Investigation of Ground Motion Variability Due to Source Complexities

Date: 4/25/2019

Time: 10:30 AM

Room: Pine

We analyze the effect of source parameters in variability of ground motions, simulated in the near field region of large earthquakes. We quantify variabilities in simulated Peak Ground Velocity (PGV) and Spectral Accelerations (Sa) with respect to observed records and GMPE-based predictions. We compute independently, the variabilities due to complexities in source that include slip distribution, hypocenter location, rupture velocity and rise time.

In this study, we consider two past events – Mw 6.9 Iwate Miyagi Earthquake (2008), Japan and Mw 6.5 Imperial Valley Earthquake, California (1979). Assuming a 1D velocity structure, the rupture models are generated using the pseudo-dynamic approach of Guatteri et al. (2004) for different slip distributions (Mai and Beroza, 2002, Thingbaijam and Mai, 2016). We create a database of rupture models, 50 scenarios for each source parameter. Synthetic low-frequency waveforms (0.1-2Hz) are computed in the near field region (Rjb <150km) using the discrete-wavenumber finite element method of Olson et al. (1984). Our results show a large reduction in variability by fixing hypocenter locations on the fault plane. We also find that locations of asperities do not alter the waveforms significantly for a given hypocenter, rupture velocity and rise time distribution. We analyze the variabilities in these waveforms at few near field stations and conjecture that as the rupture propagates towards these sites, the on-fault rupture evolution and radiation-pattern effects are similar for all the rupture models. We also compare our results with SCEC-calibrated methods (e.g. GP2016).

Presenting Author: Jayalakshmi Sivasubramonian

Authors