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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
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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
Relocation of Youngduk Offshore Micro-earthquakes
Kim, Kwang-Hee ; Ryoo, Yong-Gyu ; Yu, Chan-Ho ; Kang, Su-Young ; Kim, Han-Joon ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 267~273
A cluster of micro-earthquakes in the transition zone between the continental and oceanic crust in the East Sea was relocated using the Joint Hypocenter Determination (JHD) method. In order to increase the number of available earthquakes and to take advantage of the high detection capability of the Korea National Seismic Network (KNSN), continuously recorded seismic data were reviewed to identify 56 micro-earthquakes occurring in a 20 km
20 km region. The initial earthquake hypocenters were determined using a routine single event location method. Single event locations do not reveal any significant structures in the study area. After relocating the earthquake hypocenters using the JHD technique, the earthquakes were clustered and four potential faults responsible for earthquake generation in the subsurface were delineated. They are defined by two sub-vertical and two steeply south-dipping seismicities located next to each other.
Analysis of Characteristics of Seismic Source and Response Spectrum of Ground Motions from Recent Earthquake near the Backryoung Island
Kim, Jun-Kyoung ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 274~281
We analysed ground motions form Mw 4.3 earthquake around Backryoung Island for the seismic source focal mechanism and horizontal response spectrum. Focal mechanism of the Backryoung Islands area was compared to existing principal stress orientation of the Korean Peninsula and horizontal response spectrum was also compared to those of the US NRC Regulatory Guide (1.60) and the Korean National Building Code. The ground motions of 3 stations, including vertical, radial, and tangential components for each station, were used for grid search method of moment tensor seismic source. The principal stress orientation from this study, ENE-WSW, is consistent fairly well with that of the Korean Peninsula. The horizontal response spectrum using 30 observed ground motions analysed and then were compared to both the seismic design response spectra (Reg Guide 1.60), applied to the domestic nuclear power plants, and the Korean Standard Design Response Spectrum for general structures and buildings (1997). Response spectrum of 30 horizontal ground motions were used for normalization with respect to the peak acceleration value of each ground motion. The results showed that the horizontal response spectrum revealed higher values for frequency bands above 3 Hz than Reg. Guide (1.60). The results were also compared to the Korean Standard Response Spectrum for the 3 different soil types and showed that the vertical response spectra revealed higher values for the frequency bands below 0.8 second than the Korean Standard Response Spectrum (SD soil condition). However, through the qualitative improvements and quantitative enhancement of the observed ground motions, the conservation of horizontal seismic design response spectrum should be considered more significantly for the higher frequency bands.
Comparison of Signal Powers Generated with Metal Hammer Plate and Plastic Hammer Plate
Kim, Jin-Hoo ; Lee, Young-Hyun ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 282~288
One of the most challenging issues facing shallow seismic survey is how to generate large amplitude of high frequency signal with small seismic sources. We tested the performance of the most commonly used shallow seismic source, hammer, with four plates: PE, nylon, aluminum, and steel plates. We compared their signal powers in terms of impulsive forces, accelerations, and ground vibration velocities caused by hammer impacts. According to a previous work, hammer blowing to an aluminum plate would generate the largest amplitude among four combinations. However, it was found in this experimental research that aluminum plate delivers seismic wave energy to the ground less than that generated with steel or PE plate. Even though the amplitude is relatively small, plastic plates could provide seismic pulses of 180 ~ 200 Hz in the bandwidth, and it seems to be very hard to generate seismic energy over the frequency of 250 Hz.
A Case Study on the Data Processing to Enhance the Resolution of Chirp SBP Data
Kim, Young-Jun ; Kim, Won-Sik ; Shin, Sung-Ryul ; Kim, Jin-Ho ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 289~297
Chirp sub-bottom profilers (SBP) data are comparatively higher-resolution data than other seismic data and it's raw signal can be used as a final section after conducting basic filtering. However, Chirp SBP signal has possibility to include various noise in high-frequency band and to provide the distorted image for the complex geological structure in time domain. This study aims at the goal to establish the workflow of Chirp SBP data processing for enhanced image and to analyze the proper parameters for the domestic continental shelf. After pre-processing, we include the dynamic S/N filtering to eliminate the high-frequency component noise, the dip scan stack to enhance the continuity of reflection events and finally the post-stack depth migration to correct the distorted structure on the time domain sections. We demonstrated our workflow on the data acquired by domestically widely used equipments and then we could obtain the improved seismic sections of depth domain. This workflow seems to provide the proper seismic section to interpretation when applied to data processing of Chirp SBP that are largely used for domestic acquisition.
