Earthquake
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| 3 |
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| 2 |
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| Likelihood | |||||||||||||||||||||||||||||||||||||||||||||||||||
| ID | 44 |
|---|---|
| Risk theme | Natural and environmental hazards |
Impact & Likelihood
| 5 | Catastrophic |
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| 4 | Significant |
| 3 | Moderate |
| 2 | Limited |
| 1 | Minor |
| 5 | >25% |
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| 4 | 5-25% |
| 3 | 1-5% |
| 2 | 0.2-1% |
| 1 | <0.2% |
Background
Earthquakes in the UK are rare, and an earthquake powerful enough to inflict severe damage is unlikely. Damage from UK earthquakes would be greatest in historic buildings such as churches, monuments and Victorian or Edwardian terraced housing. The risk of damage would be greatest closest to the epicentre and decrease with distance. In 2007, a very shallow earthquake occurred near Folkestone in Kent, resulting in power outages, transport disruption and widespread superficial damage. The most damaging UK earthquake in terms of intensity occurred in 1884 in Colchester, Essex. Approximately 1,200 buildings required repairs to collapsed walls, chimneys and roofs. The maximum observed intensity for the earthquake was 8 on the European Macroseismic Scale (EMS).
The British Geological Survey (BGS) operates a network of seismometers throughout the UK to acquire seismic data on a long-term basis and to help coordinate an appropriate emergency response, plan for future events and improve confidence in seismic hazard assessments. BGS also collates information on historic earthquakes, to improve estimates of earthquake recurrence rates, a key part of hazard assessment. These activities are part of its Seismic Monitoring and Information Service.
Scenario
The reasonable worst-case scenario is based on earthquake activity in the UK that results in the ground shaking with at least an intensity of 8 on the EMS, which causes damage to buildings and infrastructure.* This could result in some fatalities and casualties due to falling masonry or interior damage. Damage to buildings would include moderate structural damage along with heavy non-structural damage, for example extensive cracks in walls, complete collapse of chimneys. More substantial damage could occur to more vulnerable structures. Such an earthquake may cause significant disruption to infrastructure, transport and communications, even if the physical damage is comparatively minor. There may be power outages caused by vibration of apparatus along with disruption to transport and communications networks. Safety inspections of high-consequence structures
and installations including nuclear power plants, dams and reservoirs, bridges and tunnels would likely be required.
*A magnitude 6 earthquake at a moderate depth in a densely populated urban area would lead to ground shaking at intensity 8 EMS at distances of up to a few kilometres from the epicentre and 7 EMS at tens of kilometres away.
Key assumptions
The risk assumes that no critical infrastructure is damaged to an extent that overwhelms existing emergency plans. It assumes one EMS 8 earthquake, with further related earthquakes having only minor impacts.
Variations
A higher magnitude earthquake, or one that affects more critical infrastructure or built-up areas would have higher impacts.
Response capability requirements
Capabilities required to deal with the aftermath from an earthquake are largely covered by plans put in place by Local Resilience Forums (LRFs). This includes the restoration of essential services (gas, water, electricity, communications) due to pipes or cables being disrupted. Damage to infrastructure such as power or communications networks will require specialist intervention. Additional support could be provided via mutual aid agreements with neighbouring local authorities or LRFs – supplemented as necessary by national support (for example specialist Fire and Rescue equipment held as national assets).
Recovery
Temporary or permanent rehousing may be necessary where residential properties are unsafe or unliveable (due to a lack of access or a lack of services), and while clearance and assessment is carried out. Temporary relocation of commercial premises or other infrastructure such as schools might be necessary where the properties have been damaged and are considered unsafe or unusable. There are unlikely to be any significant long-term implications from an earthquake, although there may be a spike
in numbers of people seeking access to mental health services for psychological support in the months after the incident. Vulnerable persons and children in particular are more likely to require support.