Seismic site-response experiments following the March 3, 1985 central Chile earthquake (topographical and geological effects)

Abstract Site-response experiments were performed 5 months after the MS = 7.8 central Chile earthquake of 3 March 1985 to identify amplification due to topography and geology. Topographical amplification at Canal Beagle, a subdivision of Viña del Mar, was hypothesized immediately after the main event, when extensive damage was observed on the ridges of Canal Beagle. Using frequency-dependent spectral ratios of aftershock data obtained from a temporarily established dense array, it is shown that there is substantial amplification of motions at the ridges of Canal Beagle. The data set constitutes the first such set depicting topographical amplification at a heavily populated region and correlates well with the damage distribution observed during the main event. Dense arrays established in Viña del Mar also yielded extensive data which are quantified to show that, in the range of frequencies of engineering interest, there was substantial amplification at different sites of different geological formations. To substantiate this, spectral ratios developed from the strong-motion records of the main event are used to show the extensive degree of amplification at an alluvial site as compared to a rock site. Similarly, spectral ratios developed from aftershocks recorded at comparable stations qualitatively confirm that the frequency ranges for which the amplification of motions occur are quite similar to those from strong-motion records. In case of weak motions, the denser arrays established temporarily as described herein can be used to identify the frequency ranges for which amplification occurs, to quantify the degree of frequency-dependent amplification and used in microzonation of closely spaced localities.

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Preliminary report of investigations of the central Chile earthquake of March 3, 1985

Open-File Report ◽

10.3133/ofr85542 ◽

1985 ◽

Cited By ~ 4

Author(s):

Sylvester Theodore Algermissen

Keyword(s):

Preliminary Report ◽

Central Chile ◽

Chile Earthquake

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Effect of Intra-layer Vs Fluctuation on Linear Seismic Site Response

KSCE Journal of Civil Engineering ◽

10.1007/s12205-021-2047-9 ◽

2021 ◽

Author(s):

Yen-Hsiang Chang ◽

Chi-Chin Tsai ◽

Chien-Chia Huang ◽

Duhee Park

Keyword(s):

Site Response ◽

Seismic Site Response

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Experimental and analytical study of seismic site response of discontinuous permafrost

Canadian Geotechnical Journal ◽

10.1139/cgj-2015-0223 ◽

2016 ◽

Vol 53 (9) ◽

pp. 1363-1375 ◽

Cited By ~ 2

Author(s):

Behrang Dadfar ◽

M. Hesham El Naggar ◽

Miroslav Nastev

Keyword(s):

Shear Wave ◽

Site Response ◽

Free Field ◽

Frozen Soil ◽

Shaking Table ◽

Experimental Program ◽

Small Scale ◽

Seismic Site Response ◽

Discontinuous Permafrost ◽

Spectral Accelerations

Seismic site response of discontinuous permafrost is discussed. The presence of frozen ground in soil deposits can significantly affect their dynamic response due to stiffer conditions characterized by higher shear-wave velocities compared to unfrozen soils. Both experimental and numerical investigations were conducted to examine the problem. The experimental program included a series of 1g shaking table tests on small-scale models. Nonlinear numerical analyses were performed employing FLAC software. The numerical model was verified using the obtained experimental results. Parametric simulations were then conducted using the verified model to study variations of the free-field spectral accelerations (on top of the frozen and unfrozen soil blocks) with the scheme of frozen–unfrozen soil, and to determine the key parameters and their effects on seismic site response. Results show that spectral accelerations were generally higher in frozen soils than in unfrozen ones. It was found that the shear-wave velocity of the frozen soil as well as the assumed geometry of the blocks and their spacing have a significant impact on the site response.

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Seismic site response in the greater Vancouver, British Columbia, area: spectral ratios from moderate earthquakes

Canadian Geotechnical Journal ◽

10.1139/t98-096 ◽

1999 ◽

Vol 36 (2) ◽

pp. 195-209 ◽

Cited By ~ 11

Author(s):

John F Cassidy ◽

Garry C Rogers

Keyword(s):

Site Response ◽

Strong Motion ◽

River Delta ◽

Data Sets ◽

Fraser River ◽

Spectral Ratios ◽

Data Set ◽

Seismic Site Response ◽

Fraser River Delta ◽

S Period

Three-component, digital recordings of two recent moderate earthquakes provide valuable new insight into the response to seismic shaking in the greater Vancouver area, particularly on the Fraser River delta. The 1996 M = 5.1 Duvall, Washington, earthquake (180 km southeast of Vancouver) triggered strong-motion seismographs at seven sites and the 1997 M = 4.3 Georgia Strait earthquake (37 km west of Vancouver) triggered instruments at 13 sites in the greater Vancouver area. The latter data set is especially important because it contains the first three-component recordings made on bedrock in greater Vancouver. Both data sets represent weak ground motion, with peak horizontal accelerations of 0.5-1.5% gravity (g) for the Duvall earthquake, and 0.2-2.4% g for the Georgia Strait earthquake. Using the method of spectral ratios, we estimate the site response for each of the strong-motion instrument soil sites. On the Fraser River delta amplification is observed over a relatively narrow frequency range of 1.5-4 Hz (0.25-0.67 s period), with peak amplification of 4-10 (relative to competent bedrock) for the thick soil delta centre sites, and about 7-11 for the delta edge sites. Relative to firm soil, the peak amplification ranges from 2 to 5 for the thick soil delta centre sites, and 2 to 6 for the delta edge sites. At higher frequencies, little or no amplification, and in many cases slight attenuation, is observed.Key words: seismic site response, Fraser delta, earthquakes.

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