Surrey earthquakes unlikely to be caused by oil activity, say researchers

190504 BGS chart newdigate

A new study has found no clear links between the recent swarm of earth tremors in Surrey and local oil drilling activity.

According to the paper, there have been 129 seismic events centred  between the villages of Newdigate and Charlwood since 1 April 2018.

But based on the available evidence, the authors concluded it was unlikely that nearby industrial activities had induced the swarm.

The study, submitted to the journal, Seismological Research Letters, uses recorded seismic data and operational information provided by operators at oil exploration sites at Horse Hill, near Gatwick Airport, and Brockham, near Dorking.

Most of these tremors were recorded on a network of temporary seismometer stations installed in the area in July and August 2018 after the first nine seismic events.

The largest tremor in the swarm had a magnitude of 3.1ML. 31 events exceeded 0.5ML but only 11 were felt, based on reports recorded by the British Geological Survey (BGS). The most recent tremor reported by the BGS was on 17 May 2019.

1810 Horse Hill UKOG2

Horse Hill oil site near Gatwick Airport, October 2018. Photo: Used with the owner’s consent

UK Oil & Gas, the main investor in the Horse Hill site, and Angus Energy, the operator at Brockham, have repeatedly said their activities did not cause the tremors.

The paper, which has not yet been peer-reviewed, has been posted online and lead author, seismologist, Dr Stephen Hicks, of Imperial College, welcomes scientific feedback. The final published version may change.

“Background seismicity”

The authors said the average depth of the tremors was 2.3km, below the target formations at Horse Hill. The well, Horse Hill-1 (HH-1) is exploring the Portland sandstone at a depth of 600m and the Kimmeridge shale at 800m, they said.

If the tremors had been induced it was a novel mechanism that has not been documented in scientific literature, Dr Hicks told BBC Radio.

He said the tremors, based on data available at present, were likely to be part of the background seismicity of the UK. Ancient faults could be stressed by tectonic forces in the Alps and Mediterranean, he said. This could cause seismic slip to be released along faults running east-west in the Weald.

The study’s conclusions were based on six key points:

  1. Timing
    The authors said the sequence of seismic events started before subsurface activity and flow testing/production began at HH-1 in 2018
  2. Location
    The earth tremors were 3km from the nearest oilfield operations at HH-1 and deeper than the target formations. This would be an unusual location for induced seismicity caused by the current scale of operations, the authors said. They found no clusters of seismicity immediately close to the drill site.
  3. Oil activities
    Based on operational logs provided by the operators, the authors said they found no clear link between the seismicity rate and cumulative oil production or activities at either HH-1 or Brockham. Some events happened when the HH-1 well was shut-in, they said. But if this were a factor, any correlation was not yet robust and such a stress transfer mechanism was unclear, Dr Hicks said.
  4. Mechanism
    The authors did not find any abnormal faulting mechanisms that had been previously observed for production-induced seismicity, such as at Groningen in the Netherlands. The observations were consistent with reactivation of a pre-existing fault, they said.
  5. Volume and stress
    The cumulative volumes of net production reported by the operators were much smaller than past reported cases of extraction-induced seismicity, the authors said.
  6. Fluid pathways
    There were no obvious connections between Horse Hill and Newdigate Faults, which could plausibly offer a permeability pathway from HH-1 to the earthquakes, the paper concluded. The borehole does not directly intersect the Horse Hill fault, it said.

The study recommended seismic monitoring should be carried out close to hydrocarbon development and production sites. Operational activities, such as well shut-in periods, and production volumes and rates should be reported to reduce uncertainties for similar cases in future, it added.

Seismological Research Letters

58 replies »

  1. KatT. Clusters happen in natural systems. From stars, to ecotopes. A cluster of earth tremors does not definitively imply a causal relationship with human activity, although clusters can be caused by human activity (e.g mining, or large dams, or geothermal operations, and yes in some cases with oil & gas operations). This scientific study is rigorously demonstrating that with regard to the oil & gas operations in the area studied, they cannot be linked to the seismic events. That’s all. Of course you are entitled to believe what you wish, think, etc., in spite of the evidence. However, unless you can show that the authors of this study have failed in doing a thorough job, then I would would advise you to take seriously their conclusions.

    • I do not question what you write Dr Riley, nor the content of this particular report. I am simply pointing out that other petroleum geologists and scientists do have concerns about fracking as the comments of some infer that only unscientific, ignorant people oppose fracking, which is clearly untrue. My comments were therefore in response to the condescending, stereotyping of opponents of fracking, which is unnecessarily rude, none factual and unscientific.

