Earthquakes: Science on Shaky Ground

As we emerge from lockdown, keeping tabs on where COVID-19 might be about to rear its ugly head again, as well as watching for the appearance of viral variants that might be able to sidestep our vaccines, is going to be key to keeping the country moving. And most scientists agree that mass testing in one form or another is crucial. But how do we do this in a way that's not inconvenient, onerous and costly? Well, researchers at the UK's National Institute for Biological Standards and Control, have found that they can use...what we put down the drain...as a sensitive way to track the activity of COVID in the population and also spot the early emergence of variants we're worried about. It stemmed from an existing project to use sewage to screen for polio; Chris Smith spoke with Javier Martin, one of the brains behind it...

Javier - There was early evidence that there was high concentration of the virus genetic material in stool samples from infected people. So since we have been carrying out surveillance for polio virus in wastewater samples, we thought that we could adapt our techniques to detect the virus causing COVID.

Chris - So you were already doing this for polio?

Javier - Yes. For many years now, yes.

Chris - Does this involve, then - not to put too fine a point on it - just going into the sewage farm and saying, "can I have a sample of what's coming down the sewer pipe, please?"

Javier - We were lucky because we've been doing this for many years now, so we regular samples supplied by the sewage plant every month. So we had samples from before and during the pandemic to look at.

Chris - Presumably, then, this bottle arrives, which is wastewater from different parts of the country; how do you process it?

Javier - Yes - you clear it up from any solids that might be there, by using filters to concentrate particles such as viruses.

Chris -
What, is it whole viruses that you're collecting, or will there just be bits of genetic information from these viruses in there?

Javier - We are not sure what if they are viable virus. We think they are not infectious, they're probably particles that are somehow damaged, but they contain genetic material that's sufficient to detect it.

Chris - And you can get that genetic material out and read it, can you?

Javier - Yes.

Chris - And can you detect things like variants doing this? If you can read genetic code, does that mean you can basically spot a variant, or spot the rate of change, how a variant is increasing its population as the infection spreads through the country, or a variant emerges, for example?

Javier - Yes. We're trying to quantify the amount of genetic material in wastewater; also sequencing so we can identify those mutations that correspond to variants, and therefore monitor them.

Chris - What's the point of doing this? Why do you think this would be useful?

Javier - I think it would be useful to help understand how these viruses meet between people, and also to possibly establish early alert systems for such variants becoming predominant in a population. Also, what you find as water is obviously what people are excreting, so you are not biased by the sampling of clinical samples; and they represent also asymptomatic infection, so a more detailed picture of what's happening.

Chris - I suppose one constraint, though, is how sensitive this is. Because if you only end up seeing it after, arguably, the virological horse has bolted, and there's already a rip roaring outbreak in a particular town, it's not going to really add anything; whereas if this could be an early warning sign - the canary in the coal mine almost - and you get early warning of a variant coming or an outbreak about to erupt, then that would be really powerful.

Javier - Yes, you're right. Sensitivity is the key. You could increase it by looking at a higher volume of your sample, by increasing the frequency, and also by maybe doing a more targeted community surveillance in areas that, for example, you have detected new concerning variants. So you can go to smaller surveillance areas to increase the sensitivity of your sampling.

Chris - You obviously straddle the time when we've seen the emergence of things like the Kent variant. So have you been able to see that appear as a blip on your radar, and then begin to dominate - as it has done - during the course of doing these experiments?

Javier - Yeah, we have seen the variant very clearly appearing in our wastewater samples since early November. So at that time, this was not obvious from clinical samples yet. And then, the proportion of this variant increased really nicely - exponentially, actually, since then - to become almost a hundred percent by the end of January.

Chris - So it does look like there is the prospect to use this, and it could provide advanced warning of a threat that's coming.

Javier - Yes, indeed. And in fact, the way we've designed the processes would also detect those variants that have been firstly detected in Brazil and South Africa, which are quite worrying, including some mutations that we know seem to affect vaccine efficacy.

Stephanie has gotten in touch with a COVID question: Please could someone explain the mechanism of immune response over time to vaccines? Given that the booster needs to be at least a few weeks after the first dose... what happens in those intermediary weeks? Chris Smith has the answer...

