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1.
—?We introduce a conceptual model for the in-plane physics of an earthquake fault. The model employs cellular automaton techniques to simulate tectonic loading, earthquake rupture, and strain redistribution. The impact of a hypothetical crustal elastodynamic Green's function is approximated by a long-range strain redistribution law with a r ?p dependance. We investigate the influence of the effective elastodynamic interaction range upon the dynamical behaviour of the model by conducting experiments with different values of the exponent (p). The results indicate that this model has two distinct, stable modes of behaviour. The first mode produces a characteristic earthquake distribution with moderate to large events preceeded by an interval of time in which the rate of energy release accelerates. A correlation function analysis reveals that accelerating sequences are associated with a systematic, global evolution of strain energy correlations within the system. The second stable mode produces Gutenberg-Richter statistics, with near-linear energy release and no significant global correlation evolution. A model with effectively short-range interactions preferentially displays Gutenberg-Richter behaviour. However, models with long-range interactions appear to switch between the characteristic and GR modes. As the range of elastodynamic interactions is increased, characteristic behaviour begins to dominate GR behaviour. These models demonstrate that evolution of strain energy correlations may occur within systems with a fixed elastodynamic interaction range. Supposing that similar mode-switching dynamical behaviour occurs within earthquake faults then intermediate-term forecasting of large earthquakes may be feasible for some earthquakes but not for others, in alignment with certain empirical seismological observations. Further numerical investigation of dynamical models of this type may lead to advances in earthquake forecasting research and theoretical seismology.  相似文献   

2.
On August 8, 2017, a M7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China, resulting in significant casualties and property damage. Therefore, it is critical to identify the areas of potential aftershocks before reconstruction and re-settling people to avoid future disasters. Based on the elastic dislocation theory and a multi-layered lithospheric model, we calculate the Coulomb failure stress changes caused by the Wenchuan and Jiuzhaigou earthquakes, discuss the relationship between the Mw7.9 Wenchuan and M7.0 Jiuzhaigou earthquakes, and analyze the influence of the aftershock distribution and stress changes on the major faults in this region caused by the Jiuzhaigou earthquake. The co- and post-seismic stress changes caused by the Wenchuan earthquake significantly increased the stress accumulation at the hypocenter of the Jiuzhaigou earthquake. Therefore, the occurrence of the Jiuzhaigou earthquake was probably stimulated by the Wenchuan earthquake. The aftershock distribution is well explained by the co-seismic stress changes of the Jiuzhaigou earthquake. The stress accumulation and corresponding seismic hazard on the Maqu-Heye segment of the East Kunlun fault and the northern extremity of the Huya fault has been further increased by the Jiuzhaigou earthquake.  相似文献   

3.
Spatiotemporal mapping the minimum magnitude of completeness Mc and b-value of the Gutenberg–Richter law is conducted for the earthquake catalog data of Greece. The data were recorded by the seismic network of the Institute of Geodynamics of the National Observatory of Athens (GINOA) in 1970–2010 and by the Hellenic Unified Seismic Network (HUSN) in 2011–2014. It is shown that with the beginning of the measurements at HUSN, the number of the recorded events more than quintupled. The magnitude of completeness Mc of the earthquake catalog for 1970–2010 varies within 2.7 to 3.5, whereas starting from April 2011 it decreases to 1.5–1.8 in the central part of the region and fluctuates around the average of 2.0 in the study region overall. The magnitude of completeness Mc and b-value for the catalogs of the earthquakes recorded by the old (GINOA) and new (HUSN) seismic networks are compared. It is hypothesized that the magnitude of completeness Mc may affect the b-value estimates. The spatial distribution of the b-value determined from the HUSN catalog data generally agrees with the main geotectonic features of the studied territory. It is shown that the b-value is below 1 in the zones of compression and is larger than or equal to 1 in the zones dominated by extension. The established depth dependence of the b-value is pretty much consistent with the hypothesis of a brittle–ductile transition zone existing in the Earth’s crust. It is assumed that the source depth of a strong earthquake can probably be estimated from the depth distribution of the b-value, which can be used for seismic hazard assessment.  相似文献   

