Shallow Seismic Exploration Research Articles

Modelling complex near-surface features to improve shallow seismic exploration

Land seismic exploration is often limited or impacted by complex structures in the near surface. These can include large variations in velocities related to weathering (low velocity) or basalts (potentially high velocity).Timing changes due to near-surface velocity variations are often accommodated by applying statics corrections during seismic processing. Shallow coal exploration requires high-resolution data to image structures and faulting. A good understanding of these features is required for both safety and economic reasons. However, in some cases small errors in statics correction may have a significant impact on the viability of the use of seismic data in these complex environments.Often near-surface structures also show non-planar characteristics which may attenuate or further complicated the seismic response.In this paper we use finite-difference visco-elastic modelling to investigate the impact that a number of common near-surface structures have on seismic data. This modelling has been used to determine the optimal acquisition and processing parameters required for a seismic program in order to achieve desired results.

Investigation of the Yellow River buried fault in the Wuhai basin, northwestern Ordos Block, China, using deep/shallow seismic reflection and drilling techniques

Studying the faults in Wuhai Basin, which is located in the northwestern corner of the Ordos Block in China, can not only guide earthquake-safe construction in the region, but also provide a greater understanding of the structure of the Wuhai Basin and the dynamic environment of Northwestern Ordos Block. In this study, we effectively detected the Yellow River buried Fault (YRF), which we believe currently presents a risk to human life in the area. First, we laid out a deep seismic reflection profile (DSRP) in the north of the Wuhai Basin and found that the YRF is composed of two subparallel faults, the east branch of the Yellow River buried Fault (EYF) and the west branch of the Yellow River buried Fault (WYF), which formed a Y-type graben in the section. We then used 25 shallow seismic exploration profiles to find out how the faults are distributed. Finally, we used drillings and Quaternary dating methods to certify their existence and obtain their activity parameters. We used the sequence stratigraphy method to compare sediment strata and identified paleo-earthquake events by finding the unequal thickness layers (UTLs) on both sides of the fault. The drillings revealed that four earthquakes occurred on the YRF around 25.6 ± 0.11 ka BP, 39.5 ± 0.45–41.7 ± 0.57 ka BP, 58.25 ± 7.13 ka BP, and 111 ± 1.21 ka BP. Since the last activity on the YRF occurred much longer ago than its estimated recurrence cycle, we believe that the fault YRF currently presents a dangerous risk. Our study confirms that the YRF is a normal fault graben and that the Wuhai Bain is an extensional basin formed by the relative movement of the Tibetan Plateau, the Alashan Block, and the Ordos Block.

Shallow structure of the Tangshan fault zone unveiled by dense seismic array and horizontal-to-vertical spectral ratio method

The Tangshan fault zone has been considered to be a potential seismogenic fault from the devastating 1976 Ms 7.8 Tangshan earthquake. Based on the dense seismic array with interstation distance of ∼1 km and length of ∼40 km, HVSR (horizontal-to-vertical spectral ratio) curves at 37 stations are obtained with the micro-tremor seismic waveforms, and the two-dimensional Quaternary sedimentary structures cross the Tangshan fault zone are imaged by frequency-to-depth conversion. Results suggest that two significant seismic impedance interfaces at ∼100 m and 300–800 m depth are clearly revealed, respectively. The interface at ∼100 m depth can be attributed to the strong contrasts between the unconsolidated sand-clay and semi-consolidated silt, which suggests very small variations and is well consistent with the seismic reflection interface from shallow seismic reflection exploration. While the deeper interface at 300–800 m depth can be attributed to the Quaternary sedimentary basement, which increases from 300 to 800 m from the west to the east, and is also consistent with the results in previous studies. Rapid variations (∼200 m) of the Quaternary sedimentary basement depth just beneath the fault zone well agrees with spatial characteristics of the fault revealed by deep seismic reflection profiling. Our work suggests that the Tangshan fault zone has been significantly ruptured and modified by strong earthquake activities since Quaternary. This study also suggests that the HVSR method with dense seismic array is an efficient, effective, non-invasive and low-cost method for investigating active faults in shallow sediments. It is useful for probing the active faults buried by thick sediments in the densely populated urban settings where seismic investigation with explosive sources are too hazardous to carry out.

An Experimental Study Among P-wave Velocity of Sandstones, Pressures and Water Saturation in Hami, Xinjiang, China

Seismic velocity of rocks have a wide range of applications in regional tectonic research and shallow seismic exploration. Hami area is one of the important production bases for oil and gas in China, but there is short of seismic velocity. This paper contributes to the measurement of Pwave velocity of sandstones from Hami under different conditions by applying AutoLab 2000 computer-controlled servo hydraulic triaxial test system. Specifically, it shows the variation of seismic wave velocity of sandstones with respect to the water saturation under various pressures. The results show that P-wave velocity of sandstones is remarkably correlated linearly with the increasing water saturation and the correlation coefficient is over 0.9. Besides, the change rate between P-wave velocity and water saturation will decrease with the increasing pressure. The fitting formulas among pressures, water saturation and P-wave velocity are suitable for Hami region. Finally, we get a new method to predict water saturation by combining the experimental result with logging curve in Hami area.

Seismic survey on an open pingo system in Adventdalen Valley, Spitsbergen, Svalbard

ABSTRACTWe present the results of a seismic survey on an open‐system pingo, the Innerhytta pingo, located in the Adventdalen Valley, Spitsbergen Island of the Svalbard Archipelago, Norway. To evaluate the temporal evolution of the permafrost, we need detailed knowledge of its heterogeneities, of which pingos are the most visible markers. The seismic velocity contrasts and inversions peculiar to these features can be a problem for a successful seismic survey. The present paper focusses on the limits and benefits of various seismic methods for imaging the subsurface structure of the pingo, with the aim of defining the best practice for shallow seismic exploration. We performed several tests, using classical reflection/refraction arrays, seismic tomography, and surface wave analysis. We tested different kinds of seismic sources and receivers. The combined use of several sources and receivers sets and patterns, and the use of surface wave analysis and body wave tomography allowed constructing a three‐dimensional model of the velocities. For this particular pingo, beneath an approximately 15‐m thick high‐velocity layer, low velocities are found to be present at an anomalously shallow depth. This low‐velocity layer is interpreted to host the ground water circulation that controls the pingo’s structural evolution. Such observations suggest feeding water flow from depth rather than from the near surface, as commonly supposed for open‐system pingos.

AVO inversion for a non-welded interface: estimating compliances of a fluid-filled fracture

Though well known for layer boundaries, the use of amplitude-versus-offset (AVO) variations for non-welded boundaries like fractures is not yet investigated. Depending on the seismic wavelength used, fractures can be regarded as thin, compliant zones in rocks, in different scales. We explore the potential of multiangle AVO inversion of P-P and P-S reflections from a fracture to estimate fracture properties.We conduct laboratory experiments to measure reflection responses of dry and wet fractures. The observed P-P reflections of the wet fracture and the fracture aperture are very well predicted by the non-welded interface model.We invert the angle-dependent P-P reflectivity of the fracture to estimate both normal and tangential fracture compliances. The estimated value of the normal compliance is accurate, and it is also possible to obtain the value of the non-zero tangential compliance.We find that supplementing the information of converted P-S reflections in theAVOinversion greatly improves the estimate of the tangential compliance. The calculated compliance ratio clearly shows the existence of fluid in the fracture. This finding can be crucial for new applications in a wide range of scale—from earthquake seismology, deep and shallow seismic exploration, to non-destructive material testing.

Applications of shallow-seismic exploration methods for mechanical characterization of soil and rock bodies at engineering project sites in Colombia

The application of seismic methods for rock and soil-mass characterization has proved to be useful for engineering projects of any kind. These methods can predict the presence and geometry of low-competent subsoil materials and can define preliminary structural designs for each project. In three studies in Colombia, refraction tomography and multichannel analysis of surface waves (MASW) were applied for road tunnels and multistory building construction, respectively. In situ rock and soil types were classified based on P- and S-wave measurements, and preliminary structural designs and construction methods were recommended for each case. Both rock and soil classifications and preliminary structural designs must be refined with direct subsoil-characterization methods such as core drilling and laboratory testing.

Latest Development of Shallow Seismic Exploration for Sandstone‐type Uranium Deposits in Erlian Basin, China

Latest Development of Shallow Seismic Exploration for Sandstone‐type Uranium Deposits in Erlian Basin, China

Remote sensing interpretation and extraction of structural information about active faults at Hangzhou, China, and their surroundings

It is important to explore active faults in urban areas and their surroundings for earthquake disaster mitigation. Satellite remote sensing techniques can play an important role in such active fault exploration. It can not only reveal the pattern of active faults and active tectonics on a macroscopic scale, but also monitor the occurrence, development and rules of temporal-spatial evolution of active faults. In this paper, we use the Hangzhou area as an example to introduce methods of extracting detailed active fault information when covered by thick unconsolidated Quaternary sediment, using image enhancement and image fusion etc. to improve the definition and precision of satellite images and presenting a three-dimensional (3D) image to illustrate tectono-geomorphic features along the relevant faults. We have also collected aeromagnetic anomaly data, shallow seismic exploration data and dating data, and carried out field surveys to validate the characteristics of active faults based on remote sensing images. The results revealed about the faults showed a high consistency with traditional geological knowledge, and demonstrate that it is feasible to explore active faults in a weakly active tectonic area by using satellite remote sensing techniques and contribute to large engineering projects and research on neotectonics.

A Laboratory Study of Seismic Wave Velocities in Sandstones Bearing Different Pore Fluids at Different Pressures

Abstract:Seismic properties of rocks have wide applications in regional tectonic research and shallow seismic exploration. The Yanchang oilfield is one of the important production bases for oil and gas in China, but lacks basic data of seismic wave properties of rocks. This work applied the AutoLab 2000 computer‐controlled servo hydraulic triaxial test system to measure accurate P‐ and S‐wave velocities at pressures up to 180 MPa on three kinds of core samples of sandstones in dry, water and oil‐saturated conditions from the Yanchang oilfield. The results show the wave velocities Vp, Vs1 and Vs2 for the three kinds of samples of sandstones change basically logarithmically with increasing (or decreasing) pressures. The relationships between wave velocities in dry, water and oil‐saturated conditions indicates obvious differences for three kinds of core samples of sandstones, mainly because rock elastic modulus, pore fluid property, and rock structure are different. For the different kinds of sandstones, the pressure dependence of the Vp, Vs1 and Vs2 in the same pore fluid condition is controlled by the porosity and grain size, and for the same kind of sandstone, the pressure dependence of the Vp, Vs1 and Vs2 in the different pore fluid conditions is affected by the effective modulus of elasticity and density. Moreover, Vs1 and Vs2 hardly vary with water and oil saturation. The experimental results can provide an important basis for the interpretation of seismic data and comparing with well log data in that region.

Recurrence Characteristics of Major Earthquakes in the Tangshan area, North China

AbstractThe Tangshan area lies in the North China plain where an Ms 7.8 earthquake occurred in 1976, which is associated with a hidden active fault. To reveal the recurrence characteristics of major quakes in this area over a relatively long time, we have conducted a comprehensive study using geological investigations, shallow seismic exploration, boreholes, trench observations and geological dating. Five paleoearthquakes were recognized in a 6.4m‐deep trench west to the Tangshan Asylum. Among them, the former three events occurred between 56.78 ± 4.83ka and 89.39 ± 7.60 ka, and the fourth event occurred around 6.9 ka, respectively, and then followed by the fifth in 1976. Seven boreholes were deployed crossing the ground fissure formed by the 1976 Tangshan earthquake at the site of No. 10 Middle School, where we have identified 25 liquefaction events in the boreholes TZC6–5 and 6–7. By the comprehensive analysis of the trench, the liquefaction events from the boreholes and the depth‐time curves of drill cores, we suggest a new recurrence model of major quakes in this area. It is not a constant recurring cycle since 210 ka, instead consisting of six alternating seismically quiet and active stages. Of them, stage I (>177 ka) was a quiescent period in seismicity, stage II (from 143 ka to 177 ka) was an active one, stage III (from 102 ka to 143 ka) was quiescent again, stage IV (from 56 ka to 102 ka) had many quakes, stage V (from 6.9 ka to 56 ka) became quiet, and stage VI (from 6.9 ka to now) was the beginning of a new seismically active period.

A HIGH-PRECISION SYNCHRONOUS SAMPLING APPROACH FOR LARGE-SCALE DISTRIBUTED WIRE SENSOR NETWORKS IN SEISMIC DATA ACQUISITION SYSTEMS

In large-scale land or marine seismic data acquisition systems, a multinode distributed wire sensor network structure is still presently the main choice. Synchronous sampling between each node in such systems is very important, which may significantly influence the results of the ensuing data analysis. A synchronous sampling approach with its implementation is introduced in this article. The main idea of this approach is combined command delay compensation with clock phase compensation of CDR (clock data recovery) to achieve high precision of synchronization. For testing, a kind of six-node land seismic data acquisition system with 100 m distance between two neighboring nodes is successfully developed using this approach. Test results indicate that the achieved precision of synchronous sampling is fixed after power-on with no time accumulation effect; the sampling clock phase difference between two neighboring nodes is maximally 1 ns in the worst case, and the command synchronization error among all the nodes is less than 1 ns independent of the number of nodes and the distance between nodes. High synchronous precision is much more significant for the shallow stratum engineering seismic exploration, because shallow exploration always needs high sampling rates; for example, 32 kilo sample per second, and hence the tolerant synchronization error is much smaller.

Stability Analysis of Shallow Stratum in Jiangshidi Nuclear Power Plant Site and its Surrounding Areas

The differential GPS navigation and positioning technique, multi-channel shallow seismic exploration and high resolution single channel seismic technique were used for the geophysical exploration of the shallow stratum in Jiangshidi nuclear power plant site and its surrounding areas. Based on seismic data post processing results, the seismic section interpretation was performed, combined with regional geological background, borehole data and shallow anatomy data. Five main seismic reflection surfaces were recognized by using seismic stratigraphic method, and eight breakpoints were found according to the active fault discrimination criteria. Then the distribution and activity characteristics of main faults were obtained. The results show that any fault and marked deformation in the quaternary sediments has not been observed in the range of 5 km away from Jiangshidi nuclear power plant site. So the stability analysis results of shallow stratum in target area can meet the requirement of nuclear power plant site selection code.

Seismic studies of frozen ground in Arctic areas

Seismiv surveys have been applied to investigate the structure of frozen ground, to identify and contour natural and man-caused unfrozen layers in permafrost (taliks), to constrain the position of the permafrost table in the Arctic inner shelf, and to study the related coastal stability. They are the classic methods common in shallow seismic exploration and new techniques specially designed at the Institute of Earth’s Cryosphere (Tyumen’) for different wave components. The joint use of compressional and shear waves provides a higher-quality interpretation of seismic data in permafrost applications. In the case of a single wave component, shear waves are advantageous over P waves.

Application of the Remote Sensing Technology in the Line Arrangement of Shallow Artificial Seismic Exploration

The remote sensing image can not only show the panorama information of the fault distribution, but also offer the information about the geology, physiognomy and digital elevation with high precision. In this paper we took the Hangzhou area as the example and systematically introduced the application of the remote sensing technology in the optimal design of the shallow artificial seismic line, and it was very important to optimize the seismic line distribution of the shallow artificial seismic exploitation, perfect the quality of the seismic materials, enhance the work efficiency and reduce the exploitation costs.

GDP: A new source for shallow high-resolution seismic exploration

Gas-Driven Piston (GDP) is a new source for shallow seismic exploration. This source works by igniting a small amount of gas inside a closed chamber connected to a vertical steel cylinder. The gas explosion drives a steel piston, mounted inside the cylinder, downward so that the piston's thick head hits a steel base at the end of the cylinder generating a strong shock wave into the ground. Experimental field tests conducted near Ismailia, Egypt, prove that the portable, inexpensive and environmentally benign GDP generates stronger seismic waves than the sledgehammer that is commonly used in shallow seismic exploration. Tests also show that GDP is a highly repeatable and controllable and that its seismic waves contain a good amount of high frequencies which makes the GDP an excellent source for shallow seismic exploration.

Seismic Exploration Method for Detecting Buried Fault and Its Upper Breakpoint in Quaternary Sediment Area—An Example of Yinchuan Buried Active Fault

AbstractSeismic exploration is an effective geophysical means for detecting buried faults. The spread geometries of seismic exploration are the main factors to affect the exploration results as well as the accuracy of fault location. Based on the shallow seismic exploration data from an active fault survey in Yinchuan city and in combination with the petroleum seismic exploration profiles and drilling data, this paper proposes an upward fault‐tracing method for determining the geometry of the target fault and its upper breakpoint in thick Quaternary sediments. The result shows that the combination of high resolution shallow seismic exploration and borehole geological section is an effective way for locating the buried fault and determining its activeness.

An active fault in southern Taiwan detected using shallow seismics and ground penetration radar

We conducted high-resolution shallow seismic exploration and ground penetrating radar (GPR) exploration to assess the earthquake hazard along the speculated north-south striking Chaujou Fault that is along the mountain foot at the western edge of the Central Range in the southern tip of Taiwan. Shallow seismic and GPR survey lines are approximately eastwest oriented, perpendicular to the speculated fault. All these survey lines run across the speculated fault. A fault plane of an 50° east-dipping angle is interpreted using shallow seismic profiles and one GPR profile. The interpreted fault locations are consistent with the scarp on the earth?s surface with an error of only a few meters, indicating that the scarp marks the Chaujou Fault?s surface location. The GPR profile even shows fault planes within a few meters depth, indicating fault rupturing within the past centuries. As Taiwan has humid climate with high erosion and deposition rate, these evidences imply that the Chaujou Fault really exists and is an active fault, that it has been displaced within the past centuries, and that it is a potential earthquake-inducing mechanism.

The Research of Rare Earth-Iron Giant Magnetostrictive Seismic Source of Shallow Seismic Exploration

Due to the lack of resolution and precision of shallow seismic reflection exploration, the seismic source made of rare earth-iron giant magnetostrictive material (GMM) is used in the shallow reflection seismic exploration, and the resolution and precision is improved. GMM seismic source has more merit than the conventional seismic source. The characteristic of GMM seismic source is that the bandwidth of the seismic wave transmitted by the source is large. It is able to sweep through a range of frequency from tens Hz to thousands Hz. The parameters of the seismic source are easy to change, such as seismic energy, waveform and time length. Portable structure makes it convenient to transport and setup. The only thing should be considered before use is coupling. Its cost is not as big as other seismic source. The seismic source mentioned above can cover the shortage of shallow seismic exploration. It is an effective method to improve the exploration. A shallow seismic reflection exploration specimen machine with GMM seismic source is designed, including seismic source, driving circuit, waveform generator, data acquisition instrument and experiment system. The speed of propagation of seismic wave and the attenuation factor of soil was tested. Echo detecting experiment has also been finished. Basal experiment result is positive and further experiment is on progress at present.

INVSP gathers of local earthquake seismograms: an approach for modelling the upper crustalPandSvelocity structure

A new approach is presented here for obtaining INVSP gathers of local earthquake seismograms in regions with adequate seismogenic depth range. The inverse vertical seismic profiling (INVSP) geometry is in principle quite similar to the up-hole surveys of shallow seismic exploration in which shots fired at various depths in boreholes are recorded on the surface at a fixed offset. Similarly, local earthquake seismograms of ‘selected’ events at different hypocentral depths can be gathered into ‘Constant offsetINVSP’ sections for various stations of a mobile seismograph network. They can be modelled for P and S velocity structure to upper crustal depths at each of the stations in the network with the aid of synthetic seismogram computations using appropriate source mechanisms of the earthquakes used. An INVSP gather, obtained to a depth range of about 10 km at a station with 28 km constant offset, is modelled for the upper crustal P and S velocity structure in the Koyna-Warna seismic region in the western Indian shield to demonstrate this approach.