Inventory of landslides triggered by the 1994 Northridge, California earthquake

The 17 January 1994 Northridge, California, earthquake (M=6.7)
triggered more than 11,000 landslides over an area of about 10,000
km². Most of the landslides were concentrated in a 1,000-km² area
that includes the Santa Susana Mountains and the mountains north of
the Santa Clara River valley. We mapped landslides triggered by the
earthquake in the field and from 1:60,000-scale aerial photography
provided by the U.S. Air Force and taken the morning of the
earthquake; these were subsequently digitized and plotted in a
GIS-based format, as shown on the accompanying maps (which also are
accessible via Internet). Most of the triggered landslides were
shallow (1-5 m), highly disrupted falls and slides in weakly
cemented Tertiary to Pleistocene clastic sediment. Average volumes
of these types of landslides were less than 1,000 m³, but many had
volumes exceeding 100,000 m³. Many of the larger disrupted slides
traveled more than 50 m, and a few moved as far as 200 m from the
bases of steep parent slopes. Deeper ( >5 m) rotational slumps and
block slides numbered in the hundreds, a few of which exceeded
100,000 m³ in volume. The largest triggered landslide was a block
slide having a volume of 8X10E06 m³. Triggered landslides damaged or
destroyed dozens of homes, blocked roads, and damaged oil-field
infrastructure. Analysis of landslide distribution with respect to
variations in (1) landslide susceptibility and (2) strong shaking
recorded by hundreds of instruments will form the basis of a seismic
landslide hazard analysis of the Los Angeles area.