Journal articles: 'EPICENTRAL DISTANCE'

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Liang, Haian, Li Ping Jing, Ze Ping Yang, and Yong Qiang Li. "Effects of Epicentral Distance and Seismogenic Fault Distance on Seismic Damage of Dams in Wenchuan Earthquake." Applied Mechanics and Materials 353-356 (August 2013): 2187–90. http://dx.doi.org/10.4028/www.scientific.net/amm.353-356.2187.

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Epicentral distance and seismogeonic fault distances as crucial ground motion parameters of attenuation relationship are widely accepted indexes for rapid assessment of seismic scenario. Based on the geographical information of 379 heavily damaged dams in Wenchuan Earthquake, 2008, China, the distribution of damaged dams is analyzed statistically. Specifically, the correlation of damage rate & epicentral distance and that of damage proportion & seismogenic fault distance are compared, and corresponding equations are developed respectively using least square methods. The investigation shows that there exists a closer relationship between seismic damage and seismogenic fault distance than between damage and epicentral distance for Wenchuan earthquake. It is concluded that the index of seismogenic fault distance is more applicable to large earthquake, while Epicentral distance is a more accurate index for small and mid-level earthquakes.

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Shayakubova, M. "ESTIMATES OF EPICENTRAL DISTANCE AND MAGNITUDE FROM ONE SEISMIC STATION." Journal of Science and Innovative Development 5, no. 5 (September 21, 2022): 20–24. http://dx.doi.org/10.36522/2181-9637-2022-5-3.

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Rapid assessment of epicentral distance and magnitude has fundamental importance for earthquake early detection and warning systems. We present a new method for estimating the epicentral distance using one seismic record in short time. To quantify the difference in the observed seismic signals, we introduced a simple function of the form Bt•exp(-At) and determined A and B from the point of view of the least squares method, fitting this function to the initial part of the signal envelope. We found that log B is inversely proportional to log Δ , where Δ represents the epicentral distance. This ratio is valid regardless of the magnitude of the earthquake. Using this ratio, we can estimate approximate epicentral distance almost immediately after the arrival of the P-wave. Then we can easily estimate the magnitude from the maximum amplitude observed during a given short time interval after the arrival of the P-wave, using the empirical magnitude-amplitude ratio, which includes the epicentral distance as a parameter.

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Nelson, J. L., and M. s. De Assumpção. "Curva de Amplitude-Distância para Ondas P de Período Curto e Correção de Estação para Magnitude Mb na América do Sul." Brazilian Journal of Geophysics 12, no. 1 (January 1, 2013): 89. http://dx.doi.org/10.22564/brjg.v12i1.2285.

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Amplitudes de ondas P, de período curto de sismos rasos registrados por estações na faixa de distância epicentral de 0° - 100°, são analisadas para a determinação dos efeitos de estação, de fonte e de distância. 56 sismos foram utilizados, 12 dos quais com epicentros no território brasileiro. As correções de estações são estimadas com limites de confiança de 95%. Os resultados mostram que o padrão das isolinhas dos efeitos de estação difere do padrão para a América do Norte. Uma curva de amplitude-distância é determinada para intervalos de 5º de distância epicentral. Essa curva indica que os efeitos de distância entre 20° e 80° não são significativos, isto é, não há desvio significativo em relação a um efeito constante nessa faixa. A curva de amplitude-distância obtida é menos irregular que a de Gutenberg-Richter. Esse resultado concorda com estudos similares de outros autores.Short Period P-Wave Amplitude-Distance Curve and Station Correction For Mb Magnitude in South America Vertical short period P-waves amplitudes from shallow earthquakes recorded by stations in the epicentral distance range 0° - 100° are analysed to determine the station, source and distance effects. 56 earthquakes were used, 12 of which having epicenters in Brazilian territory. Station corrections are estimated with 95% confidence limits. The results show that the station effect isolines pattern is different from the pattern for North America. An amplitude-distance curve is derived for 5° distance intervals. This curve indicates that distance effects between 20 and 80° are not significant, i.eThere is no significant deviation from a constant effect in this range. The amplitude-distance curve obtained here is less irregular than the Gutenberg-Richter's curve. This result is in agreement with similar studies of other authors.

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Gupta, I. D., and M. D. Trifunac. "Attenuation of intensity with epicentral distance in India." Soil Dynamics and Earthquake Engineering 7, no. 3 (July 1988): 162–69. http://dx.doi.org/10.1016/s0267-7261(88)80020-4.

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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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Su, Feng, John G. Anderson, James N. Brune, and Yuehua Zeng. "A comparison of direct S-wave and coda-wave site amplification determined from aftershocks of the Little Skull Mountain earthquake." Bulletin of the Seismological Society of America 86, no. 4 (August 1, 1996): 1006–18. http://dx.doi.org/10.1785/bssa0860041006.

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Abstract Site amplifications of direct S waves and coda waves are studied and compared using high-quality, three-component digital data from aftershocks of the Little Skull Mountain, Neveda, earthquake. We use data from 12 stations installed on a variety of geological and topographic site conditions, distributed widely in space with different azimuths and epicentral distances. S-wave site amplifications are obtained in the frequency range from about 0.5 to over 30 Hz, while coda-wave site amplifications are obtained in a frequency range from about 1.5 to over 30 Hz. A thorough statistical analysis of these results was performed. We find that (1) for S waves, all three components at a station follow a similar frequency-dependent trend. The amplitudes of the two horizontal components match more closely, while the vertical component shows consistently lower amplification than the horizontal components at low frequencies. (2) For coda waves, all three components share both similar frequency-dependent trends and amplification level. (3) S-wave and coda-wave site amplification are consistent for stations with epicentral distance greater than about 10 km (which is about the average focal depth of the earthquakes we used). Within the epicentral distance of 10 km, however, some stations show discordant S-wave and coda-wave site amplifications. Possible factors are that the direct S waves are affected by particular wave propagation paths and that at short distance SV is partitioned with more energy on the horizontal components and less on the vertical components than at larger distances.

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Keers, H., G. Nolet, and F. A. Dahlen. "Ray theoretical analysis of Lg." Bulletin of the Seismological Society of America 86, no. 3 (June 1, 1996): 726–36. http://dx.doi.org/10.1785/bssa0860030726.

