资源环境科技发展态势分析平台

We employ near‐field GPS data to determine the subsurface geometry of a collapsing caldera during the 2018 Kīlauea eruption. Collapse occurred in 6 discrete events, with ``inflationary” deformation external to the collapse, similar to previous basaltic collapses. We take advantage of GPS data from the collapsing block, and independent constraints on the magma chamber geometry from inversion of deflation prior to collapse onset. This provides an unparalleled opportunity to constrain the collapse geometry. Employin an axi‐symmetric finite element model, the co‐collapse displacements are best explained by piston‐like subsidence along a high angle (~85°) normal ring‐fault that may steepen to vertical with depth. Reservoir magma has compressibility of 2 → 15 x 10^‐10 Pa^‐1, indicating bubble volume fractions from 1 to 7% (lower if fault steepens with depth). Magma pressure increases during collapses are 1 to 3 MPa, depending on compressibility. Depressurization of a tri‐axial point source in a homogeneous half‐space fits the data well, but provides a biased representation of the source depth and process.