4.
The data from seismic stations of the Arkhangelsk network and the networks in the neighboring territories are analyzed for refining the focal parameters of the tectonic earthquakes recorded in the north of the Russian plate on October 22, 2005 (M = 2.9) and March 28, 2013 (M = 3.4). The epicenters of the earthquakes are confined to the large NW–SE striking faults which border the Arkhangelsk bulge starting from the Kara–Pinega rift in the northeast and Onega–Kandalaksha paleorift in the southwest. The calculated focal mechanism of the earthquake of March 28, 2013 agrees with the distribution of neotectonic stresses characteristic of the north of the Russian plate, and specifically, with the submeridional compression and sublatitudinal extension.  相似文献   

5.
In this paper, we calculated the seismic pattern of instrumental recorded small and moderate earthquakes near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province. According to the spatial distribution of small and moderate earthquakes, 6 seismic dense zones are delineated. Temporal distribution of M L≥2 earthquakes since 1970 in each seismic dense zone has been analyzed. Based on temporal distribution characteristics and historical earthquake activity, three types of seismicities are proposed. The relationship between seismic types and crustal medium is analyzed. The mechanism of three types is discussed. Finity of strong earthquake recurrence is proposed. Seismic hazard in mid-long term and diversity of earthquake disaster in Shanxi seismic belt are discussed.  相似文献   

6.
The complex seismotectonic studies of the pleistoseist area of the Ilin-Tas earthquake (Ms = 6.9), one of the strongest seismic events ever recorded by the regional seismic network in northeastern Russia, are carried out. The structural tectonic position, morphotectonic features of present-day topography, active faults, and types of Cenozoic deformations of the epicentral zone are analyzed. The data of the instrumental observations are summarized, and the manifestations of the strong seismic events in the Yana–Indigirka segment of the Cherskii seismotectonic zone are considered. The explanation is suggested for the dynamical tectonic setting responsible for the Andrei-Tas seismic maximum. This setting is created by the influence of the Kolyma–Omolon indenter, which intrudes into the Cherskii seismotectonic zone from the region of the North American lithospheric plate and forms the main seismogenic structures of the Yana–Indigirka segment in the frontal zone (the Ilin-Tas anticlinorium). The highest seismic potential is noted in the Andrei- Tas block—the focus of the main tectonic impacts from the Kolyma–Omolon superterrane. The general trend of this block coincides with the orientation of the major axis of isoseismal ellipses (azimuth 50°–85°), which were determined from the observations of macroseismic effects on the ground after the Uyandina (Ms = 5.6), Andrei-Tas (Ms = 6.1), and Ilin-Tas (Ms = 6.9) earthquakes.  相似文献   

7.
Since March 2014, an unusually large amount of earthquakes occur southeast of the city of Darmstadt in the northern Upper Rhine Graben. During the period, until April 2015, we have recorded 356 earthquakes with magnitudes ranging from ML?=??0.6 to 4.2. We identified two source clusters separated laterally by about 5 km. The hypocentres within these clusters are aligned vertically extending over a depth range from 1 to 8 km with a lateral extent of about 1 to 2 km. Focal mechanisms show left-lateral strike-slip movements; b values are changing with time between b?=?0.6 and b?=?0.9. This is the first time in almost 150 years that such high earthquake rates have been observed in the region. Historical accounts dating back to the nineteenth century report of over 2000 felt earthquakes over a time span from 1869 to 1871. From these, maximum intensities of VII have been estimated. Other seismic activities in the region were reported in the 1970s. The observations of the 2014–2015 earthquake series do not completely match a typical main shock–aftershock sequence or a typical earthquake swarm. Especially the activity at the beginning of the earthquake series may be considered as a mixture of a main shock–aftershock sequence and a short-lasting swarm event. Whether or not the time gap between the current seismic activity, which actually takes place at the same locations as parts of the seismic swarm in 1869–1871, and the seismic activity in the nineteenth century or the seismic activity in the 1970s can be interpreted as a seismic cycle remains unclear.  相似文献   

