M=3.5 Hayward Fault earthquake strikes East Bay

By David Jacobson, Temblor

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Last night’s M=3.5 earthquake just east of Oakland resulted in shaking across the entire Bay Area.

 

Last night, at 7:18 p.m. local time, a M=3.5 earthquake struck just 3 km east of downtown Oakland, and resulted in shaking across the entire San Francisco Bay Area. As of this morning, over 19,000 people reported feeling the quake on the USGS website. According to the USGS ShakeMap, only light shaking was felt close to the epicenter. Because of this, no damage or injuries were sustained. The quake wasn’t even large enough to disrupt the San Francisco Giants baseball game, as Giants pitcher Chris Stratton still delivered a pitch in the first inning.

hayward-fault-earthquake
This Temblor map shows the location of last night’s M=3.5 earthquake along the Hayward Fault. As can be seen in this figure, the Hayward Fault is one of three major faults in the Bay Area. According to the USGS, the Hayward has the highest probability of rupturing in a large earthquake by 2043 (33%).

 

Based on the location of last night’s earthquake, it struck along the Hayward Fault. The Hayward Fault is one of the three major Bay Area faults (in addition to the San Andreas and Calaveras faults) and snakes its way from San Pablo Bay to just north of San Jose. In the process, it cuts through the cities of Berkeley, Oakland, Hayward, and Fremont. Because of this, it threatens over 7 million people and 2 million buildings.

Hayward-fault-oblique
As it snakes its way across the East Bay, the Hayward Fault cuts through the cities of Berkeley, Oakland, Hayward, and Fremont.

 

While last night’s quake was nothing to be concerned about, the Hayward Fault is capable of rupturing in large earthquakes. In fact, the USGS gives it the highest probability of any Bay Area fault of rupturing in a large (M=6.7+) earthquake by 2043 (33%). Because of the significant threat the fault poses to the region, last month, the USGS released the second volume of their HayWired report, the impacts of a large Hayward Fault earthquake on the Bay Area. Perhaps just by coincidence, but the epicenter of last night’s quake was just a couple kilometers from the epicenter of the scenario earthquake in HayWired. To read more about that scenario, click here .

While a M=7.0 earthquake along the Hayward Fault, which is what the HayWired scenario simulates, may seem large, Bay Area residents should still be prepared for a large earthquake in their lifetime. By using the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor, we can see what people can expect. This model uses global strain rates and the last 40 years of seismicity to forecast the likely earthquake magnitude in your lifetime anywhere on earth. In the figure below, one can see that in the location of last night’s earthquake, the likely magnitude is M=6.5+. While this is smaller than the HayWired scenario, such an earthquake would still cause significant damage to the region and recovery could take months to years. Therefore, people should be aware of the hazards around them and do everything they can to prevent future losses.

california-earthquake-forecast
This Temblor map shows the Global Earthquake Activity Rate (GEAR) model for much of California. This model uses global strain rates and the last 40 years of seismicity to forecast the likely earthquake magnitude in your lifetime anywhere on earth. In this figure, one can see that for the location of last night’s earthquake, that magnitude is M=6.5+.

 

References
USGS
Detweiler, S.T., and Wein, A.M., eds., 2017, The HayWired earthquake scenario—Earthquake hazards (ver. 1.1, March 2018): U.S. Geological Survey Scientific Investigations Report 2017–5013–A–H, 126 p., https://doi.org/10.3133/sir20175013v1. Link
Detweiler, S.T., and Wein, A.M., eds., 2018, The HayWired earthquake scenario—Engineering implications: U.S. Geological Survey Scientific Investigations Report 2017–5013–I–Q, 429 p., https://doi.org/10.3133/sir20175013v2. Link

  • Kate Stillwell

    In our house it was a short thump – I just thought it was our fat cat jumping down from the table in the other room. More interesting, my kids were outside and they didn’t feel it, but they said for a moment everything went quiet and all the tree leaves started shaking.