Observation of 1- to 5- sec Microtremors and Their Application to Earthquake Engineering. Part III

Kono, Hiroshi; Ohta, Yutaka; Goto, Noriko; Shiono, Keishi; Kudo, Kazuyoshi; Sakajiri, Naomi; Naruse, Seiji; Izuhara, Kohji; Takeuchi, Fumiaki

doi:10.4294/zisin1948.29.2_147

Cited by 11 publications

(21 citation statements)

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“…7). In order to determine whether the characteristics observed in the spectra in short, as well as in long, periods have their origins in the geological characteristics and to establish what type of relationship exists between the different variables, we applied the (Kagami et al, 1982(Kagami et al, , 1986Field et al, 1990;Morales et al, 1991a sites. By using the classical method of spectral ratios between a sediment/bedrock pair of stations (Borcherdt, 1970) we obtain the relative amplification at the 11 points located on sediment, in the interior of the basin, with respect to site 12, taken here as a reference.…”

Section: The Granada Basinmentioning

confidence: 99%

“…However, the analysis of microseisms can be a useful tool for the study of the influence of deep structure such as depth to basement, on ground motion if there are no strong changes in the meteorological conditions. Clear examples of these types of studies are those of Ohta et al (1978) and Kagami et al (1982Kagami et al ( , 1986.…”

Section: Introductionmentioning

confidence: 99%

“…Another procedure is to take the spectral ratio of microtremors motion at soil site with respect to the motion recorded at a hard-rock reference site in order to retrieve the site transfer function (Kagami et al, 1982(Kagami et al, , 1986Field et al, 1990). The lack of knowledge of the origin and the exact location of the sources that generate short period microtremors (Aki, 1988) and the variation in temporal and spatial spectral characteristics make interpretation difficult, thus it should be applied carefully, especially when the spectral ratio is used to avoid source and attenuation effects, since they may not be totally canceled.…”

Section: Introductionmentioning

confidence: 99%

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Site Response on Seismic Motion in the Granada Basin (Southern Spain) Based on Microtremor Measurements.

et al. 1993

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We investigate the feasibility of using microtremor measurements in short and long period ranges for the prediction of frequency-dependent amplification effects due to local site geology in the Granada basin and Granada city (Southern Spain). Following a seismic reflection profile crossing the Granada basin, microtremor measurements were recorded at 12 different sites. Peaks centered at 0.7 s (1.5 Hz) and 3-4 s are observed in the microtremor spectra. The 0.7 s peak is interpreted in terms of microtremors and the second one in terms of ocean-generated microseisms. The former is present at all sites on Pliocene and Quaternary sedimens while the 3-4 s peak is present at all sites regardless of the surface geology, although with differences in the spectral amplitude. In order to investigate the possible influence of geologic parameters on long period motion, the maximum spectral amplitude value in the range 1 to 5 s was estimated at all sites in Granada basin. A good linear relation between the maximum spectral amplitude value and surface geology and depth to underground basement was found. However, for short period range (T<1 s), only the surface geology has any relation with the maximum spectral amplitude value. For Granada city, differences in the microtremor spectra were found to depend on the local geology. In the downtown area, situated on alluvial clay and sand from the Quaternary age, differences of up to 10 times with respect to the hill zones (located on compact conglomerates of Pliocene age) are observed. Results from coda-Q analysis from local earthquakes in the Granada basin show overestimations of Qc, for lapse times of 70 s, of up to 4 times at stations situated on sediment when compared to those obtained on bedrock for the 1.5 Hz frequency and to a lesser extent for 3 Hz. This overestimation is explained in terms of seismic-wave amplification in the Granada basin.

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Section: The Granada Basinmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Site Response on Seismic Motion in the Granada Basin (Southern Spain) Based on Microtremor Measurements.

et al. 1993

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“…In some cases predominant period is discussed with depth to bedrock (e.g., Ohta et al, 1978), while in the others attention is focused on the variation of amplitude (e.g., Kagami et al, 1982). Kagami et al (1986) studied amplification of 3-5 s microtremors in relation to the depth of bedrock in San Fernando Valley. Novaro et al (1990) accounted for the spatial distribution of soil amplification of Kagami et al (1986) by a model involving lateral resonances of horizontally propagating waves in the valley.…”

Section: Introductionmentioning

confidence: 99%

“…Kagami et al (1986) studied amplification of 3-5 s microtremors in relation to the depth of bedrock in San Fernando Valley. Novaro et al (1990) accounted for the spatial distribution of soil amplification of Kagami et al (1986) by a model involving lateral resonances of horizontally propagating waves in the valley.…”

Section: Introductionmentioning

confidence: 99%

Vibrational Characteristics of Microseisms and Their Applicability to Microzoning in a Sedimentary Basin.

1992

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In order to study the applicability of microseisms to microzoning of an urban area in a sedimentary basin, characteristics of microseisms were examined through simultaneous observations at ground sites and rock sites in and around the Kyoto Basin, southwest Japan. Time-invariant and site-specific soil amplifications were discussed on the basis of spectral ratios averaged over repeated observations (ground site/rock site):(1) horizontal amplification is larger than vertical one; (2) as the site location changes from the edge of basin to the center, the frequency range with large amplification extends to lower frequency; and (3) at the margin inside the basin, amplification in the direction parallel to the edge of basin is larger than that normal to the edge. Amplification factors thus obtained were nearly the same as those for seismic surface waves from the 1984 west Nagano Prefecture earthquake of M 6.8. Duration of vibration at a ground site during the earthquake was much longer than that at a rock site around the peak frequency of amplification for microseisms. Therefore, amplification factor for microseism can be used as a useful measure to predict long-period vibrational characteristics during earthquakes.

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A new significance on the vertical component ratio of the power spectra between two sites in the application of array methods

Zhang

Morikawa

2015

J Seismol

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Array methods like spatial auto-correlation (SPAC) method and the centerless circular array (CCA) method have provided a convenient means of inferring the phase velocity of surface waves. However, these methods are under the assumption of horizontally layered medium (lateral homogeneity) while the ground structure is actually likely to be inclined. Hence, it is expected to obtain more detailed information of ground structure such as inclination by making better use of the records. In recent years, the seismic interferometry theory has also been widely used to estimate ground structure. According to seismic interferometry theory, the cross correlation of motion between two sites is proportional to the imaginary part of the Green’s function (IOG) between the two sites in diffuse wavefield. In this study, we can obtain the ratio of IOG between two sites by taking the ratio of power spectra between the same two sites. We propose this ratio as an indicator of the lateral heterogeneity between two sites. Through numerical simulation and a field test, we demonstrate that the significance of ratio of power spectra can be interpreted from the sight of ratio of IOG successfully.

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Observation of 1- to 5- sec Microtremors and Their Application to Earthquake Engineering. Part III

Cited by 11 publications

References 0 publications

Site Response on Seismic Motion in the Granada Basin (Southern Spain) Based on Microtremor Measurements.

Site Response on Seismic Motion in the Granada Basin (Southern Spain) Based on Microtremor Measurements.

Vibrational Characteristics of Microseisms and Their Applicability to Microzoning in a Sedimentary Basin.

A new significance on the vertical component ratio of the power spectra between two sites in the application of array methods

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