Search

We estimated spatiotemporal slip distributions from three long-term slow slip events (L-SSEs) that occurred beneath the Bungo Channel at the convergent plate boundary between the subducting oceanic Philippine Sea plate and the continental Amurian plate in southwest Japan between 1997 and 1998, 2002 and 2004 and 2009 and 2011. For this purpose, we employed an inversion method using a Bayesian Information Criterion (ABIC), which included the following three prior constraints: the spatial slip distribution was smooth to some extent, slip directions were mostly oriented in the direction of plate convergence and the temporal change in slipwas smooth to some extent. Our results revealed that the three L-SSEs had a common feature: slipped regions expanded southwestward at accelerating slip velocities. We also found that major slipped regions migrated southwestward by approximately 50-100 km yr-1. In contrast, southwestward and northeastward migration of the slipped regions, whose direction differed from event to event, was also identified before or after the periods when the slip velocities were at their greatest. Comparing the obtained spatiotemporal slip distributions of the three L-SSEs with slip-deficit rate distributions obtained in our previous study, we investigated the accumulation process of the slip deficit caused by slip-deficit rate distributions and the release processes of the slip deficit caused by the obtained spatiotemporal slip distributions of the three L-SSEs. At the western plate interface of the Bungo Channel, as the slip-deficit rate was small and the amounts of slips associated with the three L-SSEs were large, most of the accumulated slip deficit was estimated to have been released. In contrast, at the eastern plate interface, as the slip-deficit rate was large and the amounts of slips associated with the three L-SSEs were small, the slip deficit was estimated to have accumulated effectively. These results suggest that the slipped regions of the three L-SSEs and the strongly coupled region are not spatially complementary; the accumulated slip deficit showed spatial variation even at approximately the same depth range along the arc. [ABSTRACT FROM AUTHOR]

To elucidate the relationship between interplate temperatures and generation mechanisms for megathrust earthquakes and slow slip events (SSEs) in the Kanto district, central Japan, we performed numerical simulations on the thermal state. For this purpose, we newly developed a 2-D box-type thermal convection model that is able to handle the subduction of two oceanic plates: the young oceanic Philippine Sea (PHS) plate subducts following subduction of the old oceanic Pacific (PAC) plate beneath it. To constrain temperatures on the upper surface of the PHS plate, we used high-density Hi-net heat flow data on land.We found that low heat flow in the Kanto district was caused mostly by subduction of the cold PHS plate. To explain the heat flowdistribution in the Kanto district inmore detail,we needed to incorporate frictional heating at the plate interface on the seaward side of the corner of the mantle wedge, and temperature changes due to surface erosion and sedimentation associated with crustal deformation during the Quaternary on land into the models. The most suitable pore pressure ratio to explain the heat flow data was 0.98. The thermally estimated seismogenic zone corresponded well to the fault planes of the 1923 Taisho Kanto earthquake and the western half of the 1707 Genroku Kanto earthquake. The eastern half of the fault plane of the 1707 Genroku Kanto earthquake could be divided into two areas; the northwestern fault plane corresponded to the thermally estimated seismogenic zone, whereas the relationship between the southeastern fault plane and interplate temperatures was ambiguous. The off-Boso SSEs occurred on the plate interface at temperatures lower than approximately 250 °C, and the slipped region passed through the 150 °C isotherm, corresponding to the clay mineral phase transformation from smectite to illite. This might suggest that the SSEs occurred in relation to a dehydration process. [ABSTRACT FROM AUTHOR]