Mount St Helens is the most active volcano within the Cascade arc; however, its location is unusual because it lies 50 km west of the main axis of arc volcanism. Subduction zone thermal models indicate that the down-going slab is decoupled from the overriding mantle wedge beneath the forearc, resulting in a cold mantle wedge that is unlikely to generate melt. Consequently, the forearc location ...

We present a shear velocity model of the crust and upper mantle beneath central Eurasia by simultaneous inversion of broadband group and phase velocity maps of fundamental-mode Love and Rayleigh waves. The model is parameterized in terms of velocity depth profiles on a discrete 2◦ × 2◦ grid. The model is isotropic for the crust and for the upper mantle below 220 km but, to fit simultaneously lo...

We present three case studies of traveltime tomography applied to regional imaging of the earth's crust and upper mantle. The first case study investigates the imaging of Poisson's ratio using measurements of compressional and shear wave traveltimes. Inversions schemes that jointly fit both types of traveltime data and that selectively damp the compressional to shear wave velocity ratio are sho...

Joint inversions are now commonly used in the earth sciences. They have been developed to better understand the structure of the earth, since they provide more constraints on the inverted parameters. We propose a new process to simultaneously invert several data sets in order to better image 3D crustal and upper mantle structures. Our inversion uses three kinds of data that present good complem...

To investigate the nature of Pn propagation, we have implemented the spectral-element method (SEM) for vertically and laterally varying media with and without attenuation. As a practical measure, essential features of the Pn waves are distilled into seismic attributes including arrival times, amplitudes and pulse frequencies. To validate the SEM simulations, we first compare the SEM results wit...

[1] Surface topography and associated gravity anomalies above a layer resembling continental lithosphere, whose mantle part is gravitationally unstable, depend strongly on the ratio of viscosities of the lower-density crustal part to that of the mantle part. For linear stability analysis, growth rates of Rayleigh-Taylor instabilities depend largely on the wave number, or wavelength, of the pert...

S U M M A R Y We investigate the crust and uppermost mantle velocity structure beneath the Laccadive Island through the inversion of teleseismic receiver functions following the neighbourhood algorithm. The velocity structure suggests that the 16-km thick-oceanic crust is underplated by 8-km thick high-velocity layer (Vs ∼ 4.25–4.4 km s−1; Vp ∼ 7.35–7.6 km s−1). The uppermost mantle shear veloc...

Introduction: The dynamics of the crust-mantle interface (Moho) underlying lunar impact basins has received considerable study, particularly those with strong positive free-air gravity anomalies associated with the locations of large basins (" mascons ") [e.g. 1-8]. These gravity anomalies, detected via orbital spacecraft observation, indicate that after surface topography and mare loads are ac...

High-quality seismic data obtained from a dense broadband array near Kimberley, South Africa, exhibit crustal reverberations of remarkable clarity that provide well-resolved constraints on the structure of the lowermost crust and Moho. Receiver function analysis of Moho conversions and crustal multiples beneath the Kimberley array shows that the crust is 35 km thick with an average Poisson’s ra...