6 research outputs found
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Modeling Temporal-Spatial Earthquake and Volcano Clustering at Yucca Mountain, Nevada
The proposed national high-level nuclear repository at Yucca Mountain is close to Quaternary faults and cinder cones. The frequency of these events is low, with indications of spatial and temporal clustering, making probabilistic assessments difficult. In an effort to identify the most likely intrusion sites, we based a 3D finite element model on the expectation that faulting and basalt intrusions are primarily sensitive to the magnitude and orientation of the least principal stress in extensional terranes. We found that in the absence of fault slip, variation in overburden pressure caused a stress state that preferentially favored intrusions at Crater Flat. However, when we allowed central Yucca Mountain faults to slip in the model, we found that magmatic clustering was not favored at Crater Flat or in the central Yucca Mountain block. Instead, we calculated that the stress field was most encouraging to intrusions near fault terminations, consistent with the location of the most recent volcanism at Yucca Mountain, the Lathrop Wells cone. We found this linked fault and magmatic system to be mutually reinforcing in the model in that dike inflation favored renewed fault slip
Community and population dynamics of spruce–fir forests on Whiteface Mountain, New York: recent trends, 1985–2000
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The use of propagation path corrections to improve seismic event location in western China
In an effort to improve ability to locate events in western China using only regional data, the authors have developed propagation path corrections to seismic travel times, and applied such corrections using both traditional location routines as well as a nonlinear grid search method. Thus far, they have concentrated on corrections to observed P arrival times. They have constructed such corrections by using travel time observations available from the USGS Earthquake Data Reports, as well as data reported by the ISC. They have also constructed corrections for six stations that are a part of the International monitoring System. For each station having sufficient data, they produce a map of the travel-time residuals from all located events. Large-amplitude residuals are removed by median filtering, and the resulting data are gridded. For a given source location, the correction at a particular station is then interpolated from the correction grid associated with the station. They have constrained the magnitude of the corrections to be {le} 3 s. They have evaluated the utility of the calculated corrections by applying the corrections to the regional relocation of 10 well-located Chinese nuclear tests, as well as a single, well-located aftershock in nearby Kyrgyzstan. The use of corrections having magnitudes > 2 s is troubling when using traditional location codes, as the corrections amount to a nonlinear perturbation correction, and when large may destabilize the location algorithm. Partly for this reason, the authors have begun using grid search methods to relocate regional events. Such methods are easy to implement and fully nonlinear. Moreover, the misfit function used to locate the event can very easily be changed; they have used L{sub 1}- and L{sub 2}-norm misfit functions, for example. Instances in which multiple local minima occur in a location problem are easily recognized by simply contouring or otherwise displaying the misfit function
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Regional location in western China
Accurately locating seismic events in western China using only regional seismic stations is a challenge. Not only is the number of seismic stations available for locating events small, but most stations available to researchers are often over 10{degree} distant. Here the authors describe the relocation, using regional stations, of both nuclear and earthquake sources near the Lop Nor test site in western China. For such relocations, they used the Earthquake Data Reports provided by the US Geological Survey (USGS) for the reported travel times. Such reports provide a listing of all phases reported to the USGS from stations throughout the world, including many stations in the People`s Republic of China. LocSAT was used as the location code. The authors systematically relocated each event int his study several times, using fewer and fewer stations at reach relocation, with the farther stations being eliminated at each step. They found that location accuracy, judged by comparing solutions from few stations to the solution provided using all available stations, remained good typically until fewer than seven stations remained.With a good station distribution, location accuracy remained surprisingly good (within 7 km) using as few as 3 stations. Because these relocations were computed without good station corrections and without source-specific station corrections (that is, path corrections), they believe that such regional locations can be substantially improved, largely using static station corrections and source-specific station corrections, at least in the Lop nor area, where sources have known locations. Elsewhere in China, one must rely upon known locations of regionally-recorded explosions. Locating such sources is clearly one of the major problems to be overcome before one can provide event locations with any assurance from regional stations