Seismic Refraction Survey Research Articles

IDENTIFATION OF LANSLIDE DIMENSION BASED ON SEISMIC REFRACTION SURVEY IN TENGKILK VILLAGE, KARANGANYAR, CENTRAL JAVA

A seismic refraction survey was conducted at a landslide site, which had destroyed a road and several houses in Tengklik Village, Karanganyar, Central Java, Indonesia. The survey provided insight into the slope stratigraphy, as well as the dimensions of sliding area and depths of the slope failure planes. Field observations and drill-hole data were used to verify the accuracy of seismic refraction data. The seismic velocity measured in the top - sliding layer of sandy silt was less than 900 m/sec, while that in the underlying layer of silty sandstone ranged from 2400 to 900 m/sec. The stable bedrock of andesite breccia underneath the sliding soil layers was about 2500 m/sec. It was apparent that the failure surface was irregular, varies in depth. This failure plane exists at the contact of the andesitic breccia (bedrock) and the sliding layer of silty sandstone. The thickness of the sandy silt ranged from 3 to 5 m at lower part of sliding mass, while at the upper part ranged from 4 to 8 m. The estimated depth of the failure surface ranged from 12 to 24 m. The volume of mass movement is estimated about 111.386 m3 . It was also found that the presence of mountain block at the bedrock of andesitic breccia may resist the movement.

Magnetic and seismic refraction survey for site investigation of an urban expansion site in Abha District, Southwest Saudi Arabia

Ground magnetic and seismic refraction survey is carried out on an urban extension site in the southwest of Ahud Rufeidah town, southwest Saudi Arabia. The purpose of the survey was to map the surface topography of the bedrock and thickness of the alluvium overburden. The ground magnetic survey based on an assumption that the alluvial sediments is less or non-magnetic relative to the underlying gneiss basement rock. In this context, a total of 3,750 survey stations were measured along 40 east–west survey profiles, striking roughly perpendicular to the extension of the expected structures. In addition, 13 seismic refraction spreads were conducted along four seismic survey profiles across the expected pathways of buried alluvial channels in order to provide additional details about the depth and boundaries of the buried channels. The ground magnetic survey results show the presence of a basin combining two sub-basins filled with alluvium sediments that occupy the middle area of the investigated site. This basin is a closed basin that has no outlet, and there are four small and narrow channels that convey water and sediments from the eastern and southern hills into sub-basins. These channels are represented by narrow and elongated low magnetic anomalies extending towards the basinal area. The thickness of the alluvial sediments is verified using seismic refraction survey that indicates a greater thickness, exceeds 20 m, of low velocity sedimentary overburden inside the interpreted sub-basins and surrounding buried alluvial channels. These soft alluvial sediments can be deceptive and dangerous for urban foundations.

High resolution seismic imaging at the planned tunnel entrance to the Forsmark repository for spent nuclear fuel, central Sweden

The Swedish Nuclear Waste Management Company (SKB) plans to build a repository for storage of high‐level radioactive spent nuclear fuel at the Forsmark site in central Sweden at a depth of about 470 m. The planned repository will cover an area of about 3.6 km2 at this depth. Prior to beginning excavation and tunneling, some detailed geophysical surveys are being performed at the planned site. One of these was a refraction seismic survey to determine depth to bedrock in the vicinity of the planned access ramp. Two lines, each about 300 m long and spaced about 35 m apart, were acquired in August 2011. Since the bedrock topography is known to be highly variable, a close receiver (2 m) and source (6 m) spacing was required to map it. This close spacing allowed the data also to be treated as reflection seismic data and some adjustments to the acquisition procedure were made in the field with this in mind to aid in the later processing. The main adjustment was that seismic data were recorded on all geophone stations simultaneously. That is, as shots were fired along one line, data were recorded along both that line and the other one. Likewise, when shots were fired along the other line, data were recorded along that line and the first line. This adjustment allowed semi‐3D coverage between the lines. Results from first break traveltime tomography along the lines indicate a depth to bedrock that is greater than that found from geotechnical observations along the lines. This discrepancy is attributed to the uppermost bedrock being highly fractured and having a velocity significantly below that expected from the intact bedrock deeper down. Reflection seismic processing of the data shows a reflection at about 20 ms (about 60 m). The reflection is interpreted to have a gentle northwesterly dip component to it. Comparison with core data in the area suggests that the reflection is from a thin (a few metres thick) fracture zone, although none of the boreholes actually penetrate the reflector where it is mapped by the seismic data. This fracture zone may be part of a larger fracture zone mapped by core drilling further to the east. The newly mapped reflector may be crossed by the ramp when excavation begins. Further seismic surveying towards the west is required to verify if this will be the case.

