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1.
Chihiro Hashimoto Eiichi Fukuyama Mitsuhiro Matsu’ura 《Pure and Applied Geophysics》2014,171(8):1705-1728
The generation of interplate earthquakes can be regarded as a process of tectonic stress accumulation and release, driven by relative plate motion. We completed a physics-based simulation system for earthquake generation cycles at plate interfaces in the Japan region, where the Pacific plate is descending beneath the North American and Philippine Sea plates, and the Philippine Sea plate is descending beneath the North American and Eurasian plates. The system is composed of a quasi-static tectonic loading model and a dynamic rupture propagation model, developed on a realistic 3-D plate interface model. The driving force of the system is relative plate motion. In the quasi-static tectonic loading model, mechanical interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity (fault slip) across them on the basis of dislocation theory for an elastic surface layer overlying Maxwell-type viscoelastic half-space. In the dynamic rupture propagation model, stress changes due to fault slip motion on non-planar plate interfaces are evaluated with the boundary integral equation method. The progress of seismic (dynamic) or aseismic (quasi-static) fault slip on plate interfaces is governed by a slip- and time-dependent fault constitutive law. As an example, we numerically simulated earthquake generation cycles at the source region of the 1968 Tokachi-oki earthquake on the North American-Pacific plate interface. From the numerical simulation, we can see that postseismic stress relaxation in the asthenosphere accelerates stress accumulation in the source region. When the stress state of the source region is close to a critical level, dynamic rupture is rapidly accelerated and develops over the whole source region. When the stress state is much lower than the critical level, the rupture is not accelerated. This means that the stress state realized by interseismic tectonic loading essentially controls the subsequent dynamic rupture process. 相似文献
2.
Interplate Earthquake Fault Slip During Periodic Earthquake Cycles in a Viscoelastic Medium at a Subduction Zone 总被引：1，自引：0，他引：1
K. Hirahara 《Pure and Applied Geophysics》2002,159(10):2201-2220
--A 2-D finite-element-method (FEM) numerical experiment of earthquake cycles at a subduction zone is performed to investigate the effect of viscoelasticity of the earth on great interplate earthquake fault slip. We construct a 2-D viscoelastic FEM model of northeast Japan, which consists of an elastic upper crust and a viscoelastic mantle wedge under gravitation overlying the subducting elastic Pacific plate. Instead of the dislocation model prescribing an amount of slip on a plate interface, we define an earthquake cycle, in which the plate interface down to a depth is locked during an interseismic period and unlocked during coseismic and postseismic periods by changing the friction on the boundary with the master-slave method. This earthquake cycle with steady plate subduction is periodically repeated to calculate the resultant earthquake fault slip.¶As simulated in a previous study (Wang, 1995), the amount of fault slip at the first earthquake cycle is smaller than the total relative plate motion. This small amount of fault slip in the viscoelastic medium was considered to be one factor explaining the small seismic coupling observed at several subduction zones. Our simulation, however, shows that the fault slip grows with an increasing number of repeated earthquake cycles and reaches an amount comparable to the total relative plate motion after more than ten earthquake cycles. This new finding indicates that the viscoelasticity of the earth is not the main factor in explaining the observed small seismic coupling. In comparison with a simple one-degree-of-freedom experiment, we demonstrate that the increase of the fault slip occurs in the transient state from the relaxed initial state to the stressed equilibrium state due to the intermittent plate loading in a viscoelastic medium. 相似文献
3.
在断层面上引入速率-状态相依摩擦本构关系、考虑铲形逆冲断层几何结构特征、断层下盘和上盘中下地壳及上地幔为黏弹性介质、上盘上地壳为弹塑性介质,本文用二维有限元动力学模型模拟了龙门山断层上大震准周期复发行为、分析了断层上地震孕育位置、地震周期不同阶段的应力/应变场演化特征.不同于近垂直走滑断层上的地震周期行为,大陆铲形逆冲断层上的构造应力的积累和释放过程更复杂、有其独特性.我们得到如下认识：（1）铲形逆冲断层上的地震复发是准周期行为.（2）龙门山断层最大库仑应力位于断层17~20 km深处,应力长期积累和同震释放都在此深度最大,说明地震会在此处孕育、发动.（3）在断层破裂的深部和浅部,同震滑动大小和构造应力释放大小并非同步,而是差异悬殊.（4）地震仅部分释放区域积累的应变能,断层上盘上地壳顶部和底部的褶皱、破裂等永久变形形式也是释放应变能的重要形式.（5）应变能密度增量的演化图像分为：震间、同震、震后期,清晰反应了龙门山断层附近的地震动力学过程.（6）地震发生除释放能量外,同时也对近断层的中地壳和断层底部有很大的应变能加载;这些加载,在震后期可能通过震后滑移、余震或中下地壳乃至上地幔的驰豫形变用几十年时间释放.以上对大陆内铲形逆冲断层上变形特征的了解,有助于我们在其地震周期行为中评估地震危险性. 相似文献
4.
