GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 the almost simultaneous activation of the two adjacent segments by the first mainshock ( May 20 th 2012) and by a M L 4.8 event that occurred a few minutes after. In fact, seismicity migrated immediately westward during the first hours from the beginning of the seismic sequence (dark purple dots in Figure 1). In addition, in the oil field area and between the two thrusts, a reduction in Vs (light blue zones in Figure 2) is visible. These velocity anomalies are interpreted as lower-density zones due to the presence of fluids. Furthermore, the two mainshocks and the larger magnitude aftershocks occurred in a volume characterized by high fluid pressure (i.e., high Vp/Vs) suggesting a hydraulic connection between the thrusts.