Its been quite awhile since we checked in on the seismicity in Oklahoma. As we’ll see, on the whole the news is good, but there are a couple of things worth watching…
First, the number of quakes has steadily dwindled…
This is what you’d hope to see with decreases in wastewater injection. Some of this is regulatory, but a big piece is because the low price of oil made the more water-rich (an thus injection-heavy) fields less attractive.
If instead we look at seismic moment, things are somewhat less clear:
Now first off you see the big drop in increase of seismic moment starting in late 2016; that rate has continued to the end of 2018 (the red curve is new since the last post). But curiously it hasn’t dropped: the M4.6 in April of 2018 offsets the seemingly slowing rate since then–a straight line from the end of 2016 through early 2018 projects right to where the cumulative seismic moment stood at the end of 2018. At present it seems the moment release rate is pretty constant. For this to coexist with a decreasing number of earthquakes means that earthquakes are getting larger even as they are less frequent.
What this means is that while things are a lot better, they might not be improving as much as you could hope.
GG recently commented on Lucy Jones’s [no relation] book on the Big Ones, disasters out of proportion to recent experience. An LA Times article on concerns that dams in the Los Angeles basin are not up to dealing with a superstorm brings up an interesting question: how big can you go? Forty days and forty nights?
For seismologists, the magic equation has often been the Gutenberg-Richter equation which basically says that the log of the number of earthquakes of a given magnitude over a specified time is inversely proportional to the magnitude (so log N = a + bM, where N is the number of earthquakes of magnitude M and a and b describe the distribution in some area). The rate of decrease in number of earthquakes with increasing magnitude, the b-value, is close to -1. So say you have 10 M5 earthquakes in a year, you expect to have one M6. You’d then expect over 10 years to have 100 M5s, 10 M6s, and 1 M7.
If you keep playing this game, you might say that in 100 years you should see a M8, and in a thousand a M9, and in ten thousand a M10. And this is where seismologists see a problem: physically, a M10 is probably impossible (and if the area we’re concerning ourselves with is anything less than a quarter of the globe, it is certainly impossible).
This is pretty unusual, but at 9:45 am MST on Nov 14, this is what the USGS earthquake map showed:
Two things stand out. Most amazing, the entire southern hemisphere lacks earthquakes sizable enough to make the map. The second is that the very largest earthquake in the last 24 hours is a just a M5.0 in Japan. Given that on any given day you expect to see 4-5 earthquakes larger than that 5.0, and that 7/7 earthquakes above M4 are all in the northern hemisphere, this is highly unusual.
Enjoy it while it lasts….
Dr. Lucy Jones has spent her career standing in front of TV cameras and telling the people of Southern California what just happened in the last earthquake and what it meant. [She is no relation to GG, if you wondered]. She developed over years of practice the ability to issue a soundbite acceptable to newscasters while still containing a scientifically defensible statement that provided useful information to a concerned public. The number of working scientists with that background probably can be counted on one hand. (GG recalls seeing her do a live stand-up while one of her children wrestled with her leg–she gave no indication to the viewing audience what was going on just below the edge of their screen nor did it affect her delivery). She has recently been leveraging that experience to try to affect public policy through the creation of her own center on science and society. An outgrowth of this is her book, The Big Ones: How Natural Disasters Have Shaped Us (and What We Can Do About Them).
It is worth reminding you of her scientific work, as many times the public face of an organization isn’t really an authority. Lucy got deeply involved in the question of just what aftershocks really represent, which includes the question of what is going on when the aftershock is bigger than the original mainshock? This has been a tremendously practical approach to better quantifying short-term earthquake hazard, and she has worked to incorporate it in the messages to the public. This has led her to respond to reporters’ queries with simple yet fact-based responses, like when asked “what should people do after this last earthquake?” she might respond “Don’t leave town, but make sure your bookshelves are securely fastened to the wall and you aren’t sleeping under something heavy that could fall on you.”
