Journal
EARTH PLANETS AND SPACE
Volume 66, Issue -, Pages -Publisher
SPRINGER HEIDELBERG
DOI: 10.1186/1880-5981-66-28
Keywords
Carbonaceous material; Thermal maturation; Fault friction; Chelungpu fault
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Funding
- Japan Ministry of Education, Culture, Sports, Science and Technology [23684039]
- Grants-in-Aid for Scientific Research [25800284, 22224010, 23684039] Funding Source: KAKEN
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To estimate the slip parameters and understand the fault lubrication mechanism during the 1999 Taiwan Chi-Chi earthquake, we applied vitrinite reflectance geothermometry to samples retrieved from the Chelungpu fault. We found a marked reflectance anomaly of 1.30%+/- 0.21% in the primary slip zone of the earthquake, whereas the reflectances in the surrounding deformed and host rocks were 0.45% to 0.77%. By applying a kinetic model of vitrinite thermal maturation together with a one-dimensional heat and thermal diffusion equation, we determined the shear stress and peak temperature in the slip zone during the earthquake to be 1.00 +/- 0.04 MPa and 626 degrees C +/- 25 degrees C, respectively. Taking into account the probable overestimation of the temperature owing to a mechanochemically enhanced reaction or flash heating at grain contacts, this temperature should be considered an upper limit. The lower limit was previously constrained to 400 degrees C by studies of fluid-mobile trace-element concentrations and magnetic minerals. Therefore, we inferred that the peak temperature during the Chi-Chi earthquake was 400 degrees C to 626 degrees C, corresponding to an apparent friction coefficient of 0.01 to 0.06. Such low friction and the previous evidence of a high-temperature fluid suggest that thermal pressurization likely contributed to dynamic weakening during the Chi-Chi earthquake.
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