2018 Hawaii earthquake

On May 4, 2018, an earthquake with a magnitude of Mw 6.9[4] struck Hawaii island in the Hawaii archipelago at around 12:33 p.m. local time.[5] The earthquake's epicenter was near the south flank of Kīlauea, which has been the site of seismic and volcanic activity since late April of that year.[6] According to the United States Geological Survey the quake was related to the new lava outbreaks at the volcano,[7] and it resulted in the Hilina Slump moving about two feet.[8] It was the largest earthquake to affect Hawaii since the 1975 earthquake, which affected the same region,[9] killing two people and injuring another 28.[10]

2018 Hawaii earthquake
Shakemap for the 2018 Hawaii earthquake
Hilo
Honolulu
UTC time2018-05-04 22:32:55
ISC event611928827
USGS-ANSSComCat
Local dateMay 4, 2018 (2018-05-04)
Local time12:33 p.m. HST
Magnitude6.9 Mww[1]
Depth5.8 km (4 mi)[2]
Epicenter19.313°N 154.998°W / 19.313; -154.998
TypeThrust fault
Max. intensityVIII (Severe)[3]
TsunamiYes (minor)
Casualties0

The earthquake had a maximum strength on the Mercalli intensity scale of VIII (Severe).[11] The earthquake was preceded by a smaller event, measuring 5.4, that was felt across the island and as far away as Oahu.[12]

The earthquake produced a minor tsunami that reached a maximum height of 40 cm (15.7 in.) in Kapoho, 20 cm (7.9 in.) in Hilo and 15 cm (5.9 in.) in Honuapo.[13]

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 associated with the gradual collapse of the island's flanks as it continues to be enlarged.[14] 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 10 cm/year (3.9 in/year). The slump moved during the May 4 earthquake by about 0.6 m (2.0 ft) and has moved during previous earthquakes, such as those in 1868 and 1975.[15]

Earthquake

The main earthquake was preceded almost exactly an hour earlier by a Mw  5.4 foreshock with a similar epicenter and focal mechanism.[16] Analysis of seismic waveforms suggest that the mainshock was most likely caused by slip on a thrust fault dipping at 20° to the northwest beneath the southeastern flank of the volcano.[17] The mainshock was followed by four aftershocks greater than Mw  4.5 over the next 30 minutes. Smaller aftershock continued to occur for months after the main earthquake.[18]

Further analysis of Love waves, whose radiation pattern gives a 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 overly 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.[19]

Damage

The quake damaged many buildings, caused landslides that damaged shorelines, and caused cracks in a road, causing it to be shut down.[20]

Foreshock and aftershock occurrence with time
Map of aftershock distribution

See also

References
  1. ANSS. "Hawaii 2018: M 6.9 – 19km SSW of Leilani Estates, Hawaii". Comprehensive Catalog. U.S. Geological Survey.
  2. ANSS: Hawaii 2018 .
  3. ANSS: Hawaii 2018, "ShakeMap" (accessed May 4, 2018).
  4. ANSS: Hawaii 2018 (accessed May 4, 2018).
  5. "USGS upgrades strength of latest Kilauea earthquake to magnitude 6.9; no tsunami". Honolulu Star-Advertiser. May 4, 2018. Retrieved May 4, 2018.
  6. "Magnitude-6.9 quake jolts Hawaii's Big Island". Associated Press. May 4, 2018. Retrieved May 4, 2018.
  7. The "lurch" of the M6.9 earthquake was prompted by pressure in the east rift zone due to the magma intrusion.,"Kīlauea Eruption FAQs: General Questions". Archived from the original on May 22, 2018. Retrieved May 22, 2018.CS1 maint: bot: original URL status unknown (link)
  8. "A Slow Emergency and a Sudden Slump". Berkeley Seismology Lab. May 7, 2018. Retrieved May 27, 2018.
  9. "6.9-magnitude quake rocks Big Island as Kilauea eruption continues". Hawaii News Now. May 4, 2018. Archived from the original on May 4, 2018. Retrieved May 4, 2018.
  10. "Hawaii: Two dead, 28 injured after 6.9-magnitude earthquake causes eruption in Kilauea volcano; residents flee – Firstpost". www.firstpost.com. Retrieved May 5, 2018.
  11. ANSS: Hawaii 2018 , "ShakeMap" (accessed May 4, 2018).
  12. "Earthquakes rock Hawaii's Big Island as Kilauea volcano erupts". CBS News. Associated Press. May 4, 2018. Retrieved May 4, 2018.
  13. "Third declaration of local information on tsunamis, Hawaii". PTWC. Archived from the original on May 5, 2018. Retrieved May 5, 2018.
  14. "About Earthquakes in Hawaii". Hawaiian Volcano Observatory. Retrieved July 30, 2018.
  15. Seismo Blog (May 7, 2018). "A Slow Emergency and a Sudden Slump". Berkeley Seismology Lab. Retrieved July 30, 2018.
  16. ANSS: Hawaii 2018 (accessed May 4, 2018).
  17. ANSS: Hawaii 2018, Finite Fault (accessed July 30, 2018).
  18. "Hawaiian Volcano Observatory Update". United States Geological Survey. September 25, 2018. Retrieved September 26, 2018. Small aftershocks from the magnitude-6.9 earthquake in early May are still being generated on faults located on Kīlauea's South Flank.
  19. Lay T.; Ye L.; Kanamori H.; Satake K. (2018). "Constraining the Dip of Shallow, Shallowly Dipping Thrust Events Using Long‐Period Love Wave Radiation Patterns: Applications to the 25 October 2010 Mentawai, Indonesia, and 4 May 2018 Hawaii Island Earthquakes". Geophysical Research Letters. 45 (19): 10, 342–10, 349. doi:10.1029/2018GL080042.
  20. "Lava from volcano's eruption destroys 2 homes, earthquake rattles Hawaii". ABC News. May 5, 2018. Retrieved May 5, 2018.
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