The Jiufengershan area is characterized by an
asymmetric fold (Taanshan syncline), which plunges
gently toward the south. The stratigraphic formations
from bottom to top in the study area are defined as
follows: Tanliaoti Shale (TL), Shihmen Formation
(SM), Changhukeng Shale (CH) and Kueichulin Formation
(KC) (Fig. 1). The Changhukeng Shale is
composed mainly of shale and sandstone. The Jiufengershan
landslide destabilized the western limb of
the Taanshan syncline, affecting rocks belonging to
the Changhukeng formation (Huang et al., 2002;
Wang et al., 2003). The dip angle of the western
limb is about 15–258 in the study area. The sliding
surface was characterized by striations parallel to the
dip of the bedding, as well as shear folds generated
by the rock avalanche. Near the main shear zone, we
observed mud injections infilling preexisting fractures
and joints. These structures were created during
the sliding process and they are probably linked to
the fluidization of saturated clay levels subjected to
high pore-water pressure. A thin layer of pseudotachylyte
(glass or cryptocrystalline material associated
with cataclasites) was also observed along some
areas of the basal shear surface, in particular in the
upper zone of the sliding surface. We suggest that
this material was formed by frictional heating during
the sliding process. Note that the minimum estimated
temperature for pseudotachylyte formation is 1100–
1600 8C for dry rocks (Lin et al., 2001). These
observations suggest that the sliding process occurred
at high velocities.