Postseismic Processes Following the 1999 Chi-Chi, Earthquake and Models of Active Crustal Deformation in Taiwan

1999年台湾集集地震的震后过程与地壳活动变形模式1999年台湾集集地震发生在密集GPS网的中心，震级为Mw = 7.5。在地震后的前200天内，水平和垂直分量的位移累积高达10厘米。密集的空间覆盖和非凡的信噪比使得集集地震的震后形变场可以说是有史以来最好的记录。 地震前的位移速率提供了关于活动断层的几何形状和滑动速率、地震加载周期以及活动弧形大陆碰撞的构造的独特信息，后滑、粘滞流和孔隙弹性松弛都被提出来解释地震后的瞬时变形。集集地震的资料具有很高的信噪比，因此有可能区分这些过程。 震后早期瞬变（3个月）最好用后滑来解释，但随后几年的变形分析可能会揭示粘弹性和/或孔隙弹性松弛。 反演结果表明，后滑包围了大的同震滑动区，与稳定的滑动由地震引起的应力变化驱动一致。 在孕震深度推断后滑提出了一个问题，为什么这种滑动发生缓慢，而不是迅速在地震期间。 与实验室推导的摩擦定律相一致的滑动力学模型结合的时空反演将有助于解决这一问题，也应该阐明断层带的性质和应力。同震和震后GPS数据的反演与车笼埔断层的斜坡平坦几何形状一致。 然而，更深处活动断层的几何形状还没有完全解决。 一个困难是，在挤压造山环境中的地震间变形的力学一致的模型是必要的。 我们建议开发物理的2D粘弹性模型的地震周期在台湾，其中包括重力的一阶效应，并在断层上的滑动速率驱动的远场板块运动，而不是强加的运动学。 这些模型，结合现有的速度场，将允许在台湾的活动断层的几何形状和滑动速率的估计。

EAR-0309148SegallPostseismic Processes Following the 1999 Chi-Chi, Earthquake and Models of Active Crustal Deformation in TaiwanThe Mw = 7.5, 1999 Chi-Chi, Taiwan earthquake occurred in the center of a dense GPS network. In the first 200 days after the earthquake displacements of as much as 10 cm accumulated in both the horizontal and vertical components. The dense spatial coverage and extraordinary signal to noise ratio make the postseismic deformation field of the Chi-Chi earthquake arguably the best ever recorded. Preseismic displacement rates provide unique information on the geometry and slip-rates of active faults, the earthquake loading cycle, and tectonics of an active arc continent collision.Afterslip, viscous flow, and poroelastic relaxation have all been proposed to explain transient postseismic deformation. The data from the Chi-Chi earthquake is of such high signal to noise ratio that it is possible to discriminate between these processes. The early postseismic transient (3 months) is best explained by afterslip, however analysis of deformation over the subsequent years may reveal viscoelastic and/or poroelastic relaxation. Inversion results reveal that afterslip encircled the zone of large coseismic slip, consistent with stable slip being driven by stress changes caused by the earthquake. Inferred afterslip at seismogenic depths raises the question of why this slip occurred slowly rather than rapidly during the earthquake. Space-time inversions combined with mechanical models of slip consistent with laboratory derived friction laws will help to address this and should also elucidate fault zone properties and stresses. Inversion of both the coseismic and postseismic GPS data are consistent with a ramp-flat geometry for the Chelungpu Fault. The geometry of active faults at greater depths is, however, not fully resolved. One difficulty has been that mechanically consistent models of interseismic deformation in compressional orogenic environments are needed. We propose to develop physical 2D viscoelastic models of the earthquake cycle in Taiwan, which include the first order effects of gravity, and in which the slip rates on faults are driven by far field plate motions rather than imposed kinematically. These models, combined with the available velocity field, will allow estimates of the geometry and slip-rates on active faults in Taiwan.