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Abstract Ray theory is used to investigate the effect that irregular crustal interfaces have on the different phases that comprise Lg. We concentrate on the effects of a variable Moho in this initial study, while keeping the surface flat. The Moho models considered are a cosinusoid, a model of the Moho below the German part of the European Geo-Traverse (EGT) and a model representing an ocean-continent transition. It is found that even slight undulations of the Moho give rise to extensive multipathing. This affects the amplitudes of the supercritically reflected crustal multiples comprising Lg in a dramatic way. Two different types of ray behavior are distinguished. The first type, corresponding to regular or weakly chaotic ray behavior, occurs at smaller values of the ray parameter and gives rise to large amplitudes at distinct epicentral distances due to focusing, accompanied by “gaps” containing very little energy due to defocusing in between. The second type, corresponding to strongly chaotic ray behavior, occurs at larger values of the ray parameter. Small changes in the take-off angle in this chaotic regime produce large fluctuations in the epicentral distance of arrivals. The Moho below Germany, for example, produces 140 supercritically reflected arrivals at an epicentral distance of 400 km. Since the amplitudes of arrivals in the chaotic region are smeared out over a large epicentral distance range, they are much less prominent than the arrivals from the regular region, even though they are supercritically reflected. Travel-time fluctuations are less sensitive to the undulations in the Moho than amplitude variations. They are more affected by the magnitude than by the wavelength of the undulations. Amplitude undulations of more than 3 km produce multiple arrivals that have differences in travel time of up to 10 sec.

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Xu, Qin, Shaofeng Chai, Shihu Zhou, Liqun Bao, and Quan Li. "Time-Frequency Characteristics of Ground Motion and Seismic Response Analysis of Typical Structures in the Yangbi Earthquake in Yunnan Province." Advances in Civil Engineering 2022 (July 20, 2022): 1–13. http://dx.doi.org/10.1155/2022/9998019.

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The ground motion records obtained by the CDSMON during the Ms6.4 earthquake in Yangbi, Yunnan Province, on May 21, 2021, were subjected to routine processing such as baseline correction and filtering. The nonstationary time-frequency characteristics of ground motion signals were analysed by the wavelet transform, and the acceleration response spectrum characteristics of typical stations under different epicentral distances, magnitudes, and site conditions were analysed. Finite element software was used to establish a model to analyse the seismic response of a typical three-span continuous beam bridge. The maximum peak ground acceleration (PGA) of this earthquake (720.29 gal) was obtained from 53YBX in the NS direction at the epicentral distance of 8.6 km. The energy at station 53YBX was mainly concentrated in 0–15 Hz range, and the low-frequency component energy caused great damage to buildings with natural frequencies in this frequency band. The Sa value near the origin of the earthquake is relatively large, as the distance from the epicentre increases, the predominant period of Sa also gradually increases, and the high-frequency component diminishes. With the increase in earthquake magnitude, the Sa peak increased, and the long-period component became more obvious. The soil station had more obvious long-period components than the bedrock station, which is consistent with the amplification result of the response spectrum of overburden thickness to surface acceleration. The earthquake had little influence on the pier displacement of the three-span continuous beam bridge with a fundamental period of 0.77 s but had a great influence on the bending moment at the bottom of the piers.

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Muratov, Pavel, Oleg Rulenko, and Yuriy Marapulets. "Manifestation features of near-surface sedimentary rock electric and acoustic responses on seismic waves from earthquakes." E3S Web of Conferences 127 (2019): 02015. http://dx.doi.org/10.1051/e3sconf/201912702015.

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The results of analysis of near-surface sedimentary rock electric and acoustic responses on seismic waves from five Kamchatka earthquakes with the magnitudes of 4.9 – 7.3 at the distances of 79 – 498 km from epicenters are presented. Manifestation features of these responses, depending upon earthquake magnitude, epicentral distance, source depth and direction to an epicenter, are considered.

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Casado, C. L. "Attenuation of Intensity with Epicentral Distance in the Iberian Peninsula." Bulletin of the Seismological Society of America 90, no. 1 (February 1, 2000): 34–47. http://dx.doi.org/10.1785/0119980116.

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Grandori, G., A. Drei, F. Perotti, and A. Tagliani. "Macroseismic intensity versus epicentral distance: the case of Central Italy." Tectonophysics 193, no. 1-3 (July 1991): 165–71. http://dx.doi.org/10.1016/0040-1951(91)90196-y.

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Bakun, W. H., and C. M. Wentworth. "Estimating earthquake location and magnitude from seismic intensity data." Bulletin of the Seismological Society of America 87, no. 6 (December 1, 1997): 1502–21. http://dx.doi.org/10.1785/bssa0870061502.

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Abstract Analysis of Modified Mercalli intensity (MMI) observations for a training set of 22 California earthquakes suggests a strategy for bounding the epicentral region and moment magnitude M from MMI observations only. We define an intensity magnitude MI that is calibrated to be equal in the mean to M. MI = mean (Mi), where Mi = (MMIi + 3.29 + 0.0206 * Δi)/1.68 and Δi is the epicentral distance (km) of observation MMIi. The epicentral region is bounded by contours of rms [MI] = rms (MI − Mi − rms0 (MI − Mi), where rms is the root mean square, rms0 (MI − Mi) is the minimum rms over a grid of assumed epicenters, and empirical site corrections and a distance weighting function are used. Empirical contour values for bounding the epicenter location and empirical bounds for M estimated from MI appropriate for different levels of confidence and different quantities of intensity observations are tabulated. The epicentral region bounds and MI obtained for an independent test set of western California earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes. The analysis strategy is particularly appropriate for the evaluation of pre-1900 earthquakes for which the only available data are a sparse set of intensity observations.

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Kuzin, I. P., L. I. Lobkovskiy, and K. A. Dozorova. "Okhotsk deep earthquake 24.05.2013: nature of coseismal earth’s oscillations and estimation of P-wave amplitudes at teleseismic distances." Доклады Академии наук 486, no. 2 (May 27, 2019): 237–42. http://dx.doi.org/10.31857/s0869-56524862237-242.

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The results of coseismic GPS observations in the epicentral area of 2013 Sea-of- Okhotsk earthquake are presented and specific features of seismic waves amplitudes variations with distance are detected basing on the records of Russian and international seismic stations. Global propagation of P-waves for the Sea-of-Okhotsk and Bolivian (09.06.1994) earthquakes was studied and their amplitudes on teleseismic distances were estimated.

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STEELE, Heather, Shunta NODA, Shunroku YAMAMOTO, and Masahiro KORENAGA. "Improved Epicentral Distance Estimations for Railway Earthquake Early Warning." Quarterly Report of RTRI 61, no. 3 (August 1, 2020): 222–27. http://dx.doi.org/10.2219/rtriqr.61.3_222.

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Piroddi, Luca, Gaetano Ranieri, Friedemann Freund, and Antonio Trogu. "Geology, tectonics and topography underlined by L'Aquila earthquake TIR precursors." Geophysical Journal International 197, no. 3 (May 16, 2014): 1532–36. http://dx.doi.org/10.1093/gji/ggu123.

