A detailed study of the aftershocks of the earthquake that devastated Managua, Nicaragua, on December 23, 1972, shows that the earthquake occurred on a fault that strikes N30° to 35°E and dips 80° to 90°E, and that this fault moved in a left-lateral sense over a zone about 15 km long extending from shallow depth to a depth of 8 or 10 km. The extensive damage accompanying an earthquake with body-wave magnitude of only 5.6 was caused primarily by the types and method of construction predominantly used in the area and because the location of this fault and the associated surface rupture and intense shaking were directly under the city. Faults of this type that strike perpendicular to volcanic axes of volcanic arcs appear to be common in many areas and need to be understood in order to determine earthquake hazards and local tectonic processes. Among the hypotheses available to explain the origin of the Tiscapa fault are that it is a transform fault, it is a product of north-south compression, or it is caused in some way by a change in dip in the slab moving under Central America from the Middle America trench.

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