Archive for May, 2008

The Big-Enough One

21 May 2008

The theme of this month’s Accretionary Wedge blog carnival is, “a geological event you consider most significant to you.” I know what that one is. It didn’t awaken my sense of awe and turn me toward science. It didn’t injure me or make me rich or poor. No famous historical figure was involved. But the very month my wife and I moved to Oakland, the Loma Prieta earthquake changed the city irreversibly.

Those first couple weeks of October 1989 were fun. We loved having a proper downtown with fine old buildings, great weather, a lively cultural scene and a city with real geography to it. We had moved our stuff from the house in Concord and were readying it for the next owner, so at 5:04 pm on 17 October we were out of town, cleaning the old house for the last time. It was totally empty. The shaking went on for a long time, but out there it wasn’t very strong. Driving back to Oakland a little later, we felt worse and worse as the news rolled in and the signs of damage appeared.

There was a pall over Oakland for a long time. I felt it for years, not just on the anniversaries but every time I went downtown; every time a new friend or neighbor told their earthquake stories and listened to ours; every time I saw the news from other places and people struck by earthquake. Even now the effects linger in the scars left on the map, buildings left empty and the new Bay Bridge yet unfinished. And while the downtown, the weather, the scene and the land have endured, I now have a deep-seated relationship with earthquakes, Oakland geology and the Hayward fault that gives me a pang every time I feel the little shakers from beneath our side of the bay and think of the Big One to come.

The US Geological Survey has unveiled three new publications on the Hayward fault, all of them well worthwhile. They are a four-page fact sheet on the current hazard, a 96-page field guide with tons of information and photos covering the whole length of the fault, and a Google-Earth virtual tour for deep background and visualization. Get learning!

The top knocker of Mountain View Cemetery

17 May 2008


Up at the very top of the public part of Mountain View Cemetery is this knocker. I think it has a mixture of rock types in it, but I haven’t lain down on it with my magnifier to tease them out. For now let’s call it greenstone, which is how the area is mapped. The stone is a bit dirty, unlike every other knocker in the yard. The groundskeepers ought to give it a good scrubbing with a water jet.

Across the road from here the other week, I passed a pile of rock and soil from a grave excavation and fingered a few of the stones—looked like a gray basalt. Greenstone is a mildly metamorphosed basalt; it often has wiggly veins of carbonate. See three examples starting here. It is somewhere between about 160 and 70 million years old, that is, Jurassic to Cretaceous.

The view of the bay and the city from up here is fantastic. The view of the hills has potential. The cemetery is slowly getting rid of the eucalyptus along the east side, and more and more of the lush hills and neighborhoods is visible every year.


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