Report IDs Pacific Northwest as ‘Mega-Earthquake’ Hotspot

The Pacific Northwest is one of five regions in the world most likely to see a mega-earthquake, according to a new report. “When The Earth Moves: Mega-Earthquakes To Come?” published by Aon Benfield in conjunction with the Aon Benfield UCL Hazard Research Centre, identifies the Caribbean, Cascadia in North America, Chile, Indonesia and Japan as areas where mega-earthquakes of moment magnitude (Mw) 8+ are most likely to occur. In addition to the scientific assessment, the report addresses the (re)insurance implications of a mega-earthquake in each region.

The Cascadia Subduction Zone extends from Cape Mendocino in Northern California to central Vancouver Island in British Columbia, Canada. According to the report, the last mega-earthquake in this area occurred 300 years ago. “While the short- to medium-term probability of a mega-earthquake may be low, insurers should not disregard the associated risks to the cities along the coast,” the report said.

“Recent work suggests clustering of earthquakes into series of up to five events over 1,500 to 2,000 years, separated by quiet periods up to 1,200 years long. There have been three earthquakes in the past 1,000 years, suggesting that we are presently in the middle of an earthquake series,” the report further noted.

Aon predicted, however, that any earthquake rupture will most likely occur beneath the sea, well to the west of Portland, Seattle and Vancouver.

“Only moderate levels of seismic shaking (MMI VI (strong) to VII (very strong)) are predicted in major cities, but these will be long lasting: liquefaction and building resonance effects will be important in determining the level of damage. Secondary hazards, such as landslides and local tsunamis, are likely to be significant in Puget Sound, west of Seattle and Vancouver areas, owing to failures in thick sequences of post-glacial unconsolidated sediments. Smaller communities on the Pacific coast are predicted to experience greater levels of shaking at MMI IX (ruinous) and also be highly vulnerable to effects of tsunamis.”

The other four regions most at risk for a mega-earthquake are:

• Caribbean (Lesser Antilles) -The 2 centimeter year rate of plate convergence is enough to produce a mega-earthquake of Mw 9.0 once every 3,000 years. A major loss in the Caribbean would quickly use up available reinsurance capacity.
• Chile – As the only segment of the Chile-Peru Subduction Zone not to have ruptured within the past 100 years, the north Chile segment is now considered to be a region at high risk from an earthquake similar in size to the 2010 event. Following this year’s earthquake in Maule, reinsurance programs are now renewing with increases of 75 percent or more.
• Indonesia (Sumatra) – Padang is regarded as being at high risk from a mega-earthquake comparable to that which occurred in 1797, with a magnitude of 8.5 or more. A mega-earthquake would undoubtedly increase the price of reinsurance following a sizeable insured loss.
• Japan – The South Japan Subduction Zone (Nankai Trough) has a complex pattern of three segments. The largest earthquakes rupturing along the whole subduction zone may have magnitudes up to 8.6. A mega-earthquake in this region would most likely be a market-moving event.

John Moore, head of international analytics at Aon Benfield, explained: “2010 has already proven to be a devastating year for earthquakes, with events in Haiti and Chile providing the world with a tragic reminder of the power and destructive capabilities of these natural perils. …By examining the fault lines and historical precedence of earthquake activity in five of the world’s most vulnerable regions, this report sets out to assess the current risk and improve our understanding of where and when the next mega-earthquake could hit,”

Dr. Simon Day, researcher at the Aon Benfield UCL Hazard Research Centre, said the Maule earthquake that struck central Chile on Feb. 27, 2010, of moment magnitude (Mw) 8.8, is the most recent example of a subduction zone mega-earthquake and the seventh largest magnitude earthquake ever recorded. Most earthquakes of this kind are produced at subduction zones where an oceanic plate slides beneath another plate, known as the upper plate, and the down-going plate descends into the interior of the Earth as a subducted slab.

The report may be obtained at: www.aon.com/attachments/reinsurance/201006_global_mega_eq_report_web.pdf.