TO SEISMICITY AND SEISMIC HAZARD IN
CAUSES OF THE SEISMICITY: THE TECTONIC ENVIRONMENT.
The tectonic plate boundaries consist of the Polochic-Motagua-Jocotan system, a right lateral strike slip fault system on the northern part of the country, and which represents the boundary between the North American and the Caribbean plates; and the subduction zone, south offshore in the Pacific Ocean, where the Cocos plate subducts under the Caribbean plate (Mann et al in prep., Anderson et al 1983).
The surface trace of the Plochic-Motagua_Jocotan fault system is better defined in the eastern part of the country and it becomes less clear towards the west (Burkart, 1978, Erdlac et al 1982, Dengo and Dengo, 1996 (in Spanish)), where the system vanishes under the Pleistocene volcanic cover, or diverts into different branches, however some of the major earthquakes that happened during the 19th century seem to be related to these faults. The relative rates of strain accumulation and therefore the potential of each of these individual faults to generate earthquakes are also poorly known (Lyon_Caen et al in prep.).
The subduction zone is part of the Central American
subduction plate boundary (Carr 1976) and
is divided in different segments. Historically it has been the most active
source of seismicity for
The local faults in the volcanic highlands, although only
representing a second order feature in tectonic terms, may represent a similar
hazard than the Polochi-Motagua-Jocotan system or the subduction zone, given
its shallow nature and its proximity to populated areas (Molina et al 1996 (in Spanish)).
Feldman (1993) compiled an extensive list of major (destructive) earthquakes encompassing the 15th through the 19th centuries. White et al (2004) analyzed the earthquakes related to subduction, over the past 5 centuries. Less research has been done on the earthquakes generated from the Polochic-Motagu-Jocotan system and the local faults, although Monzon (1996a, 1996b (in Spanish)) gives a summary of these events.
There have been around 70 important earthquakes during the
XX century in
Historic seismicity has been attributed to all the above
described sources and processes. Although the bigger events where form both
subduction (e. g. 1902 and 1942) and transform fault (e. g. 1856, 1976)
sourced, the smaller events form local fault systems have also been important
because of the damage they’ve caused.
Some relatively small earthquakes, produced in local fault systems have
produce very high intensities, like the 1917 and 1918 earthquakes, which where
estimated to have a magnitude of 5.8 and produced intensities on the MMI scale
of VIII. This earthquakes caused extensive damage in
Some specific events have been studied in more detail, due
to the availability of information and the impact they had. Peraldo and Montero
(1996a and 1996b) studied the 1717 earthquake, based
on historical documents. The 1976 earthquake has been studied in considerably
detail, being the largest disaster related to natural hazards in
Monitoring of the seismic activity over long enough periods of time is crucial to characterize the seismogenic sources, to be able to estimate the potential that these sources have to generate earthquakes of different magnitudes. Besides the earthquake catalogs based on eye witnessed reports, covering back to 500 years, instrumental records catalogs usually go back to the 70’s.
Nowadays, different institutions and seismic networks
routinely collect data on the seismicity in and near
Other regional networks that post earthquake information online
in near real time include the Mexican Servicio
Sismológico Nacional, the Salvadoran Servicio Nacional de Estudios
Territoriales (SNET (in Spanish)),
and the Nicaraguan Instituto Nacional de Estudios Territoriales (INETER (in Spanish)).
World wide networks include the USGS Earthquake
hazard program and the GEOFON
Extended virtual network, from the GFZ Centrum in