The Guatemala earthquake of 1816 on the Chixoy-Polochic fault

Abstract

Abstract Forty historical documents have been found which describe a previously unknown very large earthquake on 22 July 1816. This event occurred along the strike-slip boundary between the Caribbean and North American plates in Guatemala and southern Mexico. Modified Mercalli intensities are estimated from these accounts, and a rough isoseismal map is constructed. The damage pattern indicates that the causative fault was the left-lateral Chixoy-Polochic fault for which no damaging earthquake has previously been reported. Damage of Modified Mercalli intensity VII or greater covered an area of at least 13,000 km 2 , extending over 340 km from Alta Verapaz province in Guatemala westward to San Cristobal Ias Casas, in Chiapas, Mexico. The area of intensity VII indicates a moment of 1 × 10 28 dyne-cm, while the estimated length of the intensity VII isoseismal indicates a more likely figure of 3.5 × 10 27 dyne-cm, or an equivalent magnitude ( M w ) of 7 1 2 to 7 3 4 . The reported aftershock sequence is compatible with an earthquake in this magnitude range. These data demonstrate that the Chixoy-Polochic fault is currently an active part of the Caribbean-North American plate boundary and is capable of producing very large earthquakes.