Archive for the ‘oakland hazards’ Category

Trees and serpentine

29 March 2015

There’s a stretch of Castle Drive, up in the Piedmont Pines neighborhood, lined with huge trees. On the Walk Oakland map, it’s even labeled “Colonnade of Eucalyptus.”

CastleDrTrees

These give me mixed feelings, as tree removal projects have aroused lately elsewhere in Oakland.

First, there’s the experience the trees provide. For one thing, you basically can’t walk here, so the colonnade is not a realistic attraction for walkers. Its main effect is a momentary diversion for drivers, who really don’t need one at this location.

Second, there’s the effect on the surroundings. As you climb up in this valley, the trees emerge as a very tall fence that blocks the view of the hills and the city and the bay.

Third, there’s the geologic setting. This part of the roadway runs along a very steep 40-degree slope through pure serpentinite, visible in the small landslide scar on the right side of the photo. Serpentine rock is poor footing for these massive trees. The trees may seem like they’re buttressing the roadway, but when they inevitably tip over in a storm or earthquake, they’ll uproot it instead, forcing the locals to drive up and down Ascot Drive for many months.

But how about that rock? Here’s a hunk of it that spilled across the road.

castleserpfoot

And here’s a hand specimen. I love this stone, but roadbuilders don’t.

castleserphand

It’s not my problem, since I don’t live there, but I think the best thing to do is to turn this colonnade into a line of ground-level stumps. The root systems would bolster the soil for another decade or so, giving the city time to plan and execute a properly engineered roadway. And bollards set in the stumps would preserve the trees’ most useful current function of keeping cars out of the canyon.

Trees are supposed to be wonderful stockpiles of carbon, sequestering it from the atmosphere. For me, that argument shouldn’t apply to individual trees or even individual groves of trees. What do we do, in the long run, with the carbon in trees—pile the trunks in pyramids? Carbon is best stored in the soil, where it provides excellent tilth and maintains a thriving ecosystem that resists fire and drought. It’s like circulating money in an economy: do you hoard it in vaults or spread it around among people ready to use it as a medium of exchange? Humans have spent thousands of years degrading the world’s soils, and I’d rather we begin to restore them.

The 2015 California Earthquake Forecast

11 March 2015

The U.S. Geological Survey issued a major update to its statewide earthquake forecast yesterday, the Third Uniform California Earthquake Rupture Forecast (UCERF3). No surprise, the news media boiled it down a little too far for my taste. For our side of the bay, there wasn’t a lot of change in my mind. Click the image below for a larger and wider image showing the whole Bay area. The whole report is online.

UCERF3lilmap

The Hayward fault is now officially considered to have a much higher risk of a very large, magnitude 7.5 or so, earthquake. (The figure in parentheses shows the percentage of the change in assigned risk.) This is because now we’ve added the possibility that not only the whole fault, but its neighboring faults (Rodgers Creek on the north and Calaveras on the south) could join it in an oversize rupture. Scientists (and I) have known about this change for a while because we follow the literature, but the new forecast is a formal admission.

The headlines and radio blurbs have been easy to misinterpret. The Tribune this morning was typical: “CALIFORNIA’S CHANCES OF ‘BIG ONE’ GROWING.” But look at it this way. The state of the Earth’s crust is hardly different from what it was seven years ago when the USGS issued its previous forecast. It’s we who have changed—our knowledge and models have progressed. We have a better idea of California’s chances of a “big one.”

The people who will study this in detail are doing things like setting earthquake insurance rates and designing large structures. For the rest of us, there is no change. We still live in earthquake country. We still need to work on our personal readiness. The largest events still will be rare. Better for Oaklanders to prepare for the smaller but still destructive magnitude-6 earthquakes, like the one in Napa last year. We will experience more than ten times as many of those, and they are worrisome enough.

What I like about the new forecast is that it isn’t really a forecast. The system has grown in sophistication and flexibility to the point that it’s really a modeler’s sandbox, a software environment that can handle surprises, new information and complexities better than ever. Talk to a seismologist and they’ll instantly agree that earthquakes pretty much always take us by surprise. The giant Tohoku earthquake, which happened four years ago today, took seismologists by surprise. You name it, the quake was a surprise. It will be many decades, maybe centuries, before this state of affairs ends.

We can’t deal with the situation using simple, linear computer models based on one idea of Earth’s behavior. The third UCERF is a supple, fine-grained instrument that takes advantage of many significant advances during the last decade. When I told a USGS quake guy yesterday how much I admired the new model, his eyes twinkled. They’re proud of this.

Landslides of Outlook hill

5 March 2015

I’ve been surveying the low hill between Mills College and Holy Redeemer College, home of the Millsmont and Eastmont Hills neighborhoods. Its western face has no bedrock, either on the geologic map or in my experience. Here’s the relevant portion of the geologic map.

outlookmap

Its crest is supposedly Jurassic basalt, which would be part of the Franciscan assemblage. But the Hayward fault runs right along its length, and I lean toward calling it a pressure ridge. Long story short, it is squeezed up, shattered, and oversteepened, and these make it prone to landslides. Here are some, starting with the notable example at the top of 64th Avenue. This is its toe . . .

64th-beunaventura-slide

. . . and this is the view from its head, at Delmont Avenue.

64-buena-slide-top

Another is above Outlook Avenue, south of 76th Avenue. As you walk along its base, you’ll see bits of concrete from the homes that once stood here.

outlook-76-slide

Above it, on Hillmont Drive, there is a gap in the houses that offers a nice view. I have no business saying whether a landslide is responsible.

outlook-76-slide-top

Between these two obvious slides are some fine hillsides. This one, below Simson Street, makes a lovely backdrop to the Eastmont mall and, it seems, a nice informal park for the residents.

simson-field

It isn’t really vacant—all of the lots that subdivide it are extremely long for some reason. I think that spaces like this, shared without fuss by the landowners around it, are very precious.

