Unraveling the Slip Behavior and Evolution of the Mai'iu-Goodenough Detachment Fault System by Integrating Multi-timescale Datasets with Novel Coral Paleoseismological Evidence

Low-angle normal faults (LANFs; dip <30°) accommodate kilometers of crustal extension, but it remains unclear whether these faults can host large earthquakes or if they predominantly creep aseismically. We present ²³⁰Th ages from a sequence of distinct platforms of formerly shallow-living fossilized corals killed during uplift-induced emergence of the footwall of the Mai'iu-Goodenough detachment in Papua New Guinea, a fault system that includes one of the world's fastest-slipping active low-angle normal faults, the Mai'iu fault, which slips at rates of 8-12 mm/yr. Coastal morphology and coral ages indicate that rapid slip events on the Mai'iu-Goodenough detachment resulted in episodic uplift. Maximum uplift increments of 0.5-1.8 m imply episodic slip events with an equivalent M_w >7, which we infer to be seismic.

Our multidisciplinary research yields one of the first coral paleoseismological records of normal fault earthquakes and constrains the surface uplift patterns and timing of multiple detachment fault seismic cycles, confirming that these faults can slip in large (M_w >7) earthquakes. Finally, we integrate our kyr-scale coral paleoseismological results with recent datasets from the Mai'iu fault spanning timescales from seconds (preseismic: laboratory friction experiments on fault zone rocks) to years (interseismic: GPS velocities) to millions of years (fault zone microstructures and tectonic geomorphology) to examine the roles depth-dependent on-fault processes play in elastic strain accumulation and release. Our results indicate that heterogeneous frictional coupling and ductile creep at sub-tectonic-loading rates are key processes that facilitate both interseismic creep and coseismic slip on a detachment system hosting the world's fastest slipping active low-angle normal fault.