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1.
TheM s =6.9 Gonghe, China, earthquake of April 26, 1990 is the largest earthquake to have been documented historically as well as recorded instrumentally in the northeastern Qinghai-Xizang (Tibetan) plateau. The source process of this earthquake and the tectonic stress field in the northeastern Qinghai-Xizang plateau are investigated using geodetic and seismic data. The leveling data are used to invert the focal mechanism, the shape of the slipped region and the slip distribution on the fault plane. It is obtained through inversion of the leveling data that this earthquake was caused by a mainly reverse dip-slipping buried fault with strike 102°, dip 46° to SSW, rake 86° and a seismic moment of 9,4×1018 Nm. The stress drop, strain and energy released for this earthquake are estimated to be 4.9 MPa, 7.4×10–5 and 7.0×1014 J, respectively. The slip distributes in a region slightly deep from NWW to SEE, with two nuclei, i.e., knots with highly concentrated slip, located in a shallower depth in the NWW and a deeper depth in the SEE, respectively.Broadband body waves data recorded by the China Digital Seismograph Network (CDSN) for the Gonghe earthquake are used to retrieve the source process of the earthquakes. It is found through moment-tensor inversion that theM s =6.9 main shock is a complex rupture process dominated by shear faulting with scalar seismic moment of the best double-couple of 9.4×1018 Nm, which is identical to the seismic moment determined from leveling data. The moment rate tensor functions reveal that this earthquake consists of three consecutive events. The first event, with a scalar seismic moment of 4.7×1018 Nm, occurred between 0–12 s, and has a focal mechanism similar to that inverted from leveling data. The second event, with a smaller seismic moment of 2.1×1018 Nm, occurred between 12–31 s, and has a variable focal mechanism. The third event, with a sealar seismic moment of 2.5×1018 Nm, occurred between 31–41 s, and has a focal mechanism similar to that inverted from leveling data. The strike of the 1990 Gonghe earthquake, and the significantly reverse dip-slip with minor left-lateral strike-slip motion suggest that the pressure axis of the tectonic stress field in the northeastern Qinghai-Xizang plateau is close to horizontal and oriented NNE to SSW, consistent with the relative collision motion between the Indian and Eurasian plates. The predominant thrust mechanism and the complexity in the tempo-spatial rupture process of the Gonghe earthquake, as revealed by the geodetic and seismic data, is generally consistent with the overall distribution of isoseismals, aftershock seismicity and the geometry of intersecting faults structure in the Gonghe basin of the northeastern Qinghai-Xizang plateau.Contribution No. 96 B0006 Institute of Geophysics, State Seismological Bureau, Beijing, China.  相似文献   

2.
利用断层滑动资料反演构造应力张量从而确定出海原、六盘山断裂带至银川断陷的第四纪两期构造应力场 :早更新世末期以前 ,为北东—南西挤压型构造应力场 ,由此造成该地区断裂活动主要以逆断为主 ;早更新世末期至中更新世以后 ,构造应力场发生了调整 ,主压应力方向由早期的北东—南西改变为北东东—南西西 ,应力结构由挤压型转变为走滑型 ,并导致断裂活动由早期的逆断为主变为走滑为主 ,这种应力场格局一直持续至今。研究区现代构造应力场可划分为 :海原断裂带走滑应力区、六盘山逆断 -走滑混合应力区和银川断陷拉张应力区  相似文献   

