• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.3-7
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• 2003

The velocity structure beneath the CHNB broadband station is determined by receiver function analysis using by from teleseismic P waveforms. The detailed broadband receiver functions are obtained by stacking method for source-equalized vertical, radial and tangential components of teleseismic P waveforms. A time domain inversion uses the stacked radial receiver function to determine vertical P wave velocity structure beneath the station. The crustal velocity structures beneath the stations are estimated using the receiver function inversion method in the case at the crustal model parameterized by many thin, flat-lying, homogeneous layers. Events divide into 4 groups. four azimuths corresponding to events in group a(southwest), b(south), c(southeast), d(northeast). The result of crust at model inversion shows the crustal velocity structure beneath the CHNB station varies smoothly with increasing depth. The conard discontinuity lies around 18 km and moho discontinuity lies range from 30 to 34 km.

• International Journal of Highway Engineering
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• v.12 no.4
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• pp.139-145
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• 2010

An integrity testing for stone columns was attempted using crosshole S-wave logging. The method is conceptionally quite similar to the crosshole sonic logging (CSL) for drilled piers. The critical difference in the logging is the use of S-wave rather than P-wave, which is used in CSL, because swave is the only wave sensing the stiffness of slower unbounded materials than water. An electro-mechanical source, which can generate reversed Swave signals, was utilized in the logging. The stone column was delineated using the S-wave travel times across the stone column, the S-wave velocity profile of the crushed stone($V_{cs}$-profile) and that of surrounding soil($V_s$-profile). In the calculation of $V_{cs}$-profile of the crushed stone, its friction angle and Ko (coefficient of lateral earth pressure at rest) are recommended to be used. The calculation of the column diameter is not much affected by the values of friction angle and Ko.

• Journal of the Korean Geotechnical Society
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• v.25 no.5
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• pp.5-16
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• 2009

Preconsolidation stress is one of the important design parameters in soft soils because the behavior of saturated soft soils changes dramatically at the preconsolidation stress. For the estimation of preconsolidation stress, the global vertical settlement without considering micro strain behavior has been considered. The purpose of this study is to propose and verify a new method called the "shear wave velocity method" for determination of the preconsolidation stress reflecting on particle behavior at the small-strain. In this study, the undisturbed soft soils obtained at Busan, Incheon and Gwangyang in Korea were used. The oedometer cell incoporated with the bender elements is used for the consolidation tests under the $K_0$ condition. The preconsolidation stress determined by the proposed method is compared with that estimated by Casagrande (e-log p'), Sridharan (log (1+e)-log p'), and Onitsuka (In(1+e)-log p') methods. This study suggests that the shear wave velocity method may determine simply the preconsolidation stress with considering the small-strain behavior.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.173-182
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• 2009

In April 2008, KIGAM carried out an ocean-bottom seismometer (OBS) survey in the central Ulleung Basin where strong bottom simulating reflectors (BSRs) were revealed from previous surveys and some gas-hydrate samples were retrieved by direct sampling. The purpose of this survey is to estimate the velocity structure near the BSR in the gas hydrate prospect area using wide-angle seismic data recorded on the ocean-bottom seismometers. Along with the OBS survey, a 2-D seismic survey was performed whereby stratigraphic and preliminary velocity information was obtained. Two methods were applied to wide-angle data for estimating P wave velocity; one is velocity analysis in the $\tau$-p domain and the other is seismic traveltime inversion. A 1-D interval velocity profile was obtained by the first method, which was refined to layered velocity structure by the latter method. A layer stripping method was adopted for modeling and inversion. All velocity profiles at each OBS site clearly show velocity reversal at BSR depths due to the presence of gas hydrates. In addition, we could confirm high velocity in the column/chimney structure.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1999.10c
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• pp.265-270
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• 1999

At this study, we investigated the chemical component and the mineral granular composition of sedimentary rock and others where were distributed in Taegu area and compared correlations with each data through the various physicla and mechanical characteristic test. As the result, d and E, they are kinds of granite, which contain much albite than others were proved to be strong by mechanical tests and the correlation moduli were proved to be more than 0.8 except P wave velocity-Poisson's ration relation when examined Elastic moduluous -Poisson's ration, P, wave velocity-Uniaxial compression strength, Elastic modulous -Uniaxial compression strength and Uniaxial compression strength-Poisson's ration correlation function graph.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.12a
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• pp.43-51
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• 2007