A seismic refraction survey conducted for the Ocean Bottom Cabled Seismometer system installed in the Japan Sea

A seismic refraction survey conducted for the Ocean Bottom Cabled Seismometer system installed in the Japan Sea

Tracing of the Avenue of the Ram-Headed Sphinxes Remains Using Geophysical Investigations, Luxor, Egypt

Throughout 3000 years ago, over the New Kingdom in the Pharaonic period, the Ram-headed Sphinxes Avenue connected Karnak and the Temples of Luxor, a processional avenue was lined on both sides by 1200 statues of sphinxes. The lining of the avenue was erased. Centuries over centuries this avenue has been buried with its statues under about 2 m of silt and sand, and urban development covered it with housing, asphaltic streets, and other structures, obscuring its route and interrupting this dramatic connection. This paper focuses on the discovery of some of these Sphinx statuses and remains at a suggested part of the avenue using both near-surface magnetic and shallow seismic refraction methods. A gradiometer survey was conducted in an area that amounted 576 m2 as (48 m × 12 m) to measure the vertical magnetic gradient with a high resolution instrument with 0.25 m sampling interval. A superior detection was accomplished by using the analytic signal and Euler deconvolution techniques. The shallow seismic refraction survey was done in the same area to illustrate the lithology of layers material with 1 m interval; both P and S waves were measured to calculate the geotechnical properties of the area to sustain the sketch of structures’ boundaries. We have lucratively detected six main structures; they can be the pedestal of these Ram-headed Sphinx statues. Mining a small part of the study area has proven the reliability of, both the magnetic and shallow seismic refraction discoveries, and the shallowness and composition of the detected features.

SEISMIC REFRACTION METHOD: A TECHNIQUE FOR DETERMINING THE THICKNESS OF STRATIFIED SUBSTRATUM

The seismic refraction survey is a very important geophysical technique used in the investigation of subsurface characteristics. This is why this study was carried out to emphasize the ability of the seismic refraction method in determining the thickness of stratified layers of soil and rock. The results obtained are generalized expressions that relate travel time, offset distance, velocity and thickness of subsurface layers.

Integration of surface-based tomographic models for zonation and multimodel guided extrapolation of sparsely known petrophysical parameters

We integrate the information of multiple tomographic models acquired from the earth’s surface by modifying a statistical approach recently developed for the integration of cross-borehole tomographic models. In doing so, we introduce spectral cluster analysis as the new core of the model integration procedure to capture the spatial heterogeneity present in all considered tomographic models and describe this heterogeneity in a fuzzy sense. Because spectral cluster algorithms analyze model structure locally, they are considered relatively robust with regard to systematically and spatially varying imaging capabilities typical for geophysical tomographic surveys conducted on the earth’s surface. Using a synthetic aquifer example, a fuzzy spectral cluster algorithm can be used to integrate the information provided by 2D tomographic refraction seismic and DC resistivity surveys. The integrated information in the fuzzy membership domain is then used to derive an integrated zonal geophysical model outlining the major structural units present in both input models. We also explain how the fuzzy membership information can be used to identify optimal locations for sparse logging of additional target parameters, i.e., porosity information in our synthetic example. We demonstrate how this sparse porosity information can be extrapolated based on all tomographic input models. The resultant 2D porosity model matches the original porosity distribution reasonably well within the spatial resolution limits of the underlying tomographic models. Consecutively, we apply this approach to a field data base acquired over a former river channel. Sparse information about natural gamma radiation is available and extrapolated on the basis of the fuzzy membership information obtained by spectral cluster analysis of 2D P-wave velocity and electrical resistivity models. This field data shows that the presented parameter extrapolation procedure is robust, even if the locations of target parameter acquisition have not been optimized with regard to the fuzzy membership information.

