Late Holocene Uplift of the Chihshang segment of the Longitudinal Valley Fault at Fuli, Eastern Taiwan

Brian Thomas Gray
August 2007

Abstract

Uplifted Holocene strath terraces of the Bieh River drainage, eastern Taiwan, were analyzed in order to determine millennial-scale uplift and horizontal shortening rates of the Longitudinal Valley fault. Detrital charcoal fragments collected from three terraces within the Bieh River drainage yield ages between 1395 and 555 cal. yr B.P, suggesting an average uplift rate of 11.3±3.6 mm/yr for the last 1400 cal. yr B.P. The average horizontal shortening rate of 19.7±9.5 mm/yr was within error of present-day conventional geodetic measurements, but near the lower limit of the geodetic measurements. This suggests that present-day horizontal shortening may not reflect the millennial- scale nature of horizontal shortening across the Chihshang segment of the Longitudinal Valley fault. Based on the longitudinal profile and several distinct regional geomorphic features, the Bieh River may be experiencing differential deformation outside of the main Longitudinal Valley fault zone, possibly on the Yungfong fault, or unrecognized structures within the Lich Mélange.

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