Tecto-geomorphic analysis of paleoseismic trenching sites on active strike-slip faults

Ideal trenching sites, which directly determine the quality of the paleoseismic research, are very rare. In this paper, based on 82 research papers of paleoseismic investigations published both in Chinese and English, the authors analyzed the common geomorphological characteristics of trenching sites that recorded long series of paleoearthquakes and coseismic slips. The sites with long paeloearthquake records are usually located at the sag pond, pull-apart basin, small closed basin, or upstream of a shutter ridge, a gentle fan or the toe of a large-drainage fan, which have common depositional environment with few or no depositional hiatuses, high rates of sedimentation, and abundant carbon dating materials. We should not only analyze the modern depositional environment but also its paleoenvironment during the choice of trenching sites. On the other hand, trenching sites for the purpose of recovering coseismic slips are often located at places where frequent incision events are recorded, such as channels, which provide offset piercing markers. In these studies, trenches are opened in an array with orientations both parallel and perpendicular to fault strike. Due to the fact that good trenching sites are rare, decade-long persistent efforts are usually invested at these sites for detailed studies, to uncover as many as possible the events back in time.