3.
王华林  侯珍清 《地震研究》1994,17(1):79-107
昌马断裂带是是青藏高原北部一条活动强烈的左旋走滑断裂带。它表现为重力、航磁、地壳厚度的综合异常梯度带，属于断面陡、切割深的超岩石圈断裂。昌马断裂带由１２条长４公里至１８公里不等的不连续的主断层和４条次级断层组成，可划分为东、中、西三大段落。断裂的水平位移和滑动速率具有分段性，全新世以来，东、中、西三段的左旋水平滑动速率分别为４．１毫米／年，２．６毫米／年和１．５毫米／年。北东东、北北西和北西西三个方向断层的位移具有分级特征，不同级别的位移具有良好的同步性。全新世以来北东东、北北西和北西西三个方向断层的水平滑动速率分别为４．１毫米／年、３．８毫米／年和２．７毫米／年。白垩纪以来，昌马断裂呈天平式运动，显示了枢纽断裂运动特征，枢纽轴位于断裂中段。昌马地震震源破裂性质及其反映的震源应力场与地震破裂带的破裂性质及其反映的构造应力场不一致。昌马地震震源机制解反映了北北西～南南东挤压，作用应力近于水平的震源应力场；昌马地震破裂带的变形组合反映了东北～南西挤压的构造应力场。昌马地震破裂带长１２０公里，分为东部正走滑段、中部逆走滑段和西部尾端破裂段，显示了多个水平位移峰值。全新世以来，沿昌马断裂发生了６次强震事件，强震复发  相似文献   

4.
If aseismic slip occurs on a fault or its deeper extension, both seismicity and crustal deformation around the source would be affected. Anomalous phenomena of this kind are revealed from earthquake occurrence data and geodetic records during a period of 10 years leading up to the March 2005 M 7.0 earthquake west of Fukuoka that occurred off the northern coast of Kyushu, Japan. Seismicity rate anomalies (quiescence and activation) took place relative to the rates expected by the ETAS model in a number of seismic zones in and around the Kyushu District. The seismic zone of the relative quiescence and activation consistently corresponds to the zone of the negative and positive ΔCFS (Coulomb failure stress change), respectively, assuming the precursory aseismic slips on the M 7.0 source fault. In addition, we consider the time series of geodetic baseline distances between permanent GPS stations in the Kyushu District for the same period, which also supports the possible precursory slips rather than the known slow slips beneath the Bungo Straight, off the eastern coast of Kyushu.  相似文献   

5.
Recent high-resolution deep seismic reflection profile across the Kunlun fault in northeastern Tibet shows clearly that the Moho is cut off by a complex thrust fault system. Moho offset is a general phenomenon, but little is known about the dynamic mechanism. In this study, contact models with Maxwell materials are used to simulate the mechanical process of Moho offset induced by the aseismic slip of deeply buried faults. Based on the seismic reflection data, we project a single fault model and a complex fault system model with two faults intersecting. The deformations of the Moho, the aseismic slips, and contact stresses on faults in different models are discussed in detail. Results show that the Moho offset might be produced by aseismic slip of deeply buried faults, and the magnitude is influenced by the friction coefficient of faults and the viscosity of the lower crust. The maximum slip occurs near the Moho on the single fault or at the crossing point of two intersecting faults system. Stress concentrates mainly on the Moho, the deep end of faults, or the crossing point. This study will throw light on understanding the mechanism of Moho offset and aseismic slip of deeply buried faults. The results of complex fault system with two faults intersecting are also useful to understand the shallow intersecting faults that may cause earthquakes.  相似文献   

6.
本文利用主成分分析、震间位错反演和小波技术分析了鲜水河断裂西北段的跨断层形变资料(1986—2013).结果表明:以左旋走滑为主的断层长期运动为跨断层资料的主要信息,且符合负指数函数的运动规律,随着断层深度的增加,滑动量逐渐减弱.从炉霍段、道孚段到乾宁段,断层闭锁程度逐渐增强.2001年昆仑山M8.1地震发生后,鲜水河断裂西北段地壳浅层(地表以下30km)的左旋走滑明显减弱,到2013年的累积减弱量为3~13mm.5·12汶川M8.0地震发生前,断层滑动出现周期4~5年的增强信号.4·20芦山M7.0地震发生前,断层滑动首先出现低频信号(4~5年周期)增强,随着地震发生临近,强信号频率逐渐升高,直到出现周期为1年的强信号.  相似文献   

