Researchers say Arctic sea ice still at risk despite cold winter

 Still from animation showing ice loss. Credit: NASA
Still from animation showing ice loss. Credit: NASA

Using the latest satellite observations, NASA researchers and others report that the Arctic is still on “thin ice” when it comes to the condition of sea ice cover in the region. A colder-than-average winter in some regions of the Arctic this year has yielded an increase in the area of new sea ice, while the older sea ice that lasts for several years has continued to decline.

On March 18 the scientists said they believe that the increased area of sea ice this winter is due to recent weather conditions, while the decline in perennial ice reflects the longer-term warming climate trend and is a result of increased melting during summer and greater movement of the older ice out of the Arctic.

Perennial sea ice is the long-lived, year-round layer of ice that remains even when the surrounding short-lived seasonal sea ice melts away in summer to its minimum extent. It is this perennial sea ice, left over from the summer melt period, that has been rapidly declining from year to year, and that has gained the attention and research focus of scientists. According to NASA-processed microwave data, whereas perennial ice used to cover 50-60 percent of the Arctic, this year it covers less than 30 percent. Very old ice that remains in the Arctic for at least six years comprised over 20 percent of the Arctic area in the mid to late 1980s, but this winter it decreased to just six percent.

According to Walt Meier of the National Snow and Ice Data Center at the University of Colorado, Boulder, as ice ages it continues to grow and thicken, so that older ice is generally also thicker ice. This winter the ice cover is much thinner overall and thus in a more vulnerable state heading into the summer melt season. NASA’s ICESat satellite has contributed to understanding of the changes in ice thickness. To get a better understanding of the behavior of sea ice, NASA is planning a follow-on satellite mission, ICESat II, to launch in 2015.

Arctic sea ice grows and declines seasonally, ranging from an average minimum extent in September of 2.5 million square miles to an average winter maximum extent of 5.9 million square miles in March. This March, instruments on NASA’s Aqua satellite and NOAA and U.S. Defense Department satellites showed the maximum sea ice extent slightly increased by 3.9 percent over that of the previous three years, but it is still below the long-term average by 2.2 percent. Increases in ice extent occurred in areas where surface temperatures were colder than the historical averages. At the same time, as a result of the export of ice from the Arctic, the area of perennial ice decreased to an all-time minimum.

Joey Comiso of NASA’s Goddard Space Flight Center in Greenbelt, Md., the lead author of a 2007 related study, used data from NASA’s passive microwave data set to establish that the perennial ice cover at the summer Arctic ice minimum in 2007 was about 40 percent less than the 28-year average. According to the latest observations from the National Snow and Ice Data Center (an organization partially funded by NASA), perennial sea ice dropped from about 40 percent of the total ice pack last year to 30 percent of total ice this winter. The perennial ice is also growing younger, meaning that it is thinner and will be more vulnerable during the summer melt period.

In light of the Arctic’s cold spell this winter, NASA satellites and scientists will continue to carefully watch conditions in the Arctic Ocean as summer settles in to better determine the extent of the perennial sea ice.

Prestigious science prize awarded for 800,000 year old ice core

Shallow ice core drilling at Dome C. The core will be used to study the climate fo the last 2000 years.
Shallow ice core drilling at Dome C. The core will be used to study the climate fo the last 2000 years.

Ice core scientists from the British Antarctic Survey (BAS) are joint winners of a major European science prize. The European Project for Ice Coring in Antarctica (EPICA) – which retrieved two deep ice cores that have revealed how Earth’s climate behaved over the last 800,000 years – is one of three projects to be awarded the 2007 Descartes Prize for excellence in collaborative research. Three winning trans-national research teams share this year’s Descartes Prize of 1.36 million Euros. The prize is awarded annually to teams which have achieved outstanding scientific or technological results through collaborative research in any field of science.

The EPICA project brought together scientists and engineers from 10 European countries in a 10-year effort in one of the most hostile research environments on Earth. They drilled ice cores right through the Antarctic ice sheet at two locations, reaching bedrock at over 3200 metres depth in one case. The records of climate and atmospheric composition preserved in the ice have provided unique information about how climate works.

