The Complex Rupture Process of the 1996 Deep Flores, Indonesia Earthquake (Mw 7.9) from teleseismic P‐waves

Abstract

From an analysis of broadband teleseismic P‐waveforms we resolve the complex rupture characteristics of the 17 June 1996, Flores earthquake (Mw 7.9, depth 590 km). This earthquake was unusual because of its large rupture length and the variation in rupture velocity and stress drop. The 20 s rupture propagated westward at 2–3 km/s to a distance of 20–30 km, and eastward at 4 km/s over 75 km. Average static stress drop was about 15 MPa, but the stress drop during the episode of main moment release was a factor of four higher. The oblique normal faulting mechanism is consistent with the stress expected as the slab descends along a highly curved trench. Significant rupture complexity is also reported for the deep 1994 Mw 7.7 Fiji and Mw 8.2 Bolivia earthquakes and is evident in the source‐time functions of many smaller earthquakes at depths >300 km. Thus source complexity of deep earthquakes appears no less common than for shallow earthquakes, and requires the existence of significant heterogeneity in the physical properties that control deep earthquake rupture.