A four-dimensional viscoelastic deformation model for Long Valley Caldera, California, between 1995 and 2000

AV Newman, TH Dixon, N Gourmelen

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We investigate the effects of viscoelastic (VE) rheologies surrounding a vertically dipping prolate spheroid source during an active period of time-dependent deformation between 1995 and 2000 at Long Valley caldera. We model a rapid magmatic inflation episode and slip across the South Moat fault (SMF) in late 1997. We extend the spherical VE shell model of Newman et al. [Newman, A.V, Dixon, T.H., Ofoegbu, G., Dixon, J.E., 2001. Geodetic and seismic constraints on recent activity at Long Valley caldera, California: Evidence for viscoelastic rheology. J. Volcanol. Geotherm. Res. 105, 183-206.] to include a prolate spheroid geometry more accurately representing the probable source geometry inferred from other studies. This paper presents the first attempt to geodetically constrain the volcanic deformation source volume at Long Valley, a parameter for hazard assessment. Including fault slip along the SMF explains significant deformation observed with several EDM baselines and components of two continuous GPS time series. Additionally, the model explains the spatial extent of deformation observed by InSAR data covering the 1997-98 inflation episode. For the time period studied, the VE model requires modest pressure changes (maximum of 14.3 MPa) that are far lower than the overburden pressure (similar to 115 MPa), and less than the maximum for a purely elastic model with the same geometry and elastic strength (similar to 45 MPa). Thus, the inclusion of a realistic VE component significantly lowers the inferred pressures necessary to explain observed surface deformation. Though our model is non-unique, it is consistent with a broader variety of data compared to purely elastic models. Only right-lateral slip, and not dilitation, was necessary to explain offsets in EDM data near and crossing the SMF. (c) 2005 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)244-269
Number of pages26
JournalJournal of Volcanology and Geothermal Research
Volume150
Issue number1-3
DOIs
Publication statusPublished - 1 Feb 2006

Keywords / Materials (for Non-textual outputs)

  • global positioning system
  • finite element analysis
  • Long Valley Caldera
  • viscoelasticity
  • magma chambers
  • ALGORITHM INVERSION TECHNIQUE
  • EASTERN CALIFORNIA
  • VOLCANIC SOURCES
  • HYDROTHERMAL SYSTEM
  • 2-COLOR GEODIMETER
  • TIME-SERIES
  • HALF-SPACE
  • INFLATION
  • UNREST
  • GPS

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