Preparing for the Big One

The probability of a great Cascadia earthquake in the near future is low. The geological record suggests that they occur, on average, once every 600 years, although intervals between successive earthquakes differ considerably. Uncertainties in the number and ages of events (Atwater et al., 1995) result in a broad range of probabilities (from a few percent to perhaps 30%) that a great earthquake will occur somewhere along the Cascadia subduction zone in the next 50 years.

While a Cascadia subduction zone earthquake poses new challenges to engineers and emergency planners, it must be remembered that a large local crustal earthquake can also be devastating. One need only look at Kobe, Japan for an example. Kobe’s building code and earthquake preparedness plans, intended for a great earthquake on the Japanese subduction zone some 150 km away, proved to be totally inadequate for a much smaller, closer earthquake.

The British Columbia Ministry of Education has recently completed a $3 million seismic vulnerability assessment of most of its schools. About $600 million will be spent annually on upgrading schools, of which $30 million is specifically targeted for structural improvements related to earthquakes (Resources Inventory Committee, 1994). Since 1985, British Columbia Hydro and Power Authority has spent about $120 million upgrading its dams in southwestern British Columbia, with a significant portion going to seismic improvements (Resources Inventory Committee, 1994). The City of Vancouver has spent $1.1 million, and will be spending an additional $2.8 million, on three critical road bridges. Vancouver also has commissioned seismic vulnerability assessments of public buildings and is examining proposals to assess some 1200 private buildings (Resources Inventory Committee, 1994).

Some people question the value of spending large sums of public money preparing for a damaging earthquake. However, the devastation wrought by the Kobe earthquake, which result in 5470 deaths and damage of $200-300 billion CDN in a country widely acknowledged to have the highest level of earthquake preparedness in the world, provides a timely reminder of the need for a coordinated and well funded plan to assess hazard and reduce structural damage and loss of life due to a strong earthquake in southwestern British Columbia.