Crustal structure and seismic anisotropy near the San Andreas Fault at Parkfield, California
Crustal structure and seismic anisotropy near the San Andreas Fault at Parkfield, California
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加利福尼亚州帕克菲尔德圣安德烈亚斯断层附近的地壳结构和地震各向异性
DOI：
10.1111/j.1365-246x.2009.04198.x
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发表时间：
2009
影响因子：
2.8
通讯作者：
G. Zandt
中科院分区：
文献类型：
--
作者：
A. Ozacar;G. Zandt
位于圣安德烈亚斯断层（SAF）西南约3公里处的PKD站的接收函数（rf）对帕克菲尔德附近的萨利系地层进行了采样。地壳倍数表明地壳厚度为26 km， aVP/VS为1.88，而西部上、中地壳aVP/VS略低（1.83）。对于中地壳，观测到的到达时间与最近成像的地震反射器相对应，并且可能对应于暴露在地表的花岗岩基底部下方的一层变质沉积岩。对于下地壳，RFs显示出强烈的反向极性反转和莫霍振幅变化，这需要在低速，高VP/VS，可能是具有ENE倾斜（~ 35◦）岩石结构的蛇纹岩或充满流体的片岩层中具有强的地震各向异性（> 15%）。在位于SAF以西的一些南加州台站的rf中观测到的类似振幅变化和极性反转模式支持了这些数据特征的原因是区域普遍存在的下地壳各向异性的假设。这种各向异性结构的方向与最近的圣安德烈亚斯剪切感不一致，很可能是过去向东（法拉龙板块）俯冲的化石结构。
SUMMARY Receiver functions (RFs) from station PKD located ∼3 km SW of the San Andreas Fault (SAF) samples the Salinian terrane near Parkfield. Crustal multiples indicate a 26-km-thick crust with aVP/VS of 1.88, which is slightly lower (1.83) for the upper and middle crust in the west. For the mid-crust, arrivals are observed at times corresponding to recently imaged seismic reflectors and may correspond to a layer of metasedimentary rocks below the base of the granitic batholith exposed at the surface. For the lower crust, RFs display strong polarity reversals with backazimuth and a change in Moho amplitude that require strong seismic anisotropy (>15 per cent) in a low velocity, high VP/VS, possibly serpentinite or fluid filled schist layer that has a ENE dipping (∼35 ◦ ) rock fabric. Similar patterns of amplitude variations and polarity reversal observed in RFs for some southern California stations located west of the SAF support the hypothesis that the cause of these data characteristics is a regionally prevalent lower crustal anisotropy. The orientation of this anisotropic fabric is inconsistent with the recent San Andreas sense of shear and is most likely a fossilized fabric of past eastward-directed (Farallon Plate) subduction.