Mechanism of Dynamic Triggering for Slab-Related Fluid-Induced Tremors Occurred in Nanao, Taiwan

ABSTRACT The origin of nonvolcanic tremors has been linked to different ways the crust slips on a fault in the presence of fluids. We collected the tremors recorded by a seismic array in Nanao, Taiwan, and found a class of high-frequency tremors among ambient tremors and triggered tremors. The f-k analysis results and the large moveout implied that the triggered tremors originated from moving sources beneath the array. With seismogeodetic inversion, the triggered tremors occurred when dilation was larger than 10−8, similar to the deep low-frequency fluid-related seismic tremors in the Nankai trough. Based on previous tomographic studies, the partial melting due to the dehydration of the subducting Ryukyu slab is distributed along the slab edge and migrates upward near Nanao. Such a partial melting at shallow depth can potentially elevate the pore-fluid temperature and the pressure. According to these findings, we proposed a scenario analogous to fluid-related acoustic emission lab experiments. Dehydration near the edge of a subducting slab provides fluid and heat, and the dilational strains from the teleseismic waves cause decompression and therefore the fluid motions. Teleseismically perturbed fluids helped create at least some of the triggered tremors. This could be among the first field examples of dynamically triggered tremors associated with moving fluids from a slab and its edge.