Seismic Refraction Tomography Surveys Research Articles

Prospection of faults on the Southern Erftscholle (Germany) with individually and jointly inverted refraction seismics and electrical resistivity tomography

As part of the Lower Rhein Embayment (LRE), the Southern Erft block is characterized by a complex tectonic setting that influences hydrological and geological conditions on a local as well as regional level. The study area is located in the south of North Rhine-Westphalia and traversed by several NW-SE-oriented fault structures. Since the tectonic structures were located by past studies based on a sparse foundation of geological data, the positions include considerable uncertainties. Therefore, it was decided to re-evaluate and refine the assumed fault locations by conducting geophysical measurements. Seismic Refraction Tomography (SRT) as well as Electrical Resistivity Tomography (ERT) was performed along seven measurement profiles with a length of up to 1.1 km. In addition to compiling individual resistivity and velocity models for all deduced measurements, ERT and SRT datasets were cooperatively inverted using the Structurally Coupled Cooperative Inversion (SCCI). This algorithm strengthens structural similarities between velocity and resistivity by adapting the individual regularizations after each model iteration. Previously assumed locations of the tectonic structures diverge from the new evidence based on ERT and SRT surveys. Especially in the western and eastern parts of the research area, differences between the survey results and formerly assumed locations are in the order of 100 m. Seismic and geoelectric measurements further indicate a fault structure in the southern part of the area, which remained undetected by past studies. The cooperative inversions do not improve the geophysical models qualitatively, since the individually inverted datasets already provide results of good quality and resolution.

Determining subsurface geology with seismic refraction tomography survey

Seismic refraction tomography survey is one of the geophysical techniques that is the most popular and commonly used to determine subsurface geology in engineering application. It is fast, reliable, cheaper and cover bigger area in shorter time compared with borehole drilling and other geophysical techniques in providing continuous information on subsurface geology along the lengths of the seismic survey lines. However, the success of seismic refraction tomography survey depends on a few factors such as noise background, top soil features, geology of the site, limitation of the equipment, understanding of the theories and experiences in interpreting the seismic refraction tomography survey data. The method of seismic refraction tomography survey measures the first arrival time of the primary waves through the earth material after seismic signals were generated at several shot points with sledge hammer or explosives. In this paper, the applications of seismic refraction tomography survey in investigating the subsurface geology were discussed in two case studies. The first case study discussed the effect of geophone interval in the limit of depth penetration of seismic refraction tomography survey. Increasing the geophone interval would increase the limit of depth penetration, which helped in mapping the very deep bedrock profile. The second case study showed that the seismic refraction tomography survey results were able to indicate the highly irregular bedrock profiles and complexity of the subsurface geology such as shear zones. It was able to show the extent of the shear zones at the project area, which would have been missed by merely doing borehole drilling. Hydrothermally altered granite and quartz veins were encountered in the boreholes located along the shear zones. Both case studies showed good correlations between boreholes and seismic refraction tomography survey results.

The Effect of Aspect and Elevation on Critical Zone Architecture in the Reynolds Creek Critical Zone Observatory: A Seismic Refraction Study

In the northern hemisphere within snow-dominated mountainous watersheds north-facing slopes are commonly more deeply weathered than south-facing slopes. This has been attributed to a more persistent snowpack on the north facing aspects. A persistent snowpack releases its water into the subsurface in a single large pulse, which propagates the water deeper into the subsurface than the series of small pulses characteristic of the intermittent snowpack on south-facing slopes. Johnston Draw is an east-draining catchment in the Reynolds Creek Critical Zone Observatory, Idaho that spans a 300 m elevation gradient. The north-facing slope hosts a persistent snowpack that increases in volume up drainage, while the south-facing slope has intermittent snowpack throughout the drainage. We hypothesize that the largest difference in weathering depth between the two aspects will occur where the difference in snow accumulation between the aspects is also greatest. To test this hypothesis, we conducted four seismic refraction tomography surveys within Johnston Draw from inlet to outlet and perpendicular to drainage direction. From these measurements, we calculate the weathering zone thickness from the P-wave velocity profiles. We conclude that the maximum difference in weathering between aspects occurs ¾ of the way up the drainage from the outlet, where the difference in snow accumulation is highest. Above and below this point, the subsurface is more equally weathered and the snow accumulations are more similar. We also observed that the thickness of the weathering zone increased with decreasing elevation and interpret this to be related to the observed increase soil moisture at lower elevations. Our observations support the hypothesis that deeper snow accumulation leads to deeper weathering when all other variables are held equal. One caveat is the possibility that the denser vegetation contributes to deeper weathering on north-facing slopes via soil retention or higher rates of biological weathering.