Site-specific shear wave velocity investigation for geotechnical engineering applications using seismic refraction and 2D multi-channel analysis of surface waves

In order to quantify the near-surface seismic properties (P- and S-wave velocities, and the dynamic elastic properties) with respect to the depth at a specific area (6th of October club), we conducted a non-invasive and low cost active seismic survey. The primary wave velocity is determined by conducting a P-wave shallow seismic refraction survey. The dispersive characteristics of Rayleigh type surface waves were utilized for imaging the shallow subsurface layers by estimating the 1D (depth) and 2D (depth and surface location) shear wave velocities. The reliability of the Multi-channel Analysis of Surface Waves (MASW) depends on the accurate determination of phase velocities for horizontally traveling fundamental mode Rayleigh waves. Consequently, the elastic properties are evaluated empirically. The Vs30 (average shear wave velocity down to 30m depth), which is obtained from the MASW technique, plays a critical role in evaluating the site response of the upper 30m depth. The distribution of the obtained values of Vs30 through the studied area demonstrates site classes of C and D, according to the NEHRP (National Earthquake Hazard Reduction Program) and IBC (International Building Code) standards.

Understanding the structure of subducting plates

Seismic studies are helping scientists learn more about the structure of subducting oceanic plates. Using an air gun array and 80 ocean bottom seismometers spaced along a 500‐kilometer profile, Fujie et al. conducted a seismic reflection and refraction survey at the Kuril trench in the northwestern Pacific margin, where part of the Pacific plate is subducting beneath the Okhotsk plate. They estimated the water content of the subducting plate by measuring the velocity of seismic waves—both P waves and S waves—through the plate. The ratio of seismic wave velocities (Vp/Vs) is an indicator of the lithology, porosity, and presence of fluid in the plate. Their findings showed that the water content in the plate increased toward the trench, along with greater bending and fracturing, suggesting that water enters the plate through the fractures. The authors conclude that the bending and fracturing of the plate as it subducts play an important role in the water cycle in subduction zones. (Geophysical Research Letters, doi:10.1029/2012GL054340, 2013)

Hydrogeophysical Investigations in a Typical Khondalitic Terrain to Delineate the Kaolinised Layer using Resistivity Imaging

Abstract: Investigation for high yielding water wells in the khondalitic terrain (graneti ferrous silliminite gnesiss) is mostly faced with the problem of identification of the extent of the depth of kaolinisation of the aquifer. The traditional Vertical Electrical Sounding survey, Seismic Refraction survey and Very Low Frequency Electromagnetic survey could not identify the kaolinisation of the aquifer in the present investigations. The Two Dimensional (2D) Resistivity and Induced Polarization (IP) Imaging surveys are attempted for the identification of kaolinised layer and depth of kaolinisation. Number of 2D Resistivity and IP Imaging profiles were conducted near Chipurupally in Vizianagaram district of Andhra Pradesh, India along successful and failed wells located within short distances. Resistivity and IP measurements were carried out using an ABEM SAS 4000 Terrameter. The resistivity and I.P. images have provided a clear view of the thickness of the highly weathered zone (kaolinised zone) at both successful and failed wells. The highly weathered zone is identified with the resistivity values below 25 ohm.m. The depth of highly weathered material at failed well is extended about 8-10 m more deeper than the successful wells at some places to as much as 20 m more deep at some other places. This extended deeper kaolinisation of the aquifer is responsible for failure of wells. Layers having resistivities between 25 – 65 Ohm.m are identified as aquifer layers which are composed of moderately weathered and fractured khondalitic suit of rocks (Garnti ferrous sillimanite/biotite gneiss). Layers with resistivities greater than 65 Ohm.m are interpreted to have basement characteristics belonging to the granite gneiss. Interestingly IP imaging has not provided any greater insights in delineating the kaolinistion of the aquifer when compared to resistivity Imaging, in fact resitivity imaging has shown greater depths of kaolinisation than IP Imaging.

