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1.
《Geofísica Internacional》2013,52(2):173-196
An analysis of local and regional data produced by the shallow, thrust Ometepec-Pinotepa Nacional earthquake (Mw 7.5) of 20 March 2012 shows that it nucleated at 16.254°N 98.531°W, about 5 km offshore at a depth of about 20 km. During the first 4 seconds the slip was relatively small. It was followed by rupture of two patches with large slip, one updip of the hypocenter to the SE and the other downdip to the north. Total rupture area, estimated from inversion of near-source strong-motion recordings, is ~25 km × 60 km. The earthquake was followed by an exceptionally large number of aftershocks. The aftershock area overlaps with that of the 1982 doublet (Mw 7.0, 6.9). However, the seismic moment of the 2012 earthquake is ~3 times the sum of the moments of the doublet, indicating that the gross rupture characteristics of the two earthquake episodes differ. The small-slip area near the hypocenter and large-slip areas of the two patches are characterized by relatively small aftershock activity. A striking, intense, linear NE alignment of the aftershocks is clearly seen. The radiated energy to seismic moment ratios, (Es/M0), of five earthquakes in the region reveal that they are an order of magnitude smaller for near-trench earthquakes than those that occur further downdip (e.g., 2012 and the 1995 Copala earthquakes). The near-trench earthquakes are known to produce low Amax. The available information suggests that the plate interface in the region can be divided in three domains. (1) From the trench to a distance of about 35 km downdip. In this domain M~6 to 7 earthquakes with low values of (Es/M0) occur. These events generate large number of aftershocks. It is not known whether the remaining area on this part of the interface slips aseismically (stable sliding) or is partially locked. (2) From 35 to 100 km from the trench. This domain is seismically coupled where stick-slip sliding occurs, generating large earthquakes. Part of the area is probably conditionally stable. (3) From 100 to 200 km from the trench. In this domain slow slip events (SSE) and nonvolcanic tremors (NVT) have been reported.The earthquake caused severe damage in and near the towns of Ometepec and Pinotepa Nacional. The PGA exceeded 1 g at a soft site in the epicentral region. Observed PGAs on hard sites as a function of distance are in reasonable agreement with the expected ones from ground motion prediction equations derived using data from Mexican interplate earthquakes. The earthquake was strongly felt in Mexico City. PGA at CU, a hard site in the city, was 12 gal. Strong-motion recordings in the city since 1985 demonstrate that PGAs during the 2012 earthquake were not exceptional, and that similar motion occurs about once in three years. 相似文献
2.
3.
To better understand the mechanics of subduction and the process of breaking a mature seismic gap, we study seismic activity along the western New Britain subduction segment (147°E–151°E, 4°S–8°S) through earthquakes withm
b
5.0 in the outer-rise, the upper area of subducting slab and at intermediate depths to 250 km, from January 1964 to December 1990. The segment last broke fully in large earthquakes of December, 28, 1945 (M
s
=7.9) and May 6, 1947 (M
s
=7.7.), and its higher seismic potential has been recognized byMcCann
et al., (1979). Recently the segment broke partially in two smaller events of February, 8, 1987 (M
s
=7.4) and October 16, 1987 (M
s
=7.4), leaving still unbroken areas.We observe from focal mechanisms that the outer-rise along the whole segment was under pronounced compression from the late 60's to at least October 1987 (with exception of the tensional earthquake of December 11, 1985), signifying the mature stage of the earthquake cycle. Simultaneously the slab at intermediate depths below 40 km was under tension before the earthquake of October 16, 1987. That event, with a smooth rupture lasting 32 sec, rupture velocity of 2.0 km/sec, extent of approximately 70 km and moment of 1.2×1027 dyne-cm, did not change significantly the compressive state of stress in the outer-rise of that segment. The earthquake did not fill the gap completely and this segment is still capable of rupturing either in an earthquake which would fill the gap between the 1987 and 1971 events, or in a larger magnitude event (M
s
=7.7–7.9), comparable to earthquakes observed in that segment in 1906, 1945 and 1947. 相似文献
4.
