Document Type

Post-Print

Publication Date

2008

Abstract

Approximately 25% of the differential motion between the Pacific and North American plates occurs in the Walker Lane, a zone of dextral motion within the western margin of the Basin and Range province. At the latitude of Lake Tahoe, the central Walker Lane has been considered a zone of transtension, with strain accommodated by dip-slip, strike-slip, and oblique-slip faults. Geologic data indicate that extension and strike-slip motion are partitioned across the central Walker Lane, with dip-slip motion resulting in E–W to ESE–WNW extension along the present-day western margin of the central Walker Lane since approximately 15 Ma, and dextral strike-slip motion across a zone further east since as early as 24 Ma. GPS velocity data suggest that present-day strain continues to be strongly partitioned and localized across the same regions established by geologic data. Velocity data across the central Walker Lane suggest a minimum of 2 mm/yr extensional strain focused along the western margin of the belt, with very little extension across either the central or eastern portions of the Walker Lane. These data indicate very little dextral motion across the central and western portions of the domain, with dextral motion of 3–5 mm/yr presently focused along a discrete zone of the eastern part of the central Walker Lane, coincident with existing, mapped strike-slip faults. Historic seismic data reveal little seismic activity in areas of Late Holocene dip-slip motion in the west or dextral motion in the east, suggesting a period of quiescence in the earthquake cycle and the likelihood of future activity in both areas. Based on this and previous studies, it is likely that a combination of pre-Cenozoic crustal structure, a relatively weak lithosphere beneath the Walker Lane, and long-term low stress ratios in the crust have permitted the long-term partitioning of dextral and extensional strain exhibited across the central Walker Lane. The present-day location of dextral strain in the central Walker Lane is subparallel with dextral deformation documented in the northern Walker Lane, suggesting that as strain continues to accumulate, these two discrete zones could become a continuous strike-slip system which will play a more important role in the future accommodation of relative Pacific–North American plate motion.

Publication Information

Tectonophysics

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