The Origin of Earthquakes

A new study has simulated the formation of strike-slip faults in Earth’s crust, revealing new insight on how these earthquake-generating structures develop over time.

The researchers investigated a hypothesis known as ‘Lazy Earth,’ which suggests that faults take the easiest path for growth.

But, while they did find evidence to support the idea that faults evolve to increase their efficiency, they also found some ‘surprising’ phenomena at play.

The experiments showed that faults ‘shut off along the way,’ and even develop persistent irregularities that last for millions of years.

The researchers from the University of Massachusetts Amherst created conditions in the lab to mimic what goes on deep in Earth’s crust as the faults form.

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‘We set up the conditions for faulting on a small scale and watch them unfold,’ said structural geologist Michele Cooke.

‘People have done this before, but we’ve developed methods so we can see faults grow in very, very fine detail, at a finer resolution than anyone has documented before.’

To do this, the researchers filled a tray with china clay, or kaolin, at the right viscosity and length to represent Earth’s crust.

In their experiments, two slabs of wet clay were then moved in opposite directions under one of three conditions, to simulate the different ways of ‘loading’ the fault.

One of the experiments involved a pre-existing fault, while another focused on localized displacement beneath the clay.

The third included displacement across a wider zone.

‘We have captured very different conditions for fault formation in our experiments that represent a range of conditions that might drive faulting in the crust,’ Cooke says.

‘We found that faults do evolve to increase kinematic efficiency under different conditions, and we learned some surprising things along the way.

‘One of them is that faults shut off along the way. We suspected this, but our experiment is the first to document it in detail.

‘Another especially surprising finding is that fault irregularities, which are inefficient, persist rather than the system forming a straight, efficient fault.’

The researchers identified four stages in fault evolution: pre-faulting, localization, linkage, and slip. At first, they explain, it begins simply and later advances to the ‘peak of complexity.’ Then, the complexity suddenly ends, giving way to the return of simpler processes

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