Influence of Epistemic Uncertainty in Shear Wave Velocity on Seismic Ground Response Analyses

2019 ◽  
Vol 35 (2) ◽  
pp. 929-954 ◽  
Author(s):  
Federico Passeri ◽  
Sebastiano Foti ◽  
Brady R. Cox ◽  
Adrian Rodriguez-Marek
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Site Response ◽  
Epistemic Uncertainty ◽  
Ground Response ◽  
Soil Response ◽  
Linear Elastic ◽  
Seismic Ground Response ◽  
Study Sites

This study aims to evaluate the influence of epistemic uncertainties in shear wave velocity ( VS) on seismic ground response analyses (GRAs). A number of alternative VS profiles obtained from both invasive (i.e., borehole) and noninvasive (i.e., surface waves) testing methods are available for two blind study sites. These profiles are used to estimate epistemic uncertainties in VS, which are then propagated through equivalent linear-elastic GRAs, allowing for the quantification of intramethod uncertainty and intermethod variability in terms of spectral accelerations, amplification functions, and damage parameters (i.e., Arias and Housner intensities). This study demonstrates that nonlinearity of soil response plays a fundamental role in increasing the propagated uncertainty in GRA. Additionally, GRAs were also performed by means of VS upper/lower-range profiles developed from assumptions commonly used to account for epistemic uncertainties. These VS profiles were found to yield unrealistic site response estimates for both low strain (i.e., linear-elastic) and high strain (i.e., nonlinear) levels.

PSHA Compatible Probabilistic Seismic Site Response Analysis for Oslo, Norway

2020 ◽  
Author(s):  
Brian Carlton ◽  
Amir M. Kaynia
Keyword(s):  
Velocity Profile ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Site Response ◽  
Epistemic Uncertainty ◽  
Base Case ◽  
Response Analysis ◽  
Soil Profiles ◽  
Shear Wave Velocity Profile

ABSTRACT This article describes a probabilistic site-response analysis for the city of Oslo, Norway. We first perform a probabilistic seismic hazard analysis (PSHA) for hard rock. Then, we conduct site-response analyses using Monte Carlo simulations to capture uncertainty in the site profile. We include four base-case soil profiles to incorporate epistemic uncertainty, and we vary the shear-wave velocity profile and shear-modulus reduction and damping curves to account for aleatory variability. We base the soil profiles on over 7000 in situ tests, and the shear-wave velocity profile median, standard deviation, and interlayer correlation on over 559 cone penetration tests. Next, we perform regression analyses to estimate medians and standard deviations of site-specific amplification factors (AFs). Finally, we modify the ground-motion models for rock with the AFs and recompute the PSHA for the soil surface. The analyses show that (1) shallower soil profiles have larger uniform hazard spectra (UHS) values at short periods and smaller UHS values at long periods; (2) epistemic uncertainty of the base-case soil shear-wave velocity profile leads to alternative UHS values with a difference of a factor of 2 at short periods; (3) there is only a small difference in the mean magnitudes and distances controlling the hazard for the PSHA conducted for rock compared to soil; (4) response spectra calculated from site-response analyses with no aleatory variability of the soil properties predict significantly smaller spectral acceleration values at periods shorter than the natural site period; (5) using site amplification standard deviations based on ground-motion recordings, instead of site-response analyses, results in a 10%–20% reduction in the soil surface UHS at short periods and a 5%–10% increase at long periods; and (6) the Eurocode 8 AFs are, in general, conservative for Oslo.

Development of Deep Shear Wave Velocity Profiles with Estimates of Uncertainty in the Complex Interbedded Geology of Christchurch, New Zealand

2018 ◽  
Vol 34 (2) ◽  
pp. 639-672 ◽  
Author(s):  
David Teague ◽  
Brady Cox ◽  
Brendon Bradley ◽  
Liam Wotherspoon
Keyword(s):  
New Zealand ◽  
Surface Wave ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Site Response ◽  
Epistemic Uncertainty ◽  
Data Uncertainty ◽  
Source Surface ◽  
Dispersion Data

Deep (+500-m) shear wave velocity ( V S) profiles were developed at 14 sites throughout Christchurch, New Zealand, using a combination of active-and passive-source surface wave testing. The geology of Christchurch is complex and presents several challenges for surface wave testing. Specifically, the complex interlayering of relatively stiff gravels with soft sands, silts, and clays makes (1) the interpretation of experimental dispersion data ambiguous and (2) complicates the determination of appropriate inversion-layering parameterizations. In order to address the first issue, dispersion data uncertainty was quantified and several mode interpretations were considered during inversion. To address the second issue, 155 geotechnical boreholes and 199 geologic well logs in the vicinity of the test sites were used to guide the choice of layering parameterizations such that geologically realistic V S profiles were obtained via surface wave inversion. At each site, a suite of 1,000 V S profiles representing the combined effects of epistemic uncertainty and apparent aleatory variability in V S was obtained. These V S profiles are available on the DesignSafe-CI web site ( https://doi.org/10.17603/DS21D4D ) and are intended to aid in future seismic site response analyses.

