abstract

Triangulation surveys carried out in the vicinity of the White Wolf Fault in 1932, 1952, 1953, and 1963 are used to delineate the strain changes preceding, accompanying, and following the 1952 earthquake. The strain rate (engineering shear) during the preseismic interval (1932 to 1952) was 0.36 ± 0.10 μstrain/yr and was nearly uniform across the 70-km-long triangulation arc, with the plane of maximum left-lateral shear oriented N44° ± 7°E, nearly parallel to the White Wolf Fault. The coseismic observations (1952 to 1953), supplemented by leveling data, are matched using a dislocation model with the following characteristics

Dip = 60°SE

Strike = N50°E

Length = 70 km

Left-Lateral Strike-Slip = 2.4 ± 0.1 meter (m)

Reverse Dip-Slip = 1.9 to 0.6 m (decreasing to the NE)

Seismic moment ≧ 0.9 × 1027 dyne-cm.

The data also require most of the slip to have occurred below ∼5 km (5 to 20 km in our model), on roughly the southwest half of the fault, with the slip occurring at shallow depths to the northeast. The postseismic triangulation data (1953 to 1963) indicate that the average shear strain rate in the 10 yr following the earthquake (0.80 ± 0.20 μstrain/yr) was about twice that during the 20 yr preceding it. The postseismic strain changes were concentrated closer to the fault than those determined for the preseismic time interval, and the 1953 to 1963 data are explained well by episodic postseismic slip of about 2 m (left-lateral strike-slip) occurring on the down-dip extension of the coseismic fault plane.

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