Landslides from the February 4, 1976, Guatemala earthquake

A description of the largest landlises, a discussion of failure mechanisms, a mapping of landslides throughout most of the landslide affected area, and a mapping of landslide concentration in the Guatemala city area

Liquefaction - caused ground failure during the February 4, 1976, Guatemala earthquake

Seismically induced liquefaction (the transformation of granular materials to a liquefied state due to increased pore - water pressure) caused ground failures in the February 4, 1976, Guatemala earthquake. Failures occurred predominantly in areas of recent deposition such as deltas and stream channels, and around some small ponds and wet areas in the highlands. Water - laid saturated pumiceous sand deposits were highly susceptible to liquefaction. Lateral - spreading landslides with more than 9.6 m horizontal displacement and a meter of subsidence occurred on slopes as gentle as 3.2 percent on the youngest part of the delta in Lake Amatitlan (14 km south of Guatemala City) due to liquefaction of a shallow (1 m deep) layer of pumice sand and gravel. Associated ground cracks and sand boils formed as much as several hundred meters from the lake shore and were generally oriented parallel to the lake shore or to river banks. Lateral spreading across these cracks destroyed some well - built reinforced brick houses that appeared to have suffered no direct shaking damage. At the Rio panajachel delta on lake Atitlan, 65 km west of Guatemala City, cracking and associated subsidence due to lateral spreading caused moderate damage along the lake shore. In the swampy lower Motagua River Valley, bank collapses were common and ground cracks and sand boils were noted as far as 100 meters from river banks. Liquefaction effects were also reported from Lake Izabal, Guatemala; from Puerto Cortés, Omoa, and the San Pedro Sula area in Honduras; and from Lake Ilopango, El Salvador. The ground failures at Omoa affected houses built on sand dunes. There were ground cracks and damage to shoreline structures at a delta in Lake Ilopango about 240 km from the fault rupture (AU)