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Geophysical Research Letters

Source time function of the Great 1994 Bolivia Deep Earthquake by waveform 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) × 1021 Nm over an interval of about 50 s. Its history is highly episodic and can be divided into three stages: an initial sequence (0 ≲ t ≲ 13 s; 2 × 1020 Nm), a main-event sequence (13 ≲ t ≲ 38 s; 2.2 × 1021 Nm), and a terminal sequence (38 ≲ t ≲ 50 s; 3 × 1020 Nm). The main event is resolved into five subevents with peaks at ∼ 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.

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