Journal articles: 'Focal Depths'

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Yun, Sukyoung, Won Sang Lee, Robert P. Dziak, and Haruyoshi Matsumoto. "Numerical Study on the Characteristics of Abyssal T-Wave Envelopes Controlled by Earthquake Source Parameters." Seismological Research Letters 93, no. 4 (April 19, 2022): 2189–200. http://dx.doi.org/10.1785/0220210264.

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Abstract Hydroacoustics has been successfully applied to detect and locate small-to-intermediate submarine tectonic activities infrequently recorded in land-based seismic arrays. However, to extend the utilization of T waves to extract other important earthquake source parameters, such as source strength, the roles of earthquake focal mechanisms, and source depths in T-wave envelopes must be thoroughly understood. We performed 3D numerical modeling considering anisotropic source radiation and realistic scattering in the oceanic crust for two focal mechanisms (normal and strike-slip faults) and three depths (5, 10, and 15 km) to investigate the effect of source radiation and focal depth on abyssal T waves. By analyzing the synthetic T-wave envelopes, we showed that stronger SV-energy radiation from a normal-fault earthquake event generates higher-intensity T waves of the same source magnitude. The anisotropic source radiation of a double-couple source causes azimuthal changes in the shapes of T waves, and deeper earthquakes cause gentle-sloped envelopes; however, the slopes also vary with respect to the azimuths of receivers and focal mechanisms. Temporal changes in the slopes of T-wave envelopes of magmatic swarm events near Wordie Volcano, Bransfield Strait, Antarctic Peninsula, imply that the depth dependency can be utilized to determine relative depths for hydrothermal-vent events or sequenced earthquakes.

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Szeidovitz, Gy, Z. Bus, and K. Gribovszki. "Focal depths of earthquakes in the Carpathian Basin." Acta Geodaetica et Geophysica Hungarica 39, no. 4 (November 2004): 447–70. http://dx.doi.org/10.1556/ageod.39.2004.4.13.

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Wang, Yaheng, Li Yi, Masayoshi Tonouchi, and Tadao Nagatsuma. "High-Speed 600 GHz-Band Terahertz Imaging Scanner System with Enhanced Focal Depth." Photonics 9, no. 12 (November 28, 2022): 913. http://dx.doi.org/10.3390/photonics9120913.

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Lenses/mirrors with fast data acquisition speeds and extended focal depths have practical importance in terahertz (THz) imaging systems. Thus, a high-speed 600 GHz-band THz imaging scanner system with enhanced focal depth is presented in this work. A polygon mirror with a 250 Hz scanning frequency and an integrated off-axis parabolic (OAP) mirror with an ~170 mm focal depth were employed for 2D imaging. The simulation and experimental results show that a spatial resolution of ~2 mm can be achieved as the imaging distance varies from ~85 to 255 mm. The proposed system was applied to image a hidden metal object as a potential security application, demonstrating that this system can image targets with an enhanced focal depth.

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Palmeri, Mark L., Kristin D. Frinkley, Katherine G. Oldenburg, and Kathryn R. Nightingale. "Characterizing Acoustic Attenuation of Homogeneous Media Using Focused Impulsive Acoustic Radiation Force." Ultrasonic Imaging 28, no. 2 (April 2006): 114–28. http://dx.doi.org/10.1177/016173460602800204.

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A new method to characterize a material's attenuation using acoustic radiation force is proposed. Comparison of displacement magnitudes generated in a homogeneous material by acoustic radiation force excitations can be used to estimate the material's attenuation when the excitations are applied over a range of focal depths while maintaining a constant lateral focal configuration. Acoustic attenuations are related to the inverse of the excitation focal depth that yields the greatest focal zone displacement for this protocol. Experimental studies in calibrated tissue-mimicking phantoms are presented to demonstrate the feasibility of this method. Attenuations ranging from 0.3–1.5 dB/cm/MHz were characterized over excitation focal depths ranging from 5–30 mm, with an accuracy of 0.1 ± 0.15 dB/cm/MHz. As currently implemented, this method is limited to characterizing materials that have homogeneous material properties and acoustic attenuations. This method for characterizing acoustic attenuation can be performed using conventional diagnostic scanners without any additional hardware and could also be performed concurrently with acoustic radiation force-based imaging modalities to generate images of mechanical properties and attenuation that are spatially co-registered with B-mode images.

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Nguyen, Thanh Phuoc, Van Tu Nguyen, Sudip Mondal, Van Hiep Pham, Dinh Dat Vu, Byung-Gak Kim, and Junghwan Oh. "Improved Depth-of-Field Photoacoustic Microscopy with a Multifocal Point Transducer for Biomedical Imaging." Sensors 20, no. 7 (April 3, 2020): 2020. http://dx.doi.org/10.3390/s20072020.

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In this study, a photoacoustic microscopy (PAM) system based on a multifocal point (MFP) transducer was fabricated to produce a large depth-of-field tissue image. The customized MFP transducer has seven focal points, distributed along with the transducer’s axis, fabricated by separate spherically-focused surfaces. These surfaces generate distinct focal zones that are overlapped to extend the depth-of-field. This design allows extending the focal zone of 10 mm for the 11 MHz MFP transducer, which is a great improvement over the 0.48 mm focal zone of the 11 MHz single focal point (SFP) transducer. The PAM image penetration depths of a chicken-hemoglobin phantom using SFP and MFP transducers were measured as 5 mm and 8 mm, respectively. The significant increase in the PAM image-based penetration depth of the chicken-hemoglobin phantom was a result of using the customized MFP transducer.

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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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Li, Chuan, Wenqi Gao, Youxue Wang, and Songping Yu. "Accurate Redetermination of the Focal Depth by Using the Time Intervals between the Inner Core Phases PKIKP and pPKIKP." Applied Sciences 12, no. 15 (July 29, 2022): 7669. http://dx.doi.org/10.3390/app12157669.

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The hypocenter parameters of an earthquake may give us an insight into the Earth’s structure and tectonic processes. Among the hypocenter parameters, the focal depth is normally more difficult to estimate than the earthquake location (latitude and longitude). We propose to use the pPKIKP-PKIKP arrival time intervals for estimating the focal depth. We analyze the sensitivity of the pPKIKP-PKIKP arrival time interval to the earthquake depth. We measure the pPKIKP-PKIKP arrival time interval on seismograms (the vertical component), and invert the time interval data set using the simulated annealing inversion algorithm. We illustrate the inversion approach on two teleseismic earthquakes which have shallow and deep focal depths, and demonstrate that the approach is indeed appropriate to the shallow and deep event. We can obtain a reliable estimate on focal depth, even though the seismic station is sparse or in a remote part of the epicenter.

