Shallow Seismic Reflection Surveys Research Articles

Late Quaternary Activity Studies on the Lintong–Chang’an Fault Zone in the Weihe Graben, Central China, Using Combined Techniques

The Lintong–Chang’an Fault Zone (LCFZ) is an important active structure in the Weihe Graben (central China). The study on the activity of the LCFZ is not only of great significance to explore the regional tectonic mechanism, but also has practical value in urban seismic mitigation and disaster relief. In this study, based on high-resolution remotely sensed imagery, shallow seismic reflection survey, borehole data and excavation of a foundation pit, we determined the distribution and activity of the Wangjiabian–Houjiawan fault (a branch fault of the LCFZ) in the Shaoling Loess Tableland. Combined with previous studies, we further inferred that the vertical displacements were 0–6 m along the LCFZ, but most displacements were around 1 m. Furthermore, there are eight locations where no displacements have been found in the Late Pleistocene strata. The offsets on the fault zone since the Late Pleistocene display a wave-like pattern, which is unrelated to the regional topographic expression. Compared to other faults in the Weihe Graben, the activity of the LCFZ in vertical component is relatively weak, implying a possible strike–slip motion. In addition, a major active fault may exist on the northwest side of this fault zone, bearing part of the fault motion in this region.

Stratigraphic and geotechnical characterization of regionally extensive and highly competent shallow sand units in the southern North Sea

A detailed stratigraphic and geotechnical investigation of the uppermost 50 m below the sea floor was carried out for parts of the German North Sea sector using combined information from shallow seismic reflection surveys, 50‐m‐long sediment cores and cone penetration tests covering an area of ~150 km2. While most recent studies concentrate on unusual features such as buried tunnel‐ or river‐valleys, this study focused on the less well understood, regionally dominant sand units deposited after the retreat of the last glaciers in this region. We identified two sandy units which dominate the late‐ to post‐Saalian geology: (i) the Upper Fluvial Member, believed to be derived from deposition of the Weser, Ems and Elbe palaeorivers as well as other tributaries of the Elbe Palaeovalley in the NE during the Saalian; and (ii) the Aeolian Member, which correlates with periglacial deposits of Weichselian age. Additionally, a Saalian Buried Valley Member believed to comprise fluvial deposit was also identified. Key stratigraphic units within the uppermost 50 m below the sea floor were also identified and mapped. Detailed geotechnical properties were obtained for each of the individual stratigraphic units. The regional extent of the Aeolian and Upper Fluvial Members was documented in the region west of the Elbe Palaeovalley and south of the Dogger Bank, where their geotechnical properties are important for foundation design. In conclusion, the study complements the established regional geotechno‐stratigraphy and offers new and detailed publically accessible information beneficial for offshore wind farm development within the region.

The study of applicability of the very shallow geophysical exploration method for the strike-slip fault (part 2; S-wave shallow seismic reflection survey and two-dimensional electrical resistivity survey): the case study of the Go-mura fault zone and Yamada fault zone

The study of applicability of the very shallow geophysical exploration method for the strike-slip fault (part 2; S-wave shallow seismic reflection survey and two-dimensional electrical resistivity survey): the case study of the Go-mura fault zone and Yamada fault zone

Kinematic Characteristics of the Jiangsu Segment of the Anqiu–Juxian Fault in the Tanlu Fault Zone, Eastern China