Detection of karstic limestone bedrock by shallow seismic refraction in an area west of Assiut, Middle Egypt

The main goal of this study was the detection of complex surface and internal structures of limestone bedrock over the entire area planned for urban development on the lower Eocene plateau, west of Assiut, Egypt. A 2.5D shallow seismic refraction survey provided sufficient resolution for mapping faults and karst at the scale required for civil engineering plans. The 3D P-wave seismic velocity map was developed from integration of a series of 2D spreads recorded along a 2D grid using only inline spreads.

Systematic changes in the incoming plate structure at the Kuril trench

Recent seismic structural studies in trench‐outer rise regions have shown that Vp within the incoming oceanic plate systematically decreases toward the trench, probably owing to bending and fracturing of the plate. To understand the mechanisms acting to reduce Vp, Vs is critical because the Vp/Vs ratio is a sensitive indicator of lithology, porosity, and the presence of fluid. In the outer rise region of the Kuril trench, we conducted an extensive seismic refraction and reflection survey that revealed systematic changes in Vp, Vs, and Vp/Vs. Our results suggest that water content within the incoming oceanic plate increases toward the trench accompanied by the development of bending‐related fractures at the top of the oceanic crust, consistent with the seawater percolation. Our results support the idea that plate bending and fracturing during the bending in the outer rise of the trench play an important role in the water cycle of subduction zones.

Seismic Refraction Survey of Tar Sands Deposits in Ijebu East of Ogun State Southwestern Nigeria

The interest in unconventional oil resources such as tar sands and oil shale is known as great economic importance by the governments and industries have encouraged researches in the development of these resources. Vast tar sands resources have not been adequately explored and exploited by the Nigeria Government except for accumulation of oil, natural gas and other minerals but bitumen has proven to be of great value. This motivated this study to map the ttar sands deposit at Imeri in Ijebu-Imushin within the Ijebu- East Local government area in Ogun State using seismic refraction survey. A seismic refraction survey at Imeri, Ijebu-Imushin of Ijebu-east carried out using ABEM seismograph Terraloc Mark 6 Version 2.22. Thirteen (13) traverse were taken along five profiles in which both forward and backward shooting were measured to cover a spread of 72m in each of the traverse. Pickwin software was adopted to analyze the results obtained in order to give information on first arrival time and velocity of the first and second layers. A model of the earth structure was achieved by the used of ploterrafa (refraction) software and interpretation to determine the thickness of the first layer from the processed data based on the known geology of the area. The velocities of the first layers of five profiles ranges from (0.75-1.30)km/s and the second layers velocities ranges were from (1.31-2.51)km/s. The presence of tar sands was observed in traverse 6, 7, 8, 9&12, with velocity values (1.12-1.44)km/s, (1.12- 1.86)km/s and (1.10-1.47)km/s respectively. The depth of the first layer of the above profile ranges from (5.00- 7.10)m. traverses 1-5, 10,11 and 13 shows the presence of clayed sand, sand, sand stone clay and sand with water saturation respectively was observed. The information provided by the analysis and interpretation of the first arrival time and velocities of the first and second layers concise with geologic trends of the rock type in the study area. It was observed that the velocities of the first and second layers were related to the velocities of different earth materials and their depth to the surface.

