The best fitting depth for the earthquake was found to be 13 km, and source parameters show the focal mechanism as a strike slip fault with an almost vertically oriented fault plane. The strike-slip nature, with a ∼NW-SE compression axis relates well to the maximum compressive tectonic stresses that affects the whole UK, and appears to be in good agreement with other earthquake mechanisms in the region as well as the rest of the UK, see figure 4. The most likely mechanism is right-lateral strike-slip motion on a near vertical WNW-ESE fault, due to the proximity of the source to the Variscan Front fault.

In summary, this event represents the first large earthquake in the Swansea region to be recorded by modern instrumentation and reveals faulting that is possibly on the Variscan Front fault due to interactions (transcurrent/pinching) with the Welsh Border Fault system. Further studies between this event and larger magnitude events in this area may reveal the faulting mechanisms that cause the unexpected abundance of ∼ 5 ML events.

Further Reading

My full report write-up is available here:

The February 17, 2018 Wales Earthquake: A Moderate Sized Earthquake in the UK

Acknowledgements