7.
川滇菱形块体主要边界运动模型的GPS数据反演分析   总被引：29，自引：7，他引：29       下载免费PDF全文
利用川滇地区1991-1999年的高精度GPS观测处理结果,采用稳健 - 贝叶斯最小二乘算法与多断裂位错模型,分析研究了川滇菱形块体主要边界运动的定量模型.反演分析表明:川西鲜水河断裂带和安宁河断裂带的左旋走滑运动速率约30mm/a,倾滑运动(逆断层)速率分别约9-11mm/a;滇西红河断裂带、程海断裂带、鹤庆 - 洱源断裂带的走滑运动(分别为右旋、左旋、左旋)速率分别约、11、13mm/a,倾滑运动(正断层)速率分别约16、24、16mm/a;如将其视为弹性应力应变积累,则各断层每年有相当于6级左右的地震能量积累.依据上述反演结果,模拟了区域主要断层运动引起的水平位移、应变速率场图像,显示了边界断裂及其之间的相互作用.  相似文献   

8.
The evidence of east-west compression in northeast Japan has been reported by many investigators on the basis of geodetic, geologic and geomorphic data, but its origin still remains far from understood. In the present study we have proposed a mechanical model of tectonic loading at convergent plate boundary zones, and demonstrated its validity through the numerical simulation of internal stress fields in northeast Japan with realistic 3-D geometry of plate interfaces. At convergent plate boundary zones, in general, a part of plate convergence is consumed by steady slip along plate interfaces, and the remaining part by inelastic deformation (seismic faulting, aseismic faulting, and active folding) of overriding plates. Such a plate boundary process to be called ``partial collision' can be quantitatively described by introducing a collision rate defined as c = 1 − steady slip rate at plate interfaces/plate convergence rate. By this definition, we can simply represent the mechanical process of partial collision, which includes total subduction (c = 0) and total collision (c = 1) as two extreme cases, in terms of steady slip rates at plate interfaces. On the basis of elastic dislocation theory, first, we numerically computed the internal stress fields in northeast Japan produced by the total subduction of the Pacific plate beneath the North American plate, however the computed stress pattern was opposite in sense to observations. Then, we computed the internal stress fields by taking c = 0.1 on average, and succeeded in reproducing the observed east-west compression in northeast Japan. This indicates that the concept of partial collision is essential to understand the mechanism of intraplate tectonic loading.  相似文献   

9.
In this work we analyze the tectonic setting of the recent damaging seismic series occurred in the Internal Zones of the eastern Betic Cordillera (SE Spain) and surrounding areas, the tectonic region where took place the 11th May 2011 Mw 5.2 Lorca earthquake. We revisit and make a synthesis of the seven largest and damaging seismic series occurred from 1984 to 2011. We analyze their seismotectonic setting, and their geological sources under the light of recent advances in the knowledge on active faults, neotectonics, seismotectonics and stress regime, with special attention focused on the Lorca Earthquake. These seismic series are characterized by two types of focal mechanisms, produced mainly by two sets of active faults, NNW–SSE to NNE–SSW small (no larger than 20–30 km) extensional faults with some strike slip component, and E–W to NE–SW large strike slip faults (more than 50 km long) with some compressional component (oblique slip faults). The normal fault earthquakes related to the smaller faults are dominant in the interior of large crustal tectonic blocks that are bounded by the large E–W to NE–SW strike-slip faults. The strike slip earthquakes are associated to the reactivation of segments or intersegment regions of the large E–W to NE–SW faults bounding those crustal tectonic blocks. Most of the seismic series studied in this work can be interpreted as part of the background seismicity that occurs within the crustal blocks that are strained under a transpressional regime driven by the major strike slip shear corridors bounding the blocks. The seismotectonic analysis and the phenomenology of the studied series indicate that it is usual the occurrence of damaging compound earthquakes of M  \(\sim \)  5.0 associated with triggering processes driven by coseismic stress transfer. These processes mainly occur in the seismic series generated by NNW–SSE to NNE–SSW faults. These mechanical interaction processes may induce a higher frequency of occurrence of this kind of earthquakes than considered in traditional probabilistic seismic hazard assessments and it should be taken into account in future seismic hazard assessments.  相似文献   

