Seismic Activity in Indonesia

Indonesia is a seismically very active country. The United States Geological Survey (USGS) lists Indonesia as the country with the most earthquakes in the world¹. The archipelago's geological predisposition to seismic activity is attributed to its strategic location along the Pacific Ring of Fire, an expansive volcanic and seismic belt that encompasses approximately 81 percent of recorded earthquakes worldwide. This geological phenomenon is characterized by a convergence of intense tectonic activity, manifesting in the relentless interplay of subterranean forces. 

Indonesia lies in the intersection with three major tectonic plates: the Indo-Australian Plate, the Eurasian Plate, and the Pacific Plate. The constant interaction of these plates, along with the interaction with several other minor plates such as the Philippine Sea plate and the Caroline plate, amplifies the geological complexity of the region. This convergence of tectonic plates generates a dynamic landscape where the Earth's crust is in a constant dynamic, leading to the frequent occurrence of earthquakes and volcanic eruptions.

In this blog post, we will explore seismicity in Indonesia.

Picture 1: Ring of fire.

Earthquake and Volcano Activity in Indonesia

According to the United States Geological Survey (USGS), in 2020 within a range of 300 km, 1692 earthquakes with a magnitude of more than 4.0 occurred in Indonesia (among them were 1471 between 4.0 and 4.9, 113 earthquakes with a magnitude between 5.0 and 5.9, and 10 earthquakes with a magnitude above 6.0), which is 37 less than the subsequent year of 2021, when it witnessed 1730 earthquakes with a magnitude above 4.0 (among them were 1555 with a magnitude between 4.0 and 4.9, 121 with a magnitude between 5.0 and 5.9, and 11 above 6.0). To compare, in the year 2022, Indonesia experienced 1791 earthquakes with a magnitude of more than 4.0, among which 10 were of a magnitude larger than 6.0, according to the EMSC.

Indonesia, besides being recognized as an earthquake-prone nation, also deals with a diverse array of natural calamities, ranging from volcanic eruptions to floods and tsunamis. It has a lot of volcanoes, especially in places like Sumatra, Java, Bali, and the eastern islands. More than 200 of them are scattered across the country. While these volcanoes make Indonesia's scenery stunning, they also make the area more prone to volcanic eruptions. This means there's a continuous risk to the safety of the people who live there. The landscape might look beautiful, but it comes with a potential danger that the people have to be aware of and prepared for. Due to its disastrous natural disasters, Indonesia has made global headlines on several occasions in recent years with worldwide reports on the loss of hundreds of thousands of people’s lives and the devastating effects incurred on the infrastructure and economy.

Picture 2: Indonesia's earthquake consequences.

Lombok Earthquakes in 2018

Indonesia has experienced several significant earthquakes throughout its history. One of the recent ones were the so-called magnitude 7.5 Lombok earthquakes in 2018, a series of seismic events that struck the island of Lombok in Indonesia. The earthquakes occurred in July and August 2018, causing significant damage to buildings and infrastructure, as well as resulting in casualties and displacements. It occurred on September 28, 2018, and triggered a large tsunami causing more than 2,000 fatalities, more than 4,000 serious injuries, more than 600 missing people, and about 68,000 damaged or destroyed houses³.

Thousands of residents were displaced from their homes, seeking shelter in makeshift camps or evacuation centers. The displacement added to the challenges faced by local authorities in providing immediate assistance and addressing the humanitarian needs of the affected population. Search and rescue operations were launched to locate survivors trapped in the debris of collapsed structures. These efforts involved local authorities, national agencies, and international organizations working together to respond to the emergency and provide aid to those in need.

In the aftermath of the earthquakes, efforts were made to provide humanitarian assistance, medical aid, and temporary shelters to those affected. The Indonesian government, along with non-governmental organizations and the international community, engaged in ongoing recovery and rebuilding initiatives to help the affected communities recover and reconstruct.

2021 West Sulawesi earthquake

A magnitude 6.2 earthquake hit Majene Regency in West Sulawesi, Indonesia, on the 15th of January 2021, at 02:28 local time. with the maximum Modified Mercalli intensity of VI (Strong) in Majene and Mamuju. The epicenter was located 32 km (20 mi) south of Mamuju. It was preceded by a magnitude  5.7 foreshock several hours prior.  Four of the five regencies in West Sulawesi were affected and more than 6,000 structures were damaged or destroyed. Additionally, at least 105 people were confirmed dead; more than 3,300 were injured and thousands were displaced. The complete damage was estimated at Rp829.1 billion rupiah.

