A powerful earthquake originating in what seismologists call the Nankai Trough off the Pacific coast could cut off tap water to roughly 8.32 million people in Osaka, or 94 percent of the prefecture’s residents, the Osaka Prefectural Government said Friday.

The outage would be caused by damage to tap water infrastructure stemming from the intense oscillation, tsunami and liquefaction, it said, quoting the conclusions of an advisory panel to the prefecture.

An intense temblor would cut power to a combined 2.34 million households (55 percent) in the prefecture, and gas to 1.15 million (34 percent), according to the prefectural government.

Damage to buildings, distribution networks and other infrastructure would surpass ¥28 trillion.

Although the central government earlier predicted that a Nankai Trough quake would cut tap water to only 4.3 million people, Osaka’s projection almost doubles that estimate.

The prefecture’s estimate is more severe because it accounts for possible damage to water intakes along the Yodo River, its main source of tap water.

Any tsunami induced by the quake would put a combined 11,000 hectares of the area under water, roughly 3.6 times that estimated by the central government, it said.

Osaka also assumes the quake would trigger tsunami that would reverse the flow of the Yodo northeast toward Kyoto and reach the prefectural border in about two hours, it added.

The water intakes at 12 points along the river might be rendered useless, and direct damage to water pipelines is also feared, it says.

One option would be to open dams upstream to push the seawater back out, which would resolve the tap water problem in 40 days, it says.

Aside from drinking water, about 48 percent of Osaka’s cellphone networks could be damaged. The prefecture has about 20,000 relay stations.

Train services of all types might be disabled, the report says. In one scenario, 1.91 million people could face evacuation while 1.46 million others are left stranded in the city.

Kansai University professor Yoshiaki Kawata, who heads the panel, urged residents to get prepared.

“Numbers of this scale cannot be ignored. Residents of the prefecture must raise their alert levels and get prepared.”