Just as I did in 2016 and 2017, I thought I’d begin the new year with a look back at the earthquake activity in the last. According to the catalogue maintained by the USGS, the Earth’s ever-grinding tectonic plates produced 1,795 earthquakes of magnitude 5 or greater over the past 12 months. Below are maps of the individual locations of each of these earthquakes, as well as a global seismic ‘heat map’, scaled to represented the total energy release in each 5º grid square.
Global Map of M5+ earthquakes that occurred in 2018, from the USGS catalog.
Heat Map of global seismic activity in 2018, scaled to total moment release from all M5+ earthquakes in each 5º grid square
Based on the last 50 years or so of data from the global network of seismometers, in an average year we expect around 1500 magnitude 5-6 earthquakes; about 130 magnitude 6-7 earthquakes, about a dozen magnitude 7-8 earthquakes, and maybe one event larger than magnitude 8 (earthquakes of magnitude 9 or more are much rarer beasts, with only two so far in the 21st century). 2018 boasted about 10% more M5-6 earthquakes than the long-term average, about 10% less M6-7 earthquakes, and about 20% (2-3) more M7-8 events and that one M8+ event. All this is well within the variability we see between years in the records since 1974.
Number of earthquakes in different magnitude ranges in 2018, compared to longer term averages and ranges.
2018 earthquake frequency compared to the instrumental record since 1950 (note that M5-6 events are largely missing from the catalogue prior to the 1970s).
In a geological echo of the uncertainty principle, we can only narrow down the location of a future earthquake if we are very fuzzy about the timeframe over which it will occur, and we can only talk with any confidence about a specific period in which an earthquake of a particular size will occur by greatly expanding the area of the planet we are considering.
The same principle applies when talking about multiple earthquakes. The scale of the whole planet, and the timescale of a year, is fuzzy enough to ‘predict’ roughly how many earthquakes of particular sizes are going to happen. But the characteristics of each individual earthquake – when and particularly where – are not predictable. Yes, we got the expected magnitude 8+ earthquake, but it was almost 600 km down in the subducting Pacific slab beneath Fiji, deep enough that it only caused minor shaking on the surface and no damage.
Contrast this with the magnitude 7.5 Palu earthquake. It released less than a tenth of the energy, but the rupture occurred within 20 km of the surface. The strong ground shaking that resulted, and particularly the landslides and tsunami that the shaking triggered, killed at least 2 thousand people, making it by far the deadliest earthquake of the year. Also in unfortunate Indonesia, a sequence of magnitude 6-7 earthquakes beneath Lombok Island in August killed hundreds, when most of the dozens of others in this size range that occurred last year were, through some combination of less proximity to the surface or people and more resilient infrastructure, little more than an inconvenience. Last month’s Anchorage earthquake springs to mind. And one of those more than 1600 magnitude 5-6 earthquakes was sufficient to kill 14 people in Haiti. Even if an earthquake only severely shakes a very small area, that small area can coincide with vulnerable people.
As always, earthquake location matters. In the year ahead, we can expect roughly the same numbers of earthquakes to happen globally as in the past. But their locations and depths and timing – the factors that, far more than magnitude, tip the balance between a minor blip and a disaster – will sadly only unfold as the year itself does.
I’m pleased to announce that I’m leading a new multi-institution NSF-funded project investigating how stormwater decision making translates to environmental outcomes at the watershed scale. I’m collaborating with Aditi Bhaskar (Colorado State University), Kelly Turner (UCLA), and Dave Costello (Kent State University) on the project we’ve christened STORMS, for STream Outcomes Resulting from Management of Stormwater.
Little Dry Creek at Westminster, Colorado (Photo by Aditi Bhaskar)
Over the next three years, we’ll be working in set of watersheds and municipalities in the Cleveland and Denver regions. Cleveland and Denver have different climates, hydrology, and institutional structures affecting stormwater management, and our goal is to distill generalized knowledge from studying these contrasting regions.
