Volume 6, Issue 40
Heads Up for Earthquakes
In addition to earthquakes, Richard Allen studies Earth's shifting interior to better understand mantle flow, volcanism and interactions between tectonic plates. Image credit: courtesy Richard Allen
Life in earthquake country has always been a gamble. At any time of year, any hour of the day, once-solid ground can roll and tremble like a stormy sea.
Unlike hurricanes or volcanic eruptions, earthquakes can't be forecast days or weeks in advance. The next best solution, says seismologist Richard Allen, is an earthquake early warning system. "If there was an earthquake now, we'd want to know how much it's going to shake here, and how much time we have," says Allen, a Berkeley professor of earth and planetary sciences.
Allen is in the process of implementing an earthquake early warning system in temblor-prone California. Called ElarmS, the system is designed to detect the imminent arrival of a strong earthquake and then warn a vulnerable public.
A collaboration among UC Berkeley, Caltech, the U.S. Geological Survey and the Southern California Earthquake Center, the ElarmS system operates much like a spider's silken web. An existing network of seismographs around the state continuously transmits earth movements to several central processing hubs. Just as a spider uses vibrations to judge the size and location of trapped insects, modeling programs at the centers use this ground shaking data to calculate how serious any tremor is likely to be. If the quake looks to be a whopper, the models will generate a map of the most serious shaking areas. Civil safety systems can then alert the public to the danger.
ElarmS accurately predicted the ground shaking in the October 30, 2007 magnitude 5.4 Alum Rock earthquake centered in San Jose. ElarmS generated data for this map a few seconds before the earthquake was felt in San Francisco. Image credit: Richard Allen
Because an earthquake travels along a fault like a train speeding down a track, it can take tens of seconds to minutes for shaking to reach urban centers. Those precious moments can be enough for people to shelter under a table, slow trains and buses, or switch heavy machinery into safe mode.
"The idea is to detect the beginnings, to try to establish how much ground shaking we expect, and issue a warning," Allen says.
Allen's own research speaks to the heart of ElarmS: what happens during the earliest stages of an earthquake. The current concept of an earthquake rupture is known as the cascade model. In this view, the faces of a fault are made up of discrete patches of different sizes. As stress builds up along the fault, one patch might rupture. At this point, the fault face behaves like a fruit pyramid at a grocery store. Pull out one orange, and the structure might shudder but remain intact. Remove a different orange, and it could trigger a mini-avalanche.
But in this model, earthquakes big and small begin the same way. The failure of a given patch might cause the fault to quiver-or trigger the chain reaction leading to a big earthquake. The cascade model can't explain this inconsistent behavior.
Seismic stations, such as this one operated by the Berkeley Seismological Lab in Hopland, take continuous readings of earthquake activity in California. ElarmS uses this data to predict areas of strong ground shaking in imminent earthquakes. Image credit: John Friday
Allen is developing a more accurate way to describe how earthquakes are born. Newer data suggests that when a patch of rock fails along a fault face, the slippage radiates energy in all directions like a bomb. "If you have a large amount of initial displacement, more energy is carried across the fault plane. That energy travels further and gives a larger magnitude earthquake," Allen says. Ultimately, the new model might improve future earthquake forecasting algorithms.
As is, ElarmS has already proved its mettle. On October 30, 2007, just 20 days after ElarmS went online for testing in Northern California, the magnitude 5.4 Alum Rock earthquake rippled across urban San Jose. ElarmS accurately estimated the magnitude and the extent of ground shaking for San Francisco two seconds before the temblor reached city limits. Being in test mode slowed the system's responses. If ElarmS had been running normally, the warning time would have been closer to ten seconds-long enough for most people to reach safer ground.
At present, the California Integrated Seismic Network, a collaboration of institutions including UC Berkeley, is testing three independently developed earthquake forecasting algorithms including ElarmS. Dry runs like the Alum Rock earthquake will allow seismologists to gauge the accuracy and time cushion each method can provide. "My guess is we'll find we don't want to just choose one. If two methods say it's a magnitude 7 earthquake, then we can be much more confident," Allen says. With a system like ElarmS on duty, residents of earthquake country can be more assured of their safety, too.
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A Better View of the Planets
What's the weather like on Jupiter? Berkeley professor of astronomy Imke de Pater knows. De Pater and her colleagues have tracked the planet's titanic and long-lasting storms, observed its icy ammonia clouds, and mapped the structure of its violent atmosphere. In other work, they've discovered methane drizzle on Saturn's moon Titan, modeled Jupiter's magnetic fields, and revealed the dynamic behavior of Neptune's skies.
