A broadband P wave analysis of the large deep Fiji Island and Bolivia Earthquakes of 1994

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Abstract

The complex broadband P-wave displacement recordings of the 570 km deep March 9, 1994, Mw 7.6 Fiji Island and the 660 km deep June 9, 1994, Mw 8.2 Bolivia earthquakes are analyzed to estimate the spatial and temporal characteristics of their ruptures. We model relative arrival times and amplitudes of coherent subevents in P waveforms, and perform waveform analyses. We resolve: (1) short rupture durations relative to their seismic moments, 12 and 40 s for the Fiji and Bolivia earthquakes, respectively; (2) small areas of main moment release, for both earthquakes 30 × 40 km²; (3) high stress drops compared to shallow earthquakes, with the stress drop of the Bolivia event (283 MPa) being significantly higher than the stress drop of the Fiji event (26 MPa); (4) small changes in mechanism (up to 10° changes in fault plane orientation); and (5) a steeply dipping rupture plane for the Fiji earthquake, and a shallowly dipping rupture plane for the Bolivia earthquake. Details of the ruptures are difficult to resolve using teleseismic P waveforms.

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