Deep Sea Three Components Magnetometer Survey using ROV
Kim, Chang-Hwan ; Park, Chan-Hong ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 298~304
We conducted magnetic survey using IBRV (Ice Breaker Research Vessel) ARAON of KORDI (Korea Ocean Research and Development Institute), ROV (Remotely Operated Vehicle) of Oceaneering Co. and three components vector magnetometer, at Apr., 2011 in the western slope of the caldera of TA25 seamount, the Lau Basin, the southwestern Pacific. The depth ranges of the survey area are from about 900 m to 1200 m, below sea level. For the deep sea magnetic survey, we made the nation's first small deep sea three components magnetometer of Korea. The magnetometer sensor and the data logger was attached with the upper part and lower part of ROV, respectively. ROV followed the planning tracks at 25 ~ 30 m above seafloor using the altimeter and USBL (Ultra Short Base Line) of ROV. The three components magnetometer measured the X (North), Y (East) and Z (Vertical) vector components of the magnetic field of the survey area. A motion sensor provided us the data of pitch, roll, yaw of ROV for the motion correction of the magnetic data. The data of the magnetometer sensor and the motion sensor were recorded on a notebook through the optical cable of ROV and the network of ARON. The precision positions of magnetic data were merged by the post-processing of USBL data of ROV. The obtained three components magnetic data are entirely utilized by finding possible hydrothermal vents of the survey area.
A study on the Factors Affected on the P- and S-wave Velocity Measurement of the Acrylic and Stainless Steel Core
Lee, Sang-Kyu ; Lee, Tae-Jong ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 305~315
A total of 864 measurements for P- and S- wave velocity of acrylic and stainless steel core samples have been performed with respect to their lengths and axial load applied. S-wave velocity measurement was much harder than P-wave velocity, so that it showed higher deviation in measured S-wave velocity with respect to repeated measurement, length of the cores, and the axial load applied. Velocity measurements for acrylic cores showed more stable and less than half of the variation between the measurements than the stainless steel cores. This seems to be come from better coupling between the transducers and acrylic cores than stainless cores, and from larger value of the first arrival time in a similar system noise environments. From the analysis of the 864 measurements, it is recommended that the length of the core be 60 ~ 90 mm, axial load between 20 kg (27.7
) and 30 kg (41.6
) for measurement of wave velocity of the acrylic and stainless steel cores. Especially for measuring S-wave velocity of stainless steel core, core length should be less than 50 mm, otherwise it will be affected by mode conversion or others. These results can be used in measurement and correction for system delay in wave velocity measurement for rock cores.
3-D Resistivity Imaing of a Large Scale Tumulus
Oh, Hyun-Dok ; Yi, Myeong-Jong ; Kim, Jung-Ho ; Shin, Jong-Woo ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 316~323
To test the applicability of resistivity survey methods for the archaeological prospection of a large-scale tumulus, a three-dimensional resistivity survey was conducted at the
tumulus at Bokam-ri, in Naju city, South Korea. Since accurate topographic relief of the tumulus and electrode locations are required to obtain a high resolution image of the subsurface, electrodes were installed after making grids by threads, which is commonly used in the archaeological investigation. In the data acquisition, data were measured using a 2 m electrode spacing with the line spacing of 1 m and each survey line was shifted 1 m to form an effective grid of 1 m
1 m. Though the 3-D inversion of data, we could obtain the 3-D image of the tumulus, where we could identify the brilliant signature of buried tombs made of stones. The results were compared with the previous excavation results and we could convince that a 3-D resistivity imaging method is very useful to investigate a large-scale tumulus.
Seismic Velocity Change Due to Micro-crack Accumulation of Rock Samples from Seokmo Island, Korea
Lee, Sang-Kyu ; Choi, Ji-Hyang ; Cheon, Dae-Sung ; Lee, Tae-Jong ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 324~334
Seismic wave velocity change has been monitored due to the accumulation of micro-cracks by uniaxial loads on the rock samples from Seokmo Island with stepwise increase in 5 stages. After the load was applied up to 95% of UCS, P- and S-wave velocities varied in ranges of 0.9 ~ 18.3% and 2.8 ~ 14.8% of fresh rock sample velocities, respectively. Unlike seismic velocity of the dry rock samples that showed overall decreases after the loading, velocity changes of saturated rock samples were much more complicated. These seemed to be due to the mixture of two contradictory mechanisms; i.e. accumulation of micro-crack causes an increase in porosity and a decrease in wave velocity, while saturation causes an increase in wave velocity. Most of tested rocks showed a trend of velocity increase with low axial load and then velocity decrease at later stages. Starting stage of velocity decrease differs from samples to samples. After the failure of rock occurred, noticeable increases of porosity and decreases of wave velocity have been observed. It showed overall trend that the more the quartz contents and the lower the silicate, the higher the Young's modulus.
A Breakthrough in Sensing and Measurement Technologies: Compressed Sensing and Super-Resolution for Geophysical Exploration
Kong, Seung-Hyun ; Han, Seung-Jun ;
Geophysics and Geophysical Exploration, volume 14, issue 4, 2011, Pages 335~341
Most sensing and instrumentation systems should have very higher sampling rate than required data rate not to miss important information. This means that the system can be inefficient in some cases. This paper introduces two new research areas about information acquisition with high accuracy from less number of sampled data. One is Compressed Sensing technology (which obtains original information with as little samples as possible) and the other is Super-Resolution technology (which gains very high-resolution information from restrictively sampled data). This paper explains fundamental theories and reconstruction algorithms of compressed sensing technology and describes several applications to geophysical exploration. In addition, this paper explains the fundamentals of super-resolution technology and introduces recent research results and its applications, e.g. FRI (Finite Rate of Innovation) and LIMS (Least-squares based Iterative Multipath Super-resolution). In conclusion, this paper discusses how these technologies can be used in geophysical exploration systems.