We performed measurements of velocity variations for variable coda waves time lapse using empirical Green's functions reconstructed by autocorrelation of seismic noise recorded during a period of 17 years in the region of L'Aquila, Italy. The time lapse approach permitted us to evaluate the spatial (depth) dependence of velocity variation (dv/v). By quantitatively comparing the 17 years of dv/v time series with independent data (e.g., strain induced by earthquakes and hydrological loading), we unravel a group of physical processes inducing velocity variations in the crust over multiple time and spatial scales. We find that rapid shaking due to three magnitude 6+ earthquakes mainly induced near surface velocity variations. On the other hand, slow strain perturbation (period 5 years, in the preseismic period) associated with hydrological cycles, induced velocity changes primarily in the middle crust. The observed behavior suggests the existence of a large volume of fluid‐filled cracks exist deep in the crust. Our study highlights the possibility of using seasonal and multiyear perturbations to probe the physical properties of seismogenic fault volumes and shed new light into the depth‐dependent rheology of crustal rocks in the region or L'Aquila.

中文翻译：

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从单站测量和地壳流变学意义看拉奎拉地区的季节性和同震速度变化

我们使用经验格林函数（通过意大利拉奎拉地区17年内记录的地震噪声的自相关重建的经验格林函数）对可变尾声波时移的速度变化进行了测量。时间流逝方法使我们能够评估速度变化（dv / v）的空间（深度）依赖性。通过定量比较17年的dv / v时间序列与独立数据（例如，地震和水文负荷引起的应变），我们揭示了一组物理过程，这些过程导致了地壳在多个时间和空间尺度上的速度变化。我们发现，由于三级6+地震引起的快速晃动主要引起近地表速度变化。另一方面，缓慢的应变扰动（周期为5年，在与水文循环有关的地震前期），感应速度主要在中地壳发生变化。观察到的行为表明，地壳深处存在大量充满流体的裂缝。我们的研究突出了使用季节性和多年扰动来探查地震成因断层体积的物理性质的可能性，并为该地区或拉奎拉地壳岩石的深度依赖流变学提供了新的思路。