| Abstract |
A numerical model was used for a geomechanical analysis of dike formation beneath the Kryaksky Volcano, which was active during 2008 through 2009. We investigated whether seismicity associated with the volcanic activity may have been influenced by flow of magma into preexisting fault structures. In our conceptual model, magma flowed into a 2 km (along dip) by 2 km (along strike) fracture located at a depth of 6000 m (-3000 m abs.) with a dip angle of 60. In the model, magma was injected into the fracture over the period of one day at a rate of 2000 kg/s and a maximum pressure of 200 MPa. The initial fluid pressure in the fault was 50 MPa. The magma density was 2800 kg/m3. We tested various magma viscosities ranging from 200 Pa s (andesitic magma) to 2 Pa s (basaltic magma). The state of stress in the study are was determined in a previous study. The numerical model was used to calculate distributions of fluid pressure distribution, normal stress, fracture opening, shear displacement, and sliding velocity in the fracture. The behavior was characterized by fluid pressure of 60 to 65 MPa (overpressure of 10 to 15 MPa) within a 500 m radius of the location of magma injection. We observed opening displacements of 0.02 m in the periphery to 0.3 m at center. The volume of dyke formed by magma injection corresponded to magma flow rate and was 60.8 x 103 m3. As magma injection occurred into the fracture, a reduction in the effective normal stress caused the fracture to slip. Slip occurred in a normal faulting mechanism. The cumulative shear slip discontinuity was roughly 1 m near the fracture periphery and roughly 3 m near the location where magma injection occurred. The maximum velocities of shear displacement of the fracture walls was observed to be 2 x 10-3 m/s (for the case with reduced viscosity basaltic magma), which corresponds to the hypocentral zones of plane-oriented earthquake clusters. |