The following highlights summarize research papers that have been published in Geophysical Research Letters (GRL) or the Journal of Geophysical Research – Atmospheres (JGR-D).
In this release:
- L'Aquila earthquake source found, risk remains
- Waning sea ice bodes stormier, rainier Arctic
- New use for GPS: measuring snow depth
- Major Antarctic glacier thins at fast-increasing pace
- Slow seismic waves reveal deep-Earth slab
- Deep tremors may give earthquake warnings
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1. L'Aquila earthquake source found, risk remains
The magnitude 6.3 April 2009 L'Aquila earthquake in central Italy killed around 300 people, injured 1000, and caused extensive damage to homes and other buildings. To locate the source mechanism and study implications for future seismic hazard in the region, Walters et al. examine radar satellite images and seismology data. They locate the source of the L'Aquila earthquake as the Paganica fault, northeast of L'Aquila. From its surface appearance, this fault was thought to be slipping less rapidly than other faults nearby. This earthquake emphasizes the difficulties of assessing seismic hazard in regions where there are many closely spaced faults, the authors note. In addition to identifying the source of the L'Aquila earthquake, the authors use remote sensing and field observations along with static stress models to study how the L'Aquila earthquake caused stress changes on nearby faults. They find that several of these faults, in particular the Montereale and Campotosto faults, have been brought closer to failure as a result of the L'Aquila earthquake and continue to represent a seismic hazard in the region.
Title: The 2009 L'Aquila earthquake (central Italy): A source mechanism and implications for seismic hazard
Authors: R. J. Walters, J. R. Elliott, P. C. England, and B. Parsons: COMET, Department of Earth Sciences, University of Oxford, Oxford, UK; N. D'Agostino and I. Hunstad: Centro Nazionale Terremoti, Istituto Nazionale di Geofisica e Vulcanogia, Rome, Italy; J. A. Jackson: COMET, Department of Earth Sciences, University of Cambridge, Cambridge, UK; R. J. Phillips: School of GeoSciences, University of Edinburgh, Edinburgh, UK; G. Roberts: Research School of Earth Sciences, University College London, London, UK.
Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL039337, 2009; http://dx.doi.org/10.1029/2009GL039337
2. Waning sea ice bodes stormier, rainier Arctic
The Arctic system is changing at a record pace in response to human-induced global warming as melting sea ice affects and is affected by atmospheric circulation, precipitation, temperature, nutrient abundance, and ecosystem health. Using a technique that distills large data sets into physically meaningful representative samples, Higgins and Cassano study the role of melting sea ice with regard to atmospheric changes seen during the winter using an atmosphere-only global climate model. They find that the model indicates that low-pressure systems will be pervasive over much of the Arctic basin, causing increased cyclonic behavior and precipitation. This increase in precipitation is due to thermodynamic changes, such as increased moisture in the atmosphere due to melting ice, rather than changes in the frequency of cyclones. Such winter atmospheric changes could further reduce winter sea ice production in the Arctic.
Title: Impacts of reduced sea ice on winter arctic atmospheric circulation, precipitation, and temperature
Authors: Matthew E. Higgins and John J. Cassano: Cooperative Institute for Research in Environmental Sciences and Department of Atmospheric and Ocean Sciences, University of Colorado, Boulder, Colorado, USA.
Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2009JD011884, 2009 http://dx.doi.org/10.1029/2009JD011884
3. New use for GPS: measuring snow depth
Snow is a key component of both regional and global climate models. Knowledge of snowpack is also important for management of the water supply and flood control. However, in situ observations of snow depth are sparse, and most remote sensing observations have poor spatial resolution. It would be beneficial to develop new methods to measure snow depth to augment existing networks and remote sensing systems. There are hundreds of Global Positioning System (GPS) receivers operating in snowy regions of the United States. Although these GPS receivers were installed primarily to measure plate tectonics, they could provide a valuable, cost-effective option for measuring snow depth. To investigate whether GPS receivers are suitable for this task, Larson et al. take data during two spring 2009 snowstorms at a site near Boulder, Colorado. They compare snow depth derived from the GPS receivers with field measurements and data from three ultrasonic snow depth sensors, and find good agreement. The authors conclude that GPS receivers could potentially be a useful tool for measuring snow depth.
Title: Can we measure snow depth with GPS receivers?
