Shaken not Stirred

Introduction and caveats 

Two weeks ago Haiti suffered a devastating earthquake and a severe aftershock that killed several thousand people, followed by a tropical storm that greatly compromised recovery. Normally, these are events that would dominate MSM headlines but, instead, have been largely overshadowed by happenings in Afghanistan. Nevertheless, here and there, speculation about possible links between frequency and intensity of earthquakes and climate change reappeared, including mention of a 2013 book by Bill McGuire (Waking the Giant). These caused my geological BS hackles to rise.

I have been asked to add my thoughts upon this topic. This posed me with a dilemma. Seismology (the study of earthquakes) has been far from any area of my expertise, even though I have worked closely with oil company geophysicists whose speciality is closest to this subject. Also, when I was employed by the Saskatchewan Geological Survey the geologist in the adjacent office was tasked with assessing the Province’s subsurface for waste storage and disposal, and we would discuss our studies with each other. The relevance of this is that some locations (such as Denver, Colorado), where liquid wastes were pumped into the ground, are notorious for spawning earthquakes resulting from changes in underground fluid pressures. I also have thought much about the rate at which temperature changes migrate in the subsurface, a topic relevant to how changes in climate might influence the subsurface. Thus my expertise is limited and my opinions are potentially questionable by a more informed expert. [But when has this fact ever stopped me? I have history]. I also lived and worked in the San Francisco area for three years where you imbibe much earthquake lore and I experienced a few events, one of which scared the bejesus out of me.

Another problem is that I have not read McGuire’s 2013 book. However, it was preceded by a Guardian article (26 February, 2012) – “Climate change will shake the Earth”, which reads like a summary of the main points in the book – full of fire and brimstone prophesies. Death and destruction all round, all to be laid at the door of human induced climate change impacting the subsurface. Its message is clear, we will cause catastrophic geological harm unless we mend our ways. I am far from being convinced, except possibly in areas where thick glaciers have melted recently and even here opportunities for causing big earthquakes that would cause death and destruction to millions would seem to be somewhat limited.

Basics of earthquakes 

Adjacent sides of a fault normally cannot move past each other because of irregularities, or asperities, along the fault surface – the fault is locked. Continued movement of opposing sides creates increasing stress and increasing strain energy along the fault plane. Strain increases until the accompanying stress rises sufficiently to break the asperity, and suddenly sliding along part of the locked part of the fault is possible. The stored energy is then released. 

This elastic-rebound theory of earthquakes invokes a gradual build-up of strain and stress along locked fault planes, punctuated by episodes of sudden failure. It is estimated that around 10% of the released stress is released as seismic energy, whereas the majority powers the fracture growth within the fault or is converted into heat.    

Upward deformation that might relieve the gradual build-up of strain energy is opposed by the overburden load. This load is supported at depth by both the solid rock and by the pressure within any fluid within fractures or other porosity. If the overburden pressure is reduced or increased it can stimulate seismicity. Cases in point are earthquakes caused by excessive groundwater removal or due to pumping fluid waste into the subsurface, due to changing subsurface fluid pressures.

Most earthquake foci on continents lie at depths of several kilometres, but foci associated with plate margins with descending tectonic slabs can lie at depths of up to 600 km. All lie at depths well beneath those affected by temperature changes resulting from present-day climate change. Rocks do not transmit temperature changes quickly. In fact, past climate changes going back to past ice ages can be detected in boreholes by temperature anomalies that are still slowly migrating downward from the surface.

Earthquakes and climate change

So will climate change, induced by humans or not, cause an increase in the frequency or the magnitude of earthquakes? Bill McGuire, volcanologist, Emeritus Professor of Geophysical and Climate Hazards, former member of the U.K. Government’s Natural Hazards Working Group and the Scientific Advisory Group for Emergencies (SAGE), contributing author to the 2011 IPCC Report on climate change and extreme events, &c., &c., says yes, yes, yes. He has done so in books, newspaper articles, radio, and on blog sites. Furthermore, his views are repeated often by those who wish to scare us with the perils of man-made climate change.  

Is he to be believed? My view, partially due to prejudice, is both yes and no. Yes, where substantial thicknesses of glacial ice have disappeared as a result of warming since the Little Ice Age, especially in earthquake prone regions of the Earth; but no as a result of recent, or even expected, sea-level rises.

McGuire’s thesis

McGuire argues that rates of geological change, particularly the melting of glacial ice and coastal flooding by rising sea level, occurred most rapidly at the end of the last ice age and during the earliest part of the Holocene. These changes caused flexure of the crust and the unlocking of faults. He argues that rates of earthquake occurrence were greater then than more recently. I don’t know where he gets this information, perhaps this is explained in his book. McGuire is a volcanologist, he also argues that erupting volcanoes were more frequent and/or more violent at times when and where the crust was flexing. This should leave an identifiable record at the surface in the form of lava flows and ash deposits of that date, and a diminution of those materials during the later Holocene. I know of no published work reaching those conclusions but that may just be my ignorance.

Similar fast rates of change are believed by McGuire to be either happening today or are expected to occur in the immediate future as a result of man-made climate change. These changes should cause crustal deformation and changes in the frequency and severity of earthquakes and volcanism. This is, in his opinion, something to worry about.

Glacial melting and earthquakes

There is no question that the melting of ice sheets and glaciers, especially those of great thickness, will cause substantial changes in the deep subsurface. But the response is extremely slow. Commonly upward bobbing of the crust accompanied by lateral movements of the ductile Upper Mantle to fill the potential void beneath the upward moving crust both occur at rates compared to those at which fingernails grow.

