Hi John. Here is Steve’s reply.

Don,
Oh dear. It looks to me that a bogus earthquake location got into the
ANSS composite catalog. It’s possible that there may be more of these too. It
turns out that a few years ago we did a reformatting of our basic earthquake
files and some automatic reprocessing. Because of changes in analysts,
particularly back in the 1980s, there were inconsistencies in the way event
information was stored. When reprocessing some bogus locations were
generated. There was an earthquake at the time (1988/09/30 00:39) of the
really deep one in the composite catalog; however, it is so far outside our
network that we should not have reported a location for it. Certainly the
depth is wrong.
I have arranged to have it removed from our catalog submission. We
should go through our catalog to see if there are other similar errors and fix
them too..... when we get time.
Thanks very much for your enquiry. We try to keep our catalogs
accurate but sometimes things such as this slip through. Observations (and
reports) from our users are very valuable.
Sincerely,
Steve

I also talked to Dr. Lind Gee at the University of Berkeley and it is her opinion that the rest of the quakes are bogus. This is based on the low number of recording stations. We also talked a little about “air quakes” which I have seen. This isn’t to be confused with sonic booms which are also recorded, but don’t look anything like a quake. Take Care...Don in creepy town