Shear-Wave Velocity Site Characterization in Oklahoma from Joint Inversion of Multimethod Surface Seismic Measurements: Implications for Central U.S. Ground-Motion Prediction

2021 ◽  
Author(s):  
William J. Stephenson ◽  
Jack K. Odum ◽  
Steve H. Hartzell ◽  
Alena L. Leeds ◽  
Robert A. Williams
Keyword(s):  
Ground Motion ◽  
Wave Velocity ◽  
Joint Inversion ◽  
Site Characterization ◽  
Earthquake Ground Motion ◽  
Sh Wave ◽  
Site Class ◽  
Hypocentral Distance ◽  
Phase Velocity Dispersion

ABSTRACT We analyze multimethod shear (SH)-wave velocity (VS) site characterization data acquired at three permanent and 25 temporary seismograph stations in Oklahoma that recorded M 4+ earthquakes within a 50 km hypocentral distance of at least one of the 2016 M 5.1 Fairview, M 5.8 Pawnee, or M 5.0 Cushing earthquakes to better constrain earthquake ground-motion modeling in the region. We acquired active-source seismic data for time-averaged VS to 30 m depth (VS30) at 28 seismograph stations near the Fairview, Pawnee, and Cushing epicentral areas. The SH-wave refraction travel times coupled with Rayleigh- and Love-wave phase velocity dispersion were extracted and modeled in a nonlinear least-squares (L2) joint inversion to obtain a best-fit 1D VS versus depth profile for each site. At a subset of sites where the preferred L2 inverse model did not optimally fit each of the Love, Rayleigh, and SH travel-time datasets, we explore application of simulated annealing in a joint inversion to find a more global solution. VS30 values range from 262 to 807  m/s for the preferred measured (in situ) VS profiles, or National Earthquake Hazards Reduction Program (NEHRP) site class D to B, and are broadly comparable with estimates from previous data reports in the region. Site amplification estimates were calculated next from 1D SH transfer functions of the preferred VS profiles and then compared against observed horizontal-to-vertical spectral ratios (HVSRs) from nearby seismograph stations. We generally see good agreement between the predicted in situ model and the observed HVSR resonant frequencies, with nominal amplifications between 2 and 10 within the 2–15 Hz frequency band. Next, using 40 known in situ VS30 measurements in the region, we demonstrate that the in situ VS30 values improve the fit for selected suites of ground-motion models (GMMs) for M 4+ earthquakes within a 50 km hypocentral distance when compared with proxy methods, arguing for future development of GMMs implementing in situ VS profiles.

scholarly journals Multi-method site characterization to verify the hard rock (Site Class A) assumption at 25 seismograph stations across Eastern Canada

2021 ◽  
pp. 875529302110010
Author(s):  
Sameer Ladak ◽  
Sheri Molnar ◽  
Samantha Palmer
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Hard Rock ◽  
Site Characterization ◽  
Eastern Canada ◽  
Site Class ◽  
Paleozoic Rock ◽  
Rock Types ◽  
Site Period

Site characterization is a crucial component in assessing seismic hazard, typically involving in situ shear-wave velocity ( VS) depth profiling, and measurement of site amplification including site period. Noninvasive methods are ideal for soil sites and become challenging in terms of field logistics and interpretation in more complex geologic settings including rock sites. Multiple noninvasive active- and passive-seismic techniques are applied at 25 seismograph stations across Eastern Canada. It is typically assumed that these stations are installed on hard rock. We investigate which site characterization methods are suitable at rock sites as well as confirm the hard rock assumption by providing VS profiles. Active-source compression-wave refraction and surface wave array techniques consistently provide velocity measurements at rock sites; passive-source array testing is less consistent but it is our most suitable method in constraining the rock VS. Bayesian inversion of Rayleigh wave dispersion curves provides quantitative uncertainty in the rock VS. We succeed in estimating rock VS at 16 stations, with constrained rock VS estimates at 7 stations that are consistent with previous estimates for Precambrian and Paleozoic rock types. The National Building Code of Canada uses solely the time-averaged shear-wave velocity of the upper 30 m ( VS30) to classify rock sites. We determine a mean VS30 of ∼ 1600 m/s for 16 Eastern Canada stations; the hard rock assumption is correct (>1500 m/s) but not as hard as often assumed (∼2000 m/s). Mean variability in VS30 is ∼400 m/s and can lead to softer rock classifications, in particular, for Paleozoic rock types with lower average rock VS near the hard/soft rock boundary. Microtremor and earthquake horizontal-to-vertical spectral ratios are obtained and provide site period classifications as an alternative to VS30.

