Constraints on the location and mechanism of the 1511 Western-Slovenia earthquake from active tectonics and modeling of macroseismic data
The 1511 Western Slovenia earthquake ( M = 6.9) is the largest event occurred so far in the region of the Alps-Dinarides junction. Though it strongly influences the regional seismic hazard assessment, the epicenter and mechanism are still under debate. The complexity of the active tectonics of the Alps-Dinarides junction is reflected by the presence of both compressional and transpressional deformations. This complexity is witnessed by the recent occurrence of three main earthquake sequences, the 1976 Friuli thrust faulting events, the 1998 Bovec-Krn Mountain and the 2004 Kobarid strike-slip events. The epicenters of the 1998 and 2004 strike-slip earthquakes ( Ms = 5.7 and Ms = 4.9, respectively) lie only 50 km far from the 1976 thrust earthquake ( Ms = 6.5). We use the available macroseismic data and recent active tectonics studies, to assess a possible epicenter and mechanism for the 1511 earthquake and causative fault. According with previous works reported in the literature, we analyze both a two-and a single-event case, defining several input fault models. We compute synthetic seismograms up to 1 Hz in an extended-source approximation, testing different rupture propagations and applying a uniform seismic moment distribution on the fault segments. We extract the maximum horizontal velocities from the synthetics and we convert them into intensities by means of an empirical relation. A rounded-to-integer misfit between observed and computed intensities is performed, considering both a minimized and a maximized databases, built to avoid the use of half-degree macroseismic intensity data points. Our results are consistent with a 6.9 magnitude single event rupturing 50 km of the Idrija right-lateral strike-slip fault with bilateral rupture propagation.