Archive for the ‘the hayward fault’ Category

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

39th Avenue fault gauge revisited

27 November 2013

2-1/2 years ago, I presented a photo of a cut mark in the curb of 39th Avenue where the Hayward fault is mapped. This month I happened to visit the spot during an Oakland Urban Pathways walk, and I took the opportunity to take a new photo.

39th-faultgauge-2013

It has moved slightly, just a few millimeters, in the intervening time.

The U.S. Geological Survey monitors the fault closely through Oakland. They don’t measure this mark, or if they do it’s not definitive. The definitive survey is along a longer line across the fault, because the fault movement isn’t limited to a perfectly thin geometric plane. Their measurements show that this part of Oakland is creeping approximately 4 millimeters per year. Heck, here’s a good source, from a 2000 paper by the USGS guys that was published in Geophysical Research Letters:

HFcreeptable

The authors note that Oakland has a relatively slow rate of creep, and they interpret that as a sign that the fault here is more extensively locked than it is elsewhere. The area and degree of locking bears directly on the energy the fault is capable of releasing. Mind you, we have over a decade of new data and new thinking since that paper was published, but the data is sound.

Middleton hill

26 July 2013

Way down in the Sheffield Village neighborhood is a big hill and a little hill, but most of the place is in a flat little basin. The geologic map shows it as a patch of old alluvial sediment of the same vintage as the Fan:

sheffieldmap

The big hill is on the east side, across the Hayward fault (the black line from the lower right corner). The little hill is on the west side, butting against I-580. The road on its west side is Middleton Street, so I give the hill that name. I didn’t realize it when I poked around there earlier this month, but the hill is mapped as San Leandro Gabbro, of Jurassic age. The rock doesn’t show itself very much, but here’s a small exposure. Next time I’ll bring a hammer.

middletonhill

The highlight of the hill is the little private park inside the ring of houses there, just a microscopic piece of the original oak meadow (although this is actually a cork oak).

middletonpark

From there you get a nice view of the big hill. The fault runs along the foot of the hills, behind the homes in the center and in front of the lower set of homes on the right.

sheffield450

Click the photo for a big version.

New Lake Merritt

12 July 2013

I think it’s safe to say that everyone in town is thrilled with the improvements to Lake Merritt. After seeing the final configuration today, I’m feeling a deep satisfaction.

newlakemerritt

The new roadway and pedestrian bridge over the lake’s outlet serves vehicular traffic as well as ever, but residents and, most of all, the lake and the land get their due. The lake—actually it’s a tidal marsh—is noticeably healthier now that the tidal flow from the bay is no longer regulated with a dam. The range of the tide is greater now and the water is flushed more thoroughly. We have figured out how to trust nature with our lake. We’ll see in the future how the new lake deals with drought and flood, but I think that the city will not overreact to the occasional inundation as it might have in the past.

newlakemerritt2

The new lake is a triumph for the planners of Measure DD, where the money came from. The funds are still being spent on this and many other projects around Oakland, but I’m starting to wonder what the DD crew could do for an encore. Nature holds us in its hand with the Hayward fault, too. Can we envision better ways to live with it?

Montclair ballfield and the Hayward fault

4 May 2013

This is the view from atop the old railroad crossing at Mountain Boulevard, overlooking the south end of Montclair Playground.

montclairfield

The Hayward fault is mapped running through here from about third base on the ballfield at the left across the field of view. Two trenches were dug across the fault right here in 1981, and Jim Lienkaemper, the US Geological Survey’s (therefore the world’s) leading expert on active faults in Northern California, found evidence that the 1868 earthquake ruptured the fault here. Here’s part of the map he published in 1992 showing this area (at the REN in WARREN).

HFmontclair

The map is oriented so the fault runs vertically. The codes refer to evidence of active creep (C2) and vaguer evidence of creep (C3), geomorphic features of greater and lesser distinctness (G2, G3), and the trenches (T) I mentioned. “H2″ means there was good evidence of fault motion in the last 12,000 years—in this case, historic motion. The little oval at the WA in WARREN is a sag basin, now a water feature in the park. From top to bottom, the two-letter codes are as follows: gi, gradual inflection in slope; rw, right-offset wall; sl, linear scarp; jo, opened joints or cracks in concrete; sc, scissor point (where the up and down sides switch); rb, racking/distortion of building; as, arcuate scarp; dr, depression in a right stepover (sag basin); rc, right-offset curb; so, surveyed offset feature. The other codes refer to specific publications. This level of detail is available for the entire length of the fault, and while the USGS considers its online database of 2008 to be the most current, I like the format of this older map, Miscellaneous Field Studies Map MF-2196

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.


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