A fresh look at the tectonic structure of the Eastern Java margin using improved seismic reflection tomography

Abstract:

The Java margin is characterized by a rugged oceanic plate relief and a highly segmented in the marine-forearc. This complex structure complicates seismic imaging of the margin, especially at greater depths. To overcome this, we apply the Non-Rigid Matching (NRM) method in reflection tomography to derive a more detailed velocity structure. The detailed P-wave models inverted from the tomography are then used to obtain high-quality pre-stack depth migrated seismic reflection images for two dip-lines between Eastern Java and the Lombok Island. In the western profile off Java (BGR06-305), a broad subducting seamount is observed underneath the accretionary wedge, with a height of ~ 2 km and a width of ~ 20 km. A distinct slope break at the seafloor is observed above the apex of the seamount. Underneath the slope break we observe splay faults reaching from the décollement to the seafloor. Additionally, at the transition zone from the forearc high to the forearc basin, two distinct back-thrusts are seismically imaged to a depth of ~ 7.5 km below seafloor. In the eastern profile off Lombok (BGR06-313), a décollement is observed within the subducting sediments ~ 1200 m above the top of the oceanic basement. The décollement shows inversed-polarity relative to the seafloor and develops on the seaward flank of another subducted seamount beneath the accretionary wedge. Additionally, we image landward dipping normal faults and fragmented folding structures which may develop in response to seamount subduction. The newly processed seismic lines underline the significant impact of subducting oceanic relief on décollement development, upper-plate deformation, and seafloor morphology.