abstract

The Managua, Nicaragua, earthquake of December 23, 1972 (body-wave magnitude of 5.6, surface-wave magnitude of 6.2), and its aftershocks strongly affected an area of about 27 km2 centered on Managua. Within this area, over 11,000 people were killed and 20,000 were injured. About 75 per cent of the city's housing units were destroyed or rendered uninhabitable leaving between 200,000 and 250,000 people homeless, and property damage exceeded half a billion dollars. As a consequence, the economy and government of the city, and to a large extent the entire country, were severely disrupted.

Surface geology shows that there are at least four subparallel strike-slip faults spaced 270 to 1,150 meters apart in the Managua area that slipped in a predominantly sinistral (left-lateral) sense during the earthquake. Aftershock studies show that at least one of these northeast-trending faults extends from the surface to a depth of 8 to 10 km over a maximum length of about 15 km. The faults are mappable on land for 1.6, 5.1, 5.9 and 2.7 km; aftershock data indicate that faulting extends at least 6 km northeast of the city beneath Lake Managua. Horizontal displacements vary, with the maximum aggregate sinistral slip ranging from 2.0 to 38.0 cm. There is also a local small down-to-the-southeast vertical component of slip on three of the four faults. The nature and distribution of the surface faulting are consistent with a tectonic origin for the earthquake.

The extensive destruction and loss of life in the Managua area were caused by a combination of the following factors: (1) occurrence of the earthquake on faults directly beneath the city, (2) poor behavior of structures, chiefly tarquezal (wood frame and adobe) and masonry, during strong seismic shaking, and (3) direct displacement of structures, streets, and utilities by faulting. The historic record of seismicity and geological evidence of active Holocene faulting and volcanism together show that Managua is an unusually high-risk area in terms of geological hazards and that these hazards should be a primary consideration in evaluating reconstruction of Managua.

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