Abstract
The Median Tectonic Line (MTL) is an arc-parallel strike-slip fault that accommodates much of the arc-parallel component of the oblique convergence of the Philippine Sea and Eurasian plates at the Nankai Trough. The MTL in Shikoku is one of the fastest-slipping faults in Japan, with a late Quaternary right-lateral slip rate of 5–10 mm/yr. To estimate the right-lateral slip amounts of the past faulting events on the MTL, we acquired 2D and pseudo-3D ground-penetrating radar (GPR) sections across the ENE-trending Ikeda fault of the MTL in eastern Shikoku. We conducted the GPR surveys at the Higashi-Miyoshi site, where two terrace riser offsets mark the active fault trace. The 2D lines were about 28–64 m long, and the pseudo-3D data were sized 20 m × 30 m with a 0.5-m inline spacing. We used 50 MHz GPR antennas and conducted wide-angle measurements to estimate the electromagnetic wave velocity. We identified three paleochannels on the final depth-converted GPR sections, and two of them are deflected by the fault. A paleochannel at 0.6–1.4 m depth is observed on all inline sections of the pseudo-3D GPR data. We built a 3D model of this paleochannel and estimated the right-lateral and vertical displacements of ~ 3.5 m and ~ 0.5 m, respectively. This paleochannel offset is probably caused by the most recent surface-rupturing earthquake on the Ikeda fault, which may be the 1596 Keicho-Fushimi earthquake. This study demonstrates the usefulness of the GPR surveys to identify geological features displaced laterally and vertically by the most recent surface-rupturing earthquake.
Highlights
The Japanese Islands are a seismically active region located at the convergence zone of the Eurasian, North American, Philippine Sea, and Pacific plates (Fig. 1a)
Between horizontal distance (HD) 7 m and 9 m, these reflectors are slightly downthrown from the adjacent reflectors by the F5 fault (Fig. 5a, b)
We interpreted a reflector with a limited extent at a depth of 1.6 m between HD 33 and 38 m, which is underlain by a concave-upward reflector as a paleochannel
Summary
The Japanese Islands are a seismically active region located at the convergence zone of the Eurasian, North American, Philippine Sea, and Pacific plates (Fig. 1a). The Pacific plate subducts beneath the North American plate at the Japan Trench at a rate of ~ 10 cm/yr, while the Philippine Sea plate subducts obliquely beneath the Eurasian plate at the Nankai Trough at a rate of ~ 4 cm/yr (DeMets et al 2010). This oblique convergence partitions into trench-parallel and trench-normal slip components. Several 3D trench surveys were conducted to identify piercing point offsets associated with the most recent surface-faulting event (Goto et al 2003; Tsutsumi et al 1991)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
