An expert says large-scale rupture of an underground fault occurred at least twice in the powerful earthquake that struck the Noto Peninsula in central Japan on January 1.

The Earthquake Engineering Committee of the Japan Society of Civil Engineers discussed preliminary research reports by earthquake and tsunami experts in an online meeting on Tuesday.

Professor Goto Hiroyuki of Kyoto University reported that nearly the entire northern section of the peninsula sits on the fault where the quake originated.

Goto said the seismic wave patterns indicate that large-scale rupture of the fault took place at least twice near the quake's epicenter. He added that the ruptures caused tremors that lasted over 20 seconds.

Goto also said that the ground formation under some urban areas, including Wajima City and Anamizu Town, is relatively soft, which may have caused tremors there to be amplified.

As for the tsunami that hit coastal areas, Professor Koshimura Shunichi of Tohoku University conducted onsite investigations and simulated analysis.

Koshimura said that the cities of Wajima and Suzu are located in the area where the tsunami originated, and that waves reached them immediately after the quake.

He noted that Suzu City was especially hit badly by tidal waves estimated to be as high as 3 meters, due to the distinct seabed terrain of the Toyama Bay, which it faces.