Open-source archive of active faults for northwest South America Gabriel Veloza*, Richard Styron, and Michael Taylor, Dept. of accommodating transpression across the Caribbean–South Geology, University of Kansas, Lawrence, Kansas 66045, USA; American plate boundary (Pindell et al., 2005). and Andrés Mora, Ecopetrol, Instituto Colombiano del Petróleo, The Andes have dense population centers, concentrated mostly Bucaramanga, Colombia in elevated regions of the Venezuelan and Colombian Andes and along the Pacific coasts of Ecuador and Peru. A shared characteristic of these urban centers is their proximity to ABSTRACT seismically active faults. For example, the cities of Bucaramanga We present a publicly available database of active structures for and Santiago de Guayaquil lie adjacent to the Bucaramanga and the northern Andes based on the literature, our own field map- Guayaquil-Algeciras faults, and major cities such as Lima are ping, interpretation of digital elevation models, earthquakes, and above an active subduction zone. Earthquake hazards are not the regional velocity field obtained from Global Positioning limited to the well-described subduction zone settings— System (GPS) studies. The “Active Tectonics of the Andes” data- devastating earthquakes occur in continental settings where active base (ATA v.1.0) is a digital archive of more than 400 active faults structures are often smaller but shallower and close to population available in a variety of digital formats for use by the scientific and centers (e.g., England and Jackson, 2011); the 2008 and 2010 teaching communities. ATA v.1.0 is an open-source archive that is earthquakes in New Zealand and China, respectively (e.g., updateable based on new results obtained by the scientific com- Robinson et al., 2011), provide recent examples. To achieve the munity, and it should prove useful to scientists, teachers, policy goal of understanding the distribution and kinematics of active makers, and the general population. We use ATA v.1.0 in combi- faults, digital archives of active structures are being compiled nation with surface velocities from GPS to evaluate the regional worldwide. Attention has been paid to the Andes (e.g., Paris et al., kinematics of faulting in northwest South America. In particular, 2000; Costa et al., 2006), and similar databases have been made we find that the development of active strike-slip systems is con- for other orogens (e.g., Styron et al., 2010) and the western United trolled, in part, by the degree of convergence obliquity between States (USGS, 2006). These databases are useful for understanding subducting oceanic plates and South America. seismic hazard and the dynamic mechanisms driving deformation. We present a publicly available database, “Active Tectonics of INTRODUCTION the Andes” (ATA v.1.0), comprising over 400 active faults from Active deformation of northwest South America is character- northeast Venezuela to southern Peru. These structures were ized by interaction between the Caribbean and Nazca plates with mapped from our own field observations, interpretation of the South American margin, in sharp contrast to the classic geologic maps, topography, remote sensing data, and earthquake Andean convergent margin south of 5°S. This change in plate con- seismicity from national databases of the geological surveys of figuration is reflected in the distribution and kinematics of active Venezuela, Colombia, Ecuador, and Peru (FUNVISIS, structures in the upper plate, where strain is distributed over hun- INGEOMINAS, EPN, and IGP, respectively [see references]). dreds of active structures capable of generating damaging earth- Fault names and kinematics are compiled from academic journals quakes. In the south, Peru is dominated by thrust faulting along and regional compilations. Faults were mapped at scales ranging the forearc and sub-Andean zones, largely in response to subduc- from ~1:1,000,000 to 1:100,000, depending on the scale of the tion, whereas left-lateral strike-slip and normal faulting are char- structure, the quality of remote sensing imagery, and accounting acteristic of higher elevations and the retroarc region to the east for uncertainties in fault kinematics. ATA v.1.0 is suitable for (Dalmayrac and Molnar, 1981; Dewey and Lamb, 1992; McNulty displaying with most GIS packages (e.g., ArcGIS), the Generic et al., 1998) (Fig. 1). Ecuador’s recent deformation is similarly Mapping Tools (Wessel and Smith, 1998), and Google Earth. partitioned between well-developed thrust systems and the Where available, millennial and longer-term slip rates and Guayaquil-Algeciras right-lateral fault system (Fig. 1). Colombia references are included as metadata in .shp and .kml formats. User exhibits a more complex tectonic framework, with subduction of input is encouraged to contribute to or refine the database. the Caribbean and Nazca slabs beneath northwest South