Coseismic deformation of the 2021 MW7.4 Maduo earthquake from joint inversion of InSAR,GPS, and teleseismic data 
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下载免费PDF全文 Chaoya Liu Ling Bai Shunying Hong Yanfang Dong Yong Jiang Hongru Li Huili Zhan Zhiwen Chen 《地震科学（英文版）》2021,34(5):436-446
The MW7.4 Maduo earthquake occurred on 22 May 2021 at 02:04 CST with a large-expansion surface rupture. This earthquake was located in the Bayan Har block at the eastern Tibetan Plateau, where eight earthquakes of MS >7.0 have occurred in the past 25 years. Here, we combined interferometric synthetic aperture radar, GPS, and teleseismic data to study the coseismic slip distribution, fault geometry, and dynamic source rupture process of the Maduo earthquake. We found that the overall coseismic deformation field of the Maduo earthquake is distributed in the NWW-SEE direction along 285°. There was slight bending at the western end and two branches at the eastern end. The maximum slip is located near the eastern bending area on the northern branch of the fault system. The rupture nucleated on the Jiangcuo fault and propagated approximately 160 km along-strike in both the NWW and SEE directions. The characteristic source rupture process of the Maduo earthquake is similar to that of the 2010 MW6.8 Yushu earthquake, indicating that similar earthquakes with large-expansion surface ruptures and small shallow slip deficits can occur on both the internal fault and boundary fault of the Bayan Har block. 相似文献
5.
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We determine the rupture velocity, rupture area, stress drop and duration of four strong deep-focus earthquakes in the Philippines
by back-projecting the teleseismic P waves. Four deep-focus earthquakes occurred in a totally consumed Molucca microplate;
their focal depths were greater than 550 km and their moment magnitudes were between M
w 6.6 and M
w 7.6. By studying this deep-focus cluster, we are able to estimate the rupture velocity, rupture area and stress drop which
would assist in constraining the physical mechanism for earthquakes deeper than 500 km. Since the Molucca microplate is totally
consumed, little evidence is left on the surface for us to do research. This deep-focus cluster provides us the opportunity
to reveal the properties of this totally consumed microplate by using seismic method for the first time. Four earthquakes
in this deep-focus cluster all have multiple rupture subevents. The M
w 7.3 event ruptures in two subevents, the M
w 7.6 and M
w 7.4 events both have three subevents. The M
w 6.6 event has single peak on the amplitude as a function of time; however, its energy releases at two spatially separated
areas. Our results show that this deep-focus cluster has a slow rupture velocity which is about 0.27 to 0.43 of the shear
wave velocity, long-scaled duration, concentrated energy release area, and high stress drop. These source properties are similar
to those of other deep earthquakes occurring in warm slabs and indicate that the totally consumed Molucca microplate possibly
is a warm plate. 相似文献
7.
The 10 January 2018 MW7.5 Swan island, Honduras earthquake occurred on the Swan island fault, which is a transform plate boundary between the North American and Caribbean plates. Here we back-project the rupture process of the earthquake using dense seismic stations in Alaska, and find that the earthquake ruptured at least three faults (three stages) for a duration of ~40 s. The rupture speed for the longest fault (stage 3) is as fast as 5 km/s, which is much faster than the local shear wave velocity of ~4 km/s. Supershear rupture was incidentally observed on long and straight strike-slip faults. This study shows a supershear rupture that occured on a strike-slip fault with moderate length, implying that supershear rupture might commonly occur on large strike-slip earthquakes. The common occurrence of supershear rupture on strike-slip earthquakes will challenge present understanding of crack physics, as well as strong ground motion evaluation in earthquake engineering. 相似文献
8.
Maximum earthquake size varies considerably amongst the subduction zones. This has been interpreted as a variation in the seismic coupling, which is presumably related to the mechanical conditions of the fault zone. The rupture process of a great earthquake indicates the distribution of strong (asperities) and weak regions of the fault. The rupture process of three great earthquakes (1963 Kurile Islands, MW = 8.5; 1965 Rat Islands, MW = 8.7; 1964 Alaska, MW = 9.2) are studied by using WWSSN stations in the core shadow zone. Diffraction around the core attenuates the P-wave amplitudes such that on-scale long-period P-waves are recorded. There are striking differences between the seismograms of the great earthquakes; the Alaskan earthquake has the largest amplitude and a very long-period nature, while the Kurile Islands earthquake appears to be a sequence of magnitude 7.5 events.The source time functions are deconvolved from the observed records. The Kurile Islands rupture process is characterized by the breaking of asperities with a length scale of 40–60 km, and for the Alaskan earthquake the dominant length scale in the epicentral region is 140–200 km. The variation of length scale and MW suggests that larger asperities cause larger earthquakes. The source time function of the 1979 Colombia earthquake (MW = 8.3) is also deconvolved. This earthquake is characterized by a single asperity of length scale 100–120 km, which is consistent with the above pattern, as the Colombia subduction zone was previously ruptured by a great (MW = 8.8) earthquake in 1906.The main result is that maximum earthquake size is related to the asperity distribution on the fault. The subduction zones with the largest earthquakes have very large asperities (e.g. the Alaskan earthquake), while the zones with the smaller great earthquakes (e.g. Kurile Islands) have smaller scattered asperities. 相似文献
9.
