Titre : Near-fault ground-motion simulation....

Titre : Near-fault ground-motion simulation. Application to the Mw 5.9 2012 Emilia-Romagna earthquake

Laboratoryt : ISTerre

Supervisor : Mathieu Causse

Tel : 0033476635179

Key words : seismic hazard, ground motion, seismic rupture

Goals of the training period :
The prediction of synthetic ground-motion time histories due to an hypothetical future earthquake is a fundamental stage to anticipate damage. Ground motion depends on the seismic energy released on the ruptured fault and on the geological structures crossed by the waves. The prediction of ground-motion at the vicinity of a fault, where damage is expected to be the highest, is particularly challenging because ground motion strongly depends on the details of the rupture process on the fault area.

On May 29, 2012 occurred a Mw=5.9 earthquake in the Po plain (Emilia-Romagna, Northern Italy) on a thrust fault system, followed by hundreds of smaller aftershocks. This sequence was well recorded by an array of 15 strong motion stations located less than 15 km away from the fault plane, with 4 stations located just above the fault. The geological features of this area are unique, the Po plain being one of the largest sedimentary basin in the world. This context results in a particularly complex wave propagation, which makes it even more difficult to predict ground motion. A question arises : could have we anticipated the generated ground motion ? With what accuracy ?

The goal of this work is to model the ground motion recorded during this earthquake. The proposed strategy is the following : first, the rupture on the fault (that is, the spatial and temporal evolution of the slip on the fault) will be modeled by means of spatial random fields. Second, we will take advantage of the large set of recorded aftershocks, considered as point sources, to model wave propagation (up to 10Hz). Due to the heterogeneous distributions of the aftershocks on the fault plane, an interpolation technique will be developed so as to compute an approximation of the Green’s function between each fault points and each strong motion station. Next, the Green’s functions will be convolved with the local fault slip to compute ground motion at the target stations. The set of simulated ground motion time-histories will be finally analyzed and compared with the real data.

Skills : quantitative seismology and/or engineering seismology, signal processing, programming in Matlab