America, TECTONIC SETTING and the arc collision of the Chocó–Panamá indenter (Farris et al., 2011). The northern margin of South America is also partitioned Slip partitioning in the northern Andes is highly dependent on between south-directed thrusting along the southern Merida the plate boundary configuration relative to the surface velocity Andes, which contrasts with high rates of dextral shear across the field. Where convergence is orthogonal, we generally expect to central and northern portions of the range (Fig. 1), observe pure shear deformation (in map view), whereas in regions GSA TODAY | OCTOBER 2012 GSA Today, v. 22, no. 10, doi: 10.1130/GSAT-G156A.1. *E-mail: [email protected] 4 -85 -80 -75 -70 -65 -85 -80 -75 -70 20 mm/yr CB 14 14 10 14 CCR 5 CF OA MA 0 BAP CR SSJ BAP LV PT LV LB SA SMB VF CM SM SM 60 mm/yr TB -5 9 ss GU 9 BAP NZ PH ES Venezuela -10 JR MD PF CM SMB MRB B RM AT BM CY GR GA GRB IB GT 4 MPR Neotectonic map of the Northern Andes 4 RM LEFT SLIP FAULTS JI: Jipijapa fault AY: Ayacucho fault system LVP: La Victoria- Pisayambo fault CH ES: Espíritu Santo fault MC: La Macarena fault system MC HY: Huaytalpallana fault MN: Manu thrust TB JR: Jaque River fault MO: Mocoa fault GA OC: Ocolpa fault NB: Numbalá fault RM PF: Palestina fault PA: Pasco fault Colombia QU: Quiches fault system PH: Pierre Hills fault system MO RP: Rapaz fault system PLL: Pallatanga fault RC SMB: Santa Marta Bucaramanga fault system PT: Perijá - El Tigre fault system VF: Valera fault system PU: Pucallpa fault QI: Quinindé fault QI CA RIGHT SLIP FAULTS RM: Romeral fault system CC BAP: Boconó - Ancon - El Pilar fault system SH: Shitari fault CF: Cuisa Fault SM: South Merida thrust front GA: Guayaquil-Algeciras fault system SS: Sansón fault system JI -1 LVP Ecuador GR: Garrapatas fault SSJ: Sinú - San Jacinto fult system -1 DL BF CR TP IB: Ibagué fault ST: Santiago fault CL LB: Los Bajos fault system TB: Tambor fault LV: La Victoria fault system TP: Tena - Pusuno faults PO TS MD: Murindó fault TS: Taisha fault ST OA: Oca - Ancón Fault GA RC: Río Canandé NORMAL FAULTS TB PLL CA: Cayesh fault system CZ THRUST FAULTS CB: Cordillera Blanca fault system CMA AT: Alto del Trigo fault CM: Campearito fault system SB BF: Buena Fé fault CZ: Cuzco fault system Peru BM: Bituima fault HL: El Huevo - Lomas fault system GRI CA: Cascales fault system HU: Huancayo fault NB CC: Calceta fault PO: Posorja fault EP CH: Chusma fault system RG: Rio Gatún fault CL: Colonche fault system VN: Vilcanota fault system -6 SH CM: Cimitarra fault -6 CMA: Célica - Macará - Amotape fault system OCEANIC RIDGES EP CY: Cusiana - Yopal fault system CR: Carnegie ridge NB CZ: Campanquiz fault GRI: Grijalva Fault Zone DL: Daule fault MD: Mendaña Fault Zone EP Brazil EP: Eastern Perú thrust front MPR: Malpelo Ridge GT: Guaicáramo thrust GU: Guanare fault QU Map Symbology PU CB PA Thrust fault Right Lateral slip fault Left Lateral slip fault Normal fault RP Quaternary volcano CA -11 Ridge/Oceanic Country border -11 OC plate fault zone HY MN -6000 0 6000 MD Elevation HU AY MN CZ Bolivia 500 km VN HL A -16 -16 -85 -80 -75 -70 -65 Figure 1. (A) Active faults of northwest South America. Thrust faults and normal faults have barbs and balls on the hanging wall. Arrows indicate horizontal motion for strike slip faults. GRB—Guaviare River basin; MA—Mérida Andes; MRB—Meta River basin; SB—Santiago basin; TB—Talara bend. (B) Schematic model for slip partitioning of northwest South America. Eastward motion of Nazca Plate is partitioned into trench-parallel (red arrows) and trench-normal (blue arrows) components. Velocities for Nazca and Caribbean plates from Trenkamp et al. (2002). Trench-parallel components of the velocity field increase away from Figure 1 GSA TODAY | OCTOBER 2012 the Talara Bend, with the maximum velocity gradient located in that area. Note the position of the Carnegie Ridge relative to the Talara Bend, where strike-slip faults initiate. CB—Caribbean plate; CCR—Cocos Ridge; CR—Carnegie Ridge; NZ—Nazca plate; SA—South American plate; TB—Talara bend. 5 of oblique convergence, an element of simple shear deformation is Other first-order fault systems of the Colombian Andes include expected. Orthogonal convergence between the Nazca and South the northwest-striking Santa Marta–Bucaramanga fault system, American plates is restricted to the region near 5°S latitude, which is a left-slip fault system, ~500 km in length (Fig. 1). Its whereas the Caribbean plate is underthrusting obliquely below southeastern tip is located near the central portion of the eastern northern South America (Fig. 1). To the north and south, rapid Cordillera and sits above the Bucaramanga seismic nest. The increases in convergence obliquity lead to the development of Santa Marta–Bucaramanga fault system is thought to be the significant trench-parallel strike-slip faults (Dewey and Lamb, surface response to slab collision (Taboada et al., 2000).