• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.4
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• pp.759-768
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• 2015

The ground motions of large dimensional structures such as long span bridges at different stations during an earthquake, are inevitably different, which is known as the ground motion spatial variation effect. There are many causes that may result in the spatial variability in seismic ground motion, e.g., the wave passage effect due to the different arrival times of waves at different locations; the loss of coherency due to seismic waves scattering in the heterogeneous medium of the ground; the site amplification effect owing to different local soil properties. In previous researches, the site amplification effects have not been considered or considered by a single-layered soil model only. In this study, however, the ground motion amplification and filtering effects are evaluated by multi-layered soil model. Spatially varying ground motion at the sites with different number of layers, depths, and soil characteristics are generated and the variation characteristics of ground motion time histories according to the correlation of coherency loss function and soil conditions are evaluated. For the bridge system composed of two unit bridges, seismic behavior characteristics are analyzed using the generated seismic waves as input ground motion. Especially, relative displacement due to coherency loss and site effect which can cause the unseating and pounding between girders are evaluated. As a result, considering the soil conditions of each site are always important and should not be neglected for an accurate structural response analysis.

• Proceedings of the KSEG Conference
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• 2005.04a
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• pp.101-106
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• 2005

The three-dimensional Tomography developed by Kim and Bae(2004) was applied to 64,024 P and 64,618 S wave arrival times observed at 238 seismic stations for 4050 local earthquakes in the depth range from 0 to 300 km in and around Hokkaido, Japan. High and low velocity zones for Vp/Vs were clearly imaged in and around Hokkaido. The upper seismic planes of the double seismic zone (DSZ) were found in the subducted Pacific Plate beneath Hokkaido at depth of 40- 80 km, which produced high seismicity around Hokkaido. The findings of high Vp/Vs anomalies beneath the Moho discontinuity supports an evidence of a surface triple-collision hypothesis prepared by Moriya(1994) that the Kuril Arc(Okhotsk Plate or North American Plate) is colliding against the NE Japanese Arc(Amurian Plate or Eurasian Plate), along and beneath the Hidaka Mountain Range, and at the same time the Pacific Plate is subducting into these two plates, making an equilibrium of tectonic forces along the Hikada Mountain Range (HMR) corner and the central tectonic axis(142 ~ 143E) in Hokkaido. The low Vp and Vs were also found in east and west along the central tectonic axis in which the focal mechanism represents the extensional forces. These phenomena are also consistent with low Bouguer gravity anomalies in this region. It is understood why most of great earthquakes occurred outside Hokkaido where the balance of tectonic forces are breaking from the triple junction of three tectonic forces in Hokkaido.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.5
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• pp.513-522
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• 2021

A smartphone (SMP) includes a MEMS sensor that can record 3-components motions and has a wireless network device to transmit data in live. These features and relatively low maintenance costs are the advantage of using SMPs as an auxiliary seismic observation network. Currently, 279 SMPs are monitoring seismic motions. In this study, we compare the SMP records with the seismic station (SS) records to validate SMP records. The data used for comparison are records for five earthquakes that occurred in 2019, which are 321 SS data recorded by the Korea Meteorological Administration and the Korea Institute of Geoscience and Mineral Resources and 145 recorded by SMPs. The analysis shows that the event-term corrected average residual of the SMP MEMS sensor records is 0.59 which indicating that the peak horizontal acceleration by SMP is 1.8 factor bigger than the peak ground acceleration by SS. In addition, the residuals tend to decrease as the installation floor of the smartphone MEMS sensor increases, which is the similar trend with response spectra from SS.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.1
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• pp.19-24
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• 1997

The seismic of the main shock and two after shocks of the Yeongwol Earthquake are studied based on the phase analysis. The travel time curves and two point ray tracing with 12 different possible phases are used to analyze the phases of the records, which were provided by KIGAM seismic network. The results of phase analysis of the Yeongwol Earthquake show the characteristics as follows 1) The main shock ($M_s$=4.5) clearly shows Pn phase but two after shocks ($M_s$=3.8 and $M_s$=2.5) do not show Pn phase. 2) The Pg PmP looks as first arrival phase in the after shock records whose epicentral distance is smaller or larger than 145 km, 3). It is very difficult to identify the phases in the seismic records, which ae related to the Conrad discontinulty, even if the Conrad discontiulty exists. 4) The record of GRE station located outside of the Kyeongsan Basin shows different arrival time of Pn phase, P-S duration time and frequency comared with those of the other stations located within the Kyeongsan Basin.

• Journal of the Korean Geophysical Society
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• v.5 no.3
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• pp.165-174
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• 2002

Seismic velocity and attenuation coefficient of the rocks under the broad-band earthquake observatories of the Korea Meteorological Administration have been measured in the laboratory by using very high frequency seismic waves. Estimated P velocities of the rocks range from 3.2 km/s to 5.6 km/s, depending on the rock type, mineral, and weathering, while, the attenuation coefficients vary from 0.06 to 4.3 db/kHz-m. It seems that P velocities is inversely proportional to the attenuation coefficients of the rocks. Average travel-time delays of the broad-band stations seem to be related with the measured P velocities in the laboratory.

• The Journal of Engineering Geology
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• v.22 no.4
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• pp.399-408
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• 2012

To estimate seismic source and soil-structure interaction more reliably, site amplification characteristics should be considered. Among the various estimation methods, we used Nakamura's method (1989) to estimate site amplification. This method was originally applied to background noise; however, it has recently been successfully applied to S-wave and Coda-wave energy, and is applied to S-waves in the present study. We used more than 180 observed ground motions from 23 macro-earthquakes and then analyzed site amplification characteristics at eight seismic stations. Each station showed characteristics of site amplification properties in the low-, high- and resonance-frequency ranges. Comparison of the present results with those of other studies provide successful information regarding the dynamic amplification of domestic site characteristics and site classification.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.527-536
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• 2016

This paper investigates seismic damage potential of recent September 12 M5.8 Gyeongju earthquake from diverse earthquake engineering perspectives using the accelerograms recorded at three stations near the epicenter. In time domain, strong motion durations are evaluated based on the accelerograms and compared with statistical averages of the ground motions with similar magnitude, epicentral distance and soil conditions, while Fourier analysis using FFT is performed to identify damaging frequency contents contained in the earthquake. Effective peak ground accelerations are evaluated from the calculated response spectra and compared with apparent peak ground accelerations and the design spectrum in KBC 2016. All these results are used to consistently explain the reason why most of seismic damage in the earthquake was concentrated on low-rise stiff buildings but not quite significant. In order to comparatively appraise the damage potential, the constant ductility spectrum constructed from the Gyeongju earthquake is compared with that of the well-known 1940 El Centro earthquake. Deconvolution analysis by using one accelerogram speculated to be recorded at a stiff soil site is also performed to estimate the soil profile conforming to the response spectrum characteristics. Finally, response history analysis for 39- and 61-story tall buildings is performed as a case study to explain significant building vibration felt on the upper floors of some tall buildings in Busan area during the Gyeongju earthquake. Seismic design and retrofit implications of M5.8 Gyeongju earthquake are summarized for further research efforts and improvements of relevant practice.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.4 s.15
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• pp.43-54
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• 2004

The broadband receiver functions are developed from teleseismic P waveforms recorded at Wonju(KSRS), Inchon(IRIS), and Pohang(PHN), and are analyzed to examine the crustal structure beneath these stations. The teleseismic receiver functions are inverted in the time domain of the vertical P wave velocity structures beneath the stations. Clear P-to-S converted phases from the Moho interface are observed in teleseismic seismograms recorded at these stations. The crustal velocity structures beneath the stations are estimated by using the receiver function inversion method(Ammon et al., 1990). The general features of inversion results are as follows: (1) For the Inchon station, the Conrad discontinuity exists at 17.5 Km(SW) deep and the Moho discontinuity exists at 29.5 Km(NW) and 30.5 Km(SE, SW) deep. (2) The shallow crustal structure beneath Wonju station may be covered with a sedimentary rock of a 3 Km thickness. The average Moho depth is assumed about 33.0 Km, and the Conrad discontinuity may exist at 17.0 Km(NE) and 21.0 Km(NW) deep. (3) For Pohang station, the thickness of shallow sedimentary layer is a 3.0 Km in the direction of NE and NW. The Moho depth is 28.0 Km in the direction of the NE and NW. The Conrad discontinuity can be estimated to be existed at 21.0 Km deep for the NE and NW directions.

• Geophysics and Geophysical Exploration
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• v.14 no.4
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• pp.274-281
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• 2011

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.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.51-60
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• 2002

In this study we developed the visualization scheme of spatial ground-motion measurements in real time by using DSS data. Even though this scheme itself is useful for national earthquake mitigation plans, this scheme could be served as the crucial core for constructing rapid earthquake damage evaluation system. DSS is the abbreviation of Data Subscription Service and this is the pre-assigned request for the seismic stations to send very limited brief data with high priority and negligible transmission load. In addition to visualize the damage area with intensity, the corresponding epicenter can be estimated roughly for quick event alarm. For the interpolation of spatially irregular PGA data, the program, named as surface. of GMT was used with NetCDF grid file format. Since the grid file is similar to a postscript file, the program, called as shading, was coded with C language by using Matpak library in order to convert grid files into image files.