• Title/Summary/Keyword: Seismic refraction

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Shallow Crustal Structure of the Bransfield Basin Using an Autonomous Underwater Hydrophone

  • Kim, Kee-Hoon;Park, Min-Kyu;Hong, Jong-Kuk;Lee, Joo-Han
    • Journal of the Korean Geophysical Society
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    • v.9 no.4
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    • pp.351-359
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    • 2006
  • We investigated subsurface structures of the Bransfield Basin, the Antarctic with AUH (Autonomous Underwater Hydrophne) which was designed to record abyssal T-waves generated from submarine earthquakes. The data obtained from a multi-channel seismic survey and an AUH were used for this study. A seismic reflection method was applied to the multi-channel seismic survey data in order to identify bathymetry and sedimentary structures, and the signals recorded in the AUH were used to obtain deep structures as we applied a seismic refraction method. Even though we couldn’t investigate deeper and detailed structure in study area because of lack of Airgun’s capacity, the AUH showed possibilities for being used for a marine seismic survey. From this experiment, we decided the upper and lower sediment layer velocities, detected irregular basement topography probably caused by submarine volcanic/magmatic activities, and retrieved the velocity of the basement and the depth of the sediment layer/basement boundary.

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Seismic Refraction Survey for Installation of Water Pipe on a Side of the Seomjin River near Namwon (남원 섬진강변 관로 매설을 위한 굴절파 탐사)

  • Kim, Gi Yeong;U, Nam Cheol;Kim, Hyeong Su
    • Journal of the Korean Geophysical Society
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    • v.2 no.3
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    • pp.209-216
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    • 1999
  • In order to get geologic information necessary for underground installation of water pipe, seismic refraction profiling was applied to the southwest side of the Seomjin River which flows between Namwon-gun, Cholabuk-do and Gokseong-gun, Cholanam-do. Before obtaining the in-line refraction data, walkaway data were recorded with 1 m geophone interval and -36∼+36 m offset range. From the walkaway data, it is interpreted that a dry soil layer with the average velocity of 585 m/s covers wet sediments with the average velocity of 1,326 m/s. The second layer overlies basements nearly horizontally with the average velocity of 4,218 m/s. Refraction profiling of 220 m long with the geophone interval of 2 m is interpreted with the Generalized Reciprocal Method (GRM). Three layers are identified with average velocities of 688 m/s, 1,473 m/s, and 3,776 m/s, respectively. The depth to the bedrock impossible for ripping ranges between two extremes, 1.51∼2.43 m and 2.25∼3.54 m, depending upon thickness of the hidden layer. A typical shortcoming of refraction method, the hidden layer problem, prevents accurate estimation in depth of the second layer.

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Case Study of the Shallow Seismic Refraction Survey using Wave Glider (웨이브글라이더를 이용한 천해저 탄성파 굴절법 탐사 사례)

  • Kim, Young-Jun;Cheong, Snons;Koo, Nam-Hyung;Chun, Jong-Hwa;Kim, Jeong-Ki;Hwang, Kyu-Duk;Lee, Ho-Young;Heo, Sin;Moon, Ki-Don;Jeong, Cheol-Hun;Hong, Sung-Du
    • Geophysics and Geophysical Exploration
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    • v.20 no.1
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    • pp.43-48
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    • 2017
  • The applicability of refraction survey has been tested using a wave glider widely used in long-term ocean observations around the world. To record seismic refractions, a single channel streamer with metal weight and a seismic recording system were mounted on the wave glider. We used GPS precise time synchronization signal and radio frequency (RF) communication to synchronize shot and recorder triggers and to control acquired data quality in real time. When the wave glider is positioned close to the set point, a 2,000 J sparker is exploded along the designed track at 2 second intervals. Through the test survey, we were able to successfully acquire refractions from the subsurface.

Rock Quality using Seismic Tomography in Deep Tunnel Depths (대심도 탄성파 토모그래피 탐사를 이용한 암반분류)

  • Koo, Ja-Kab;Kim, Young-Duck;Kwon, So-Jin
    • Journal of the Korean GEO-environmental Society
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    • v.3 no.3
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    • pp.5-13
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    • 2002
  • In tunnel design, geotechnical survey of over 200m tunnel depth is required because of its characteristical topography. For this reason, there are difficulties in collecting information of basic data in tunnel design because of large-scale costs in borehole tests, of limits to a geotechnical analysis by the existing refraction seismic survey and of analytical errors in steep mountainous area. Seismic tomography has many advantages as follows; 1) seismic velocity as absolute value is more reliable than electrical resistivity, 2) geotechnical analysis in deep tunnel depth is available by seismic velocity, 3) analytical errors is reduced in steep mountainous area. In this paper, it was found out a correlation of seismic velocity and Q in tunnel design in the neighborhood of the National Capital region and the reduction effect of tunnel construction cost using reliable rock quality by seismic tomography compared with by borehole data and electricity resistivity data.

