Geostatistical simulation for geophysical applications—Part II: Geophysical modeling

Geophysics ◽  
1990 ◽  
Vol 55 (11) ◽  
pp. 1441-1446 ◽  
Author(s):  
P. N. Shive ◽  
T. Lowry ◽  
D. H. Easley ◽  
L. E. Borgman
Keyword(s):  
Physical Properties ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Three Dimensional ◽  
Companion Paper ◽  
Geostatistical Simulation ◽  
Near Surface ◽  
Geophysical Modeling ◽  
Karst Environment ◽  
Geophysical Surveys

A companion paper (this issue) describes a method for producing three‐dimensional simulations of physical properties for different geologic situations. Here we create a simulation for a particular case, which is a near‐surface (<80 ft deep) description of a karst environment. We simulate seismic velocity, density, resistivity, and the dielectric constant for this situation. We then conduct (in the computer) hypothetical geophysical surveys at the surface of the model. These surveys are seismic refraction, microgravity, dc resistivity, and ground‐probing radar. Physical properties appropriate for cavities are then entered in the model. Repeating the geophysical surveys over the model with cavities provides a convenient method of evaluating their potential for cavity detection. Anomalies produced by normal variations in physical properties may simulate or obscure anomalies from target features. More data about the correlation of physical properties, particularly in the horizontal directions, will be required to evaluate this problem properly.

scholarly journals Shallow geophysical techniques to investigate the groundwater table at the Great Pyramids of Giza, Egypt

2019 ◽  
Vol 8 (1) ◽  
pp. 29-43 ◽  
Author(s):  
Sharafeldin M. Sharafeldin ◽  
Khalid S. Essa ◽  
Mohamed A. S. Youssef ◽  
Hakan Karsli ◽  
Zein E. Diab ◽  
...  
Keyword(s):  
Water Table ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Groundwater Table ◽  
Near Surface ◽  
Groundwater Aquifer ◽  
Geophysical Surveys ◽  
Subsurface Layers ◽  
Average Water ◽  
Ground Penetrating

Abstract. The near-surface groundwater aquifer that threatened the Great Pyramids of Giza, Egypt, was investigated using integrated geophysical surveys. A total of 10 electrical resistivity imaging, 26 shallow seismic refraction, and 19 ground-penetrating radar surveys were conducted in the Giza Plateau. Collected data for each method were evaluated by state-of-the art processing and modeling techniques. A three-layer model depicts the subsurface layers and better delineates the groundwater aquifer and water table elevation. The resistivity of the aquifer layer and seismic velocity vary between 40 and 80 Ωm and between 1500 and 2500 m s−1, respectively. The average water table elevation is about +15 m, which is safe for the Great Sphinx, but it is still subjected to potential hazards from the Nazlet El-Samman suburb where the water table elevation reaches 17 m. A shallower water table at the Valley Temple and the tomb of Queen Khentkawes, with a low topographic relief, represents severe hazards. It can be concluded that a perched groundwater table is detected in the elevated topography to the west and southwest that might be due to runoff and capillary seepage.

Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

2020 ◽  
Vol 25 (3) ◽  
pp. 415-423
Author(s):  
Ahmed Lachhab ◽  
El Mehdi Benyassine ◽  
Mohamed Rouai ◽  
Abdelilah Dekayir ◽  
Jean C. Parisot ◽  
...  
Keyword(s):  
Heavy Metals ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Low Frequency ◽  
Electrical Current ◽  
P Wave ◽  
Low Resistivity ◽  
Refraction Tomography ◽  
Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

Interpretation of three-dimensional seismic refraction data from western Hecate Strait, British Columbia: structure of the crust

1993 ◽  
Vol 30 (7) ◽  
pp. 1440-1452 ◽  
Author(s):  
J. A. Hole ◽  
R. M. Clowes ◽  
R. M. Ellis
Keyword(s):  
Velocity Structure ◽  
Seismic Refraction ◽  
Three Dimensional ◽  
Surface Expression ◽  
Wide Angle ◽  
Lateral Velocity ◽  
Near Surface ◽  
Velocity Anomaly ◽  
Air Gun ◽  
Refraction Data

