Relevant bibliographies by topics / Backazimuth determination

Academic literature on the topic 'Backazimuth determination'

Author: Grafiati
Published: 10 December 2022
Last updated: 19 February 2023

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Journal articles on the topic "Backazimuth determination"

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Lin, Cheng-Horng, and S. W. Roecker. "P-wave backazimuth anomalies observed by a small-aperture seismic array at Pinyon Flat, southern California: Implications for structure and source location." Bulletin of the Seismological Society of America 86, no. 2 (April 1, 1996): 470–76. http://dx.doi.org/10.1785/bssa0860020470.

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Abstract Seismograms of earthquakes and explosions recorded at local, regional, and teleseismic distances by a small-aperture, dense seismic array located on Pinyon Flat, in southern California, reveal large (±15°) backazimuth anomalies. We investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques: the broadband frequency-wavenumber (BBFK) technique, the polarization technique, and the beamforming technique. While each technique provided nearly the same direction as a most likely estimate, the beamforming estimate was associated with the smallest uncertainties. Backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the Anza and Caltech seismic networks and the Preliminary Determination of Epicenters (PDE) Bulletin. These backazimuth anomalies have a simple sinelike dependence on azimuth, with the largest anomalies observed from the southeast and northwest directions. Such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array. A best-fit model of a single interface has a dip and strike of 20° and 315°, respectively, and a velocity contrast of 0.82 km/sec. Application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions, suggesting that this is an upper crustal feature. We confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models.
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Pirli, M., E. Pirlis, and N. Voulgaris. "Mislocation vectors for the Tripoli seismic array, Greece, and structural effect implications from backazimuth and slowness residual analysis." Bulletin of the Geological Society of Greece 40, no. 3 (June 5, 2018): 1234. http://dx.doi.org/10.12681/bgsg.16876.

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Tripoli Seismic Array, Greece, performance in terms of event location is restricted by its very small aperture and limited number of sensors. Detailed investigation of errors in automatic location results suggests structural and local geology effects. In order to investigate the possibility to correct for systematic errors automatically, mis location vectors were calculated for an extended data-set. Theoretical values were calculated based on earthquake catalogues compiled by the National Observatory of Athens and the ISC. Resulting mis location vectors are characterized by significant vector length, consistent with the large observed backazimuth and slowness residuals, the smaller values being met in the area NE of the array and for epicentral distance values less than 200 km. As expected, resulting corrections mostly concern backazimuth values and are not able to sufficiently affect the final epicentre solution, as the largest automatic algorithm errors are observed in epicentral distance determination. However, the possibility to automatically correct for systematic deviations is verified, and future research with an extended array configuration is expected to provide clearer results, due to significantly lower scatter.
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Nakamura, Ayako, Shigeki Horiuchi, and Akira Hasegawa. "Joint focal mechanism determination with source-region station corrections using short-period body-wave amplitude data." Bulletin of the Seismological Society of America 89, no. 2 (April 1, 1999): 373–83. http://dx.doi.org/10.1785/bssa0890020373.

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Abstract We have developed a method that simultaneously determines focal mechanism solutions of many small earthquakes and source-region station corrections for short-period body-wave amplitudes by inverting amplitude data of P, SH, and SV waves, together with P-wave polarity data. The observed seismic waveform includes the effects of site amplification and attenuation along its ray path in addition to the radiation pattern of earthquake source. The amplitude of seismograms at frequencies higher than a few Hertz is extremely sensitive to heterogeneous structure near the ground surface. Consequently, we need to know in detail the effects of site amplification and attenuation in order to estimate focal mechanisms by using short-period waveforms. However, at present, we do not know the detailed crustal structure with a resolution necessary for this estimation. In the present study, we assume that P- and S-wave attenuation factors along ray paths from hypocenters to each station can be expressed as a function of hypocentral distance, backazimuth, and incident angle. Based on this assumption, we determined focal mechanism solutions of many earthquakes and the coefficients in the function for each station simultaneously, by using P-, SH-, and SV-wave amplitudes and P-wave polarities. We applied the present method to 170 aftershocks of the 1996 Onikobe earthquake (M 5.9), which occurred in the central part of northeastern Japan. We obtained focal mechanism solutions of many microearthquakes whose mechanism solutions could not be determined by using P-wave polarity data alone. P axes of almost all the obtained focal mechanism solutions are horizontal and oriented in the east-west direction. T axes are, on average, near vertical at the shallowest depth. As the depth approaches 5 km, the T axes become horizontal and then gradually become near vertical again.
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Pirli, M., Ν. Voulgaris, J. Alexopoulos, and K. Makropoulos. "INSTALLATION AND PRELIMINARY RESULTS FROM A SMALL APERTURE SEISMIC ARRAY IN TRIPOLI, GREECE." Bulletin of the Geological Society of Greece 36, no. 3 (January 1, 2004): 1499. http://dx.doi.org/10.12681/bgsg.16540.