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González-Salido, Nuria, and Jorge Camacho. "Normalization of Multifocal Acoustic Radiation Force Impulse Images." Archives of Acoustics 42, no. 2 (June 27, 2017): 321–31. http://dx.doi.org/10.1515/aoa-2017-0034.

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Abstract Imaging the tissue displacements caused by Acoustic Radiation Force Impulse (ARFI) provides qualitative tissue elasticity maps around the focus. To increase imaging range, multi-focus techniques combine several images obtained with different focal depths. Since the acoustic radiation force depends on focus depth, axial distance and steering angle, a normalization process is required before blending multi-focal ARFI images so that changes in the displayed displacements represent true tissue elasticity variations. This work analyzes the sources of displacement variability in multi-focal-zone ARFI and proposes a procedure to normalize and combine partial images. The proposal is based on the system focal configuration, transducer characteristics and global tissue parameters found by ultrasonic measurements. Performance of the proposed algorithm is experimentally evaluated with tissue mimicking phantoms.

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Plourde, Alexandre P., and Mladen R. Nedimović. "Earthquake Depths, Focal Mechanisms, and Stress in the Lower St. Lawrence Seismic Zone." Seismological Research Letters 92, no. 4 (May 5, 2021): 2562–72. http://dx.doi.org/10.1785/0220200429.

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Abstract We examine earthquake hypocenters, focal mechanisms, and the state of tectonic stress in the Lower St. Lawrence Seismic Zone (LSZ), a paleorift zone in eastern Canada. The largest earthquake recorded in the region is the 1999 Côte–Nord MN 5.1, which was followed by ∼80 aftershocks of MN>1. It is not known if the region is capable of producing hazardous Mw>6 earthquakes, similar to the Charlevoix Seismic Zone ∼250 km upriver. Focusing on 2015–2020, we apply a machine-learning-based phase picker to detect 72 earthquakes in addition to the 150 catalog earthquakes in the same region over this time span. We produce an updated 1D, gradient velocity model via a Monte Carlo search using a uniform VP/VS=1.77, which we computed with the Wadati method. We refine hypocenter estimates using the triple-difference method, with sP depth phases as additional constraints on earthquake depth. We estimate focal mechanisms for >100 earthquakes with automatically picked P-wave first motions and absolute value P-SV-SH amplitude ratios, and we use the focal mechanisms to invert for the state of tectonic stress. Grid searches and Bayesian analysis allow for robust uncertainty estimates of focal mechanisms, which in turn allow for uncertainty estimates of the stress tensor. The recovered west-northwest–east-southeast σ1 is consistent with previous estimates and with a stress tensor controlled by glacial isostatic adjustment, although a contrast between deep and shallow focal mechanisms suggests that these stresses may be concentrated in the lower crust. Epicenter lineations up to ∼40 km long may be indicative of sizable faults in the LSZ capable of generating Mw>6 earthquakes, but hypocenter and focal mechanism uncertainties are too high to say so definitively, thus pointing to a need for denser station coverage, including ocean-bottom seismometers.

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Kulchitsky, V. E., B. G. Pustovitenko, and V. A. Svidlova. "Focal Depths of Earthquakes in the Crimea–Black Sea Region." Seismic Instruments 54, no. 3 (May 2018): 340–61. http://dx.doi.org/10.3103/s0747923918030155.

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Radziminovich, N. A. "Focal depths of earthquakes in the Baikal region: A review." Izvestiya, Physics of the Solid Earth 46, no. 3 (March 2010): 216–29. http://dx.doi.org/10.1134/s1069351310030043.

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Dong, Yibing, Sidao Ni, David A. Yuen, and Zhiwei Li. "Crustal rheology from focal depths in the North China Basin." Earth and Planetary Science Letters 497 (September 2018): 123–38. http://dx.doi.org/10.1016/j.epsl.2018.06.018.

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Hu, Huakui, Fulin Cao, and Yue Zhao. "Extending Focal Depth of Flower-Shaped Optical Vortex with Composited Spiral Zone Plate Grating." Photonics 9, no. 6 (May 25, 2022): 371. http://dx.doi.org/10.3390/photonics9060371.

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By combining a spiral zone plate (SZP) and a grating, we propose a single optical element, termed a composited spiral zone plate grating (CSZPG), to generate flower mode vortices with the equicohesive petals and has long focal depths. Theoretical analysis reveals that the CSZPG can generate flower mode vortices with approximately equicohesive petals, and that it has longer focal depths compared with the conventional SZP. Moreover, the performance of the CSZPG on the period, focal length and radius is investigated. The experimental results are also presented, agreeing well with the theoretical predictions. The unique characteristics of the proposed CSZPG make it attractive for many applications such as particle trapping and optical imaging.

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Martinez, P., M. Beaulieu, K. Barjot, O. Guyon, C. Gouvret, A. Marcotto, M. Belhadi, et al. "Design and manufacturing of a multi-zone phase-shifting coronagraph mask for extremely large telescopes." Astronomy & Astrophysics 635 (March 2020): A126. http://dx.doi.org/10.1051/0004-6361/201936903.

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Context. High-contrast imaging of exoplanets around nearby stars with future large-segmented apertures requires starlight suppression systems optimized for complex aperture geometries. Future extremely large telescopes (ELTs) equipped with high-contrast instruments operating as close as possible to the diffraction limit will open a bulk of targets in the habitable zone around M-stars. In this context, the phase-induced amplitude apodization complex mask coronagraph (PIAACMC) is a promising concept for high-efficiency coronagraphic imaging at small angular separations with segmented telescopes. Aims. The complex focal plane mask of the PIAACMC is a multi-zone, phase-shifting mask comprised of tiled hexagons that vary in depth. The mask requires micro-fabrication techniques because it is generally made of hundreds micron-scale hexagonal zones with depths ranging over a few microns. We aim to demonstrate that the complex focal plane mask of a PIAACMC with a small inner working angle can be designed and manufactured for segmented apertures. Methods. We report on the numerical design, specifications, manufacturing, and characterization of a PIAACMC complex focal plane mask for the segmented pupil experiment for exoplanet detection facility. Results. Our PIAACMC design offers an inner working angle of 1.3 λ/D and is optimized for a 30% telescope-central-obscuration ratio including six secondary support structures (ESO/ELT design). The fabricated reflective focal plane mask is made of 499 hexagons, and the characteristic size of the mask features is 25 μm, with depths ranging over ±0.4 μm. The mask sag local deviation is measured to an average error of 3 nm and standard deviation of 6 nm rms. The metrological analysis of the mask using interferential microscopy gives access to an in-depth understanding of the component’s optical quality, including a complete mapping of the zone depth distribution zone-depth distribution. The amplitude of the errors in the fabricated mask are within the wavefront control dynamic range. Conclusions. We demonstrate the feasibility of fabricating and characterizing high-quality PIAA complex focal plane masks.

