A Signal in Giant Earthquakes That Could Save Lives

Taking a break from the general political hubbub that floods the site regularly, I present this thread discussing the possibility that before a large (~M7+) quake is complete there are signals within the recorded data that can help to estimate the final magnitude of said quake.

With the advent of technology, more and more information is recorded in regards to earthquakes than has heretofore been available. This additional data, along with complex computer modelling has allowed scientists to tease out information about the an earthquake while it is in the process of the rupture.

Large quakes aren't instantaneous, they can take minutes from initial rupture to when the movement is completed. For example, the Great Tōhoku Quake of 2011 in Japan lasted approximately 6 minutes.

These signals allow scientists to estimate the final size of an earthquake well before the rupture is complete:

Seismologists have never had a better understanding of earthquakes. But tragedy after tragedy shows that quakes still surprise and shock people with their mercurial behavior. Precise predictions of when and where quakes will occur, and how deadly they may be, are not yet possible. If, however, researchers could chronicle how quakes grow, they might be able to better forecast how powerful they will become.

The mightiest quakes are far from instantaneous. They can last minutes, which makes them less like a single subterranean blast and more like a series of explosions moving outward. A new study, published on Wednesday in Science Advances, explains that the outward journey of these explosions differs depending on the power of the quake.

That means that the final magnitude of a quake could be determined in as little as 10 to 15 seconds after it begins, and long before it ends.

New York Times

This is new research, and as such is still in need of further verification and study, but if it pans out it could lead to a much more robust warning systems for areas in which seismic instability represents a danger to life and property.

The abstract from the study the New York Times article references:

Whether earthquakes of different sizes are distinguishable early in their rupture process is a subject of debate. Studies have shown that the frequency content of radiated seismic energy in the first seconds of earthquakes scales with magnitude, implying determinism. Other studies have shown that recordings of ground displacement from small to moderate-sized earthquakes are indistinguishable, implying a universal early rupture process. Regardless of how earthquakes start, events of different sizes must be distinguishable at some point. If that difference occurs before the rupture duration of the smaller event, this implies some level of determinism. We show through analysis of a database of source time functions and near-source displacement records that, after an initiation phase, ruptures of M7 to M9 earthquakes organize into a slip pulse, the kinematic properties of which scale with magnitude. Hence, early in the rupture process—after about 10 s—large and very large earthquakes can be distinguished.

That has been found is that there is a measurable difference in the signals generated by large earthquakes early on in the process:

We find that individual events of a given magnitude demonstrate substantial variability (Fig. 2), a reflection of natural differences between earthquake ruptures. However, their median behavior over a range of magnitude bins shows systematic differences that scale with magnitude. On average, earthquakes with a larger final magnitude grow faster early on in the source process.

If this new research is verified and built upon, it could lead to more accurate warnings for areas which would be affected by large seismic events.

These findings are relevant for hazard warning systems, in particular for earthquake early warning (EEW), where every second gained matters. The modern EEW paradigm centers on forecasting the shaking intensity at a site of interest some distance away from an earthquake. Recent studies have shown that uncertainty of an event’s final magnitude leads to a tradeoff between the possible warning time and the certainty of the ground motion forecast (7). At present, a fast warning can only be made with large uncertainty in the associated shaking. While waiting for more information about the source significantly reduces the uncertainty, this comes at the cost of shrinking the warning time and enlarging the blind zone where no warning is possible. Modern EEW systems rely on a combination of point source and finite fault algorithms, neither of which is designed to exploit weak determinism. Point source algorithms focus on the first 1 to 3 s of a P wave as measured by inertial seismic sensors (18–20); thus, it is unlikely that they will overcome the familiar problem of magnitude saturation for the largest events. Of course, for the smaller events in our dataset, by 10 to 15 s, the earthquakes are in the later portion of their source processes. As a result, from an early warning perspective, the results here would still leave room for future improvements in speeding up warning times. Finite fault algorithms (21–23) can more effectively deal with large magnitude events but rely on the entire rupture (or a significant portion of it) being complete before they produce reliable magnitude estimates.

Much work has yet to be done with this, but this could certainly present benefits to huge numbers of people. Millions of people live in areas in which large seismic events could play a crucial role in any sort of natural disaster as can be seen in the results of the Sumatra and Japanese tsunamis.

Characterizing large earthquakes before rupture is complete - Science Advances

The new York Times piece ends with a quote from ATS member, John Vidale:

“It’s a good speculative idea, we just need to fill it in before we can have a lot of confidence in it,” said John Vidale, a professor of seismology at the University of Southern California.

What says ATS?

I may have read this and totally misunderstood.

BUT they are talking of determining the scale of the quake in the first few seconds of it starting.

To me, this doesnt seem like such a break through! what am I missing?

|BTW thanks for the post of anything other than politics.

a reply to: FawnyKate

BUT they are talking of determining the scale of the quake in the first few seconds of it starting.

