Situated on the Ring of Fire, the ASEAN region faces one of the greatest threats of natural disaster due to geophysical activity along this active belt of tectonic plates. Following on from volcanoes in the last edition, another key disaster threat categorised into the geophysical type are earthquakes, as well as a range of related disasters that can occur as the result of earthquake activity. Earthquakes are another form of geophysical events that have triggered disasters in ASEAN during recent times. Therefore, understanding the varieties and impacts of earthquakes is important for disaster management across the region.

The AHA Centre receives ongoing information regarding earthquakes as they take place across the region. Considered relatively unpredictable, earthquake occurrences are therefore more often than not the focus of both response and preparedness activities for the AHA Centre team. As with volcanoes, Indonesia’s geographical location sees it experience earthquakes of various sizes on an almost daily basis, with their impact highly dependent upon a range of influencing factors such as force, depth, location and vicinity to human populations and infrastructure.

2018 has seen more than its fair share of significant earthquake events, particularly across Indonesia. A number of major earthquakes during August and September caused widespread death and damage on the island of Lombok and its surrounds, while most recently a 7.4M event shook central Sulawesi, causing not only extreme devastation from the earthquake itself, but a resulting tsunami that has affected millions of people. Other significant ASEAN earthquakes in recent times include:

7.2M quake that killed over 200 people in Bohol, the Philippines 2013;
6.9M earthquake that killed approximately 100 people in Myanmar, 2011;
7.6M earthquake that caused over 1,000 deaths in Padang, Indonesia 2009; and
9.1-9.3M earthquake (and resulting tsunami) with an epicentre off Aceh, Indonesia, that resulted in the loss of over 220,000 lives, and displaced millions across 14 countries, including Indonesia, Thailand, Myanmar and Malaysia.

ABOUT EARTHQUAKES

An earthquake, identified by a shaking of the earth, are most often caused by movement of geological fault lines (along the edges of the earth’s tectonic plates) – known as an inter-plate earthquake. The three main types of faults that can result in these earthquakes are known as ‘normal’, ‘reverse thrust’ and ‘strike-slip’ faults. The first two types of fault occur when two plates meet, resulting in movement that is vertical in nature (dip-slip movement). The third, strike-slip faults, are characterised by two plates meeting and sliding past each other horizontally. While most of the earthquakes we experience are related to these naturally occurring faults, earthquakes are also caused by other events such as volcanic activity, or human-induced occurrences such as mine blasts or nuclear testing.

MEASURING EARTHQUAKES

The power of an earthquake is measured by the use of the Richter scale, most commonly used to describe the magnitude (for example 6M or 6MR) and impact of a quake. An earthquake’s impact and force will decrease further from its epicentre, and also depend upon the location and depth of the initial fault occurrence. In general, earthquakes felt with higher magnitude measurement will result in greater damage, with general guidelines shown below.

RELATED HAZARDS

Aside from being powerful and deadly in themselves, earthquakes also lead to a range of other dangerous natural disasters. Well-known to the ASEAN region is the tsunami, which is caused by shallow earthquakes with an epicentre in the ocean, resulting in giant waves that make their way towards land. Alongside this, the shaking of the earth from a quake can cause landslides in hilly or mountainous regions, as well as phenomenon such as soil liquefaction, which was a major cause of death and destruction after the most recent earthquake in Central Sulawesi, Indonesia..

Written by : William Shea 

Situated on the Ring of Fire, the ASEAN region faces one of the greatest threats of natural disaster due to geophysical activity along this unstable belt of tectonic plates. One of the key disaster threats categorised into the geophysical type are volcanoes, as well as a range of related disasters that can occur as the result of volcanic activity. During 2018 ASEAN has experienced a range of geophysical events that have triggered disasters. Therefore, understanding the varieties and impacts of such occurrences is highly important for disaster management across the region.

The AHA Centre closely monitors the ongoing dynamic conditions of 150 volcanoes in the ASEAN region that are active and have a recent historical record of eruptions.127 of these volcanoes are located in Indonesia, with 23 in the Philippines, while volcanoes found in other areas of the region are currently dormant. Volcanoes in other ASEAN countries are in dormant condition, such as those in Viet Nam with its last eruptions dated back in the early Holocene era or underwater volcanoes in Andaman Sea between Thailand and Myanmar. Most recently in late 2017 to early 2018, monitoring, preparedness, and pre-emptive evacuations were undertaken by respective local and national agencies due to increased activities on Mount Agung (Bali, Indonesia) and Mount Mayon (Albay, the Philippines). However no lives were lost due to this increased activity. As of September 2018, only Mount Sinabung (North Sumatra, Indonesia) remains at Alert Level IV (out of the maximum 4 alert levels) – which means it may experience major eruptions at any point – with the level IV status ongoing throughout the past five years. Mount Agung remains at Alert Level III, while all other volcanoes in Indonesia and the Philippines are currently at Alert Level II (localised activity with no serious eruption risk).

ABOUT VOLCANOES

A volcano is an opening in the Earth’s crust that allows molten rock, gases and debris to escape to the surface, often exploding through the surface with severe strength and impact on nearby geography. Volcano eruptions are categorised into geophysical hazards that occur when magma (molten rock) is released from a volcanic vent, with eruptions classified into a range of different types including phreatic, phreatomagmatic, surtseyan and effusive (lava-bearing) eruptions.

RELATED HAZARDS

Most hazards, phenomena and disasters associated with volcanic eruptions affect areas close to the volcano itself. Of high importance is the realisation that volcanic activity may also trigger other natural disaster events, including tsunamis, landscape deformation, floods, and tremor-provoked landslides.

LINK TO EARTHQUAKES

Earthquakes and volcanoes are intrinsically linked, as they result from tectonic plate processes that constantly reshape the earth’s surface. Earthquakes form a key clue that a volcano is preparing to erupt, as the movement of magma exerts significant force on the earth above it as pushes through the crust. This pressure from the rising magma causes many of the earthquakes that occur in volcanically active areas. However, such earthquakes also rarely exceed magnitude 5, and are barely noticeable outside the vicinity of the volcano itself. Such earthquakes do help volcanologists to map and track underground lava flows, with different types of earthquakes often resulting based the signature of tremors, then used to determine if the volcano is heading towards an eruption. Seismic information such as this is valuable for volcanologists who are monitoring eruption events such as explosions or lahars.

Written by : William Shea 

Since its foundation, the AHA Centre has actively monitored seven types of natural disasters that have occurred on a frequent basis across the Southeast Asian region. The natural disasters types that have registered on the AHA Centre’s radar include drought, earthquake, flood, wind, storm, volcano, and landslides.

Throughout the previous six years, a total of 1380 disasters have been recorded by the AHA Centre’s team. While floods, winds, storms, and landslides top the list for frequency, slower-onset disasters, such as drought, still pose significant risk, primarily for ASEAN’s agricultural-based communities.

The most recent recorded disasters have been the floods in Cambodia, Lao PDR, Myanmar, the Philippines, Thailand, and Viet Nam, that occurred due to the accumulated impact of the monsoon season and Tropical Storm 11 (Son-Tinh/ Henry). Between end of July and early August, the AHA Centre activated three emergency responses, responding to severe flooding in Southern Lao PDR and 4 states/regions of Myanmar, as well as powerful earthquakes in Lombok, Indonesia. The following chart may support further development of mitigation plans for disaster managers, as part of wider disaster-preparedness strategies.

Written by : Shintya Kurniawan