Evidence for Fluid Migration During the 2016 Meinong, Taiwan, Aftershock Sequence

Abstract

AbstractAn important question of earthquake science is to what extent fluids such as water play an important role in modulating seismicity. While many models of earthquake rupture assume that fluids are critical for dynamic weakening during slip and evidence for fluids is well documented for shallow injection‐induced or hydrothermally induced earthquakes, there has been limited conclusive evidence for the role of fluids for tectonic earthquakes in the middle‐to‐lower crust. Here, we provide evidence for fluid migration during the 2016 Meinong, Taiwan, aftershock sequence, occurring at 10–20 km depth within a classic fold‐and‐thrust belt. We find high Vp/Vs ratios, characteristic of highly fluid saturated regions, in the Meinong aftershock region and that the Vp/Vs ratios in the central aftershock region change with time during the aftershock sequence. The central aftershock sequence distinguishes itself from other aftershocks by having a swarm‐like magnitude distribution and aftershock decay rate, as well as a slower migration rate that may be related to fluid diffusion. The estimated permeability (~3.8 × 10−15 m2) and temporal changes in Vp/Vs suggest that moderate earthquakes may be able to strongly affect permeabilities in the midcrust. The results also suggest that fluid processes play a critical role in regulating seismicity in a classic continental collision tectonic setting and may also have a role in modifying earthquake hazards more generally.