DataSheet2_Crustal permeability changes inferred from seismic attenuation: Impacts on multi-mainshock sequences.CSV

We use amplitude ratios from narrowband-filtered earthquake seismograms to measure variations of seismic attenuation over time, providing unique insights into the dynamic state of stress in the Earth’s crust at depth. Our dataset from earthquakes of the 2016–2017 Central Apennines sequence allows us to obtain high-resolution time histories of seismic attenuation (frequency band: 0.5–30 Hz) characterized by strong earthquake dilatation-induced fluctuations at seismogenic depths, caused by the cumulative elastic stress drop after the sequence, as well as damage-induced ones at shallow depths caused by energetic surface waves. Cumulative stress drop causes negative dilatation, reduced permeability, and seismic attenuation, whereas strong-motion surface waves produce an increase in crack density, and so in permeability and seismic attenuation. In the aftermath of the main shocks of the sequence, we show that the M ≥ 3.5 earthquake occurrence vs. time and distance is consistent with fluid diffusion: diffusion signatures are associated with changes in seismic attenuation during the first days of the Amatrice, Visso-Norcia, and Capitignano sub-sequences. We hypothesize that coseismic permeability changes create fluid diffusion pathways that are at least partly responsible for triggering multi-mainshock seismic sequences. Here we show that anelastic seismic attenuation fluctuates coherently with our hypothesis.

本研究利用经窄带滤波的地震波形记录的振幅比，随时间监测地震衰减的变化，为深入理解深部地壳的动态应力状态提供了独特研究视角。我们依托2016—2017年亚平宁山脉中部地震序列的数据集，获得了频带范围为0.5~30 Hz的高分辨率地震衰减时间序列；该序列在发震深度处表现出由该地震序列发生后累积弹性应力降引发的显著地震扩容诱导波动，同时在浅部圈层呈现出由强能量面波导致的损伤诱导波动。累积应力降会引发负扩容、渗透率降低以及地震衰减；而强动面波则会提升裂隙密度，进而提高渗透率与地震衰减。在该序列主震发生后的震后阶段，我们发现震级M≥3.5的地震发生的时间与空间分布符合流体扩散规律：在阿马特里切（Amatrice）、维索-诺尔恰（Visso-Norcia）以及卡皮蒂尼亚诺（Capitignano）子序列的初始阶段，流体扩散特征与地震衰减的变化存在显著关联。我们提出假说：同震过程中的渗透率变化形成了流体扩散通道，该通道至少部分触发了多主震地震序列的发生。本研究证实，非弹性地震衰减的波动与我们提出的假说具有良好的一致性。