We employ near‐field GPS data to determine the subsurface geometry of a collapsing caldera during the 2018 Kīlauea eruption. Collapse occurred in 62 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. Employing an axisymmetric 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 × 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 triaxial point source in a homogeneous half‐space fits the data well but provides a biased representation of the source depth and process.

From August 2018 to May 2019, Kīlauea’s summit exhibited unique, simultaneous, inflation and deflation, apparent in both GPS time series and cumulative InSAR displacement maps. This deformation pattern provides clear evidence that the Halema‘uma‘u (HMM) and South Caldera (SC) reservoirs are distinct. Post‐collapse inflation of the East Rift Zone (ERZ), as captured by InSAR, indicates concurrent magma transfer from the summit reservoirs to the ERZ. We present a physics‐based model that couples pressure‐driven flow between these magma reservoirs to simulate time dependent summit deformation. We take a two‐step approach to quantitatively constrain Kīlauea’s magmatic plumbing system. First, we jointly invert the InSAR displacement maps and GPS offsets for the location and geometry of the summit reservoirs, approximated as spheroidal chambers. We find that HMM reservoir has an aspect ratio of ∼1.8 (prolate) and a depth of ∼2.2 km (below surface). The SC reservoir has an aspect ratio of ∼0.14 (oblate) and a depth of ∼3.6 km. Second, we utilize the flux model to invert GPS time series from 8 summit stations. Results favor a shallow HMM‐ERZ pathway an order of magnitude more hydraulically conductive than the deep SC‐ERZ pathway. Further analysis shows that the HMM‐ERZ pathway is required to explain the deformation time series. Given high‐quality geodetic data, such an approach promises to quantify the connectivity of magmatic pathways between reservoirs in other similar volcanic systems.

In this work, we investigate the April 4, 2010, M_w 7.2 El Mayor Cucapah (EMC) earthquake. Existing studies modeled the EMC area as an elastic half‐space in a homogeneous or vertically layered structure, which, along with differences in data and inversion methodologies, led to considerable variability in the resultant fault slip models. To investigate the EMC earthquake more realistically, we first examine how published coseismic fault slip models have approached the problem and what are their findings, then we select the optimal geometry and slip of one most recent and comprehensive coseismic fault slip model, obtained through analytical inversions, and adapt them in a three‐dimensional finite element numerical environment where we assess the effects of topography and material heterogeneities. Numerically optimized slip models are obtained via joint inversion of GPS, interferometric synthetic aperture radar, and subpixel offset data sets. We find the effect of topography to be negligible while the inclusion of material heterogeneities enhances the slip at depth, as might be expected where the medium has higher rigidity, and better fits the displacements at both near and far field, especially around the Salton Sea area. The match with geodetic data is significantly improved when the fault slip is increased at the fault planes close to the epicenter and deeper at the southernmost plane, with respect to the slip of the chosen analytical model. Our findings suggest that this earthquake was associated with a higher and more spatially concentrated slip than previously thought implying a greater stress drop at depth.

The Long Valley Caldera, located at the eastern edge of the Sierra Nevada range in California, has been in a state of unrest since the late 1970s. Seismic, gravity and geodetic data strongly suggest that the source of unrest is an intrusion beneath the caldera resurgent dome. However, it is not clear yet if the main contribution to the deformation comes from pulses of ascending high-pressure hydrothermal fluids or low viscosity magmatic melts. To characterize the nature of the intrusion, we developed a 3D finite element model which includes topography and crust heterogeneities. We first performed joint numerical inversions of uplift and Electronic Distance Measurement baseline length change data, collected during the period 1985–1999, to infer the deformation-source size, position, and overpressure. Successively, we used this information to refine the source overpressure estimation, compute the gravity potential and infer the intrusion density from the inversion of deformation and gravity data collected in 1982–1998. The deformation source is located beneath the resurgent dome, at a depth of 7.5 ± 0.5 km and a volume change of 0.21 ± 0.04 km³. We assumed a rhyolite compressibility of 0.026 ± 0.0011 GPa⁻¹ (volume fraction of water between 0% and 30%) and estimated a reservoir compressibility of 0.147 ± 0.037 GPa⁻¹. We obtained a density of 1856 ± 72 kg/m³. This density is consistent with a rhyolite melt, with 20% to 30% of dissolved hydrothermal fluids.

We employ near-field GPS data to determine the subsurface geometry of a collapsing caldera during the 2018 Kilauea eruption. Collapse occurred in 62 discrete events with “inflationary’ deformation external to the collapse similar to previous basaltic collapses. We employ GPS data from the collapsing block, and constraints on the magma chamber geometry from inversion of deflation prior to collapse. This provides an unparalleled opportunity to constrain the collapse geometry. Employing an axisymmetric finite element model, the co-collapse displacements are best explained by piston-like subsidence along a steep (~85 degree) normal ring-fault that may steepen with depth. Magma compressibility is 2-15 x 10 Pa, indicating bubble volume fractions from 1 to 7 % (lower if fault steepens with depth). Magma pressure increases during collapses are 1-3 MPa, depending on compressibility. A point source in a half-space fits the data well, but provides a biased representation of the source depth and process.