A Japanese seismic expert says the biggest jolt of the earthquake in Morocco was probably equivalent to upper 5 to lower 6 on the Japanese seismic scale of zero to 7.

The US Geological Survey reports that the magnitude 6.8 quake struck late Friday, with the epicenter about 70 kilometers from the central city of Marrakesh.

Professor Satake Kenji at the University of Tokyo's Earthquake Research Institute says the quake likely occurred at an active fault in the African Plate. He says it was a reverse-fault type, which occurs when two blocks of tectonic plates grind against each other and one block moves up over the other.

He says the northern part of Morocco is seismically active, as it is close to the border between the African Plate and the Eurasian Plate, but central Morocco, where this latest quake occurred, is not.

Professor Satake says buildings in the quake-hit area are therefore likely not built to withstand strong jolts like this one. He says the timing of the quake, in the middle of the night, may also have contributed to the extensive damage.

Satake warns that quakes with a similar intensity can occur over the next week or so, causing more damage to buildings and landslides in mountainous areas.