GNSS VELOCITY AND STRAIN FIELD IN THE NORTHERN SUMATRA 15 YEARS AFTER THE 2004 M9.2 SUMATRA ANDAMAN EARTHQUAKE

The 2004 M9.2 Sumatra-Andaman earthquake in the tectonically active northern Sumatra, could generate postseismic deformation up to a recent period and needs to be considered for earthquake potential study. The GNSS velocities before and 15 years after the earthquake were used to obtain preliminary indicator of whether the postseismic deformation still takes place. Recent velocities were calculated from the horizontal coordinate time series that is obtained using Bernese GNSS software version 5.2. To do this, a comparison was made of velocities and strain rates over two periods. The velocities of 5.5 to 40.5 mm/yr and the strain rate up to 47.2 μstrain/yr were obtained from the recently acquired GNSS data. The pattern for the two-period values can be defined where the direction of vector velocities is trenchward, and extensional behavior occurs more often in the northern area. This indicates that postseismic deformation still occurs therein even 15 years after the earthquake.