LIDAR MEASUREMENT OF FAULT SURFACE TOPOGRAPHY
We present systematic measurements of several fault surfaces using ground-based LiDAR and a laboratory profilometer. Thousands of fault profiles ranging from 10 micron to >100 m in length show that small-slip faults (slip <1 m) are rougher than large-slip faults (slip 10 to 100 m or more) on profiles parallel to the slip direction. Surfaces of small-slip faults have asperities on all scales, while large-slip faults surfaces are polished, with RMS roughness (average deviation from a planar surface) values of <3mm up to 1-2 m profile length. Surprisingly, the large-slip surfaces show smooth, elongate, semi-elliptical bumps that are meters long and up to several centimeters high. We infer that these bumps evolve during fault maturation. This roughness characteristic implies that the nucleation, growth and termination of earthquakes on evolved faults are fundamentally different than on new ones.