We examined the hypothesis that minima in local recurrence time, TL, or equivalently maxima in local probability, PL, may map asperities in the Kanto and Tokai areas of Japan, where the earthquake catalog of the National Research Institute for Earth Science and Disaster Prevention (NIED) is complete at the M=1.5 (M1.5) level. We mapped TL (PL) based on the a- and b-values of the nearest earthquakes within 20 km of every node of a grid spaced 0.01° for M7 target events. Only earthquakes within the top 33 km were used. The b-values increase strongly with depth, in several areas. Therefore, some of the TL (PL) anomalies are not revealed if data from the entire crustal seismogenic zone are mixed. Thus, we mapped TL (PL) separately for the top 15 km and the rest of the depth range, as well as for the entire seismogenic crust. The resulting TL- and PL-maps show that approximately 12% of the total area shows anomalously short recurrence times. Out of six shallow target events with M≥6.5 and which occurred since 1890, five are located within the anomalous areas with TL <450 years. We interpret this to mean that areas with anomalously short TL map asperities, which are more likely than other areas to generate future target events. The probability that this result is due to chance is vanishingly small. The great Kanto rupture of 1923 appears to have initiated in the most significant asperity we mapped in the study area. One anomaly is located in the northeastern part of the area of the proposed future rupture of the Tokai earthquake, and another one at its southwestern corner. The absolute values of TL calculated are uncertain because they depend on the size of the volume used for the calculation. 相似文献
10.
Emile A. Okal 《Physics of the Earth and Planetary Interiors》1976,12(4):319-328
Long-period records of multiple Love waves from the 1957 earthquake in Mongolia (MS = 8.0) at Pasadena are analysed and compared to synthetic seismograms, generated by the method of Kanamori. A fit in the time domain shows that the records are not consistent with the previous solution, achieved through a frequency-domain analysis of directivity by Ben-Menahem and Toksöz. The solution asks for a shorter rupture of 270 km at a velocity of 3.5 km/s. The focal parameters are constrained by updating all the reported first motion and are found to be: strike = 103°, dip = 53°, slip = 32°. A seismic moment of 1.8 · 1028 dyn · cm is obtained. These figures are also consistent with a time-domain analysis of Love waves at Palisades and Strasbourg, and of Rayleigh waves at Pasadena, with a directivity study of Love waves at Pasadena, and with static deformation and isoseismal data. A discussion is given of the relation between moment, magnitude and rupture area, and a comparison is made with other events in the same region: it is concluded that this earthquake does not exhibit an “intra-plate” behavior, but rather compares better with “inter-plate” events, such as the great Assam earthquake. 相似文献
11.
12.
Recent seismic activity in southern Lebanon is of particular interest since the tectonic framework of this region is poorly understood. In addition, seismicity in this region is very infrequent compared with the Roum fault to the east, which is seismically active. Between early 2008 and the end of 2010, intense seismic activity occurred in the area. This was manifested by several swarm-like sequences and continuous trickling seismicity over many days, amounting in total to more than 900 earthquakes in the magnitude range of 0.5?≤?M d?≤?5.2. The region of activity extended in a 40-km long zone mainly in a N-S direction and was located about 10 km west of the Roum fault. The largest earthquake, with a duration magnitude of M d?=?5.2, occurred on February 15, 2008, and was located at 33.327° N, 35.406° E at a depth of 3 km. The mean-horizontal peak ground acceleration observed at two nearby accelerometers exceeded 0.05 g, where the strongest peak horizontal acceleration was 55 cm/s2 at about 20 km SE of the epicenter. Application of the HypoDD algorithm yielded a pronounced N-S zone, parallel to the Roum fault, which was not known to be seismically active. Focal mechanism, based on full waveform inversion and the directivity effect of the strongest earthquake, suggests left-lateral strike-slip NNW-SSE faulting that crosses the NE-SW traverse faults in southern Lebanon. 相似文献
13.
