Difference in acoustic properties at seismogenic fault along a subduction interface: Application to estimation of effective pressure and fluid pressure ratio

Yoshitaka Hashimoto, Noriaki Doi, Takeshi Tsuji

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Fluid pressure along subduction plate boundaries plays a role in seismogenesis and tsunami genesis because it is strongly related to the physical properties of faults. In this study, we conducted P-wave velocity (Vp) and S-wave velocity (Vs) measurements for the hanging wall and footwall of a fossil subduction interface with pseudotachylyte located at the northern edge of the Mugi mélange in the Cretaceous Shimanto Belt, Shikoku, southwest Japan. This area corresponds to the depth of the shallow seismogenic zone in the transition zone between the inner and outer wedges. By combining the acoustic properties with parameters obtained from Amplitude Variation with Offset (AVO) analysis on the Nankai seismic profile, we estimated the fluid pressure at the seismogenic fault.The Mugi mélanges are composed of shale matrices and are juxtaposed with the coherent unit of the Hiwasa formation in the north, which is composed mainly of sandstone. We collected 5 sandstone samples from the hanging wall (Hiwasa formation) and 4 mudstone samples from the footwall (Mugi mélange). We conducted velocity measurements while controlling both the fluid pressure and confining pressure by using two pumps. The effective pressure in each measurement ranged from 5 to 65. MPa with intervals of 5. MPa.The Vp and Vs of sandstone increase exponentially with effective pressure from ~. 4500 to ~. 5000. m/s and ~. 2500 to ~. 3000. m/s, respectively. The Vp and Vs of the mudstone also increased exponentially from ~. 4100 to ~. 4500. m/s and ~. 1900 to ~. 2200. m/s, respectively.We used AVO parameters along the décollement based upon a seismic profile of the Nankai trough, which is off Muroto 40-45. km landward from the trench axis, corresponding to approximately 66. MPa of effective pressure under a hydrostatic condition. By combining the velocities obtained from this study and the AVO parameters derived from the Muroto seismic data, we estimate the mean effective pressures for the hanging wall and the footwall as approximately 10-20. MPa and 8-10. MPa, respectively. The normalized fluid pressure ratios for the hanging wall and the footwall correspond to approximately 0.82-0.91 and 0.91-0.93, respectively. This high fluid pressure indicates a very low effective friction coefficient along the décollement in the transition zone, possibly causing a rupture to propagate to the shallower outer wedge and thus generating a large tsunami.

Original languageEnglish
Pages (from-to)134-141
Number of pages8
JournalTectonophysics
Volume600
DOIs
Publication statusPublished - Jul 17 2013

Fingerprint

acoustic property
fluid pressure
pressure ratio
acoustic properties
hanging wall
footwall
subduction
sandstones
sandstone
velocity measurement
tsunami
transition zone
wedges
mudstone
wave velocity
pseudotachylite
fossils
profiles
confining pressure
hydrostatics

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth-Surface Processes

Cite this

Difference in acoustic properties at seismogenic fault along a subduction interface : Application to estimation of effective pressure and fluid pressure ratio. / Hashimoto, Yoshitaka; Doi, Noriaki; Tsuji, Takeshi.

In: Tectonophysics, Vol. 600, 17.07.2013, p. 134-141.

Research output: Contribution to journalArticle

@article{3727ab48e81b47b7b916e9d2ab253b66,
title = "Difference in acoustic properties at seismogenic fault along a subduction interface: Application to estimation of effective pressure and fluid pressure ratio",
abstract = "Fluid pressure along subduction plate boundaries plays a role in seismogenesis and tsunami genesis because it is strongly related to the physical properties of faults. In this study, we conducted P-wave velocity (Vp) and S-wave velocity (Vs) measurements for the hanging wall and footwall of a fossil subduction interface with pseudotachylyte located at the northern edge of the Mugi m{\'e}lange in the Cretaceous Shimanto Belt, Shikoku, southwest Japan. This area corresponds to the depth of the shallow seismogenic zone in the transition zone between the inner and outer wedges. By combining the acoustic properties with parameters obtained from Amplitude Variation with Offset (AVO) analysis on the Nankai seismic profile, we estimated the fluid pressure at the seismogenic fault.The Mugi m{\'e}langes are composed of shale matrices and are juxtaposed with the coherent unit of the Hiwasa formation in the north, which is composed mainly of sandstone. We collected 5 sandstone samples from the hanging wall (Hiwasa formation) and 4 mudstone samples from the footwall (Mugi m{\'e}lange). We conducted velocity measurements while controlling both the fluid pressure and confining pressure by using two pumps. The effective pressure in each measurement ranged from 5 to 65. MPa with intervals of 5. MPa.The Vp and Vs of sandstone increase exponentially with effective pressure from ~. 4500 to ~. 5000. m/s and ~. 2500 to ~. 3000. m/s, respectively. The Vp and Vs of the mudstone also increased exponentially from ~. 4100 to ~. 4500. m/s and ~. 1900 to ~. 2200. m/s, respectively.We used AVO parameters along the d{\'e}collement based upon a seismic profile of the Nankai trough, which is off Muroto 40-45. km landward from the trench axis, corresponding to approximately 66. MPa of effective pressure under a hydrostatic condition. By combining the velocities obtained from this study and the AVO parameters derived from the Muroto seismic data, we estimate the mean effective pressures for the hanging wall and the footwall as approximately 10-20. MPa and 8-10. MPa, respectively. The normalized fluid pressure ratios for the hanging wall and the footwall correspond to approximately 0.82-0.91 and 0.91-0.93, respectively. This high fluid pressure indicates a very low effective friction coefficient along the d{\'e}collement in the transition zone, possibly causing a rupture to propagate to the shallower outer wedge and thus generating a large tsunami.",
author = "Yoshitaka Hashimoto and Noriaki Doi and Takeshi Tsuji",
year = "2013",
month = "7",
day = "17",
doi = "10.1016/j.tecto.2013.03.016",
language = "English",
volume = "600",
pages = "134--141",
journal = "Tectonophysics",
issn = "0040-1951",
publisher = "Elsevier",

