Journal articles on the topic 'Teleseismic events'
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1
Baer, M., and U. Kradolfer. "An automatic phase picker for local and teleseismic events." Bulletin of the Seismological Society of America 77, no. 4 (August 1, 1987): 1437–45. http://dx.doi.org/10.1785/bssa0770041437.
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Abstract An automatic detection algorithm has been developed which is capable of time P-phase arrivals of both local and teleseismic earthquakes, but rejects noise bursts and transient events. For each signal trace, the envelope function is calculated and passed through a nonlinear amplifier. The resulting signal is then subjected to a statistical analysis to yield arrival time, first motion, and a measure of reliability to be placed on the P-arrival pick. An incorporated dynamic threshold lets the algorithm become very sensitive; thus, even weak signals are timed precisely. During an extended performance evaluation on a data set comprising 789 P phases of local events and 1857 P phases of teleseismic events picked by an analyst, the automatic picker selected 66 per cent of the local phases and 90 per cent of the teleseismic phases. The accuracy of the automatic picks was “ideal” (i.e., could not be improved by the analyst) for 60 per cent of the local events and 63 per cent of the teleseismic events.
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Short, Kevin M. "Detection of Teleseismic Events in Seismic Sensor Data Using Nonlinear Dynamic Forecasting." International Journal of Bifurcation and Chaos 07, no. 08 (August 1997): 1833–45. http://dx.doi.org/10.1142/s0218127497001400.
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In this paper we consider the use of nonlinear dynamic (NLD) forecasting as a signal processing tool for seismic applications. The specific problem considered here arises in monitoring nuclear tests and nuclear treaty compliance, where the presence of ubiquitous background noise obscures the seismic signals associated with the tests. The problem is that the signal from a distant teleseismic event can be attenuated so that it is lost in the background noise, and since the noise overlaps the frequency band occupied by the teleseisms, frequency-based techniques provide only marginal improvements in detection capabilities. For the work in this paper, we studied a test set of actual seismic sensor data prepared by the Air Force Technical Applications Center (AFTAC). The data set was composed of background seismic noise which contained or had added to it a number of hidden teleseismic signals. This data was analyzed to determine if techniques of NLD forecasting could be used to detect the hidden signals. For this test case, it was possible to predict the behavior of the seismic background sufficiently well that when the predicted background behavior was removed, the hidden signals became evident. However, some of the weaker signals were very close to the residual noise level, so the ability to detect these events is compromised.
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Pirli, M., and J. Schweitzer. "Regional and teleseismic event detection capability of the small-aperture Tripoli seismic array, Greece." Bulletin of the Geological Society of Greece 40, no. 3 (June 5, 2018): 1246. http://dx.doi.org/10.12681/bgsg.16877.
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The Tripoli Seismic Array (TRISAR) is a small-aperture array designed to monitor and locate the seismicity in the area of Greece. In this study, its detection capabilities are discussed for regional and teleseismic events. A reference event list is compiled, consisting of events ofmb>5.0for regional and teleseismic distances (A>6°), according to the ISC On-line Bulletin. TRISAR automatically detected approximately 25% of these events over the entire investigated distance range. Although TRISAR slowness vector residuals are rather large, as expected for an array of such small aperture, the benefits resulting from the use of such a system for reporting regional and teleseismic activity is obvious.
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van Ginkel, Janneke, Elmer Ruigrok, and Rien Herber. "Using horizontal-to-vertical spectral ratios to construct shear-wave velocity profiles." Solid Earth 11, no. 6 (November 9, 2020): 2015–30. http://dx.doi.org/10.5194/se-11-2015-2020.
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Abstract. For seismic hazard assessment and earthquake hypocentre localization, detailed shear-wave velocity profiles are an important input parameter. Here, we present a method to construct a shear-wave velocity profiles for a deep unconsolidated sedimentary layer by using strong teleseismic phases and the ambient noise field. Gas extraction in the Groningen field, in the northern part of the Netherlands, is causing low-magnitude, induced seismic events. This region forms an excellent case study due to the presence of a permanent borehole network and detailed subsurface knowledge. Instead of conventional horizontal-to-vertical spectral ratios (H∕V ratios) from amplitude spectra, we calculate power spectral densities and use those as input for H∕V calculations. The strong teleseisms provide resonance recordings at low frequencies, where the seismic noise field is too weak to be recorded well with the employed geophones and accelerometers. The H∕V ratios of the ambient noise field are compared with several forward modelling approaches to quality check the teleseism-based shear-wave velocity profiles. Using the well-constrained depth of the sedimentary basin, we invert the H∕V ratios for velocity profiles. A close relationship is observed between the H∕V spectral ratios from the ambient noise field, shear-wave resonance frequencies and Rayleigh-wave ellipticity. By processing only five teleseismic events, we are able to derive shear-wave velocities for the deeper sedimentary sequence with a 7 % bias in comparison with the existing detailed velocity model for the Cenozoic sediments overlying the Groningen gas field. Furthermore, a relation between resonance frequency and unconsolidated sediment thickness is derived, to be used in other areas in the Netherlands, where detailed depth maps are not available.
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Tiira, Timo. "Detecting teleseismic events using artificial neural networks." Computers & Geosciences 25, no. 8 (September 1999): 929–38. http://dx.doi.org/10.1016/s0098-3004(99)00056-4.
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Kanao, Masaki, Akira Yamada, and Mikiya Yamashita. "Characteristic Seismic Waves Associated with Cryosphere Dynamics in Eastern Dronning Maud Land, East Antarctica." International Journal of Geophysics 2012 (2012): 1–19. http://dx.doi.org/10.1155/2012/389297.
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Several kinds of natural source signals are recorded by seismic exploration stations on the continental ice sheet in Eastern Dronning Maud Land, East Antarctica, during 2002 austral summer. They include not only tectonic earthquakes, but also ice-related phenomena possibly involving recent global climate change. The recorded signals are classified into (1) teleseismic events, (2) local ice quakes, and (3) unidentified events (X-phases). The teleseismic waves show the high signal-to-noise ratio in spite of the small magnitude of the event; this indicates that it is highly feasible to study not only the local shallow structure but also the deep structure of the earth by using teleseismic events. Frequency spectra of the all waveforms represent discordances along the observation seismic profile. The abrupt change of topography in the valley along the seismic profile might cause both the anomalous frequency content and travel times. Finally, an origin of the X-phases is speculated as the intraplate earthquakes or possibly large ice-quakes (glacial earthquakes) around Antarctica, involving global warming appeared in polar region.
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Li, Chenyu, Zhigang Peng, Julien A. Chaput, Jacob I. Walter, and Richard C. Aster. "Remote Triggering of Icequakes at Mt. Erebus, Antarctica by Large Teleseismic Earthquakes." Seismological Research Letters 92, no. 5 (May 12, 2021): 2866–75. http://dx.doi.org/10.1785/0220210027.
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Abstract Recent studies have shown that the Antarctic cryosphere is sensitive to external disturbances such as tidal stresses or dynamic stresses from remote large earthquakes. In this study, we systematically examine evidence of remotely triggered microseismicity around Mount (Mt.) Erebus, an active high elevation stratovolcano located on Ross Island, Antarctica. We detect microearthquakes recorded by multiple stations from the Mt. Erebus Volcano Observatory Seismic Network one day before and after 43 large teleseismic earthquakes, and find that seven large earthquakes (including the 2010 Mw 8.8 Maule, Chile, and 2012 Mw 8.6 Indian Ocean events) triggered local seismicity on the volcano, with most triggered events occurring during the passage of the shorter-period Rayleigh waves. In addition, their waveforms and locations for the triggered events are different when comparing with seismic events arising from the persistent small-scale eruptions, but similar to other detected events before and after the mainshocks. Based on the waveform characteristics and their locations, we infer that these triggered events are likely shallow icequakes triggered by dilatational stress perturbations from teleseismic surface waves. We show that teleseismic earthquakes with higher peak dynamic stress changes are more capable of triggering icequakes at Mt. Erebus. We also find that the icequakes in this study are more likely to be triggered during the austral summer months. Our study motivates the continued monitoring of Mount Erebus with dense seismic instrumentation to better understand interactions between dynamic seismic triggering, crospheric processes, and volcanic activity.
