1999 Ambrym earthquake

Earthquake and tsunami in Vanuatu 1999 Ambrym earthquake Vanuatu#Oceania 1999-11-26 13:21:17 1651802 iscgem1651802 1999 11 27 00:21:17 7.4 w y 30 km mi 0 on -16.41 168.15 region:VU_type:event inline,title New Hebrides Subduction Zone Back arc thrust belt Oblique-thrust Moderate 7 6.6 m on 5–10 dead, 40–100 injured The 1999 Ambrym earthquake occurred on November 27 at 00:21:17 local time 13:21:17 UTC with a moment magnitude of 7.4 and a maximum Mercalli intensity of VII (Very strong). The back arc thrust event occurred within the Vanuatu archipelago, just to the south of the volcanic island of Ambrym. Vanuatu, which was previously known as New Hebrides, is subject to volcanic and earthquake activity because it lies on an active and destructive plate boundary called the New Hebrides Subduction Zone. While the National Geophysical Data Center classified the total damage as moderate, a destructive local tsunami did result in some deaths, with at least five killed and up to 100 injured. This was one of very few events along the New Hebrides Subduction Zone that has been studied. Scientists from technical institutes in the region submitted papers to the scientific journals about the event, and while not all data on each of the aspects of the event are in agreement, what is certain is that the d'Entrecasteaux Ridge is producing unusual effects where it infringes into the subduction zone via the Indo-Australian plate. Tectonic setting The primary tectonic feature of the 1200 km on island chain is the New Hebrides Subduction Zone, the convergent boundary between the Indo-Australian and Pacific plates. Along the Wadati–Benioff zone, earthquake activity has been observed as shallow, intermediate, and deep-focus events at depths of up to 700 km on. Volcanic activity is also present along this north-northwest trending and northeast-dipping subduction zone.Active Faults of the World https://books.google.com/books?id=aQUgAwAAQBAJ Yeats R. 2012 Cambridge University Press 978-0521190855 478 While much of the island arc experiences intermediate-depth earthquakes along a Wadati–Benioff zone that dips steeply at 70°, the area adjacent to the d'Entrecasteaux Ridge does not. There is a corresponding gap in seismicity that occurs below 50 km on where it enters the subduction zone from the west. According to the NUVEL-1 global relative plate motion model, convergence is occurring at roughly 8 cm on per year. The uncertainty, which also affects the Tonga arc, is due to the influence of spreading at the North Fiji Basin. Of the 58 M7 or greater events that occurred between 1909 and 2001, few were studied.Deep Earthquakes C. Frolich 2006 Cambridge University Press 978-0805836523 399–401 Earthquake Scientists with the Institut de recherche pour le développement in New Caledonia investigated the extent of the aftershock zone and estimated that the rupture area was about 50 x 25 km on, but an inversion of GPS-based displacement data showed a smaller rupture area of 35 x 20 km on. It was also described as an intraplate event that occurred away from the east-dipping subduction interface on a west-dipping fault in an area with an uncertain type of convergence (either subduction or crustal thickening). The Harvard Centroid Moment Tensor project lists the slip vector as 67°, indicating that the mechanism was mostly thrust, with a significant amount of left-lateral strike-slip motion. Their submission for other fault parameters showed that the north-striking fault dipped shallowly at 30°. Damage thumb|USGS ShakeMap for the event Earthquake damage was limited to northern Pentecost Island, but the tsunami destroyed the village of Baie Martelli (population 300) on the southern tip of Pentecost. The loss of life there was minimal and could be attributed to well-educated people with regard to tsunami hazard, that even at the late hour, the villagers were awake because of a wedding celebration, and because of quick access to a safe area. Eyewitnesses described the initial phase of the tsunami as negative (withdrawal). This wave action came within 10 minutes of the earthquake and was followed shortly after by two larger waves that were separated by about 15 minutes. These waves destroyed all the buildings that were made of woven grass and corrugated metal roofs. The maximum height of the waves above sea level was 6.6 m on.Vanuatu Earthquake and Tsunami Cause Much Damage, Few Casualties P. Caminade D. Charlie U. Kanoglu S. Koshimura H. Matsutomi C. Ruscher C. Synolakis T. Takahashi 2000 Earth & Space Science News 81 52 641–647 10.1029/EO081i052p00641-02 2000EOSTr..81..641C free To the west of the epicenter on the island of Malakula, a moderate runup of just 1.8 m on caused the wooden cargo ship Halimon to sink while it was at anchor in 10 m on of water. The ship was loaded with 18 tons of copra (dried coconut meat). While the crew were asleep on board, the initial withdrawal of the tsunami caused the vessel to settle onto the bottom of the bay and list severely. Later, the first positive tsunami wave entered the harbor and swamped the vessel. Investigators were reminded of a similar situation from the much more destructive tsunami that followed the 1868 Arica earthquake in Chile that affected multiple vessels in a similar fashion. Tsunami A 6.6 m on wave height was recorded at the southern tip of Pentecost at the village of Baie Martelli. There, all simple structures were destroyed, except for a church. While the USGS placed the epicenter to the south of Ambrym island (very close to the ISC-GEM coordinates on the map), the Harvard epicenter is to the north (somewhat between Pentecost and Ambrym). The northerly location could account for the greatest runup that was observed on the south shore of Pentecost and the north shore of Ambrym. The wave heights decreased with distance from that location, but scientists lacked a source for the unexpected runups (1.6 m on to 2.6 m on) that were seen well to the south on the island of Efate.Numerical modeling of the 26 November 1999 Vanuatu tsunami M. Ioualalen B. Pelletier P. Watts M. Regnier 2006 Journal of Geophysical Research 111 C6 C06030 10.1029/2005JC003249 2006JGRC..111.6030I https://hal.archives-ouvertes.fr/hal-00407598/file/2005JC003249.pdf See also 2009 Vanuatu earthquakes Geography of Vanuatu List of earthquakes in 1999 List of earthquakes in Vanuatu References EXPO-CAT Earthquake Catalog https://earthquake.usgs.gov/static/lfs/data/pager/catalogs/ December 1, 2008 United States Geological Survey Version 2007-12 ISC-GEM Global Instrumental Earthquake Catalogue (1900–2012) https://www.isc.ac.uk/iscgem/index.php ISC 2016 International Seismological Centre Version 3.0 Significant Earthquake Database https://www.ngdc.noaa.gov/nndc/struts/form?t=101650&s=1&d=1 https://web.archive.org/web/20060929000601/http://www.ngdc.noaa.gov/nndc/struts/form?t=101650&s=1&d=1 dead September 29, 2006 National Geophysical Data Center / World Data Service (NGDC/WDS) National Geophysical Data Center, NOAA 10.7289/V5TD9V7K 1972 PAGER-CAT Earthquake Catalog https://earthquake.usgs.gov/static/lfs/data/pager/catalogs/ September 4, 2009 United States Geological Survey Version 2008_06.1 The Mw 7.5 1999 Ambrym earthquake, Vanuatu: A back arc intraplate thrust event M. Regnier S. Calmant B. Pelletier Y. Lagabrielle G. Cabioch 2003 Tectonics 22 4 1034 10.1029/2002TC001422 2003Tecto..22.1034R 128580339 free External links M7.5 – Vanuatu – United States Geological Survey Unusual mechanism of the Ambrym and Pentecost – Eurekalert! 1651802 Category:1999 earthquakes Ambrym Category:Earthquakes in Vanuatu Category:1999 in Vanuatu Category:November 1999 in Oceania Category:Malampa Province