Largest earthquakes in Indonesia

The catastrophic earthquake that struck Indonesia on the 26th of December 2004, was a seismic event of unprecedented magnitude and devastating consequences. This underwater earthquake, measuring a staggering 9.1 in magnitude, occurred off the west coast of northern Sumatra. The impact of this seismic activity extended far beyond the initial tremors, as it triggered one of the most destructive tsunamis in recorded history, a 100-foot-tall tsunami killing more than 200,000 people and leaving thousands of communities in ruins². These tsunamis surged towards the coastal regions of several countries bordering the Indian Ocean, including Indonesia, Thailand, Sri Lanka, India, and many others.

Picture 4: Indonesia's strongest and deadliest earthquake location.

The toll of this catastrophic event was both immediate and profound. The tsunamis struck with relentless force, inundating coastal areas, sweeping away entire communities, and leaving a path of destruction in their wake. The human cost was staggering, with the loss of over 200,000 lives. The scale of the disaster left thousands of families bereaved, and countless others faced the arduous task of rebuilding their lives amidst the ruins.

Furthermore, the impact on infrastructure was equally severe, as homes, schools, hospitals, and vital services were displaced by the force of the waves. The widespread devastation prompted an international humanitarian response, with nations, organizations, and individuals around the world mobilizing to provide emergency aid, medical assistance, and support for the displaced survivors.

In the aftermath of the 2004 Indian Ocean earthquake and tsunami, significant efforts were made to enhance early warning systems and disaster preparedness measures globally, particularly in regions prone to seismic activity and tsunamis. The tragedy underscored the need for international collaboration in monitoring and responding to natural disasters, with the establishment of the Indian Ocean Tsunami Warning System (IOTWS) being one notable outcome.

The five largest earthquakes since 2000 in Indonesia are:
- M8.2 Wharton Basin 2012-04-11 earthquake;
- M8.4 Sumatra 2007-09-12 earthquake (23 fatalities, 88 injured);
- M8.6 Wharton Basin 2012-04-11 earthquake (10 fatalities, 12 injured);
- M8.6 Sumatra 2005-03-28 earthquake (1,314 fatalities, 1,145 injured);
- M9.1 Sumatra-Andaman 2004-12-26 earthquake (167,540 fatalities in Indonesia, more than 200,000 injured).

Below is a selected list of recent earthquakes that caused severe damage and at least 20 fatalities⁴:

Earthquakes are one of the biggest threats to Indonesia in terms of natural disasters as they often strike in populous areas such as the bigger cities, making many people lose their lives, homes, and property. According to the USGS, earthquakes with a magnitude of around five on the Richter scale occur almost daily in Indonesia, but often with little to no damage. More devastating earthquakes are the ones with a magnitude above six on the Richter scale.

The great degree of material damage is exacerbated by the poor state of the country’s infrastructure, which only increases the devastating consequences of earthquakes.

You might ask, why haven’t more solid, earthquake-resistant facilities been developed in such an earthquake-prone country? It could be because of mismanagement, limited financial resources, a lack of skills, or corruption⁴.

Because of the weak infrastructure, even moderately strong earthquakes can result in the collapse of buildings and the loss of lives. If a strong earthquake were to strike a mega-city such as Jakarta, Surabaya, Medan, or another with an extremely high population density, the consequences could be as never seen before.

Pictures 3: Indonesia's strongest and deadliest earthquake consequences.

When it comes to natural disasters in Indonesia, we need to keep in mind that we are talking about a relatively poor country, where many people struggle to get through the day. A poor country that lacks basic necessities needs even more time and resources to recover after suffering a natural disaster. The most vulnerable victims are people with low incomes and those living in poverty.

What lies ahead?

To sum it up, Indonesia experiences a lot of earthquakes daily because of its position on the Ring of Fire. The place is like a hot zone for these ground-shaking events due to big tectonic plates moving around underneath. It is, therefore, essential for Indonesia to be ready for these natural challenges, making sure people, buildings, and communities are prepared.

Sources:
1) USGS. Which country has the most earthquakes? Accessed on 15-Jun-2022. Available at: https://www.usgs.gov/faqs/which-country-has-most-earthquakes
2) National Public Radio (NPR). 2022. Searchers dig into the rubble after an earthquake hit Indonesia. Accessed on 15-Jun-2022. Available at: https://www.npr.org/2022/02/26/1083275522/indonesia-earthquake-search-victims?t=165527229606
3) Worldvision. 2018 Indonesia quakes and tsunamis: Facts, FAQs, and how to help. Accessed on 15-Jun-2022. Available at: https://www.worldvision.org/disaster-relief-news-stories/2018-indonesia-earthquake-facts#:~:text=28%2C%202018%2C%20triggering%20a%20tsunami,the%20Indonesia%20disaster%20management%20agency
4) Indonesia Investments. Natural Disasters in Indonesia. Accessed on 15-Jun-2022. Available at: https://www.indonesia-investments.com/business/risks/natural-disasters/item243