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Title: Effects of the Truckee, California Earthquake of September 12, 1966 (PH 15-16b)(1967) Collection Type: Directories and Documents Collection Name: Pamphlets Catalog #: PH 15-16b Author: Reuben Kachadoorian, R. F. Yerkes, & A. O. Waananen Published: 1967 Subjects: Truckee Earthquake, Earthquake, Truckee # of Pages: 25 Download PDF: User Login Required Download OCR Text: User Login Required

Metadata By: Shelby Figueroa Printed or handwritten: All printed text Date Scanned: 2024-12-04 15:45:47 Scanned By: Shelby Figueroa Scanning Equipment: CZUR Book Scanner OCR Software Version #: tesseract 5.4.1 Item Sourced From: JPGs First Created: 2025-03-17 05:46:38 Last Updated: 2025-03-17 05:46:38

Original Held At: Searls Historical Library Location: 161 Nevada City Hwy, Nevada City, CA 95959

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Minor but extensive ground breakage occurred in a zone about 10 miles long that trends about N. 30° E.; the zone ranges in width from about 75 ft near Prosser Reservoir and Hoke Valley to about 1 mile in Russel Valley. Ground breakage was confined to low elongated areas of unconsolidated natural fill, commonly subparallel to the zone. The breakage is expressed locally as eracks, slightly sinuous small ridges, wedges, and mounds of freshly disturbed soil and turf; the linear features are commonly oriented subparallel to the zone and are as much as 20 ft long. Pebbles were locally overturned. All these effects are attributed entirely to shaking but are in no ease associated with lateral spreading of the ground toward an unconfined face. They may be, however, associated with the effects of topography on the passage of gravitational waves. (See Coulter and Migliaccio, 1966, p. 20.) Alinement of the zone of ground breakage with the trend of a fault exposed at the Stampede damsite (fig. 2) suggests an association with the fault; however, a thin veneer of undisturbed soil overlying the fault trace indicates that movement did not occur here during the earthquake. Dry natural slopes as low as 20° underlain by semiconsolidated alluvial and colluvial deposits showed minor slumping at two localities along the Little Truckee River north of Russel Valley. Headwall fissures opened as much as 1 inch and the ground surface dropped as much as 3 in. across these fissures; a buried telephone cable was damaged by one of the slumps. A small slide occurred just above water level on the west side of Prosser Reservoir (fig. 3). FIGURE 3.—Small slump in unconsolidated alluvial deposits on west bank of Prosser Reservoir; top of slump about 10 ft above water level; upstream face of Prosser Dam in lower left. EFFECTS OF TRUCKEE, CALIFORNTA, EARTHQUAKE OF SEPT, 12, 1966 Effects on structures DAMS Three dams were studied—two earthfill and one conerete. Both the Prosser and Boea earthfill dams were damaged, whereas the conerete structure, located at Tahoe City 20 miles south of the epicentral area, sustained slight damage. Prosser Dam is located about 3 miles southeast of Russel Valley and within a mile of the zone of ground breakage (fig. 2). The dam rests upon lake sediments and apparently received severe seismie shaking. Two axial cracks, one on the downstream side and one on the upstream side of the dam, developed along the northeastward-trending erest and extended over most of its length (figs. 4 and 5). A third less conspicuous crack was confined to the center of the crest. Drill holes by the Bureau of Reclamation indicate that the eracks do not extend into the impervious core of the dam (Brent Crater, oral commun., 1966). Maximum downslope displacement of the well-graded selected compacted fill of 2 in. vertically and 3 in. horizontally occurred in the vicinity of the spillway (fig. 6). Boca Dam, which also lies 3 miles southeast of Russel Valley, but about 3 miles from the zone of breakage (fig 2) and three-fourths of a mile south of the instrumental epicenter, was less severely damaged than Prosser Dam. Damage to Boca Dam was restricted to small cracks in the earthfill crest of the dam at its junction with the conerete spillway structure. The conerete dam on the Truckee River at Tahoe City controls the outflow from Lake Tahoe. This structure is reported to have cracked slightly during the earthquake, but the only cracks noted by the writers during a brief examination of the dam were along construction joints, particularly in the counterfort buttresses, and all appeared to be preearthquake. BRIDGES Most of the damage to highway bridges occurred on Interstate Highway 80 between Donner Lake and Floristan, but one bridge along Highway 89 north of Truckee was damaged slightly. The ensuing discussion on bridge damage is based on information collected by Mr. H. C. Johnson, California Division of Highways, and by R. Kachadoorian and R. F. Yerkes.