The international community has offered condolences and aid pledges for victims of Saturday's massive earthquake in Kashmir that officials fear killed thousands. In Washington, President Bush said initial U.S. deployments of assistance are underway. Seismologists say the quake is perhaps the region's strongest in 70 years, and is the direct result of the Indian subcontinent's steady push northward.

A father comforts his son injured by the earthquake at a makeshift hospital in Pakistan

Saturday's earthquake hit shortly before 9 a.m. local time in the rugged Hindu Kush mountains of northern Pakistan.

Initial estimates rank it as a 7.6 magnitude tremor, which would be the strongest quake to strike the region since 1935.

Pakistani Army spokesman Major General Shaukat Sultan described the devastation. "The damage caused is mostly in the mountainous areas where the landslides have been triggered and the houses were mostly mud or the semi-permanent types of houses," he explained. "So in certain areas the entire villages, they have collapsed and in certain areas almost entire towns have vanished from the scene."

Search teams comb a collapsed apartment building in Islamabad

The earthquake also flattened concrete multi-story buildings some 100 kilometers away in the Pakistani capital of Islamabad, and was felt hundreds of kilometers away in Kabul, Afghanistan and New Delhi, India.

The region has a long history of seismic activity because it is located on the Indian plate, a piece of the earth's crust moving north at the rate of some 40 millimeters per year. As the plate collides into and slips under the massive Eurasian plate to the north, it lifts the world's highest mountain ranges, the Himalayas, even higher. But major fault lines exist at the plate's edge, where sudden jolts have wreaked massive devastation.

The 9.0 magnitude quake that caused the 2004 Indian Ocean tsunami occurred on the sea floor, where the India plate rubs against the Burma plate. The movement pushed up a wall of ocean water that smashed into coastlines, killing more than 200,000 people. This past March, a magnitude 8.7 quake in the same region killed more than 1,000 people, but did not create a tsunami.

On land, a 5.8 magnitude quake in northern Afghanistan's Hindu Kush mountains in 2002 killed about 700 people, and in western India in 2001, a 7.6 magnitude earthquake killed at least 11,000 people in Gujarat.

US Geologic Survey image shows the approximate epicenter of the October 8 quake in Pakistan

Massive quakes on the Indian subcontinent were also reported in 1935, when some 35,000 people were estimated killed in a tremor in western Pakistan; and in 1905, when nearly 20,000 died in a 7.9 magnitude quake in northern India.

An earthquake's magnitude indicates how much energy it releases, but other factors affect the extent of its devastation, including where tremors strike, the type of terrain around them, and how deep within the earth they occur.

In 1974, a magnitude 6.2 earthquake in the same region as Saturday's tremor killed more than 5,000 people.

Some seismologists say because Saturday's magnitude 7.6 quake appears to have been very shallow, with much of the violent activity occurring near the earth's surface, it could be more damaging compared to other quakes of similar magnitude.