Silverdale tremors: how a village’s quakes compare to Britain’s largest built-up area

Residents of the Lancashire village of Silverdale have been left puzzled after experiencing a swarm of 25 small earthquakes over the past twelve months. The largest of these tremors, recorded earlier this year, was strong enough to be felt more than 12 miles from the epicentre, rattling windows and unsettling locals across a wide stretch of the north-west.

Seismologists from the British Geological Survey have been monitoring the cluster, which remains unusually persistent for a region not typically associated with high seismic activity. While most of the quakes have been too weak to cause damage, the frequency has prompted questions about underlying geological faults and whether the swarm might be linked to historical mining works or natural stress release in the bedrock.

How far can a small tremor travel?

Putting village tremors in a built-up context

While Silverdale itself is a compact rural settlement, the felt effects of its largest earthquake reached across an area that would comfortably swallow many of Britain's largest towns and cities. To grasp the scale, consider the built-up area of the largest town in our ranking: Birmingham in the West Midlands covers 219.1 square kilometres. That is a continuous urban footprint housing over a million people, yet it represents just a fraction of the circle within which the tremor was perceptible.

This single data point, drawn from Postcodes UK's built-up area dataset, highlights how even the most expansive postcode districts are dwarfed by the reach of a modest seismic event. A village epicentre can send vibrations through multiple counties, crossing administrative boundaries and reminding us that the ground beneath our feet does not respect the lines we draw on maps.

The data behind this

Built-up area figures are from the Postcodes UK built-up area dataset.

In response to reporting by BBC England. Analysis and figures by Postcodes UK.