Geology topics

Scott Lindvall

Publications and source records attributed to Scott Lindvall.

4 recordsLinked to original sources

USGS2020

Late Quaternary slip rates on the Sierra Madre fault zone and paleoseismic evidence on the size and frequency of past ruptures

The Sierra Madre fault zone is a south-vergent, active reverse fault that accommodates shortening between basins on the northern margin of the Los Angeles region and the San Gabriel Mountains. The preservation of late Quaternary alluvial fill and fan surfaces in the hanging wall of the fault provides evidence of long-term uplift. Surface rupture from the 1971 Mw 6.6 San Fernando earthquake and evidence of large prehistoric displacements from trenching investigations emphasize the ongoing hazard posed by the fault system to the region. This one-day field trip visits some of the key locations near Pasadena and San Fernando, California, where slip rates have been determined from cosmogenic and luminescence dating of abandoned surfaces dating to 50–70, ca. 30, and ca. 12 ka and surface offsets measured from lidar and pre-development topographic maps. Another stop is the site of a paleoseismic trench, which provided key evidence on the timing and displacement of past ruptures on the fault. In combination, results from these field investigations converge on a slip rate for the eastern ~100 km of the fault zone of 1–2 mm/yr, which matches or exceeds the rates for other reverse faults in southern California. This rate, in combination with trenching data that show no evidence of post–mid Holocene ruptures along the central and eastern portions of the fault, indicate the fault zone poses a significant seismic hazard to the region.

California↗

USGS2018

Characterizing the Los Angeles Aqueduct crossing of the San Andreas Fault for improved earthquake resilience

The five-mile-long Elizabeth Tunnel, which crosses the San Andreas fault (SAF) zone near Lake Hughes, California, is part of the Los Angeles Aqueduct (LAA) that delivers water from Owens Valley to the City of Los Angeles. Geologic characterization of the Elizabeth Tunnel alignment is focused on developing a better understanding of fault displacement hazards at the SAF crossing to support design of both short- and long-term strategies to increase the earthquake resilience of the City’s water supply system. The results of this study define a fault zone that is wider and more complex at the surface than at tunnel depth. A 750-ft transect of deep, angled core borings, located ~ 100 ft west of, and parallel to the tunnel alignment, penetrated a wide zone (>550 ft) of fault-damaged granitic and gneissic rocks containing a few thick fault zones that can be correlated confidently between borings as well as a multitude of very thin faults and shears throughout the rock mass. Fault rocks are predominantly defined as coherent cataclasites and ultracataclasites, as opposed to incoherent clay gouge, even at this relatively shallow sampling depth. Integrating geomorphic, geologic, petrographic, and geophysical data defines a steeply south-dipping SAF that splays upward and increases in complexity toward the surface, and provides the basis for engineering design considerations at this critical SAF crossing.

California↗

USGS2002

Lateral offsets on surveyed cultural features resulting from the 1999 İzmit and Düzce earthquakes, Turkey

Surveys of offset linear cultural features that cross the surface ruptures of the 17 August and 12 November 1999 earthquakes on the North Anatolian fault in Turkey yield slip values as large as or larger than those recorded by near-field measurements in the same areas immediately after the earthquake. Using long, linear alignments of trees, fence lines, walls, and canals, we demonstrate as much as a 2-m increase in observed slip over the initial field measurements. On an average, we observed about 15% of the total lateral slip as off-fault deformation, with values ranging from 0% to 40% of the total slip. Part of this lateral deformation is accommodated by bending or drag in a zone as much as 30 m in width, although usually the zone varies between 5 and 20 m in width. This supports the idea that substantial nonbrittle, off-fault deformation is associated with ruptures in areas of alluvial fill. Alternatively, there may have been substantial afterslip, although none has been recognized on postearthquake repaired structures. Our observations suggest that postearthquake measurements of fault slip, using tape measures on offset geomorphic features, may underestimate the actual amount of slip in that event, where the nonlinearity of the offset feature does not allow recognition of the warping. Surveys of multiple tree lines within groves of poplar trees, planted in straight lines across the fault prior to the earthquake, show surprisingly large lateral variations. In one grove, slip increases by nearly 1.8 m, or 35% of the maximum measured value, over a lateral distance of nearly 100 m. This and other observations along the 1999 ruptures suggest that the lateral variability of slip observed from displaced geomorphic features in many earthquakes of the past may represent a combination of (1) actual differences in slip at the surface and (2) the difficulty in recognizing distributed nonbrittle deformation.

Bulletin of the Seismological Society of America↗

USGS1993

Near-field investigations of the Landers earthquake sequence, April to July 1992

The Landers earthquake, which had a moment magnitude ( M w ) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its M w 6.1 preshock and M w 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.

California↗