Seismic Imaging of a Bimaterial Interface Along the Hayward Fault, CA, with Fault Zone Head Waves and Direct P Arrivals
Seismic Imaging of a Bimaterial Interface Along the Hayward Fault, CA, with Fault Zone Head Waves and Direct P Arrivals
复制标题
加利福尼亚州海沃德断层沿线双材料界面的地震成像，包含断层带头波和直接 P 到达
DOI：
10.1007/s00024-014-0784-0
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发表时间：
2012
影响因子：
2
通讯作者：
Zhigang Peng
中科院分区：
文献类型：
--
作者：
A. Allam;Y. Ben‐Zion;Zhigang Peng
我们观察到由旧金山湾区海沃德断层约 80 公里的一段产生并传播的断层带头波 (FZHW)。 FZHW 和直达 P 波到达时间之间的时差值用于获得断层不同部分的平均 P 波速度对比。结果基于 5,800 多次地震产生的波形，并在伯克利数字地震台网 (BDSN) 和北加州地震台网 (NCSN) 的多达 12 个台站记录。由于 BDSN 和 NCSN 的仪器不同，FZHW 的鲁棒识别需要多种技术的结合。对于单分量短周期仪器，FZHW 的识别方法是检查故障两侧的波形组，并在直接 P 波之前在一侧（慢速）侧发现出现的反向极性到达。对于三分量宽带和强运动仪器，FZHW 通过偏振分析来识别，该分析可以在沿源-接收器后方位角具有偏振的常规体波之前检测来自断层方向的早期到达。结果表明，沿海沃德断层的平均速度对比为 3-8%，西南侧具有更快的 P 波速度，与断层扫描图像一致。约 80 公里长的断层部分的 FZHW 和直达 P 波之间的系统性时差表明，在该距离上的发震带中存在单个连续界面。我们在东南部卡拉维拉斯断层交界处和奥克兰市附近观察到一些复杂情况。产生可变 FZHW 到达时间的区域可以与存在岩性复杂性（例如高速变质蛇纹岩碎片和相对分布的地震活动）的一阶相关。地震速度对比和地质复杂性对海沃德断层的地震和破裂动力学具有重要意义，包括统计上地震破裂向东南传播的首选方向。
We observe fault zone head waves (FZHW) that are generated by and propagate along a roughly 80 km section of the Hayward fault in the San Francisco Bay area. Moveout values between the arrival times of FZHW and direct P waves are used to obtain average P-wave velocity contrasts across different sections of the fault. The results are based on waveforms generated by more than 5,800 earthquakes and recorded at up to 12 stations of the Berkeley digital seismic network (BDSN) and the Northern California seismic network (NCSN). Robust identification of FZHW requires the combination of multiple techniques due to the diverse instrumentation of the BDSN and NCSN. For single-component short-period instruments, FZHW are identified by examining sets of waveforms from both sides of the fault, and finding on one (the slow) side emergent reversed-polarity arrivals before the direct P waves. For three-component broadband and strong-motion instruments, the FZHW are identified with polarization analysis that detects early arrivals from the fault direction before the regular body waves which have polarizations along the source-receiver backazimuth. The results indicate average velocity contrasts of 3–8 % along the Hayward fault, with the southwest side having faster P wave velocities in agreement with tomographic images. A systematic moveout between the FZHW and direct P waves for about a 80 km long fault section suggests a single continuous interface in the seismogenic zone over that distance. We observe some complexities near the junction with the Calaveras fault in the SE-most portion and near the city of Oakland. Regions giving rise to variable FZHW arrival times can be correlated to first order with the presence of lithological complexity such as slivers of high-velocity metamorphic serpentinized rocks and relatively distributed seismicity. The seismic velocity contrast and geological complexity have important implications for earthquake and rupture dynamics of the Hayward fault, including a statistically preferred propagation direction of earthquake ruptures to the SE.