Aftershocks of the Truckee, California, earthquake of September 12, 1966

Abstract On September 12, 1966, at 16h 41m, an earthquake of magnitude 6.0 to 6.5 occurred about 10 km northeast of Truckee, California. Hypocenters of 158 after-shocks that occurred between September 14 and 25 were found to be within a volume 3 km wide by 10 km long by 12 km deep. The magnitude-frequency curve appears anomalous, as there seem to be too many shocks greater than magnitude 2 compared to the number of small ones under magnitude 0.5. Nodal-plane determinations indicate two modes of faulting for the aftershocks. Strike-slip faulting with nodal planes striking N. 40°W. and N. 50°E. is dominant; secondary normal faulting occurs on nodal planes striking nearly north. An attempt is made to relate the strain release pattern of these aftershocks to major regional right-lateral shear and extension.