Preliminary characterization of the magnitude frequency distributions of multi-fault rupture hypotheses at the Eastern Betic shear zone (SE Spain) by using the sherifs approach

Abstract

Earthquake ruptures can be accommodated through the implication of multiple different fault sections within a specific fault or fault system (multi-fault ruptures). Accordingly, seismic hazard assessments should move from considering faults as individual sources to consider them as an interacting system. In this preliminary study we explored the magnitude-frequency distributions (MFDs) of five different hypotheses of fault ruptures for the Eastern Betic Shear Zone (EBSZ), each one determined by rules that allow or prevent particular fault sections from rupturing together. We used the computer code SHERIFS in order to obtain the MFDs of each hypothesis. Then, we performed a consistency check to analyse the fit between every modelled MFD and the short-term seismicity rates deduced from the regional seismic catalogue. The hypotheses that allow ruptures to propagate through a part or the whole fault system produce mean maximum magnitudes (Mwmax) over 7.0-7.6 with cumulative annual rates between 10-4-10-7 earthquakes/year (eq/yr), depending on the model considered. These annual rates are much lower than those obtained from the hypotheses that prevent multi-fault ruptures, but maximum magnitudes are almost one order higher (10-4-10-6 eq/yr for Mwmax~ 6.5-7.0). For the consistency check we observed that the hypothesis that fits best the catalog is the one that allows the occurrence of long multi-fault ruptures between several major faults of the system, so this is our preferred model, but other hypotheses cannot be discarded. It is important to consider that the results of this study are preliminary, since the research is still ongoing. Improvements on the rupture models (e.g. by including more fault sources), exploration of the buffer area, completeness of the catalogue and other variables (e.g. b value) need to be done in the future to obtain more accurate results.