Finite difference forward modelling across the Tyrrhenian basin

2021 ◽  
Author(s):  
Chiara Nardoni ◽  
Luca De Siena ◽  
Fabio Cammarano ◽  
Elisabetta Mattei ◽  
Fabrizio Magrini
Keyword(s):  
Wave Propagation ◽  
Finite Difference ◽  
Wave Attenuation ◽  
Software Tool ◽  
Seismic Wave Propagation ◽  
Tyrrhenian Sea ◽  
Forward Modelling ◽  
Crustal Thinning ◽  
Energy Leakage ◽  
Radiative Transfer Equations

<p>Strong lateral variations in medium properties affect the response of seismic wavefields. The Tyrrhenian Sea is ideally suited to explore these effects in a mixed continental-oceanic crust that comprises magmatic systems. The study aims at investigating the effects of crustal thinning and sedimentary layers on wave propagation, especially the reverberating (e.g., Lg) phases, across the oceanic basin. We model regional seismograms (600-800 km) using the software tool OpenSWPC (Maeda et al., 2017, EPS) based on the finite difference simulation of the wave equation. The code simulates the seismic wave propagation in heterogeneous viscoelastic media including the statistical velocity fluctuations as well as heterogeneous topography, typical of mixed settings. This approach allows to evaluate the role of interfaces and layer thicknesses on phase arrivals and direct and coda attenuation measurements. The results are compared with previous simulations of the radiative-transfer equations. They provide an improved understanding of the complex wave attenuation and energy leakage in the mantle characterizing the southern part of the Tyrrhenian Sea and the Italian peninsula. The forward modelling is to be embedded in future applications of attenuation, absorption and scattering tomography performed with MuRAT (the Multi-Resolution Attenuation Tomography code – De Siena et al. 2014, JVGR) available at https://github.com/LucaDeSiena/MuRAT.</p>

On: “Wave Propagation in heterogeneous, porous media: A velocity‐stress, finite difference method,” by N. Dai, A. Vafidis, and E. R. Kanasewich (March‐April 1995 GEOPHYSICS, p. 327–340).

Geophysics ◽  
1996 ◽  
Vol 61 (4) ◽  
pp. 1230-1231 ◽  
Author(s):  
Boris Gurevich
Keyword(s):  
Porous Media ◽  
Wave Propagation ◽  
Finite Difference ◽  
Finite Difference Method ◽  
Seismic Wave Propagation ◽  
Heterogeneous Porous Media ◽  
Two Dimensions ◽  
Seismic Modeling ◽  
Modeling Technology ◽  
Interesting Paper

In their interesting paper the authors present a new advanced approach to the simulation of seismic wave propagation in media described by Biot’s theory of dynamic poroelasticity in two dimensions. The algorithm developed can be used to accurately simulate the effect of dynamic poroelasticity on seismic wavefields over hydrocarbon reservoirs. In cases where this effect proves significant this algorithm can be incorporated in the seismic modeling technology.

An adaptive node-distribution method for radial-basis-function finite-difference modeling with optimal shape parameter

Geophysics ◽  
2021 ◽  
Vol 86 (1) ◽  
pp. T1-T18
Author(s):  
Peiran Duan ◽  
Bingluo Gu ◽  
Zhenchun Li ◽  
Zhiming Ren ◽  
Qingyang Li
Keyword(s):  
Wave Propagation ◽  
Dispersion Relation ◽  
Finite Difference ◽  
Stability Condition ◽  
Seismic Wave Propagation ◽  
Optimal Shape ◽  
Shape Parameters ◽  
Seismic Modeling ◽  
Distribution Method ◽  
Node Distribution

The radial-basis-function finite-difference (RBF-FD) method has been proven successful in modeling seismic-wave propagation. Node distribution is typically the first and most critical step in RBF-FD. Regarding the difficulties in seismic modeling, such as node distribution of complex geologic structures, we have designed an adaptive node-distribution method that can generate nodes automatically and flexibly as the computation proceeds with the adaptive grain-radius satisfied dispersion relation and stability condition of seismic-wave propagation. Our method consists of two novel points. The first one is that we adopt an adaptive grain-radius generation method, which can automatically provide a wider scope of grain radius in seismic modeling while satisfying the dispersion relation and stability condition; the second one is that the node-generation algorithm is built by a smoothed model, which significantly improves the modeling stability at a reduced computational cost. Excessive or undesirable shape parameters will create a very ill-conditioned problem. A set of optimal shape parameters for different numbers of neighbor nodes is found quantitatively by minimizing root-mean-square error functions. This optimization method enables us to achieve an improved meshfree modeling process with higher accuracy and practicability and fewer spurious diffractions caused by the transition of different sampling areas. Several numerical results verify the feasibility of our adaptive node-distribution method and the optimal shape parameters.

The effects of pore‐fluid salinity on ultrasonic wave propagation in sandstones

Geophysics ◽  
1998 ◽  
Vol 63 (3) ◽  
pp. 928-934 ◽  
Author(s):  
Simon M. Jones ◽  
Clive McCann ◽  
Timothy R. Astin ◽  
Jeremy Sothcott
Keyword(s):  
Wave Propagation ◽  
Ultrasonic Wave ◽  
Wave Attenuation ◽  
Clay Content ◽  
Seismic Wave Propagation ◽  
Ultrasonic Pulse ◽  
Pore Fluid ◽  
P Wave ◽  
S Wave ◽  
Shear Moduli

Petrophysical interpretation of increasingly refined seismic data from subsurface formations requires a more fundamental understanding of seismic wave propagation in sedimentary rocks. We consider the variation of ultrasonic wave velocity and attenuation in sandstones with pore‐fluid salinity and show that wave propagation is modified in proportion to the clay content of the rock and the salinity of the pore fluid. Using an ultrasonic pulse reflection technique (590–890 kHz), we have measured the P-wave and S-wave velocities and attenuations of 15 saturated sandstones with variable effective pressure (5–60 MPa) and pore‐fluid salinity (0.0–3.4 M). In clean sandstones, there was close agreement between experimental and Biot model values of [Formula: see text], but they diverged progressively in rocks containing more than 5% clay. However, this effect is small: [Formula: see text] changed by only 0.6% per molar change in salinity for a rock with a clay content of 29%. The variation of [Formula: see text] with brine molarity exhibited Biot behavior in some samples but not in others; there was no obvious relationship with clay content. P-wave attenuation was independent of pore‐fluid salinity, while S-wave attenuation was weakly dependent. The velocity data suggest the frame bulk and shear moduli of sandstones are altered by changes in the pore‐fluid salinity. One possible mechanism is the formation damage caused by clay swelling and migration of fines in low‐molarity electrolytes. The absence of variation between the attenuation in water‐saturated and brine‐saturated samples indicates the attenuation mechanism is relatively unaffected by changes in the frame moduli.

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