August 17, 2015

Wake-up call from the Hayward Fault

Posted by Austin Elliott

During a brief visit to California this week, I, along with a metroregionfull of people, was treated to a rattling little temblor from the Hayward Fault. The quick jolt struck conveniently just before everyone’s morning alarms went off, serving as a wakeup call for the day, and as this season’s broader “wakeup call” reminder that there are big active seams in the crust inching along around and below our cities.

In this nexus of tech, design, and urban geography, folks were quick to record and display this earthquake’s place in our lives, with CartoDB producing a lovely map of shaking intensity contours:

The Bay Area’s rapid transit system, BART, early adopters of earthquake early warning technology, halted all their trains as the earthquake hit, for safety and subsequent inspection.

 

Of course plenty of Bay Area residents submitted their own accounts of the shaking to the USGS’s Did You Feel It survey (and those of you who haven’t yet should!). The map reveals a pretty small radius within which the quake was felt, elongated NW-SE along the geologic grain of the state, all of which is to be expected.

USGS DYFI Community Intensity Map

This was a modest little quake that emanated from the Hayward Fault zone, not unlike many others that have happened over the past few years. As with any earthquake, it has a very small chance of being a foreshock to a larger temblor, but this should generally not be a cause for alarm: in the Bay Area, a larger temblor could happen at any moment anyway, so a small one doesn’t inherently change how prepared you should be. What it does do is remind you that our cities lie atop straining, creaking regions of the crust that are periodically prone to snap. Review your preparedness plans, strap down your furniture, and refresh your earthquake kit! For more info on the Hayward fault and potential earthquakes it may produce, refer to this post by the Berkeley Seismo Lab, and links therein.

As today’s quake struck at 6:49am, several TV networks’ morning news shows were on air and recorded reactions to the shaking. At San Francisco’s Fox affiliate, KTVU, the weatherman has a start when the shaking starts.

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The CBS station KPIX was doing a segment on drones and didn’t film the shaking, but you can hear the rattling precede their reactions, then their scramble for information. Update, 17 Aug 15:19 PDT: This video appears to have been taken down for copyright violation; can’t find an original from KPIX. 

A pair of pups gets jolted from sleep by the quake in this scene that’s being widely circulated. This is about what it felt like here in San Francisco. Importantly with this video, as with many involving dogs, note that the dogs awaken at the arrival of the compressional P-wave, which you can hear rumbling in the house (it’s like a big sound wave, in the ground); the proper shaking that follows are the S waves, jerking side-to-side. This video does NOT show dogs having some sort of premonition–you can hear the earthquake starting at the same time the dogs do.

The fourth video this morning shows the interior of a consignment store in Oakland, very near the epicenter. Shaking is sharp and moderate, but importantly most things stay shelved. It’s noisy, as most quakes are when you’re inside a building.

If other videos crop up, I’ll try to update the post with them here. Meanwhile feel free to bring any to my/our attention in the comments below! Did You Feel It?