Francis Anthony Dahlen

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We present tomographic evidence for the existence of deep-mantle thermal convection plumes. P-wave velocity images show at least six well-resolved plumes that extend into the lowermost mantle: Ascension, Azores, Canary, Easter, Samoa, and Tahiti. Other less well-resolved plumes, including Hawaii, may also reach the lowermost mantle. We also see several(More)
An active fold-and-thrust belt in unchanging tectonic and climatic conditions attains a dynamic steady-state in which the influx of accreted material at the toe is balanced by the erosive efflux off the top. The overall balance of energy in such a steady-state fold-and-thrust belt is described by the equation E = W(G) + Q, where E is the rate at which both(More)
S U M M A R Y We propose the use of 1 regularization in a wavelet basis for the solution of linearized seismic tomography problems Am = d, allowing for the possibility of sharp discontinuities superimposed on a smoothly varying background. An iterative method is used to find a sparse solution m that contains no more fine-scale structure than is necessary to(More)
S U M M A R Y This paper presents a comparison of ray-theoretical and finite-frequency traveltime tomography for compressional waves. Our data set consists of 86 405 long-period P and PP–P traveltimes measured by cross-correlation. The traveltime of a finite-frequency wave is sensitive to anomalies in a hollow banana-shaped region surrounding the(More)
The efficient computation of finite-frequency traveltime and amplitude sensitivity kernels for velocity and attenuation perturbations in global seismic tomography poses problems both of numerical precision and of validity of the paraxial approximation used. We investigate these aspects, using a local model parameterization in the form of a tetrahedral grid(More)
We present a dynamic ray tracing program for a spherically symmetric Earth that may be used to compute Fréchet kernels for traveltime and amplitude anomalies at finite frequency. The program works for arbitrarily defined phases and background models. The numerical precisions of kinematic and dynamic ray tracing are optimized to produce traveltime errors(More)
Earthquake seismology is being nourished by a growing body of observational constraints on the structure of fault zones, including geological field studies of exhumed faults (Chester et al., 1993), classical and guided-wave fault-zone tomographic studies (Catchings et al., 2002; Thurber et al., 2003; Ben-Zion, 1998; Li et al., 2000), high-resolution(More)
We propose the use of l1 regularization in a wavelet basis for the solution of linearized seismic tomography problems Am = d, allowing for the possibility of sharp discontinuities superimposed on a smoothly varying background. An iterative method is used to find a sparse solution m that contains no more fine-scale structure than is necessary to fit the data(More)
We use ray theory to model the propagation of Lg waves through 2D and 3D layered crustal models. The layers are homogeneous, and the discontinuities are undulating. The Lg wave train is modelled by multiple S reflections within the crustal layers. The ray tracing system is reduced from a set of linear differential equations to a set of maps. If the medium(More)