HOME

ABOUT US

SERVICES

 ESS 287C Seismology Seminar - Spring Quarter 2007

Abstract: Global seismic tomography has now been around for more than 20 years. It is a mature field, and it is no longer possible to simply assemble a larger dataset and publish a higher resolution S and/or P model. There are, however, still many open avenues for research in seismic tomography. Future tomographic discoveries have to originate from the 4 components of the inverse problem: the data, the model, the forward theory, and the inverse method. In recent years, advances in computational power have made several improvements to both the forward theory and the inverse method more practical (e.g. 3D finite frequency sensitivity kernels, and adjoint inverse techniques taking advantage of numerical wavefield modeling tools). However, the limitations of data coverage, and the regularization of the inverse problem required by that limited coverage, may mean much of the theoretical advances map into the null space of the final model. This means that, in the long term, cooperative efforts among Earth scientists to instrument the ocean bottoms to improve the data coverage will yield big returns in terms of expanding our knowledge of deep Earth structure. Until then, however, we can still make significant progress by carefully revising how we consider our models. For example, we can look for anisotropic and anelastic structure, which can eventually better constrain the quantities most of interest to other geoscientists looking at the mantle, such as the temperature, composition, and flow patterns of the mantle. In this talk, I will discuss some of the specific tools I have already used and am currently developing to approach these challenges, and the most likely avenues for progress in the next decade.

Abstract: The biotic response to climate change, as indicated by species extinctions, changes in community composition, and the potential for ecosystem deterioration, is of particular relevance given the prospects for future global warming. The fossil record provides a deep-time perspective on the extent of biotic disruption during major climate fluctuations such as the Early Permian aftermath of the late Paleozoic ice age. Biotic change at the regional scale is assessed through counts of relative abundance in marine fossil assemblages from the Early Permian of eastern Australia, which contains richly fossiliferous sections through the deglaciation interval (Sakmarian-Kungurian). Quantitative data from 73 fossil assemblages reveal pronounced change, from glacial communities dominated by the bivalve Eurydesma and the brachiopod Trigonotreta to postglacial assemblages with abundant brachiopods Terrakea and Echinalosia. Cluster analysis suggests that this shift was synchronous across latitudinal zones, from polar regions in Tasmania to temperate settings in Queensland, but may have occurred earlier in offshore habitats. Detrended correspondence analysis reveals that Artinskian communities, during the transition from glacial to postglacial climates, were substantially more variable than either glacial or postglacial assemblages. This variability, including the development of communities dominated by unusual or otherwise rare genera, is similar to the rapid fluctuations observed in terrestrial plant communities during the Artinskian. A GIS database analysis of biogeographic changes provides global context, indicating that numerically abundant genera of the glacial biota were also widespread during the earliest Permian but became progressively restricted to the coldest regions during deglaciation and/or became extinct as climate warmed. Biogeographic patterns also indicate that dominant postglacial genera evolved in Gondwana during climate warming, rather than invading from lower latitudes as temperatures rose. These results indicate that marine communities are strongly influenced by climate change, at least at the million year timescales during the aftermath of the late Paleozoic ice age.