Dennise C. Templeton Robert M. Nadeau Roland Bürgmann 《Earth and Planetary Science Letters》2009,277(1-2):1-8
Repeating earthquakes (REs) are sequences of events that have virtually identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth. To investigate the postseismic deformation after the 1984 M6.2 Morgan Hill earthquake, we identify RE sequences occurring on the central Calaveras fault between 1984 and 2005 using a combination of cross-correlation and spectral coherence techniques. Both the accelerated slip transients due to the earthquake as well as the return to interseismic background creep rates can be imaged from our dataset. A comparison between the regions of the fault that ruptured coseismically and the locations of the REs show that REs preferentially occur in areas adjacent to the coseismic rupture. Using calculated RE-derived subsurface slip distributions at 6 months and 18 months after the mainshock, we predict surface electronic distance meter (EDM) line length changes between stations near the Morgan Hill rupture area. The RE-derived slip model underpredicts a subset of the observed line-length changes. Inclusion of transient aseismic slip below the seismogenic zone is needed to better match the measured surface deformation. 相似文献
5.
THE SOURCE PARAMETERS AND RUPTURE PROCESS OF THE MW7.0 EARTHQUAKE IN ALASKA,USA ON DECEMBER 1, 2018 
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下载免费PDF全文 XU Zhi-guo ZHANG Huai ZHOU Yuan-ze LIANG Shan-shan SU Zhe SHI Jian-yu ZHAO-Bo 《地震地质》2019,41(5):1223-1238
A magnitude MW7.0 earthquake struck north of Anchorage, Alaska, USA on 1 December 2018. This earthquake occurred in the Alaska-Aleutian subduction zone, on a fault within the subducting Pacific slab rather than on the shallower boundary between the Pacific and North American plates. In order to better understand the earthquake source characteristics and slip distribution of source rupture process as well as to explore the effect of tectonic environment on dynamic triggering of earthquake, the faulting geometry, slip distribution, seismic moment, source time function are estimated from broadband waveforms downloaded from IRIS Data Management Center. We use the regional broadband waveforms to infer the source parameters with ISOLA package and the teleseismic body wave recorded by stations of the Global Seismic Network is employed to conduct slip distribution inversion with iterative deconvolution method. The focal mechanism solution indicates that the Alaska earthquake occurred as the result of tensile-type normal faulting, the estimated centroid depth from waveform inversion shows that the earthquake occurred at the depth of 56.5km, and the centroid location is 10km far away in northeast direction relative to the location of initial epicenter. We use the aftershock distribution to constrain the fault-plane strike of a normal fault to set up the finite fault model, the finite fault inversion shows that the earthquake slip distribution is concentrated mainly on a rectangular area with 30km×20km, and the maximum slip is up to 3.6m. In addition, the slip distribution shows an asymmetrical distribution and the range of possible rupture direction, the direction of rupture extends to the northeast direction, which is same as that of aftershock distribution for a period of ten days after the mainshock. It is interesting to note that a seismic gap appears in the southwest of the seismogenic fault, we initially determined that the earthquake was a typical normal fault-type earthquake that occurred in the back-arc extensional environment of the subduction collision zone between the Pacific plate and the North American plate, this earthquake was not related to tectonic movement of faults near the Earth's surface. Due to the influence of high temperature and pressure during the subduction of the Pacific plate toward to the north, the subduction angle of the Pacific plate becomes steep, causing consequently the backward bending deformation, thus forming to a tensile environment at the trailing edge of the collision zone and generating the MW7.0 earthquake in Alaska. 相似文献
6.
