Holocene activity of the strike-slip faults revealed by sediment cores and ground penetrating radar profiling, the northern area of the Izu Peninsula, central Japan
Dr. Haruo Kimura1, Prof. Toshimichi Nakanishi2, Ms. Mei Yukawa1, Mr. Takashi Hosoya3, Dr. Wan Hong4
1Central Research Institute Of Electric Power Industry, Abiko, Japan, 2Museum of Natural and Environmental History, Shizuoka, Shizuoka, Japan, 3Chuo Kaihatsu Corporation, , Japan, 4Korea Institute of Geoscience & Mineral Resources, Daejeon, Republic of Korea
The Mjma=7.3 1930 Kita-Izu earthquake ruptured the N-S trending Kita-Izu fault zone, which was also called as the Tanna fault zone. The fault zone is located in the Izu Peninsula, northern tip of the Izu-Bonin-Mariana arc, and it consists of many sinistral strands and some conjugate dextral ones. The Sagiriko fault located to the south of the Kita-Izu fault zone also consists of N-S trending strands and conjugate ones. The Tanna fault zone and a N-S trending strand of the Sagiriko fault were ruptured during the 1930 earthquake, but Holocene activity of the conjugate E-W trending strands of the fault have not been revealed. We analyzed the near-surface structure profiled by ground penetrating radar (GPR) and accelerator mass spectrometry (AMS) radiocarbon ages of drill cores to estimate Holocene activity on the main strand of the Tanna fault, which caused the largest surface displacement in the fault zone during the 1930 earthquake, and one of the E-W trending strands of the Sagiriko fault, which have been reported no deformation during the earthquake. In order to detect detailed location of the fault trace on the surface, we first carried out aerial photograph interpretation and field observation before the drilling and GPR surveys. The drilling sites were arrayed near the Tanna fault and the Sagiriko fault, respectively. The GPR surveys were conducted along the arrays of the drilling sites. The GPR profiling data were collected by common-offset modes using pulseEKKO PRO GPR systems manufactured by Sensors and Software Inc., and we also carried out wide-angle measurements to estimate the electromagnetic wave velocity used in the time-to-depth conversion of the GPR sections. We interpreted several horizons showing local subsidence and past seismic events on the final depth-converted GPR sections of the Tanna and the Sagiriko faults, respectively. The horizons were dated by AMS radiocarbon ages of plant fragments and organic soil samples in the drilled cores. The chronology was confirmed by tephra layers such as the Kawago-daita pumice and Aira-Tanzawa ash. The horizons explained the Holocene activity of the E-W trending strand of the Sagiriko fault as well as the main strand of the Tanna fault. This work was started as a research project funded by the Izu Peninsula UNESCO Global Geopark. This study was partially funded by the Japan Society for the Promotion of Science Kakenhi grant numbers 15K01255 and 18K03768.
After getting a Doctor of Science from the University of Tokyo, he worked at the Earthquake Research Institute of the university and the Geological Survey of Japan. Currently, he is studying active tectonics and structural geology at the Central Research Institute of Electric Power Industry.