}

TY - JOUR

T1 - Difference in acoustic properties at seismogenic fault along a subduction interface

T2 - Application to estimation of effective pressure and fluid pressure ratio

AU - Hashimoto, Yoshitaka

AU - Doi, Noriaki

AU - Tsuji, Takeshi

PY - 2013/7/17

Y1 - 2013/7/17

N2 - Fluid pressure along subduction plate boundaries plays a role in seismogenesis and tsunami genesis because it is strongly related to the physical properties of faults. In this study, we conducted P-wave velocity (Vp) and S-wave velocity (Vs) measurements for the hanging wall and footwall of a fossil subduction interface with pseudotachylyte located at the northern edge of the Mugi mélange in the Cretaceous Shimanto Belt, Shikoku, southwest Japan. This area corresponds to the depth of the shallow seismogenic zone in the transition zone between the inner and outer wedges. By combining the acoustic properties with parameters obtained from Amplitude Variation with Offset (AVO) analysis on the Nankai seismic profile, we estimated the fluid pressure at the seismogenic fault.The Mugi mélanges are composed of shale matrices and are juxtaposed with the coherent unit of the Hiwasa formation in the north, which is composed mainly of sandstone. We collected 5 sandstone samples from the hanging wall (Hiwasa formation) and 4 mudstone samples from the footwall (Mugi mélange). We conducted velocity measurements while controlling both the fluid pressure and confining pressure by using two pumps. The effective pressure in each measurement ranged from 5 to 65. MPa with intervals of 5. MPa.The Vp and Vs of sandstone increase exponentially with effective pressure from ~. 4500 to ~. 5000. m/s and ~. 2500 to ~. 3000. m/s, respectively. The Vp and Vs of the mudstone also increased exponentially from ~. 4100 to ~. 4500. m/s and ~. 1900 to ~. 2200. m/s, respectively.We used AVO parameters along the décollement based upon a seismic profile of the Nankai trough, which is off Muroto 40-45. km landward from the trench axis, corresponding to approximately 66. MPa of effective pressure under a hydrostatic condition. By combining the velocities obtained from this study and the AVO parameters derived from the Muroto seismic data, we estimate the mean effective pressures for the hanging wall and the footwall as approximately 10-20. MPa and 8-10. MPa, respectively. The normalized fluid pressure ratios for the hanging wall and the footwall correspond to approximately 0.82-0.91 and 0.91-0.93, respectively. This high fluid pressure indicates a very low effective friction coefficient along the décollement in the transition zone, possibly causing a rupture to propagate to the shallower outer wedge and thus generating a large tsunami.

AB - Fluid pressure along subduction plate boundaries plays a role in seismogenesis and tsunami genesis because it is strongly related to the physical properties of faults. In this study, we conducted P-wave velocity (Vp) and S-wave velocity (Vs) measurements for the hanging wall and footwall of a fossil subduction interface with pseudotachylyte located at the northern edge of the Mugi mélange in the Cretaceous Shimanto Belt, Shikoku, southwest Japan. This area corresponds to the depth of the shallow seismogenic zone in the transition zone between the inner and outer wedges. By combining the acoustic properties with parameters obtained from Amplitude Variation with Offset (AVO) analysis on the Nankai seismic profile, we estimated the fluid pressure at the seismogenic fault.The Mugi mélanges are composed of shale matrices and are juxtaposed with the coherent unit of the Hiwasa formation in the north, which is composed mainly of sandstone. We collected 5 sandstone samples from the hanging wall (Hiwasa formation) and 4 mudstone samples from the footwall (Mugi mélange). We conducted velocity measurements while controlling both the fluid pressure and confining pressure by using two pumps. The effective pressure in each measurement ranged from 5 to 65. MPa with intervals of 5. MPa.The Vp and Vs of sandstone increase exponentially with effective pressure from ~. 4500 to ~. 5000. m/s and ~. 2500 to ~. 3000. m/s, respectively. The Vp and Vs of the mudstone also increased exponentially from ~. 4100 to ~. 4500. m/s and ~. 1900 to ~. 2200. m/s, respectively.We used AVO parameters along the décollement based upon a seismic profile of the Nankai trough, which is off Muroto 40-45. km landward from the trench axis, corresponding to approximately 66. MPa of effective pressure under a hydrostatic condition. By combining the velocities obtained from this study and the AVO parameters derived from the Muroto seismic data, we estimate the mean effective pressures for the hanging wall and the footwall as approximately 10-20. MPa and 8-10. MPa, respectively. The normalized fluid pressure ratios for the hanging wall and the footwall correspond to approximately 0.82-0.91 and 0.91-0.93, respectively. This high fluid pressure indicates a very low effective friction coefficient along the décollement in the transition zone, possibly causing a rupture to propagate to the shallower outer wedge and thus generating a large tsunami.

UR - http://www.scopus.com/inward/record.url?scp=84879793083&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84879793083&partnerID=8YFLogxK

U2 - 10.1016/j.tecto.2013.03.016

DO - 10.1016/j.tecto.2013.03.016

M3 - Article

AN - SCOPUS:84879793083

VL - 600

SP - 134

EP - 141

JO - Tectonophysics

JF - Tectonophysics

SN - 0040-1951

ER -