Stefanie Donner Dirk Rößler Frank Krüger Abdolreza Ghods Manfred R. Strecker 《Journal of Seismology》2013,17(3):925-959
The M w 6.2 Baladeh earthquake occurred on 28 May 2004 in the Alborz Mountains, northern Iran. This earthquake was the first strong shock in this intracontinental orogen for which digital regional broadband data are available. The Baladeh event provides a rare opportunity to study fault geometry and ongoing deformation processes using modern seismological methods. A joint inversion for hypocentres and a velocity model plus a surface-wave group dispersion curve analysis were used to obtain an adapted velocity model, customised for mid- and long-period waveform modelling. Based on the new velocity model, regional waveform data of the mainshock and larger aftershocks (M w ?≥3.3) were inverted for moment tensors. For the Baladeh mainshock, this included inversion for kinematic parameters. All analysed earthquakes show dominant thrust mechanisms at depths between 14 and 26 km, with NW–SE striking fault planes. The mainshock ruptured a 28° south-dipping area of 24 × 21 km along a north-easterly direction. The rupture plane of the mainshock does not coincide with the aftershock distribution, neither in map view nor with respect to depth. The considered aftershocks form two main clusters. The eastern cluster is associated with the mainshock. The western cluster does not appear to be connected with the rupture plane of the mainshock but, instead, indicates a second activated fault plane dipping at 85° towards the north. 相似文献
14.
Pulse-like ground motion observed during the 6 February 2023 MW7.8 Pazarcık Earthquake (Kahramanmaraş, SE Türkiye) 下载免费PDF全文
下载免费PDF全文 Fan Wu Junju Xie Zhao An Chenghao Lyu Tuncay Taymaz Tahir Serkan Irmak Xiaojun Li Zengping Wen Baofeng Zhou 《地震科学（英文版）》2023,36(4):328-339
In this study, we analyzed 100 three-component strong ground motion records observed within 200 km of the causative fault of the 6 February 2023 MW7.8 Pazarcık (Kahramanmaraş) Earthquake in SE Türkiye. The wavelet method was utilized to identify and analyze the characteristics of pulse-like ground motions in the near-fault region, while considering the uncertainty of the pulse orientation during the analysis. Our investigation focused on the effects of the focal mechanism and rupture process on the spatial distribution, pulse orientation, and maximum pulse direction of the observed pulse-like ground motion. We also analyzed the amplitude and period of the observed ground pulses and the effect of long-period amplification on the ground motion response spectra. Our results indicated the following: (1) A total of 21 typical ground velocity pulses were observed during this earthquake, exhibiting complex characteristics due to the influence of the strike-slip mechanism and rupture directivity. Most ground pulses (17 out of 21) were recorded within 20 km of the fault, in a wide range of orientations, including normal and parallel to the fault direction. The waveforms exhibited unidirectional features, indicating the effects of left-lateral fault slip. Distinct pulses observed more than 20 km from the fault were mainly oriented normal to the fault. The waveforms were bidirectional with double- or multi-round trips as a result of rupture directivity. (2) The amplitudes of the observed pulses ranged from 30.5 to 220.0 cm/s, with the largest peak velocity of 220.0 cm/s observed at Station 3138. The pulse periods ranged from 2.3 to 14.5 s, with the longest pulse period of 14.5 s observed at Station 3116. The amplitude and period of the pulses observed during this earthquake were comparable to those of similar-magnitude global earthquakes. The amplitude of the pulses decreased significantly with increasing fault distance, whereas the pulse period was not significantly affected by the fault distance. (3) Compared with non-pulse records, the velocity pulse records had a pronounced amplification effect on the acceleration response spectra near the pulse period, with factors ranging from 2.1 to 5.8. The larger velocity pulses also significantly amplified the velocity response spectra, particularly over the long periods. This significant amplification effect of the pulses on the response spectra leads to empirical models underestimating the long-period earthquake ground motion. 相似文献
15.
