The 1996 Peru tsunamigenic earthquake: Broadband source process

Abstract

We investigate the spatio‐temporal complexity of moment release of the February 21, 1996 Peru earthquake (Mw 7.5). We use a non‐linear source tomographic technique, based on simulated annealing, to invert surface wave source spectra for the slip distribution on a gently dipping fault plane. The spectra (5–65 mHz) are obtained using an empirical Green's function (EGF) method applied to first and second orbit fundamental mode Rayleigh waves. Spectra are well fit by a 110 km bilateral rupture, subparallel to the trench, updip of the hypocenter, with a total moment of 2.0×1020 Nm. The non‐linear inversion reveals a 30×30 km² major slip patch south the onset, where rupture velocities attain 1.5–2.0 km/s. Inversions of teleseismic broadband P and SH waves (10–500 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 (∼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 seismicity regions near the trench should be globally reassessed.