For what it's worth, the 2001 Nisqually earthquake was not on any of the faults in the Puget Lowland, it was in the subducting Juan de Fuca slab, and was quite

For what it's worth, the 2001 Nisqually earthquake was not on any of the faults in the Puget Lowland, it was in the subducting Juan de Fuca slab, and was quite deep (57 km) which reduced the ground shaking considerably. That said there are cracks in my office walls from it, and the chem labs in the building were decomissioned following seismic damage. You are right, though, that there are a host of active faults in the upper crust in the region [1]. Seattle itself sits on the Seattle Fault (running from west of Bremerton, through Bainbridge Island, Alki Point, Beacon Hill, through Mercer Island to the east; subsidiary strands run through White Center and Issaquah), which is thought to have produced M7+ earthquakes in the past few thousand years [1]. These are shallow and surface-breaking and would be extremely destructive to the city. They are fairly infrequent (~5 in the past 16,000 years) but travel in packs [2]. Atkinson and Macias [3] estimate peak ground accelerations at ~2 m/s^2 (i.e., 20% gravity) in Seattle for a Cascadia event. Graves et al [4] (see Supplemental Fig 1) estimate PGA at about the same for most of LA given a M7.8 event on the San Andreas (which is the maximum estimated from paleoseismology and various other inferences). The SAF is 30 km from LA; the areas with much stronger local shaking are relatively sparsely populated desert regions. LA also has a lot of faults in the basin itself that are similar in size and slip rate to the Puget Lowland faults. I think the recurrence intervals for the largest Cascadia events are very roughly 2-3 times those for the San Andreas (i.e. earthquakes are 1/2 to 1/3 less frequent). [1]: http://geosphere.gsapubs.org/content/early/2014/06/24/GES00967.1.full.pdf http://geosphere.gsapubs.org/content/early/2014/06/24/GES009... [2]: http://onlinelibrary.wiley.com/doi/10.1002/2013JB010635/epdf http://onlinelibrary.wiley.com/doi/10.1002/2013JB010635/epdf [3]: http://www.openseismo.org/contributors/Lee/MoWorking_Backups/Mo2012_0424backup/MoWorking/Paper_Pending/Atkinson-Macias_BSSA2009_p1552.pdf http://www.openseismo.org/contributors/Lee/MoWorking_Backups... [4]: http://onlinelibrary.wiley.com/doi/10.1029/2008GL035750/full http://onlinelibrary.wiley.com/doi/10.1029/2008GL035750/full