Observations of Wave Propagation Effects through the UCLA Factor Building

1. Center for Embedded Networked Sensing Observations of Wave Propagation Effects through the UCLA Factor Building Monica Kohler, Paul Davis, Igor Stubailo Seismology Group – www.cens.ucla.edu/Project-Descriptions/Seismology/index.html and factor.gps.caltech.edu Introduction:System identification through wave propagation properties On using Impulse Response Functions Sources of Excitations • Motion of building depends on properties of structure and coupling with ground. • Need to separate building response from the excitation and the ground coupling by deconvolution to obtain the impulse response function. • The resulting imulse response functions account for the wave propagation effects between receivers. • Shear-wave velocity and attenuation can be computed from the deconvolved displacement waveforms. • Relate shear-wave velocities and attenuation to the changes in system properties (e.g., stiffness, mass). 20 small and intermediate, local and regional earthquakes (stars). UCLA and downtown Los Angeles (squares). Problem Description:Characterize the effects of a traveling seismic wave on a structure through the dense observations • The deconvolution of two time series signals, d1() and d2(w) in the frequency domain is given by D()=d1()/d2(), where d1()/ is the higher floor displacement, and d2(), is the subbasement displacement which is used as a proxy for the free-field.. • In order to keep the division stable, we use relatively short time series that contain an earthquake signal, and we add a low-amplitude frequency shift if the spectral amplitude equals zero. • We use displacement records that have been bandpass filtered for frequencies between 1 and 10 Hz, and decimated by 4 (100 sps down to 25 sps). • Shear-wave velocity is obtained by fitting a line through the distance-time measurements after obtaining the travel time by a Gaussian fit to the Green’s functions. Proposed Solution:Pre-event characterization in order to compare with post-event data Resulting deconvolution for 4 sample earthquakes Stack of 20 earthquakes Travel-time and velocity calculation UCLA – UCR – Caltech – USC – CSU – JPL – UC Merced