UC Berkeley’s Roland Burgmann is describing two large earthquakes that occurred in April of this year, in the Indian Ocean, off the coast of Sumatra. While the two ‘quakes caused little damage, the first, measuring magnitude 8.7, was the largest strike-slip temblor ever recorded, and the events seem to be triggering much more than shaking.

Three papers this week in Nature analyze the before, during, and after of the two earthquakes, and all three seem to arrive at the same conclusion: the Indo-Australian tectonic plate is breaking into two separate plates.

If you’ve visited the Academy’s Earthquake exhibit and planetarium show (and you can now do so virtually, through an iTunes course), you know that earthquakes result when continents break apart and plates grind against each other. Scientists say that’s exactly what is happening in this Indo-Australian region right now. Not surprisingly, very slowly.

Thorne Lay, of UC Santa Cruz and co-author on one of the Nature papers, says that the process of forming a new plate boundary will take millions of years and is likely to require hundreds if not thousands of earthquakes like the larger one in April. “This was a huge earthquake, but it’s going to happen again and again to make a through-going fracture that separates the plates.”

Lay and his colleagues’ paper analyzes what happened during the 8.7 quake. It appears that it ruptured over a complex network of at least four faults lying at right angles to one another. According to Lay, the energy released on each fault individually was about magnitude 8, adding up to a total event magnitude of 8.7 (a revised estimate higher than the 8.6 value initially reported). The initial shock was followed two hours later by a magnitude 8.2 aftershock on yet another fault to the south.

The paper by Burgmann and his colleagues from the USGS in Menlo Park, takes it from there. The study shows that these two quakes triggered other, distant earthquakes hours and days later. In fact, the seismologists’ analysis found five times the expected number of quakes during the six days following the April 11 quake and aftershock!

“We found a lot of big events around the world, including a 7.0 quake in Baja California and quakes in Indonesia and Japan, that created significant local shaking,” Burgmann says. “If those quakes had been in an urban area, it could potentially have been disastrous.

“Until now, we seismologists have always said, ‘Don’t worry about distant earthquakes triggering local quakes.’ This study now says that, while it is very rare—it may only happen every few decades—it is a real possibility if the right kind of earthquake happens.”

Image: Thorne Lay/UCSC

An international research team, which includes astronomers from UC Santa Cruz, has discovered a new exoplanet in a system about 22 light years from Earth (pretty close, in the scheme of things). The planet, called GJ 667Cc, has an orbital period of 28.15 days and a minimum mass of 4.5 times that of Earth—and it sits smack dab in the parent star’s habitable zone.

Its host star is a member of a triple-star system and has a different makeup than our sun, with a much lower abundance of elements heavier than helium (such as iron, carbon, and silicon). This discovery indicates that potentially habitable planets can occur in a greater variety of environments than previously believed.

The new planet receives 90 percent of the light that Earth receives. However, because most of its incoming light is in infrared wavelengths, the researchers speculate that the planet absorbs a higher percentage of this incoming energy. When both these effects are taken into account, the planet is expected to absorb about the same amount of energy from its star that the Earth absorbs from the sun.

The researchers used public data from the European Southern Observatory and analyzed it with a novel data-analysis method. They also incorporated new measurements from the W. M. Keck Observatory’s High Resolution Echelle Spectrograph and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope. Their planet-finding technique involved measuring the small wobbles in the star’s motion caused by the gravitational tug of a planet.

The team found that the system might also contain a giant planet and an additional super-Earth with an orbital period of 75 days. However, further observations are needed to confirm these two possibilities.

“This was expected to be a rather unlikely star to host planets. Yet there they are, around a very nearby, metal-poor example of the most common type of star in our galaxy,” says Steven Vogt, a professor of astronomy and astrophysics at UCSC. “The detection of this planet, this nearby and this soon, implies that our galaxy must be teeming with billions of potentially habitable rocky planets.”

“This planet is the new best candidate to support liquid water and, perhaps, life as we know it,” according to team lead Guillem Anglada-Escudé of the Carnegie Institution for Science.

The finding is published in Astrophysical Journal Letters.

Image: Guillem Anglada-Escudé, Carnegie Institution

So imagine the surprise, forty years ago, when the Apollo astronauts brought back moon rocks with magnetic properties. How is that possible?

This week, two teams of scientists attempt to solve the mystery with separate papers in Nature.

Christina Dwyer, of UC Santa Cruz, and her team offer one theory. Early in its history, the Moon orbited Earth at a much closer distance than it does now, and it continues to gradually recede from Earth—even today! At close distances, tidal interactions between Earth and the Moon caused the Moon’s mantle to rotate slightly differently than the core. This differential motion of the mantle relative to the core stirred the liquid core, creating fluid motions that could give rise to a magnetic field.

Michael Le Bars, of Non-Equilibrium Phenomena Research Institute in Marseille, France, and his team have another theory. Large impact events like asteroids a few billion years ago could have caused sloshing within the lunar core for up to 10,000 years at a time.

So is it the asteroids’ fault or Earth’s? New Scientist doesn’t take sides:

Both models offer “a way out of a pretty major conundrum,” says Ben Weiss at the Massachusetts Institute of Technology.

