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1.
The Geological Survey of India (GSI) established a twelve-station temporary microearthquake (MEQ) network to monitor the aftershocks in the epicenter area of the Bhuj earthquake (M w7.5) of 26th January 2001. The main shock occurred in the Kutch rift basin with the epicenter to the north of Bhachao village, at an estimated depth of 25 km (IMD). About 3000 aftershocks (M d ≥ 1.0), were recorded by the GSI network over a monitoring period of about two and half months from 29th January 2001 to 15th April 2001. About 800 aftershocks (M d ≥ 2.0) are located in this study. The epicenters are clustered in an area 60 km × 30 km, between 23.3‡N and 23.6‡N and 70‡E and 70.6‡E. The main shock epicenter is also located within this zone. Two major aftershock trends are observed; one in the NE direction and other in the NW direction. Out of these two trends, the NE trend was more pronounced with depth. The major NE-SW trend is parallel to the Anjar-Rapar lineament. The other trend along NW-SE is parallel to the Bhachao lineament. The aftershocks at a shallower depth (<10km) are aligned only along the NW-SE direction. The depth slice at 10 km to 20 km shows both the NE-SW trend and the NW-SE trend. At greater depth (20 km–38 km) the NE-SW trend becomes more predominant. This observation suggests that the major rupture of the main shock took place at a depth level more than 20 km; it propagated along the NE-SW direction, and a conjugate rupture followed the NW-SE direction. A N-S depth section of the aftershocks shows that some aftershocks are clustered at shallower depth ≤ 10 km, but intense activity is observed at 15–38 km depth. There is almost an aseismic layer at 10–15 km depth. The activity is sparse below 38 km. The estimated depth of the main shock at 25 km is consistent with the cluster of maximum number of the aftershocks at 20–38 km. A NW-SE depth section of the aftershocks, perpendicular to the major NE-SW trend, indicates a SE dipping plane and a NE-SW depth section across the NW-SE trend shows a SW dipping plane. The epicentral map of the stronger aftershocksM ≥ 4.0 shows a prominent NE trend. Stronger aftershocks have followed the major rupture trend of the main shock. The depth section of these stronger aftershocks reveals that it occurred in the depth range of 20 to 38 km, and corroborates with a south dipping seismogenic plane.  相似文献   

2.
The 13 March 1992 Erzincan earthquake, M=6.8, occurred in the eastern half of the Erzincan basin. The largest aftershock took place near Pülümür on 15 March 1992. No clear surface breaks were observed, although teleseismic studies suggested that it was a strike-slip earthquake striking parallel to the North Anatolian fault, with a focus of approximately 10±2 km depth, 30 km rupture length, 95 cm of slip, and a 1.16×1026 dyn.cm seismic moment. The aftershock distribution concentrated at an area of the intersection between the North Anatolian fault and the Ovacik fault. These results indicate that the previously suggested seismic gap along the North Anatolian fault, east of Erzincan, still remains unruptured.  相似文献   

3.
We present the estimated source parameters from SH-wave spectral modeling of selected 463 aftershocks (2002–06) of the 26 January 2001 Bhuj earthquake, the well-recorded largest continental intraplate earthquake. The estimated seismic moment (Mo), corner frequency (fc), source radius (r) and stress drop (Δσ) for aftershocks of moment magnitude 1.7 to 5.6 range from 3.55×1011 to 2.84×1017 N-m, 1.3 to 11.83 Hz, 107 to 1515 m and 0.13 to 26.7 MPa, respectively, while the errors in fc and Δσ are found to be 1.1 Hz and 1.1 MPa, respectively. We also notice that the near surface attenuation factor (k) values vary from 0.02 to 0.03. Our estimates reveal that the stress drop values show more scatter (Mo0.5 to 1 is proportional to Δσ) toward the larger Mo values (≥1014.5 N-m), while they show a more systematic nature (Mo3 is proportional to Δσ) for smaller Mo values (<1014.5 N-m), which can be explained as a consequence of a nearly constant rupture radius for smaller aftershocks in the region. The large stress drops (= 10 MPa) associated with events on the north Wagad fault (at 15–30 km depth) and Gedi fault (at 3–15 km depth) can be attributed to the large stress developed at hypocentral depths as a result of high fluid pressure and the presence of mafic intrusive bodies beneath these two fault zones.  相似文献   

