Why Almost 150 Earthquakes Struck Japan in Less Than a Day

A big earthquake rattled Japan's northwestern coast on New Year's day, killing dozens and rekindling fears of the tsunami that ravaged the nation's northern region in 2011. It was one of about 150 to strike the region over the day. 

Japan is located in one of the most active seismic regions in the world, with the whole country at risk of being affected by quakes. Here's a look at the quake and its effects.    

What happened?

A magnitude 7.6 earthquake struck off the Noto Peninsula on Japan's northwest coast on Jan. 1 just after 4 p.m. locally, killing at least 48 people and injuring many more, according to local officials.    

Collapsed houses following an earthquake in Nanao, Ishikawa Prefecture, Japan, on January 2.

The quake triggered a tsunami warning for almost all of the country's Sea of Japan coastline on Jan. 1, gripping the nation at the start of the New Year, when many were celebrating with friends and family. The Japan Meteorological Agency issued a warning for a wave of up five meters (16 feet) on January 1, but it lifted all tsunami alerts on Tuesday at 10 a.m. after recording a wave of at least 1.2 meters in height.

This was one of the largest quakes in Japan since 2018 and resulted in damage to at least 200 structures, left thousands without power and running water, and caused stoppages to rail and road traffic around the region.

Are more quakes expected imminently?      

Past instances show there is a risk of up to 20% that another quake of the same size could take place, the Japan Meteorological Agency said in a press briefing. Residents in the area continue to be hit by frequent aftershocks, which are putting structures in the region at even greater risk. 

People in areas worst affected should be on alert over the next week for the possibility of large earthquakes and potentially tsunami, according to JMA.

What's the worst case scenario?

The worst case scenario is that an additional large earthquake could hit the northwest and trigger a tsunami of the scale that authorities initially warned about on Jan. 1.  

Why did the quakes occur in a cluster?

There are a number of active faults off the Noto Peninsula, with the compression pushing underground plates together and forcing one above the other, according to Japan's Headquarters for Earthquake Research Promotion. This is known as a reverse-type fault mechanism. Earthquakes have been increasing in the area since 2018, with seismic activity becoming higher over the past three years.

There were more than 14,000 small earthquakes occurring off the Noto peninsula in seismic swarm from November 2020 to February 2023 with a magnitude of 1 or more, according to a paper by experts at Japanese universities. A 6.5 magnitude earthquake in the Noto area killed at least one person in May last year.

Considering the changes in crustal deformation zones in the region, it's possible that fluid movements were involved in earlier quakes, according to a report released by the government's earthquake research council.

The biggest earthquake in the Noto peninsula over the last century was the Noto-Hanto earthquake that occurred on March 25, 2007 with a magnitude of 6.9.

How dangerous can quakes be in Japan?

In Japan, thousands of people have died due to major earthquakes in recent decades, with a large part of the northern region needing to be rebuilt after what is locally called the Great East Japan Earthquake of 2011. That earthquake and subsequent tsunami resulted in about 20,000 deaths with about 2,500 going missing, according to government statistics.

Thousands of buildings were damaged, with more than 120,000 totally collapsing in 2011. The disaster also resulted in Japan's worst nuclear disaster at Tokyo Electric's Fukushima plant, requiring the government to bail out the utility. The government raised taxes to rebuild its northern regions. 

In 1995, more than 6,000 people died in the Kobe earthquake, while in more recent years, the Kumamoto earthquake in 2016 killed over 200 people. The death count from an earthquake that struck Tokyo in 1923 is believed to have exceeded 100,000, according to official statistics. 

Does Japan have a warning system in place?

Japan's meteorological agency has an earthquake early warning (EEW) system that has been in place since 2007. Authorities have improved measurement techniques since the events of 2011 and 2016 to better judge the size of multiple earthquakes occurring at the same time. But the EEW system has still sent false alarms, including in 2018 and 2020, causing concern.

Japanese residents with smartphones receive loud alerts on their phones in the case of a sizable earthquake, warning them to take safety precautions. In Japan, residents are well used to earthquakes and one of the first things they do when feeling a tremor is to turn on the national broadcaster NHK which carries extensive coverage, while other TV stations also flash quake alerts across their screen.

People also increasingly rely on the Internet for quick information, even though it contains inaccurate or misleading information. Prime Minister Fumio Kishida urged strict caution against the spread of misinformation that could amplify confusion in the field. Also, despite the growing importance of mobile services, major telecommunications carriers have often reported connection failures after earthquakes.

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)