I have been seeing them for years on my 4D. I have been logging them when they trigger the alarm I have set up to monitor for quakes. Since Sept of 2019: 67. The majority seem to occur in the late afternoon between 4p to 6p. I can go a month or two without seeing one at times.
My theory is that something is expanding/contracting near the RShake’s vault in the late afternoon heat or when the sea breeze cools things down rapidly. Vynil fencing maybe??? Just theory, however.
Here is a thread I started on the topic about a year ago: The Spike Mystery
A spike from 5/26:
–Steve Caron
RS4D RD29A Chino Hills, Ca