Subsurface geometry and structural evolution of the eastern margin fault zone of the Yokote basin based on seismic reflection data, northeast Japan

Kagohara, Kyoko; Ishiyama, Tatsuya*; Imaizumi, Toshifumi*; Miyauchi, Takahiro*; Sato, Hiroshi*; Matsuta, Nobuhisa*; Miwa, Atsushi*; Ikawa, Takeshi*

Tectonophysics, 470(3-4), p.319 - 328, 2009/05

https://doi.org/10.1016/j.tecto.2009.02.007

Seismic reflection profiles across coseismic fault scarps of the A.D. 1896 Rikuu earthquake along the eastern margin of the Yokote basin fault zone (EYBFZ), correlated with borehole stratigraphy and geologic mapping, provide insights into its detailed structural evolution. In spite of along-strike variations of thrust geometries both at ground surface and at shallow depth, the EYBFZ has commonly formed as forward breaking imbricate thrust systems. Spatial variations in the long-term uplift rates estimated from cross-section balancing are consistent with mountain topography, in contrast to their weak coupling with the magnitudes of short-term uplift rates and coseismic uplift during the A.D. 1896 earthquake. This suggests that mechanical decoupling of Miocene mudstone that formed frontal emergent thrust faults may have enhanced the slip at shallowest structural levels at shorter timescales.

Active tectonics of the Senya Hills and evolution of the Senya Active Fault, Eastern margin of the Yokote Basin Fault Zone, Northeast Japan

Kagohara, Kyoko*; Imaizumi, Toshifumi*; Miyauchi, Takahiro*; Sato, Hiroshi*; Uchida, Takuma*; Echigo, Tomoo*; Ishiyama, Tatsuya*; Matsuta, Nobuhisa*; Okada, Shinsuke*; Ikeda, Yasutaka*; et al.

Chigaku Zasshi, 115(6), p.691 - 714, 2006/12

https://doi.org/10.5026/jgeography.115.6_691

The eastern marginal fault zone of the Yokote Basin is one of seismogenic reverse faults developed in Northeast Japan, generating the 1896 Riku-u Earthquake (M7.2). We discussed the relationship among fault traces, geomorphic displacements and fault geometries on the Senya fault, based on a data from high-resolution seismic reflection profiling, investigations in tectonic geomorphology and structural geology, with the help of the balanced cross section method. By the restoring the balanced cross sections, the horizontal shortening amount is estimated to be totally 3 km through the thrust system, and the thrusting is retroactive to 2.4 Ma. Depending on the strike of fault traces and the morphotectonic features, the Senya fault is subdivided into three, the northern, central and southern portion. The initiation of thrust front migration is ca.1.6 Ma at the central portion and 0.6 Ma at the northern portion. This means that the central portion preceded the northern portion as an emergent fault, and suggests that the initial propagated fault extends from the fault end to the boundary fault.

Report of Horonobe technical review meetings (FY 2004); 1st to 4th meetings (Document on present state of affairs)

Shirato, Nobuaki*; Matsui, Hiroya; Morioka, Hiroshi; Hatanaka, Koichiro; Takeuchi, Ryuji; Hatakeyama, Nobuya; Ohara, Hidefumi; Nakajima, Takahiro; Kunitomo, Takahiro

JNC TN5440 2005-001, 412 Pages, 2005/06

JNC-TN5440-2005-001.pdf:20.87MB

We held Horonobe technical review meeting 4 times a year. The first meeting is for the plan of Horonobe underground research laboratory and others. The secound meeting is for geology of Horonobe area and modeling study and data acquisition for safety assessment methodology and others. The third meeting is for ventilation network analyses on URL plan. The fourth meeting is for the remote monitoring system using ACROSS. This report is records of these meetings.

The Horonobe Underground Research Laboratory project; Outline and progress of development of remote monitoring system (ACROSS)

Ohara, Hidefumi; Tsukui, Rota; Kunitomo, Takahiro; Nakajima, Takahiro; Niizato, Tadafumi; Aoki, Kazuhiro; Shigeta, Naotaka; Kumazawa, Mineo

no journal, , 

Japan Atomic Energy Agency (JAEA) is developing a remote monitoring system using seismic and electromagnetic ACROSS(Accurately Controlled Routinely Operated Signal System), to monitor changes in the geological environment. ACROSS has been researched and developed in Tono Geoscience Center for 9 years, and we introduce it to the Horonobe Underground Research Laboratory (URL) project. The Horonobe URL project is devoted to the technological development over 20-years from March 2001 for a safe geological disposal of high level radioactive wastes in Horonobe-cho in northern Hokkaido, Japan. We install the monitoring system before the shaft excavation, and collect data before, during and after the excavation, in order to permit assessment of the system's reliability. The source and receivers of electromagnetic ACROSS were installed in the winter before last, and we are carrying out the test of the system. In last December, the source and receivers of a seismic ACROSS were installed in Horonobe. Then we are going to examine the practicability of ACROSS.