Geology topics

Hoby N. T. Razafindrakoto

Publications and source records attributed to Hoby N. T. Razafindrakoto.

3 recordsLinked to original sources

USGS2021

Regional calibration of hybrid ground‐motion simulations in moderate seismicity areas: Application to the Upper Rhine Graben

This study presents the coupling of the spectral decomposition results for anelastic attenuation, stress drop, and site effects with the Graves‐Pitarka (GP) hybrid ground‐motion simulation methodology, as implemented on the Southern California Earthquake Center (SCEC) broadband platform (BBP). It is targeted to applications in the Upper Rhine graben (URG), which is among the seismically active areas in western Europe, yet a moderate seismicity area. Our development consists of three main steps: (1) calibration of regional high‐frequency (HF) attenuation properties; (2) modification of the hybrid approach to add compressional waves in the HF computation and examine various strategies to evaluate site amplification factors in the Fourier domain (e.g., V S 30 "> V S 30 VS30 ‐based or site‐specific factors); (3) testing of the simulations using earthquake records from the URG ( ⁠ 3.7 < M w < 5 "> 3.7 < M w < 5 3.7<Mw<5 ⁠ ). The validation process of the simulated time histories is performed first on rock sites, and, then subsequently at all stations, whatever their site conditions. The performance of the simulations for rock sites is assessed through the standard validation technique in the BBP (comparison of the waveforms, intensity measures, and estimation of the response spectra model bias). We additionally compare the Fourier amplitude spectrum of the simulations and observations, and compute their corresponding bias. The results show that the simulated ground motions match the general characteristics of the recorded motions, and that the model bias generally fluctuates around zero across the broadband frequency range. Hence, the hybrid ground‐motion methodology implemented in the SCEC BBP can be successfully applied outside high‐seismicity areas and outside those areas for which it had been generally calibrated. Our results also show that HF modification and calibration were necessary to improve the fits with the observation, and demonstrate the potential benefits of using site‐specific amplification factors compared to V S 30 "> V S 30 VS30 ‐based amplification factors.

Upper Rhine Graben↗

USGS2018

Broadband ground‐motion simulation of the 2011 Mw 6.2 Christchurch, New Zealand, earthquake

This study presents the details and results of hybrid broadband (0–10 Hz) ground‐motion simulations for the 2011 M w "> M w Mw 6.2 Christchurch, New Zealand, earthquake. The simulations utilize a 3D velocity model and a kinematic source model with stochastic realizations of the slip amplitude, rise time, and rake angle. The resulting ground motions capture the salient basin amplification effects that are seen in the observed ground motions in central Christchurch city. Quantitative comparisons of the simulations with both observed recordings and empirical ground‐motion models (GMMs), considering peak ground acceleration, 5% damped pseudospectral acceleration, and 5%–95% significant duration, indicate that the simulations exhibit lower bias than empirical GMMs over the T = 1 – 10    s "> T = 1 – 10 s T=1–10 s period range, and are comparable at short periods ( ⁠ T < 1    s "> T < 1 s T<1 s ⁠ ). Sensitivity analyses suggest that the effect of stochastic realizations of different slip distributions is relatively small because of the fault dimensions. It is also illustrated that the effect of slip distribution variability is only a small component of the total uncertainty in ground‐motion simulation. As well as the important implications toward ground‐motion simulation validation, the presented simulations provide ground‐motion time series that can be used for forensic structural and geotechnical case histories that are located sufficiently far from strong‐motion station recordings.

Christchurch↗

USGS2016

The Earthquake‐Source Inversion Validation (SIV) Project

Finite‐fault earthquake source inversions infer the (time‐dependent) displacement on the rupture surface from geophysical data. The resulting earthquake source models document the complexity of the rupture process. However, multiple source models for the same earthquake, obtained by different research teams, often exhibit remarkable dissimilarities. To address the uncertainties in earthquake‐source inversion methods and to understand strengths and weaknesses of the various approaches used, the Source Inversion Validation (SIV) project conducts a set of forward‐modeling exercises and inversion benchmarks. In this article, we describe the SIV strategy, the initial benchmarks, and current SIV results. Furthermore, we apply statistical tools for quantitative waveform comparison and for investigating source‐model (dis)similarities that enable us to rank the solutions, and to identify particularly promising source inversion approaches. All SIV exercises (with related data and descriptions) and statistical comparison tools are available via an online collaboration platform, and we encourage source modelers to use the SIV benchmarks for developing and testing new methods. We envision that the SIV efforts will lead to new developments for tackling the earthquake‐source imaging problem.

Seismological Research Letters↗