8.
Based on the results from seismogeological study, aeromagnetic inversion and deep seismic sounding (DSS), it is found that the M≥8.0 earthquakes in North China have three common deep structural characteristics, i.e., they all took place above the ultra-crustal deep faults or on the edges of the tectonic blocks with higher intensity, and there are low-velocity, low-density and high-conductive layers deep in the epicentral regions. The origins of the earthquakes are also discussed and the two possibilities of seismogenesis are proposed, i.e., tectonic movement and intracrustal explosion.  相似文献   

9.
To study the prospective areas of upcoming strong-to-major earthquakes, i.e., M w  ≥ 6.0, a catalog of seismicity in the vicinity of the Thailand-Laos-Myanmar border region was generated and then investigated statistically. Based on the successful investigations of previous works, the seismicity rate change (Z value) technique was applied in this study. According to the completeness earthquake dataset, eight available case studies of strong-to-major earthquakes were investigated retrospectively. After iterative tests of the characteristic parameters concerning the number of earthquakes (N) and time window (T w ), the values of 50 and 1.2 years, respectively, were found to reveal an anomalous high Z-value peak (seismic quiescence) prior to the occurrence of six out of the eight major earthquake events studied. In addition, the location of the Z-value anomalies conformed fairly well to the epicenters of those earthquakes. Based on the investigation of correlation coefficient and the stochastic test of the Z values, the parameters used here (N = 50 events and T w  = 1.2 years) were suitable to determine the precursory Z value and not random phenomena. The Z values of this study and the frequency-magnitude distribution b values of a previous work both highlighted the same prospective areas that might generate an upcoming major earthquake: (i) some areas in the northern part of Laos and (ii) the eastern part of Myanmar.  相似文献   

10.
On April 29, 2017 at 0:56 UTC (2:56 local time), an MW =?2.8 earthquake struck the metropolitan area between Leipzig and Halle, Germany, near the small town of Markranstädt. The earthquake was felt within 50 km from the epicenter and reached a local intensity of I0 = IV. Already in 2015 and only 15 km northwest of the epicenter, a MW =?3.2 earthquake struck the area with a similar large felt radius and I0 = IV. More than 1.1 million people live in the region, and the unusual occurrence of the two earthquakes led to public attention, because the tectonic activity is unclear and induced earthquakes have occurred in neighboring regions. Historical earthquakes south of Leipzig had estimated magnitudes up to MW ≈?5 and coincide with NW-SE striking crustal basement faults. We use different seismological methods to analyze the two recent earthquakes and discuss them in the context of the known tectonic structures and historical seismicity. Novel stochastic full waveform simulation and inversion approaches are adapted for the application to weak, local earthquakes, to analyze mechanisms and ground motions and their relation to observed intensities. We find NW-SE striking normal faulting mechanisms for both earthquakes and centroid depths of 26 and 29 km. The earthquakes are located where faults with large vertical offsets of several hundred meters and Hercynian strike have developed since the Mesozoic. We use a stochastic full waveform simulation to explain the local peak ground velocities and calibrate the method to simulate intensities. Since the area is densely populated and has sensitive infrastructure, we simulate scenarios assuming that a 12-km long fault segment between the two recent earthquakes is ruptured and study the impact of rupture parameters on ground motions and expected damage.  相似文献   