力学上,地震可以看作在应力场作用下由于断层带介质的突然损伤或软化导致的断层带失稳事件.本文基于这个地震动力学模型,利用一种可以模拟断层大位错的有限元方法,研究了2011年MW9.0东日本大地震(Tohoku-Oki)的动力学破裂过程.比较了无障碍体和具有不同刚度障碍体的断层带模型产生的断层位移、位错和应力降.主要结果表明,障碍体的存在并不明显地改变障碍体区域的初始构造应力场.对有障碍体情形,准静态结果显示断层上盘最大逆冲位移和最大剪切位错分别为51m和58m,均发生在海底表面海沟处,与无障碍体的结果(最大剪切位错约55m)相比差别不大;下盘最大倾向位移(-10m)并不与上盘最大值出现在同一位置,而是在障碍体处.障碍体处剪应力降(约11 MPa)大于周围非障碍体区域.障碍体处正应力降的最大值约为3 MPa.模拟结果似乎不支持海山是导致本次地震异乎寻常大位错的原因,而倾向于断层带剪切刚度在地震过程中极度损伤或软化. 相似文献
7.
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
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.
--The earthquake generation cycle consists of tectonic loading, quasi-static rupture nucleation, dynamic rupture propagation and stop, and subsequent stress redistribution and fault restrengthening. From a macroscopic point of view, the entire process of earthquake generation cycles should be consistently described by a coupled nonlinear system of a slip-response function, a fault constitutive law and a driving force. On the basis of such a general idea, we constructed a realistic 3-D simulation model for earthquake generation cycles at a transcurrent plate boundary by combining the viscoelastic slip-response function derived for a two-layered elastic-viscoelastic structure model, the slip- and time-dependent fault constitutive law that has an inherent mechanism of fault restrengthening, and the steady relative plate motion as a driving force into a single closed system. With this model we numerically simulated the earthquake generation cycles repeated in a seismogenic region on a plate interface, and examined space-time changes in shear stress, slip deficits and fault constitutive properties during one complete cycle in detail. The occurrence of unstable dynamic slip brings about decrease both in fault strength and shear stress to a constant residual level. After the arrest of dynamic slip, the breakdown strength drop j†p of fault is restored rapidly and the process of stress accumulation resumes in the seismogenic region. On the other hand, the restoration of the critical weakening displacement Dc proceeds gradually with time through the interseismic period. The restoration of Dc can be regarded as the macroscopic manifestation of the microscopic recovery process of fractal fault surface structure. Through numerical simulation with a multi-segmented fault model, we examined the effects of viscoelastic fault-to-fault interaction. The effect of transient viscoelastic stress transfer through the asthenosphere is significant as well as the direct effect of elastic stress transfer, and it possibly explains the time lag of the sequential occurrence of large events along a plate boundary. 相似文献
10.
An M8.3 earthquake struck the southwestern part of the Hellenic Arc, near the Island of Crete, in AD 365, generating a tsunami
that affected almost the entire eastern Mediterranean region. Taking into account that the time history of seismicity in this
region is fairly complete for such earthquakes in the historical catalog, which can be dated as back as the 5th century B.C.,
there is no indication that this segment of plate boundary has been fully ruptured again. The seismic hazard associated with
this part of the Hellenic Arc necessitates the evaluation of the rupture characteristics of this great event. The constraint
of the faulting geometry was initially achieved by using information from seismicity, and the focal mechanisms of earthquakes
that occurred during the instrumental period. A rupture model for this great earthquake is constructed by assuming an elastic
medium and calculating the theoretical surface displacements for various fault models that are matched with the observed surface
deformation gleaned from historical reports. The resulted fault model concerns thrust faulting with a rupture length of 160
km and a seismic moment of 5.7 × 1028 dyn·cm, an average slip of 8.9 m and a corresponding moment magnitude equal to 8.4, in excellent agreement with the macroseismic
estimation. The absence of such events recurrence is an indication of the lack of complete seismic coupling that is common
in subduction zones, which is in accordance with the back arc spreading of the Aegean microplate and with previous results
showing low coupling for extensional strain of the upper plate. 相似文献
11.
-- Daily averaged tilt component data from four sites of the Central Apennines (Italy) revealed intermediate-term tilts of a few months as possible precursors of the seismic sequence occurred in the Umbria-Marche region during 1997. A change was also observed in the secular tectonic trend recorded at one site and referred to the same seismic sequence. The observed intermediate-term preseismic tilts are considered as the manifestation of aseismic creep episodes in the fault materials close to the tilt sites. The mechanism refers to a strain field slowly propagating from the dilatancy (focal) area to the tiltmeters, through rigid crustal blocks separated by weak transition zones with viscoelastic rheology. This propagation is thought to be the cause of the local aseismic fault slip recorded by tiltmeters. In one case such creep strains revealed to have larger amplitude and higher frequency content than those accepted for fault materials, and this was attributed to an amplified response of the heterogeneous ground surface at the site. The existence of a propagating strain field is confirmed by the different onset time delays in the preseismic tilt signals recorded at different distances from the same earthquake. In particular, the onset time delays observed at each tilt site appear to increase with increasing distance of such site from the epicentral area. At greatest distances, where the preseismic strain becomes negligible, the characteristic intermediate-term ground tilts vanish completely. 相似文献
12.