4.
The East Anatolian Fault Zone is a continental transform fault accommodating westward motion of the Anatolian fault. This study aims to investigate the source properties of two moderately large and damaging earthquakes which occurred along the transform fault in the last two decades using the teleseismic broadband P and SH body waveforms. The first earthquake, the 27 June 1998 Adana earthquake, occurred beneath the Adana basin, located close to the eastern extreme of Turkey’s Mediterranean coast. The faulting associated with the 1998 Adana earthquake is unilateral to the NE and confined to depths below 15 km with a length of 30 km along the strike (53°) and a dipping of 81° SE. The fixed-rake models fit the data less well than the variable-rake model. The main slip area centered at depth of about 27 km and to the NE of the hypocenter, covering a circular area of 10 km in diameter with a peak slip of about 60 cm. The slip model yields a seismic moment of 3.5?×?1018 N-m (Mw???6.4). The second earthquake, the 1 May 2003 Bingöl earthquake, occurred along a dextral conjugate fault of the East Anatolian Fault Zone. The preferred slip model with a seismic moment of 4.1?×?1018 N-m (Mw???6.4) suggests that the rupture was unilateral toward SE and was controlled by a failure of large asperity roughly circular in shape and centered at a depth of 5 km with peak displacement of about 55 cm. Our results suggest that the 1998 Adana earthquake did not occur on the mapped Göksun Yakap?nar Fault Zone but rather on a SE dipping unmapped fault that may be a split fault of it and buried under the thick (about 6 km) deposits of the Adana basin. For the 2003 Bingöl earthquake, the final slip model requires a rupture plane having 15° different strike than the most possible mapped fault.  相似文献   

5.
The Jiashian earthquake (ML 6.4) occurred on 4 March 2010. It was the largest inland event in southern Taiwan of 2010. The mainshock location was unexpected since it occurred in an area with relatively low background seismicity. In addition, reports of earthquake focal mechanisms do not fit with any known active fault geometry. In order to understand the origin of this earthquake, especially its rupture process, we perform a joint source inversion by using teleseismic body wave, GPS coseismic displacements and near field ground motion data. In this study, we considered a northwest–southeast trending fault with a northeast dip retrieved from GPS coseismic data and aftershocks distribution. To analyze the detailed slip distribution in space and time, we used near field 3D Green’s functions provided by spectral-element method and a full time–space inversion technique. We find a complex rupture process with several slip patches distributed inside two main asperities. The slip map reveals a mean slip of 12.9 cm for a maximum slip of 27.3 cm leading to a Mw 6.47 for this event. The rupture initiates in the deepest portion of the fault at 20 km depth, and propagated upward up to 2 km depth to form the two asperities. The source time function of this event revealed two pulses corresponding to the two asperities, for a total duration time of about 16 s. Most aftershocks occurred near the upper boundary of the deepest asperity while no aftershocks are located close to the shallowest one. We infer that the locations of these slip patches are related to the surrounding fault systems that may have restricted the rupture propagation during the earthquake.  相似文献   

6.
Spatial-temporal patterns of aftershocks of the 2001 Mw7.7 Bhuj earthquake during 2001–2008 reveal a northward spatial migration of seismic activity in the Kachchh seismic zone, which could be related with the loading stresses caused by the continued occurrences of aftershocks on the north Wagad fault (NWF), the causative fault of the 2001-mainshock. Aiming at explaining the observed northward migration of activity, we modelled the Coulomb failure stress change (DCFS) produced by the 2001-mainshock, the 2006 Mw5.6 Gedi fault (GF) and the 2007 Mw4.5 Allah bund fault (ABF) events on optimally oriented plane. A strong correlation between occurrences of earthquakes and regions of increased DCFS is obtained on the associated three faults i.e. NWF, ABF and GF. Predicted DCFS on the GF increased by 0.9 MPa at 3 km depth, where the 7th March 2006 Mw5.6 event occurred, whereas predicted DCFS on the ABF increased by 0.07 MPa at 30 km depth, where the 15th December 2007 Mw4.5 event occurred. Focal mechanism solutions of three events on the ABF have been estimated using the iterative inversion of broadband data from 5–10 stations, which are also constrained by the first P-motion data from 8–12 stations. These focal mechanism solutions for the ABF events reveal a dominant reverse movement with a strike-slip component along a preferred northwest or northeast dipping plane (∼50–70°). Focal mechanisms of the events on all the three fault zones reveal an N-S oriented P- axis or maximum principal stress in the region, which agrees with the prevailing N-S compression over the Indian plate. It is apparent that the northward migration of the static stress changes from the NWF, resulting from the occurrence 2001 Bhuj mainshock, might have caused the occurrence of the events on the GF and ABF during 2006–08.  相似文献   

