Finite source modelling of magmatic unrest in Socorro, New Mexico, and Long Valley, California

Abstract

SUMMARY We investigate surface deformation associated with currently active crustal magma bodies in Socorro, New Mexico, and Long Valley, California, USA. We invert available geodetic data from these locations to constrain the overall geometry and dynamics of the inferred deformation sources at depth. Our best‐fitting model for the Socorro magma body is a sill with a depth of 19 km, an effective diameter of 70 km and a rate of increase in the excess magma pressure of 0.6 kPa yr−1. We show that the corresponding volumetric inflation rate is ∼6×10−3 km3 yr−1, which is considerably less than previously suggested. The measured inflation rate of the Socorro magma body may result from a steady influx of magma from a deep source, or a volume increase associated with melting of the magma chamber roof (i.e. crustal anatexis). In the latter case, the most recent major injection of mantle‐derived melts into the middle crust beneath Socorro may have occurred within the last several tens to several hundreds of years. The Synthetic Interferometric Aperture Radar (InSAR) data collected in the area of the Long Valley caldera, CA, between June 1996 and July 1998 reveal an intracaldera uplift with a maximum amplitude of ∼11 cm and a volume of 3.5×10−2 km3. Modelling of the InSAR data suggests that the observed deformation might be due to either a sill‐like magma body at a depth of ∼12 km or a pluton‐like magma body at a depth of ∼8 km beneath the resurgent dome. Assuming that the caldera fill deforms as an isotropic linear elastic solid, a joint inversion of the InSAR data and two‐colour laser geodimeter data (which provide independent constraints on horizontal displacements at the surface) suggests that the inferred magma chamber is a steeply dipping prolate spheroid with a depth of 7–9 km and an aspect ratio in excess of 2:1. Our results highlight the need for large radar look angles and multiple look directions in future InSAR missions.

Phase unwrapping in three dimensions with application to InSAR time series

“…Hooper et al [7] unwrapped PS time series over Long Valley using a 2D algorithm and also found the unwrapping between the two benchmarks to be reasonable. However, the overall pattern of the displacements found by Hooper et al [7] differs to that observed by Fialko et al [28], especially on the west side of the caldera where there appears to be a discontinuity in the former data set. The overall pattern we find using the stepwise 3D algorithm, on the other hand, matches well.…”

Sombrero Uplift Above the Altiplano-Puna Magma Body: Evidence of a Ballooning Mid-Crustal Diapir

“…In both cases, the modeled source of inflation is smaller than the seismically imaged magma body (22). There is indication of subsidence around the central uplift due to the SMB (10,21,22), although the rates of both uplift and subsidence due to the SMB are smaller than those due to the Altiplano-Puna Magma Body and therefore subject to greater uncertainties (Fig. 3).…”

Error estimation in multitemporal InSAR deformation time series, with application to Lanzarote, Canary Islands

“…Successful geophysical applications of classical differential InSAR have started from avoiding error quantification [ Massonnet et al , 1995; Fialko and Simons , 2001] to gradually incorporate some error assessment [ Simons et al , 2002; Knospe and Jonsson , 2010]. Several authors have suggested how to incorporate estimated observational errors for the extraction of geophysical parameters (magma volume, earthquake source parameters, etc.)…”