Chris - What we don't know is what the perfect time to administer these two doses is. Because the only reason we used three weeks or four weeks initially was because that was the time set by the manufacturers in their trials, because they wanted to get the data quickly. And in fact, we've resorted to 12 weeks between doses because there's some data suggesting that actually the longer you leave it, the better the immune response is. And you might think, "well, why is that?" And the reason is that the immune response is not just a static thing. You don't just see something you want to respond to, make the response, and then call it a day. The immune system is continuously evolving, optimising, and maturing its response. So as more time goes by, the response that you make initially is slowly petered out and dissipates, and out of that emerges a much more focused, much better response, that's more finely tuned, but it takes time to get there. So waiting a bit longer between doses can in fact mean, when you do come back with the booster, you in fact then boost the really finely tuned, even better response you've now made - rather than a more broad, less finely tuned one you would have made if you stimulated with a booster too soon. And actually if you come back too quickly, with another booster too quickly after the first dose, you can in fact do the opposite and de-tune your immune response completely. It's finding that sweet spot that researchers are still trying to find at the moment.

Above ground, there are a lot more factors than just the geophysics, that determine the degree of damage that ensues in an earthquake. Wendy Bohon is in Washington DC where she’s part of the Incorporated Research Institutions for Seismology, and she spoke to Chris Smith about the different causes of earthquake damages...

Wendy - Not all buildings are created equal. So it depends on the type of material that the buildings are made out of and where the buildings are built. So there are certain types of soil that can be really bad during earthquakes. When seismic waves travel through rock, they go pretty quickly. But in areas that have soft sand and soil, like in valleys or on the edges of rivers, those areas actually trap the seismic waves. And so if you have a building that's built there, you'll shake harder. And for a longer period of time, which obviously is bad.

Additionally, certain types of building construction are more likely to fail during earthquakes. So the kinds of structures that have like car ports underneath, or parking lots underneath. Those can't take the side to side motion of the earthquakes. And often that soft first story will pancake causing complete destruction of the building. Additionally, wood frame structures are nice and flexible just like trees. So they're really good in earthquake shaking, but structures that may be more stiff that are made out of concrete or other types of materials like brick. Those can sometimes fail during earthquake shaking.

Chris - A lot to unpack there. Very interesting what you were saying about the location of where you put your building because what's underfoot really matters. Is it not just a question of - when you shake the ground, it's not just like the ground staying hard, can not the characteristics of the ground also change if you shake it up? I'm thinking we were talking about avalanches on the programme a year or so ago. And showing that actually snow, when you shake it, behaves quite differently than when it's just a snow pack.

Wendy - That's absolutely right. One of the things that we're concerned about in areas that have that soft sand and soil, but that also have a high water table, they can experience something called liquefaction. And this is where the ground turns almost into quicksand. So as the seismic waves pass through the ground, they push that water up towards the surface. This forces all those little pieces of sand and dirt apart, which means that the surface of the ground loses its strength. So anything that's built there or anything that may be standing there, like say a car, that will sort of sink down into the ground. Now it's not going to sit down and get totally swallowed, but you can imagine if your house is built on an area that experiences liquefaction and your whole house tips the side, even if your home doesn't fall down, that could still be a total loss.

Chris - Do we know roughly what fraction of the housing stock the world has are in those rather inopportune places? Because this is presumably something we've learned since. And we tended to live where it was nice to live rather than having done a survey of what was underfoot before we built a city there.

Wendy - Right! If only we had known what we know now! But we can improve those things moving forward. I'm not sure about the total amount of construction in the world that are built in seismic hazard zones. And there's lots of different areas that will experience landslides or liquefaction or ground shaking. But we can definitely make sure that we know what those hazards are. We can let the people that live in those areas know what they can do to help mitigate or solve those hazards. And we can build any new structures up to seismic standards. So we can take those older buildings also and do things called seismic retrofitting - things like strapping homes down to their foundation. So they don't slide off during earthquake shaking. Making sure that we put in shear walls, because when the earthquake passes through it doesn't just shake a building back and forth, it gives it an upward push, a sideways thrust, a downward drop, and then a sideways thrust in the other direction. So we need to have the building strong in all different directions. And we can do that even after the buildings have been built. So a combination of policy changes, making sure that we're putting money into the system so that we don't have to put money in after the earthquake happens to rebuild. And then also educating the people that live in those areas about what those hazards might be during the earthquake.

