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Dynamical triggering of tremors near Nanao, Taiwan, by the 2011 Tohoku earthquake: Slab-related fluid-induced seismicity
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  • Yi-Hsuan Wu,
  • Wu-Cheng Chi,
  • Liam Chai,
  • Chin-Jen Lin
Yi-Hsuan Wu
Institute of Earth Sciences, Academia Sinica

Corresponding Author:maomaowyh@gmail.com

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Wu-Cheng Chi
Academia Sinica
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Liam Chai
University of Chicago
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Chin-Jen Lin
Institute of Earth Sciences, Academia Sinica, Taiwan
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Dynamic triggering has been documented in many places in both seismic active and inactive regions, and most triggered events are tremors. These tremors provide a scaling relationship that bridges natural earthquakes and laboratory experiments. In particular, dynamic triggering may help understand the rupture mechanism of natural earthquakes. The Nanao array, a small aperture array composed of 4 dual broadband and strong motion seismic stations in Taiwan, recorded the 2011 Tohoku M9 earthquake and locally triggered tremors, in addition to the ambient tremors. Using Spudich’s method to derive shallow crustal shear strain, dilation, and rotation during tremor episodes, we found that tremors occurred when dilation was larger than 10–8, similar to Nankai Trough cases. Previous tomographic studies have shown partial melting coming from the dehydration of the subducting Ryukyu slab and the slab edge corner. Such a partial melt zone extends to shallow depth near the Nanao array and could potentially elevate the pore fluid temperature. A systematic check of all the seismic stations in Northern Taiwan shows clear increased triggered tremors only near Nanao right after the Tohoku earthquake. We applied array processing methods to the Nanao array data and derived a NE to SW back azimuth directions of the tremors, filling a seismic gap in northeastern Taiwan seismicity six months after Tohoku earthquake. Analogous to fluid-related acoustic emission lab experiments, we propose that this is among the first field examples of dynamically triggered tremors associated with moving fluids from a slab and its edge.