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. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.
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. Earthquakes can also trigger landslides, and occasionally volcanic activity.
Pakistani troops race to rescue earthquake victims
Pakistani troops scrambled yesterday to reach remote villages to aid victims of a powerful earthquake centred in nearby Iran, as the US offered help and a strong aftershock jolted the region.
The Pakistani army deployed hundreds of soldiers to help the relief effort in Mashkeel, the area of Baluchistan province hit hardest by Tuesday's magnitude 7.8 quake. But many residents in Mashkeel, where nearly every home was destroyed, said they were unhappy with the response.
"I appeal to the government. I appeal to the international community to help us with food, medicine, tents and blankets," Syed Mureed Shah, an official in the surrounding Washak district, said. "Come and see with your own eyes the damage caused."
The epicentre of Tuesday's 7.8-magnitude quake lay in southeast Iran but all 40 estimated deaths reported so far have been across the border, in Pakistan's dirt-poor province of Baluchistan, where hundreds of mud-built homes suffered damage.
The powerful tremor shook the ground and caused panic as far afield as Kuwait and the Indian capital, New Delhi.
A new aftershock early yesterday frayed nerves on the Iran-Pakistan border. The US Geological Survey measured its magnitude at 5.7.
In Pakistan, officials said that regular army and paramilitary forces had deployed to help the relief effort after the quake brought down homes in the Mashkail area of Baluchistan.
Military helicopters carrying medical teams had been sent to the area, while paramilitary troops were supplementing the relief efforts, they said.
Some 650 personnel are involved in the rescue operation in Mashkail town.
"When I felt the tremors, I saw within seconds houses razed to the ground. It was like doomsday," said Abdul Bari, a 32-year-old tailor whose leg was broken.
"I saw three small children taken out from the debris of a collapsed wall by local people."
Thousands of people remained homeless and desperate for aid in southwestern Pakistan after the deadly earthquake centred in neighbouring Iran that toppled scores of mud brick homes and killed at least 36 people.
At least 35 people were killed and 150 injured in Pakistan. Only one person was killed in Iran - a woman struck by falling rocks while she was collecting herbs - and 12 people were injured.
An estimated 700 houses were reported damaged in Mashkeel. But Shah said the damage was more widespread. He said more than 3,000 homes were destroyed in the district, leaving about 19,000 people without shelter.
He said only about 60 tents had been received from the provincial government.
The provision of supplies was hampered yesterday by a sand storm that stopped helicopters from landing in Mashkeel.