Comparison of Site-Adjustment Methods in Broadband Simulated Waveforms for Moderate Magnitude Earthquakes

Sajan K C, Chukwuebuka C. Nweke, Jonathan P. Stewart, & Robert W. Graves

Submitted September 10, 2023, SCEC Contribution #13231, 2023 SCEC Annual Meeting Poster #185

Earthquake simulation platforms like the SCEC Broadband platform are attractive tools for predicting ground motion intensities particularly in data-scarce regions. The Broadband platform can generate simulated time series with and without accounting for local site conditions. The site modification of earthquake ground shaking amplitude, frequency, and duration is significantly influenced by local features related to the near-surface geology and the deep structure of sedimentary basins, making them a crucial factor to account for in ground-motion simulations. There are different site adjustment methods available such as Boore et al (2014), Bayless and Abrahamson (2019) and Shi and Asimaki (2017) that consider the effect of local geology using different parameters such as Vs30 and/or Z1.0 in seismic wave propagation. Before fully embracing simulated ground motions, validating their accuracy is crucial, which is done by performing simulations for earthquakes with well-recorded data. It is key to investigate the behavior and characteristics of the different site adjustment methodologies as this influences the accuracy of simulation. In the present study, 27 well recorded earthquakes in southern California have been simulated using the Broadband platform. The present study has found that time series data generated with and without different site adjustment modules give different levels of bias when comparing with corresponding observed recordings. Residuals computed as the difference between pseudo spectral acceleration of data and simulation for 1 to 10s range are used as the metric to assess the performance of the various site adjustment methodologies for the study region. In the next step, other aspects of the simulation models (e.g., source scaling) can be calibrated to further reduce the bias and enhance accuracy.

Key Words
simulation, Broadband platform, site adjustment, bias

K C, S., Nweke, C. C., Stewart, J. P., & Graves, R. W. (2023, 09). Comparison of Site-Adjustment Methods in Broadband Simulated Waveforms for Moderate Magnitude Earthquakes. Poster Presentation at 2023 SCEC Annual Meeting.

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