The 1996 June 17 Flores Sea and 1994 March 9 Fiji-Tonga earthquakes: source processes and deep earthquake mechanisms

Abstract

Source parameters of the 1996 Flores Sea and 1994 Fiji–Tonga deep earthquakes are derived from teleseismic body waves recorded by the global seismic network of broad-band seismograph stations. Both events consisted of several subevents. Models to approximate the spatial and temporal extent of the source process include point sources, propagating point sources and a combination of these. For the Flores Sea event, rupture lasted about 23 s and terminated some 70 km east of the nucleation point as inferred from the duration of P-wave pulses, in agreement with the findings reported by other investigators. Our preferred model suggests bilateral rupture propagation. It consists of four point sources that have variable double-couple radiation patterns and source time histories, and explains well the large compensated linear vector dipole (CLVD) component inferred from the Harvard centroid moment tensor (CMT) solution. The main moment release in the Fiji–Tonga event lasted only about 15 s. Our best model consists of two point sources with a total moment release of 2.8 × 1020 N m. Rupture propagated subhorizontally from the nucleation point to the north. The termination of rupture was located about 40 km to the north of rupture initiation. The inferred velocity of moment release in the Flores Sea and Fiji–Tonga events was 3–5 km s-1, a value which is higher than that inferred for the great Bolivian earthquake of June 1994. Other derived source parameters (static stress drop, radiated seismic energy and maximum seismic efficiency) are also significantly different from those inferred for the 1994 Bolivian event, suggesting that deep earthquake processes do not follow an easily detectable common mechanism.