Authors: Kristine M. Larson and Felipe G. Nievinski: Department of Aerospace Engineering Sciences, University of Colorado, Boulder, Colorado, USA; Ethan D. Gutmann: ASP, RAL, ISP, NCAR, Boulder, Colorado, USA; Valery U. Zavorotny: Earth System Research Laboratory, NOAA, Boulder, Colorado, USA; John J. Braun: COSMIC, UCAR, Boulder, Colorado, USA; Mark W. Williams: INSTAAR and Department of Geography, University of Colorado, Boulder, Colorado, USA.
Source: Geophysical Research Letters (GRL) paper 10.10292009GL039430, 2009; http://dx.doi.org/10.1029/2009GL039430
4. Major Antarctic glacier thins at fast-increasing pace
The West Antarctic ice sheet is known to be thinning, with potentially dramatic consequences for sea level rise. To learn more about the rate and extent of thinning of the Pine Island Glacier, one of the largest ice streams in West Antarctica, Wingham et al. analyze satellite radar altimeter data covering the period from 1995 to 2006. The authors find that within the central trunk of the glacier, the rate of ice thinning quadrupled from 1995 to 2006. In addition, the extent of ice thinning has spread inland from the trunk, so that all tributaries to the central trunk are now thinning rapidly as well. The changes indicate a prolonged disturbance to ice flow. The authors estimate that if the thinning trend continues, the main trunk of the glacier will be entirely afloat within 100 years, much sooner than previous estimates had suggested. They conclude that predictions of sea level rise due to West Antarctic ice melting should take these new findings into account.
Title: Spatial and temporal evolution of Pine Island Glacier thinning, 1995�
Authors: D. J. Wingham and D. W. Wallis: Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, London, UK; A. Shepherd: Centre for Polar Observation and Modelling, School of Geosciences, University of Edinburgh, Edinburgh, UK.
Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL039126, 2009; http://dx.doi.org/10.1029/2009GL039126
5. Slow seismic waves reveal deep-Earth slab
In recent decades, scientists have used seismic waves to discover interesting structural features at the bottom of Earth's mantle, just above the core. These features include ultralow-velocity zones, regions of thin, partly melted, lower-density material that slows seismic waves. To learn more about these zones and their locations, Xu and Koper analyze seismic wave data from 1371 shallow earthquakes detected by the Yellowknife seismic array. They find a long, narrow region in the lower mantle beneath the northwestern Pacific Ocean where seismic waves travel as much as 6 percent slower than average. The authors suggest that this newly discovered ultralow-velocity zone is caused by a slab of old material that is creating partial melting of mantle material as it moves laterally from the northwestern Pacific subduction zones toward a large, chemically distinct region beneath the south central Pacific. The authors believe the study will help improve understanding of processes in the lower mantle and the nature of ultralow-velocity zones.
Title: Detection of a ULVZ at the base of the mantle beneath the northwest Pacific
Authors: Yan Xu and Keith D. Koper: Earth and Atmospheric Sciences, Saint Louis University, Saint Louis, Missouri, USA.
Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL039387, 2009; http://dx.doi.org/10.1029/2009GL039387
6. Deep tremors may give earthquake warnings
Any change in seismic activity that precedes earthquakes could potentially be useful in predicting them. Looking for possible precursor events, Shelly analyzes data from the Parkfield borehole High Resolution Seismic Network covering the period before and after the 2004 magnitude 6.0 earthquake in Parkfield, Calif. The author looks in detail at deep tectonic tremor, the rumbling that occurs deeper in the Earth than the movement that generates earthquakes. Although Shelly finds no obvious short-term precursor to the earthquake, he does find some changes in the deep tectonic tremor activity. His analysis shows that in the 3 months before the Parkfield earthquake, the rate of deep tremor increased and the direction in which the tremor propagated changed from a mix of northward and southward to exclusively southward. According to the author, these changes in tremor activity suggest that before the earthquake, a deep slow slip event occurred about 16 kilometers (9.9 miles) below the earthquake hypocenter. He notes that further studies of deep tremor could shed light on deep fault slip events and could eventually lead to a means of forecasting earthquakes in some regions.
Title: Possible deep fault slip preceding the 2004 Parkfield earthquake, inferred from detailed observations of tectonic tremor
Author: David R. Shelly: U.S. Geological Survey, Menlo Park, California, USA.
Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL039589, 2009 http://dx.doi.org/10.1029/2009GL039589
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Journal
Geophysical Research Letters