Extraction of crustal deformation from seafloor hydraulic pressure gauges to estimate interplate coupling for subduction plate boundaries

To estimate seismic plate coupling and crustal deformation near the trench along the Nankai Trough, we perform a trial simulation of earthquake cycle in the Tonakai district, applying a rate- and state dependent friction law on the plate boundary and assuming the 1944 Tonankai earthquake and slow earthquakes occurring in numerous small asperities. Our simulation suggests that the observed activity of the shallow slow earthquakes locally around the fault segmentation boundary between the source regions of the Tonankai and Nankai megathrust earthquakes may be due to weak coupling between the two segments, while quiescence of the shallow slow earthquake around the segmentation boundary between the Tonankai and Tokai megathrust earthquakes may indicate strong plate coupling between the two segments. To evaluate these characteristics quantitatively, we also estimate leveling change at seafloor due to shallow VLFE swarms. Since the levelling change is expected to be so local as to be incoherent, removal of the moving-averaged data from the data stacked by four nearby observation point in the same node may be useful to detect the short-term local levelling change. In the future, we have to extract the crustal deformation component by separating other components such as instrumental drift and oceanic changes in order to consider coherent change among the same science node.