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Abstract Anomalous thermal infrared (TIR) emissions have widely been detected by satellite sensors before the major earthquakes. A recent processing technique for geostationary thermal data, developed for the case of the 2009 April 6, magnitude 6.3 L'Aquila earthquake, makes it possible to identify areas of enhanced TIR emissions around the epicentral region at a mean distance of less than 50 km but inside a radius of about 100 km. The index, called Night Thermal Gradient (NTG), derived from 4-D time-series data (two spatial and two temporal coordinates), identifies TIR anomalies by following the temperature trend during night, when the surface of the Earth is expected to cool. Leading up to the L'Aquila earthquake, an anomalous warming trend was observed. In this study, the anomalous NTG pattern is compared to the expected normal trend, taking into account the seismogenic faults, the overall tectonic setting, lithological spatial features, the orography and world stress map near the epicentral region. Main results are that a certain lithological selectivity can be recognized and that the known main stress field and seismogenic faults seem to be less important than certain tectonic lineaments, which are classified as non-seismogenic. The strong correlation between the topography and the TIR anomalies is in agreement with proposed physical mechanism for the generation of TIR anomalies. This relation is, in turn, present mainly in correspondence to two tectonic lineaments which in particular are thrusts: therefore, strong compressive states seem to be a positive condition for the generation of TIR anomalies. The temporary modification of these stress fields have triggered the Paganica Fault to its normal rupture mechanism. It is important to note that the distances, over which the TIR anomalies occurred, are an order of magnitude larger than the estimated length of the main fault rupture. Pixel-by-pixel time-series comparisons between the maximum TIR anomaly area and the epicentre of the main shock show that the increase in radiative emission occurred in the areas of maximum TIR anomalies and did not start by spreading outward from the epicentral region.

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Yang, Zongji, Bo Pang, Wufan Dong, and Dehua Li. "Spatial Pattern and Intensity Mapping of Coseismic Landslides Triggered by the 2022 Luding Earthquake in China." Remote Sensing 15, no. 5 (February 27, 2023): 1323. http://dx.doi.org/10.3390/rs15051323.

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On 5 September 2022, an Mw 6.6 earthquake occurred in Luding County in China, resulting in extensive surface rupture and casualties. Sufficient study on distribution characteristics and susceptibility regionalization of the earthquake-induced disasters (especially coseismic landslides) in the region has great significance to mitigation of seismic hazards. In this study, a complete coseismic landslide inventory, including 6233 landslides with 32.4 km2 in area, was present through multi-temporal satellite images. We explored the distribution and controlling conditions of coseismic landslides induced by the 2022 Luding event from the perspective of epicentral distance. According to the maximum value of landslide area density, the geographical location with the strongest coseismic landslide activity intensity under the influence of seismic energy, the macro-epicenter, was determined, and we found a remarkable relationship with the landslide distribution and macro-epicentral distance, that is, both the landslide area and number density associatively decreased with the increase in macro-epicentral distance. Then, a fast and effective method for coseismic landslide intensity zoning based on the obvious attenuation relationship was proposed, which could provide theoretical reference for susceptibility mapping of coseismic landslides induced by earthquakes in mountainous areas. Additionally, to quantitatively assess the impact of topographic, seismogenic and lithological factors on the spatial pattern of coseismic landslides, the relationships between the occurrences of coseismic landslides and influencing factors, i.e., elevation, slope angle, local relief, aspect, distance to fault and lithology, were examined. This study provides a fresh perspective on intensity zoning of coseismic landslides and has important guiding significance for post-earthquake reconstruction and land use in the disaster area.

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Ochoa Gutierrez, Luis Hernán, Carlos Alberto Vargas Jimenez, and Luis Fernando Niño Vasquez. "Fast estimation of earthquake epicenter distance using a single seismological station with machine learning techniques." DYNA 85, no. 204 (January 1, 2018): 161–68. http://dx.doi.org/10.15446/dyna.v85n204.68408.

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Se aplicó un algoritmo de máquinas de vector de soporte para calcular la distancia epicentral utilizando una señal de diez segundos, después del arribo de ondas primarias a una estación sismológica cercana a Bogotá - Colombia. Este algoritmo fue probado con 863 registros de terremotos donde los parámetros de entrada fueron una función exponencial de la envolvente estimada para los mínimos cuadrados y el valor máximo de las formas de ondas registradas en cada componente de la estación sísmica. Validación cruzada fue aplicada a funciones kernel polinomiales normalizadas, obteniendo la media del error absoluto para diferentes exponentes y parámetros de complejidad. La distancia epicentral se estimó con 10.3 kilómetros de error absoluto, mejorando los resultados previamente obtenidos para este parámetro hipocentral. El algoritmo propuesto es fácil de implementar y puede ser empleado directamente en campo, generando decisiones rápidas en centros de control sismológico incrementado posibilidades de tener reacciones efectivas.

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Kopylova, G. N., and S. V. Boldina. "Hydrogeological precursors of earthquakes and volcanic activations according to observation data in Kamchatka Peninsula wells." Earth sciences and subsoil use 44, no. 2 (June 17, 2021): 141–50. http://dx.doi.org/10.21285/2686-9993-2021-44-2-141-150.

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The purpose of the study is generalization of data on the manifestations of hydrogeological earthquake precursors and volcanic activations based on long-term observations in the wells of the eastern part of the Kamchatka Peninsula. The main problem under consideration is the connection between the manifestations of hydrogeological precursors in several wells with the values of the magnitude Mw and epicentral distance of earthquakes to the wells de as well as with the parameters of seismic action in the observation area including specific density of seismic wave energy e and macroseismic intensity of shaking IMSK-64. The study results revealed that hydrogeological precursors in two-four wells had been manifesting for the period from 1 to 9 months before the strongest earthquakes with Mw = 6.6–7.8 at the epicentral distances de = 90–300 km. Such earthquakes were accompanied by the shakings of the intensity of IMSK-64 = 4–6 points. The specific density of seismic energy under such earthquakes was minimum 0.1 J/m3. The hydrogeological precursors were confined to the area for which the ratios of the earthquake epicentral distance de to the maximum linear size of the earthquake source L, km ranged from 1 to 3.7. Using the established relationships between the manifestations of hydrogeological precursors and earthquake parameters, weekly prognostic conclusions were made for expert earthquake prediction councils based on the data of current observations in wells. The well located at the distance of 15 and 20 km from the Koryaksky and Avacha active volcanoes featured the anomalous rise of groundwater pressure before the eruptions in 1991 and 2008– 2009. Therefore, a conclusion can be drawn that observation equipment operating in wells, the study results of hydrogeological precursors of earthquakes and volcanic eruptions as well as their application experience in the work of expert councils can form the scientific and technical basis for the development of geoinformation prediction technology for natural disasters in the Kamchatka Krai.

