Transcript ASCENT - California Institute of Technology

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
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On using Impulse Response Functions
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).
Sources of Excitations
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 displac
• 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 spec
• 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 functio
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