Abstract The Tancheng–Lujiang (Tanlu) fault zone is the most active fault zone in eastern China. In this zone, the Anqiu–Juxian fault represents the most recently active fault and has the clearest surface traces and the highest seismic risk. This study comprehensively analyzes the kinematic characteristics of the Jiangsu segment of the Anqiu–Juxian fault using field geological surveys, trenches, shallow seismic reflection surveys, combined borehole section exploration, and middepth seismic reflection surveys. The results show that the Jiangsu segment of the Anqiu–Juxian fault features a single branch in the bedrock outcrop area, with reverse strike-slip motion near North Maling Mountain and Chonggang Mountain and normal strike-slip motion near South Maling Mountain. The sedimentary zone features two normal strike-slip faults (east and western branches), which represent the synsedimentary boundaries of a half-graben rift basin. The kinematic process is represented by rotational movement along the strike-slip fault with a curved path. The resulting tensile and compressive stresses are accommodated by dip-slip movement at both ends of the strike-slip fault. The activity of the Jiangsu segment of the Anqiu-Juxian fault can be divided into two periods. The first period of activity occurred before the later part of the Late Pleistocene, when movement along this curved segment occurred, forming the western branch of the Xinyi segment and the eastern branch of the Suqian segment. The second period of activity started in the later part of the Late Pleistocene and continues today. It is characterized by activity on the western branch of the Xinyi segment and the western branch of the Suqian segment of the Jiangsu segment, while the eastern branch of the Xinyi segment and the eastern branch of the Suqian segment became inactive and can be considered Late Pleistocene faults. The maximum vertical slip rate of the Jiangsu segment of the Anqiu–Juxian fault since the Pleistocene has been 0.28 mm/a. The Jiangsu segment of the Anqiu–Juxian fault formed via dextral strike-slip faulting, mainly due to the southward movement of the region to the east of the fault.

A New Approach to Predict Hydrogeological Parameters Using Shear Waves from the Multichannel Analysis of Surface Waves Method

For near-surface contaminant characterization, the accurate prediction of hydrogeological parameters in anisotropic and heterogeneous environments has been a challenge since the last decades. However, recent advances in near-surface geophysics have facilitated the use of geophysical data for hydrogeological characterization in the last few years. A pseudo 3-D high resolution P-wave shallow seismic reflection survey was performed at the P Reactor Area, Savannah River Site, South Carolina in order to delineate and predict migration pathways of a large contaminant plume including trichloroethylene. This contaminant plume originates from the northwest section of the reactor facility that is located within the Upper Atlantic Coastal Plain. The data were collected with 40 Hz geophones, an accelerated weight-drop as seismic source and 1 m receiver spacing with near- and far-offsets of 0.5 and 119.5 m, respectively. In such areas with near-surface contaminants, a detailed subsurface characterization of the vadose zone hydraulic parameters is very important. Indeed, an inexpensive method of deriving such parameters by the use of seismic reflection surveys is beneficial, and our approach uses the relationship between seismic velocity and hydrogeological parameters together with empirical observations relating porosity to permeability and hydraulic conductivity. Shear wave velocity ( Vs) profiles were estimated from surface wave dispersion analysis of the seismic reflection data and were subsequently used to derive hydraulic parameters such as porosity, permeability, and hydraulic conductivity. Additional geophysical data including core samples, vertical seismic profiling, surface electrical resistivity tomography, natural gamma and electrical resistivity logs allowed for a robust assessment of the validity and geological significance of the estimated Vs and hydrogeological models. The results demonstrate the usefulness of this approach for the upper 15 m of shallow unconsolidated sediments even though the survey design parameters were not optimal for surface wave analysis due to the higher than desired frequency geophones.

Shallow seismic reflection survey for imaging deep-seated coal layer - Case study from Muara Enim coal

Indonesia has a great potential for deep-seated coal resources. To assist and support the deep-seated coal exploration, a shallow seismic reflection method is applicable for this purpose. This study has conducted a shallow seismic reflection method in Musi Banyuasin Regency, South Sumatera Province. The Muara Enim coal target varies from 100 to 500 meters from the surface. The thickness of the coal layer varies from 2 to 10.65 meters. This study uses 48 channels with 14 Hz single geophone and MiniSosie as the energy source. The receiver and source interval is 15 meters. This study uses a fixed receiver and moving source configuration. From the interpreted seismic section, this study identified a deep-seated coal layer target. These layers are Mangus, Burung, Benuang, Kebon and Benakat layers. A simple interpretation is analyzed by combining the seismic amplitude characteristics and the thickness of the coal layer from the borehole data. From the interpreted seismic section, deep-seated coal layer targets have strong amplitude characteristics and are continuous from southwest to the northeast with a down-dip of around 20-30°. This study helps to inform the operator companies who develop the utilization of deep-seated coal (coalbed methane, underground coal gasification and underground coal mining) about the effective and proper geophysical method for imaging deep-seated coal layer.