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Rodríguez-Pradilla, Germán, and David W. Eaton. "Ground-Motion Analysis of Hydraulic-Fracturing Induced Seismicity at Close Epicentral Distance." Bulletin of the Seismological Society of America 110, no. 1 (December 31, 2019): 331–44. http://dx.doi.org/10.1785/0120190103.

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ABSTRACT The application of seismic hazard analysis methods developed for natural earthquakes can provide an effective framework for managing risks of induced seismicity (IS) sequences, particularly for assessment of potential risk to nearby infrastructure. Among various factors, the reliability of these methods depends on the accuracy of the ground-motion prediction equation (GMPE)—especially at close epicentral distances where ground motions are expected to be highest. In addition, potential impacts on local infrastructure can be assessed based on ground-motion-derived intensity values, which provide a basis for some traffic-light protocols that are used for managing fluid IS. GMPEs in many areas of the world, however, are poorly calibrated at close epicentral distances, because the availability of near-source seismograph stations is generally very sparse. This study investigates ground motions generated by an IS sequence, up to local magnitude (ML) 3.77 that occurred during a hydraulic-fracturing stimulation in the Duvernay shale play in central Alberta, western Canada. The sequence was monitored using a near-surface array that was located directly above the hydraulically fractured horizontal wells, providing accurate ground-motion measurements at hypocentral distances <10 km. The local array consisted of a combination of geophones cemented in shallow wellbores to depth of ∼27 m, shallow buried broadband seismometers, and a strong-motion accelerometer. This configuration enabled direct measurement of near-surface seismic velocities in the top 27 m, which provided robust VS30 data used to correct observed ground motions for local site-amplification effects. Our data set extends previous analyses in this region by providing new measurements very close to the epicenters of moderate earthquakes and shows that a recently developed GMPE provides accurate near-source ground-motion estimates.

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Allen, J. R. L. "Earthquake magnitude-frequency, epicentral distance, and soft-sediment deformation in sedimentary basins." Sedimentary Geology 46, no. 1-2 (January 1986): 67–75. http://dx.doi.org/10.1016/0037-0738(86)90006-0.

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MOHANTY, WILLIAM K., AKHILESH K. VERMA, FRANCO VACCARI, and GIULIANO F. PANZA. "Influence of epicentral distance on local seismic response in Kolkata City, India." Journal of Earth System Science 122, no. 2 (March 26, 2013): 321–38. http://dx.doi.org/10.1007/s12040-013-0275-1.

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DUBE, RK. "The variation of the angle of incidence of p waves with epicentral distance." MAUSAM 18, no. 2 (April 30, 2022): 279–84. http://dx.doi.org/10.54302/mausam.v18i2.4452.

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Angles of incidence of p waves were obtained from the records of the short and long period seismographs of W.W.S.S.N. at Shillong. The study covers the range of epicentral distances from 200 to 1000. The observations indicate that the velocity of P waves at the earth’s surface is approximately 6 km/sec which is the velocity of the upper layer (granitic layer) of the earth.

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Cassidy, John F., Garry C. Rogers, and Dieter H. Weichert. "Soil response on the Fraser delta to the MW = 5.1 Duvall, Washington, earthquake." Bulletin of the Seismological Society of America 87, no. 5 (October 1, 1997): 1354–61. http://dx.doi.org/10.1785/bssa0870051354.

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Abstract Strong-motion recordings of the 3 May 1996 MW = 5.1 Duvall, Washington, earthquake made in southwestern British Columbia provide the best constraints, to date, on soil response to seismic shaking on the Fraser delta, just south of Vancouver. A total of nine strong-motion instruments in southern B.C. triggered during this earthquake, seven of which are on or near the Fraser delta. These recordings were made at epicentral distances of 140 to 180 km. A preliminary analysis of these data clearly shows that for low frequencies (<3 Hz) seismic spectral amplification (by a factor of 2 to 7) occurs on the Fraser delta relative to nearby bedrock or thin firm-soil sites. However, at higher frequencies, moderate attenuation is observed at the Fraser delta sites. The largest peak ground accelerations recorded (generally around 2 to 3 Hz) were not on the thickest delta sediments but nearer the edge of the delta. Peak amplification is more pronounced in the horizontal component of ground motion than in the vertical. The average SH/Z ratio for peak values at the Fraser delta sites is 4.5 ± 0.9 compared to 1.6 ± 0.6 for the bedrock and firm-soil sites. In addition to the strong-motion records, we also utilize five three-component broadband recordings of this earthquake made in southern B.C. (epicentral distances of 140 to 520 km), and 12 short-period vertical-component recordings (epicentral distances of 130 to 380 km) to document attenuation of peak acceleration with distance for this earthquake. The observed values are slightly lower than those predicted by the ground-motion relations proposed for the year 2000 National Building Code of Canada.

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Cibeira Urtiaga, Ángel, Manuel Berrocoso, Belén Rosado, and Antonio Pazos. "Detection and study of a high magnitude seismic event from GPS data: Case study of the 2011 Tohoku-Oki earthquake." Earth Sciences Research Journal 26, no. 2 (September 8, 2022): 91–106. http://dx.doi.org/10.15446/esrj.v26n2.97735.

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The advent of GPS provided a new way of measuring surface displacements due to earthquakes by deploying GPS networks within active seismic areas. Japan is located in the confluence of several tectonic plates, hence its seismicity. In order to surveille this activity, one of wider GPS network in the world was deployed, i.e., GEONET. By processing data from 93 GEONET reference stations, we analyze the 2011 Tohoku-Oki earthquake using PPP strategy. We studied the time series during the event setting up a threshold value at we consider the time series are being altered by the earthquake. We also identified the time after the occurrence when the maximum displacements happen. With the study of these two parameters, we aim to show their different behavior as the main shock propagates along the Japan islands, with a focus on a better understanding of the earthquake and its propagation. To achieving this, a least square adjustment method was used to relate epicentral distance to topocentric displacements and the time of detection to epicentral distance. The results show an exponential behavior of the distance-displacement regression versus a linear behavior of the distance-time regression. Besides, we use the former linear regression to calculate and approximation of the velocity of the shock waves.

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Bowers, David. "On the probability of mistaking an earthquake for an explosion using the simplicity of P." Bulletin of the Seismological Society of America 86, no. 6 (December 1, 1996): 1925–34. http://dx.doi.org/10.1785/bssa0860061925.