The research team has published its findings in nearly 200 peer-reviewed scientific papers, including several in the leading journals Nature and Science. Their data are widely quoted in many influential publications including the recent Intergovernmental Panel on Climate Change (IPCC) report.

Dr. Eric Wolff from the British Antarctic Survey, and the chair of the EPICA science group said:

“EPICA is an example of a successful European cooperation that made ground-breaking discoveries that could not have been achieved by working separately. The ice core research has shown us how our climate works, and therefore helps us to predict how it will work in the future. It is an honour for all of us to have this effort recognised by the Descartes Prize.”

The Prize will be awarded at a The European Science Awards 2007, Celebrating Excellence in European Research, in Brussels on Wednesday 12th March.

Seismologists set up telemetry system in wake of Wells earthquake

University researchers from the Nevada Seismological Laboratory, with the help of Wells Electric Company Snowcats and in cooperation with the U.S. Geological Survey, set up a telemetry system near Wells, Nev., in the wake of that rural Nevada community's magnitude 6.0 earthquake last month. Photo by Ken Smith.
University researchers from the Nevada Seismological Laboratory, with the help of Wells Electric Company Snowcats and in cooperation with the U.S. Geological Survey, set up a telemetry system near Wells, Nev., in the wake of that rural Nevada community’s magnitude 6.0 earthquake last month. Photo by Ken Smith.

Even now, several days after traveling to Wells, Nev., to set up a telemetry network to gain a better understanding of the magnitude 6.0 earthquake that rocked the rural Nevada community last month, Nathan Edwards shakes his head with a sense of amazement.

Just a few years ago, before any of the current technology was available, such an undertaking would’ve been impossible.

Wells, a community of about 1,600 residents, is located in a remote area of Nevada, about 60 miles west of the Utah state line. Damage to Wells, estimated at close to $1 million, included the ruin of several buildings in the town’s historic district.

“It was very difficult,” Edwards, a development technician II in the University’s Nevada Seismological Laboratory, said. “Most of the stations were about at 6,000 feet or so, so there was snow everywhere … we needed Snowcats just to get there.”

Although the process was difficult, the results have been notable.

Scientists and technicians from the Nevada Seismological Laboratory, working with representatives from the United States Geological Survey in Golden, Colo., and the University of Utah in Salt Lake City, Utah, began setting up a telemetry system within days of the Feb. 21 earthquake.

It was up and running by Tuesday, Feb. 26, and has been supplying scientists with data on the quake – the strongest in Nevada in 14 years – in real time ever since.

“We hadn’t had an event like this in a long time,” said Ken Smith, associate research professor and manager of the Nevada Seismological Laboratory’s seismic network. “In fact, we had never installed a wireless network on short order like this before. It’s been probably about 10 years since we had a similar earthquake response. Now we’re in an IP environment, plus we have cell phones and mobile internet devices – we didn’t have those things 10 years ago.

As Smith said, it took the collective effort of many different agencies and organizations to make the system a reality, and many thanks to the community of Wells.

The path of the data from the eight monitoring stations located a few miles northeast of Wells requires good knowledge of Nevada geography. Smith said that 8 of the 20 stations have telemetry, which can deliver information in real time via remote IP radios that communicate through DOIT’s microwave network. The University of Utah subsequently installed analog telemetry to four more among the 20 total.

To do this, though, the data is transmitted from radios at remote sites to a link at the State Microwave system at Turner Station near Wells, to the State’s Angel Peak site outside of Las Vegas, then to UNLV, where the data, as Smith puts it, “jumps on the University network. The way the network is configured it’s literally on the Seismology Lab’s private network, giving us better control of the instrumentation.”

Similar approaches have been used in the wake of volcanic eruptions, Smith said, but this could be one of the first times that such a comprehensive IP network has been deployed in the wake of a significant earthquake in the United States.

