Why earthquakes happen more frequently in Britain than Ireland

Newswise — A recent discovery by researchers from the University of Cambridge and the Dublin Institute for Advanced Studies reveals a direct relationship between variations in the thickness of tectonic plates and the distribution of earthquakes. This finding applies not only to regions like Britain and Ireland but also has global implications. The thickness of tectonic plates plays a crucial role in determining seismic activity patterns.

In addition to the aforementioned discovery, the study also provides an explanation for a longstanding mystery: the frequent occurrence of small earthquakes in Britain and their near absence in neighboring Ireland. The variations in the thickness of tectonic plates help clarify this disparity, shedding light on the underlying geological processes responsible for the occurrence and distribution of earthquakes in these regions.

To examine Earth's interior and gather insights into the thickness of the solid outer layer called the lithosphere, the researchers employed a technique called seismic tomography. This method, akin to a medical CT scan, allowed them to create a computer-generated image of Earth's interior. By collecting and analyzing seismic data, they identified variations in the thickness of the lithosphere across Ireland and Britain. This information proved instrumental in their study and contributed to the understanding of earthquake distribution in the region.

Sergei Lebedev, the lead author of the research from Cambridge's Department of Earth Sciences, highlights the surprising irregularity in earthquake occurrences throughout Britain and Ireland. He emphasizes that the study has successfully provided an explanation for this long-standing disparity, which has perplexed scientists for more than a century. The newfound understanding of the relationship between variations in tectonic plate thickness and earthquake distribution has finally resolved this enduring puzzle.

Through their research, the scientists made a notable discovery regarding the lithosphere beneath western Britain and Ireland. They found that the lithosphere in western Britain is relatively thin and weak, making the rocks more prone to bending and leading to frequent earthquake activity in that region. On the other hand, Ireland rests upon thick and robust lithosphere, which explains the absence of significant seismic activity in the country. This discrepancy in lithosphere characteristics provides a clear explanation for the differing earthquake patterns observed between the two regions.

Despite being geographically distant from the nearest plate boundary, where most earthquakes occur globally, the United Kingdom experiences a relatively frequent occurrence of minor tremors. According to the British Geological Survey (BGS), the UK encounters approximately 200 to 300 small to moderately-sized tremors each year. These earthquakes primarily take place along the western side of mainland Britain. Among these tremors, less than 30 are strong enough to be felt by people, although there are rare instances where they can cause more significant damage.

Sergei Lebedev acknowledges that earthquakes in the UK do not reach the magnitudes observed in other regions of the world. Nevertheless, he emphasizes the importance of understanding the reasons behind the occurrence of earthquakes in specific locations within the UK. This knowledge is crucial for engineering projects to effectively consider and mitigate potential seismic hazards. By comprehending the patterns and factors influencing earthquake occurrences, appropriate measures can be taken to enhance preparedness and minimize risks associated with seismic activity.

The notable contrast between the frequency of small earthquakes in western Britain and the relative absence of seismic activity in neighboring Ireland was initially observed by Irish seismologist Joseph O'Reilly in 1884. O'Reilly meticulously mapped the historical earthquake occurrences across Britain and Ireland, drawing attention to this distinctive difference in seismic activity between the two regions. This observation laid the foundation for further investigations and the recent study by researchers from the University of Cambridge and the Dublin Institute for Advanced Studies.

Since Joseph O'Reilly's initial observation, scientists have been working to unravel the reasons behind the occurrence of earthquakes in Britain while their absence in Ireland remains a puzzle. One theory proposes that seismic activity in Britain might be concentrated in specific localized areas where land has experienced differential shifts after the melting of the ice sheets that once covered the region around 12,000 years ago. However, Sergei Lebedev points out that this theory, along with others, fails to fully explain the precise location of seismic activity observed in the region. The quest for a comprehensive understanding of this phenomenon continues among researchers.

To gain a more comprehensive understanding of the seismic activity in Ireland, the researchers utilized a network of seismometers strategically placed across the country. These seismometers enabled them to measure the paths and behavior of seismic waves generated by earthquakes, providing valuable insights into the structure and composition of the Earth's crust beneath Ireland. This detailed examination of the subsurface crust aided the researchers in unraveling the factors contributing to the absence of significant seismic activity in Ireland compared to its neighboring regions.

The research conducted by the scientists revealed a compelling correlation between the distribution of earthquakes in Britain and Ireland and the thickness and strength of the underlying tectonic plate. The properties of the lithosphere, specifically the lithospheric thickness and strength, were identified as the primary factors determining the location of seismic activity. Sergei Lebedev expressed surprise at the remarkable connection between lithosphere characteristics and earthquake occurrence, emphasizing the significance of this finding in deepening our understanding of seismic processes in the region.

The researchers' investigation revealed that the lithosphere beneath Ireland is characterized by greater strength and thickness compared to the seismically active regions of western Britain. This added strength prevents the tectonic plate from buckling or undergoing significant deformation. As a result, seismic activity, such as earthquakes, is less frequent in Ireland. Sergei Lebedev explains that the lithosphere's enhanced ability to withstand deformation in this area contributes to the relatively low occurrence of earthquakes in Ireland compared to its neighboring regions.

Sergei Lebedev highlights that the presence of a thin and weak lithosphere extending along western Britain provides a clear explanation for the higher frequency of earthquakes in that region. The contrast in lithosphere characteristics allows the tectonic plate to crumple and fracture more easily, activating pre-existing faults near the Earth's surface and resulting in seismic tremors. The vulnerability of the lithosphere in western Britain plays a crucial role in facilitating the occurrence of earthquakes in the region.

The team's findings also provide an explanation for specific patterns of earthquake locations in Britain and Ireland. For instance, in Ireland, earthquakes only occur in one area, Co. Donegal, which happens to be situated above a region with weak lithosphere. In contrast, in certain parts of Britain, like eastern Scotland and south-eastern England, there are patches of stronger tectonic plates where fewer earthquakes occur.

Professor Chris Bean from the Dublin Institute for Advanced Studies said that the research findings are very important because they reveal that small details are significant even within the same plate. This helps us understand why there are more earthquakes happening in Britain compared to Ireland, and it gives us new knowledge about the places where earthquakes are more likely to occur.

In addition to figuring out the puzzling distribution of earthquakes in Britain and Ireland, the findings also provide insights into the forces that influence earthquake patterns in other parts of the world. The researchers are now interested in studying earthquakes in Africa and other continents, where they have observed a similar concentration of earthquakes in regions with thinner and weaker lithosphere.