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Lewis, Brian T. R., and LeRoy M. Dorman. "Recording teleseisms on the seafloor; an example from the Juan de Fuca plate." Bulletin of the Seismological Society of America 88, no. 1 (February 1, 1998): 107–16. http://dx.doi.org/10.1785/bssa0880010107.
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Abstract In 1991, during an experiment to compare low-frequency seismic noise on a basaltic and a sediment covered seafloor (NOBS), we recorded teleseisms on the Juan de Fuca ridge, the Gorda ridge, and the adjacent Cascadia Basin with the SNAG ocean-bottom seismometers (OBS). These data provide an indication of the type of data that may be obtained from future experiments to record teleseisms and may be helpful in designing these experiments and analyzing the results. We found that although seafloor noise is dominated by microseisms in the band 0.1 to 0.3 Hz, there is a well-developed minimum in noise from about 0.03 to 0.1 Hz (the noise notch). In this noise notch, teleseisms can be most easily detected. In the Cascadia area, the overall noise levels are such that only teleseismic events with magnitude greater than 6.5 were usefully recorded. A magnitude 6.6 event in the New Britain area (Δ = 89°) produced usable P- and surface-wave data only in this noise notch. In the band 0.03 to 0.1 Hz, the character of compressional waves is very sensitive to water depth and the type of sensor. We show that pressure sensors are especially sensitive to reverberation in the ocean and that motion sensors (seismometers) are less sensitive to ocean reverberations and will record teleseismic phases with less distortion than pressure sensors. The Cascadia data indicate enhanced P amplitudes at sites on the ridge axes that could be due to focusing caused by a low-velocity lens. These data suggest that amplitude information may be as, or even more, useful than P delay times for determining upper mantle structure.
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Shragge, J., B. Artman, and C. Wilson. "Teleseismic shot-profile migration." GEOPHYSICS 71, no. 4 (July 2006): SI221—SI229. http://dx.doi.org/10.1190/1.2208263.
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The shot-profile migration approach of wave-equation migration generates subsurface images using the interferometric principle of crosscorrelating two passive wavefields. These wavefields are typically a source wavefield containing energy from an excited source and a receiver wavefield comprised of scattered-source wavefield energy by the discontinuous earth structure. Shot-profile migration can be recast as a novel way of imaging the earth’s lithosphere using teleseismic wavefield data, where the source wavefield is the directly arriving wavefront and the receiver wavefield is the following wavefield coda. We demonstrate that the shot-profile technique can be tailored to suit teleseismic acquisition geometry and wavefields. Assuming an acoustic framework and 2.5D experimental geometry, we develop procedures that enable kinematic and structural imaging (migration) using both transmission and free-surface reflected passive wavefields. Experiments with synthetic data demonstrate the method’s applicability and illustrate the negative imaging consequence of using inaccurate migration velocity profiles. We apply shot-profile migration to a suite of teleseismic events acquired during the IRIS-PASSCAL CASC-1993 experiment in central Oregon. The imaging results are interpreted to show the Juan de Fuca plate subducting beneath the North American plate. We attribute the observed dissimilarities between these results and other Juan de Fuca subduction- zone images to the combination of different imaging goals and the use of more accurate migration velocity profiles.
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Tiira, Timo. "Slowness vector correction for teleseismic events with artificial neural networks." Physics of the Earth and Planetary Interiors 112, no. 1-2 (March 1999): 101–9. http://dx.doi.org/10.1016/s0031-9201(98)00179-4.
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Uski, Marja. "Event detection and location performance of the FINESA array in Finland." Bulletin of the Seismological Society of America 80, no. 6B (December 1, 1990): 1818–32. http://dx.doi.org/10.1785/bssa08006b1818.
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Abstract The experimental seismic array FINESA in Finland is designed to monitor weak seismic events at regional and teleseismic distances. The array geometry currently comprises 15 short-period vertical seismometers in three concentric rings (A-, B-, and C-rings), with a diameter of the outer ring of about 2 km. In late 1989, the data acquisition system of the array was completely modernized. Signals are now transferred continuously via high-speed telephone lines to the processing centers at the Institute of Seismology in Helsinki and NORSAR in Norway, therefore allowing automatic real-time processing of the recorded data. In this paper, the detection performance of the array in the current configuration has been evaluated. The results are encouraging: during a 2-week test period, FINESA detected at least one P and one S phase for 84 per cent of the events reported in the regional bulletin of the University of Helsinki, and 99 per cent of the events in the weekly teleseismic bulletins. Many additional events at both distance ranges were also found. The estimated phase velocities obtained by the broadband frequency-wave-number analysis confidently identify the phase type (teleseismic Pgional PgionalS). However, the resolution of the analysis is not sufficient to separate Pg from Pn and Lg from Sn. The estimated backazimuths are reliable for phase association, the standard deviation of the estimates being 7° for regional P phases, 6° for regional S phases, and 23° for teleseismic P phases. Finally, preliminary results from FINESA's on-line event location capability showed that the average error in the location estimates is 21 per cent of the true epicentral distance. The greatest error sources are uncertainty in the estimated azimuths and occasional misidentification of secondary phases (Lg, Sn and Rg). The error could be reduced by constructing a regional correction term for the azimuth estimates and “tuning” the phase identification algorithms for FINESA. The characteristics of the Rg-phase need to be especially considered.
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Jerkins, Annie E., Hasbi Ash Shiddiqi, Tormod Kværna, Steven J. Gibbons, Johannes Schweitzer, Lars Ottemöller, and Hilmar Bungum. "The 30 June 2017 North Sea Earthquake: Location, Characteristics, and Context." Bulletin of the Seismological Society of America 110, no. 2 (January 21, 2020): 937–52. http://dx.doi.org/10.1785/0120190181.
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ABSTRACT The Mw 4.5 southern Viking graben earthquake on 30 June 2017 was one of the largest seismic events in the Norwegian part of the North Sea during the last century. It was well recorded on surrounding broadband seismic stations at regional distances, and it generated high signal-to-noise ratio teleseismic P arrivals at up to 90° with good azimuthal coverage. Here, the teleseismic signals provide a unique opportunity to constrain the event hypocenter. Depth phases are visible globally and indicate a surface reflection in the P-wave coda some 4 s after the initial P arrival, giving a much better depth constraint than regional S-P time differences provide. Moment tensor inversion results in a reverse thrust faulting mechanism. The fit between synthetic and observed surface waves at regional distances is improved by including a sedimentary layer. Synthetic teleseismic waveforms generated based on the moment tensor solution, and a near-source 1D velocity model indicates a depth of 7 km. Correlation detectors using the S-wave coda from the main event were run on almost 30 yr of continuous multichannel seismic data searching for repeating signals. In addition to a magnitude 1.9 aftershock 33 min later, and a few magnitude ∼1 events in the following days, a magnitude 2.5 earthquake on 13 November 2016 was the only event found to match the 30 June 2017 event well. Using double-difference techniques, we find that the two largest events are located within 1 km of the main event. We present a Bayesloc probabilistic multiple event location including the 30 June event and all additional seismic events in the region well recorded on the regional networks. The Bayesloc relocation gave a more consistent seismicity pattern and moved several of the events more toward the west. The results of this study are also discussed within the regional seismotectonic frame of reference.
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Sugioka, Hiroko, Yoshio Fukao, and Shin'ichi Sakai. "Anomalously Early First Arrivals to the J-Array from Teleseismic Events." Journal of Physics of the Earth 44, no. 6 (1996): 687–99. http://dx.doi.org/10.4294/jpe1952.44.687.
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Wilde-Piórko, M., and M. Grad. "Regional and teleseismic events recorded across the TESZ during POLONAISE'97." Tectonophysics 314, no. 1-3 (December 1999): 161–74. http://dx.doi.org/10.1016/s0040-1951(99)00242-5.
