Nav: Home

Dissection of the 2015 Bonin deep earthquake

March 15, 2017

Researchers at Tohoku University's Department of Geophysics, have been studying the deep earthquake which occurred on May 30, 2015, to the west of Japan's Bonin Islands.

The earthquake, which registered at about 670 km depth with moment magnitude (Mw) of 7.9 (Fig. 1), was the deepest global seismic event on record with M ≥ 7.8. It was also an isolated event located over 100 km deeper than the mainstream seismic zones recorded so far (Fig. 1). The event has attracted great interest among researchers because high pressure and high temperature at such great depth make it unusual for earthquakes to generate there.

In the Izu-Bonin region, the Pacific plate is subducting northwestward beneath the Philippine Sea plate. Subduction is a process where one of Earth's tectonic plates sinks under another. To date, several studies have investigated the source location of the Bonin deep earthquake relative to the subducting Pacific plate (slab*1). But there have been conflicting results because the mantle structure in and around the source zone is still unclear.

The Tohoku University team, led by Professor Dapeng Zhao, applied a method of seismic tomography to over five million P-wave arrival-time data recorded by world-wide seismic stations to determine a high-resolution mantle tomography beneath the Izu-Bonin region. The stations included those from the dense seismic networks in Japan and East China.

Seismic tomography*2 is an effective tool for investigating the three-dimensional (3-D) structure of the Earth's interior, in particular, for clarifying the morphology and structure of subducting slabs. Using that method, the team received clear images of the subducting Pacific slab as a high-velocity zone , and showed that the Bonin deep event occurred within the Pacific slab, which is penetrating the lower mantle (Fig. 2). Moreover, its hypocenter is located just beside the eastern slab boundary to the ambient mantle within the mantle transition zone*3.

They also found that the Pacific slab is split at about 28° north latitude, i.e., slightly north of the 2015 deep event hypocenter. In the north, the slab is flat in the mantle transition zone. Whereas in the south, the slab is nearly vertical and directly penetrating the lower mantle (Fig. 3).

These results suggest that this deep earthquake was caused by the joint effects of several factors. These include the Pacific slab's fast deep subduction, slab tearing, slab thermal variation, stress changes and phase transformations in the slab, as well as complex interactions between the slab and the ambient mantle. This work sheds new light on the deep slab structure and subduction dynamics.
-end-
Notes:

*1 Slab: the subducting oceanic plate.

*2 Seismic tomography: a method to image the three-dimensional structure of the Earth's interior by inverting abundant seismic wave data generated by many earthquakes and recorded at many seismic stations.

*3 Mantle transition zone: a part of the Earth's mantle between depths of approximately 410 and 670 km, separating the upper mantle from the lower mantle.

Acknowledgements:

The authors wish to thank the data centers of the Japanese Kiban Seismic Network, the China Seismic Network, and the International Seismological Center for providing the high-quality arrival-time data used in this study. This work was supported by research grants from the Japan Society for the Promotion of Science (Kiban-S 23224012) and MEXT (grant No. 26106005).

Tohoku University

Related Earthquake Articles:

Earthquake symmetry
A recent study investigated around 100,000 localized seismic events to search for patterns in the data.
Crowdsourcing speeds up earthquake monitoring
Data produced by Internet users can help to speed up the detection of earthquakes.
Geophysics: A surprising, cascading earthquake
The Kaikoura earthquake in New Zealand in 2016 caused widespread damage.
How fluid viscosity affects earthquake intensity
A young researcher at EPFL has demonstrated that the viscosity of fluids present in faults has a direct effect on the intensity of earthquakes.
Earthquake in super slo-mo
A big earthquake occurred south of Istanbul in the summer of 2016, but it was so slow that nobody noticed.
A milestone for forecasting earthquake hazards
In a new study in Science Advances, researchers report that their physics-based model of California earthquake hazards replicated estimates from the state's leading statistical model.
Mw 5.4 Pohang earthquake tied to geothermal activity?
The Mw 5.4 Pohang earthquake that occurred near a geothermal site in South Korea last year was likely triggered by fluid injection at the geothermal plant, two separate reports conclude.
Seismologists introduce new measure of earthquake ruptures
A team of seismologists has developed a new measurement of seismic energy release that can be applied to large earthquakes.
Residual strain despite mega earthquake
On Christmas Day 2016, the earth trembled in southern Chile.
The losses that come after the earthquake: Devastating and costly
The study, titled, 'Losses Associated with Secondary Effects in Earthquakes,' published by Frontiers in Built Environmen, looks at the devastation resulting from secondary disasters, such as tsunamis, liquefaction of sediments, fires, landslides, and flooding that occurred during 100 key earthquakes that occurred from 1900 to the present.
More Earthquake News and Earthquake Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.