scholarly journals Vertical seismic profiling of glaciers: appraising multi-phase mixing models

2013 ◽  
Vol 54 (64) ◽  
pp. 115-123 ◽  
Author(s):  
Alessio Gusmeroli ◽  
Tavi Murray ◽  
Roger A. Clark ◽  
Bernd Kulessa ◽  
Peter Jansson
Keyword(s):  
Water Content ◽  
Wave Speed ◽  
P Wave ◽  
Water Model ◽  
Seismic Profiles ◽  
Compressional Waves ◽  
Vertical Seismic Profiles ◽  
Polythermal Glacier ◽  
Multi Phase ◽  
Ground Penetrating

Abstract We have investigated the speed of compressional waves in a polythermal glacier by, first, predicting them from a simple three-phase (ice, air, water) model derived from a published ground-penetrating radar study, and then comparing them with field data from four orthogonally orientated walkaway vertical seismic profiles (VSPs) acquired in an 80 m deep borehole drilled in the ablation area of Storglaciären, northern Sweden. The model predicts that the P-wave speed increases gradually with depth from 3700ms–1 at the surface to 3760ms–1 at 80m depth, and this change is almost wholly caused by a reduction in air content from 3% at the surface to <0.5% at depth. Changes in P-wave speed due to water content variations are small (<10 ms–1); the model’s seismic cold–temperate transition surface (CTS) is characterized by a 0.3% decrease downwards in P-wave speed (about ten times smaller than the radar CTS). This lack of sensitivity, and the small contrast at the CTS, makes seismically derived water content estimation very challenging. Nevertheless, for down-going direct-wave first arrivals for zero- and near-offset VSP shots, we find that the model-predicted travel times and field observations agree to within 0.2 ms, i.e. less than the observational uncertainties.

scholarly journals Pressure in a fluid‐filled borehole caused by a seismic source in stratified media

Geophysics ◽  
1996 ◽  
Vol 61 (1) ◽  
pp. 43-55 ◽  
Author(s):  
Chengbin Peng ◽  
Jung M. Lee ◽  
M. Nafi Toksöz
Keyword(s):  
Field Measurements ◽  
Seismic Source ◽  
P Wave ◽  
Stratified Medium ◽  
Stratified Media ◽  
Coupling Theory ◽  
Seismic Profiles ◽  
Matrix Formulation ◽  
Vertical Seismic Profiles ◽  
Vsp Data

A method for numerically simulating hydrophone vertical seismic profiles (VSP) and crosswell data measured in a fluid‐filled borehole (either open or cased) embedded in stratified media is presented. The method makes use of both the borehole coupling theory and the global matrix formulation for computing synthetic seismograms in a stratified medium. The global matrix formulation is used to calculate the stress field at the borehole location. Borehole coupling theory is then employed to obtain the pressure in the borehole fluid. Comparisons with exact solutions for an open borehole in a homogeneous and unbounded formation show that this method is accurate for frequencies below 2 kHz. This method is used to model the Kent Cliffs hydrophone VSP data, where good agreement between the numerical simulations and the field measurements has been found, in both traveltimes and rms amplitudes of the direct P‐wave. Examples show that this method is efficient and accurate, and can be applied to model VSP and crosswell experiments using an array of hydrophones.

scholarly journals Compressional and EM wave velocity anisotropy in a temperate glacier due to basal crevasses, and implications for water content estimation

2013 ◽  
Vol 54 (64) ◽  
pp. 168-178 ◽  
Author(s):  
John H. Bradford ◽  
Joshua Nichols ◽  
Joel T. Harper ◽  
Toby Meierbachtol
Keyword(s):  
Water Content ◽  
Seismic Velocity ◽  
Three Dimensional ◽  
Compressional Wave ◽  
P Wave ◽  
Velocity Anisotropy ◽  
South Central ◽  
Glacier Flow ◽  
Ground Penetrating ◽  
Wave Normal

AbstractWe have conducted a series of experiments designed to investigate elastic and electromagnetic (EM) velocity anisotropy associated with a preferentially aligned fracture system on a temperate valley glacier in south-central Alaska, USA. Measurements include a three-dimensional compressional wave (P-wave) seismic reflection survey conducted over a 300 m x 300 m survey patch, with uniform source grid and static checkerboard receiver pattern. Additionally, we acquired a multi-azimuth, multi-offset, polarimetric ground-penetrating radar (GPR) reflection experiment in a wagon-wheel geometry with 94° of azimuthal coverage. Results show azimuthal variation in the P-wave normal-moveout velocity of >3% (3765 and 3630 m s–1in the fast and slow directions respectively) and difference of nearly 5% between the fast (0.164 m ns–1) and slow (0.156 m ns–1) EM velocities. Fracture orientations estimated from the GPR and seismic velocity data are consistent and indicate a preferred fracture orientation that is 30-45° oblique to glacier flow; these measurements agree with borehole observations. Anisotropic analysis of the polarimetric data gives a single volumetric water content estimate of 0.73 ±0.11%. We conclude that meaningful estimates of physical properties in glaciers based on EM or seismic velocity measurements require collecting data such that the presence of anisotropy can be evaluated and an anisotropic analysis employed when necessary.