Yes, that is precisely what this is saying. Currently earthquake magnitudes are calculated utilizing things such as the length of the rupture, how much the ruptured area moves and how long it moves for. All of the previous parameters are not known until after an earthquake has finished its motion. What this research shows is that within the first few seconds of an earthquake, the seismic signature of larger quakes have specific characteristics which scale to the final magnitude.

Initial magnitudes are determined by an algorithm many times, then once the datasets have been reviewed, it will be adjusted based upon the final waveforms of the earthquake. This is why you will often see earthquake magnitudes change from initial reports.

The scientists were able to determine this by going back and looking at recorded data for several large quakes.

This is groundbreaking research in the field of seismology.

These are very subtle and difficult to measure differences in the seismic waveform. One of the things that was found was that these signals are stronger the closer the instrument is to the hypocenter and that the further the seismic signal propagates, the weaker these signals are:

For these events, we find that the near-source records finish growing to their final value (or very close to it) in a time much shorter than the event duration. This behavior is a strong function of distance to the source. While the records will be affected by complexities in the STFs, such as multiple moment rate peaks, at close distances, and at long periods, HR-GNSS records will be mostly unaffected by elastic wave propagation and are dominated by the ramp-like growth to PGD and to the static offset. Thus, they more accurately reflect the behavior of slip at adjacent portions of the fault (10). At greater distances, this relationship breaks down and HR-GNSS records reflect mostly S waves and surface waves.

Source link is in OP.

|BTW thanks for the post of anything other than politics.

You're quite welcome. I like to do these threads from time to time when I find something of interest as ATS was a lot less political when I joined and even though I do wade into the fray since that seems to take a large segment of the existing threads, my original interests were nowhere near politics.

a reply to: jadedANDcynical

i too - am failing to comprehend how :

knowing the exact peak magnitude of an event that lasts a few minuites - withing seconds of its start point will " save lives "

Treat every earthquake like " the big one"

That's our best strategy, and we won't have a better one for a while.

I want to say around 2035-ish we get a better prediction system, but I'm not 100%, sometime between 2030's and 2050's for sure though.

a reply to: ignorant_ape

When dealing with earthquakes, especially of the tsunamigenic variety, seconds count. There is a significant difference between an M8 and an M9 quake. If people can gain even a few minutes head start on activating their emergency procedures that might make the difference between life and death.

Japan has one of the most robust early warning systems for earthquakes in the world and they still suffered tremendous loss of life to go with the property damage inflicted by not only the tremendous shaking but the tsunami that washed ashore afterwards; see the Fukushima Nuclear Power Plant as an example. Had FNPP had an extra few minutes notice additional precautions could have been implemented prior to the arrival of the tsunami had they the information that this study discovered available to them. Or it might not have made any difference at all due to the incredible amount of corporate/government corruption in the Japanese Nuclear industry.

In the US, we are facing a similar danger with the Cascadian Seismic Zone in which the possibility of a M9+ quake is a real and present danger. Adding just a few minutes to the time people have to react to such an occurrence could potentially save hundreds of thousands of lives.

a reply to: jadedANDcynical

Ever since I was about 6 yrs old and remember asking about how earthquakes happen and the answers I got did not make any sense,they say"the magma becomes unstable and shakes the earth" I would ask what makes it become unstable? I got patronizing at best answers,and was told I was crazy about outside objects and their effects on earth,but the same story they gave on moon and how it had similar effects on tides,was also told the earth had a solid core ,now it has a plasma one,the reason is I've been lied top by schools,colleges,government licence agents,now as things piece together we are headed into another destructive cycle just like before

a reply to: jadedANDcynical

my issue with that = final magnitude is not a good index of " tsunami probability " -

a reply to: ignorant_ape

This is true as far as it goes. For example, there was a high M8 quake that happened in Indonesia I believe that did not produce a tsunami. This was due to the fact that even though it was a high magnitude earthquake, it was a strike slip quake rather than a reverse slip fault, or as it is more commonly known, a mega-thrust fault.

The main difference is in the direction of motion between the two relative fractured pieced of crustal rock. In a strike slip, the motion is sideways as one portion of rock slide past the other. In a reverse slip fault, there is one piece of crust that is being pushed parallel to the motion of the crust causing massive amounts of water (if underwater) to be displaced. It is this displacement of water which is what causes the tsunami; the Great Tohoku Quake of 2011 displaced somewhere around 257 cubic kilometers of water due to the motion, and direction of motion of the ruptured crust.

The depth of the quake also plays a role in whether or not a tsunami will be generated. Deeper quakes just don't have as much surface motion for there to be the amount of displacement of water that a shallower quake will produce.

All in all though, any kind of advantage that could be gained for people living in highly dangerous seismic zones should be sought out.