We’ll be collecting social, physical, and ecological datasets to generate an integrated understanding of stormwater management decision making and environmental consequences. We’ll start by looking at how formal institutional rules and informal norms shape the decisions made at the local and regional scale and translate to specific management actions (like building ponds versus rain gardens). The next step is to see how those management actions affect urban watersheds’ hydrologic regime, and we’ll do that by using stakeholder-informed modeling, as well as retrospective analysis of hydrology and stormwater actions. We’ll use stream metabolism and suspended sediment transport as our measures of environmental outcomes, so there will be field work in six watersheds to draw the connections between hydrologic and sediment dynamics and ecosystem health. By the end of the project, we’ll tie all of our findings together using a Bayesian network.
Throughout the project, we’ll be working with stakeholders, including watershed groups and decision-making authorities, to both shape our approach and share results. We’ll also be working with Cleveland Metroparks and Denver KIC-NET educators to develop Data Nuggets, that they can use with middle school and high school students. Collaborator Lauren Kinsman-Costello helped develop Data Nuggets, which give students practice making claims based on quantitative evidence. We’ll draw from the data collected over the course of the project and connect the nuggets to Next Generation Science Standards relevant to the engineering and environmental science within the project.
I’ll be seeking a PhD student to work on the hydrological aspects of the project, and Dave Costello will be recruiting a MS student to lead the ecosystem metabolism piece of the project. Look for those ads in the coming weeks and months. We’ll also be recruiting undergraduate researchers from Kent State University and Colorado State University.
West Creek in Brooklyn, Ohio. (Photo by Anne Jefferson)
If you want to make earthquake scientists jumpy, all you need to do is ask, "can you predict the next earthquake?"
In fact, any variation on the theme of ‘earthquake’ and ‘prediction’ will do – unless it is one which informs you that their combination is impossible.
Use of the word ‘prediction’ implies precise knowledge about an upcoming event, both in space and in time: we think that fault will fail, in an earthquake so big, over this timeframe. But such specificity is exactly what we don’t have, and may never have, when we’re considering the future risk of large earthquakes.
In a geological echo of the uncertainty principle, we can only narrow down the location of a future earthquake if we are very fuzzy about the timeframe over which it will occur, and we can only talk with any confidence about a specific period in which an earthquake of a particular size will occur by greatly expanding the area of the planet we are considering. So we can ‘predict’ there will be a magnitude 6 or greater earthquake somewhere in the world in the next fortnight. We can ‘predict’ that the San Andreas Fault will rupture at some point in the next 250 years. But neither of these predictions are useful: we don’t know even roughly where in the world that magnitude 6 will occur, let alone which fault will rupture to produce it. And we don’t know when in the next 250 years the San Andreas will rupture. It could be tomorrow; it could be two centuries from now; it could be any point in between.
If we confine ourselves geographically to a particular fault or collection of faults, there are two specific timeframes over which a bona fide prediction would be actionable, giving us the chance to meaningfully act to mitigate the worst of the damage and devastation. One is short – days to weeks. If we knew that there was going to be a major rupture on a particular fault in the next few days or weeks, we could evacuate the area at risk, and disaster response could be ramped up in advance of the inevitable damage and casualties. This is the realm of claimed earthquake precursors – a subject which I have written about many, many, many, many times. At best, we don’t understand enough to interpret potential precursor signals ahead of time. At worst, large earthquakes don’t actually generate precursors, because they’re just small earthquakes that happened to keep going.
