Tipping the balance: what makes slow earthquakes episodic?

Subduction zones, where one tectonic plate descends beneath another, produce the planet’s largest earthquakes and tsunami; but what controls the timing of fault slip in these events? The recent discovery of frequent, semi-predictable slow-motion earthquakes (lasting days to years) on subduction faults, provide an untapped opportunity to investigate what tips the balance on these faults, causing them to fail. Slow-motion earthquakes on the Hikurangi subduction zone offshore New Zealand’s east coast are remarkable for the range of slow and fast (seismic) slip processes occurring at shallow depths (