“Eight real-time stations right on top of the earthquake sequence up and running within a week is pretty unique,” he said. “It’s surely never been done before in Nevada. It’s the model for how we want to respond to future significant earthquakes in the State.”

Adds John Torrisi, an associate engineer at the Nevada Seismological Laboratory who helped get the system running: “We’ve set out portable deployments over the years, but this is my first time doing a telemetered array. Just coordinating this effort with all the different people out there has been one of the really unique aspects of this.”

Smith says that in addition to the cooperating research entities, help from an amalgam of concerned groups, including the Elko County Sheriff’s Department, Wells Rural Electric, the Division of Information Technology (DOIT) and the Division of Emergency Management for the State of Nevada, helped make the undertaking a success.

“They all played important roles in this,” Smith said. He pauses and gestures, holding his hands several feet apart. “We had snow this deep out there. If we didn’t have Snowcats, we never could have gotten out there … the DOIT guys went down to Angel Peak outside of Las Vegas and completed the circuit (the signal from Wells) for us. We really appreciate their help.

“All of the people in Wells have been so concerned about the earthquake, and they want to have as much information about it as they possibly can.”

Good data, recording the hundreds of aftershocks that have continued since the quake, have been pouring in since the system went live.

“Our job now is to try to isolate the geometry of the fault underground,” said Smith, explaining that the earthquake occurred on what is called a “normal fault.” A “normal fault” features a process where one side of a fault drops down relative to other.

“This was a normal fault, and there is a lot of interest in normal faults,” Smith added. “There’s not been a normal faulting event that has been as well recorded at this one. We can use this data to estimate what the effects of a magnitude 6.0 earthquake will be in other parts of the State”.

“The important thing is, we got out there quickly, we got the telemetry system up, and now we’re sharing the ‘live’ data with the rest of the country.”

Glacier Melt Impact on Sea-Level is Underestimated

Global sea level has been climbing steadily over the past 80 years-and the contribution from melting ice has been more substantial than previously estimated, according to new research in Science Express.

The missing factor in earlier calculations: how much of the Earth’s water is impounded in artificial reservoirs, say Benjamin Chao and colleagues at National Central University in Chung-Li, Taiwan.

The total rise in sea level over the past century is due mostly to ocean water expanding in volume as it warms up, and ice melt from mountain glaciers and Greenland and Antarctic ice sheets. Subtracting the effect of thermal expansion from the observed rate of sea level rise should give a reasonable estimate of the rate of ice melting, the researchers say, but the equation leaves out the amount of water locked up in reservoirs.

They estimate that trapping the reservoir waters has artificially dropped sea levels by 30 millimeters over the past half-century. Add that water back in, they say, and the contribution of ice melt must be higher than previously thought.

The paper was published in the 13 March issue of Science Express (“Impact of Artificial Reservoir Water Impoundment on Global Sea Level”). The Web site provides electronic publication of selected Science papers in advance of print; some editorial changes may occur between the online version and the final printed version.

10 questions shaping 21st-century earth science identified

Ten questions driving the geological and planetary sciences were identified today in a new report by the National Research Council. Aimed at reflecting the major scientific issues facing earth science at the start of the 21st century, the questions represent where the field stands, how it arrived at this point, and where it may be headed.

“With all the advancements over the last 20 years, we can now get a better picture of Earth by looking at it from micro- to macro-perspectives, such as discerning individual atoms in minerals or watching continents drift and mountains grow,” said Donald J. DePaolo, professor of geochemistry at the University of California at Berkeley and chair of the committee that wrote the report. “To keep the field moving forward, we have to look to the past and ask deeper fundamental questions, about the origins of the Earth and life, the structure and dynamics of planets, and the connections between life and climate, for example.”

The report was requested by the U.S. Department of Energy, National Science Foundation, U.S. Geological Survey, and NASA. The committee selected the question topics, without regard to agency-specific issues, and covered a variety of spatial scales — subatomic to planetary — and temporal scales — from the past to the present and beyond.

