Fine details of the Wadati‐Benioff zone under Indonesia and its geodynamic implications

Abstract

Abstract.Using about 5200 handpicked P, $, pP, sP, PcP, and $cP phases from digitally recorded seismograms, together with International Seismological Centre reported phases, we obtain improved hypocentral locations for -01790 earthquakes, -0983 of them having 90% confidence limits <30 km, at depths >50 km, in the period 1962 to September 1996, along the Indonesian subduction zone. We use an improved joint hypocenter determination method in which the solution is more stable than in the original one. We show that for deep earthquakes, use of the core-reflected phases is as good as use of depth phases, and since such core phases often have larger amplitudes and sharper onsets than the depth phases, their arrival times can be read very accurately. The positions of the relocated hypocenters show that (1) a portion of the Indonesian arc between •0 110øE and 123øE longitude, and deeper than -0500 km, is dipping southward at an angle of -075 ø, that is, in a direction opposite to the upper part of the north dipping slab, and (2) east of about 108øE, the seismic zone is wider near 670 km than near the 500 km depth. The first suggests southward lateral flow in the mantle, relative to the plate motion vector here. From •he contortion of the seismic zone along the eastern portion of the Indonesian arc, we can estimate the average lateral shear strain rate in the 300 to 670 km depth range to be of the order of 10-16s -1, over the last 10-20 Myr.

Multitaper coherence method for appraising the elastic thickness of the Indonesian active continental margin

“…1) is a prototype of a complex subduction zone lying at the boundary of the Indo-Australian plate (IAP) (Schoffel and Das, 1999). The Sumatran Fault Zone (SFZ) is characterized by the presence of an active volcanic arc and several fore-arc structures.…”

Comparison of the rupture and radiation characteristics of intermediate and deep earthquakes

“…Kanamori et al [1998] have suggested that melting of the fault plane after rupture initiation could have reduced fault friction and led to runaway slip in the 1994 Bolivian earthquake. Detailed study of the deep Indonesia seismic zone [SchOffel and Das, 1999] shows that the seismic zone is much wider near 650 km than near 500 km, with the sudden disappearance of seismic activity below 670 km. This means that the seismic zone is not slowly tapering with depth, as is generally believed on the basis of the simple idea that the slab is heating up as it subducts.…”

Evolution of Ataúro Island: Temporal constraints on subduction processes beneath the Wetar zone, Banda Arc

“…Previous work investigating the nature of earthquakes in the Banda Arc includes both regional (Das, 2004;McCaffrey, 1988;Schoffel and Das, 1999) and more focussed studies (Ely and Sandiford, 2010;McCaffrey et al, 1985;Sandiford, 2008). Compared to other parts of the Banda Arc, seismicity in the Wetar zone has unique characteristics that have important implications for understanding the development of the collision zone.…”