4.0 and 5.0 earthquakes off the Oregon coast happen with some regularity. The epicenter was directly overhead the
subduction zone and every so often a big chunk of plate can get subducted at once, which sends shockwaves
through the adjoining plate fractures. This would explain the seismic activity in the western ranges
of Oregon and Washington. Had this been a fault thrust or slip, it would've registered in a higher frequency
on the experimental spectrograms.
As to the increased frequency in seismic activity worldwide, no doubt the winter solstice is affecting
gravity patterns, which could in turn cause seismic activity. I was thinking HAARP for awhile and there are
some peculiar readings but... I've been wathcing ElfRad like a hawk and it has barely chirped.