Bangalore, Apr 12 (IANS): Scientists had been expecting Wednesday's great earthquake off Sumatra but it occurred a little sooner, according to Arun Bapat, an Indian seismologist in Pune.
Bapat is one of the associate scientists of the newly formed International Earthquake and Volcano Prediction Center (IEVPC) based in Orlando, Florida in the United States.
Asked why the IEVPC failed to predict Wednesday's 8.6 Richter earthquake that triggered tsunami fears in Indian Ocean countries, Bapat said they did suspect an impending quake on April 5 itself.
In an email to IANS Bapat said: "We were expecting occurrence of a large magnitude earthquake in Indonesia…. We were debating it and the expected time window was about 10 to 15 days." But it has occurred earlier, he said.
Bapat said he sensed the possible occurrence of the earthquake first on March 21 itself after having observed the satellite picture of the Total Electron Content (TEC). The TEC is the total number of electrons present between any two points in the Earth's ionosphere and is measured as the number of electrons per square meter.
"I kept thinking," Bapat said. "Subsequently on April 5 I had two more satellite photos of TEC. We have been monitoring the TEC every day. We get inputs from Russia."
According to Bapat, it is known that there is a statistical association between large earthquakes and TEC anomalies as changes in the electron concentration occur a few days before earthquake. "It was found during the recent Tohoku (Fukushima) Japan earthquake that the TEC had increased very high," Bapat said. It was about three to four times the normal electron concentration.
Similarly, Kyushu earthquake of March 20, 2005 (M = 6.6) had revealed an earthquake-associated TEC anomaly 11 days before that quake.
Bapat said that from the TEC pictures he obtained (on March 21 and April 5) "it would be seen that the area of potential earthquake epicentre had very high concentration of electrons", suggesting that the Sumatra earthquake was imminent. However, the earthquake came before any warning could be issued.
According to Bapat, the IEVPC warned earlier this week that a major earthquake and possible tsunami will strike Kamchatka Peninsula of Russia between now and the end of June 2012.