• Geomechanics and Engineering
• /
• v.3 no.3
• /
• pp.189-206
• /
• 2011

Amplification based on empirical relations is widely used for seismic microzonation of urban centers. Amplifications are used to represent the site effects of a particular soil column. Many empirical correlations are available to estimate the amplification of seismic waves. These correlations are based on the ratio of shear wave velocity of foundation/rock to soil velocity or 30 m equivalent shear wave velocity ($Vs^{30}$) and are developed considering deep soil data. The aim of this work is to examine the applicability of available amplification relations in the literature for shallow engineering bedrock sites by carrying out site response studies. Shear wave velocity of thirteen sites having shallow engineering bedrock have been selected for the study. In these locations, the depth of engineering bedrock (> 760 ${\pm}$ 60 m/s) is matched with the drilled bore hole. Shear wave velocity (SWV) has been measured using Multichannel Analysis of Surface Wave survey. These sites are classified according to the National Earthquake Hazards Reduction Program (NEHRP) classification system. Amplifications for an earthquake are arrived for these sites using empirical relations and measured SWV data. Site response analysis has been carried out in SHAKE using SWV and using synthetic and real earthquake data. Amplification from site response analysis and empirical relations are compared. Study shows that the amplification arrived using empirical relations does not match with the site response amplification. Site response amplification is much more than empirical values for same shear wave velocity.

• Economic and Environmental Geology
• /
• v.44 no.3
• /
• pp.229-238
• /
• 2011

S-wave, which provides lithology and pore fluid information, plays a key role in estimating gas-hydrate saturation. In general, P- and S-wave velocities increase in the presence of gas-hydrate and the P-wave velocity decreases in the presence of free gas under the gas-hydrate layer. Whereas there are very small changes, even slightly increases, in the S-wave velocity in the free gas layer because S-wave is not affected by the pore fluid when propagating in the free gas layer. To verify those velocity properties of the BSR (bottom-simulating reflector) depth in the gas-hydrate prospect area in the Ulleung Basin, P- and S-wave velocity profiles were derived from multi-component ocean-bottom seismic data which were acquired by Korea Institute of Geoscience and Mineral Resources (KIGAM) in May 2009. OBS (ocean-bottom seismometer) hydrophone component data were modeled and inverted first through the traveltime inversion method to derive P-wave velocity and depth model of survey area. 2-D multichannel stacked data were incorporated as an initial model. Two horizontal geophone component data, then, were polarization filtered and rotated to make radial component section. Traveltimes of main S-wave events were picked and used for forward modeling incorporating Poisson's ratio. This modeling provides S-wave profiles and Poisson's ratio profiles at every OBS site. The results shows that P-wave velocities in most OBS sites decrease beneath the BSR, whereas S-wave velocities slightly increase. Consequently, Poisson's ratio decreased strongly beneath the BSR indicating the presence of a free gas layer under the BSR.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.58 no.4
• /
• pp.588-591
• /
• 2009

We had experimental studies of microwave output generator. We experimented with a corrugate-shped K-band slow wave guide in the backward wave oscillator. It generated output 표 interaction between electron beam's generation and magnetic field. We estimated oscillation frequency at 24GHz by changing propagation velocity and group velocity. We identified movement by second harmonic of Cherencov interaction and slow cyclotron mode. In our study we achieved oscillation stabilization, generation of long pulse, improvement of oscillation efficiency and output.

• Tunnel and Underground Space
• /
• v.23 no.3
• /
• pp.212-218
• /
• 2013

Tuff specimens were thermally treated with predetermined temperatures of 200, 400 and $600^{\circ}C$ to construct specimens simulating weathered tuff rocks. Specific gravity, absorption ratio, elastic wave velocity, uniaxial compressive strength, Brazilian tensile strength, Young's modulus, Poisson's ratio and slake-durability index were measured for pre-heated specimens. Heating of rock specimens entailed the degradation of material properties except for slake-durability index. It was found that correlations among P-wave velocity, uniaxial compressive strength, Brazilian tensile strength, Young's modulus and absorption ratio are high. Regression equations which use the P-wave velocity as an independent variable were presented to evaluate uniaxial compressive strength, Brazilian tensile strength, Young's modulus and absorption ratio.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.10a
• /
• pp.352-359
• /
• 2005

In this study, seismic refraction survey and MASW at dam crest and down-hole test and cross hole test in the boring holes located in dam crest through the core are performed to fin out dynamic material properties, are needed to evaluate dynamic safety of rockfill dam using dynamic analysis method. From the field test and geophysical exploration, applied such as above, p-wave and s-wave velocity profile of each layer of dam body. Dynamic material properties, such as elastic modulus, shear modulus, poissong's ration, are obtained from p-wave and s-wave velocity profile and density profile from formation density logging test.

