Subsurface structure of the Median Tectonic Line in the northeastern part of the Wakayama plain, central Japan

OKADA Atsumasa, MATSUI Kazuo, YOKOTA Hiroshi, SAITO Masaru, ENDO Satoru, NODA Toshikazu, KAGAWA Toshiyuki

doi:10.11462/afr1985.1998.17_84

The western extension of the Negoro fault, a segment of the Median Tectonic Line active fault system at the western part of Kink District, cuts the Middle Pleistocene deposits and is covered with Holocene alluvial deposits in the Wakayama plain, central Japan. We have carried out several drillings and a seismic reflection study using the S waves in this plain to clarify the subsurface structure around the MTL and to date recent faulting events;<BR>The buried reverse fault structure and stratigr a phic evidence with dates were clarified by seismic reflection method and a 80 meters deep drilling. As the fault shattered zone accampanies the Cretaceous Izumi sedimentary rocks, Sambagawa metamorphic rocks and ryolite intruded to the zone in the Miocene, this structure corresponds to the geologically defined MTL in the narrow sense and make a fault zone with the subordinary faults.<BR>The vertical displacement along th i s fault is estimated to be about 1 meter on the uncomformity between the Holocene sediments and the horizons of late Quaternary formations.<BR>The latest event of this fault may be younger than 8,000yBP, though the detailed age of the event and recurrence interval along the fault were not obtained by this study.

Subsurface structure of the Median Tectonic Line in the northeastern part of the Wakayama plain, central Japan

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