Fault slip and Coulomb stress variations around a pressured magma reservoir: consequences on seismicity and magma intrusion

Pressure variations in a magma reservoir may cause deformation at the surface and a redistribution of the stress in the surrounding rock. In this study, we use two‐dimensional numerical models and elaborate how magma chamber inflation and deflation affect the stress field around and surface displacement. We test how a pre‐existing normal fault near the magma reservoir may influence the pattern of stress. We demonstrate the possibility of initiating both normal and reverse slip on faults during the inflation of the magma reservoir. The Coulomb failure stress changes are calculated during the periods of pressure variation. An increase of Coulomb failure stress can be predicted above and below the magma chamber during increasing magma chamber pressure that may encourage earthquakes. This process can produce cracks and fault growth encouraging magma propagation along the cracked zone. A different distribution of the stress change is expected in the case of subsequent deflation of the overpressured magma reservoir. In this case, seismicity is expected on a plane at equal depth than the magma chamber, laterally offset from the extent of the magma chamber. Magma could propagate laterally from the magma reservoir into zones where cracks have been generated, but only if the resolved shear stress on the fault is small compared with the excess magma pressure.