Neotectonic Activity in the Low-Strain Broken Foreland (Santa Bárbara System) of the North-Western Argentinean Andes (26°S)

AbstractUplift in the broken Andean foreland of the Argentine Santa Bárbara System (SBS) is associated with the contractional reactivation of basement anisotropies, similar to those reported from the thick-skinned Cretaceous-Eocene Laramide province of North America. Fault scarps, deformed Quaternary deposits and landforms, disrupted drainage patterns, and medium-sized earthquakes within the SBS suggest that movement along these structures may be a recurring phenomenon, with yet to be defined repeat intervals and rupture lengths. In contrast to the Subandes thrust belt farther north, where eastward-migrating deformation has generated a well-defined thrust front, the SBS records spatiotemporally disparate deformation along structures that are only known to the first order. We present herein the results of geomorphic desktop analyses, structural field observations, and 2D electrical resistivity tomography and seismic-refraction tomography surveys and an interpretation of seismic reflection profiles across suspected fault scarps in the sedimentary basins adjacent to the Candelaria Range (CR) basement uplift, in the south-central part of the SBS. Our analysis in the CR piedmont areas reveals consistency between the results of near-surface electrical resistivity and seismic-refraction tomography surveys, the locations of prominent fault scarps, and structural geometries at greater depth imaged by seismic reflection data. We suggest that this deformation is driven by deep-seated blind thrusting beneath the CR and associated regional warping, while shortening involving Mesozoic and Cenozoic sedimentary strata in the adjacent basins was accommodated by layer-parallel folding and flexural-slip faults that cut through Quaternary landforms and deposits at the surface.

Integrated geophysical and hydrochemical investigations for seawater intrusion: a case study in southwestern Saudi Arabia

The objective of the present study was to assess the deterioration in groundwater quality due to saline water intrusion in the Ad-Darb region of southwestern Saudi Arabia. An integrated approach using geochemical and geophysical methods was applied to assess the extent of saline water intrusion. Geochemical methods involved the determination of main groundwater facies present in the region using Piper and extended Durov plots. The geophysical methods used in the study included seismic refraction (SR), seismic refraction tomography (SRT), vertical electrical soundings (VES), and electrical resistivity tomography (ERT). Two SR and SRT surveys, three ERT surveys, and nine VES surveys were carried out. Piper plot shows that the water mainly belongs to the SO4-Cl type of anionic facies. The Durov plot indicates base ion exchange, linear mixing, and saline water intrusion as the main factors influencing the groundwater chemistry of the area. The TDS increases towards the coast, with values reaching as high as 9000 mg/l. These results confirm the interpretation of the vertical electrical sounding (VES) and electrical resistivity tomography (ERT) sections which indicates the presence of saline water intrusion, with the thickness of the intruded zone increasing towards the sea. The geoelectric resistivity results indicate four geoelectric resistivity layers. The average thickness of upper layer is 2.5 m and the resistivity ranges from 22.5 to 280 Ωm. The P wave velocity of this layer varies from 488 to 787 m/s. The second geoelectric resistivity zone consists of relatively disconnected layers with 10 to 33 m thickness and 52 to 120 Ωm resistivity. The third zone is a low resistivity zone, increasing in thickness westwards towards the sea and with resistivities of 0.3 to 19.5 Ωm. This is the main zone (consisting of unconsolidated Quaternary sediments) affected by saline water intrusion. This zone is intercalated with muddy marine intercalations, as indicated by its low resistivity (as low as 0.3 Ωm) The second and third geoelectric resistivity layer is represented by a single seismic zone with P wave seismic velocities ranging from 1231 to 1524 m/s, indicating the presence of water. The resistivity of the lowest layer ranges from 56 to 822 Ωm and corresponds to the basement. This bedrock layer has seismic velocities varying between 2315 and 3164 m/s.