In order to investigate the velocity structure of the southern part of the Korean peninsula, exploded seismic signals were recorded for 120 s along a 294-km WNW-ESE line and 150 s along a 335-km NNW-SSE line in 2002 and 2004, respectively. Velocity tomograms were derived from inverting P-wave and S-wave first arrival times. The raypaths indicate several midcrust interfaces. The shallowest one is at the approximate depth of $2{\sim}3\;km$ with refraction velocities of approximately Vp=6.0 and Vs=3.5 km/s, respectively. The second one of $15{\sim}17\;km$ depth has refraction velocities of approximately Vp=7.1 and Vs=3.7 km/s, respectively. The deepest significant interface varies in depth from 30.8 km to 36.1 km. The critically refracting Vp of $7.8{\sim}8.1\;km/s$ and Vs of $4.2{\sim}4.6\;km/s$ along this interface which may correspond to the Moho discontinuity. The velocity tomograms show (1) existence of a low-velocity zone centered at $6{\sim}7\;km$ depth under the Okchon fold belt and the Yeongnam massif, (2) extension of the Yeongdon fault down to greater than 10 km, and (3) existence of high-velocity materials under the Gyeongsan basin less than 4.2 km thick.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.129-129
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• 2009

• Journal of the Korean Geophysical Society
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• v.4 no.1
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• pp.21-33
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• 2001

Simultaneous inversion of first-arrivals of local earthquakes recorded by the Korea Meteorological Administration(KMA) seismograph network from 1991 to 1998 is made to derive 1D crustal velocity structure of the Korean peninsula. Twenty-nine events with 178 observations are used in the inversion. Average crustal P-wave velocity turns out to be about 6.3 km/sec, and crustal thickness and upper mantle P-wave velocity are estimated as 33 km and 7.9 km/sec, respectively. Results of inversion indicate the possibility of the low velocity layer in the lower crust. Joint inversion is applied to estimate hypocenters, station delays, and velocities simultaneously. Relative station corrections for 11 stations range from zero to about 1.2 sec. Analysis of the synthetic data shows that estimates of hypocenter locations and station corrections as well as averaged crustal structure are reliable for the given data set..

• Economic and Environmental Geology
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• v.30 no.4
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• pp.353-362
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• 1997

P wave velocities of core samples from the Pocheon granite were measured before and after applications of cyclic loading. Then. distribution of the pre-existing microcracks and microcracks developed due to the cyclic loading was investigated by analyzing P wave velocity anisotropies and microscopic observations from thin sections. Anisotropy constants were calculated with three different ways: (1) $C_A$ between the maximum and the minimum velocities, (2) $C_AI$ between velocities measured along the axial direction and the average of six velocities measured in the planes perpendicular to the loading axis (rift plane) and (3) $C_AII$ between the maximum and the minimum velocities measured in the plane perpendicular to the loading axis. Among anisotropy constants. $C_AI$ was the most effective anisotropy constant to identify the rift plane whose orientation is parallel to the pre-existing microcracks as well as the distribution of stress induced microcracks. $C_AI$ decreased after cyclic loading and the relationship between $C_AI$ and number of cycles shows comparatively coherent negative trends. indicating that stress induced microcracks are aligned perpendicular to the orientation of pre-existing microcracks and that the amounts are proportional to the number of loading cycles. The difference of anisotropy constants before and after cyclic loading was effective in delineating the level of cracks and we called it Induced Crack Index. Velocity measurements and microscopic observations show that anisotropy was caused mainly due to microcracks aligned to a particular direction.

• Atmosphere
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• v.31 no.4
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• pp.395-404
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• 2021

In order to investigate downslope windstorm by using more detailed observation, we observed 6 cases at 3 sites - Inje, Yongpyeong, and Bukgangneung - during "3-D Meteorological Observation Project in Yeongdong region of Gangwon province, South Korea in 2020." The results from analysis of the project data were as follows. First, AWS data showed that a subsidence inversion layer appeared in 800~700 hPa on the windward side and 900~850 hPa on the leeward side. Second, before strong wind occurred, the inversion layer had descended to about 880~800 hPa. Third, with mountain wave breaking, downslope wind was intensified at the height of 2~3 km above sea level. After the downslope wind began to descend, the subsidence inversion layer developed. When the subsidence inversion layer got close to the ground, wind peak occurred. In general, UM (Unified Model) GDAPS (Global Data Assimilation Prediction System) have had negative bias in wind speed around peak area of Taebaek mountain range, and positive bias in that of East Sea coast area. The stronger wind blew, the larger the gap between observed and predicted wind speed by GDAPS became. GDAPS predicted strong p-velocity at 0600 LST 25 Apr 2020 (4^th case) and weak p-velocity at 2100 LST 01 Jun 2020 (6^th case) on the lee-side of Taebaek mountain range near Yangyang. As hydraulic jump theory was proved, which is known as a mechanism of downslope windstorm in Yeongdong region, it was confirmed that there is a relationship between p-velocity of lee-side and wind speed of eastern slope of Taebaek mountain range.