Researchers installed moorings containing fiber-optic cables hundreds of meters down into the McMurdo Ice Shelf in West Antarctica to collect temperature information about the base of the ice shelf, where the thick platform of floating ice meets the ocean. The sensors were able to measure mere millimeters of ice loss at the interface, demonstrating that the new fiber-optic method could be used to remotely monitor the ice shelves in real-time. GeoSpace spoke with Scott Tyler, a hydrologist at the University of Nevada, Reno and the study's principal investigator, about the new research that has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
From 1957 to 1965, 46 research vessels operating under 14 flags collected data for the International Indian Ocean Expedition. Now, 50 years later, the time is ripe for a fresh effort to study the Indian Ocean.
Coastal Oregon is home to a number of slow, recurrent landslides. During bouts of heavy rain, water gets into the soil, reducing friction and causing the ground to slip. Often, these landslides creep along at a barely perceptible rate--less than a centimeter per day. Yet the landslides are a lurking threat, as past events that have damaged infrastructure and cut communities off for months at a time have demonstrated.
Of particular concern is how these landslide regions would respond to the more potent shaking of an earthquake, a process which is not well understood. Based on new laboratory experiments, Schulz and Wang suggest that many of Oregon's slow creeping coastal areas would fail catastrophically during an earthquake, an added threat in the seismically active region.
Between the smaller recurrent landslide events, the hillslopes are propped up by the constant friction that develops in the soil during the slow movements, known as its "residual shear strength." A small amount of jostling, however, can actually change the strength of a hillslope, as soil particles are rearranged into either a more shear-resistant or shear-compliant state.
The question posed by the authors was how the soil from two of Oregon's landslide regions would respond to different kinds of pressure. The authors tested soil samples from two recurrent landslides under constant and increasing displacement rate and under loading forces that mimicked historical earthquakes.
They find that a small rapid displacement causes a pronounced drop in shear strength. Yet, if the displacement rate is increasing, rather than constant, the shear strength actually increases--up to a point. Under shaking conditions drawn from historical earthquakes, however, the soils' residual strength could not hold up.
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