--> New Broadband Seismic Unveils the Complexity of the Timor-Leste Offshore Subduction Zone

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New Broadband Seismic Unveils the Complexity of the Timor-Leste Offshore Subduction Zone

Abstract

A new regional 2D seismic survey was completed in Timor-Leste water in 2014 using CGG's BroadSeis technology. Early geological interpretation of these broadband data shows tremendous seismic image improvements revealing new information about the subduction margin. The additional low frequencies penetrate deep below the Timor Island accretionary prism to image what happens to the subducted Australian Plate. Furthermore, good quality high frequencies have enabled geologists to interpret in greater detail the Triassic-Holocene section of the Australian plate along with the inner structure of the Timor Island accretionary wedge. Deep beneath the accretionary prism, the seismic data reveal the behaviour of horsts and grabens from the Australian Plate under-going subduction. We observe a general thinning of the Mesozoic section towards the NE leading to think there was a prevalent monocline ramp in Late Permian. In addition, a large normal fault trending NNW-SSE with up to 2300m vertical offset splits the Timor-Leste offshore in two distinct sub-basins. This fault bounds the SW flank of a regional paleo-high, which was clearly active during Cretaceous times with visible thickening of the sediments in the hanging wall. This paleo-high probably acts as an obstacle for subduction giving rise to collision-like features at depth such as inverted faults and thrust duplexes below the regional decollement. Spatial relationship between the overriding and subducting plates suggests uplift and isostatic rebound due to slab detachment also proved by P-wave tomography models. These observations have multiple implications on the potential existence of petroleum systems in the Timor-Leste Offshore acreage.