The average seismic velocity and density jumps across the 410- and 660-kilometer discontinuities in the upper mantle were determined by modeling the observed range dependence in long-period seismic wave arrivals that reflect off of these interfaces. The preliminary reference Earth model (PREM) is within the computed 95 percent confidence ellipse for the 410-km discontinuity but outside the allo...

One strategy for discriminating between explosions and natural events depends on accurate determinations of event locations, including focal depths. If a seismic event could be reliably determined to have a focal depth greater than a few kilometers, one could be confident that the event is not an explosion. But to determine focal depths accurately, one must first have a fairly accurate model of...

In this study, we apply advanced numerical optimization techniques to extend the work of Imhof and Sharma (2005, 2006) to integrate geological and geophysical data and infer the sedimentary parameters that produce a match to seismic data. In particular, we seek to match not just event timing (phase) but also reflection strength (amplitude). This inverse problem of quantitatively matching presen...

The internal structure of the core-mantle boundary (CMB) region of the Earth plays a crucial role in controlling the dynamics and evolution of our planet. We have developed a comprehensive model based on the radial variations of shear velocity in the D'' layer (the base of the lower mantle) and the high-P,T elastic properties of major candidate minerals, including the effects of post-perovskite...

A limited seismic investigation of Ball Mountain Dam, an earthen dam near Jamaica, Vermont, was conducted using multiple seismic methods including multi-channel analysis of surface waves (MASW), refraction tomography, and vertical seismic profiling (VSP). The refraction and MASW data were efficiently collected in one survey using a towed land streamer containing vertical-displacement geophones ...

In order to produce an accurate depth migration of a seismic line, one needs an accurate velocity model. This model should reflect the lithology and lithostatic load that the rocks have experienced through burial and deformation. If we understand the geometry of these rocks, and their behaviour upon deformation, we can produce a more accurate velocity model. Performing palinspastic restoration ...

In subduction zones, elevated pore fluid pressure, generally linked to metamorphic dehydration reactions, has a profound influence on the mechanical behavior of the plate interface and forearc crust through its control on effective stress. We use seismic noise-based monitoring to characterize seismic velocity variations following the 2012 Nicoya Peninsula, Costa Rica earthquake [M w (moment mag...

Processes within the lowest several hundred kilometers of Earth's rocky mantle play a critical role in the evolution of the planet. Understanding Earth's lower mantle requires putting recent seismic and mineral physics discoveries into a self-consistent, geodynamically feasible context. Two nearly antipodal large low-shear-velocity provinces in the deep mantle likely represent chemically distin...