Abstract
Abstract. Recent researches have indicated coupling between volcanic eruptions and earthquakes. Some of them calculated static stress transfer in subsurface induced by the occurrences of earthquakes. Most of their analyses ignored the spatial heterogeneity in subsurface, or only took into account the rigidity layering in the crust. On the other hand, a smaller scale heterogeneity of around hundreds of meters has been suggested by geophysical investigations. It is difficult to reflect that kind of heterogeneity in analysis models because accurate distributions of fluctuation are not well understood in many cases. Thus, the effect of the ignorance of the smaller scale heterogeneity on evaluating the earthquake triggering of volcanic eruptions is also not well understood. In the present study, we investigate the influence of the assumption of homogeneity on evaluating earthquake triggering of volcanic eruptions using finite element simulations. The crust is treated as a stochastic media with different heterogeneous parameters (correlation length and magnitude of velocity perturbation) in our simulations. We adopt exponential and von Karman functions as spatial auto-correlation functions (ACF). In all our simulation results, the ignorance of the smaller scale heterogeneity leads to underestimation of the failure pressure around a chamber wall, which relates to dyke initiation. The magnitude of the velocity perturbation has a larger effect on the tensile failure at the chamber wall than the difference of the ACF and the correlation length. The maximum effect on the failure pressure in all our simulations is about twice larger than that in the homogeneous case. This indicates that the estimation of the earthquake triggering due to static stress transfer should take account of the heterogeneity of around hundreds of meters.
Highlights
A causal relationship betweenolafrgthe eearPthqausaktes and followthe spatial heterogeneity in subsurface, or only took into ac- ing volcanic eruptions has been indicated by many researches count the rigidity layering in the crust
We investigate the effect of the ignorance of the smaller spatial scale heterogeneity on evaluating the earthquake triggering of volcanic eruptions by means of calculating failure pressure change around a magma chamber wall (Pinel and Jaupart, 2003; Albino et al, 2010), using finite element simulations
The average of the failure pressure and the standard deviation of that increases with increasing the magnitude of the velocity perturbation
Summary
The mechanical properties of the host rock are characterized by P-wave velocity Vp, mass density ρ and Poisson’s ratio σ. Mass density and Poisson’s ratio are fixed to 2700 kg m−3 and 0.25, respectively. Circular magma chamber, whose diameter D is fixed to 800 m, is embedded in the host rock. The bulk modulus of magma is fixed to 10 GPa. The governing equation in this study is a static equilibrium equation as follows:. The large scale strain is fixed to 1.0 × 10−6. Using a different strain value affects the magnitude of the calculated stress field, the relative magnitude is not changed. We change the correlation length, the magnitude of the velocity perturbation, ACFs and the diameter of the strong heterogeneous region in order to investigate the effect of the smaller scale heterogeneities on evaluating the earthquake triggering of volcanic eruptions
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