SCEC Award Number 17234 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title ESTIMATING PATH AND SOURCE PARAMETERS IN THE SOUTHERN SIERRA NEVADA USING A NON-PARAMETRIC APPROACH AND SPECIAL SOURCE CONSTRAINTS
Investigator(s)
Name Organization
Jorge Crempien University of California, Santa Barbara Ralph Archuleta University of California, Santa Barbara
Other Participants
SCEC Priorities 4a, 4b, 2b SCEC Groups CCSP, GM, Seismology
Report Due Date 12/31/2018 Date Report Submitted 01/07/2019
Project Abstract
 The main objective of this work was to determine Q for direct S-waves, as well as κ in the Central California Sierra Nevada region. For this we calculated the smoothed Fourier spectra for each ground motion recording, and used a non-parametric to invert for both path and source parameters. From the inverted source spectra, we determined κ, which on average was ~ 35 ms. Qs is ~ 33f^0.78.
Intellectual Merit Attenuation is a critical parameter for high frequency ground motion. Because attenuation can strongly affect the spectrum derived from a seismogram, it can lead to a misinterpretation of the stress drop and stress parameter. Consequently, simulations based on the incorrect stress drop/parameter will incorrectly predict ground motion from future events. Attenuation is often divided into a site and a path effect. Separating these is also important because the site attenuation can be masked by site amplification. A major SCEC emphasis is the prediction of ground motions from simulations. The correct attenuation parameters are critical for realistic simulated ground motions. We have determined important seismic parameters which are useful to quantify seismic hazard in the Central California Sierra Nevada region with a new approach that takes into advantage relative observed source spectra. To our knowledge, there have been no prior attempts to calculate regional κ values in this region, which are important to simulate ground motion and to estimate response spectra for engineering purposes. Also, we have developed a new method to perform an inversion for both path and source properties by relying on double difference measurements of the earthquake source.
Broader Impacts During this project, we were able to determine important seismic parameters such as Q and regional κ values, which will be useful for the Central California Coastal region in terms of hazard determination.
An outcome of the project was a Python code to determine Q and κ values, that in the future will be used to teach students on how to determine these important parameters. We plan to make this code freely available at a computer code repository.
Exemplary Figure Figure (4): (a) Ground motion produced by a Mw 4.0 earthquake. The blue lines are the time window in which the continuous wavelet transform integrated along the time domain to produce a smoothed spectrum of the S-wave, (b) smoothed Spectrum of the S-wave, (c) the anelastic attenuation with distance at different frequency ranges. We also show a theoretical 1/R attenuation depicted as a purple line, and (d) source spectra for four earthquakes of the total earthquakes we analyzed, where the dashed red line in a theoretical omega-squared model in acceleration.