Allowable Bearing Capacity for Shallow Foundation in Eket Local Government Area, Akwa Ibom State, Southern Nigeria

P-wave and S-wave velocities were obtained from seismic refraction survey in the foundation layer of Eket, the study area. The Tezcan’s approach discussed extensively in the work was used in conjunction with the existing mathematical relations between elastic parameters and seismic refraction velocities for the study of foundation layers in the study area. Based on the results, the elastic constants, allowable bearing pressure/capacity, ultimate bearing capacity and other parameters in Table 1 were determined. The result shows that allowable bearing pressure increases with increase in shear modulus and shear wave velocity. The empirical relation between allowable bearing capacity and shear modulus shows that the allowable bearing capacity increases with depth. Comparing our findings with some ranges of safe allowable bearing capacities of similar non cohesive/granular soils in literatures, the second layer with allowable bearing capacity range of 72.56 - 206.63 kN·m-2 (average = 154.78 kN·m-2) has been considered to be the safe shallow engineering foundation in the study area. The empirical relations between allowable bearing capacities shear modulus and shear wave velocity, in conjunction with the inferred maps, which serve as our findings, will be used as guide in the location of foundations. The inferred ultimate and allowable capacities correlate maximally for the two shallow foundations penetrated by the seismic waves. This perfect correlation reflects the uniqueness of the method.

Integration of Seismic Refraction and 2D Electrical Resistivity in Locating Geological Contact

The aim of this research is to locate the geological contact for engineering purpose applying seismic refraction and 2D electrical resistivity method. Resistivity and seismic refraction method was conducted on four survey lines with 3 lines running from NW to SE which about parallel to each other and 40 m apart while the fourth line was running from SW to NE. The 2D resistivity survey used minimum electrode spacing of 5 m and the survey used pole-dipole array with minimum current was 2 mA and maximum was 20 mA. The seismic refraction survey used 5 m geophone spacing with offset shot was + 30 m and - 30 m. Resistivity results generally show the area was divided into two main zones, alluvium with resistivity value of 10 - 800 ohm-m, and granite bedrock with resistivity value of > 2500 ohm-m. There is a geological contact between granite and alluvium. The seismic results show the area consists of two layers. The first layer (top layer) with velocity of 460 - 900 m/s which was alluvium mixed with boulders. The second layer with velocity of 2060 - 3140 m/s with depth 71 - 90 MSL. The thickness of the overburden is 5 - 15 m.

A comparison of seismic and radar methods to establish the thickness and density of glacier snow cover

AbstractWe show that geophysical methods offer an effective means of quantifying snow thickness and density. Opportunistic (efficient but non-optimized) seismic refraction and ground-penetrating radar (GPR) surveys were performed on Storglaciären, Sweden, co-located with a snow pit that shows the snowpack to be 1.73 m thick, with density increasing from ∼120 to ∼500 kg m–3 (with a +50 kg m–3 anomaly between 0.73 and 0.83 m depth). Depths estimated for two detectable GPR reflectors, 0.76 ±0.02 and 1.71 ± 0.03 m, correlate extremely well with ground-truth observations. Refraction seismic predicts an interface at 1.90 ± 0.31 m depth, with a refraction velocity (3730 ± 190 ms–1) indicative of underlying glacier ice. For density estimates, several standard velocity-density relationships are trialled. In the best case, GPR delivers an excellent density estimate for the upper snow layer (observed = 321 ± 74 kg m–3, estimated = 319 ± 10 kgm–3) but overestimates the density of the lower layer by 20%. Refraction seismic delivers a bulk density of 404 ±22 kgm–3 compared with a ground-truth average of 356 ± 22 kg m–3. We suggest that geophysical surveys are an effective complement to mass-balance measurements (particularly for controlling estimates of snow thickness between pits) but should always be validated against ground-truth observations.

