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

Abstract

Summary 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.

Source characteristics of the deep Philippine earthquake cluster, 23 and 24 July 2010

“…The results show that the source properties of this deep-focus cluster are similar in characters to those of Kikuchi and Kanamori (1994), Kanamori et al (1998) b Fukao and Kikuchi (1987) c McGuire et al (1997) d Tibi et al (1999) other deep earthquakes occurring in warmer slabs and indicate that the totally consumed Molucca plate possibly is a warmer slab.…”

“…However, Antolik et al (1999) suggests that isobaric process might control the progression of the rupture and results in a tendency of horizontal rupture propagation through determining the source characteristics of five large, deep-focus earthquakes. Several deep-focus earthquake studies also indicate horizontal fault planes and horizontal rupture propagation direction (Warreni et al 2007;Tibi et al 1999;Park and Mori 2008;Tibi et al 2003;Wu and Chen 2001). CMT solutions show that every member in this Philippine deep-focus cluster has similar mechanism consisting of a near-vertical nodal plane trending north-south, and a subhorizontal nodal plane striking east-south.…”

“…These two source parameters are slab thermal state dependent (Wiens 2001;Tibi et al 2003;Houston 2007). The previous studies suggest that deep earthquakes in warmer and young subducting slabs tend to have a slow rupture velocity and high stress drop (Kikuchi and Kanamori 1994;Kanamori et al 1998;Goes and Ritsema 1995;Antolik et al 1999;Wiens 2001;Tibi et al 2003), and deep events in cold slabs have a fast rupture velocity and low stress drop (Fukao and Kikuchi 1987;McGuire et al 1997;Tibi et al 1999).…”

DIRDOP: a directivity approach to determining the seismic rupture velocity vector

“…1), including the Fig. 1 Effects of rupture directivity: a common pulse duration at different azimuths from the rupture, b corner frequency variation on spectra diagrams of body wave displacement, c pulse duration variation observed in relative source time functions, and d symmetric change of the radiation pattern with maximum amplitude related to the direction of the rupture following: (a) a variation of pulse duration observed in waveforms at stations with differing azimuths (e.g., Fukao 1972; Tibi et al 1999;Caldeira et al 2004), (b) variations of corner frequencies observed in the amplitude spectra (e.g., Tumarkin and Archuleta 1994;Hoshiba 2003), (c) pulse duration variations observed in relative source time functions (RSTF; e.g., Ihmlé 1998;Baumont et al 2002;Kraeva 2004), and (d) symmetric changes of the radiation pattern in which the maximum amplitude is related to the direction of the rupture (e.g., Benioff 1955;Ben-Menahem and Singh 1981;Kasahara 1981).…”

“…(b) The second approach uses the apparent duration of the rupture gathered from seismic waveforms or from the apparent source time functions, which are both azimuthally distributed. Equation 2 is then applied to estimate the parameters of source finiteness (e.g., Fukao 1972;Boore and Joyner 1978;Cipar 1979;Beck et al 1995;Ihmlé 1998;Tibi et al 1999;Kraeva 2004) In this study, we use a similar scheme to determine the direction and rupture velocity and the corresponding errors. The directivity by Doppler effect (DIRDOP) program uses time delays between common pulses selected in broadband seismic body waves with an azimuthal distribution around the epicenter; it calculates the source parameters through a subsequent Doppler analysis.…”