Extremely weak fault planes: An estimate of focal mechanisms from stationary seismic activity in the San'in district, Japan
| Autor: | Itaru Yoneda, Setsuro Nakao, Hiroshi Katao, Yoshihisa Iio, Tsutomu Miura, Shinji Kishimoto, Masayo Sawada |
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| Rok vydání: | 2018 |
| Předmět: |
geography
Focal mechanism geography.geographical_feature_category 010504 meteorology & atmospheric sciences Magnitude (mathematics) Pore fluid pressure Fault (geology) 010502 geochemistry & geophysics 01 natural sciences Stress (mechanics) Stress field Geophysics Shear stress Intraplate earthquake human activities Geology Seismology 0105 earth and related environmental sciences Earth-Surface Processes |
| Zdroj: | Tectonophysics. 723:136-148 |
| ISSN: | 0040-1951 |
| Popis: | In this paper, using data from dense seismic observations in and around the seismic belt of the San'in district, Japan, we describe our analysis of focal mechanisms of stationary seismic activity, estimated stress states, and pore fluid pressures. We found these focal mechanisms to be described by the estimated stress field, suggesting that the stress field can be treated as uniform in each sub-region of the study area. We also found that events occurred even on unfavorably oriented fault planes with small shear stress. Further, we inferred that pore fluid pressures of approximately 20% of the faults analyzed are greater than the magnitude of minimum principal stress, when we assume μ = 0.6. A possible explanation is localized high pore fluid pressure anomalies; another is the coefficient of friction of at least a part of faults analyzed in the study area being substantially smaller than 0.6, which we view as more plausible, since it is difficult to maintain pore fluid pressures higher than the magnitude of minimum principal stress for long periods of time. |
| Databáze: | OpenAIRE |
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