SCEC Award Number 12064 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Improving High-Frequency Site Response with Ambient Noise
Investigator(s)
Name Organization
Victor Tsai California Institute of Technology
Other Participants 1 graduate student (4.5 months)
1 undergraduate (summer research fellow)
SCEC Priorities 6c, 6a, 6d SCEC Groups Seismology, GMP, EarthScope
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 The long-term goal of this project is to achieve improved high-frequency (>0.5 Hz) site amplification maps by utilizing ambient noise observations. To accomplish this, we need improved understanding of how ambient noise fields affect amplitudes as well as improved methods for robustly measuring wavefield amplitudes. In this work, we accomplish both of these goals. Firstly, we perform a theoretical analysis of ambient noise amplitudes that highlights the sensitivity of the measurement to noise distributions. Secondly, we develop the array-based method of Helmholtz tomography to apply to measuring site amplification and attenuation. Preliminary testing of the method on earthquake data is favorable.
Intellectual Merit The research firstly tackles important conceptual problems related to how to make useful ambient noise amplitude observations. With the rising popularity of ambient noise observations, this understanding will be key to interpreting future results. Secondly, our development of a new array-based amplification mapping method is unique and will be useful for all researchers attempting to use array data in a combined robust manner.
Broader Impacts Throughout the project, the PI has brought his research to the public through talks for middle school students and displaying results to group tours of the Seismological Laboratory. Once the long-term goals are met, the research should help identify variability in earthquake hazards that cannot easily be distinguished with other methods. This information may be useful for cities in determining how to deal with earthquake risk.
Exemplary Figure Figure 3 (from Lin et al., 2012a): (a) Observed amplification across USArray for 60-s Rayleigh waves, using the improved Helmholtz tomography method. (b) Predicted amplification for 60-s Rayleigh waves based on one of our inverted velocity models. Figure is taken from Lin, FC, VC Tsai, and MH Ritzwoller (2012), JGR, 117, B06302.