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KOMPAS.com – Research results by researchers from the Bandung Institute of Technology (ITB) related to the possibility of a 20-meter tsunami in southern Java going viral and have been widely discussed by the public.
Research results that have been published in journals Nature science report On (9/17/2020), it is considered concerning if it actually happens later.
Daryono, as Head of the Earthquake and Tsunami Mitigation Division at BMKG, relayed this to Kompas.com, Friday (9/25/2020), this research should be appreciated because it has determined the maximum potential magnitude of the earthquake megathrust and the worst case.
However, what is an earthquake? megathrust?
Also read: Potential for a 20 meter tsunami in South Java, follow these 3 mitigation tips
Earthquake megathrust Many times it is understood as something new and that will happen in the near future, of enormous magnitude, and that will cause devastating damage and a tsunami.
“Understanding this is, of course, inaccurate,” said Daryono, head of BMKG Earthquake and Tsunami Mitigation in his official statement to Kompas.com, Saturday (9/26/2020).
He explained that the megathrust zone is actually just a term to describe the source of the shallow plate collision.
In this case, the oceanic plate sinking below the continental plate forms a stress field in the area of contact between the plates that can then suddenly shift causing an earthquake.
“If an earthquake occurs, then the part of the continental plate that is above the oceanic plate will be pushed up,” he explained.
Daryono explained that the subduction pathways of the plates are generally very long with little depth covering the contact areas between the plates.
He continued, the subduction zone in its development was supposed to be a “large upward fault”, which is now popularly known as the mega-fusion zone.
Nothing new
The megathrust area is nothing new. In Indonesia, this earthquake source zone has existed for millions of years when the Indonesian archipelago was formed.
Daryono said that the megathrust zone is in an active subduction zone, like:
- Sundanese subduction covers Sumatra, Java, Bali, Lombok, and Sumba
- Subduction band
- Subduction of the Maluku Marine Plate
- Sulawesi Subduction
- Subduction of the Philippine oceanic plate
- North Papua Subduction.
“Today, Indonesia’s megatrust zone segment has recognized its potential,” said Daryono.
He continued, all seismic activity originating from the mega melt zone is called an earthquake. megathrust and not always powerful.
However, as the source of the earthquake, the area megathrust It can generate earthquakes of various magnitudes and depths.
BMKG monitoring data shows that small earthquakes are more common in the mega melt zone. However, the mega melt zone can also trigger major earthquakes.
Read also: ITB research reveals the potential of a 20 meter tsunami in South Java, here is the explanation
Megathrust South Java
In the book Sources and Earthquake Hazards Maps for Indonesia in 2017, it is stated that in the Indian Ocean south of Java there are 3 mega-incident segments, namely (1) East Java Segment, (2) Central Java-West Java Segment and (3) Banten-Sunda Strait Segment.
These three mega-thrust segments have a target magnitude of M 8.7.
However, if the model scenario is performed with the assumption that 2 mega-thrust segments are moving simultaneously, the magnitude of the resulting earthquake can be greater than 8.7.
According to the analysis of Indonesia earthquake map and book update sources, if an earthquake with a magnitude of 8.9 occurs in the Nias Mentawai megathrust segment, a tsunami is likely to occur. Tsunami waves can reach the mainland Nias Islands in less than 7 minutes.The magnitude of the declared magnitude of the earthquake is a possible worst case scenario (worst of cases) is not a prediction of what will happen in the near future, so no one knows when it will happen.
“For that, given the uncertainty of when it will happen, we all have to make mitigation efforts,” Daryono warned.
The results of the BMKG monitoring show that the southern megafusion zone of Java is indeed very active as seen on the seismic activity map.
In historical records, since 1700, the megathrust area of southern Java has occurred several times a major earthquake and a major earthquake.
Large earthquakes with magnitudes between 7.0 and 7.9 that originated in the southern megathrust area of Java have occurred 8 times, namely:
- 1903 (M7.9)
- 1921 (M7.5)
- 1937 (M7.2)
- 1981 (M7.0)
- 1994 (M7.6)
- Year 2006 (M7.8)
- Year 2009 (M7.3)
Meanwhile, devastating earthquakes with a magnitude of 8.0 or more that originated in the mega-melt zone south of Java have occurred 3 times, namely:
- 1780 (M8.5)
- 1859 (M8.5)
- 1943 (M8.1).
Meanwhile, earthquakes with a magnitude of 9.0 or more in southern Java have not been recorded in the earthquake history catalog.
Also read: Potential tsunami 20 meters south of Java, BMKG: Don’t panic and focus on mitigation
South Java Tsunami
The southern Java region has experienced several tsunamis.
Evidence for a tsunami in southern Java can be found in the BMKG’s Indonesian tsunami catalog, where tsunamis occurred in 1840, 1859, 1921, 1921, 1994, and 2006.
Apart from these data, research results on paleotsunamis also confirm the existence of repeated tsunami traces in southern Java in the past.
Frequent earthquakes and tsunamis in southern Java are a risk faced by people who live and live at the junction of plate tectonic boundaries.
“So whether we like it or not, like it or not, this is a risk that we must face,” Daryono said.
“Do we live near the megathrust area where we are always trapped by anxiety and fear? It is not necessary, because by making concrete mitigation efforts, we can minimize risks, so that we can still live safely and comfortably in areas prone to disasters, “he concluded.
