Having just remembered the 1906 San Francisco Earthquake brings to mind Harry Fielding Reid’s model of elastic rebound for earthquakes developed from observations of that 1906 quake. The idea that the earth’s surface was slowly moving in opposite directions across a fault over a long time period, straining the rocks near the fault until a critical point was reached when the strained rocks would cause the fault to rupture, allowing each side of the fault to “catch up” with the more distant parts of the earth’s surface farther away.
Much later, when plate tectonics was developed, earth scientists could tell what the average velocity of plates were over a couple million years from analysis of magnetic anomalies on the seafloor. When space-based geodesy came along, first with VLBI and then with GPS, geodesists found that the plates were moving today at a rate equal to that seen over millions of years. It seemed as though the earth ran at a smooth and even pace.
The combination of ideas would suggest that one hope expressed about a hundred years ago was that faults would be triggered like clockwork. Every so many years, termed the recurrence interval, a fault would rupture with what would be called a characteristic earthquake. Ideally you could then predict the next earthquake if you knew when the last couple had happened.
This ideal view of the earthquake world has gradually unravelled, with a couple of observations in the past decade indicating that there really is something more variable in how geologic strain is created than the elastic rebound model and smooth plate motions would have suggested.
The New York Times has a very nice piece on the risks of high rises in San Francisco. And although the story focuses on San Francisco, the issues brought up apply as well to Los Angeles (which, for a very long time, forbid any building to be taller than 13 stories, the exception being city hall). [Later note: the LA Times also celebrated the 112th anniversary of the 18 April 1906 earthquake with a story on preparedness and a look at the potential for disaster on the Hayward Fault in the East Bay].
Some of the quotes in the New York Times article are priceless:
“Buildings falling on top of other buildings — that’s not going to happen,” Mr. Klemencic [the chief executive of Magnusson Klemencic Associates, designer of the tallest SF skyscraper] said.
Er, has he looked at what has happened?
(And those are just a few of the collapses in M6-ish EQs. Just wait for the right M7+, where the ground shaking will last longer).
GG has heard this kind of hubris before, and it is not comforting. Buildings do fall over, and if they are close enough together, they do fall over onto other buildings. All too often this is because the foundation is compromised by liquefaction–which is the very risk in the part of San Francisco where the building Mr. Klemencic’s firm designed sits–next to another building already tilting and sinking.
(Engineering certainty probably increases the closer to a CEO a person sits, but many Japanese were confident they would not see structural failures like California saw in the 1989 Loma Prieta or 1994 Northridge earthquakes until the 1995 Kobe earthquake proved them wrong. And Americans were able to design an overpass that failed not in just one earthquake, but two: the high overpass of the I-5/SR14/I-210 interchange failed in both the 1971 Sylmar quake and the 1994 Northridge earthquake.)
Mr. Macris [who led the planning board under four mayors] said the issue of seismic safety of high rises was “never a factor” in the redevelopment plans of the South of Market area.
Astounding. Look at the USGS liquefaction susceptibility map. The whole area is at an extreme risk. How–HOW!–could seismic safety NOT be a factor in a community that as recently as 1989 saw much smaller structures destroyed in the Marina District from the Loma Prieta earthquake.
All this is amazing. Years ago, there was the 1971 documentary, “The City that Waits to Die” about San Francisco’s disinterest in any kind of seismic safety. GG remembers seeing this long ago, and it was just amazing that San Franciscans were so oblivious to the obvious risk. This extends to how they interpret their own history: the 1906 quake is often buried under the subsequent fire, with claims of fatalities both downplayed (probably more than 3000 died instead of the 498 claimed at the time) and tied to the fire (a more common urban problem seemingly cured with brick buildings). All this was to make San Francisco appear safer to businesses and visitors from other places.
And if you want to feel safe in LA, don’t. The welding failure mentioned in the NY Times piece was recognized from the 1994 Northridge earthquake–but the failures were not remediated. The broken welds are not obvious in buildings that did not fail in that quake, but most likely will in then next one. (If you want the gory details, look at Tom Heaton’s notes from a class he taught).
