More than seven decades have passed since the 1923 Great Kanto Earthquake killed more than 100,000 in temblor-prone Tokyo, and seismologists say another "big one" may be overdue.

The experts agree that the possibility of a major earthquake striking beneath Tokyo has increased, a prediction that has recently prompted the Tokyo Metropolitan Government to revise its projections of damages from a major quake. The city government's latest report predicts that about 7,200 people would die if an earthquake of 7.2 on the Richter scale directly hits Tokyo's 23 wards; 1,820 would be killed if it hit beneath the Tama district of western Tokyo.

The Tokyo Metropolitan Government began studies to revise earthquake projections in 1994 for an inland-type earthquake. It is estimated that earthquakes similar to the 1923 quake, which occurred in a sub-marine trench, hit the region about every 220 years as the Pacific plate moves and slides beneath the Philippine Sea plate. This releases accumulated pressure when it becomes excessive in a sub-marine trench.

But the accumulated pressure between the sea plates also distorts underground rock slabs and sometimes destroys portions of them, which can cause temblors directly beneath an inland area. Based on research, this type of inland earthquake occurs about 70 to 80 years after a quake along a sub-marine trench, seismologists say, which means pressure has continued to build since the 1923 quake.