As part of a multidisciplinary investigation of the structure and tectonics of the Queen Charlotte Basin and underlying crust, deep multichannel seismic reflection and coincident crustal refraction data were collected in 1988. Energy from the reflection air-gun array source was recorded at land sites at offsets appropriate to record crustal refraction and wide-angle reflection data. Refraction data recorded in a broadside geometry provide good three-dimensional coverage of western Hecate Strait. These data are modelled using tomographic inversion techniques to determine the three-dimensional velocity structure of the crust in this region. The one-dimensional average velocity increases rapidly with depth to 6.5 km/s at 7 km depth. Velocities from 7 to at least 12 km depth remain approximately constant and are associated with rocks of the Wrangellia terrane. Significant lateral velocity variations, including large differences in near-surface velocities attributable to surface features, relatively low velocities representing interbedded Tertiary sediments and volcanics, and a deep high-velocity anomaly that may represent the root of an igneous intrusion, are mapped. Wide-angle reflections from the Moho are used to determine the thickness of the crust. The Moho is at 29 km depth beneath the east coast of the Queen Charlotte Islands. This is deeper than the Moho observed below Queen Charlotte Sound and as deep as, or deeper than, that below Hecate Strait. Crustal thinning during Tertiary extension was thus greatest beneath the surface expression of the Queen Charlotte Basin, leaving the crust under the islands considerably thicker than under the basin. In an alternate or additional explanation, compression at the continental margin during the last 4 Ma may have been taken up by thickening or underplating of the continental crust beneath the islands. If the Pacific plate is subducting beneath the islands, the Moho observations constrain the slab to dip greater than 20–26°.

scholarly journals Geostatistical FDEM inversion: a three-dimensional real case application

2021 ◽  
Author(s):  
Leonardo Azevedo ◽  
João Narciso ◽  
Ellen Van De Vijver
Keyword(s):  
Spatial Distribution ◽  
Physical Properties ◽  
Three Dimensional ◽  
Real Case ◽  
Small Scale ◽  
Inversion Method ◽  
Two Dimensional ◽  
Data Set ◽  
Near Surface ◽  
Direct Observations

&lt;p&gt;The near surface is a complex and often highly heterogeneous system as its current status results from interacting processes of both natural and anthropogenic origin. Effective sustainable management and land use planning, especially in urban environments, demands high-resolution subsurface property models enabling to capture small-scale processes of interest. The modelling methods based only on discrete direct observations from conventional invasive sampling techniques have limitations with respect to capturing the spatial variability of these systems. Near-surface geophysical surveys are emerging as powerful techniques to provide indirect measurements of subsurface properties. Their integration with direct observations has the potential for better predicting the spatial distribution of the subsurface physical properties of interest and capture the heterogeneities of the near-surface systems.&lt;/p&gt;&lt;p&gt;Within the most common geophysical techniques, frequency-domain electromagnetic (FDEM) induction methods have demonstrated their potential and efficiency to characterize heterogeneous deposits due to their simultaneous sensitivity to electrical conductivity (EC) and magnetic susceptibility (MS). The inverse modelling of FDEM data based on geostatistical techniques allows to go beyond conventional analyses of FDEM data. This geostatistical FDEM inversion method uses stochastic sequential simulation and co-simulation to perturbate the model parameter space and the corresponding FDEM forward model solutions, including both the synthetic FDEM responses and their sensitivity to changes on the physical properties of interest. A stochastic optimization driven by the misfit between true and synthetic FDEM data is applied to iterative towards a final subsurface model. This method not only improve the confidence of the obtained EC and MS inverted models but also allows to quantify the uncertainty related to them. Furthermore, taking into account spatial correlations enables more accurate prediction of the spatial distribution of subsurface properties and a more realistic reconstruction of small-scale spatial variations, even when considering highly heterogeneous near surface systems. Moreover, a main advantage of this iterative geostatistical FDEM inversion method is its ability to flexibly integrate data with different resolution in the same framework.&lt;/p&gt;&lt;p&gt;In this work, we apply this iterative geostatistical FDEM inversion technique, which has already been successfully demonstrated for one- and two-dimensional applications, to invert a real case FDEM data set in three dimensions. The FDEM survey data set was collected on a site located near Knowlton (Dorset, UK), which is geologically characterized by Cretaceous chalk overlain by Quaternary siliciclastic sand deposits. The subsurface at the site is known to contain several archaeological features, which produces strong local in-phase anomalies in the FDEM survey data. We discuss the particular challenges involved in the three-dimensional application of the inversion method to a real case data set and compare our results against previously obtained ones for one- and two-dimensional approximations.&lt;/p&gt;

scholarly journals Geophysical site assessment of an active urban development site, southeastern suburb of Cairo, Egypt

