Archive for the ‘the hayward fault’ Category

MapView: Not ready for Oakland (updated)

11 March 2013

The U.S. Geological Survey’s programmers have made a nifty nationwide map server called MapView that lets you play with geologic maps from most of the country. Naturally I zoomed in on Oakland. I expected to see something like this when I looked at the Toler Heights area.

graymerbit

It’s kinda garish, but it’s from the USGS and as authoritative as these things can be. Instead, MapView shows me this:

dibbleebit

It’s crisp, it’s suitable for colorblind readers, but it’s wildly different. It shows simpler divisions and more limited areas of bedrock. It shows the active trace of the Hayward fault running on the opposite side of the hill from where it actually moves. Then there are things I notice: the names of the rock units have an antique feel and very few faults are mapped. And what’s with the ludicrously small landslide (“Qls”) and serpentinite pod (“sp”) in the middle? Why such a mixture of vagueness and precision?

In fact, this is not a USGS map at all, but a map issued by the Dibblee Foundation. Dibblee is the late and distinguished Tom Dibblee (1911–2004), popularly considered “the greatest geologic mapper who ever lived.” I consider him one of the greatest reconnaissance geologic mappers ever because that was his M.O.: to take his Jeep out to various high spots in poorly mapped territory and sketch out the bedrocks in the landscape onto a map base, then do field-checking until it was ready to publish. His skills were more than just fieldwork; he knew the literature and the community too, both scientific and industrial. I don’t have the talent to question his talent.

But. If you download the map and look at its sources, you’ll see that it’s based on Dibblee’s fieldwork in 1963 and a short return visit in 1977, plus three “preliminary maps” issued by the USGS, one of them in 1967 and all of them superseded by the map I use, Russ Graymer’s USGS Map MF-2342 published in 2000. I can only infer that this map was based on Dibblee’s old field notes as edited, posthumously, by John Minch in his role as official map editor for the Dibblee Foundation. I don’t question his talent, either, but it would be a major undertaking to update this map, one that has not been done.

What’s a few years, you might ask; the rocks never change. Well, consider that this map misplaces the Hayward fault. How do I know? It ignores the experience of Jim Lienkaemper’s meticulous mapping, which checks out in the field wherever I’ve looked. This is from his 1992 compilation of the fault trace and the supporting evidence.

lienkaemperbit

The Dibblee Foundation map is beautiful, but in this respect it is simply wrong. It didn’t go through the rigorous USGS review process; in fact I am confident that if it were submitted it would be rejected.

I’m going to ask the MapView people to reconsider using these maps in preference to USGS maps. For now I have to say that MapView is not curated to my standards.

UPDATE: The MapView administrator responded to me promptly and politely; I’ll excerpt his reply: “the point you raise has been a real concern . . . but [we] didn’t know the entire story nor had we been presented with a clear example of the problem, as you did in your blog. . . Our starting assumption is that newer maps supersede older mapping, and so unless there’s a compelling reason to not do so, we show the newer map. . . . The most effective way to improve upon what’s shown in MapView is for local and regional experts to weigh in with their opinion and experience, as you have done. I sincerely thank you for contacting us, and assure you that we’ll remove the Dibblee Foundation maps in all cases where there isn’t an older map of that scale that is ‘better’.” Translation: We pick maps by their release date and we won’t adjust that until someone squawks.

The other attractive feature of the Dibblee maps is that they’re standard 7.5-minute quadrangles, which makes things much easier for the MapView programmers. But ease of programming is not the same as usefulness.

Broadway Terrace fault crossing

9 November 2012

The Hayward fault is mapped as crossing Broadway Terrace here, just west of the route 13 overcrossing.

hayward fault

The pavement is a wreck and has been repeatedly patched. You may see a dip in the concrete berm in the road’s centerline, too.

On the other side is the old concrete supports for the railroad line that used to go through here.

Fault valley

21 October 2012

October 21, not October 17, is Oakland’s real Earthquake Day. While many of us remember the 17th vividly, the day of the Loma Prieta quake in 1989, the morning of October 21, 1868 was when the original Great San Francisco Earthquake struck. It was on this side of the bay, on our own earthquake fault, and the ground cracked from Fremont all the way to the edge of this view from the end of Pali Court, in the neighborhood just across route 24 from Lake Temescal.

hayward fault valley

The Hayward fault runs from the notch on the skyline, which is in Montclair, to the right edge behind the house in the middle distance. This part of the fault, between Mills College and Lake Temescal, is the only place that has large areas of bedrock on both sides. What that means for the purposes of today’s post is that it’s the most rugged and picturesque part of the fault and has probably the greatest concentration of million-dollar homes.

Today I invite you to review this blog’s category “the hayward fault.” I seem to have rattled on at great length on this subject. Some day the fault will rattle all of us at great length.

Today’s Oakland Tribune has an article about newly mapped faults in the Hayward fault zone; I won’t link to it because the Trib’s links die quickly. But the new Alquist-Priolo zone map can be accessed here.