Chris - And are earthquakes made equal? As in, I know there can be stronger and weaker, but do they tend to all shake the ground the same way, or do they come in different varieties, which actually might shake the ground differently? And therefore it's all very well to say, well, we'll build our buildings to resist an earthquake like this, but because there are so many varieties, it could be really tricky therefore to defend against all those threats.

Wendy - The first thing is that we spend a lot of time talking about the big ones, the ones that affect, you know, really large areas, like say the San Andreas fault, all of California, something like that. But we're actually more likely to feel shaking or to have damage from smaller earthquakes because they happen so much more frequently. We need to think about the big ones and plan for those really, really big events. But we also really kind of need to think a lot about what's happening locally and plan for that. Luckily scientists can go and figure out exactly where the faults are moving, where that stress is building up. We can go and dig down into the fault zones to figure out when earthquakes happened before and how big those earthquakes were. So that we get an idea of what might happen and how hard the ground might shake in these places. That way we can go and work with engineers and architects and say, this is the type of shaking that's been felt here in the past. And this is we think we can experience in the future. So taking what's happened in the past and applying it to the here and now I think will make a big difference.

Chris - That's certainly true in countries that have the resources, the wherewithal, and they don't have the pressures on the environment, the climate, food supplies, and so on to do that where you can make a rational choice. But in many places, as population climbs we're finding that people are resorting to living in areas that were a second choice previously, and that often does push them into the path of danger, doesn't it?

Wendy - It really does. What we know for certain is that disasters do discriminate and the people that are the least able to prepare for those disasters are often the ones who are going to be the most impacted when they happen. And so we really need to take into account vulnerable populations and the equity of how we're doing our communication about earthquakes, our communication about what those hazards are and working within populations that may be more vulnerable. Working with countries that may not have the infrastructure or the resources to go in and do the types of improvements that will really help to save lives and property during these big events.

Chris - Well, what then must scientists bear in mind? Or what must be the bottom line in terms of what we need to communicate to people going forward about earthquake threats and how they're likely to impact on us in the years ahead?

Wendy - Earthquakes can happen anywhere. We need to be ready when they do happen. And know that scientists are working very hard on your behalf. This is our science and we love it. But we recognise that these kinds of events impact people's homes, their businesses, it affects their lives. And that matters to us. We are working as hard as we can to make the changes that we need to make in order to keep everyone safe.

Protection against the effects of earthquakes matters of course, but if we could predict their impending arrival, that would be even better: we could evacuate people; put rescue services on standby; prepare to turn off gas or electricity supplies if necessary, and so on. But, regrettably, it’s not that easy. And to explain why, Chris Smith was joined by UCL's Joanna Faure-Walker…

Joanna - The problem is it's, as you mentioned, very difficult to actually predict an earthquake. So when you're talking about prediction, you're saying, you know, how big will the earthquake be and exactly where and when is it going to occur? So is it going to be on Tuesday at 5:20 PM and magnitude 8 on this particular fault? We're nowhere near that. The problem is to be able to do that - let's just consider one fault in isolation at the moment. If we wanted to be able to predict when the earthquake would occur, we would need to know how large we expect the earthquake to be, so how much movement on that particular fault do expect that to be? And how long would it take to build up the stress required for that amount of movement? So how fast is the fault moving? We'd also need to know how much of that movement is taken up, what we say seismically, so in earthquakes, versus aseismically, so not in earthquakes. And then we would also need to know when was the last earthquake on that fault so we know where we're starting our timer. Now, all of those things are actually very difficult to measure. We know some of them on some faults, we actually know almost all of them on particular faults, but in most places in the world, most of those elude us. Even if we did know all of those things, it's more complicated than that because faults don't behave on their own. They're not isolated structures, they interact with each other. So the forces that are governing the timing of these earthquakes is just more complicated than at the moment our models can deal with.

