Open AccessGPS‐derived coupling estimates for the Central America subduction zone and volcanic arc faults: El Salvador, Honduras and Nicaragua
Author(s) -
CorreaMora F.,
DeMets C.,
Alvarado D.,
Turner H. L.,
Mattioli G.,
Hernandez D.,
Pullinger C.,
Rodriguez M.,
Tenorio C.
Publication year - 2009
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2009.04371.x
Subject(s) - forearc , subduction , geology , seismology , volcanic arc , volcano , episodic tremor and slip , coupling (piping) , volcanic belt , global positioning system , geodesy , volcanic rock , tectonics , mechanical engineering , engineering , telecommunications , computer science
SUMMARY We invert GPS velocities from 32 sites in El Salvador, Honduras and Nicaragua to estimate the rate of long‐term forearc motion and distributions of interseismic coupling across the Middle America subduction zone offshore from these countries and faults in the Salvadoran and Nicaraguan volcanic arcs. A 3‐D finite element model is used to approximate the geometries of the subduction interface and strike‐slip faults in the volcanic arc and determine the elastic response to coupling across these faults. The GPS velocities are best fit by a model in which the forearc moves 14–16 mm yr −1 and has coupling of 85–100 per cent across faults in the volcanic arc, in agreement with the high level of historic and recent earthquake activity in the volcanic arc. Our velocity inversion indicates that coupling across the potentially seismogenic areas of the subduction interface is remarkably weak, averaging no more than 3 per cent of the plate convergence rate and with only two poorly resolved patches where coupling might be higher along the 550‐km‐long segment we modelled. Our geodetic evidence for weak subduction coupling disagrees with a seismically derived coupling estimate of 60 ± 10 per cent from a published analysis of earthquake damage back to 1690, but agrees with three other seismologic studies that infer weak subduction coupling from 20th century earthquakes. Most large historical earthquakes offshore from El Salvador and western Nicaragua may therefore have been intraslab normal faulting events similar to the M w 7.3 1982 and M w 7.7 2001 earthquakes offshore from El Salvador. Alternatively, the degree of coupling might vary with time. The evidence for weak coupling indirectly supports a recently published hypothesis that much of the Middle American forearc is escaping to the west or northwest away from the Cocos Ridge collision zone in Costa Rica. Such a hypothesis is particularly attractive for El Salvador, where there is little or no convergence obliquity to drive the observed trench‐parallel forearc motion.