The committee canvassed the geological community and deliberated at length to arrive at 10 questions. Some of the questions present challenges that scientists may not understand for decades, if ever, while others are more tractable, and significant progress could be made in a matter of years, the report says. The committee did not prioritize the 10 questions — listed with associated illustrative issues below — nor did it recommend specific measures for implementing them.


While scientists generally agree that this solar system’s sun and planets came from the same nebular cloud, they do not know enough about how Earth obtained its chemical composition to understand its evolution or why the other planets are different from one other. Although credible models of planet formation now exist, further measurements of solar system bodies and extrasolar objects could offer insight to the origin of Earth and the solar system.


Scientists believe that another planet collided with Earth during the latter stages of its formation, creating debris that became the moon and causing Earth to melt down to its core. This period is critical to understanding planetary evolution, especially how the Earth developed its atmosphere and oceans, but scientists have little information because few rocks from this age are preserved.


The origin of life is one of the most intriguing, difficult, and enduring questions in science. The only remaining evidence of where, when, and in what form life first appeared springs from geological investigations of rocks and minerals. To help answer the question, scientists are also turning toward Mars, where the sedimentary record of early planetary history predates the oldest Earth rocks, and other star systems with planets.


Scientists know that the mantle and core are in constant convective motion. Core convection produces Earth’s magnetic field, which may influence surface conditions, and mantle convection causes volcanism, seafloor generation, and mountain building. However, scientists can neither precisely describe these motions, nor calculate how they were different in the past, hindering scientific understanding of the past and prediction of Earth’s future surface environment.


Although plate tectonic theory is well established, scientists wonder why Earth has plate tectonics and how closely it is related to other aspects of Earth, such as the abundance of water and the existence of the continents, oceans, and life. Moreover, scientists still do not know when continents first formed, how they remained preserved for billions of years, or how they are likely to evolve in the future. These are especially important questions as weathering of the continental crust plays a role in regulating Earth’s climate.


Scientists now recognize that macroscale behaviors, such as plate tectonics and mantle convection, arise from the microscale properties of Earth materials, including the smallest details of their atomic structures. Understanding materials at this microscale is essential to comprehending Earth’s history and making reasonable predictions about how planetary processes may change in the future.


Earth’s surface temperature has remained within a relatively narrow range for most of the last 4 billion years, but how does it stay well-regulated in the long run, even though it can change so abruptly” Study of Earth’s climate extremes through history — when climate was extremely cold or hot or changed quickly — may lead to improved climate models that could enable scientists to predict the magnitude and consequences of climate change.


The exact ways in which geology and biology influence each other are still elusive. Scientists are interested in life’s role in oxygenating the atmosphere and reshaping the surface through weathering and erosion. They also seek to understand how geological events caused mass extinctions and influenced the course of evolution.


Progress has been made in estimating the probability of future earthquakes, but scientists may never be able to predict the exact time and place an earthquake will strike. Nevertheless, they continue to decipher how fault ruptures start and stop and how much shaking can be expected near large earthquakes. For volcanic eruptions, geologists are moving toward predictive capabilities, but face the challenge of developing a clear picture of the movement of magma, from its sources in the upper mantle, through Earth’s crust, to the surface where it erupts.


Good management of natural resources and the environment requires knowledge of the behavior of fluids, both below ground and at the surface, and scientists ultimately want to produce mathematical models that can predict the performance of these natural systems. Yet, it remains difficult to determine how subsurface fluids are distributed in heterogeneous rock and soil formations, how fast they flow, how effectively they transport dissolved and suspended materials, and how they are affected by chemical and thermal exchange with the host formations.

Are existing large-scale simulations of water dynamics wrong?

Researchers find that a much smaller spatial resolution should be used for modeling soil water

Soils are complicated porous media that are highly relevant for the sustainable use of water resources. Not only the essential basis for agriculture, soils also act as a filter for clean drinking water, and, depending on soil properties, they dampen or intensify surface runoff and thus susceptibility to floods. Moreover, the interaction of soil water with the atmosphere and the related energy flux is an important part of modern weather and climate models.

