Analysis of Fault Zone Resonance Modes Recorded by a Dense Seismic Array Across the San Jacinto Fault Zone at Blackburn Saddle
Analysis of Fault Zone Resonance Modes Recorded by a Dense Seismic Array Across the San Jacinto Fault Zone at Blackburn Saddle
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DOI：
10.1029/2020jb019756
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发表时间：
2020-10-01
影响因子：
3.9
通讯作者：
Ben-Zion, Yehuda
中科院分区：
文献类型：
--
作者：
Qiu, Hongrui;Allam, Amir A.;Ben-Zion, Yehuda
我们目前的观测和建模的空间特征函数的共振波在断层带波导，使用的数据记录在一个密集的地震阵列在圣哈辛托断层带（SJFZ）在南加州。该阵列由5-Hz地震检波器组成，在靠近Hemet Stepover的Blackburn Saddle处以类似于10-30 m的间距穿过SJFZ。S波到达后的波场快照是一致的50多个近断层事件，这表明这种模式是由断裂带结构，而不是源属性控制。高信噪比地震实例资料显示，在断层附近测站平均的共振波振幅谱中，有三个主频率峰值，分别位于1.3、2.0和2.8Hz附近。数据建模与共振波的本征函数在两个四分之一空间之间的低速层（断层带）的解析表达式。使用网格搜索为基础的方法，我们调查可能的宽度的波导管，阵列内的位置，以及剪切波速度的介质，适合在类似于1.3 Hz的谐振信号。结果表明，类似于300米宽的破坏断层带层，与围岩相比，S波速度降低了65%。低速带的SW边缘靠近映射的断层面迹线，表明损伤带不对称地位于区域性较快的NE地壳块体上。将断层共振模式和陷波结合起来进行建模，可以提高断层构造的成像分辨率。
We present observations and modeling of spatial eigen-functions of resonating waves within fault zone waveguide, using data recorded on a dense seismic array across the San Jacinto Fault Zone (SJFZ) in southern California. The array consists of 5-Hz geophones that cross the SJFZ with similar to 10-30 m spacing at the Blackburn Saddle near the Hemet Stepover. Wavefield snapshots after the S wave arrival are consistent for more than 50 near-fault events, suggesting that this pattern is controlled by the fault zone structure rather than source properties. Data from example event with high signal to noise ratio show three main frequency peaks at similar to 1.3, similar to 2.0, and similar to 2.8 Hz in the amplitude spectra of resonance waves averaged over stations near the fault. The data are modeled with analytical expressions for eigen-functions of resonance waves in a low-velocity layer (fault zone) between two quarter-spaces. Using a grid search-based method, we investigate the possible width of the waveguide, location within the array, and shear wave velocities of the media that fit well the resonance signal at similar to 1.3 Hz. The results indicate a similar to 300 m wide damaged fault zone layer with similar to 65% S wave velocity reduction compared to the host rock. The SW edge of the low-velocity zone is near the mapped fault surface trace, indicating that the damage zone is asymmetrically located at the regionally faster NE crustal block. The imaging resolution of the fault zone structure can be improved by modeling fault zone resonance modes and trapped waves together.