Is global warming causing more earthquakes?

The allegation: global warming is melting ice caps and glaciers, thereby unloading weight. This causes an isostatic readjustment of the Earth’s crust which results in earthquakes.

The reality according to the U.S. Geological Survey:

We continue to be asked by many people throughout the world if earthquakes are on the increase. Although it may seem that we are having more earthquakes, earthquakes of magnitude 7.0 or greater have remained fairly constant.

 A partial explanation may lie in the fact that in the last twenty years, we have definitely had an increase in the number of earthquakes we have been able to locate each year. This is because of the tremendous increase in the number of seismograph stations in the world and the many improvements in global communications. In 1931, there were about 350 stations operating in the world; today, there are more than 8,000 stations and the data now comes in rapidly from these stations by electronic mail, internet and satellite. This increase in the number of stations and the more timely receipt of data has allowed us and other seismological centers to locate earthquakes more rapidly and to locate many small earthquakes which were undetected in earlier years. The NEIC now locates about 20,000 earthquakes each year or approximately 50 per day. Also, because of the improvements in communications and the increased interest in the environment and natural disasters, the public now learns about more earthquakes.

 According to long-term records (since about 1900), we expect about 17 major earthquakes (7.0 – 7.9) and one great earthquake (8.0 or above) in any given year.

See a video of the apparent increase of earthquakes in Arizona due to the increase in number of seismic stations: Arizona earthquakes, 1852-2011, a video time line

 

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5 comments

  1. Post-glacial rebound, or as Jon more properly calls it, isostatic adjustment; is the rise of land masses that were depressed by the huge weight of ice sheets during glacial periods through a process known as isostasy. The fact that processes associated with isostasy have been shown to cause increases in seismicity is  well known. As Jon is a geologist, he would know better than I, but I don’t think this is a contentious issue. Perhaps he could provide a link to the specific “allegation” to which he’s referring. 

    There has been research on deglaciation, such as is now occurring, and numerical modeling study has demonstrated that seismicity does increase during unloading, due to the removal of ice.  [Hampel, et al (2010). “Response of faults to climate-driven changes in ice and water volumes on Earth’s surface”].

    Another significant affect of deglaciation is the possible increase in volcanism. Reduction in ice cover reduces the confining pressure exerted on a volcano, increasing the stress differences  and potentially causing the volcano to erupt. This reduction of pressure can also cause decompression melting of material in the mantle, resulting in the generation of more magma (Pagli,et al (2008). Researchers in Iceland have shown that the rate of volcanic rock production there following deglaciation (10,000 to 4500 years before present) was 20–30 times greater than that observed after 2900 years before present (Sigvadason, et al (1992). This work in Iceland has been corroborated by a study in California, in which scientists found a strong correlation between volcanism and periods of global deglaciation (Jellinek, A. Mark (2004).

    If major deglaciation occurs due to a warming climate, there is a  definite potential for subsequent increases in seismic and volcanic activity. My understanding of the literature is that these effects would manifest on longer timescales than others associated with AGW.   JP

    1. What absolute rubbish, the idea that a tiny reduction in ice cover caused by “global warming” in the last 100 years can some how be compared to the deglaciation  that occurred over the last 18K years is absurd. Most of the ice cover reduction in the last 100 years has been over the arctic ocean and therefore no impact on land pressure at all.  

      One would have to show that ice cover has reduced in the last 100 years has had a material impact on pressure over areas subject to earth quakes and that simply cant be shown. In terms of volcanoes I find the link between above ground pressure and volcanism implausible and from real world distribution there is no correlation on the number of active volcanoes to areas either covered or devoid of ice.

      This is another piece of global warming alarmist nonsense that undermines the whole issue. Its like the nonsense about animal movements in response to climate change when a 1 degree increase is simply noise in the 30C changes that happen within a day. To me this article simply doesn’t pass the smell test      

      1. Craig, I hope you have an opportunity to do a little research on the topic. It’s a really an interesting subject. For instance, enough ice was lost from the Greenland and Antarctic ice sheets in the years between 2003 and 2010 (1000 cubic miles!) to actually measurably alter the rotation of the planet. These masses are so large, 4.3 trillion tons in this case, that their gravitational pull causes sea levels to be higher in some parts of the ocean than others.

        Like you, I assumed that these forces would need to be near areas prone to earthquakes. It turns out not to be the case. The giant earthquake centered around New Madrid, Missouri in 1811-1812 was caused by isostatic adjustment precipitated by deglaciation. This is still the largest recorded earthquake to hit the eastern U.S., even though it is nowhere near one of the major tectonic plate boundaries. Your point is well taken though, as Iceland does lie directly over such a plate boundary and is of course very near Greenland.

        Contrary to you intuition, there is a large body of evidence that points to a strong correlation between past deglaciations and seismic and volcanic activity. Researching isostasy gives a whole new perspective on some amazing geologic forces, regardless of one’s opinions about anthropogenic climate change. I believe Jon, a trained Geologist, would agree that isostatic adjustment is very real. 

        Your last comment about the 1 degree C change has some merit. Most climatologists are not so concerned about a 1 degree C change in average global surface temps. They are concerned that the trend appears to be heading toward 3 or 4 degrees C by 2090. That’s ten to twelve percent of the “30 degree changes…in a day” you mentioned. I think a twelve percent hotter August day in Tucson might get your attention.   JP

      2. Thanks for the reply on this but I think we need to get some perspective. I have no doubt the large isostatic rebound could in theory (no hard evidence exists other than correlation) cause earthquakes. Its the application of this theory of massive changes in overbearing weight to tiny changes (just measurable versus 25% of the earth coverage reduction after the last ice age) that irks me. In terms of the Antarctic ice sheet reduction that is patiently incorrect, yes there was a reduction in ice over a tiny percentage of Antarctica western peninsular (most due to a very large erupting volcano under very ice) but overall the sea ice and continental ice grew in those years. Again it is very strange how people believe that ice is melting in Antarctica when temp over the vast majority of the continent never gets above -10c mid summer. Sea ice cover has increased every year for the last 15 (satellite record).
        Tropical earthquakes by definition are not caused by ice reduction or isostatic rebound as I would contend is the same for all sea  floor quakes. I would rather the scientists focused on real issues like land clearance, habitat destruction, real pollution like sulfur output in Asia etc etc because wasting research dollars on this kind of nonsense simply diverts funds from really important issues.     

      3. Craig, Your statements are largely correct. I would however, point out the need to recognize that there are two large ice sheets on the Antarctic continent. They are separated by a large mountain range. The west antarctic ice sheet (WAIS) and the east Antarctic ice sheet (EAIS). GRACE-based studies data indicate that the EAIS is losing mass at a rate of 57 billion tons per year and that the total Antarctic ice sheet (including WAIS, and EAIS coastal areas) is losing mass at a rate of 152 cubic kilometers (~139 billion tons) per year. Although these are huge volumes of ice; from my understanding of the literature, it’s unlikely they would cause any substantial isostatic readjustment. 

        But secondly Craig, the ice loss from the Greenland Ice Sheet is far greater, the trend far faster and (as you rightly pointed out) the location relative to an active seismic zone much more worrisome. 

        Being completely fair, I must say that the potential seismic and volcanic effects of AGW will likely manifest quite some time after other, better known issues. But they are real.

        Lastly, although I try to stay out of the policy debate because I lack expertise in that area, I generally agree with your submission that the focus (and the money) could do more good in other areas. Thanks for the thoughtful exchange.   JP

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