Reevaluation of the Panjang Fault as a Potential Seismic Source in Eastern Lampung, Indonesia: Insights from Integrated Gravity, Seismicity, and Morphotectonic Analyses

Eastern Lampung occupies a complex back-arc tectonic setting, yet its seismic potential remains insufficiently constrained. This study investigates the Panjang Fault, a previously underrepresented Quaternary structure in eastern Lampung, through an integrated analysis of Bouguer gravity anomalies, seismicity, focal mechanisms, morphotectonic indices, and published GNSS (Global Navigation Satellite System) observations. The results reveal a segmented normal-fault system expressed by gravity lineaments, shallow seismicity, and fault-controlled drainage morphology. Low bifurcation ratios (Rb) and locally high Stream Length–Gradient index (SL) indices provide geomorphic evidence of tectonic control on drainage development, while published GNSS observations indicate ongoing crustal deformation within the broader Lampung–Sunda Strait region. The GNSS data is consistent with the extensional tectonic framework inferred from the geological, geophysical, and geomorphological data. Empirical scaling based on fault-segment lengths of 20–60 km yields potential earthquake magnitudes of approximately Mw 6.57–7.20. The findings demonstrate that the back-arc position of the Panjang Fault does not necessarily imply low seismic hazard and highlights the need to consider this structure in future seismic source models and regional hazard assessments. The study provides an integrated framework for recognizing potentially active back-arc faults and improving seismic risk assessment in eastern Lampung.