REGIONAL TSUNAMI SOURCES (Cont) Southern New Hebrides The central and southern parts of the New Hebrides subduction zone are regional sources according to our criteria based on travel-time, while the northern part is a distant source. Large earthquakes with magnitude up to 8.5, causing tsunami with run-ups of 12 m locally, have occurred near Vanuatu in the central part of the New Hebrides region. The central part of the New Hebrides subduction zone is not well oriented to direct tsunami towards New Zealand. The southern part is well oriented, but here the record of earthquakes is probably complete only from 1960 onward. The historical record of earthquakes in the Southern New Hebrides is short, and complete for major earthquakes (MW >~7.5) only over the past century. This is primarily a consequence of their remote location, the largely uninhabited nature of the few islands in the eastern part of the arc, and the lack of surviving oral history accounts from the pre-colonisation cultures on the islands. The largest historical event occurred in August 1901, with an estimated magnitude of 7.9–8.4, and several lives were lost on islands close to the earthquake due to the tsunami. The observed maximum water heights in Hawaii from this tsunami were up to 1.2 metres, and were significantly larger than those of the 2009 MW 8.1 Samoa earthquake. On this basis, favour the interpretation of a moment magnitude for this event of around 8.4. show that earthquakes larger than an MW 8.0 on the southern section of the New Hebrides trench (Figure 5.1) could present a significant hazard for Northland. An under-sea ridge (the Three Kings Ridge) extends north from Cape Reinga and acts as a waveguide, leading to potentially hazardous wave heights in the northern North Island. Numerical models show that earthquake scenarios ranging from MW 8.15 to MW 8.8 on the southern New Hebrides Trench could lead to maximum tsunami heights of 2 to 15 m respectively at highly amplifying sites in the far north, such as the Aupouri Peninsula. Along the eastern and western coastlines of Northland, maximum expected tsunami heights range from less than 1 to ~5 metres as the magnitude ranges from MW 8.15 to MW 8.8.
Posted on: Sat, 15 Mar 2014 00:34:23 +0000