TECTONIC GEOMORPHOLOGY, STRUCTURAL GEOLOGY, AND PALEOSEISMOLOGY OF FAULT ZONES FROM HIGH RESOLUTION TOPOGRAPHY

Bridging the gap in measurements of lithospheric deformation between the seconds to decades of earthquake seismology and geodesy and the million year time scale of geology and structural seismology, tectonic landforms and earthquake geology contribute information about strain release over 10² to 10⁵ years. Airborne LiDAR topography efforts in western North America and elsewhere have illuminated thousands of kilometers of active fault traces at decimeter resolution with at least a few returns per square meter. Cm-scale terrestrial laser scanning observations may be embedded within the airborne coverage. Such measurements of the earth’s surface characterize meter scale tectonic landforms and are typically used in several different ways: 1) as base data for high accuracy fault trace delineation; 2) for direct measurement of offset along fault traces (in particular where the ability to strip laser returns from vegetative canopies permit us to work with “bare earth” digital elevation models); 3) to assess the geomorphic response to active deformation along faults and within fault-bounded blocks; and 4) repeat measurement (especially following large earthquakes) to directly measure surface displacements. Fault traces when mapped at high spatial accuracy and associated with high resolution topography and be used to reconstruct the discontinuous three dimensional geometry of the upper few hundred meters of the fault zone. Along strike-slip faults such as the south-central San Andreas Fault, these geometric models include elongate blocks (with aspect ratios of >5:1 parallel:perpendicular to the fault zone). Holocene offsets along the arcuate Teton normal fault zone are indicated by displaced moraines. Deformed fluvial terraces and piedmont landforms demonstrate the subsurface dip variation along thrust faults such as the San Cayetano and the Little Salmon in southern and Northern California respectively.