Gravity signatures at the upper plate above subducting asperities along Sunda Arc

Abstract The subducting Indo-Australian plate along the Sunda Arc has various degrees of roughness near the trench. The variation in the subducted plate’s seafloor morphology should affect the upper plate’s dynamic at the forearc region and further in land, which would appear in the form of variation in seismicity along the arc. In this paper, we explored the pattern in topography and gravity along the forearc at two regions. First is northern Sumatra, where some ridges have been subducted. The second is east Java, where part of the oceanic plateau of Roo Rise has been subducted. In addition, we also examined the seismicity in those two regions. The elongated ridges pattern of the subducted ridges was observed in the forearc region of Sumatra as the higher anomalies. It is probably due to the continuous nature of the ridge. The broader ruggedness, such as in Roo Rise, does not reflect directly at the Java forearc. However, the anomalies are chaotic and might represent the condition of the rugged subducted plate. The seismicity events at the area of the subducted ridge formed a straight line at the same position where the ridges are assumed to be. Meanwhile, the events on the opposite side of the plateau showed more sporadic distribution, which might indicate the condition of the irregular morphology of the subducted plate.