De Pater uses a technique called adaptive optics that dramatically improves that sharpness of images taken from ground-based telescopes. This is Uranus as seen by the Keck telescope in two different wavelengths with (right) and without AO (left). Image credit: Heidi B. Hammel and Imke de Pater
A planetary scientist, de Pater studies the climate, composition, rings, and physical forces at play on and around Earth's nearest neighbors. She uses a combination of traditional optical, infrared, and radio telescopes, combining and layering the data from each in innovative ways to lift the veil between us and these neighboring worlds.
Most astronomers use ground-based telescopes to study the skies. But the drawback of viewing the cosmos from Earth is the turbulence in our atmosphere. True to her innovative style, de Pater has been pushing the limits of a newer technique known as adaptive optics (AO) to improve the quality of ground-based observations.
The method uses a reference light source near the target, such as a laser beam or adjacent moon, or in some cases the object of interest itself to quantify the degree of atmospheric turbulence, and correct the data online with help of a deformable mirror. The result: a crisp and astonishingly detailed picture.
De Pater and colleagues have discovered a new, blue ring around the planet Uranus. The outermost rings of both Saturn (above) and Uranus (below) are blue rather than red because they are composed of tiny, dust-sized particles. Both planets are depicted with the same diameter. Image credit: Showalter, de Pater, Hammel
With AO, says de Pater, "we start to really see things that in the past you could only see from spacecraft, but now you can see from the ground." De Pater's images of Uranus are a stunning example of how well the method works. "If you look through a conventional telescope, you can just barely see the rings around Uranus, and you certainly don't see atmospheric details," de Pater says. By contrast, the details in her AO images of the planet rival the shots sent back by the Voyager spacecraft during its 1986 Uranus flyby. de De Pater's AO images have helped prove that the planet's newly-discovered outermost ring is blue rather than red, indicating its particles must be no larger than dust motes.
Only one other blue ring, Saturn's E ring, is known to exist. The two blue circlets have much in common. Saturn's moon Enceladus is located in the midst of the E ring; icy plumes erupting from its surface probably supply the ring's fine particles. Uranus's blue ring harbors a moon as well, a tiny world called Mab. But Mab is rocky and dead, suggesting that meteorite impacts on the moon are a more likely dust source.
During a study of Jupiter's moon Io, a team led by Imke de Pater and Franck Marchis observed a large eruption originating near the volcano Surt in February of 2001. Credit: Franck Marchis
But many other questions about the ring remain unanswered. "Why not a range of particle sizes, including bigger ones? Is there a reason why only small grains appear to "survive"? The answers all come down to the dynamics of meteorite impacts on moons," says de Pater, and the physical processes that play a role within the rings themselves.
To that end, de Pater is using her images to construct the most detailed model of the planet's rings to date. Scientists will use the model to study how Uranus's rings were formed and are maintained.
De Pater studies Jupiter's dynamic weather systems by comparing images taken at different wavelengths with different instruments. This false-color composite near-infrared image of Jupiter, taken with the Hubble Space telescope, shows the Great Red Spot (a storm about twice the diameter of Earth) and two smaller storms (each about the diameter of Earth) which were eventually swallowed by the Great Red Spot. Image credit: Wong and de Pater
Ultimately, says de Pater, "Rings offer a laboratory for planetary formation. If you have a star with a disk around it, we know planets will form in those disks. If you look at planetary rings, you can see these processes up close."
De Pater has also been using AO to observe Jupiter's moon Io. The moon is riddled with active volcanoes that appear on infrared images as bright hotspots. These look particularly spectacular when Io is in Jupiter's shadow. "Every time we look at Io through a telescope, it looks different," de Pater says. By observing Io using a combination of infrared and radio telescopes, she has been able to identify different gases in Io's atmosphere. She is now working on mapping the distributions of these gases to identify their sources, and by extension learn more about Io's volcanoes and the moon itself. Larger radio telescopes such as CARMA in California and, in the future, ALMA in Chile promise to give de Pater an even better view. "These arrays have become so large that we now have the power to resolve planets and satellites which appear as mere specks of light on the sky." Those who watch the weather should stay tuned.
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Sniffing Out Smog
Atmospheric chemist Ron Cohen studies air quality in places ranging from UC's Sagehen Creek Reserve to the Canadian tundra. Image credit: Michael Barnes.