Detecting the Weathering Structure of Shallow Geology via for Ground-Penetrating Radar

ABSTRACT Taiwan exhibits very complicated features (Figure 1). Under the subtropical climate of high temperatures and moisture, the weathering reactions are both powerful and fast. The result, after weathering is the formation of regolith which often accumulates at hills, tablelands and slopes, and which can easily induce engineering problems such as slides and collapse during the rainy season. At present, the engineering industry often adopts methods such as shallow seismic reflection survey and drilling sample to investigate the properties and depth of regolith profiles. The drawback is that it not only damages the structure of the existing ground, but the sampling range is also limited, cost is higher and operation speed is slower. For shallow seismic reflection survey, on the other hand, scattered energy of reflection waves and slow speed of weathering, have entailed a poor resolution of stacked profile and the impossibility of accurate reading. In order to seek an accurate, fast, economic and non-destructive method that can thoroughly investigate weathering and characteristics of underground geology, an attempt has been made to adopt GPR for detecting underground weathering of shallow layer. The experiment is done in mountainous area of Houlong Township, Miaoli County; the rock type of stratum is Shangshan sand rock of Pleistocene Toukoshan Formation. The research results indicate that there is an obvious reflection surface of electromagnetic waves, where the GPR can easily and accurately read out underground weathering. The result verifies that the method is not only accurate, fast and capable of reducing the high cost of seismic survey and drilling, but can also act as reference for regolith surveys for future industry.

Geological prediction ahead of tunnel face using the Shallow Seismic Reflection survey for Tunnel (SSRT) from the tunnel and the ground surface

Geological prediction ahead of tunnel face using the Shallow Seismic Reflection survey for Tunnel (SSRT) from the tunnel and the ground surface

An Improved Technique for Static Correction in a High Resolution Shallow Seismic Reflection Data using Difference in Reflection Times.

Shallow Seismic reflection survey was carried out in Zaria, located in the basement complex of central northern Nigeria, with the aim of characterising the granitic batholith. However, the effect of near surface material, which could make reflection events appear disjointed or deeper than they really are, could be enormous if not corrected for. This work sets out to correct for this events by making use of difference in reflection times estimated from initially known models of the subsurface. During the data acquisition the receivers where placed at 1 m interval, with a constant offset of 1 m. the common midpoint (CMP) method with a 12 fold coverage was employed. Previous refraction tomography model carried out in the area was used as a guide during the 2D velocity model generation, making use of the observed travel times. The observe time was used to generate the initial model, which was later corrected using the previous known subsurface model, thereby noting the difference in travel time induced by the near surface materials. The results obtained showed that the reflection events were more coherent and in their actual reflecting point on the statically corrected seismic sections, than the section without static correction because of the excess time from the near surface material with variable p wave velocity. This experiment has proved that difference in reflection travel times obtained from previous known model or borehole information in conjunction with the observed travel times serve as a better tool in applying static correction to seismic reflection data, than any previous known conventional methods that relies on a single technique. Key Words: Static correction, High resolution, Seismic reflection, Reflection times

Structural and stratigraphic control on the migration of a contaminant plume at the P Reactor area, Savannah River site, South Carolina

