We have conducted geodetic and geomorphic observations in the northernmost part of Sumatra, Indonesia to monitor strain accumulation in the vicinity of the northern Sumatran fault. Evaluation of the earthquake generation potential in this region is highly urgent because of a large fault slip rate, absence of major earthquakes for more than 100 years and recent Coulomb stress increase on the fault due to the 2004 Sumatra-Andaman earthquake (Mw 9:2).We have deployed Aceh GPS Network for the Sumatran Fault System (AGNeSS) since 2005. The data collected have been used for estimating slip/locking distribution of the Sumatran fault and constructing a comprehensive model for postseismic deformation after the 2004 event. Tectonic geomorphic features are also important to reveal long-term slip history of the fault. We have used high-resolution stereo-paired ALOS (Advanced Land Observing Satellite) PRISM (Panchromatic Remote-sensing Instrument for Stereo Mapping) satellite images to map the surface trace of the Sumatran fault and conducted field observations to ensure the trace by geomorphic and geologic evidence. We introduce preliminary results of the fault mapping together with a brief description of the crustal deformation field detected by GPS.