Cascadia earthquake damage may be less than initially assumed

Updated earthquake research by the United States Geological Survey is reporting that expected damage to buildings as a result of a Pacific Northwest earthquake in the Cascadia Subduction Region (which also affects B.C.) could be lower than initially assumed.The research includes the use of “Next-Generation Attenuation (NGA) Equations,” which predict how ground motion decays with increasing distance from an earthquake’s epicenter.Based on its use of NGA equations, the latest earthquake research shows a changing modelled hazard of between -15% and +5% in the Pacific Northwest region of the United States. The changing modelled hazard could possibly mean a change to the modelled damage to buildings as a result of the earthquake, according to a report released by Willis, ‘Preparing for a New View of U.S. Earthquake Risk.’The Willis report notes that if ground motion and hence the hazard risk decreases in a region, then all other things being equal, so too will the expected damage to buildings.”Based on the shape of a building damage function for earthquakes, the amount of damage a building incurs rapidly decreases as the ground motion decreases (all other components remaining unchanged),” the report notes. “Therefore, a 20% increase in hazard can equal a 30-50% decrease in expected damage.”These observations could have a bearing on earthquake modelling done by AIR, EQECAT and RMS, Willis notes.The Willis report also notes that: “There is a 10% chance in the next 30 years the Cascadia Subduction Zone will generate a8-9 [magnitude] event along the subduction zone somewhere between Northern California and Washington State.”