Elastic Block Model in the North Andean Sliver

Journal of South American Earth Sciences, 2018

We present a velocity field for northwestern South America and the southwest Caribbean based on GPS Continuously Operating Reference Stations in Colombia, Panama, Ecuador and Venezuela. This paper presents the first comprehensive model of North Andean block (NAB) motion. We estimate that the NAB is moving to the northeast (060°) at a rate of 8.6 mm/yr relative to the South America plate. The NAB vector can be resolved into a margin-parallel (035°) component of 8.1 mm/yr rigid block motion and a margin-normal (125°) component of 4.3 mm/yr. This present-day margin-normal shortening rate across the Eastern Cordillera (EC) of Colombia is surprising in view of paleobotanical, fission-track, and seismic reflection data that suggest rapid uplift (7 km) and shortening (120 km) in the last 10 Ma. We propose a "broken indenter" model for the Panama-Choco arc, in which the Choco arc has been recently accreted to the NAB, resulting in a rapid decrease in shortening in the EC. The Panama arc is colliding eastward with the NAB at approximately 15-18 mm/yr, and the Panama-Choco collision may have been responsible for much of the uplift of the EC. The present ongoing collision poses a major earthquake hazard in northwestern Colombia from the Panama border to Medellin area. Since the northeastward margin-parallel motion of the NAB is now greater than the rate of shortening in the EC, northeast trending rightlateral strike-slip faulting is the primary seismic hazard for the 8 million inhabitants of Bogota, the capital city of Colombia. There continues to be a high risk of a great megathrust earthquakes in southern Colombia along the Ecuador-Colombia trench. Trench earthquakes have only released a fraction of the energy accumulated in the Ecuador-Colombia trench since the 1906 Ecuador earthquake, and interseismic strain is accumulating rapidly at least as far north as Tumaco, the rupture area of the 1979 earthquake.

Journal of Geophysical Research, 1993

Repeated geodetic measurements with the Global Positioning System (GPS) provide direct measurements of displacements due to plate motions and active crustal deformation in Central America and northern South America, an area of complex interaction of the Nazca, Cocos, Caribbean and South American plates. The displacement rates for the period 1988-1991, obtained from the results of the first three Central And South America (CASA) GPS campaigns, are in general agreement with the predictions of the NUVEL-1 plate motion model, but there are differences in detail between the observations and the model. The Nazca-North Andes convergence rate vector measured by GPS is different from the NUVF.•I vector at 95% confidence. The difference implies that the North Andes are moving northward relative to South America. The measured convergence between the Caribbean plate and the North Andes suggests that the southern margin of the Caribbean plate is located in the South Caribbean deformed belt. The April 1991 Costa Rica earthquake and the Cocos-Caribbean convergence rate determined by GPS suggest the possibility of significant ongoing deformation between Central America and the stable interior of the Caribbean plate. Our GPS results are consistent with deformation of the overriding plates at the convergent margins of Central and South America and confirm that active convergence is occurring around much of the southern margin of the Caribbean plate, from Colombia west to Costa Rica. Costa Rica and Panam• are not part of the stable Caribbean plate. Instead, the South Caribbean deformed belt and the North Panam• fold belt probably represent the southern margin of the Caribbean plate.

Geophysical Journal International, 2019

We describe a new elastic-kinematic model for the present tectonics of northern Central America and southern Mexico, where the Motagua-Polochic fault zone, Middle America subduction zone and faults in the Central America volcanic arc pose significant seismic hazards. The new model, which consists of the angular velocities for eight plates and blocks, interseismic locking solutions for some of the block-bounding faults and strain-rate tensors for three blocks with significant internal deformation, optimizes the fit to regional fault azimuths and earthquake slip directions and a new 200+ station GPS velocity field that has been corrected for the coseismic and post-seismic effects of three large regional earthquakes in 2009 and 2012. From our new observations and modelling thereof, we find evidence for the following: (1) 13±1 mm yr −1 of ≈E-W stretching between undeformed Caribbean plate in central Honduras and a location ≈50 km west of the Guatemala City graben; (2) accommodation of the above extension via slow W-to-WNW motions of newly defined Chortis and Ipala blocks and distributed ENE-WSW stretching within both blocks; (3) 80 per cent of Chortis-North America plate motion in eastern Guatemala occurs on the Motagua fault versus only 20 per cent on the Polochic fault; (4) Motagua fault slip rates that decrease westwards from 14 ± 1.5 mm yr −1 to 9-10 ± 2 mm yr −1 to less than 2 mm yr −1 in eastern Guatemala, central Guatemala and west of the Guatemala City graben, respectively; (5) Slip rates along Central America volcanic arc faults that decrease from 12.5 ± 1.0 mm yr −1 in Nicaragua to 10 ± 1.3 mm yr −1 in central El Salvador to 7.6 ± 2.1 mm yr −1 on the Jalpatagua fault of southern Guatemala to 2-3 mm yr −1 or less across the volcanic arc west of Guatemala City; (6) a transition near the Mexico-Guatemala border from moderate-to-high locking of the subduction interface offshore from southern Mexico to low locking below the Central America forearc sliver; (7) Subduction of the Cocos plate beneath the Central America forearc sliver up to 10 mm yr −1 faster than and 7-8 • clockwise from all previous estimates; (8) 12 ± 6 mm yr −1 of E-W