The other useful timescale is longer. If we could make confident predictions about a major fault rupture in the next few decades, then that could inform specific decisions about where to build the most resilient infrastructure, which populations need to be prepared, and how to train emergency personnel. Unfortunately, the behaviour of faults is highly variable over precisely the sort of 50-100* year timescales that would be useful to us. In places where we can use paleoseismology – the study of the geological record left by earthquakes – to construct a history of multiple large earthquakes over hundreds or thousands of years, we see quasi-periodic behaviour: the average interval between dozens of earthquakes often remains fairly constant, but the interval between any two earthquakes can vary quite significantly from that average. A couple of examples:
Earthquakes can never really be ‘overdue’, because they don’t have a fixed schedule. All we can say for sure is that an active fault will rupture eventually. If scientists have done the hard work of reconstructing the paleoseismic record, we may also know that over many events, the average time gap between them is so many years. But because the gap between individual large earthquakes on a fault can vary by a century or more, we cannot truly know for sure if there is going to be a major earthquake in the next 50 years. This uncertainty will always be with us: it is a fundamental aspect of how large earthquakes seem to work. And, as such, making specific predictions about when the next big earthquake will strike is folly – arguably, even attempting to do so is dangerously misleading, because it tacitly accepts the premise that such a thing is possible, when it isn’t.
Our certainty about an earthquake occurring within a particular timeframe is only high over periods of centuries or more. For anything less, our prediction has a very high chance of being wrong.
Rather than stating that a large earthquake will definitely happen (or not) in the next 50 years, earthquake scientists must instead grapple with the uncertainties in fault behaviour and estimate the 50 (or 25, or 100) year probability of such an event occurring. Using our knowledge of a fault’s past behaviour, and our assumptions about how deformation in the crust works, we ask the question: if we could run the next 50 years multiple times, how often would we see a big quake?
This approach has it’s limitations. Our knowledge and understanding of the system is not complete, and different assumptions can lead to very different estimated probabilities (here is a good start for understanding these issues). People are also exceedingly bad at interpreting probabilities correctly, particularly in cases such as this: we only get to live through the next 50 years once, and for a single roll of the seismic dice, although certain outcomes are more likely, any scenario with a non-zero probability could happen.
That is not to say these forecasts should be ignored. They represent our current best guess about the seismic risks a region faces, and are a valuable starting point for preparing to meet them. But their core message is that the dice exists, and bad rolls are possible. Even if we don’t know exactly how many sides spell bad things for us, we know that some of them do, and we should prepare accordingly. We don’t know when in the next few hundred years the San Andreas Fault, the Alpine Fault, or the Cascadia subduction zone will rupture, just that they will. We must prepare like it might be tomorrow, and not be surprised if it is instead two centuries from now. With faults, you never can tell which it will be.
* 50 years – the interval for which we generally construct seismic hazard maps – is the average lifetime of a building.
All of this has been accompanied by lots of earthquakes, produced directly by magma squeezing its way through the surrounding rock, and also by the deformation of the landscape around the summit as it it moves from one place to another. But can we link the earthquake activity to the volcanic activity on the surface? To answer this question, we can take advantage of the USGS earthquake catalogue search tool, which allows you to export the results in the form of an animated kml file to display in Google Earth:
Earthquakes around Kilauea on the Big Island of Hawaii between 28 April and 4 May 2018. Orange circles occurred in the final 24 hours of the record. Data from the USGS catalogue.
What’s cool about this animation is that the patterns you can see in the seismic data match the activity on the volcano described above. As the Pu’u O’o lava lake started to drain on the 1st May, causing the crater floor to collapse, you can see a series of earthquakes migrating eastwards from Pu’u O’o, tracking the underground migration of the magma before it began to emerge from the fissures on the Leilani Estates subdivision (which is located exactly at the eastern edge of the yellow earthquake swarm). This nicely processed radar interferogram from Pablo Gonàzlez shows ground displacements that also match up with this narrative, with a long linear zone of intense deformation in the same region as the earthquake swarm. Both are caused by the magma draining sideways and down the Kilauea rift zone.
Ground displacements on Kilauea from comparisons of satellite radar measurements in Mid-April and early May.
Then yesterday evening, a large magnitude 6.9 earthquake struck the region, and the seismic activity afterwards appears to have largely shifted again, with main three clusters (orange and red circles) to the west of the epicentre and the fissure eruptions.