2020 ◽  
Vol 54 (1) ◽  
pp. qjegh2018-151
Author(s):  
N. I. Medhat ◽  
M. Atya ◽  
E. A. Ragab ◽  
A. A. El-Kenawy ◽  
M. Abdel Zaher ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Structural Damage ◽  
Residential Buildings ◽  
Seismic Refraction ◽  
Urban Site ◽  
Site Assessment ◽  
Near Surface ◽  
Geophysical Surveys ◽  
Quarry Blasting ◽  
Ground Stability

There has been significant structural damage of newly built residential buildings in Quarter-27 District in the SE of Cairo, Egypt. A nearby active limestone quarry may also be affecting ground stability. This paper shows how a near-surface geophysical survey could characterize the site, unusually after the initial housing construction had already been undertaken. Geophysical surveys included seismic refraction (acquired between phases of quarry blasting), electrical resistivity and ground penetrating radar (GPR) 1D and 2D datasets. Geophysical results produced maps of a 3D ground model that also included water table depth, known major faults and a saturated layer that may have caused the building damage. Of the geophysical techniques trialled electrical resistivity tomography and GPR data were deemed optimal. This study shows that it is possible to undertake geophysical surveys to characterize a restricted urban site development.

An integrated methodological approach for the three-dimensional modeling of the subsurface structures: the case of Borgo Montello, in Latina, Italy.

2021 ◽  
Author(s):  
Klodian Skrame ◽  
Diego Albini ◽  
Carlo Moriconi ◽  
Christian Comotti ◽  
Redi Muci ◽  
...  
Keyword(s):  
Seismic Refraction ◽  
Three Dimensional ◽  
Geophysical Data ◽  
Electrical Tomography ◽  
Subsurface Structures ◽  
Three Dimensional Modeling ◽  
Dimensional Modeling ◽  
Stratigraphic Model ◽  
Local Seismic Response ◽  
Geophysical Surveys

&lt;p&gt;In this work, it is intended to highlight the indispensable significance of the geophysical surveys on the hydrogeological research and on the seismic risk mitigation.&lt;/p&gt;&lt;p&gt;This paper describes the acquisition methodologies, the instrumentation used, the techniques and methods of inversion / interpretation and the results of a hybrid geophysical survey carried out for the reconstruction of the 3-D geological modeling of the Borgo Montello case study, in the Province of Latina, in Italy.&lt;/p&gt;&lt;p&gt;The aim of the study was to test the use of hybrid geophysical surveys in order to obtain a detailed geological-stratigraphic and hydrogeological modeling of the subsoil, its interpretation in terms of flow model and to identify the relationships between the parameters that define the geological-hydrogeological-stratigraphic model with the local seismic ground motion amplification of the site.&lt;/p&gt;&lt;p&gt;From a geological point of view, the study area in composed by two main geological formations. The most superficial one is characterized by sedimentary deposits linked to the filling of the Pontine depression: composed by alternations of clays, silty clays and silts, with a subordinate component of silty sands. The second lithological type is linked to the deposition of pyroclastic deposits from the Lazio volcano and in particular from the deposits of reddish pozzolane alternating with thickened tuff, the so-called &quot;Tufo lionato&quot;.&lt;/p&gt;&lt;p&gt;A research approach that integrated different geophysical methods, as: resistivity, induced polarization electrical tomography and seismic refraction and high resolution reflection methods were carried out to reproduce the thickness and the extension of the over mentioned deposits.&lt;/p&gt;&lt;p&gt;Afterwards, having obtained 5 independent models (seismic reflection section, seismic refraction section, electrical resistivity tomography, electrical tomography and local seismic amplification section) the authors proceeded, through the k-means algorithm methods, for the analysis of the bivariate dataset cluster, in order to identify the relationships between the 5 sets of variables. The proposed methodology was focuses on characterizing the aquifer potential by using simultaneously all the geophysical parameters obtained together with the stratigraphic data, in order to reduce the uncertainties and ambiguity in the interpretation of the geophysical data for a better modeling of the subsoil.&lt;/p&gt;&lt;p&gt;The obtained results were compared with a collection of existing boreholes, well logs, geotechnical and geophysical data. The 3-D geological models match quite well with the information determined from these previous works.&lt;/p&gt;&lt;p&gt;Lastly, based on the three-dimensional modeling of the subsurface structures, a Local Seismic Response study was carried out.&lt;/p&gt;