      • KatT. Thank you for clarifying what you meant. I agree. There are some very good scientists who have concerns about fracking. There are also some very poor scientists who have concerns too. One has to discern on a case by case basis, looking at the best available rigorous evidence, who is most likely to be wrong & who is most likely to be close to what is reality. Science can never be certain, & all good scientists should constantly evaluate their view each time new evidence emerges, Uncertainty is nothing unique to science, it is part of all human experience. All science can do is reduce uncertainty & get a closer approximation to what is real, based on the best evidence & understanding available.

      • Kat – I know quite a bit about this subject and Nick is 100% correct. I’ve got a very large network of geoscientists and I only know two (Smythe and Haszledine) that argue that shale gas extraction is an intrinsically risky process. In my opinion they are commenting outside their area of competency. I’m sure you won’t take up my advice but if you were open minded you might just try and check out how many peer reviewed articles either of them have on geomechanics, induced-seismicity, linking fluid flow to seismicity etc. I can assure you that they have no expertise or publications on those subjects. You seem incapable of differentiating your values and beliefs from scientific fact. Don’t feel bad about it – you are not alone.

    • Hi Nick
      To be strictly accurate, the report says that “Surrey earthquakes are UNLIKELY to be caused by oil and gas operations”.

      It’s worth noting too the last line of the DoD report:

      Operational activities, such as well shut-in periods, and production volumes and rates should be reported to reduce uncertainties for similar cases in future, [the report] added.

      Ruth has discussed her article with Dr Hicks, who described it as “a good summary”.

      • Paul, UNLIKELY expresses the fact that science can never be absolutely certain. See discussion between KatT & myself.

      • Judith, You do have a propensity to assert your over-inflated ego. Sad really, As you keep pointing out in your diatribe that all antis know diddly squat about “science facts” As it has been pointed out to you already, irrespective of what causes the earthquakes is neither here or there. The IPCC has warned us that if we don’t tackle climate change within the next 11 years then it will be too late. The fossil fuel industry has had its day, but of course, you know that already Judith. Sadly, too many people like you have helped to speed up the process of climate change. The earth is approximately 4.5 billion years old but within the last couple of hundred years, we as a species have single-handedly caused more harm than we could have ever imagined. Whilst there have been some incredible advances, in technology and medicine etc, …which in some respects could be argued about the necessity of them, enough is enough. We should have been getting out of the fossil fuel game a couple of decades ago. Money should have been poured in R&D for renewables 20/30 years ago.

        The on-shore o&g industry has proven many times to flout the law and simply can’t be trusted in mine and countless others opinion who spend a lot of time researching this industry. Money does change hands and little brown envelopes do find their way into the hands of officialdom. Sadly this is the way the world works, However, changes are afoot and there seems to be a much greater call for transparency nowadays and about time too.
        So, Judith if you still need to continue to massage your inflated ego, then try to be somewhat less patronising in doing so.

        • Candore – the article is about seismicity – I’m not sure why you are mentioning climate change – I guess the antis just can’t stop themselves from conflating issues

          • Judith, It is rather simple. The fossil fuel industry is the leading cause of climate change. Unless serious funding is put into the renewable technology industry el-pronto, we will be leaving an ecological disaster for future generations. We should have already learned from the effects of the industrial revolution. This government has stifled the funding for the renewable technology industry. We have desecrated the natural resources of this planet to the great cost of its health and the wildlife that we share it with.

        • Candoure

          You say that ‘money does change hands’ and ‘little brown envelopes do find their way into officialdom’. Just after noting you have done a lot of research into the onshore oil and gas industry.

          Have you any examples at hand to back up this assertion ( brown envelopes to planners or councillors say, or a bung to local politicians of any description, or maybe a bung to civil servants? ).

          Graft is something to keep an eye on as those old enough to remember the Donnygate scandals

          Or that the NCB subsidence claims department issues many years ago.

          But you seem to indicate that there may be ( or you have ) evidence or perhaps justifiable suspicion that this has actually happened?

          • hewes62,

            Regarding ‘graft’ aka bribery and corruption, in the late 1970s it was established practice to leave a folded sheet of newspaper containing £10 in a foolscap envelope under the passenger seat of vehicles having fitness to work examinations at the council run testing depot.
            No £10 no pass and mysterious faults would be discovered during the inspection that were absent before presentation!
            No more details but the matter was dealt with!

            • Peter K R

              Indeed. A similar scam is still running I suspect when people take their cars in for a service. Mysterious faults are found, which, to fix would cost inordinate amounts of money.

