Variations in mantle lithosphere buoyancy reveal seismogenic behaviour in the Sunda-Andaman subduction zone

The distribution of historic earthquakes in the Sumatra subduction zone reveals, in the forearc region, the intense seismic activity and frequent occurrences of M_w > 8 earthquakes throughout the whole area. In contrast, the neighbouring region has less dense seismicity and no large earthquake greater than M_w8 has been observed in the Java subduction zone. Such different seismic behaviours may be due to distinct degrees of the stress accumulation and release. In this study, the strength of plate coupling inferred from mantle lithosphere buoyancy (H_m) estimation is used to explain the seismogenic behaviour in the Sunda-Andaman subduction zone. Strong and weak plate coupling status are obtained in the Sumatra and Java subduction zones, respectively. These results can explain the significant differences in seismogenic behaviours in the Sunda-Andaman subduction zone. In assessing the global implications of this finding, we observe that uplifted serpentinized forearc mantle peridotite is the critical phenomenon in weak plate coupling cases and leads to a limit on the width of the coupling zone. Strong plate coupling can cause a relatively low gravity anomaly as well as a negative trench-parallel gravity anomaly (TPGA) in the forearc regions and correlates well with the occurrence of large earthquakes, whereas weak plate coupling can cause a positive TPGA and constrain the potential occurrence of large earthquakes.