Earthquakes around Kilauea in the roughly 24 hours following a large magnitude 6.9 earthquake on 4th May 2018.
The focal mechanism of the earthquake – the largest earthquake recorded on Hawaii since a magnitude 7.4 in 1975 – indicates compression on a fault about 5 km below the surface. It is probably related the fact that the whole flank of Kilauea is sliding towards the sea. As the volcano is built upwards by eruptive activity, it spreads outwards along a weak detachment at the contact between the strong oceanic crust that the Big Island is built on top of, and the weaker jumble of fractured lavas and other volcanic debris that it is built from.
The most likely explanation is that the large earthquake yesterday evening was caused by sudden motion along this detachment or a fault associated with it: some preliminary GPS data from the USGS indicates that this is indeed the case.
GPS data showing up to 0.5 m of motion due to M6.9 earthquake on 4th May, and displacements of up to 2.5 m on simulated rupture. Source: USGS Volcanoes on Twitter.
The three patches of earthquake activity after the earthquake are therefore probably located on the fault surface, and at the top and western edge of the bit of the volcano flank that just moved towards the sea.
What I am pondering right now is the relationship between this earthquake and the earlier magma movement from Pu’u O’o down to Leilani. I have annotated the radar image from above with the approximate location of the magnitude 6.9 earthquake. I think it is possible that the additional seaward stress applied by the dike intrusion helped to trigger this earthquake – although that is a little speculative at this point.
Large earthquake on May 4th located on radar interferogram, showing relationship between earthquake location and magma movement in preceding days.
We’ll also have to wait and see if this wider collapse of the flank of the volcano is going to have an effect on eruptive activity.
Yes – the dipolar component (the dominant, bar-magnet like part) of the Earth’s magnetic field has been decreasing in intensity over the couple of hundred years we have had the ability to directly measure it. Based on the records of the Earth’s magnetic field intensity over previous reversals, preserved in igneous and sedimentary rocks formed at the time, reversals are associated with a substantial weakening of the dipole field.
Records of dipole intensity over the last five reversals, showing a steady decrease over several tens of thousands of years before the actual reversal, which lasts of the order of 10,000 years. Source: Valet et al. 2005.
But no – the recent weakening trend doesn’t mean a reversal is necessarily imminent. It turns out that baking clay to make pottery is a great way of taking accurate snapshots of the Earth’s magnetic field, so thanks to archeology, we have a fairly good idea of the strength of the dipole field over the past few thousand years. When plotted on the geological records of reversals above, we can see that the current dipole field is still 2-4 times stronger than it seems to be during an actual reversal, despite the recent decrease. A closer look at the record for the last 10,000 years shows we’re actually coming down from a fairly significant peak in field strength at around 0 AD.
A figure summarising several different models of dipole strength over the past few thousand years, based on different compilations of paleomagnetic measurements of geological and archeological samples. All show a peak in field strength about 2000 years ago. Source: Korte & Muscheler (2012)
Yes – regardless of present trends, the field will reverse eventually. The rate has varied over geological time, but the recent rate of reversals is somewhere between 2-5 every million years; at 780,000 years and counting, the current polarity chron is definitely pretty long by recent standards. It is certainly possible that the current decrease is part of the run up to the next one.
But no – when it does happen, a reversal will not happen overnight. Look again at the record of past reversals above, which shows a 30,000-50,000 year period of decaying dipole strength (which could be what we are witnessing the early stages of right now) before the dipole reverses and then more quickly recovers its strength. We can estimate the length of the transition period, when the dipole is weak and the higher-order components of the field dominate, from records of cosmogenic isotope production, which will be boosted in a weaker field because the atmosphere is less shielded from incoming high energy solar and cosmic particles. These records suggest a transition period of around 10,000-20,000 years, at least for the last reversal 780,000 years ago. If the field had started reversing when the Pyramids or Stonehenge were being built, we would still be waiting for the polarity switch to be completed. On current trends, even if the dipole continues to steadily weaken, the Empire State Building and the Eiffel Tower would be well into their second millennia of existence before the dipole field truly started to fail. Our many-times-great-grandchildren could easily be wondering about an ‘impending’ reversal in much the same way as we are.
