Multiscale estimation of GPS velocity fields
We present a spherical wavelet-based multiscale approach for estimating a spatial velocity field on the sphere from a set of irregularly spaced geodetic displacement observations. Because the adopted spherical wavelets are analytically differentiable, spatial gradient tensor quantities such as dilatation rate, strain rate and rotation rate can be directly computed using the same coefficients. In a series of synthetic and real examples,we illustrate the benefit of themultiscale approach, in particular, the inherent ability of the method to localize a given deformation field in space and scale as well as to detect outliers in the set of observations. This approach has the added benefit of being able to locally match the smallest resolved process to the local spatial density of observations, thereby both maximizing the amount of derived information while also allowing the comparison of derived quantities at the same scale but in different regions.We also consider the vertical component of the velocity field in our synthetic and real examples, showing that in some cases the spatial gradients of the vertical velocity field may constitute a significant part of the deformation. This formulation may be easily applied either regionally or globally and is ideally suited as the spatial parametrization used in any automatic time-dependent geodetic transient detector.
Additional Information© 2009 The Authors. Journal compilation © 2009 RAS. Accepted 2009 July 11. Received 2009 July 10; in original form 2009 March 9. Article first published online: 25 Aug. 2009 We are grateful to John Haines, an anonymous reviewer, and editor John Beavan for comments that improved this manuscript. We thank Jean-Philippe Avouac for helpful discussions. We acknowledge the Southern California Integrated GPS Network and its sponsors, the W.M. Keck Foundation, NASA, NSF, USGS and SCEC, for providing data used in this study. This research was supported in part by the Gordon and Betty Moore Foundation. This is Caltech Tectonic Observatory Contribution 112.
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