              A couple of years ago I was quoted £1400 to change a brake pipe (which involved dropping out the rear axle ), but a wire brush on a stick removed the bit of mud pretending to be corrosion and all was ( and is ) OK.

              So .. as you note, one has to keep an eye out for graft in all its forms.

  2. KatT. I don’t know whether you have been watching the events leading up to the timing of the D Day landings. The timing boiled down to 2 meteorologists advising the timing. One thought it OK to proceed with D-Day to be June 5th, the other strongly disagreed. General Eisenhower, & the allied leaders had to make a choice between the conflicting advise of 2 scientists. Eisenhower rigorously cross examined each meteorologist. He chose the right advise, & despite all the difficulties of postponing D Day by 24 hrs, had he not done so D Day would have been a disaster. The timing of D Day was based on the best available science & understanding. Eisenhower, thank fully, had the ability to see that.

    • Quote from previous post from Paul at Drill or Drop.

      “From now on, all comments drawing parallels with fascists, Nazis, the Second World War or the Mafia will be removed in full.

      Dr Nick Riley MBE, C.Geol., FGS
      June 6, 2019 at 8:43 pm
      Paul, Thank for removing such inappropriate & disrespectful posts.

      Phil C
      June 6, 2019 at 11:57 pm

      Paul Seaman, please remove that innapropriate and disrespectful post.

        • Never mind Paul, i’ll pick them up for you, just as our children and future generations will have to do after you lot have ransacked the entire planet…..

          Have a nice day, to children everywhere…

  3. Paul, UNLIKELY expresses the fact that science can never be absolutely certain. See discussion between KatT & myself.

  4. Well, they do say that if a monkey is sat in front of a typewriter eventually it will type all the works of Shakespeare . So I guess we have to accept that the very clear correlations (the paper says a 30-50% correlation) in Fig3 between well activity and earthquakes could just be coincidence. Interestingly, I note that we have now moved on from the OGA report “no causal link” between Hydrocarbon activity and the earthquakes to “unlikely causal link”. So maybe, just maybe, the authors are beginning to think that the coincidences are starting to look implausable.

    Maybe all the experts commenting here would like to ask themselves what might have changed a benign fault into a critically stressed fault and what role the drilling of a well might have played in that. I doubt there are too many options and the discussion would be much more interesting

    • reffords

      The faults are assumed to be critically stressed in the Haszeldine et al presentation.

      So, nowhere on either side of the discussion had a benign fault been considered to become critically stressed by the drilling of a well or subsequent activities.

      Maybe looking at the Haszeldine et al gas migration route and subsequent seismic activity causation would result in a good discussion as i believe that routing of gas and list of assumptions is quite comprehensive.

      I would also note that the drilling of a well is not considered to cause seismic activity by any expert. It is always subsequent activity that is the issue at hand ( be it the firing of a perforation gun or the re injection of water into existing reservoirs et al ).

      But all those faults have some stress.

        • reffolds

          Thanks, and I should have noted that my comment re drilling relates to the Weald seismic issues above.

          You would be correct in that drilling itself can cause issues. The example you link is fascinating, if only in that as reported ( start at page 6 of the report ) it seems that € millions of damage has been caused in what could be called a ‘dash for easy geothermal’. The report gives the impression that small drilling companies could just rock up and ( on the request of a home owner ) drill you a geothermal well which then causes a sink hole and damages all your neighbours houses. Though the larger events were council planned ( the drilling that is, not the damage ).

          Hopefully future drilling for geothermal through anhydride beds et al will be ( or maybe now is ) properly regulated and planned.

          So, it just goes to show how careful you need to be when drilling, if only for a water well.

          Other examples can be the salt mine example ( linked on here before ).

          • Hewes62- geothermal isn’t particularly well regulated in the UK. One just needs local planning permission. Unlike fracking for gas, there is no traffic light system for seismicity in the UK.

          • Huwes62
            Thank you for the links. It seems that drilling into water is quite common and can cause catastrophic unintended consequences. Do you think that could have happened at Horsehill? Both the nearby wells at Brockham and Balcombe have hit high pressure water and have had to halt production.The geology is said to be the same. Could water have been released and travelled to the fault and made it critically stressed?

            • reffolds

              It will be the other way round here. The faults are stressed ( formed by the same forces that caused the Alps ) and keen to move up, down or sideways but held in place by the weight of rock. Critically stressed means that you do not need much of an event to make them move.

              A situation they have been in for many millions of years.

