Crustal structure of the Java margin from seismic wide‐angle and multichannel reflection data

Abstract

[1] Seismic investigations across the convergent Sunda margin off Indonesia provide a detailed image of the crustal architecture of the Sunda plate boundary. The combined analysis and interpretation of wide-angle and reflection seismic data along two coincident profiles across the subduction zone are complemented by additional lines within the forearc domain, which yield some three-dimensional (3-D) constraints on the velocity-depth structure across the margin. A detailed cross section of the subduction zone is presented, which is confirmed by supplementary gravity modeling. The Sunda convergence zone is a prime example of an accretionary margin, where sediment accretion has led to the formation of a massive accretionary prism, with a total width of >110 km between the trench and the forearc basin. It is composed of a frontal wedge which documents ongoing accretion and a fossil part behind the present backstop structure which constitutes the outer high. Moderate seismic velocities derived from wide-angle modeling indicate a sedimentary composition of the outer high. The subducting oceanic slab is traced to a depth of almost 30 km underneath the accretionary prism. The adjacent forearc domain is characterized by a pronounced morphological basin which is underlain by a layer of increased seismic velocities and a shallow upper plate Moho at 16 km depth. We speculate that remnant fragments of oceanic crust might be involved in the formation of this oceanic-type crust found at the leading edge of the upper plate beneath the forearc basin.

Perkembangan Tektonik Daerah Busur Muka Selat Sunda dan Hubungannya dengan Zona Sesar Sumatera

“…Oleh sebab itu, dapat dipastikan adanya zona ekstensi di busur muka Selat Sunda. Terdapat banyak bukti adanya ekstensi dan juga struktur graben di daerah ini (Harjono et al, 1991;Gaedicke, et al, 2003, Kopp et al, 2002 sehingga sangat kecil keraguan akan adanya kelanjutan Sesar Sumatera melintasi busur muka dan berakhir di palung. Berdasarkan pergerakan lempeng dan sesar yang telah diketahui dan fitur-fitur lainnya yang diperoleh dari penelitian ini, model pergerakan tektonik disusun untuk menjelaskan kemungkinan perkembangan tektonik daerah busur muka Selat Sunda.…”

Audio-Magnetotelluric Modeling of Cimandiri Fault Zone at Cibeber, Cianjur

“…Furthermore, Malod et al (1995) suggested that Cimandiri Fault Zone was extended to offshore and connected to Sumatra Fault Zone in a forearc region and formed a conjugate dextral strike-slip fault. The argument was rather weak since several offshore seimic reflection surveys indicated that more complex structures existed in the Sunda Strait forearc region (Kopp et al, 2002;Susilohadi et al, 2005).…”

Bathymetry of the Indonesian Sunda margin-relating morphological features of the upper plate slopes to the location and extent of the seismogenic zone

“…The downdip limit for the Sunda Strait transect is constrained by gravity modelling with a distance of 140 km from the deformation front at a depth of 25 km (Kopp et al, 2001). Kopp et al (2002) reveal a shallow upper plate mantle in a depth of ∼22 km in the western part of Java (106/107 • E) at a distance of about 100 km from the trench from wide-angle seismic studies (landward dashed line, Figs. 3, 5).…”

“…They noted major (M w 7.0 − 7.9) earthquakes to occur off Java and the Lesser Sunda islands, whereas great thrust earthquakes were missing in that region. The main target of later studies was the deep structure of the subduction systems offshore southern Sumatra and the Sunda Strait (Kopp et al, 2001(Kopp et al, , 2003 and western Java (Kopp et al, 2002 of the Indonesian island arc.…”