Is the Risk of Big Earthquakes on the Rise?
S11A-2186 · Monday, Dec. 5, 8 a.m. - 12:20 p.m. · Moscone Halls A-C
From March's devastating magnitude 9.0 earthquake in Japan to last year's 8.8 quake off Chile and the 9.0 Sumatra-Andaman event of 2004, seismologists have recently wondered whether such massive events are on the rise. Perhaps such giant quakes are not independent, random events, but rather somehow connected, even triggering one another?
Peter Shearer of Scripps Institution of Oceanography at UC San Diego and Philip Stark of UC Berkeley explored these issues in a new study that evaluated the question of
whether the cluster of recent large earthquakes is statistically significant compared with models of random event occurrence.
The short answer: no. The researchers say smaller earthquakes are near their historic norms, so it's difficult to imagine a physical mechanism that would increase the rate of the largest earthquakes but not the smaller quakes. "This suggests that the global risk of large earthquakes is no higher today than it has been in the past," the researchers note. However, they also conclude: "Even if the risk has not increased recently, that does not mean that the ongoing risk is small or should be ignored."
PRESENTATION TITLE: "HAS THE RISK OF BIG EARTHQUAKES RECENTLY INCREASED?"
Sea-level Rise May Return to the West Coast
G24A-03 · Tuesday, Dec. 6, 4:30 p.m. · Moscone Room 3024
North America's West Coast has gone through a period in which sea level in the eastern North Pacific Ocean has been steady during the last few decades, but there is evidence that a change in wind patterns may be occurring that could cause coastal sea-level rise to accelerate beginning
this decade. Research led by Peter Bromirski of Scripps Institution of Oceanography at UC San Diego shows that conditions dominated by cold surface waters along the West Coast could soon flip to an opposite state.
Global sea level rose during the 20th Century at a rate of about two millimeters (.08 inches) per year. That rate increased by 50 percent during the 1990s to a global rate of three millimeters (.12 inches) per year, an uptick frequently linked to global warming. Rising sea level has consequences for coastal development, beach erosion and wetlands inundation. Higher sea levels could cause increased damage to coastal communities and beaches, especially during coincident high tides, storm surges and extreme wave conditions.
When the cycle shifts to its negative "cold" phase, coastal ocean waters will become characterized more by a downwelling regime, where the amount of colder, denser water currently brought to the surface will be reduced. Resulting warmer surface water will raise sea level.
PRESENTATION TITLE: "DYNAMICAL SUPPRESSION OF SEA LEVEL RISE ALONG THE EASTERN BOUNDARY OF THE NORTH PACIFIC" (INVITED)
A New View of Japan's Devastating Earthquake
S33B-05 · Wednesday, Dec. 7, 2:40 p.m. · Moscone Room 2009
Scientists at Scripps Institution of Oceanography at UC San Diego have developed a new method for imaging how the Earth ruptures during large earthquakes, using the first-arriving seismic waves as recorded by an array of seismometers in the United States.
Scripps researchers Huajian Yao, Peter Gerstoft and Peter Shearer with colleague Christoph Mecklenbräuker of Austria's Vienna University of Technology used a data-inversion technique called "compressive sensing," which simplifies the problem by assuming that the seismic energy is radiated from a small number of discrete sources. Application of the method to the disastrous March 11, 2011, earthquake in Japan shows a strong frequency dependence in the seismic radiation. The lowest frequencies were generated in the shallow part of the fault near the offshore trench, where the tsunami is known to have originated. In contrast, the higher-frequency seismic radiation originated from the deeper part of the fault closer to the Japanese mainland. These results have important implications for the stress state and frictional properties of the faults that cause giant earthquakes and tsunamis.
PRESENTATION TITLE: "COMPRESSIVE SENSING OF THE TOHOKU-OKI MW 9.0 EARTHQUAKE: FREQUENCY-DEPENDENT RUPTURE MODES"
Prospecting for Plates
DI43B-01 · Thursday, Dec. 8, 1:40 p.m. · Moscone Room 3022
When tectonic plates get recycled back into Earth's interior, they can usually be imaged using tomographic techniques that utilize seismic waves. Underneath North America, the Farallon plate was subducting for more than 100 million years, but only the oldest-and deepest-portion of it was clearly identifiable, while the most recent portion closer to the surface seemed to be missing.
Scientists working through EarthScope, an ambitious scientific program focused on the structure and evolution of the North American continent, have revealed an extremely complex mantle structure beneath the western United States, including clues about missing parts of the subducted Farallon plate. Using geodynamic models to simulate these plate tectonic processes, Scripps Institution of Oceanography at UC San Diego geophysicists Lijun Liu and Dave Stegman convincingly show how the Farallon-Juan de Fuca plate broke up as it subducted below western North America.
The study demonstrates that around 15 million years ago the once continuous Juan de Fuca slab segmented into three portions that became highly contorted as they sank, resulting in the configuration presently observed by EarthScope. The findings indicate that both the shrinking width of the subducting oceanic plate and its very weak mechanical strength allowed the plate to break. The new model provides a reliable framework for understanding the unique magmatic and geologic history of the western U.S.
PRESENTATION TITLE: "SEGMENTATION OF THE FARALLON SLAB" (INVITED)
Exploring Dark Antarctic Ice Caves for Microbes
B44B-08 · Thursday, Dec. 8, 5:45 p.m. · Moscone Room 2004
As far as desolate locations go, this one's tough to beat. A team of scientists including Hubert Staudigel of Scripps Institution of Oceanography at UC San Diego has withstood the brutal conditions of Antarctica's Mount Erebus volcano and its dark ice caves to study microbes and how they subsist in an environment with nothing to eat except rocks. Such microscopic "extremophiles" (see story and video) are yielding clues that may resemble the harsh conditions of a young planet Earth.
"If we find microbes that rely on things like iron oxidation or chemical reactions for energy, we are one step closer to identifying the ones that are specialized to situations inside the surface of volcanoes," said Staudigel.
"These microbes will help us understand who lives in the deep volcanic biosphere, or maybe even whether these microbes were among the earliest life on Earth."
PRESENTATION TITLE: "DARK OLIGOTROPHIC VOLCANIC ECOSYSTEMS (DOVEs) IN FUMAROLIC ICE CAVES OF MT. EREBUS VOLCANO".