An important question in understanding the potential magnitude of earthquakes, and consequently the hazard certain faults may pose, is the distance over which earthquakes can jump during rupture. This is because a critical observation of earthquake scaling which holds true is that the longer a fault rupture, the larger the earthquake. In a bigger earthquake, the ground shaking is more severe, it occurs over a wider area and lasts longer; exposing more buildings and people to a greater level of hazard.

The previous consensus on the control of the maximum likely leap in an earthquake was that an offset between faults of 5 km would probably be enough to stop a rupture – the gap being too much of a physical barrier for the earthquake to jump across. This limit of 5 km is used in some standard seismic hazard assessments.

However, an international team of researchers, have forensically unpicked from a seismic event that struck Pakistan in 1997, a pair of large earthquakes that had been previously catalogued as one. In a study published in Nature Geoscience, they combine satellite observations with seismology, to show that this pair of earthquakes involved a massive jump of 50 km between fault segments during the rupture – this is 10 times larger than the current accepted rule that is used in assessing earthquake hazard.

Research Paper: Nissen, E. K., Elliott, J. R., R. A. Sloan, T. J. Craig, G. J. Funning, A. Hutko, B. E. Parsons & T. J. Wright (2016) Dynamic triggering of an earthquake doublet exposes limitations to rupture forecasting, Nature Geoscience, doi:10.1038/NGEO2653