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1.
强震后地表变形的动力学机制是地球动力学研究的重要方面,现在普遍认为震后变形主要由断层的震后余滑或由介质的黏弹性松弛所至。1999年台湾集集地震GPS观测系统记录到了空前的资料,为研究震后变形的动力学机制提供了难得的机会。本研究认为集集地震后地表变形由震后断层余滑、下地壳／上地幔的黏弹性松弛、震源区介质的破裂、孔隙弹性回跳、地下流体的运移、介质孔隙度及孔隙压的变化等多种因素共同影响决定。为抓住重点,研究中将介质的破裂、地下流体的运移和孔隙弹性回跳等因素等效为震源区介质的物性变化。文中运用黏弹性有限单元模型（麦克斯威尔体）、利用GPS观测的时间序列资料对震后余滑、地壳／地幔黏度以及等效的震源区介质物性变化进行了反演。反演模型给出了震后余滑的分布及变化特征,反演结果初步显示台湾地区的下地壳／上地幔的黏度分别为2.7×10^18,4.2×10^20Pa·s。此外,反演结果还给出每种影响因素对地表变形的贡献大小,在集集地震后的450d时间里,断层的震后余滑引起的地表变形占总变形的44.6％,下地壳／上地幔的黏性松弛占34.7％,等效的震源区介质的物性变化占20.7％。 相似文献
2.
震后变形是地震周期中一个重要阶段,深入研究其产生机制有助于提高对地震演化过程、断层性质及地震危险性评估的认识.2017年伊朗MW7.3地震InSAR观测资料丰富,为研究扎格罗斯造山带山前褶皱带盲逆冲断层震后变形机制提供了切入点.合理详细的震源模型及高精度的形变观测是开展震后余滑或黏弹松弛研究的首要前提,本文采用多视角InSAR资料联合远场波形数据反演该地震的破裂滑动分布,并解算得到伪三维地表位移,利用InSAR时序分析提取震源区主震后一年半内变形特征,显示震源区震后形变特征与同震位移场类似,LOS向形变速率最大值约8 cm·a-1,震后变形预示震源区可能存在明显的震后应力调整现象.利用震后半年内形变资料约束的纯运动学余滑模型表明同时期释放能量为矩震级MW6.7,进一步探讨应力驱动震后余滑及下地壳黏弹性松弛对震后变形的贡献,基于分层黏弹模型的模拟计算表明震后余滑和黏弹松弛效应的耦合模型可以更好地解释地表震后变形特征,其中震后余滑主要分布在同震破裂区的上方浅部,对主震后一年半内震后地表变形起主导作用,震源区壳下黏滞系数量级下... 相似文献
3.
使用GPS同震位移资料和远场P波记录,研究了1999年台湾集集地震震源破裂过程．根据地质构造和余震分布引入了一个由弯曲断层面构造的三段“铲状”断层模型．在使用静态GPS位移资料反演集集地震的断层破裂滑动分布时,由于集集地震断层北部近地表破裂的复杂性,在位错模型中考虑拉张分量对地表同震位移的贡献,可更好地同时拟合GPS观测资料的水平和垂向分量．而纯剪切位错弹性半空间模型和分层地壳模型都无法同时拟合水平和垂向GPS观测资料．在此基础上,同时使用静力学同震位移资料和远场地震波形记录,反演集集地震的震源破裂过程．结果表明,一种垂直于断层面的“挤压性”(负)拉张分量几乎集中分布于地震断层的浅部和北部转折处,而这一带地表破裂远较没有(负)拉张分量出现的南部断层复杂．“冒起构造”的数字模拟表明,这种在集集地震破裂转折处及北部断裂带广为出现的典型破裂造成的地表位移可以用具有负拉张分量(挤压)的逆冲断层更好地模拟．而这种负拉张分量(挤压)的分布正是地震破裂性质和几何复杂性的综合反映,震源破裂过程也显示北部转折处破裂在空间和时间上的复杂性.高滑区域与余震分布表现为负相关. 相似文献
4.
台湾集集921地震地壳形变的简介与讨论 总被引：4，自引：0，他引：4
台湾集集921地震是20世纪末发生在我国的一次影响很大的地震。地震性一年后，笔者有幸考察了地震现场。本文展示部分地震遗迹照片和收集到的GPS观测资料，分析讨论了这次地震的震前震后地壳形变特征。 相似文献
5.
