On 1 January 2024, at 16:10:09 JST (07:10:09 UTC), a 7.6 (7.5) earthquake struck north-northeast of Suzu, located on the Noto Peninsula of Ishikawa Prefecture, Japan. The reverse-faulting shock achieved a maximum JMA seismic intensity of Shindo 7 and Modified Mercalli intensity of X–XI (Extreme). The shaking and accompanying tsunami caused widespread destruction on the Noto Peninsula, particularly in the towns of Suzu, Wajima, Noto and Anamizu. Damage was also recorded in Toyama and Niigata prefectures.
There were 732 deaths confirmed and two people remain missing. At least 718 fatalities occurred in Ishikawa, 8 in Toyama and 6 more in Niigata. The mainshock also injured more than 1,400 people and damaged 204,903 structures across nine prefectures. Of these, 228 deaths were directly attributed to the earthquake, and the other 504 were disaster-related deaths aggravated by fear of aftershocks, electricity and water outages and evacuations to temporary shelters and other locations. It was the deadliest earthquake in Japan since the 2016 Kumamoto earthquake.
The Japan Meteorological Agency (JMA) officially named this earthquake the . It led to Japan's first major tsunami warning since the 2011 Tōhoku earthquake, and a tsunami of was measured in Wajima on the peninsula.
Tectonic setting Overview
Noto Peninsula lies on the southeastern margin of the Sea of Japan, which was formed by back-arc rifting related to subduction of the Pacific plate beneath the Eurasian plate along the Japan Trench. This process began during the Early Miocene, ending in the Middle Miocene. By the late Pliocene the tectonic regime changed to compression, probably associated with collision between the Izu–Bonin Arc and Honshu. This led to reactivation of the rift faults in reverse sense, combined with inversion of the basins formed by these faults. Currently Japan is situated on the convergent boundaries between the Pacific, Philippine Sea, North American and Eurasian Plates. Along the island arc's east and southeast coasts, subduction of the Pacific and Philippine Sea plates occurs at the Japan Trench and Nankai Trough, respectively. The west coast of Honshu, bordering the Sea of Japan, is a north–south trending convergent boundary between the Eurasian and North American Plates. It has been proposed that it is an incipient subduction zone, consisting of eastward-dipping thrust faults.
The rifting and subsequent inversion has created a series of faults along the coast that have the potential to move and cause earthquakes, in the range of 6.8–7.9, in many cases with tsunamis. Major earthquakes and tsunamis along this boundary occurred in 1833, 1940, 1964, 1983 and 1993. The largest and most destructive tsunami in the Sea of Japan occurred in 1741 and was attributed to the eruption of Oshima. A fault known as the F43 (in the list of 60 faults evaluated) reaches the seabed just north of the Noto peninsula trending WSW–ENE. This southeast-dipping fault, which consists of two segments with a combined length of , has been judged to be capable of producing an earthquake of 7.6.
Earthquake swarm
The northeastern tip of the Noto Peninsula has been subject to an earthquake swarm for the last three years, with the largest earthquake being a MJMA 6.5 event that took place in May 2023. The 1 January 2024 mainshock was the strongest to hit the peninsula since records began in 1885.
The swarm began in December 2020 at depths greater than beneath the peninsula's northeast. By mid-March 2021, the earthquake swarm migrated to shallower depths above . Most earthquakes after May 2021 occurred at depth. The 7.5 earthquake occurring after the swarm was deemed "rare". The general understanding of earthquake swarms are that due to the high intensity in crustal fracturing, such areas experiencing them are unlikely to generate large earthquakes. The swarm may have been triggered by the intrusion of fluids at deeper depths in response to crustal deformation.
Fluid upwelling may be occurring beneath the peninsula as evidenced by a uplift of the surface above the swarm. Seismologists considered the swarm unexpected as the peninsula lacked active volcanic or geothermal features to produce high-pressure fluids that would promote such seismic activity. These fluids may have originated from the upper mantle and migrated upwards into the crust through faults. Lubricated by fluids, these faults began producing earthquakes. No direct connection between the swarm and mainshock has been established, however, the swarm may have induced stress on these faults as they moved.
Earthquake
The United States Geological Survey (USGS) reported a moment magnitude of 7.5 and a focal depth of for the earthquake. The Japan Meteorological Agency recorded a magnitude of 7.6. It was the largest earthquake to strike Ishikawa since at least 1885, and the largest to strike Mainland Japan since the 2011 Tōhoku earthquake.
The focal mechanism of the mainshock corresponded to shallow reverse faulting along a northeast-trending plane dipping northwest or southeast, happening along the convergent boundary between the Okhotsk Plate and Amurian Plate. A magnitude 5.8 foreshock struck four minutes before the mainshock, while a magnitude 6.2 aftershock struck nine minutes later. More than 1,200 aftershocks were recorded across a zone. At least seven of them registered a magnitude of 5.0 and above.
According to a finite fault model released by the , the earthquake rupture extended over by from the southwestern Noto Peninsula to Sado Island along a southeast-dipping fault. Slip was mostly concentrated entirely beneath the peninsula. The zones of the largest slip occurred southwest of the hypocenter while little to no slip occurred on the segment offshore between the peninsula and island. The patch immediately southwest of the epicenter produced a displacement of beneath the peninsula's coast. Another zone of slip occurred further southwest beneath the same stretch of coastline, producing up to of slip beneath Motoichi. The fault likely ruptured towards the seafloor at the peninsula while little to no slip was observed on the seafloor between the peninsula and Sado Island. The entire rupture process took about 50 seconds with the greatest phase of seismic moment release occurring some 25 seconds after initiation.