Geophysical Journal International, 2018

We examine the hypocentral distribution of seismicity and a series of geodetic velocity vectors obtained from Global Positioning System observations between 1994 and 2015 both offshore and mainland northwestern South America (66 • W-77 • W; 8 • N-14 • N). Our analysis, that includes a kinematic block modelling, shows that east of the Caribbean-South American-North Andes plates triple junction at ∼68 • W; 10.7 • N, right-lateral easterly oriented shear motion (∼19.6 ± 2.0 mm yr −1) between the Caribbean and South America plates is split along two easterly striking, right-lateral strike-slip subparallel fault zones: the San Sebastián fault that runs offshore the Venezuelan coast and slips about 17.0 ± 0.5 mm yr −1 and the La Victoria fault, located onshore to the south, which is accumulating strain equivalent to 2.6 ± 0.4 mm yr −1. West of the triple junction, relative right-lateral motion between the Caribbean and South American plates is mostly divided between the Morrocoy and Boconó fault systems that strike northwest and southwest from the triple junction, respectively, and bound the intervening North Andes plate that shows an easterly oriented geodetic slip of 15.0 ± 1.0 mm yr −1 relative to the South American plate. Slip on the Morrocoy fault is right-lateral and transtensional. Motion across the Boconó fault is also right-lateral but instead transpressional, divided between ∼9 and 11 mm yr −1 of right-slip on the Boconó fault and 2-5 mm yr −1 of convergence across adjacent and subparallel thrust faults. Farther west of the triple junction, ∼800 km away in northern Colombia, the Caribbean plate subducts to the southeast beneath the North Andes plate at a geodetically estimated rate of ∼5-7 mm yr −1 .

2006

Northern Central America is located in a complex zone of interraction between three major tectonic plates: The North American (NA), the Caribbean (CA) and the Cocos (CO) plates. While the CO plate is subducting under the NA and CA plates along the Mid-American trench, the on-land relative motion between the NA and CA plates is mainly accomodated by the east-west-trending left-lateral Polochic-Motagua fault system. The relative contributions of the Polochic and Motagua left-lateral faults, of a series of north-south grabens on the CA plate, and of the Mid-American Volcanic Arc (MAVA) in the accomodation of the deformation related to the CO-NA-CA triple junction remain poorly constrained. To adress these issues, we have analyzed GPS campaign data from geodetic networks in Guatemala (24 sites measured in 1999, 2003 and 2006), Salvador (3 sites measured in 2003 and 2006), and Chiapas in Mexico (8 sites measured in 2002, 2003, 2004 and 2005). These data were combined with GPS data from 14 permanent stations (including 11 stations in Mexico and 3 in Guatemala) and selected IGS stations. They were processed using the GAMIT and GLOBK softwares. Preliminary results computing the 1999-2003 data from the Guatemalan GPS network show that the relative velocity between the NA and CA plates is about 20 mm/yr. The obtained velocity field can be fitted using simple elastic models with a single fault centered on the Motagua fault, locked at a depth of 20 km with a slip-rate decreasing from eastern (20 mm/yr) to central Guatemala (12 mm/yr) towards the CO-NA-CA triple junction. This decrease seems to be accomodated by a 8 mm/yr east-west extension across the grabens south of the Motagua fault. We also observe about 10 mm/yr of dextral slip across MAVA. We will present a new regional velocity field, combining all the available Guatemalan, Salvadorian and Mexican GPS data set in order to better quantify the deformation of northern Central America at a regional scale, and to present a refined kinematic model of this complex area.

