1868 Hawaii earthquake: Difference between revisions
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| UTC time | ?? |
|---|---|
| Magnitude | 7.9 ML |
| Epicenter | 19°12′N 155°30′W / 19.2°N 155.5°W |
| Areas affected |  United States, Hawaii |
| Tsunami | yes |
| Casualties | 77 |
The 1868 Hawaii earthquake was the largest recorded in the island's history, causing a landslide and tsunami that led to 77 deaths. The earthquake occurred at 4 p.m. local time on April 2, 1868. The aftershock sequence for this event has continued up to the present day.[1]
Background
The island of Hawaii is the currently active volcanic centre formed over the Hawaii hotspot. The two active volcanoes on the Big Island are Kilauea and Mauna Loa with a newer submarine volcano forming the Loihi Seamount 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.[2] This flank displacement is linked to extension within the rift zones associated with both of the active volcanoes, the Mauna Loa and Kilauea 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.[3]
The Hilina Slump
This is the largest of the active slumps around the Hawaiian islands. The '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.[4]
Damage
Wooden houses were knocked off their foundations in Keiawa, Punaluu and Ninole, while straw houses supported by posts in the same areas were torn to shreds.[5] At Kau nearly every stone wall and house was demolished in an instant.[6] At Waiohinu, a large stone church collapsed and in Hilo the shaking destroyed the few stone buildings and most walls.[5]
Landslides occurred over a wide area, the largest of which at Kapapala, on the flanks of Mauna Loa, swept away trees, animals and people, causing 31 fatalities.[5]
A tsunami struck the Kau-Puna coast, causing major destruction at Honuapo, Keauhou and Punaluu. 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.[5]
Characteristics
Earthquake
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.[6] 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 12 miles (19 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 Kilauea on the basal detachment at an estimated depth of 9 km,[7] and was probably triggered by the earlier event.[6]
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.[1]
Landslide
The earthquake triggered a mudslide 3 km wide and 9 m thick, that swept down the hillside at Kapapala.
Tsunami
The 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.[5]
Effect on volcanic eruptions
Kilauea was the most affected by the lateral displacement associated with the earthquake, as it did not have another major eruption until 1919.[6] 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.[8]
References
- ^ a b Klein, F.W. (2008). "Exponential decline of aftershocks of the M7.9 1868 great Kau earthquake, Hawaii, through the 20th century". Journal of geophysical research. 113 (B9): B09310.1-B09310.11. Retrieved 2009-11-09.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Bryan, C.J. (1991). "Block tectonics of the island of Hawaii from a focal mechanism analysis of basal slip". Bulletin of the Seismological Society of America. 81: 491–507. Retrieved 2009-11-12.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Morgan, J.K. (2000). "Overthrusting and sediment accretion along Kilauea's mobile south flank, Hawaii: Evidence for volcanic spreading from marine seismic reflection data". Geology. 28 (7): 667–670. Retrieved 2009-11-12.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Cannon, E.C. (2001). "Shallow Normal Faulting and Block Rotation Associated with the 1975 Kalapana Earthquake, Kilauea Volcano, Hawaii". Bulletin of the Seismological Society of America. 91 (6): 1553–1562. Retrieved 2009-11-12.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ a b c d e USGS. "Ka'u District, Island of Hawaii 1868 04 03 02:25 UTC (04/02/1868 local) Magnitude 7.9, Largest Earthquake in Hawaii". Retrieved 2009-11-11.
- ^ a b c d Hawaiian Volcano Observatory (2008). "The Great Ka`u Earthquake of 1868". Retrieved 2009-11-09.
- ^ Wyss, M. (1988). "A proposed source model for the great Kau, Hawaii, earthquake of 1868". Bulletin of the Seismological Society of America. 78 (4): 1450–1462. Retrieved 2009-11-12.
- ^ Tilling, R.I. (1987). "Disruption of the Mauna Loa Magma System by the 1868 Hawaiian Earthquake: Geochemical Evidence". Science. 235 (4785): 196–199. Retrieved 2009-11-11.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)