If smog were a kitchen creation, the recipe would go something like this: Start with a miasma of organic hydrocarbons from spilled gasoline, incomplete combustion and trees. Add nitrogen oxides from combustion in factory furnaces and vehicle engines. Zap with a dose of sunlight, and wait. The result: a heaping serving of photochemical smog.
Made up of components such as nitric acid and ozone gas, smog is nasty stuff. Nitric acid is a component of acid rain, while ozone kills human lung cells and contributes to global warming.
Atmospheric chemist Ron Cohen studies how these pollutants form, tracks where and how far they travel, and how they get removed from the atmosphere. He then uses this knowledge to understand air quality and the interactions of pollutants with climate. A Berkeley professor of chemistry and earth and planetary sciences, his work provides the factual underpinnings for climate and air pollution models that, ultimately, help keep us all breathing more easily.
Cohen's studies in the Sierra Nevada proved that smog forms twice as fast as previously thought. The effect makes daytime air cleaner within Sacramento than around foothill forests. Image credit: courtesy Ron Cohen
"Most of my work is figuring out how to make observations that test parts of these models; I ground truth them," Cohen says. "The goal is to provide the underlying science for the people who have to make social and policy judgments."
Cohen tracks air pollution from its molecular origins through its metamorphosis into ugly yellow smog. To do this, he designs and builds instruments capable of measuring minute amounts of the chemicals that contribute to air pollution. Armed with these super sniffers, he can track exactly how fast smog forms and how much of it is in the environment.
"We try to understand how these molecules get into the atmosphere, what their chemistry is, and what they're doing to climate," Cohen says.
Cohen's smog-sniffing instruments are mounted high above UC's Blodgett Forest Research Station.
For the past decade, Cohen has deployed these instruments to study smog formation in the Sacramento Valley. Air patterns there are as regular as the tides. During the day, winds sweep nitrogen oxides belched out by trucks and businesses up into the Sierra Nevada. At night, the cooling air tumbles back into the valley again.
"We can see how factors such as temperature or decreases in emissions on weekends affect the chemistry because everything else holds more or less constant. It lets us tease apart how the chemistry works much better than we've been able to do anywhere else," he says.
Cohen placed his instruments around Sacramento, in the Sierra foothills and just west of Lake Tahoe. Each step of the way, he measured the relative concentrations of smog components. By combining this data with wind speed and temperature information, Cohen could measure precisely how fast these reactions were occurring.
Weekday versus weekend air quality in the Bay Area. Weekend air is much cleaner because fewer big rigs are on the road. Image credits: SCIAMACHY instrument, courtesy Tim Bertram and Andreas Richter
In the foothills, Cohen found double the nitric acid he expected, indicating the photochemical reactions that produce smog run twice as fast as previously thought. And by the time the air masses near Lake Tahoe, most of the nitric acid has already disappeared. That means ozone levels in hamlets like Auburn and Kyburz can be far worse than at the state capitol. And air pollution from Sacramento isn't fouling the lake; the nitric acid entering its limpid waters comes from local traffic instead. From a broader perspective, his results help link regional air quality to larger climate trends.
One big question mark that remains in the models is how much ozone comes from natural sources like lightning. Cohen seeks to quantify this natural background by testing the air over some of the world's most remote places. He sets up the sampling instruments inside a specially outfitted NASA DC-8, straps himself into the extra comfy seats, and settles in for up to 12 hours of cruising across places such as the Canadian tundra and the unbroken waves between Hawaii and Alaska.
"Even there we see quite a strong signature of emissions from Asia. There's no place, at least in the Northern Hemisphere, where you can escape," Cohen says.
Cohen loads his custom-built smog detecting instruments into a NASA DC-8 to study air quality over pristine environments. Here, the plane is at Diamond Head, Hawaii, for a sampling mission over the Pacific Ocean. Image credit: Scott Sandholm
Despite these trace plumes of pollution, nitrogen oxide levels past Midway Island are so low that they don't inhibit natural ozone removal processes. Cohen is trying to identify the threshold concentrations where that shift back to ozone production starts to occur. If nitrogen oxide levels over the Central Pacific are already near that threshold, then lowering pollution a smidgen more might make a tremendous difference in air quality and maybe even global warming.
"As a society, we're in an amazing spot," Cohen says. "We have a pending catastrophe-climate change- that we can do something about if we use science wisely. And as a scientist, there's an incredible wealth of fun, interesting questions to work on while trying to help the social system address the question."
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