A large-scale obliquely inclined bedding rockslide, activated by a heavy rainstorm, occurred on July 8, 2020, at 7:05 (UTC?+?8) in Shiban Village, Songtao Miao Autonomous County, Guizhou Province, China. The loss of life in this event was greatly reduced owing to the local warning system for rainstorm-induced geohazards. To understand the failure characteristics, triggering factors, the genetic mechanism of the landslide, the geomorphological features, geological characteristics, hydrological conditions, and rainfall characteristics were systematically studied by a synthetic approach including field investigations, satellite imagery, unmanned aerial vehicle (UAV) photography, laboratory tests, and rainfall data statistics. The results indicated that the interface between the soft and hard rock, the well-developed joints, and the free face in front of the slope constituted the boundaries of this landslide. The concave topography at the back and southern edge of the landslide, the bare ground, and the cataclastic structure of the rock mass provided favorable conditions for the collection or infiltration of rainwater. The concentrated rainstorm was the direct trigger for the landslide, which led to a rapid inflow and retention of rainfall in the landslide through favorable landform and geological conditions. The groundwater recharge that cannot be drained in time caused the mechanical deterioration of rock mass and induced a rapid increase in pore water pressure in the landslide. Moreover, the water level of the Ganlong River at the toe of the slope also rose rapidly, and the uplift pressure in front of the slope increased accordingly. Under the combined action of these adverse factors, the overall anti-sliding force of the slope was less than the sliding force, finally resulting in the landslide. Remarkably, the local warning system for rainstorm-induced geohazards successfully forecasted the landslide, but the shortcoming is that the forecast time in advance is short. Nevertheless, the prediction has significantly reduced human casualties and provided valuable experience for the prediction of this type of landslide.
The anisotropy of a periodically layered isotropic medium is numerically modeled in order to study the effect of the scale
of heterogeneity on seismic observations. An important motivation is to delineate the wavelength ranges over which a pulse
propagating obliquely through the structure will be described by either ray (short wavelength) or effective medium (long wavelength)
theory. The same band-limited pulse is propagated obliquely at a variety of incidence angles through a compositionally uniform
layered structure as a function of the layer thicknesses. The resulting seismograms display similar behavior to that encountered
for normal incidence including the effects of stop- and pass-bands. Velocities determined from time picks on these seismograms
show a large difference in velocities between the long and short wavelength limits as has been previously demonstrated for
normal incidence propagation. The bulk of the transition between these two limits is independent of incidence angle and occurs
when the ratio between the wavelength and the layering thickness is near a value of 10. Two more geologically reasonable models
show that these effects are diminished with smaller contrasts between the layers. 相似文献