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Alemayehu, Sisay, and Jima Asefa. "A Review of Earthquake Source Parameters in the Main Ethiopian Rift." International Journal of Geophysics 2023 (May 11, 2023): 1–14. http://dx.doi.org/10.1155/2023/8368175.

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We assessed earthquake source parameters compiled from previous studies and international databases. In addition, moment tensor inversion is made from the broadband seismic data of two earthquakes that occurred in the region in 2017 and 2018 with magnitudes Mw 5.0 and 5.1, respectively. As a result, the two events’ reliable source parameters are retrieved. We found that earthquakes are distributed in the rift floor, at margins and adjacent plateaus. Because the majority of earthquakes occur on the rift floor, deformation is most likely caused by strain accumulation transferred from border faults to magmatic segments along the rift floor. Predominantly normal faulting is observed, but some strike-slip events are also observed. Normal faulting mechanisms are consistent with major plate divergence, whereas the strike-slip components observed in the region might be associated with the counterclockwise rotation of the Danakil microplate, and the mechanism would indicate an oblique-slip deformation between the Nubian plate and the Danakil microplate. However, the focal mechanism obtained from the moment tensor inversion for the Mw 5.1 event indicates dominant normal faulting accompanied by a minor strike-slip component at the western margin of Afar, whereas the Mw 5.0 event has a significant strike-slip component at the central part of MER. The majority of focal depths of earthquakes are found within the upper crust, including the 2017 (Mw 5.0) event with a focal depth of 9.7 km that was computed using moment tensor inversion. A significant number of earthquakes are also found within the lower crust, including the 2018 (Mw 5.1) event with a focal depth of 20.2 km. However, earthquakes with focal depths within the upper mantle are also found in the compiled international database, which may not be consistent with the previously published works in the region. The observed focal depth may suggest a widespread deformation throughout the upper and lower crusts, implying that magmatic intrusions and faulting play a central role in facilitating the seismicity of the main Ethiopian rift (MER). The current investigation will provide further information on the earthquake source parameters and seismogenic depth of earthquake occurrence in the MER.

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Poulin, Andrew, Ron Weir, David Eaton, Nadine Igonin, Yukuan Chen, Laurence Lines, and Donald Lawton. "Focal-time analysis: A new method for stratigraphic depth control of microseismicity and induced seismic events." GEOPHYSICS 84, no. 6 (November 1, 2019): KS173—KS182. http://dx.doi.org/10.1190/geo2019-0046.1.

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Focal-time analysis is a straightforward data-driven method to obtain robust stratigraphic depth control for microseismicity or induced seismic events. The method eliminates the necessity to build an explicit, calibrated velocity model for hypocenter depth estimation, although it requires multicomponent 3D seismic data that are colocated with surface or near-surface microseismic observations. Event focal depths are initially expressed in terms of zero-offset focal time (two-way P-P reflection time) to facilitate registration and visualization with 3D seismic data. Application of the focal-time method requires (1) high-quality P- and S-wave time picks, which are extrapolated to zero offset and (2) registration of correlative P-P and P-S reflections to provide [Formula: see text] and [Formula: see text] time-depth control. We determine the utility of this method by applying it to a microseismic and induced-seismicity data set recorded with a shallow-borehole monitoring array in Alberta, Canada, combined with high-quality multicomponent surface seismic data. The calculated depth distribution of events is in good agreement with hypocenter locations obtained independently using a nonlinear global-search method. Our results reveal that individual event clusters have distinct depth distributions that can provide important clues about the mechanisms of fault activation.

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Wang, Qingdong, and Risheng Chu. "Earthquake Source Parameters in Southwestern China and Their Rheological Implications." Seismological Research Letters 91, no. 2A (January 2, 2020): 936–47. http://dx.doi.org/10.1785/0220190193.

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Abstract Earthquake depth distribution provides key information on rheological behavior of the crust, which usually shows a brittle–ductile transition at a depth of about 10 km. In this study, we use the generalized cut-and-paste method to obtain source parameters of 571 earthquakes in the Sichuan–Yunnan region of China between 2009 and 2017. We were able to successfully determine focal mechanisms, moment magnitudes, and centroid depths of 536 earthquakes with a minimum moment magnitude of 3.2. Our moment magnitudes and centroid depths are systematically smaller than the magnitudes (Ms and mb) and hypocenter depths from the China Earthquake Network Center and International Seismological Centre catalogs for M≥4.0 earthquakes. The earthquake depths in the Sichuan–Yunnan region are mostly in a 5–9 km range, with an average at 7.6 km. About 23% earthquakes have centroid depths <5 km and are concentrated in the southern Sichuan basin. Only very few earthquakes are deeper than 19 km. Compared with the earthquake depth distribution in southern California, the Sichuan–Yunnan region has many shallower earthquakes. The depth distribution suggests that the brittle–ductile transition in the Sichuan–Yunnan region is shallower than the transition beneath southern California, which is probably due to the existence of newborn faults in the Sichuan–Yunnan region.

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Bollinger, G. A., M. C. Chapman, M. S. Sibol, and J. K. Costain. "An analysis of earthquake focal depths in the southeastern U. S." Geophysical Research Letters 12, no. 11 (November 1985): 785–88. http://dx.doi.org/10.1029/gl012i011p00785.

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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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Olson, Jean A., and Mary Lou Zoback. "Source character of microseismicity in the San Francisco Bay block, California, and implications for seismic hazard." Bulletin of the Seismological Society of America 88, no. 2 (April 1, 1998): 543–55. http://dx.doi.org/10.1785/bssa0880020543.

