Precursory Rise of P-Wave Attenuation before the 2004 Parkfield Earthquake
Precursory Rise of P-Wave Attenuation before the 2004 Parkfield Earthquake
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2004 年帕克菲尔德地震前 P 波衰减的先兆上升
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
G. Henderson
中科院分区：
文献类型：
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作者：
K. Chun;Qiang Yuan;G. Henderson
摘要2004年9月28日，加利福尼亚州帕克菲尔德附近发生6.0级地震，圣安德烈亚斯断裂长达30公里。自1980年代中期以来，美国地质调查局曾长期预测，1993年以前帕克菲尔德附近将发生一次具有∼6级特征的地震，因此自1980年代中期以来，该断层段一直处于密切监测之下。多重地震使研究与主震有关的地震传播特征的时间变化成为可能。结果表明，在迟发地震发生前18个月左右，P波衰减算子t*开始急剧上升，并伴随着P/S比值在频域和时间域的迅速下降。询问即将到来的破裂带北半部的P波，那里的同震滑动最大，产生了最强烈的t*异常。这些异常在帕克菲尔德地震后六周达到顶峰，然后在接下来的几个月里迅速减弱。震前t*的上升，伴随着P/S比值的迅速下降，表明微破裂导致的孔隙-流体饱和度下降，最终导致了断层破裂期间的灾难性岩石破坏。
Abstract On 28 September 2004 an M 6.0 earthquake occurred, rupturing a 30-km stretch of the San Andreas fault near Parkfield, California. The fault segment, which hosted a cluster of nearly identical microearthquakes (a multiplet), had been under close surveillance since the mid-1980s following a long-term prediction by the United States Geological Survey that a characteristic earthquake of M ∼6.0 would occur near Parkfield before 1993. The multiplet made possible a study of temporal changes in seismic propagation characteristics associated with the mainshock. We show that a sharp rise in P -wave attenuation operator t * began to appear about 18 months before the belated seismic event, accompanied by a rapid fall in P / S ratio, in both the frequency and time domains. The P waves that interrogated the northern half of the impending rupture zone, where the coseismic slip was to be the largest, yielded the strongest t * anomalies. The anomalies peaked six weeks after the Parkfield earthquake and then diminished rapidly in the months ensuing. The preseismic rise of the t * , accompanied by a rapidly falling P / S ratio, pointed to a decline in pore-fluid saturation due to microcracking that culminated in the catastrophic rock failure during the fault rupture.