HR: 16:15h
AN: T14B-02    [Abstracts]
TI: LIDAR Measurements of Fault Roughness
AU: * Sagy, A
EM: asagy@moho.ess.ucla.edu
AF: University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095
AU: Axen, G J
EM: gaxen@ees.nmt.edu
AF: New Mexico Tech, 801 Leroy Place, Socorro, NM 87801
AU: Brodsky, E E
EM: brodsky@ess.ucla.edu
AF: University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095
AB: Fault zones contain several discrete slip surfaces that accommodate most of the displacement across the zone. The geometrical properties of a given slip surface and the geometrical relation between surfaces can control the friction and deformation properties. We present the first measurements of fault surfaces using ground-based LiDAR (Light Detection and Ranging). The Laser-based system can measure precise distances over an area hundreds of squares meters large with individual points spaced as close as 3mm apart. We can then extract thousands of fault-surface profiles in any direction along the scanned surface. Our measurements of 8 large-scale, natural fault exposures in the Western US suggest the following preliminary results: (1) Not surprisingly, at any measurable wavelength, individual coherent striated slip surfaces are smooth relative to nearby erosional surfaces. For wavelengths of 1 m (which is the scale of slip on large earthquakes), we find that the average asperity height of slip surfaces is 1.8 cm, while that of erosional surfaces is 10 cm. (2) Like previous studies, we find that the wavelength λ is related to the asperity height h by h=Cλ#^ζ over a range of wavelengths of 2 cm to a few meters. However, our more precise measurements show that the constants are different than in previous estimates. We find that C ranges between 0.01-0.0025, and ζ ranges between 0.4-0.7. Surfaces with low values of C also have low values of ζ. (3) An extrapolation of the self-affine relationship with the measured parameters implies that the heights and lengths of asperities have similar dimensions at scales of microns up to tens of microns. The geometry implies that below these scales sliding breaks asperities, while at larger scales the surfaces are riding up on each other during sliding. This scale of 10s of microns is consistent with previous laboratory measurements of Dc. (4) In some cases the fault ``surface'' is an ensemble of striated surfaces at non-uniform orientation and a single exposure may have non-stationary spectral properties with variations in both ζ and C (although not Dc) over the 1-10 meter scale. Other surfaces have consistent spectra for nearly 100 m.
DE: 3902 Creep and deformation
DE: 7209 Earthquake dynamics (1242)
DE: 8010 Fractures and faults
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005