Earthquakes Are Common in Indonesia, but Mitigation Measures Are Lacking

On November 21, at 1:21 p.m. local time, an earthquake with a magnitude of 5.6 struck Cianjur Regency in West Java. The 10-kilometer-deep earthquake caused buildings and cliffs to collapse, killing up to 327 people.

Meanwhile, the number of people missing following the earthquake in Cianjur Regency has risen to 13. The earthquake also resulted in 108 serious injuries, which were all treated at nearby hospitals. Outpatient treatment is continuing for 40 of the 108 injured victims. So far, 73,874 people have been displaced because of the Cianjur earthquake. They are distributed across 194 evacuation points in eight districts in Cianjur, West Java.

Active fault activity caused the earthquake. The characteristics of these active faults, however, are unknown. The site was in the northeastern part of the Cimandiri fault zone. Until November 28, or eight days after the first earthquake, there had been 305 aftershocks. However, the activity of aftershocks with fluctuating magnitudes is getting smaller, as is the frequency of occurrence, which is getting rarer.

Indonesia Is Prone to Earthquakes

Indonesia is prone to geological disasters like earthquakes. The interaction of four tectonic plates in Indonesia, namely the Eurasian Plate, the Indo-Australian Plate, the Pacific Plate, and the Philippine Sea Plate, handles this.

When these plates collide, they form front basins, back basins, magmatic pathways, geological structural patterns, and earthquake sources known as subduction zones, collision zones, and active faults.

From 2000 to 2021, Indonesia experienced 5 to 26 destructive earthquakes per year, with the most occurring in 2021 with 26 events. The occurrence of a destructive earthquake means the earthquake caused casualties, building damage, environmental damage, and property loss.

The number of destructive earthquakes expected in 2021 is the highest in the last 20 years. Most of the damaging earthquakes in 2021 occurred on active faults, with some occurring on subduction zones. Since 2015, the frequency of damaging earthquakes has been fluctuating.

Aside from 2021, Indonesia experienced a significant number of destructive earthquakes in 2017, with 19 incidents. Returning to 2021, the occurrence of damaging earthquakes began on January 4, 2021, with an earthquake in Morowali, Central Sulawesi Province, and ended on December 30, 2021, with an earthquake in Southwest Maluku, Maluku Province.

The active Matano fault caused the Morowali earthquake, which had a magnitude of 4.9. While the subduction of the Banda Sea Plate caused the 7.4-magnitude earthquake in Southwest Maluku. There were no fatalities because of the two earthquakes.

The most severe earthquake in 2021 occurred on January 15, 2021, in Mamuju and Majene Regencies, West Sulawesi. This earthquake, with a magnitude of 6.2, killed 106 people and seriously injured 278 others. There were 6,478 minor injury victims reported in Mamuju Regency, with 2,493 in Majene. The total damage and losses caused by the West Sulawesi earthquake reached IDR 829.1 billion.

When viewed from a global perspective, earthquakes continue to be a disaster that claims many lives. Since the 2000s, earthquakes have claimed many lives, reaching 100 thousand in 2004 and 2010. The Aceh earthquake and tsunami in 2004 and the Port-au-Prince earthquake in Haiti in 2010 were the two events.

The magnitude-9 earthquake that struck Aceh on December 26, 2004, caused a tsunami and killed at least 165 thousand people. According to Our World in Data, the total number of deaths is close to 228 thousand people. While the earthquake in Haiti killed 316 thousand of people, the exact number of victims is still being debated.

Aceh's earthquake and tsunami is ranked seventh out of ten major deadly earthquakes in history. The first deadly earthquake sequence occurred in China in 1556, killing about 830 thousand people. The magnitude of the earthquake was 8 on the Richter scale.

Mitigation Is Minimal

Indonesia is a disaster-prone area. Some areas are more dangerous than others. Fifteen provinces are classified as having a high disaster risk, while 19 are classified as having a moderate disaster risk. No province is immune from natural disasters.

West Sulawesi, the Bangka Belitung Islands, and Maluku are the provinces most at risk. At the regional level, Cianjur Regency is listed as one of the top 20 areas with high disaster risk. Southwest Maluku and Majene, which were recently hit by a powerful earthquake in 2021, are the areas most vulnerable to disaster.

Aside from the 20 regions, there are 221 areas in Indonesia classified as having a high disaster risk out of 514 regencies or cities. This means that 42.99 percent of areas in Indonesia have a high disaster risk potential, accounting for nearly half of all regencies or cities. Meanwhile, the remaining 292 regions have a moderate disaster risk index, accounting for 56.8 percent of the total area. There are no areas with a low disaster risk index, as previously stated.

From 2015 to 2021, Cianjur Regency has been classified as having a high disaster risk. Unfortunately, the Cianjur Regency government provides disaster mitigation funds in 2022 that are quite small, accounting for only about 0.05 percent of the total regional budget. The capital expenditure for river/coastal protection and disaster management amounted to IDR 2.1 billion of the IDR 4.34 trillion total regional expenditure budget.

During the Palu earthquake and tsunami in 2018, a similar pattern was observed in Central Sulawesi Province. In 2017, the Central Sulawesi government provided only 0.1 to 0.3 percent of the total regional budget for disaster mitigation.

Disaster mitigation funds should ideally amount to 1 percent of the total regional budget. Other preparations, such as natural disaster early warning systems, tsunami early warning systems, safety equipment, and evacuation routes in the regions, must be improved besides the allocation of funds.

In West Java, for example, only 823 villages and sub-districts out of 5,957 have an early warning system for natural disasters as of 2018. Only 147 of Maluku's 1,240 villages and sub-districts have early warning systems for natural disasters.

Indeed, based on the historical occurrence of earthquakes in Indonesia that claimed thousands to hundreds of thousands of lives, as well as earthquake records, and the location of the Indonesian country that is prone to disasters, damaging earthquakes could occur again.

The Cimandiri fault, for example, has caused earthquakes frequently. At least seven major earthquakes have occurred in the twentieth century, including the Pelabuhan Ratu earthquake, the Cibadak earthquake, the Gandasoli earthquake, the Padalarang earthquake, the Tanjungsari earthquake, the Conggeang earthquake, and the Sukabumi earthquake.

A magnitude 8.9 megathrust earthquake in southern Java and southwest Sumatra is possible. This earthquake has the potential to cause a 34-meter tsunami. The government must prepare by implementing mitigation measures so that the impact is not as severe as the earthquake in Cianjur, which killed hundreds of people.

Natural disasters have previously been predicted, besides a 34-meter tsunami caused by a megathrust earthquake in the south of Java Island to Sumatra, like the Palu liquefaction phenomenon, which was predicted in 2012 and occurred in 2018. However, this prediction received little attention, as the government took only minor mitigation measures during the Palu earthquake.