Broadband Ground‐Motion Simulation with Interfrequency Correlations

Abstract

Ground‐motion simulations can be viable alternatives to empirical relations for seismic hazard analysis when data are sparse. Interfrequency correlation is revealed in recorded seismic data, which has implications for seismic risk (Bayless and Abrahamson, 2018a). However, in many cases, simulated ground‐motion time series, in particular those originating from stochastic methods, lack interfrequency correlation. Here, we develop a postprocessing method to rectify simulation techniques that otherwise produce synthetic time histories deficient in an interfrequency correlation structure. An empirical correlation matrix is used in our approach to generate correlated random variables that are multiplied in the frequency domain with the Fourier amplitudes of the synthetic ground‐motion time series. The method is tested using the San Diego State University broadband ground‐motion generation module, which is a broadband ground‐motion generator that combines deterministic low‐frequency and stochastic high‐frequency signals, validated for the median of the spectral acceleration. Using our method, the results for seven western U.S. earthquakes with magnitude between 5.0 and 7.2 show that empirical interfrequency correlations are well simulated for a large number of realizations without biasing the fit of the median of the spectral accelerations to data. The best fit of the interfrequency correlation to data is obtained assuming that the horizontal components are correlated with a correlation coefficient of about 0.7.

A frequency-dependent ground-motion spatial correlation model of within-event residuals for Fourier amplitude spectra

“…HC2 Â Ã is used here (Wang et al, 2019 The following steps are then the same for the two components, so the ''HC1'' and ''HC2'' subscripts are dropped for notational brevity and Rs 1 , Rs 2 , Rs 3 refer to either of the two components of the three n by m random variables, if not specified.…”

“…In that implementation, the empirical EAS correlation model is used to generate separate but correlated FAS adjustments to the two horizontal components at a given site. Specifically, we use the findings for inter-frequency correlation by Wang et al (2019) to generate correlated horizontal-component FAS residuals with correlation coefficient 0.7.…”

Sensitivity Analysis of the Interfrequency Correlation of Synthetic Ground Motions to Pseudodynamic Source Models

“…There have been several attempts to understand how well the physics-based ground motion simulation models reproduce the mean and the standard deviation of ground motion intensity measures, produced by empirical GMPEs (Cotton et al, 2013;Causse and Song, 2015;Imtiaz et al, 2015;Vyas et al, 2016;Crempien and Archuleta, 2017;Moschetti et al, 2017;Wirth et al, 2017). Recently, Wang et al (2019) implemented an inter-frequency correlation model obtained by analyzing recorded ground motion data in their physics-based broadband ground motion simulation platform. In other words, they developed a post-processing method for their synthetic ground motion waveforms to mimic the inter-frequency correlation structure observed in the empirical model.…”

Platform approach to diversification: bio-based methyl coumalate to functionalized aromatics via a Diels-Alder strategy

“…The principles address a broad expanse of topics with an emphasis on reaction and process design to decrease toxicity and auxiliary substances while increasing the use of catalytic reagents and improving biodegradability. Atom economy is featured in the second principle which was also promoted by Trost 6,7 to transfer as many atoms as possible from the starting material…”

“…Discovered in 1924 from yeast fermentation, 4 malic acid is a naturally-inherent C4 dicarboxylic acid, as defined by Lee and co-workers 5. It can be generated during the native glucose fermentation pathway in a variety of prokaryotic and eukaryotic microorganisms 6. Its corresponding petroleumbased route is through the hydration of maleic anhydride which ultimately arises from benzene.7 Malic acid's application in the food and beverage industry as a flavor modifier resulted in its annual production of 40,000 tons in 2006.7 Its potential as a platform molecule alongside other C4 diacids and its sizeable production volume stimulates research into bio-based alternatives, especially as they stereoselectively generate L-malic acid instead of racemic mixtures.…”