One Year After Solomon Islands Disaster, Scientists Realize Geological Barrier to Earthquakes Weaker than Expected

On the one year anniversary of a devastating earthquake and tsunami in the Solomon Islands that killed 52 people and displaced more than 6,000, scientists are revising their understanding of the potential for similar giant earthquakes in other parts of the globe.

Geoscientists from The University of Texas at Austin’s Jackson School of Geosciences and their colleagues report this week that the rupture, which produced an 8.1 magnitude earthquake, broke through a geological province previously thought to form a barrier to earthquakes. This could mean that other sites with similar geological barriers, such as the Cascadia Subduction Zone in northwestern North America, have the potential for more severe earthquakes than once thought.

In an advance online publication in the journal Nature Geoscience, the scientists report that the rupture started on the Pacific seafloor near a spot where two of Earth’s tectonic plates are subducting, or diving below, a third plate.

The two subducting plates-the Australian and Woodlark plates-are also spreading apart and sliding past one another. The boundary between them, called Simbo Ridge, was thought to work as a barrier to the propagation of a rupture because the two plates are sliding under the overriding Pacific plate at different rates, in different directions, and each is likely to have a different amount of built-up stress and friction with the overlying rock. But the boundary did not stop the rupture from spreading from one plate to the other.

“Both sides of that boundary had accumulated elastic strain,” says Fred Taylor, a researcher at the university’s Institute for Geophysics and principal investigator for the project. “Those plates hadn’t had an earthquake for quite a while and they were both ready to rupture. When the first segment ruptured, there was probably stress transferred from one to the other.

“What our work shows is that this is a barrier, but not a reliable one,” says Taylor. In other words, it resists rupturing, but not insurmountably. The work has implications for earthquakes in other parts of the world.

“Cascadia is an important boundary because of its potential for a great earthquake in the future,” says Taylor. “You have these transform faults separating the plates-Juan de Fuca, Gorda and Explorer. If such boundaries are not a barrier to rupture in the Solomons, there’s no reason to believe they are in Cascadia either.”

The last great earthquake along the Cascadia Subduction Zone was in the year 1700. The intensity of the quake has been estimated at around magnitude 9. If it happened today, it could be devastating to people living in the northwestern U.S. and western Canada. The geological record suggests such great quakes occur there every few hundred years.

The scientists were able to piece together where and how the fault near the Solomons ruptured by observing how it affected corals living in shallow water around the islands. Because corals normally grow right up to the low-tide water mark, scientists can readily measure how far they have been displaced up or down by an earthquake. In the case of uplift, scientists measure how far the coral dies back from its previous height as a result of being thrust up out of the water. In the case of subsidence, scientists measure how deep the coral is compared to its usual maximum depth below sea level.

“In many ways the corals are much better than manmade instruments as you don’t need to deploy corals or change their batteries-they just go on measuring uplift and subsidence for you anyhow,” says Taylor.

With funds from the Jackson School of Geosciences, Taylor was able to travel to the Solomons just 10 days after the earthquake to make observations, an extremely swift trip in the world of scientific field work. It was part of a new rapid response capability the Jackson School is developing for research that cannot wait several months for government or foundation grants to be approved.

“The trip wouldn’t have happened without the Jackson School support,” said Taylor. “We are extremely grateful for that.”

Taylor’s co-authors include Cliff Frohlich and Matt Hornbach, also at the Institute for Geophysics, Richard W. Briggs and Aron Meltzner at the California Institute of Technology, Abel Brown at Ohio State University, and Alison K. Papabatu and Douglas Billy at the Department of Mines, Energy and Water in the Solomon Islands.

New findings from Tibetan Plateau suggest uplift occurred in stages

 UCSC graduate student Peter Lippert and coworker Igor Villa of the University of Bern collect samples from an outcrop in Tibet - Credit: Xixi Zhao
UCSC graduate student Peter Lippert and coworker Igor Villa of the University of Bern collect samples from an outcrop in Tibet – Credit: Xixi Zhao

The vast Tibetan Plateau–the world’s highest and largest plateau, bordered by the world’s highest mountains–has long challenged geologists trying to understand how and when the region rose to such spectacular heights. New evidence from an eight-year study by U.S. and Chinese researchers indicates that the plateau rose in stages, with uplift occurring first in the central plateau and later in regions to the north and south.