11.
The paper addresses the collection and analysis of new data on aftershocks that occurred within 20 days of the main shock of the December 7, 1988, Spitak earthquake, Mw = 6.8. The data were used to improve the location of aftershock hypocenters and magnitudes. Available data concerning this 20-day period were the least reliable in terms of completeness, representativeness, and the accuracy of hypocenter location and, in particular, estimation of energy classes and magnitudes. New data were retrieved from the records and bulletins of the seismic stations of the regional and global networks. Hypocenter parameters were determined by means of the minimization of wave travel-time residuals and subsequent double-difference hypocenter relocation. Digital records of the Obninsk and Arti seismic stations (Δ = 15°–18°) and five more distant stations (Δ = 34°–53°) were used to more accurately estimate the surface-wave magnitude of the main shock and strongest aftershock. The aftershock catalog of the Spitak earthquake was substantially revised. First, the previous hypocenter locations (Aref’ev et al., 1991) were improved using the double-difference method; second, new data were retrieved from the bulletins of Caucasian seismic stations. The minimum magnitude of completeness (M c = 1.9) of the new catalog for the first 20 days after the main shock (when there were no epicentral observations) is the same as that for the period from December 7, 1988, to December 31, 1989. The new catalog contains information on 2090 aftershocks with magnitude M = 1.9 and more for the period from December 7, 1988, to December 31, 1989. The double-difference method allowed the location of the epicenters of clustered earthquakes to be reliably estimated with a longitude error of no more than 4.6 km, a latitude error of 4 km, and a depth error of 5 km. The new spatial distribution of the aftershock hypocenters is better correlated with the tectonic setting than the old data. The new catalog can be used to assess seismic hazard after strong earthquakes in the region.  相似文献   

12.
The paper presents results of analysis of spatiotemporal variations in the rigidity of seismically active rock masses obtained from California Integrated Seismic Network data on first arrivals of P waves from local background (M < 5.0) earthquakes. The main goal was to determine sizes of zones of an anomalous response to the nucleation of strong earthquakes and to reveal specific features of dynamic manifestations of anomalies in crustal fault zones. As a result, conclusions are drawn on the nature of the variations, their implications for the development of strong earthquake sources, and their suitability for earthquake prediction.  相似文献   

13.
The locations of possible earthquake occurrence (magnitudes M ≥ 6) have been determined for mountainous Crimea and the adjacent sea shelf, including the continental slope zone. The earthquake-generating structures were assumed to be intersections of morphostructural lineaments as found by morphostructural zoning. The measurement of geological and geophysical characteristics was followed by applying a decision rule that was derived previously using the CORA-3 pattern recognition algorithm in order to find possible locations of M ≥ 6 earthquakes in the Caucasus. The results corroborate the high seismic potential for the Yalta area where two events with magnitudes of 6.0 and 6.8 occurred in 1927, as well as indicating the possibility of M ≥ 6 earthquakes in other areas in mountainous Crimea and in the adjacent Black Sea area where no such events have yet been recorded.  相似文献   

14.
The time variations in the Gutenberg–Richter b-value are minutely studied based on the data of highly accurate seismological observations at the Garm prognostic site, Tajikistan, where a stationary network of seismic stations of the Complex Seismological Expedition (CSE) of Schmidt Institute of Physics of the Earth (IPE) of the USSR (Russian) Academy of Sciences was in operation from 1955 to 1992. A total of 93035 local earthquakes ranging from 0.0 to 6.3 in the Ml magnitudes are considered. The spatiotemporal fluctuations in the minimal magnitude of completeness of the earthquakes, Mc, are analyzed. The study considers a 25-year interval of the observations at the center of the observation system within which Mc = 0.9. It is shown that in most cases, the b-value and log10E2/3 experience characteristic time variations before the earthquakes with magnitudes higher than the minimal magnitude of the predicted earthquake (MPE). The 6-year anomaly in the parameters’ b-value, log10E2/3, and log10N associated with the single strongest earthquake with M = 6.3 that occurred in the observation region on October 26, 1984 is revealed. The inversely proportional relationship is established between the time variations in the b-value and the time variations in the velocities of seismic waves Vp and Vp/Vs. It is shown that the exponent p in the power function which links the time variations of the b-value and log10E2/3 is higher in the zones of crustal compression than in the zones of extension. It is simultaneously confirmed that the average b-value in the zones of compression is lower than in the zones of extension. It is established that in the case of earthquakes with M ≥ 2.6, the time series of seismic activity log10Ni and the time series of the b-value are highly cross correlated with a coefficient of r ≈ 0.75, whereas in the case of earthquakes with M ≥ 0.9, the coefficient of cross correlation between these time series is close to zero (r ≈ 0.06). The law of variations in the slope of the lines approximating the relationship between the log10Ni time series in the different magnitude ranges (M ≥ Mci) and b-value time series is obtained. It is hypothesized that the seismic activity of the earthquakes with high magnitudes can be estimated provided that the parameters of the time series of the b-value and time series of the number of earthquakes logN(ΔMi) in the range of low magnitudes are known. It is concluded that using the parameter log10N for prognostic estimates of the strong earthquakes only makes sense for earthquakes having moderate and large magnitudes. It is inferred that the time variations in the b-value are predominantly contributed by the time variations of the earthquakes with relatively large magnitudes.  相似文献   