2010年4月14日青海玉树MS7.1地震发生在青藏高原东南部甘孜-玉树地震带,在震后7~10天内,我们快速建立了由15个GPS测站组成的跨地震破裂带观测剖面,包括1个连续站,3个半连续站和11个流动站,对所有站进行了240多天的观测,获取了该次地震的震后形变时空特征.采用欧拉矢量和位错模型解算了背景速度场,并从GPS观测的形变场中扣除该分量.采用分层黏弹性位错模型计算余震引起的地表形变,结果表明余震对部分测站的位移造成不可忽视的影响.采用对数模型拟合位移时间序列,表明特征衰减时间为6.7±1.2天.利用最速下降法反演震后余滑时空分布,反演结果表明震后断层活动以左旋滑动为主,断层南盘具有少量的抬升.在空间分布上,余滑主要位于同震破裂区的两侧,西北侧的余滑几乎达到地表,而东南区的余滑基本在同震破裂区的下方,余滑最大的区域位于结古镇东南下方10~20 km的深度范围.随着震后离逝时间的增加,2个余滑区在空间上保持不变,余滑区的面积逐渐扩大.余滑的矩释放为（1.5~5.1）×1018Nm,相当于1个MW6.1~6.4地震释放的能量.分层岩石圈黏弹性模型计算的地壳孔隙弹性反弹形变与地表观测值相差较大,不能解释观测到的震后变形.采用麦克斯维尔流变体模型计算下地壳和上地幔松弛引起的地表形变,显示出其对地表形变的贡献较小.GPS观测得到的震后形变所具有的快速衰减特征,以及余滑模型能够较好地拟合GPS地表形变,表明2010年玉树MS7.1地震后早期阶段的地壳形变主要是由余滑机制决定的. 相似文献
6.
汶川地震震后短期青藏高原东北缘地壳变形特征成因讨论 总被引：1，自引：0，他引：1
2007—2009年时段GPS数据资料显示青藏高原东北缘地区地壳运动较前期(1999-2007年时段)发生明显变化.本文分别对汶川地震同震影响、震后粘弹性松弛影响和震后余滑影响进行了分析.结果表明,同震对该区域地壳变形特征的形成存在一定影响,而震后粘弹性松弛和余滑产生的影响均可忽略不计.分析认为,对于中国大陆这种多块体系统而言,现有的震后变形机制并不能充分解释震后短期某些区域地壳运动变形特征的形成,汶川地震震后短期青藏高原东北缘的地壳变形特征的形成可能主要与震后块体运动调整有关. 相似文献
7.
1996年丽江MS7.0地震的余震深度分布明显具有时间依赖性,主震发生后短时间内余震震源深度较深,随着时间的延续,余震震源深度变得越来越浅。余震的这种深度分布受地壳脆塑性转化带深度控制,而脆塑性转化带的深度变化与地震前后断层的应变速率有关。由震后GPS地表变形数据得到的地表变形模型表明,震后地表变形主要来自地壳深部,震后滑动与地壳深部弹性松弛有关。根据鲜水河断层地表的滑动数据和按Marone's(1991)给出的方程确定的震后滑动模型,估计的应变速率显示,主震发生后应变速率较高,随时间延续,应变速率逐渐下降。基于地壳P波速度结构和利用热流数据估计的丽江地区地壳温度,采用含水石英的塑性流变参数,估计了中地壳脆塑性转化带深度随震后应变速率的变化。结果表明,主震震源深度与余震深度分布下限与中地壳脆塑性转化带的深度随时间变化趋势一致。由于断层的震后快速滑动致使断层带深部具有很高的应变速率,高应变速率引起断层脆塑性转化带深度下移,主震之后短时间内发生了较深的余震;随着震后时间的延续,断层逐渐进入蠕变阶段,断层滑动速率逐渐减小,地壳应变速率逐渐降低,断层脆塑性转化带也逐渐恢复到间震期的深度,相应余震深度随之变化。因此,余震分布的深度变化是中地壳流变结构和脆塑性转化带深度变化的直接反映。 相似文献
8.
2004年苏门答腊地震后, 不同学者根据不同观测数据(地震波、 GPS), 得到了此次地震的断层滑动模型。 反演过程中使用半无限空间模型时, 无法利用远场观测数据进行约束, 势必影响远场形变的解释。 基于Hoechner等使用的断层几何模型和GPS同震位移数据, 本研究利用球体位错理论反演方法反演了2004年苏门答腊地震断层滑动模型, 得到的矩震级为9.24, 最大滑移量为30.4 m, 由于考虑了曲率的效应, 该模型在远场同震位移的计算结果与GPS数据吻合较好。 然后, 选取了2001—2004年和2004—2007年两期的GPS水平位移速度场, 研究2004年苏门答腊地震对华南地区地壳水平活动的影响, 从两期的GPS水平位移速度场差异可以看出地震后华南块体有向西南方向的运动趋势, 华南块体受到此次地震明显的震后影响。 最后, 基于反演得到的断层模型, 利用Tanaka等提出的粘弹性球体位错理论对华南块体两期GPS水平位移速度场差异进行模拟, 得到华南块体内部粘滞性系数为2×1019 Pa·s, 当考虑地幔粘滞性松弛效应后, 两期的速度场差异的均方根值由3.2 mm减少为1.9 mm。 可见在研究2004年前后中国大陆GPS水平位移速度场时, 若继续以华南块体为基准, 需考虑此次地震的地幔粘滞性松弛效应。 相似文献
9.