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Abstract The observation that P waves from an earthquake are generally more complex than those from an underground explosion was first noted in the 1960s. This difference in P-wave character may still be the only way of identifying small earthquakes close to the detection threshold of a given station network. However, there are certain earthquakes that produce simple seismograms. The frequency at which such earthquakes are mistaken for explosions, using the complexity criterion, is known as the false alarm rate. A simple seismogram can be defined as having only one large-amplitude phase that can be caused by several mechanisms. We examine the proportion of simple seismograms produced by a randomly oriented double-couple source buried in three different crustal structures, observed at a single station at a range of epicentral distances. The model predicts that if the hypocenter of a small earthquake (near the detection threshold) is in a region with thick sediments, then the false alarm rate at a single station can be as high as 50% in the teleseismic distance range (30° to 90°). The results suggest that the false alarm rate is minimized if (1) array stations are used, (2) the station is at a large epicentral distance, (3) the source region structure has few layers, or (4) the disturbance is recorded at more than one station.

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Zhang, Baolong, Xiangfang Zeng, Jun Xie, and Vernon F. Cormier. "Validity of Resolving the 785 km Discontinuity in the Lower Mantle with P′P′ Precursors?" Seismological Research Letters 91, no. 6 (August 19, 2020): 3278–85. http://dx.doi.org/10.1785/0220200210.

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Abstract P ′ P ′ precursors have been used to detect discontinuities in the lower mantle of the Earth, but some seismic phases propagating along asymmetric ray paths or scattered waves could be misinterpreted as reflections from mantle discontinuities. By forward modeling in standard 1D Earth models, we demonstrate that the frequency content, slowness, and decay with distance of precursors about 180 s before P′P′ arrival are consistent with those of the PKPPdiff phase (or PdiffPKP) at epicentral distances around 78° rather than a reflection from a lower mantle interface. Furthermore, a beamforming technique applied to waveform data recorded at the USArray demonstrates that PKPPdiff can be commonly observed from numerous earthquakes. Hence, a reference 1D Earth model without lower mantle discontinuities can explain many of the observed P′P′ precursors signals if they are interpreted as PKPPdiff, instead of P′785P′. However, this study does not exclude the possibility of 785 km interface beneath the Africa. If this interface indeed exists, P′P′ precursors at distances around 78° would better not be used for its detection to avoid interference from PKPPdiff. Indeed, it could be detected with P′P′ precursors at epicentral distances less than 76° or with other seismic phases such as backscattered PKP·PKP waves.

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Chávez, David E., and Keith F. Priestley. "ML observations in the Great Basin and M0 versus ML relationships for the 1980 Mammoth Lakes, California, earthquake sequence." Bulletin of the Seismological Society of America 75, no. 6 (December 1, 1985): 1583–98. http://dx.doi.org/10.1785/bssa0750061583.

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Abstract The local magnitude distance correction term, log A0(Δ), has been estimated for paths within the Great Basin by converting seismograms of earthquakes in the vicinity of Mammoth Lakes, California, into equivalent Wood-Anderson seismograms and measuring the decay of peak amplitude with distance. The shape of the log A0(Δ) curve which results suggests more attenuation of energy in the Wood-Anderson passband than in southern California. For Great Basin paths we find, for events with ML ≦ 5.5, that log A 0 ( Δ ) = { log 10 [ e − 0.016 R R ] − 0.31 0 ≦ Δ ≦ 9 0 km log 10 [ e − 0.006 R R 0.83 ] − 1.08 90 ≦ Δ ≦ 6 0 0 km where Δ is epicentral distance, R=Δ2+h2 is hypocentral distance, and h is focal depth. Our data also suggest a magnitude bias in the correction term, in that for events above ML ≈ 5.5, peak amplitudes recorded at epicentral distances below 20 km decay less rapidly than those for smaller events recorded at the same sites. This observation is consistent with the hypothesis that there is a near-source saturation of ML due to the effects of a finite source size for large earthquakes. Using the revised magnitude scale and seismic moments, M0, estimated from spectral analysis, the data are well fit by the straight line log ⁡ M 0 = ( 1.20 ± 0.05 ) M L + ( 17.49 ± 0.19 ) for 1 ≦ ML ≦ 6. M0 versus ML values from model calculations which assume constant stress drop predict curved moment-magnitude plots over this magnitude range. The fact that we observe a linear relationship suggests that the stress drop of these events is not constant but rather increases with ML, in particular for events above ML ≈ 5.5.

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Markušić, Snježana, Davor Stanko, Davorin Penava, Ines Ivančić, Olga Bjelotomić Oršulić, Tvrtko Korbar, and Vasilis Sarhosis. "Destructive M6.2 Petrinja Earthquake (Croatia) in 2020—Preliminary Multidisciplinary Research." Remote Sensing 13, no. 6 (March 13, 2021): 1095. http://dx.doi.org/10.3390/rs13061095.

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On 28 December 2020, seismic activity in the wider Petrinja area strongly intensified after a period of relative seismological quiescence that had lasted more than 100 years (since the well-known M5.8 Kupa Valley earthquake of 1909, which is known based on the discovery of the Mohorovičić discontinuity). The day after the M5 foreshock, a destructive M6.2 mainshock occurred. Outcomes of preliminary seismological, geological and SAR image analyses indicate that the foreshocks, mainshock and aftershocks were generated due to the (re)activation of a complex fault system—the intersection of longitudinal NW–SE right-lateral and transverse NE–SW left-lateral faults along the transitional contact zone of the Dinarides and the Pannonian Basin. According to a survey of damage to buildings, approximately 15% of buildings were very heavily damaged or collapsed. Buildings of special or outstanding historical or cultural heritage significance mostly collapsed or became unserviceable. A preliminary analysis of the earthquake ground motion showed that in the epicentral area, the estimated peak ground acceleration PGA values for the bedrock ranged from 0.29 to 0.44 g. In the close Petrinja epicentral area that is characterized by the superficial deposits, significant ground failures were reported within local site effects. Based on that finding and building damage, we assume that the resulting peak ground acceleration (PGAsite) values were likely between 0.4 and 0.6 g depending on the local site characteristics and the distance from the epicentre.

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Bilham, Roger, and Bryan Castillo. "The July 2019 Ridgecrest, California, Earthquake Sequence Recorded by Creepmeters: Negligible Epicentral Afterslip and Prolonged Triggered Slip at Teleseismic Distances." Seismological Research Letters 91, no. 2A (January 15, 2020): 707–20. http://dx.doi.org/10.1785/0220190293.

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Abstract We report sequential triggered slip at 271–384 km distances on the San Andreas, Superstition Hills, and Imperial faults with an apparent travel-time speed of 2.2 ± 0.1 km/s, following the passage of surface waves from the 4 July 2019 (17:33:49 UTC) Mw 6.4 and 6 July 2019 (03:19:53 UTC) Mw 7.1 Ridgecrest earthquakes. Slip on remote faults was not triggered instantaneously but developed over several minutes, increasing in duration with distance. Maximum slip amplitudes varied from 10 μm to 5 mm within minutes of slip nucleation, but on the southernmost San Andreas fault slip continued for two months and was followed on 16 September 2019 by a swarm of microearthquakes (Mw≤3.8) near Bombay Beach. These observations add to a growing body of evidence that fault creep may result in delayed triggered seismicity. Displacements across surface faults in the southern epicentral region and on the Garlock fault in the months following the Ridgecrest earthquakes were negligible (<1.1 mm), and they are interpreted to characterize surface strain adjustments in the epicentral region, rather than to result from discrete slip on surface faults.