15.
In the paper, the feature of strong earthquake orderly distribution in time, space and intensity before the Western Kunlun Mountain Pass M=8.1 earthquake is preliminarily studied. The modulation and triggering factors such as the earth rotation, earth tides are analyzed. The results show that: the giant earthquakes with the magnitude more than 8 occurred about every 24 years and the earthquakes with the magnitude more than 7 about every 7 years in Chinese mainland. The Western Kunlun Mountain M=8.1 earthquake exactly occurred at the expected time; The spatial distance show approximately the same distances between each two swarms. The earth rotation, earth tide, sun tide and sun magnetic field have played a role of modulation and triggering in the intensity. At last, the conditions for earthquake generation and occurrence are also discussed.  相似文献   

16.
The purpose of this work is to define a seismic regionalization of Mexico for seismic hazard and risk analyses. This seismic regionalization is based on seismic, geologic, and tectonic characteristics. To this end, a seismic catalog was compiled using the more reliable sources available. The catalog was made homogeneous in magnitude in order to avoid the differences in the way this parameter is reported by various agencies. Instead of using a linear regression to converts from m b and M d to M s or M w , using only events for which estimates of both magnitudes are available (i.e., paired data), we used the frequency-magnitude relations relying on the a and b values of the Gutenberg-Richter relation. The seismic regions are divided into three main categories: seismicity associated with the subduction process along the Pacific coast of Mexico, in-slab events within the down-going COC and RIV plates, and crustal seismicity associated to various geologic and tectonic regions. In total, 18 seismic regions were identified and delimited. For each, the a and b values of the Gutenberg-Richter relation were determined using a maximum likelihood estimation. The a and b parameters were repeatedly estimated as a function of time for each region, in order to confirm their reliability and stability. The recurrence times predicted by the resulting Gutenberg-Richter relations obtained are compared with the observed recurrence times of the larger events in each region of both historical and instrumental earthquakes.  相似文献   

17.
Introduction The northeast margin of Qinghai-Xizang block has become the place with close attentions from geo-specialists at home and abroad for its significant tectonic movement and intensive seismicity. Quite a number of achievements have been obtained from the studies on geological structures and strong earthquake activities (DING, LU, 1989, 1991; GUO, et al, 1992, 2000; GUO, XIANG, 1993; HOU, et al, 1999; Tapponnier, et al, 1990; Gaudemer, et al, 1995). In the Development Program…  相似文献   

18.
We present the seismic source zoning of the tectonically active Greater Kashmir territory of the Northwestern Himalaya and seismicity analysis (Gutenberg-Richter parameters) and maximum credible earthquake (m max) estimation of each zone. The earthquake catalogue used in the analysis is an extensive one compiled from various sources which spans from 1907 to 2012. Five seismogenic zones were delineated, viz. Hazara-Kashmir Syntaxis, Karakorum Seismic Zone, Kohistan Seismic Zone, Nanga Parbat Syntaxis, and SE-Kashmir Seismic Zone. Then, the seismicity analysis and maximum credible earthquake estimation were carried out for each zone. The low b value (<1.0) indicates a higher stress regime in all the zones except Nanga Parbat Syntaxis Seismic Zone and SE-Kashmir Seismic Zone. The m max was estimated following three different methodologies, the fault parameter approach, convergence rates using geodetic measurements, and the probabilistic approach using the earthquake catalogue and is estimated to be M w 7.7, M w 8.5, and M w 8.1, respectively. The maximum credible earthquake (m max) estimated for each zone shows that Hazara Kashmir Syntaxis Seismic Zone has the highest m max of M w 8.1 (±0.36), which is espoused by the historical 1555 Kashmir earthquake of M w 7.6 as well as the recent 8 October 2005 Kashmir earthquake of M w 7.6. The variation in the estimated m max by the above discussed methodologies is obvious, as the definition and interpretation of the m max change with the method. Interestingly, historical archives (～900 years) do not speak of a great earthquake in this region, which is attributed to the complex and unique tectonic and geologic setup of the Kashmir Himalaya. The convergence is this part of the Himalaya is distributed not only along the main boundary faults but also along the various active out-of-sequence faults as compared to the Central Himalaya, where it is mainly adjusted along the main boundary fault.  相似文献   

