Large surface wave of the 2004 Sumatra-Andaman earthquake captured by the very long baseline kinematic analysis of 1-Hz GPS data

The 26 December 2004 Sumatra-Andaman great earthquake had a -1500 km long rupture of more than 600 seconds duration, and may have involved a complex rupture process including slow slip. We processed International GNSS Service (IGS) 1-Hz Global Positioning System (GPS) data using kinematic analysis to investigate ground motion caused by this large earthquake. Since there are few 1-Hz stations, we had to process long baseline up to several thousand kilometers long. Long baselines degrade the GPS carrier phase ambiguity resolution. Nevertheless, clear seismic surface waves of the earthquake are recorded in our longdistance kinematic GPS solutions, which are in good agreement with response-corrected broadband seismic record. Our long baseline kinematic GPS solutions clearly indicated directivity of the seismic wave associated by rupture process of this earthquake. Also at the GPS stations that are 2,000 km away from the epicenter, dynamic displacements exceeding 5-10 cm were detected. In contrast, short baseline kinematic analysis shows large strain change caused by passage of surface wave, which reaches 6 x 10(-6). Based on the comparison with seismometer and spectrum analysis of GPS results, it is difficult to discuss for very long time period displacement such as with a period more than 600 seconds in this study.