On November 21st, the Indonesian Java Island got hit by a harmful seism classified as 5.6 magnitude on the Richter scale. The power unleashed by the earthquake was mixed with an epicentre which is not very deep, estimated to be 10 km under the surface. The earthquake, due to the habitation density and the fragile construction of buildings, caused hundreds of damages to the building, deaths, and more than 300 missing people.
The emergency services were working non-stop to save the ones still trapped under the rubble of the collapsed buildings, while the minor wounded individuals were treated in the hospital parking lot because of the power failure caused by the quake.
The area is known to be seismic like the geographic area of Java Island, Sumatra island, which got struck by a stronger seism of a magnitude 6.2 on the Richter scale, resulting in 25 deaths and more than 450 injured. The Sulawesi Island earthquake, which happened in January 2021, caused 105 victims and around 6500 wounded. This represents a reconfirmation of the area's seismicity.
The area is under the observation of the United States Geological Surveys (USGS) as part of the Earthquake Hazard Program. The USGS is an American geological institute which studies USA territory natural resources and the natural hazard threatening it; the Earthquake Hazard Program delivers studies on the seismic phenomenon to understand the earthquakes occurring, their effects, and their consequences.
What is the cause behind the seisms?
According to the studies conducted by the USGS, the seism seems to be caused by clashes between tectonic plates. The Indonesian Sumatra Island is in a seismic zone between the Indo-Australian Plate (at Ovest) and the Sunda Plate (at west)
The clash between tectonic plates is a natural occurrence consisting of two tectonic plates interacting, moved by the heat power of the inside of the hearth, resulting in "convection" and, by the force of gravity, movements of "ridge push" and "slab pull". The Indonesian area affected by those seismic phenomena is prone to subduction movements.
What are the tectonic plates' subduction movements?
Subduction is a natural, geologic, tectonic plate movement which has a fundamental role in the Tectonic Plates Theory and the lithosphere morphological state. The subduction consists of the slipping of a lithospheric plate under a second one and the consequent drag down of the first one, resulting in the creation of oceanic trenches and volcanic arches, along with forearc and avanarc regions.
The Sunda arch is a volcanic arch which forms the Sunda and Java Islands, along with Small Probe Islands and the Probe Strait. It is the result of the subduction between the Indo-Australian and Sunda plates, which created a volcanic island range characterised by intense seismic activity.
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