An accurate modeling of soil water dynamics thus has been an important research challenge for decades, but the prediction of water movement, especially at large spatial scales, is complicated by the heterogeneity of soils and the sometimes complicated topography.

Simulation models are typically based on Richards’ equation, a nonlinear partial differential equation, which can be solved using numerical solution methods. A prerequisite of most solution algorithms is the partitioning of the simulated region into discrete grid cells. For any fixed region, such as a soil profile, a hill slope, or an entire watershed, the grid resolution is usually limited by the available computer power. But how does this grid resolution affect the quality of the solution?

This problem was explored by Hans-Joerg Vogel from the UFZ – Helmholtz Center of Environmental Research in Leipzig, Germany and Olaf Ippisch from the Institute for Parallel and Distributed Systems of the University of Stuttgart, Germany. The results are published in the article “Estimation of a Critical Spatial Discretization Limit for Solving Richards’ Equation at Large Scales,” Vadose Zone J. Vol. 7, p. 112-114, in the February 2008 issue of Vadose Zone Journal.

Vogel and Ippisch found that the critical limit for the spatial resolution can be estimated based on more easily available soil properties: the soil water retention characteristic. Most importantly, this limit came out to be on the order of decimeters for loamy soils, and is even lower, on the order of millimeters, for sandy soils. This is much smaller than the resolution used in many practical applications.

This study implies that large-scale simulations of water dynamics in soil may be imprecise to completely wrong. But, it also opens new options for a specific refinement of simulation techniques using locally adaptive grids. The derived critical limit could serve as an indicator that shows where a refinement is necessary. These findings should be transferable to applications such as the simulation of oil reservoirs or models for soil remediation techniques.

The full article is available for no charge for 30 days following the date of this summary. View the abstract at:

Mediterranean ‘due a tsunami’ research suggests

Calculation of the sea wave (tsunami) caused by the AD 365 earthquake at 30 minutes after the earthquake. Red and blue shades correspond to peaks and troughs of about 50 cm.
Calculation of the sea wave (tsunami) caused by the AD 365 earthquake at 30 minutes after the earthquake. Red and blue shades correspond to peaks and troughs of about 50 cm.

Studying an ancient earthquake has enabled Oxford University researchers to quantify the likelihood of a tsunami in the Eastern Mediterranean.

They estimate that a ring of faults around the south of Greece and the Aegean Sea generates tsunami earthquakes approximately once every 800 years and, because the last such earthquake took place in 1303, the probability of a tsunami affecting the region is much higher than had been thought.

The Oxford researchers – working with colleagues from the Universities of Cambridge, Nice and Imperial College London – identified the cause of an earthquake that generated a tsunami that destroyed Alexandria on 21 July AD 365. Reporting in Nature Geoscience, the group describe how they tracked down the origin of this ancient quake to a fault beneath western Crete. Very precise radiocarbon dates of uplifted shorelines show that western Crete was lifted by about ten metres within a few decades of AD 365, and the shape of the uplifted shorelines is diagnostic of distortion of the land surface by an earthquake.

The researchers then used GPS stations to take very precise measurements of how the Earth’s surface is being slowly compressed all around the southern Aegean Sea today. From these measurements they predict that the energy being built up will be released in tsunami-earthquakes somewhere along this fault approximately every 800 years.

Professor Philip England, Head of Oxford’s Department of Earth Sciences and a co-author of the paper, said: ‘The AD 365 event is important because it is the only earthquake in the Mediterranean where the evidence can be studied on land, rather than being hidden under the ocean. It was one of the most devastating events in the ancient world: destroying cities and drowning thousands of people in coastal regions from the Nile Delta to modern day Dubrovnik.’

Calculations suggest that, as it crossed the open ocean, the wave height of the AD 365 tsunami was similar to that of the 2004 Sumatra tsunami – around one metre high. This leads the researchers to believe that, when it hit the shore, this sea wave would have been highly destructive.