SHEAR‐WAVE DETECTION IN NEAR‐SURFACE SEISMIC REFRACTION STUDlES

Geophysics ◽  
1966 ◽  
Vol 31 (5) ◽  
pp. 981-983 ◽  
Author(s):  
James H. Whitcomb
Keyword(s):  
Physical Properties ◽  
Shear Wave ◽  
Shear Waves ◽  
Seismic Refraction ◽  
Geological Survey ◽  
Near Surface ◽  
Wave Detection

The U. S. Geological Survey, on behalf of the National Aeronautics and Space Administration, has begun investigations designed to relate the data obtained from seismic refraction profiles to the physical properties of lunar analog earth materials. The velocity of shear waves is a significant property, but the recording of these waves presented a serious problem.

scholarly journals Near surface shear wave velocity in Bucharest, Romania

2008 ◽  
Vol 8 (6) ◽  
pp. 1299-1307 ◽  
Author(s):  
M. von Steht ◽  
B. Jaskolla ◽  
J. R. R. Ritter
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Compressional Wave ◽  
Seismic Zone ◽  
Surface Shear ◽  
Near Surface ◽  
Surface Shear Wave

Abstract. Bucharest, the capital of Romania with nearly 2 1/2 million inhabitants, is endangered by the strong earthquakes in the Vrancea seismic zone. To obtain information on the near surface shear-wave velocity Vs structure and to improve the available microzonations we conducted seismic refraction measurements in two parks of the city. There the shallow Vs structure is determined along five profiles, and the compressional-wave velocity (Vp) structure is obtained along one profile. Although the amount of data collected is limited, they offer a reasonable idea about the seismic velocity distribution in these two locations. This knowledge is useful for a city like Bucharest where seismic velocity information so far is sparse and poorly documented. Using sledge-hammer blows on a steel plate and a 24-channel recording unit, we observe clear shear-wave arrivals in a very noisy environment up to a distance of 300 m from the source. The Vp model along profile 1 can be correlated with the known near surface sedimentary layers. Vp increases from 320 m/s near the surface to 1280 m/s above 55–65 m depth. The Vs models along all five profiles are characterized by low Vs (<350 m/s) in the upper 60 m depth and a maximum Vs of about 1000 m/s below this depth. In the upper 30 m the average Vs30 varies from 210 m/s to 290 m/s. The Vp-Vs relations lead to a high Poisson's ratio of 0.45–0.49 in the upper ~60 m depth, which is an indication for water-saturated clayey sediments. Such ground conditions may severely influence the ground motion during strong Vrancea earthquakes.

The Application of Near-Surface Geophysics at Proposed Pipeline River Crossings: A Comparative Overview of Various Techniques and Their Associated Capabilities and Limitations

2002 ◽  
Author(s):  
Paul Tarrant ◽  
David Baines
Keyword(s):  
Large Diameter ◽  
Seismic Refraction ◽  
Directional Drilling ◽  
Near Surface ◽  
Design Engineers ◽  
Geotechnical Investigations ◽  
Geophysical Surveys ◽  
Ground Conditions ◽  
Borehole Drilling ◽  
Near Surface Geophysics

The cost, design, and in some instances, feasibility of directional drilling large diameter or lengthy pipeline river crossings is primarily dependent on ground conditions encountered during construction. Geotechnical investigations are commonly used to explore and assess subsurface conditions at proposed crossings. Ground conditions are determined using borehole drilling and near surface geophysics. Borehole drilling provides subsurface sediment stratigraphy and depth to bedrock information. Geophysics is used to provide information between borehole locations or where borehole drilling is determined to be too difficult or too costly. When used to augment borehole results, geophysical surveys provide more complete geologic cross-section models throughout the length of a proposed directional drill path. This paper presents an overview of the more common geophysical methodologies used to profile subsurface conditions at proposed pipeline crossings. The methods discussed include ground penetrating radar (GPR), seismic refraction profiling and electrical resistivity tomography (ERT). The appropriateness and feasibility of each method is discussed in terms relating to investigation objectives of geotechnical and pipeline design engineers. All three methods were applied to two survey lines at a typical river crossing site on the Bow River, downstream from Calgary, Alberta. Results from the overlapping surveys are presented and the capabilities and limitations for each method compared. Borehole information obtained within the survey area is used to corroborate the interpreted geophysical results.

Sign in / Sign up

Export Citation Format

Share Document