Estimation of site amplification and S-wave velocity profiles in metropolitan Manila, the Philippines, from earthquake ground motion records

2011 ◽  
Vol 42 (1) ◽  
pp. 69-79 ◽  
Author(s):  
Hiroaki Yamanaka ◽  
Kaoru Ohtawara ◽  
Rhommel Grutas ◽  
Robert B. Tiglao ◽  
Melchor Lasala ◽  
...  
Keyword(s):  
Ground Motion ◽  
Wave Velocity ◽  
Site Amplification ◽  
Velocity Profiles ◽  
The Philippines ◽  
Earthquake Ground Motion ◽  
S Wave ◽  
Ground Motion Records

scholarly journals Risks of Solely Relying on VS30 in Ground Motion Response Studies

2018 ◽  
Vol 4 (12) ◽  
pp. 2937
Author(s):  
Amin Ghanbari ◽  
Younes Daghigh ◽  
Forough Hassanvand
Keyword(s):  
Shear Wave ◽  
Ground Motion ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ground Surface ◽  
Earthquake Excitation ◽  
Site Class ◽  
Velocity Models ◽  
Average Shear ◽  
Classification Tool

The average shear wave velocity of the uppermost 30 m of earth (Vs30) is widely used in seismic geotechnical engineering and soil-structure interaction studies. In this regard, any given subsurface profile is assigned to a specific site class according to its average shear wave velocity. However, in a real-world scenario, entirely different velocity models could be considered in the same class type due to their identical average velocities. The objective of the present study is to underline some of the risks associated with solely using Vs30 as a classification tool. To do so, three imaginary soil profiles that are quite different in nature, but all with the same average Vs were considered and were subjected to the same earthquake excitation. Seismic records acquired at the ground surface demonstrated that the three sites have different ground motion amplifications. Then, the different ground responses were used to excite a five-story structure. Results confirmed that even sites from the same class can indeed exhibit different responses under identical seismic excitations. Our results demonstrated that caution should be practiced when large-contrast velocity models are involved as such profiles are prone to pronounced ground motion amplification. This study, which serves as link between soil dynamics and structural dynamics, warns practitioners about the risks associated with oversimplifying the subsurface profile. Such oversimplifications can potentially undermine the safety of existing or future structures.

Exploration of Deep S-Wave Velocity Structure in Niigata and Shonai Plains to Estimate Long-period Earthquake Ground Motion

2009 ◽  
Vol 61 (4) ◽  
pp. 191-205
Author(s):  
Hiroaki SATO ◽  
Hiroaki YAMANAKA ◽  
Sadanori HIGASHI ◽  
Kiyotaka SATO ◽  
Yoshiaki SHIBA ◽  
...  
Keyword(s):  
Ground Motion ◽  
Wave Velocity ◽  
Velocity Structure ◽  
Earthquake Ground Motion ◽  
S Wave ◽  
Long Period

Effect of underground cavities on surface earthquake ground motion under SH wave propagation

2009 ◽  
Vol 38 (12) ◽  
pp. 1441-1460 ◽  
Author(s):  
C. Smerzini ◽  
J. Avilés ◽  
R. Paolucci ◽  
F. J. Sánchez-Sesma
Keyword(s):  
Wave Propagation ◽  
Ground Motion ◽  
Earthquake Ground Motion ◽  
Sh Wave ◽  
Underground Cavities

Site Characterization Using Microtremor Array and Seismic Hazard Assessment for Jakarta, Indonesia

2019 ◽  
Vol 109 (6) ◽  
pp. 2644-2657 ◽  
Author(s):  
Mohamad Ridwan ◽  
Phil R. Cummins ◽  
Sri Widiyantoro ◽  
Masyhur Irsyam
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Soft Soil ◽  
Site Characterization ◽  
Standard Penetration Test ◽  
Alluvial Fan ◽  
Earthquake Hazards ◽  
Ground Acceleration ◽  
Site Class ◽  
Near Surface

Abstract Site characterization is one of the most important components in seismic hazard analysis because it accounts for the important effects of near‐surface geology on ground motion. It is usually quantified based on the time‐averaged S‐wave velocity (VS) for the top 30 m of the profile (VS30). In this study, we estimate the site class in Jakarta based on VS structure estimated using microtremor array observations. The results show that microtremor‐derived VS profiles agree well with standard penetration test‐derived profiles at nine sites. The site‐class estimates in the Jakarta area can be divided into two National Earthquake Hazards Reduction Program classes: (a) site class E (soft soil) located in alluvium, beach ridge, and alluvial fan deposits in northern and western Jakarta, and (b) site class D (stiff soil) found mainly in alluvial fan deposits in southeastern Jakarta. The variation of VS30 in Jakarta leads to different soil amplification factors that will impact the seismic hazard at the surface. We show that the seismic hazard resulting from selected ground‐motion models (GMMs) illustrates a clear influence of site effects at long periods (>1  s). However, the effect on peak ground acceleration and response spectra for short periods (0.2 s) appear to be less pronounced, due to the GMMs’ treatment of basin effects and nonlinear soil behavior. Available GMMs may not accurately account for such effects in the Jakarta basin, and GMMs specific to Indonesia should be developed to accurately assess seismic hazard there.

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