Seismotectonic setting of the Wakayama district, Japan, and location of the linear seismic array. Distributions of 86 portable seismic stations (yellow triangles) deployed from December 2010 to June 2011 and grid nodes used in the tomographic analysis (black crosses). Open squares denote permanent stations. Relocated ordinary earthquakes are shown as circles scaled to earthquake magnitude and color-coded by depth. Red stars represent epicenters of LFEs relocated in the present study. Gray circles denote all of the earthquakes identified by JMA during the seismic observing period. Solid contours represent annual rate of uplift ≥4 mm/year (with an interval of 1 mm/year) observed by geodetic measurements (Yoshida et al. 2011). Major active faults are drawn as red lines. The inset shows the location of the dense seismic array deployed in the present study. Small dots denote epicenters of LFEs. Red triangles denote active volcanoes. EP, Eurasian Plate; PSP, Philippine Sea Plate.