Dix Seismo Lab Seminar

  The northern half of the emerging West-coast-wide ShakeAlert earthquake  early warning (EEW) system is comprised by Cascadian subduction. To speed  development and initial deployment of ShakeAlert, the Pacific Northwest is  using seismic algorithms developed in California in our prototype  demonstration EEW system (PNWShakeAlert). However,  in contrast with the  transform plate boundary through California, where quite active shallow  faults onshore traverse nearby or beneath sprawling major population  centers, the Cascadian boundary lies chiefly offshore and remote from the  rather sparse seismic network while onshore faults are poorly defined,  less active, and even the megathrust fault itself is seismically silent.  PNWShakeAlert has operated for a couple of years with an audience of about  2 dozen error-tolerant alert recipients representing a variety of  industries and agencies. To date our PNWShakeAlert has been tuned for the  regional network using both recorded and real-time data, and has performed  well. Because our most feared earthquakes will be great megathrust  subduction earthquakes 100s of kilometers long, we focus on issues of  scaling in this presentation. We expect current ShakeAlert to work well  for earthquakes up to magnitudes about 7. For larger earthquakes the  closest onshore monitoring sites will be in the near-field, and using GNSS  geodetic positioning data (the G-FAST system) becomes a very useful tool  for rapidly characterizing a fault rupture in progress. This presentation  summarizes progress to date and seeks to identify scientific questions as  well as engineering needs for future development of EEW in Cascadia.