Survey on 3-D soil structure of Fukui Plain through microtremor H/V spectrum method

Three-dimensional soil structure in Fukui Plain was estimated from microtremor observations at 1 km mesh points. Depth of alluvial, diluvial, tertiary layers and seismic bedrock were evaluated from the observed H/V spectrum ratios through the GA method. The main features on the seismic bedrock depth in the target area are as follows. There is a deep domain along the west edge of the plain. The depth becomes quickly shallower to westward and gently shallower to eastward. Another deep linear domain estimated along the east edge has possibility of corresponding to the 1948 Fukui Earthquake Fault. Moreover a steep change of bedrock depth is found at the northern side of Asuwayama Hill