Monday January 22, 2018
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Arunachal fortunate to be safe from quake damage

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Kolkata: Arunachal Pradesh, one of the seven sisters state, located at the tip of northeast India was luckily protected from the destructive Manipur earthquake  because of it’s geography and geology, experts said. Proper quake-resilient structures should be built, they added.

Famous for its biodiversity, Arunachal Pradesh, sharing international borders with Myanmar, China and Bhutan, was perhaps the least affected when a 6.7-magnitude temblor along the Indo-Myanmar border jolted India’s northeast and east and neighbours Myanmar, Bhutan and Bangladesh.

At least eight people were killed and more than 120 injured in the Manipur temblor that affected its other northeast sisters including Assam, Meghalaya, Tripura, Sikkim and Nagaland. A six-storey under-construction building toppled in Manipur’s capital Imphal where the iconic Mothers’ Market also took a hit.

“Arunachal was outside a 50 km radius range from the epicentre at Manipur’s Tamenglong region. In addition, the geology in Arunachal Pradesh is different,” B K Rastogi, former director general of Gandhinagar-based Institute of Seismological Research (ISR) said.

The soil in Manipur’s quake-hot areas is alluvial which magnified the seismic waves, but most of Arunachal is rocky which doesn’t have similar amplification effects, explained Rastogi.

Common principles of geography and energy distribution played a key role in the state escaping the disaster.

“As the distance from the epicentre increases there is an equal decrease in the energy released and subsequently a decrease in the effect.

“This is one of the factors why Arunachal Pradesh did not see damage during the Monday’s quake,” said Gibji Nimasow, a professor in the geography department of the Rajiv Gandhi University, Arunachal Pradesh.

Manipur bore the brunt of the temblor, which struck at 4.35 AM and left a trail of devastation in the region: at least four people were injured in southern Assam, walls of some residences and other buildings cracked in Tripura, Mizoram and Nagaland where the intensity was strong.

IIT-Guwahati’s Chandan Mahanta pointed out the quake was distinguishable from other temblors in the region because of its duration (more than 30-plus seconds) but Arunachal, home to the great Indian hornbills, was lucky time-wise too.

“While the first quake was only for a second in Arunachal Pradesh, the second quake on Monday lasted for few seconds, less than a minute, which saved the state from disaster,” Nimasow elaborated.

While the magnitude of the tremor was 6.7 in Manipur and Assam, it slumped below 6 in Arunachal, said Nimasow.

“The potential to cause damage was low as the temblor’s intensity was less,” disaster management coordinator for UNDP project Sarat Das said, from Tripura, adding the quake was classified as a moderate intensity one.

According to the USGS, moderate to large earthquakes in the region around northeast India, where the subcontinent collides with the Eurasia plate, are fairly common.

India’s northeast region is considered the world’s sixth most earthquake-prone belt.

In the last 100 years, some 19 other quakes greater than magnitude-6 have occurred within a 250 km range from the site of Monday’s temblor. The largest was a magnitude-8 quake in 1946.

But northeast India has not learnt its lessons yet despite its vulnerability, lamented Durgesh C Rai, of IIT-Kanpur’s National Information Centre of Earthquake Engineering.

“Copying building designs from other cities for modernisation is not right. Buildings in earthquake prone regions should be according to the site-specific codes,” Rai said.(IANS)(image: orrissapost.com)

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Researchers Suggest Studying Aquifer Water Levels in the Himalayas to Predict an Earthquake

Whenever earthquakes occur, widespread cracks and deformations on the earth's surface are common, resulting in changes in groundwater levels, believe researchers

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Can water levels in the foothills of Himalayas forewarn about earthquakes? The blinking red light on a seismograph shows the epicentre of an earthquake. (representational image) Wikimedia

Bengaluru, October 16, 2017 : Continuous monitoring of water levels in the foothills of the Himalayas can warn about an impending earthquake in the region, which is due for a major temblor.

This recommendation to the Ministry of Earth Sciences has come from Ramesh Singh, professor of environmental sciences at California’s Chapman University, who is also president of the Natural Hazards Group of the American Geological Union.

Singh says the utility of monitoring the water levels of underground aquifers for predicting earthquakes in quake-prone regions has been confirmed from analysis of water level data in a bore hole collected during the earthquake that rocked Nepal’s Gorkha district on April 25, 2015.

The findings of the study carried out by Singh and three seismologists from China have recently been published in the journal Techtonophysics.

The Gorkha quake, one of the deadliest in Nepal, killed about 5,000 people mainly in Nepal, a few in bordering India, two in Bangladesh and one in China, and injured about 9,200 people.

Whenever earthquakes occur, widespread cracks and deformations on the earth’s surface are common, resulting in changes in groundwater levels, Singh told this correspondent in an email.

In China, many parameters are being monitored in water wells, including water level, water temperature, and water radon concentrations to detect any signal prior to an impending earthquake.

According to the scientists, due to seismic wave propagation, the volume of an aquifer expands and contracts, forming fractures that change the water flow in a bore well sunk into the aquifer.

In the case of the Gorkha quake, the scientists considered the water level in a bore well — called “Jingle” well — atop an aquifer in China’s Shanxi province, 2,769 kilometres from the temblor’s epicenter. The data was analysed soon after the Nepal earthquake.

A “spectrum analysis” of the co-seismic response of the bore hole water level showed large amplitude oscillations with a maximum peak-to-peak value of about 1.75 metres associated with ground vibrations generated by the earthquake, says their report.

In addition, the analysis revealed the arrival of a possible precursor wave at the “Jingle” well about 6.5 hours prior to the actual occurrence.

ALSO READ Indian Seismologist Arun Bapat had Predicted China Earthquake on August 8

“The study of co-seismic changes in groundwater has emerged as an important research area which can provide an improved understanding of earthquake processes and corresponding changes in surface and subsurface parameters,” Singh said.

Water level data in close proximity to the epicenter may be of great importance in getting early warning signals of an impending earthquake, he said. China and the United States routinely monitor aquifer water levels at 15-minute intervals.

In the light of the finding, Singh said that “India’s Ministry of Earth Sciences may consider deploying water level sensors in the Himalayan foothills areas, which may provide valuable information about an impending earthquake in the Himalayan region, which is due for a major earthquake.”

Such data, he added, “is also useful in understanding the dynamic nature of the Indian plate”.

However Arun Bapat, former head of Earthquake Engineering Research at the Central Water and Power Research Station in Pune, says he has some reservations about the study’s conclusion that water level changes observed in the bore hole were the warning signal for the Gorkha earthquake.

“Various effects associated with a large earthquake (Magnitude 7.5 or more) such as electrical, magnetic, geological, tectonic, hydraulic, radioactivity, etc., have been observed within about 600 to 800 km from the epicenter (but not beyond),” Bapat told IANS.

Bapat said the magnitude of the Gorkha quake was about 6.5 to 6.75 which is considered as moderate. “The effect of this quake on water level changes at a distance of 2,769 kilometres from its epicenter is almost not possible.” (IANS)