Nonuniform and Unsteady Sliding of a Plate Boundary in a Great Earthquake Cycle: A Numerical Simulation Using a Laboratory-derived Friction Law 总被引：1，自引：0，他引：1
—A numerical study is conducted to simulate complicated sliding behavior and earthquake activity on a subducting plate boundary. A 2-D model of a uniform elastic half-space with a semi-infinite thrust fault is set up, and the frictional stress prescribed by a rate- and state-dependent friction law is assumed to act on the plate boundary fault. Spatial nonuniformity of friction parameters representing rate-dependence of friction and of slip-dependence of friction are introduced in the model to obtain complicated sliding behavior in the numerical simulation. Analogs of great earthquakes that break the entire seismogenic plate boundary repeatedly occur at a constant time interval. Smaller events of seismic or aseismic sliding occur during a great earthquake cycle. Regions of rate-strengthening of friction and of a large characteristic distance in slip-dependence of friction behave as barriers or asperities. Rupture propagation is often arrested in such a region and a great earthquake occurs later when the region is broken. The variety of earthquake activity observed in many regions along real plate boundaries may be explained by similar nonuniformity in friction parameters. Conversely, the friction parameters on plate boundaries might be estimated from comparison of theoretical simulations with observations of earthquake activity. Simulation results indicate that spatiotemporal variation in stress due to aseismic sliding may play an important part in generating earthquakes. 相似文献
13.
The seismogenic zone of subduction thrust faults 总被引：13，自引：0，他引：13
Abstract Subduction thrust faults generate earthquakes over a limited depth range. They are aseismic in their seaward updip portions and landward downdip of a critical point. The seaward shallow aseismic zone, commonly beneath accreted sediments, may be a consequence of unconsolidated sediments, especially stable-sliding smectite clays. Such clays are dehydrated and the fault may become seismogenic where the temperature reaches 100--150°C, that is, at a 5--15 km depth. Two factors may determine the downdip seismogenic limit. For subduction of young hot oceanic lithosphere beneath large accretionary sedimentary prisms and beneath continental crust, the transition to aseismic stable sliding is temperature controlled. The maximum temperature for seismic behavior in crustal rocks is ～ 350°C, regardless of the presence of water. In addition, great earthquake ruptures initiated at less than this temperature may propagate with decreasing slip to where the temperature is ～ 450°C. For subduction beneath thin island arc crust and beneath continental crust in some areas, the forearc mantle is reached by the thrust shallower than the 350°C temperature. The forearc upper mantle probably is aseismic because of stable-sliding serpentinite hydrated by water from the underthrusting oceanic crust and sediments. For many subduction zones the downdip seismogenic width defined by these limits is much less than previously assumed. Within the narrowly defined seismic zone, most of the convergence may occur in earthquakes. Numerical thermal models have been employed to estimate temperatures on the subduction thrust planes of four continental subduction zones. For Cascadia and Southwest Japan where very young and hot plates are subducting, the downdip seismogenic limit on the subduction thrust is thermally controlled and is shallow. For Alaska and most of Chile, the forearc mantle is reached before the critical temperature, and mantle serpentinite provides the limit. In all four regions, the seismogenic zones so defined agree with estimates of the extent of great earthquake rupture, and with the downdip extent of the interseismic locked zone. 相似文献
14.
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
15.
2008年5月12日在青藏高原与四川盆地交界的龙门山山脉发生了Ms8.0级强烈地震,引发山体滑坡等地质灾害,造成了巨大的人员伤亡和经济损失.本文利用远场体波波形记录结合近场同震位移数据,根据地质资料和地震形成的地表破裂轨迹,构造了一个双“铲状”有限地震断层模型,利用反演技术重建地震的破裂过程.结果显示汶川大地震主要是沿龙门山构造带的映秀-北川断裂和灌县-江油断裂发生的逆冲兼右旋走滑破裂事件.断层面上的滑动分布显示两个高滑动区先后发生在地震破坏最为严重的映秀和北川地区,最大滑动量高达1200～1250 cm,且破裂过程也显示一定的复杂性.地震破裂的平均走滑量略大于平均倾滑量,与多种观测资料获得的震前龙门山断裂带构造变形相一致,推断是由于长期区域应力场作用和龙门山地区特殊的物质组成和结构孕育了这次千年尺度的强烈地震. 相似文献
16.