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Retailleau, L., N. M. Shapiro, J. Guilbert, M. Campillo, and P. Roux. "Detecting and locating seismic events with using USArray as a large antenna." Advances in Geosciences 40 (January 12, 2015): 27–30. http://dx.doi.org/10.5194/adgeo-40-27-2015.
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Abstract. We design an earthquake detection and location algorithm that explores coherence and characteristic behavior of teleseismic waves recorded by a large-scale seismic network. The procedure consists of three steps. First, for every tested source location we construct a time-distance gather by computing great-circle distances to all stations of the network and aligning the signals respectively. Second, we use the constructed gather to compute a Tau-P transform. For waves emitted by teleseismic sources, the amplitude of this transform has a very characteristic behavior with maxima corresponding to different seismic phases. Relative location of these maxima on the time-slowness plane strongly depends on the distance to the earthquake. To explore this dependence, in a third step, we convolve the Tau-P amplitude with a time-slowness filter whose maxima are computed based on prediction of a global travel-time calculator. As a result of this three-step procedure, we obtain a function that characterizes a likelihood of occurrence of a seismic event at a given position in space and time. We test the developed algorithm by applying it to vertical-component records of USArray to locate a set of earthquakes distributed around the Globe with magnitudes between 6.1 and 7.2.
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Hwang, Lorraine J., and Hiroo Kanamori. "Teleseismic and strong-motion source spectra from two earthquakes in eastern Taiwan." Bulletin of the Seismological Society of America 79, no. 4 (August 1, 1989): 935–44. http://dx.doi.org/10.1785/bssa0790040935.
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Abstract The 20 May and 14 November 1986 Hualien earthquakes occurred in a seismically active region of Taiwan. Locally determined focal mechanisms and aftershock patterns from the Taiwan Telemetered Seismographic Network indicate that both earthquakes occurred on steeply dipping reverse faults that trend NNE. This agrees with teleseismic first-motion data for the May event but not for the November event. This discrepancy is due to a moderate foreshock before the November event. Surface-wave analysis gives a solution for the November event of: dip 57°, rake 100°, and strike 43°, which is similar to the locally reported focal mechanism. The seismic moment of the November event is M0 = 1.7 × 1027 dynecm and the magnitudes determined from WWSSN data are m^b = 6.4, Ms = 7.3. Teleseismic source spectra show that the two events also have similar spectral signatures above 0.15 Hz. Reference acceleration spectra are computed from the average teleseismic source spectra and compared to the averaged acceleration spectra computed from strong-motion stations for both events. Correlations between the spectral amplitudes of the strong-motion spectra obtained from the main portion of the SMART 1 array and the teleseismically estimated reference spectra are poor above 0.2 Hz. Data from the hard-rock site situated outside of the basin indicates that amplification of the ground motion between 0.17-1.7 Hz is due to the alluvial valley where the SMART 1 array is located. The amplitude of the observed spectrum is five times the reference spectrum at the hard-rock site. This is consistent with similar observations from the 1985 Michoacan and 1983 Akita-Oki earthquakes. The analysis of these and more teleseismic and strong-motion records will lead to a better understanding of the relationship between their spectra.
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Smith, Gideon P., and Göran Ekström. "Improving teleseismic event locations using a three-dimensional Earth model." Bulletin of the Seismological Society of America 86, no. 3 (June 1, 1996): 788–96. http://dx.doi.org/10.1785/bssa0860030788.
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Abstract A comparison is made between seismic event locations derived from standard spherically symmetric Earth models (JB, PREM, IASP91) and a recent Earth model (S&P12/WM13) that incorporates large-scale lateral heterogeneity of P- and S-wave velocities in the mantle. Events with known hypocentral coordinates are located in the different Earth models using standard methods. Two sets of events are considered: a data set of 26 explosions, including primarily nuclear weapons test explosions and peaceful nuclear explosions in the United States and former USSR; and a published data set of 82 well-located earthquakes with a more even global distribution. IASP91 and PREM are shown to offer similar errors in event location and origin time estimates with respect to the JB model. The three-dimensional (3D) model S&P12/WM13 offers improvement in event locations over all three one-dimensional (1D) models with, or without, station corrections. For the explosion events, the average mislocation distance is reduced by approximately 40%; for the earthquakes, the improvements are smaller. Corrections for crustal thickness beneath source and receiver are found to be of similar magnitude to the mantle corrections, but use of station corrections together with the three-dimensional mantle model provide the best locations.
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Engdahl, E. Robert, Rob van der Hilst, and Raymond Buland. "Global teleseismic earthquake relocation with improved travel times and procedures for depth determination." Bulletin of the Seismological Society of America 88, no. 3 (June 1, 1998): 722–43. http://dx.doi.org/10.1785/bssa0880030722.
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Abstract We relocate nearly 100,000 events that occurred during the period 1964 to 1995 and are well-constrained teleseismically by arrival-time data reported to the International Seismological Centre (ISC) and to the U.S. Geological Survey's National Earthquake Information Center (NEIC). Hypocenter determination is significantly improved by using, in addition to regional and teleseismic P and S phases, the arrival times of PKiKP, PKPdf, and the teleseismic depth phases pP, pwP, and sP in the relocation procedure. A global probability model developed for later-arriving phases is used to independently identify the depth phases. The relocations are compared to hypocenters reported in the ISC and NEIC catalogs and by other sources. Differences in our epicenters with respect to ISC and NEIC estimates are generally small and regionally systematic due to the combined effects of the observing station network and plate geometry regionally, differences in upper mantle travel times between the reference earth models used, and the use of later-arriving phases. Focal depths are improved substantially over most other independent estimates, demonstrating (for example) how regional structures such as downgoing slabs can severely bias depth estimation when only regional and teleseismic P arrivals are used to determine the hypocenter. The new data base, which is complete to about Mw 5.2 and includes all events for which moment-tensor solutions are available, has immediate application to high-resolution definition of Wadati-Benioff Zones (WBZs) worldwide, regional and global tomographic imaging, and other studies of earth structure.
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Kanao, Masaki, Dmitry Storchak, and Ben Dando. "Evaluation of Long-Period Detectability of Teleseismic Events at Syowa Station, Antarctica." International Journal of Geosciences 03, no. 04 (2012): 809–21. http://dx.doi.org/10.4236/ijg.2012.324082.
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Hao, Chunyue, and Zhong Zheng. "Slowness–azimuth corrections of teleseismic events for IMS primary arrays in China." Journal of Seismology 13, no. 4 (October 14, 2008): 437–48. http://dx.doi.org/10.1007/s10950-008-9137-8.
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Paffrath, Marcel, and Wolfgang Friederich. "Teleseismic P waves at the AlpArray seismic network: wave fronts, absolute travel times and travel-time residuals." Solid Earth 12, no. 7 (July 20, 2021): 1635–60. http://dx.doi.org/10.5194/se-12-1635-2021.
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Abstract. We present an extensive dataset of highly accurate absolute travel times and travel-time residuals of teleseismic P waves recorded by the AlpArray Seismic Network and complementary field experiments in the years from 2015 to 2019. The dataset is intended to serve as the basis for teleseismic travel-time tomography of the upper mantle below the greater Alpine region. In addition, the data may be used as constraints in full-waveform inversion of AlpArray recordings. The dataset comprises about 170 000 onsets derived from records filtered to an upper-corner frequency of 0.5 Hz and 214 000 onsets from records filtered to an upper-corner frequency of 0.1 Hz. The high accuracy of absolute and residual travel times was obtained by applying a specially designed combination of automatic picking, waveform cross-correlation and beamforming. Taking travel-time data for individual events, we are able to visualise in detail the wave fronts of teleseismic P waves as they propagate across AlpArray. Variations of distances between isochrons indicate structural perturbations in the mantle below. Travel-time residuals for individual events exhibit spatially coherent patterns that prove to be stable if events of similar epicentral distance and azimuth are considered. When residuals for all available events are stacked, conspicuous areas of negative residuals emerge that indicate the lateral location of subducting slabs beneath the Apennines and the western, central and eastern Alps. Stacking residuals for events from 90∘ wide azimuthal sectors results in lateral distributions of negative and positive residuals that are generally consistent but differ in detail due to the differing direction of illumination of mantle structures by the incident P waves. Uncertainties of travel-time residuals are estimated from the peak width of the cross-correlation function and its maximum value. The median uncertainty is 0.15 s at 0.5 Hz and 0.18 s at 0.1 Hz, which is more than 10 times lower than the typical travel-time residuals of up to ±2 s. Uncertainties display a regional dependence caused by quality differences between temporary and permanent stations as well as site-specific noise conditions.