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Sohn, Dong-Hyo, Byung-Kyu Choi, Sungshil Kim, Sun-Cheon Park, Won-Jin Lee, and Pil-Ho Park. "Decaying Post-Seismic Deformation Observed on the Korean Peninsula Following the 2011 Tohoku-Oki Earthquake." Sensors 21, no. 13 (June 30, 2021): 4493. http://dx.doi.org/10.3390/s21134493.

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We investigated decaying post-seismic deformation observed on the Korean Peninsula associated with the 2011 Mw 9.0 Tohoku-Oki earthquake using Global Navigation Satellite System (GNSS). The GNSS velocity vectors were estimated in five periods from 2005 to 2019. A co-seismic offset of the Korean Peninsula caused by the 2011 earthquake was inversely proportional to epicentral distances. According to the temporal variations of two components (magnitude and direction) of the GNSS velocity vector with the epicentral distance, the difference between the eastern and western regions for the two components becomes smaller over time. For approximately nine years after the 2011 event, the direction for the crustal movement in South Korea showed a recovery pattern returning to the pre-earthquake motion. In addition, the recovery patterns of the crustal movement were observed differently with the regional geologic structure (e.g., the crustal thickness) and each period. Our estimates of the decay in post-seismic deformation of the Korean Peninsula suggest that post-seismic relaxation will be complete within 5–20 years after the 2011 earthquake. The results suggest that the crustal movement on the Korean Peninsula is gradually recovering to its pre-earthquake motion.

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Seinassinov, N. A., and N. N. Mikhailova. "MAGNITUDE SENSITIVITY OF KARATAYU SEISMIC ARRAY IN MONITORING OF SEISMICITY IN CENTRAL ASIA." NNC RK Bulletin, no. 2 (June 23, 2022): 23–31. http://dx.doi.org/10.52676/1729-7885-2022-2-23-31.

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The capability to record events of different magnitude at various epicentral distances (magnitude sensitivity of the station) was studied basing on representative statistical material ontained by the results of Karatayu seismic array operation for more than 10 years period. The dependence of magnitude sensitivity on azimuth of seismic waves arrival was studied. It is shown that depending on the direction, the station has different capabilities in recoding of small earthquakes at the same distance. The examples of small events recorded by Karatayu station are shown by a series of two explosions of shells at military warehouses in the south Kazakhstan in 2019 and 2021.

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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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Qiao, Zhiyuan, Guangcai Wang, Hong Fu, and Xiaojing Hu. "Identification of Groundwater Radon Precursory Anomalies by Critical Slowing down Theory: A Case Study in Yunnan Region, Southwest China." Water 14, no. 4 (February 11, 2022): 541. http://dx.doi.org/10.3390/w14040541.

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In this study, we use the critical slowing down (CSD) theory to identify the precursory anomalies of groundwater radon based on the 1000-day continuous data from 8 monitoring stations in Yunnan Province, China during the seismically active period of 1993–1996. The low-frequency and high-frequency information were extracted from raw groundwater radon data to calculate their one-step lag autocorrelation (AR-1) and variance, respectively, in order to identify the precursory anomalies. The results show that the anomaly characteristics can be divided into three categories: sudden jump anomalies, persistent anomalies, and fluctuation anomalies. The highest average seismic recognition rate is 72.78%, based on the high-frequency information’s autocorrelation, while the lowest is 45.08%, based on the low-frequency information’s variance. The crustal activity and the change in hydrogeological conditions are possibly the main factors influencing groundwater radon anomalies in the selected period in the study area. There is a positive correlation between the anomaly occurrence time and epicentral distance when epicentral distance is less than 300 km, which may be related to the seismogenic modes and hydrogeological conditions. This study provides a reference for identifying groundwater radon anomalies before earthquakes by mathematical methods.

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Lu, Yong, Yongming Huang, Jing Liu, Wei Xue, and Guobao Zhang. "Analysis of Geomagnetic Signals Based on Wavelet Transform and Fractal Algorithm." International Journal of Pattern Recognition and Artificial Intelligence 34, no. 09 (December 30, 2019): 2058011. http://dx.doi.org/10.1142/s0218001420580112.

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In this paper, in order to figure out the variations before an earthquake and extract abnormal signals related to it, the geomagnetic three component Z, H, F minute values of 15 geomagnetic stations within 600[Formula: see text]km of the epicentral distance before the MS 6.6 Minxian–Zhangxian earthquake in Gansu were analyzed. The following are the results. (1) After the fractal analysis was used directly, only three geomagnetic stations in 15 geomagnetic stations showed synchronous anomalous signals; (2) After the method of this paper was used, 9 of the 15 geomagnetic stations (including the three stations in the first point) extracted two synchronous anomalous signals, and six of the nine geomagnetic stations presented additional synchronous anomalous signals. (3) Of the three abnormal signals extracted, one had a medium-term effect and two had short-term effects. (4) The anomalous duration of the Z component of nine geomagnetic stations was longer than that of H and F. And as the epicentral distance increased, duration decreased. While the proposed method could not clearly indicate the exact relationship between the anomalous signals and the earthquake, it was proved that the signals extracted are effective and well-correlative to the earthquake.

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Brown, R. James. "Elimination of near-source ellipticity corrections to body-wave travel times by use of equidistant latitudes." Bulletin of the Seismological Society of America 75, no. 6 (December 1, 1985): 1713–18. http://dx.doi.org/10.1785/bssa0750061713.

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Abstract The use of equidistant latitudes has been proposed by the author to eliminate discrepancies between angular and kilometric epicentral distances. This is done in combination with a path-length correction which depends on the inclination of the great ellipse containing the epicenter-receiver path. If there were a one-to-one correspondence between source-receiver surface arc length (in kilometers) and, say, P-wave travel time (for constant focal depth) for a standard spheroidal Earth, the ellipticity (time) correction could then be replaced by the distance correction described. However, one would only expect this to be approximately valid for small epicentral distances Δ. In this paper, the travel-time corrections made by using equidistant latitudes (and the great-ellipse correction) are compared with the “true” ellipticity corrections due to Dziewonski and Gilbert. It is seen that the present equidistant-latitude method gives P-wave correction values that, for example, are always within 0.05 sec of the “true” values for Δ ≦ 14° and normal focal depth (h ≦ 40 km). For large Δ(⪞ 45°) and/or great focal depth (h⪞ 475 km), these values may differ by more than 0.2 sec. This equidistant-latitude method of correcting body-wave travel times is thus not recommended for routine use, but it could be used to advantage in special studies involving smaller Δ and h.