The overconfidence and denial evident in the construction habits in San Francisco are probably not limited to that jurisdiction. There will be deaths and monetary damages that could be devastating if the right quake is the next one to occur. Maybe San Francisco will get a solid warning shot across its bow if, say, the Hayward Fault on the east side of the Bay ruptures from north to south–shaking San Francisco enough to maybe demonstrate enough that these problems are real to make the city take care to prepare better while not producing the truly devastating outcome that seems possible.
A year ago GG posted on the Kaikoura M7.8 earthquake with the title “Single quake slip partitioning”. With a year past, it seems a quick look at the literature that has appeared is in order. Was this diagnosis correct? In some work, it seems the answer is yes; in others, it seems no.
The most comprehensive overview is probably a paper by Kaiser et al. in Seismological Research Letters. This paper summarizes geologic, seismologic, geodetic, and engineering observations from this quake. They note that 13 separate mapped faults all ruptured together, more than was anticipated prior to the quake. It took about two minutes for things to unwind from south to north along this collection of faults, with substantial step-overs was one strand to the next. Most of the energy released came in two distinct jumps, one 20 seconds into the quake, the next about 70 seconds in.
But as to GG’s hypothesis of slip-partitioning during the quake, the interpretation of the slip history from high-frequency seismic data is no; the faulting was dominantly strike-slip to oblique-slip on land, though the authors do note a period during the rupture when they don’t really locate the source of seismic energy very well.
A second paper comes at this from a different angle. Read More…
Last November, a M5.0 quake caused some damage in Cushing, Oklahoma. A number of folks at the time were relieved that there wasn’t any noticeable damage to the nation’s largest oil storage facility. This was only a few months after the Oklahoma Corporation Commission ordered a cutback in disposal of wastewater in injection wells. Since then, seismicity has mostly quieted down, but it seems that recognition of the scale of the hazard has been seeping into the awareness of a broader part of the media, leading to a lengthy piece in Politico Magazine on the potential disaster lurking in Cushing from facilities not really designed to survive an earthquake. While most of the stories of earthquake hazards in Oklahoma have been more focused on falling chimneys and old brick buildings, this piece exposes a pretty critical flaw in Oklahoma’s infrastructure.
So we will hope that there isn’t another unrecognized fault slowly being lubed up under Cushing. But remember, the largest events from the infamous Rocky Mountain Arsenal injection adventure in the 1960s came more than a year after injection was totally stopped. Oklahoma hasn’t stopped injecting fluids, and the volume of water injected so far dwarfs anything that happened in Denver in the 1960s…
For those of us in earth science, this past week has highlighted an awful lot of potential “told you so” moments. Like how warming climate and a warming ocean will lead to higher precipitation events. Like how you really do need to plan for floods. And we just missed hearing more about the barrier island/marsh protection talking point. And almost at the same time we’ve been greeted with ever more evidence that the Trump administration has little or no use for scientific input–not even choosing to ignore it, they seem more eager to simply not have any scientific input at all. Just as it is ever clearer that we are facing real decisions in trying to prepare for a warmer world, we seem the have a government yelling “la la LA LA” with its fingers in its ears.
But that isn’t the point here today.
One aspect of the tragedy in Houston is that the absence of any sensible planning has led to more flooding (the worst example might well be letting houses be built within the basin and below the spillway elevation of flood control dams); this is exacerbated by the combination of government subsidized flood insurance and the out-of-date or inadequate flood zone maps. Of course some now point to the zoning-free and laissez-faire approach to building in Texas as the bargain they made with the devil, implying that other places where strict zoning has been enforced will be safer.
