Erosion's Impact On Fault Segmentation In Thrust Belts

Along the southern Longmen Shan thrust belt in eastern Tibet,the Dayi subsegment stood out as it remained unruptured in both the 2008 Wenchuan and the 2013 Lushan earthquakes.Whether localized weak materials or differential erosion caused this fault segmentation is unclear.According to the critical-taper wedge theory,above two different mechanisms would lead to distinct morphotectonic features and erosional distribution across and along the thrust belt.To examine these different mechanisms,we obtained 10 apatite fission track dates(?3-44 Ma)and deduced an average erosion rate of 0.5-0.6 mm/yr and 0.3-0.4 mm/yr since ?6-8 Ma in the hangingwall and footwall of the Shuangshi-Dachuan fault,respectively,in the Dayi subsegment.We further calculated the fluvial shear stress and erosion rate at 708 sites.The two methods yield consistent mean erosion rates,implying an exhumational steady state since at least 5 Ma.A heterogeneous,systematic pattern of erosion is found on a 3-by-3 grid along and across the Dayi subsegment.In the hinterland,the erosion rate in the Dayi subsegment is lower than that of adjacent areas along strike,whereas at the range front,the erosion rate in the Dayi subsegment is greater.The spatial patterns of erosion and topography suggest that differential erosion plays a major,but not exclusive,role in regulating the fault segmentation and earthquakes in the study area.In addition,the Dayi subsegment acted as a barrier during the recent great earthquakes,posing substantial seismic potential to this region.