Boi-Yee Liao Tian-Wei Sheu Yeong-Tien Yeh Huey-Chu Huang Lien-Shiang Yang 《Pure and Applied Geophysics》2013,170(3):391-407
This study investigates the kinematics of the rupture process of the M L 7.3 Chi–Chi, Taiwan, earthquake on September 21, 1999. By applying the proposed hybrid homomorphic deconvolution method to deconvolve teleseismic broadband P-wave displacement recordings of the earthquake, this study derives the apparent source time functions (ASTFs) at ten stations located around the epicenter. To further characterize the fault, the kinematic history of the rupture was inverted from ASTFs using a genetic algorithm, coupled with nonlinear iterative technique. The calculated ASFTs reveal that the total rupture event lasted for approximately 27 s. Static slip distribution images indicate that most slip occurred at shallower portions of the fault plane, especially 20–55 km north of the epicenter. The maximum slip reached 20 m at 45 km north of the epicenter, and the average slip throughout the observed rupture area was approximately 2 m. Large asperities on the fault appeared at 25–35 km and 40–50 km north of the hypocenter, and coincided with relatively high rupture velocity. This suggests that the earthquake’s energy may have been released quickly. The rupture velocity decreased upon encountering an asperity, and increased again after passing the asperity. This implies that the rupture required more time to overcome the resistances of the asperities. The maximum rupture velocity was 3.8 km/s, while the average rupture velocity was approximately 2.2 km/s. The rise time distribution suggests that larger slip amplitudes generally correspond to shorter rise times on the subfaults. 相似文献
16.
Ari Ben-Menahem Ezra Aboodi Rivka Schild 《Physics of the Earth and Planetary Interiors》1974,9(4):265-289
The source of the Assam earthquake of Aug. 15, 1950 is revealed from amplitude observations of surface and body waves at Pasadena, Tokyo and Bergen. Seiches' amplitudes in Norway, initial P motions throughout the world, aftershocks and landslides distribution, PP/P ratio at Tokyo, R/L ratio and directivity at Pasadena, are also used. The ensuing fault geometry and kinematics is consistent with the phenomenology of the event and the known geology of the source area. It is found that a progressive strike-slip rupture with velocity 3 km/sec took place on a fault of length 250 km and width 80 km striking 330–337° east of north and dipping 55–60° to ENE. The use of exact surface-wave theory and asymptotic body-wave theory which takes into account finiteness and absorption, rendered an average shear dislocation of 35 m. A three-dimensional theory for the excitation of seiches in lakes by the horizontal acceleration of surface waves was developed. It is confirmed that Love waves near Bergen generated seiches with peak amplitude up to 70 cm depending strongly on the width of the channel.It is believed that the earthquake was caused by a motion of the Asian plate relative to the eastern flank of the Indian plate where the NE Assam block is imparted a tendency of rotation with fracture lines being developed along its periphery.Comparison with other well-studied earthquakes shows that although the magnitude of the Assam event superseded that of all earthquakes since 1950, its potency U0dS (700,000 m × km2) was inferior to that of Alaska 1964 (1,560,000 m × km2) and Chile 1960 (1,020,000 m × km2). 相似文献
17.
Fracture characteristics of the 1997 Jiashi, Xinjiang, China, earthquake swarm inferred from source spectra 总被引：2，自引：0，他引：2
SHI-YONG ZHOU 《地震学报(英文版)》2000,13(2):125-135
Broadband P and S waves source spectra of 12 MS5.0 earthquakes of the 1997 Jiashi, Xinjiang, China, earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propagation of the earthquake faulting has also been inferred from the azimuthal variation of the corner frequency. The main results are as follows: ①The rupture size of MS6.0 strong earthquakes is in the range of 10～20 km, while that of MS=5.0～5.5 earthquakes is 6～10 km.② The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. ③ Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earthquakes. ④ For each MS6.0 earthquake there exists an apparent azimuthal variation of the corner frequencies. Azimuthally variation pattern of corner frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists. 相似文献
18.
