Taiwan is bounded by the 2200-km long Ryukyu subduction zone to the north and the 1100-km long Manila subduction zone to the south. The convergence rate across the Taiwan plate boundary is close to 90 mm/yr; whereas historic records document infrequent large earthquakes (M>8) over the past few hundred years. On the other hand, geological records across the South China Sea have reported more than one hundred tsunami events. Attempts to study megathrust earthquakes and tsunamis from these two subduction zones have obtained different results due to insufficient data. Recent development of seafloor geodetic techniques in Taiwan provides a means to evaluate the spatial extent of locked fault zones and creeping segments on the plate interface, the fraction of fault slip released seismically, and the magnitude of potential destructive subduction zone earthquakes.

In this talk, I will give an overview of the Taiwan seafloor geodetic array which consists of GNSS-acoustic stations, seafloor pressure gauges (APGs) and ocean-bottom seismometers. I then present data collected by the GNSS-acoustic technique and APGs along the southern Ryukyu Trench. I speculate that the cumulative strain is possibly partitioned between large dextral strike-slip faults in the accretionary wedge and thrust faults on the plate interface. Due to a low-angle plate interface at shallow depths, seafloor vertical movements may be difficult to be detected by APGs.
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