5:15 PM - 6:45 PM
[SSS05-P14] Modified EASY%Ro model considering the comminution during faulting
Keywords:Vitrinite reflectance, frictional heating, Nankai Trough
Quantifying the temperature due to frictional heating within a fault zone is important for estimating the physical parameters of fault slip during earthquakes. During the International Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), the core sample from the toe of the megasplay fault at Site C0004 off the Kii Peninsula was obtained and was found significantly high vitrinite reflectance as evidence of frictional heating during fault slip (Sakaguchi et al., 2011). Friction experiments using simulated fault gouge containing vitrinite grains have confirmed that vitrinite reflectance increases significantly due to frictional heating during seismic slip (e.g., Kitamura et al., 2012). They also suggested that the increase in vitrinite reflectance within the fault zone cannot be explained by the EASY%Ro model (Sweeney and Burnham, 1990), which has commonly used to estimate the maximum burial temperature. In the EASY%Ro model, the complex maturation processes of vitrinite grains are formulated as a linear combination of several first-order reactions whose reaction rate obey the Arrhenius equation. Although its activation energies are constants dependent on each reaction component, some previous studies have reported that the shear-induced comminution can reduce the activation energies. For instance, Hirono et al. (2013) performed a series of rotary-shear friction experiments using illite powders and demonstrated that the activation energy for illite dehydration progressively decreases with increasing the applied frictional work. Such comminution-induced enhancement of chemical reactions could also happen for the vitrinite maturation, as discussed by Kitamura et al. (2012). Heating experiments after griding friction tests with coal materials have also shown that coal materials tend to mature with grinding (Kaneki et al., 2018). Considering the above, we attempt to develop a vitrinite fault-thermometer to estimate the temperature of frictional heating considering the effect of the shear-induced comminution with seismic fault slip.
In the present study, we modified the EASY%Ro model such that its activation energies are exponentially decreasing functions of frictional work. Our modified model newly requires two constants, i.e., the coefficient that determines the lower limit of activation energies and the characteristic work. Preliminarily modeling results of the parameter study for these two constants demonstrated that the increase in the vitrinite reflectance observed by Kitamura et al. (2012), which is unlikely to be explained by the EASY%Ro model, is reasonably achieved within the parameter range consistent with those reported for clay dehydration. For optimizing the model parameters, we will use the results of vitrinite reflectance measurements and temperature estimation based on the finite element method which are obtained from the friction experiments conducted by Kitamura et al. (2012).
In the present study, we modified the EASY%Ro model such that its activation energies are exponentially decreasing functions of frictional work. Our modified model newly requires two constants, i.e., the coefficient that determines the lower limit of activation energies and the characteristic work. Preliminarily modeling results of the parameter study for these two constants demonstrated that the increase in the vitrinite reflectance observed by Kitamura et al. (2012), which is unlikely to be explained by the EASY%Ro model, is reasonably achieved within the parameter range consistent with those reported for clay dehydration. For optimizing the model parameters, we will use the results of vitrinite reflectance measurements and temperature estimation based on the finite element method which are obtained from the friction experiments conducted by Kitamura et al. (2012).