The earthquake itself was a Strike-slip fault whose mechanism generally does not trigger tsunamis. It can be perceived that something which occurred at sea floor or along the coast may have caused the multiple tsunamis. As a result of his survey at Palu and surrounding areas, Professor Imamura concludes that the quake caused a landslide at sea floor, thus triggering the tsunamis. This is due to the geographical features of Palu Bay that is vulnerable to landslides.

BMKG (Badan Meteorologi, Klimatologi, dan Geofisika; the Meteorology, Climatology, and Geophysical Agency of Indonesia) states that a tsunami warning was issued, but the warning was cancelled in less than an hour because the epicenter was on land, the magnitude was low (too low to cause a significant tsunami) and the mechanism lateral.

Additionally, real-time observation data of the tsunami could not be transmitted due to the blackout in several areas. The actual time the tsunami that reached the island and the time the tsunami warning was canceled is unidentified. Such a tsunami is difficult to predict even in Japan and remains an issue.

Because of difficulties in traveling to the affected area due to the damages by earthquake and tsunami, in-depth survey was limited to the inner part and east coast of Palu Bay. The area located 50 meters from the coastline had especially significant damage, where buildings were swept away leaving only the foundations. The overpass destroyed by the tsunami bears marks which show that the tsunami reached 5 meters. On the other hand, the more inland area had approximately 1 to 2 meters and the damage was relatively small compared to an average tsunami. According to local citizens, the statue of a white horse was swallowed up by the tsunami or the water level reached the hooves of the horse, it is estimated that the tsunami may have reached a height of 10 meters.

Tsunamis caused by sea bottom landslides have also previously occurred in Japan. On August 11, 2009, a 6.5-magnitude earthquake with a seismic intensity of 6, struck Suruga Bay causing a landslide at sea bottom, triggering a 1-meter tsunami. Fortunately, there was no damage. We hope to continue supporting the recovery of the affected area and utilize our knowledge and experience in regards to tsunami disasters in Japan--especially about warning systems—in planning future countermeasures.