Seismic wave propagation in poro-viscoelastic hot rocks

Seismic-wave modelling is a key tool to characterize the Earth’s structure, nearby geothermal areas where the presence of high temperatures can cause the existence of supercritical fluids and also partial melting. The seismic characterization of these areas is very important especially in deep drilling and highenthalpy systems. Carcione and Poletto (2013) study the seismic properties variations in the presence of a transition between zones with brittle and ductile behaviour. Carcione et al. (2014) propose an algorithm, based on the Burger mechanical model, to simulate full-waveform propagation in this areas. The presented full-wave solver is based on the Burger mechanical model, which allows us to describe the anelastic behaviour due to shear deformation and plastic flow, and the Gassmann equation to account for the fluid properties in the poro-viscoelastic model. The shear viscosity that relates the stiffness components of the brittle and ductile formation to temperature, is calculated by the Arrhenius equation and the octahedral-stress criterion. The algorithm is based on a direct grid method, and the equations of motion are solved in the time domain by using memory variables (Carcione 2014), spatial derivatives and time integration are obtained with Fourier pseudospectral method and Runge-Kutta technique, respectively. We present synthetic seismograms recorded, along a vertical seismic profile (VSP), in wet and dry viscoelastic media characterized by different temperature profiles, in order to analyse the observability of the associated variations by borehole seismic methods (Poletto and Miranda, 2004).