Postseismic relaxation and aftershocks
Postseismic relaxation and aftershocks
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震后弛豫和余震
DOI：
10.1029/2006jb004584
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发表时间：
2007
影响因子：
--
通讯作者：
Shui‐Beih Yu
中科院分区：
文献类型：
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作者：
J. C. Savage;J. Svarc;Shui‐Beih Yu
[1]Perfettini等人（2005）提出，地震后在震中区测量的地表位移u（t）的时间依赖性与余震累积次数N（t）有关，方程为u（t）= a + bt + cN（t）+ d（1 − e−αt），其中a、B、c、d和α是选择来拟合数据的常数，t是震后时间。N（t）出现在u（t）的表达式中，因为余震和u（t）的一部分被认为是由相同的震源驱动的，即在同震破裂下倾延伸的次震孕育深度处的震后断层蠕动。我们表明，这个方程与实际观测到的N（t）拟合了五次地震后在几个基线上记录的震后位移：1999年M7.6集集（台湾），1999年M7.1赫克托矿山（加州南部）、2002年7.9级德纳里（阿拉斯加中部）、2003年6.5级圣西蒙（加州中部）和2004年6.0级帕克菲尔德（加州中部）地震。虽然对于u（t）表达式中的每一项都有合理的物理解释，但拟合相当简单的震后位移所涉及的大量可调常数（a、B、c、d和α）降低了拟合的重要性。由于观测到的N（t）与修正的大森定律很好地拟合，断层在深度的蠕动可能表现出相同的时间依赖性。如果同震破裂引起的断层下倾的流变学与普通的瞬态蠕变一致，则可以解释这种依赖性。Montesi（2004）证明，在深部剪切带上的幂律蠕变也会产生这种时间信号。
[1] Perfettini et al. (2005) suggested that the temporal dependence of surface displacements u(t) measured in the epicentral area following an earthquake is related to N(t), the cumulative number of aftershocks, by the equation u(t) = a + bt + cN(t) + d(1 − e−αt), where a, b, c, d, and α are constants chosen to fit the data and t is the postearthquake time. N(t) appears in the expression for u(t) because both the aftershocks and a portion of u(t) are thought to be driven by the same source, postseismic fault creep at subseismogenic depths on the downdip extension of the coseismic rupture. We show that this equation with the actually observed N(t) fits the postseismic displacements recorded on several baselines following each of five earthquakes: 1999 M7.6 Chi-Chi (Taiwan), 1999 M7.1 Hector Mine (southern California), 2002 M7.9 Denali (central Alaska), 2003 M6.5 San Simeon (central California), and 2004 M6.0 Parkfield (central California) earthquakes. Although there are plausible physical interpretations for each of the terms in the expression for u(t), the large number of adjustable constants (a, b, c, d, and α) involved in fitting the rather simple postseismic displacements diminishes the significance of the fit. Because the observed N(t) is well fit by the modified Omori's law, fault creep at depth presumably exhibits the same temporal dependence. That dependence could be explained if the rheology of the fault downdip from the coseismic rupture is consistent with ordinary transient creep. Montesi (2004) demonstrated that power law creep across a shear zone at depth would also produce that temporal signal.