Earthquakes are totally unpredictable. Plate tectonics easily explain the workings of earthquakes but leave us in the dark as to their frequency and time of occurrence. Nancy Gibbs wrote in this weeks special report of Time Magazine “what happens when disaster strikes even the most prepared of nations?” Sadly, the only possible answer to tragic events like the recent magnitude 9 quake in Japan is to help those in need, clean up and brace for the next one.
Scientists have discovered a law in earthquake behaviour, however, that might not be the key to earthquake prediction, yet will help fine-tune preparations. A law discovered through geological observations and advances in complexity science, fractals and self-organised criticality. I am reading Mark Buchanan’s ‘Ubiquity’ at the moment, which is all about this natural law and uses a lot of examples from earthquake patterns.
It turns out that earthquakes happen all the time but differ strongly in magnitude. Friction and slipping between plates on faults constantly release energy as minor bursts. Observations in California, for example, have shown that on average as many as twenty quakes lower than magnitude 3 occur every day. As an inhabitant of that region you might be blissfully unaware of this fact, as these small shakes would not even disturb the water surface in your cup. The friction can also build up to release massive bursts with sometimes catastrophic consequences for communities and, indeed, the entire world. Slipping in one case is much greater than in others making some earthquakes small and others large, but why is this? It is within this relationship between the frequency of low and high magnitude earthquakes that this ubiquitous law in nature is manifested.
Exploring a worldwide catalogue of earthquake frequencies and magnitudes, and by plotting both on different axes of a logarithmic graph (see fig), Gutenberg and Richter discovered an interesting pattern in earthquake behaviour. It turns out that the bigger a quake, the rarer it is. But this behaviour actually shows a very distinct type of pattern, that of a power-law. An earthquake A with double the magnitude of another earthquake B happens four times less frequently. This power-law in quake behaviour implies that earthquakes are scale invariant. That means Gutenberg and Richter came to the baffling conclusion that the processes triggering small and large quakes are precisely the same. So apparently it does not make sense to look for special explanations why massive earthquakes happen. As Mark Buchanan put it: “They are no more special or unusual than the tiny shudders constantly rippling beneath our feet”.
How can something so simple as this power-law behaviour emerge as a worldwide phenomenon from the complex particular and local processes in the earth’s crust? Geologists and physicists argue that it is due to the fact that the earth’s crust is tuned to be in a critical state, and lives on the edge of upheaval. This basically comes down to changes in a fundamentally instable system, like rocks slipping on a particularly unstable section of a fault. Catastrophic earthquakes happen for no reason at all.
Is this archaeology? No, probably not. There is a very real reason why I discuss this here, however. Catastrophic events sometimes just happen for no reason at all but are meaningful to people, nowadays as well as in the past. They might not be explainable, predictable, or even describable. But that does not take away the fact that they happened and affected people’s lives and behaviours. As archaeologists we might find traces of catastrophic natural events like earthquakes and volcanic eruptions, and they are worth exploring. This does not mean that such events explain anything at all. Indeed, they cannot even be explained themselves. Like these natural events emerging from local actions at any conceivable scale, individual people shape the full complexity of their reality through their local actions and interactions. The Japanese government has a long tradition in preparing for earthquakes to strike. The Japanese people live their lives under the constant threat of quakes. After the tragic events of the last few weeks individuals in Japan have decided to live on, despair, rebuild or prepare for worse. Their collective actions, guided by their own motivations and influenced by natural and social events, shapes the past, present and future of Japan.
In the end, what intrigues me in such a complex systems perspective is nothing more than what we try to do as archaeologists. We are confronted with reflections of past processes. If we are to understand these processes we have to acknowledge the importance of individual actions as well as their role in collectively creating something that cannot be understood as the mere sum of its parts. A very real complex reality that matters.