One century of tectonic deformation along the Sumatran fault from triangulation and Global Positioning System surveys

An analysis combining historical triangulation and recent Global Positioning System (GPS) survey measurements in west and north Sumatra, Indonesia, reveals a detailed slip history along the central part of the Sumatran fault. The are-parallel components of the combined velocity field are consistent with slip rates inferred from GPS data, ranging from 23 to 24 mm/yr. Between 1.0 degreesS and 1.3 degreesN the Sumatran fault appears to be characterized by deep locking depths, of the order of 20 km, and the occurrence of large (M-W similar to 7) earthquakes. The long-term (1883-1993) strains show simple right-lateral shear, with rates similar to GPS-measured, 1989-1993 strain rates. Coseismic deformation due to the 1892 Tapanuli and 1926 Padang Panjang earthquakes, estimated from triangulation measurements taken before and after the events, indicates that the main shocks were significantly larger than previously reported. The 1892 earthquake had a likely magnitude of M-W approximate to 7.6, while the 1926 events appear to be comparable in size to the subsequent (M similar to 7) 1943 events and an order of magnitude higher than previously reported.