Paglialunga F, Passelègue F X, Acosta M, Violay M
École Polytechnique Fédérale de Lausanne LEMR Lausanne Switzerland.
Geophys Res Lett. 2021 Jun 28;48(12):e2021GL093619. doi: 10.1029/2021GL093619. Epub 2021 Jun 22.
Seismological observations highlighted that earthquakes are often followed by changes in elastic properties around the fault zone. Here, we studied the origin of these variations using stick-slip experiments on saw-cut granite samples presenting different degrees of bulk damage (i.e., microcracks). Stick-slip events were induced under triaxial compression configuration with continuous active ultrasonic measurements at confining pressures representative of upper crustal conditions (15-120 MPa). Both the P-wave velocity ( ) and amplitude ( ) showed drops, concurrently with stress drops, and had a non-monotonic dependence toward the fault's stress state. Our experimental results suggest that co-seismic changes in were mostly controlled by the elastic re-opening of microcracks in the bulk, rather than by co-seismic damage or the formation of fault gouge. Co-seismic changes in were controlled by a combination of elastic re-opening of microcracks in the bulk and inelastic processes (i.e., co-seismic damage and gouge formation and dilation).
地震学观测结果表明，地震之后，断层带周围的弹性性质常常会发生变化。在此，我们通过对呈现不同程度整体损伤（即微裂纹）的锯切花岗岩样品进行粘滑实验，研究了这些变化的起源。在代表上地壳条件的围压（15 - 120兆帕）下，采用连续主动超声测量，在三轴压缩配置下诱发粘滑事件。纵波速度（ ）和振幅（ ）均随应力降出现下降，并且对断层应力状态具有非单调依赖性。我们的实验结果表明，纵波速度的同震变化主要受整体微裂纹的弹性重新张开控制，而非同震损伤或断层泥的形成。横波速度的同震变化受整体微裂纹的弹性重新张开和非弹性过程（即同震损伤、断层泥形成和扩张）的共同控制。