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A small aperture seismic array was installed by the University of Athens, in the area of Tripoli, Greece, on July 16th 2003, in order to test the performance of seismic array processing in the area of Greece and assess its contribution to earthquake location, especially in offshore areas not azimuthally covered by the existing, conventional seismological networks. The array consists of four three-component seismological stations, one of them in the middle of a small, almost equilateral triangle, formed by the deployment of the other three stations. Despite the fact that array siting is a compromise of array installation criteria, equipment safety and logistics, the test character of the experiment can be served successfully. The array transfer function depicts good azimuthal coverage nonetheless the existence of side-lobes and a rather wide main lobe is characteristic of spatial aliasing and low resolution in the two-dimensional wavenumber domain. The resolvable wavenumber passband of the array permits the determination of most of the common seismic body wave phases (Pn, Pg, Sn, Sg, etc.) for local and regional events in the area of Greece. Location of recorded events was performed using slowness and backazimuth data, calculated by f-k analysis of the seismic waveforms. Preliminary results have been compared to epicentres calculated by the Geodynamic Institute of the National Observatory of Athens. Although some differences are observed, these are not significant and location results as well as overall array performance can be improved by array calibration and travel-time, azimuth and slowness correction calculations.
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Ritter, Joachim R. R., Yvonne Fröhlich, Yasmin Sanz Alonso, and Michael Grund. "Short-scale laterally varying SK(K)S shear wave splitting at BFO, Germany — implications for the determination of anisotropic structures." Journal of Seismology, October 6, 2022. http://dx.doi.org/10.1007/s10950-022-10112-w.

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AbstractThe splitting of SK(K)S phases is an important observational constraint to study past and present geodynamic processes in the Earth based on seismic anisotropy. The uniqueness of the derived models is unclear in most cases, because the azimuthal data coverage is often limited due to recordings from only a few backazimuthal directions. Here, we analyze an exceptional dataset from the permanent broadband seismological recording station Black Forest Observatory (BFO) in SW Germany with a very good backazimuthal coverage. This dataset well represents the potential teleseismic ray paths, which can be observed at Central European stations. Our results indicate that averaging splitting parameters over a wide or the whole backazimuthal range can blur both vertical and lateral variations of anisotropy. Within the narrow backazimuthal interval of 30–100°, we observe a complete flip of the fast polarization direction. Such a splitting pattern can be caused by two layers with about NW–SE (lower layer) and NE-SW (upper layer) fast polarization directions for shear wave propagation. However, the possible model parameters have quite a large scatter and represent only the structure to the northeast of BFO. In contrast, within the wide backazimuthal range 155–335°, we prevailingly determine null splits, hence, no signs for anisotropy. This null anomaly cannot be explained satisfactorily yet and is partly different to published regional anisotropy models. Our findings demonstrate that there is significant small-scale lateral variation of upper mantle anisotropy below SW Germany. Furthermore, even low-noise long-term recording over 25 years cannot properly resolve these anisotropic structural variations.
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Dissertations / Theses on the topic "Backazimuth determination"

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(12547160), Jennifer Kay Hafner. "Earthquake backazimuth determination using a single three-component digital seismograph." Thesis, 1997. https://figshare.com/articles/thesis/Earthquake_backazimuth_determination_using_a_single_three-component_digital_seismograph/19769053.

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Earthquake backazimuth estimation using a single three -component digital seismograph has been investigated. A three-dimensional principal components method formed the basic computational technique. Other details of the backazimuth estimation procedure were varied to determine the optimum approach. The data set comprised aftershocks of the 1988 Tennant Creek earthquakes, recorded on a number of stations in, or close to, the source zone. Epicentral distances (3.5 to 25 km) were unusually small compared to the data sets of others who have used similar techniques.

Complex geology challenged the accuracy of results. The most likely causes of error were believed to be the interruption of source -receiver wave travel paths by fault planes, and complex site geology. This included outcrops of highly deformed rocks, and proximity to a large intrusive body of anomalous character. Errors of 180° were common, possibly due to the low velocity surface layers.

Single station estimates were compared to reference backazimuths from network locations, determined by "EQLOCL" (SRC, RMIT), a program based on the least -squares travel -time approach. Approximately 75% of backazimuth discrepancies, projected into the range -90 to +90°, were less than or equal to 20°. This outcome indicates that the investigated technique can be successfully used to estimate earthquake backazimuth in at least some complex geologic receiver settings, and at short epicentral distances.

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Conference papers on the topic "Backazimuth determination"

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Fischer, T., L. Eisner, S. Buske, and S. Shapiro. "Determination of S-wave Backazimuth from a Linear Array of Receivers." In 70th EAGE Conference and Exhibition - Workshops and Fieldtrips. European Association of Geoscientists & Engineers, 2008. http://dx.doi.org/10.3997/2214-4609.20147853.

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