Two interesting quakes in the last few days have been the 5.6 magnitude quake near Eureka California and the 6.0 quake off of the coast of Oregon. Both of them shallow quakes, but being close together they are not on the same fault line.
The Eureka quake is on the southern end of the Cascadia fault line that runs from here to the north end of Vancouver Island Canada. If you draw a line of the historic quakes in this area they draw a 3d curve of the fault boundary as the Juan de Fuca plate is subducted below the north american plate. This end of the fault is actually quite active but only for a short distance into the fault.
The Oregon quake is right smack on the mid pacific ridge (which isn’t so mid pacific) and while the two quakes are on the sides of the same plate, they are on opposite sides and only related in that there is plat tectonics that causes them both.
So neither of these quakes is any real cause for alarm as neither is an indicator of the Cascadia fault letting go any time soon. (Seattle still has time to fix it’s quake susceptible buildings.)
- 6.0 quake in Pacific off S. OR; no damage reports (seattletimes.nwsource.com)
- Feb 4 Vancouver Island Quake (echlinm.wordpress.com)