BERKELEY (CBS SF) – The 3.6-magnitude earthquake that shook parts of the East Bay and San Francisco Thursday morning was the fourth quake in a week centered in Berkeley.

Construction crews retrofitting Memorial Stadium had just started their shifts when a jolt at 5:36 a.m. caused shaking throughout Berkeley, Alameda and San Francisco.

“The guys thought that it was just a big thing of steel that fell on the ground from above,” said plumber Neil Hake.

The US Geological Survey recorded the quake 2 miles east of Berkeley with a depth of about 6 miles.

KCBS’ Holly Quan Reports:

Hake said it was ironic some of the workers on the job site felt a quake that woke up parts of San Francisco while other colleagues nearby didn’t notice a thing.

The same area was jolted by a pair of quakes the previous Thursday that measured 4.0 and 3.8. Those were followed by a 2.5 on Saturday night. On Wednesday, a similarly powerful quake struck near Blackhawk.

CBS SF Earthquake Section: Quake News And Preparedness Tips

Kimberly Hudson, one of the electricians laying the new electrical work for the 60,000-seat football stadium, said all the recent seismic activity put her work in perspective.

“There’s a fault line that runs directly underneath our stadium here, so we are constantly being put to the test each and every time an earthquake happens,” she said with a laugh.

The $321 million retrofit of the historic stadium situated above the Hayward fault is on schedule to be finished in time for the 2012 football season.

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