7.
Locally recorded data for eighteen aftershocks of a magnitude(mb) 4.6 earthquake occurring near Ukhimath in the Garhwal Himalaya were analysed. A master event technique was adopted to locate seventeen individual aftershock hypocentres relative to the hypocentre of the eighteenth aftershock chosen as the master event. The aftershock epicentres define an approximately 30 km2 rupture zone commensurate with the magnitude of the earthquake. The distribution of epicentres within this zone and the limited amount of first motion data support the view that a group of parallel, sub-vertical, sinistral strike-slip faults oriented N46°, transverse to the regional NW-SE trend of the Garhwal Himalaya, was involved in this seismic episode. Since the estimated focal depth range for aftershocks of this sequence is 3–14 km, we infer that this transverse fault zone extends through the upper crustal layer to a depth of 14 km at least.  相似文献   

8.
We herein present source parameters and focal mechanism of a rare cratonic upper crustal earthquake of Mw4.0, which occurred at 8 km depth (centroid depth) below a region near Deogarh, Jharkhand. For our study, we used broadband waveform data from a seismic network of 15 three-component seismographs in the eastern Indian craton. The average seismic moment, moment magnitude and source radius are estimated to be 1.1 × 1015 N-m, 4.0 and 180.6 m, respectively. The high average stress drop of 14.27 MPa could be attributed to its lower-crustal origin. The mean corner frequency is calculated to be 4.1 Hz. To study the source mechanism, we perform a deviatoric constrained full waveform moment tensor inversion of multiple point sources on the band-passed (0.06 – 0.14 Hz) broadband displacement data of the Deogarh event, using ISOLA software. The best fit is obtained for the source at 8 km centroid depth, with a moment magnitude 3.7, and a right-lateral strike-slip mechanism with strike 162°, dip 72° and rake 169°. The P-axis orients N24°E, which is parallel to the direction of the absolute plate motion direction of Indian plate, while T-axis orients E-W, which is parallel to the strike of the pre-existing Damodar Graben (DG) of Gondwana age. The occurrence of this earthquake is attributed to the neotectonic reactivation of a fault associated with the E-W trending DG shear zone.  相似文献   

9.
This paper gives macroseismic and instrumental data on the 17 August 1983 Kamchatka earthquake which occurred in the center of the Kamchatka Gulf bend at a depth of 98 km with an epicentral intensity of VI–VII (MSK-64 scale), energy class 15, and magnitude MLH = 6.9. The focal mechanism represents a thrust along the inclined surface across the strike of the Kamchatka Gulf coastal line. The Primary-wave seismic moment M 0 is 6.3 × 1019 Nm, the Rayleigh wave M 0 is 1.6 × 1019 Nm, and the stress drop is 2.5 MPa. Copies of displacement and acceleration records are presented and the temporal and spatial distribution of the aftershocks is analyzed.  相似文献   

10.
Papadimitriou  P.  Voulgaris  N.  Kassaras  I.  Kaviris  G.  Delibasis  N.  Makropoulos  K. 《Natural Hazards》2002,27(1-2):15-33
On 7 September 1999 at 11:56 GMT a destructive earthquake (Mw = 6.0) occurred close to Athens (Greece). The rupture process is examined using data from the Cornet local permanent network, as well as teleseismic recordings. Data recorded by a temporary seismological network were analyzed to study the aftershock sequence. The mainshock was relocated at 38.105°N, 23.565°E, about 20 km northwest of Athens. Four foreshocks were also relocated close to the mainshock. The modeling of teleseismic P and SH waves provides a well-constrained focal mechanism of the mainshock (strike = 105°, dip = 55° and rake = -80°) at a depth of 8 km and a seismic moment M0 = 1.01025 dyn·cm. The obtained fault plane solution represents normal faulting indicating an almost north-south extension. More than 3500 aftershocks were located, 1813 of which present RMS < 0.1 s and ERH, ERZ < 1.0 km. Two main clusters were distinguished, while the depth distribution is concentrated between 2 and 11 km. Over 1000 fault plane solutions of aftershocks were constrained, the majority of which also correspond to N–S extension. No surface breaks were observed but the fault plane solution of the mainshock is in agreement with the tectonics of the area and with the focal mechanisms obtained by aftershocks. The hypocenter of the mainshock is located on the deep western edge of the fault plane. The relocated epicenter coincides with the fringe that represents the highest deformation observed on the differential interferometric image. The calculated source duration is 5 sec, while the estimated dimensions of the fault are 15 km length and 10 km width. The source process is characterized by unilateral eastward rupture propagation, towards the city of Athens. An evident stop phase observed in the recordings of the Cornet local stations is interpreted as a barrier caused by the Aegaleo Mountain.  相似文献   

