Estimation of slip parameters associated with frictional heating during the 1999 Taiwan Chi-Chi earthquake by vitrinite reflectance geothermometry
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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°C ± 25°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°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°C to 626°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.
This study was supported by a Japan Ministry of Education, Culture, Sports, Science and Technology Grant-in-Aid for Young Scientists (A) 23684039, 2013.
Earth, Planets and Space
© 2014 Maekawa et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.