Figure 6

Conceptual diagram to illustrate the mechanism for triggering eruptions at Axial Seamount. Diagrams are not to scale, and gray shading is shown to relate model predictions of Mohr-Coulomb failure to the area of anticipated seismicity in this context. When the pressurization of the magma reservoir is equal to the confining strength of the rock surrounding it, the system is in a state of lithostatic equilibrium and seismicity and surface deformation are not observed (a). As the magma reservoir pressurizes (b) microseismicity, represented by red dots, is observed on shallow faults which accommodate some deformation of the host rock. Deformation and seismicity likely relieve some of the stresses induced on the host rock by pressurization of the reservoir and buffer the system from eruption. Eventually the pressure threshold of ~12–14 MPa is exceeded, at which time high rates of seismicity are observed as magma is intruded to the surface during an eruption (c). Rapid underpressurization of the magma reservoir immediately after eruption causes subsidence of the surface over magma reservoir (d).