Canie,
I have attached a listing of earthquakes (Ml>=3) within 20 km of
today's events near Gustine, CA. It appears the area is not
above an occasional earthquake in the M>=3 range. I can't
answer your question regarding reservoir triggering, however,
since I have no information on when those reservoirs were
formed. Usually reservoir triggering discontinues after 10-15
years after filling, though.

Lowell

MO DA HR MN SC YEAR N LAT W LONG DEP ML
12 8 4 37 0 1933 37.000 -121.000 0 4.0
2 4 9 8 24 1942 37.000 -121.300 0 4.0
12 8 3 43 49 1943 37.100 -121.070 0 3.5
5 16 0 43 33 1944 37.000 -121.000 0 3.9
9 27 5 24 47 1945 37.070 -121.080 0 3.5
2 6 23 32 36 1946 37.000 -121.200 0 3.1
11 26 8 46 0 1947 37.000 -121.100 0 3.3
10 17 2 41 45 1949 37.000 -121.220 0 3.8
10 17 4 38 6 1949 37.000 -121.220 0 3.6
10 17 4 45 4 1949 37.000 -121.220 0 3.0
10 18 12 25 38 1949 37.000 -121.220 0 3.6
10 25 9 59 52 1959 37.000 -121.300 0 3.6
9 18 14 35 15 1964 37.060 -121.040 9 3.0
10 8 15 32 24 1964 37.160 -121.130 14 3.2
5 19 5 20 14 1975 37.190 -120.960 8 3.1
5 25 6 15 48 1975 37.197 -120.974 0 3.3
6 11 11 38 18 1975 37.186 -120.955 0 3.2
6 18 17 50 20 1975 37.188 -120.954 2 4.2
6 26 20 1 28 1979 37.040 -121.090 14 3.0
5 19 22 19 39 1980 37.088 -121.165 9 3.1
5 20 17 21 31 1981 36.978 -121.042 10 3.9
12 26 23 19 38 1985 37.064 -121.112 14 3.0
3 21 1 23 48 1986 36.939 -120.998 12 3.0
8 26 9 49 47 1987 37.149 -121.149 12 3.8
1 15 16 15 2 1988 36.986 -121.043 3 3.1
1 21 16 2 6 1988 36.988 -121.032 9 3.0
5 1 1 2 29 1992 37.111 -120.979 16 3.5
5 1 11 55 50 1992 37.103 -121.003 8 3.0
5 3 23 26 2 1992 37.097 -121.016 5 3.2
9 7 19 10 4 1994 37.255 -120.996 6 4.1
9 27 21 22 2 1994 37.123 -121.028 1 3.1
8 8 13 56 50 1995 37.111 -120.996 5 3.1
4 18 21 41 40 1997 37.065 -121.272 2 3.0
7 27 6 51 41 2000 36.957 -120.945 5 3.1
2 16 3 40 33 2001 37.090 -121.030 7 3.0
2 23 20 58 46 2001 37.088 -121.030 4 3.3