Archive for the ‘The Hayward fault’ Category

The Hillside School and the Hayward fault

20 November 2017

It was a most enjoyable hike that I led on Saturday for the Berkeley Path Wanderers Association, wandering for 3-plus miles in the city’s wonderful rock parks and along the Hayward fault. As usual, visiting the fault has its troubling side, and here I couldn’t ignore the implications of this splendid building, the old Hillside Elementary School on Le Roy Avenue.

This is the second Hillside School, built after the first one burned in the 1923 Berkeley Hills fire. For its time it was well designed, well made and well appointed, but after 50 years scientists confirmed that an active trace of the Hayward fault runs under it. The next major earthquake on this fault will rupture and ruin the structure. Besides that, the site is on a deep-seated active landslide.

The clear and present danger to children and teachers led the authorities to abandon the building in 1980.

In 2011 the German International School of Silicon Valley bought the site and pledged to do right by the building. In 2016 they fixed the roof with new, historically authentic materials, but at year’s end they moved out after deciding they couldn’t afford any more of the needed work.

There are two facts on the ground here. It’s a geological fact that this building is doomed and dangerous. But it’s an emotional and political fact that this building is precious.

The city declared the school a historic landmark in 1980, and it’s on the national register too. People love it and have strengthened the structure twice since 1925. But after the next major quake — not to mention a repeat of the 1923 fire — the school will be kindling, or ashes. Spending good money in a lost cause is an example of escalation of commitment, or the fallacy of sunk costs.

Without a building here, the site would be an excellent resource throughout the disaster period, and in between disasters an excellent little park.

During the walk, I made the modest proposal that we remove the building, and give it a nice funeral, before disaster strikes. Because now is the time that one day we’ll remember as “before.”

By holding a funeral for a building I mean, for starters, a respectful demolition. Make a virtual-reality model of the structure, recording the rooms and their beautiful wood beams and floors. Collect stories from the people who taught or attended school there. Hold a farewell concert in the old auditorium (with everyone signing waivers). Salvage the good materials. Build a memorial and have ceremonies.

All that stuff and more would befit the facts on the ground. I think it would raise the community’s consciousness of disaster preparedness, and at the same time mark the fact that in this case our ancestors won their bet against geology.

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South Dunsmuir Ridge

29 May 2017

I finally got to a sweet corner of town last week, the sunny side of Dunsmuir Ridge, this lovely hill in the Google Maps 3D view.

The view is to the north-northwest, such that the Hayward fault runs straight up about a thumb’s width from the left edge. The maps below start with the 1915 topo map, in which the ridge’s top is the lobed outline of the 625-foot contour.

That straight creek valley along the hill’s south side — the gorge in the foreground of the top image — keeps catching my eye, but it seems to be inaccessible, which might make it Oakland’s wildest piece of land. The watershed map below may help in visualizing the hill and its surroundings. The two black dots are where the fire trail I took starts and ends.

Dunsmuir Ridge is city land, rescued from development after several aborted attempts to put high-end estates on this broad hilltop overlooking (in both senses) the deadly Hayward fault. The fire trail starts at the end of Cranford Way and winds up the ridge to join the fire road from the other side, which I’ve featured here before.

The walk is very scenic. To the north, downtown rises against Mount Tam.

Or if you prefer, there’s the new profile of San Francisco.

Higher up, the view opens out. Here San Leandro Creek is made visible as a line of trees coming out of the canyon toward its mouth near the airport.

But the main attraction is to the south. This is the best place to take portraits of Fairmont Ridge and its quarry scar. Unlike most places, this trail sets off the hill with a foreground of wild, forested land.

The prominent cleared space midway up the trail — a staging pad for firefighters — has regular visitors who find the spot special.

Interestingly, this spot is mapped as a patch of the peculiar Irvington-aged gravel that first brought me to Dunsmuir Ridge in 2009. However, I didn’t notice much of it, if any. See it on the geologic map — the white dots mark the ends of the fire trail.

There are rocks to be seen too. The soil is thin in most places. This little cut displays a profile of the soil and the decaying bedrock — saprolite — just beneath it.

The bedrock varies, and it doesn’t match the geologic map very closely. I would say nearly all of the lower part is not Leona volcanics (Jsv) but San Leandro Gabbro (gb). It has the gabbro’s pepper-and-salt appearance but is stained orange instead of the pristine rock’s bluish gray (as I saw earlier that day in San Leandro). You’ll see it well exposed in the trail itself, where this winter’s heavy rains carved fresh runnels.

If the city fills them before you get there (which it should before they become gullies), there are still roadside exposures that display the rock well, and it’s unmistakably gabbro where the map says volcanics. The top of the hill, though, is unquestionably Leona volcanics.

My long-term plan is to revisit every bit of bedrock in Oakland and log it. Besides sheer nerdery and the chance to improve the map, my motive is to come back to views like this one over and over again.

