Velocity-Based Earthquake Detection Using Downhole Distributed Acoustic Sensing-Examples from the San Andreas Fault Observatory at Depth
Velocity-Based Earthquake Detection Using Downhole Distributed Acoustic Sensing-Examples from the San Andreas Fault Observatory at Depth
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DOI：
10.1785/0120190176
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发表时间：
2019-12-01
影响因子：
3
通讯作者：
Biondi, Biondo
中科院分区：
文献类型：
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作者：
Lellouch, Ariel;Yuan, Siyuan;Biondi, Biondo
传统的地震台网对地震激发的波场进行稀疏采样。因此，标准的事件检测是通过分析单独的台站并合并它们的结果来进行的。新兴的分布式声传感记录技术允许对波场进行无偏空间采样，因此可以对记录的信号进行基于阵列的处理。在深度主孔的圣安德烈亚斯断层观测站使用胶结光纤，从地面到800米深度每隔1米采样800个虚拟接收器。记录的地震近似为平面波首先到达阵列的底部。根据这个假设，记录的事件的相对传播时间取决于阵列位置的本地速度和面波前到达该位置的入射角。在给定地震速度的情况下，一种新提出的检测算法相当于对入射角进行单参数扫描，并沿着不同可能的走时曲线测量数据相干性。使用整个记录阵列，与单个通道处理相比，可以获得更高的有效信噪比。本文分析了圣安德烈亚斯断层约20天的地震活动记录。使用井下单阵列，可以检测到该区域的大多数已编目事件。此外，一个以前不为人知的事件被揭开。我们估计它的大小大约是-0.5。
Conventional seismographic networks sparsely sample the wavefields excited by earthquakes. Thus, standard event detection is conducted by analyzing separate stations and merging their results. Emerging distributed acoustic sensing recording technologies allow for unbiased spatial sampling of the wavefield and, as a result, array-based processing of the recorded signals. Using a cemented fiber in the San Andreas Fault Observatory at Depth main hole, 800 virtual receivers are sampled at a 1 m interval from the surface to 800 m depth. Recorded earthquakes are approximated as plane waves reaching the bottom of the array first. Following this assumption, the relative travel times of the recorded event depend on the local velocity at the array location and the angle of incidence at which the planar wavefront reaches it. Given the seismic velocity, a newly proposed detection algorithm amounts to a single-parameter scan of the incidence angle and measurement of data coherency along the different possible travel-time curves. Using the entire recording array, a much higher effective signal-to-noise ratio can be obtained when compared to individual channel processing. About 20 days of recorded seismic activity from the San Andreas Fault is analyzed. Using a downhole single array, the majority of cataloged events in the area are detected. In addition, a previously unknown event is unveiled. We estimate its magnitude at roughly -0.5.