Sergio Cimbaro

Virtual array beamforming of GPS TEC observations of coseismic ionospheric disturbances near the Geomagnetic South Pole triggered by teleseismic megathrusts

We identified co-seismic ionospheric disturbances (CID) in Antarctica generated by the 2010 Maule and the 2011 Tohoku-Oki earthquakes analyzing TEC data with a modified beamforming technique. Beamforming in Antarctica, however, is not straightforward due to the effects of array deformation and atmospheric neutral wave-ionospheric plasma coupling. We take these effects into account and present a method to invert for the seismically generated acoustic wave using TEC observations. The back azimuths, speeds and waveforms obtained by the beamform are in excellent agreement with the hypothesis that the TEC signals are generated by the passage of Rayleigh waves from the Maule and Tohoku-Oki earthquakes. The Tohoku-Oki earthquake is ~12,500 km from Antarctica, making this the farthest observation of CIDs to date using GPS.

The History, State, and Future of the Argentine Continuous Satellite Monitoring Network and Its Contributions to Geodesy in Latin America

Since its creation in 1998, the Argentine Continuous Satellite Monitoring Network (Red Argentina de Monitoreo Satelital Continuo [RAMSAC]) has grown to include more than 100 continuously operating Global Navigation Satellite Systems (GNSS) stations in Argentina. RAMSAC Receiver Independent Exchange Format (RINEX) data and their derived positioning products (e.g., Networked Transport of RTCM via Internet Protocol [NTRIP] streams and time series) have been used in more than 20 peer-reviewed publications studying the inter-, co-, and postseismic geodynamic evolution of the subduction interface between the South America and Nazca plates. Most of this research has focused on the deformation associated with the near-field megathrust earthquake cycle. Nevertheless, many authors have begun to include in their analyses far-field GNSS observations, which in general do not follow the elastic/viscoelastic deformation predicted by current models. We review the contribution of RAMSAC to scientific knowledge of earthquake elastic deformation and associated phenomena. We also describe the future plans for RAMSAC and the societal impact beyond geodetic and geophysical science. INTRODUCTION AND HISTORY OF RAMSAC In 1993, the Argentine Military Geographic Institute (Instituto Geográfico Militar [IGM]), now the Argentine National Geographic Institute (Instituto Geográfico Nacional [IGN]), began a campaign to acquire Global Positioning System (GPS) measurements on ∼120 benchmarks to produce Argentina’s first GPS-based geodetic reference frame (RF), the Geodetic Argentine Positions (Posiciones Geodésicas Argentinas [POSGAR]) RF. This RF, later called POSGAR94, replaced the original national local system (Campo Inchauspe 69) and was based on GPS observations obtained during field campaigns (Lauría et al., 2002) in collaboration with the National Science Foundation-funded Central Andes GPS Project (CAP). In the mid 1990s, the Jet Propulsion Laboratory at National Aeronautics and Space Administration (NASA) and the Deutsches GeoForschungsZentrum (GFZ) deployed the first three continuous GPS (CGPS) stations at the Universidad Nacional de La Plata (Buenos Aires), Universidad Nacional de Salta (Salta), and Estación Astronómica Río Grande (Tierra del Fuego) as part of the early global International GNSS Service (IGS) network. At the same time, CAP deployed stations at the seismic station Coronel Fontana (San Juan),Universidad Nacional de Tucumán (Tucumán), Parque Nacional Lihué Calel (La Pampa), and Aeropuerto de Ushuaia (Tierra del Fuego). Both the NASA/GFZ and CAP groups collaborated with Argentine universities and national laboratories, and CAP also collaborated with the IGN and the National Parks Administration. The IGN proposed creation of an open collaborative GPS network using data provided by these seven sites in Argentina to support governmental, commercial, and scientific geodesy and surveying. This network was named the Argentine Continuous Satellite Monitoring Network (Red Argentina de Monitoreo Satelital Continuo [RAMSAC]), and its main goal was to be the foundation for the development and maintenance of the national geodetic RF. Figure 1 shows a summary of the RAMSAC stations grouped by installation date. Until 2009, RAMSAC depended mainly on other agencies and institutions (both national and international) to provide GPS/Global Navigation Satellite Systems (GNSS) stations to expand the network. During this period, thanks to the effort of multiple national and international collaborators, the network incorporated stations such as Universidad Nacional de Rosario (Santa Fe), and Centro Regional de Investigaciones Científicas y Tecnológicas (Mendoza; MZAC), among others. In late 2009, IGN obtained Argentine government funding to begin to build and operate its own GPS/GNSS stations. This triggered the rapid RAMSAC expansion shown in Figure 1. One of the strengths of RAMSAC is that all installations are performed using monumentation that guarantees the stability of the GPS/GNSS antennas. Also, in an effort to maintain the best possible continuity of the time series (with the least possible time-series jumps), IGN has always tried to keep the antenna changes to a minimum unless a degradation in the solutions quality is noticed. doi: 10.1785/0220170162 Seismological Research Letters Volume XX, Number XX – 2018 1 SRL Early Edition

Correction to “Coseismic slip distribution of the February 27, 2010 Mw 8.8 Maule, Chile earthquake”

[1] In the paper “Coseismic slip distribution of the February 27, 2010 Mw 8.8 Maule, Chile earthquake” by Fred F. Pollitz et al. (Geophysical Research Letters, 38, L09309, doi:10.1029/2011GL047065, 2011) the captions for Figure 1–3 are ordered incorrectly. The correct captions for Figures 1–3 appear here. [2] Figure 1. Rupture areas associated with historic earthquakes along the Andean megathrust and aftershocks of the February 27, 2010 event. Historical epicenters are provided by Centro Regional de Sismologia para America del Sur and aftershock locations are provided by the National Earthquake Information Center. White lines indicate the surface projection of the fault plane used to model the 2010 event. Nazca–South America relative plate motion vector is from Ruegg et al. [2009]. [3] Figure 2. Observed coseismic GPS offsets (black vectors) with 95% uncertainties compared with model horizontal offsets using the coseismic slip model obtained by the joint InSAR/GPS inversion, which is contoured in gray (values in meters). White lines indicate the surface projection of the fault plane. [4] Figure 3. Coseismic slip models derived from (a) InSAR data only, (b) GPS data only, and (c) combined GPS and InSAR data, with seismic moment indicated for each model. Contour interval is 3 m. Star symbol indicates the Global CMT epicenter.