The old quarry is still for sale. Developers have tried to put houses there, but they keep getting shot down. Better, I say, for the Regional Parks District to acquire the land and develop it for quiet recreation.

The Hayward fault at Warm Springs

17 April 2017

Every extension of BART opens up a new region accessible to geologizers using public transit. So the other week I paid a visit to the far end of the Hayward fault, less than a mile from the new Warm Springs station in south Fremont. The station has nice views of the San Mateo Peninsula mountains to the west and Mission Peak to the east.

It appears, too, that the Irvington Gravels site to the north is accessible for determined walkers who bring provisions — that is, hikers.

To get to the fault just walk east on South Grimmer Boulevard toward the place marked “Weibel” on Google Maps.

Here’s the same area in Jim Lienkaemper’s detailed 1992 map of the fault. The map has a key to all the annotations. Note that both images are tilted to make the fault vertical; north is at about 1:30.

The fault runs through the “D” in “Blvd.”

Look back at the Google Maps image. See the line of green along the fault trace? That’s because of the 1972 Alquist-Priolo Act, which forbids new construction within 50 feet of an active fault. The area in the middle must have been built up before the act took effect. That’s where I went.

South Grimmer reveals the offset from fault creep well. This view is looking east toward Mission Peak. On the fault map, the locality (just below the horizontal dashed line) is circled and labeled “C1,rc,rf” signifying “strongly pronounced” evidence of creep in the form of right-offset curbs and a right-offset fence line.

And this is the other side of the road, looking west. Notice that the sidewalk is offset as well as the curb.

There’s another, much smaller offset higher up the slope that I didn’t get a good picture of. Repeated measurements show that together these offsets add up to about 6 millimeters per year. The slope itself is a sign of the fault, too.

To the north across little Arroyo Agua Caliente Park on Gardenia Way, this nice set of echelon cracks marks the fault trace. That’s what the “ec” in the circle labeled “C1,ec,rc,cc” stands for.

The fault nips the corner of Gardenia and Ivy Way, bending this curb (the “rc” in the label).

The city or the homeowner copes with the sidewalk by patching it as needed. You’ll see stuff like this everywhere on the Hayward fault.

Walking north through the park to Parkmeadow Drive on its north edge, you can look west down the street and see both an offset curb and the change in slope that marks the fault.

You can do this yourself all along the fault. The map has all the evidence (and the USGS has an updated version as of 2008).

A week later I hosted two French journalists — a writer and a photographer — for an afternoon, showing them fault offset features like these up in Hayward and Oakland. The writer went and spoke to a resident whose home was on the fault, and his fatalistic response took her aback a bit. She said “we don’t have attitudes like this in France.” I told her we Californians have been this way since the Gold Rush.

The East Bay Seismic Investigation

12 September 2016

On Friday I got my first look at a seismic survey that will be visualizing the Hayward fault (and the Chabot fault for good measure) this fall. It involves a 15-kilometer line of several hundred seismometers stretching from the San Leandro shoreline to Cull Canyon. A team of geologists from the US Geological Survey and Cal State East Bay will set off 19 small explosions along the line to serve as energy sources, and the seismometers will record the sound waves as they arrive, after traveling through the various layers of the ground. Here’s the line of charges (as usual, click it for the full-size version); the seismic stations are too numerous to bother showing.

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The Hayward fault is the red line, the Chabot fault is the blue line, and I’ve added the lidar swath along the fault between the light-blue lines. The purple line is the little-known Miller Creek fault.

The occasion on Friday was a photo op for the press. The team drilled a 30-foot hole in which charge number 9 will be placed, and a bunch of reporters took a bunch of footage and asked a bunch of questions.

It was a pretty spartan setup. That’s USGS press officers Leslie Gordon waving on the left and Susan Garcia standing on the right. I see them all the time at science meetings.

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It can be very helpful to have press officers around to answer basic questions in press-friendly ways, follow up with extra pictures and so forth.

Here’s the press gathering footage as Joanne Chan of the USGS works the Bobcat.

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Off to the side, the radio and TV people were talking to the chief scientists, Rufus Catchings of the USGS and Luther Strayer of CSUEB. The photogs put their bodies on the line seeking that grab-you image.

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On the table was one of the seismometers — it’s the orange dealie with the prongs. The can holds the power supply and electronics. You stick it firmly into the ground, hook everything up, and stand very still while the shots are fired.

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They’ll do the shots late at night to avoid vehicle vibrations. then they’ll put all the instruments away and fill in the holes. Also, thank all the property owners whose permission was required for this important research. As you can imagine, a boatload of planning had to happen before reaching this stage. The USGS’s National Earthquake Hazards Reduction Program is paying for the project.

I hope to see more of the project as it proceeds and will report back. Meanwhile, see how the press did:

Mercury News

SFGate

KPIX