You may have been jostled awake, or you may have been up and felt the rumble of this morning's earthquake, which gave San Francisco a small shake at 7:02 am. You also might not have felt it.

It measured 3.7 in magnitude, and was centered under the Pacific, 3.3 miles east-southeast of the San Francisco Zoo, according to the US Geological Survey.

This is the first measurable earthquake felt in San Francisco in over a month, since the 7.0M Mendocino Fault quake that triggered that tsunami warning on December 5, and its aftershocks.

The epicenter appears consistant with where the San Andreas Fault runs off the San Francisco Coast, but it occurred in an area not far from where the fault intersects with the San Gregorio Fault, around the Marin Headlands.

The Chronicle points out that the epicenter is near where experts believe the 1906 earthquake rupture began.

The USGS's Shake Map shows that all of San Francisco, and parts of the Peninsula and East Bay, experienced "weak" shaking, with the eastern half of the city feeling the equivalent of a 3.1M earthquake or lesser.

Update: A 3.0M aftershock followed, center 3.5 miles east-southeast of the zoo, at 10:48 am.