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Yang, X. "Validation of Regional and Teleseismic Travel-Time Models by Relocating Ground-Truth Events." Bulletin of the Seismological Society of America 94, no. 3 (June 1, 2004): 897–919. http://dx.doi.org/10.1785/0120030148.
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Saikia, Sowrav, Sumer Chopra, Santanu Baruah, P. R. Baidya, and Upendra K. Singh. "Crustal imaging of the Northwest Himalaya and its foredeep region from teleseismic events." Geomatics, Natural Hazards and Risk 7, no. 4 (September 11, 2015): 1265–86. http://dx.doi.org/10.1080/19475705.2015.1063095.
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Suteau-Henson, Anne. "Estimating azimuth and slowness from three-component and array stations." Bulletin of the Seismological Society of America 80, no. 6B (December 1, 1990): 1987–98. http://dx.doi.org/10.1785/bssa08006b1987.
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Abstract The capabilities of three-component (3-C) and array stations for estimating azimuth and slowness are compared for short-period P-type phases recorded at the NORESS array. For vertical array data, azimuth and slowness estimates are obtained from broadband frequency-wavenumber (f-k) analysis. For 3-C data, polarization analysis is performed. The data processing is automated, using arrival time and dominant frequency information from the NORESS Bulletin. Independent determinations of azimuth and/or slowness, obtained from locations in the NEIS or regional network bulletins, are used as reference estimates. Over 100 events are analyzed, both teleseismic and regional. They were selected from a variety of distances and azimuths, and cover a wide range of signal-to-noise ratios (SNR). The capability of 3-C stations for azimuth and slowness estimation critically depends on SNR. For SNR below a threshold of ∼2, the scatter in the estimates is very large for both parameters, and the slowness of teleseismic events tends to be overestimated. Also, the results are site-dependent within the NORESS array. The array measurements obtained with the broadband f-k method are not significantly affected by noise at the levels of SNR considered. For events with sufficient SNR, both methods compare well, and only a slightly better performance is observed with the f-k method.
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Piana Agostinetti, Nicola, and Alberto Malinverno. "Assessing uncertainties in high-resolution, multifrequency receiver-function inversion: A comparison with borehole data." GEOPHYSICS 83, no. 3 (May 1, 2018): KS11—KS22. http://dx.doi.org/10.1190/geo2017-0350.1.
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We use teleseismic P-to-S converted waves from a permanent station to estimate the uncertainties in a 1D elastic model of the shallow crust (0–7 km depth) obtained from the inversion of receiver function (RF) data. Our earth model consists of layers with a constant S-wave velocity [Formula: see text] and P- to S-wave velocity ratio ([Formula: see text]). We apply a Bayesian formulation and transdimensional Monte Carlo sampling to compute the posterior uncertainties of the earth model. The model uncertainties rely on a realistic representation of the data uncertainties, and we estimate directly from the stacking of the teleseismic data, a full-error covariance matrix. To explore the effect of the number of teleseismic events and the RF frequency content, we compare the results of inverting a single RF computed for a cut-off filter frequency of 4 Hz with the joint inversion of four RFs computed from independent ensembles in a larger pool of events for cut-off frequencies of 0.5, 1, 2, and 4 Hz. The inversion results are compared with the lithostratigraphy and sonic-log measurements from a 7 km deep borehole drilled near the seismic station. The inversion of a single RF results in larger uncertainties in the recovered [Formula: see text] profile and in the depth to seismic discontinuities compared with the multifrequency inversion. Moreover, the multifrequency inversion predicts more accurately the depth to a velocity inversion at approximately 6 km below the surface and matches more closely the borehole sonic-log data. Our results indicate that RF data can be used to map shallow (3–5 km depth) crustal interfaces with uncertainties in the order of 300–500 m, whereas uncertainties are consistently smaller (<300 m) for interfaces in the top kilometer.
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Clark, R. A., and R. G. Pearce. "Identification of multiple underground explosions using the relative amplitude method." Bulletin of the Seismological Society of America 78, no. 2 (April 1, 1988): 885–97. http://dx.doi.org/10.1785/bssa0780020885.
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Abstract The relative amplitude method is applied to the few available good quality teleseismic P-wave seismograms from five presumed double nuclear explosions and one known multiple chemical explosion, under the “naive” assumption that the observed multiple arrivals correspond to P, pP, and sP from a single earthquake—an interpretation which is indeed consistent with the body-wave arrival time data in most cases. The purpose is to investigate the ability of relative amplitudes to identify correctly such multiple events for which established discrimination criteria may give earthquake-like or ambiguous results. For five of the examples, observed relative amplitudes from only four azimuthally well-distributed array seismograms are sufficient to exclude the single-earthquake interpretation. Deliberate attempts to simulate earthquake teleseismic P wave-forms using multiple explosions are restricted to simulation studies, and one of these is analyzed here using the same approach. We conclude that relative amplitudes can act as a valuable aid to source discrimination in cases where complexity gives rise to fallibility of conventional discriminants, even where only a small number of well-distributed teleseismic short-period array seismograms are available, their signal-to-noise ratios being maximized by suitable array design and careful choice of array site. The network need not be dense, since closely spaced observations of the focal sphere generally embody a large measure of redundancy.
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Woodgold, Catherine R. D. "Wide-aperture beamforming of depth phases by timescale contraction." Bulletin of the Seismological Society of America 89, no. 1 (February 1, 1999): 165–77. http://dx.doi.org/10.1785/bssa0890010165.
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Abstract Teleseismic depth phase signals can be combined with constructive interference from stations spaced as much as 1000 km apart. Each trace is first deconvolved using an operator based on the P phase of that trace, then its timescale is stretched or contracted to eliminate the moveout of pP-P time with distance. Traces can then be added with constructive interference of depth phases out to 10° or more angular distance between the stations on the focal sphere. Depth phases (pP or sP) representing hypocentral depths ranging from 6 to 204 km were found using Canadian National Seismograph Network (CNSN) data for 45 events, recorded at ranges of 2000 to 10,800 km, which had been reported in the Reviewed Event Bulletins (REB) of the Prototype International Data Center (PIDC), including 23 events for which the REB reported no depth phases. For 28 events for which a catalog depth (REB; or PDE from USGS) was available for comparison, 18 had depths agreeing either within 6 km or within 15%, 7 can be explained by assuming an sP phase was misassociated as pP, 1 is just outside the error bar of the free depth reported in the REB, and only 2 disagree significantly. Thus, using only Canadian data, depth phases were found by beamforming for many events for which no depth phases had been found by the PIDC using worldwide data including arrays. The depth phase beamforming method has the potential of substantially increasing the number of earthquakes for which teleseismic depth phases can be detected.
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Bryan, Carol J. "A possible triggering mechanism for large Hawaiian earthquakes derived from analysis of the 26 June 1989 Kilauea south flank sequence." Bulletin of the Seismological Society of America 82, no. 6 (December 1, 1992): 2368–90. http://dx.doi.org/10.1785/bssa0820062368.
