In central California, periodic earthquake occurrence suggests a relationship with annual hydrological, atmospheric, thermal, and tidal loadings. In catalogs of declustered earthquakes within 100 km from Parkfield, CA, we study a semiannual periodicity for the monthly number of ≤7.2‐km‐deep earthquakes and the monthly median hypocenter depth over 1994–2002 and 2006–2014. Peak‐trough months in fitted periodic components differ between time spans and event populations. Deeper earthquakes present no semiannual and a weak annual periodicity. Although modeled pore pressure shows a Spring peak, when added to the elastic Coulomb stress from surface hydrospheric loads, it fails to predict a 6‐month periodicity for 2006–2014. In 1994–2002, the pore‐pressure amplitude appears to be of same order as the elastic stress and may have had a stronger effect. In 2006–2014, we did not find load model parameters explaining the observed pattern or apparent changes following the 2003 San Simeon and 2004 Parkfield earthquakes.

中文翻译：

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加利福尼亚帕克菲尔德附近地震发生和震源深度的周期性分析，1994-2002年与2006-2014年之间

在加利福尼亚中部，周期性地震的发生表明与每年的水文，大气，热力和潮汐负荷有关。在距加州帕克菲尔德（Parkfield）100公里以内的减震地震目录中，我们研究了1994-2002年和2006-2014年每月≤7.2-km深地震的每月周期和每月震中深度的中位数。拟合的周期性成分中的高峰谷月在时间跨度和事件总体之间有所不同。较深的地震没有半年期，并且年周期很弱。尽管模拟的孔隙压力显示出一个春季峰值，但当将其添加到来自表面水圈载荷的弹性库仑应力中时，它无法预测2006-2014年的6个月周期。在1994–2002年期间，孔隙压力振幅似乎与弹性应力处于同一数量级，并且可能具有更强的作用。