Present-day Interseismic Deformation in Northern Sumatra and Its Seismic Implications Derived from GNSS Data

The Sumatra region exhibits a complex tectonic configuration resulting from the oblique subduction of the Indian/Australian plate beneath the Sunda Block. This process has generated several great earthquakes, including the 2004 M_W9.2 Sumatra-Andaman and the 2005 M_W8.7 Nias-Simeulue earthquakes. In contrast, the central segment near Siberut Island has remained unruptured in recent history, indicating a seismic gap that continues to accumulate strain. Global Navigation Satellite System (GNSS) observations from 70 continuous stations operated by the Sumatran GPS Array (SuGAr) and the Geospatial Information Agency of Indonesia (BIG), with the time period from 2015 to mid-2023, were analyzed to quantify interseismic strain accumulation and evaluate earthquake potential along the Sumatra subduction zone. The interseismic deformation model reveals that the overall slip deficit rate corresponds to an earthquake of approximately M_W8.9 using a recurrence interval of ~ 226 years. This research highlights the current end stage of the 1797 seismic cycle, which may culminate in a future rupture, and estimates a recurrence interval of approximately 258 years for the 2005 Nias earthquake.