- Università degli Studi di Bari Aldo Moro, Università degli Studi di Bari Aldo Moro, Department of Earth and Geo-Environmental Sciences, Italy (f.perrucci5@phd.uniba.it)
A method is proposed for determining the most likely fault plane of an earthquake from the modeling of the directivity effect of the seismic source, which affects the half- and total- duration (rise time and pulse width) of the first P-wave at a fixed takeoff angle. The method is based on previously inferred relationships relating rise time and pulse width to source parameters and Q (Zollo and de Lorenzo, 2001; de Lorenzo et al., 2004; de Lorenzo and Zollo, 2006).
These studies employed a Sato-Hirasawa (1973) circular crack model with a constant rupture velocity, set to 90% of the S-wave velocity at the source. A set of nonlinear equations relate rise time and pulse width to the anelastic intrinsic factor (Q) and the source characteristics (strike, dip, fault radius). These equations allow determining which of the two solutions of the focal mechanism better reproduces the observed trend of rise time (and pulse width) vs. travel time.
Using a constant Q in the medium causes a problem of underfitting between theoretical and observed rise times (Filippucci et al., 2006). To overcome this problem, the novel technique accounts for the variability of Q along each source-to-receiver path.
In this new approach, after inferring an average Q for the study area, a line-search inversion is carried out to estimate the fault radius, for each of the two possible fault planes of each event. Differences between data and their theoretical estimates can be attributed to heterogeneity of Q along each path. When using data coming from different events, the retrieved Q differences can be averaged to reduce the misfit between data and their theoretical estimates. Data can therefore be corrected for the path effect. An iterative inversion procedure is stopped when the misfit between data and their theoretical estimates is less than the error of data.
The technique has been applied to a dataset of 21 earthquakes from the Amatrice-Visso-Norcia Sequence (2016) with ML ranging between 3 and 4, hypocentral depths between 8 km and 13 km and known focal mechanisms. For data selection, analysis, and plotting, custom software was developed in Matlab for this study.
How to cite: Perrucci, F., de Lorenzo, S., and Zollo, A.: A method for the determination of the fault plane from the analysis of data in the time domain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12660, https://doi.org/10.5194/egusphere-egu25-12660, 2025.