“The middle part of the plateau was uplifted first at least 40 million years ago, while the Himalayan Range in the south and also the mountains to the north were uplifted significantly later,” said Xixi Zhao, a research scientist at the University of California, Santa Cruz.

The team found marine fossils suggesting that the now lofty Himalayas remained below sea level at a time when the central plateau was already at or near its modern elevation, Zhao said. The average elevation of the plateau today is more than 4,500 meters (14,850 feet).

The researchers published their findings in the Proceedings of the National Academy of Sciences (online the week of March 24 and later in a print edition). Zhao, who is affiliated with the Institute of Geophysics and Planetary Physics at UCSC, is the second author of the paper. First author Chengshan Wang of the China University of Geosciences in Beijing has been collaborating with Zhao and other UCSC researchers since 1996.

Known as “the roof of the world,” the Tibetan Plateau was created by the ongoing collision of tectonic plates as India plows northward into Asia. Coauthor Robert Coe, a professor of Earth and planetary sciences at UCSC, said ideas about how the uplift of the plateau occurred have been evolving since well before his first visit to Tibet in 1988.

“People used to talk about the whole plateau coming up at once, but it has become clear that different parts of the plateau were elevated at different times,” Coe said. “Our work shows that the central part of the plateau was uplifted first, and it seems to fit pretty well with other studies.”

The rise of the Tibetan Plateau led to dramatic changes in the climate, both regionally and globally. For climate researchers trying to understand major episodes of global climate change in Earth’s past, the timing of the uplift is a crucial piece of information.

“One of the traditional views of when Tibet became a high plateau is that it’s a relatively recent phenomenon that happened in the last 15 million years,” said coauthor Peter Lippert, a UCSC graduate student who has spent five field seasons studying the geology of the plateau. “The existence of a high plateau at least 40 million years ago could have important climatic implications.”

The team of U.S. and Chinese geologists based their findings on extensive field studies conducted mostly in a remote interior region of the Tibetan Plateau. They focused on an area called the Hoh Xil Basin in the north-central part of the plateau. The area’s geologic history is recorded in layers of sedimentary rock 5,000 meters thick. Now a part of the high plateau, it was once a basin on the northern edge of the central plateau, Lippert said.

“The structure of the basin and way the sediments were deposited show that it is the type of basin that forms at the base of large mountains. So we’ve shown that there was high topography to the south of the Hoh Xil Basin at least 40 million years ago,” he said.

Several lines of evidence support the team’s conclusions. In addition to field studies, the researchers used a variety of laboratory techniques to analyze and date the rocks. Past changes in Earth’s magnetic field, recorded in the magnetization of the rocks, provide one method of dating. Called magnetostratigraphy, this analysis was performed in Coe’s laboratory at UCSC. Another dating technique used in the study, called apatite fission-track analysis, is based on the damage trails left in apatite crystals by the decay of radiogenic isotopes.

The researchers also discovered volcanic rock in an area of the central plateau south of the Hoh Xil Basin. The flat bed of hardened lava lies on top of tilted and folded layers of sedimentary rocks; geochronology techniques dated it to 40 million years ago.

“The presence of these flat-lying volcanic rocks tells us that the sedimentary rock was deformed prior to the volcanism, and it extends the age of volcanism in this part of Tibet from 15 million to 40 million years ago,” Lippert said.

In the Himalayas, the team found fossils of marine plankton called radiolarians that turned out to be 5 million years younger than any previously discovered marine fossils from that area. The discovery narrows the window of time during which the Himalayas could have been uplifted. When the central part of the Tibetan plateau was uplifted more than 40 million years ago, Mount Everest and the rest of the Himalayas were still part of a deep ocean basin, Zhao said.

The Himalayan region is very complicated, however, and other groups are working to determine the timing of its uplift more precisely, said Lippert. “Our main contribution has been the data we gathered from the north-central part of the plateau, which has not been well studied,” he said.

