The Chilean National Seismic Network

Abstract eng:
Chile, along 3000 km of it 4200 km long coast, is regularly affected by very large earthquakes (up to magnitude 9.5) resulting from the convergence and subduction of the Nazca plate beneath the South American plate. These megathrust earthquakes exhibit long rupture regions reaching several hundreds of km with fault displacements of several tens of meters. Minimum delay characterization of these giant events to establish their rupture extent and slip distribution is of the utmost importance for rapid estimations of the shaking area and their corresponding tsunamigenic potential evaluation, particularly when there are only few minutes to warn the coastal population for immediate actions. The task of a rapid evaluation of large earthquakes is accomplished in Chile through a network of sensors being implemented by the National Seismological Center of the University of Chile. The network is mainly composed approximately by one hundred broad-band and strong motion instruments and 130 GNSS devices; all connected in real time. Forty units present an optional RTX capability, where precise satellite orbits and clock corrections are sent to the field device producing a 1-Hz stream at 4-cm level. In the other units, raw data will be sent in real-time to be later processed at the central facility. Hypocentral locations and magnitudes are estimated after few minutes by automatic processing software based on wave arrival; for magnitudes less than 7.0 the rapid estimation works within acceptable bounds. For larger events, automatic detectors and amplitude estimators of displacement have been developed from the real time GNSS streams. This software has been tested for several cases showing that, for plate interface events, the minimum magnitude threshold detectability reaches values within 6.2 and 6.5 (1-2 cm coastal horizontal displacement), providing an excellent tool for earthquake early characterization from a tsunamigenic perspective.

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