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Mainshock-strongest aftershock relation in Northeastern Italy and Western Slovenia
  • Stefania Gentili,
  • Rita Di Giovambattista
Stefania Gentili
Istituto Nazionale di Oceanografia e di Geofisica Sperimentale

Corresponding Author:sgentili@inogs.it

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Rita Di Giovambattista
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In this study, we have applied to northeastern Italy and western Slovenia medium-low seismicity an algorithm for strong aftershock forecasting we originally developed for medium-high seismicity in Italy (Gentili and Di Giovambattista, 2017). This study is possible thanks to the OGS bulletins, an accurate local catalogue, characterized by low completeness magnitude, that has been compiled by the National Institute of Oceanography and Experimental Geophysics, Centre of Seismological Research, since 1977. The method is based on a pattern recognition approach which uses statistical features based on the number of the early aftershocks and on the spatio-temporal evolution of the radiated energy in the first hours/days after the mainshock. The analysis was performed on different time-spans after the mainshock to simulate the increase of information available as time passes during the seismic clusters. Following the approach of Gentili and Giovambattista (2017), we used an operational definition of clusters that defines “mainshock” as the first shock of the cluster over a given threshold. We have adopted this criterion in order to be able to apply the procedure immediately after the occurrence of a shock without waiting to verify if a stronger earthquake followed. If the difference in magnitude between the “mainshock” and the strongest aftershock is lower than 1 the clusters are classified as “Type A”, otherwise as “Type B”,. The Type A and B clusters’ distribution is analyzed also considering a draft subdivision of the region into two sub-regions characterized by different complexity of the clusters (Peresan and Gentili, 2018) Vp/Vs (Bressan et al., 2012) and attenuation characteristcs (Gentili and Gentile, 2015).