A spike in the levels of the cosmogenic isotope Beryllium-10 in sediment and ice-core records over a 20,000 year period 780,000 years ago seems to record the interval when the Earth’s magnetic field was more disorganised and weaker during the last reversal. Source: Valet & Fournier (2016)
Yes, there are potential problems arising from a weaker and more disorganised field during a reversal. Lower and more changeable ionospheric currents could disrupt electrical grids (as they can today during geomagnetic storms). Orbiting satellites will also face a more hostile radiation environment.
But no – a global cataclysm is not on the cards. There is zero evidence of any species extinctions associated with a magnetic reversal. Beyond the field not being dipolar, the actual behaviour of the field during the transition, particularly the rate of change, is not well constrained by the geological record*, but if we use recent behaviour as a guide, variation of the non-dipolar components of the field appears to mainly happen over centuries, not months and years. Migratory animals that have been shown to at least partially rely on sensing the magnetic field to navigate seem to have coped with past reversals just fine. And if you think about things from an evolutionary perspective, the fact that they have also retained this ability suggests that the changes during the thousands of years that the dipole is weak are not so rapid that successive generations are getting totally lost on their migrations.
What our civilisation would actually face during a magnetic field reversal would not be a quick catastrophe, but something more akin to the effects of sea-level rise: a long-term deterioration in the conditions that we are used to, and our society and infrastructure are tuned for. As the decades pass, we might start seeing more frequent disruptions of the grid due to ionospheric interference, and not just when there was an intense geomagnetic storm; we might see a drop in the average lifetime of orbiting satellites, and more random losses. Increased surface radiation levels in particular locations could also affect background cancer rates. These long-term trends present challenges, but not insurmountable ones. And again, we are talking about this playing out over centuries, or even thousands of years.
What do all these terms have in common? They all suggest an abrupt, rapid, violent event. The use of the present tense also strongly suggests an event that is on the verge of happening, if not happening right now. And that is true: from a certain point of view. If you ask a geologist if magnetic reversals are rapid, they would say yes. If you asked if a field reversal was imminent, I would say maybe, but you could definitely find scientists who would express more confidence. But these are Deep Time answers, where ‘rapid’ and ‘imminent’ have durations that are considerably more stretched out than their more everyday meanings.
If asked to name an abrupt geological event, most people would name things like earthquakes, volcanoes, and catastrophic landslides: processes that cause quick, violent upheavals over the space of a few hours or days. Geologists, reading the history of the Earth from preserved sequences of rocks, don’t quite see things this way. Each layer – of limestone, of sandstone, of volcanic ash, of mudstone – is a page that describes the prevailing conditions on the Earth at the time it formed. By reading through the book, from bottom to top, we can chart how those conditions change over time. But geological narratives are rarely exhaustive: they are more like a fast-paced thriller that you buy at the airport to read on your holidays. A lot of narrative can be squashed into a relatively small thickness of rock: a cliff-face built from sedimentary rocks might recount the passage of millions of years, and thousands of years might be missed in the turn of a page – between the end of one unit being deposited and the start of another.
So when geologists start talking about ‘rapid’ events, what we really mean is that in the compressed and fragmented books of Earth history, we can observe a change with a clearly identifiable ‘before’ that differs significantly from ‘after’, but the details of the transition are squashed into a single thin horizon, or even lost in the transition between two different rock units. When a centimetre or two of rock can span thousands of years, you can start to see that for geologists, an event that lasts millennia can be rapid: an event that is going to happen in a few thousand years can be imminent. From a geological perspective, the last 35 years of eruptive activity at Kilauea is a tiny blip in Earth history. An earthquake is part of a longer cycle that involves centuries – or millennia – of strain accumulation across a fault, which means there is little difference in terms of the record left behind whether it occurs tomorrow or a century from now. And the resolution of most geological records is such that changes that take several thousand years – longer than the length of recorded human history – are often more like punctuation marks than complete sentences.
