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形变模式1999年集集地震的Mw = 7.5发生在密集的GPS台网中心。在地震后的前200天内，水平和垂直分量都累积了多达10厘米的位移。密集的空间覆盖和非凡的信噪比，使得集集地震的震后变形场可以说是有史以来最好的。震前位移率提供了有关活动断层的几何形状和滑动率、地震荷载周期和活动弧大陆碰撞构造的独特信息。余震、粘性流动和孔弹性松弛都被用来解释地震后的瞬态变形。集集地震的资料具有很高的信噪比，因此可以区分这两个过程。早期的震后瞬态（3个月）最好用余震来解释，但是对随后几年的变形分析可能会揭示粘弹性和/或孔弹性松弛。反演结果表明，余震围绕同震大滑动带，与地震引起的应力变化驱动的稳定滑动一致。在发震深度推断出的余震引发了这样一个问题：为什么这种余震在地震期间发生得很慢而不是很快？与实验室推导的摩擦定律相一致的滑移力学模型相结合的时空反演将有助于解决这一问题，并应阐明断裂带的性质和应力。同震和震后GPS反演结果显示，车隆堡断裂呈斜平状。然而，更深层活动断层的几何形状尚未完全确定。一个困难是需要在挤压造山环境中建立力学上一致的震间变形模型。我们建议发展台湾地震周期的物理二维粘弹性模型，其中包括重力的一阶效应，其中断层的滑动率是由远场板块运动驱动的，而不是运动学强加的。这些模型与可用的速度场相结合，将可以估计台湾活动断层的几何形状和滑动速率。

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.