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Twin Earthquakes Epicentered In Concord Rumble The Numbers

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A layered pair of earthquakes registering 4.0 and 2.7 on the Richter Scale rumbled through The Numbers Sunday, causing no outward signs of damage but generally seen as a reminder from Mother Nature that she can still make the earth move when she wants to.

Sunday’s initial temblor originated just south of Concord and registered 4.0, according to USGS sensors, with an almost simultaneous quake recorded almost immediately afterward originating under Concord and registering at 2.7. The U.S. Geological Survey reported the quake occurred at 3:13 p.m.

Residents from San Ramon to Benicia reported feeling the shaker, which set joists and rafters moaning and prompted some precautionary inspections of rail lines and infrastructure vulnerable to ground movement.

Did you know there was a fault line under Concord? We didn’t either. The USGS tells us the Concord-Green Valley Fault is mostly a right-lateral strike-slip fault with up to approximately 4 mm/yr (1/6 inch/year) of creep. The Concord Fault lies to the south of the Green Valley Fault. The total slip rate on the Concord Fault segment is 4 mm/yr (1/6 inch/year) and on the Green Valley Fault segment is about 5 mm/yr (1/5 inches/yr).