Figure 4

Vertical section of V_P and V_P/V_S (top) across the 2018 intrusive dyke (segment O-A in Fig. 1) and along the lateral collapse fault (segment A-B in Fig. 1). The white box indicates the extent of the intrusive dyke, while dashed white line indicates the decollement layer. Red stars are M_L ≥ 4.0 earthquakes and yellow star is the M_W = 4.9 event. The lower panel shows V_P and V_P/V_S changes during the intrusive period. Note the increase of V_P (increase of stiffness) around the intruded dyke that propagates at the base of the decollement. High V_P/V_S on top of the decollement and along the FPF (black polygon) is observed, as well as an increase during the intrusion.