" L" Street landslide, Anchorage, Alaska

A subsidence trough (or graben) formed at the head of the L Street landslide in Anchorage during the earthquake. The slide block, which is virtually unbroken ground to the left of the graben, moved to the left. The subsidence trough sank 7 to 10 feet in response to 11 feet of horizontal movement of the slide block. The volume of the trough is theoretically equal to the volume of the void created at the head of the slide by movement of the slide block. A number of houses were undercut or tilted by subsidence of the graben. Note also the collapsed Four Seasons Apartment Building and the undamaged three-story reinforced concrete frame building behind it, which are on the stable block beyond the graben.
Published in U.S. Geological Survey Circular 491, Figure 18-A, p.31.