Paleo-stress and temperatures based on calcite twin and vitrinite reflectance in the Nojima Fault, SW Japan
Abstract
The seismogenic fault must experience rupture propagation and frictional slip during earthquakes. The record of this process can be estimated from heat and stress records at principal shear zone of fault. In recent, some methods were developed to detect heat and stress from fault rocks. The organic materials in sediment are delicate with heating to be sensitive geo-thermometer. The vitrinite reflectance and Raman spectra analysis were applied for detection of fault heating. The mechanical twin of calcite depends on shear stress, and twin density method is proposed to estimate paleo-stress for fault rock in brittle regime. The Nojima Fault develops at Awaji Island SW Japan is the seismogenic fault of the 1995 Kobe earthquake. The Nojima Fault strikes northeast - south west and bounds Ryoke Granite and Pleistocene Osaka Groups. The Ryoke Granite thrusts up the Osaka Group and suffers deformation more than several ten meters. This damage zone is characterized by brittle failure, and some cracks are filled with fine calcite minerals. The Osaka Group is composed of a sandstone and silt layers, and contacts with Ryoke Granite at silt layer. The fault related folds are observed around the fault zone, and some granite blokes are scattered within the Osaka Group . In micro structure, possible principal shear zone of narrow dark seem of 5 mm in thickness is developed within the silt layer of the Osaka Group. Some coal laminas are included in the Osaka Group, and the vitrinite reflectance was approximately 0.2%. The estimated paleo-temperature of the host rock is approximately several ten degrees. Such low temperature of the sediment must be obtained shallow burial depth, and the sediment may record recent fault activity. Low temperature host rock can detect small signal of frictional heat.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T43D3081O
- Keywords:
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- 1140 Thermochronology;
- GEOCHRONOLOGYDE: 8010 Fractures and faults;
- STRUCTURAL GEOLOGYDE: 8030 Microstructures;
- STRUCTURAL GEOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS