Go to the main menu
Skip to content
Go to bottom
REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Geophysics and Geophysical Exploration
Journal Basic Information
Journal DOI :
Korean Society of Earth and Exploration Geophysicists
Editor in Chief :
Volume & Issues
Volume 14, Issue 4 - Nov 2011
Volume 14, Issue 3 - Aug 2011
Volume 14, Issue 2 - May 2011
Volume 14, Issue 1 - Feb 2011
Selecting the target year
Dispersion constraints and the Hilbert transform for electromagnetic system response validation
Macnae, James ; Springall, Ryan ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 1~6
As a check on calibration and drift in each discrete sub-system of a commercial frequency-domain airborne electromagnetic system, we aim to use causality constraints alone to predict in-phase from wide-band quadrature data. There are several possible applications of the prediction of in-phase response from quadrature data including: (1) quality control on base level drift, calibration and phase checks; (2) prediction and validation of noise levels in in-phase from quadrature measurements and vice versa and in future; and (3) interpolation and extrapolation of sparsely sampled data enforcing causality and better frequency-domain-time-domain transformations. In practice, using tests on both synthetic and measured Resolve helicopter-borne electromagnetic frequency domain data, in-phase data points could be predicted using a scaled Hilbert transform with a standard deviation between 40 and 80 ppm. However, relative differences between base levels between flight could be resolved to better than 1 ppm, which allows an independent quality control check on the accuracy of drift corrections.
Three-dimensional anisotropic inversion of resistivity tomography data in an abandoned mine area
Yi, Myeong-Jong ; Kim, Jung-Ho ; Son, Jeong-Sul ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 7~17
We have developed an inversion code for three-dimensional (3D) resistivity tomography including the anisotropy effect. The algorithm is based on the finite element approximations for the forward modelling and Active Constraint Balancing method is adopted to enhance the resolving power of the smoothness constraint least-squares inversion. Using numerical experiments, we have shown that anisotropic inversion is viable to get an accurate image of the subsurface when the subsurface shows strong electrical anisotropy. Moreover, anisotropy can be used as additional information in the interpretation of subsurface. This algorithm was also applied to the field dataset acquired in the abandoned old mine area, where a high-rise apartment block has been built up over a mining tunnel. The main purpose of the investigation was to evaluate the safety analysis of the building due to old mining activities. Strong electrical anisotropy has been observed and it was proven to be caused by geological setting of the site. To handle the anisotropy problem, field data were inverted by a 3D anisotropic tomography algorithm and we could obtain 3D subsurface images, which matches well with geology mapping observations. The inversion results have been used to provide the subsurface model for the safety analysis in rock engineering and we could assure the residents that the apartment has no problem in its safety after the completion of investigation works.
Seismic reflection imaging of a Warm Core Ring south of Hokkaido
Yamashita, Mikiya ; Yokota, Kanako ; Fukao, Yoshio ; Kodaira, Shuichi ; Miura, Seiichi ; Katsumata, Katsuro ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 18~24
A multi-channel seismic reflection (MCS) survey was conducted in 2009 to explore the deep crustal structure of the Pacific Plate south of Hokkaido. The survey line happened to traverse a 250-km-wide Warm Core Ring (WCR), a current eddy that had been generated by the Kuroshio Extension. We attempted to use these MCS data to delineate the WCR fine structure. The survey line consists of two profiles: one with a shot interval of 200m and the other with a shot interval of 50 m. Records from the denser shot point line show much higher background noise than the records from the sparser shot point line. We identified the origin of this noise as acoustic reverberations between the sea surface, seafloor and subsurface discontinuities, from previous shots. Results showed that a prestack migration technique could enhance the signal buried in this background noise efficiently, if the sound speed information acquired from concurrent temperature measurements is available. The WCR is acoustically an assemblage of concave reflectors dipping inward, with steeper slopes (
) on th ocean side and gentler slopes (
) on the coastal side. Within the WCR, we recognised a 30-km-wide lens-shaped structure with reflectors on the perimeter.
AVO analysis using crossplot and amplitude polynomial methods for characterisation of hydrocarbon reservoirs
Kim, Ji-Soo ; Kim, Won-Ki ; Ha, Hee-Sang ; Kim, Sung-Soo ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 25~41
AVO analysis was conducted on hydrocarbon-bearing structures by applying the crossplot and offset-coordinate amplitude polynomial techniques. To evaluate the applicability of the AVO analysis, it was conducted on synthetic data that were generated with an anticline model, and field data from the hydrocarbon-bearing Colony Sand bed in Canada. Analysis of synthetic data from the anticline model demonstrates that the crossplot method yields zero-offset reflection amplitude and amplitude variation with negative values for the upper interface of the hydrocarbon-bearing layer. The crossplot values are clustered in the third quadrant. The results of AVO analysis based on the coefficients of the amplitude polynomial are similar to those from the crossplots. These well correlated results of AVO analysis on field and synthetic data suggest that both methods successfully investigate the characteristics of the reflections from the upper interface of a hydrocarbon-bearing layer. Analysis based on the incident-angle equation facilitates the application of various interpretation methods. However, it requires the conversion of seismic data to an incident angle gather. By contrast, analysis using coefficients of the amplitude polynomial is cost-effective because it allows examining amplitude variation with offset without involving the conversion process. However, it warrants further investigation into versatile application. The two different techniques can be complement each other effectively as AVO-analysis tools for the detection of hydrocarbon reservoirs.
Detection of anomalous features in an earthen dam using inversion of P-wave first-arrival times and surface-wave dispersion curves
Kim, K.Y. ; Jeon, K.M. ; Hong, M.H. ; Park, Young-Gyu ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 42~49
To locate anomalous features including seepage pathways through the Daeryong earth-fill dam, P and Rayleigh waves were recorded along a 250-m profile on the crest of the dam. Seismic energy was generated using a 5-kg sledgehammer and detected by 24 4.5-Hz vertical-axis geophones installed at 3-m intervals. P-wave and apparent S-wave velocities of the reservoir dam and underlying bedrock were then inverted from first-arrival traveltimes and dispersion curves of Rayleigh waves, respectively. Apparent dynamic Poisson's ratios as high as 0.46 were obtained at the base of the dam near its north-east end, where an outlet conduit occurs, and in the clay core body near the south-west end of the profile where the dam was repeatedly grouted to abate seepage before our survey. These anomalies of higher Poisson's ratios in the upper part of clay core were also associated with effusion of grout on the downstream slope of the dam during post-survey grouting to abate leakage. Combining P-wave traveltime tomography and inversion of Rayleigh wave velocities was very effective in detecting potential pathways for seepage and previous grouted zones in this earthen dam.
Overpressure prediction of the Efomeh field using synthetic data, onshore Niger Delta, Nigeria
Omolaiye, Gabriel Efomeh ; Ojo, John Sunday ; Oladapo, Michael Ilesanmi ; Ayolabi, Elijah A. ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 50~57
For effective and accurate prediction of overpressure in the Efomeh field, located in the Niger delta basin of Nigeria, integrated seismic and borehole analyses were undertaken. Normal and abnormal pore pressure zones were delineated based on the principle of normal and deviation from normal velocity trends. The transition between the two trends signifies the top of overpressure. The overpressure tops were picked at regular intervals from seismic data using interval velocities obtained by applying Dix's approximation. The accuracy of the predicted overpressure zone was confirmed from the sonic velocity data of the Efomeh 01 well. The variation to the depth of overpressure between the predicted and observed values was less than 10mat the Efomeh 01 well location, with confidence of over 99 per cent. The depth map generated shows that the depth distribution to the top of the overpressure zone of the Efomeh field falls within the sub-sea depth range of 2655
2m (2550 ms) to 3720
2m (2900 ms). This depth conforms to thick marine shales using the Efomeh 01 composite log. The lower part of the Agbada Formation within the Efomeh field is overpressured and the depth of the top of the overpressure does not follow any time-stratigraphic boundary across the field. Prediction of the top of the overpressure zone within the Efomeh field for potential wells that will total depth beyond 2440m sub-sea is very important for safer drilling practice as well as the prevention of lost circulation.
Monitoring and detecting
injected into water-saturated sandstone with joint seismic and resistivity measurements
Kim, Jong-Wook ; Matsuoka, Toshifumi ; Xue, Ziqiu ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 58~68
As part of basic studies of monitoring carbon dioxide (
) storage using electrical and seismic surveys, laboratory experiments have been conducted to measure resistivity and P-wave velocity changes due to the injection of
into water-saturated sandstone. The rock sample used is a cylinder of Berea sandstone.
was injected under supercritical conditions (10 MPa,
). The experimental results show that resistivity increases monotonously throughout the injection period, while P-wave velocity and amplitude decrease drastically due to the supercritical
injection. A reconstructed P-wave velocity tomogram clearly images
migration in the sandstone sample. Both resistivity and seismic velocity are useful for monitoring
behaviour. P-wave velocity, however, is less sensitive than resistivity when the
saturation is greater than ~20%. The result indicates that the saturation estimation from resistivity can effectively complement the difficulty of
saturation estimations from seismic velocity variations. By combining resistivity and seismic velocity we were able to estimate
saturation distribution and the injected
behaviour in our sample.
Estimation of site amplification and S-wave velocity profiles in metropolitan Manila, the Philippines, from earthquake ground motion records
Yamanaka, Hiroaki ; Ohtawara, Kaoru ; Grutas, Rhommel ; Tiglao, Robert B. ; Lasala, Melchor ; Narag, Ishmael C. ; Bautista, Bartlome C. ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 69~79
In this study, empirical site amplifications and S-wave velocity profiles for shallow and deep soils are estimated using earthquake ground motion records in metropolitan Manila, the Philippines. We first apply a spectral inversion technique to the earthquake records to estimate effects of source, path, and local site amplification. The earthquake data used were obtained during 36 moderate earthquakes at 10 strong-motion stations of an earthquake observation network in Manila. The estimated Q value of the propagation path is modelled as
. Most of the source spectra can be approximated with the omega-square model. The site amplifications show characteristic features according to surface geological conditions. The amplifications at the sites in the coastal lowland and Marikina Valley shows predominant peaks at frequencies from 1 to 5 Hz, while those in the central plateau are characterised by no dominant peaks. These site amplifications are inverted to subsurface S-wave velocity. We, next, discuss the relationship between the amplifications and average S-wave velocity in the top 30m of the S-wave velocity profiles. The amplifications at low frequencies are well correlated with the averaged S-wave velocity. However, high-frequency amplifications cannot be sufficiently explained by the averaged S-wave velocity in the top 30 m. They are correlated more with the average of S-wave velocity over depths less than 30 m.
Acoustic images of the submarine fan system of the northern Kumano Basin obtained during the experimental dives of the Deep Sea AUV URASHIMA
Kasaya, Takafumi ; Kanamatsu, Toshiya ; Sawa, Takao ; Kinosita, Masataka ; Tukioka, Satoshi ; Yamamoto, Fujio ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 80~87
Autonomous underwater vehicles (AUVs) present the important advantage of being able to approach the seafloor more closely than surface vessel surveys can. To collect bathymetric data, bottom material information, and sub-surface images, multibeam echosounder, sidescan sonar (SSS) and subbottom profiler (SBP) equipment mounted on an AUV are powerful tools. The 3000m class AUV URASHIMA was developed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). After finishing the engineering development and examination phase of a fuel-cell system used for the vehicle's power supply system, a renovated lithium-ion battery power system was installed in URASHIMA. The AUV was redeployed from its prior engineering tasks to scientific use. Various scientific instruments were loaded on the vehicle, and experimental dives for science-oriented missions conducted from 2006. During the experimental cruise of 2007, high-resolution acoustic images were obtained by SSS and SBP on the URASHIMA around the northern Kumano Basin off Japan's Kii Peninsula. The map of backscatter intensity data revealed many debris objects, and SBP images revealed the subsurface structure around the north-eastern end of our study area. These features suggest a structure related to the formation of the latest submarine fan. However, a strong reflection layer exists below ~20 ms below the seafloor in the south-western area, which we interpret as a denudation feature, now covered with younger surface sediments. We continue to improve the vehicle's performance, and expect that many fruitful results will be obtained using URASHIMA.
Rapid gravity and gravity gradiometry terrain corrections via an adaptive quadtree mesh discretization
Davis, Kristofer ; Kass, M.Andy ; Li, Yaoguo ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 88~97
We present a method for modelling the terrain response of gravity gradiometry surveys utilising an adaptive quadtree mesh discretization. The data- and terrain-dependent method is tailored to provide rapid and accurate terrain corrections for draped and barometric airborne surveys. The surface used in the modelling of the terrain effect for each datum is discretized automatically to the largest cell size that will yield the desired accuracy, resulting in much faster modelling than full-resolution calculations. The largest cell sizes within the model occur in areas of minimal terrain variation and at large distances away from the datum location. We show synthetic and field examples for proof of concept. In the presented field example, the adaptive quadtree method reduces the computational cost by performing 351 times fewer calculations than the full model would require while retaining an accuracy of one E
s for the gradient data. The method is also used for the terrain correction of the gravity field and performed 310 times faster compared with a calculation of the full digital elevation model.
