SOURCE TIME FUNCTION OF THE GREAT 1994 BOLIVIA DEEP EARTHQUAKE BY WAVE-FORM AND SPECTRAL INVERSIONS

The source time function of the great 1994 Bolivia deep earthquake is estimated from far-field seismograms by two techniques: time-domain inversion of direct P and S waveforms, and spectral-domain inversion of a combination of body waves, first-orbit traveling modes, and free oscillations. Both methods give consistent estimates, but the latter provides more bandwidth (1-300 mHz) and is more robust with respect to source-directivity effects and wave scattering. The earthquake released a total moment of 2.7 (+/- 0.1) x 10(21) Nm over an interval of about 50 s. Its history is highly episodic and can be divided into three stages: an initial sequence (0 less than or similar to t less than or similar to 13 s; 2 x 10(20) Nm), a main-event sequence (13 less than or similar to t less than or similar to 38 s; 2.2 x 10(21) Nm), and a terminal sequence (38 less than or similar to t less than or similar to 50 s; 3 x 10(20) Nm). The main event is resolved into five subevents with peaks at similar to 16, 20, 26, 29, and 36 s. The spatial pattern of moment release suggests that the main event was confined to the cold slab core, while the initial and terminal stages were part of a distinct westward-propagating rupture in the lower reaches of the former oceanic plate.