The balsawood boulders of the Kaiser Roof Garden

26 September 2016

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Ever since 1960 when the rooftop garden on the Kaiser Center’s garage, largest in the world at the time, was built, it’s been heralded by American landscaping pros, Kaiser Center employees and appreciative residents. After the garden’s recent rehabbing, now (specifically, any weekday) is a good time to visit.

Putting a garden on a roof, even one made of the best Kaiser reinforced concrete, takes careful design and execution. The heaviest plantings and features were situated directly over the strongest supporting columns.

Even so, the designers had to minimize the weight of everything. The soil, a blend of lava rock, expanded shale and peat moss, is practically potting mix. The concrete is a lightweight formula. And then there are these impressive boulders.

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Each one is a generously sized hunk of pumice, the nearest thing to balsa wood in the mineral kingdom. Well, diatomite is lighter, but so friable you can crumble it in your hands. Pumice, basically a foam of expanded lava, stands up to weather beautifully with its relatively inert glassy composition. And close up, it’s handsome.

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If you see this stuff in a landscaping-supply yard, kick it around or pick it up. It’s so light, you’ll feel like Superman — but pumice will cut your bare skin, so be careful.

Oakland building stones: Sandstone

19 September 2016

For many years, timber was the default material for Bay Area buildings. Only substantial institutions like governments, banks and a few wealthy churches were sheathed in masonry — solid stone — and time and again, earthquakes were their undoing. Sandstone was chosen for the walls of two major Oakland churches, First Baptist and First Unitarian.

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First Baptist, on Telegraph Avenue at 22nd Street, was one of Julia Morgan’s earliest commissions, although she didn’t have a say in its looks. The Romanesque Revival building, inspired by the Aachen Kaiserdom, was designed by another architect whose delays in getting it built led the congregation to fire him once the exterior walls were up, in 1904. The day the church was to vote on Morgan’s design for the interior was 18 April 1906, and early that morning the San Francisco earthquake badly damaged the exterior. She took on the job of rebuilding it, then finishing to her own specifications a magnificent sanctuary inside.

The stone, to all appearances, is from the Greystone Quarry south of San Jose. It’s the same golden sandstone of Eocene age (~35 million years) used for the core buildings of Stanford University and other landmark structures like the Carson City Mint in Nevada, Lick Observatory and the old San Jose Post Office, now part of the San Jose Art Museum. I wrote about this stone for KQED a few years back. The stone blocks have a rugged “quarry face” on the exterior but are nicely dressed on the sides. The flat sides qualify them as ashlars, as opposed to fieldstone like you’d use in free-standing stone walls.

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The building also suffered damage during the 1989 earthquake. In this view you can see the seismic bracing, covered in gray, on the north wall that was installed at the time.

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The First Unitarian Church, at 685 14th Street, was designed by Walter Mathews in the elegant Richardsonian Romanesque style. Construction began in 1890.

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Stone was an important design choice, inspired by “a spirit of civic pride.” All of the building’s materials were sourced in California. The sandstone is a thick veneer, in quarry-faced ashlars like first Baptist. However, the stone is a cool gray, very fine grained, and is apparently not from Greystone Quarry. Parts of the building are faced in neat rows (courses) and arches.

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This stairwell bay is pleasingly laid in random-coursed ashlars, a system that avoids a regimented look and is probably stronger too.

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At its opening on 6 September 1891, a hymn written for the occasion began with the verse,

“The forests gave their oak and pine,
The hills their stone and clay,
And fashioned by the builder’s art
Our temple stands today.”

The building suffered light damage in 1906 and 1989, but repairs in both cases took several years.

The church’s Historic American Buildings Survey (HABS) report is full of deep technical and historical detail.

In both buildings, the sandstone shows signs of deterioration after more than a century of exposure.

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