abstract

The earthquakes of December 16, 1954, were accompanied by offsets along many faults in four main zones of a north-trending belt 60 miles long by 20 miles wide. Minor geologic effects included changed flow of springs and wells, formation of water fountains and craters, landslips, landslides, mudflows, and rockfalls, and secondary fracturing of unconsolidated sediments.

The fault displacements were mainly along normal faults of the Basin-Range type in the following zones: (1) west of Dixie Valley, (2) southeast of Dixie Valley, (3) east of Fairview Peak, and (4) east of Stingaree Valley. The maximum strike-slip component was 12 feet (right-lateral) at Fairview Peak, and the maximum vertical-slip component was about 12 feet at Bell Flat.

Most of the faults are at or near the alluvium-bedrock contact. A tectonic origin is proposed for these faults, however, since most of the faults have segments which cross bedrock or follow prehistoric scarps in alluvium. Dip-slip displacements were prevalent in the northern part of the area, and diagonal-slip or even strike-slip displacements characterized the southern part.

The four main types of fault structure are herein defined as simple, subsidence, gravity-graben, and longitudinal step-fault types. The origin and nature of each type is discussed. Measurement of dip-slip components of displacement is complicated by the nature of these structures and earthfalls. In general, the scarp height is greater than the dip-slip component or throw.

Comparison of geodetic data with field geologic data shows that the field geologist can, with care, measure fault displacements accurately, even across complex fault structures.

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