TY - JOUR
T1 - An evaluation of linear site-response parameters in the central and eastern United States and the importance of empirical site-response estimations
AU - Seth Carpenter, N.
AU - Wang, Zhenming
AU - Woolery, Edward W.
N1 - Publisher Copyright:
© Seismological Society of America.
PY - 2020/4/1
Y1 - 2020/4/1
N2 - Site response at many locations in the central and eastern United States is a resonance-based phenomenon, which site factors based on the VS30 proxy may not reliably capture. Alternative factors, fundamental frequency, f0, and fundamental-mode amplification, A0, calculated from simplified expressions were evaluated against 1D linear, viscoelastic SH-wave full-resonance (FR) site responses. Tests were conducted using S-wave velocity profiles to bedrock at 11 seismic stations. The results showed that simplified expressions approximate FR f0 and A0 at most stations. However, at two sites with intermediate-depth strong impedance contrasts, the simplified approach underestimates A0 by ∼ 40%. In addi-tion, FR f0 and A0 were compared with weak-motion earthquake S-wave horizontal-to-vertical (H/V) spectral ratios. Measuring f0 and A0 from S-wave H/V for our comparisons required considering multiple observations at the regional scale. The first S-wave H/V peaks occurred between ∼ 1 and ∼ 3 Hz at all seven stations in the Illinois basin (IB), which is a much lower f0 than expected for five of these sites. Thus, we used the first S-wave H/V peaks at f > 3 Hz at these five sites in our comparisons. The S-wave H/V peaks we evaluated indicate that S-wave H/V can approximate FR f0 . However, although the A0 measured from S-wave H/V is positively correlated with theoretical A0, it overestimated FR A0 by more than 40% at all but three sites, indicating that additional study is needed to determine the appropriate use of A0 from S-wave H/V. The observed, unmodeled amplifications between ∼ 1 and ∼ 3 Hz are of similar magnitudes as those from the shallower sediment layers at most stations, which highlights the importance of collecting empirical site-response estimations. Furthermore, the amplifications indicate the need to investigate deeper velocity structures in the IB to account for site responses within the frequency band of engineering interest.
AB - Site response at many locations in the central and eastern United States is a resonance-based phenomenon, which site factors based on the VS30 proxy may not reliably capture. Alternative factors, fundamental frequency, f0, and fundamental-mode amplification, A0, calculated from simplified expressions were evaluated against 1D linear, viscoelastic SH-wave full-resonance (FR) site responses. Tests were conducted using S-wave velocity profiles to bedrock at 11 seismic stations. The results showed that simplified expressions approximate FR f0 and A0 at most stations. However, at two sites with intermediate-depth strong impedance contrasts, the simplified approach underestimates A0 by ∼ 40%. In addi-tion, FR f0 and A0 were compared with weak-motion earthquake S-wave horizontal-to-vertical (H/V) spectral ratios. Measuring f0 and A0 from S-wave H/V for our comparisons required considering multiple observations at the regional scale. The first S-wave H/V peaks occurred between ∼ 1 and ∼ 3 Hz at all seven stations in the Illinois basin (IB), which is a much lower f0 than expected for five of these sites. Thus, we used the first S-wave H/V peaks at f > 3 Hz at these five sites in our comparisons. The S-wave H/V peaks we evaluated indicate that S-wave H/V can approximate FR f0 . However, although the A0 measured from S-wave H/V is positively correlated with theoretical A0, it overestimated FR A0 by more than 40% at all but three sites, indicating that additional study is needed to determine the appropriate use of A0 from S-wave H/V. The observed, unmodeled amplifications between ∼ 1 and ∼ 3 Hz are of similar magnitudes as those from the shallower sediment layers at most stations, which highlights the importance of collecting empirical site-response estimations. Furthermore, the amplifications indicate the need to investigate deeper velocity structures in the IB to account for site responses within the frequency band of engineering interest.
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U2 - 10.1785/0120190217
DO - 10.1785/0120190217
M3 - Article
AN - SCOPUS:85083081884
SN - 0037-1106
VL - 110
SP - 489
EP - 507
JO - Bulletin of the Seismological Society of America
JF - Bulletin of the Seismological Society of America
IS - 2
ER -