Changes in Frequency of Moderate-Size Earthquakes and Coulomb Failure Stress before and after the Landers, California, Earthquake of 1992
Changes in Frequency of Moderate-Size Earthquakes and Coulomb Failure Stress before and after the Landers, California, Earthquake of 1992
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1992年加利福尼亚州兰德斯地震前后中型地震频率和库仑破坏应力的变化
DOI：
10.1785/0120000224
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发表时间：
2001
影响因子：
3
通讯作者：
L. Sykes
中科院分区：
文献类型：
--
作者：
W. Du;L. Sykes
本文研究了1992年6月28日兰德斯地震前后中等规模地震发生频率的变化，并结合1812年以来南加州库仑破裂应力（CFS）的演变讨论了它们的意义。我们系统地考虑了以兰德斯地震震中为中心的圆形区域和等面积环。比较了兰德斯事件前两个10年周期和前后两个5年周期的频率-震级关系。仅包括震级为M ≥ 4.0的事件;排除余震。对于半径为140至160公里的较大的圆形区域，在主震之前的中等规模的事件的频率-震级分布的速率和斜率似乎是异常的，与之前或之后的时期相比。然而，对于更接近1992年震中的地区，事件数量很少，分布上的差异也不太明显。然而，当我们检查相等面积的环带中的地震活动时，最大的变化发生在距离主震震中约150公里处，而不是像兰德斯事件的前兆那样更近。我们还推导出一个指数值，以更好地量化作为时间函数的中等规模事件发生频率的差异。指数值和频率-震级分布具有相似的空间依赖性。自1812年以来，兰德斯附近的一个大区域已经接近故障的变化，在CFS的圣安德烈亚斯类型的故障。然而，这些变化主要是由与1812年和1857年地震相关的同震变化和与圣安德烈亚斯断层相关的构造应力积累所主导，而不是由兰德斯断层本身相关的应力积累所主导，兰德斯断层的特点是非常缓慢的长期位移。因此，1992年之前中等规模地震频率的最显著变化似乎与兰德斯序列本身的应力积累无关。它们，沿着兰德斯序列，可能预示着一个广阔的区域，在未来最终的大地震之前正接近高应力状态。没有发现兰德斯附近中等规模地震的明显增加与这样一种观点是雅阁的，即这种在几年到几十年的时间尺度上的增加与沿着高（而不是低）长期滑动率断层的大地震应力的区域积累有关。
Changes in the frequency of moderate-size events before and after the 28 June 1992 Landers earthquake are investigated, and their implications are discussed in the context of Coulomb failure stress (CFS) evolution since 1812 in southern California. We systematically considered circular regions and equal-area annuli centered on the epicenter of the Landers earthquake. Frequency-magnitude relationships for two 10-year periods before and two 5-year periods around the Landers event are compared. Only events with magnitude, M ≥ 4.0 are included; aftershocks are removed. For the larger circular regions with radii of 140 to 160 km, the rate and slope of the frequency-magnitude distribution for moderate-size events just before the mainshock appear to be anomalous compared to those for either the preceding or subsequent periods. For areas closer to the 1992 epicenter, however, the number of events is few, and the differences in the distributions are less obvious. When we examined the seismic activity in annuli of equal area, however, the largest changes occurred about 150 km from the epicenter of the mainshock, not closer as would be expected for a precursor to the Landers event. We also derive an index value to better quantify differences in the frequency of occurrence of moderate-size events as a function of time. The index value and the frequency-magnitude distribution show similar spatial dependence. Since 1812 a large region near Landers has moved closer to failure in terms of changes in CFS for faults of San Andreas type. These changes, however, are dominated by coseismic changes associated with the 1812 and 1857 earthquakes and by tectonic stress buildup related to the San Andreas fault, not by stress buildup associated with the Landers faults themselves, which are characterized by very slow long-term displacements. Hence, the most pronounced changes in the frequency of moderate-size earthquakes before 1992 do not appear to be related to stress buildup to the Landers sequence itself. They, along with the Landers sequence, may be indicative of a broad region that is approaching a high stress state prior to an eventual future great earthquake. The failure to find a pronounced increase in moderate-size shocks close in to Landers is in accord with the idea that such increases on a timescale of years to decades are associated with the regional buildup of stress to large earthquake along faults of high (not low) long-term slip rates.
影响因子：
3
作者：
Y. Okada
通讯作者：
Y. Okada