Geophysical methods, including a shallow seismic reflection (SSR) survey, surface and borehole ground-penetrating radar (GPR) data, and electrical resistivity imaging (ERI), were conducted at the Savannah River site (SRS), South Carolina, to investigate the shallow stratigraphy, hydrogeophysical zonation, and the applicability and performance of these geophysical techniques for hydrogeological characterization in contaminant areas. The study site is the P Reactor area located within the upper Atlantic coastal plain, with clastic sediments ranging from Late Cretaceous to Miocene in age. The target of this research was the delineation and prediction of migration pathways of a trichloroethylene (TCE) contaminant plume that originates from the northwest section of the reactor facility and discharges into the nearby Steel Creek. This contaminant plume has been migrating in an east-to-west direction and narrowing away from the source in an area where the general stratigraphy along with the groundwater flow dips to the southeast. Here, we present the results from a stratigraphic and hydrogeophysical characterization of the site using the SSR, GPR, and ERI methods. Although detailed stratigraphic layers were identified in the upper approximately 50 m (164 ft), other major findings include (1) the discovery of a shallow (23 m [75 ft] from the ground surface) inverse fault, (2) the detection of a paleochannel system that was previously reported but that seems to be controlled by the reactivation of the interpreted fault, and (3) the finding that the hydraulic gradient seems to have a convergence of groundwater flow near the area. The interpreted fault at the study site appears to be of upper Eocene age and may be associated with other known reactivated faults within the Dunbarton Triassic Basin. The coincident use of the SSR and ERI methods in conjunction with the complementary 50-, 100-, and 200-MHz GPR antennas allowed us to generate a detailed geologic model of the shallow subsurface, suggesting that the migration of the TCE plume is constrained by (1) the paleochannel system with respect to its migration direction, (2) the presence of an inverse fault that may also contribute to the paleochannel growth and structural evolution, and (3) the local groundwater flow volume with respect to its longer and narrower shape away from the source updip stratigraphic bedding.

Significance of shallow seismic reflection (SSR) and ground penetrating radar (GPR) profiling on the Modern Coast line History of the Bedre area, Eğirdir Lake, Isparta, Turkey

Lake level changes and settlement places constitute the main problems in controlling the coastal environment along the Eğirdir Lake, SW Turkey. The Quaternary geology in the Bedre Coast was studied based on shallow seismic reflection (SSR) survey, ground penetrating radar (GPR) profiles, and the data derived from boreholes and investigations in the field. Thus, six seismic and five radar facies were determined respectively. The geological units from the basement rock to the Holocene deposits were imaged by the SSR technique. GPR technique is used for the shallower part, ranging from the ancient to the Modern lacustrin sediments. The Quaternary lake level changes, borehole, seismic and radar data indicate that a pond with a connected to the Lake around the Bedre area existed in the last century. Sand barriers, climate, topographical elevation and erosions of the basement rocks control the sedimentation of the back barrier of the coastal line. Marsh muddies and ancient beach sands are the main sediments of the pond area. From the profiles, ancient buried sand barriers were also seen in the lake side. In our view, as the previous lake level dropped from the highstand, the ancient sand barrier was formed which divided the lake and the pond and isolated a small inland lake which lies 4 m below the level of the coastal barrier. For agricultural purposes, artificial man-made constructions were done on the barrier and channels. Thus, dry agricultural land appeared in the last 50 years on the pond side.

Shallow seismic reflection survey across the North Matsuda fault in the Kozu-Matsuda fault system, central Japan

Shallow seismic reflection survey across the North Matsuda fault in the Kozu-Matsuda fault system, central Japan

Application of seismic stratigraphy and sedimentology to regional hydrogeological investigations: an example from Oak Ridges Moraine, southern Ontario, Canada