              The idea, or worry, is that they have moved due to oil and gas activity, specifically the recent drilling has upset stressed faults, and if water, it has lubricated them making it easier for them to move.

              We should keep an eye out for any PEER review information that turns up on the back of the paper.

              Should there be any more tremors it will be well commented about on here one suspects.

  5. Judith

    Thanks. I guess that when we go for deep thermal ( rather than the shallow stuff above ) a fact finding trip to NZ will be in order to ensure appropriate regulation.

    • Hewes62 – that’s a good idea but it might be a bit late for that given that the well currently being drilled in Cornwall is relatively deep! It seems pretty hypocritical of the anti’s to cause a massive fuss about the possibility of tremors at PNR will ignoring the possibility of far large events in the geothermal well.

    • Hewes62

      There hasn’t been an earthquake in this region since 1551 according to the BGS. WW2 bombs falling in the area and the test flows in 2016 at Horsehill didn’t cause earthquakes. So it seems as if the fault wasn’t critically stressed at that time. Then in April 2018 we get our first earthquake as work started again at Hoesehill after a 2 year shutin. So I am wondering whether drilling the well in 2014 and or the work in 2016 released water which found its way over 2 year period to the fault and made if critical.

      There were 2 more small tremors last Sunday 9th June

      • reffolds

        Apologies for a delayed response.

        Re water and faults, i would not think so as the water is likely to be in contact with the fault anyway.

        Re critical stressed faults. Yes …. I think you still need a fair amount of activity ( be it extraction or injection ) to make faults move, not the limited activity carried out so far. This point is one still being discussed on DOD in one of the recent posts.

        My only experience of faults first hand is tunnelling through them ( by machine or by explosives ) or undermining them completely by removing 3ft or so of coal. We cursed them as well if they turned up in the middle of a coal face.

  6. I still haven’t managed to get around to reading the report despite my best intentions, but I assume there is nothing new in it?

    • Hi Dorkinian, i have been trawling through the actual document, and its not very enlightening, all questions and no answers.

      This is the text of the, not yet peer reviewed document is here:

      It is worth also looking at the following abstract on the introduction page:


      Earthquakes induced by subsurface industrial activities are a globally emotive issue, with a growing catalogue of induced earthquake sequences. However, attempts at discriminating between natural and induced causes, particularly for anomalously shallow seismicity, can be challenging. An earthquake swarm during 2018–19 in south-east England with a maximum magnitude of ML 3.2 received great public and media attention because of its proximity to operating oilfields. It is therefore vital and timely to provide a detailed characterisation of the earthquake sequence at present, and to decide based on current evidence, whether the earthquakes were likely natural or induced. We detected 129 earthquakes and computed detailed source parameters of these events. Most earthquakes occurred at a shallow depth of 2.3 km, >1 km deeper than the geological formations targeted by the oilfields, and laterally >3 km away from the drill-sites. We combine the east-west trending cluster of the seismicity with 2-D seismic reflection profiles to find the causative fault system for the earthquakes. A b-value close to unity and strike-slip faulting mechanisms are consistent with tectonic reactivation along a pre-existing fault. Overall, we find no indicators in the earthquake parameters that would strongly suggest an induced source. Nor do we find any clear trends between drilling activities and seismicity based on operational logs provided by the operators. Injected volumes are near-zero and monthly production amounts are many orders of magnitude smaller than other reported cases of extraction-induced seismicity. On balance, and based on the available evidence, we find it currently unlikely that nearby industrial activities induced the seismic swarm. Most likely, the Surrey earthquakes offer a uniquely detailed insight into shallow seismicity within sedimentary basins. Nevertheless, the way that activity reporting by operators themselves is regulated remains a controversial issue when discriminating between natural and induced seismicity for industrial methods that have not been expected to induce earthquakes.”

      This is how vague it is, enough holes in the logic to run a convoy of HGV’s through.

      “On balance, and based on the available evidence, we find it currently unlikely that nearby industrial activities induced the seismic swarm.”

      Lots of double speak, if’s and’s or but’s and caveats there, not a scientific document at all, no scope of statistics, no information that points indisputably to the vague conclusions, in fact no actual facts at all, merely presumptions and suppositions.

      This last sentence from the conclusions:

      “Nevertheless, the way that activity reporting by operators themselves is regulated remains a controversial issue when discriminating between natural and induced seismicity for industrial methods that have not been expected to induce earthquakes.”

