Numerical comparative analysis of functional mechanism of typical reservoir triggered earthquake

Since the 1960s, with the development of economy and the improvement of living standard, the demand for water resource of industrial consumption and agricultural water and domestic water is increasing. This in turn led reservoir quickly become one of the most important measures in water conservancy projects. However, after the impoundment of reservoir, not only water load put enormous compressive stress on the bottom rock of the reservoir area, but also cause head pressure and pore pressure which would diffuse along the stratum, fracture zone, faults, fissures and other tectonics structure. So, after Carder firstly pointed out the relationship between the Boulder Reservoir and local earthquake activities in the 1940s, there are four well acknowledged reservoir triggered earthquakes (RTE) with magnitude ≥ 6.0 to date. And the M_s 6.1 earthquake in the Xinfengjiang Reservoir in China in 1962 is well acknowledged as one of the four.

In this study, based on the existing research of the geological background of the typical RTEs (M _s6.3 in Koyna, M_s6.1 in Xinfengjiang, M_L5.7 in Aswan, M6.1 in Kariba), we apply the fully poroelastic theory to discuss the physical mechanism of RTE. To better understand the RTE mechanism, three-dimensional high-resolution finite element models which adopting precise topography and dynamic water level are employed to simulate the complicated stress and pore pressure fields. Besides, distribution of Coulomb failure stress changes (ΔCFS) varying with time and accumulation of strain energy in the reservoir region are also calculated.

Primary results suggest that diffused pore pressure was likely the main factor that triggered the Answan and Xinfengjiang RTEs, whereas the elastic water load directly induced the M6.1 Kariba earthquake. ΔCFS values of hypocenters can be vary from several kPa to 0.1MPa. However, diffusion coefficient or permeability dramatically affected the computational results. Besides, the accumulated strain energy caused by the Xinfengjiang Reservoir was less than 1% of the energy released by the Ms6.1 earthquake. In addition, more studies about specific geological information, geological structure, and geodynamic environment are needed.