Deep rock damage in the San Andreas Fault revealed by P- and S-type fault-zone-guided waves
Deep rock damage in the San Andreas Fault revealed by P- and S-type fault-zone-guided waves
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P 型和 S 型断层带导波揭示了圣安德烈亚斯断层的深层岩石损伤
DOI：
10.1144/sp359.3
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发表时间：
2011
影响因子：
2.8
通讯作者：
P. Malin
中科院分区：
文献类型：
--
作者：
W. Ellsworth;P. Malin
断层滑动对断裂带岩石的破坏导致低地震波速度通道的形成。在这样的通道内，由Fg表示的被引导的地震波可以传播。在这里，我们显示与岩心样品，测井曲线和FG波，这样的通道是由SAFOD（圣安德烈亚斯断层观测深度）钻孔在2.7公里的深度附近的帕克菲尔德，加州，美国穿过。这条横向延伸的通道向下延伸到至少一半的发震地壳，超过7公里。该通道不仅支持已有的洛夫型（FL）和瑞利型（FR）导波，而且还支持一种新的断层导波，我们称之为FΦ。在地下2.7公里处记录到的FΦ通常是分散的，在艾里相位结束，并在P波和S波之间到达。模拟结果表明，FΦ在断裂带核部以漏模传播。结合岩心样本、测井记录和其他两种类型的导波，SAFOD的FΦ揭示了一个极深的岩石损伤区。起源于在断层运动的最近历史积累的损害，我们建议它是通过断裂附近的滑动面的地震，如1857年的特洪堡M 7.9，或者是一个无法解释的一部分，已知是活跃在这个网站的断层蠕动过程。
Abstract Damage to fault-zone rocks during fault slip results in the formation of a channel of low seismic-wave velocities. Within such channels guided seismic waves, denoted by Fg, can propagate. Here we show with core samples, well logs and Fg-waves that such a channel is crossed by the SAFOD (San Andreas Fault Observatory at Depth) borehole at a depth of 2.7 km near Parkfield, California, USA. This laterally extensive channel extends downwards to at least half way through the seismogenic crust, more than about 7 km. The channel supports not only the previously recognized Love-type- (FL) and Rayleigh-type- (FR) guided waves, but also a new fault-guided wave, which we name FΦ. As recorded 2.7 km underground, FΦ is normally dispersed, ends in an Airy phase, and arrives between the P- and S-waves. Modelling shows that FΦ travels as a leaky mode within the core of the fault zone. Combined with the drill core samples, well logs and the two other types of guided waves, FΦ at SAFOD reveals a zone of profound, deep, rock damage. Originating from damage accumulated over the recent history of fault movement, we suggest it is maintained either by fracturing near the slip surface of earthquakes, such as the 1857 Fort Tejon M 7.9, or is an unexplained part of the fault-creep process known to be active at this site.