Zhao noted that the U.S. researchers could not have gained access to this area without the support of their Chinese colleagues. This long-term collaboration has included exchanges of graduate students between UCSC and Chinese universities, as well as opportunities for UCSC undergraduates to conduct field research in Tibet. “It has been a very good research collaboration, with a strong educational component as well,” Zhao said.

In addition to Wang, Zhao, Lippert, and Coe, the coauthors of the paper include Zhifei Liu of Tongji University in Shanghai; Stephan Graham of Stanford University; Haisheng Yi, Lidong Zhu, and Shun Liu of Chengdu University of Technology in Chengdu; and Yalin Li of China University of Geosciences in Beijing. This research was supported in part by grants from the National Key Basic Research Program of China, the U.S. National Science Foundation, and the Institute of Geophysics and Planetary Physics at UCSC.

Earthquake predictions prove accurate for researchers

The area around Indonesia is geologically unstable most of the time
This images shows the earthquakes in the Indonesia area during the last 7 days – Image Credit: USGS

Two large earthquakes have occurred in quick succession in Sumatra, Western Indonesia, only months after University of Queensland researchers publicly identified the area as a high-risk zone for seismic activity.

The quakes, which were measured at 7.5 and 7.0 on the Richter scale and caused significant damage and at least three deaths between them, occurred on February 20 and 25 respectively, precisely in the regions pinpointed by researchers.

The successful forecast is just the latest in a string of accurate predictions made by researchers at the University’s Earth Systems Science Computational Centre (ESSCC), using their pioneering advanced computer simulation software.

In December last year, centre scientist Dr Huilin Xing presented the accompanying research at the 40thannual meeting of the American Geophysical Union, to much international interest.

“We have been focusing on the computational mode and development for simulating earth crustal dynamics on supercomputers [for some time now],” Dr Xing said.

“The successful predictions so far have demonstrated the capability of our software, which has already drawn the attention of earthquake scientists from around the world‚Ķ and some from China and the USA have already applied or will apply it to study earthquake behaviour of their own regions.”

Building on this breakthrough work, Dr Xing and team member Dr Can Yin are continuing to apply the modelling software to the southern Indonesian region that has become notorious since the 2004 Boxing Day tsunami.

With the Eurasian and Indian/Australian tectonic plates converging just off the coast, Sumatran waters will likely be the site of seismic activity for some time to come.

“The question is how big and where it will happen in the near future, and whether it will induce a deadly tsunami,” Dr Xing said.

In the meantime, ESSCC researchers will continue to perfect simulation software and the prediction process, hoping to contribute to significant improvements in this important area.

“As we gain more experience in model construction and parameter selection, as well as more experience and confidence in the process, we will no doubt work towards a more accurate and reliable earthquake forecasting platform and filling more wide applications,” he said.

This will include the application of the crustal dynamics software in supercomputer simulation of hot fractured geothermal reservoir systems in the field of alternative energy; and with ongoing funding, exploration of other applications in regards to modelling the deep geological disposal of nuclear waste and carbon dioxide.

Dr Xing said these endeavours owed much to the ongoing support of the Department of Education, Science and Training, the Australian Research Council, and industry collaborators such as Geodynamics Ltd.

The ESSCC conducts research on the mechanics and physics of solid Earth processes on all scales using supercomputer simulation and by applying the methodologies of geophysical fluid and solid mechanics.

Earthquake theory stretched in Central Asia study

Scientists discover cause of seismic instability in Pakistan
Scientists discover cause of seismic instability in Pakistan

The entrenched political instability in Pakistan and Afghanistan is of grave concern to many in the West – but now geologists at ANU have suggested a new cause for the seismic instability that regularly rocks the region.

Scientists from the Research School of Earth Sciences at ANU argue that the frequent and dramatic earthquakes in the Hindu Kush mountain range are likely to be the result of a slow, elastic stretching of a sub-surface feature called a boudin. Their findings, published in the journal Nature Geoscience today, run contrary to the theory that earthquakes usually result from the abrasive collisions between tectonic plates.

