September 5, 2018 Earthquake: Hokkaido, Japan

41 people killed, including 36 from several landslides at Atsuma, and about 680 people injured in southern Hokkaido. Numerous buildings and roads damaged or destroyed at Sapporo. Dozens of houses destroyed from multiple landslides at Atsuma. Damage and fires occurred at Hokkaido's largest coal-fired plant causing power outages throughout the island. Liquefaction damaged roads in the epicentral area, as far away as Kiyota-ku.

The September 5, 2018, M 6.6 earthquake east of Tomakomai, on the island of Hokkaido, Japan, occurred as the result of shallow reverse faulting. Focal mechanism solutions for the earthquake indicate faulting occurred on either a moderately dipping reverse fault striking northwest, or on a shallow-to-moderately dipping fault striking southeast. At the location of this earthquake, the Pacific plate is moving towards the west-northwest at a velocity of about 87 mm/yr relative to the North America plate, subducting beneath Japan and Eurasia at the Japan and Kuril-Kamchatka Trenches to the east of the September 5th earthquake. Given the depth and focal mechanism solutions of this earthquake, the event likely represents rupture of a fault within the North America (upper) plate (or Okhotsk microplate), rather than on the subduction zone plate boundary interface between the Pacific and North America plates, which is at a depth of approximately 100 km at the location of this earthquake. Slip on a fault aligned with either nodal plane of the focal mechanism solution is consistent with this intraplate setting.

This reverse-faulting earthquake occurred in a collisional belt whose tectonics are driven by the convergence of the Pacific, Eurasia and North America plates. Hokkaido is made up of accreted terrain that roughly parallels the plate boundary to the east, and today's earthquake is located in the Oshima Belt region. Japanese seismic hazard maps indicate this earthquake was located in close proximity to the Nohoro-Kyuryo fault zone, with high hazard and an expected maximum magnitude of M~7.

While large earthquakes are common in Japan, and regularly cause damage, few moderate-to-large shallow intraplate earthquakes have occurred in the vicinity of today's earthquake. Over the preceding century, 70 earthquakes of M 6 or larger have occurred within 250 km of the September 5th earthquake, though only 6 of these occurred at shallow depths beneath Hokkaido. The most recent of these six upper plate events was a M 6.4 earthquake about 100 km to the east of today's event in January, 1970.

Chitose, Hokkaido, Japan - CDI: 8; Shizunai, Hokkaido, Japan - CDI: 7; Mombetsu, Hokkaido, Japan - CDI: 7

(above ref #13456)

damage to Hokkaido Electric's Tomato-Atsuma plant (ref #12219)

The death toll from a powerful earthquake in northern Japan last week rose to 44, with 660 injured, the government said on Monday (ref #12221)

The Hokkaido prefectural government in northern Japan reports this month's powerful earthquake has caused economic loss exceeding 350 million dollars to the local forestry, agriculture, and fishery industries. Officials say landslides triggered by the September 6th quake caused an estimated 200 million dollars' damage to mountain forests in Atsuma, Abira and Mukawa towns (ref #12227)

USD 2 bn losses (ref #12634)

max intensity of 7 was registered in Atsuma [...] 41 lives were lost and approximately 15000 buildings were damaged (partially or fully)[...] earthquake triggered nearly 6000 landslides, which claimed 36 lives (ref #12824)

The 2018 Hokkaido Eastern Iburi Earthquake [...] triggered more than 6000 landslides and 259 rockslides in the area. Of the total of 44 fatalities resulted from this earthquake, 36 were caused by earthslides and rockslides in Atsuma town (ref#13072)

42 fatalities 762 injured. Housing: Complete collapse: 462, partial collapse: 1570, partial damage: 12,600 (ref# 13217)