10.
用形变资料反演1976年唐山地震序列的破裂分布   总被引：2，自引：0，他引：2       下载免费PDF全文
1976年唐山发生了7.8级地震,相继又发生了两次大余震——滦县7.1级地震和宁河6.9级地震.地震发生在观测条件比较好的地区,水准测量和三角测量测得了地震的同震位移场.本研究采用原始水准测量数据,而不是采用根据水准数据处理的地面沉降图像,和三角测量数据反演了该地震序列的破裂分布.模型构建中考虑了滦县地震和宁河地震的断层形态和大小.结果表明,唐山地震主震断层有明显的右旋走滑性质,最大走向滑动错距>6 m,位于断层南段,北段的走滑分量明显小于南段.主震总地震矩达2.58×1020N·m,与地震波反演得到的地震矩的量级相当;滦县地震断层总体表现为左旋正断层,释放地震矩达4.95×1019N·m;宁河地震断层总体表现为右旋正断层,释放地震矩达3.94×1019N·m,比地震波反演的地震矩大一个量级.据此可以推测唐山地震的无震滑移主要发生在宁河地震断层的西部上,滑动性质以正断层为主.该结果对于唐山地震序列后的动力学演变过程及余震发生机理有一定参考.  相似文献   

11.
Historical seismicity is used in order to map spatial distribution of seismic moment released by past earthquakes and to compare strain rate deduced from seismicity to those measured by geodetic GPS survey. Spatial analyses are performed on the seismicity of northern boundary of Central Iranian Block which coincides with the Alborz Mountains. This belt has been responsible for several catastrophic earthquakes in the past. In this study, the records of historical and instrumental earthquakes in the Alborz Mountains are used to calculate and plot geographical distribution of seismic moment released in time. A two-dimensional distribution function is proposed and used here to spread seismic moment along causative tectonic features. Using accumulated seismic moment, average slip rates across active faults are estimated for 32 sub-zones along the Alborz Mountains and western Kopet Dag. Seismic moment released by historical and recent earthquakes on this belt accounts for slip rate of 3–5 mm/year which is in good agreement with the geodetic vectors recently deduced from GPS survey in this region. The study also reveals geographical variations of slip rates along some 900 km length of this zone based on seismic history. The results are compared against finding from similar study in this region. Portions of Central and Eastern Alborz show lower seismic strain rate which could imply aseismic motion or overdue earthquakes. Completeness of historical earthquake catalogue and its reliability with regard to earthquake magnitudes, locations, and rupturing systems are among many plausible factors controlling the credibility of such results. Therefore, any conclusions derived from these results remain as reliable as the data and assumptions used for the analyses.  相似文献   

12.
以青藏高原北缘及东北缘的柴达木-祁连山地块内的活动断裂、由断裂所围限的微小块体为研究对象,系统收集整理区内活动断裂定量参数和GPS速度场等资料,使用球面应变率计算方法分析研究区内GPS 速度场得到现今构造应变率场,讨论区内最大剪应变率、面膨胀率与旋转率等参数与区域构造变形之间的关系;同时,依据区内详实的活动断裂资料建立精细的微小活动块体模型,利用Backslip模型反演断裂所围限的各个块体边界断裂的滑动速率、块体内部统一应变率及块体欧拉运动学参数等,并与活动构造方法获得的滑动速率做对比;最后,讨论研究区内由GPS速度场所揭示的地壳运动变形模式.结果表明:(1)柴达木-祁连山地区地壳运动,在沿着山脉走向上具有带状区域分块运动特征,大范围内具有弥散变形特征;(2)青藏高原北部变形场应是通过不同断裂差异性相对运动、区域内部逆冲挤压和块体旋转共同作用的结果.从鄂拉山到古浪民勤一带具有强烈的逆冲活动,其两侧地壳块体分别具有逆向旋转的运动性质;(3)在研究区东部GPS速度场所呈现顺时针旋转的形态,应是处于不同地块边界处的中下地壳与地幔介质差异驱动机制对上地壳块体所产生的作用,并以近地表断层应变率积累形式表现的结果,是祁连山地块、阿拉善块体、鄂尔多斯地块等大型块体推挤旋转影响下的复杂运动学形态.  相似文献   

