Figure 3
From: Combining stress transfer and source directivity: the case of the 2012 Emilia seismic sequence
Static and dynamic stress transfer and permeability change.
Panel (a): local cumulative ΔCFS at hypocentral locations and on preferential focal mechanisms of target main events. Cumulative ΔCFS is estimated considering the contribution of all the earthquakes occurred before the target event. The dataset used for Coulomb stress estimation contains 22 events for which locations and focal mechanisms are available3. For the events 2 and 7 in Table 1 the fault plane solutions are not available and a mean focal mechanism is then assumed. The dashed line represents the commonly accepted triggering threshold for static ΔCFS8,9. Below this threshold, stress changes are considered too small to significantly contribute to the triggering process. Panel (b): local dynamic stress change obtained from the peak dynamic strain (assuming a rigidity value of 30 GPa) induced by each considered event at the hypocenter of the next main earthquake in the sequence. The local dynamic stress is estimated both considering the directivity function Cd, (squares) and ignoring it (open circles). Panel (c): permeability change ΔK induced by each considered event at the hypocenter of the next main earthquake in the sequence. The two horizontal dashed lines define the seismogenic permeability range (5 × 10−16 – 5 × 10−14 m2)27,28. ΔK changes are estimated through PGV values: i) modified by the source directivity function Cd (squares); and ii) not modified by Cd (open circles). The gray triangles represent ΔK obtained by using the upper and lower R bounds (see equation 2). The relative hypocentral distance (in km) between each triggering and target events, is provided in the bottom of the panel. In the three panels, the numbering on x-axis refers to the seismic events as listed in Table 1.
