Cause of tsunami waves unknown

Japan's Meteorological Agency reported tsunami activity in the Izu Islands south of Tokyo on Monday morning. A 60 centimeter tsunami struck Hachijojima Island, and 50-centimeter tsunami waves hit the islands of Kozushima and Miyakejima.

The Tokyo Metropolitan Police Department, which has jurisdiction over the Islands, conducted coastal patrols and said there were no casualties.

Tsunami waves ranging in height from 10 to 40 centimeters were also observed Monday morning in Chiba, Kochi, Miyazaki and Kagoshima prefectures.

'The cause remains unclear'

A Japan Meteorological Agency official speaks at a news conference on Monday.

The first tsunami advisories were issued for the Izu and Ogasawara Islands. Tremors had occurred near the Izu Islands about an hour earlier, but their magnitudes were not known. It has, however, been confirmed that no quakes took place with an intensity of 1 or higher on the Japanese seismic scale of zero to 7.

Advisories were issued for increasingly wide areas after tsunami waves were observed.

An official noted at the news conference that the JMA was unable to accurately identify the epicenter or magnitude of any of the tremors because they took place in areas with few observation points.

He said they could have been caused by volcanic activity, a volcanic eruption, a large-scale underwater crustal deformation or a landslide.

Quakes may be related to magma and crustal movements

Sandanbata Osamu is an assistant professor at the University of Tokyo Earthquake Research Institute.

Sandanbata Osamu, an assistant professor at the University of Tokyo Earthquake Research Institute, says although the earthquake was fairly small, relatively large tsunami waves have been observed — which is not a normal phenomenon. He says he was surprised as he hadn't seen tsunami activity in this area before.

Sandanbata says tsunami waves can also be caused by activities such as explosive eruptions of undersea volcanoes, shock waves caused by eruptions, crustal movements on the seabed triggered by magma activity and seabed landslides.

He says many undersea volcanoes are located around the epicenter of the latest earthquake, and there is a possibility that magma-related crustal movements occurred on the seabed.

He says people should keep abreast of the latest information.