Chris - I was going to ask you - do faults talk to each other? in the sense that if you've got one that starts to unzip or move, does that actually have an impact or knock on effect at encouraging another fault to unload itself as well? Does it transfer the stress elsewhere, if you like?

Joanna - It does exactly that. I like your expression there of talking to each other. When an earthquake occurs on a fault, we lose the stress on that fault. It releases the stress there. But it also is causing movement throughout the crust, that's where we're standing on now and that's where these earthquakes occur. So other faults will either be accelerated or you can actually bring delays so you can slow down that rupture. So the problem with this is the idea you'll sometimes hear about recurrence intervals on faults - so the average time interval between earthquakes. But if we've got all these interactions taking place, it's not a regular time interval and so it's much more difficult to predict again.

Chris - It becomes a massive, massive problem doesn't it with so many different dimensions to it. Have new tools helped us though? Because we've got things like GPS that can make very accurate movement assessments of how the land is moving that would previously have been very difficult to do at the sort of scale that we can now do them. Does bringing more data to the table help with these sorts of predictions?

Joanna - It really does. It really helps us understand the fundamental mechanics - so how fast are these faults moving? But the problem is we're looking at timescales here. Now as a geologist, when I talk about short term time periods, I'm talking about hundreds or even maybe thousands of years. So as a geologist, that's a short time period. Now these GPS records that you just referred to can look at years or tens of years, but they're not going back hundreds of thousands of years. Now, if we consider an individual fault, they can move at parts of millimetres or centimetres per year. So about as fast as our fingernails grow. How long would you need to not cut your fingernail before you could have, you know, a metre or even 20 metres of slip in one event? So on an individual fault, it may be hundreds or thousands of years between individual earthquakes. And with these modern methods of analysing the movement, yes, they're giving us a lot of information, but we're looking at such a short time period compared to the length of what we call the seismic cycle.

Chris - Are there any other kinds of markers that might be proxy markers of energy that's being stored in compression in these faults that's slowly building up? Because, you know, I know people say the animals change their behaviour ahead of earthquakes. Now this might just be attaching significance to coincidence might'n it because about 10 years ago there was this lovely paper - unfortunately it came out around the time of April fool's day which meant everyone kind of said they thought it was a joke, but it was a bunch of toads that just disappeared from when they would normally be mating around a site in Italy that then a few days later had a huge earthquake. And the researchers there speculated perhaps there were changes in the Earth's ionosphere, the pattern of how the earth guides radiation round its outer part of space. Are there any markers we might be able to plug into that would point us towards a critical stress building up at certain fault points?

Joanna - There are some ideas and some of them are more promising than others. I mean, the problem with animal behaviour is we are yet to see a statistical study. Something like the toad behaviour, or dogs barking, things like this, if you actually monitored the toads every single day of the year, and you kept doing this year after year, and you actually said that there was statistically significant different behaviour on those dates, then you might be able to start using some of these methods. But as yet, I do not know of any studies where they actually look at these. So you hear people saying things like the toads moved or the dogs barked, and it's like, well, yes, toads move and dogs bark. So I don't think those are particularly promising at the moment. But what we can do, and a lot of the work that I'm involved in, is trying to look at long term rates of deformation. So geological timescales for thousands of years, tens of thousands of years, and we can use markers on the longterm where we look at how rocks have been displaced relative to each other, to try and understand how fast are these faults moving in the long term? And then compare these to things like the GPS records to see where are we in that cycle of stress building up, and is there any helpful information about imminent failure.

Chris - And are we better at doing this these days? Or are we just better at knowing we're no good at it, if you see what I mean.

Joanna - We are better. So we are producing what we call probabilistic seismic hazard approaches. So this is where we use probabilities - so how likely is an event to occur in the next 5, 10, or even a thousand years, depending on what you're interested in, and on those we are making very good progress. It helps us make relative risk decisions. But in terms of actually saying whether we expect an earthquake at 5:00 PM on Tuesday we still have a way to go.