Investigations of the 2004 Parkfield Earthquake Sequence

圣安德烈亚斯断层的帕克菲尔德段受到了广泛的地球物理仪器的密集监测，预计将记录平均每隔22年重复发生的一系列地震中的下一次。虽然官方对1988-5年(巴昆和林德，1985年)发生这一事件的预测失败，但幸运的是，监测工作仍在继续。2004年9月28日发生6级地震，为同震(主震时)和震后研究断裂过程的力学提供了丰富的新资料。2004年帕克菲尔德地震可以说是迄今为止记录最好的地震，观测到了近断层的强烈地面运动、连续的GPS、地表蠕变、钻孔应变、地下水和电磁信号，以及区域宽带波形数据。在拟议的研究中，将利用当地和更远的地震仪器以及GPS获得的地表形变来确定破裂过程的高分辨率模型，即断层滑动在空间和时间上的分布。此外，还将从连续的GPS数据中获得震后滑动模型。这些高分辨率模型将被用来计算断层上的应力变化，并将其与余震的行为、具有特征的重复地震(其行为因主震的发生而改变)以及震后滑动联系起来，从而深入了解断裂带的流变性。已有1922年、1934年和1966年帕克菲尔德地震的区域和远震记录，并将与2004年地震的类似记录进行比较，以评估该地区大地震的特征地震假说。这个项目将解决有关主震、余震、震前地震活动和震后形变之间关系的基本问题。它还将讨论断层滑动反演的震源参数解析问题，目的是更好地了解潜在的破裂动力学和近实时地震动报告在地震危险方面的应用。

The Parkfield segment of the San Andreas fault has been intensively monitored with a broad array of geophysical instrumentation in anticipation of recording the next in a series of earthquakes that repeat on average approximately every 22 years. Although the official prediction for the occurrence of the event in 1988 +- 5 years (Bakun and Lindh, 1985) failed, fortunately the monitoring efforts continued. On September 28, 2004 a magnitude 6 earthquake occurred, and it has produced a wealth of new data to study the mechanics of the faulting process both coseismically (at the time of the mainshock) and postseismically. The 2004 Parkfield earthquake is arguably the best recorded to date with observations of near-fault strong ground motion, continuous GPS, surface creep, borehole strain, ground water and EM signals, as well as regional broadband waveform data. In the proposed research a high-resolution model of the rupture process, namely the distribution of fault slip in both space and time will be determined from local and more distant seismic instruments as well as surface deformation obtained from GPS. Additionally a postseismic slip model will be obtained from the continuous GPS data. These high-resolution models will then be used to calculate the stress change on the fault and relate it to the behavior of aftershocks, characteristically repeating earthquakes (whose behavior was changed by the occurrence of the mainshock), and postseismic slip giving insight into the fault zone rheology. Regional and teleseismic records of the previous Parkfield earthquakes in 1922, 1934, and 1966 are available and will be compared with similar records for the 2004 event to evaluate the characteristic earthquake hypothesis for large events in the region. This project will address fundamental questions about the relationships between mainshocks, aftershocks, pre-event seismicity, and post-seismic deformation. It will also address the question of source parameter resolution of fault slip inversions with the goal of better understanding underlying rupture dynamics and the earthquake hazard application of near-realtime ground motion reporting.