Proportionally, ten thousand years in the multibillion-year lifetime of the Earth is the equivalent of an hour or two in the average human life. So there is a certain narrative sense to this stretching out of the timespans implied by commonplace words; it helps us translate the vast tracts of geological time into a frame of reference we can more easily grasp. But the downside of this linguistic appropriation is that while geologists recognise and understand code switching between the Deep Time meanings and the everyday meanings of ‘abrupt’ and ‘rapid’, the rest of the world does not. Field reversals are abrupt? Then we’re in disaster movie territory when it happens, aren’t we***?
Or, as Alanna Mitchell puts it, in the section of her piece which I do think treads a bit too far into scaremongering territory:
"NO LIGHTS. No computers. No cellphones. Even flushing a toilet or filling a car’s gas tank would be impossible. And that’s just for starters."
This mismatch is why I periodicallyfind myself trying to tamp down magnetic field collapse hysteria – and will surely end up doing so again in the future. And yet: there is one further layer of complication, which at the very least makes me sympathetic to what ‘The Poles May Flip’ was (I suspect) aiming to do. If ‘rapid’ changes can last thousands of years, then threats can also slowly develop over similar timeframes. As our response to the threat of climate change rather depressingly illustrates, we are very bad at prioritising problems that manifest over timescales of decades, let alone centuries. The earlier we act, the less we have to do to stave off danger. But the harder it is to convince ourselves into action, because we take on all the pain and our distant ancestors reap all of the benefit.
Alanna Mitchell is right that the long-term deterioration of the field in the run-up to a reversal – should that be what ends up happening over the next century or five – is eventually going to be a problem. Coping with these changes may not technically present an insurmountable challenge. But spending the money required to build infrastructure that is not just fit for the conditions it faces today, but is also resilient to the threats that we know are coming in its working lifetime, turns out to be a tough ask. To our ape brains, urgent threats that accumulate over decades and centuries seem like a contradiction in terms; such things are so far outside of the way we think about time that we lack the language to even properly describe such things.
So how do we present such problems in a way that people actually perceive them as a problem that might require action? We have been discussing an example of the most obvious tactic: using words like ‘rapid’ and ‘abrupt’, which are technically correct in the Deep Time sense, and letting peoples’ more common understanding of these words add the sense of urgency. It surely works to grab attention, and sometimes inspire concern. But I question if it is effective at actually building a consensus for long-term action. Eventually, someone has to explain that we are not talking about the Day After Tomorrow, but the century or millennium after next. Once this happens, people will probably stop worrying again, and may also feel resentful that they were made to worry in the first place.
But what do we do instead? Sadly, I don’t have the answers. If our species is to face and survive the long-term threats presented by our geologically active planet, and our alteration of it, we need to find that new language, that expresses the fierce urgency of acting now to avoid trouble centuries hence.
But for today: your compass will continue to point north. Your children’s compasses will continue to point north. And their children’s too.
Footnotes
*if you want the gory, highly technical details of what we do – and don’t – know about reversals based on the paleomagnetic record, this excellent review is a good place to start.
**from a sneak peek, she even visited the site in France where the first reversed polarity paleomagnetic samples were collected, which makes me more than a little jealous.
***I love The Core. The fact that I know how gloriously wrong it is is probably what elevates it above your standard terrible disaster movie.
Nice plan for content warnings on Mastodon and the Fediverse. Now you need a Mastodon/Fediverse button on this blog.
For lot's more videos on soil moisture topics, see Drs Selker and Or's text-book support videos https://www.youtube.com/channel/UCoMb5YOZuaGtn8pZyQMSLuQ/playlists
[…] Announcing STORMS | Highly Allochthonous on Recent News […]
Nice plan for content warnings on Mastodon and the Fediverse. Now you need a Mastodon/Fediverse button on this blog.