The M_w 6.1 (6 April 2009) L’Aquila (Italy) earthquake occurred in one of the most seismically active areas of central Italy and was preceded by a three-month-long foreshock period. Thanks to recordings by a regional permanent network, we derive for the first time P- and S-wave velocity tomographic models of a major fault prone to an imminent main shock. Close to the M_w 6.1 hypocenter, we observe high Vp (>6.8 km/s) and high Vp/Vs (>1.9) consistent with thick dolomitic volumes filled with fluids sealed by impermeable anhydritic layers. Significant changes in velocities defined by time-lapse imaging during the foreshock period suggest rapid fluid migration through the locked fault zone. The complex positive feedback between fluid pressure buildup and hydrofracturing of the dolomitic reservoir, testified by foreshock production, eventually provoked the catastrophic coseismic breaching of the fault seal. Our results show that foreshock time-lapse tomography provides clues on the preparatory phase of a large normal-faulting earthquake.

中文翻译：

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通过前震延时层析成像追踪的2009年意大利拉奎拉6.1兆瓦正常断层地震的筹备阶段

在M _{w ^} 6.1（2009年4月6日）L'Aquila（意大利）地震发生在意大利中部的地震活动最活跃的地区之一，是由三个月之久的前震前时期。借助区域性永久性网络的记录，我们首次得出了容易发生主震的重大断层的P波和S波速度层析成像模型。接近M _w6.1震中，我们观察到较高的Vp（> 6.8 km / s）和较高的Vp / Vs（> 1.9），这与由不透水的无水层密封的流体所填充的白云岩厚实的体积一致。在前震期间，通过延时成像确定的速度的显着变化表明流体快速移动通过了锁定的断层带。白云岩油藏流体压力与水力压裂之间的复杂正反馈，由前震的产生证明，最终引起了断层封堵的灾难性同震破坏。我们的结果表明，前震延时断层扫描为正常大地震的准备阶段提供了线索。