Linear scarps

1 September 2012

Next Saturday, 8 September, I’ll be leading a short, rugged urban walk for Oakland Urban Paths that among other things will visit these faceted spurs along the Hayward fault. Seen from the north . . .

view south

and from the south:

view north

The downhill side is moving north with respect to the near side. The open land in the foreground is the King Estates Open Space.

This will not be a stairway walk. The off-street passages are steep, weedy dirt paths that have not been maintained. The land along the fault is steep, making for nice residential view lots. I haven’t finished the route yet but it will take no more than 90 minutes, 10 to 11:30—I have a lunch destination I’m anxious to make. So I would like to set a good geologist’s pace. Details and questions as they come to you over at Oakland Urban Paths.

Heritage in a dynamic place

10 February 2012

I gave my talk last night to the Oakland Heritage Alliance and I think it turned out well. I tried to talk about our geology not on its own terms, but weighted toward its relevance in Oakland’s general civic life. One of my slides was this lovely digital elevation model that makes the Hayward fault obvious. Click to see the whole thing. Sadly, I can’t recall exactly where I got it.

oakland DEM

Here are my concluding remarks from the talk.

Oakland is situated in an area that falls down every century or so. Today, a repeat of the 1868 earthquake would erase large areas of our city. I don’t see how we can prevent that. How can we hang on to our history in the face of nature? And how can we hang on to our history in the face of human nature? By that I refer to well-known tendencies in cities that are traumatized. Citizens have a strong, almost overwhelming urge to return to normal, and that drive is amplified in their leaders.

We have the example of San Francisco after 1906, which underwent a furious rebuilding and whose leaders had no tolerance for delay. San Francisco was the leading city of the West, and the stakes were very high. Democracy was short-circuited for a time. The development-driven city leaders, led by “mover and shaker” James Phelan, were prepared to obliterate Chinatown before the Asian-American community rallied to save it. There was no heritage community at the time, and who knows how it would have fared had there been one.

After our earthquake—and it’s coming—Oakland will still have all the geographical gifts that I showed you at the start of my talk. We can assume that the seaport and airport and rail lines and highways will be rebuilt as soon as possible. The stakes will again be very high. There will be little conflict with the heritage community over any of that. The hard part will begin once the emergency ends.

Earthquakes are part of our geography. These days we like to talk about sustainable living: in tornado country, for instance, that means everyone has a storm cellar. What does it mean in Oakland? Some of our most beautiful neighborhoods lie along the fault, and they probably will not be reoccupied once destroyed. The city that arises after the next Big One will be very different in some ways.

I think I can foresee a more sustainable Oakland in which more people will live in well designed multi-family buildings and recreate in a long greenbelt where route 13 runs today. On the other hand, much will endure. City Hall should survive thanks to its retrofit after 1989. Landmarks like Tech High, the Camron-Stanford House, Peralta Hacienda, and Dunsmuir will be restored if they survive the tumult. I know that the Oakland Heritage Alliance will be there, doing its utmost to save what can be saved. In the end, much depends on the citizenry at large: the values they hold most strongly, the values we are teaching them today, will be those that prevail.

The Oakland seismic landslide map

3 August 2011

A few years back, two guys at the U.S. Geological Survey did an exercise with a database that was subjected to a mathematical version of the Big One on the Hayward fault in the middle of the wet season. Their result was published as Miscellaneous Field Studies Map MF-2379, “Seismic Landslide Hazard for the Cities of Oakland and Piedmont, California.” Here’s a piece of it.

oakland landslide map

Dark-green areas are relatively fine, red areas are relatively awful, and the in-between colors are in between. Gray areas have slopes less than 5 degrees and don’t count. There’s a purple line running from top left to bottom right representing the Hayward fault; students of our street patterns may recognize the upper left corner as the intersection of 580 and 13. The lower right corner is 580 at the exit to the zoo. The left edge of the band of orange down the middle is Outlook Avenue. There are two bits of blue; the upper left one is the pond at Mills College and the lower one is the big hilltop reservoir near Toler Heights.

This map is of very little real use, because it’s just one worst-case scenario of one particular simulation, but it’s well worth studying anyway. (For real uses, like assessing your own property, you should hire a pro.) One big point is that bedrock matters. The big dark-green swath represents the solid metavolcanic rocks that are exposed in the Leona Quarry; they also underlie King Estates Open Space and part of the hill with the reservoir on top.

Fault gauge, 39th Avenue

27 May 2011

South of the LDS Temple, the Hayward fault runs down a well-defined gulch, past the stream offset at Rettig canyon, and becomes more subtle as it traverses Redwood Heights. It’s mapped going down Jordan Road and then Victor Avenue. Here’s where Victor butts against 39th Avenue.

hayward fault

It only takes a moment with a concrete saw to set an unobtrusive fiduciary mark like this. It will document offset along the fault, whether it’s aseismic creep or a more massive wrench when the fault lets loose.


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