Geophysical Journal International

We use continuous and campaign measurements from 215 GPS sites in northern Central America and southern Mexico to estimate coseismic and afterslip solutions for the 2009 M w = 7.3 Swan Islands fault strike-slip earthquake and the 2012 M w = 7.3 El Salvador and M w = 7.4 Guatemala thrust-faulting earthquakes on the Middle America trench. Our simultaneous, time-dependent inversion of more than 350 000 daily GPS site positions gives the first jointly consistent estimates of the coseismic slips for all three earthquakes, their combined time-dependent post-seismic effects and secular station velocities corrected for both the coseismic and post-seismic deformation. Our geodetic slip solutions for all three earthquakes agree with previous estimates that were derived via static coseismic-offset modelling. Our time-dependent model, which attributes all transient post-seismic deformation to earthquake afterslip, fits nearly all of the continuous GPS site position time-series within their severalmillimetre position noise. Afterslip moments for the three earthquakes range from 35 to 140 per cent of the geodetic coseismic moments, with the largest afterslip estimated for the 2012 El Salvador earthquake along the weakly coupled El Salvador trench segment. Forward modelling of viscoelastic deformation triggered by all three earthquakes for a range of assumed mantle and lower crustal viscosities suggests that it accounts for under 20 per cent of the observed post-seismic deformation and possibly under 10 per cent. Our results thus point to afterslip as the primary and perhaps dominant mode of post-seismic deformation for these C The Author(s)

Journal of Geophysical Research, 1998

Global Positioning System (GPS) measurements in 1986, 1994, and 1995 at sites in Dominican Republic, Puerto Rico, Cuba, and Grand Turk define the velocity of the Caribbean plate relative to North America. The data show eastward motion of the Caribbean plate at a rate of 21 ñ I mm/yr (l standard error) in the vicinity of southern Dominican Republic, a factor of 2 higher than the NUVEL-1A plate motion model prediction of l I ñ 3 mm/yr. Independent measurements on San Andres Island, and an Euler vector derived from these data, also suggest a rate that is much higher than the NUVEL-lA model. Available data, combined with simple elastic strain models, give the following slip rate estimates for major left-lateral faults in Hispaniola: (1) the North Hispaniola fault offshore the north coast of Hispaniola, 4 ñ 3 mm/yr; (2) the Septentrional fault in northern Dominican Republic, 8 ñ 3 mm/yr; and (3) the Enriquillo fault in southern Dominican Republic and Haiti, 8 ñ 4 mm yr. The relatively high plate motion rate and fault slip rates suggested by our study, combined with evidence for strain accumulation and historical seismicity, imply that seismic risk in the region may be higher than previous estimates based on low plate rate/low fault slip rate models and the relatively low rate of seismicity over the last century. 1. Introduction One of the important discoveries in the last decade was the recognition that the velocities of Earth's major lithospheric plates, as measured by marine magnetic anomalies averaged over several million years or predicted by plate motion models based on these and other data [e.g., DeMets et al., 1990], are equivalent, within small uncertainties, to velocities measured by independent space geodetic techniques over 5 to 10 years, including satellite laser ranging [Smith et al., 1990; Robbins et al., 1993; Cazenave et al., 1993], very long baseline interferometry [Robaudo and Harrison, 1993], and the Global Positioning System [Argus •tnd Heftin, 1995; Dixon and Mao, 1997; Larson et al., 1997]. This equivalence is generally interpreted not only as an indication of the steadiness of plate motion over several million years but also, with some circularity, as validation of both the space •Rosenstiel School of Marine and Atmospheric Sciences, Paper number 97JB03575. 0148-0227/98/97JB-03575509.00 geodetic techniques and the models. However, a complete test of this equivalence remains to be done. For logistical and economic reasons the space geodetic sites used in these pioneering studies necessarily omitted several plates, including the Caribbean plate. This is a critical omission because the velocity of this plate with respect to its neighbors is poorly known on both geologic and geodetic timescales. While there has been much research on this topic using global models [•!ordan, 1975; Stein et al., 1988; DeMets et al., 1990] and models based on local earthquake slip vectors [Sykes et al., 1982; Deng and Sykes, 1995], large uncertainties remain, reflecting complex regional geology. Transform fault azimuths, earthquake slip vectors, midocean ridge spreading rates, and other relative motion indicators are poorly def'med, inconsistent, sparse, or nonexistent around the boundary of the Caribbean plate. Most parts of this boundary are actually broad, deforming zones of continental or transitional arc continental crust, complicating interpretation of kinematic indicators. The most poorly determined Euler vectors in global plate motion models such as NUVEL-l and 1A [DeMets et al., 1990, 1994] generally involve the Caribbean plate, reflecting these problems. This paper reports the first geodetic measurements of Caribbean plate motion. We use Global Positioning System (GPS) data acquired in several experiments spanning up to a decade to derive a velocity estimate and uncertainties for the Caribbean plate. We also discuss implications for strain partitioning and earthquake hazard in the northeastern Caribbean. Although our data are too sparse to develop a detailed picture of strain distribution, we can put broad constraints on the slip rates of major faults in Hispaniola, and assess the influence of elastic 15,157 15,158 DIXON ET AL.: NORTHERN CARIBBEAN GPS strain accumulation on measured site velocities for the

