One of the problems with on-line data is we tend to take it as GOD's WORD, especially
NEIS data - which is exceptionally poor for local studies. I repeated your search
on our data base which contains NEIS and local data. I got 603 events within
10 km of the Hawthorne earthquake of which 521 were shallower than 2.8 km -

The problem with using the NEIS data is that only the events of Ml>about 3 (sometimes
they include events of 2.8 and 2.9, but there is no consistency) are included.
Larger events do tend to occur at greater depth - near the brittle/ductile transition
zone. So this database is biased not only in the events they include, but in the
depths of the events they include.

Better to get your data from the Caltech Catalog and ignore NEIS for local studies.
You can ftp their catalog from:
ftp://scec.gps.caltech.edu

• Southern California earthquake catalog