GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 earthquakes irrespectve of the event azimuth, due to the high velocity contrast between the bedrock and the basin, the main diference being in the P to S diferental tme owing to the distance between the fber and the event hypocenter. The high impedance contrast at the base of the dry lake leads to considerable site amplifcaton and allows to detect local microearthquakes without stacking. We developed an integral approach for convertng strain-rate data into kinematc quanttes (Trabatoni et al., 2023), based on moving average flters, that allows retrieving the high-pass displacement from DAS records. Using converted data, we performed automatc arrival phase identfcaton using ML based detectors (e.g., EQTransformer, Mousavi et al., 2020; PhaseNet, Zhu et al., 2019). We found phase picking consistent with manual measurements, and an enhanced sensitvity when compared to strain rate data, in terms of number and quality of picks. This approach also enables for event detecton when informaton is integrated across the whole fber. We used displacement converted data for local magnitude (ML) computaton. The fnal magnitude was estmated as the median value of the ML distributon at all the usable channels, while uncertaintes have been quantfed by the standard median absolute deviaton (SMAD). Magnitude estmates provided by the DAS are compatble with those computed from the INFO network showing that using DAS recovered velocity enables simple and accurate ML estmaton. We also investgated the correlaton between the elastc energy release rate estmated at the fber and the kinetc energy release rate from the closest staton (< 2 km) and we used this scaling to retrieve the energy magnitude from the integral of elastc energy. We found that our observatons are compatble with the detecton threshold as a functon of the distance associated with the signal to noise level of the DAS recordings. Finally, we evaluated seismic moment and source size by invertng the spectral amplitude of DAS records, afer removal of site efects, according to the Anderson and Hough (1984) model. In conclusion, this workfow enables for automatc event detecton and characterizaton from DAS records, even in presence of longer cables and larger bunches of data. References Anderson, J. G., Hough, S. E.; 1984: A model for the shape of the Fourier amplitude spectrum of acceleraton at high frequencies, Bulletn of the Seismological Society of America , 74(5), 1969-1993. Chiaraluce, L., Festa, G., Bernard, P., Caracausi, A., Carluccio, I., Clinton, J., et al.; 2022: the near fault observatory community in Europe: A new resource for faultng and hazard studies, Annals of Geophysics , 65(3), DM316. htps://doi.org/10.4401/ag-8778. Current, G., Jousset, P., Napoli, R., Krawczyk, C., & Weber, M.; 2021: On the comparison of strain measurements from fbre optcs with a dense seismometer array at Etna volcano (Italy), Solid Earth , 12 (4), 993–1003. htps://doi.org/10.5194/se-12-993-2021