Multiple Fold Earthquakes Recorded by the Paleoseismic Surface Ruptures of Bending-Moment Faults in the Qiulitage Anticline, South Tianshan, China

Abstract

Bending-moment faults (BMFs), as a fundamental type of secondary faulting, are intrinsically linked to the primary causative faults within active thrust-fold belts. When these faults thrust through the ground surface, the resulting geomorphic scarps offer the characteristics of local earthquake recurrence. This information helps to fill a gap left by main faults, which often lack coseismic surface ruptures. The Qiulitage anticline where the 1949 M 7¼ Kuqa earthquake occurred is an active thrust-and-fold belt predominantly governed by blind faults. In addition, several typical BMFs extensively crop out as surface scarps in the front of the mountain. Our research concentrates on the well-developed BMF scarps in this region and seeks to explore the recurrence characteristics of paleoearthquakes, which remain inadequately comprehended. Our study reveals that (1) secondary BMF with high enough magnitude can directly generate coseismic ground ruptures, and (2) the seismic behavior of BMFs exhibits a degree of repeatability, potentially linked to the concurrent movement of various BMFs or the solitary action of a single fault. However, the case study presented in this article also highlights the limitation of fold earthquake research because of the swift attenuation of coseismic fault slip as it approaches the ground surface.