Sri Lanka is unlikely to experience another tsunami triggered by a large-scale earthquake for at least the next 50 years or more, former Vice Chancellor of the Peradeniya University and Geology Professor Athula Senaratne yesterday told The Sunday Observer.
He was addressing growing public concerns over the potential threat of a major earthquake or tsunami which could occur in the country due to distant seismic activities in the Indian Ocean, driven by a surge in reports of minor tremors within the country coupled with lingering memories of the devastating 2004 boxing-day tsunami and the deadly earthquake that struck Morocco earlier this month.
Prof. Senaratne underscored the rarity of a large-scale earthquake in the Southern or Eastern seas triggering a catastrophic impact on Sri Lanka. He said that while distant seismic activities in the Indian Ocean are a cause for concern, the specific geological conditions necessary for a major earthquake or a tsunami in Sri Lanka are infrequent.
Contrary to the prevalent anxieties, Prof. Senaratne said that the specific geological conditions required to generate a tsunami in Sri Lanka are rare. He said that the epicentre of the Moroccan earthquake was far removed from the tectonic boundaries encompassing Sri Lanka.
He attributed public fears to the frequent exposure to seismic wave reports and minor tremors. “They have become more common due to the proliferation of earthquake measuring instruments, “he said. According to him, the Government has recently employed about eight or nine seismic monitoring instruments on the advice of geologists.
He said the increased availability of earthquake measuring instruments, now numbering thirteen in the country, has led to greater public awareness of seismic events. He said, “While these instruments provide valuable data, they can also contribute to a heightened sense of impending earthquakes, even when the actual risk is low.”
Sri Lanka’s geological location on the Indian Plate, adjacent to the Indian and Australian Plates, makes it susceptible to geological movements; Prof. Senaratne said.
“Earthquakes occurring 500 to 2,000 kilometres away from Sri Lanka are often felt due to these tectonic dynamics,” he said.
Central highlands
Referring to the earthquakes within Sri Lanka, he said that they commonly occur in the central highlands, apparently in elevated locations in the Southern and Eastern provinces. “They are linked to large reservoirs in the central highlands. When these reservoirs fill, they can induce geological formations underground, releasing energy and tremors,” he said.
In 1972, Prof. P.W. Withanage, a prominent geologist and former Vice Chancellor of the Peradeniya University, shed light on the causes of earthquakes in Sri Lanka.
He said that the island nation is slowly rising, ascending at a rate of approximately 2 millimetres per year. This gradual uplift leads to the formation of cracks in the earth’s crust, setting the stage for potential tremors.
Prof. Senaratna said that the tremors experienced in Sri Lanka’s western regions are a consequence of the country moving away from the Indian subcontinent.
This geological phenomenon can be traced back millions of years when Sri Lanka and India were once part of a massive landmass that included Africa, Antarctica, and Australia. Over time, this landmass began to shift upward, eventually connecting with the Eurasian Plate.
Evidence of this ongoing movement can be observed in the form of long faults and cracks on the seabed between Sri Lanka and India, a clear indication that Sri Lanka continues to distance itself from the Indian landmass. These geological conditions give rise to minor disturbances that, when amplified, result in seismic events.
As Prof. Senaratna elaborated, Sri Lanka rests upon the Indo-Australian Plate, an expansive geological entity stretching from the Himalayas to the Indian Ocean and the Tasman Sea, encompassing a significant portion of the Earth’s crust.
Recent geological observations have noted earthquakes approximately 1,500 kilometres from Sri Lanka, signalling the potential splitting of the Indo-Australian Plate into the Indian and Australian Plates.
“It’s important to understand that the root causes of earthquakes lie deep beneath the Earth’s surface, extending hundreds of kilometres into the ground. These phenomena are unrelated to surface activities and environmental factors. At great depths, underground convection currents, analogous to the ripples in boiling water, play a crucial role.
These convection currents are a common occurrence in the earth’s deep layers, particularly in the mantle, which extends from the top of the crust to a depth of about 7,000 kilometres, with the core lying beneath.
Molten rock
The upper part of the core consists of molten rock, energised by various deep-seated reactions. These convection currents induce movements in the semi-solid mantle just above them, which, in turn, affect the crust.
The resulting movements in the earth’s crust can take various forms, including blocks colliding with each other, ultimately leading to the release of seismic energy in the form of earthquakes.
