Early Warning of Cascadian Megaquakes for Pacific Northwestern cities

The Cascadia subduction zone offers great utility from earthquake early warning for the Puget Sound, Portland, Vancouver, and the tsunami-vulnerable coast. The 1000-km length allows minutes of warning when a megaquake starts at a distance, as is likely. The 10,000-year record of the last several dozen great earthquakes from offshore turbidites allows good guessing of the chance of a big earthquake growing into a turbulent giant. We are far enough into the 500-year M9 cycle to have 150% of the long term odds - 1/300 odds each year. The southern stretch of Cascadia, which is prone to M8s as well as M9s, is even more primed for action. Challenges are also outsized. Instrumentation is relatively sparse. Discrimination between a wide range of possible styles and depths of strong earthquakes will be difficult. Means of relaying warnings, discussions with potential users, and long-term funding are not yet mature. The UW and UC Berkeley, with the support of the Moore Foundation, are constructing a prototype early warning system. We are beginning with duplicate installations of the ElarmS algorithm in Seattle and Berkeley, and sharing data across borders. We are also exploring inclusion of GPS displacements in verifying the magnitude and development of large earthquakes.