Late holocene earthquakes on the aeropuerto fault, Managua, Nicaragua

Managua, capital of Nicaragua, is built on the shore of Lake Managua, within a densely faulted graben at a major discontinuity in the Central American volcanic chain. Shallow moderate earthquakes (M-s 6-6:2) ruptured faults with devastating effect at the heart of urban Managua in 1931 and 1972, and damaging earthquakes are cataloged in the earlier history of the surrounding region. The Aeropuerto fault is a major structure in the Managua Graben, but like other faults in this area its behavior is little understood. Paleoseismic investigations now suggest that the most recent large earthquake on this fault occurred sometime during the interval A.D. 1650-1810. An earlier earthquake on this fault occurred prior to A.D. 1390 and possibly around 2000 B.P. On the basis of stratigraphic correlations we estimate the ages of two shorelines associated with former high stands of Lake Managua to be less than 6.4 ka and approximately 2 ka, respectively. Deformation of these abandoned shorelines adjacent to the Aeropuerto fault implies a vertical slip rate of 0.3 to 0.9 mm/yr. Strike-slip movement on this fault is also expected, but no direct measurement could be performed. By comparison with faults of similar geometry in the Managua area that ruptured in 1931 and 1972, we suspect a left-lateral component of horizontal slip that is higher than the vertical one but less than 5 mm/yr. Additional data on slip rate and timing of paleoearthquakes are needed to better assess the Holocene behavior of the Managua faults and to investigate the influence of magmatic processes on the nature of faulting in the Managua Graben.