      So it does indicate that the operators own self regulation reporting and supplied figures, or not reporting or even recording of events in the old style permissions lack of any transparency at all, may also put into doubt the only really significant factor asides from all the avoidances and non conclusive elements, and that is, what was the timing between the first earthquakes and the first on site activities of whatever manner. all that depends upon the operators figures which depend entirely upon dates and accuracy for the conclusions such as they are.

      There mere fact that these earthquake storms only occurred when the exploratory and extraction activities were happening and not prior to that at all for 40 years, may only be explained by what activities were not recorded or timed correctly?

      Maybe the peer review will be more discerning?

      Interesting isnt it?

  7. Good morning ladies and gentlemen, boys and girls, its Sunday 9th June 2019 and its the first Sunday since Theresa May resigned.
    And its also the 35th Sunday since fracking was attempted to be resurrected by Cuadrilla in PNR, and we all now know that the earthquake swarms closed that down and the subsequent attempts to bypass the TLS regulations limit and change the operations to Nationally Significant Infrastructure and Permitted Development also came to nought.

    So now it seems that there are moves to exonerate the drilling and extraction operations in Surrey in this paper by Stephen Hicks James Verdon, Brian Baptie, Richard Luckett, Zoë Mildon and Thomas Gernon which reports that the very causes of earthquake swarms in relation to drilling and extraction is “unlikely” to be the local fossil fuel exploration and extraction operations. Except that the report does not go so far as to actually suggest an possible alternative reason for the earthquake swarm that occurred during that time period.
    Perhaps the term “unlikely” also applies to the lack of any hard evidence for the “unlikely” conclusions? Maybe a peer review will clarify that?
    I find the last sentence in the extract from the report to be significant at the very least:
    “Nevertheless, the way that activity reporting by operators themselves is regulated remains a controversial issue when discriminating between natural and induced seismicity for industrial methods that have not been expected to induce earthquakes.”

    So perhaps the operators simply did not record activities that were supposed to be “before the drilling operations began”? Seismic testing perhaps? And only 2d seismic modelling was used, not the 3d version that seems to reveal so much more?
    Interesting isn’t it?

    Maybe a subsequent relevant question is that does this constitute a move to attempt to also exonerate the earthquake swarms in Lancashire by Cuadrilla at PNR? Now that is an interesting question isn’t it?

    Watch this space…..

    Theresa May departed after her resignation this week on 7th June, the day after….can i still mention a date?

    Yes folks, EUlvis has well and truly left the building and with Donald Trump and the lovely Emmanuel Macron to wish her a fond farewell.

    Thangyouverymuchhh laydees an’ gennelmen…..

    And now what about fracking considering the government that supported them got cold feet and appear to have fragmented into competing camps, the DUP disappeared off in a huff over the brexit borders and resignations left right a centre, to enable MP’s to line up for the next madhatters tea party?

    Boris! Gove! Javid! …..Nigel! Dear me, do we even deserve these nightmares again?

    I see the anti antis are hoping for a fracking spring with a new government, but i seriously doubt that this present government are capable of sheathing their Huwawei long knives for long enough to actually become one government again and maybe there will be a general election after all.

    God help us all.

    So now, of course we see the frantic scramble for the PM’s still warm seat at Number 10 Downing Street, while the political fall out still wet on the floors?

    Talking about throwing their toys out of the pram, this is the Tories throwing their decoys out of the sham.

    Strange days indeed.

    Have a great Sunday with family and friends and perhaps take this paper that is not yet peer reviewed with a large pinch of salt.

  8. These are the Reith Lectures presently on Radio 4 with Lord Jonathan Sumption looking the present moves to make the legal courts deal with social issues that were never their original purpose, such as we saw with the injunctions being taken out against “persons unknown” and only failing after challenges by people on the grounds of inappropriate and intrusive legislation into common law and human rights.

    These are very much worth listening to, if you haven’t all ready been following them, there are two more to come in the series.

    1/5. Law’s Expanding Empire
    The Reith Lectures2019: Jonathan Sumption
    Jonathan Sumption argues that the law is taking over the space once occupied by politics. Lord Sumption is a former justice of the UK’s Supreme Court.

    2/5. In Praise of Politics
    The Reith Lectures2019: Jonathan Sumption
    Jonathan Sumption explains how democracy has the unique power to accommodate opposing opinions and interests.

    3/5. Human Rights and Wrongs
    The Reith Lectures2019: Jonathan Sumption
    Jonathan Sumption argues that judges – especially those of the European Court of Human Rights – have usurped power by expanding the interpretation of human rights law.

    [Typo corrected at poster’s request]

  9. this is parts 1 and 2 of the DW documentary which is also worth watching.

    the power struggle between corporations and the state:



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