There's been quite a bit of tremor activity in the last month. I don't know if it is a change from before, but over the last month (2021-04-01 - 2021-05-06) basically everything west of I-5 from Portland, OR to Redding, CA has had deep tremors.

https://pnsn.org/tremor?starttime=2021-04-01T00:00:00&endtim...