In the 4th century B.C., the Greek Philosopher Aristotle believed that earthquakes were the result of air escaping violently from subterranean caves. While that exact mechanism has been known for some time to be incorrect, it turns out that there may be a connection between climate and earthquakes and other seismic activity as well.
The modern understanding of plate tectonics—the realization that the earth's land masses, rigid plates that make up the earth's crust both above the oceans and below them, are in constant motion and tension with respect to each other—was confirmed only in the 1960s. The movement of these plates, however, is slow. For example, the subduction of the Nazca plate under the South American plate is just 70–80 millimeters per year. But the movement is relentless. After eons, the result is the configuration of the Earth's surface as we know it today. In the tectonic play of irresistible forces, eventually something gives, or breaks, or moves aside. The Earth quakes. How and when pressure is relieved depends in part on the load that a plate is carrying. The load can be in many forms such as rock, water, or ice.
Glacial rebounding is a phenomenon where the crust rises due to melting of ice (unloading). The Canadian shield has been experiencing glacial rebounding since the last glacial retreat in the North America continent. As the climate continues to warm and reduce the amount of ice in some places and increase the mass of water (e.g., from oceans, precipitation), the stress on tectonic plates can change—sometimes abruptly. The topic of climate’s contribution to earthquakes, tsunamis, and even volcanic eruptions is not new and has been studied for the last few decades, with continued research interest.
A recent article, for example, discussed the contribution of glacial melt to a 1958 M7.8 earthquake in Alaska. That earthquake unleashed 30 million cubic meters of rock, causing a massive rockslide that slammed into the waters of the Gilbert Inlet and caused the world’s largest tsunami runup ever recorded—1720 meters.
The study noted that the event occurred in July, which is the warmest month of the year in Alaska, and that 1958 was the warmest year since 1944. The authors estimated that glacial melt increased the probability of the event occurring by 2%. While this may not be a big impact for that event, Arctic amplification is causing rapid glacial melt in high latitudes, so the possibility exists for more activity like this to occur in the future.
The reduction of glacial ice on and around volcanoes has also been shown to correlate with increased volcanic activity. This makes for a potentially interesting negative feedback mechanism between climate change and increased sulfate aerosols that would form from the activity and slightly reduce incoming solar radiation.
Melting glaciers and thermal expansion of oceans from climate change may also contribute to another earthquake-related hazard. Rising seas are raising the water table in many places of the world, which can translate to an increased tendency for liquefaction during earthquakes. Liquefaction occurs when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking. It was significant during the Christchurch, New Zealand earthquake in 2011. The impact of sea level rise on liquefaction has been studied recently by Quilter et al. (2015) who examined several different sea level rise scenarios for the South Island, where Christchurch is located. The study found a several fold increase in the number of properties that would be damaged depending on the amount of sea level rise and the magnitude of the earthquake.
As mentioned earlier, load can take the form of water as well. Earthquakes in the Himalayas have been linked to heavy rainfall in the region. During monsoon season, the addition of water weight reduces micro-seismic activity and in the dry season it is enhanced (Panda et al. 2018). The extra weight causes plates to move horizontally as well as vertically.
Again, while climate change is not mentioned as the ultimate driver, monsoon rainfall is expected to increase because of the Clausius-Clapeyron effect and increased land-ocean temperature contrast. The precipitation loading and unloading mechanism could be even more significant in the future.
The water weight effect is not trivial. To put it into perspective, Argus et al. (2017) noted that the 2011-2015 period of drought in the Sierra Nevada, a mountain range between the Central Valley of California and the Great Basin, resulted in a one-inch rise in the height of this range owing to the 11 cubic miles of water that evaporated (was removed) during that period. That amount of water would service all of Los Angeles’ current water needs for nearly 50 years.
In the subsequent two years, increased rainfall caused a one-half inch decrease in the Sierra Nevada’s height. The vertical motions may seem small but are comparable to the displacements caused by actual seismic movement and such climate impacts have been found to modulate the timing of earthquakes in California (Johnson et al. 2017).
Reduced Atmospheric Pressure
In other parts of the world, typhoon activity has been found to have a small impact on seismic activity in Taiwan, not from the precipitation falling on the mountains, and not from the wind buffeting them, but from the reduced atmospheric pressure causing small changes in stress. Liu et al. (2008) found that the lower pressure associated with a typhoon results in a very small unclamping of the fault that must be close to the failure condition for the typhoon to act as a trigger.
This effect relieves stress from building up that would otherwise cause stronger earthquakes. Climate change will bring stronger typhoons with lower central pressure but even an expected 10% reduction in the center-to-periphery pressure will not likely have an increased impact on this effect.
Climate Change Is Rarely Mentioned
It is important to keep in mind that with many of the examples mentioned, processes described, and the studies cited, climate change is mentioned rarely, if at all. The connection of seismic activity to climate—from melting ice or changes in rainfall patterns has, however, been demonstrated using historical information and there is relatively high confidence that glacial melt and heavy rainfall events will continue to increase.
One also has to keep in mind that climate change attribution studies, even for specific weather events, aren’t exactly commonplace yet either, so quantifying the impact on significant seismic effects may just take a while longer. Given the relative infrequency compared to events like floods and hurricanes, it could take several decades before the right event comes along. Then again, maybe just one drop of water from a Pacific coastal storm on Mt. Whitney in the Sierra Nevada in the near future may be the seismic “butterfly” for a ground-shaking case study.