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AIST:Research Highlights, Retention of High Fluid Pressure Near Plate Boundaries After Earthquakes

Geological Survey of Japan

Retention of High Fluid Pressure Near Plate Boundaries After Earthquakes

OTSUBO Makoto
Research Institute of Earthquake and Volcano Geology
MIYAKAWA Ayumu
Research Institute of Geology and Geoinformation

Released: August 3, 2020

Fluid pressure near plate boundaries maintained at a higher level after earthquakes than previously predicted

We estimated the fluid pressure near a past plate boundary similar to the Nankai Trough. The results showed that the change in fluid pressure before and after an earthquake was less than previously predicted, and fluid pressure was maintained at a higher level after the earthquake than previously predicted.

(a) Schematic diagram of drainage from cracks formed after a large earthquake, (b)
Relationship between fluid pressure and conditions leading to repeated earthquakes. Earthquakes could occur near a plate boundary when the fluid pressure accumulating near the plate boundary builds up to around the maximum level.

Fluid pressure near the plate boundary is the key to earthquake occurrence

Understanding the mechanism of large earthquakes along plate boundaries such as the Nankai Trough is essential to estimate the risk of earthquake disasters. The temporal buildup of pore fluid pressure during the seismic cycle may promote the earthquake occurrences. But the decrease in the fluid pressure is not estimated. Accurate estimation of the order of the fluid pressure change contributes to the understanding of the conditions under which the next earthquake would occur.

Fluid pressure near the focal area in the Nankai Trough is maintained at a higher level than previous assumptions

A "crack model" based on observation and analysis results of the Nobeoka Thrust in Miyazaki Prefecture (on-land analog of the Nankai Trough) indicates the temporal changes of the fluid pressure. Results by the crack model show that the fluid pressure near the focal area in the Nankai Trough is maintained at a higher level than the estimation by previous studies. Our estimated temporal changes (10 MPa) are one-tenth of previous studies (~120 MPa).

Long-term monitoring of fluid pressure near the plate boundary is proposed to contribute to the prediction of the occurrences of large Nankai Trough earthquakes

We intend to quantitatively study the behavior of fluid near the plate boundary using the rock samples obtained in excavation surveys off the Kii Peninsula by the Deep-sea Scientific Drilling Vessel "CHIKYU". We propose long-term monitoring of the fluid pressure (long-term observation of temporal changes of 10 MPa order) near the plate boundary to increase the prediction accuracy for large earthquakes occurring in the Nankai Trough.

Contact for inquiries related to this theme

Geodynamics Research Group, Research Institute of Earthquake and Volcano Geology

OTSUBO Makoto, Chief Senior Researcher

AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567 Japan

E-mail: ievg-webmaster-ml*aist.go.jp (Please convert "*" to "@".)

Web: https://unit.aist.go.jp/ievg/en/index.html

Geophysics Research Group, Research Institute of Geology and Geoinformation

MIYAKAWA Ayumu, Senior Researcher

AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567 Japan

E-mail: igg-webmaster-ml*aist.go.jp (Please convert "*" to "@".)

Web: https://unit.aist.go.jp/igg/geophy-rg/

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