13.
Because of the viscoelastic behaviour of the earth, accumulation of elastic strain energy by tectonic loading and release of such energy by earthquake fault slips at subduction zones may take place on different spatial scales. If the lithospheric plate is acted upon by distant tectonic forces, strain accumulation must occur in a broad region. However, an earthquake releases strain only in a region comparable to the size of the rupture area. A two-dimensional finite-element model of a subduction zone with viscoelastic rheology has been used to investigate the coupling of tectonic loading and earthquake fault slips. A fault lock-and-unlock technique is employed so that the amount of fault slip in an earthquake is not prescribed, but determined by the accumulated stress. The amount of earthquake fault slip as a fraction of the total relative plate motion depends on the relative sizes of the earthquake rupture area and the region of tectonic strain accumulation, as well as the rheology of the rock material. The larger the region of strain accumulation is compared to the earthquake rupture, the smaller is the earthquake fault slip. The reason for the limited earthquake fault slip is that the elastic shear stress in the asthenosphere induced by the earthquake resists the elastic rebound of the overlying plate. Since rapid permanent plate shortening is not observed at subduction zones, there must be either strain release over a large region or strain accumulation over a small region over earthquake cycles. The former can be achieved only by significant aseismic fault slip between large subduction earthquakes. The most likely mechanism for the latter is the accumulation of elastic strain around isolated locked asperities of the fault, which requires significant aseismic fault slip between asperities.  相似文献   

14.
In this study we analyse coseismic GPS displacements and DInSAR data to constrain a dislocation model for the three largest earthquakes of the 1997 Umbria-Marche seismic sequence. The first two events, which occurred on September 26 at 00:33 GMT (Mw 5.7) and 09:40 GMT (Mw 6.0) respectively, are investigated using both GPS displacements and DInSAR interferograms. We discuss and compare the results of previous studies which separately modeled a smaller subset of geodetic data. We provide a dislocation model for these two earthquakes which fits well both GPS and DInSAR data and agrees with the results of seismological and geological investigations. The first event consists of a unilateral rupture towards the southeast with a uniform dislocation. The strike, rake and dip angles are those resulting from the CMT solution. The second event consists of an unilateral rupture towards the northwest and a variable slip distribution on the fault plane. The strike and the rake are consistent with the CMT solution, but the dip angle has been slightly modified to improve the simultaneous fit of GPS and DInSAR data. While the second rupture (09:40 GMT) arrived very close to the surface, the fit to geodetic data shows that the first rupture (00:33 GMT) is deeper (2 km), despite the more evident surface geological effects. The analysis of new SAR interferograms allows the identification of a 5–6 cm additional displacement caused by the October 3 (Mw 5.2) and 6 (Mw 5.4) seismic events.We use data from a new DInSAR interferogram to model the displacement field of the Sellano earthquake of October 14, 1997. For this event significant GPS measurements were not available. We tested two different fault plane geometries: a blind, planar fault (top depth = 2.4 km), and a curved (listric) fault reaching the surface. The two models provide a generally similar fit to the data, and show that most of the slip was released at depths greater than 2.4 km along a gently dipping (40°–45°) fault surface. They also show that a unilateral rupture does not allow fitting the interferometric fringes since there is evident surface deformation to the northwest of the hypocenter. Moreover, we suggest that the concentration of high residuals in the southern part of our uniform slip model may in fact indicate a certain slip variability in this area.We conclude that, despite the moderate magnitudes and the lack of significant surface faulting, the space geodetic data allowed to constrain dislocation models giving new insights in the rupture process of the three largest events of the sequence.  相似文献   

