Co-seismic and post-seismic pore-fluid pressure changes in the Philippine Sea plate and Nankai decollement in response to a seismogenic strain event off Kii Peninsula, Japan

Earl Davis, Keir Becker, Kelin Wang, Masa Kinoshita

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

New pressure data from a pair of Ocean Drilling Program (ODP) hydrologic borehole observatories at ODP Sites 1173 and 808, located off Japan in the subducting Philippine Sea plate and in the nearby Nankai accretionary prism, respectively, show clear signals associated with an earthquake swarm off the Kii Peninsula that began on September 5, 2004, roughly 220 km away from the observatory sites. At Site 1173, formation pressures rose by 1.0-1.5 kPa at the time of the largest earthquake (Mw = 7.5), then continued to rise to a total anomaly of 4 kPa during the following 200-300 days. These transients are inferred to reflect co-seismic and slow continuing volumetric contraction of the plate by amounts of roughly 0.2 × 106 and 0.5 × 106, respectively. The sign of the estimated strain is consistent with that predicted with a seismic-moment-constrained elastic half-space dislocation model, but the amplitude is much larger, by roughly a factor of 6 at the time of the main earthquake, and by nearly a factor of 20 when the total pressure-estimated strain at the end of the post-seismic period is compared to that estimated from the total cumulative seismic moment including aftershocks. The simplest inference that can be drawn is that a large component of aseismic slip occurred in the epicentral area. At Site 808, pressure at the deepest monitoring zone just above the subduction decollement fell at the time of the largest earthquakes. This may reflect shear-induced dilatation which would be consistent with strain- or velocity- hardening behaviour alone this seaward-most part of the subduction thrust interface.

Original languageEnglish (US)
Pages (from-to)649-657
Number of pages9
JournalEarth, Planets and Space
Volume61
Issue number6
StatePublished - 2009

Fingerprint

Philippines
Philippine Sea plate
fluid pressure
decollement
peninsulas
pore pressure
Japan
earthquakes
porosity
seismic moment
drilling
Ocean Drilling Program
earthquake
observatories
oceans
subduction
observatory
moments
earthquake swarm
accretionary prism

Keywords

  • Co-seismic strain
  • CORK borehole observatory
  • Ocean Drilling Program
  • Post-seismic strain

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science

Cite this

@article{1eca6d77158a46c3bfb5295d79f74f1e,
title = "Co-seismic and post-seismic pore-fluid pressure changes in the Philippine Sea plate and Nankai decollement in response to a seismogenic strain event off Kii Peninsula, Japan",
abstract = "New pressure data from a pair of Ocean Drilling Program (ODP) hydrologic borehole observatories at ODP Sites 1173 and 808, located off Japan in the subducting Philippine Sea plate and in the nearby Nankai accretionary prism, respectively, show clear signals associated with an earthquake swarm off the Kii Peninsula that began on September 5, 2004, roughly 220 km away from the observatory sites. At Site 1173, formation pressures rose by 1.0-1.5 kPa at the time of the largest earthquake (Mw = 7.5), then continued to rise to a total anomaly of 4 kPa during the following 200-300 days. These transients are inferred to reflect co-seismic and slow continuing volumetric contraction of the plate by amounts of roughly 0.2 × 106 and 0.5 × 106, respectively. The sign of the estimated strain is consistent with that predicted with a seismic-moment-constrained elastic half-space dislocation model, but the amplitude is much larger, by roughly a factor of 6 at the time of the main earthquake, and by nearly a factor of 20 when the total pressure-estimated strain at the end of the post-seismic period is compared to that estimated from the total cumulative seismic moment including aftershocks. The simplest inference that can be drawn is that a large component of aseismic slip occurred in the epicentral area. At Site 808, pressure at the deepest monitoring zone just above the subduction decollement fell at the time of the largest earthquakes. This may reflect shear-induced dilatation which would be consistent with strain- or velocity- hardening behaviour alone this seaward-most part of the subduction thrust interface.",
keywords = "Co-seismic strain, CORK borehole observatory, Ocean Drilling Program, Post-seismic strain",
author = "Earl Davis and Keir Becker and Kelin Wang and Masa Kinoshita",
year = "2009",
language = "English (US)",
volume = "61",
pages = "649--657",
journal = "Earth, Planets and Space",
issn = "1343-8832",
publisher = "Terra Scientific Publishing Company",
number = "6",

