5:15 PM - 7:15 PM
[SSS10-P17] Quantitative evaluation of surface fracture energy in minor fault adjacent to the Taiwan Chelungpu fault
Keywords:surface fracture energy, breakdown work, seismic moment
The earthquake drives the release of stored elastic strain energy accumulated on the fault, which is distributed as dissipated energy and radiated energy. The energy budget is essential to estimate the earthquake's scale and the fault's stress level. However, the energetics of minor faults, which is here defined as a fault has roughly a small thickness less than 1cm and/or a slip distance under 1 m, rarely have been studied. Thus, we tried to estimate the surface fracture energy from the minor fault obtained TCDP, having 1-cm thick black gouge, by analyzing grain images under scanning electron microscope (SEM) and optical microscope.
We obtained the surface fracture energy by applying the formula of U = ASZγλ(Chester et al. , 2005), in which ASZ is the surface area per meters squared area during the slip, γ is a specific fracture energy, and λ is the correction value. We obtained ASZ = 1.5×104 m2 per meter squared area by calculating through images of microscopes for the minor fault. By assumingγ= 1 J/m2 and λ= 6.6, we estimated that the surface fracture energy of the minor fault is 0.1 MJ/m2. In addition, we tried to assess the breakdown work of the minor fault by using this value. Assuming the ratio calculated by Ma et al. (2006) of breakdown work to surface fracture energy, 6%, we estimated the value of 1.68 MJ/m2. We also estimated the seismic moment of the minor fault. By assuming that the fault length is several cracks length observed on outcrops, 2–60 m and by apllying empirical formulas for Matsuda (1975) and Iio (1986), we obtained the values of the seismic moment to be 4.6×109 –1.1×1013 Nm.
We compared these data with the scaling law which was estimated the breakdown work and the seismic moment through earthquake observations by Cocco et al. (2008), and found that the values of the minor fault is out of the law. In the presentation, we will show more updated discussion.
We obtained the surface fracture energy by applying the formula of U = ASZγλ(Chester et al. , 2005), in which ASZ is the surface area per meters squared area during the slip, γ is a specific fracture energy, and λ is the correction value. We obtained ASZ = 1.5×104 m2 per meter squared area by calculating through images of microscopes for the minor fault. By assumingγ= 1 J/m2 and λ= 6.6, we estimated that the surface fracture energy of the minor fault is 0.1 MJ/m2. In addition, we tried to assess the breakdown work of the minor fault by using this value. Assuming the ratio calculated by Ma et al. (2006) of breakdown work to surface fracture energy, 6%, we estimated the value of 1.68 MJ/m2. We also estimated the seismic moment of the minor fault. By assuming that the fault length is several cracks length observed on outcrops, 2–60 m and by apllying empirical formulas for Matsuda (1975) and Iio (1986), we obtained the values of the seismic moment to be 4.6×109 –1.1×1013 Nm.
We compared these data with the scaling law which was estimated the breakdown work and the seismic moment through earthquake observations by Cocco et al. (2008), and found that the values of the minor fault is out of the law. In the presentation, we will show more updated discussion.