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Abstract Examination of short-period seismic data from the ML = 6.1 Kilauea south flank earthquake and aftershock sequence indicates that the rupture process in large Hawaiian earthquakes is more complex than previously modeled. In contrast to the low-angle thrust solution determined for the mainshock from long-period teleseismic body waves by other workers, I find an intermediate- to high-angle reverse solution; I find, however, that focal mechanisms for coastal aftershocks of ML > 3.0 are similar to the teleseismic mechanism for the mainshock. A difference in focal mechanisms determined from short-period local-network seismic data and from long-period teleseismic data has been noted for other recent large Hawaiian earthquakes. Both the mapping of surface cracks and the focal mechanism derived from short-period seismic data for the ML = 6.6 1983 Kaoiki earthquake show strike-slip motion, whereas the centroid moment tensor solution shows low-angle thrusting. The focal mechanism calculated from short-period seismic data for the ML = 7.2 1975 Kalapana mainshock shows low-angle thrusting according to some workers, but intermediate- to high-angle reverse faulting according to others, whereas focal mechanisms calculated from long-period seismic data show low-angle thrusting. This result suggests that rupture initiation in large Hawaiian earthquakes, as represented by the short-period focal mechanisms, differs significantly from the overall rupture process, as represented by the teleseismic mechanisms. I propose that small earthquakes trigger the large-scale energy release at the bases of the volcanic edifices, the type of energy release often observed in large Hawaiian earthquakes. These triggering events may occur along rupture surfaces that differ from those along which the long-period moment release occurs and thus may represent release of a local stress concentration superposed upon the regional stress field.
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Simmons, N. A., S. C. Myers, C. Morency, A. Chiang, and D. R. Knapp. "SPiRaL: a multiresolution global tomography model of seismic wave speeds and radial anisotropy variations in the crust and mantle." Geophysical Journal International 227, no. 2 (July 20, 2021): 1366–91. http://dx.doi.org/10.1093/gji/ggab277.
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SUMMARY SPiRaL is a joint global-scale model of wave speeds (P and S) and anisotropy (vertical transverse isotropy, VTI) variations in the crust and mantle. The model is comprised of >2.1 million nodes with five parameters at each node that capture velocity variations for P- and S-waves travelling at arbitrary directions in transversely isotropic media with a vertical symmetry axis (VTI). The crust (including ice, water, sediments and crystalline layers) is directly incorporated into the model. The default node spacing is approximately 2° in the lower mantle and 1° in the crust and upper mantle. The grid is refined with ∼0.25° minimum node spacing in highly sampled regions of the crust and upper mantle throughout North America and Eurasia. The data considered in the construction of SPiRaL includes millions of body wave traveltimes (crustal, regional and teleseismic phases with multiples) and surface wave (Rayleigh and Love) dispersion. A multiresolution inversion approach is employed to capture long-wavelength heterogeneities commonly depicted in global-scale tomography images as well as more localized details that are typically resolved in more focused regional-scale studies. Our previous work has demonstrated that such global-scale models with regional-scale detail can accurately predict both teleseismic and regional body wave traveltimes, which is necessary for more accurate location of small seismic events that may have limited signal at teleseismic distances. SPiRaL was constructed to predict traveltimes for event location and long-period waveform dispersion for seismic source inversion applications in regions without sufficiently tuned models. SPiRaL may also serve as a starting model for full-waveform inversion (FWI) with the goal of fitting waves with periods 10–50 s over multiple broad regions (thousands of kilometres) and potentially the globe. To gain insight to this possibility, we simulated waveforms for a small set of events using SPiRaL and independent waveform-based models for comparison. For the events tested, the performance of the traveltime-based SPiRaL model is shown to be generally on par with regional 3-D waveform-based models in three regions (western United States, Middle East, Korean Peninsula) suggesting SPiRaL may serve as a starting model for FWI over broad regions.
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Zhao, Dapeng, Akira Hasegawa, and Hiroo Kanamori. "Deep structure of Japan subduction zone as derived from local, regional, and teleseismic events." Journal of Geophysical Research: Solid Earth 99, B11 (November 10, 1994): 22313–29. http://dx.doi.org/10.1029/94jb01149.
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DYRDAL, IDAR. "TELESEISMIC DISCRIMINATION OF EARTHQUAKES AND NUCLEAR DETONATIONS WITH FEATURES DERIVED FROM MAXIMUM ENTROPY POWER SPECTRAL ESTIMATES." International Journal of Pattern Recognition and Artificial Intelligence 01, no. 03n04 (December 1987): 323–33. http://dx.doi.org/10.1142/s0218001487000229.
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This paper describes pattern recognition techniques for discriminating between earthquakes and underground nuclear detonations from teleseismic signals. The features investigated are obtained by Maximum Entropy Spectral Analysis techniques. Classification performance is evaluated on a seismic database recorded at the Large Aperture Seismic Array (LASA) in Montana. The events are randomly divided into design and test subsets. Several pattern recognition algorithms including Baye's quadratic classifier, the minimum distance classifier and the nearest neighbor rule are applied. The best results are obtained with spectral ratios from windows taken at regular intervals within the coda combined with bodywave magnitude. With the Baye's classifier, 85% correct classification was achieved for the test set events. For a reduced dataset containing only central Asian events, 96% was achieved.
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Qin, Lei, Pieter-Ewald Share, Hongrui Qiu, Amir A. Allam, Frank L. Vernon, and Yehuda Ben-Zion. "Internal structure of the San Jacinto fault zone at the Ramona Reservation, north of Anza, California, from dense array seismic data." Geophysical Journal International 224, no. 2 (October 23, 2020): 1225–41. http://dx.doi.org/10.1093/gji/ggaa482.
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SUMMARY We image the internal structure of the San Jacinto fault zone (SJFZ) near Anza, California, with seismic data recorded by two dense arrays (RA and RR) from ∼42 000 local and ∼180 teleseismic events occurring between 2012 and 2017. The RA linear array has short aperture (∼470 m long with 12 strong motion sensors) and recorded for the entire analysed time window, whereas the RR is a large three-component nodal array (97 geophones across a ∼2.4 km × 1.4 km area) that operated for about a month in September–October 2016. The SJFZ at the site contains three near-parallel surface traces F1, F2 and F3 from SW to NE that have accommodated several Mw > 6 earthquakes in the past 15 000 yr. Waveform changes in the fault normal direction indicate structural discontinuities that are consistent with the three fault surface traces. Relative slowness from local events and delay time analysis of teleseismic arrivals in the fault normal direction suggest a slower SW side than the NE with a core damage zone between F1 and F2. This core damage zone causes ∼0.05 s delay at stations RR26–31 in the teleseismic P arrivals compared with the SW-most station, and generates both P- and S-type fault zone trapped waves. Inversion of S trapped waves indicates the core damaged structure is ∼100 m wide, ∼4 km deep with a Q value of ∼20 and 40 per cent S-wave velocity reduction compared with bounding rocks. Fault zone head waves observed at stations SW of F3 indicate a local bimaterial interface that separates the locally faster NE block from the broad damage zone in the SW at shallow depth and merges with a deep interface that separates the regionally faster NE block from rocks to the SW with slower velocities at greater depth. The multiscale structural components observed at the site are related to the geological and earthquake rupture history at the site, and provide important information on the preferred NW propagation of earthquake ruptures on the San Jacinto fault.
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Silvennoinen, H., E. Kozlovskaya, and E. Kissling. "POLENET/LAPNET teleseismic P-wave traveltime tomography model of the upper mantle beneath northern Fennoscandia." Solid Earth Discussions 7, no. 3 (September 10, 2015): 2527–62. http://dx.doi.org/10.5194/sed-7-2527-2015.
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Abstract. The POLENET/LAPNET broadband seismic array was deployed in northern Fennoscandia (Finland, Sweden, Norway, and Russia) during the third International Polar Year 2007–2009. The array consisted of roughly 60 seismic stations. In our study we estimate the 3-D architecture of the upper mantle beneath the northern Fennoscandian shield using high-resolution teleseismic P-wave tomography. For this purpose 111 clearly recorded teleseismic events were selected and the data from the stations handpicked and analysed. Our study reveals a highly heterogeneous lithospheric mantle beneath the northern Fennoscandian shield though without any large high P-wave velocity area that may indicate presence of thick depleted lithospheric "keel". The most significant feature seen in the velocity model is a large elongated negative velocity anomaly (up to −3.5 %) in depth range 100–150 km in the central part of our study area that can be followed down to a depth of 200 km in some local areas. This low-velocity area separates three high-velocity regions corresponding to the cratons and it extends to greater depth below the Karelian craton.
