The excitement around the Bowen earthquake last week reminded me of this now dated 1999 report I stumbled upon some time ago, with a foreword from a more youthful Warren Entsch. The building construction and location data would be well out of date by now I presume: COMMUNITY RISK IN CAIRNS A MULTI-HAZARD RISK ASSESSMENT
The earthquake hazard in Cairns is moderate by global standards, but it is not negligible. Over the past 100 years there have been at least 11 significant earthquakes reported within 200 km of Cairns, the most damaging being the Richter magnitude 4.3 event of 1896. In many places of Australia, probably including Cairns, moderate to strong earthquakes of Richter magnitudes 5 to 6 make up about 90% of the total contribution to the overall earthquake hazard. The occurrence of such an earthquake close to Cairns would be a rare event. However, its impact could be great. An earthquake in this magnitude range (Richter magnitude 5.6) near Newcastle in 1989 caused arguably Australia’s most costly 20th Century natural disaster.
We have constructed earthquake urban hazard zonation maps and, from the building database, produced an inventory of buildings, by construction type and usage, in the zones in these maps. Any earthquake of a magnitude likely to cause damage in Cairns will have an effect across all suburbs. The amount of damage, and consequently risk, will increase with the intensity of the event.
Whilst all suburbs have some degree of exposure, Risk-GIS analysis of the earthquake hazard reveals that some 86% of Cairns buildings stand on ‘soft’ sediments of the coastal plains and riverine deltas, or the sands, silts and clays of the lower footslopes. These sediments amplify earthquake shaking. The extensive ‘soft’ sediments beneath the coastal suburbs, in particular, would aggravate the impact of any significant earthquake. These are also the suburbs that contain many of the critical facilities and have significant concentrations of people, buildings and infrastructure. The remaining 14% of the buildings are mostly modern and are situated on the upper slope soils or rock of the hills where ground motions will be less damaging. Some of these buildings conform to the earthquake loading provisions of the Australian Building Code, and the majority conform to wind loading provisions.
In order to produce a suburb-by-suburb ranking of Cairns for earthquake risk from direct damage to buildings, we have introduced a vulnerability ranking of building construction types. The profile of risk exposure to earthquake and a total earthquake risk profile, which takes account of community vulnerability as well as the exposure to the hazard, are shown in Figures (v) and (vi