In a post below Billion Watts queried whether we were at a low
level of activity in California at the present time. I have done some
statistics to answer that question. It is likely that the count that
BW is making is off the web data which is substantially increased
after the final catalogs are prepared. The web data shows only
confirmed (immediately) events. Since SCSN has stopped providing
preliminary determinations to the web site, the count is probably
down in immediate events as BW observes.
However, BW's question deserves some statistical checking. I have combined
the NCSN and SCSN catalogs for the period Jan 1, 2001 through
October 8, 2001 (their extent) and counted the number of total
events in California per week. The average including the weeks
of the swarm at Coso Junction is 599 events per week with a
standard deviation of 397. Taking out the weeks during which Coso
Junction was active, the average number per week is 496 with a
standard deviation of 86. In the non-Coso statistics, seismicity
of the region has actually been slightly above average during the
past 6 weeks.
Below are two tables of numbers of events per week with and
without Coso swarm. The first column is the week number, followed
by the number of events during that week and the z-statistic of
that number measured against the average and standard deviation.
If the z-value is negative the number is less than expected, if
positive, more. Z-values of 1.93 are significant at the 0.05 level,
of 2.73 at the 0.01 level.

In this regard, the only weeks with significant increases in
seismicity were weeks 17 and 20. No weeks during 2001 have shown
significant decreases in seismicity.

Numbers with Coso Junction swarm:

AVERAGE: 599.25000 STD: 397.59909

WEEK # # of Events z-statistic

1.00000 473.000000 -0.317531
2.00000 417.000000 -0.458376
3.00000 377.000000 -0.558980
4.00000 375.000000 -0.564010
5.00000 505.000000 -0.237048
6.00000 530.000000 -0.174170
7.00000 485.000000 -0.287350
8.00000 440.000000 -0.400529
9.00000 526.000000 -0.184231
10.00000 436.000000 -0.410589
11.00000 419.000000 -0.453346
12.00000 487.000000 -0.282320
13.00000 361.000000 -0.599222
14.00000 380.000000 -0.551435
15.00000 533.000000 -0.166625
16.00000 505.000000 -0.237048
17.00000 737.000000 0.346455
18.00000 438.000000 -0.405559
19.00000 539.000000 -0.151535
20.00000 697.000000 0.245851
21.00000 594.000000 -0.013204
22.00000 425.000000 -0.438256
23.00000 482.000000 -0.294895
24.00000 426.000000 -0.435740
25.00000 405.000000 -0.488557
26.00000 382.000000 -0.546405
27.00000 481.000000 -0.297410
28.00000 705.000000 0.265971
29.00000 2863.000000 5.693549 Coso Swarm begins
30.00000 1072.000000 1.189012
31.00000 1072.000000 1.189012
32.00000 872.000000 0.685993
33.00000 706.000000 0.268487
34.00000 593.000000 -0.015719
35.00000 570.000000 -0.073567
36.00000 579.000000 -0.050931
37.00000 540.000000 -0.149019
38.00000 524.000000 -0.189261
39.00000 488.000000 -0.279804
40.00000 531.000000 -0.171655

Numbers with weeks of Coso Swarm removed

AVERAGE: 490.58823 STD: 86.33591

WEEK # # of Events z-statistic

1.00000 473.000000 -0.203719
2.00000 417.000000 -0.852348
3.00000 377.000000 -1.315654
4.00000 375.000000 -1.338820
5.00000 505.000000 0.166927
6.00000 530.000000 0.456493
7.00000 485.000000 -0.064727
8.00000 440.000000 -0.585947
9.00000 526.000000 0.410163
10.00000 436.000000 -0.632277
11.00000 419.000000 -0.829182
12.00000 487.000000 -0.041561
13.00000 361.000000 -1.500977
14.00000 380.000000 -1.280906
15.00000 533.000000 0.491241
16.00000 505.000000 0.166927
17.00000 737.000000 2.854105
18.00000 438.000000 -0.609112
19.00000 539.000000 0.560737
20.00000 697.000000 2.390799
21.00000 594.000000 1.197784
22.00000 425.000000 -0.759686
23.00000 482.000000 -0.099475
24.00000 426.000000 -0.748104
25.00000 405.000000 -0.991340
26.00000 382.000000 -1.257741
27.00000 481.000000 -0.111057
28.00000 593.000000 1.186201
29.00000 570.000000 0.919800
30.00000 579.000000 1.024044
31.00000 540.000000 0.572320
32.00000 524.000000 0.386997
33.00000 488.000000 -0.029979
34.00000 531.000000 0.468076