We examine the cyclic amplitude variation of seismic noise recorded by continuous three-component broad-band seismic data with durations spanning 91–713 d (2008–2011) from three different networks: Anza seismic network, IDA network and the transportable seismic array. These stations surround the San Jacinto Fault Zone (SJFZ) in southern California. We find the seismic noise amplitudes exhibit a cyclical variation between 0.3 and 7.2 Hz. The high-frequency (≥0.9 Hz) noise variations can be linked to human activity and are not a concern. Our primary interest is signals in the low frequencies (0.3–0.9 Hz), where the seismic noise is modulated by semi-diurnal tidal mode M₂. These long-period (low-frequency) variations of seismic noise can be attributed to a temporal change of the ocean waves breaking at the shoreline, driven by ocean tidal loading. We focus on the M₂ variation of seismic noise at f = 0.6 Hz, travelling distances of ∼92 km through the crust from offshore California to the inland Anza, California, region. Relative to the shoreline station, data from the inland stations show a phase lag of ∼ –12°, which we attribute to the cyclic change in M₂ that can alter crustal seismic attenuation. We also find that for mode M₂ at 0.6 Hz, the amplitude variations of the seismic quality factor (Q) depend on azimuth and varies from 0.22 per cent (southeast to northwest) to 1.28 per cent (northeast to southwest) with Q = 25 for Rayleigh waves. We propose the direction dependence of the Q variation at 0.6 Hz reflects the preferred orientation of subfaults parallel to the main faulting defined by the primarily N45°W strike of the SJFZ.

中文翻译：

---

加利福尼亚南部圣哈辛托断裂附近的地震噪声调制：周期性时间相关性和相关地壳特性的起源和观测

我们研究了来自三个不同网络（Anza地震网络，IDA网络和可移动地震阵列）的连续三分量宽带地震数据（持续时间跨度91-713 d（2008-2011））记录的地震噪声的循环振幅变化。这些站围绕着加利福尼亚南部的圣哈辛托断裂带（SJFZ）。我们发现地震噪声振幅呈现出0.3到7.2 Hz之间的周期性变化。高频（≥0.9Hz）噪声变化可能与人类活动有关，因此不必担心。我们的主要兴趣是低频（0.3–0.9 Hz）信号，其中地震噪声由半日潮汐模式M ₂调制。地震噪声的这些长时间（低频）变化可以归因于由海潮负荷驱动的在海岸线处破裂的海浪随时间的变化。我们关注的焦点是f  = 0.6 Hz时地震噪声的M ₂变化，从地壳加利福尼亚到加利福尼亚内陆地区安扎，穿过地壳的传播距离约为92 km。相对于海岸线站，来自内陆站的数据显示出约–12°的相位滞后，我们将其归因于M ₂的周期性变化，它可以改变地壳地震衰减。我们还发现，对于模式中号₂在0.6赫兹，地震质量因子的幅度变化（Q）取决于方位角，其变化范围为0.22％（东南到西北）到1.28％（东北到西南），瑞利波的Q  = 25。我们提出在0.6 Hz处Q变化的方向相关性反映了与SJFZ的主要N45°W走向定义的主要断层平行的子断层的优选方向。