Quakes

Bay Area hit by M6 quake, strongest since Loma Prieta

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Damage. Twitter: Jeff Ranieri

An earthquake centered between the cities of Napa and Vallejo woke up the entire Bay Area and a swath of Northern California at 3:20 Sunday morning. At least 70 people have gone to hospitals with an assortment of injuries, and there is damage reported to highway bridges, gas and water pipes, and some buildings. Downtown Napa has bricks, chunks of concrete and broken glass on the ground and on parked cars. There is visible damage to foundations, chimneys and pavement. A fire in the Napa Valley Mobile Home Park destroyed at least four homes. Of course the contents of markets and homes have been left in disarray closest to the quake.

The USGS seems to have settled on 6.0 as the magnitude (SCEDC says 6.1 still.) That is the strongest temblor in the Bay Area since the 6.9 magnitude Loma Prieta quake rolled out of the Santa Cruz area during the 1989 World Series, leaving 63 people dead.

Dozens of small aftershocks have followed this morning, the largest a 3.6 magnitude quake at 5:47 a.m. Further aftershocks are considered likely. Gov. Jerry Brown has already declared a state of emergency for the area.

The proprietor of Matthiasson Wines posted on Twitter that "All of our 2013 red barrels are on the ground, don't know how much wine is lost yet."

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Seismically speaking, USGS says "the earthquake lies within a 70-km-wide (44 miles) set of major faults of the San Andreas Fault system that forms the boundary between the Pacific and North American tectonic plates….The earthquake is located at the eastern shore of San Pablo Bay between two major active fault systems: the Hayward-Rodgers Creek Fault system on the west and the Concord-Green Valley Fault system on the east. The earthquake occurred near the well-known West Napa Fault, and the less well known Carneros-Franklin Faults, which juxtapose different suites of rocks."

There's earthquake history to the area, USGS notes. "The Hayward-Rodgers Creek Fault system, which is approximately 7 km (4 miles) west of the site, generated damaging earthquakes in 1868 and probably in 1898. The Concord-Green Valley Fault system, which is 12 km (7 miles) east of the site, produced a M5.5 earthquake in 1954; while it has not generated a large historical event, there is strong evidence for recent pre-historic activity...The bayshore areas in the San Francisco Bay region are underlain by landfill and bay mud and have experienced disproportionately greater damage during historic earthquakes. Such damage is caused by soil failure in the fills and amplification of ground shaking by the soft bay mud."

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Damage to building at Brown and Second streets in Napa. Alvin Jornada.

The UC Berkeley Seismo Lab posted a short video showing a ten-second warning that was received before the shaking arrived in some of the Bay Area.


LA Observed earthquake page


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