Basement structure across Renun segment near Toba caldera inferred from the gravity anomaly: Implication for potential earthquake rupture barrier

Basement structures may influence how ruptures propagate during an earthquake. However, most structural evidence is beneath the thick layer of younger volcanic sediments. In this study, gravity method was applied to discover more features of the basement structure. A land survey of gravity measurement was conducted at 383 stations south of Toba. The observed gravity was then used to generate Complete Bouguer Anomaly and residual-regional anomaly maps. In addition, several edge enhancements based on derivations were applied. All results presented lineations that could be linked to previously recognized active faults and structures. Additionally, the most prominent feature is a large northwest-southeast elongated high anomaly, almost sub-parallel to the Sumatra Fault Zone (SFZ). Since the feature is also located at the continuation of the Medial Sumatra Tectonic Zone (MSTZ), the body might be the hidden part of this major tectonic zone. The occurrence of MSTZ across the SFZ would affect the rupture propagation of earthquake events in the fault segment of the SFZ.