If GG has noticed one thing about strict zoning (and Boulder has a pretty heavy hand on building), it is that it is rarely used to prevent building in stupid places–it is mainly used to keep people from building on land other people enjoy as it is. Some years ago when Colorado Springs was approached by a developer who wanted to build houses on an active landslide, the city council had to look away from the evidence they were given in order to approve this ongoing disaster. You can find similar stories elsewhere. Yes, fear of flooding is brought up when a new development is proposed…but mainly as part of the larger arsenal serving Fort NIMBY (sometimes there is a legitimate fear, but sometimes it is greatly exaggerated). California has the Alquist-Priolo act to prevent construction near active faults, but it only moves buildings 50 feet from an active fault. Direct destruction of a building by a fault being directly under it is one of the least likely modes of destruction (even some dams do OK on faults: the Upper Crystal Springs dam survived having several feet of offset in the 1906 earthquake). Earthquakes do most damage by shaking weak soils: recall the Marina District in San Francisco, far from surface faulting, where shaking from the Loma Prieta earthquake damaged dozens of structures. What strict zoning clearly does is raise housing prices.
The main exceptions to non-use of zoning as a disaster preventative is in the wake of disasters. Even then, the most common refrain after a disaster is “we’re going to rebuild and bring it back better than before.” After a tornado, this makes sense. After a flood, whether storm surge or heavy rain? Not so much. The harder statement? “We learned a lesson and we aren’t going to make that mistake again.” It is very hard to say, but if we are going to avoid paying to rebuild over and over again in increasingly vulnerable places, risking the lives of inhabitants in the meantime, it’s time to start saying it and then walking the walk.
Its been awhile since Oklahoma earthquakes made news and so it seems timely to look in on the Sooner State to see how things are going.
Last we looked in, numbers of earthquakes were down but the moment release was still pretty high. Predictions from Stanford late last year were that the decreased injection of wastewater would lead to a decrease in earthquakes over the succeeding five years. The USGS, in contrast, has continued to note that the decrease in the number of events does not mean a decrease in damaging earthquakes.
So far, the news is good. Not too surprisingly, the number of earthquakes continues to drop:
So that continues the trend from 2016. What about moment release? Well, given the absence of news reports, you’d guess there is a decline there, too, and you’d be right:
And, indeed, 2017 has been dead quiet moment-wise as well.
Does this mean that the seismic risk is now gone? Well, no. That M5.7 earthquake in late summer last year was on an unrecognized fault. The fluids migrating in the basement could encounter another critically stressed fault and trigger a significant earthquake. But for now, this is good news for Oklahoma residents.
With 2016 coming to a close, GG thought we might want to see just how things are shaking out in Oklahoma, home of the great induced earthquake experiment. And there is something for everybody, depending on how you want to look at it.
For the optimists hoping that Oklahoma’s actions to slow wastewater injection will end the plague of induced earthquakes, we have plot number one: number of quakes with a magnitude of 3.0 or higher by month:
The rate of such earthquakes dropped from nearly 4 a day in January to about one a day this month. And you could hope that this had something to do with this:
The 25% reduction during the year in the rate of injection in the area where triggered seismicity has been observed might be responsible for this. But there are other things to watch as well. First, these are still pretty high volumes of water going back into the Arbuckle, and all the water that went down earlier is still making its way through the subsurface. Second, presumably a lot of produced water is going to other wells, either in the Arbuckle outside the area of interest or into other formations. Third, a decrease in the number of M3+ events is not the same thing as a decline in seismic moment:
The 9/3/2016 M5.8 Pawnee, Oklahoma earthquake put a big damper on any celebration of a decrease in seismicity. The overall moment release of 7.8 x 1024 dyne cm is the largest single year moment release in Oklahoma history. As we noted before, this isn’t unexpected: the Rocky Mountain Arsenal sequence in the 1960s produced its largest quakes after the injection ended.
So we enter 2017 on a note of caution. If you bought earthquake insurance in Oklahoma, don’t let it lapse just yet. You might get shaken a bit less often, but when you do get a quake, it might still be pretty big.
P.S.: there are a couple of nice visualizations out there. Tulsa World put together an interactive map a year ago showing how produced water injection was varying over time and by county. The Oklahoma state government has an interactive figure with recent earthquakes and disposal well locations.