“We’ve always thought of earthquakes as being brittle, but our research that the slow, ductile stretching of certain geological features can build up energy that is then suddenly released, causing major seismic upheaval,” said lead author Professor Gordon Lister.

Using computer modelling, the researchers were able to show that the long, hard boudin that sits vertically beneath the Hindu Kush is being stretched as its lower parts are pulled into the Earth’s mantle. “It’s like a metal rod that is being pulled at both ends,” Professor Lister explained. “Eventually the stretching will suddenly accelerate, releasing energy in the process.”

The boudin is thought to be a remnant of the oceanic plate that was pushed into the Earth’s mantle when India collided with Asia. Professor Lister said that eventually it too will eventually drop into the deeper mantle, but that is likely to take thousands, if not millions, of years.

“This is important work, as it suggests a new way of understanding how earthquakes happen. It feeds into the potential for us to eventually develop new and innovative long-range forecasting techniques” Professor Lister said.

“It’s no accident that nations like Afghanistan and Pakistan are places of unrest, because the people there are living in constant hardship, and this results in part from periodic catastrophe’s they must endure, for example related to earthquakes. If we don’t put more effort into understanding the how and why, and also into how we might eventually better forecast earthquakes, humankind is forever doomed to deal with the consequences.”

The researchers have developed a software program called eQuakes that allows them to model earthquake patterns against geological features.

Surprise On Journey To Center Of The Earth: Light Tectonic Plates Lead The Way

Andes Mountains, Peru. When two tectonic plates collide, with one sliding below the other and sinking into mantle, it can lead to the formation of mountain belts, like the Andes.
Andes Mountains, Peru. When two tectonic plates collide, with one sliding below the other and sinking into mantle, it can lead to the formation of mountain belts, like the Andes.

The first direct evidence of how and when tectonic plates move into the deepest reaches of the Earth has been detailed in Nature. Scientists hope their description of how plates collide with one sliding below the other into the rocky mantle could potentially improve their ability to assess earthquake risks.

The UK and Swiss team found that, contrary to common scientific predictions, dense plates tend to be held in the upper mantle, while younger and lighter plates sink more readily into the lower mantle.

The mantle is a zone underneath the Earth’s crust encompassing its super hot molten core. It is divided into an upper and lower area, and is made up of a 2,900 km circumference of churning, viscous rock. It is constantly fed with new material from parts of tectonic plates which slide down from the surface into it.

The researchers’ numerical models show how old, dense and relatively stiff plates tend to flatten upon reaching the upper-lower mantle boundary, ‘draping’ on top of it. Their models are helping to explain plate movements and earthquakes in the Western Pacific, where old plates currently sink below Tonga, the Mariana Islands and Japan.

By contrast, younger more malleable plates tend to bend and fold above the boundary of the lower mantle for tens of millions of years until they form a critical mass that can sink rapidly into the lower mantle.

When this mass moves into the lower mantle, the part of the plate still at the surface is pulled along at high speed. This explains why plate movements below Central and northern South America are much higher than expected for such young plates.

The scientists came to these conclusions by using a numerical model, originally used to show how buildings buckle and fold, which calculates the brittleness, stiffness and elasticity of tectonic plates alongside how the pressures and stresses inside the mantle would affect the plate on its downward descent.

They then compared the modelling with plate movement data. By comparing the two models, the team was able to build up a clear picture of how plates should move when stalled in the upper mantle and also show, for the first time, how tectonic plate rock is mixing within the mantle.

Commenting about the study,* lead researcher Dr Saskia Goes, from Imperial College London’s Department of Earth Science and Engineering, said: “It is exciting to see direct evidence of plates transiting from the upper and lower mantle. This process has been predicted by models before, but no one has been able to link these predictions with observations, as we now do for plate motions.”

When two tectonic plates collide, with one sliding below the other and sinking into mantle, it can lead to the formation of mountain belts, like the Andes, and island arcs, like Japan and, in some places, cause explosive volcanism and earthquakes. Dr Goes say more research is needed, but believes this study could potentially help scientists determine earthquake risks in parts of these zones where none have ever been recorded before.

