Browsing by Author "Bahrampouri, Mahdi"

Now showing 1 - 4 of 4
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    A database of ground motion recordings, site profiles, and amplification factors from the Groningen gas field in the Netherlands
    Ntinalexis, Michail; Kruiver, Pauline P.; Bommer, Julian J.; Ruigrok, Elmer; Rodriguez-Marek, Adrian; Edwards, Ben; Pinho, Rui; Spetzler, Jesper; Hernandez, Edwin Obando; Pefkos, Manos; Bahrampouri, Mahdi; van Onselen, Erik P.; Dost, Bernard; van Elk, Jan (Sage Publications, 2023-02)
    A comprehensive database that has been used to develop ground motion models for induced earthquakes in the Groningen gas field is provided in a freely accessible online repository. The database includes more than 8500 processed ground motion recordings from 87 earthquakes of local magnitude M-L between 1.8 and 3.6, obtained from a large network of surface accelerographs and borehole geophones placed at 50 m depth intervals to a depth of 200 m. The 5%-damped pseudo-acceleration spectra and Fourier amplitude spectra of the records are also provided. Measured shear-wave velocity (V-S) profiles, obtained primarily from seismic Cone Penetration Tests (CPTs), are provided for 80 of the similar to 100 recording stations. A model representing the regional dynamic soil properties is presented for the entire gas field plus a 5 km onshore buffer zone, specifying lithology, V-S, and damping for all layers above the reference baserock horizon located at about 800 m depth. Transfer functions and frequency-dependent amplification factors from the reference rock horizon to the surface for the locations of the recording stations are also included. The database provides a valuable resource for further refinement of induced seismic hazard and risk modeling in Groningen as well as for generic research in site response of thick, soft soil deposits and the characteristics of ground motions from small-magnitude, shallow-focus induced earthquakes.
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    Ground Motion Prediction Equations for Non-Spectral Parameters using the KiK-net Database
    Bahrampouri, Mahdi (Virginia Tech, 2017-08-24)
    The KiK-net ground motion database is used to develop ground motion prediction equations for Arias Intensity (Ia), 5-95% Significant Duration (Ds5-95), and 5-75% Significant Duration (Ds5-75). Relationships are developed both for shallow crustal earthquakes and subduction zone earthquakes (hypocentral depth less than 45 km). The models developed consider site amplification using VS30 and the depth to a layer with VS=800 m/s (h₈₀₀). We observe that the site effect for Iα is magnitude dependent. For Ds5-95 and Ds5-75, we also observe strong magnitude dependency in distance attenuation. We compare the results with previous GMPEs for Japanese earthquakes and observe that the relationships are similar. The results of this study also allow a comparison between earthquakes in shallow-crustal regions, and subduction regions. This comparison shows that Arias Intensity has similar magnitude and distance scaling between both regions and generally Arias Intensity of shallow crustal motions are higher than subduction motions. On the other hand, the duration of shallow crustal motions are longer than subduction earthquakes except for records with large distance and small magnitude causative earthquakes. Because small shallow crustal events saturate with distance, ground motions with large distances and small magnitudes have shorter duration for shallow crustal events than subduction earthquakes.
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    The impact of hazard-consistent ground motion scenarios selection on structural seismic risk estimation
    Zaker Esteghamati, Mohsen; Bahrampouri, Mahdi; Rodriguez-Marek, Adrian (The Geo-Institute of ASCE, 2021)
    Structural risk-based evaluation requires a large number of time-history analyses at different ground motion (GM) intensity levels, where the scenarios (e.g. magnitude and distance) of the GMs used in the time-history analyses should be consistent with the site's hazard. The current practice of GM selection typically simplifies the choice of scenario to either an average scenario or the modal scenarios based on the site's hazard deaggregation results. This paper investigates the impact of hazard deaggregation and scenario selection on estimating structural seismic risk. For a hypothetical site in the Eastern US, a Monte Carlo seismic hazard analysis is performed to derive a site-consistent GM suite that captures 1,000,000 years of the site's seismic activity. The complete GM suite consisting of 99,917 records is then used to perform nonlinear dynamic analyses on a mid-rise concrete office building to derive a benchmark seismic demand curve. Subsequently, four GM sets are selected based on average and modal scenarios from two different hazard deaggregation formulation, and the resulting demand curves are compared to the benchmark. The results show that the hazard deaggregation method and scenario choice impacts the demand curve estimation. When deaggregation is performed on IM exceedance, GMs that were selected based on both methods agree well with the benchmark up to higher damage states where mode-based records outperform average-based records. On the other hand, when deaggregation is formulated based on IM occurrence, average scenario-based GMs better match the benchmark, except for higher damage states where again modal scenario-based GMs are in better agreement with the benchmark.
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    Quantification of Uncertainties for Conducting Partially Non-ergodic Probabilistic Seismic Hazard Analysis
    Bahrampouri, Mahdi (Virginia Tech, 2021-07-01)
    Estimating local site effects and modifying the uncertainty in ground motion predictions are two indispensable parts of partially non-ergodic site-specific PSHA. Local site effects can be estimated using site response simulations or recorded ground motions at the site. When such predictions are available, the aleatory variability of ground motions used in PSHA can be changed to the single station sigma value. However, in these cases, the epistemic uncertainty in predicting site effects must be incorporated into the hazard analyses. This research focuses on the challenges specific to conducting partially non-ergodic site-specific PSHA using recorded ground motions or site response analysis. The main challenge in estimating local site effects using recorded data is whether ground motions collected in a relatively short time can be used to estimate site effects for long return period events. We first develop a database for recorded ground motions at the KiK-net array to investigate this question and use this database to develop a predictive model for the Fourier Amplitude Spectra of ground motions. The ground motion model (GMM) residuals are used to investigate the stability of site terms across different tectonic regimes. We observe that empirical site terms are stable across different tectonic regimes. This observation allows the use of ground motions from any tectonic regime (whether they belong to the tectonic regime that controls the hazard or not) to estimate local site effects. Moreover, in Fourier amplitude, site effects are not dependent on event magnitude and source to site distance; therefore, estimates of site effects from low magnitude events can be easily extrapolated to larger events. The Fourier amplitude GMM developed in this study adds to the library of Fourier amplitude models to be used in future partially non-ergodic site-specific PSHAs. In practice, one of the most common tools for simulating wave propagation is 1-D site response analysis. Two central assumptions in 1-D site response analysis are that the soil profile is comprised of horizontal soil layers of infinite extent and that the vertically propagating SH-waves control the horizontal component of ground motion. SH-waves tend to propagate vertically near the surface because as earthquake waves hit softer layers traveling from the source to the site, they refract until the path becomes steeply inclined. The validity of both assumptions in 1-D site response depends on the geological setting at the site and the geology between the earthquake source and the site, raising the question of which sites are suitable for 1-D site response analysis and what the model error in 1-D site response analysis is. We use the GMM developed for FAS to estimate observed and empirical site terms. The empirical site effects are then compared with the theoretical site effects to determine whether sites are amenable to 1-D site response analyses, and to quantify the model error in the analyses.