As an emeritus member of the Seismological Society of America, I have grave concerns about building multi-story structures on the unconsolidated sediments that lie beneath Arcata's Gateway Project footprint. During an earthquake, ground shaking in these bay and river deposits can be amplified by two to five times as compared to bedrock sites, such as that which Founders Hall sits on.
Compounding this site's amplification problem, Arcata has the distinction of sitting directly over the locked portion of the southern Cascadia subduction zone. This means that the boundary between the North American plate and the subducting Gorda plate is building up stored strain energy (locked), and when it reaches a certain limit as it did in January 1700, it will snap and shake Arcata violently for more than one minute. This has happened in the past and will happen in the future. In all the world, only two locations have a population sited directly over a locked subduction zone interface. We also have to consider the more frequent offshore Gorda plate earthquakes ("Turns Out the Dec. 20 Earthquake was Actually Two," posted online Jan. 30) and the San Andreas and Mendocino faults as sources of damaging ground shaking.
I have no problem with infilling, for that is the proper thing to do. I think the project has many merits, but I would advise that the height of future buildings be limited on ground that behaves as Jello during earthquakes to avoid potential structural failures (even if engineered) that may cause loss of life.
R.C. McPherson, Bayside