“The speed with which the two plates converge, and the force with which they are pushed together, determine the size of the largest earthquakes and time between large tremors. Understanding what forces control the plate motions will ultimately help us determine the chances for large earthquakes in areas where plates converge, in places like the northern U.S., Java and northern Peru, but where no large earthquakes have been recorded in historic times,” she adds.

About tectonic plates

There are 8 major and a further 7 minor tectonic plates which cover the Earth’s surface. These plates move across the surface of the Earth. When some plates meet they undergo a process which pushes them upward to create geological formations like mountain ranges. Some plates pull apart, causing fault lines and others undergo a process known as subduction. Subduction occurs when one plate is pushed underneath another and moves into the Earth’s mantle – a rocky zone underneath the crust.

*Journal reference: Saskia Goes, Fabio A. Capitanio and Gabriele Morra. “Evidence of lower mantle slab penetration phases in plate motions.” Nature, 21 February 2008.

This work was supported by a Schweizerischer Nationalfonds Fo¨rderungsprofessur (to S.G.).

Paired earthquakes separated in time and space

Earthquakes occurring at the edges of tectonic plates can trigger events at a distance and much later in time, according to a team of researchers reporting in today’s (Jan. 31) issue of Nature. These doublet earthquakes may hold an underestimated hazard, but may also shed light on earthquake dynamics.

“The last great outer rise earthquakes that occurred were in the 1930s and 1970s,” said Charles J. Ammon, associate professor of geoscience, Penn State. “We did not then have the equipment to record the details of those events.” The outer rise is the region seaward of the deep-sea trench that marks the top of the plate boundary.

In late 2006 and early 2007, two large earthquakes occurred near Japan separated by about 60 days. These earthquakes took place in the area of the Kuril Islands that are located from the westernmost point of the Japanese Island of Hokkaido to the southern tip of the Kamchatka Peninsula. The first event took place on Nov. 15, 2006 when the edge of the Pacific plate thrust under the arc of the Kuril Islands, initiating a magnitude 8.3 event and causing some damage in Japan and a small tsunami that caused minor damage in Crescent City, California. About 60 days later, on Jan. 13, 2007, a magnitude 8.1 earthquake occurred in “the upper portion of the Pacific plate, producing one of the largest recorded shallow extensional earthquakes.”

This second earthquake was not at a plate boundary and was not directly caused by subduction – the moving of one plate beneath the other. Rather, it was a normal faulting event, where the Pacific plate stretched, bent and broke.

While Japan and the Kamchatka Peninsula are active earthquake areas, the region of the Kuril Islands where the large November earthquake occurred, had not had a large earthquake since 1915 and researchers are unsure of the exact nature of that event.

Working with Hiroo Kanamori, the John E. and Hazel S. Smits professor of geophysics, emeritus, California Institute of Technology, and Thorne Lay, professor of Earth & planetary sciences, University of California, Santa Cruz, the Penn State researcher looked at the sequence of seismic activity that link these two earthquakes into a doublet.

“Such large doublet earthquakes, though rare, could be an underestimated hazard,” says Ammon. “We are also interested in what these events tell us about how earthquakes interact, how the stresses and interactions allow one earthquake to trigger another.”

Looking at the seismic record, the researchers found a series of smaller, foreshock earthquakes beginning about 45 days before Nov. 15. On Nov. 15, there was the magnitude 8.3 earthquake on the plate boundary, the largest event of 2006.

“Within minutes of the Nov. 15 earthquake, seismic activity began on the Pacific plate in the area where the January earthquake would take place,” says Ammon. “This large second earthquake generated a larger amplitude of shaking in the frequency range that affects human-made structures than the first earthquake.”

Usually, aftershocks from a large earthquake are at least one order of magnitude less than the main event and taper off rapidly. In this case, the events within the Pacific plate east of the plate boundary did not taper off, and the second event that occurred in January was about the same size as the first earthquake.

