--> Abstract: Landslides and Groundwater Related to the 1992-1993 Winter Storms Along the Liberty Canyon Fault Zone in the Central Santa Monica Mountains, City of Agoura Hills, California, by F. E. Denison; #90981 (1994).
[First Hit]

Datapages, Inc.Print this page

Abstract: Landslides and Groundwater Related to the 1992-1993 Winter Storms Along the Liberty Canyon Previous HitFaultNext Hit Zone in the Central Santa Monica Mountains, City of Agoura Hills, California

Frank E. Denison

The Liberty Canyon Previous HitfaultNext Hit is a northwest-trending Previous HitfaultNext Hit about 15 km long. The Previous HitfaultNext Hit is bifurcated to the south or even two separate parallel faults. The north end of the Previous HitfaultNext Hit appears to be braided. The Previous HitfaultNext Hit is concealed by alluvium over most of its trace. New data from landslide investigation suggests that the Previous HitfaultNext Hit turns westward at the north end of Liberty Canyon at the intersection of the Ventura Freeway. The Previous HitfaultNext Hit either becomes a low-angle thrust Previous HitfaultNext Hit or several parallel normal faults to the west. In addition to the Previous HitfaultNext Hit zone, there are numerous folds in the Miocene marine sediments with axial traces that are parallel to and bend around the north end of the Previous HitfaultNext Hit.

The Liberty Canyon Previous HitfaultNext Hit zone and its related folds are only now being recognized as a significant groundwater barrier that localizes the development of pore-water pressures that activate landslides. The intense rains of 1993 triggered these conditions and reactivated landslides threatening numerous residences at the top and toe of the slides. In the study area, two recent landslides can be attributed to an accumulation of groundwater along faults, folds, and broken bedrock thus increasing the amount of water available for infiltration. Several residences were threatened and only one was lost in 1993 as a result of poor placement/construction of subdrainage and also to the lack of recognition and understanding of the significance of the folds and associated Previous HitfaultNext Hit zone. Additional slop failures also occurred along this Previous HitfaultNext Hit zone in 1969, 1978, and 1990 during periods of intense rainstorms.

The study area has been mapped by several researchers over the last 40 to 50 yr, however, there is no consensus as to the location of the Liberty Canyon Previous HitfaultNext Hit, since it has not been observed at the surface. Subsurface data suggest that several hundred vertical feet of offset are on the east side of the Previous HitfaultNext Hit.

The land use has changed from ranching to housing. Portions of the western Santa Monica Mountains along the Ventura Freeway corridor have now become an urbanized community within the cities of Agoura Hills and Calabasas. Initial construction of these residences began in the early 1960s and 1970s. The lack of a clear understanding of the geologic structure of this Previous HitfaultTop has allowed placement of some residences within an area with a previously unrecognized potential for storm damage during intense rainstorms.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994