From US — 7.7 and don’t blame Indians

Behind the bland number and minor decimal changes is a story of mother nature’s unpredictable ways and raw power of mathematical progression. The Richter scale that measures earthquakes is expressed in multiples, which means an earthquake that measures 7 on the Richter Scale is 30 times more powerful than a quake that measures 6. An earthquake that measures 8 on theRichter scale is 900 times (30×30) more powerful than one that measures 6.

The Bhuj `bhukamp’ came closer to an 8 than any quake in recent times. Experts say that if you consider the nuclear bomb dropped on Hiroshima had a force of 15,000 tons of TNT, a magnitude 8 quake is 400 times more powerful than that nuclear bomb. The Bhuj catastrophe would approximate some 300 Hiroshima type bombs, or, more pertinently, a single modern nuclear weapon.

Quakes measuring 8 and above occur once in three or four years on an average, while there are an average of 3 temblors each year in the 7.5 to 7.9 range. Casualties depend on how close the epicenter is to human habitation. Unfortunately in the case of Gujarat, it was too close to Bhuj. Most earthquakes measuring 8 have occurred in the sparsely populatedAlaska region.

But how and why did Indian seismologists err so badly in calling the Bhuj quake at 6.9? All the U.S experts this correspondent spoke to defended Indian seismologists, explaining that seismographic equipment in the quake zone would not be capable of reading the entire energy released by a temblor right away.

“It is a very common problem. Even the Taiwan and Turkey quakes were under read. Indian seismologists could have measured only a part of the wave train,” said Dr Mary Lou Zoback, Chief Scientist of the U.S.Geological Survey in Menlo Park, California.

“It’s like trying to measure the size of a forest fire when you are in the middle of it. Instruments that are far away have a better scope of seeing theevent,” explained Dr John Anderson, Director of the Seismological Laboratory in the University of Nevada.

The experts also said none of them had red-flagged the Kutch area although it had a past history of seismic activity. Traditionally, seismologists across the world have been more concerned with the Himalayan region. The process of the formation of Himalayas — during which the peninsular landmass of India went up and nudged what would be mainland China — resulted ingreat seismic activity.

“When I first heard there was a big quake in India, my mind immediately went to the Himalayan region. The other fault lines in India haven’t been studied a great deal,” Dr Anderson said.

But it turns out that two Indian researchers who trained in the U.S did study the Kutch region. The wife-husband team of Kusala and C.P.Rajendra, whoworked with Dr Zoback some years ago, returned to India and spoored the Kutch region. An abstract of a paper they wrote says based on the data they gathered, an earthquake of the same magnitude as Kutch’s 1819 event (there was no instrumentation then, but it was a big one) occurred some 800-1000 years ago in the same place.

The Rajendrans’ conclusion that their observations from the Kutch seismic zone may have implications for the mechanism of similar 19th century earthquakes in New Madrid and Charleston lay buried as a case study till the latest quake. It has now galvanised the American seismological community and e-mails have zinged to and fro in recent days.

“I want to pass along a conversation I had with Otto Nuttli around 1973 about intraplate earthquakes. We agreed that, short of another great New Madrid earthquake, one of the most interesting and important events that could occur would be a repeat of the 1819 Kutch earthquake. Well, here we are!” Jim Zollweg, a seismologist at the University of Idaho, wrote in ane-mail to his colleagues soon after the Bhuj temblor, his academic excitement totally dissonant to the human tragedy in India.

“The 2001 earthquake is extremely important to earthquake studies in the central US. If we ignore or fail to obtain data from the Indian earthquakesequence, it is difficult to say whether we will ever have another chance to constrain central/eastern US ground motion models at high magnitude levels prior to the next great New Madrid event,” Zollweg told fellow seismologists, urging a “science plan” to study the Bhuj quake.