The field of crustal velocity in Asia calculated from Quaternary rates of slip on faults

Abstract

Rates of Quaternary faulting, when treated as measures of strain rates within regions several times larger than the depths of brittle faulting, yield a velocity field for Asia that matches the average relative velocity between the Indian and Eurasian plates over the past 2 Myr (NUVEL-1A), and the velocity of Shanghai with respect to Eurasia, measured with Very Long Baseline Interferometry (VLBI). By using rates of slip on discrete surfaces (faults) to define average strain rates, we explicitly assume that the large-scale deformation can be treated as that of a continuum. Depending on the jcales over which strain rates are averaged, 87 to 93 per cent of the assumed strain ites are fit within assigned 1-sigma uncertainties, and 97 to 99 per cent are fit within 2-sigma. The internal consistency of these data and the agreement with independent rates (NUVEL-1A and VLBI) test the validity of treating large-scale deformation of continents as that of a continuum. In the calculated velocity field, a large fraction, ∼ 85 per cent, of India's convergence with Eurasia is absorbed by crustal, or lithospheric, thickening. Among consistently misfit assumed strain rates are those dominated by high rates of strike-slip faulting. Strain associated with 20-30 mm a-1 of slip on the Altyn Tagh, Karakax, and Karakorum faults is inconsistent with the distributions of strain in surrounding regions. We conclude that these rates, all of which are based on correlations of ages of offset landforms with changes in global climate, and not on radiometric dating, have been systematically overestimated. Lateral transport out of India's northward path is relatively minor; South China is calculated to move east-southeast at less than 10 mm a-1.