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VELVET

 

Velocity Versus Time

People:

Pasquale De Gori pasquale.degori@ingv.it

Francesco Pio Lucente pio.lucente@ingv.it

Claudio Chiarabba claudio.chiarabba@ingv.it

With VELVET we study the spatial and-temporal variations of the physical properties of the crustal volume containing this low angle normal fault system (ATF). The goal is to provide critical constraints on the relationship between seismicity and rock rheology in a rock volume where over-pressured fluids has been proposed as a key factor controlling the mechanical behaviour of the fault (a, b). We develop procedures to compute 4D changes of VP and VP/VS starting from a huge amount of high quality seismic phases readings and high precision hypocentral parameters. The applied methodologies are summarized below:

VP/VS through the timeWe measure the ratio between the compressional (P-wave) and the shear (S-wave) seismic velocities, the VP/VS starting from P wave travel times and S-P differential times (c, d, e). Assuming a homogeneous transmission medium, the slope of the line through the data from the origin is a measure of the function (VP/VS – 1; f, g, h). This method differs form the classical Wadati diagram (i) by the use of the P-wave travel time instead of the P-wave arrival time. This requires to hypocentral parameters to be known but offers the chance to compute the VP/VS values at single stations, which will be crucial when interpreting the observation.

High-Resolution time repeated seismic tomographySeismic tomography is a powerful tool for imaging lateral heterogeneities in the upper crust. In particular, the time repeated seismic tomography, defined as several tomographic models of the same region computed with dataset recorded in different time intervals, allow to investigate the temporal variations of the elastic properties within the target volume (l, m, d, n). We adopt classic tomographic method (o, p) where local earthquake arrival time data are simultaneously inverted to compute hypocentres and 3D, VP and VP/VS structure.

Reference

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