2018 Sulawesi earthquake and tsunami

Date: September 28, 2018

Place: Central Sulawesi Province on the island of Sulawesi in Indonesia

Result: A 7.5 magnitude earthquake followed by several aftershocks struck a mountainous region of Indonesia’s Sulawesi island, triggering a deadly tsunami. The earthquakes and tsunami left more than 4,300 people dead and damaged or destroyed more than 40,000 structures.

Overview

Sulawesi is the fourth largest island of Indonesia, a Southeast Asian nation consisting of more than 13,400 islands. Indonesia is very geologically active and earthquakes and volcanic eruptions are common in the region. Sulawesi itself is located near the point where three major sections of Earth’s crust—the Australian, Philippine, and Sunda plates—come together. The areas where these plates meet are called fault zones, one of which, the Palu-Koro fault, runs through the northeastern section of the island. The Palu-Koro fault is an example of a slip-strike fault, a type of fault where the plates move either left or right horizontally along the fault line with very little upward or downward motion.

On the afternoon of September 28, 2018, the Palu-Koro fault began moving and triggered a strong magnitude 6.1 earthquake. Early reports claimed one person was killed and several buildings damaged by the quake. The initial shock was followed by twenty-seven aftershocks before an even stronger 7.5 magnitude earthquake struck about three hours later. The quake’s epicenter was located in the mountains about 48 miles (77 kilometers) north of Palu, a city with a population of about 330,000 people. The earthquake caused severe damage and a number of fatalities in Palu and in the province of Central Sulawesi. It also raised concerns of a possible tsunami.

The Indonesian Agency for Meteorology, Climatology and Geophysics initially issued a tsunami warning, but later canceled it. Typically, a slip-strike fault does not produce powerful tsunamis as the horizontal moment of the fault does not displace large amounts of water. While the quake was powerful, it occurred on land, which also would have seemed to lessen the chance for a devastating tsunami. However, some scientists believe that the quake may have caused a tsunami that was funnelled by the narrow geography of Palu Bay and magnified into a stronger wave. Another theory states that the tsunami was caused by massive landslides cascading into the waters of the bay.

No matter the cause, a large series of tsunami surges formed in Palu Bay and began crashing into the coastline, reaching heights of about 18- to 20-feet (5.5- to 6.1-meters) tall. The tsunami hit so quickly that many people were taken by surprise by the wall of water. Compounding the problem was that more than five hundred of the region’s communication towers had been damaged by the earthquake and were inoperable. Tsunami sensors placed in the bay also did not work properly or provided inaccurate data, leading officials to underestimate the threat.

The first tsunami surge hit just after 6 p.m. and smashed into beachfront structures, turning debris into deadly floating wreckage and carrying away hundreds of people. The powerful water surges liquefied the soil and pulled whole houses from the ground, wiping out entire neighborhoods in some places. The waves flattened numerous structures including bridges, mosques, hotels, and shopping centers, leaving dozens trapped amid the rubble. News accounts after the waters began to recede reported that the beaches of Palu were strewn with hundreds of bodies. Many victims were feared to have been washed out to sea.

Impact

The city of Palu and the nearby region of Donggala were hardest hit by the earthquake and tsunami. Palu itself was devastated and left with no drinking water or electricity for days after the disaster. Rescue workers were slowed in their attempts to reach trapped people by a lack of heavy equipment and were forced to search the rubble by hand. More than fifty people were believed to have been trapped in the collapsed rubble of the eight-story Roa Roa Hotel in Palu. Six survivors were later pulled out alive. With so many people killed, authorities were forced to bury many of them in mass graves soon after the victims were identified. At the time of the disaster, the city was hosting the Palu Nomoni Festival, an annual cultural event that attracts thousands of people. Some of those killed were in Palu for the three-day festival.

As of May 2019, the death toll from the Sulawesi earthquake and tsunami was estimated at 4,340 people, with 2,141 of the deaths occurring in Palu. More than 1,000 bodies had not been identified into 2019. Another 667 people were declared missing and more than 10,000 people were injured. The disaster was the world’s deadliest in 2018 and the worst to hit Indonesia since a 2004 earthquake and tsunami killed more than 225,000 people across the Indian Ocean.

More than 3,600 buildings were completely destroyed and another 9,181 were severely damaged. In total, more than 42,000 structures were reported to have suffered some form of damage. A state of emergency was declared in the province of Central Sulawesi and remained in place until October 26, 2018. Some survivors were still living in emergency shelters as of February 2019, prompting complaints of a poorly planned and slow disaster response by the government.

Some researchers believe the soil liquefaction caused by the earthquake and tsunami surges was the most widespread ever observed during such an event. The soil liquefaction was blamed for several mudslides near Palu. Scientists investigating the disaster claimed the unexpected way the earthquake and tsunami occurred made it difficult for the early-warning system to properly forecast the event correctly. Sensors indicated the incoming waves would come ashore at a height of 2–9 feet (0.6–2.7 meters), not with the devastating force that actually occurred.

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