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Geophysical Research Letters

A very broadband study of the 1994 Deep Bolivia Earthquake Sequence



We have examined the source process of the June 9, 1994 Bolivia earthquake in the period range of body waves to free oscillations. A series of moment tensor inversions were performed on various teleseismic wave types and frequency bands to infer the source parameters and to map the temporal character of the source process. Time independent moment tensor inversion of the body waves (P and SH) yields a source time function of 46 seconds duration with four major “pulses” of moment release, with moment release dominated by the third pulse. The focal mechanism is dominantly dip-slip on the sub-horizontal nodal plane (strike 287°, dip 8° and slip −74°). The best bodywave fit requires a non-double-couple component of approximately 7%; although this could be due to an isotropic component of the source, it is at the margin of resolution. Time dependent moment tensor inversion of the body waves, which yields independent time histories for each moment tensor element, shows that the source orientations (fault plane and slip direction) change very little throughout the rupture duration. Analysis at several frequencies shows that the seismic moment is very stable (3.0 × 1021 Nm ± 6%) at periods greater than 150 seconds and that the isotropic moment is negligible given the resolution.

We also modeled the P-waves for the January 10, 1994 event, the strong aftershock of June 9, 1994 and the August 8, 1994 earthquake. Rotation of the P axes for events after the mainshock may suggest a possible stress adjustment.

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