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Der, Z. A., M. R. Hirano, and R. H. Shumway. "Coherent processing of regional signals at small seismic arrays." Bulletin of the Seismological Society of America 80, no. 6B (December 1, 1990): 2161–76. http://dx.doi.org/10.1785/bssa08006b2161.
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Abstract Regional arrivals, similarly to short-period teleseismic P waves, have a spectral structure that the Fourier transforms of individual sensors at arrays for events located in limited source regions can be decomposed into source and site spectral factors. This structure has been demonstrated to be valid for Pn and Lg arrivals at NORESS. This property of regional arrivals can be exploited for: (a) Grouping events with respect to relative location; (b) Identifying events with differing source mechanisms; and (c) Finding differences in the source time functions between closely spaced events. Potentially useful techniques for accomplishing such analyses consist of computing site-averaged interevent coherences, interevent and intersite equalization methods combined with correlation techniques. The advantage of such approaches is that we need not know much about the propagation characteristics (Green's functions) along the paths to an array.
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Peng, Xiaohua, and Eugene D. Humphreys. "Moho dip and crustal anisotropy in northwestern Nevada from teleseismic receiver functions." Bulletin of the Seismological Society of America 87, no. 3 (June 1, 1997): 745–54. http://dx.doi.org/10.1785/bssa0870030745.
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Abstract Receiver functions are derived from teleseismic waves recorded during the 1988 to 1989 PASSCAL Basin and Range passive-source seismic experiment in northwestern Nevada. A velocity model involving both a planar dipping Moho and crustal anisotropy is needed to explain the radial and tangential motions of the observed PS conversions. An arrival-time difference often observed between radial and tangential Moho PS conversions suggests an anisotropic crust. The PS conversions are large and indicate a major discontinuity under the area. The particle motion directions for most of the tangential components change sign between South American events and events from the other two source areas (Japan and Tonga regions), providing good evidence for a Moho dipping approximately to the north. Also, the PS conversions from the Moho follow direct P arrivals by about 3.2 sec under the southern part of the array, 3.4 sec under the southern central part of the array, and 3.7 sec under the northern part of the array, indicating a Moho that varies in depth from about 26 to 31 km. A velocity model with the Moho dipping ∼9° in a nearly northerly direction and an anisotropic crust with a split time of ∼0.25 sec and a fast axis of ∼130° best explain these observations.
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Ambraseys, N. N., and R. D. Adams. "Seismicity of the Sudan." Bulletin of the Seismological Society of America 76, no. 2 (April 1, 1986): 483–93. http://dx.doi.org/10.1785/bssa0760020483.
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abstract This paper presents a record of information on the seismicity of the Sudan. In addition to events for which only felt information exists, there are a number of early teleseismic locations of earthquakes which have been reexamined using information from contemporary station bulletins. Most activity is close to the southern borders of Sudan, near the African rift system, but the northeast is affected by earthquakes in the Red Sea, and the central intraplate region has also experienced earthquakes capable of producing damage.
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Woods, Bradley B., Sharon Kedar, and Donald V. Helmberger. "ML:M0 as a regional seismic discriminant." Bulletin of the Seismological Society of America 83, no. 4 (August 1, 1993): 1167–83. http://dx.doi.org/10.1785/bssa0830041167.
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Abstract The mb:MS ratio determined by teleseismic observations has proven to be an effective discriminant, for explosive sources tend to be significantly richer in short-period energy than are earthquakes. Unfortunately, this method is limited by the detection threshold of teleseismic surface waves. However, recent advances in instrumentation allowing low amplitude surface wave measurements coupled with new analytical techniques make it feasible to use regional waveform data to determine the long-period source excitation level of low magnitude events. We propose using the ratio of ML (local magnitude) to M0 (scalar seismic moment) as an analogous regional discriminant. We applied this criterion to a data set of 299 earthquakes and 178 explosions and found that this ratio seems to be diagnostic of source type. For a given M0, the ML of an explosion is more than 0.5 magnitude units larger than that of an earthquake. This separation of populations with respect to source type can be attributed to the fact that ML is a short-period (1 Hz) energy measurement, whereas seismic moment is determined from long-period body wave phases (period > 4 s) and surface waves (10 to 40 sec). Using regional stations with sources 200 to 600 km away, the effective threshold for magnitude measurements for this discriminant is found to be ML = 3.1 for earthquakes and ML = 3.6 for explosions. This method does require the determination of regional crustal models and path calibrations from master events or by other means.
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Langston, Charles A., and Mariaclare Franco-Spera. "Modeling of the Koyna, India, aftershock of 12 December 1967." Bulletin of the Seismological Society of America 75, no. 3 (June 1, 1985): 651–60. http://dx.doi.org/10.1785/bssa0750030651.
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Abstract Short-period teleseismic and near-regional long-period waveforms from a large aftershock (mb = 5.3, origin time 06:18:36.8 UTC) of the 10 December 1967 Koyna main event were modeled to determine source depth and focal mechanism. Identification of pP and sP on the short-period waveforms yielded a well-constrained source depth of 3.5 to 4.0 km. The focal mechanism was determined using a systematic trial and error (grid-testing) technique in which seven P first motions, two SH first motions, two teleseismic pP/P ratios, one teleseismic sP/P ratio, and one regional SH/P ratio were included. This heterogeneous, but sparse, data set yielded a constrained normal fault mechanism at 100° ± 20° strike, 40° ± 10° dip, and 240° ± 20° rake. Rupture directivity is inferred from consistently high surface reflection/direct wave amplitude ratios. A circular fault of 1 km radius with a rupture initiation point at the lower edge and an assumed rupture velocity of 0.9 Vs explains the anomalously high amplitude ratios and yields a seismic moment of 3.8 × 1023 dyne-cm. The shallow source depth is similar to that found for the main event (4.5 km) and the 13 September foreshocks (5 km) in previous modeling studies and is consistent with the premise that the Koyna earthquakes were triggered by the impoundment of the Koyna reservoir. However, the normal fault mechanism differs substantially from the previous events which were left-lateral strike-slip faults trending NNE. The differing aftershock mechanism is probably due to the reactivation of old faults in the Koyna area caused by stress readjustment after the Koyna main event.
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Wald, David J., Hiroo Kanamori, Donald V. Helmberger, and Thomas H. Heaton. "Source study of the 1906 San Francisco earthquake." Bulletin of the Seismological Society of America 83, no. 4 (August 1, 1993): 981–1019. http://dx.doi.org/10.1785/bssa0830040981.
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Abstract All quality teleseismic recordings of the great 1906 San Francisco earthquake archived in the 1908 Carnegie Report by the State Earthquake Investigation Commission were scanned and digitized. First order results were obtained by comparing complexity and amplitudes of teleseismic waveforms from the 1906 earthquake with well calibrated, similarly located, more recent earthquakes (1979 Coyote Lake, 1984 Morgan Hill, and 1989 Loma Prieta earthquakes) at nearly co-located modern stations. Peak amplitude ratios for calibration events indicated that a localized moment release of about 1 to 1.5 × 1027 dyne-cm was responsible for producing the peak the teleseismic body wave arrivals. At longer periods (50 to 80 sec), we found spectral amplitude ratios of the surface waves require a total moment release between 4 and 6 × 1027 dyne-cm for the 1906 earthquake, comparable to previous geodetic and surface wave estimates (Thatcher, 1975). We then made a more detailed source analysis using Morgan Hill S body waves as empirical Green's Functions in a finite fault subevent summation. The Morgan Hill earthquake was deemed most appropriate for this purpose as its mechanism is that of the 1906 earthquake in the central portion of the rupture. From forward and inverse empirical summations of Morgan Hill Green's functions, we obtained a good fit to the best quality teleseismic waveforms with a relatively simple source model having two regions of localized strong radiation separated spatially by about 110 km. Assuming the 1906 epicenter determined by Bolt (1968), this corresponds with a large asperity (on the order of the Loma Prieta earthquake) in the Golden Gate/San Francisco region and one about three times larger located northwest along strike between Point Reyes and Fort Ross. This model implies that much of the 1906 rupture zone may have occurred with relatively little 10 to 20 sec radiation. Consideration of the amplitude and frequency content of the 1906 teleseismic data allowed us to estimate the scale length of the largest asperity to be less than about 40 km. With rough constraints on the largest asperity (size and magnitude) we produced a suite of estimated synthetic ground velocities assuming a slip distribution similar to that of the Loma Prieta earthquake but with three times as much slip. For purposes of comparison with the recent, abundant Loma Prieta strong motion data set, we “moved” the largest 1906 asperity into Loma Prieta region. Peak ground velocity amplitudes are substantially greater than those recorded during the Loma Prieta earthquake, and are comparable to those predicted by the attenuation relationship of Joyner and Boore (1988) for a magnitude MW = 7.7 earthquake.
