Linear site-response characteristics at central and eastern U.S. seismic stations
Earthquake S waves can become trapped, or resonate, between the free surface and high-impedance basal layers, strongly contributing to site response at specific frequencies. Strong S-wave resonances have been observed in the central and eastern U.S., where many sites sit on unlithified sediments und...
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| Format: | Article |
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Frontiers Media S.A.
2023-09-01
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| Series: | Frontiers in Earth Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/feart.2023.1216467/full |
| _version_ | 1827822648926666752 |
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| author | N. Seth Carpenter N. Seth Carpenter Zhenming Wang Zhenming Wang Edward W. Woolery |
| author_facet | N. Seth Carpenter N. Seth Carpenter Zhenming Wang Zhenming Wang Edward W. Woolery |
| author_sort | N. Seth Carpenter |
| collection | DOAJ |
| description | Earthquake S waves can become trapped, or resonate, between the free surface and high-impedance basal layers, strongly contributing to site response at specific frequencies. Strong S-wave resonances have been observed in the central and eastern U.S., where many sites sit on unlithified sediments underlain by stiff bedrock. To evaluate S-wave resonances in this region, we calculated 1D linear site-responses at 89 seismic stations with developed S-wave velocity profiles into bedrock. We found that S-wave resonances at the fundamental and strongest (peak) modes occur across large ranges of frequencies, each spanning more than two orders of magnitude — 0.21–54.0 Hz and 0.29–71.5 Hz, respectively. Amplifications of ∼5 and ∼6 are common at the fundamental frequency and peak modes, respectively; the largest amplification calculated was 13.2. Using simple regression analyses, we evaluated the skills of six proxies derived from the S-wave velocity profiles to predict the frequencies and corresponding amplifications of the fundamental and peak modes. We found that the depths to the 1.0 km/s and 2.5 km/s horizons, consistent with other studies, and to the maximum impedance contrasts strongly correlate with the resonance frequencies and that the fundamental-mode and peak amplifications correlate with the maximum impedance ratios. Correlations improved for data subsets based on the number and magnitude of impedance ratios underlying the sites and are the strongest at sites underlain by a single impedance ratio of 3.0 or greater. Finally, we calculated the S-wave horizontal-to-vertical spectral ratios (HVSR) at each possible seismic station and found, consistent with other studies, that the first peak can be used to estimate fundamental-mode frequencies and the corresponding amplifications. Thus, S-wave HVSR, can provide useful estimates of the fundamental-mode linear site response parameters at sites lacking S-wave velocity profiles. Furthermore, S-wave HVSR curves appear to be useful to broadly categorize impedance-ratio profiles. |
| first_indexed | 2024-03-12T01:59:41Z |
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| id | doaj.art-d5a4c3d2863144b98674a240cbf4f98a |
| institution | Directory Open Access Journal |
| issn | 2296-6463 |
| language | English |
| last_indexed | 2024-03-12T01:59:41Z |
| publishDate | 2023-09-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Earth Science |
| spelling | doaj.art-d5a4c3d2863144b98674a240cbf4f98a2023-09-07T20:53:09ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632023-09-011110.3389/feart.2023.12164671216467Linear site-response characteristics at central and eastern U.S. seismic stationsN. Seth Carpenter0N. Seth Carpenter1Zhenming Wang2Zhenming Wang3Edward W. Woolery4Kentucky Geological Survey, University of Kentucky, Lexington, KY, United StatesDepartment of Earth and Environmental Sciences, College of Arts and Sciences, University of Kentucky, Lexington, KaY, United StatesKentucky Geological Survey, University of Kentucky, Lexington, KY, United StatesDepartment of Earth and Environmental Sciences, College of Arts and Sciences, University of Kentucky, Lexington, KaY, United StatesDepartment of Earth and Environmental Sciences, College of Arts and Sciences, University of Kentucky, Lexington, KaY, United StatesEarthquake S waves can become trapped, or resonate, between the free surface and high-impedance basal layers, strongly contributing to site response at specific frequencies. Strong S-wave resonances have been observed in the central and eastern U.S., where many sites sit on unlithified sediments underlain by stiff bedrock. To evaluate S-wave resonances in this region, we calculated 1D linear site-responses at 89 seismic stations with developed S-wave velocity profiles into bedrock. We found that S-wave resonances at the fundamental and strongest (peak) modes occur across large ranges of frequencies, each spanning more than two orders of magnitude — 0.21–54.0 Hz and 0.29–71.5 Hz, respectively. Amplifications of ∼5 and ∼6 are common at the fundamental frequency and peak modes, respectively; the largest amplification calculated was 13.2. Using simple regression analyses, we evaluated the skills of six proxies derived from the S-wave velocity profiles to predict the frequencies and corresponding amplifications of the fundamental and peak modes. We found that the depths to the 1.0 km/s and 2.5 km/s horizons, consistent with other studies, and to the maximum impedance contrasts strongly correlate with the resonance frequencies and that the fundamental-mode and peak amplifications correlate with the maximum impedance ratios. Correlations improved for data subsets based on the number and magnitude of impedance ratios underlying the sites and are the strongest at sites underlain by a single impedance ratio of 3.0 or greater. Finally, we calculated the S-wave horizontal-to-vertical spectral ratios (HVSR) at each possible seismic station and found, consistent with other studies, that the first peak can be used to estimate fundamental-mode frequencies and the corresponding amplifications. Thus, S-wave HVSR, can provide useful estimates of the fundamental-mode linear site response parameters at sites lacking S-wave velocity profiles. Furthermore, S-wave HVSR curves appear to be useful to broadly categorize impedance-ratio profiles.https://www.frontiersin.org/articles/10.3389/feart.2023.1216467/fullsite responsesite effect proxiesresonanceimpedance contrastHVSRCEUS seismic hazard |
| spellingShingle | N. Seth Carpenter N. Seth Carpenter Zhenming Wang Zhenming Wang Edward W. Woolery Linear site-response characteristics at central and eastern U.S. seismic stations Frontiers in Earth Science site response site effect proxies resonance impedance contrast HVSR CEUS seismic hazard |
| title | Linear site-response characteristics at central and eastern U.S. seismic stations |
| title_full | Linear site-response characteristics at central and eastern U.S. seismic stations |
| title_fullStr | Linear site-response characteristics at central and eastern U.S. seismic stations |
| title_full_unstemmed | Linear site-response characteristics at central and eastern U.S. seismic stations |
| title_short | Linear site-response characteristics at central and eastern U.S. seismic stations |
| title_sort | linear site response characteristics at central and eastern u s seismic stations |
| topic | site response site effect proxies resonance impedance contrast HVSR CEUS seismic hazard |
| url | https://www.frontiersin.org/articles/10.3389/feart.2023.1216467/full |
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