Journal of South American Earth Sciences, 2002

These data reveal wide plate boundary deformation and escape tectonics occurring along an approximately 1400 km length of the North Andes, locking of the subducting Nazca plate and 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 re¯ect 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.

J Geophys Res, 1997

Global Positioning System (GPS) measurements in 1986, 1994, and 1995 at sites in Dominican Republic, Puerto Rico, Cuba, and Grand Turk define the velocity of the Caribbean plate relative to North America. The data show eastward motion of the Caribbean plate at a rate of 21 ñ I mm/yr (l standard error) in the vicinity of southern Dominican Republic, a factor of 2 higher than the NUVEL-1A plate motion model prediction of l I ñ 3 mm/yr. Independent measurements on San Andres Island, and an Euler vector derived from these data, also suggest a rate that is much higher than the NUVEL-lA model. Available data, combined with simple elastic strain models, give the following slip rate estimates for major left-lateral faults in Hispaniola: (1) the North Hispaniola fault offshore the north coast of Hispaniola, 4 ñ 3 mm/yr; (2) the Septentrional fault in northern Dominican Republic, 8 ñ 3 mm/yr; and (3) the Enriquillo fault in southern Dominican Republic and Haiti, 8 ñ 4 mm yr. The relatively high plate motion rate and fault slip rates suggested by our study, combined with evidence for strain accumulation and historical seismicity, imply that seismic risk in the region may be higher than previous estimates based on low plate rate/low fault slip rate models and the relatively low rate of seismicity over the last century. 1. Introduction One of the important discoveries in the last decade was the recognition that the velocities of Earth's major lithospheric plates, as measured by marine magnetic anomalies averaged over several million years or predicted by plate motion models based on these and other data [e.g., DeMets et al., 1990], are equivalent, within small uncertainties, to velocities measured by independent space geodetic techniques over 5 to 10 years, including satellite laser ranging [Smith et al., 1990; Robbins et al., 1993; Cazenave et al., 1993], very long baseline interferometry [Robaudo and Harrison, 1993], and the Global Positioning System [Argus •tnd Heftin, 1995; Dixon and Mao, 1997; Larson et al., 1997]. This equivalence is generally interpreted not only as an indication of the steadiness of plate motion over several million years but also, with some circularity, as validation of both the space •Rosenstiel School of Marine and Atmospheric Sciences, Paper number 97JB03575. 0148-0227/98/97JB-03575509.00 geodetic techniques and the models. However, a complete test of this equivalence remains to be done. For logistical and economic reasons the space geodetic sites used in these pioneering studies necessarily omitted several plates, including the Caribbean plate. This is a critical omission because the velocity of this plate with respect to its neighbors is poorly known on both geologic and geodetic timescales. While there has been much research on this topic using global models [•!ordan, 1975; Stein et al., 1988; DeMets et al., 1990] and models based on local earthquake slip vectors [Sykes et al., 1982; Deng and Sykes, 1995], large uncertainties remain, reflecting complex regional geology. Transform fault azimuths, earthquake slip vectors, midocean ridge spreading rates, and other relative motion indicators are poorly def'med, inconsistent, sparse, or nonexistent around the boundary of the Caribbean plate. Most parts of this boundary are actually broad, deforming zones of continental or transitional arc continental crust, complicating interpretation of kinematic indicators. The most poorly determined Euler vectors in global plate motion models such as NUVEL-l and 1A [DeMets et al., 1990, 1994] generally involve the Caribbean plate, reflecting these problems. This paper reports the first geodetic measurements of Caribbean plate motion. We use Global Positioning System (GPS) data acquired in several experiments spanning up to a decade to derive a velocity estimate and uncertainties for the Caribbean plate. We also discuss implications for strain partitioning and earthquake hazard in the northeastern Caribbean. Although our data are too sparse to develop a detailed picture of strain distribution, we can put broad constraints on the slip rates of major faults in Hispaniola, and assess the influence of elastic 15,157 15,158 DIXON ET AL.: NORTHERN CARIBBEAN GPS strain accumulation on measured site velocities for the

Tectonics, 2011