Influences human activity on earthquake probability

Tiny earthquakes as harbingers

In between larger earthquakes there are many smaller earthquakes that are not noticeable to humans. These mini-quakes could provide information on the physical properties of the fault - i.e. the point of fracture in the rock - and perhaps also on the next larger quake. This is now shown by measurement data from the laboratory and from real earthquakes, which two teams led by Claudia Hulbert and Bertrand Rouet-Leduc from Los Alamos National Laboratory in the USA evaluated using machine learning.

In their laboratory, Hulbert and her colleagues first put quartz powder under pressure in a special device. Similar to nature, stronger vibrations occur, which are accompanied by a jolt. But very small vibrations could also be observed, during which the powder slowly shifted against each other. These micro-fractures create sound waves with frequencies between 0.02 and 2 megahertz, which the scientists registered with the help of piezo sensors. They then used the measurement data to train a statistical model. It turned out that the time, duration and strength of the stronger laboratory tremors could be predicted on the basis of the acoustic signals. According to this, larger earthquakes are heralded by a characteristic cascade of microquakes.

The researchers working with Rouet-Leduc investigated the extent to which this relationship can also be transferred to nature using earthquakes near Vancouver in Canada. At the Cascadia Fault, so-called mega tremors occur at irregular intervals, which can cause severe devastation. In the time between the great quakes, the tectonic plates are entangled and hardly move. The scientists now analyzed - also using machine learning methods - seismic measurements and data from GPS stations that record displacements in the area around the fault.

In this way, the scientists found that a constant tremor can be observed - similar to the micro-fractures in quartz powder. Meanwhile, there are slow shifts in the fault area. According to the study, the strength of the tremor is proportional to the strength of the shift. Rouet-Leduc and his team hope that the analysis of the tremor can provide new insights into the physical processes at the Cascadia Fault. In the future, for example, it could be investigated whether and how slow displacements at the fault can develop into a major earthquake. In this way, the earthquake hazard in the region could possibly be better estimated.