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Use of the Second Seismic Moments to Estimate Source Parameters and Rupture Directivity of Moderate Earthquakes in Central Italy

Description: 

Although directivity effect is usually associated with high magnitude earthquakes, it can also be relevant in moderate and small events. This effect results in azimuthal and spectral variations in ground motion that can be used to estimate the orientation of the fault plane or a prevailing rupture propagation. The associated spectral variations can strongly amplify the ground motion at locations that are in the forward-direction of the rupture propagation, so that even moderate magnitude earthquakes can cause severe unexpected damages.
Knowledge of rupture directivity is therefore important for understanding seismic hazard and in the design of safe and resilient structures. However, determining directivity and source parameters for small to moderate magnitude earthquakes remains a challenge.

A common method for estimating the directivity is based on measuring the duration of the source pulse (the apparent source time function) at each location and then modelling it with a line source. Some approaches rely on the deconvolution of waveforms by an empirical Green’s function to overcome the problems associated with the presence of path and site effects. A promising approach for estimating the rupture directivity effect and the associated source properties is based on the calculation of the second seismic moments. In this study we apply a method based on the calculation of the second seismic moments to estimate the rupture process and source parameters of moderate earthquakes that occurred in central Italy in 2016 using waveforms recorded by the RAN (Acceletrometic National Network) and the RSN (Seismic National Network) italian networks.
We first used synthetic apparent source time functions computed from a geometric source model obtained from a real event to test the robustness of the method. Then, we applied the second-seismic moments method on moderate earthquakes occurred in Central Italy in 2016 trying two different deconvolution processes: one in the time domain and the other one in the frequency domain. The results are discussed and the strengths and weakness of the two approaches are highlighted.

Session: Earthquake Source Parameters: Theory, Observations and Interpretations

Type: Oral

Date: 4/18/2023

Presentation Time: 08:30 AM (local time)

Presenting Author: Arianna Cuius

Student Presenter: Yes

Invited Presentation: 

Authors