1868 Hawaii earthquake

The island of Hawai{{okina}}i (commonly called the "Big Island") is the currently active volcanic center of the Hawaiian Islands formed over the Hawaii hotspot. Two of the active volcanoes on the Big Island are Kīlauea and Mauna Loa with a newer submarine volcano forming the Kamaʻehuakanaloa Seamount (formerly Lōʻihi) to the southeast of the island. Continued growth of the southeastern part of the island is accompanied by major slumping and southeastward movement of the flanks of the two volcanoes.{{cite journal|last=Bryan|first=C.J.|author2=Johnson C.E.|year=1991|title=Block tectonics of the island of Hawaii from a focal mechanism analysis of basal slip|journal=Bulletin of the Seismological Society of America|publisher=Seismological Society of America|volume=81|issue=2|pages=491–507|url=http://www.bssaonline.org/cgi/content/abstract/81/2/491|access-date=2009-11-12|archive-date=2011-09-30|archive-url=https://web.archive.org/web/20110930202541/http://www.bssaonline.org/cgi/content/abstract/81/2/491|url-status=dead}}

This flank displacement is linked to extension within the rift zones associated with both of the active volcanoes, the Mauna Loa and Kīlauea rifts. From the interpretation of seismic reflection data, it has been proposed that the southeastward displacement takes place on a decollement surface near the top of the oceanic crust. The slumping is thought to affect only the upper part of the flank as the amount of shortening observed in the toe thrust zone is much larger than that observed in the extensional faults associated with the slumps, but matches well with estimates of extension within the volcanic rift systems.{{cite journal|doi=10.1130/0091-7613(2000)28<667:OASAAK>2.0.CO;2|last=Morgan|first=J.K.|author2=Moore G.F.|author3=Hills D.J.|author4=Leslie S.|name-list-style=amp|year=2000|title=Overthrusting and sediment accretion along Kīlauea's mobile south flank, Hawaii: Evidence for volcanic spreading from marine seismic reflection data|journal=Geology|publisher=The Geological Society of America|volume=28|issue=7|pages=667–670|bibcode = 2000Geo....28..667M }}

{{Main|Hilina Slump}}

The Hilina Slump is the largest of the active slumps around the Hawaiian islands. The '{{Not a typo|backscarp}}' to the slump is formed by the Hilina extensional fault system, which is known to have moved in both the 1868 event and the 1975 Kalapana earthquake.{{cite journal|doi=10.1785/0120000072|last=Cannon|first=E.C.|author2=Bürgmann R.|author3=Owen S.E.|name-list-style=amp|year=2001|title=Shallow Normal Faulting and Block Rotation Associated with the 1975 Kalapana Earthquake, Kilauea Volcano, Hawaii|journal=Bulletin of the Seismological Society of America|publisher=Seismological Society of America|volume=91|issue=6|pages=1553–1562|url=http://bssa.geoscienceworld.org/cgi/content/abstract/91/6/1553|access-date=2009-11-12|bibcode = 2001BuSSA..91.1553C }}

A firsthand description of the events was written by Frederick S. Lyman, a goat and sheep rancher at Keaīwa near the epicenter of the events.{{cite journal |title= Recent Eruption of Mauna Loa and Kilauea, Hawaii |journal= American Journal of Science and Arts |publisher=American Journal of Science|volume= 96 |date= July 1868 |pages= 105–123 |url= https://books.google.com/books?id=U_YQAAAAIAAJ&pg=PA111 |access-date= December 11, 2010 |issue= 136 |bibcode= 1868AmJS...46..105D |last1= Dana |first1= J. D |last2= Coan |first2= T |doi= 10.2475/ajs.s2-46.136.105 |s2cid= 130168932 }} A sequence of foreshocks began on March 27, with tremors every few minutes. They increased steadily in intensity, including one on March 28 that had an estimated magnitude of 7.1. The sequence continued until 4 p.m. on April 2, when the mainshock occurred. One interpretation of this sequence of events is that they were related to the movement of two separate landslide structures on the south side of the island. The first, triggered by an eruption that began in the upper part of Mauna Loa's southwest rift, involved movement of a block that extended seawards for at least {{convert|12|mi|km}}. The tremors over the next four days are regarded as aftershocks of the 7.1 event caused by this movement. The mainshock involved movement of the entire southern flank of Kīlauea on the basal detachment at an estimated depth of {{convert |9|km|sp=us}},{{cite journal |author=Max Wyss |year=1988 |title=A proposed source model for the great Kau, Hawaii, earthquake of 1868 |journal=Bulletin of the Seismological Society of America |publisher=Seismological Society of America |volume=78 |issue=4 |pages=1450–1462 |doi=10.1785/BSSA0780041450 |bibcode=1988BuSSA..78.1450W |url=http://www.bssaonline.org/cgi/reprint/78/4/1450 |access-date=2009-11-12 |archive-date=2008-09-05 |archive-url=https://web.archive.org/web/20080905080420/http://www.bssaonline.org/cgi/reprint/78/4/1450 |url-status=dead }} and was probably triggered by the earlier event.