11.
Earthquakes in Kenya are common along the Kenya Rift Valley because of the slow divergent movement of the rift and hydrothermal processes in the geothermal fields. This implies slow but continuous radiation of seismic energy, which relieves stress in the subsurface rocks. On the contrary, the NW-SE trending rift/fault zones such as the Aswa-Nyangia fault zone and the Muglad-Anza-Lamu rift zone are the likely sites of major earthquakes in Kenya and the East African region. These rift/fault zones have been the sites of a number of strong earthquakes in the past such as the M w = 7.2 southern Sudan earthquake of 20 May 1990 and aftershocks of M w = 6.5 and 7.1 on 24 May 1990, the 1937 M s = 6.1 earthquake north of Lake Turkana close to the Kenya-Ethiopian border, and the 1913 M s = 6.0 Turkana earthquake, among others. Source parameters of the 20 May 1990 southern Sudan earthquake show that this earthquake consists of only one event on a fault having strike, dip, and rake of 315°, 84°, and ?3°. The fault plane is characterized by a left-lateral strike slip fault mechanism. The focal depth for this earthquake is 12.1 km, seismic moment M o = 7.65 × 1019 Nm, and moment magnitude, M w = 7.19 (?7.2). The fault rupture started 15 s earlier and lasted for 17 s along a fault plane having dimensions of ?60 km × 40 km. The average fault dislocation is 1.1 m, and the stress drop, ?σ, is 1.63 MPa. The distribution of historical earthquakes (M w ≥ 5) from southern Sudan through central Kenya generally shows a NW-SE alignment of epicenters. On a local scale in Kenya, the NW–SE alignment of epicenters is characterized by earthquakes of local magnitude M l ≤ 4.0, except the 1928 Subukia earthquake (M s = 6.9) in central Kenya. This NW–SE alignment of epicenters is consistent with the trend of the Aswa-Nyangia Fault Zone, from southern Sudan through central Kenya and further southwards into the Indian Ocean. We therefore conclude that the NW–SE trending rift/fault zones are sites of strong earthquakes likely to pose the greatest earthquake hazard in Kenya and the East African region in general.  相似文献   

12.
Following a large-sized Bhuj earthquake (M s = 7.6) of January 26th, 2001, a small aperture 4-station temporary local network was deployed, in the epicentral area, for a period of about three weeks and resulted in the recording of more than 1800 aftershocks (-0.07 ≤M L <5.0). Preliminary locations of epicenters of 297 aftershocks (2.0 ≤M L <5.0) have brought out a dense cluster of aftershock activity, the center of which falls 20 km NW of Bhachau. Epicentral locations of after-shocks encompass a surface area of about 50 × 40 km2 that seems to indicate the surface projection of the rupture area associated with the earthquake. The distribution of aftershock activity above magnitude 3, shows that aftershocks are nonuniformly distributed and are aligned in the north, northwest and northeast directions. The epicenter of the mainshock falls on the southern edge of the delineated zone of aftershock activity and the maximum clustering of activity occurs in close proximity of the mainshock. Well-constrained focal depths of 122 aftershocks show that 89% of the aftershocks occurred at depths ranging between 6 and 25 km and only 7% and 4% aftershocks occur at depths less than 5 and more than 25 km respectively. The Gutenberg-Richter (GR) relationship, logN = 4.52 - 0.89ML, is fitted to the aftershock data (1.0<-M L<5.0) and theb-value of 0.89 has been estimated for the aftershock activity.  相似文献   

