Seismic quiescence before the landers (M = 7.5) and big bear (M = 6.5) 1992 earthquakes
Seismic quiescence before the landers (M = 7.5) and big bear (M = 6.5) 1992 earthquakes
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1992 年登陆器 (M = 7.5) 和大熊 (M = 6.5) 地震前的地震静止状态
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
M. Wyss
中科院分区：
文献类型：
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作者：
S. Wiemer;M. Wyss
在1992年6月28日兰德斯地震之前，在震中附近和以北约11乘23乘15公里的区域内，地震活动率下降了75%。这种异常开始，所有震级带，在1988年1月，持续4.5年的主震。震中以南的一个较小的体积（7 × 14 × 15公里）显示，从1989年11月开始，地震活动率下降了75%。在同一天的大熊地震之前，在震源周围约13 × 22 × 15公里的体积内，地震活动率下降了100%。该卷包含了9年背景期内的192次M1.6级地震，但在1990年12月至1992年6月27日的1.6年中没有。表征这些速率变化的标准偏差z值非常高，分别为6.3和12.3，并且异常是唯一的，在所检查的南加州地震目录的部分（117°06′W至115°40′W和33°45′N至35°10′N）中，其显著性没有被任何其他速率下降超过。在1992年4月23日约书亚特里6.1级地震附近没有发现地震活动率的变化。根据震级特征和频率-震级分析，我们得出结论，这两个平静异常可能不是由于移动或压缩的震级尺度，我们解释为前兆异常。这一分析是使用兰德斯地区的去聚类地震目录进行的，对两次疑似震级变化进行了0.2和0.1（1985年8月和1990年5月）的校正。通过一种新的可视化技术，我们可以研究地震活动率作为时间和空间函数的稳定性和变化。通过在每个时间间隔映射z值的速率变化，并在以密集的点网格（纬度，经度）为中心的体积中，该计算机代码显示了速率变化程度的平滑等高线图的几乎连续的序列。因此，任何人为的或真实的异常都可以被准确地定义。
The Landers earthquake of 28 June 1992 was preceded by a seismicity rate decrease of 75% in a volume approximately 11 by 23 by 15 km, located adjacent to and north of the epicenter. This anomaly started, for all magnitude bands, in January 1988, lasting 4.5 yr up to the mainshock. A smaller volume (7 by 14 by 15 km), to the south of the epicenter, showed a seismicity rate decrease of 75% starting in November 1989. The Big Bear earthquake of the same day was preceded by a 100% decrease of the seismicity rate, within a volume of approximately 13 by 22 by 15 km around the hypocenter. This volume contained 192 earthquakes of M ≧ 1.6 during the background period of 9 yr, but none during the 1.6 yr from December 1990 to 27 June 1992. The standard deviate z values characterizing these rate changes are very high, 6.3 and 12.3, respectively, and the anomalies are unique, not surpassed in significance by any other rate decrease in portion of the southern California earthquake catalog examined (117°06′W to 115°40′W and 33°45′N to 35°10′N). No seismicity rate change was found in the vicinity of the M = 6.1 Joshua Tree earthquake of 23 April 1992. Based on magnitude signatures and frequency-magnitude analyses, we conclude that the two quiescence anomalies could not have been due to a shift or a compression of the magnitude scale, and we interpret them as precursor anomalies. This analysis was carried out using the declustered earthquake catalog for the Landers area with corrections of 0.2 and 0.1 (August 1985 and May 1990) for two suspected magnitude shifts. With a new visualization technique we can investigate the stability, and changes, of the seismicity rate as a function of time and space. By mapping z values for rate changes at every time interval, and in volumes centered on a dense grid of points (latitude, longitude), this computer code furnishes an almost continuous sequence of smooth contour maps of the degree of rate changes. Any anomalies, artificial or real, may thus be defined accurately.