Hmmm, USGS says 4.0

Earthquake Details
Magnitude 4.0
Date-Time Saturday, September 06, 2008 at 04:00:15 UTC
Friday, September 05, 2008 at 09:00:15 PM at epicenter
Time of Earthquake in other Time Zones

Location 37.866°N, 121.996°W
Depth 16.2 km (10.1 miles)
Region SAN FRANCISCO BAY AREA, CALIFORNIA
Distances 3 km (2 miles) ENE (77°) from Alamo, CA
5 km (3 miles) NW (315°) from Diablo, CA
6 km (4 miles) NNW (343°) from Danville, CA
11 km (7 miles) S (172°) from Concord, CA
22 km (14 miles) ENE (69°) from Oakland, CA