August 19, 2018 Earthquake: Fiji Islands

The August 18, 2018, M 8.2 earthquake near Fiji occurred as the result of deep, normal faulting approximately 560 km beneath the South Pacific Ocean several hundred kilometers to the west of the Tonga Trench. Focal mechanism solutions indicate that rupture occurred on a moderately dipping normal fault striking to the west-northwest or the east-southeast. At the location of this earthquake, the Pacific plate moves approximately due west relative to the Australia plate at a velocity of about 81 mm/yr. The location, depth, and focal mechanism solutions of the August 18th event indicate that the earthquake is related to faulting within the subducted Pacific slab.

Earthquakes that have focal depths greater than 300 km are commonly termed "deep-focus" earthquakes. Deep-focus earthquakes cause less damage on the ground surface above their foci than similar-magnitude shallow-focus earthquakes, but large deep-focus earthquakes may be felt at great distance from their epicenters. This earthquake is similar in size to the largest observed deep-focus earthquakes. The largest recorded deep-focus earthquake to date was the M 8.3 event that occurred at a depth of 600 km within the subducted Pacific plate beneath the Sea of Okhotsk offshore of northeastern Russia in 2013. The M 8.3 Okhotsk earthquake was felt all over Asia, as far away as Moscow, and across the Pacific Ocean along the western seaboard of the United States (though at distant locations, individuals reporting having felt the event were likely very favorably situated for the perception of small ground motions). The M 8.2 Bolivian deep-focus earthquake in 1994 had similarly been reported by individuals in North America at great distance from the epicenter.

Deep focus earthquakes are common near this event. Over the past century, 9 earthquakes with a magnitude of M 7+ have occurred within 250 km of this event, all at depths greater than 300 km. The largest of these prior to this event was an M 7.8 earthquake in January 1919.

Suva, Central, Fiji Islands - CDI: 5; Levuka, Eastern, Fiji Islands - CDI: 5; Nadi, Western, Fiji Islands - CDI: 5; Nausori, Central, Fiji Islands - CDI: 5; Haveloloto, Tongatapu, Tonga - CDI: 4

(all above from reference #13456)