Hydrogeological models need to be supported by a clear understanding of the subsurface geology to provide effective assessment, flow modelling, or management of groundwater regimes. This paper illustrates how geophysical and sedimentological data can be used to significantly improve watershed-scale hydrostratigraphic models by advancing our understanding of the subsurface through regional hydrogeological investigations in the Greater Toronto Area. The example of a 3 km shallow seismic reflection survey that traverses a buried channel within Bowmanville Creek watershed, Oak Ridges Moraine, Ontario, illustrates a basis for linking geophysical and sedimentological properties to regional hydrostratigraphic parameters. Seismic reflection methods plus seismic stratigraphy and a well-constrained three-dimensional geological framework have helped to (i) identify regional hydrostratigraphic units, (ii) define properties and trends of these units–facies, (iii) improve depositional models that assist hydrogeological analysis, and (iv) establish a hydrostratigraphic framework within a watershed. The extent, proportions, boundaries, and variation in internal properties of major hydrostratigraphic units could be identified to greater than 100 m depth. Geostatistical analysis of seismic amplitudes was used to provide a quantitative measure of heterogeneity in a glaciofluvial aquifer with inadequate parameter support. Benefits to engineering practice include improved siting of monitors and tests from portrayal of the spatial organization, geometry, and variability of hydrostratigraphic units based on sedimentary architecture and environments of deposition. Hydrogeological modelling can be improved with better knowledge of the geometry of aquifers and aquitards and grid-cell boundaries that correspond with the defined sediment boundaries that control properties.Key words: Oak Ridges Moraine, hydrogeology, seismic stratigraphy, southern Ontario, sedimentology.

Shallow subsurface applications of high-resolution seismic reflection

Shallow seismic reflection surveys have been applied to a wide variety of problems. For example, in many geologic settings, variations and discontinuities on the surface of bedrock can influence the transport and eventual fate of contaminants introduced at or near the ground surface. Using seismic methods to determine the nature and location of anomalous bedrock can be an essential component of hydrologic characterization. Shallow seismic surveys can also be used to detect earthquake faults and to image underground voids. During the early 1980s, the advent of digital engineering seismographs designed for shallow, high-resolution surveying spurred significant improvements in engineering and environmental reflection seismology. Commonly, shallow seismic reflection methods are used in conjunction with other geophysical and geological methods, supported by a well-planned drilling-verification effort. To the extent that seismic reflection, refraction, and surface-wave methods can constrain shallow stratigraphy, geologic structure, engineering properties, and relative permeability, these methods are useful in civil-engineering applications and in characterizing environmental sites. Case histories from Kansas, California, and Texas illustrate how seismic reflection can be used to map bedrock beneath alluvium at hazardous waste sites, detect abandoned coal mines, follow the top of the saturated zone during an alluvial aquifer pumping test, and map shallow faults that serve as contaminant flowpaths.

Mapping the northern portion of the Chelungpu fault, Taiwan by shallow reflection seismics

The Chelungpu fault was activated by the 1999 Chi‐Chi earthquake (Mw = 7.6), Taiwan. This fault exhibited extraordinarily large surface ruptures (up to 9.8 m) as well as underground fault slippages (up to 12 m) during the earthquake. These large displacements were concentrated along the northern portion of the fault, 40 km north of the epicenter. To prepare data for the future drilling of deep wells in this area, many shallow seismic reflection surveys were conducted to investigate the sites. An approximate 3D structure of the fault surface can be deduced by this cost‐effective approach. Although the depth penetration may be limited (e.g., 3 km), the method still provides reliable information to study large ruptures, and to better plan future deep wells.

Some considerations on shallow seismic reflection surveys

High-resolution shallow seismic reflection surveys require more attention to the choice of source and configuration, receivers and recording geometry for optimizing data acquisition than conventional oil exploration surveys. Moreover, some standard processing techniques to increase signal/noise (S/N) ratio need special accuracy (for example, surgically precise removal of early-time coherent noise and iterative, small time shift static corrections). This paper compares results obtained using different sources at two test sites: explosive, cap, shotgun, hammer and weight drop. Data from experiments using geophones with different natural frequencies and using various acquisition geometries are also compared. In data processing, it is demonstrated how increasing the S/N ratio for high-resolution results requires special consideration in some common processing steps (F–K filter, first arrivals muting, elimination of air wave and static corrections). The comparison, based on shot gathers and stack sections, shows that attenuation of high frequencies by the earth is the most significant influence on the spectral properties of the data, as expected the source itself also does have some influence on frequency content, depending to some extent on surface conditions. The high-velocity explosive sources produced the highest frequency reflections and best S/N ratio, because they have higher energy related to higher burn/blast velocity and source containment then the other sources and they are used in hole (i.e. below ground surface where the air wave energy is more attenuated) but the shotgun also an explosive source was reasonably comparable to high explosive when used in hole. Special care must be taken during processing to insure artifacts are distinguished from real reflection events.