It is this clear-spoken and practical approach that informs the book. She concerns herself with disasters of a magnitude large enough to threaten societies, such as the great Lisbon earthquake and tsunami, 1783-4 Laki eruption, the 1861-2 California flood, Katrina, and the Boxing Day and Tohoku tsunamis. (The one category she leaves out is drought). She argues that these events are of a totally different scale than more routine floods, earthquakes, and eruptions and that we are unprepared for just how destructive these things can be. In the end she argues (based on her own experiences with government) that making a more resilient society is the necessary goal and sets out guidelines for how to get there.
The disasters discussed range from the obscure (not many people know of Laki or the Lisbon earthquake these days) and the well known (Pompeii shows up with Katrina). In some instances she can shed light on events in ways most others could not (the Tangshen earthquake tragedy following the fortunate if lucky prediction of the Haicheng quake, the inability of California flood planners to accept the reality and possible recurrence of the 1862 floods, and the mistakes made in the L’Aquila earthquake prediction/unprediction and court case). The summaries of each are placed in a brief social context and provide a human dimension to the catastrophe (focusing on what happened to Pliny the Elder in the Pompeii eruption, for instance). Each has a bit of a moral about what this tells us about such mega disasters.
The book is a success, an easy read with good storylines for the reader and some twists and turns of interest even to seismologists, but there are a couple things that might have made its point more powerful. One is the absence of examples of societies that failed in the face of natural disasters; the closest example in the book is a small society wiped away in the Banda Aceh tsunami. Others seem not to be failures of societies so much as adaptations to some changes (did New Orleans go away? Did Sacramento rebuild? Did Rome fall from Pompeii? Would the Chinese Gang of Four really have ruled in the absence of the Tangshen earthquake?). Real failures might not be a lengthy list, which brings into question whether these Big Ones really are as challenging to societies as Dr. Jones would like us to believe. Perhaps the collapse of Minoan civilization in the face of the Santorini eruption or the abandonment of Anasazi centers or Chaco culture due to drought might make the case that there is a real to a society’s continued survival. The devastation of Haiti or Puerto Rico might yet make the case, but Haiti’s quake isn’t mentioned and Puerto Rico is a brief aside.
The other loss is Jones’s dodge of the really Big One: climate change. While Dr. Jones does a nice job of illustrating how the global reach of media and social media in particular is bringing home to all the terror and impact of big disasters, the presence of an ongoing global disaster seems to just not fit her narrative. Was this a decision to avoid alienating parts of her audience with a more politically charged topic, or just a disaster that was in a totally different class? Given concerns about storms described in the book becoming more common with a warmer climate, going beyond the resilient community recommendations in this case would have been welcome. After all, we can’t lower the intensity of an earthquake, but we can undercut the most extreme storms, making communities more resilient on both ends of the spectrum.
Those are minor objections, though. Dr. Jones discusses her time with the City of Los Angeles working to get a program in place to retrofit the most dangerous buildings in the city. Her perspective is an interesting one for scientists loathe to step into the fray, as she is neither encouraging taking over the role of making policy or simply pitching academic studies over the fence for policy makers to do with what they will. Whether others can follow in her footsteps is yet to be seen, but she has laid out a case that big disasters are in our future and we are far better off preparing to mitigate their effects than preparing to respond once the emergency is underway.
A op-ed-ish piece at CNN takes the devastation of hurricane Michael and seeks it to be labelled something other than a ‘natural disaster’. The main argument is that human emissions have led to warmer ocean waters, a warmer atmosphere and higher sea level, all of which allow for stronger and more impactful hurricanes. This is not news in the climate community, which has been striving the past few years to be able to say something about the effect of global warming on major storms, heat waves and droughts. But, of course, this is not the only way that humanity makes disasters worse.
A seismological aphorism is “earthquakes don’t kill people, buildings kill people.” Although an approximation (tsunamis are pretty capable of dealing death, as are quake-triggered landslides and avalanches), this does highlight the other way that humanity makes nature even more powerful. As a result, geoscientists often walk around shaking their head and muttering under their breath “Why’d they do that?” Adobe buildings in earthquake prone areas. Beach houses on barrier islands. Developments at the base of landslide-prone mountainsides–or on active landslides themselves. Cities in floodplains. Insurance designed to force the reconstruction of things in the same hazardous places. Frankly, it is so bloody obvious that these are stupid things that you want to throw your hands up in the air and embrace the inevitable extinction of such an incompetent species.
Of course these are all things that make natural disasters worse for people, but they don’t actually make the actual trigger worse, right? Um, true, but we already do plenty more than just supercharge hurricanes. Injection of waste water into deep wells has produced quite the swarm of earthquakes in Oklahoma. Paving over wetlands made floods in Houston that much worse than they would have been without paving. Human-caused fires set the stage for catastrophic landslides and mudflows that might not have happened without the fires. Subdivision have been crushed and roads destroyed because bulldozers removed the toe of stable landslides that then failed. Excessive watering and water from septic systems is likely the cause of the Portuguese Bend landslide in Southern California as the old slip planes got lubricated and the soils above increased in weight.
In sum, we’ve been at this business of making our own “natural disasters” for some time. All we’ve done with global warming is to carry our local disaster mania on the road. Arguably we’ve reached the point where a truly natural disaster is a rarity.
So FiveThirtyEight has a story about how inadequate hurricane intensity numbers (Saffir-Simpson scale categories) are. Basically the destructive potential of a hurricane is poorly linked to that number. But the funny thing in reading the piece is that you could substitute Richter magnitude for Saffir-Simpson scale and make almost no other changes and the article would sound about right. Richter magnitudes (as popularly understood; the numbers reported for events are usually moment magnitudes these days) tell you almost nothing about the destructive potential of an earthquake.
Just as with hurricanes, where an earthquake strikes is critical in determining its damage. Magnitude 8 earthquakes 600 km under western Brazil are barely even noticed, while a M5.9 in northern Haiti kills over a dozen. The details can be amazingly important: a M6.3 earthquake in Christchurch devastated the city center and killed nearly 200 but the earlier M7.0 earthquake only a few miles away produced little damage and no fatalities.
Just as with hurricanes, the details of the earthquake will affect its ability to do damage. When an earthquake ruptures in one direction, damage will be greater in that direction than 180 degrees away. Another New Zealand quake, the 2016 M7.8 Kaikoura earthquake, ruptured from south to north, sparing areas closer to the epicenter but causing enough shaking in Wellington, across Cook Strait from the event, that several buildings had to be torn down. Toss in intrinsic variations in frequencies due to variations in stress drop and it is clear that a magnitude by itself doesn’t carry the whole story.
A popular pastime in southern California is guessing the magnitude of an earthquake solely from what was felt. GG recalls a radio news program years ago when there was an earthquake near GG, who felt the quake before the radio broadcaster did. Callers speculated on where and how large this was: “I’m in San Bernardino and it was a slow rolling event so probably on the San Andreas to the north” “It was a sharp event that must have been a magnitude 6” and so on. (In fact, when you are close you tend to get a very sharp movement from the P-waves, but farther away it is the surface wave train that produces a more rolling movement).
The Richter magnitude is about forty years older than the Saffir-Simpson scale and as a result, seismologists have had that much more time to try and clarify all the things that go into earthquake damage. Look into the earthquakes.usgs.gov page at a recent large event and you see far more than the magnitude. Their Pager page tries to estimate damage and deaths almost immediately after an event to help gauge the need for emergency assistance. Stories about the “Big One” that dominated California media for decades are being replaced with more nuanced stories highlighting the risk from faults through urban areas like the Malibu Coast/Hollywood Hills fault system or the Hayward Fault. And the interaction with the engineering community is far more sophisticated than 40 or 50 years ago, with power spectra and 50 year exceedence criteria being passed on from the seismological community.
And yet we get stories about the earthquake proof house that can withstand “an earthquake registering up to 9.0 on the Richter scale”. Well, GG’s house survived a M9 earthquake–sure, it was across the globe, but the point is that distance and environment matter. Would these buildings make it if right on a 20m fault rupture? Doubtful. That surviving a M9 means nothing. Surviving some threshold of ground motion? That might be useful, but probably the public wouldn’t get a max acceleration of 2g as a useful number.
So good luck meteorologists. Your best hope might be in scaling total kinetic energy in a hurricane to a level from 1 to 5, where you could add decimals. Oh wait, they’ve done that. So why isn’t this on TV and the web now?
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.