Nav: Home

Scientists get first look at cause of 'slow motion' earthquakes

March 25, 2020

An international team of scientists has for the first time identified the conditions deep below the Earth's surface that lead to the triggering of so-called 'slow motion' earthquakes.

These events, more commonly known as slow slip events, are similar to regular sudden and catastrophic earthquakes but take place on much longer timescales, usually from days to months.

By drilling down to just over 1km deep in water depths of 3.5km off the coast of New Zealand, the team have shown that the fault zone areas in which slow slip events occur are characterised by a 'mash up' of different rock types.

The results, published today in the journal Science Advances, showed that the areas are comprised of extremely rough sea floor topography made of rocks that varied markedly in size, type and physical characteristics.

The lead author of the paper, Dr Philip Barnes of New Zealand's National Institute of Water and Atmospheric Research (NIWA), described that 'some rocks were mushy and weak, whilst others were hard, cemented and strong.'

This has given scientists the first-ever look at the types and properties of rocks directly involved in slow motion earthquakes and begins to answer some of the major outstanding questions surrounding these unique events, such as whether or not they can trigger larger, more damaging earthquakes and tsunamis.

Co-author of the study Dr Ake Fagereng, from Cardiff University's School of Earth and Ocean Sciences, said: "This was the first effort to sample the rocks that host slow slip events, and the striking, immediate observation is that their strengths are hugely variable. One can therefore visualise the slow slip source as a mixture of hard and weak rocks, and use this as a starting point for models of how slow slip occurs."

First discovered on the San Andreas fault in California, but since 2002 found to occur in several other locations, slow slip events remain a relative mystery to scientists, who are endeavouring to find out how, where and why they occur and what drives their behaviour.

As part of their study, the international team undertook two International Ocean Discovery Program (IODP) expeditions aboard the JOIDES Resolution research vessel to the Hikurangi subduction zone off the east coast of the North Island in 2017 and 2018.

This was the first time that scientists had studied, and directly sampled, rocks from the source region of slow slip events using ocean floor scientific drilling methods.

The Hikurangi subduction zone is New Zealand's largest earthquake fault and is one of the best places in the world to study slow slip because here these events occur close to the sea floor which makes drilling to collect rock samples a lot easier.

For instance, Laura Wallace of GNS Science, New Zealand, describes that the 2016 Kaik?ura earthquake triggered a series of major slow slip events on the Hikurangi subduction zone - where the Pacific Plate dives beneath the eastern North Island - and was the most widespread episode of slow slip seen in New Zealand since they were first discovered in the country.

These slow slip events following the Kaikoura earthquake released a large amount of built-up tectonic energy and lasted over the weeks and months following the earthquake.

During the expedition the team drilled two boreholes to obtain a sequence of rocks and sediments on the incoming (Pacific) plate approaching the North Island.

The drilling data were interpreted together with seismic reflection profiles - or pictures of the layers under the surface of the earth which are created at sea by sound waves.

The study has indicated that the co-existence of these contrasting rock types in the fault zone may lead to the slow slip movements observed offshore from Gisborne, and perhaps elsewhere at subduction boundaries around the world.

Indeed, Dr Barnes says that the research will have direct relevance not only to New Zealand, but to areas like Japan and Costa Rica, which sit on the Ring of Fire - the perimeter of the Pacific Ocean basin where many earthquakes and volcanic eruptions occur.

"We now know that a highly variable mixture of rock strengths is part of the recipe for slow slip. This opens for new studies of how such mixtures deform, why they can generate slow slip, and under what conditions (if any) they can also generate damaging earthquakes. This may help address the outstanding question of how earthquakes and slow slip events interact," continued Dr Fagereng.
-end-
The study was led by jointly led by researchers from NIWA, GNS Science, The University of Texas at Austin, and the University of Auckland. The International Ocean Discovery Program is sponsored by the National Science Foundation in the USA, the Natural Environment Research Council in the UK, and other participating countries.

Notes to editors

1). For more information, please contact:

Michael Bishop
Cardiff University
02920874499/07713325300
Bishopm1@cardiff.ac.uk

2). Cardiff University is recognised in independent government assessments as one of Britain's leading teaching and research universities and is a member of the Russell Group of the UK's most research intensive universities. The 2014 Research Excellence Framework ranked the University 5th in the UK for research excellence. Among its academic staff are two Nobel Laureates, including the winner of the 2007 Nobel Prize for Medicine, Professor Sir Martin Evans. Founded by Royal Charter in 1883, today the University combines impressive modern facilities and a dynamic approach to teaching and research. The University's breadth of expertise encompasses: the College of Arts, Humanities and Social Sciences; the College of Biomedical and Life Sciences; and the College of Physical Sciences and Engineering, along with a longstanding commitment to lifelong learning.

Cardiff University

Related Earthquake Articles:

New clues to deep earthquake mystery
A new understanding of our planet's deepest earthquakes could help unravel one of the most mysterious geophysical processes on Earth.
Fracking and earthquake risk
Earthquakes caused by hydraulic fracturing can damage property and endanger lives.
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.
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: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.