• Tunnel and Underground Space
• /
• v.21 no.2
• /
• pp.145-150
• /
• 2011

Variations of physical properties such as weight loss rate, wave velocity and uniaxial compressive strength after performing freeze-thaw cyclic test were measured in order to define weathering characteristics of sandstone and andesite. Weight change in specimens of the two rocks decreased with increasing the repetition number of freeze-thaw cyclic test. In particular, weight loss of andesite specimens was very irregular. P-wave velocity of sandstone specimens decreased more than 5%. On the other hand, P-wave velocity of andesite specimens do not vary up to 500 cycles and decreased more than 5% after 1000 cycles. This implies that the sandstone are easily weakened and loosened by weathering processes, while the andesite are relatively strong. In addition, the wave velocity changes of the andesite specimens coincident with the weight change. Uniaxial compressive strengths of the sandstone specimens slightly decreased at the early stage of the freezing-thawing cyclic test, then tended to be irregular after 64 cycles. In conclusion, the rock specimens showed smaller weight loss, less had lower strength reduction rate.

• Geophysics and Geophysical Exploration
• /
• v.15 no.1
• /
• pp.8-15
• /
• 2012

To estimate the S-wave velocity structure beneath the KS31 broad-band station in Wonju, Korea, we used $H-{\kappa}$ stacking and joint inversion of receiver functions and surface-wave dispersion curves derived from 297 teleseismic events (Mw > 5.5) recorded during the period between 2002 and 2009. We thereby determined that the average depth to a nearly flat Moho is $32.4{\pm}0.5\;km$ within tens of kilometer radius of the seismic station. For the crust at this location, we estimate an average shear-wave velocity of 3.69 km/s and a ratio of P- to S-wave velocities, $V_p/V_s$, of $1.72{\pm}0.04$, as is typical for continental crust. A negative phase in the receiver functions at 1 s indicates the presence of a shearwave low velocity layer in a depth interval of 10 to 18 km in the upper crust beneath the KS31 station.

• Tunnel and Underground Space
• /
• v.21 no.6
• /
• pp.460-470
• /
• 2011

Wave velocity was measured to define the weathering characteristics of rock and the strength evaluation of weathered rock on a target of the Aso gravestones with various sizes under the natural environment. As a result, the size correction method which was changed sample of the different size to one of the same size for evaluating wave velocity was proposed, and also suggested the NET (Normalized Elapsed Time) as a new weathering index of rock. In addition, the strength of the weathered rock was estimated from the weathering classification of rock using the NET. Wave velocity of welded tuff was high and didn't show velocity degradation, on the other hand, one of andesite was low and showed velocity degradation. The degree of weathering between rocks of the different size is considered to be comparable, applying the NET based on the on the $V_p/V_o$-NET curve. Furthermore, the classification of rock weathering stages using the NET based on the $S_c/S_o$-NET curve was available, and the estimation of strength for the weathered rock was also possible.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2005.05a
• /
• pp.287-291
• /
• 2005

Two-dimensional velocity tomograms of P- and S-waves were obtained by inverting traveltimes of first arrivals. The two sections of shear-wave velocity show similar features as a whole, with smaller values on the section from surface wave dispersions. Difficulties in picking SH-wave phases due to noise and later arrivals than P waves and PS converted waves are experienced. In addition, a flat layer model based on the surface wave inversion prohibits applications of the method where sgear wave velocities vary strongly in the lateral direction.

• Journal of the Korean Geotechnical Society
• /
• v.18 no.4
• /
• pp.271-283
• /
• 2002

P-wave velocity of concrete is a crucial parameter in determining the thickness of concrete lining, the location of cracks or other defects in Impact-Echo(IE) method. This study introduces an IE-SASW method that may determine the P-wave velocity on a surface of each testing area using the Spectral Analysis of Surface Wave (SASW) method. In numerical studies(Part I), it was verified that P-wave velocities could be obtained from SASW. In this paper(Part II), experimental studies were made in slab type concrete model specimens in which voids and waterproof sheet were included at the known locations. Accordingly, the feasibility of the proposed method was evaluated. The IE-SASW method was also performed in the precast model tunnel on ground and open-cut tunnel in ground. SASW tests were performed to determine the P-wave velocity of the concrete and then IE tests were carried at regularly spaced points along the testing lines to determine the thickness of structures. The nondestructive testing method which combined SASW and IE tests showed the great potential in the field applications.