Abstract
Abstract. Earthquake history shows that the Sunda subduction zone of the Indonesian margin produces great earthquakes offshore Sumatra, whereas earthquakes of comparable magnitude are lacking offshore Java and the Lesser Sunda islands. Morphological structures in multibeam bathymetric data across the forearc relate with the extent of the seismogenic zone. Its updip limit corresponds to the slope break, most distinct off Java and Lesser Sunda islands, where we find coincident narrow, uniform, continuous outer arc ridges. Their landward termination and a shallow upper plate mantle mark the downdip limit of the seismogenic zone. In contrast the outer arc ridges off Sumatra are wider and partly elevated above sea level forming the forearc islands. The downdip limit of the seismogenic zone coincides with a deeper upper plate mantle. Sunda Strait marks a transition zone between the Sumatra and Java margins. We find the differences along the Sunda margin, especially the wider extent of the seismogenic zone off Sumatra, producing larger earthquakes, to result from the interaction of different age and subduction direction of the oceanic plate. We attribute a major role to the sediment income and continental/oceanic upper plate nature of Sumatra/Java influencing the composition and deformation style along the forearc and subduction fault.
Highlights
The seismogenic zone (SZ) is the unstable regime of the plate interface at a subduction zone, where the largest earthquakes in the world are produced (Scholz, 1998)
We find the differences along the Sunda margin, especially the wider extent of the seismogenic zone off Sumatra, producing larger earthquakes, to result from the interaction of different age and subduction direction of the oceanic plate
Off Simeulue and further South, the updip limit of the SZ is shifted landward to ∼70 km from the deformation front
Summary
The seismogenic zone (SZ) is the unstable regime of the plate interface at a subduction zone, where the largest earthquakes in the world are produced (Scholz, 1998). Moore and Saffer (2001) and Moore, J.C. et al (2007) relate the updip limit to temperature dependent processes These take place between 100 ◦C and 150 ◦C and cause progressive rheological changes on subducted and accreted sediment. We use the term of inner and outer wedge as introduced by Wang and Hu (2006) to describe the transition zone of the updip limit of the SZ. Thermal modelling and locations of earthquakes verify the updip limit of the SZ, whereas the downdip termination of the SZ is constrained by seismic wide-angle and seismological analyses. We investigate the upper plate morphology with respect to the localized occurrence (spatial distribution) of major (Mw7.0–7.9) and great (Mw ≥ 8) earthquakes produced along the subduction fault (Fig. 1)
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