Abstract
AbstractThe 1992 7.3 Landers earthquake in the Mojave Desert (California) provided exceptional observations of surface faulting in a large, continental earthquake. The U. S. Geological Survey obtained nadir angle, overlapping aerial photographs at 1:6,000 scale for the entire 85 km rupture length. Recent advances in Structure from Motion photogrammetry allow for archival photographic data sets such as these to be reprocessed, generating digital topography that can be reanalyzed quantitatively in a way that was not previously possible. In this proof‐of‐concept study, we generated a georectified, 10 points/m topographic point cloud over nearly the entire Landers rupture length and a higher‐resolution 40 points/m point cloud over a smaller ( 5 km) rupture segment along the Emerson fault. We estimated the accuracy and explore the utility of our point cloud in two tests. First, we observe close geometric agreement (average closest point distance 2.1 cm and standard deviation 14.0 cm) between our point cloud and a 2008 terrestrial lidar survey of the Galway Lake Road site on the Emerson fault. Second, we made 173 vertical offset measurements within a small, structurally complex pull‐apart basin, also on the Emerson fault, and find visual and statistical similarity with 21 local field measurements. These two tests demonstrate that point clouds generated from legacy aerial surveys and georeferenced using free Google Earth and National Elevation Dataset imagery are geometrically accurate and can be used to densify geomorphic offset measurements even along well‐studied surface ruptures. Applied to other historical events, such measurements could provide new insights into earthquake rupture processes.
Highlights
The 28 June 1992 Mw 7.3 Landers earthquake generated an ∼85-km-long surface rupture distributed across five major and numerous minor predominantly dextral faults within the Mojave desert of California (Figure 1)
Following ICP closest point alignment, we compare the two surveys using a map of cloud-to-mesh distance from the registered Structure from motion (SfM) point cloud to the meshed terrestrial lidar scanning (TLS) survey (Figure 3b)
The average cloud-to-mesh distance is 2.1 cm with a standard deviation of ∼14.0 cm. These centimeter level values demonstrate that the multimeter translations needed to align the clouds with ICP mostly represent differences in geographic projections for ground control between the two surveys, as opposed to internal geometric inaccuracies in the SfM point cloud
Summary
The 28 June 1992 Mw 7.3 Landers earthquake generated an ∼85-km-long surface rupture distributed across five major and numerous minor predominantly dextral faults within the Mojave desert of California (Figure 1) It has since become one of the most important earthquakes for the advancement of earthquake seismology, geodesy and geology. The intricate and well-exposed surface ruptures were surveyed aerially by the United States Geological Survey (USGS) 2 days after the earthquake, principally to assist with field-based mapping
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