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Abstract We examine relocated seismicity within a 30-km-wide crustal block containing San Francisco Bay and bounded by two major right-lateral strike-slip fault systems, the Hayward and San Andreas faults, to determine seismicity distribution, source character, and possible relationship to proposed faults. Well-located low-level seismicity (Md ≦ 3.0) has occurred persistently within this block throughout the recording interval (1969 to 1995), with the highest levels of activity occurring along or directly adjacent to (within ∼5 km) the bounding faults and falling off toward the long axis of the bay. The total seismic moment release within the interior of the Bay block since 1969 is equivalent to one ML 3.8 earthquake, one to two orders of magnitude lower than activity along and within 5 km of the bounding faults. Focal depths of reliably located events within the Bay block are generally less than 13 km with most seismicity in the depth range of 7 to 12 km, similar to focal depths along both the adjacent portions of the San Andreas and Hayward faults. Focal mechanisms for Md 2 to 3 events within the Bay block mimic focal mechanisms along the adjacent San Andreas fault zone and in the East Bay, suggesting that Bay block is responding to a similar regional stress field. Two potential seismic source zones have been suggested within the Bay block. Our hypocentral depths and focal mechanisms suggest that a proposed subhorizontal detachment fault 15 to 18 km beneath the Bay is not seismically active. Several large-scale linear NW-trending aeromagnetic anomalies within the Bay block were previously suggested to represent large through-going subvertical fault zones. The two largest earthquakes (both Md 3.0) in the Bay block since 1969 occur near two of these large-scale linear aeromagnetic anomalies; both have subvertical nodal planes with right-lateral slip subparallel to the magnetic anomalies, suggesting that structures related to the anomalies may be capable of brittle failure. Geodetic, focal mechanism and seismicity data all suggest the Bay block is responding elastically to the same regional stresses affecting the bounding faults; however, continuous Holocene reflectors across the proposed fault zones suggest that if the magnetic anomalies represent basement fault zones, then these faults must have recurrence times one to several orders of magnitude longer than on the bounding faults.

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DATTATRAYAM, R. S. "Earthquake source parameter estimation using synthetic waveform modelling." MAUSAM 43, no. 4 (December 31, 2021): 365–70. http://dx.doi.org/10.54302/mausam.v43i4.3503.

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Fault plane solutions and focal depths for three crustal events occurring in the Himalayan collision zone have been obtained using synthetic waveform modelling. Two crustal events with their epicenters in the Tibetan plateau show large component of normal faulting with east-west trading T-axes. The third event with It’s epicenter north of Main Boundary Thrust (MBT) shows reverse faulting with the nodal planes paralleling the local structural trend. All the three crustal events studied have occurred at shallow focal depths of less than 15 km. The Inferred source parameters of these events are discussed In the light of active tectonics of the region.

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Astiz, Luciana, and Hiroo Kanamori. "Interplate coupling and temporal variation of mechanisms of intermediate-depth earthquakes in Chile." Bulletin of the Seismological Society of America 76, no. 6 (December 1, 1986): 1614–22. http://dx.doi.org/10.1785/bssa0760061614.

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Abstract We investigated the temporal variation of the mechanism of large intraplate earthquakes at intermediate depths in relation to the occurrence of large under-thrusting earthquakes in Chile. Focal mechanisms were determined for three large events (1 March 1934: M = 7.1, d = 120 km; 20 April 1949: M = 7.3, d = 70 km; and 8 May 1971: MW = 7.2, d = 150 km) which occurred down-dip of the great 1960 Chilean earthquake (MW = 9.5) rupture zone. The 1971 event is down-dip compressional: θ (strike) = 12°, δ (dip) = 80°, and λ (rake) = 100°. The 1949 earthquake focal mechanisms is θ = 350°, δ = 70°, and λ = −130°. The data available for the 1934 event are consistent with a down-dip tensional mechanism. Thus, the two events which occurred prior to the great 1960 Chilean earthquake are down-dip tensional. Published fault plane solutions of large intermediate-depth earthquakes (28 March 1965 and 7 November 1981) which occurred down-dip of the Valparaiso earthquakes of 1971 (MW = 7.8) and 1985 (MW = 8.0) are also down-dip tensional. These results suggest that before a major thrust earthquake, the interplate boundary is strongly coupled, and the subducted slab is under tension at intermediate depths; after the occurrence of an interplate thrust event, the displacement on the thrust boundary induces transient compressional stress at intermediate depth in the down-going slab. This interpretation is consistent with the hypothesis that temporal variations of focal mechanisms of outer-rise events are due to changes of interplate coupling.

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Tralli, David M., and Lane R. Johnson. "Estimation of slowness-dependent source and receiver corrections for P-wave travel times." Bulletin of the Seismological Society of America 76, no. 6 (December 1, 1986): 1718–38. http://dx.doi.org/10.1785/bssa0760061718.

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Abstract Tectonically regionalized tau estimates are used to obtain seismic P-wave travel-time corrections for lateral variations in the Earth's crust and shallow-mantle velocity structure. The corrections, in the form of estimates of tau perturbations, are functions of slowness and are assessed for both the source and receiver regions. The functional form is derived analytically and allows interpretations of causative velocity anomalies. Corrections for both ray path endpoints constrain effects typically assigned solely to the receiver, thereby helping assess systematic errors in hypocentral parameters. Over 1.25 million ISC Bulletin P-wave ray paths are used to estimate tau perturbation functions for seven types of tectonic regions. Particular attention is given to the problem of uniformly sampling all tectonic regions at all propagation depths in the mantle. Estimates of source and receiver tau perturbations are consistently less than 1 sec and show a definite and systematic difference between the travel-time correction functions for oceans and continents. Source tau perturbations are indicative of negative velocity anomalies in the shallow mantle beneath oceanic regions and positive anomalies beneath continental regions and oceanic trenches. Heterogeneity confined to the upper 250 km of the mantle suggests velocity variations within ±5 per cent of the lateral mean over a depth interval of approximately 100 km. Differences between the receiver and source perturbations for a common tectonic region are attributed to variations in the characteristic crustal structure of the region, constrained by the receiver perturbation, and errors in origin time and/or focal depth, determined from the source perturbation. The estimates of perturbation functions therefore suggest systematic regional biases in crustal structure and hypocentral parameters. A less than average crustal thickness in oceanic regions and greater thickness in stable continental regions is indicated. Furthermore, it appears that the origin times of sources in oceanic regions are systematically determined too late and/or focal depths located too shallow, whereas origin times of sources in continental regions are systematically determined too early and/or focal depths located too deep.

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Mitra, Supriyo, Keith Priestley, Anjan Kr Bhattacharyya, and V. K. Gaur. "Crustal structure and earthquake focal depths beneath northeastern India and southern Tibet." Geophysical Journal International 160, no. 1 (December 21, 2004): 227–48. http://dx.doi.org/10.1111/j.1365-246x.2004.02470.x.

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Bai, Ling, Guohui Li, Nangyal G. Khan, Junmeng Zhao, and Lin Ding. "Focal depths and mechanisms of shallow earthquakes in the Himalayan–Tibetan region." Gondwana Research 41 (January 2017): 390–99. http://dx.doi.org/10.1016/j.gr.2015.07.009.

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Riazi, Naimeh, David W. Eaton, Alemayehu Aklilu, and Andrew Poulin. "Application of focal-time analysis for improved induced seismicity depth control: A case study from the Montney Formation, British Columbia, Canada." GEOPHYSICS 85, no. 6 (October 22, 2020): KS185—KS196. http://dx.doi.org/10.1190/geo2019-0833.1.

