LASSCI2009.2: layered earthquake rupture forecast model for central Italy, submitted to the CSEP project

Abstract

The Collaboratory for the Study of Earthquake Predictability (CSEP) selected Italy as a testing region for probabilistic earthquake forecast models in October, 2008. The model we have submitted for the two medium-term forecast periods of 5 and 10 years (from 2009) is a time-dependent, geologically based, earthquake rupture forecast that is defined for central Italy only (11-15 ̊ E; 41-45 ̊ N). The model took into account three separate layers of seismogenic sources: background seismicity; seismotectonic provinces; and individual faults that can produce major earthquakes (seismogenic boxes). For CSEP testing purposes, the background seismicity layer covered a range of magnitudes from 5.0 to 5.3 and the seismicity rates were obtained by truncated Gutenberg-Richter relationships for cells centered on the CSEP grid. Then the seismotectonic provinces layer returned the expected rates of medium-to-large earthquakes following a traditional Cornell-type approach. Finally, for the seismogenic boxes layer, the rates were based on the geometry and kinematics of the faults that different earthquake recurrence models have been assigned to, ranging from pure Gutenberg- Richter behavior to characteristic events, with the intermediate behavior named as the hybrid model. The results for different magnitude ranges highlight the contribution of each of the three layers to the total computation. The expected rates for M > 6.0 on April 1, 2009 (thus computed before the L'Aquila, 2009, Mw = 6.3 earthquake) are of particular interest. They showed local maxima in the two seismogenic-box sources of Paganica and Sulmona, one of which was activated by the L'Aquila earthquake of April 6, 2009. Earthquake rates as of August 1, 2009, (now under test) also showed a maximum close to the Sulmona source for Mw ~ 6.5; significant seismicity rates (10-4 to 10-3 in 5 years) for destructive events (magnitude up to 7.0) were located in other individual sources identified as being capable of such earthquakes in the central part of this area of the Apennines.