 Ramba uchinyora ndima iyi - Gungwa reToba riri pedyo neGreat Sumatra Fault, iyo inoenda nechepakati peSumatra muSumatra Fracture Zone. Makomo anoputika eSumatra neJava chikamu cheSunda Arc, mugumisiro wokufamba kuchamhembe kwakadziva kumabvazuva kweIndo-Australian Plate, iyo iri kutsvedza pasi peEurasian Plate iri kufamba ichienda kumabvazuva. Nzvimbo inochera mvura iri munharaunda iyi inoshanda zvikuru: pasi pegungwa riri pedyo nemhenderekedzo yokumadokero yeSumatra pakava nokudengenyeka kukuru kwakawanda kubvira muna 1995, kusanganisira kudengenyeka kwenyika kwakaitika muna 2004 muIndian Ocean kwakakura 9.1 uye kudengenyeka kwenyika kwakaitika muna 2005 kuNiasSimeulue kwakakura 8.7, ine nzvimbo dzayo dzakakomberedza Toba. 