Velocity dispersion and attenuation in rocks are coupled properties that depend on the pore fluids and fluid flow. Attenuation shows a peak at high partial gas saturation. The amplitude of this peak increases with frequency. With full saturation, velocities rise but dispersion remains approximately constant. A substantial frequency shift occurs with decreasing permeability or fluid mobility. Th...

Isochron rays are lines perpendicular to isochrons, which represent surfaces of constant two-way traveltime. The image of a temporal sequence of seismic impulses is a sequence of isochrons in depth. The later the time impulse the deeper the isochron. The term isochron ray arises from an analogy between the isochron “movement” and the wave propagation. While isochrons behave as wavefronts, its p...

Seismic imaging produces images of contrasts in physical parameters in the subsurface, e.g., velocity or impedance. To build such images, a background model describing the wave kinematics in the earth is necessary. In practice, the structural image and background velocity model are unknown and have to be estimated from the acquired data. Migration velocity analysis deals with estimation of the ...

In this paper, we summarize some recent results of measurements of temporal changes of active volcanoes using seismic noise cross-correlations. We first present a novel approach to estimate volcano interior temporal seismic velocity changes. The proposed method allows to measure very small velocity changes (≈ 0.1%) with a time resolution as small as one day. The application of that method to Pi...

We calculate the vertical mass discharge rate from Mount St. Helens for the first few minutes of the May 18, 1980 cataclysmic eruption using a new method based on seismic constraints. The observed seismic waves indicate that the seismic source is a series of single forces. We model these forces as thrusts due to a combination of the momentum flux of the erupted products and the pressure of the ...

The Initial stages of velocity model building (VMB) start off from smooth models that capture geological assumptions of the subsurface region under analysis. Acceptable velocity models result from successive iterations of human intervention (interpreter) and seismic data processing within complex workflows. The interpreters ensure that any additions or corrections made by seismic processing are...

We propose a methodology to propagate uncertainties in seismic pore pressure prediction using a 3-D Probabilistic Mechanical Earth Model (P-MEM). An extended form of Bowers formula is used to link pore pressure to seismic velocity, overburden stress, porosity and clay volume. Probability Distribution Functions (PDFs) for all input variables are stored as attributes in the 3-D MEM. An output PDF...

S U M M A R Y Since W. J. Morgan proposed that intraplate volcanism at some Pacific hotspots is caused by hot plumes rising from the lower mantle, geophysicists have been actively pursuing physical evidence for mantle plumes. Several seismic studies have mapped low-velocity anomalies below a number of hotspots. However, the association of low-velocity structures with plume tails has remained co...

Thermodynamic (Anderson 2005) and elastic properties (Musgrave 1970) of minerals provide the fundamental information needed to analyze seismic observations and to model Earth’s dynamic state. The connection between pressure, temperature, chemical composition, and mineralogy that produce seismic velocity gradients, heterogeneities, and discontinuities, can be established with knowledge of thermo...

Temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviors including slow earthquakes, tremor and low frequency earthquakes1. Laboratory and theoretical studies predict changes in seismic velocity prior to earthquake failure2, however tectonic fault...