ERS卫星雷达干涉测量:1999年台湾集集大地震震前和同震地表位移 总被引：4，自引：1，他引：4
1999年集集大地震(Mw=7.6)是20世纪以来台湾岛内最大的地震.在本研究中,5个不同时间获取的ERS-1/2卫星合成孔径雷达图像被组合,并被处理成多个差分干涉图,以此来考查与该地震相关的地表位移场.这些差分干涉图(空间分辨率为50m×50m)详细地揭示了沿台湾西海岸震中附近150km2陆地范围内的震前和同震地表形变.几个具有较长时间(2-3a)跨度的震前干涉图呈现出高度的相关性和一致性,并均显示出约1个干涉条纹,相当于沿kd 雷达视线方向的地表位移在空间尺度上呈相对总量为28.3mm的分布;而具有短时间跨度(0.5-la)的同震干涉图呈现出显著的反映地震形变的干涉条纹(9-10个条纹),相当于沿雷达视线方向的地表位移在空间尺度上呈相对总量为25.5-28.3cm的分布,这些由干涉处理所得到的形变观测结果与GPS测量结果吻合程度很高(相关系数达0.95),证实了干涉形变精度可达1cm.特别地,这些高分辨率的同震形变干涉结果可以为该地震的物理机制解释提供极好的观测数据,同时也展示了使用短波段InSAR监测长时间累积的微小震前地表位移是可能的. 相似文献
10.
利用GPS和GRACE观测数据研究了日本MW9.0地震的震后变形特征.GPS观测显示,区域震后位移呈现随指数函数变化特征,变化速率符合大森公式的衰减特性;近五年的震后水平位移累积已达到东向60~165 cm,南向20~65 cm的量值,距震中较远站点已超过同震变化量,且震后变形仍然持续.GRACE观测到显著的震后重力变化,地震破裂两侧的重力变化总体均呈上升趋势,但海洋侧的变化速率较快.联合震后余滑和黏弹性位错理论对震后变形进行了模拟,探索了GPS和GRACE观测的综合应用方法.研究发现,综合考虑震后余滑和黏滞性松弛效应可以对日本地震的震后变形做出较合理的解释,震后初期余滑起主要作用,1至2年以后逐渐减弱,黏滞性松弛作用逐渐增强.在震后变形模拟和区域黏滞性结构反演中形成GPS和GRACE观测结合应用的方法,先基于震后GPS形变估算区域黏滞性结构,而后利用GRACE观测修正深部的黏滞系数,并综合利用这两种观测微调浅层黏滞系数,最终确定区域黏滞性结构.基于该方法反演了日本震源区的地幔黏滞性结构,地震断层破裂两侧的流变参数存在差异,大陆侧的地幔顶层黏滞系数在1.0×1019 Pa·s量级,而海洋侧的则略小于大陆的,在6.0×1018 Pa·s量级. 相似文献
11.
The mechanism of postseismic deformation related to strong earthquakes is important in geodynamics, and presumably afterslip
or viscoelastic relaxation is responsible for the postsesimic deformation. The 1999 Chi-Chi, Taiwan of China, earthquake occurred
in the region where GPS observation station is most densely deployed in the world. The unprecedented GPS data provides a unique
opportunity to study the physical processes of postseismic deformation. Here we assume that the interactions of viscoelastic
relaxation, afterslip, fault zone collapse, poroelastic rebound, flow of underground fluids, and all these combined contribute
to the surface displacements following the main shock. In order to know the essence of the postseismic deformation after the
strong event, fault zone collapse, poroelastic rebound, flow of underground fluids, and so on, are represented equivalently
by the variations of the focal medium properties. Therefore, the viscoelastic relaxation, afterslip, and the variations of
the equivalent focal medium properties are inverted by applying the GPS temporal series measurement data with viscoelastic
finite element method. Both the afterslip rate distribution along the fault and the afterslip evolution with time are obtained
by means of inversion. Also, the preliminary result suggests that viscosities of the lower crust and the upper mantle in Taiwan
region is 2.7×1018 and 4.2×1020 Pa·s, respectively. Moreover, the inversion results indicate that the afterslip contributing to postseismic deformation of
44.6% in 450 days after the Chi-Chi earthquake, with 34.7% caused by the viscous relaxation and 20.7% by other factors such
as fault zone collapse, poroelastic rebound, and the flow of liquids. 相似文献
12.
