Mechanisms of the Creep‐seismic Slip Transition along the Guanxian–Anxian Fault Zone, Longmen Shan: Evidence from the WFSD‐3 Core

Abstract The Guanxian–Anxian fault zone in the Longmen Shan, Sichuan, China, exhibits long‐term creep‐slip but ruptured during the 2008 Wenchuan earthquake, challenging the view that creeping faults rarely generate strong earthquakes. To investigate the transition from creep‐slip to stick‐slip, we analyzed fault rocks from the WFSD‐3, using microstructural observations, XRD, μXRF, Raman spectroscopy, and quartz grain size statistics. Fault rocks show intense foliation, pressure‐solution structures, and abundant clay minerals, reflecting long‐term aseismic creep. At the interface between black and gray fault gouges at ∼1249.98 m, microstructures indicate stick‐slip behavior, including truncated grains, angular fragments, and finer grain sizes. Here, clay content drops sharply while strong minerals (quartz, feldspar, calcite, dolomite) increase. Elemental mapping shows Al and K enriched in black gouge, whereas Ca and Si in gray gouge; Raman spectroscopy indicates possible graphitization; the finest quartz grains occur in black gouge. These features mark co‐seismic principal slip zone of the Wenchuan earthquake. We propose that fluid‐driven transformation of strong minerals into clays facilitates creep‐slip, whereas localized precipitation of strong minerals strengthens the fault, causing stress accumulation and controlling the creep‐slip to stick‐slip transition. This mechanism has implications for reassessing seismic hazards of creeping faults.