Acceleration of computation speed for elastic wave simulation using a Graphic Processing Unit
Nakata, Norimitsu ; Tsuji, Takeshi ; Matsuoka, Toshifumi ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 98~104
Numerical simulation in exploration geophysics provides important insights into subsurface wave propagation phenomena. Although elastic wave simulations take longer to compute than acoustic simulations, an elastic simulator can construct more realistic wavefields including shear components. Therefore, it is suitable for exploration of the responses of elastic bodies. To overcome the long duration of the calculations, we use a Graphic Processing Unit (GPU) to accelerate the elastic wave simulation. Because a GPU has many processors and a wide memory bandwidth, we can use it in a parallelised computing architecture. The GPU board used in this study is an NVIDIA Tesla C1060, which has 240 processors and a 102 GB/s memory bandwidth. Despite the availability of a parallel computing architecture (CUDA), developed by NVIDIA, we must optimise the usage of the different types of memory on the GPU device, and the sequence of calculations, to obtain a significant speedup of the computation. In this study, we simulate two- (2D) and threedimensional (3D) elastic wave propagation using the Finite-Difference Time-Domain (FDTD) method on GPUs. In the wave propagation simulation, we adopt the staggered-grid method, which is one of the conventional FD schemes, since this method can achieve sufficient accuracy for use in numerical modelling in geophysics. Our simulator optimises the usage of memory on the GPU device to reduce data access times, and uses faster memory as much as possible. This is a key factor in GPU computing. By using one GPU device and optimising its memory usage, we improved the computation time by more than 14 times in the 2D simulation, and over six times in the 3D simulation, compared with one CPU. Furthermore, by using three GPUs, we succeeded in accelerating the 3D simulation 10 times.
A poroelastic model for ultrasonic wave attenuation in partially frozen brines
Matsushima, Jun ; Nibe, Takao ; Suzuki, Makoto ; Kato, Yoshibumi ; Rokugawa, Shuichi ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 105~115
Although there are many possible mechanisms for the intrinsic seismic attenuation in composite materials that include fluids, relative motion between solids and fluids during seismic wave propagation is one of the most important attenuation mechanisms. In our previous study, we conducted ultrasonic wave transmission measurements on an ice-brine coexisting system to examine the influence on ultrasonic waves of the unfrozen brine in the pore microstructure of ice. In order to elucidate the physical mechanism responsible for ultrasonic wave attenuation in the frequency range of 350.600 kHz, measured at different temperatures in partially frozen brines, we employed a poroelastic model based on the Biot theory to describe the propagation of ultrasonic waves through partially frozen brines. By assuming that the solid phase is ice and the liquid phase is the unfrozen brine, fluid properties measured by a pulsed nuclear magnetic resonance technique were used to calculate porosities at different temperatures. The computed intrinsic attenuation at 500 kHz cannot completely predict the measured attenuation results from the experimental study in an ice-brine coexisting system, which suggests that other attenuation mechanisms such as the squirt-flow mechanism and wave scattering effect should be taken into account.
Short note: on the use of radioelement ratios to enhance gamma-ray spectrometric data
Minty, Brian ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 116~120
Radioelement ratios are useful for mapping subtle variations in radiometric signatures in map data. But the conventional method for calculating radioelement ratios has the significant limitation that if just one of the radioelements comprising the ratio has a small spread of concentration estimates relative to its mean, then it will not contribute significantly to the ratio map. However, if both the numerator and denominator are first normalised to approximately the same mean and spread prior to ratioing, then they will contribute equally to the enhancement of the differences between them across the map area.
Discussion: On 'Magnetization structure of Aogashima Island using vector magnetic anomalies obtained by a helicopter-borne magnetometer' (Isezaki, N., and J. Matsuo, 2009, Exploration Geophysics, 40, 17.26; Butsuri-Tansa, 62, 17.26; Mulli-Tamsa, 12, 17.26).
Nakatsuka, Tadashi ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 121~122
Reply by the authors to the discussion by Nakatsuka
Matsuo, Jun ; Isezaki, Nobuhiro ;
Geophysics and Geophysical Exploration, volume 14, issue 1, 2011, Pages 123~126