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It has been more than 300 years since the last megathrust earthquake hit the Pacific Northwest,��and it may only be a matter of time before it happens again.

Referring to “The Big One,” scientists have long believed it’s not a matter of “if” another magnitude-9.0 (or greater) earthquake will rock North America’s west coast, but “when.”

The last one struck the region on Jan. 26, 1700, and researchers believe the probability of a similar disaster happening in within the next 50 years has risen from 10 per cent to 37 per cent. They worry that such a natural��disaster could��result in thousands of deaths and billions of dollars in infrastructure and property damage, as well as generate subsequent tsunamis that would affect other parts of the world.

• Photo above:��From left: Zahra Ashena, MJ Dehghan, Dr. Hojjat Kabirzadeh, Dr. Emad Ghaleh Noei, Masume Akbari, and Luis Silva pose with Prof. Jeong Woo Kim (front row), and the A10 absolute gravity meter. Photo by Riley Brandt, ����ɫ��

The last megathrust earthquake to hit��North America was the 9.2-magnitude Anchorage, Alaska, earthquake of 1964; it generated tsunami waves that reached as far as Antarctica.��

A team of researchers, including four from the ����ɫ��, believe they are one step closer to helping predict when The Big One might next happen.

Their new report, “,” published in Nature Communications Earth and Environment, analyzes years of gravity measurements and reveals periodic changes in gravity related to seismic activities.

Measuring earthquake energy

The project, including Schulich School of Engineering researchers prof. , PhD;��Dr. Hojjat Kabirzadeh, �ʳ��’16, PDF; Dr. Ricky Kao, PDF;��and prof Dr. Michael Sideris, MSc’84, PhD’88, took place between July 2012 and April 2015 along the Cascadia Subduction Zone, which stretches from Alaska to California. In this tectonically active zone, the young and heavy Pacific Ocean plate subducts beneath the North American continental plate.

“A part of the contact interface between the two plates is, however, in a locked situation and mechanical energy is being accumulated,” Kim says. “Eventually, when the locked zone is unlocked, a significant amount of energy may be released, resulting in megathrust earthquakes at intervals ranging from 500 to 600 years.”

During their research, large earthquakes occurred in Haida Gwaii, B.C., and Craig, Alaska, with magnitudes of 7.8 and 7.5, respectively, giving the team some valuable data.

“For the first time, we demonstrated that the observed gravity increase results from a density increase due to crustal compression and that this is mostly a result of inter-seismic strain accumulation during the subduction,” Kim says. “We believe the anomalous behaviour in this trend, whether an acceleration or deceleration of the density and subsequent gravity changes, combined with other evidence from plate movement and microseismic activities, may be a warning signal for the next mega-earthquake.”

Better technology for forecasting

Plate tectonic-originated earthquakes are the most common and devastating types of natural earthquakes.

Kim, a professor in the and the microgravity project leader, says the findings from this project will help other regions with similar geological settings like in South America and Japan, where mega-earthquakes have also occurred in recent years (a 1960 quake in Chile, of an estimated 9.4-9.6 magnitude, was the most powerful on record and killed thousands).

“There are many geophysical, geodetic and geotechnical technologies that can detect earthquakes, but continuous monitoring of microgravity is the most promising technology that can detect its precursor at present because changes in underground density usually occur before earthquakes,” Kim says. “The most common seismometers detect vibrations in the crust caused by earthquakes, so it is almost impossible to catch the density change, which is a very obvious and reliable precursor of earthquakes.”

However, analysis of earthquakes in this way is limited, so Kim says it is necessary to integrate data from modern technologies such as a GPS network, borehole strainmeters (a geophysical sensor which measures deformation of the Earth's crust),��and broadband seismometers.

International implications

Among the many international collaborations Kim has developed with this project, he is working with researchers at , a deep-underground astrophysics and geophysics lab recently built under the remote mountain area in Jeongsun, South Korea.

In October, through a research agreement between the University of��Calgary and the National Institute for Mathematical Sciences of Korea Institute for Basic Science, Kim installed the iGrav superconducting gravimeter at YemiLab.��Located nearly 1,100 metres below the Earth’s surface, making it is the closest-to-source gravimeter ever installed for continuous operation and the first microgravity meter about 120 metres below mean sea level.��

With minimal environmental noise and unprecedented precision of iGrav, Kim says the site provides optimal research conditions for observation of underground gravitational waves and detection of precursor of mega-earthquakes.

“Our goal is not only to establish an integrated monitoring system for catastrophic earthquakes, active volcanoes and active faults located within 500 kilometers of YemiLab, but also to detect the potential hazard areas prone to devastating natural disasters,” he says.