Improved 2-D attenuation analysis for Northern Italy using a merged dataset from selected regional seismic networks

Abstract

A merged, high-quality waveform data set from different seismic networks has been used to improve our understanding of lateral seismic attenuation for Northern Italy. In a previous study on the same region, Morasca et al. (2008) were able to resolve only a small area due to limited data coverage. For this reason the interpretation of the attenuation anomalies was difficult given the complexity of the region and the poor resolution of the available data. In order to better understand the lateral changes in the crustal structure and thickness of this region, we selected 770 earthquakes recorded by 54 stations for a total of almost 16000 waveforms derived from seismic networks operating totally or partially in Northern Italy. Direct S-wave and coda attenuation images were obtained using an amplitude ratio technique that eliminates source terms from the formulation. Both direct and early-coda amplitudes are used as input for the inversions and the results are compared.Results were obtained for various frequency bands ranging between 0.3-25.0 Hz, and in all cases show significant improvement with respect to the previous study since the resolved area has been extended and more crossing paths have been used to image smaller scale anomalies. Quality-factor estimates are consistent with the regional tectonic structure exhibiting a general trend of low attenuation under the Po Plain basin and higher values for the western Alps and northern Apennines. The interpretation of the results for the Eastern Alps is not simple, possibly because our resolution for this area is still not adequate to resolve small scale structures.Response to Reviewers: Dear Dr. ZahradnikBelow is our response to the two reviewers' comments and we have uploaded both the revision and another copy with highlighted changes. Both reviewers had very good suggestions and we tried to address each item. We feel fortunate to have received such thorough reviews, particularly reviewer #2 who had numerous comments that ultimately made the paper more clear. We emphasize that this current study is an extension of the 2008 Western Alps study by Morasca et al. (BSSA) but incorporating a much larger data set. The inversion methodology and assumptions on using the early coda is described in detail in the previous work. In addition, we cite in the current study other supporting papers that describe in great detail more of the method. Including this once again in this paper would seem redundant. In addition, we have highlighted changes in the revision as well. COMMENTS FOR THE AUTHOR:Reviewer #1: This paper presents a 2-D Attenuation study for Northern Italy. The authors use earthquakes recorded by several stations deployed in the region. This study extends geographically the knowledge of Q distribution especially north eastern of the studied zone. The presented results agree with previously reported. I found this manuscript to be well written and presenting a very complete study. I support its publication in JOSE. I have some minor comments:1.-Abstract shows ...

Comment on egusphere-2024-721

“…A similar behaviour of such coherence was observed in this region from the previous works where source characteristics of local and regional earthquakes were examined using empirical coda methods assuming simple 1-D radially symmetric path correction (e.g., Eken et al, 2004;Gök et al, 2016). Previous empirical coda envelope modelling studies (e.g., Mayeda et al, 2005b;Morasca et al, 2010) were able to estimate accurate coda-wave-derived source parameters using 2-D path-corrected station techniques that account for amplitude-distance relationships. However, noticeable outliers in our estimates (Fig.…”