Earthquake risk in Managua: a critical view

Abstract

A critical interpretation of the 1972 Managua earthquake is proposed. Tiscapa Fault, a 16 km strike-slip fault, controls the local earthquake hazard in Managua. Faulting in the basement occurred along a single vertical plane striking N 32° E through Lake Tiscapa; there is no proof of multiple foulting. The complex surface fracture patterns may be accounted for by strain release' in the sediments, partly as a result of Tiscapa Crater acting as a cylindrical obstacle astride the fault. There is no clear historical precedent for destructive earthquakes on the Tiscapa Fault, except for the 1931 earthquake (M = 5.8). The entire region is intensely fractured by faults having Holocene displacements, and it has yet to be shown that there are acceptable sites that are geologically safer than that of present-day Managua.
An upper-bound computation of seismic risk in Managua leads to an actualized estimate of 3.33 x 109 cordobas for damage over an indefinite time period. The investment required for earthquake-resistant construction will reach at most 30% of this amount. An immediate adoption of adequate measures of earthquake risk control, through urban planning and building regulations, represents a sound first-level strategy not only for Nicaragua but also for the en tire seismic region including the Pacific seaboard and the Median Trough of Central America.