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Bai, Qipeng, Sidao Ni, Risheng Chu, and Zhe Jia. "gCAPjoint, A Software Package for Full Moment Tensor Inversion of Moderately Strong Earthquakes with Local and Teleseismic Waveforms." Seismological Research Letters 91, no. 6 (August 19, 2020): 3550–62. http://dx.doi.org/10.1785/0220200031.
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Abstract Earthquake moment tensors and focal depths are crucial to assessing seismic hazards and studying active tectonic and volcanic processes. Although less powerful than strong earthquakes (M 7+), moderately strong earthquakes (M 5–6.5) occur more frequently and extensively, which can cause severe damages in populated areas. The inversion of moment tensors is usually affected by insufficient local waveform data (epicentral distance <5°) in sparse seismic networks. It would be necessary to combine local and teleseismic data (epicentral distance 30°–90°) for a joint inversion. In this study, we present the generalized cut-and-paste joint (gCAPjoint) algorithm to jointly invert full moment tensor and centroid depth with local and teleseismic broadband waveforms. To demonstrate the effectiveness and explore the limitations of this algorithm, we perform case studies on three earthquakes with different tectonic settings and source properties. Comparison of our results with global centroid moment tensor and other catalog solutions illustrates that both non-double-couple compositions of the focal mechanisms and centroid depths can be reliably recovered for very shallow (<10 km) earthquakes and intermediate-depth events with this software package.
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Ma, Shutian, and Dariush Motazedian. "Focal depth distribution of the 1982 Miramichi earthquake sequence determined by modelling depth phases." Canadian Journal of Earth Sciences 54, no. 4 (April 2017): 359–69. http://dx.doi.org/10.1139/cjes-2016-0111.
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On 9 January 1982, in the Miramichi region of New Brunswick, Canada, an earthquake with body-wave magnitude (mb) 5.7 occurred, and extensive aftershocks followed. The mainshock was felt throughout Eastern Canada and New England, USA. The mainshock and several principal aftershocks were digitally recorded worldwide, but smaller aftershocks were digitally recorded only at regional stations. Digital stations were not yet popular in 1982; therefore, available regional digital waveform records for modelling are very limited. Fortunately, two Eastern Canada Telemetered Network (ECTN) stations, EBN and KLN, produced excellent waveform records for most of the aftershocks until their closure at the end of 1990. The waveform records can be retrieved from the archive database at the Geological Survey of Canada (GSC). Since EBN had clear sPmP records of the larger aftershocks (with magnitude mN ≥ 2.8), we were able to determine focal depths for these larger events. Most of the focal depth solutions for the 113 larger aftershocks were within a depth range of 3–6 km. The majority of the depths were at about 4.5 km. Some aftershocks had depths of about 1–2 km. The focal depth solutions for the shallow events were confirmed by the existence of prominent crustal Rayleigh waves. As the records for the foreshock and the mainshock at EBN were not available, we used the records at station LMN for the foreshock and a teleseismic depth phase for the mainshock. The teleseismic depth phase comparison shows that the mainshock and its three principal aftershocks migrated from a depth of about 7 km to near the Earth’s surface.
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Finlay, Tori S., Lindsay L. Worthington, Brandon Schmandt, Nishath R. Ranasinghe, Susan L. Bilek, and Richard C. Aster. "Teleseismic Scattered‐Wave Imaging Using a Large‐N Array in the Albuquerque Basin, New Mexico." Seismological Research Letters 91, no. 1 (October 30, 2019): 287–303. http://dx.doi.org/10.1785/0220190146.
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Abstract The advent of low‐cost continuously recording cable‐free autonomous seismographs, commonly referred to as nodes, enables dense spatiotemporal sampling of seismic wavefields. We create virtual source reflection profiles using P waves from five teleseismic events recorded by the Sevilleta node array experiment in the southern Albuquerque basin. The basin geology records a structurally complex history, including multiple Phanerozoic orogenies, Rio Grande rift extension, and ongoing uplift from a midcrustal magma body. The Sevilleta experiment densified the long term, regionally sparse seismograph network with 801 single channel vertical‐component 10 Hz geophone nodes deployed at ∼300 m spacing for 14 days in February 2015. Results show sediment‐basement reflections at <5 km depth and numerous sub‐basin structures. Comparisons to legacy crustal‐scale reflection images from the Consortium for Continental Reflection Profiling show agreement with structural geometries in the rift basin and upper crust. Comparisons of the teleseismic virtual reflection profiles to synthetic tests using 2D finite‐difference elastic wave propagation show strong P‐to‐Rayleigh scattering from steep basin edges. These high‐amplitude conversions dominate the record sections near the western rift margin and originate at the Loma Pelada fault, which acts as the primary contact between rift‐bounding basement‐cored fault blocks and rift basin sediments. At near offsets, these signals may interfere with interpretation of upper crustal structure, but their relatively slow moveout compared to teleseismic P‐wave multiples provides clear temporal separation from sediment‐basement reflections across most of the array. The high‐signal‐to‐noise ratio of these converted Rayleigh‐wave signals suggests that they may be useful for constraining short‐period (∼1 Hz) dispersion with strong sensitivity in the uppermost ∼1 km of the rift basin sediments.
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Shi, Huiyan, Tonglin Li, Rui Sun, Gongbo Zhang, Rongzhe Zhang, and Xinze Kang. "Insights from the P Wave Travel Time Tomography in the Upper Mantle Beneath the Central Philippines." Remote Sensing 13, no. 13 (June 23, 2021): 2449. http://dx.doi.org/10.3390/rs13132449.
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In this paper, we present a high resolution 3-D tomographic model of the upper mantle obtained from a large number of teleseismic travel time data from the ISC in the central Philippines. There are 2921 teleseismic events and 32,224 useful relative travel time residuals picked to compute the velocity structure in the upper mantle, which was recorded by 87 receivers and satisfied the requirements of teleseismic tomography. Crustal correction was conducted to these data before inversion. The fast-marching method (FMM) and a subspace method were adopted in the forward step and inversion step, respectively. The present tomographic model clearly images steeply subducting high velocity anomalies along the Manila trench in the South China Sea (SCS), which reveals a gradual changing of the subduction angle and a gradual shallowing of the subduction depth from the north to the south. It is speculated that the change in its subduction depth and angle indicates the cessation of the SCS spreading from the north to the south, which also implies that the northern part of the SCS opened earlier than the southern part. Subduction of the Philippine Sea (PS) plate is exhibited between 14° N and 9° N, with its subduction direction changing from westward to eastward near 13° N. In the range of 11° N–9° N, the subduction of the Sulu Sea (SS) lies on the west side of PS plate. It is notable that obvious high velocity anomalies are imaged in the mantle transition zone (MTZ) between 14° N and 9° N, which are identified as the proto-SCS (PSCS) slabs and paleo-Pacific (PP) plate. It extends the location of the paleo-suture of PSCS-PP eastward from Borneo to the Philippines, which should be considered in studying the mechanism of the SCS and the tectonic evolution in SE Asia.
