GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 The sensitvity analysis performed in this study shows that the uncertaintes in the input data have diferent efects on the calculaton of the source parameters and that an accurate measurement of the ASTF as well as the velocity model play the most important role in infuencing the inversion process. The results of our tests (Tab. 2 and Fig. 3) show that the main source parameters, i.e. fracture size, swelling duraton and centroid velocity, are generally well reproduced within the standard deviaton. The source duraton resultng from the inversion process is strongly infuenced by the duraton of the input ASTF, and even 10 % infuences the inversion of the second moment tensor. In the case of dense instrumentaton, the horizontal locaton of the earthquake can be well resolved, but the resoluton of the earthquake depth is largely determined by the velocity model, and an inaccurate earthquake locaton can lead to uncertaintes in the resolved second moments. Care must also be taken to avoid artfacts due to the discretzaton of the velocity model when the hypocenter is located at an interface between two layers with high velocity contrast. Fig. 2 Flowchart of the perturbaton test. For each test, we computed 1000 random staton confguratons or perturbed input variables (depth, velocity model, focal mechanism, or observed c) with a given standard deviaton. Then we performed the inversion and calculated the source parameters and directvity. Finally, we calculated the mean and dispersion of the output variables of the 1000 scenarios. The values of the directvity depend on the ASTF duraton, the choice of velocity model and the focal mechanism (Fig. 3). To ensure good resoluton of the fault plane, good coverage of the ray path is critcal for both upward and downward waves (McGuire, 2004). The component of rupture directvity along the dip can only be well determined if statons directly above the hypocenter are available, as the seismic rays are nearly horizontal at most other statons.