The interactions between tectonic movement, erosion and sedimentation
can modify linear geomorphic features. Offset channels associated with strike-slip faults are good examples of linear geomorphic markers that can be used to determine the rate and nature of tectonic movement. While tectonic landforms can be found in many parts of the world, the south-central San Andreas Fault (SAF) in California has arguably some of the world’s best-preserved tectonic landforms at 10s and 1000s of meter scale [5
]. The most famous offset feature is the offset channel at Wallace Creek across the San Andreas Fault zone in the Carrizo Plain, California [8
The acquisition of LiDAR data by the B4 project [9
] provides new research opportunities for better understanding of the tectonic geomorphology and neotectonic deformation history of the SAF. Arrowsmith and Zielke [10
] evaluated the use of LiDAR data for mapping recently active breaks in the Cholame segment of the south-central SAF, and concluded that a LiDAR-only approach compares well with a combination of aerial photographic and field-based methods. Zielke et al. [11
] determined that the average slip along the Carrizo segment of the south-central SAF during the 1857 Mw 7.9 earthquake was 5.3 ± 1.4 meters. Zielke et al. [12
] employed LiDAR data to reevaluate the distribution of surface displacement along the rupture trace of the 1857 Mw 7.9 earthquake using 450 offset measurements with displacements below 60 m. Their results show that the 1857 earthquake
had an average displacement of less than 3.5 m with 4-6 m released along the northwestern half of the rupture. To measure lateral displacements of offset linear geomorphic features such as stream channels and alluvial fan edges, Zielke and Arrowsmith [13
] developed a Matlab-based tool to visually reconstruct and assess lateral displacements through slicing a digital elevation models (DEM) and back slipping. The LiDAR data for the south-central SAF and relevant case studies have facilitated the application of LiDAR for the quantification of linear geomorphic markers and active faults in general.
In the Lake Tahoe Basin, California, tectonic offsets of linear glacial moraines have been used to calculate slip rates of active normal faults obscured by dense vegetation. Howle et al. [14
] used bare-earth point cloud data to mathematically reconstruct linear lateral moraine crests on both sides of faults. The reconstructed moraine crests produced statistically significant ‘piercing lines’ that were projected to intersection with modeled fault planes to define ‘piercing points’ in 3D space. The measured tectonic displacements were coupled with 10
Be and 26
Al terrestrial cosmogenic nuclide (TCN) surface exposure ages and optically stimulated luminescence (OSL) ages of the displaced moraines to estimate late Pleistocene slip rates. The results of the study yielded a two to three fold increase over previous estimates of tectonic slip rates in the Lake Tahoe region.
LiDAR data have also been used for discovering new active faults and delineating earthquake surface ruptures in vegetated areas. While LiDAR data have been collected over known active fault zones for fine-scale study of tectonic-geomorphic features (e.g. [9
]), new active faults have been discovered using LiDAR data collected from areas that have been overlooked by scientists. For example, Hunter et al. [17
] discovered a previously unmapped fault using LiDAR data near the Martis Creek Dam, Truckee, California. Székely et al. [18
] used LiDAR data in an extremely flat area, east of Neusiedlersee in Hungary, and discovered linear geomorphic features, which are several hundred meters to several kilometers long. Field investigation and analysis of other geological and geophysical
data indicate that the linear features have a neotectonic origin, representing the surface expression of a seismically active fault. In areas with dense vegetation cover in the U.S. Pacific Northwest and Europe, 2-m resolution DEMs derived from LiDAR data have been successfully used for delineating earthquake surface ruptures [19
]. Using 2-m and 3-m resolution DEMs derived from LiDAR data along portions of the Alpine and Hope faults in New Zealand, Langridge et al. [22
] found that the surface strike variations of the Alpine Fault are more variant than previously mapped, and that unprecedented views of the surface geomorphology of these active faults can be revealed by LiDAR data. However, some other LiDAR studies on the northern San Andreas Fault and central Japanese mountains indicated that 2-m resolution DEMs could not identify some small tectonic breaks [23
]. Using airborne LiDAR data collected from orthogonal flight lines, Lin et al. [25
] created 0.5-m resolution DEMs along the Neodani Fault in Japan, and revealed a number of previously unknown fault scarps and active fault traces hidden under dense vegetation. Although the cost of data collection will increase with overlapping flight lines, the greater bare-earth data density, collected from different angles, will likely enhance the imaging of subtle geomorphic markers in densely forested areas.