Measuring Seismic Waves Induced by Large Earthquakes with GPS

Independent GPS position solutions at 1-sec interval, derived from the International GPS Service (IGS) data and orbit÷clock products, clearly show seismic waves generated by the magnitude 7.9 Denali Fault, Alaska earthquake of November 3, 2002. Surface seismic waves with periods of about 20 sec and amplitudes of up to 20 cm were detected up to 4,000 km from the epicenter. This confirms the previous findings reported by Larson et al. (2003); we use additional station data along with different processing software and strategies. The seismic waves from the May 26, 2003 magnitude 7.0 Japanese earthquake were also observed in the 1-sec position solution series at station MIZU, about 80 km from the epicenter. This earthquake, however, could not be detected by GPS at station USUD, about 410 km away. Similarly, the Algerian May 21, 2003 earthquake of magnitude 6.8 could not be detected by GPS at the nearest IGS station located approximately 800 km from the epicenter.