APPLICATIONS OF LIDAR DATA AND GIS DERIVATIVES FOR FAULT ANALYSIS AND EVALUATION: EXAMPLES FROM THREE STUDIES IN CALIFORNIA

High-resolution elevation data collected with LiDAR techniques play a crucial role in the geomorphic analysis of three active seismic sources: the Kern Canyon Fault (KCF) in the southern Sierra Nevada, the Santa Cruz Mountains section of the San Andreas Fault (SAF), and the Contra Costa Shear Zone (CCSZ) in the eastern San Francisco Bay area. The employment of LiDAR data is particularly suitable in these projects because the faults are located in rugged, vegetation-covered terrain, thus allowing development of preliminary office-based detailed analyses to be followed by ground truthing.

Specifically, along the KCF, LiDAR-derived digital elevation models (DEMs) and their manipulation in the GIS environment have been the basis for identifying investigation sites, presence of secondary faults and structural stepovers, width of the fault zone, and initial estimates of fault displacement. Mapping of faulted and unfaulted alluvial terraces using GIS analyses of the LiDAR data provides additional details on fault behavior.

Analysis of shaded relief representations derived from DEMs, through the variation of illumination angle and shadows, allows developing both generalized and detailed mapping of fault lineaments and joints otherwise not apparent by means of more traditional air-photo and topographic map analysis.

In addition, the LiDAR-derived DEMs are used for developing fault-normal scarp profiles along the 140-km long fault, with accuracy and efficiency well beyond that possible by field-based surveys and mapping. The profiles illuminate the pattern of west-down Quaternary ruptures and the geomorphic expression in various bedrock types.

In the SAF study, hillshade and slope maps based on LiDAR data are fundamental for revealing micro-topographic features such as linear scarps not otherwise identifiable by analyzing map-derived DEMs and for helping to identify sites suited for field investigation focusing on timing past earthquakes and evaluating slip rate.

LiDAR-based data analyses of the CCSZ demonstrate the complexity of deformation between the northern Calaveras Fault and the southern extension of the West Napa Fault. Using various hillshade illuminations allows documentation of fault-related lineaments previously only identified via air-photo analysis and field reconnaissance.