2022年1月8日,青海省门源县发生MS6.9地震。使用青海、甘肃等区域数字台网所观测到的2009年1月1日—2022年2月8日间青海门源及周边地区(36°～39°N,101°～104°E)14 869次地震事件的地震观测资料,基于双差成像(TomoDD)方法进行重定位分析,结果表明：门源及周边地区地震震源深度较浅,主要集中在5～15 km深度范围,其中10 km附近分布最多。推断该深度区域为门源及周边地区的主要孕震区。基于地震重定位结果和主震区三维速度结构分别对2016年门源MS6.4地震和此次地震序列的发震机理进行分析对比,发现两次地震都位于高速异常体边缘,速度结构与断裂、地震序列吻合较好。2022年门源地震位于高速体的西端末梢位置,是该高速体受青藏高原东北缘顺时针应力作用导致的滑动产生的走滑型地震。 相似文献
19.
On July 20, 1995, an earthquake of M
L=4.1 occurred in Huailai basin, northwest of Beijing, with epicenter coordinates 40.326°N, 115.448°E and focal depth 5.5 km.
Following the main shock, seismicity sharply increased in the basin. This earthquake sequence was recorded by Sino-European
Cooperative Huailai Digital Seismograph Network (HDSN) and the hypocentres were precisely located. About 2 hours after the
occurrence of the main shock, a smaller event of M
L=2.0 took place at 40.323°N, 115.447°E with a focal depth of 5.0 km, which is very close to the main shock. Using the M
L=2.0 earthquake as an empirical Green’s function, a regularization method was applied to retrieve the far-field source-time
function (STF) of the main shock. Considering the records of HDSN are the type of velocity, to depress high frequency noise,
we removed instrument response from the records of the two events, then integrated them to get displacement seismogram before
applying the regularization method. From the 5 field stations, P phases in vertical direction which mostly are about 0.5 s
in length were used. The STFs obtained from each seismic phases are in good agreement, showing that the M
L=4.1 earthquake consisted of two events. STFs from each station demonstrate an obvious “seismic Doppler effect”. Assuming
the nodal plane striking 37° and dipping 40°, determined by using P wave first motion data and aftershock distribution, is
the fault plane, through a trial and error method, the following results were drawn: Both of the events lasted about 0.1 s,
the rupture length of the first one is 0.5 km, longer than the second one which is 0.3 km, and the rupture velocity of the
first event is 5.0 km/s, larger than that of the second one which is about 3.0 km/s; the second event took place 0.06 s later
than the first one; on the fault plane, the first event ruptured in the direction γ=140° measured clockwise from the strike
of the fault, while the second event ruptured at γ=80°, the initial point of the second one locates at γ=−100° and 0.52 km
from the beginning point of the first one. Using far-field ground displacement spectrum measurement method, the following
source parameters about the M
L=4.1 earthquake were also reached: the scalar earthquake moment is 3.3×1013 N·m, stress drop 4.6 MPa, rupture radius 0.16 km.
Contribution No. 99FE2022, Institute of Geophysics, China Seismological Bureau.
This study is supported by the Chinese Joint Seismological Science Foundation (95-07-411). 相似文献
20.
S. S. Arefiev E. A. Rogozhin Zh. Ya. Aptekman V. V. Bykova C. Dorbath 《Izvestiya Physics of the Solid Earth》2006,42(10):850-863
This work generalizes the results of tomographic imaging performed by the authors for epicentral zones. Seismic events in North Africa (the M w = 5.8 earthquake of 1985 near the town of Constantine), eastern Anatolia (the Erzincan M w = 6.7 earthquake of 1992), the Lesser and Greater Caucasus (the 1988 Spitak M w = 6.8 and the 1991 Racha M w = 7.0 earthquakes), and northern Sakhalin (the 1995 Neftegorsk M w = 7.1 earthquake) are examined. It is shown how various morphokinematic types of active faults differ in the resulting tomographic images at various depths. A classification of tomographic images of strong earthquake source zones is proposed in accordance with the rank of their generating faults. The sources of the Spitak, Racha, and Erzincan earthquakes are confined to large boundary faults separating tectonic zones. Lower velocity bands are revealed in the tomographic images, and low velocity “pockets” 1–2 km or somewhat more in width penetrating to a depth of up to 15 km are observed near the fault zones. The Constantine and Neftegorsk earthquakes were generated by faults of a lower rank. The source zones of these events are imaged tomographically as narrow gradient zones. 相似文献