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Characterization of induced seismicity and associated microseismicity is an important challenge for enhanced oil recovery and development of tight hydrocarbon reservoirs. In particular, accurately correlating hypocenters of induced events to stratigraphic layers plays an important role in understanding the mechanisms of fault activation. Existing methods for estimating focal depth, however, are prone to a high degree of uncertainty. A comprehensive analysis of inferred focal depths is applied to induced events that occurred during completions of horizontal wells targeting the Montney Formation in British Columbia, Canada. Our workflow includes a probabilistic, nonlinear global-search algorithm (NonLinLoc), a hierarchical clustering algorithm for relative relocation (GrowClust), and depth refinement using the recently developed focal-time method. The focal-time method leverages stratigraphic correlations between P-P and P-S reflections to eliminate the need for an explicit velocity model developed specifically for hypocenter depth estimation. We find that this approach is robust in the presence of noisy picks and location errors from epicenters obtained using a global-search algorithm, but it is limited to areas where multicomponent 3D seismic data are available. We have developed a novel method to determine statics corrections to ensure that the passive seismic observations and 3D seismic data share a common datum in areas of moderate to high topography. Our results highlight the importance of transverse faults, which appear to provide permeable pathways for activation of other faults at distances of up to 2 km from hydraulic fracturing operations.

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Frohlich, Cliff. "Does maximum earthquake size depend on focal depth?" Bulletin of the Seismological Society of America 88, no. 2 (April 1, 1998): 329–36. http://dx.doi.org/10.1785/bssa0880020329.

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Abstract While the Gutenberg-Richter “law” (GR) with b-value of 1.0 is an inexact description of the earthquake frequency-magnitude distribution, it does provide a convenient statistical basis for identifying when the largest earthquakes in a catalog are either anomalously large or anomalously small. When the largest earthquakes are as predicted by the GR distribution, it is inappropriate to infer that the largest historically known earthquake is the largest possible. Only when the largest observed earthquakes are significantly smaller than predicted can we infer that the largest possible earthquakes have occurred. Analysis of the global historical catalog demonstrates that at nearly all depths, the largest deep and intermediate earthquakes have sizes close to those predicted by a GR distribution with b of 1.0. Only between about 300 to 450 km and beneath 600 km are the largest known earthquakes somewhat larger than predicted. However, when geographically isolatable subgroups within catalogs are considered separately, largest earthquakes that are either anomalously large or small are quite common. Often this is because individual regions have b-values much different than 1.0; alternatively, sometimes there appear to be physical constraints limiting the size of the largest possible earthquake. As examples illustrating these assertions, this article evaluates two subgroups—deep-focus earthquakes occurring beneath Spain and intermediate-depth earthquakes in the Bucaramanga, Colombia, “nest.”

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Huang, Paul Y., Sean C. Solomon, Eric A. Bergman, and John L. Nabelek. "Focal depths and mechanism of Mid-Atlantic Ridge earthquakes from body waveform inversion." Journal of Geophysical Research 91, B1 (1986): 579. http://dx.doi.org/10.1029/jb091ib01p00579.

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Maggi, A., J. A. Jackson, D. McKenzie, and K. Priestley. "Earthquake focal depths, effective elastic thickness, and the strength of the continental lithosphere." Geology 28, no. 6 (June 2000): 495–98. http://dx.doi.org/10.1130/0091-7613(2000)028<0495:efdeet>2.3.co;2.

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Maggi, A., J. A. Jackson, D. McKenzie, and K. Priestley. "Earthquake focal depths, effective elastic thickness, and the strength of the continental lithosphere." Geology 28, no. 6 (2000): 495. http://dx.doi.org/10.1130/0091-7613(2000)28<495:efdeet>2.0.co;2.

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Bai, Ling, Lorena Medina Luna, Eric A. Hetland, and Jeroen Ritsema. "Focal depths and mechanisms of Tohoku-Oki aftershocks from teleseismic P wave modeling." Earthquake Science 27, no. 1 (December 10, 2013): 1–13. http://dx.doi.org/10.1007/s11589-013-0036-x.

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Yang, Hongfeng, Pengcheng Zhou, Nan Fang, Gaohua Zhu, Wenbin Xu, Jinrong Su, Fanbao Meng, and Risheng Chu. "A Shallow Shock: The 25 February 2019 ML 4.9 Earthquake in the Weiyuan Shale Gas Field in Sichuan, China." Seismological Research Letters 91, no. 6 (October 7, 2020): 3182–94. http://dx.doi.org/10.1785/0220200202.

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Abstract Earthquakes rarely occur at extremely shallow depths, for example, less than 2 km. Even for induced earthquakes that are typically shallower than tectonic events, only very small ones have been reported in such depths. The ML 4.9 earthquake (Mw 4.3) that struck the Rongxian County, Sichuan, China on 25 February 2019 was an extremely shallow event. Seismological and geodetic data constrained the mainshock depth at ∼1 km with a thrust-faulting mechanism, consistent with the Molin fault orienting northwest. Two foreshocks with magnitudes larger than 4 occurred on an unmapped fault striking northeast, right next to an injection well where hydraulic fracturing (HF) was conducted. The focal depths of the two foreshocks were at ∼2.7 km, coinciding with the depth of HF. Coulomb failure stresses of the two foreshocks on the Molin fault was ∼3 kPa, smaller than typical static triggering threshold (10 kPa), and thus their triggering effects were mild. As the fault was hydraulically sealed from HF, we suggested that the ML 4.9 earthquake was possibly triggered by nearby HF activities through poroelastic stress transfer. Such findings held significant implications for shale gas development by considering seismic hazard associated with shallow faults.

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Jaimes, Miguel A., and Adrián D. García-Soto. "Updated ground motion prediction model for Mexican intermediate-depth intraslab earthquakes including V/H ratios." Earthquake Spectra 36, no. 3 (February 18, 2020): 1298–330. http://dx.doi.org/10.1177/8755293019899947.

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This article presents an updated ground motion prediction equation for pseudo acceleration values from Mexican intermediate-depth intraslab earthquakes at rock sites (National Earthquake Hazards Reduction Program (NEHRP) class B) for the horizontal and the vertical components. The equations were built as functions of magnitude, distance to the fault surface of the earthquake and focal depth, using 23 event recordings (366 records). The database is extended from a previous one used to develop a ground motion prediction equation for intraslab earthquakes, including 7 more events and over 80 accelerograms recorded from 2005 to 2017. The previous model neither included the ground motion parameters from the two significant normal-faulting events occurred in 2017, nor the computing of V/ H ratios. Differences in the predicted ground motion parameters are found. Therefore, an updated attenuation model for intraslab earthquakes is developed for distances up to around 400 km and Mw from approximately 5 to 8.2. The model includes a depth-scaling term with focal depths restricted up to 75 km.

