Nonlinear Source Tomography Of The Mw=8.4, 23 June 2001 Arequipa, Peru, Earthquake.

We investigate on the rupture process of the Mw=8.4 tsunami-genic earthquake of June 23, 2001 in Arequipa, Peru, putting special emphasis on the determination of rupture velocity. Since the determination of rupture velocity is nonlinear we use the Neighbourhood algorithm for the inversion. We use 16 broad band far field seismograms band pass filtered between 0.01 and 0.4Hz. The goodness of the fit between observed and synthetics is mesured with an L² norm. The fault is parameterized with a model containing 57 patch of size 9× 20km. Because of computer time problems the final steps in the inversion, once the solution has converged to a well defined minimum, are done with a downhill simplex algorithm. The best solution for this unilateral event is found to have propagated southward at a very low speed (1,6km/s) with 80% of the final moment released as one patch 80s after the onset of rupture. The general features of the inversion are compatible with results of linearized inversion and the slow rupture speed is similar to that observed for tsunami earthquakes. The location of the main energy patch is confirmed by a CMT grid search over the whole area of rupture and by tsunami observations.