The Flores Thrust and Its Interplay With Volcanism

Abstract The 2018 Lombok, Indonesia, earthquake sequence demonstrated the important interplay between the deep root of an active volcano and rupture patterns on the Flores Thrust. This backarc fault runs along the north side of the Lesser Sunda Islands and is co‐located with several other large volcanoes that also likely influence its seismogenic zone. As a first step toward better understanding these fault‐volcano interactions, we construct a new 3D model of the Flores Thrust using relocated seismicity and geological constraints. We then develop simple thermal models of the volcanoes and map their interaction with the seismogenic zone of the Flores Thrust. The geometry of our preferred fault model varies along strike, with southward dips ranging from 25° to 32° in eastern Java to Bali, 7°–38° in eastern Bali to western Sumbawa, 31°–47° in eastern Sumbawa to Komodo, 41°–54° in western Flores, and 31°–38° in eastern Flores. Our models exhibit flat‐ramp geometry between eastern Bali and western Sumbawa, corresponding to the extent of the North Bali‐Lombok Basin where its basement acts as a thrust décollement; farther east, the fault is a simple ramp. The maximum seismogenic depth is approximated based on the estimated depth of the 450°C isotherm, which varies depending on the presence of volcanoes. The complex geological history in the region, involving rifting and tectonic inversion, controls the segmented and varying dips of the thrust. Moreover, the progressive growth of the Flores Thrust and the evolution of arc volcanism would also mutually influence each other, modifying both fault geometry and volcano distributions.