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Zhakeyev, Adilet, and Jose Marques-Hueso. "Centimeter-Scale Curing Depths in Laser-Assisted 3D Printing of Photopolymers Enabled by Er3+ Upconversion and Green Light-Absorbing Photosensitizer." Photonics 9, no. 7 (July 16, 2022): 498. http://dx.doi.org/10.3390/photonics9070498.

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Photopolymer resins used in stereolithographic 3D printing are limited to penetration depths of less than 1 mm. Our approach explores the use of near-infrared (NIR) to visible upconversion (UC) emissions from lanthanide-based phosphors to initiate photopolymer crosslinking at a much higher depth. This concept relies on the use of invisibility windows and non-linear optical effects to achieve selective crosslinking in photopolymers. SLA resin formulation capable of absorbing light in the visible region (420–550 nm) was developed, in order to take advantage of efficient green-UC of Er3+/Yb3+ doped phosphor. NIR-green light UC shows versatility in enhancing curing depths in laser patterning. For instance, a structure with a curing depth of 11 ± 0.2 mm, cured width of 496 ± 5 µm and aspect ratios of over 22.2:1 in a single pass via NIR-green light UC. The penetration depth of the reported formulation approached 39 mm. Therefore, this technique would allow curing depths of up to 4 cm. Moreover, it was also demonstrated that this technique can initiate cross-linking directly at the focal point. This shows the potential of NIR-assisted UC as a low-cost method for direct laser writing in volume and 3D printing.

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Umino, Norihito, and Akira Hasegawa. "Aftershock Focal Depths of the 1993 Hokkaido-Nansei-Oki Earthquake Estimated from sP Depth Phase at Small Epicentral Distances." Journal of Physics of the Earth 42, no. 4 (1994): 321–29. http://dx.doi.org/10.4294/jpe1952.42.321.

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Davison, Frederick C., and Melissa J. Bodé. "A Note on the December 1986 - January 1987 Richmond, Virginia, Felt Earthquake Sequence." Seismological Research Letters 58, no. 3 (July 1, 1987): 73–80. http://dx.doi.org/10.1785/gssrl.58.3.73.

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Abstract A series of small, felt earthquakes occurred in Richmond, Virginia, during December 1986 and January 1987. Historie records show that such a sequence is unique for Richmond. There were at least 11 felt events, of which six were instrumentally recorded and four were located. Duration magnitudes of these four ranged from 1.5 to 2.2. A focal mechanism solution was calculated and indicates reverse faulting on a plane striking north-northwest and dipping either 45° northeast or 44° southwest. Epicentral intensity reports, up to MMI V, and felt areas do not conform to usual intensity - magnitude relationships. Independent estimates of depth suggest that extremely shallow foei (<2.5 km) may be the cause for this anomaly. The shallow focal depths have important implications concerning the stability of the crust around any shallow underground facilities sited in the area, especially with respect to protection of the groundwater environment.

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Lin, Guoqing. "Waveform Cross-Correlation Relocation and Focal Mechanisms for the 2019 Ridgecrest Earthquake Sequence." Seismological Research Letters 91, no. 4 (February 26, 2020): 2055–61. http://dx.doi.org/10.1785/0220190277.

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Abstract I present a high-precision earthquake relocation catalog and first-motion focal mechanisms before and during the 2019 Ridgecrest earthquake sequence in eastern California. I obtain phase arrivals, first-motion polarities, and waveform data from the Southern California Earthquake Data Center for more than 24,000 earthquakes with the magnitudes varying between −0.7 and 7.1 from 1 January to 31 July 2019. I first relocate all the earthquakes using phase arrivals through a previously developed 3D seismic-velocity model and then improve relative location accuracies using differential times from waveform cross correlation. The majority of the relocated seismicity is distributed above 12 km depth. The seismicity migration along the northwest–southeast direction can be clearly seen with an aseismic zone near the Coso volcanic field. Focal mechanisms are solved for all the relocated events based on the first-motion polarity data with dominant strike-slip fault solutions. The Mw 6.4 and 7.1 earthquakes are positioned at 12.45 and 4.16 km depths after the 3D relocation, respectively, with strike-slip focal solutions. These results can help our understanding of the 2019 Ridgecrest earthquake sequence and can be used in other seismological and geophysical studies.

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Acree, Steven D., Jill R. Acree, and Pradeep Talwani. "The Lake Keowee, South Carolina Earthquakes of February through July 1986." Seismological Research Letters 59, no. 2 (April 1987): 63–70. http://dx.doi.org/10.1785/gssrl.59.2.63.

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Abstract In the early morning of 13 February 1986, an earthquake with a duration magnitude (MD) of 3.2 rumbled through northwestern South Carolina. The event was centered near Lake Keowee in Oconee County in a region of prior low level seismicity. Approximately eighty aftershocks with magnitudes ranging from −1.0 to 2.0 were recorded during the next six days. The locations of five aftershocks were accurately determined, utilizing data from portable seismographs deployed in the epicentral area. Depths of the two earthquakes with a location quality of B or better were between 3 and 4 km. First motion focal mechanism solutions for the mainshock suggest oblique slip along a plane striking northeast or northwest. The P axis was oriented northeast-southwest in support of the directions obtained from mechanisms of other local earthquakes and from direct measurements of the maximum horizontal stress in the regions. A second mainshock (MD = 2.8) occurred in the vicinity of Lake Keowee on 11 June 1986 and was followed by over sixty earthquakes during the next five weeks. Focal mechanism solutions from first motion data obtained for the mainshock resemble those of the 13 February event and suggest oblique slip along a northeast or northwest striking plane. Depths of the best located aftershocks were approximately 1 km. Two tests were applied to the data to assess the reliability of the depth estimates. These involve the determination that the plot of RMS travel time residual versus fixed solution depth exhibits a single, sharp RMS minimum at the depth obtained from a free solution (depth uniqueness) and that the final free solution depth is not dependent upon the choice of starting depth (depth stability). Free solution depths obtained for the majority of the better located aftershocks were found to be unique and stable at depths between 1 and 4 km. A northeast trending anomaly is prominent in the geophysical data for this area. This anomaly is interpreted to result from an abrupt, lateral change in lithology along a shallow, northeast striking plane. The earthquakes do not appear to be associated with this feature. Instead, these earthquakes appear to be associated with a shallow body and may represent slip along northeast or northwest striking joints. The proximity of these earthquakes to Lake Keowee suggests the possibility of reservoir triggering. No correlation between seismicity and reservoir level is evident prior to the February events. Rapid fluctuations in water level did precede the events in June and July, providing possible triggering mechanisms.