High Resolution in Seismic Refraction Tomography for Environmental Study

Seismic refraction tomography (SRT) involves more complex mathematic algorithms to fit more flexible model. In the field procedure SRT in generally needs more shot points than standard seismic refraction survey to obtain high resolution profile. In this seismic refraction study, we have used 9 shot-points for inline and 10 shot-points for offset in purpose to obtaine high resolution of seismic refraction tomography. During a recent geophysical test site, the subsurface material was mapped along survey line using seismic refraction method. Analyses of the site investigation data revealed that the studied site was made up of two layers of the subsurface. The upper layer has velocity values with range of 500 m/s to1500 m/s which can be classified as unconsolidated surface deposits and mixtures of unsaturated sands and gravels. Meanwhile the lower layer has velocity values with range of2000 m/s to5500 m/s which is classified as compacted fine’s soil due to high pressure of the overburden. Analysis of seismic refraction data demonstrated that refraction tomography software systems are able to reveal subsurface material which represented by their seismic velocity value. Furthermore, the velocity model obtained in this study is agreed with its synthetic modelling result as initial model. This validity and reasonable results was able to assist in interpretation of the seismic refraction method for the environmental study.

Applying the Seismic Refraction Tomography for Site Characterization

Seismic refraction method is a geophysical method that has been developed for shallow subsurface investigation. It provides 2-dimensional profiles including depth and distance that simplified the characterization of relatively large volumes of the subsurface. Interpretation of seismic refraction data using seismic tomography involves continuous velocity gradient across a subsurface which is more effective for site characterization compared to conventional seismic refraction. Three parallel seismic refraction survey lines were conducted at Kaki Bukit, Perlis with the aim of characterizing the subsurface of the area. 2m geophone spacing was used with total length of 46m. The separation between lines is 20m. Weight drop of 20kg and steel plate were used as seismic source. A total of 20 shotpoints were performed for survey line L1, 23 shotpoints for survey line L2 and 22 shotpoints for survey line L3. The high quality seismic data obtained were then processed using SeisOptPicker and SeisOpt2D software to produce a seismic tomography section for each survey line. Results indicate that the study area is said to have 4 main layers with velocity increase fairly with depth. The first layer with velocity 300-500 m/s predominantly consists of top soil and form overburden. Second layer with velocity 500-800 m/s is suggested to be a highly weathered limestone. The third layer represents by highly fractured limestone with velocity 800-1500m/s. Limestone bedrock represent by the fourth layer with velocity > 2000m/s. Competent limestone bedrock is identified at survey line L3 with velocity > 3000m/s.

Landslide investigation study using seismic refraction and 2D electrical resistivity imaging (ERI) technique in Ooty, Nilgiri District, Tamilnadu

The aim of this paper is to investigate landslide prone areas in Nilgiri hills which have caused damage to people and properties and to devise preventive steps to be taken in the events of future landslides. Our study area was situated at Ooty region, Nilgiri District, Tamilnadu. In this study we use the seismic refraction survey carried out across landslides located near the villages in Allanchi, Kundha, The 2D electrical resistivity imaging (ERI) surveys are acquired near the villages of katerri, Kunda. Topographic models of landslide surface are made for all three sites. Seismic and resistivity imaging method give detailed of the soil, lithomorphic clay and weathered gnessic rocks in the study area. In the study area there are two types of landslides; thin soil slides, and lesser rock mass slides. Landsliding in the study area can be caused by high rainfall and seismic activity. This case study focuses on paleo slides and look at predicting areas of future landslide in Ooty area. Key words: Landslide, seismic refraction, 2D electrical resistivity imaging (ERI), resistivity, Ooty.

From two-way time to depth and pressure for interpretation of seismic geometries and velocities offshore

SUMMARY The effect of water and rock loading on seismic velocities and consequently on interpreted geometries is often underestimated in offshore studies. Direct comparative analysis of interval velocity patterns between areas of significantly different water depth and thickness of rock overburden requires various pressure related changes in velocity to be accounted for. Presentation of velocity models as a function of pressure rather than two-way time, or depth, emerges as a possible solution. An accurate velocity model is essential for meaningful timeto-depth conversion of interpreted seismic horizons. Ideally, it should be based on integration of seismic velocities from well log measurements, refraction seismic surveys and from stacking of multi-channel marine reflection data. In some cases velocities derived from stacking of high quality long streamer marine reflection seismic data correlate reasonably with well log measurements and velocities derived from refraction seismic studies, and provide clues to reasonable depth conversion and lithology interpretation.