Damage and Strain Localization Around a Pressurized Shallow‐Level Magma Reservoir

Abstract

Structures developing above long‐term growing shallow‐level magma reservoirs, such as resurgent domes, may contain information on the reservoir itself. To understand the formation of such tectonic features, we have investigated the deformation process around a shallow pressurized magma reservoir embedded in a damaging elastic volcanic edifice. Our model allows evidencing the effect of the progressive damage in producing the fault pattern associated to tectonic surface deformation. Damage is first isotropic around the cavity and constitutes a damaged zone. Then the free‐surface effect appears, and an anisotropic shear strain develops from the boundary of the damaged zone; it localizes on reverse faults that propagate upward to the surface. When the surface deformation is sufficient, normal faulting appears. Finally, the complete structure shows an undeformed wedge above the damaged zone. This structure is similar to those found by analog modeling and from field geologic observations. From this model, we found a relation to estimate the reservoir radius and depth from the graben and dome widths. From limit analysis, we deduced an analytical expression of the magma reservoir pressure which provides a better understanding of the magma pressure buildup during doming. The dip of reverse faults limiting the dome can be inferred from the minimal pressure required to rupture the crust around the reservoir. Finally, the magma reservoir overpressure, the dip of the faults, the reservoir depth, and the damaged zone radius are inferred from three parameters: the ratio ρR computed from the dome and graben widths, the cohesion, and the friction angle.

Fault inversion contributes to ground deformation above inflating igneous sills

“…These relationships between sill and restored overburden geometry imply that space for the intruding magma was primarily generated by roof uplift, which itself was facilitated by the localisation of host rock damage (folding) above the western sill termination [e.g. Got et al 2019]. We also note that the monoclinal fold has a present-day relief of ∼50 m above the resolved western sill tip and appears to extend beyond the mapped edge of the sill (Figure 4D and 6).…”

What causes the persistent seismicity below the eastern flank of Piton de la Fournaise (la Réunion Island)? Elasto-plastic models of magma inflation

“…by creep (e.g. Poland et al, 2017;Villeneuve et al, 2018;Got et al, 2019;De Barros et al, 2019). Note that seismicity actually does not necessarily occur in damaged domains but rather at its boundaries with surrounding intact rock mass where there are still cohesive bonds to break; in that sense, the seismic "cup" can draw this contour boundary between intact material at depth and already damaged (e.g.…”

Migration of Mechanical Perturbations Estimated by Seismic Coda Wave Interferometry During the 2018 Pre‐Eruptive Period at Kīlauea Volcano, Hawaii

“…When the magma pressure and reservoir volume still increase, the free‐surface effect deeply modifies the stress field and the associated plastic strain; it induces shear and extension strain along bands and faults above the reservoir (Got et al., 2019). Due to the asymmetric topography of the Kīlauea and the progressive nature of the damage and weakening process, these shear and extension bands are localized along the decollement plane and the ERZ, rather than being distributed homogeneously and randomly all around the caldera.…”

“…(2015), Got et al. (2017, 2019) used a damage approach to model the surface displacements from pre‐eruptive earthquake time series.…”