Abstract Recently, an earthquake sequence formed by a series of subsequences characterized by large earthquakes (three events M ≥ 6.0 and five events M ≥ 5.0) occurred in the Central Apennines in 6–7 months during 2016–2017. Several studies interpreted this cascading type of earthquake occurrence as associated with fluid movements through an interconnected network of cracks around the active faults that triggered the subsequences in different time and location. In the present study we aim to verify if the presence of fluids is confirmed by the pattern of seismic wave attenuation. To do so we separately estimate the space-averaged parameters intrinsic Qi−1 and scattering Qs−1, proportional to the correspondent attenuation parameters, by applying a modified Multiple Lapse Time Window Analysis (MLTWA), in order to establish reference background values for the study region. MLTWA measures the decay of S-wave energy with distance and lapse time and fit it to the Energy Transport Equation solution for scattering, yielding the seismic albedo, B0 = Qs−1/Qt−1 and the extinction Length, Le,∝Qt−1 parameters as a function of frequency. The knowledge of the separated attenuation parameters allows determining which process of seismic energy dissipation dominates in the region. In the present study B0 results to be around0.6 (at 1.5 Hz) and decreases with increasing frequency down to 0.2 indicating that the attenuation of the seismic energy carried by S-wave is controlled by intrinsic dissipation rather than by scattering. Moreover, the intrinsic attenuation is frequency dependent (f −0.9 for the uniform model and f −0.4 for the crust/Moho model). This behavior well matches with the presence of fluids in the faults and fracture zones in the central Apennines, in agreement with results from other independent studies in the region. Finally, a comparison among the attenuation parameters estimated for this area and those measured in several areas of Italy and other parts of the world is presented together with a discussion on the comparison between the present MLTWA attenuation estimates and homologous results obtained for the same area with different approaches.

中文翻译：

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中亚平宁山脉的本征和散射地震波衰减（意大利）

摘要 近期，2016-2017年中亚平宁山脉在6-7个月内发生了一系列以大地震（3次M≥6.0和5次M≥5.0）为特征的子序列形成的地震序列。几项研究将这种级联地震的发生解释为与通过活动断层周围相互连接的裂缝网络的流体运动有关，这些裂缝在不同的时间和位置触发了子序列。在本研究中，我们的目标是验证地震波衰减模式是否证实了流体的存在。为此，我们通过应用修改后的多重间隔时间窗口分析 (MLTWA)，分别估计空间平均参数内在 Qi−1 和散射 Qs−1，与相应的衰减参数成正比，为研究区域建立参考背景值。MLTWA 测量 S 波能量随距离和经过时间的衰减，并将其拟合到散射的能量传输方程解中，产生地震反照率 B0 = Qs−1/Qt−1 和消光长度 Le,∝Qt− 1 作为频率函数的参数。分离衰减参数的知识允许确定哪个地震能量耗散过程在该区域中占主导地位。在本研究中，B0 结果约为 0.6（在 1.5 Hz 时），并且随着频率的增加而降低至 0.2，表明 S 波携带的地震能量的衰减受本征耗散而不是散射控制。此外，固有衰减与频率有关（均匀模型为 f -0.9，地壳/莫霍面模型为 f -0.4）。这种行为与亚平宁山脉中部断层和断裂带中存在的流体非常吻合，与该地区其他独立研究的结果一致。最后，介绍了对该地区估计的衰减参数与在意大利和世界其他地区的几个地区测量的衰减参数之间的比较，并讨论了当前 MLTWA 衰减估计与同一地区获得的同源结果之间的比较不同的方法。