Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

• Nakajima Junichi

  Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University

• Hasegawa Akira

  Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University

• Horiuchi Shigeki

  National Research Institute for Earth Science and Disaster Prevention

• Yoshimoto Kazuo

  Graduate School of Integrated Science, Yokohama City University

• Yoshida Takeyoshi

  Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University

• Umino Norihito

  Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University

Abstract

AnM=5 earthquake occurred on September 15, 1998, in the Nagamachi-Rifu fault (NRF), northeastern Japan. In the aftermath of this event, many seismograph stations were constructed temporarily around the fault, forming a dense network of stations with a spatial separation of 5 km. We report here our estimation of the threedimensional velocity structures of the P and S waves using arrival-time data recorded at these stations with the aim of understanding the heterogeneous structure around the NRF. Low-Velocity and high Poisson's ratio anomalies are imaged in the lower crust beneath the volcanic area, which are probably associated with the partially molten materials conveyed through the upwelling flow in the mantle wedge. A distinct low-velocity anomaly, which is explainable by the existence of H₂O-filled pores, is observed in the mid crust at the deeper extension of the NRF. Two low-velocity anomalies that are probably associated with the remnants of magmatic activity that formed the Shirasawa caldera and with the existence of thick late-Cenozoic sedimentary layers are observed at depths shallower than 10 km in the hanging wall of the NRF. Our results successfully characterize the major features of the complex velocity structure around the NRF, with implications for the existence of fluid-rich regions in the mid to lower crust.

Journal

• Earth, Planets and Space

  Earth, Planets and Space 58 (7), 843-853, 2006

  Society of Geomagnetism and Earth, Planetary and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan , The Geodetic Society of Japan , The Japanese Society for Planetary Sciences

Keywords

• seismic velocity structure
• northeastern Japan
• Nagamachi-Rifu fault
• fluids
• magma
• caldera
• active fault

Details

• CRID: 1390001206511885696
• NII Article ID: 10024493005
• NII Article ID: 130003781199
• NII Book ID: AA11211921
• DOI: 10.1186/bf03351989
• ISSN: 18805981
• ISSN: 13438832
• NDL BIB ID: 8002925
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I8002925
• Web Site: https://link.springer.com/content/pdf/10.1186/BF03351989.pdf
• Web Site: https://link.springer.com/article/10.1186/BF03351989/fulltext.html
• Web Site: http://link.springer.com/content/pdf/10.1186/BF03351989
• Text Lang: en
• Data Source:
  • JaLC
  • NDL
  • Crossref
  • CiNii Articles
• Abstract License Flag: Disallowed