Tsai, Victor C. (2011) A model for seasonal changes in GPS positions and seismic wave speeds due to thermoelastic and hydrologic variations. Journal of Geophysical Research B, 116 (B4). Art. No. B04404. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20140616-103542486
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It is known that GPS time series contain a seasonal variation that is not due to tectonic motions, and it has recently been shown that crustal seismic velocities may also vary seasonally. In order to explain these changes, a number of hypotheses have been given, among which thermoelastic and hydrology-induced stresses and strains are leading candidates. Unfortunately, though, since a general framework does not exist for understanding such seasonal variations, it is currently not possible to quickly evaluate the plausibility of these hypotheses. To fill this gap in the literature, I generalize a two-dimensional thermoelastic strain model to provide an analytic solution for the displacements and wave speed changes due to either thermoelastic stresses or hydrologic loading, which consists of poroelastic stresses and purely elastic stresses. The thermoelastic model assumes a periodic surface temperature, and the hydrologic models similarly assume a periodic near-surface water load. Since all three models are two-dimensional and periodic, they are expected to only approximate any realistic scenario; but the models nonetheless provide a quantitative framework for estimating the effects of thermoelastic and hydrologic variations. Quantitative comparison between the models and observations is further complicated by the large uncertainty in some of the relevant parameters. Despite this uncertainty, though, I find that maximum realistic thermoelastic effects are unlikely to explain a large fraction of the observed annual variation in a typical GPS displacement time series or of the observed annual variations in seismic wave speeds in southern California. Hydrologic loading, on the other hand, may be able to explain a larger fraction of both the annual variations in displacements and seismic wave speeds. Neither model is likely to explain all of the seismic wave speed variations inferred from observations. However, more definitive conclusions cannot be made until the model parameters are better constrained.
|Additional Information:||This paper is not subject to U.S. copyright. Published in 2011 by the American Geophysical Union. Received 8 December 2010; revised 9 February 2011; accepted 10 February 2011; published 19 April 2011. The author thanks P. A. Johnson and two anonymous reviewers for helpful comments. This research was supported by the Mendenhall Postdoctoral Fellowship program of the United States Geological Survey.|
|Subject Keywords:||thermoelasticity; poroelasticity; seasonal variations; analytic model|
|Official Citation:||Tsai, V. C. (2011), A model for seasonal changes in GPS positions and seismic wave speeds due to thermoelastic and hydrologic variations, J. Geophys. Res., 116, B04404, doi:10.1029/2010JB008156|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||16 Jun 2014 19:52|
|Last Modified:||23 Nov 2016 20:00|
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