Landslides triggered by the 1994 Northridge, California, earthquake

TLDR

The 1994 Northridge earthquake (Mw 6.7) triggered more than 11,000 landslides across roughly 10,000 km², mainly concentrated in a 1,000 km² area that includes the Santa Susana Mountains and the mountains north of the Santa Clara River valley. The authors aim to use the mapped landslide distribution, together with landslide susceptibility and strong‑shaking data, to develop a seismic landslide hazard analysis for the Los Angeles area. Landslides were mapped in the field and from 1:60,000 aerial photographs taken the morning of the quake, then digitized and plotted in a GIS format. Most triggered landslides were shallow 1–5 m thick falls and slides in weakly cemented clastic sediment, with average volumes under 1,000 m³ but many exceeding 100,000 m³; larger slides ran over 50 m, some up to 200 m, while deeper rotational slumps and block slides were fewer but some exceeded 100,000 m³, and the largest single landslide had a volume of 8 × 10⁶ m³.

Abstract

Abstract The 17 January 1994 Northridge, California, earthquake (Mw = 6.7) triggered more than 11,000 landslides over an area of about 10,000 km2. Most of the landslides were concentrated in a 1000-km2 area that included 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-nominal-scale aerial photography provided by the U.S. Air Force and taken the morning of the earthquake; these mapped landslides were subsequently digitized and plotted in a GIS-based format. Most of the triggered landslides were shallow (1- to 5-m thick), highly disrupted falls and slides within weakly cemented Tertiary to Pleistocene clastic sediment. Average volumes of these types of landslides were less than 1000 m3, but many had volumes exceeding 100,000 m3. The larger disrupted slides commonly had runout paths of more than 50 m, and a few traveled as far as 200 m from the bases of steep parent slopes. Deeper (>5-m thick) rotational slumps and block slides numbered in the tens to perhaps hundreds, a few of which exceeded 100,000 m3 in volume. Most of these were reactivations of previously existing landslides. The largest single landslide triggered by the earthquake was a rotational slump/block slide having a volume of 8 × 106 m3. Analysis of the mapped 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.