Both theories produce a magnetic field of the right strength—about one fiftieth of what we experience here on Earth’s surface—but how do we decide which one is correct?  Sky & Telescope explains:

Distinguishing between these theories will depend in part on figuring out which rocks were magnetized when. Big bull’s-eyes happened pretty rarely in lunar history. If an impact created a dynamo, any molten surface rock around the time of the crash—such as lava created by the hit itself—would record the magnetic field created. But lava that erupted on the surface between these infrequent events wouldn’t. If most lunar rocks everywhere were magnetized during a particular time period, including rocks not made by impacts, that would sway the balance toward the precession argument, Weiss says. If impact melts are always associated with a magnetic field, the balance swings the other way.

Or maybe a combination of both? Wired makes the point that the two ideas aren’t mutually exclusive:

Dwyer herself has suggested that both models could have some parts correct, with tidal forces pushing the mantle steadily for a time and giant impacts speeding up the motion occasionally.

Image: Luc Viatour / www.Lucnix.be

But it’s quality, not quantity right? Our Moon is spectacular and well-studied, yet still a mystery. Take the differences of each side of the moon.

The near side is relatively low and flat, while the topography of the far side is high and mountainous, with a much thicker crust. “The fact that the near side of the moon looks so different to the far side has been a puzzle since the dawn of the space age, perhaps second only to the origin of the moon itself,” says Francis Nimmo, a professor of Earth and planetary sciences at UC Santa Cruz.

Last year, Nimmo and another UC Santa Cruz researcher published a theory for these differences; they suggested that tidal forces were responsible for shaping the thickness of the moon’s crust.

This week, two other UC Santa Cruz colleagues published a very different theory in the journal Nature. Their study builds on the “giant impact” model for the origin of the moon, in which a Mars-sized object collided with Earth early in the history of the solar system and ejected debris that coalesced to form the moon. The study suggests that this giant impact also created another, smaller body, initially sharing an orbit with the moon, that eventually fell back onto the moon and coated one side with an extra layer of solid crust tens of kilometers thick.

That means that at one point, Earth possibly had two moons. New Scientist cries cannibalism!

Family squabbles rarely result in cannibalism, but that may be just what happened in the moon’s youth. It may have gobbled up a smaller sibling, making itself permanently lopsided.

In the new study, Erik Asphaug and Martin Jutzi used computer simulations of an impact between the moon and a smaller companion (about one-thirtieth the mass of the moon) to study the dynamics of the collision and track the evolution and distribution of lunar material in its aftermath. In such a low-velocity collision, the impact does not form a crater and does not cause much melting. Instead, most of the colliding material is piled onto the impacted hemisphere as a thick new layer of solid crust, forming a mountainous region comparable in extent to the lunar farside highlands.

“Of course, impact modelers try to explain everything with collisions. In this case, it requires an odd collision: being slow, it does not form a crater, but splats material onto one side,” Asphaug said. “It is something new to think about.”

ScienceNOW explains how this new study of a slow collision does build upon previous work:

… the slowest-moving impacter would be one in the same orbit as the moon. Earlier work by others had shown that smaller, secondary bodies would also coalesce from the debris of the collision with Earth that created the moon. Studies had also shown that only a secondary moon orbiting Earth at a gravitational balance point just ahead of or behind the moon would survive more than a few million years before slowly colliding with the moon.

Asphaug agrees. “Our model works well with models of the moon-forming giant impact, which predict there should be massive debris left in orbit about the Earth, besides the moon itself. It agrees with what is known about the dynamical stability of such a system, the timing of the cooling of the moon, and the ages of lunar rocks.”

And while Nimmo may disagree on the specifics, he values his colleagues’ work. “One of the elegant aspects of Erik’s article is that it links these two puzzles together: perhaps the giant collision that formed the moon also spalled off some smaller bodies, one of which later fell back to the moon to cause the dichotomy that we see today.”

For now, he said, there is not enough data to say which of the alternative models offers the best explanation for the lunar dichotomy. “As further spacecraft data (and, hopefully, lunar samples) are obtained, which of these two hypotheses is more nearly correct will become clear.”

Image: Martin Jutzi and Erik Asphaug/Nature

But it’s what they do in the water might surprise you. They dive to extraordinary depths for feeding – down to between 1000 and 2600 feet! During their migrations in the Pacific, they will travel the open ocean for several months at a time. According to Dan Costa, Professor of Ecology and Evolutionary Biology at UC Santa Cruz and supervisor of elephant seal research at Año Nuevo, one migration (after they wean their pups) lasts two to three months and the other (after they molt) lasts seven months.

This fact has long puzzled researchers.  How do elephant seals rest while migrating at sea for such long periods of time?

Dr. Costa and other researchers believe they have found the answer to this question, and they published their theory in the April 23^rd issue of Biology Letters.

According to the paper, northern elephant seals rest as they perform drift dives, which resemble a type of scuba diving and allow the seal to drift with the currents.  “We found that seals rolled over and sank on their backs during the drift phase, wobbling periodically so that they resembled a falling leaf… this allows them time to rest, process food or possibly sleep during the descent phase of these dives where they are probably less susceptible to predation.”

These drift dives are slower than their other dives. On average, they may last 25 minutes and reach about 1400 feet below sea level. How often are they making these dives? “Mostly they do it more after a series of feeding dives. A few times a day if things are going well,” according to Dr. Costa via email.

Sounds a little like siestas or catnaps, doesn’t it? Making me sleepy… Yawn.

Creative Commons image by Mike Baird