Rapid afterslip and short-term viscoelastic relaxation following the 2008 M_W7.9 Wenchuan earthquake
Zhigang Shao Rongjiang Wang Yanqiang Wu Langping Zhang Institute of Earthquake Science China Earthquake Administration Beijing China GFZ German Research Center for Geosciences D- Potsdam Germany 《地震学报(英文版)》2011,(2):163-175
Significant postseismic deformation of the 2008 M W 7.9 Wenchuan earthquake has been observed from GPS data of the first 14 days after the earthquake. The possible mechanisms for the rapid postseismic deformation are assumed to be afterslip on the earthquake rupture plane and viscoelastic relaxation of coseismiclly stress change in the lower crust or upper mantle. We firstly use the constrained least squares method to find an afterslip model which can fit the GPS data best. The afterslip model can explain n... 相似文献
13.
Relaxation of the coseismic stresses following an earthquake causes postseismic crustal deformation, which can last for days
to years. Continuous monitoring of postseismic deformation facilitates the understanding of the mechanism of deformation and
postseismic relaxation and viscous rheology. After the October 8, 2005 Kashmir earthquake, global positioning system data
for 8 months, starting from October, 2005 have been analyzed from three continuous sites located at Gulmarg, Amritsar, and
Jaipur. The average velocity during the observation period at Gulmarg (8.6 cm/year) is significantly higher than the Indian
plate velocity exhibiting postseismic crustal deformation. The velocity at Amritsar (5.9 cm/year) and Jaipur (5.1 cm/year)
is comparable to the Indian plate velocity. At Gulmarg, the logarithmic function fits well to the north–south component of
postseismic transients (~in the coseismic slip direction). The nature of decay in these transients suggests that the deformation
is mainly due to an afterslip, and the second possible contribution may be from the viscous relaxation process. This paper
presents the characteristics of postseismic transients and possible contributions from various postseismic mechanisms subsequent
to the Kashmir earthquake. 相似文献
14.
Christopher Rollins Sylvain Barbot Jean-Philippe Avouac 《Pure and Applied Geophysics》2015,172(5):1305-1358
Due to its location on a transtensional section of the Pacific-North American plate boundary, the Salton Trough is a region featuring large strike-slip earthquakes within a regime of shallow asthenosphere, high heat flow, and complex faulting, and so postseismic deformation there may feature enhanced viscoelastic relaxation and afterslip that is particularly detectable at the surface. The 2010 \(M = 7.2\) El Mayor-Cucapah earthquake was the largest shock in the Salton Trough since 1892 and occurred close to the US-Mexico border, and so the postseismic deformation recorded by the continuous GPS network of southern California provides an opportunity to study the rheology of this region. Three-year postseismic transients extracted from GPS displacement time-series show four key features: (1) 1–2 cm of cumulative uplift in the Imperial Valley and \(\sim\)1 cm of subsidence in the Peninsular Ranges, (2) relatively large cumulative horizontal displacements \(>\)150 km from the rupture in the Peninsular Ranges, (3) rapidly decaying horizontal displacement rates in the first few months after the earthquake in the Imperial Valley, and (4) sustained horizontal velocities, following the rapid early motions, that were still visibly ongoing 3 years after the earthquake. Kinematic inversions show that the cumulative 3-year postseismic displacement field can be well fit by afterslip on and below the coseismic rupture, though these solutions require afterslip with a total moment equivalent to at least a \(M = 7.2\) earthquake and higher slip magnitudes than those predicted by coseismic stress changes. Forward modeling shows that stress-driven afterslip and viscoelastic relaxation in various configurations within the lithosphere can reproduce the early and later horizontal velocities in the Imperial Valley, while Newtonian viscoelastic relaxation in the asthenosphere can reproduce the uplift in the Imperial Valley and the subsidence and large westward displacements in the Peninsular Ranges. We present two forward models of dynamically coupled deformation mechanisms that fit the postseismic transient well: a model combining afterslip in the lower crust, Newtonian viscoelastic relaxation in a localized zone in the lower crust beneath areas of high heat flow and geothermal activity, and Newtonian viscoelastic relaxation in the asthenosphere; and a second model that replaces the afterslip in the first model with viscoelastic relaxation with a stress-dependent viscosity in the mantle. The rheology of this high-heat-flow, high-strain-rate region may incorporate elements of both these models and may well be more complex than either of them. 相似文献
15.
