The Argentinean National Network of Seismic and Strong-Motion Stations by Gerardo Sánchez, Rodolfo Recio, Oscar Marcuzzi, Marcelo Moreno, Mario Araujo, Carlos Navarro, Juan Carlos Suárez, Jens Havskov, and Lars Ottemöller INTRODUCTION The history of seismic studies in Argentina dates back to the first decades of the last century and is based on historical material and archeological evidence. The first institution in the country devoted to geophysical aspects (mainly seismology) was the Astronomic Observatory of La Plata, created in 1882. But it was not until 1906 that this institution included seismic observations by installing the first seismological equipment, consisting of a three-component Vicentini seismograph, in 1907. Between 1913 and 1925 two more mechanical seismo- graphs were installed by the Astronomic Observatory of La Plata. This institution started publishing its first annual bul- letin in 1922. In 1951, two electromagnetic-type seismographs were installed at the Observatory, which increased significantly the registration of seismic events. One of the stations of this Observatory became part of the World Wide Standardized Seismograph Network (WWSN) in 1962. In January 1944 a large earthquake (M w 7.0; Alvarado and Beck, 2006) almost completely destroyed the city of San Juan, the capital of San Juan province, located in the west-central part of Argentina, killing at least 5000 people. This earthquake was the trigger for seismological research and seismic observa- tions in Argentina, especially in San Juan province. Following this earthquake in 1944, the Federal Govern- ment created the Consejo Nacional de Construcciones Anti- sísmicas y de Reconstrucción de San Juan (CONCAR), an institution devoted to develop a new building code and to plan and carry out the reconstruction process of San Juan city. On 8 May 1972, the CONCAR was transformed into the National Institute for Seismic Prevention (INPRES). INPRES is a federal agency of the Argentine government depending on the Secretary of Public Services and is situated in the city of San Juan. Its main objective is to carry out the national policy for seismic prevention, operate the national network of seismic stations (46) and accelerometers (146), do research in seismology and earthquake engineering, and de- velop standards for earthquake resistant constructions. In this paper the INPRES national seismic and strong- motion network will be presented with an overview of data acquisition, processing, and analysis. SEISMICITY The seismic activity of Argentina is mainly concentrated in the central and northwest part, along the Andean backarc region (Fig. 1). This is a consequence of the compressive tectonic set- ting, produced by ongoing eastward subduction of the oceanic Nazca plate beneath the continental South American plate, which moves to the west. The axis of the convergence between the Nazca plate and the South American plate occurs along the Peru–Chile trench, and the relative velocity between the two plates is about 8:0 cm=year. The eastward movement of the Nazca plate at ∼100 km depth develops a compressive stress regime in the South Ameri- can plate resulting in active deformation of the plate along its broad western margin. This results in active superficial geo- logical structures, which mostly have reverse-type faulting as deduced from field observations, for example, trenches and fo- cal mechanisms. Some faults are strike slip with faulting parallel to the folding of the Andes in the north–south direction. The subducted Nazca plate changes its normal inclination angle of ∼30° to nearly horizontal between 29° S and 33° S (Fig. 2). This is probably caused by the subduction of the Juan Fernan- dez ridge beneath the South American plate (Fig. 2), thereby creating a strong interaction between the plates (Nazca and South American) in the northern part of Mendoza and south- ern part of San Juan. This phenomenon could be the cause of large crustal earthquakes that occur in the provinces of San Juan and Mendoza. Thus, there are two seismogenic zones that produce seismic hazard in Argentina. Shallow thrust faults within the South American plate (INPRES, 1982, 1995) and intermediate-depth normal faults (Regnier et al., 1992; Regnier et al., 1994; Costa et al., 2000) within the subducted Nazca plate. The first historical damaging earthquake records that are known after the Spanish colonization come from Talavera de Esteco in the province of Salta, located in the northwest part of Argentina. The first earthquake that killed thousands of people oc- curred on 20 March 1861. This damaging earthquake destroyed the city of Mendoza in the central west part of Argentina with a magnitude estimated to be equivalent to M S 7.0. The last de- structive earthquake occurred in Jujuy on 6 October 2011 doi: 10.1785/0220120045 Seismological Research Letters Volume 84, Number 5 September/October 2013 729