Bay Area residents got an early, shaky wake-up call today. At 2:39 a.m. to be exact.

A 4.4 magnitude earthquake in Berkeley jolted residents awake early Thursday morning. The quake struck on the Hayward Fault, which runs through the East Bay from San Pablo Bay in the north to Fremont in the south, passing through Berkeley, Oakland and Hayward. There hasn’t been a major quake on this fault since a 6.8 magnitude earthquake struck in Oct. 1868, causing massive destruction. U.S. Geological Survey scientists say the fault is “a tectonic time bomb,” due anytime for another big one.

For those of you who (like me) slept through most of geology class, a fault is a fracture in the Earth’s crust (its outermost rocky layer), the line where blocks of crust on either side have shifted past each other.

As USGS explains more precisely than I can: “Not every crack in the ground is a fault. What defines a fault is the movement of the rock on either side. When that movement is sudden, the released energy causes an earthquake. Some faults are tiny, but others are part of great fault systems along which rocks have slid past each other for hundreds of miles. These fault systems are the boundaries of the huge plates that make up the Earth’s crust. In the San Francisco Bay region, the Quaternary-active faults are part of the boundary between the Pacific and North American plates.”

As you can see from this map, the Bay Area is a veritable conference of faults. Mouseover to see the names of the faults (in red) nearest you. Click on the fault line for its description. Zoom in and click on any recent quake for more specific location data. Zoom out to see the locations and sizes of other recent earthquakes around the world. View a full-screen version of the official USGS map here.

 

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Interactive Earthquake Map: Get to Know Your Local Faults 16 February,2018Matthew Green

Author

Matthew Green

Matthew Green is a digital media producer for KQED News. He previously produced The Lowdown, KQED’s multimedia news education blog. Matthew's written for numerous Bay Area publications, including the Oakland Tribune and San Francisco Chronicle. He also taught journalism classes at Fremont High School in East Oakland.

Email: mgreen@kqed.org; Twitter: @MGreenKQED

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