The new equation developed by geoscientists from Heriot-Watt University in Edinburgh, the University of Liverpool and Utrecht University could improve how earthquakes are predicted.
Dr Sabine den Hartog from the Lyell Centre, a strategic partnership between Heriot-Watt University and the British Geological Survey, has developed a model that can help geophysicists better predict when and where earthquakes might happen.
Using maths rather than laboratory experiments, their aim was to predict the strength of the type of a key rock that lies at the heart of faults in the Earth’s crust where earthquakes happen.
Earthquakes happen during movement along faults at the weakest part of the crust, which usually comprises phyllosilicates, a type of mineral that consists of tiny, very thin plates.
While experiments have helped scientists understand fault processes and earthquakes much better, these are limited because it is difficult to recreate the complex conditions at depth in the Earth’s crust in the laboratory.
Dr den Hartog and her collaborators wanted to be able to predict the frictional strength, (the force needed to cause movement along a fault) of the phyllosilicates rather than to rely on laboratory experiments.
“Fault zones usually form at locations with a high concentration of phyllosilicates,” Dr den Hartog said.
“We’ve created a model so that we can predict the frictional strength of phyllosilicates under conditions that cannot be attained in the lab.
“We analysed artificial fault zones on the microscopic scale to identify the processes that happened during the experiment, like the splitting of the platy phyllosilicate minerals.”
Based on the fault zone analysis, the scientists formulated a set of equations to predict how the frictional strength of phyllosilicates changes with an alteration in conditions such as the humidity or the speed of fault movement.
“This allows prediction at conditions that are not accessible in the laboratory, making it much easier for modellers to simulate fault movement at natural conditions, including earthquakes,” she added.
“Our model predicts that movement along phyllosilicate-rich fault zones becomes more difficult as the movement goes faster, which is consistent with experiments. This behaviour prevents earthquakes and suggests that other minerals than phyllosilicates are important to cause earthquakes.”
Dr den Hartog stressed that more research was needed to improve the model and to predict all experimental trends.
“We couldn’t explain the relation between the force that holds a fault together and the force needed to move the fault, so there is still work to be done in this area.”
The findings were published in the Journal of Geophysical Research: Solid Earth.
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