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Jakarta, CNN Indonesia –
Council of Meteorology, Climatology and Geophysics (BMKG) gave an explanation about the PA earthquake following an ITB investigation that said tsunami large due to the great earthquake in South Java.
The 20-meter tsunami in southern Java in recent days has been busy speaking for the public. This devastating tsunami followed an ITB investigation some time ago.
Daryono, head of the Tsunami and Earthquake Mitigation Division, said many people misunderstand the meaning of the megathrust area.
“The mega earthquake is understood as something new and will happen in the near future, of enormous magnitude, and will cause devastating damage and a tsunami. This kind of understanding is of course inaccurate,” Daryono said in an official statement received. CNNIndonesia.com, Monday (28/9).
Daryono 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 that is submerged below the continental plate forms a stress field in the area of contact between the plates. This field can change suddenly causing an earthquake.
“If an earthquake happens, the part of the continental plate that is above the oceanic plate will be pushed upward,” Daryono said.
The subduction pathways of the plates are generally very long with a shallow depth covering the contact areas between the plates. During its development, the subduction zone was assumed to be a “large upward fault”, now popularly known as the mega-shock zone.
Daryono explained that the megathrust area is not new. In Indonesia, this earthquake source zone has existed for millions of years when the Indonesian archipelago was formed.
The megathrust zone is in an active subduction zone, such as: (1) Sunda subduction covering Sumatra, Java, Bali, Lombok and Sumba, (2) Banda subduction, (3) Maluku marine plate subduction, (4) Sulawesi subduction, (5) Philippine Sea plate subduction, and (6) North Papua subduction.
“Today the segment of the megathrust zone in Indonesia has been recognized for its potential. All seismic activity originating from the megathrust zone is known as a megathrust earthquake and is not always of great magnitude,” he said. Daryono.
As a source of earthquakes, the mega melt zone can generate earthquakes of various magnitudes and depths. However, Daryono said that most of the earthquakes that occur in the megathrust area are “minor earthquakes.” On the other hand, Daryono did not deny that the megathrust area could trigger a major earthquake.
Megathrust South Java
In the book Map of Indonesian Earthquake Hazards and Sources in 2017, it is stated that in the Indian Ocean south of Java there are three segments of megathrust, namely the East Java segment, the Central Java-West Java segment, and the West Java segment from the Banten-Sunda Strait.
“The three mega-thrust segments have a target magnitude of M8.7.
However, if the model scenario is made with the assumption that 2 mega-thrust segments are ‘moving’ simultaneously, the magnitude of the resulting earthquake could be greater than 8.7, “said Daryono.
However, Daryono explained that the magnitude of the earthquake that was transmitted was the worst possible potential, not a prediction that it will occur in the near future. He emphasized that no one knows when the earthquake occurred.
“For that, given the uncertainty of when it will happen, we all have to make mitigation efforts,” said Daryono.
Daryono explained that the results of the BMKG monitoring show that the southern Java megathrust zone 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), 2006 (M7.8) and 2009 (M7.3)
Meanwhile, devastating earthquakes with a magnitude of 8.0 or more originating in the southern megafusion area of Java have occurred 3 times, namely in 1780 (M8.5), 1859 (M8.5) and 1943 (M8, one). Daryono emphasized that there had not been an earthquake with a strength of M9.0 or higher in southern Java.
“Meanwhile, earthquakes with a magnitude of 9.0 or more in southern Java have not been recorded in the earthquake history catalog,” Daryono said.
South Java Tsunami
The southern Java region has experienced several tsunamis. Evidence for a tsunami in South Java can be found in the BMKG Indonesia Tsunami Catalog. In the catalog, there have been tsunamis included 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.
Furthermore, Daryono said that the high intensity of the earthquake and tsunami in southern Java was a risk faced by people who live and live at the confluence of tectonic plate boundaries.
However, Daryono said that people living near the megathrust should not be afraid if they have undertaken mitigation efforts.
So that we can live safely and comfortably in disaster-prone areas, “said Daryono.
(dd / mm)
[Gambas:Video CNN]
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