Estimation Study on Shear Wave Velocity of Seabed Using GRNN

2014 ◽  
Vol 580-583 ◽  
pp. 264-267
Author(s):  
Sheng Jie Di ◽  
Zhi Gang Shan ◽  
Xue Yong Xu
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Seismic Analysis ◽  
Site Response ◽  
Estimation Method ◽  
Response Analysis ◽  
Generalized Regression Neural Network ◽  
Engineering Practice ◽  
Site Classification

Characterization of the shear wave velocity of soils is an integral component of various seismic analysis, including site classification, hazard analysis, site response analysis, and soil-structure interaction. Shear wave velocity at offshore sites of the coastal regions can be measured by the suspension logging method according to the economic applicability. The study presents some methods for estimating the shear wave velocity profiles in the absence of site-specific shear wave velocity data. By applying generalized regression neural network (GRNN) for the estimation of in-situ shear wave velocity, it shows good performances. Therefore, this estimation method is worthy of being recommended in the later engineering practice.

An Empirical Geotechnical Seismic Site Response Procedure

2001 ◽  
Vol 17 (1) ◽  
pp. 65-87 ◽  
Author(s):  
Adrián Rodríguez-Marek ◽  
Jonathan D. Bray ◽  
Norman A. Abrahamson
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Classification System ◽  
Soil Depth ◽  
Site Response ◽  
Dynamic Stiffness ◽  
Evaluation Procedure ◽  
Site Classification ◽  
Seismic Site Response

A simplified empirically based seismic site response evaluation procedure that includes measures of the dynamic stiffness of the surficial materials and the depth to bedrock as primary parameters is introduced. This geotechnical site classification scheme provides an alternative to geologic-based and shear wave velocity-based site classification schemes. The proposed scheme is used to analyze the ground motion data from the 1989 Loma Prieta and 1994 Northridge earthquakes. Period-dependent and intensity-dependent spectral acceleration amplification factors for different site conditions are presented. The proposed scheme results in a significant reduction in standard error when compared with a simpler “rock vs. soil” classification system. Moreover, results show that sites previously grouped as “rock” should be subdivided as competent rock sites and weathered soft rock/shallow stiff soil sites to reduce uncertainty in defining site-dependent ground motions. Results also show that soil depth is an important parameter in estimating seismic site response. The standard errors resulting from the proposed site classification system are comparable with those obtained using the more elaborate code-based average shear-wave velocity classification system.

scholarly journals A Comparative Study on the VS30 and N30 Based Seismic Site Classification in Kahramanmaras, Turkey

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Dalia Munaff Naji ◽  
Muge K. Akin ◽  
Ali Firat Cabalar
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Soil Structure ◽  
Site Response ◽  
Dead Sea ◽  
Site Classification ◽  
Earthquake Hazards ◽  
Class D ◽  
Average Shear

Assessment of seismic site classification (SSC) using either the average shear wave velocity (VS30) or the average SPT-N values (N30) for upper 30 m in soils is the simplest method to carry out various studies including site response and soil-structure interactions. Either the VS30- or the N30-based SSC maps designed according to the National Earthquake Hazards Reduction Program (NEHRP) classification system are effectively used to predict possible locations for future seismic events. The main goal of this study is to generate maps using the Geographic Information System (GIS) for the SSC in Kahramanmaras city, influenced by both East Anatolian Fault and Dead Sea Fault Zones, using both VS30 and N30 values. The study also presents a series of GIS maps produced using the shear wave velocity (VS) and SPT-N values at the depths of 5 m, 10 m, 15 m, 20 m, and 25 m. Furthermore, the study estimates the bed rock level and generates the SSC maps for the average VS values through overburden soils by using the NEHRP system. The VS30 maps categorize the study area mainly under class C and limited number of areas under classes B and D, whereas the N30 maps classify the study area mainly under class D. Both maps indicate that the soil classes in the study area are different to a high extent. Eventually, the GIS maps complied for the purpose of urban development may be utilized effectively by engineers in the field.

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