‘This is our first real stab at quantifying the risk of a tsunami event in the Eastern Mediterranean,’ said Professor England. ‘What we can say for sure is that if the AD 365 earthquake were to be repeated it would have a devastating impact on the Mediterranean region.’

This work was supported by the UK’s Natural Environment Research Council (NERC) and by Oxford University.

Researchers confirm discovery of Earth’s inner, innermost core

3D illustrations of the Earth's inner core structure and the texturing of its iron crystals. The transparent outer surface is the inner core boundary (at radius 1220 km). The opaque inner sphere is the inner inner core (slightly less than half of the inner core radius) found in this study. The sticks represent the alignments of iron crystals in the outer part of the inner core. The longer the stick is, the higher the degree of alignment is and the stronger the seismic anisotropy is. The fast direction is parallel to the spin axis. The illustration A is a 3D view. The illustrations B, C, and D are cut-away views along the longitudes as labeled. The labels NP and SP stands for the North Pole and the South Pole, respectively. The anisotropy at the top 100 km is weak. The anisotropy at greater depth is stronger in the western part than in the eastern part. The form of anisotropy in the inner inner core is different from that in the outer part.
3D illustrations of the Earth’s inner core structure and the texturing of its iron crystals. The transparent outer surface is the inner core boundary (at radius 1220 km). The opaque inner sphere is the inner inner core (slightly less than half of the inner core radius) found in this study. The sticks represent the alignments of iron crystals in the outer part of the inner core. The longer the stick is, the higher the degree of alignment is and the stronger the seismic anisotropy is. The fast direction is parallel to the spin axis. The illustration A is a 3D view. The illustrations B, C, and D are cut-away views along the longitudes as labeled. The labels NP and SP stands for the North Pole and the South Pole, respectively. The anisotropy at the top 100 km is weak. The anisotropy at greater depth is stronger in the western part than in the eastern part. The form of anisotropy in the inner inner core is different from that in the outer part.

Geologists at the University of Illinois have confirmed the discovery of Earth’s inner, innermost core, and have created a three-dimensional model that describes the seismic anisotropy and texturing of iron crystals within the inner core.

“For many years, we have been like blind men touching different parts of an elephant,” said U. of I. geologist Xiaodong Song. “Now, for the fist time, we have a sense of the entire elephant, and see what the inner core of Earth really looks like.”

Using both newly acquired data and legacy data collected around the world, Song and postdoctoral research associate Xinlei Sun painstakingly probed the shape of Earth’s core. The researchers report their findings in a paper accepted for publication in the journal Earth and Planetary Science Letters, and posted on its Web site.

Composed mainly of iron, Earth’s core consists of a solid inner core about 2,400 kilometers in diameter and a fluid outer core about 7,000 kilometers in diameter. The inner core plays an important role in the geodynamo that generates Earth’s magnetic field.

The solid inner core is elastically anisotropic; that is, seismic waves have different speeds along different directions. The anisotropy has been found to change with hemisphere and with radius. In the latest work, Sun and Song describe another anomaly – a global structure – found within the inner core.

“To constrain the shape of the inner core anisotropy, we needed a uniform distribution of seismic waves traveling in all directions through the core,” Sun said. “Since the seismic waves we studied were generated by earthquakes, one challenge was acquiring enough seismic waves recorded at enough stations.”

In their analysis, Sun and Song used a three-dimensional tomography technique to invert the anisotropy of the inner core. They parameterized the anisotropy of the inner core in both radial and longitudinal directions. The researchers then used a three-dimensional ray tracing method to trace and retrace the seismic waves through the inner core iteratively.

What they found was a distinct change in the inner core anisotropy, clearly marking the presence of an inner inner core with a diameter of about 1,180 kilometers, slightly less than half the diameter of the inner core.

The layering of the core is interpreted as different texturing, or crystalline phase, of iron in the inner core, the researchers say.

