High‐resolution electromagnetic imaging of the San Andreas Fault in central California
High‐resolution electromagnetic imaging of the San Andreas Fault in central California
复制标题
加利福尼亚州中部圣安德烈亚斯断层的高分辨率电磁成像
DOI：
10.1029/98jb01755
复制
发表时间：
1999
影响因子：
--
通讯作者：
J. Booker
中科院分区：
文献类型：
--
作者：
M. Unsworth;G. Egbert;J. Booker
虽然越来越多的证据表明，流体可能在地震破裂过程中发挥重要作用，但在活动断层带中直接观察流体仍然很困难。由于导电流体（如含盐孔隙水）的存在强烈影响地壳岩石的整体导电性，因此电学和电磁方法为克服这一困难提供了巨大的潜力。在这里，我们提出和比较结果，从高分辨率大地电磁（MT）剖面的两个部分的圣安德烈亚斯断层（SAF），表现出非常不同的模式的地震活动：帕克菲尔德，有规律的小地震和蠕变事件，并在卡里佐平原，在那里的故障是地震静止，显然锁定。在这两个调查中，电场连续采样，100米长的偶极子端到端放置在整个故障。从100到0.1赫兹的数据从两个配置文件是一致的二维（2-D）故障平行电阻率模型。当解释中包括横向电磁（TE和TM）模式数据时，在两个位置都需要在断层核心中延伸至2{endash}4 km深度的低电阻率狭窄（{约}300{endash}600 m宽）区域。然而，在帕克菲尔德，异常区域的电导率（电导率厚度积）比卡里佐平原大一个数量级，这表明地震活动更活跃的帕克菲尔德段的流体浓度更高。我们还对两个部分之间的结构差异进行了成像。在卡里佐平原，电阻，推测结晶，岩石存在于断层两侧的深度低于3{endash}4公里。特别是，我们清楚地形象电阻基底延伸{约}10公里或更多的SAF以东，下面的埃尔克霍恩山和Temblor范围。在帕克菲尔德的情况是完全不同的电阻块的Salinian花岗岩西部的故障和导电，推测流体丰富的Franciscan复杂的东部。这些结构差异可能直接通过影响断层强度或间接通过控制流体供应来控制断层力学行为的差异。{copyright} 1999美国地球物理联合会« less
Although there is increasing evidence that fluids may play a significant role in the earthquake rupture process, direct observation of fluids in active fault zones remains difficult. Since the presence of an electrically conducting fluid, such as saline pore water, strongly influences the overall conductivity of crustal rocks, electrical and electromagnetic methods offer great potential for overcoming this difficulty. Here we present and compare results from high-resolution magnetotelluric (MT) profiles across two segments of the San Andreas Fault (SAF) which exhibit very different patterns of seismicity: Parkfield, which has regular small earthquakes and creep events, and in the Carrizo Plain, where the fault is seismically quiescent and apparently locked. In both surveys, electric fields were sampled continuously, with 100 m long dipoles laid end-to-end across the fault. From 100 to 0.1 Hz the data from both profiles are consistent with a two-dimensional (2-D) fault-parallel resistivity model. When both transverse electric and magnetic (TE and TM) mode data are included in the interpretation, narrow ({approximately}300{endash}600 m wide) zones of low resistivity extending to depths of 2{endash}4 km in the core of the fault are required at both locations. However, at Parkfield the conductance (conductivity thickness product) of the anomalous region ismore » an order of magnitude larger than at Carrizo Plain, suggesting much higher concentrations of fluids for the more seismically active Parkfield segment. We also image structural differences between the two segments. At Carrizo Plain, resistive, presumably crystalline, rocks are present on both sides of the fault at depths below 3{endash}4 km. In particular, we clearly image resistive basement extending {approximately}10 km or more east of the SAF, beneath the Elkhorn Hills and Temblor Range. At Parkfield the situation is quite different with a resistive block of Salinian granite west of the fault and an electrically conductive, presumably fluid rich Franciscan complex to the east. It is possible that these structural differences control the difference in mechanical behavior of the fault, either directly by affecting fault strength or indirectly by controlling fluid supply. {copyright} 1999 American Geophysical Union« less
影响因子：
--
作者：
BRUNE, JN;HENYEY, TL;ROY, RF
通讯作者：
ROY, RF