}

TY - JOUR

T1 - Co-seismic and post-seismic pore-fluid pressure changes in the Philippine Sea plate and Nankai decollement in response to a seismogenic strain event off Kii Peninsula, Japan

AU - Davis, Earl

AU - Becker, Keir

AU - Wang, Kelin

AU - Kinoshita, Masa

PY - 2009

Y1 - 2009

N2 - New pressure data from a pair of Ocean Drilling Program (ODP) hydrologic borehole observatories at ODP Sites 1173 and 808, located off Japan in the subducting Philippine Sea plate and in the nearby Nankai accretionary prism, respectively, show clear signals associated with an earthquake swarm off the Kii Peninsula that began on September 5, 2004, roughly 220 km away from the observatory sites. At Site 1173, formation pressures rose by 1.0-1.5 kPa at the time of the largest earthquake (Mw = 7.5), then continued to rise to a total anomaly of 4 kPa during the following 200-300 days. These transients are inferred to reflect co-seismic and slow continuing volumetric contraction of the plate by amounts of roughly 0.2 × 106 and 0.5 × 106, respectively. The sign of the estimated strain is consistent with that predicted with a seismic-moment-constrained elastic half-space dislocation model, but the amplitude is much larger, by roughly a factor of 6 at the time of the main earthquake, and by nearly a factor of 20 when the total pressure-estimated strain at the end of the post-seismic period is compared to that estimated from the total cumulative seismic moment including aftershocks. The simplest inference that can be drawn is that a large component of aseismic slip occurred in the epicentral area. At Site 808, pressure at the deepest monitoring zone just above the subduction decollement fell at the time of the largest earthquakes. This may reflect shear-induced dilatation which would be consistent with strain- or velocity- hardening behaviour alone this seaward-most part of the subduction thrust interface.

AB - New pressure data from a pair of Ocean Drilling Program (ODP) hydrologic borehole observatories at ODP Sites 1173 and 808, located off Japan in the subducting Philippine Sea plate and in the nearby Nankai accretionary prism, respectively, show clear signals associated with an earthquake swarm off the Kii Peninsula that began on September 5, 2004, roughly 220 km away from the observatory sites. At Site 1173, formation pressures rose by 1.0-1.5 kPa at the time of the largest earthquake (Mw = 7.5), then continued to rise to a total anomaly of 4 kPa during the following 200-300 days. These transients are inferred to reflect co-seismic and slow continuing volumetric contraction of the plate by amounts of roughly 0.2 × 106 and 0.5 × 106, respectively. The sign of the estimated strain is consistent with that predicted with a seismic-moment-constrained elastic half-space dislocation model, but the amplitude is much larger, by roughly a factor of 6 at the time of the main earthquake, and by nearly a factor of 20 when the total pressure-estimated strain at the end of the post-seismic period is compared to that estimated from the total cumulative seismic moment including aftershocks. The simplest inference that can be drawn is that a large component of aseismic slip occurred in the epicentral area. At Site 808, pressure at the deepest monitoring zone just above the subduction decollement fell at the time of the largest earthquakes. This may reflect shear-induced dilatation which would be consistent with strain- or velocity- hardening behaviour alone this seaward-most part of the subduction thrust interface.

KW - Co-seismic strain

KW - CORK borehole observatory

KW - Ocean Drilling Program

KW - Post-seismic strain

UR - http://www.scopus.com/inward/record.url?scp=70350158684&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=70350158684&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:70350158684

VL - 61

SP - 649

EP - 657

JO - Earth, Planets and Space

JF - Earth, Planets and Space

SN - 1343-8832

IS - 6

ER -