A New GPS Velocity Field T ∗ Héctor Mora-Páeza, , James N
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Journal of South American Earth Sciences 89 (2019) 76–91 Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames Crustal deformation in the northern Andes – A new GPS velocity field T ∗ Héctor Mora-Páeza, , James N. Kelloggb, Jeffrey T. Freymuellerc, Dave Mencind, Rui M.S. Fernandese, Hans Diederixa, Peter LaFeminaf, Leonardo Cardona-Piedrahitaa, Sindy Lizarazoa,g, Juan-Ramón Peláez-Gaviriaa, Fredy Díaz-Milaa, Olga Bohórquez-Orozcoa, Leidy Giraldo-Londoñoa, Yuli Corchuelo-Cuervoa a Colombian Geological Survey, Space Geodesy Research Group, Colombia b University of South Carolina, USA c University of Alaska, Fairbanks, USA d University of Colorado and UNAVCO, USA e University of Beira Interior, Instituto D. Luiz, Portugal f The Pennsylvania State University, USA g Now at the University of Nagoya, Japan ARTICLE INFO ABSTRACT Keywords: We present a velocity field for northwestern South America and the southwest Caribbean based onGPS Space geodesy Continuously Operating Reference Stations in Colombia, Panama, Ecuador and Venezuela. This paper presents North Andean block the first comprehensive model of North Andean block (NAB) motion. We estimate that the NAB ismovingtothe Crustal deformation 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 (7km) 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 on-going 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 right- lateral 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. 1. Introduction measurements performed in Costa Rica, Panama, Colombia, Venezuela and Ecuador, from the late 1980s and early 1990s demonstrated the Given the controversies over whether continental deformation is northeastward movement of the North Andes, Caribbean – North Andes best described as relative movements of rigid blocks or continuous convergence, and the ongoing rapid collision of the Panama arc with deformation, whether mountain building rates can be compared to the North Andes (e.g., Kellogg et al., 1990; Freymueller et al., 1993; convergent boundary processes, and how slip is partitioned at complex Trenkamp et al., 2002). convergent plate boundaries, northwestern South America offers a good Using GPS results from the first three CASA GPS campaigns field laboratory because it includes an active arc-continent collision, (1988–1991), Freymueller et al. (1993) showed evidence for northward margin-parallel slip, and active “flat-slab” and “normal” subduction. movement of the North Andes and convergence at the South Caribbean CASA (Central And South America) GPS Project campaign deformed belt. Kellogg and Vega (1995) used CASA GPS results to ∗ Corresponding author. E-mail addresses: [email protected], [email protected] (H. Mora-Páez). https://doi.org/10.1016/j.jsames.2018.11.002 Received 20 July 2018; Received in revised form 13 October 2018; Accepted 1 November 2018 Available online 03 November 2018 0895-9811/ © 2018 Elsevier Ltd. All rights reserved. H. Mora-Páez et al. Journal of South American Earth Sciences 89 (2019) 76–91 propose a rigid Panama block and rapid Panama-North Andes con- Panama; one station on Cocos Island, Costa Rica; seven stations in vergence. Trenkamp et al. (2002) presented CASA campaign data from Ecuador, including two IGS stations, GLPS and RIOP; and two stations 1991 to 1998 that showed wide plate boundary deformation and escape in Venezuela. Nine of the stations used are part of the COCONet Project tectonics from the subducting Carnegie Ridge along an approximately (Braun et al., 2012). This precise velocity field is based on permanent 2000 km long transform fault belt, known as the Eastern frontal Fault stations with a minimum of 2.5 years of observations (e.g., Blewitt and zone, or perhaps better named the North Andean Boundary Fault. This Lavallee, 2002). fault extends from the Gulf of Guayaquil in Ecuador to Venezuela, and Colombian data are from the GeoRED Project (Geodesia: Red de which could be a manifestation of the incipient dismemberment of the Estudios de Deformación), which is run by the Space Geodesy Research northwestern South American plate. That study also showed locking of Group of the Colombian Geological Survey (CGS, Servicio Geológico the subducting Nazca plate and strain accumulation in the Ecuador- Colombiano; formerly