Earthquake shakes up SF Bay Area but no, it wasn't the big one

Posted Aug 19, 2015 by Nathan Salant
Monday's 4.0 earthquake that awakened hundreds of thousands of Bay Area residents at 6:49 a.m. was surprising and interesting, yes, but it was nothing like the massive shaker still overdue on the Hayward fault.
SHAKING: Overview of Hayward fault zone is shown  using data gathered by the U.S. Geological Survey.
SHAKING: Overview of Hayward fault zone is shown, using data gathered by the U.S. Geological Survey.
U.S. Geological Survey - Leonard G./Wikimedia Commons
Seismologists based nearby at the University of California in Berkeley and the U.S. Geological Survey in Menlo Park agreed that Monday's shaker was centered in Oakland and measured 4.0 on the Richter scale, causing pictures to fall off walls and other minor disturbances, but no major damage.
The quake appeared to be centered a mile north of the Oakland-Piedmont border, east of Mountain View Cemetery near Mddoc Avenue, according to the San Francisco Chronicle newspaper.
The shaker was felt strongly in San Francisco, where a traffic light at Geary Boulevard and 20th Street in the Richmond District fell over, as far east as Walnut Creek, and throughout the North Bay.
Seven aftershocks followed the quake with the strongest measured at 2.4 on the Richter scale.
The quake was felt strongly by 4.5 million people, the USGS said, with as many as 600,000 feeling moderate or strong shaking.
Sean Lydon of La Salle Avenue, just yards from the Hayward fault and near the quake epicenter, said he saw some new cracks in his home's plaster walls, but that was it so far.
“Everyone’s outside to see if their homes were damaged,” he said after running from his home because of the quake.
"It was relatively shallow and intense for a magnitude 4," said seismologist Keith Knudsen, deputy director of the USGS Earthquake Science Center in Menlo Park, Calif.
"People near the epicenter felt more intense than they would if it was deeper," he said.
While there is no indication that Monday's quake was anything more than an isolated occurrence, a major quake is expected in the future on the Hayward fault because it is nearly 150 years since the last major event in 1868.
Knudsen conceded there was a "small likelihood" that Monday's shaker was a precursor to a much larger quake.
"“There is a low likelihood that this could be a foreshock," Knudsen said.
"There is a 5 to 10 percent chance that we could have a bigger earthquake in the coming weeks,” he said.
Another USGS seismologist caused an uproar last month when news outlets reported he had predicted a major quake along the Hayward fault within days.
The major quake did not occur, and the seismologist, Tom Brocher, said his comments had been taken out of context.
The Hayward fault runs along the eastern shore of San Francisco Bay from Fremont to San Pablo Bay.