We must also consider that glacial ice is not very dense compared with other geological materials. Ice has a density less than half that of most crustal rocks, so that removal of 1,000 m of ice is equivalent to the loss of much less than 500 m of rock. Of perhaps greater significance is the very fast rate that glacial ice can melt (compared with removal of most other geological materials).

Two locations have been identified as suffering more earthquakes as a consequence of ice melting. The first region is coastal Alaska, where valley glaciers have gone AWOL (shown by ground surveys by the US Geological Survey and aerial photography). However, like much of climate attribution “science” there is much to question here. The region is already earthquake-prone. I have now read more than several dozen papers and reports that claim an increase in earthquakes and attribute this to loss of glacial ice. But nowhere in my reading do I find statistics that would confirm such a link or even prove an increase in seismicity. After all, an earthquake, however caused, releases subsurface strain, commonly passing it along the fault plane to another locality not beneath an area of ice-loss. I am perfectly willing to accept a strong possibility that glacial melting could induce more earthquakes, but given how difficult or impossible it is to predict large earthquakes ahead of time, I cannot imagine how any increase in frequency or intensity can be calculated, let alone be attributed to ice loss and climate change.

There also is the possibility that increased strain and stress caused by ice melting is mostly relieved by micro-seismic events, in which case there would be no increase in more intense quakes that could cause damage and be felt. In fact large earthquakes might actually decrease.

Ice melting in Alaska is not just a recent phenomenon. I have visited Glacier Bay near Juneau. Apparently this huge bay was entirely ice choked to its entrance in the first part of the eighteenth century when the first Russian explorers sailed by not suspecting its existence. Now (or at least 20 years ago when I was there) most of the Bay is empty of ice, although many glaciers still flow into it (two of which are not retreating). [The whales and the falling ice masses at the termini of glaciers were spectacular.  Mind-blowing in fact. I only wish the coastal fog would have abated so that we could have viewed it all from the air. I particularly wished to see the huge Malaspina Glacier, but sadly that was not to be].

The other region mentioned as suffering increased seismicity due to recent glacial ice loss is coastal Greenland. I know nothing about this, other than to note that the ice-free fringe of much of coastal Greenland must be largely due to earlier Holocene melting. Any increase of seismicity would be mainly the result of this earlier melting and not due to increased CO2 in the atmosphere.

Finally, it should be noted that if there is increased seismicity in Alaska and coastal Greenland these are areas of low to no population. If indeed seismicity is now increasing in areas losing glacial ice I would have expected the message to come from more populated seismic-prone areas like New Zealand or northern Japan. But then many glaciers in New Zealand refuse to obey climate heating rules and insist upon advancing at times.

Increased seismicity due to sea-level rise

Part of McGuire’s 2012 Guardian article is pure alarmist scaremongering:

Across the world, as sea levels climb remorselessly, the load-related bending of the crust around the margins of the ocean basins might – in time – act to sufficiently “unclamp” coastal faults such as California’s San Andreas, allowing them to move more easily; at the same time acting to squeeze magma out of susceptible volcanoes that are primed and ready to blow.”

Perhaps at the end of the Pleistocene, when thick continental ice sheets melted and caused at least a 125m sea level rise, this extra loading might have caused crustal flexure severe enough to cause extra earthquake activity. But in otherwise aseismic regions this would have largely relieved any residual stresses present (however we must remember that the largest U.K. earthquake occurred near Colchester in 1884: a previously identified aseismic area). But we are only talking about crustal loading by addition of seawater due to climate change of, at most, a few millimetres a year. I cannot conceive of the Earth’s crust as being so weak as not to slowly accommodate to this minute change in loading. Thus any suggestion that the recent Haiti earthquake could be due to additional seawater loading resulting from climate heating is IMHO highly unlikely.

Seismicity as a consequence of crustal loading by water is definitely possible. The huge water reservoir behind the Aswan High Dam in Egypt (Lake Nasser), filled after 1971, to an average depth of around 25m -maximum depth 180m) has spawned numerous earthquakes, some above magnitude 4 on the Richter scale. However, the rate at which the subsurface beneath the reservoir was subjected to this additional loading is many magnitudes greater than any coastal flooding as a consequence of even the most extreme modelled rate of sea-level rise.

It’s about strength

The impression Bill McGuire gives is of the Earth’s crust being extremely weak and sensitive to even the slightest change in loading – even that produced by climate heating. Over parts of the Earth this could be true, but these areas already suffer from earthquakes and volcanoes, so a slight increase in activity would be difficult to recognise, let alone ascribe to climate change. In other areas the crust seems to be strong and few earthquakes occur. This affects areas where mass has been added, such as European river deltas where sediment has been dumped, yet the only earthquakes are very shallow and can be attributed to uneven settling. Similarly large masses of limestone and chalk have been removed from the Mendips, North-western Kent and the Island of Portland. Earthquakes? None that I know of.  And what of the 600+ marble quarries near Carrera in Italy?  As I have argued elsewhere (Humans as Super Agents) humans have and are shifting enormous masses of earth and rock. Somewhere, if McGuire is correct about the sensitivity of the Earth’s crust, this activity should be recognisable seismically.

As with many other apocalyptic warnings about climate change, there are grains of scientific truth that should be acknowledged and respected. However, there is nothing in these particular truths that suggest that the human race is at any greater serious risk, and certainly nothing that helps to justify the mad scramble for Net Zero. I may be shaken but I am certainly not stirred.

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via Climate Scepticism

August 27, 2021 at 04:47AM

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