Uemachi flexure zone investigated by borehole database and numeical simulation

Abstract:

The Uemachi fault zone extending north and south, locates in the center of the Osaka City, in Japan. The Uemachi fault is a blind reverse fault and forms the flexure zone. The effects of the Uemachi flexure zone are considered in constructing of lifelines and buildings. In this region, the geomorphological survey is difficult because of the regression of transgression. Many organizations have carried out investigations of fault structures. Various surveys have been conducted, such as seismic reflection survey in and around Osaka. Many borehole data for construction conformations have been collected and the geotechnical borehole database has been constructed. The investigation with several geological borehole data provides the subsurface geological information to the geotechnical borehole database.

Various numerical simulations have been carried out to investigate the growth of a blind reverse fault in unconsolidated sediments. The displacement of the basement was given in two ways. One is based on the fault movement, such as dislocation model, the other is a movement of basement block of hanging wall. The Drucker-Prager and elastic model were used for the sediment and basement, respectively. The simulation with low and high angle fault movements, show the good agree with the actual distribution of the marine clay inferred from borehole data in the northern and southern Uemachi fault flexure zone, respectively. This research is partly funded by the Comprehensive Research on the Uemachi Fault Zone (from FY2010 to FY2012) by The Ministry of Education, Culture, Sports, Science and Technology (MEXT).