Two improved version of the Load / Unload Response Ratio method for forecasting large earthquakes and strong aftershocks
Speaker: Shao Yi-lien
Abstract
From the viewpoint of fracture mechanics, the preparation process of an earthquake is basically the damage process of the hypocentral media. LURR has been proposed as a measure characterizing the evolution of the damage process of the crust and is calculated from the seismicity variations during loading cycles respectively during the unloading cycles. The loading-unloading cycles are performed by the stress changes induced by the Earth tides acting upon some specific fault plane. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. First, Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. Yu et al. replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. Second, Earthquake clustering effects, such as the rapid decay of aftershocks and second-stage aftershocks, cause large fluctuations in the LURR. In order to eliminate the influence of such clustering, Zhang and Zhuagn introduce a new formula for calculating the LURR, taking the epidemictype aftershock sequence (ETAS) model as the baseline seismicity. These new LURR performs better than the original LURR.
Reference
Yin Xiang-chu, H.Z. Yu, et al (2004). Load-Unload Response Ratio (LURR), Accelerating Moment / Energy Release (AM/ER) and State Vector Saltation as precursors to failure of rock specimens. Pure and Applied Geophysics 161, 2405-2416.
Yu Huai-zhong, Z. Shen, et al (2006). Increasing critical sensitivity of the Load / Unload Response Ratio before large earthquakes with identified stress accumulation pattern. Tectonophysics 428, 87-94.
Zhang Lang-ping and J. Zhuang (2011). An improved version of the Load / Unload Response Ratio method for forecasting strong aftershocks. Tectonophysics 509, 191-197.