13.
A 12-station temporary microearthquake network was established by the Geological Survey of India for aftershock monitoring of the January 26th, 2001 Bhuj earthquake (M w 7.6) in the Kutch district of Gujarat state, western India. The epicentres of the aftershocks show two major trends: one in the NE direction and the other in the NW direction. Fault-plane solutions of the best-located and selected cluster of events that occurred along the NE trend, at a depth of 15–38 km, show reverse faulting with a large left-lateral strike-slip motion, which are comparable with the main-shock solution. The NW trending upper crustal aftershocks at depth <10 km, on the other hand, show reverse faulting with right-lateral strike-slip motion, and the mid crustal and lower crustal aftershocks, at a depth of 15–38 km, show pure reverse faulting as well as reverse faulting with right-lateral and left-lateral strike-slip motions; these solutions are not comparable with the main-shock solution. It is inferred that the intersection of two faults has been the source area for stress concentration to generate the main shock and the aftershocks.  相似文献   

14.
The paper presents a detailed analysis of 1st April 2015 earthquake, whose epicenter (30.16° N, 79.28° E) was located near Simtoli village of Chamoli district, Uttarakhand. The focal depth is refined to 7 km by the grid search technique using moment tensor inversion. The source parameters of the earthquake as estimated by spectral analysis method suggested the source radius of ~1.0 km, seismic moment as 1.99E+23 dyne-cm with moment magnitude (Mw) of 4.8 and stress drop of 69 bar. The fault plane solution inferred using full waveform inversion indicated two nodal planes, the northeast dipping plane having strike 334° and dip 5° and the southwest dipping plane with dip 86° and strike 118°. The parallelism of the nodal plane striking 334° with dip 5° as indicated in depth cross sections of the tectonic elements suggested the north dipping Main Boundary Thrust (MBT) to be the causative fault for this earthquake. Spatio-temporal distribution of earthquakes during the period 1960-2015 showed seismic quiescence during 2006-2010 and migration of seismicity towards south.  相似文献   

15.
On February 13, 1981 a relatively strong earthquake occurred in the Lake Vänern region in south-central Sweden. The shock had a magnitude ofML = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 ≤ ML ≤ 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg-wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5·1020 resp. 4·1018dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant.  相似文献   

16.
The November 27, 2005 Qeshm Island earthquake (Mw 6.0) occurred along the Zagros Thrust and Fold Belt which accommodates about half of the deformation caused by the Arabian and Eurasian Plates convergence. As typical for the belt, the earthquake was associated with buried reverse faulting and produced no surface rupture. Here, teleseismic broadband P velocity waveforms of the earthquake are inverted to obtain coseismic finite-fault slip distribution of the earthquake. It is obtained that rupture was controlled by failure of a single asperity with largest displacement of approximately 0.6 m, which occurred at a depth of 9 km. The slip model indicated radial rupture propagation from the hypocentre and confirmed blind reverse faulting within deeper part (below the depth of 6 km) of the sedimentary cover above the Hormuz Salt, lying between the cover and the basement, releasing a seismic moment of about 1.3?×?1018 Nm (MW?=?6.0). The results also confirm that the Hormuz Salt behaves as a barrier for rupture propagation to the basement below and occurrence of the aftershock activity downdip from the rupture within the Hormuz Salt. Calculated Coulomb stress variations caused by the coseismic rupture indicates stress coupling between the 2005 Qeshm Island earthquake and both the largest aftershock several hours later and the 2008 Qeshm Island earthquake (MW?=?5.9). The stress calculations further indicated stress load at the depth range (15–20 km) of the well-located aftershocks, corresponding to depths of the Hormuz Salt and top of the basement and providing plausible explanation for occurrence of the aftershocks within those layers.  相似文献   

