Mechanism of slab thickening near 670 km under Indonesia

Mantle structure and tectonic history of SE Asia

“…They explained this using a model of Ringwood and Irifune (1988) by suggesting the subducted slab thickened and buckled to form a megalith above the 660-km discontinuity which then sank into the lower mantle because of its higher density. A similar mechanism for slab thickening was proposed by Das et al (2000) in the Indonesian region although in their model the thickened slab dips steeply. Puspito et al (1993) presented a P-wave travel-time tomography model for the Indonesian region showing several of the main morphological features of slabs.…”

“…In contrast, Fauzi et al (1996) suggested there was no conclusive evidence of a tear in the slab but that high seismicity along the subducted portion of the Investigator Fracture Zone was the result of the intersection of the fracture zone and the bend in the slab where it is under compressive stress. Das et al (2000) also suggested lateral compression and thickening would be produced in the Sunda slab as it subducts and encounters a barrier at the transition zone; beneath Sumatra lateral compression could result from deformation caused by the strong curvature of the subduction zone.…”

Deep Earth Structure - Subduction Zone Structure in the Mantle Transition Zone

“…Such a slab configuration may be related to the deep hypocentral distribution (at depths greater than $ 500 km) that dips steeply in the slightly backward (southward) direction in agreement with the slightly backward orientation of the near-vertical compressional axes in the focal mechanisms of deep shocks (Das et al, 2000;Schö ffel and Das, 1999). A slight backward spread of the slab image is also observed in Figure 6 of Hafkenscheid et al (2001) but not obvious in Replumaz et al (2004) and Li et al (2008).…”

Seismicity gaps and the shape of the seismic zone in the Banda Sea region from relocated hypocenters

“… McCaffrey [1988] used ISC hypocenters to ∼100 km depth, available Harvard centroid moment tensor (CMT) solutions, and modeled P and SH waveforms from the World‐Wide Standardized Seismograph Network (WWSSN) and some Global Digital Seismic network (GDSN) stations for earthquakes between 1962 and 1984. Recent studies by us in the adjacent Sunda region to the west [ Schöffel and Das , 1999; Das and Schöffel , 2000; Das et al , 2000] showed that relocating the earthquakes accurately allows one to see details not seen before. In that study of the Sunda arc, thousands of additional phases ( pP , sP , PcP , ScP ) not reported by the ISC were handpicked and used to relocate the earthquakes, using the method of joint hypocenter determination (JHD).…”

“…Under Sunda, it was found that the slab is contorted along strike and, below about 500 km in one region, actually bends antithetically to its direction of subduction at the surface. Using the relocated hypocenters together with centroid moment tensor solutions, they proposed their “slab‐shattering” model, in which the Sunda slab thickens, shortens and weakens by shearing along conjugate faults on the upper and lower portions of the Wadati‐Benioff zone (WBZ), before penetrating below 670 km [ Das et al , 2000]. The reliability of the locations permitted differentiation between earthquakes on the upper and lower sides of the seismic zone.…”