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Yi, Donghui, Fengbin Zhou, Jianyu Hua, Linsen Chen, and Wen Qiao. "Diffractive Achromat with Freeform Slope for Broadband Imaging over a Long Focal Depth." Micromachines 14, no. 7 (July 9, 2023): 1401. http://dx.doi.org/10.3390/mi14071401.

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We propose a method for designing a long-focal-depth diffractive achromat (LFDA). By applying rotational symmetric parameterization, an LFDA with a diameter of 10.89 mm is designed over three wavelengths at six focal planes. The smoothly changed slope designed by the binary variable slope search (BVSS) algorithm greatly reduces the discontinuity in depth, thus it is a fabrication-friendly process for grayscale laser direct writing lithography, involving less fabrication error and cost. The deviation between the designed and fabricated profiles amounts to 9.68%. The LFDA operates at multiple wavelengths (654 nm, 545 nm, and 467 nm) with a DOF of 500 mm~7.65λ × 105 (λ = 654 nm). The simulated and measured full-width at half-maximum (FWHM) of the focused beam is close to the diffraction limit. Experimental studies suggest that the LFDA possesses a superior capability to form high-quality chromatic images in a wide range of depths of field. The LFDA opens a new avenue to achieve compact achromatic systems for imaging, sensing, and 3D display.

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Fan, Gang, Jun Wang, Shunchao Qi, Gongda Lu, Xingguo Yang, and Jiawen Zhou. "Spatiotemporal Evolution of Earthquakes in Longmenshan Fault and Adjacent Area, before and after the 2008 Wenchuan Earthquake." Shock and Vibration 2021 (November 24, 2021): 1–13. http://dx.doi.org/10.1155/2021/9400276.

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Seismicity sequence following a main earthquake usually contains much meaningful information for unveiling the focal mechanism and predicting the reoccurrence interval of large earthquakes. The spatiotemporal evolution of earthquakes before and after the 2008 Wenchuan earthquake (Ms 8.0) is analysed comprehensively in this study. The frequency-magnitude relation of the 3493 earthquake events retrieved from the database of the International Seismological Centre indicates that the adopted catalogue is complete for magnitudes ≥Ms 3.4. The seismicity during the 10 years before the Wenchuan earthquake remained stable, including the magnitudes and focal depths. However, seismicity attenuated sharply in the year following the Wenchuan earthquake, and the magnitude of earthquakes before the Wenchuan earthquake decreased gradually. The area of the seismogenic zone of the 2008 Wenchuan earthquake was smaller than the earthquake stricken area. The earthquakes that occurred in the Longmenshan fault area and adjacent area in the study period were mainly shallow earthquakes. The focal depths of earthquakes in the study area became stable gradually after the Wenchuan earthquake, mainly within the range from 10 to 16 km. The earthquakes in the study area were mainly distributed with an along-dip distance of 0–20 km, and the seismicity was distributed uniformly along the fault strike.

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Yan, Rui, and Chilou Zhou. "Analysis of Focusing Performance in Phased Array Probe Using COMSOL." Journal of Physics: Conference Series 2610, no. 1 (October 1, 2023): 012059. http://dx.doi.org/10.1088/1742-6596/2610/1/012059.

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Abstract To improve the detection ability of ultrasonic phased array detection for hydrogen storage vessel, COMSOL was used to simulate the main parameters of phased array probes. The influence of the number of array elements, array element spacing and excitation frequency on the sound propagation characteristics was analysed. The results showed that the number of array elements has a significant effect on the focused sound field. When the number of array elements is 8, effective focus cannot be formed at the pre-set focus position, and the maximum sound pressure value does not change significantly at the three pre-set focus depths. At a focus depth of 30mm, the maximum sound pressure in the 32-element mode is more than twice that in the 8-element mode. The relationship between excitation frequency and focal sound pressure is non-linear. In addition, as the array element spacing increases, the length of the focal column decreases. And the smaller the array element spacing, the higher the sound pressure at a deeper depth.

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Liu, Chao, Yi Zheng, Nan-Nan Li, Ye-Hao Hou, Zhao Jiang, and Qiong-Hua Wang. "Real scene acquisition and holographic near-eye display system based on a zoom industrial endoscope." Optics Express 30, no. 18 (August 25, 2022): 33170. http://dx.doi.org/10.1364/oe.468267.

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In this paper, we propose a real scene acquisition and holographic near-eye display system based on a zoom industrial endoscope. By controlling the driving current of the liquid lens, the working distance and focal length of the zoom industrial endoscope can be tuned accordingly. Thus, the object at different depths can be captured. Then, the sub-sampling algorithm is used to generate the hologram. By adjusting the hologram sampling rate of the objects with different depths, the holographic near-eye 3D display can be realized. Experimental results demonstrate that the working distance of the zoom industrial endoscope can be tuned from 20 mm to 200 mm with the driving current changing from 80 mA to 190 mA. With the proposed system, the human eye can intuitively see the depth relationships among the real objects. The proposed system is expected to be applied to 3D display and industrial inspection fields.

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Allamehzadeh, M., M. Dezvareh, A. M. Farahbod, D. Hatzfeld, M. Mokhtari, A. S. Moradi, M. Mostafazadeh, A. Paul, and M. Tatar. "Seismological Aspects of the 2003 Bam, Iran, Earthquake and Its Aftershock Analysis." Earthquake Spectra 21, no. 1_suppl (December 2005): 101–12. http://dx.doi.org/10.1193/1.2098167.

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The source mechanism derived from the inversion of long-period body waves revealed that the earthquake occurred on a north-south trending strike-slip fault with a thrust component. According to the source model estimated in this study, the 2003 Bam, Iran, earthquake was a multiple event formed by two subevents. The rupture following subevent one started at a depth of about 8 km. However, the depth of subevent two is about 10 km. The total seismic moment estimated from inversion processes is 8.34×1018Nm. The pulse duration of subevent one and subevent two was determined from source time function as 1.7 s and 0.8 s, respectively. Corner frequency and source radius have been calculated by using major pulse duration. The corner frequency and source radius are 0.187 Hz and 5.47 km, respectively. The aftershock events distributed along a 30 km north-south striking fault. The focal depths of aftershocks distribution show a nearly vertical alignment of aftershocks located between 6 and 20 km depth. The focal mechanism solutions of aftershocks indicate right-lateral strike-slip faulting on a north-south trending fault, parallel to the previously known Bam fault trace in the east of Bam.

