fresh after shock of Earthquake rattles Pakistan

Heard somewhere of the proverb ‘disasters never come alone’ not sure of its origin nor correctness

An earthquake (also known as a quake, tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are measured using observations from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe. The most recent large earthquake of magnitude 9.0 or larger was a 9.0 magnitude earthquake in Japan in 2011. At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami.

News reports state that  today, several cities of Pakistan's Sindh and Balochistan provinces were hit by a massive aftershock measuring 6.8, three days after a 7.7 magnitude earthquake struck the region killed over 500 people.  The US Geological Survey said the quake struck approximately 250 kilometres (155 miles) north of the port city of Karachi.  There has been no immediate reports of casualties or damage. Local media reported that the quake affected Balochistan and Sindh regions. It reportedly was also felt in Quetta, close to Pakistan's border with Afghanistan, and Karachi. Pakistan's Meteorological Department however measured the quake at 7.2 magnitude. Chief Pakistani meteorologist is quoted as telling Pakistani television that it was an aftershock from this week's earthquake and similar tremors could continue for weeks, Associated Press reported.  The National Seismic Centre stated that the origin of this earthquake was once again Awaran.

Reports state that rescue teams are still to reach several remote areas, including the worst-hit Balochistan's Awaran district near the epicentre of Tuesday's temblor. While the official death count stands at 515, unofficial figures are as high as 700, with more than 800 injured. The earthquake left more than 50,000 people homeless in these areas. In another disturbing news, an army helicopter carrying relief goods to the quake-hit areas was fired at in Mashkay area of Awaran district by suspected militants on Friday. The helicopter was not damaged in the attack. This was the second attack on an army helicopter in the area. Yesterday, two army generals, including the head of the National Disaster Management Authority, had a narrow escape when rockets were fired at their helicopter. Security personnel accompanying a team of doctors for relief operations were fired at on Wednesday.

As one would recall on September 24, 2013, a major strike-slip earthquake rattled western Pakistan. On September 26, 2013, the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured the top image of that new island, which sits roughly one kilometer (0.6 miles) offshore. Likely a “mud volcano,” the island rose from the seafloor near Gwadar on September 24, shortly after the earthquake struck about 380 kilometers (230 miles) inland.

In the satellite images, released by NASA,  lighter shades of green and tan in the water reveal shallow seafloor or suspended sediment. The water depth around the new island is roughly 15 to 20 meters, according to marine geologist Asif Inam of Pakistan’s National Institute of Oceanography. “The floor in that area is generally flat, but the gradient in this area changes quite abruptly,” Inam said.

“The island is really just a big pile of mud from the seafloor that got pushed up,” said Bill Barnhart, a geologist at the U.S. Geological Survey who studies earthquakes in Pakistan and Iran. “This area of the world seems to see so many of these features because the geology is correct for their formation. You need a shallow, buried layer of pressurized gas—methane, carbon dioxide, or something else—and fluids. When that layer becomes disturbed by seismic waves (like an earthquake), the gases and fluids become buoyant and rush to the surface, bringing the rock and mud with them.” Inam asserted that the underground pressure in this case came from expanding natural gas.

The life of this island is likely to be short. That underground pocket of gas will cool, compress, or escape over time, allowing the crust to collapse and settle back down. Waves, storms, and tidal action from the Arabian Sea will also wash away the loose sand, soft clay, and mud. Barnhart says such islands usually last a few months to a year before sinking back below the water line.

The latter part is largely reproduced from - http://earthobservatory.nasa.gov/ - which is the source for photos too.

With regards – S. Sampathkumar