Hi Petra. I�m not really sure as to why USGS uses an M=5.0 quake as a guideline to prepare for a larger quake. Here is a list of all quakes above M=5.0 that have occurred in the Bay Area since 1950 and as you can see there was only one large quake that occurred after an M=5.0 quake. That was the Loma Prieta quake. There were two of them. One was 15 months prior to the quake and the other was 2 months prior to the quake.

There was no M=5.0 quake before the 1984 M=6.2 near Morgan Hill. There was an M=5.8 in 1979 just south of the 1984 quake. That quake may have been sufficient enough to load the fault in the area of the 1984 quake, but I don�t think anyone really knows one way or the other.

I think it may depend on which fault and where on that fault the quake occurs. I can�t help but feel that when the next major strikes the Bay Area it will be without a warning of any kind. It will strike with a bang. Take Care�Don in creepy town

catalog=ANSS
start_time=1950/01/01,00:00:00
end_time=2005/10/28,02:58:31
minimum_magnitude=5.0
maximum_magnitude=10
event_type=E
delta=0 km to 160 km from (37.342,-121.734)
Date Time Lat Lon Depth Mag Magt Nst Gap Clo RMS SRC Event ID
----------------------------------------------------------------------------------------------
1951/07/29 10:53:45.00 36.5800 -121.1800 5.00 ML BK ��
1954/04/25 20:33:28.00 36.9300 -121.6800 5.30 ML BK
1955/09/05 02:01:18.00 37.3700 -121.7800 5.50 ML BK
1955/10/24 04:10:44.00 37.9700 -122.0500 5.40 ML BK
1957/03/22 19:44:21.00 37.6700 -122.4800 5.30 ML BK
1959/03/02 23:27:17.00 36.9800 -121.6000 5.30 ML BK
1960/01/20 03:25:53.00 36.7800 -121.4300 5.00 ML BK
1961/04/09 07:23:16.00 36.6800 -121.3000 5.60 ML BK
1961/04/09 07:25:41.00 36.7000 -121.3000 5.50 ML BK
1963/09/14 19:46:17.00 36.8700 -121.6300 5.40 ML 19 BK
1964/11/16 02:46:41.70 37.0600 -121.6900 5.00 ML 17 BK
1967/09/28 15:38:35.90 37.2233 -121.6117 0.00 5.00 ML 0 0.00 CI 0
1967/12/18 17:24:31.90 37.0100 -121.7883 0.00 5.20 Mc 0 0.00 CI 0
1969/10/02 04:56:45.33 38.4963 -122.6638 0.07 5.27 Md 39 104 52 0.20 NC -1003132
1969/10/02 06:19:56.33 38.4515 -122.7522 4.16 5.22 Md 52 170 58 0.20 NC -1003135
1974/11/28 23:01:24.56 36.9202 -121.4663 6.11 5.37 Md 51 61 4 0.13 NC -1021953
1975/08/03 06:35:17.66 36.4477 -120.4532 18.81 5.23 Md 89 168 34 0.16 NC -1025217
1979/08/06 17:05:22.91 37.1042 -121.5127 8.93 5.80 ML 84 97 6 0.06 NC -1046969
1980/01/24 19:00:08.63 37.8367 -121.7708 14.72 5.23 Md 73 133 13 0.12 NC -1050047
1980/01/24 19:01:01.53 37.8115 -121.7772 7.07 5.10 ML 9 148 2 0.13 NC -1050048
1980/01/27 02:33:35.32 37.7493 -121.7062 14.69 5.18 Md 74 102 9 0.10 NC -1050444
1982/10/25 22:26:03.61 36.3198 -120.5090 12.27 5.39 Md 66 87 12 0.13 NC -1080786
1984/01/23 05:40:19.93 36.3650 -121.8878 8.19 5.12 Md 74 199 18 0.08 NC -1110311
1984/04/24 21:15:18.76 37.3097 -121.6788 8.53 6.20 ML 98 26 6 0.06 NC 17204
1986/01/26 19:20:50.93 36.8040 -121.2847 8.72 5.50 ML 76 26 7 0.07 NC 64626
1986/03/31 11:55:39.80 37.4788 -121.6858 9.17 5.70 ML 84 65 3 0.06 NC 68932
1988/02/20 08:39:57.24 36.7957 -121.3117 9.62 5.03 z 75 26 3 0.08 NC 10086194
1988/06/13 01:45:36.52 37.3923 -121.7415 9.71 5.30 ML 94 29 4 0.07 NC 10087352
1988/06/27 18:43:22.32 37.1268 -121.8962 13.15 5.30 ML 90 46 5 0.10 NC 10139668
1989/08/08 08:13:27.36 37.1458 -121.9282 14.23 5.40 ML 87 51 3 0.10 NC 10089897
1989/10/18 00:04:15.20 37.0362 -121.8802 17.29 7.00 ML 79 91 1 0.08 NC 216859
1989/10/18 00:41:23.70 37.1873 -122.0548 16.78 5.10 ML 46 59 10 0.10 NC 10090725
1990/04/18 13:53:51.30 36.9320 -121.6577 5.68 5.75 z 93 29 0 0.11 NC 20091154
1990/04/18 15:46:03.44 36.9583 -121.6848 6.67 5.36 z 81 30 1 0.10 NC 20091155
1993/01/16 06:29:35.00 37.0182 -121.4630 7.90 5.10 z 84 68 2 0.08 NC 332444
1993/08/11 22:33:04.00 37.3120 -121.6793 9.35 5.00 z 95 41 6 0.08 NC 374372
1995/04/23 08:41:36.63 36.6025 -121.2015 7.84 5.14 z 74 33 3 0.08 NC 30071966
1998/08/12 14:10:25.12 36.7533 -121.4622 9.13 5.35 ML 78 35 4 0.21 NC 30190473
2000/09/03 08:36:30.09 38.3788 -122.4127 10.12 5.17 ML 75 34 3 0.17 NC 21123384