“Our results suggest the outer inner core is composed of iron crystals of a single phase with different degrees of preferred alignment along Earth’s spin axis,” Sun said. “The inner inner core may be composed of a different phase of crystalline iron or have a different pattern of alignment.”

Although the anisotropy of the inner core was proposed 20 years ago, “this is the first time we have been able to piece everything together to create a three-dimensional view,” Song said. “This view should help us better understand the character, mineral properties and evolution of Earth’s inner core.”

The work was funded by the National Science Foundation.

Researchers find a new mineral

Mineralogists from the CAS Guangzhou Institute of Geochemistry (GIG) recently discovered Xieite, a chromium-iron oxide in its natural state. It has been authorized as a new mineral by Commission on New Minerals Nomenclature and Classification under the International Mineralogical Association (CNMNC-IMA).

In addition to diamond, according to experts, it is the 10th ultra-high pressure (UHP) mineral recognized in the world so far. The other nine UHP minerals include oesite, stishovite, seifertite, ringwoodite, wadsleyite, majorite, akimotoite, lingunite and tuite.

The diamond-like super-crystalline mineral was first recovered from an aerolite fallen in Suizhou city of central China’s Hubei Province. Although it is from the space, explain researchers, this new discovery is of significance for understanding the deep underground of the Earth, especially the composition and structure of the mantle material 500 kilometers below the Earth surface.

The new finding is named after XIE Xiande, a GIG mineralogist of world renown who has made major contribution to the field of mineral shock effects, says CHEN Ming, one of the discoverers of the new mineral and director of the GIG Laboratory of Extreme Condition Geology and Geochemistry. Prof. Xie was elected as the IMA chairman and a foreign academician in Russian Academy of Sciences in 1990 and1994, respectively.

This is not a drill: The earth actually is moving beneath western Washington

While the annual Sound Shake exercise on Wednesday produced a simulated magnitude 6.7 earthquake on the Seattle fault, a real though unfelt seismic event is taking place beneath western Washington.

Earlier in the week, seismographs in the southern Hood Canal area began recording bursts of low-level shaking associated with what is called an episodic tremor-and-slip event. If this episode behaves true to form, the tremor will move north beneath the Olympic Mountains and across to Vancouver Island during the next two to three weeks.

This the fifth so-called slow-slip event to be recorded since the phenomenon was discovered in 2002, and it will be the most closely studied such event so far. University of Washington scientists and students are hurrying to deploy a special set of instruments, 100 temporary seismographs set in a close formation in the Olympic mountains, to record the current episode. The temporary stations will augment readings from the permanent seismograph network that covers all of Washington and Oregon.

“We hope to record unprecedented detail as the tremor moves beneath the seismometer array,” said John Vidale, a UW professor of Earth and space sciences and director of the Pacific Northwest Seismic Network.

Slow-slip events, or silent earthquakes, occur at a depth of about 25 miles and can last for several weeks. Though they are unfelt by humans, they can release as much energy as a large earthquake.

Since they were first discovered in the Puget Sound region, such events have occurred regularly about every 14 months. The current slow-slip event was expected to start between mid-February and mid-April, and the first evidence that it had begun turned up on Sunday.

It is expected that as the tremor runs its course, GPS stations in western Washington will move ever so slightly — about one-tenth of an inch — to the southwest. Then they will resume their normal slow march to the northeast at a rate of about a half-inch per year as the North American plate that lies under much of the Pacific Northwest is compressed by the Juan de Fuca plate where the two meet just off the Pacific coast.

Scientists have found that the fairly continuous tremor associated with slow-slip episodes is very difficult to locate precisely using standard techniques, so they hope special processing and the use of the temporary seismic arrays will help to pinpoint the exact location and source of the tremor, as well as its relationship to earthquake faults.

Future such studies could help to determine when the region might experience major earthquakes, and provide an understanding of just how large such quakes will be, Vidale said.

Details of the current work, along with scientific commentary, can be found at