IGPP Seminar Series

Resolving the "slip-rate discrepancy" between GPS and geomorphic rates along the central Altyn Tagh Fault

by Prof. Eric Cowgill
UC Davis

Abstract

GPS and paleoseismic studies have shown that the first-order faults of the Indo-Asian collision zone slip at "slow" rates of 5-10 mm/yr at decadal to centennial timescales, whereas studies of displaced landforms have yielded "fast" rates that are up to a factor of 3 higher (10-30 mm/yr) at millennial timescales. I'll report the first tightly bracketed millennial-scale slip rate for the central Altyn Tagh Fault, and in particular show that the maximum bound on the slip rate is 13.6 1.3 mm/y over the last 4 kyr (3830 to 4068 calBP), with a minimum bound of 9.3 0.9 mm/y over the last 6 kyr (5889 to 5658 calBP). These determinations are based on displaced late Holocene fluvial landforms that are well-dated using ^14 C analyses. Because the millennial scale rate bracket I've found is compatible with the decadal and centenial scale rates determined using GPS and paleoseismic data, there appears to be no evidence of long-term variation in slip rate at Holocene time scales along the Altyn Tagh Fault. This study also shows that previous determinations of the millennial scale rate along this fault and other major faults within the Indo-Asian collision are upper bounds on the true rates and do not fully report the true range of possible slip rates permitted by the age and offset measurements. Alternative reconstructions based on the same age and offset data yield slower rates that are compatible with those derived from GPS data.
Tuesday, 06 March 2007
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM