Between a rock and a fluid place

US researchers have found a way to monitor geological faults deep in the Earth that could help them predict an imminent earthquake more precisely than with other methods. This is the first time that scientists have been able to detect temporal changes in fault strength at seismogenic depth from the Earth’s surface.

The late Paul Silver and Taka’aki Taira of the Carnegie Institution’s Department of Terrestrial Magnetism, working with Fenglin Niu of Rice University and Robert Nadeau of the University of California, Berkeley, used highly sensitive seismometers to detect subtle changes in earthquake waves that travel through the San Andreas Fault zone near Parkfield, California, over a two-decade time span.

“Fault strength is a fundamental property of seismic zones,” explains Taira, who has moved to the Berkeley since the research was done. “Earthquakes are caused when a fault fails, either because of the build-up of stress or because of a weakening of the fault. Changes in fault strength are much harder to measure than changes in stress, especially for faults deep in the crust. Our result opens up exciting possibilities for monitoring seismic risk and understanding the causes of earthquakes.”

Seismologists have focused the San Andreas Fault near Parkfield, the “Earthquake Capital of the World,” for years. The site has a sophisticated array of borehole seismometers, the High-Resolution Seismic Network, as well as other geophysical instruments in situ. Researchers consider it a natural laboratory for seismology because of the frequent quakes that occur there.

Earlier studies have suggested that there are fluid-filled fractures within the fault zone and that these shift. When this happens, “repeating” earthquakes apparently become smaller and more frequent, which researchers say is indicative of a weakened fault. “Movement of the fluid in these fractures lubricates the fault zone and thereby weakens the fault,” says Niu.

“The total displacement of the fluids is only about 10 metres at a depth of about three kilometres, so it takes very sensitive seismometers to detect the changes, such as we have at Parkfield.” Niu further explains that it seems to be distant earthquakes that cause the fluids to shift, such as the 2004 Sumatra-Andaman Earthquake, which led to tsunamis throughout the Indian Ocean that year.

It is San Andreas fault (Adapted from Wikipedia image)
It is San Andreas fault (Adapted from Wikipedia image)

The authors speculate that such large events should produce a temporal clustering of global seismicity, a hypothesis that appears to be supported by the unusually high number of large earthquakes occurring in the three years following the 2004 earthquake. The team presents additional evidence that a similar phenomenon occurred following the 1992 Landers earthquake.

LINKS

Nature, 2009, 461, 636-640
Department of Terrestrial Magnetism at the Carnegie Institution of Washington
Northern California Earthquake Data Center (NCEDC)

One fell swoop

Despite the conspiracy theories that claim the killing was down to a network of terror, the latest undercover investigations, just made public, reveal that the dinosaurs and the vast majority of animal life on Earth died in a mass extinction about 65 million years ago because of a single hit.

The likely assassin was an enormous body – the Chicxulub meteorite – that smashed into what we now refer to as the Yucatan Peninsula in Mexico. The new research provides compelling evidence that one and only one impact caused the mass extinction, says its lead author Ken MacLeod, associate professor of geological sciences at Missouri University Columbia.

Ken MacLeod

Ken MacLeod

The samples we found strongly support the single impact hypothesis, he explains, they come from very complete, expanded sections without deposits related to large, direct effects of the impact – for example, landslides – that can shuffle the record, so we can resolve the sequence of events well.

MacLeod adds that, What we see is a unique layer composed of impact-related material precisely at the level of the disappearance of many species of marine plankton that were contemporaries of the youngest dinosaurs. We do not find any sedimentological or geochemical evidence for additional impacts above or below this level, as proposed in multiple impact scenarios.

The Chicxulub crater (Credit: NASA)

The Chicxulub crater (Credit: NASA)

The Chicxulub impact probably caused massive earthquakes and tsunami, while dust from the impact would have filled the atmosphere, blocking out sunlight, and leading to the death of plants. Temperatures likely also cooled significantly around the globe. MacLeod and many other scientists believe that these effects led to the relatively rapid extinction of most species on the planet.

Nooooooooooooo! (Credit: LBL)

Nooooooooooooo! (Credit: LBL)

However, not everyone is convinced of the one-hit wonder theory. Princeton University paleontologist Gerta Keller and her collaborators Thierry Adatte from the University of Neuchatel, Switzerland, and Zsolt Berner and Doris Stueben from Karlsruhe University in Germany suggest there is growing evidence that the dinosaurs and their contemporaries were not wiped out by the Chicxulub meteor impact alone.

They say that it was multiple meteor impacts, massive volcanism in India, and climate change culminated in the end of the Cretaceous Period. Keller and her colleagues reason that Chicxulub may have been the lesser and earlier of a series of meteors and volcanic eruptions that pounded life on Earth for more than 500,000 years.

Further reading

Ken MacLeod homepage
http://rcp.missouri.edu/geosci_macleod/index.html

Suggested searches

dinosaurs
meteorites

Canary holidays safe…for now

Those worried that a holiday in the Canary Islands might be interrupted by a devastating collapse of the volcanic island of La Palma and an ensuing tsunami can relax. According to researchers in the Netherlands, La Palma is a lot more stable than is generally assumed, and holidays can go ahead as planned, at least for the next 10000 years, they say.

Jan Nieuwenhuis and his colleagues have cast doubts on pessimistic estimates of the effects of a collapse of the southwestern flank of La Palma caused by a volcanic eruption. Geologists had previously calculated that such a collapse would cause a mega tsunami that might roar across the Atlantic wreaking havoc on the US eastern seaboard, Europe, and Africa, with waves initially 650 metres high moving at 800 kilometres per hour. A tsunami on this scale could wipe New York, Boston, Lisbon, and Casablanca from the face of the map.

Robert Jan Labeur

Robert Jan Labeur

However, according to the new research, the volcano Cumbre Vieja is simply too small to fall apart…yet. So, a mega tsunami should not happen any time soon. Nieuwenhuis and his colleagues, Robert Jan Labeur and Ronald Brinkgreve, modelled the inside of the flank and then simulated several volcanic eruptions and steam explosions. Cumbre Vieja remained intact in every simulation. This is simply a very stable island’, explains Nieuwenhuis in the journal Delft Integraal.

According to his calculations, a force of at least 12 million million Newtons would be necessary to tear the island apart. That would be the equivalent of the combined strength of 600 million fighter jet engines. A volcanic outburst on La Palma would exert far less force than this, the team says. Nieuwenhuis cautions that under incredibly extreme conditions, however, the flank could become unstable. An exceptionally powerful outburst of magma coinciding with usually heavy rainfall or some other unlikely combination of circumstances would be needed. Based on what we know now, so many things must go wrong that a disaster seems very, very unlikely’, adds colleague Janneke van Berlo.

The Space Shuttle’s view of La Palma (Credit: NASA)

The Space Shuttle’s view of La Palma (Credit: NASA)

However, as the years pass, so the Cumbre Vieja will grow and its sides become steeper. 10,000 years from now, its flanks may be rendered unstable. A combination of substantial vertical growth and eruption forces will most probably act to trigger failure, van Berlo says.

But, Nieuwenhuis’s calculation does not appear in accord with the present state of La Palma, which doesn’t look very solid even today. It has lost chunks of its flanks at least twice in prehistoric time and during the last eruption, in 1949, a two kilometre rip appeared at the top of Cumbre Vieja’s southwestern flank. The Delft researchers explain that the rip was caused by innocent, shallow phenomenon that won’t lead to tsunami-producing conditions. That said, this work is, like that of the originators of the original risk assessment, the Benfield Greig Hazard Research Centre, theoretical. If I were holidaying in the Canaries, I’d keep one eye on your book and the other on that rip, just in case.

Further reading

More about mega-tsunamis
http://www.benfieldhrc.org/tsunamis/mega_tsunami_more.htm

Suggested searches

tsunamis
volcanoes<