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Modeling of Ground-motion Amplitude Saturation at Large Magnitudes and Short Distances

Description: 

As part of the NGA-West3 project, ground-motion models (GMM) are being developed for the Fourier amplitude spectra (FAS). Current observational datasets of ground motions are sparsely populated at large magnitudes and short distances, a range that usually governs the seismic hazard for sites close to active faults. To better constrain near-fault shaking effects for the FAS GMMs, we consider multiple approaches to evaluate the near-fault scaling. First, we adopted empirical modeling based on the available sparse data, which is better constrained at distances beyond 50 km from the rupture, a domain in which the dataset is more populated. Second, we performed a series of simulations using the Graves and Pitarka (GP) method for kinematic rupture modeling as implemented in the Broadband Platform (BBP) of SCEC. An initial exploration led us to remove the stochastic scheme of the GP method and extend the deterministic simulations up to frequencies of 10 Hz. We are using the GP method in an experimental range, in which not only are the small-scale heterogeneities in the source more important, but also the wave propagation becomes more complex. Thus, we included a third element to constrain our modeling based on macrointensity data set which includes more observations at short distances from large magnitudes than the ground-motion data sets. We developed an empirical model to convert intensity measures into Fourier amplitudes. The GP simulations show that there is a partial saturation of the ground-motion amplitude at short distances and large magnitudes: for magnitudes above 6.7 and at short distances, the ground-motion amplitude continues increasing, suggesting a scaling of a factor around 1.5 to 2 at high frequencies between earthquakes of M6.7 compared to M7.5. The intensity measure analysis also supports these findings. As the next step, we will develop constraints on the near-fault scaling based on the three approaches for use in the NGA-West3 project.

Session: Recent Advances in Modeling Near-source Ground Motions for Seismic Hazard Applications - I

Type: Oral

Date: 4/16/2025

Presentation Time: 08:15 AM (local time)

Presenting Author: Camilo Ignacio

Student Presenter: No

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