The Use of the Seismic Refraction Tomography Survey Method and the Multi-Channel Analysis Technique of Surface Waves in the Geotechnical Assessment of the Al-Amal Apartments Site in Kirkuk, Northern Iraq Ali

The Use of the Seismic Refraction Tomography Survey Method and the Multi-Channel Analysis Technique of Surface Waves in the Geotechnical Assessment of the Al-Amal Apartments Site in Kirkuk, Northern Iraq Ali

Seismic refraction tomography surveys as a method for voids detection: an application to the archaeological park of Cava Ispica, Sicily, Italy

ABSTRACTGeophysical surveys are commonly used in areas where the presence of ancient civilizations is historically documented. These investigations are able to detect through indirect methods the presence of bodies or structures in the subsoil measuring the variations of some physical parameters, obtaining information about archaeological remains without causing harm to them.In the present study, we investigated the presence of anthropogenic buried cavities partially filled with rubble material, in an area located in the northern part of Cava Ispica, one of the most important archaeological sites located in south-eastern Sicily. The results of seismic refraction prospections, processed with tomographic methods, are presented and discussed. The entire valley contains prehistoric burial sites, Christian catacombs and residential units of various kinds. Despite the numerous searches made over past years, much still remains to be discovered.The seismic refraction tomographic data, analyzed in 3D, revealed the presence of low velocity values (<400 m/s) areas that, considering the lithotypes locally present and the features of other archaeological structures discovered during previous surveys, can be ascribed to the presence of possible cavities. The obtained results show how such geophysical inspections represent an important preliminary tool for archaeological surveys.

Application of 2D Resistivity Imaging and Seismic Refraction Tomography to Identify Sungai Batu Sediment Depositional Origin

Geophysical survey such as 2D resistivity imaging and seismic refraction tomography are non-destructive methods that widely used in subsurface exploration including archaeological study. The purpose of this survey is to identify the sediment deposition types of Sungai Batu area for Ancient River. Two study sites were chosen to conduct 2D resistivity imaging and seismic refraction tomography surveys. The 2D resistivity imaging survey was conducted using Poledipole array with 2.5 m minimum electrode spacing while seismic refraction tomography was performed using 5 kg sledgehammer as seismic source with 5 m geophone spacing. Roll along techniques are apply for the two methods in the study site 1 and 2. The study concludes that the subsurface of the study area comprise of 3 major soil types. The top soil (1st type) consists of loose and dry alluvium which indicated with resistivity value of >100 Ohm.m. The second type was saturated alluvium (clay and sand) with resistivity and velocity values of 10-50 Ohm.m and 300 Ohm.m and >3600 m/s respectively. The correlation of 2D resistivity imaging and seismic refraction tomography show that the depositional environment for this survey is causes by land sediments deposit.

Seismic velocity model and near‐surface geology at Mycenaean Tiryns, Argive Basin, Peloponnese, Greece

ABSTRACTA near‐surface seismic refraction tomography survey was completed in the surroundings of the Mycenaean citadel of Tiryns in the Argive Basin, Peloponnese, Greece. The survey encompassed 11 hectares at the Tiryns citadel, an archaeological site listed by the United Nations Educational, Scientific and Cultural Organization as world heritage with over 120 years of excavation history. Site characterization of the shallow subsurface was performed using two‐dimensional seismic refraction tomography of compressional (P) and horizontally polarized shear (SH) wave data along 12 and 9 profiles, respectively. The interpretation of the seismic refraction results is complemented by available archaeological stratigraphy, stratigraphic logs, and new structural data of the exposed bedrock. The tomograms show a transition from unconsolidated fine alluvium at the surface to consolidated clays and silts to hard limestone bedrock. The soil–bedrock boundary dips away from the citadel, influencing the geometry of overlying soils into wedges. Based on twodimensional tomograms of P‐and SH‐wave velocities, the Poisson ratio, shear modulus, Young’s modulus, and bulk modulus were estimated for a four‐layer geotechnical model, which will be used to study seismic site effects. The rock mass quality index of the bedrock at Tiryns is classified as fair to very poor.

