Reading the Ground — Why Earthquakes Cannot Be Forecast

How to see underground

An earthquake sends its shaking clean through the planet. Those are seismic waves.

Stations around the world record when each arrives. Collect where they sped up, where they bent, and where they never arrived at all, and the layering inside emerges. That the core is liquid was found this way: one kind of wave simply failed to cross it.

Layers are an order of time

The other way to read ground is to look at a cut cliff, where strata lie stacked.

Things settle from the bottom, so lower is earlier and upper is later. It looks obvious, and it was the beginning of geology: time could now be read out of rock.

Fossils sit between those layers, and comparing which layer holds what gives the order. The pieces on display at the geological museum in Daejeon are fragments of that order. The museum is run together with the geoscience institute.

A little further in

Why earthquakes cannot be forecast

We are told whether it will rain tomorrow. Nobody can say whether there will be an earthquake next month. Both are natural. Why the difference?

Because the weather's present state can be measured. Temperature, pressure and wind, taken everywhere and fed in, give the next few hours. The atmosphere is spread out in front of us.

Underground is not. Earthquakes begin tens of kilometres down, and there is no way to measure how much stress is stored there now.

So two other things are done instead

Forecasting being impossible, other work takes its place.

One is knowing where the danger lies. Map the faults and how often and how hard the ground has moved before, and you may not know when, but you know where to build strongly. Mapping active faults in Korea is exactly this work.

The other is early warning — which is not forecasting at all. It happens after the earthquake has begun.

Knowing without digging

The institute's other axis is exploration: finding what lies buried and how much. Here too, digging comes last.

Heavy minerals make gravity very slightly stronger overhead. Iron disturbs the magnetic field. Ground with water conducts differently from ground without. Measuring those differences at the surface draws a picture of what is below — and only then is the single most promising spot drilled.

What you would study to do this

You do not have to love rocks.

1. Someone who reads strata and rock — geology.
2. Someone who draws the underground with waves — geophysics, which is half physics and half computation.
3. Someone who separates out what rock and water are made of — geochemistry and analysis.
4. Someone who handles the flood of monitoring data — computing and statistics.
5. Someone who goes out to the mountains and the sea to measure and drill — field survey and drilling.
6. Someone who catalogues and preserves specimens — museum and collection work.

The second line may surprise. Earth science suggests the outdoors, but geophysics is a day spent computing wave data. It is how someone who likes mathematics ends up working on the planet.

The last line is a real job too. Fossils and minerals survive a century only if someone numbers them and holds the conditions. What hangs in the geological museum passed through those hands.

The work is done at the Korea Institute of Geoscience and Mineral Resources in Yuseong-gu, Daejeon, with the geological museum inside it.

The question that remainsIf we can know where but never when — how far does preparing actually reach?