19.
An interpretation of the parameters of earthquake sources is proposed for the two large earthquakes in the Rat Islands of February 4, 1965 (M W = 8.7), and November 17, 2003 (M W = 7.7–7.8), based on the analysis of focal mechanisms, the manifestation of aftershocks, and the specific features of the geological structure of the island slope of the Rat Islands. The source of the earthquake of 1965 is a reverse fault of longitudinal strike, with a length of ～350 km. It is located in the lower part of the Aleutian Terrace and probably is genetically connected with the development of the Rat submarine ridge. The westward boundary of the earthquake source is determined by the Heck Canyon structures, and the eastward boundary is determined by the end of Rat Ridge in the region of λ ～ 179°E–179.5°E. The source of the earthquake of 2003 is a steep E-W reverse fault extending for about 100 km. It is located in the eastern part of the Rat Islands, higher on the slope than the source of the earthquake of 1965. The westward end of the earthquake source is determined by Rat Canyon structures, and the eastward end is an abrupt change in isobaths in the region of λ ～ 179°E. According to the aftershock hypocenters, the depth of occurrence of the reverse fault could reach ～60 km. According to our interpretation, on the southern slope of the Rat and Near islands, there is a complex system of seismogenic faults that is caused by tectonic development of different structural elements. The dominant types of faults here are reverse faults, as in other island arcs. During earthquakes, reverse faults oriented along the island arc and also faults that intersect it exhibit themselves. The reverse faults of northeastern strike that intersect the arc characterize the type of tectonic motions in a series of canyons of the western part of the Aleutian Islands.  相似文献   

20.
Aftershock hazard maps contain the essential information for search and rescue process, and re-occupation after a main-shock. Accordingly, the main purposes of this article are to study the aftershock decay parameters and to estimate the expected high-frequency ground motions (i.e., Peak Ground Acceleration (PGA)) for recent large earthquakes in the Iranian plateau. For this aim, the Ahar-Varzaghan doublet earthquake (August 11, 2012; M N =6.5, M N =6.3), and the Ilam (Murmuri) earthquake (August 18, 2014 ; M N =6.2) have been selected. The earthquake catalogue has been collected based on the Gardner and Knopoff (Bull Seismol Soc Am 64(5), 1363-1367, 1974) temporal and spatial windowing technique. The magnitude of completeness and the seismicity parameters (a,??b) and the modified Omori law parameters (P,??K,??C) have been determined for these two earthquakes in the 14, 30, and 60 days after the mainshocks. Also, the temporal changes of parameters (a,??b,??P,??K,??C) have been studied. The aftershock hazard maps for the probability of exceedance (33%) have been computed in the time periods of 14, 30, and 60 days after the Ahar-Varzaghan and Ilam (Murmuri) earthquakes. For calculating the expected PGA of aftershocks, the regional and global ground motion prediction equations have been utilized. Amplification factor based on the site classes has also been implied in the calculation of PGA. These aftershock hazard maps show an agreement between the PGAs of large aftershocks and the forecasted PGAs. Also, the significant role of b parameter in the Ilam (Murmuri) probabilistic aftershock hazard maps has been investigated.  相似文献   

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