Earthquakes at plate boundaries in subduction zones occur when the plate that is going under – being subducted – gets temporarily stuck and causes compression in the plate away from the edge. Tension builds and when the plate overcomes the friction holding it, it moves downward, slipping under the top plate and causing an earthquake. According to the researchers, the second earthquake that occurred on the Pacific plate happened because of bending experienced by the pacific plate that occurs before it subducts beneath the upper plate. As the front edge of the plate slipped, the plate east of the November earthquake bent, cracked and broke in January.

Like pie crust, when the Earth’s crust bends, small cracks begin to appear – these were the small shocks that began immediately after the first earthquake – but when the bending becomes severe, a larger region of the crust breaks – creating the second, very large event.

In the United States, subduction zones exist only in the Pacific Northwest, Alaska and the area around Puerto Rico. The researchers note, “Triggering of a large outer rise rupture with strong high-frequency shaking constitutes an important potential seismic hazard that needs to be considered in other regions.”

The National Science Foundation and the U.S. Geological Survey funded this research.

Deep-ocean researchers target tsunami zone near Japan

Rice University Earth scientist Dale Sawyer and colleagues last month reported the discovery of a strong variation in the tectonic stresses in a region of the Pacific Ocean notorious for generating devastating earthquakes and tsunamis in southeastern Japan.

The results came from an eight-week expedition by Sawyer and 15 scientists from six countries at the Nankai Trough, about 100 miles from Kobe, Japan. Using the new scientific drilling vessel “Chikyu,” the team drilled deep into a zone responsible for undersea earthquakes that have caused tsunamis and will likely cause more. They collected physical measurements and images using new rugged instruments designed to capture scientific data from deep within a well while it is being drilled.

The Nankai Trough is known as a subduction zone, because it marks the place where one tectonic plate slides beneath another. Tectonic plates are pieces of the Earth’s crust, and earthquakes often occur in regions like subduction zones where plates grate and rub against one another. For reasons scientists don’t yet understand, plates that should move smoothly relative to each other sometimes become locked. In spite of this, the plates continue moving and stress builds at the points where the plates are locked. The stored energy at these sites is eventually released as large earthquakes, which occur when the locked area breaks and the the plates move past one another very rapidly, creating a devastating tsunami like the one in Sumatra and the Indian Ocean three years ago.

“Earthquakes don’t nucleate just anywhere,” Sawyer said. “While the slip zone for quakes in this region may be hundreds of kilometers long and tens of kilometers deep, the initiation point of the big quakes is often just about five to six kilometers below the seafloor. We want to know why.”

Sawyer said scientists with the Integrated Ocean Drilling Program (IODP) plan to return to the Nankai Trough aboard the Chikyu each year through 2012, with the ultimate goal of drilling a six-kilometer-deep well to explore the region where the quakes originate. If they succeed, the well will be more than three times deeper than previous wells drilled by scientific drill ships, and it will provide the first direct evidence from this geological region where tsunami-causing quakes originate.

The drilling done by Sawyer and colleagues marked the beginning of this massive project, which IODP has dubbed the Nankai Trough Seismogenic Zone Experiment, or NanTroSEIZE. In addition to the objective of drilling across the plate boundary fault, NanTroSEIZE scientists also hope to sample the rocks and fluids inside the fault, and they want to place instruments inside the fault zone to monitor activity and conditions leading up to the next great earthquake.

“The Chikyu is a brand new ship — the largest science vessel ever constructed — and it uses state-of-the-art drilling technology,” Sawyer said.

The Chikyu is the first scientific drill ship to incorporate riser drilling technology. Pioneered by the oil industry, a riser system includes an outer casing that surrounds the drill pipe to provide return-circulation of drilling fluid to maintain balanced pressure within the borehole. The technology is necessary for drilling several thousand meters into the Earth.

IODP offers research opportunities to geoscientists and oceanographers in 21 member countries. It is an international scientific research program dedicated to advancing scientific understanding of the Earth by monitoring and sampling subseafloor environments. Using multiple ocean drilling platforms, IODP scientists explore the program’s principal themes: the deep biosphere, solid earth cycles and climate change.