15.
We propose a model which may explain seismic sequences which are often observed in seismogenic regions, as for example in the Apenninic chain (Italy). In particular, we consider a normal fault and earthquakes taking place at different depths: a first shock in a shallower layer and a second in a deeper one. The normal fault is embedded in a viscoelastic half-space. As a consequence of the rheology, there are two different brittle layers, a shallower and a deeper one, where earthquakes can nucleate. Between these two layers, the rheological behavior is ductile. The thicknesses of the layers depend on the geothermal profile that is calculated taking into account the profile of the thermal and rheological parameters with depth. The fault plane, crossing layers with different rheological behavior, is heterogeneous in respect to the slip style: seismic in the brittle layers, aseismic in the ductile layer. Dislocations in the shallower layer are assumed to produce aseismic slip in the area of the fault belonging to the ductile layer. The stress concentrated, by the seismic and aseismic dislocations, on the fault plane section in the deeper brittle layer is evaluated. It is compared with the tectonic stress rate in order to calculate how much earlier the second earthquake would occur compared to if just the bare tectonic sstress was acting. It results that such an advance is comparable with typical recurrence times of earthquakes and so a mechanism of interaction between different seismic sources, mediated by aseismic slip, can be supposed. The strains and displacements at the Earth’s surface due to seismic and aseismic slip are calculated. They are large enough to be detected by present geodetic techniques.  相似文献   

16.
In 1988 two large earthquakes with magnitude of Ms 7.6 and Ms 7.2 occurred in Lancang-Genma area, Southwest China. This paper discusses the determination of the spatial distribution of fault slip caused by the earthquakes using geodetic surveys. The prior information obtained from geological surveys and seismological investigations was used to determine the geometry of the fault plane and the average fault slip. The smooth constraints on the fault slips have been described by a normal distribution with hyperparameters, which are incorporated in the inversion analysis with a Bayesian model. Akaike’s Bayesian Information Criterion (ABIC) is used to get the optimal values of hyperparameters. Once the hyperparameters are determined, the maximum likelihood method is employed to estimate the patterns of a fault slip. Based on the results of inverse analysis monitoring geodetic surveys can be properly designed and conducted to obtain crust deformations and predict potential earthquake sources.  相似文献   

17.
The southern part of the Outer Zone of Southwest Japan including the Kii peninsula belongs to the tectonic ‘shadow zone’, where fewer conspicuous active faults and less Quaternary sediments develop than in the Nankai subduction zone and Inner Zone of Southwest Japan. In order to study the paleostress sequence of the Kii peninsula, we analyzed fault‐slip data and tension gashes at pilot sites of Early–Middle Miocene forearc sediments and Late Cretaceous accretionary complex. According to the results, six faulting events are reconstructed in sequence: (i) east–west extension (normal faulting); (ii) east–west compression and north–south extension (strike‐slip faulting); (iii) NNW–SSE compression and ENE–WSW extension (strike‐slip faulting); (iv) northeast–southwest compression and northwest–southeast extension (strike‐slip faulting); (v) WNW–ESE compression (strike‐slip or reverse faulting); and (vi) NNE–SSW extension. The north–south to NNW–SSE trending dyke swarm of Middle Miocene age in the Kii peninsula is thought to be related to Event 3, implying that Event 3 was active at least during the Middle Miocene. Because Event 6 is recognized solely at a site, the overall latest faulting event seems to be Event 5. Assuming that the compression results from the motion of the crust or plate, the compression direction of Event 5 is in good accordance with the present‐day WNW crustal velocity vectors of the Kii peninsula. The stress trajectory map of Southeast Korea and Southwest Japan reveals that the current compression directions of the Kii peninsula correspond to the combinatory stress fields of the Himalayan and Philippine Sea tectonic domains.  相似文献   

