Real-time monitoring of crustal deformation using large GPS geodetic networks - Replay of two major earthquakes with Japanese GEONET 1 Hz data

Dense regional GPS geodetic networks have been successfully established to monitor crustal deformation and associated natural hazards. Procedures for early warning and rapid damage assessment, which are especially important in heavily populated areas, however, have, in most cases, not yet been fully incorporated into the data analysis of these networks. The GPS Earth Observation Network System (GEONET) in Japan, maintained by the Geographical Survey Institute (GSI), consists of an analysis center and an array of 1200 GPS stations that cover the entire country with an average spacing of about 20 km. In the past, precise site positions were calculated only once per day. Since 2001 GSI has been working toward real-time observations and analysis. Now, most sites sample at 1 Hz and transmit the measurements in real time to the analysis center. Using GEONET data from the time of the Mw=8.0 Tokachi-Oki earthquake (September 25, 2003) and the Mw=9.2 Aceh-Andaman earthquake (December 26, 2004) as test cases, this study demonstrates a real-time applicable bootstrapping method to determine accurate absolute static and dynamic station motion for these two major events. We demonstrate that coherent instantaneous (horizontal) position changes detected by a dense GPS network (like GEONET) could be used as part of an early warning system for mitigating natural hazards.