Department of Physics,
Univ. of Colorado, Boulder;
Boulder, CO 80309-0390
ritzwoller@lemond.colorado.edu
303-492-7075
poster/oral:
We report on the construction and characteristics of a new catalogue of normal mode structure coefficients below 3 mHz. Seismic spectra obtained from the GSN, GEOSCOPE, GDSN, and IDA networks following 35 very large earthquakes dating from 1977 - 1995 have been analyzed to yield structure coefficient estimates for 90 multiplets. Improvements in data quality and quantity as well as technical advances in normal mode spectral fitting have resulted in coefficient estimates at structural degrees as high as 12 and at odd degrees. A Monte Carlo error estimation procedure appears to produce reasonable uncertainty estimates. This catalogue is useful to test existing mantle models and is straightforward to use in seismic inversions. We believe that it will prove most useful in placing constraints on mantle structures which are most poorly sampled by surface and body waves; namely at depths between about 500 and 2000 km where current global models disagree most appreciably. Research in the next two years will concentrate on extending the catalogue to 5 mHz. The current catalogue is available at the following web site:
http://phys-geophys.colorado.edu/geophysics/nm.dir/nm.html. We plan to add software to facilitate the use of the catalogue in testing mantle models and in inversions by other researchers.
Department of Physics,
Univ. of Colorado, Boulder;
Boulder, CO 80309-0390
ritzwoller@lemond.colorado.edu
303-492-7075
poster/oral:
Broadband Rayleigh and Love wave group velocity maps have been constructed across Eurasia, South America and the surrounding oceans, and Antarctica and the southern oceans using intermediate and large events (Ms > 4.9) in and around each region. Tomographic maps extend from about 15 s period to 150 - 200 s period. At present, about 1600 events have been processed to yield approximately 20,000 paths across these continents. These maps are useful both to test existing models of the crust and upper mantle under these continents and as data in inversions to improve crustal and lithospheric structures. In particular, the short period dispersion maps provide important information on crustal structures since sensitivity kernels at these periods are nearly entirely contained within the continental crust. We report (1) on comparisons between the estimated group velocity maps and predictions from CRUST-5.1/S16B30, concentrating on Eurasia, and (2) on inversions for crustal and upper mantle structures in Central Asia. The Central Asian model as well as all measured group velocity curves and the estimated group velocity maps across the three continents are available at the following web sites:
http://phys-geophys.colorado.edu/geophysics/eurasia.dir/eurasia.html