Evolution of stress in Southern California for the past 200 years from coseismic, postseismic and interseismic stress changes
Evolution of stress in Southern California for the past 200 years from coseismic, postseismic and interseismic stress changes
复制标题
DOI：
10.1111/j.1365-246x.2007.03391.x
复制
发表时间：
2007-06-01
影响因子：
2.8
通讯作者：
Burgmann, Roland
中科院分区：
文献类型：
--
作者：
Freed, Andrew M.;Ali, Syed Tabrez;Burgmann, Roland
南加州的地震活动是由太平洋和北美板块沿着圣安德烈斯断层（SAF）系统和东加州剪切带（ECSZ）的相对运动产生的应力引起的。在这里，我们计算如何在南加州的应力场已经演变了在过去的两个世纪，由于地震间的负荷，从目前的GPS观测表面速度，从静应力的重新分布引起的大自1812年Wrightwood地震以来的M-w ≥ 6.5地震，以及与这些事件相关的震后粘弹性松弛，其作用是从深部转移同震应力，温暖的下地壳和上地幔到上覆的孕震上地壳。本文计算了近两百年来所有M-w >= 6地震破裂面上平行于SAF走向的垂直走滑断层和震源处的库仑应力变化。我们的研究结果表明，1857年M-w = 8.2的特洪堡地震，迄今为止最大的事件发生在该地区在过去的两个世纪，有一个深刻的影响，在南加州的应力状态在世纪，诱导显着的应力增加到北部（帕克菲尔德地区和相邻的蠕变SAF）和南部（南部SAF和圣哈辛托断层），并在南部ECSZ应力缓解。这些应力变化随后在整个世纪早期被震后松弛作用大大放大。缓慢的地震间应力积累进一步加载了所有主要的走滑断层，并重新加载了1857年地震释放应力的ECSZ地区。我们的计算表明，只有56%的震源被推近失败的同震应力变化，这表明大地震的发生并不强烈地确定同震库仑应力变化。当考虑震后应力变化时，这一比例上升到70%。我们的计算表明，在大地震后的应力重新分布的震后粘弹性松弛的重要性。然而，我们发现，地震后的过程与事件超过约十年的老接近完成，因此没有显着影响目前在南加州观察到的区域速度场。
The seismicity of southern California results from stresses that arise from the relative motion of the Pacific and North American Plates being accommodated along the San Andreas Fault (SAF) system and the Eastern California Shear Zone (ECSZ). Here we calculate how the stress field in southern California has evolved over the past two centuries due to interseismic loading, as inferred from current GPS observations of surface velocities, from redistributions of static stress induced by large (M-w >= 6.5) earthquakes since the 1812 Wrightwood quake, and postseismic viscoelastic relaxation associated with these events that serves to transfer coseismic stresses from the deep, warm, lower crust and upper mantle to the overlying seismogenic upper crust. We calculate Coulomb stress changes on vertical strike-slip faults striking parallel to the SAF and at the hypocenters on the rupture planes of all M-w >= 6 events over the past two centuries. Our results suggest that the 1857 M-w = 8.2 Fort Tejon earthquake, by far the largest event to have occurred in the region over the past two centuries, had a profound influence on the state of stress in Southern California during the 19th century, inducing significant stress increases to the north (Parkfield region and adjoining creeping SAF) and south (southern SAF and San Jacinto fault), and stress relief across the southern ECSZ. These stress changes were then greatly magnified by postseismic relaxation through the early part of the 20th century. Slow interseismic build-up of stress further loads all major strike-slip faults and works to reload the areas of the ECSZ where stress was relieved by the 1857 quake. Our calculations suggest that only 56% of hypocenters were pushed closer to failure by preceding coseismic stress changes, suggesting that the occurrence of large earthquakes is not strongly determined by coseismic Coulomb stress changes. This percentage rises to 70% when postseismic stress changes are also considered. Our calculations demonstrate the importance of postseismic viscoelastic relaxation in the redistribution of stress following large earthquakes. We find, however, that postseismic processes associated with events more than about a decade old are near completion and thus do not significantly influence the regional velocity field presently observed in southern California.