Geophysical investigation of a landslide: The Altındağ landslide site, İzmir (western Turkey)

A geophysical survey including electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) was carried out to study a landslide site in the Altındağ district of İzmir city, western Turkey. In the city, landslide is one of the causes of natural hazard, and one of the most important landslide sites is located in the Altındağ district. The ERT studies were performed along four profiles over the landslide body in the directions of N–S and E–W. A Wenner–Schlumberger configuration was used during the resistivity measurements. The SRT survey was carried out using vertical geophones along a profile coincident with one of N–S trending resistivity profiles. Both the resistivity and the seismic data sets were processed by least-squares inversion techniques. In the first-arrival traveltime inversion of the surface refraction data, a method which is not based on ray tracing was used. Instead, the method used the functional description of traveltimes to generate the Jacobian and this matrix was calculated by using a finite-difference approximation based on the perturbation of the cell slownesses. Traveltime calculations were performed by an eikonal solver. Each technique produced useful results on the internal structure of the landslide, physical properties of the landslide material and sliding surface geometry. The landslide material was characterized by low resistivity and low seismic velocity. The resistivity results also indicated the zones associated with the high water and clay contents within the landslide mass. A layer of consolidated clastic rocks was considered to be the landslide bedrock, and it was represented by relatively high (moderate) resistivity and high velocity. Integrated interpretation of the resistivity and the seismic refraction data along one of N–S trending profiles helped us identify the geometry of the failure surface and the changes in the thickness of the landslide material. An undulating sliding surface is present along that profile and the landslide material gets thicker in the middle and the northern parts (the toe area) of the profile. Moreover, the water content is thought to have a key role in the mass movement in the landslide site.

2D Seismic Refraction Tomography Survey on Metasediment at a Proposed Development Site in Dengkil, Selangor

A geophysical survey using seismic refraction technique was carried out at a proposed development site at MINT­ Oengkil. The aim of the study was to characterize the subsurface materials based on seismic P-S wave velocities as well as to correlate those data with the lithologic logs and the standard penetration test (SPT) N-values. The study area is about 40 km squares, consisting of shale, slate and siltstones of the Kenny Hill Formation. Seismic surveys were carried out using ABEM MK 3 as a recording seismograph, and 24 units of 14Hz-frequency geophones 'to record the incoming seismic waves. The data were processed using an OPTIM software to produce sections of 20 velocity model profiles. Results show P-wave velocity of clayey silt (SPT=3-11) is ranging from 300-500mls and S-wave velocity is ranging from 80-100mls. P-wave velocity value for sandy silt (N=12-16) is ranging from 500-800mls and S-wave velocity is found ranging from 100-300mls. P-wave velocity value representing hard silt with gravel (N=20-50) is ranging from 900-1600mls and S-wave velocity is ranging from 300- 450mls. The S-wave velocity obtained from seismic surveys show only slight difference in values compared with those calculated using SPT N values. The calculated Poisson ratio value ranging from 0.43-0.47, representing clayey-silt and sandy­ silt. Velocity model sections were correlated well with the lithologic and SPT N values at each borehole. In the study area, the SPT test was terminated when the N value reached 50 which corresponds to the hard gravelly silt soil. The SPT test was only conducted in soft soil zone without penetrating the bedrock, whereas for the seismic survey, some of the 20 velocity model cross sections show P-wave velocity values range from 3500 to 4000mls at a depth of more than 15m. This high velocity values can be interpreted as representing slightly weathered to fresh rock.