How fast can low-angle normal faults slip? Insights from cosmogenic exposure dating of the active Mai’iu fault, Papua New Guinea

Abstract

Abstract Is there an upper limit to normal fault slip rates? The Mai’iu fault, located within the rapidly extending Woodlark Rift, Papua New Guinea, is one of few active continental low-angle normal faults (LANFs) globally. There is ongoing debate regarding how commonly normal faults slip at shallow (<30°) dips, and at what rates. We present a global compilation of reported slip rates on active and inactive extensional detachments that suggests that such faults may slip at >10–20 mm/yr—faster than any reported high-angle normal fault. Cosmogenic nuclide exposure dating (10Be in quartz) of the lowermost Mai’iu fault scarp supports this finding, indicating slip at 11.7 ± 3.5 mm/yr over the past ∼5.5 k.y. Our results highlight the long-term viability of LANFs, and show that the Mai’iu fault represents one of Earth’s fastest active continental normal faults. Rapid and large-displacement slip is likely enabled by extremely low fault frictional strength.