Due to the lack of significant slip on the segment offshore between the peninsula and Sado Island, seismologist Kenji Satake said there is still potential for another magnitude 7.0 or larger earthquake and tsunami. Research led by Kimiyuki Asano at the Disaster Prevention Research Institute at Kyoto University analysed waveforms recorded by seismometers and determined the earthquake consisted of two subevents. The first subevent, measuring 7.3, ruptured a fault beneath the peninsula, causing coastal uplift. A second subevent identical in magnitude ruptured the offshore segment 13 seconds after the completion of the first subevent.
Ground effects
About of coastline spanning Suzu, Wajima and Shika was raised and the shore moved seawards by up to . Wajima's Minazuki Bay was uplifted while at Nagahashimachi's fishing port, a tide gauge was rendered unusable because the seafloor was exposed.
The Geospatial Information Authority of Japan (GSI) said parts of the country moved up to westwards with the maximum displacement observed at Wajima due to crustal deformation. At Anamizu, land shifted westwards. However, the agency said these movements could be slope or local ground movement instead. The agency also added that crustal uplift of occurred in western Wajima and in northern Suzu. Near Wajima's port, the shoreline of a sandy beach was moved seawards due to the coastal uplift. Uplift at Kaiso Fishing Port in Wajima by exposed parts of the seafloor.: – NHK : Three photo images with comment by AOKI Tatsuto 金沢大学, 青木賢人准教授– Kanazawa University; Caption (text); 4 m uplift in only one minute, a once-in-a-several-thousand-year (たった1分で4m隆起「数千年に1回」) Caption (text) in images are Kaiso Fishing Port (鹿磯漁港), Isikawa, Wajima-city, day before yesterday (2024/January/03) (石川 輪島市 おととい), Approx. 4 m uplift (約4 m 隆起) Slide down "Scrollbar" 23% to see; Ground effects of Seabed, Seabed uplift, photo images before and after the 2024 Noto earthquake – Fuji News Network Slide down "Scrollbar" 42% to see; Ground effects of Seabed, – Fuji News Network
The coastline in the Kawaura district of Suzu moved seawards due to the coastal uplift, while the land area expanded by a total of . A port in the Ozawa district of Wajima was entirely drained. A seaward movement of was detected in the coasts of Monzenmachi and Kuroshimamachi districts in Wajima, as well as an expansion of in the Noto Peninsula. Areas in the northern part of the peninsula were also found to have risen while the southern sections, particularly in Anamizu, had subsided.
The said due to the land expansion by , Ishikawa Prefecture may have become larger than Fukui Prefecture in land area. The latter, having an area of , is larger than Ishikawa Prefecture, according to a survey in October 2023. However, this difference was expected to be temporary due to the effects of coastal erosion. It has been theorized that the coastal uplift may have fortuitously lessened the effects of the tsunami which followed the earthquake.
Across the mountainous region of the peninsula, landslides were widespread. There were also extensive slope failures, particularly in the northeastern part of the peninsula. The number of landslides was estimated at 1,000. At least nine landslide dams were discovered in the Wajima area on 9 January, which had the potential to cause debris avalanches. In Wajima, a landslide dam caused water to overflow downstream into fields, potentially causing a collapse. In Jōetsu, Niigata, a landslide measuring buried a section of National Route 8.
A scarp trending east–west across a zone long and wide occurred along the Wakayama River in Suzu. The maximum vertical offset was in Naka district, Wakayama town. These scarps did not display any observable horizontal displacement. It propagated through and displaced rice fields, roads and rivers among other features. The said these scarps may represent a fold in response to compressive forces due to the geology of the area. However, they did not rule out the scarp being the toe of a landslide, though this is a less probable explanation.
Surveys by the Japan Coast Guard revealed a section of uplifted seafloor south of the active fault trace. The seabed north of the Noto Peninsula lies beneath the sea. The recent survey and survey results from the previous year suggested a uplift of the seafloor.
Intensity The Japan Meteorological Agency said it recorded a maximum seismic intensity of 7 (Shindo 7), the highest level on its seismic intensity scale, the first time that an earthquake of that intensity had been observed in the country since 2018. It corresponded to a maximum Modified Mercalli intensity of X–XI (Extreme). The USGS assigned a maximum intensity of IX (Violent). The maximum intensity was reported in Shika and Wajima, Ishikawa Prefecture. Intensity 6+ was recorded in Nanao, Suzu, Noto and Anamizu. Intensity 6– was recorded in Nagaoka in Niigata Prefecture and in Ishikawa's Nakanoto. The earthquake was also felt by residents in Tokyo and across the Kanto Region and as far as Aomori Prefecture in the northern tip of Honshu to Kyushu in the south of the country. A peak ground acceleration of 2,826 gal was observed in Shika, which was close to that recorded during the 2011 Tōhoku earthquake which measured 2,934 gal. Due to the ground beneath Wajima and Anamizu comprising soft sediments, ground motions were amplified. However, the amplification was strongly influenced by soil softening processes directly caused by the strong shaking. This also affected the observed intensity in Anamizu, Wajima, Monzen, and Noto Island.