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Physical hypotheses for adjusting coarse profiles and improving 1D site-response estimation assessed at 10 KiK-net sites

James Kaklamanos, Brendon A. Bradley, Aiswarya N. Moolacattu and Bradley M. Picard
Physical hypotheses for adjusting coarse profiles and improving 1D site-response estimation assessed at 10 KiK-net sites
Bulletin of the Seismological Society of America (March 2020) 110 (3): 1338-1358

Abstract

One-dimensional (1D) linear, equivalent-linear, and nonlinear site-response models have been shown to be biased toward underprediction at high frequencies in the aggregate, particularly at small-to-medium strains. Because this bias persists among various constitutive models, we hypothesize that breakdowns in the 1D site-response assumptions and/or poorly characterized soil properties are responsible for the consistent underpredictions. We test four physical hypotheses for this persistent bias using 398 ground motions at 10 selected sites in Japan's Kiban-Kyoshin (KiK-net) database that are adequately modeled by 1D wave propagation. Specifically, we (1) apply a depth-dependent shear-wave velocity (VS) gradient within layers, (2) decrease the small-strain damping ratio by half, (3) increase the small-strain shear modulus by 10%, and (4) randomize the VS profile. We find that the application of a depth-dependent VS gradient and the reduction of the small-strain damping ratio most greatly reduce the high-frequency bias; that the randomized VS profiles sometimes improve predictions at the fundamental site frequency but often lead to greater underpredictions at high frequencies; and that the 10% adjustment of the small-strain shear modulus has a minimal effect. A significant finding of this study is that overly coarse VS profiles, which are inadequately sampled in depth, induce considerable underprediction bias in site-response models at high frequencies. With regard to 1D site-response model improvement, this study suggests that greater attention should be paid to the coarseness of VS profiles and excessive impedance contrasts, and that profile corrections using depth-dependent VS gradients may be warranted in some cases.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 110
Serial Issue: 3
Title: Physical hypotheses for adjusting coarse profiles and improving 1D site-response estimation assessed at 10 KiK-net sites
Affiliation: Merrimack College, Department of Civil Engineering, North Andover, MA, United States
Pages: 1338-1358
Published: 20200331
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 75
Accession Number: 2020-039345
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch maps
N30°00'00" - N45°00'00", E129°00'00" - E147°00'00"
Secondary Affiliation: University of Canterbury, NZL, New Zealand
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202025
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