3-D geometry and physical property of the mega-splay fault in Nankai Trough

Author(s): Masui, R.; Tsuji, T.; Yamada, Y.
Environmental Resource and System Engineering Laboratory
Author Affiliation(s): Primary:
Kyoto University, Engineering, Kyoto, Japan
Volume Title: AGU 2011 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2011; American Geophysical Union 2011 fall meeting, San Francisco, CA, Dec. 5-9, 2011. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Nankai Trough is a subduction zone, where the Philippine Sea Plate is being subducted beneath southwest Japan at a rate of ∼4-6.5 cm/y at an azimuth of ∼300°-315°. A lot of operations have been done in Nankai, such as three-dimensional seismic reflection surveys and Deep Sea Drilling Project (DSDP), Ocean Drilling Program (ODP), Integrated Ocean Drilling Program (IODP). They revealed that there is a large splay fault, referred to as "Mega-Splay". The Mega-Splay Fault has caused a series of catastrophic earthquakes and submarine landslides, which may have led to TSUNAMI. Since fault development history may have affected the geometry of the Mega-Splay Fault and physical property within the fault zone, they need to be examined in detail. In this research, we used 3-D pre-stack depth migration (PSDM), 3-D pre-stack time migration (PSTM) and P-wave velocity in C0004B well (Logging data), in order to interpret 3-D structure of Mega-Splay Fault. The analysis in this research is basically divided into two parts. One is structural interpretation of Splay Fault, based on the high amplitude reflection surface on seismic profiles. The other part is acoustic impedance inversion (AI inversion), in which we inverted seismic waveform into physical property (in this study, acoustic impedance), with the P-wave velocity data at C0004B near Mega-Splay Fault. The 3-D PSDM (or PSTM) clearly images details of Splay Fault, with good continuity of reflections along the fault. It is possible on each seismic profile to trace the high amplitude lines, where rock-properties significantly change. Since Mega-Splay Fault has 45-59m width along the wells, we interpreted the upper limit and the lower limit of the Mega-Splay Fault, based on the high amplitude surfaces along 3-D PSDM. Our interpretation shows that the width of Mega-Splay Fault has variation along the fault, and the plan geometry of the fault toe has a salient at the middle of the 3D box area, suggesting the fault could be divided into two segments: the eastern part and western part. In AI inversion, the 3-D PSTM and P-wave velocity at C0004B were used to build a physical property model around Mega-Splay Fault. AI Inversion is a methodology to invert seismic waveforms with physical property data, into acoustic impedance. Acoustic Impedance governs the ability of a rock to allow the passage of an acoustic wave. In this analysis, we used Hampson-Russell STRATA to perform post-stack seismic inversion. Our results show that there is a low acoustic impedance layer in the upper zone of Splay Fault. 3-D distribution of the low acoustic impedance layer in the fault zone has a variation in the width, similar to the 3-D interpretation of the geometry. This suggests that there are a relationship between structural geometry and physical property along the Mega-Splay Fault.
Year of Publication: 2011
Research Program: DSDP Deep Sea Drilling Project
ODP Ocean Drilling Program
Key Words: 16 Structural Geology; 19 Geophysics, Seismology; Asia; Body waves; Deep Sea Drilling Project; Earthquakes; Elastic waves; Far East; Fault zones; Faults; Geometry; Geophysical methods; Japan; Large splay faults; Mass movements; Nankai Trough; North Pacific; Northwest Pacific; Ocean Drilling Program; Ocean floors; P-waves; Pacific Ocean; Philippine Sea Plate; Physical properties; Plate tectonics; Prestack migration; Seismic methods; Seismic migration; Seismic waves; Slumping; Subduction; Subduction zones; Three-dimensional models; Tsunamis; Velocity structure; West Pacific
Record ID: 2015079659
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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