Research for deep back-arc structure in Mariana by Japan-US joint long-term seismic observation

• Project/Area Number: 16540378
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Solid earth and planetary physics
• Research Institution: The University of Tokyo
• Principal Investigator: SHIOBARA Hajime The University of Tokyo, Earthquake Research Institute, Associate Professor, 地震研究所, 助教授 (60211950)
• Project Period (FY): 2004 – 2005
• Project Status: Completed (Fiscal Year 2005)
• Budget Amount: ¥3,800,000 (Direct Cost: ¥3,800,000); Fiscal Year 2005: ¥1,200,000 (Direct Cost: ¥1,200,000); Fiscal Year 2004: ¥2,600,000 (Direct Cost: ¥2,600,000)
• Keywords: Mariana / deep events / mantle structure / double seismic zone / ocean bottom seismic observation

Research Abstract

FY2004
Recovery of LTOBS deployed for the US-JP joint long-term seismic observation in Mariana started in 2004 was performed in April and May. Although 58 LTOBS were deployed, the overall data recovery was about 80%. On 20-21 May, the US side chief, Prof.Wiens visited Japan and we discussed about the data exchange and analysis. Preliminary analysis of this data, hypocenter determination, seismic activities along the spreading center in the back-arc and around the large serpentine seamount in the fore-arc were found. As these were also found in the pilot study experiment in 2001, these are assumed as steady activities. Farther more, a simultaneous inversion for hypocenter and 3-D velocity structure had been performed too by using arrival data for one year. Due to more than 3000 events originally detected, it could image the subducting Pacific plate even if without priori information of it. More precise hypocenter distribution obtained certified the systematic shift of epicenters determin ed by land stations. These result was presented in the AGU meeting in Dec.
FY2005
Cooperative study with US scientists was continued as same in the previous year. Further more, a dive recovery for un-recovered LTOBS in Mariana was conducted in July, and 3 LTOBS related with this study were successfully recovered. So that, all usable data obtained from two experiments became available, and the final data exchange between Japan and USA was also finished. From the 2001 data with 2 more LTOBS recovered this year, whole arrival data was checked again, then the simultaneous inversion was performed again. As additional LTOBS improved the station distribution, shallow seismic activity in the back-arc was revealed with high resolution. The double seismic zone also shows a fine structure, which starts from beneath the serpentine seamount of its upper plane. The new data obtained in 2003 was analyzed mainly in US side such as S-wave splitting, surface wave analysis, hypocenter determination and body wave tomography. These results were presented in the AGU meeting by aural and posters.

Research Products

• [Journal Article] Depth of the 660-km discontinuity near the Mariana slab from an array of ocean bottom seismographs (2006)
  • Author(s): Tibi, R., D.A.Wiens, H.Shiobara, H.Sugioka, P.J.Shore
  • Journal Title: Geophys. Res. Lett. 33・L02313
  • Description: 「研究成果報告書概要(和文)」より
• [Journal Article] Depth of the 660-km discontinuity near the Mariana slab from an array of ocean bottom seismographs (2006)
  • Author(s): Tibi, R., D.A.Wiens, H.Shiobara, H.Sugioka, P.J.Shore
  • Journal Title: Geophys.Res.Lett. 33
  • Description: 「研究成果報告書概要(欧文)」より
• [Journal Article] Depth of the 660-km discontinuity near the Mariana slab from an array of ocean bottom seismographs (2006)
  • Author(s): Tibi, R., D.A.Wiens, H.Shiobara, H.Sugioka, P.J.Shore
  • Journal Title: Geophys.Res.Lett. 33・L02313
• [Journal Article] Long Term Seismic Observation in Mariana by OBSs : Double Seismic Zone and Upper Mantle Structure (2005)
  • Author(s): Shiobara, H., Sugioka, H., Mochizuki, K., Oki, S., Kanazawa, T., Fukao, Y., Suyehiro, K.
  • Journal Title: Eos Trans. AGU, Fall Meet. Suppl., Abstract 86・52
  • Description: 「研究成果報告書概要(和文)」より
• [Journal Article] Long Term Seismic Observation in Mariana by OBSs : Double Seismic Zone and Upper Mantle Structure (2005)
  • Author(s): Shiobara, H., Sugioka, H., Mochizuki, K., Oki, S., Kanazawa, T., Fukao, Y., Suyehiro, K.
  • Journal Title: Eos Trans.AGU, Fall Meet.Suppl., Abstract 86 52
  • Description: 「研究成果報告書概要(欧文)」より
• [Journal Article] Long Term Seismic Observation in Mariana by OBSs : Double Seismic Zone and Upper Mantle Structure (2005)
  • Author(s): Shiobara, H., Sugioka, H., Mochizuki, K., Oki, S., Kanazawa, T., Fukao, Y., Suyehiro, K.
  • Journal Title: Eos Trans.AGU, Fall Meet.Suppl., Abstract 86・52