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The Application of Geophysical Prospecting for Detecting Substructure and Boundary of Layer In Limestone Area (석회암 지역의 기반암 및 경계면 조사를 위한 지구물리 탐사법의 적용)

  • Suh, Beak-Su;Lee, Duk-Jae
    • Journal of Industrial Technology
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    • v.20 no.A
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    • pp.285-293
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    • 2000
  • In 1970's, the analysis of shallow substructure was the interests of geological engineering and environmental problems. And seismic refraction method was applied to detect those structures. From 1980's, digital electric industry is rapidly developed and high resolution prospecting equipment is supplied. And seismic reflection method is applied to achieve various data gathering and data analysis. In this study, geophysical prospecting method is applied to calculate the basic data of limestone yield production. Seismic shallow reflection method is used to detect the depth of bedrock and electrical resistivity method is used to detect of limestone layer boundary.

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금강 부여 군수리 충적 대수층 조사를 위한 고해상도 지구물리탐사 - 탄성파 탐사 및 GPR 조사를 중심으로 -

  • 김형수;서만철;이철우;진세화
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • 2003.04a
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    • pp.287-291
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    • 2003
  • To delineate the internal structures of alluvial aquifer, high resolution seismic and GPR methods were adopted in Buyeo Gunsu-Ri area. The result of seismic refraction survey shows the water table of the aquifer and the result of seismic reflection reveals the basement and somewhat dominant internal structures of alluvial aquifer. The internal heterogeneity due to variations in channel behavior can be delineated using GPR survey. GPR profiles for the point bar deposits near Buyeo county reveals two different stratigraphic units the lower inclined heterogeneous strata and the upper horizontally stratified strata. According to the increase of demand for water resource using artificial recharge in alluvium, it is believed that the information acquired by high resolution geophysical methods will have an important roles for the effective and sustainable development and usage of groundwater in alluvial aquifer.

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Seismic Surface Wave Cloaking by Acoustic Wave Refraction (음향파 굴절을 이용한 지진파의 표면파 가림)

  • Lee, Dong-Woo;Kang, Young-Hoon;Kim, Sang-Hoon
    • Journal of the Earthquake Engineering Society of Korea
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    • v.19 no.6
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    • pp.257-263
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    • 2015
  • Recently two seismic cloaking methods of earthquake engineering have been suggested. One is the seismic wave deflection method that makes the seismic wave bend away and the other is the shadow zone method that makes an area that seismic waves cannot pass through. It is called as seismic cloaking. The fundamental principles of the seismic cloaking by variable refractive index were explained. A two-dimensional cylindrical model which was composed of 40 layers of different density and modulus was tested by numerical simulation. The center region of the model to be protected is called 'cloaked area' and the outer region of it to deflect the incoming wave is called 'cloaking area' or 'cloak area.' As the incoming surface wave is approaching to the cloaking area, the refractive index is decreasing and, therefore, the velocity and impedance are increasing. Then, the wave bends away the cloaked area instead of passing it. Three cases are tested depending on the comparison between the seismic wavelength and the diameter of the cloaked region. The advantage and disadvantage of the method were compared with conventional earthquake engineering method. Some practical requirements for realization in fields were discussed.

Case Study on the Seismic Refraction Survey in a Subsidence Area (지반침하지역에서의 탄성파 굴절법 탐사 적용사례)

  • Yun, Sang-Ho;Ji, Jun;Lee, Doo-Sung
    • Proceedings of the Korean Geotechical Society Conference
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    • 2000.11a
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    • pp.577-584
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    • 2000
  • Seismic refraction survey was peformed for 10 lines along NE-SW and NW-SE directions above Nampoong gallery at Makyo-ri, Dogye, Samcheok, Kangwon-do. 48 geophones were laid in line with the interval of 1m, and a 5Kg hammer was used as a source at 5 points for each line. Data processing was done using reciprocal time method, GRM, and traveltime tomography which utilizes wavefront expansion method for forward process and SIRT for inversion. The result shows that the first layer has its lower boundary between 3.49m and 8.88m. The P-wave velocity of the first and the second layer were estimated as 270 360m/s and 1550 1940m/s respectively. When the boundary of the first and second layer is smooth enough and the velocity difference is large enough, GRM has little advantage over reciprocal time method. The result of reciprocal method and traveltime tomography shows consistency. The northeast part of the boundary has syncline structure, which is similar to the topography above. This implies that the collapse of the cavities of Nampoong gallery result in the subsidence of the ground surface. The subsidence is in progress across the Youngdong railroad, therefore a proper reinforcement work is required.

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Rock Mass Classification by Surface-borehole Hybrid Array Seismic Refraction Tomography in the Region of Serious Electrical Noises (전기적 잡음이 심한 지역에서 지표-시추공 복합배열 탄성파탐사에 의한 암반등급 산정)

  • Kim Ye Ryun;Sha Sang Ho;Nam Soon Sung;Jo Cheol Hyun;Cha Young Ho;Park Jong Bum;Shin Kyung Jin
    • Proceedings of the KSR Conference
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    • 2005.05a
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    • pp.610-614
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    • 2005
  • Rock mass classification by using electrical resistivity tomography(ERT) method is widely performed for the determination of rock support type in tunnel design. In the region of high electrical noise level, however, the result of the ERT will have many erroneous features. In this study, the back ground electrical noise had been measured to find out the reason why the results of ERT in this area did not agree to the expected geology confirmed by boreholes. In order to overcome this limitation of ERT, a hybrid surface-borehole array seismic refraction tomography had been followed. Using this technique, we could get P-wave velocity section including the depth level of tunnel. The comparison of the P-wave velocity and RMR shows fairly good statistical relationship to make it possible to set up the rock mass classification for the entire tunnel line.

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