Seismicity

 

  • Natural seismicity in the UK is low by world standards

  • Risk of tremors from hydraulic fracturing is low

  • Risk of any structural damage caused by hydraulic fracturing extremely unlikely

 

What causes earthquakes?

Naturally occurring earthquakes are caused by tectonic activity. The majority of these earthquakes occur along plate boundaries but natural seismic activity can occur anywhere in the world.

 

How are earthquakes measured?

Earthquakes measuring below 3.0 on the Richter Scale are generally not felt on the surface

The size or magnitude of an earthquake is measured using the Richter scale. The way the scale works means that when measured from the same distance, an earthquake of magnitude 5 produces vibrations with amplitudes 10 times greater than those from a magnitude 4 earthquake and 100 times greater than those from a magnitude 3.0 earthquake.

Therefore, an earthquake of measuring 5 on the Richter scale releases 32 times more energy than an earthquake of measuring 4 and about 1000 times more energy than an earthquake measuring 3.

 

Are there earthquakes in the UK?

Yes. Natural seismicity in the UK is low compared to the rest of the world. On average, the UK experiences seismic events measuring 5 (felt by everyone nearby) every 20 years and events measuring 4 (felt by many people) every three to four years.

The British Geological Survey (BGS) publishes a record of all earthquakes around the British Isles in the past 50 days. Based on a search conducted on the 28th September 2015, there were 18 recorded earthquakes in the previous 50 days, including one in Oakham, Rutland which measured 2.8.

According to the BGS, an earthquake is only considered to be “significant” if it measures above 4 and an earthquake measuring below 3 is generally not felt at the surface, let alone causing any damage.

For example, a minor earthquake measuring 4.2 on the Richter scale was measured in Sandwich, Kent on the 22th of May 2015. There were no reports of any damage or injury from Kent Police nor Kent Fire & Rescue Services.

 

Can hydraulic fracturing (fracking) cause earthquakes?

Unlike natural seismicity, induced seismicity is caused by human activities such as mining, deep quarrying, hydrogeological extraction or fluid disposal and activities associated with non-conventional hydrocarbon extraction (fracking).

seismicityAccording to the Royal Society and Royal Academy of Engineering the level of seismicity brought on by hydraulic fracturing (fracking) is likely to be even smaller than mining. It is now being widely accepted that the magnitude of seismicity induced by hydraulic fracturing would be no greater than 3 (felt by few people and resulting in negligible, if any, surface impacts).

In 2011, two earth tremors, measuring 1.5 and 2.3 on the Richter scale were registered at Preese Hall near Blackpool, Lancashire. After an extensive study into these events, a report published by the Department of Energy and Climate Change in conjunction with the BGS concluded that this seismic activity was induced by hydraulic fracture treatments in the area.

However, the report concluded that the sizes of the seismic events at Preese Hall were considered to be somewhat unique due to the surrounding geology of the region. The state of stress which was released by these events was pre-existing. Magnitudes of any earthquakes recorded during hydraulic fracture stimulation in reservoirs such as the Barnett Shale in the US are typically less than 1.0 and are therefore not observable by humans.

The report also concludes that further small earthquakes cannot be ruled out, however the risk from these tremors is low, and structural damage is extremely unlikely.

 

What is the industry doing to mitigate induced seismicity?

New controls are being introduced to address the possibility of any seismic risks. A Hydraulic Fracturing Programme (HFP) is prepared by the Operator and signed off by the Oil and Gas Authority (OGA) before drilling can commence.

Operators will be required to confirm that wells are not to be drilled into, or close to, existing faults which could provide the mechanism for triggering an earth tremor. Background seismicity and “real time” seismic monitoring will be used before and during activities and a “traffic-light” warning protocol will be employed. If any site records a seismic event of magnitude greater than 0.5, operations will be halted and pressures immediately reduced. This magnitude is well below the energy level that could be felt at the surface, and the protocol would enable a review of the possible causes of the event and allow further steps to be taken to prevent the occurrence of larger events.

 

Who regulates this?

The OGA (Oil and Gas Authority) www.ogauthority.co.uk regulate manmade, or induced, seismicity from oil and gas operations in the UK. Where hydraulic fracturing is planned, the OGA requires the operator to produce a 'Hydraulic Fracturing Plan', detailing how the risks of any potential induced seismicity will be managed. This ensures that the risk of felt seismicity is very low and within existing background levels.

 

Who do I speak to if I have concerns?

In the first instance you should constant your local operator helpline, for example;

  • Cuadrilla
    Lancashire Helpline: 0800 170 1115
  • Third Energy
    Yorkshire Helpline: 0800 133 7352

If you have further concerns you should speak to the regulator the Oil and Gas Authority by either emailing them at This email address is being protected from spambots. You need JavaScript enabled to view it. or telephoning 0300 020 1010.

 

What does a 0.5ML mean?

The value 0.5 ML refers to the detection level set by the OGA at which hydraulic fracturing operations must be paused by the operator. The ML (Local Magnitude) refers to the location deep in the ground at which the tremor is detected. The threshold of 0.5ML has been set by Government as this typically cannot be felt as 'ground motion' (felt earthquakes) at the surface and is below normal background levels of seismicity caused by lorries and trains.

 

Operations have been paused because a 0.5ML was reached. Does this mean that a larger earthquake will happen soon?

If a 0.5ML is reached, an operator must stop operations and release the pressure in the well. Once the pressure is released, then it is highly unlikely that a larger event will happen, as the energy required to create further seismicity has been removed from the well. The operator will continue to monitor the ground in the area and may modify future operations to avoid further 0.5ML events occurring.

 

Is there going to be damage to my house?

The thresholds set by Government are very low and typically will not result in 'ground motion' (felt earthquakes) at the surface. Homes and commercial buildings are designed to stringent British standards and can withstand 'ground motions' (Peak Ground Velocity – PGV) at much higher levels than can be created through hydraulic fracturing. Operators are required to monitor 'ground motion' around their sites to protect sensitive buildings, for example; ancient monuments. This ensures that more delicate structures are not impacted and levels of ground motion are far below any levels that could impact local receptors, such as homes and commercial premises.

 

What is the difference between the Traffic Light System and Peak Ground Velocity (PGV)/Peak Particle Velocity (PPV)?

The traffic light system, covering seismic events from 0 to 0.5ML, is designed to limit the amount of energy released during fracturing operations and control the level of seismicity deep in the ground, such that larger events are unlikely to occur. This limits the chance of felt 'ground motion' (felt earthquakes) at the surface. Peak Ground Velocity (PGV) or Peak Particle Velocity (PPV) monitoring is a way of detecting ground motion at the surface. Operators will undertake PGV/PPV monitoring to ensure sensitive buildings are protected.

 

Why are there two 'vibration threshold' levels, VT1 and VT2?

British Standard (BS7385-2:1993) 'Guide to damage levels from ground-borne vibration', provides the framework for understanding how vibration at the surface of the ground might impact a building. The traffic light system uses the vibration levels recommended within the British Standard to ensure that damage to properties cannot occur.


Is the UK going to become the next 'Oklahoma' with earthquakes every day?

The 0.5ML threshold set by Government is very low and seismic activity of this size typically cannot be felt at the surface. In Oklahoma, virtually all of the earthquakes reported are due to the disposal of waste water into rock deep in the ground, a practice that is strictly forbidden in the UK.

 

You can read our seismic protocol guidance here

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KEY FACTS

4.2
Strength on Richter scale of natural earthquake recorded in Sandwich, Kent on 22nd May 2015

 

 

2.3
Strength on Richter scale of tremor at Preese Hall, Lancashire in 2011 caused by hydraulic fracturing