THE SUMATRAN FAULT ZONE — FROM SOURCE TO HAZARD

The substantial portion of the dextral component of the Sumatran oblique convergence is accommodated by the Sumatran fault. This 1900 km-long active strike-slip fault zone runs along the backbone of Sumatra pose seismic and fault hazards to dense population on and around the fault zones. The Sumatran fault is highly segmented, and consists of 20 major geometrically defined segments, which range in length from about 60 to 200 km. These segment lengths influenced seismic source dimensions and have limited the magnitudes of large historical fault ruptures to between Mw 6.5 and about 7.7. Slip rates along the fault increase northwestward, from about 5 mm/yr around the Sunda Strait to 27 mm/yr around Toba Lake. These sliprate values provide a quantitative basis for calculation of average expected recurrence periods for large earthquakes on each segment. Deterministic and probabilistic hazard assessments are constructed based on these active fault data.