From the news: Evidence that tidal forces influence earthquakes

Large earthquakes can have immense impacts on humankind, killing thousands of people and creating widespread devastation. While decades of research have helped us understand an earthquake’s complex processes, predicting earthquakes remains a scientific dream.

However, a new study in Nature Geoscience may help us begin to make that dream a reality. “Earthquake potential revealed by tidal influence on earthquake size-frequency statistics” by Ide et al. (2016) provides evidence that large earthquakes are more likely to occur during times of high tidal stresses that affect the Earth’s crust.

Ocean tides are the result of the Moon’s gravity pulling on the ocean as it travels around the Earth. The moon also pulls the surface of the Earth toward it, creating a solid earth tide. These solid tides raise and lower the Earth’s surface imperceptibly over a period of twelve hours, so we cannot see them without scientific instruments.

However, these small ocean and earth tidal stresses may have significant effects. To analyze these effects, Ide et al. looked at the relationship between the amplitude of tidal stresses during large earthquakes. Several large earthquakes occurred during periods of high amplitude tidal stresses, including the 2004 Sumatra earthquake, the 2010 Maule earthquake, and the 2011 Tohoku-Oki earthquake. Ide et al. also found several large earthquakes that did not occur during these periods of high tidal stress.

To examine this relationship more closely, Ide et al. looked at more than 10,000 earthquakes worldwide with magnitudes greater than 5.5 and found that a greater number of large earthquakes occur when tidal stresses are high. Ide et al. interpret this to be the result of high amplitude tidal stresses causing small fractures to rupture into large fractures, turning small earthquakes into large earthquakes. According to Ide et al., a M5 earthquake is six times more likely to become a M9 earthquake during times of high tidal stresses.
                  Further study is needed to verify the causal interpretation of Ide et al. and to more fully understand the implications of this study. But if a causal link is found behind the statistical correlation of large earthquakes and high amplitude tidal stresses, this study could be instrumental in building an earthquake prediction model.

Read the paper at: Ide, Satoshi, Suguru Yabe, and Yoshiyuki Tanaka. "Earthquake potential revealed by tidal influence on earthquake size-frequency statistics." Nature Geoscience (2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2796.html

Development of the Tibetan Plateau: Talk Summary

The Tibetan Plateau is the largest high elevation area on the Earth today, and is so elevated and large that it causes the jet stream to seasonally migrate hundreds of miles- but how and when did it develop?

Figure 1. A topographic map highlighting the current location of Tibetan Plateau, the Indian subcontinent, and the jet stream, as well as the location of the Indian subcontinent and the proto-Tibetan Plateau 50 million years ago, which are known from paleomagnetic data.

Dr. Petr Yakovlev, a geologist at the Montana Bureau of Mines and Geology, kicked off the ISU Geosciences Department Colloquium Series by providing insights into those questions from his PhD work at the University of Michigan. He calculated the crustal mass balance for the region, and determined that the current crustal volume and total convergence requires a thick proto-plateau and redistribution of Indian crust under that plateau. Dr. Yakovlev also spent time in the field in Tibet mapping and dating faults, and there he observed an unusual type of high-elevation compressional deformation that is driven by simple shear and does not produce crustal thickening. Finally, he worked with other scientists studying the Tibetan Plateau to compile a geochemical database for all lavas measured in the region, and found that volcanism with similar evolved-mantle sourcing was widespread across the Plateau beginning around 30 million years ago. He suggests this occurred because the subducted slab of Indian crust broke off into the mantle at that time, 20 million years earlier than previously thought.

Figure 2. Dr. Yakovlev digging a pit in the permafrost-bound soils of the Tibetan Plateau to recover sediment for cosmogenic nuclide dating, which he used to date the age of the surface and estimate rates of uplift.

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In other Geology Department news, Professor Sarah Godsey hosted a contest to guess the opening day of Pebble Creek Ski Area and the winners have been announced! No one correctly guessed the opening day of December 16^th, but four people guessed the 15^th and three people guessed the 17^th. Two winners out of this pool were chosen to split the $50 prize. Congratulations to Dave and Jeff!

And for the data nerds out there, here are the guesses from this year’s contest compared with the opening dates from the past five years:

Figure 3. Results of Dr. Sarah Godsey’s contest to guess the opening day of Pebble Creek Ski Area. Blue circles indicating guesses from the contestants and the orange circles show the opening dates of record. Opening day in 2016 was on December 16^th.

Special thanks to Petr and Sarah for sharing their figures and data for this story. Writing by Caitlin Rushlow.