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Jin, Ping, Changzhou Pan, Chengliu Zhang, Xufeng Shen, Hongchun Wang, and Na Lu. "A novel progressive signal association algorithm for detecting teleseismic/network-outside events using regional seismic networks." Geophysical Journal International 201, no. 3 (April 17, 2015): 1950–60. http://dx.doi.org/10.1093/gji/ggv113.
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Casas, José Augusto, Gabriela Alejandra Badi, Luis Franco, and Deyan Draganov. "Seismic interferometry applied to regional and teleseismic events recorded at Planchón-Peteroa Volcanic Complex, Argentina-Chile." Journal of Volcanology and Geothermal Research 393 (March 2020): 106805. http://dx.doi.org/10.1016/j.jvolgeores.2020.106805.
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Agalos, A., P. Papadimitriou, N. Voulgaris, and K. Makropoulos. "Source parameters estimation from broadband regional seismograms for earthquakes in the Aegean region and the Gorda plate." Bulletin of the Geological Society of Greece 40, no. 3 (June 5, 2018): 1032. http://dx.doi.org/10.12681/bgsg.16795.
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Seismic moment tensors are estimated for earthquakes offshore Northern California and Greece using inversion of regionally recorded broadband seismograms. This study includes inversion results for the strongest events that occurred inside the Gorda plate and near the Mendocino triple junction from 1991 to 2005. The regional results are in good agreement with obtained teleseismic results. We finally applied the moment tensor inversion methodology and validation mainly to moderate sized earthquakes, with magnitude greater than M~4.0, in the Aegean area. The focal mechanisms of HI earthquakes that occurred during the time period between June 2003 and March 2007 were estimated using this procedure.
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Bello, Mohammed, David G. Cornwell, Nicholas Rawlinson, Anya M. Reading, and Othaniel K. Likkason. "Crustal structure of southeast Australia from teleseismic receiver functions." Solid Earth 12, no. 2 (February 24, 2021): 463–81. http://dx.doi.org/10.5194/se-12-463-2021.
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Abstract. In an effort to improve our understanding of the seismic character of the crust beneath southeast Australia and how it relates to the tectonic evolution of the region, we analyse teleseismic earthquakes recorded by 24 temporary and 8 permanent broadband stations using the receiver function method. Due to the proximity of the temporary stations to Bass Strait, only 13 of these stations yielded usable receiver functions, whereas seven permanent stations produced receiver functions for subsequent analysis. Crustal thickness, bulk seismic velocity properties, and internal crustal structure of the southern Tasmanides – an assemblage of Palaeozoic accretionary orogens that occupy eastern Australia – are constrained by H–κ stacking and receiver function inversion, which point to the following: a ∼ 39.0 km thick crust; an intermediate–high Vp/Vs ratio (∼ 1.70–1.76), relative to ak135; and a broad (> 10 km) crust–mantle transition beneath the Lachlan Fold Belt. These results are interpreted to represent magmatic underplating of mafic materials at the base of the crust. a complex crustal structure beneath VanDieland, a putative Precambrian continental fragment embedded in the southernmost Tasmanides, that features strong variability in the crustal thickness (23–37 km) and Vp/Vs ratio (1.65–193), the latter of which likely represents compositional variability and the presence of melt. The complex origins of VanDieland, which comprises multiple continental ribbons, coupled with recent failed rifting and intraplate volcanism, likely contributes to these observations. stations located in the East Tasmania Terrane and eastern Bass Strait (ETT + EB) collectively indicate a crust of uniform thickness (31–32 km), which clearly distinguishes it from VanDieland to the west. Moho depths are also compared with the continent-wide AusMoho model in southeast Australia and are shown to be largely consistent, except in regions where AusMoho has few constraints (e.g. Flinders Island). A joint interpretation of the new results with ambient noise, teleseismic tomography, and teleseismic shear wave splitting anisotropy helps provide new insight into the way that the crust has been shaped by recent events, including failed rifting during the break-up of Australia and Antarctica and recent intraplate volcanism.
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Lay, Thorne. "Direct Estimation of Explosion Pn Green’s Functions Applied to Teleseismic P-wave Intercorrelations for North Korean Nuclear Tests." Seismic Record 2, no. 1 (January 1, 2022): 11–19. http://dx.doi.org/10.1785/0320210045.
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Abstract Seismic yields and explosion source time functions for the six declared underground nuclear tests at the North Korean test site are estimated using teleseismic waveform equalization (intercorrelation) incorporating improved source structure inferred from regional distance Pn phases. Explosion source time functions estimated by previous modeling efforts are deconvolved from the broadband Pn observations to extract direct estimates of the Pn Green’s functions. Very consistent signals are found for station MDJ (to the north) for all but the 2006 event, and a 1D layered elastic model is determined that matches the corresponding pPn signals for the larger events. The much simpler Pn Green’s functions found for INCN (to the south) are well modeled using a half-space structure. The 1D structures are incorporated into intercorrelations for teleseismic P observations. Very similar results are found using the layered MDJ model for all azimuths, or when azimuthally varying the source velocity model to have a half-space structure for stations to the south, and/or using a half-space structure for the 2006 event at all azimuths. The relative yield estimates from intercorrelation are thus stable with respect to specific 1D source structures; the full effects of 3D elastic and nonelastic structures are yet to be considered.
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Silvennoinen, Hanna, Elena Kozlovskaya, and Eduard Kissling. "POLENET/LAPNET teleseismic <i>P</i> wave travel time tomography model of the upper mantle beneath northern Fennoscandia." Solid Earth 7, no. 2 (March 24, 2016): 425–39. http://dx.doi.org/10.5194/se-7-425-2016.
Full textAbstract:
Abstract. The POLENET/LAPNET (Polar Earth Observing Network) broadband seismic network was deployed in northern Fennoscandia (Finland, Sweden, Norway, and Russia) during the third International Polar Year 2007–2009. The array consisted of roughly 60 seismic stations. In our study, we estimate the 3-D architecture of the upper mantle beneath the northern Fennoscandian Shield using high-resolution teleseismic P wave tomography. The P wave tomography method can complement previous studies in the area by efficiently mapping lateral velocity variations in the mantle. For this purpose 111 clearly recorded teleseismic events were selected and the data from the stations hand-picked and analysed. Our study reveals a highly heterogeneous lithospheric mantle beneath the northern Fennoscandian Shield though without any large high P wave velocity area that may indicate the presence of thick depleted lithospheric “keel”. The most significant feature seen in the velocity model is a large elongated negative velocity anomaly (up to −3.5 %) in depth range 100–150 km in the central part of our study area that can be followed down to a depth of 200 km in some local areas. This low-velocity area separates three high-velocity regions corresponding to the cratonic units forming the area.
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Pacheco, Javier F., and Shri Krishna Singh. "Estimation of Ground Motions in the Valley of Mexico from Normal-Faulting, Intermediate-Depth Earthquakes in the Subducted Cocos Plate." Earthquake Spectra 11, no. 2 (May 1995): 233–47. http://dx.doi.org/10.1193/1.1585813.
Full textAbstract:
The Valley of Mexico is exposed to seismic risk from normal-faulting, large intermediate-depth earthquakes. We explore two approaches to estimate future ground motions from such events at CU, a hill-zone site in the valley. In the first we obtain parameters of an ω2 seismic source model and determine amplification of seismic waves due to local site effects at CU. This permits estimation of Fourier spectrum of expected ground motion at CU from postulated earthquakes. We find that the S-waves suffer an amplification of 2.5 between 0.2 to 3.0 Hz. This amplification is similar to that observed from deep teleseismic events but differs from that obtained from shallow coastal events. In the second approach the available recordings at CU are used as empirical Green's functions (EGF) to synthesize motions from future large earthquakes. This approach is very powerful if the smaller event is truly an empirical Green's function for the postulated earthquake.