17.
据中国地震台网测定，2021年5月21日21时48分在云南省大理州漾濞县发生MS6.4地震，及时查明此次地震的发震构造及震源破裂特征，可为认识该区孕震条件和判别未来强震危险性提供关键依据。采用双差定位方法对漾濞地震序列进行重新定位，得到3863次地震事件的精确震源位置。结果显示:漾濞地震序列整体呈北西—南东向分布，长约25 km；整体走向135°；MS6.4主震震中位置为25.688°N，99.877°E；震源深度约9.6 km。综合地震序列深度剖面和震源机制解结果可知，发震断层应为北西走向、整体向西南方向陡倾的右旋走滑断层，倾角具有自北西向南东逐渐变缓的趋势。进一步分析地震序列的时空演化过程发现，该地震具有典型的"前震-主震-余震型"地震序列活动特点，其破裂过程主要包括3个阶段。破裂成核阶段:首先在发震断层10~12 km深度处相对脆弱部位产生小尺度破裂，之后失稳加速破裂，发生MS5.6地震；主震破裂阶段:在构造应力场持续加载和周围小尺度破裂的共同影响下，促使浅部较高强度断层闭锁区破裂，形成MS6.4主震；尾端拉张破裂阶段:主震破裂向东南扩展过程中，在东南端形成与之呈马尾状斜交的、具有正断性质的次级破裂，并产生MS5.2余震。而且此次地震还在源区北东侧触发了北北东向的左旋走滑破裂。综合分析认为，漾濞地震是兰坪-思茅地块内部北西向草坪断裂在近南北向区域应力挤压作用下发生右旋走滑运动的结果，具有明显的新生断裂特征。近年来兰坪-思茅地块内部一系列中强地震的发生表明，青藏高原物质向东南持续挤出的过程中，遇到该地块的阻挡，正在导致地块内部早期断层贯通形成新的活动断裂。因此，川滇地块西南边界带上或相邻地块内部老断层的复活和新生断裂的产生是区域中强地震危险性分析评价中值得关注的重要课题，同时建议需重视未来该区中强地震进一步向东南和向北的迁移或扩展的可能性。   相似文献   

18.
The Vienna Basin Transfer Fault (VBTF) is a slow active fault with moderate seismicity (I max~8–9, M max~5.7) passing through the most vulnerable regions of Austria and Slovakia. We use different data to constrain the seismic potential of the VBTF including slip values computed from the seismic energy release during the 20th century, geological data on fault segmentation and a depth-extrapolated 3-D model of a generalized fault surface, which is used to define potential rupture zones. The seismic slip of the VBTF as a whole is in the range of 0.22–0.31 mm/year for a seismogenic fault thickness of 8 km. Seismic slip rates for individual segments vary from 0.00 to 0.77 mm/year. Comparing these data to geologically and GPS-derived slip velocities (>1 mm/year) proofs that the fault yields a significant seismic slip deficit. Segments of the fault with high seismic slip contrast from segments with no slip representing locked segments. Fault surfaces of segments within the seismogenic zone (4–14 km depth) vary from 55 to 400 km2. Empirical scaling relations show that these segments are sufficiently large to explain both, earthquakes observed in the last centuries, and the 4th century Carnuntum earthquake, for which archeo-seismological data suggest a magnitude of M ≥ 6. Based on the combination of all data (incomplete earthquake catalog, seismic slip deficits, locked segments, potential rupture areas, indications of strong pre-catalog earthquakes) we argue, that the maximum credible earthquake for the VBTF is in the range M max = 6.0–6.8, significantly larger than the magnitude of the strongest recorded events (M = 5.7).  相似文献   

19.
贵州的断裂与地震   总被引：1，自引：0，他引：1  
贵州的地震明显受（活动性）断裂控制和影响,地震的平面分布分区边界受区域断裂控制,地震多发生在断裂附近或多组断裂交汇区附近。1819年以来,贵州境内发生的4次6级左右地震,震中都在多组断裂交汇区附近。1875年6月8日发生的6.5级地震,震中在开远-平塘断裂和垭都-紫云断裂交汇区附近的床井背斜,地理位置位于罗甸县西部,紧邻望谟县和紫云县,即北纬25°18',东经106°36'。   相似文献   

20.
Spatial variation of seismicity parameters across India and adjoining areas   总被引：2，自引：2，他引：0  
An attempt has been made to quantify the variability in the seismic activity rate across the whole of India and adjoining areas (0–45°N and 60–105°E) using earthquake database compiled from various sources. Both historical and instrumental data were compiled and the complete catalog of Indian earthquakes till 2010 has been prepared. Region-specific earthquake magnitude scaling relations correlating different magnitude scales were achieved to develop a homogenous earthquake catalog for the region in unified moment magnitude scale. The dependent events (75.3%) in the raw catalog have been removed and the effect of aftershocks on the variation of b value has been quantified. The study area was divided into 2,025 grid points (1°×1°) and the spatial variation of the seismicity across the region have been analyzed considering all the events within 300 km radius from each grid point. A significant decrease in seismic b value was seen when declustered catalog was used which illustrates that a larger proportion of dependent events in the earthquake catalog are related to lower magnitude events. A list of 203,448 earthquakes (including aftershocks and foreshocks) occurred in the region covering the period from 250 B.C. to 2010 A.D. with all available details is uploaded in the website .  相似文献   

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