Nepal faces larger and more deadly earthquakes, even after the magnitude-7.8 temblor that killed more than 4,000 people on Saturday (April 25).

Earthquake experts say Saturday's Nepal earthquake did not release all of the pent-up seismic pressure in the region near Kathmandu. According to GPS monitoring and geologic studies, some 33 to 50 feet (10 to 15 meters) of motion may need to be released, said Eric Kirby, a geologist at Oregon State University. The earth jumped by about 10 feet (3 m) during the devastating April 25 quake, the U.S. Geological Survey reported.

"The earthquakes in this region can be much, much larger," said Walter Szeliga, a geophysicist at Central Washington University.

Seismologists have extensively studied the possibility of damaging earthquakes in the central Himalayas. Through analyzing written histories, looking for clues from damaged buildings and digging along faults, researchers know of several damaging earthquakes in the past, but not their precise size. [See Photos of This Millennium's Destructive Earthquakes]

Nepal was overdue for a major earthquake, said Marin Clark, a geophysicist at the University of Michigan. "It has been a long time since the last big rupture, so this is not unexpected," Clark said.

One of the region's most devastating recent quakes occurred in 1934, when a magnitude-8.2 earthquake killed over 8,500 people in Kathmandu. Before then, the last time such an immense quake struck Kathmandu was on July 7, 1255. That quake killed about 30 percent of the population. The region west of Kathmandu has been seismically quiet since June 6, 1505, when a great earthquake toppled buildings from Tibet to India.