First-Arrival Alignment Static Corrections Applied to Shallow Seismic Reflection Data

The proper handling of static corrections is an issue that is of critical importance to shallow seismic reflection surveys because of the high frequencies used, and the significant velocity and thickness variations that frequently exist in the very-near surface. The application of standard conventional methods of determining static corrections must be very carefully considered, as these are sometimes inadequate for shallow seismic reflection data. This paper addresses the problem of static corrections for shallow reflection data in terms of long-, medium-, and short-wavelength statics related to topography and variations in the very-low-velocity, near-surface layer, and presents a first-arrival alignment method of static corrections which is an adaptation of refraction and common offset methods. First-break picking is completed on the entire data set, and a refraction analysis of first-arrival data at selected intervals along the survey line is used to estimate a laterally-interpolated, layered, near-surface velocity structure. The first arrivals on all shot gathers are then aligned to the determined velocity function. This process corrects for medium- (i.e., within spread length), and long-wavelength ([Formula: see text] length), near-surface velocity variations, as well as most of the static contributions related to individual geophone locations and elevations (i.e., short-wavelength corrections). Residual statics are used to correct any remaining short-wavelength errors. Finally, topographic variations (long-wavelength) are corrected post-stack. Both model results and application of this method to actual shallow seismic reflection data show this to be a robust and effective method of correcting for statics related to a very-low-velocity near-surface layer, though the method (based on refraction analyses) cannot account for near-surface velocity inversions, if these exist.

Shallow seismic reflection section—Introduction

For those interested in shallow seismic reflection (SSR) techniques, this special issue of Geophysics is likely to serve as a useful reference for years to come. The idea for this issue grew out of discussions that took place at the Shallow Seismic Reflection Workshop at the Lawrence Berkeley Laboratory, California, in September 1996. The content of those discussions is the subject of a published report elsewhere (Steeples et al., 1997). Several workshop participants and their colleagues contributed to the papers in this issue as authors and as reviewers. The articles include case histories, novel uses of the SSR technique, state‐of‐the‐art planning considerations for 3-D SSR surveys, and some examples of problems unique to SSR surveying.

Integrating high‐resolution refraction data into near‐surface seismic reflection data processing and interpretation

Shallow seismic reflection surveys commonly suffer from poor data quality in the upper 100 to 150 ms of the stacked seismic record because of shot‐associated noise, surface waves, and direct arrivals that obscure the reflected energy. Nevertheless, insight into lateral changes in shallow structure and stratigraphy can still be obtained from these data by using first‐arrival picks in a refraction analysis to derive a near‐surface velocity model. We have used turning‐ray tomography to model near‐surface velocities from seismic reflection profiles recorded in the Hueco Bolson of West Texas and southern New Mexico. The results of this analysis are interval‐velocity models for the upper 150 to 300 m of the seismic profiles which delineate geologic features that were not interpretable from the stacked records alone. In addition, the interval‐velocity models lead to improved time‐to‐depth conversion; when converted to stacking velocities, they may provide a better estimate of stacking velocities at early traveltimes than other methods.

Subsurface geological structure by the shallow seismic reflection survey in the central area of the Kanto plain(<Special issue>Quaternary crustal movement and its relation to seismisity)

Subsurface geological structure by the shallow seismic reflection survey in the central area of the Kanto plain(<Special issue>Quaternary crustal movement and its relation to seismisity)