Evidence for hydrologically-induced, short-term variations in subduction interplate coupling in Taiwan

The island of Taiwan is situated in a complex tectonic setting at the top of a triple junction, where the Eurasian plate is subducting under the Philippine Sea plate and vice versa. These opposing subductions generate intense deformation, culminating in frequent megathrust earthquakes, and, at greater depths, produce seismic tremors. In addition to seismic extreme events, Taiwan experiences strong monsoon seasons during which typhoons deliver up to 1 m of precipitation locally. Here, we observe a transient reduction in megathrust slip rates following major typhoons, as evidenced by decreased geodetic velocities and reduced tremor and earthquake rates, lasting for approximately 15 days. We interpret the apparent reduction in subduction rates as a result of water-load-induced increases in normal stress on the plate interface, which, in turn, increases interplate coupling. While correlations between individual crustal fault activity and hydrological cycles have been previously reported, our study demonstrates that such effects operate at much larger scales, temporarily slowing an entire subducting slab. Our observations highlight the importance of studying the coupling between climate and tectonic dynamics.