scholarly journals Seismic inversion analysis for sedimentary layers in the Nankai Trough off Kumano, southwest Japan

2014 ◽  
Vol 67 (3) ◽  
pp. 181-194
Author(s):  
Kazuya Naito ◽  
Jin-Oh Park
Keyword(s):  
Nankai Trough ◽  
Seismic Inversion ◽  
Southwest Japan ◽  
Inversion Analysis

scholarly journals Driving stress and seismotectonic implications of the 2013 Mw5.8 Awaji Island earthquake, southwestern Japan, based on earthquake focal mechanisms before and after the mainshock

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Kazutoshi Imanishi ◽  
Makiko Ohtani ◽  
Takahiko Uchide
Keyword(s):  
Stress Field ◽  
Stress Tensor ◽  
Nankai Trough ◽  
Source Region ◽  
Local Scale ◽  
Southwest Japan ◽  
Stress Tensor Inversion ◽  
Earthquake Fault ◽  
Reverse Faulting ◽  
Before And After

Abstract A driving stress of the Mw5.8 reverse-faulting Awaji Island earthquake (2013), southwest Japan, was investigated using focal mechanism solutions of earthquakes before and after the mainshock. The seismic records from regional high-sensitivity seismic stations were used. Further, the stress tensor inversion method was applied to infer the stress fields in the source region. The results of the stress tensor inversion and the slip tendency analysis revealed that the stress field within the source region deviates from the surrounding area, in which the stress field locally contains a reverse-faulting component with ENE–WSW compression. This local fluctuation in the stress field is key to producing reverse-faulting earthquakes. The existing knowledge on regional-scale stress (tens to hundreds of km) cannot predict the occurrence of the Awaji Island earthquake, emphasizing the importance of estimating local-scale (< tens of km) stress information. It is possible that the local-scale stress heterogeneity has been formed by local tectonic movement, i.e., the formation of flexures in combination with recurring deep aseismic slips. The coseismic Coulomb stress change, induced by the disastrous 1995 Mw6.9 Kobe earthquake, increased along the fault plane of the Awaji Island earthquake; however, the postseismic stress change was negative. We concluded that the gradual stress build-up, due to the interseismic plate locking along the Nankai trough, overcame the postseismic stress reduction in a few years, pushing the Awaji Island earthquake fault over its failure threshold in 2013. The observation that the earthquake occurred in response to the interseismic plate locking has an important implication in terms of seismotectonics in southwest Japan, facilitating further research on the causal relationship between the inland earthquake activity and the Nankai trough earthquake. Furthermore, this study highlighted that the dataset before the mainshock may not have sufficient information to reflect the stress field in the source region due to the lack of earthquakes in that region. This is because the earthquake fault is generally locked prior to the mainshock. Further research is needed for estimating the stress field in the vicinity of an earthquake fault via seismicity before the mainshock alone.

Experimental Evaluation of Initial Characteristics of DONET Pressure Sensors

2018 ◽  
Vol 52 (3) ◽  
pp. 109-119
Author(s):  
Hiroyuki Matsumoto ◽  
Eiichiro Aaraki ◽  
Katsuyoshi Kawaguchi
Keyword(s):  
Nankai Trough ◽  
Pressure Sensors ◽  
Initial Response ◽  
Hydraulic Pressure ◽  
Network System ◽  
Southwest Japan ◽  
Operational Life ◽  
Pressure Standard ◽  
Pressure Changes

AbstractThe dense ocean floor network system for detecting earthquakes and tsunamis, DONET, began its operations in the Nankai Trough, southwest Japan, in 2010. The present study focuses on the pressure sensors used in DONET observatories to measure hydraulic pressure changes. Pressure sensors specify their performance for both hysteresis and repeatability; however, no details of the sensors' stability are currently available. It is known that pressure sensors typically show a drift in their readings over their operational life span. We evaluated the initial behavior of the pressure sensors before deployment into the deep sea by using our own high accuracy pressure standard. In our experiment, 20 MPa of hydrostatic pressure is applied to the pressure sensors under a constant temperature of 2°C for a duration of 1 month. Our experiment suggests that the procedure is effective at clarifying the initial response and stability of the pressure sensors before deployment. It is proved that the repeatability of the initial response is well reproduced. Then the in situ measurements are processed and compared to the experimental measurements. The pressure sensors, to which a pressure equivalent to the deployed depth is applied, show that the sensor drift in the experiment corresponds in rate and direction to that from the in situ measurements.

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