Co-seismic mole track structures produced by the 2001 Ms 8.1 Central Kunlun earthquake, China

Extensive co-seismic mole track structures have been observed along a 400-km-long surface rupture zone associated with the 2001 Ms 8.1 Central Kunlun earthquake, north Tibet. The mole track structures appear in an angular-ridge pattern, which resembles an angular triangle-shaped frame, and in a bulge pattern forming small flat hillocks. The mole tracks are developed within alluvial fans, river channels, and bajada, and form a linked array of structures along the rupture zone. The angular-ridge structures resulted from flexural slip folding and faulting of frozen alluvial deposits and surface ice, whereas bulge-type structures developed by squeezing-up of unconsolidated to weakly consolidated alluvial sediments. The mole tracks generally formed within the co-seismic rupture zone due to contraction in the right-bend and right-stepover areas between sinistral shear faults and are controlled by the pre-existing fault and fold structures along the left-lateral strike-slip Kunlun fault.