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The Quiet Hemisphere

This is pretty unusual, but at 9:45 am MST on Nov 14, this is what the USGS earthquake map showed:

NoShemiEQ

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.

[Just so there isn’t too much confusion– there was a M2.9 in New Zealand and Chile had some M3s over this time period–just not big enough to get on the USGS map]

Enjoy it while it lasts….

Big Ones (Book Review)

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.

Unnatural Degrees of Disaster

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.

Ratings Failure

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?

The Reign of Strain Isn’t Very Plain

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.

Read More…

Hubris

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?

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6 February Hualian, Taiwan M6.4 earthquake, http://www.bbc.com/news/world-asia-42966916

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5 February 2016 M6.4 Yujing, Taiwan earthquake. From https://www.theguardian.com/world/gallery/2016/feb/06/earthquake-in-southern-taiwan-in-pictures

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9 February 1971 Sylmar, California M6.5 earthquake. From https://www.dailynews.com/2016/02/08/sylmar-san-fernando-earthquake-45-years-ago-tuesday-64-killed/

(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.

Kaikoura A Year Later

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.

KaikouraFaults-Kaiser

Faults ruptures in the Kaikoura earthquake, from Kaiser et al, SRL, 2017.

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…