Paleoseismic ruptures and evolution of a small triangular pull-apart basin on the Zemuhe fault

Trenching is a primary technique on paleoseismology to reveal evidence of surface deformation produced by large earthquakes. A good trenching site requires completeness of geologic recording on paleoseismic events and corresponding reliable dating from radiocarbon samples. Based on three-dimension trenching, we show a structure of a small triangular pull-apart basin at the Daqingliangzi section on the Zemuhe fault, then explore interrelation between paleoseismic surface rupturing and evolution of the pull-apart basin, and give a corresponding identification model. Sedimentary boundary of the pull-apart basin is tightly bounded by two branch faults, which produced multiple paleoseismic events with deformation of some large fissures in sequence. Strata are thinner at north of the pull-apart basin, however thicker at south. These above characteristics show that evolution of the pull-apart basin is a continuous sedimentation process accompanying extensional deformation produced by multiple paleoseismic events. Small pull-apart basins are favorable sites for trenching and paleoseismic study on active strike-slip faults.