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2019 Ridgecrest Earthquake Reveals Areas of Los Angeles That Amplify Shaking of High-Rises

Kohler, Monica D. and Filippitzis, Filippos and Heaton, Thomas and Clayton, Robert W. and Guy, Richard and Bunn, Julian and Chandy, K. Mani (2020) 2019 Ridgecrest Earthquake Reveals Areas of Los Angeles That Amplify Shaking of High-Rises. Seismological Research Letters, 91 (6). pp. 3370-3380. ISSN 0895-0695. https://resolver.caltech.edu/CaltechAUTHORS:20210107-103141484

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Abstract

The populace of Los Angeles, California, was startled by shaking from the M 7.1 earthquake that struck the city of Ridgecrest located 200 km to the north on 6 July 2019. Although the earthquake did not cause damage in Los Angeles, the experience in high‐rise buildings was frightening in contrast to the shaking felt in short buildings. Observations from 560 ground‐level accelerometers reveal large variations in shaking in the Los Angeles basin that occurred for more than 2 min. The observations come from the spatially dense Community Seismic Network (CSN), combined with the sparser Southern California Seismic Network and California Strong Motion Instrumentation Program networks. Site amplification factors for periods of 1, 3, 6, and 8 s are computed as the ratio of each station’s response spectral values combined for the two horizontal directions, relative to the average of three bedrock sites. Spatially coherent behavior in site amplification emerges for periods ≥3  s⁠, and the maximum calculated site amplifications are the largest, by factors of 7, 10, and 8, respectively, for 3, 6, and 8 s periods. The dense CSN observations show that the long‐period amplification is clearly, but only partially, correlated with the depth to basement. Sites with the largest amplifications for the long periods (⁠≥3  s⁠) are not close to the deepest portion of the basin. At 6 and 8 s periods, the maximum amplifications occur in the western part of the Los Angeles basin and in the south‐central San Fernando Valley sedimentary basin. The observations suggest that the excitation of a hypothetical high‐rise located in an area characterized by the largest site amplifications could be four times larger than in a downtown Los Angeles location.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1785/0220200170DOIArticle
ORCID:
AuthorORCID
Kohler, Monica D.0000-0002-4703-190X
Filippitzis, Filippos0000-0001-8377-4914
Heaton, Thomas0000-0003-3363-2197
Clayton, Robert W.0000-0003-3323-3508
Guy, Richard0000-0002-8651-5608
Bunn, Julian0000-0002-3798-298X
Chandy, K. Mani0000-0001-9190-1290
Additional Information:© 2020 Seismological Society of America. Manuscript received 4 May 2020; Published online 30 September 2020. This article greatly benefitted from thoughtful reviews provided by Art Frankel and an anonymous reviewer. The authors are grateful to Caltech, the Betty and Gordon Moore Foundation, the Conrad N. Hilton Foundation, and Computers & Structures, Inc. for providing support for the Community Seismic Network and for this study. Data and Resources: Community Seismic Network (CSN) strong‐motion data for the Ridgecrest earthquake are available from csn.caltech.edu/data. Southern California Seismic Network (SCSN) data are available from the Southern California Earthquake Data Center (scedc.caltech.edu). The authors acknowledge accessing strong‐motion data through the Center for Engineering Strong Motion Data (CESMD; strongmotioncenter.org. All websites were last accessed August 2020. The networks or agencies providing the data used in this article are the California Strong Motion Instrumentation Program (CSMIP) and the U.S. Geological Survey (USGS) National Strong Motion Project (NSMP). The unpublished manuscript by F. Filippitzis, M. D. Kohler, T. H. Heaton, R. W. Graves, R. W. Clayton, R. G. Guy, J. J. Bunn, and K. M. Chandy (2020), “Ground motion response in urban Los Angeles from the 2019 Ridgecrest earthquake sequence,” submitted to Earthq. Spectra. The supplemental material contains seven figures (Figs. S1–S7) cited in the main article.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Conrad N. Hilton FoundationUNSPECIFIED
Computers and Structures, Inc.UNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20210107-103141484
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210107-103141484
Official Citation:Monica D. Kohler, Filippos Filippitzis, Thomas Heaton, Robert W. Clayton, Richard Guy, Julian Bunn, K. Mani Chandy; 2019 Ridgecrest Earthquake Reveals Areas of Los Angeles That Amplify Shaking of High‐Rises. Seismological Research Letters ; 91 (6): 3370–3380. doi: https://doi.org/10.1785/0220200170
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107360
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:08 Jan 2021 18:21
Last Modified:08 Jan 2021 18:21

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