Using global positioning system (GPS) technology, significant postseismic surface displacements were observed within the first
4 months after the 2001 Mw 7.8 Kunlun earthquake which occurred in China. In this study, we investigated the mechanisms that
may have possibly contributed to the postseismic deformations that have been observed. Based on the modeling results, we find
that an afterslip model can interpret postseismic displacements in the near field even when the fault plane is extended to
the bottom of the crust (~70 km). Models based on the viscoelastic relaxation theory showed a large discrepancy in the spatial
pattern of the deformation compared with what has been observed. Thus, we infer that both mechanisms cannot interpret the
observed postseismic deformation independently. A combination of afterslip and viscoelastic relaxation can further improve
the data fit, especially at sites far from the fault. With maximum afterslip of ~0.4 m occurring at a depth of 10 km in the
central section, the combined model shows that the estimated afterslip occurred mostly on and below the coseismic rupture
plane, as well as on its eastern extension. The estimated moment released by the afterslip in the first 4 months is almost
40% of that released by the coseismic slip. The best-fitting viscoelastic relaxation model shows a “weak” upper mantle with
a viscosity of ~1.0 × 1018 Pa s. The combined model also suggests the existence of a lower crust with viscosity larger than 1.0 × 1018 Pa s, although it cannot be constrained accurately. 相似文献
16.
--Models of combined Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data collected in the region of the Northridge earthquake indicate that significant afterslip on the main fault occurred following the earthquake. Additional shallow deformation occurred to the west of the main rupture plane. Both data sets are consistent with logarithmic time-dependent behavior following the earthquake indicative of afterslip rather than postseismic relaxation. Aftershocks account for only about 10% of the postseismic motion. The two data sets are complimentary in determining the postseismic processes. Fault afterslip and shallow deformation dominate the deformation field in the two years following the earthquake. Lower crustal deformation may play an important role later in the earthquake cycle. 相似文献
17.
2001年11月14日,在青海和新疆交界处发生了昆仑山Ms8.1级强烈地震,GPS后观测显示,此次地震震后形变不仅在断裂南北两侧存在很大的差异,而且在短时间调整后断裂南北两侧表现为同向运动.本文以观测的地震形变为约束,通过有限元数值模拟分析昆仑山地震震后形变的物理机制.建立有关的有限元虚功方程,通过有限元数值方法模拟震后形变,从理论上分析介质的非均匀性、黏滞性松弛、流体调整对震后形变的影响.采用网格搜索确定昆仑断裂南北两侧下地壳的黏滞系数分别为5.0×1017Pa·s, 9.0×1018Pa·s左右,正是这十余倍的差异引起了断裂两侧震后形变的非对称性和同向运动,这一差异既是长期地质作用的结果,又是现代地球动力学环境的决定因素之一.通过数值模拟定性讨论了断裂北侧地表形变在震后短期内的调整,对于靠近断裂附近的测点可能是黏弹性松弛和孔隙流体调整共同作用的结果,所以在分析短期震后形变时综合考虑黏弹松弛和孔隙流体调整是很有必要的. 相似文献
18.
根据1990年青海共和地震震后地表垂直形变,通过模型拟合得到了支配共和地区震后形变场时空演化的形变源及其力学机制.分析穿过断层的震前1期和震后6期水准数据,结果表明震后垂直形变具有以下特征:①震后震区上盘继续发生继承性的大幅度上升,其中震后头一年上升速率最大;②震后上升区范围显著,范围随时间变化不大,但较同震形变上升区范围增大;③震后相邻测站高差观测值的时间序列明显具有对数衰减特征或指数衰减特征,衰减特征时间分别为0.165年和1.344年.本文还发展了一个利用水准数据与连续介质位错模型研究震后形变机制的新方法.该方法用相邻水准点之间的原始高差观测值而非它们相对参照点的积分值来约束连续介质位错模型,可以有效减少误差累积带来的偏差并充分利用观测数据.利用这一方法的初步分析结果表明,断层震后滑移和介质黏弹性松弛共同导致了共和地震震后形变.前者表现为发生在断层面及其延伸部分的滑移,特别是位于主破裂上方沉积层内的滑移;后者则表现为下地壳与上地幔内的黏弹性松弛,黏滞系数为1020Pa.s量级. 相似文献