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HOSONO, Kohji, and Akio YOSHIDA. "On the Distribution of Epicentral Distance between the Largest Aftershock and the Main Shock." Zisin (Journal of the Seismological Society of Japan. 2nd ser.) 44, no. 3 (1991): 259–61. http://dx.doi.org/10.4294/zisin1948.44.3_259.

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Ma, Qiang, Fuchen Wang, Dongwang Tao, Quancai Xie, Heyi Liu, and Peng Jiang. "Topographic site effects of Xishan Park ridge in Zigong city, Sichuan considering epicentral distance." Journal of Seismology 25, no. 6 (October 5, 2021): 1537–55. http://dx.doi.org/10.1007/s10950-021-10048-7.

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Heidari, Reza. "Quick Estimation of the Magnitude and Epicentral Distance Using thePWave for Earthquakes in Iran." Bulletin of the Seismological Society of America 106, no. 1 (December 29, 2015): 225–31. http://dx.doi.org/10.1785/0120150090.

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Jung, Seula, Hyun‐Me Rhee, and Dong‐Hoon Sheen. "Rapid Assessment of Epicentral Distance Using the Initial P Waves Observed in South Korea." Bulletin of the Seismological Society of America 108, no. 1 (January 2, 2018): 511–16. http://dx.doi.org/10.1785/0120170199.

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Tian, Yu-Hong, and Pei-De Wang. "Acceleration record and characteristics of ground motion at an epicentral distance of 200 km." Acta Seismologica Sinica 7, no. 3 (August 1994): 501–5. http://dx.doi.org/10.1007/bf02650690.

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41

Mikhailova, N. N., A. N. Sokolov, and I. N. Sokolova. "QUANTITATIVE CHARACTERISTICS OF SEISMIC GROUND OSCILLATIONS BY STRONG MOTION RECORDS ON THE EAST KAZAKHSTAN TERRITORY." NNC RK Bulletin, no. 1 (March 30, 2022): 28–35. http://dx.doi.org/10.52676/1729-7885-2022-1-28-35.

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The paper describes the strong motions database that contains digital records and processing results of analogue and digital stations from the east Kazakhstan region. The database includes more than 150 records by digital data of the strong motion network, and by analogue stations at epicentral distance 7–4883 km. The peak acceleration for this period was recorded by Buran station for the aftershocks of Zaysan earthquake in 1990.

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Hough, S. E., K. Jacob, R. Busby, and P. A. Friberg. "Ground Motion From A Magnitude 3.5 Earthquake Near Massena, New York: Evidence For Poor Resolution of Corner Frequency For Small Events." Seismological Research Letters 60, no. 3 (July 1, 1989): 95–100. http://dx.doi.org/10.1785/gssrl.60.3.95.

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Abstract We present analysis of a magnitude 3.5 event which occurred at 9 km epicentral distance from a digital strong motion instrument operated by the National Center for Earthquake Engineering Research. Although the size of this isolated event is such that it can scarcely be considered to be a significant earthquake, a careful analysis of this high quality recording does yield several interesting results: 1) the S-wave spectra can be interpreted in terms of a simple omega-squared source spectrum and frequency-independent attenuation, 2) there is the suggestion of a poorly-resolved resonance in the P-wave spectrum, and perhaps most importantly, 3) the apparently simple S-wave spectra can be fit almost equally well with a surprisingly wide range of seismic corner frequencies, from roughly 5 to 25 Hz. This uncertainty in corner frequency translates into uncertainties in inferred Q values of almost an order of magnitude, and into uncertainties in stress drop of two orders of magnitude. Given the high quality of the data and the short epicentral distance to the station, we consider it likely that resolution of spectral decay and corner frequency will be at least as poor for any other recording of earthquakes with comparable or smaller magnitudes.

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Dong, Yinfeng, Hui Tian, Man Zhang, and Lejun Wei. "Long-term monitoring of dynamic characteristics of high-rise and super high-rise buildings using strong motion records." Advances in Mechanical Engineering 13, no. 12 (December 2021): 168781402110672. http://dx.doi.org/10.1177/16878140211067279.

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Seismic behavior of a structure is directly related to its dynamic characteristics, which include natural frequency, damping ratio, and mode shape. This study focuses on the long-term monitoring of dynamic characteristics of six selected target structures. The covariance-driven stochastic subspace identification (SSI) approach is used to estimate the fundamental natural frequency and damping ratio of target buildings based on long-term motion records in order to examine the temporal variation of dynamic properties. The fundamental natural frequency and damping ratio variations over time are first discussed. It is found that the fundamental natural frequency of some structures reduces dramatically after the 2011 Tohoku Earthquake, accompanied by a rise in damping ratio. Then, regression analysis is used to assess the relationship between dynamic characteristics and ground motion parameters (Peak ground acceleration (PGA), magnitude, focal depth, and epicentral distance) and structural response (root mean square acceleration, maximum response amplitude). It is discovered that the identified natural frequency has no clear correlation with the focal depth, a slight negative correlation with the epicentral distance, and a strong negative correlation with the magnitude and PGA. The root mean square acceleration and the maximum response amplitude are negatively correlated to the target buildings’ natural frequencies. Finally, the influence of environmental factors on dynamic properties is investigated.

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Heidebrecht, A. C., and N. Naumoski. "Evaluation of site-specific seismic design requirements for three Canadian cities." Canadian Journal of Civil Engineering 15, no. 3 (June 1, 1988): 409–23. http://dx.doi.org/10.1139/l88-056.

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Siesmic design requirements as specified in building codes normally use a generic approach in which the seismic response is independent of the site location, except for a single intensity-related parameter used to define the severity of the expected ground motion. In reality, the characteristics of earthquakes that influence structural response depend on both the level of seismic motion and the seismo-tectonic environment at the specific location. This paper describes a methodology for determining seismic design requirements that uses both magnitude (M) and epicentral distance (R) to define the seismo-tectonic environment. Ensembles of actual seismic strong motion records are selected to match the combinations of M and R that dominate the seismic risk at a specific location. These time histories are used to determine both response spectra and seismic response factors (as used in the 1985 edition of the National Building Code, NBCC 1985) for the location in question. This paper applies this methodology to Vancouver, Ottawa, and Quebec City and compares the results with the response spectra and seismic response factors specified in NBCC 1985. The results indicate that a site-specific investigation of seismic design requirements is important in distinguishing between locations having different seismo-tectonic environments. Key words: structures, design, seismic, code, dynamic, acceleration, velocity, spectra, magnitude, epicentral distance.

