When the earthquake struck on September 28, 2018, Indonesia's Sulawesi island flowed like water. Currents of mud swallowed anything in their paths, sweeping away entire sections of the city of Palu and crosscutting the region's neat patchwork of crop fields. Minutes after the shaking began, locals were caught unaware by a wall of water that crashed onshore with devastating results.

As the sun set that evening, thousands were missing. Within days, the smell of corpses permeated the air. The 7.5-magnitude event was 2018's deadliest quake, killing more than 2,000 people.

In the efforts to understand how this fatal series of events clicked into place, much attention has focused on the surprise tsunami. But a pair of new