A synoptic view of the natural time distribution and contemporary earthquake hazards in Sumatra, Indonesia

Abstract

Tectonic plate interactions in Sumatra have caused a range of devastating earthquake events. In this study, we develop an analytical framework, known as earthquake nowcasting (Rundle et al. in Earth and Space Science 3:480–486, 2016. 10.1002/2016EA000185), to assess the current dynamical state of earthquake hazards in Sumatra and adjacent islands from the empirical distribution of natural times, the cumulative counts of “small” events (say, M ≥ 4) between two successive “large” earthquakes (say, M ≥ 6.5). Based on 50 years of instrumental earthquake data, the best fit Weibull distribution assigns earthquake potential score between 29 and 96% to 19 large cities in the study region with the values (%) of Aceh (72), Bengkulu (34), Binjai (81), Jambi (35), Lahat (29), Lampung (45), Lhoksuemawe (54), Medan (75), Mentawai (76), Meulaboh (71), Nias (95), Palembang (80), Padang (74), Pekanbaru (39), Sabang (72), Siantar (82), Sibolga (92), Sinabang (96), and Tanjung Balai (55). These areal-source based nowcast scores, analogous to the tectonic stress buildup since the last major event, essentially provides a unique characterization of the current level of seismic progression of a city through its repetitive cycle of regional earthquakes. Inclusion of dependent events with aftershocks being more common and the concept of natural times are some of the distinctive advantages of the proposed method. The resulting natural time statistics and consequent earthquake potential scores will facilitate seismic risk estimation, multistate decision-making, and community awareness, leading to an efficient seismic risk reduction strategy in the densely populated study region.