Timor Collision Front Segmentation Reveals Potential for Great Earthquakes in the Western Outer Banda Arc, Eastern Indonesia

Aurélie Coudurier-Curveur,Ian Deighton,Satish C. Singh

doi:10.3389/feart.2021.640928

Abstract

In Eastern Indonesia, the western Outer Banda arc accommodates a part of the oblique Australian margin collision with Eurasia along the Timor Trough. Yet, unlike the Wetar and Alor thrusts of the Inner Banda arc in the north and the adjacent Java subduction zone in the west, both recent and historical seismicity along the Timor Trough are extremely low. This long-term seismic quiescence questions whether the Banda Arc collision front along the Timor Trough is actually fully locked or simply aseismic and raises major concerns on the possible occurrence of large magnitude and tsunamigenic earthquakes in this vulnerable and densely populated region. Here, we jointly analyze multibeam bathymetry and 2D seismic reflection data acquired along the Timor Trough to characterize the location, nature, and geometry of active faults. Discontinuous narrow folds forming a young accretionary prism at the base of the Timor wedge and spatially correlated outcropping normal faults on the bending northwest Australian shelf reveal two concurrent contrasting styles of deformation: underthrusting and frontal accretion. We find that those tectonic regimes and their associated seismic behaviors depend on 1) the thickness of the incoming and underthrusting Cenozoic sedimentary sequence, 2) the vergence of inherited normal faults developed within the continental shelf, and 3) the depth of the décollement beneath the Timor wedge. Based on the along-strike, interchanging distinct deformation style, we identify the mechanical and seismic segmentation along the Banda arc collision front and discuss the implications for earthquake and tsunami hazards along the western Outer Banda arc region.

Highlights

The deadliest Mw 7.8, 1992 Flores and the Mw 7.5, 2004 Alor earthquakes and tsunamis have forced the scientific community to reassess the geohazards potential in the vulnerable, densely populated coastal Banda arc region (e.g., Harris and Major, 2016; Koulali et al, 2016; Cummins, 2017)
Topographic, and seismic data analyses reveal two distinct tectonic regimes varying from total underthrusting to total accretion, which are seemingly controlled by inherited structures of the northwest shelf in the Jamdena region (Figures 5, 6A)
Based on similar morphological characteristics highlighted both on the northwest Australian shelf and in the Timor wedge, we assume that comparable tectonic wedge architectures and tectonic regimes lie in the Roti region as well, for which we do not have any seismic constraints

Summary

Introduction

The deadliest Mw 7.8, 1992 Flores and the Mw 7.5, 2004 Alor earthquakes and tsunamis have forced the scientific community to reassess the geohazards potential in the vulnerable, densely populated coastal Banda arc region (e.g., Harris and Major, 2016; Koulali et al, 2016; Cummins, 2017). These earthquakes occurred on northward verging backthrust north of the Inner Banda arc. Historical earthquake records of the past four centuries point toward sources along those same structures, revealing devastating, megathrust earthquakes and tsunamis along the Seram and Tanimbar troughs (e.g., M8.2/8.5, 1629 Seram Trough; Mw > 8.4, 1852 Banda arc; M8.5, 1938 Banda Sea, Figure 1) (Wichmann, 1918; Okal and Reymond, 2003; Liu and Harris, 2013; Fisher and Harris, 2016; Harris and Major, 2016)

Objectives

Findings

Discussion

Conclusion