According to a Science News report, drill cores and photos of the seabed, taken in January and February of 1999, showed signs of repeated slumps. Tappin was a co-leader of the research team whose results were reported in the July 27 edition of the journal Eos. The slump theory sidesteps several problems that arise from trying to blame the New Guinea waves on an earthquake alone. It didn't directly. Instead, it destabilized rocks and mud that slid down the steep hillside and displaced enough water to cause the giant waves.
Slumps commonly follow earthquakes by several minutes.
Computer models of the waves worked better if a slump, not a quake, was the cause. Unfortunately, solving a scientific problem may raise a practical one for people living along earthquake-plagued coastlines. If minor quakes can trigger major slumps, areas like the West Coast of the United States could face larger tsunami hazards than indicated by the size of undersea earthquakes.