Experts still in dark on scale and focus of tsunami-causing quake off Torishima

The Japan Meteorological Agency is still unable to pinpoint the scale and focus of an earthquake that occurred on Monday which triggered tsunami of up to 60 centimeters in the Izu Islands in the Pacific Ocean, south of Tokyo.

The agency says the quake took place at around 5:25 a.m. Monday, somewhere near Torishima in the Izu Islands. It says an unusual seismic wave pattern is making it difficult to ascertain the quake's mechanism.

The focus of an earthquake can normally be estimated by calculating the time lag between the initial small vertical waves and larger horizontal waves that follow.

But agency officials say the patterns of the two waves are not clearly distinguishable in Monday's quake.

The scarcity of observation points near the islands and a mix-up with data from other tremors are also said to be complicating the task.

The 60-centimeter tsunami was observed on Hachijojima Island. Smaller waves were recorded in other parts of the Izu Islands and the Ogasawara Islands; as well as along Chiba Prefecture in eastern Japan; and Kochi, Miyazaki and Kagoshima prefectures in western Japan.

The Meteorological Agency says seismic activity off Torishima Island appears to have subsided since Monday afternoon. But officials are urging residents to remain cautious.