Simulations of dike intrusion and ground deformation by SPH and DEM

Precise seismic and geodetic observation networks reveal the detail migration beneath volcano. For example, successive dike intrusions in several years were observed in 1990s at East-off of Izu-Peninsula, Japan, revealed by hypocenter distribution (Morita et al., 2006) and magma intrusion and lateral migration was observed at Miyakejima volcano, Japan, in 2000 (Ueda et al., 2005). To detect the locations and volumetric changes of the source of ground deformation, Mogi-model (1958) and Okada-model (1985, 1992) have been widely used and these enables us to identify the source quickly, in some cases, automatically. However these models assume isotropic and homogeneous crust, it is necessary to evaluate the effect of anisotropy and heterogeneity of volcanic body, as well as the fractures due to dike intrusion. We will discuss multi-scale phenomena, i.e. microscopic fracture to macroscopic ground deformation, so we adapt the smoothed particle hydrodynamics method (SPH) and discrete element method (DEM). 1. SPH simulation: SPH method defines the kernel function to characterize the coupling between particles as a smoothing scheme. The algorithm and discretization procedures are easy. In our preliminary analysis (both 2D and 3D), we assume a fluid magma chamber / dike in an elastic medium, and triggers magma particle to move, then we obtain some fractured region around intruded magma and ground deformations. 2. DEM simulation: DEM defines the spring and dash-pot coefficient between particles and introduces failure criterion. Our preliminary analysis (2D) simulates the rectangular magma (dike) expansion and the result shows some nearby fractures and ground deformation of inflation. (The SPH and DEM programs are originally coded by Takashi Matsushima, Tsukuba Univ.)