18.
1999年山西大同Ms 5.6地震的震源断层   总被引：9，自引：0，他引：9  
大同震区先后在 1989、1991和 1999年发生MS >5地震 ,利用大同遥测地震台网的记录资料进行比较精确的地震序列震源定位 ,结合宏观烈度分布和震源机制解资料 ,详细地分析对比了 3次子序列的异同。结果显示 ,1999年MS5 .6地震的震源断层是走向NWW、长 16km、宽12km、埋深 5km以下、倾角近直立的左旋走滑断层。而前 2个子序列是NNE为主的右旋走滑断层活动所致 ,表明地震破裂方向发生了变化。这种 2个以上方向先后出现、并且强弱有别的地震破裂是普遍存在的 ,表明震源环境的复杂程度与地震序列的类型有关。虽然震区存在NE向的大王村断裂和NW向的团堡断裂 ,但目前没有证据说明震源断层和 2条构造断层连通。 3次子序列的震源断层都是走滑断层 ,也和 2条构造正断层有别。 1999年的子序列可能属于新破裂。  相似文献   

19.
We analyze observations from eight GPS campaigns carried out between 1997 and 2005 on a network of 13 sites in the Suez–Sinai area, where separation between the African and the Arabian plates takes place. This is the key area to understand if and in which way Sinai behaves like a sub-plate of the African plate and the role played by seismic and geodetic (long-term) deformation release.Our analysis shows that, on average, the Suez–Sinai area motion, in terms of ITRF00 velocities, matches the African plate motion defined by the NNR-NUVEL-1A model.The horizontal principal strain rate axes estimated separately in the Gulf of Suez area and in the northern Sinai vary from compression across the Gulf (−2.2 ± 1.2) × 10−8 year−1 to NE extension (1.0 ± 1.5) × 10−8 year−1 in the North, showing the presence of two distinct domains, so that in our opinion Sinai cannot be considered simply a unique rigid block.The analysis of GPS baseline length variations shows short-term deformations across the Gulf of Suez, reaching up a maximum value of more than 1 cm in 8 years.Since current geodynamical models do not predict significant tectonic deformation in this area, we work under the hypothesis that a contribute may be expected by post-seismic relaxation effects. Under this hypothesis, we compare the baselines length variations with the post-seismic relaxation field associated with five major local earthquakes occurred in the area, testing two different viscoelastic models. Our results show that the detected short-term deformations are better modeled for viscosity values of 1018 Pa s in the lower crust and 1020 Pa s in the asthenosphere. However, since the modeled post-seismic effect results modest and a certain amount of the detected deformation is not accounted for, we think that an improved modeling should take into account the lateral heterogeneities of crust and upper mantle structures.  相似文献   

20.
Fault slip rate is one of the most important subjects in active tectonics research, which reveals the activity and seismic potential of a fault. Due to the improvement of dating precision with the development of dating methods, Holocene geological markers, even the young markers of thousands or hundreds of years old, are widely used in fault slip rate calculation. Usually, uncertainties from a single event and erosion of the accumulated offsets are involved in fault slip rate determination. Two types of uncertainties are related to a single event; the first is the time elapsed since the latest (the most recent) event; the second is the period since the formation of the geological marker to the occurrence of the first event. High‐slip‐rate faults are more sensitive to these uncertainties than low‐slip‐rate faults. In this study, we studied quantitatively the effects of a single event on fault slip rate following the three classic earthquake models: the characteristic earthquake, uniform slip and variable slip models. We suggest that the erosion of the accumulated offset–lateral erosion on a strike‐slip fault, should also be considered in fault slip estimation. Therefore, we propose a differential method to obtain a reliable fault slip rate. In the differential method, the slip rate is the ratio of offset differentials and corresponding age differentials between the older and younger terraces along strike‐slip faults. This kind of differential method could avoid the uncertainties from the first and latest events, as well as that from the lateral erosion. By applying the differential method, we got the revised slip rates of ∼5–10 mm/year on the Altyn Tagh and Kunlun faults. These low slip rates could fit previous geodetic and geological fault slip rates and shortening rates as well as the millennial recurrence intervals of strong earthquakes along the major segments of these faults.  相似文献   

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