Poster Presentation

Correct identification and modeling of ground motion sources are important for many studies including detection of small earthquakes and seismic imaging. To understand signals generated by common vehicle traffic, we use seismic data recorded at two sites on the San Jacinto fault zone by closely-spaced geophones normal to the roads. A simple analytical solution for propagation and attenuation of surface waves is developed to quantify the spatiotemporal and frequency variations of seismic waveforms. The model reproduces well bell-shaped spectrograms of car signals close to roads and it allows estimating frequency-dependent Q values of the subsurface. The data analysis indicates Q values of 3 to 40 up to 150 Hz for road-receiver paths at the two sites. The derived Q values are consistent with attenuation factors of surface waves obtained with other methods. The analytical results and analysis procedure provide highly efficient method for deriving Q values of shallow subsurface materials.