INGEOMINAS). Initiated in 2007 by the CGS, Colombia forearc at the latitude of the border between the two coun- GeoRED is a research and development project based on space geodesy tries, collision of the Panama arc with Colombia, and Caribbean-North technology to catalog and interpret the geodynamics and associated Andes convergence. Elastic modeling of horizontal displacements were hazards within the broad northwestern South America plate margin consistent with partial locking in the Ecuador subduction zone and a deformation zone, (Mora-Páez et al., 2018; Mora-Páez, 2006). The fully locked Panama-Colombia collision zone. GeoRED network currently has 108 operating sites, located on the Significant deformation in the region is driven by Cocos Ridge Nazca, South America and Caribbean plates, (Mora-Páez et al., 2018), subduction, Panama collision and subduction of the Caribbean plate although sites with less than 2.5 years are not used in this study. Data (e.g., van Benthem and Govers, 2010; Kobayashi et al., 2014). from Ecuadorean stations have been provided by the Geophysics In- Kobayashi et al. (2014) used GPS data from Panama, Costa Rica and stitute of the National Polytechnic University (Escuela Politécnica Na- Colombia and elastic block modeling to conclude that tectonic escape cional), (Mothes et al., 2013). Data from stations located in Panama, from Cocos Ridge collision drives northeast motion of the Panama re- Venezuela and Costa Rica have been obtained from the COCONet gion and subsequent collision with the North Andes and Choco blocks. Project (https://www.unavco.org/data/gps-gnss/gps-gnss.html) and Mora-Páez et al. (2016) measured velocities from nine GPS Con- two stations from the Panama Canal Authority. tinuously Operating Reference Stations (CORS) and twenty campaign sites in the northeast trending Eastern Cordillera of Colombia that 2.2. GPS data processing and analysis constrain the rate of this motion, showing oblique convergence, con- sisting of 8 mm/yr of right-lateral strike-slip and only 4 mm/yr of All GPS data have been processed with GIPSY-OASIS II software, v northwest-southeast shortening. Perez et al. (2018) used GPS data 6.3 developed by the Jet Propulsion Laboratory (JPL), California primarily from Venezuela, to estimate motion of the North Andean Institute of Technology (Bertiger et al., 2010; Zumberge et al., 1997). block (NAB) relative to South America, but their estimate only included Daily station coordinates are expressed in ITRF2008. The station velo- four sites in northern Colombia. Nocquet et al. (2014) used GPS data, cities (Supp. Data 1) are computed using the HECTOR software (Bos primarily from Ecuador and Peru, to quantify the margin-parallel et al., 2013), software developed at SEGAL (Space & Earth Geodetic northeastward motion of the North Andean sliver (NAS) or North An- Analysis Laboratory at the University of Beira Interior, Portugal) that is dean block (NAB) and the southeastward motion of the Peru sliver, but used to estimate the linear trend in time-series with temporal correlated their estimate for the NAB used only two sites in Colombia. noise. On the Pacific coast of Ecuador and southernmost Colombia, ob- A power-law plus white noise model was assumed. For each time served deformation includes a large contribution from elastic de- series a power-spectrum plot was generated from the residuals, and formation due to the locked part of the subduction interface (Trenkamp compared to the predicted power-spectrum of the noise model was et al., 2002; Kobayashi et al., 2014). However, that contribution varies compared with the observed power spectrum to verify that the proper considerably along strike, with high elastic strain observed in northern noise model has been used. Ecuador and nearly zero in southern Ecuador (Chlieh et al., 2014; Seasonal signals (an annual and semi-annual signal) have been in- Nocquet et al., 2014). Vallée at al. (2013) documented a long slow-slip cluded in the estimation of the secular velocities in order to reduce their event on a shallow locked patch along one part of the Ecuador sub- influence on the estimated velocities. We follow the current state-of-art duction interface (near Isla la Plata) using continuous GPS and broad- approach that assumes that the amplitude of such signals is constant at band seismic data.