On May 4, 2018, an earthquake with a magnitude of 6.9 struck

Hawaii island Hawaii ( ; haw, Hawaii ) is the largest island in the United States, located in the state of Hawaii. It is the southeasternmost of the Hawaiian Islands, a chain of volcanic islands in the North Pacific Ocean. With an area of , it has 63% o ...

in the

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only ...

archipelago at around 12:33 p.m.

local time Local time is the time observed in a specific locality. There is no canonical definition. Originally it was mean solar time, but since the introduction of time zones it is generally the time as determined by the time zone in effect, with dayligh ...

. The earthquake's

epicenter The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

was near the south flank of

Kīlauea Kīlauea ( , ) is an active shield volcano in the Hawaiian Islands. Located along the southeastern shore of the Big Island of Hawaii, the volcano is between 210,000 and 280,000 years old and emerged above sea level about 100,000 years ago. Hi ...

, which has been the site of seismic and volcanic activity since late April of that year. According to the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

the quake was related to the new lava outbreaks at the volcano, and it resulted in the Hilina Slump moving about two feet. It was the largest earthquake to affect Hawaii since the 1975 earthquake, which affected the same region, killing two people and injuring another 28. The earthquake had a maximum strength on the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the effe ...

of VIII (''Severe''). The earthquake was preceded by a smaller event, measuring 5.4, that was felt across the island and as far away as

Oahu Oahu () ( Hawaiian: ''Oʻahu'' ()), also known as "The Gathering Place", is the third-largest of the Hawaiian Islands. It is home to roughly one million people—over two-thirds of the population of the U.S. state of Hawaii. The island of O� ...

. The earthquake produced a minor

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...

that reached a maximum height of 40 cm (15.7 in.) in

Kapoho Kapoho, Hawaii, is a now-uninhabited unincorporated area in Puna district, Hawaii County, Hawaii, located near the eastern tip of the island of Hawaii, in the easternmost subaerial end of the graben overlying Kīlauea's east rift zone. Originally ...

, 20 cm (7.9 in.) in

Hilo Hilo () is a census-designated place (CDP) and the largest settlement in Hawaii County, Hawaii, United States, which encompasses the Island of Hawaii. The population was 44,186 according to the 2020 census. It is the fourth-largest settlement i ...

and 15 cm (5.9 in.) in

Honuapo Honuapo or Honuʻapo is a ghost town on the island of Hawaii in the U.S. state of Hawaii. It was a thriving port town from the 1870s to the 1930s. The port was used to transport ''Colocasia esculenta'' (taro), and sugarcane Sugarcane or suga ...

Tectonic setting

Hawaii island is affected by a large number of minor earthquakes related to the movement of magma beneath its active volcanoes. Additionally there are less frequent tectonic earthquakes that are caused either by faulting within the volcanoes or by slip along the basal detachment surface at the top of the

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafi ...

associated with the gradual collapse of the island's flanks as it continues to be enlarged. Near Kilauea volcano, the largest structure formed by the collapse of the southeastern flank of the island is the Hilina slump. This slump moves seaward at an average rate of . The slump moved during the May 4 earthquake by about and has moved during previous earthquakes, such as those in

1868 Events January–March * January 2 – British Expedition to Abyssinia: Robert Napier leads an expedition to free captive British officials and missionaries. * January 3 – The 15-year-old Mutsuhito, Emperor Meiji of Ja ...

and

1975 It was also declared the ''International Women's Year'' by the United Nations and the European Architectural Heritage Year by the Council of Europe. Events January * January 1 - Watergate scandal (United States): John N. Mitchell, H. R. ...

Earthquake

The main earthquake was preceded almost exactly an hour earlier by a 5.4

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full sequ ...

with a similar epicenter and

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and ...

. Analysis of seismic waveforms suggest that the mainshock was most likely caused by slip on a

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

dipping at 20° to the northwest beneath the southeastern flank of the volcano. The mainshock was followed by four aftershocks greater than 4.5 over the next 30 minutes. Smaller aftershock continued to occur for months after the main earthquake. Further analysis of

Love wave In elastodynamics, Love waves, named after Augustus Edward Hough Love, are horizontally polarized surface waves. The Love wave is a result of the interference of many shear waves (S-waves) guided by an elastic layer, which is ''welded'' to a ...

s, whose radiation pattern gives greater discrimination on low-angle dips, indicate that the rupture occurred on a plane dipping at about 7°, consistent with it happening at the base of the Hawaiian volcanic rocks, where they overlie sedimentary rocks on the earlier seafloor. The calculated low rupture speed is also consistent with propagation along a relatively weak zone. This would make it similar to the 1975 Kalapana earthquake.

Damage

The quake damaged many buildings, caused landslides that damaged shorelines, and caused cracks in a road, causing it to be shut down.

References

External links

* {{Earthquakes in 2018 2018 earthquakes 2018 in Hawaii Earthquakes in Hawaii May 2018 events in the United States May 2018 events in Oceania 2018 tsunamis

Tectonic setting

Earthquake

Damage

See also

References

External links