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Yang, Pengtao, Xiaolong Sun, Dongying Liu, Zhongtai He, and Yongsheng Li. "Hydrochemical Characteristics of Groundwater at the Epicenter of the 2021 Biru M6.1 Earthquake in Central Tibet." Water 13, no. 21 (November 4, 2021): 3111. http://dx.doi.org/10.3390/w13213111.

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Groundwater is undoubtedly important for water security and eco-environmental protection, especially in areas that experience earthquakes. Analyzing the characteristics and variation of groundwater after an earthquake is significant to obtain a better understanding of the seismic risk and rational management of groundwater resources. This study investigated the hydrogeochemical characteristics of groundwater at the epicenter of the 2021 Biru M6.1 earthquake in central Tibet, southwest China, using 23 water samples. The results showed that: (1) the hydrochemical type, hydrogen and oxygen isotope ratios, and SiO2 concentrations of three hot spring water samples in the study area were significantly different from those of samples taken elsewhere, indicating that the hot spring water originates from deeper geothermal reservoirs and has undergone more distant migration and longer fractionation processes; (2) the geochemical characteristics of groundwater from some sampling sites in the epicentral area were apparently distinct from those of other shallow groundwater or surface water samples, suggesting that the groundwater environment in the epicentral area has been affected by the earthquake. Along with the macroscopic groundwater responses in the epicentral area after the earthquake, we investigated the influencing mechanisms of the earthquake on the regional groundwater environment. We conclude that a shorter distance from the epicenter to the seismogenic fault leads to a greater possibility of the generation of new fractures, which then induce macroscopic responses and chemical characteristic variations for groundwater.

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Odaka, T. "A New Method of Quickly Estimating Epicentral Distance and Magnitude from a Single Seismic Record." Bulletin of the Seismological Society of America 93, no. 1 (February 1, 2003): 526–32. http://dx.doi.org/10.1785/0120020008.

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47

Friedmann, H. "A theoretical model for change of shape of spring-water radon anomalies with epicentral distance." Pure and Applied Geophysics PAGEOPH 122, no. 2-4 (1985): 531–44. http://dx.doi.org/10.1007/bf00874615.

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Ida, Y., D. Yang, Q. Li, H. Sun, and M. Hayakawa. "Detection of ULF electromagnetic emissions as a precursor to an earthquake in China with an improved polarization analysis." Natural Hazards and Earth System Sciences 8, no. 4 (July 30, 2008): 775–77. http://dx.doi.org/10.5194/nhess-8-775-2008.

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Abstract. An improved analysis of polarization (as the ratio of vertical magnetic field component to the horizontal one) has been developed, and applied to the approximately four years data (from 1 March 2003 to 31 December 2006) observed at Kashi station in China. It is concluded that the polarization ratio has exhibited an apparent increase only just before the earthquake on 1 September 2003 (magnitude = 6.1 and epicentral distance of 116 km).

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Pachhai, Surya, Michael S. Thorne, and Tarje Nissen-Meyer. "Quantification of Small-Scale Heterogeneity at the Core–Mantle Boundary Using Sample Entropy of SKS and SPdKS Synthetic Waveforms." Minerals 12, no. 7 (June 26, 2022): 813. http://dx.doi.org/10.3390/min12070813.

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Qualitative and quantitative analysis of seismic waveforms sensitive to the core–mantle boundary (CMB) region reveal the presence of ultralow-velocity zones (ULVZs) that have a strong decrease in compressional (P) and shear (S) wave velocity, and an increase in density within thin structures. However, understanding their physical origin and relation to the other large-scale structures in the lowermost mantle are limited due to an incomplete mapping of ULVZs at the CMB. The SKS and SPdKS seismic waveforms is routinely used to infer ULVZ presence, but has thus far only been used in a limited epicentral distance range. As the SKS/SPdKS wavefield interacts with a ULVZ it generates additional seismic arrivals, thus increasing the complexity of the recorded wavefield. Here, we explore utilization of the multi-scale sample entropy method to search for ULVZ structures. We investigate the feasibility of this approach through analysis of synthetic seismograms computed for PREM, 1-, 2.5-, and 3-D ULVZs as well as heterogeneous structures with a strong increase in velocity in the lowermost mantle in 1- and 2.5-D. We find that the sample entropy technique may be useful across a wide range of epicentral distances from 100° to 130°. Such an analysis, when applied to real waveforms, could provide coverage of roughly 85% by surface area of the CMB.

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Drilleau, Mélanie, Henri Samuel, Attilio Rivoldini, Mark Panning, and Philippe Lognonné. "Bayesian inversion of the Martian structure using geodynamic constraints." Geophysical Journal International 226, no. 3 (March 13, 2021): 1615–44. http://dx.doi.org/10.1093/gji/ggab105.

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SUMMARY The ongoing InSight mission has recently deployed very broad band seismometers to record the Martian seismic activity. These recordings constitute the first seismic data set collected at the surface of Mars. This unique but sparse record compels for the development of new techniques tailored to make the best use of the specific context of single station-multiple events with several possible ranges of uncertainties on the event location. To this end, we conducted sets of Markov chain Monte Carlo inversions for the 1-D seismic structure of Mars. We compared two inversion techniques that differ from the nature of the parametrization on which they rely. A first classical approach based on a parametrization of the 1-D seismic profile using Bézier curves. A second, less conventional approach that relies on a parametrization in terms of quantities that influence the thermochemical evolution of the planet (mantle rheology, initial thermal state and composition), which accounts for 4.5 Gyr of planetary evolution. We considered several combinations of true model parameters to retrieve, and explored the influence of the type of seismic data (body waves with or without surface waves), the number of events and their associated epicentral distances and uncertainties, and the presence of potential constraints on Moho depth inferred from independent measurements/considerations (receiver functions and gravity data). We show that due to its inherent tighter constraints the coupled approach allows a considerably better retrieval of Moho depth and the seismic structure underneath it than the classical inversion, under the condition that the physical assumptions made in the coupled approach are valid for Mars. In addition, our tests indicate that in order to constrain the seismic structure of Mars with InSight data, the following independent conditions must be met: (1) The presence of surface waves triggered by an internal source to constrain the epicentral distance. (2) The presence of just a few well-localized impact sources, with at least one located at close epicentral distance (<5°) to illuminate independently the crust and the mantle. In addition to providing tighter constraints of Mars seismic structure, geodynamically constrained inversions allow one to reconstruct the thermochemical and rheological history of Mars until present. Therefore, even with a relatively small amount of large events and in absence of surface waves, constraining the present-day structure and long-term evolution of the red planet remains possible through the use of tailored hybrid inversion schemes.

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Journal articles on the topic 'EPICENTRAL DISTANCE'

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