根据龙门山断裂带地区的主要构造特征,建立该地区的有限元模型,同时考虑地下深处的黏弹性蠕动和不同部位间的接触关系,模拟计算了研究区在强震轮回活动中的时间演化历程.模拟结果表明:龙门山断裂带深处的滑动速率比浅表的滑动速率大,龙门山断裂带周围是相对容易发生应变积累的地区,其5~19km深度也是高应力聚集成核区,随时间推移的应力集中程度加剧而引发强震.本模拟分析证实了重复地震观测所揭示的龙门山断裂带存在深浅活动速率差异的现象,这在一定程度上可以解释出乎预料的汶川MW7.9地震的孕育机理.综合分析研究提出:应充分利用重复地震这一天然的"地下蠕变计(subsurface creepmeter)"来探测深部构造变形的活动,为强震危险性分析提供必要的"原位(in situ)观测"约束信息. 相似文献
17.
《Physics of the Earth and Planetary Interiors》2002,129(1-2):67-82
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
18.
We present a realistic model of the San Andreas fault zone. We propose that aseismic ground displacement is a sum of visco-elastic relaxation following large earthquakes, transient fault slip, steady fault slip and a large-scale relative plate motion. We used the model to explain the aseismic ground displacements observed after the San Francisco earthquake of 1906.The data do not resolve the question of which is the dominant mechanism, but viscoelastic relaxation can contribute a significant fraction of the displacement if the elastic plate thickness is 50 km or less. If the relative plate motion is taken to be 5.5 cm/yr, as found from plate rotation pole studies, then the zone of significant shearing in the mantle is probably at least 100 km thick beneath California. 相似文献
19.
J. Klotz D. Angermann G. W. Michel R. Porth C. Reigber J. Reinking J. Viramonte R. Perdomo V. H. Rios S. Barrientos R. Barriga O. Cifuentes 《Pure and Applied Geophysics》1999,154(3-4):709-730
—In order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the Andes, a 215 site GPS network covering Chile and the western part of Argentina was selected, monumented and observed in 1993 and 1994. A dense part of the network in northern Chile and northwest Argentina, comprising some 70 sites, was re-observed after two years in October/November, 1995. The M w = 8.0 Antofagasta (North Chile) earthquake of 30th July, 1995 took place between the two observations. The city of Antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench. Three different deformation processes have been considered for modeling the measured displacements (1) interseismic accumulation of elastic strain due to subduction coupling, (2) coseismic strain release during the Antofagasta earthquake and (3) crustal shortening in the Sub-Andes.¶Eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation. Assuming a uniform slip model of interseismic coupling, the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km. The geodetically derived fault plane parameters of the Antofagasta earthquake are consistent with results derived from wave-form modeling of seismolog ical data. The coseismic slip predicted by the variable slip model reaches values of 3.2 m in the dip-slip and 1.4 m in the strike-slip directions. The derived rake is 66°. Our geodetic results suggest that the oblique Nazca–South American plate convergence is accommodated by oblique earthquake slip with no slip partitioning. The observed displacements in the back-arc indicate a present-day crustal shortening rate of 3–4 mm/year which is significantly slower than the average of 10 mm/year experienced during the evolution of the Andean plateau. 相似文献
20.
Scott M White Robert Trenkamp James N Kellogg 《Earth and Planetary Science Letters》2003,216(3):231-242
Recent results from Global Positioning System (GPS) measurements show deformation along the coast of Ecuador and Colombia that can be linked to the rupture zone of the earthquake in 1979. A 3D elastic boundary element model is used to simulate crustal deformation observed by GPS campaigns in 1991, 1994, 1996, and 1998. Deformation in Ecuador can be explained best by 50% apparent locking on the subduction interface. Although there have not been any historic large earthquakes (Mw>7) south of the 1906 earthquake rupture zone, 50% apparent elastic locking is necessary to model the deformation observed there. In Colombia, only 30% apparent elastic locking is occurring along the subduction interface in the 1979 earthquake rupture zone (Mw 8.2), and no elastic locking is necessary to explain the crustal deformation observed at two GPS sites north of there. There is no evidence from seismicity or plate geometry that plate coupling on the subduction zone is reduced in Colombia. However, simple viscoelastic models suggest that the apparent reduction in elastic locking can be explained entirely by the response of a viscous upper mantle to the 1979 earthquake. These results suggest that elastic strain accumulation is occurring evenly throughout the study area, but postseismic relaxation masks the true total strain rate. 相似文献