THE 1996 PERU TSUNAMIGENIC EARTHQUAKE - BROAD-BAND SOURCE PROCESS

We investigate the spatio-temporal complexity of moment release of the February 21, 1996 Peru earthquake (M-W 7.5). We use a non-linear sour ce tomographic technique, based on simulated annealing, to invert surf ace wave source spectra for the slip distribution on a gently dipping fault plane. The spectra (5-65 mHz) are obtained using an empirical Gr een's function (EGF) method applied to first and second orbit fundamen tal mode Rayleigh waves. Spectra are well fit by a 110 km bilateral ru pture, subparallel to the trench, updip of the hypocenter, with a tota l moment of 2.0x10(20) Nm. The non-linear inversion reveals a 30x30 km (2) major slip patch south the onset, where rupture velocities attain 1.5-2.0 km/s. Inversions of teleseismic broadband P and SH waves (10-5 00 mHz) indicate little or no directivity, consistent with the surface wave data. The average source time functions for both the surface and body wave data are similar in shape and in duration (similar to 50 s) . Part of the slip during the 1996 Peru event occurred in a region of reduced background seismicity, as was the case for the 1992 Nicaragua slow event, suggesting that the seismogenic potential of low seismicit y regions near the trench should be globally reassessed.