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 language | English (US) |
|---|---|
| Pages (from-to) | 649-657 |
| Number of pages | 9 |
| Journal | Earth, Planets and Space |
| Volume | 61 |
| Issue number | 6 |
| State | Published - 2009 |
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Keywords
- Co-seismic strain
- CORK borehole observatory
- Ocean Drilling Program
- Post-seismic strain
ASJC Scopus subject areas
- Geology
- Space and Planetary Science
Cite this
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. / Davis, Earl; Becker, Keir; Wang, Kelin; Kinoshita, Masa.
In: Earth, Planets and Space, Vol. 61, No. 6, 2009, p. 649-657.Research output: Contribution to journal › Article
}
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 -