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Chakrabarti, Surajit, Sanjoy Kumar Pal, and Soumen Sarkar. "An accurate determination of the refractive indices of water and glass by smartphone photography." Physics Education 58, no. 3 (February 22, 2023): 035010. http://dx.doi.org/10.1088/1361-6552/acb8f9.

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Abstract A smartphone can be used for many physics experiments by using the sensors built into the phone. The complementary metal oxide semiconductor (CMOS) (charge-coupled device, CCD) sensor of the camera records the images of objects photographed in pixels. The width of the image can be read off with micron level accuracy with the help of software available freely from the internet. If the dimensions of the object in the direction transverse to the viewing direction of the camera are known, the magnification of the object photographed can be determined accurately. A smartphone camera is a compound lens comprising a number of very thin lenses. A single thin lens is equivalent, as far as the transverse magnification is concerned, to a compound lens of the smartphone, when the thin lens has the same focal length as the effective focal length of the compound lens and is placed at its first principal plane. This property allows us to find experimentally the effective focal length of the compound lens of the camera accurately, using the thin lens equation. Once the focal length of the camera is known, the distance of an object can be determined by finding its magnification from the photograph. We have determined the refractive index of water accurately by photographing the apparent position of an object immersed in it. By determining the magnifications, we have found the real and apparent depths of the object. The ratio of these depths gives the refractive index. We have determined the refractive index of glass also using some thin glass slides.

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Grimison, Nina L., and Wang-Ping Chen. "The Azores-Gibraltar Plate Boundary: Focal mechanisms, depths of earthquakes, and their tectonic implications." Journal of Geophysical Research 91, B2 (1986): 2029. http://dx.doi.org/10.1029/jb091ib02p02029.

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Jemsek, John P., Eric A. Bergman, John L. Nabelek, and Sean C. Solomon. "Focal depths and mechanisms of large earthquakes on the Arctic Mid-Ocean Ridge System." Journal of Geophysical Research 91, B14 (1986): 13993. http://dx.doi.org/10.1029/jb091ib14p13993.

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Shi, Haofei, Chunlei Du, and Xiangang Luo. "Focal length modulation based on a metallic slit surrounded with grooves in curved depths." Applied Physics Letters 91, no. 9 (August 27, 2007): 093111. http://dx.doi.org/10.1063/1.2776875.

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Buttinelli, M., D. De Rita, C. Cremisini, and C. Cimarelli. "Deep explosive focal depths during maar forming magmatic-hydrothermal eruption: Baccano Crater, Central Italy." Bulletin of Volcanology 73, no. 7 (April 28, 2011): 899–915. http://dx.doi.org/10.1007/s00445-011-0466-z.

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Sun, Lesheng, Ying Xu, Zhikang Rao, Juntao Chen, Zhe Liu, and Ning Lu. "YOLO Algorithm for Long-Term Tracking and Detection of Escherichia Coli at Different Depths of Microchannels Based on Microsphere Positioning Assistance." Sensors 22, no. 19 (September 30, 2022): 7454. http://dx.doi.org/10.3390/s22197454.

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The effect evaluation of the antibiotic susceptibility test based on bacterial solution is of great significance for clinical diagnosis and prevention of antibiotic abuse. Applying a microfluidic chip as the detection platform, the detection method of using microscopic images to observe bacteria under antibiotic can greatly speed up the detection time, which is more suitable for high-throughput detection. However, due to the influence of the depth of the microchannel, there are multiple layers of bacteria under the focal depth of the microscope, which greatly affects the counting and recognition accuracy and increases the difficulty of relocation of the target bacteria, as well as extracting the characteristics of bacterial liquid changes under the action of antibiotics. After the focal depth of the target bacteria is determined, although the z-axis can be controlled with the help of a three-dimensional micro-operator, the equipment is difficult to operate and the long-term changes of the target bacteria cannot be tracked quickly and accurately. In this paper, the YOLOv5 algorithm is adopted to accurately identify bacteria with different focusing states of multi-layer bacteria at the z-axis with any focal depth. In the meantime, a certain amount of microspheres were mixed into bacteria to assist in locating bacteria, which was convenient for tracking the growth state of bacteria over a long period, and the recognition rates of both bacteria and microspheres were high. The recognition accuracy and counting accuracy of bacteria are 0.734 and 0.714, and the two recognition rates of microspheres are 0.910 and 0.927, respectively, which are much higher than the counting accuracy of 0.142 for bacteria and 0.781 for microspheres with the method of enhanced depth of field (EDF method). Moreover, during long-term bacterial tracking and detection, target bacteria at multiple z-axis focal depth positions can be recorded by the aid of microspheres as a positioning aid for 3D reconstruction, and the focal depth positions can be repositioned within 3–10 h. The structural similarity (SSIM) of microscopic image structure differences at the same focal depth fluctuates between 0.960 and 0.975 at different times, and the root-mean-square error (RMSE) fluctuates between 8 and 12, which indicates that the method also has good relocation accuracy. Thus, this method provides the basis for rapid, high-throughput, and long-term analysis of microscopic changes (e.g., morphology, size) of bacteria detection under the addition of antibiotics with different concentrations based on microfluidic channels in the future.

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Safonov, D. A. "RECONSTRUCTION OF THE TECTONIC STRESS FIELD IN THE DEEP PARTS OF THE SOUTHERN KURIL-KAMCHATKA AND NORTHERN JAPAN SUBDUCTION ZONES." Geodynamics & Tectonophysics 11, no. 4 (December 15, 2020): 743–55. http://dx.doi.org/10.5800/gt-2020-11-4-0504.

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Earthquake focal mechanisms in the Southern Kuril-Kamchatka and Northern Japan subduction zones were analysed to investigate the features of the tectonic stress field inside the Pacific lithospheric plate subducting into the upper mantle. Earthquake focal mechanism (hypocenter depths of more than 200 km) were taken from the 1966– 2018 NIED, IMGiG FEB RAS and GlobalCMT catalogues. The tectonic stress field was reconstructed by the cataclastic analysis method, using a coordinate system related to the subducting plate. In most parts of the studied seismic focal zone, the axis of the principal compression stress approximately coincides with the direction of the Pacific lithospheric plate subduction beneath the Sea of Okhotsk. It slightly deviates towards the hinge zone separating the studied regions. The principal tension stress axis is most often perpendicular to the plate movement, but less stable in direction. This leads to compression relative to the slab in some parts of the studied regions, and causes shearing in others. The hinge zone is marked by the unstable position of the tension axis and high values of the Lode–Nadai coefficient, corresponding to the conditions of uniaxial compression, while the compression direction remains the same, towards the slab movement. Two more areas of uniaxial compression are located below the Sea of Japan at depths of 400–500 km.

Journal articles on the topic 'Focal Depths'

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