Fault mechanism and evolution of the seismogenic splay fault in subduction zone

2014 Fiscal Year Final Research Report

• Project/Area Number: 23244099
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Geology
• Research Institution: The University of Tokyo
• Principal Investigator: KIMURA Gaku 東京大学, 理学(系)研究科(研究院), 教授 (80153188)
• Co-Investigator(Kenkyū-buntansha): HASHIMOTO Yoshitaka 高知大学, 自然科学系, 准教授 (40346698)
• Project Period (FY): 2011-04-01 – 2015-03-31
• Keywords: 固体地球物理学 / 地震 / 大深度地下 / 地球変動予測 / 地質学

Outline of Final Research Achievements

Scientific Drilling was conducted to reveal the fault mechanism and evolution of the seismogenic splay fault in subduction zone. Target fault is the Nobeoka Thrust in Kyushu, which is a fossilized splay fault. Core analysis recoverd by drilling and bore-hole logging was operated.
The result presents that the physical properties of elastic wave velocity, porosity, and electoric resistivity clearly show a systematic variation around the fault core of cataclasite originated from fault gouge and surrounding damaged zone.
Micro cracks and faults with slicken-sided fault surface present ancient stress field in terms of inversion method of fault analysis. The result clearly suggests that the stresss field changed from reverse fault regime to normal fault regime. This change in stresss field might be related to the dynamic change before and after the seismogenic thrust.

Free Research Field

テクトニクス、構造地質学