Date 18/09/2011
Emergency Management Academy of New Zealand
Introduction
The Greater Wellington Region is vulnerable to a number of natural hazards including: earthquakes, tsunamis, storms, flooding, and volcanic events. This essay, aimed at Emergency Management Officers, provides a basic overview of these natural hazards that could affect the region.
The hazards have been identified using the US Federal Emergency Management Agency (FEMA) model of hazard assessment (Tonkin and Taylor Ltd, 2006). This determines risk based on four criteria; history; probability; vulnerability and maximum threat. The earthquake intensity measurement used is the Modified Mercalli scale (MMI) (USGS, 2009). This information is used by the Emergency Management Office to evaluate the impact on social, build, natural and economic effects on the community. Hazard: Earthquake
i) Recent Events
The largest earthquake in the Greater Wellington Region occurred in 1855, registering a magnitude 8.2 (MMI) in the Wairarapa region (Cousins et al., 2008). More recent events occurred in the region in 1942, measuring 7.2 (24th June) and 6.8 (2nd August) with many aftershocks (McSaveny, 2009). ii) Frequency of Event
The estimated frequency of major earthquakes in the region areas is: Wellington fault 7.5 MMI every 500 to 1000 years, 335 to 485 has elapsed since the last major event; the Wairarapa fault 8.2 MMI 1 in 1000 years; the Boo Boo fault 7.4 MMI returning event 1 in 500 years; the Sub Conduction Zone Cook Strait area returning 1 in 1200 years (Cousins et al., 2008).
iii) Impact of Event
At the time of the 1942 event, the population and urbanization density was low in the region. The event caused injury to people, major structural damage and affected an 80 km wide area from the centre. Records at the time reported 5,000 homes and businesses affected, main transport routes and lifeline utilities were disrupted. Complete recovery took several years (McSaveny, 2009).
iv) Maximum likely event scenario Earthquakes occur without warning and the region-wide impact would be severe. A 7.0 intensity earthquake would result in death and mass casualties; extensive damage to private and public facilities; disruption of transport routes and communications and public utilities. In addition to the earthquake event, other hazards such as a tsunami, fire, landslips, and hazardous material spills could ensue (Cousins et al., 2008; Van Dissen et al., 2001).
The maximum scenario using current research puts the event risk as likely, the results catastrophic rated an extreme event; however, effects depend on which fault ruptures (Van Dissen et al., 2009). (FEMA Rating 181)
Hazard: Storms
i) Recent Events
In 1968 there was a cyclone (Gisele) (NIWA, 2011). Eight years later the 1976 storm events caused extensive flooding of the Hutt Valley, Johnsonville and Tawa (Tomlinson, 1978). The 2004 storm event cause flooding in the Hutt Valley and Wairarapa areas (GWRC, 2011). ii) Frequency of Event
Extreme storm events -the ex–tropical cyclone - typically occurs between December and April and the frequency is estimated to be between once every three to six years. The intensity is dependent on the phases of the El Nino/La Niño cycle (NIWA, 2002). Severe storms can be another source; numerous warnings are issued yearly, on average the region experiences 173 days per year of high wind warnings (NIWA, 2002). iii) Impact of Event
The 1968 Cyclone caused the Wahine ferry sinking, with 51 lives lost, flooding, high wind damage to private and business properties, and transport disruption throughout the region (NIWA, 2011). The1976 and 2004 storm events caused evacuation of houses due to flooding, disruption occurred to transport routes and power disruption with high wind damage to commercial