Loma Prieta plus 25

17 October 2014

Yesterday I attended the Loma Prieta 25 Symposium at the Kaiser Center. It was a quake geek’s Woodstock, where a motley host of experts got together to schmooze, celebrate 25 years of progress since the 1989 earthquake, and look ahead. At 10:16 a.m., along with 27 million other people around the world, we participated in the ShakeOut drill.

dropcoverhold

Since the Loma Prieta earthquake, Caltrans has finished reinforcing all of the state’s freeway overpasses, EBMUD and Hetch Hetchy have strengthened their principal water mains where they cross the Hayward fault, BART has strengthened its tracks and stations, and PG&E has made huge changes to make the power and gas system more robust. The airports and ports have been upgraded. The big bridges have been fixed or replaced (with only the Golden Gate Bridge upgrade to go).

The work done since Loma Prieta has also made governments work better. The mayor of Napa, Jill Techel, had high praise for the city, county and state emergency service agencies. She said PG&E did a wonderful job during the August earthquake. The federal agency FEMA was on top of things too. And the regional authority ABAG, the main sponsor of the symposium, was charged with energy and ideas to piggyback on the public awareness that followed the Napa quake.

Magnitude-6 events like the Napa earthquake will happen 10 times as often as the “big ones” we’re warned against. Even if the big ones will surely overwhelm some aspect of our preparations, the mitigation and preparedness in place can work wonders with the smaller events like the Napa quake.

The next steps that the experts laid out, the things they want done by Loma Prieta 50, involve increasing the Bay area’s resilience to disasters. Resilience means that people will not just avoid death and injury from a major earthquake, they’ll stay in their homes and return to their jobs quickly. The work of upgrading the infrastructure needs to move beyond the backbones to the limbs and arteries: neighborhood water and gas lines, smaller bridges, individual privately owned buildings. Oakland is ready to begin a program aimed at some 1800 soft-story residences in the city. The state’s earthquake insurance chief and the state senator heading the Insurance Committee were there to describe the advances they want to make in 2015. Progress works this way: inch by inch and year by year.

Oakland Harbor will save the nation when the Big One hits

3 September 2014

harborcranes

I’m attending the Third International Conference on Earthquake Early Warning, which is happening at UC Berkeley through Friday. It’s a lively gathering of specialists and officials from earthquake country all over the world. What’s galvanizing everybody is the possibility of dramatic progress in California, now that the government has passed a law that establishes a statewide early-warning system modeled on ShakeAlert, which has been quietly beta testing for more than two years.

It came up during discussion today that the West Coast has five of America’s largest seaports, and a major earthquake that disables one or more of them will affect not just the nation’s, but the entire world’s economy. OK: the West Coast has three areas that produce major earthquakes. Ours, the Bay area’s part of the San Andreas fault complex, is the least of them. The 1906 San Francisco earthquake (M 7.8) and the similarly large 1868 Hayward quake? Those are our signature quakes, and we’re third on the list. Southern California is capable of larger ones (M 8), and Cascadia, which reaches from Cape Mendocino up past the Canadian border, produces the largest quakes by far (M 9).

A Big One that knocks out Long Beach and Los Angeles harbors will not affect Oakland. Neither will the Monster One that disables Seattle, Tacoma and Portland. Oakland Harbor will be the backup port of call after either of those events. And of course they’ll share the load if we’re out of action.

harbordolphin

In any case, Oakland Harbor is a natural facility for using an early-alert system. So is Oakland Airport—imagine an alert coming in to the control tower that strong shaking will arrive in 20 seconds. This is exactly the kind of rapid decision-making information that the airline community is trained to respond to already. I foresee our airport and our port being early early-warning adopters. BART is already part of the ShakeAlert beta testing network. Watch those guys.

Our slides

26 March 2014

A large, deadly landslide in northern Washington has been making news. Smaller ones around here aren’t deadly, thank goodness, but they are sneaky and expensive and everywhere.

slidescarp

This isn’t a landslide yet, but these concentric cracks in Skyline Boulevard are typical signs of slumping ground. A city with more money to maintain streets would have dribbled tar over these cracks when they first appeared, a year or two ago. As it is, each crack lets rainwater into the hillside where it promotes more slumping. Keeping the road sealed will buy a few years’ time.

This location is underlain by the same incompetent Sobrante Formation that gave the Caldecott Tunnel builders such trouble. But landslides occur in Oakland on nearly every geologic unit, from the lower streambanks to the highest hills.

The Kitchener scarp

30 November 2013

The recent walk by the Oakland Urban Paths group took us past a catastrophe I hadn’t seen before: the landslide of 15 January 1970. It removed nearly all the homes on the east side of Kitchener Court, just south of the LDS Temple, and dumped the ground into the valley of upper Peralta Creek. The land is still empty and uninhabitable. Here’s a look south over the scarp from Kitchener.

kitchenerscarp

The slide wiped out the middle of London Road between a tiny stub at the top of Maple Street and the forlorn end trailing off of Maiden Lane. The Hayward fault is mapped right through the foot of the slide. The site of my photo is across the pink strip opposite the “J” on this portion of the Oakland geologic map.

kitchenergeomap

I frankly can’t vouch for any of the bedrock divisions shown here, but the dashed line of the fault is close enough to reality. For orientation, here’s the equivalent area in Google Maps. Rettig canyon, where Peralta Creek cuts through the bedrock ridge of Leona keratophyre (pink) and mixed Franciscan rocks (KJf), is in the patch of green at lower center.

kitchenergoogmap


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