Waveform modeling of moderate earthquakes for the comprehension of the seismic structure and the fluid-seismicity interaction beneath the southern Apennines (Italy)
Authors: Scarponi Matteo , Di Luccio Francesca , Piromallo Claudia 
Published: February 2023

The Apennines mountain range develops all along Italy, presenting important variations in terms of both structural and tectonic environments, and seismogenic patterns as well. This is observed not only along the main NW-SE chain axis, but also by comparing multidisciplinary observations between the western Tyrrhenian and the eastern Adriatic domains (Di Luccio et al., 2022).We focus on the southern Apennines, where the Adriatic plate subducts westward under the thinner Tyrrhenian plate and the highest seismic release is documented.Recent studies showed that fluids play an important role in the seismic behavior of the area. The western domain is associated with heterogeneous and distributed patterns of CO2 gas emission at the surface; the latter ceasing in the east, where high-pressure fluids are trapped in crustal pockets and affect the seismogenic cycle (Chiodini et al., 2004; Improta et al., 2014; Di Luccio et al., 2022 and references therein).We perform regional-scale P- and S-body waveform analysis and forward numerical modeling, for a selected catalog of crustal events recorded by the broadband seismic stations of the italian network, as well as of temporary passive seismic experiments. We focus on a SW-NE transect, which cross-cuts the southern portion of the Apennines chain, and along which the recorded waveforms exhibit important differences in terms of frequency content and pulse shape. Along the same transect, the waveforms from two events (2013 Mw5 Sannio-Matese and 2014 Mw4.5 Gargano earthquakes) show significant differences in the propagation towards the east and west, respectively.Starting from two velocity models such as EPcrust (Molinari et al. 2011) and the adjoint tomographic model of Magnoni et al. (2022), we use the finite difference numerical modeling code nbpsv2d (Li et al. 2014) to produce synthetic waveforms to fit and explain the observations. By including information on the earthquake source mechanism and by improving the waveform fit in terms of both arrival time and body-wave coda, we provide new, preliminary information on the crustal structure of the southern Apennines, aimed at improving our understanding of the fluid-seismicity interaction in the area.&#160;Research performed in the framework of FURTHER project (https://progetti.ingv.it/en/further).&#160;References:&#160;Chiodini G., Cardellini, C., Amato, A., Boschi, E., Caliro, S., Frondini, F., and Ventura, G. (2004). Carbon dioxide Earth degassing and seismogenesis in central and southern Italy. Geophys. Res. Lett., 31, L07615, doi:10.1029/2004GL019480.
Di Luccio et al., (2022). Geodynamics, geophysical and geochemical observations, and the role of CO2 degassing in the Apennines. Earth-Sci. Rev., https://doi.org/10.1016/j.earscirev.2022.104236
Improta L., P. De Gori, and C. Chiarabba (2014). New insights into crustal structure, Cenozoic magmatism, CO2 degassing, and seismogenesis in the southern Apennines and Irpinia region from local earthquake tomography, J. Geophys. Res. Solid Earth, 119, 8283&#8211;8311, doi:10.1002/ 2013JB010890.
Li, D., Helmberger, D., Clayton, R. W., & Sun, D. (2014). Global synthetic seismograms using a 2-D finite-difference method. Geophysical Journal International, 197(2),1166-1183.
Magnoni, F., Casarotti, E., Komatitsch, D., Di Stefano, R., Ciaccio, M. G., Tape, C., ... & Tromp, J. (2022). Adjoint tomography of the Italian lithosphere.&#160;Communications Earth & Environment,&#160;3(1),1-12.
Molinari, I., & Morelli, A. (2011). EPcrust: a reference crustal model for the European Plate.&#160;Geophysical Journal International,&#160;185(1), 352-364.