Interplate strain, wide plate margin deformation, intraplate strain: The GPS analysis spectrum

Global Positioning System (GPS) data from southern Central America and northwestern South America collected during 1991, 1994, 1996, and 1998 reveal wide plate boundary deformation and escape tectonics occurring along an 1400 km length of the North Andes; locking of the subducting Nazca plate, strain accumulation in the Ecuador-Colombia forearc; ongoing collision of the Panama arc and Colombia; and convergence of the Caribbean plate with Panama and South America. Elastic modeling of observed horizontal displacements in the Ecuador forearc is consistent with partial locking (50%) in the subduction zone and partial transfer of motion to the overriding South American plate. The deformation is hypothesized to reflect elastic recoverable strain accumulation associated with the historic seismicity of the area and active faulting associated with permanent shortening of 6 mm/a. Deformation associated with the Panama-Colombia collision is consistent with elastic strain accumulation on a fully locked Atrato-Uraba Fault Zone suture.; On August 4, 1998, a magnitude M_w = 7.1 earthquake occurred near Bahia Caraquez, Ecuador. Prior to the earthquake, geodetic control had been established during a GPS survey carried out throughout central and northern Ecuador. GPS measurements are consistent with slip on an ∼40 x 30 km section of the subducting Nazca plate and a complete release of the strain that has accummulated on that section since the 1942 event. Repeat occupations of the 1998 and 1999 sites in 2001 suggest a volume undergoing near-field and far-field post-seismic relaxation/after-slip.; Recent reoccupation of a 20 station grid near the location of current seismicity (the inferred location of the 1886 Charleston earthquake) have refined and are consistent with the previous shear strain calculations and suggest an average shear strain rate over the area that is at least an order of magnitude higher than the average intraplate strain rate for the eastern North American Plate. Further, subnet strain analysis suggests that the higher strained areas within the study area coincide with the regions of current seismicity and span the area of inferred seismogenic structures and the orientation is consistent with S_Hmax.