New methodologies of GPR Assessment for analysing water content in sedimentary deposits; Application to the Hospital Sant Pau Urban Area in Barcelona, Spain

2021 ◽  
Author(s):  
Mezgeen Rasol ◽  
Vega Perez-Gracia ◽  
Sonia Santos
Keyword(s):  
Water Content ◽  
Radar Data ◽  
Seismic Behaviour ◽  
Soil Response ◽  
Site Analysis ◽  
Sedimentary Deposits ◽  
Centre Frequency ◽  
Soil Site ◽  
New Methodologies ◽  
Ground Penetrating

<p>Ground Penetrating Radar was used in this study as a non-destructive geophysical method. The main objective of this research is focused on enhancing the local seismic soil site analysis. The study employs GPR images to determine changes in the ground that can be associated with changes on the seismic soil response. To determine the GPR capacity in detecting changes in the ground materials and improve new methodologies of the radar data processing.</p><p>Results could be used to improve the selection of areas for more intensive scrutiny, enhancing the analysis of local seismic behaviour studies. Soil site studies are crucial in the analysis of seismic hazard in populated areas. This study and analysis will be carried out in an urban environment at the Sant Pau Hospital in Barcelona city (Spain). Data were acquired in the field along with two different directions: parallel and perpendicular to the coastline of the Mediterranean Sea in Barcelona city.</p><p>The procedure is based in integrated data from the laboratory experiments by using 1600 MHz centre frequency and obtaining real GPR field images in the field by using 25 MHz centre frequency antenna in the Sant Pau Hospital. Therefore, radar data will be first processed using the commercial software ReflexW, followed by a more specific processing sequence (both in amplitude and frequency domains) with a specific algorithm developed with MATLAB.</p><p>Finally, the mathematical processing of the radargrams in terms of water content compared to the information based on historical maps. Results show that GPR is a promising method and compared to previous studies a good agreement was observed in this specific case study. </p>

scholarly journals Vertical to Horizontal Spectral Ratio (VHSR) Response of Seismic Wave Propagation in a Homogeneous Elastic – Poroelastic Medium Using The Spectral Finite Element Method

2021 ◽  
Vol 11 (1) ◽  
pp. 95
Author(s):  
Sudarmaji Saroji ◽  
Budi Eka Nurcahya ◽  
Nivan Ramadhan Sugiantoro
Keyword(s):  
Finite Element Method ◽  
Elastic Medium ◽  
Seismic Waves ◽  
Low Frequency ◽  
Seismic Wave Propagation ◽  
P Wave ◽  
Poroelastic Medium ◽  
Compressional Waves ◽  
Spectral Finite Element Method ◽  
Spectral Finite Element

<p>Numerical modeling of 2D seismic wave propagation using spectral finite element method to estimate the response of seismic waves passing through the poroelastic medium from a hydrocarbon reservoir has been carried out. A hybrid simple model of the elastic - poroelastic - elastic with a mesoscopic scale element size of about 50cm was created. Seismic waves which was in the form of the ricker function are generated on the first elastic medium, propagated into the poroelastic medium and then transmitted to the second elastic medium. Pororoelastic medium is bearing hydrocarbon fluid in the form of gas, oil or water. Vertical and horizontal component of velocity seismograms are recorded on all mediums. Seismograms which are recorded in the poroelastic and second elastic medium show the existence of slow P compressional waves following fast P compressional waves that do not appear on the seismogram of the first elastic medium. The slow P wave is generated when the fast P wave enters the interface of the elastic - poroelastic boundary, propagated in the poroelastic medium and is transmited to the second elastic medium. The curves of Vertical to horizontal spectrum ratio (VHSR) which are observed from seismograms recorded in the poroelastic and the second elastic medium show that the peak of VHSR values at low frequency correlated with the fluid of poroelastic reservoir. The highest VHSR value at the low frequency which is recorded on the seismogram is above the 2.5 Hz frequency for reservoirs containing gas and oil in the second elastic medium, while for the medium containing water is the highest VHSR value is below the 2.5 Hz frequency.</p>

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