The aftershock sequence has continued for over 140 years until the present day. The aftershock frequency fits a modified Omori (power law) for the first few decades and an exponential function thereafter.

File:Waiohinu Church destroyed by the earthquake, 1868, photograph by H. L. Chase, Mission Houses Museum Archives.jpg, 1868]]

Wooden houses were knocked off their foundations in Keaīwa, Punalu{{okina}}u Beach and Nīnole, while thatched houses supported by posts in the same areas were torn to shreds.{{cite web|url=https://earthquake.usgs.gov/earthquakes/states/events/1868_04_03.php|title=Ka'u District, Island of Hawaii 1868 04 03 02:25 UTC (04/02/1868 local) Magnitude 7.9, Largest Earthquake in Hawaii|publisher=United States Geological Survey|access-date=2009-11-11|archive-url=https://web.archive.org/web/20161110065202/http://earthquake.usgs.gov/earthquakes/states/events/1868_04_03.php|archive-date=2016-11-10|url-status=dead}} The earthquake demolished nearly every stone wall and house within the Ka{{okina}}ū district in an instant.{{cite web |url=http://hvo.wr.usgs.gov/volcanowatch/1994/94_04_01.html |title= The Great Ka'u Earthquake of 1868 |publisher= Hawaiian Volcano Observatory |date= April 1, 1994 |access-date= December 11, 2010 |archive-url=https://web.archive.org/web/20160629175821/http://hvo.wr.usgs.gov/volcanowatch/archive/1994/94_04_01.html|archive-date=June 29, 2016}} At Wai{{okina}}ōhinu, a large stone church built by Reverend John D. Paris collapsed, and in Hilo the shaking destroyed the few stone buildings and most walls.

A tsunami was caused by coastal subsidence associated with reactivation of the Hilina Slump, triggered by the earthquake. At Kapapala the land subsided by as much as 2 m and formerly dry land was flooded to a depth of 1.5 m.

The tsunami on the Ka{{okina}}ū and Puna coasts caused major destruction at Honu‘apo, Keauhou and Punalu{{okina}}u. The greatest damage was caused at Keauhou, where a wave height of 12–15 m was reported. All houses and warehouses were destroyed and 46 people were drowned.

Many villages, such as {{okina}}Āpua, were never resettled.{{Hawaiian Dictionaries |Apua |dic=pp |accessdate= December 11, 2010 }}

The earthquake triggered landslides over a wide area. The largest was a mudslide 3 km wide and 9 m thick, that swept down the flanks of Mauna Loa at Kapapala. It swept away trees, animals and people, causing 31 fatalities.

File:Lava bed at Kahuku, Hawaii, 1868, photograph by H. L. Chase, Mission Houses Museum Archives.jpg

Kīlauea was the most affected by the lateral displacement associated with the earthquake, as it did not have another major eruption until 1919. It also disrupted the magma system beneath Mauna Loa, as is shown both in reduced lava volumes and an abrupt change in the lava chemistry.{{cite journal|doi=10.1126/science.235.4785.196|last=Tilling|first=R.I.|author2=Rhodes J.M.|author3=Sparks J.W.|author4=Lockwood J.P.|author5=Lipman P.W.|name-list-style=amp|year=1987|title=Disruption of the Mauna Loa Magma System by the 1868 Hawaiian Earthquake: Geochemical Evidence|journal=Science|publisher=American Association for the Advancement of Science|volume=235|issue=4785|pages=196–199|url=http://www.sciencemag.org/cgi/content/abstract/235/4785/196|access-date=2009-11-11|pmid=17778633|bibcode = 1987Sci...235..196T |s2cid=37524089 }}

• List of earthquakes in Hawaii
• List of earthquakes in the United States
• List of historical earthquakes
• List of tsunamis

{{Reflist|30em|refs=

{{citation|title=Significant Earthquake Information|url=https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/21251|author=National Geophysical Data Center / World Data Service (NGDC/WDS)|work=NCEI/WDS Global Significant Earthquake Database|publisher=National Geophysical Data Center, NOAA|doi=10.7289/V5TD9V7K|year = 1972|type = Data Set}}

{{citation|last1=Stover|first1=C. W.|last2=Coffman|first2=J. L.|title=Seismicity of the United States, 1568–1989 (Revised)|series=U.S. Geological Survey Professional Paper 1527|url=https://books.google.com/books?id=bY0KAQAAIAAJ|year=1993|publisher=United States Government Printing Office|page=207}}

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{{Earthquakes in 1868}}

{{Earthquakes in the United States}}

{{Hawaiian volcanism}}

{{DEFAULTSORT:Hawaii earthquake, 1868}}

Hawaii Earthquake, 1868

1868

Category:Geography of Hawaii (island)

Category:19th-century tsunamis

Category:1868 natural disasters

Earthquake

Category:April 1868

Category:Volcano tectonic earthquakes

Category:19th-century volcanic events

Category:Volcanic tsunamis