Refinement and Application of an Estimation Procedure for Site Natural Periods Using Microtremor

Ohmachi, Tatsuo; Konno, Katsuaki; Endoh, T.; Toshinawa, Takumi

doi:10.2208/jscej.1994.489_251

Cited by 27 publications

(7 citation statements)

References 3 publications

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“…Horizontal to vertical spectral ratio is called the H/V spectral ratio. By looking at the peak frequency of the H/V spectral ratio, predominant frequency of ground can be estimated [9]. This information can be effectively referred to when we need to choose inherent frequency of the levee from the peak frequencies of transfer functions.…”

Section: Calculation Of H/v Spectral Ratiomentioning

confidence: 99%

Application of Microtremor Measurement for Estimate of Overall Stiffness of Levees

Mikami¹

2014

geomate

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This study explores the feasibility of estimating overall shear wave velocity for levees to detect weak sections by using microtremor measurement. Microtremor measurement is carried out on the crest and near the toe of the levee embankment simultaneously by placing servo-type velocity sensors perpendicular to the levee axis. Then, transfer functions are calculated using the horizontal motions. Finally, overall shear wave velocity structure is identified so that the peak frequency of the transfer function and the fundamental frequency of finite element model of the levee that has the same cross section coincide. The identified shear wave velocities are mostly consistent with shear wave velocities estimated based on SPT blow counts. Hence, this method is feasible to detect weak sections along levees.

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Section: Calculation Of H/v Spectral Ratiomentioning

confidence: 99%

Application of Microtremor Measurement for Estimate of Overall Stiffness of Levees

Mikami¹

2014

geomate

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“…As for the method of ascertaining ground motion characteristics, soil boring, which can provide accurate data on the subsurface structure of the target area, is ideal, but is time-consuming and expensive. Therefore, microtremor observation, a simple method of identifying ground motion characteristics, has gained a great deal of attention and many studies have been carried out using this method (Example, Nakamura [1], Ohmachi et al [2], Maruyama et al [3], Motoki et al [4]).…”

Section: Introductionmentioning

confidence: 99%

Analysis on Predominant Periods Distribution by Microtremor Observations for Seismic Disaster Prevention in Yokohama, Japan Using GIS

Ochiai¹,

Enomoto²

2019

JGIS

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In recent years, predictions of damage from earthquakes have been made on a prefectural scale, and expectations exist that more detailed damage forecasts should be made even on a city/town/village scale. It is important to know detailed ground characteristics to do damage prediction on a fine scale. Using GIS is the best way to communicate this planar disaster prevention information to the general public. Yokohama City is the second largest city in Japan and developed as part of the capital region of Metropolitan Tokyo. Recently, the population of this city has reached about 3,000,000, and economic and cultural facilities, social infrastructure, and residential complexes are concentrated in this city. The capital region, including Yokohama City, was attacked by the 1923 Great Kanto Earthquake (M7.9) and Yokohama City was devastated by this earthquake. From the research so far, it is known that the H/V spectrum obtained from microtremor observation has a good correlation with the ground characteristics. The authors have been conducting high-density tremor observations that have been ongoing since the 1990s, mainly in Kanagawa Prefecture, Japan. Here, we have organized the predominant periods obtained from the observation results for Yokohama City. The entirety of Yokohama City was divided into 250 m × 250 m meshes and their centers were used as microtremor observation sites. Excluding sites that could not be used due to geographical conditions, observations were made at approximately 5700 sites. So, we compared the data obtained separately, such as the period, terrain classification, and amplification characteristics. The distribution maps of predominant periods in Yokohama City show that the city contains a lot of artificially transformed land, and consequently, the distribution of predominant periods is not uniform. However, it can be seen that the periods become

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“…The H/V technique which evaluate the horizontal-to-vertical spectral ratios of the microtremors was popularised by Nakamura [9] to estimate the site effects. This technique was further applied in estimating the fundamental periods [10][11] and relative amplification factors of the sites (e.g., Lermo and Chavez-Garcia [12]; Konno and Ohmachi [13]). The peak of horizontal-to-vertical spectral ratios were empirically found to match the Rayleigh wave's ellipticity of the sites with layered medium [14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Estimation of Ground Structure at USM using Microtremor Observation Technique

2018

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Determination of ground structure is important for seismic hazard analysis and earthquake design of structures. Different types of ground structure at site, depending on its profile of shear-wave velocity, will amplify seismic wave at different extents. Therefore, structures should be designed accordingly to withstand the expected surface ground motion considering seismic site amplification. Microtremor observations were conducted in this study due to its simplicity, less field effort and economy. Field measurement was carried out at two sites at Universiti Sains Malaysia Engineering Campus where the actual soil profiles were known from the existing borelog data. Two sizes of circular array formed by three three-component velocity sensors along the circumference of circle and a three-component velocity sensor at the center for each array were performed. The recorded data were analysed using Spatial Autocorrelation (SPAC) method. Shear wave velocity profile for the site was then estimated through inversion of phase velocity. To produce convincing estimation of ground structure, the horizontal to vertical (H/V) spectra at the center of the circular array was compared with the computed ellipticity of the fundamental mode of Rayleigh wave. The obtained results were also compared with the borelog data. The accuracy for the estimation of ground structure based on various microtremor array sizes and analysis techniques was assessed.

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Refinement and Application of an Estimation Procedure for Site Natural Periods Using Microtremor

Cited by 27 publications

References 3 publications

Application of Microtremor Measurement for Estimate of Overall Stiffness of Levees

Application of Microtremor Measurement for Estimate of Overall Stiffness of Levees

Analysis on Predominant Periods Distribution by Microtremor Observations for Seismic Disaster Prevention in Yokohama, Japan Using GIS

Estimation of Ground Structure at USM using Microtremor Observation Technique

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