Tohoku on EARTH Magazine

Gravity changes portended 2011 Tohoku earthquake

Fri, 03 Aug 2018 13:19:38 -0400

The tectonic setting of the 2011 Tohoku quake. Credit: K. Cantner, AGI.

A new analysis of satellite data has revealed a distinct change in the gravity signal measured across the Japanese archipelago starting several months before the March 11, 2011, magnitude-9.1 Tohoku-Oki earthquake — one of the largest seismic events in recorded history. The gravity change reflects interactions among shifting tectonic plates in the region, and its timing shortly before the earthquake raises the tantalizing notion that such signals could portend impending seismicity elsewhere. But researchers say it’s unclear if the signal seen in the new study is unique to the Tohoku quake or if it represents a phenomenon common to other large subduction zone quakes.

Opportunist organisms rafted across the Pacific on plastic

Tue, 21 Nov 2017 17:02:02 -0500

This Japanese boat washed ashore in Oregon, carrying a load of nonnative species, following the 2011 Tohoku earthquake and tsunami. Credit: John W. Chapman

Since World War II, fiberglass and plastic — which are stronger, lighter and require less maintenance than wood — have become the materials of choice for coastal infrastructure like docks. An unforeseen consequence of this transition, however, is that when structures built from these durable materials break free from their moorings and drift out to sea, they can serve as resilient rafts for opportunistic organisms. In a new study in Science, researchers document hundreds of marine species that made their way 7,000 kilometers across the Pacific Ocean from Japan on debris — much of it made of plastic and other modern materials — following the magnitude-9 Tohoku earthquake and tsunami in March 2011.

Alaskan subduction zone mirrors Tohoku zone that unleashed tsunami

Thu, 09 Nov 2017 15:21:06 -0500

This diagram shows the generalized structure of the subduction zone off the Alaska Peninsula near the Shumagin Islands. A large normal fault cuts through the entire overriding North American Plate at a roughly 45-degree angle and connects to the megathrust fault along which the North American and Pacific plates move against each other. Credit: K. Cantner, AGI, based on data from Bécel et al., Nature Geoscience, 2017.

In 2011, a large swath of coastal Japan was devastated and more than 15,000 people were killed when the magnitude-9.1 Tohoku earthquake unleashed massive tsunami waves that inundated land with run-up heights of 30 meters in places. In a new study, researchers have discovered that the seafloor off the Alaska Peninsula exhibits structures and fault patterns similar to the region where the Tohoku quake originated — a finding that may indicate a higher tsunami risk for coastal Alaska than previously thought.

Gravity changes may warn of large earthquakes

Thu, 16 Feb 2017 11:04:10 -0500

Debris lines a canal in the coastal Japanese town of Ofunato following the March 2011 Tohoku earthquake. Credit: U.S. Navy photo by Mass Communication Specialist 1st Class Matthew M. Bradley.

Large earthquakes alter the planet’s gravitational field by displacing big portions of the crust. In a new study looking at earthquake-induced gravity signals produced by Japan’s magnitude-9 Tohoku quake in 2011, researchers conclude that such signals may prove useful in earthquake early warning systems.

Surprise quake at Mount Fuji triggered by rising gases

Thu, 19 May 2016 21:58:28 -0400

With a peak elevation of 2,335 meters, Mount Fuji is the highest mountain in Japan. Credit: Midori, CC BY 3.0.

On March 15, 2011, four days after the magnitude-9 Tohoku megathrust earthquake and tsunami struck Japan, a magnitude-5.9 earthquake shook the southern flank of Mount Fuji. Seismicity has been rare at the volcano since its last eruption in 1707, leading many researchers to suspect that the Fuji quake — which hit about 300 kilometers southwest of the megaquake — was remotely triggered by the Tohoku event. In a new study, scientists looking at the volcano’s underlying structure and plumbing have offered a potential mechanism for how Tohoku’s shaking could have touched off the Fuji earthquake: through rising gas-rich fluids released from the magma chamber beneath the volcano.

A decade of slow slip may have preceded Japan's 2011 earthquake

Mon, 20 Apr 2015 11:44:10 -0400

Shaking intensities (based on USGS data) on Honshu Island during the 2011 Tohoku earthquake in Japan. Warmer colors indicate greater intensity. Credit: NASA Earth Observatory Image by Jesse Allen and Robert Simmon.

Everyone notices when a fault ruptures quickly — the ground shakes and shudders, and sometimes, the seas churn. However, tectonic plates can also creep past each other so slowly that it’s almost imperceptible. Researchers say they’ve now identified the longest example to date of this type of movement along the Japan Trench in the decade leading up to the devastating magnitude-9.0 earthquake that shook the island of Honshu in 2011.

Giant quake sloshed fjords half a world away

Wed, 20 Nov 2013 11:43:45 -0500

On the morning of March 11, 2011, Leif Hus and his wife Gry Melas Hus were having breakfast in their kitchen overlooking Sognefjord in Leikanger, Norway. It was low tide on a calm and windless day with near-freezing temperatures. As they stood, coffee cups in hand, looking out the window at the fjord, they saw an unusual wave roll in. The wave continued to rise, surging over the seawall into their backyard before receding back into the fjord. Then another wave surged in, and another. As the water rose, engulfing the ladder on their dock, Leif grabbed his cell phone and started filming.

Well-healed faults produce high-frequency earthquake waves

Tue, 12 Feb 2013 08:16:29 -0500

This tabletop model consisting of adjacent Plexiglas slabs is used to simulate earthquakes and study fault healing. Gregory McLaskey

Much like our voices create sound waves with a variety of low and high pitches, or frequencies, earthquakes also produce seismic waves over a spectrum of frequencies. The seismic waves’ frequencies determine, in part, how far they travel and how damaging they are to human-made structures. But teasing out the details of how quake-generating faults influence seismic frequencies is no easy task, mainly because faults tend to be buried deep underground. Now, with the help of a tabletop earthquake model, researchers have identified how a process known as fault healing can shape seismic waves.

Voices: From Haiti to Japan: A tale of two disaster recoveries

Mon, 05 Mar 2012 15:22:23 -0500

A year ago this month, a devastating earthquake and tsunami struck northern Japan. Two years and two months earlier, on Jan. 12, 2010, a much smaller earthquake devastated Haiti. Both earthquakes occurred on a weekday and in the afternoon, but there is very little else that is similar about these two events or how the countries have recovered. Both offer reminders about the uncertainties of the effects of disasters.