Changes in physical properties of the Nankai Trough megasplay fault induced by earthquakes, detected by continuous pressure monitoring

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doi: 10.1002/2017JB014924
Author(s): Kinoshita, Chihiro; Saffer, D.; Kopf, A.; Roesner, A.; Wallace, L. M.; Araki, E.; Kimura, T.; Machida, Y.; Kobayashi, R.; Davis, E.; Toczko, S.; Carr, S.
Author Affiliation(s): Primary:
Kyoto University, Disaster Prevention Research Institute, Kyoto, Japan
Other:
Pennsylvania State University, United States
University of Bremen, Germany
University of Texas at Austin, United States
Japan Agency for Marine-Earth Science and Technology, Japan
Kagoshima University, Japan
Canadian Geological Survey, Canada
Bigelow Laboratory for Ocean Sciences, United States
Volume Title: Journal of Geophysical Research: Solid Earth
Source: Journal of Geophysical Research: Solid Earth, 123(2), p.1072-1088. Publisher: Wiley-Blackwell for American Geophysical Union, Washington, DC, United States. ISSN: 2169-9313
Note: In English. 73 refs.; illus., incl. sect., 2 tables, sketch map
Summary: One primary objective of Integrated Ocean Drilling Program Expedition 365, conducted as part of the Nankai Trough Seismogenic Zone Experiment, was to recover a temporary observatory emplaced to monitor formation pore fluid pressure and temperature within a splay fault in the Nankai subduction zone offshore SW Honshu, Japan. Here we use a 5.3 year time series of formation pore fluid pressure, and in particular the response to ocean tidal loading, to evaluate changes in pore pressure and formation and fluid elastic properties induced by earthquakes. Our analysis reveals 31 earthquake-induced perturbations. These are dominantly characterized by small transient increases in pressure (28 events) and decreases in ocean tidal loading efficiency (14 events) that reflect changes to formation or fluid compressibility. The observed perturbations follow a magnitude-distance threshold similar to that reported for earthquake-driven hydrological effects in other settings. To explore the mechanisms that cause these changes, we evaluate the expected static and dynamic strains from each earthquake. The expected static strains are too small to explain the observed pressure changes. In contrast, estimated dynamic strains correlate with the magnitude of changes in both pressure and loading efficiency. We propose potential mechanism for the changes and subsequent recovery, which is exsolution of dissolved gas in interstitial fluids in response to shaking. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
Year of Publication: 2018
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 16 Structural Geology; 19 Geophysics, Seismology; Detection; Earthquakes; Expedition 319; Expedition 365; Faults; IODP Site C0010; Instruments; Integrated Ocean Drilling Program; International Ocean Discovery Program; Loading; Mechanism; Monitoring; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Ocean floors; P-T conditions; Pacific Ocean; Physical properties; Pore pressure; Pore water; Pressure; Seismotectonics; Solution; Statistical analysis; Strain; Stress; Subduction zones; Tectonics; Time series analysis; Variations; West Pacific
Coordinates: N331236 N331236 E1364112 E1364112
Record ID: 2018083202
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom