scholarly journals Deep-towed high resolution seismic imaging II: Determination of P-wave velocity distribution

2018 ◽  
Vol 132 ◽  
pp. 29-36 ◽  
Author(s):  
B. Marsset ◽  
S. Ker ◽  
Y. Thomas ◽  
F. Colin
Keyword(s):  
High Resolution ◽  
Velocity Distribution ◽  
Wave Velocity ◽  
Seismic Imaging ◽  
P Wave ◽  
P Wave Velocity

scholarly journals P-wave velocity and density structure beneath Mt. Vesuvius: a magma body in the upper edifice?

2013 ◽  
Vol 56 (4) ◽  
Author(s):  
Paolo Capuano ◽  
Guido Russo ◽  
Roberto Scarpa
Keyword(s):  
High Resolution ◽  
Wave Velocity ◽  
Gravity Data ◽  
High Energy ◽  
P Wave ◽  
Gravity Inversion ◽  
Density Structure ◽  
Resolution Image ◽  
High Resolution Image ◽  
P Wave Velocity

<p>A high-resolution image of the compressional wave velocity and density structure in the shallow edifice of Mount Vesuvius has been derived from simultaneous inversion of travel times and hypocentral parameters of local earthquakes and from gravity inversion. The robustness of the tomography solution has been improved by adding to the earthquake data a set of land based shots, used for constraining the travel time residuals. The results give a high resolution image of the P-wave velocity structure with details down to 300-500 m. The relocated local seismicity appears to extend down to 5 km depth below the central crater, distributed into two clusters, and separated by an anomalously high Vp region positioned at around 1 km depth. A zone with high Vp/Vs ratio in the upper layers is interpreted as produced by the presence of intense fluid circulation alternatively to the interpretation in terms of a small magma chamber inferred by petrologic studies. In this shallower zone the seismicity has the minimum energy, whilst most of the high-energy quakes (up to Magnitude 3.6) occur in the cluster located at greater depth. The seismicity appears to be located along almost vertical cracks, delimited by a high velocity body located along past intrusive body, corresponding to remnants of Mt. Somma. In this framework a gravity data inversion has been performed to study the shallower part of the volcano. Gravity data have been inverted using a method suitable for the application to scattered data in presence of relevant topography based on a discretization of the investigated medium performed by establishing an approximation of the topography by a triangular mesh. The tomography results, the retrieved density distribution, and the pattern of relocated seismicity exclude the presence of significant shallow magma reservoirs close to the central conduit. These should be located at depth higher than that of the base of the hypocenter volume, as evidenced by previous studies.</p>

scholarly journals Determination of vp/vs on Bali Province: Case of Bali Earthquake March 22, 2017

2018 ◽  
Vol 19 (2) ◽  
pp. 73
Author(s):  
Febi Niswatul Auliyah ◽  
Komang Ngurah Suarbawa ◽  
Indira Indira
Keyword(s):  
Case Studies ◽  
Wave Velocity ◽  
P Wave ◽  
S Wave ◽  
Diagram Method ◽  
P Wave Velocity ◽  
Before And After ◽  
Earthquake Data

P-wave velocity and S-wave velocity have been investigated in the Bali Province by using earthquake case studies on March 22, 2017. The study was focused on finding out whether there were anomalies in the values of vp/vs before and after the earthquake. Earthquake data was obtained from the Meteorology, Climatology and Geophysics Agency (BMKG) Region III Denpasar, which consisted of the main earthquake on March 22, 2017 and earthquake data in August 2016 to May 2017. Data was processed using the wadati diagram method, obtained that the vp/vs on SRBI, IGBI, DNP and RTBI stations are shifted from 1.5062 to 1.8261. Before the earthquake occurred the anomaly of the value of vp/vs was found on the four stations, at the SRBI station at 10.35%, at the IGBI station at 16.16%, at DNP station at 12.27% and at RTBI station at 4.62%.

High-resolution three-term AVO inversion by means of a Trivariate Cauchy probability distribution

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. R43-R55 ◽  
Author(s):  
Wubshet Alemie ◽  
Mauricio D. Sacchi
Keyword(s):  
High Resolution ◽  
Wave Velocity ◽  
P Wave ◽  
S Wave ◽  
Avo Inversion ◽  
P Wave Velocity ◽  
Multivariate Gaussian ◽  
Density Perturbations ◽  
Gaussian Prior ◽  
Scale Matrix

Three-term AVO inversion can be used to estimate P-wave velocity, S-wave velocity, and density perturbations from reflection seismic data. The density term, however, exhibits little sensitivity to amplitudes and, therefore, its inversion is unstable. One way to stabilize the density term is by including a scale matrix that provides correlation information between the three unknown AVO parameters. We investigate a Bayesian procedure to include sparsity and a scale matrix in the three-term AVO inversion problem. To this end, we model the prior distribution of the AVO parameters via a Trivariate Cauchy distribution. We found an iterative algorithm to solve the Bayesian inversion and, in addition, comparisons are provided with the classical inversion approach that uses a Multivariate Gaussian prior. It is important to point out that the Multivariate Gaussian prior allows us to include the correlation of the AVO parameters in the solution of the inverse problem. The Trivariate Cauchy prior not only permits us to incorporate correlation but also leads to high-resolution (broadband) P-wave velocity, S-wave velocity, and density perturbations.

P‐wave velocity and permeability distribution of sandstones from a fractured tight gas reservoir

Geophysics ◽  
2002 ◽  
Vol 67 (1) ◽  
pp. 241-253 ◽  
Author(s):  
Helmut Dürrast ◽  
P. N. J. Rasolofosaon ◽  
Siegfried Siegesmund
Keyword(s):  
Velocity Distribution ◽  
Wave Velocity ◽  
Confining Pressure ◽  
P Wave ◽  
Tight Gas ◽  
Rock Fabric ◽  
The Core ◽  
Wave Velocities ◽  
P Wave Velocity ◽  
Tight Gas Reservoir

Fractures are an important fabric element in many tight gas reservoirs because they provide the necessary channels for fluid flow in rocks which usually have low matrix permeabilities. Several sandstone samples of such a reservoir type were chosen for a combined study of rock fabric elements and petrophysical properties. Geological investigations of the distribution and orientation of the fractures and sedimentary layering were performed. In addition, laboratory measurements were carried out to determine the directional dependence of the permeability and P‐wave velocities. Higher permeability values are generally in the plane of the nearly horizontal sedimentary layering with regard to the core axis. With the occurrence of subvertical fractures, however, the highest permeabilities were determined to be parallel to the core axis. Compressional wave velocities were measured on spherical samples in more than 100 directions to get the VP symmetry without prior assumptions. Below 50 MPa confining pressure, all samples show a monoclinic symmetry of the P wave velocity distribution, caused by sedimentary layering, fractures, and crossbedding. At higher confining pressure, sedimentary layering is approximately the only effective fabric element, resulting in a more transverse isotropic VP symmetry. Using the geological‐petrophysical model introduced here, the complex symmetry of the VP distributions can only be explained by the rock fabric elements. Furthermore, water saturation increases the velocities and decreases the anisotropy but does not change VP symmetry. This indicates that at this state, all fabric elements, including the fractures, have an influence on P‐wave velocity distribution.

scholarly journals Quantitative seismic characterization of CO2 at the Sleipner storage site, North Sea

2017 ◽  
Vol 5 (4) ◽  
pp. SS23-SS42 ◽  
Author(s):  
Bastien Dupuy ◽  
Anouar Romdhane ◽  
Peder Eliasson ◽  
Etor Querendez ◽  
Hong Yan ◽  
...  
Keyword(s):  
High Resolution ◽  
Wave Velocity ◽  
Rock Physics ◽  
Joint Estimation ◽  
P Wave ◽  
Storage Site ◽  
Seismic Waveform ◽  
P Wave Velocity ◽  
Seismic Characterization

Reliable quantification of carbon dioxide ([Formula: see text]) properties and saturation is crucial in the monitoring of [Formula: see text] underground storage projects. We have focused on quantitative seismic characterization of [Formula: see text] at the Sleipner storage pilot site. We evaluate a methodology combining high-resolution seismic waveform tomography, with uncertainty quantification and rock physics inversion. We use full-waveform inversion (FWI) to provide high-resolution estimates of P-wave velocity [Formula: see text] and perform an evaluation of the reliability of the derived model based on posterior covariance matrix analysis. To get realistic estimates of [Formula: see text] saturation, we implement advanced rock physics models taking into account effective fluid phase theory and patchy saturation. We determine through sensitivity tests that the estimation of [Formula: see text] saturation is possible even when using only the P-wave velocity as input. After a characterization of rock frame properties based on log data prior to the [Formula: see text] injection at Sleipner, we apply our two-step methodology. The FWI result provides clear indications of the injected [Formula: see text] plume being observed as low-velocity zones corresponding to thin [Formula: see text] filled layers. Several tests, varying the rock physics model and [Formula: see text] properties, are then performed to estimate [Formula: see text] saturation. The results suggest saturations reaching 30%–35% in the thin sand layers and up to 75% when patchy mixing is considered. We have carried out a joint estimation of saturation with distribution type and, even if the inversion is not well-constrained due to limited input data, we conclude that the [Formula: see text] has an intermediate pattern between uniform and patchy mixing, which leads to saturation levels of approximately [Formula: see text]. It is worth noting that the 2D section used in this work is located 533 m east of the injection point. We also conclude that the joint estimation of [Formula: see text] properties with saturation is not crucial and consequently that knowing the pressure and temperature state of the reservoir does not prevent reliable estimation of [Formula: see text] saturation.

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