SEMINAR - Christian Koeberl

Meteorite impact cratering on Earth:
Geological and biological consequences

Dr. Christian Koeberl
Department of Geological Sciences
University of Vienna, Austria

Wednesday, December 5th, 1:00pm GMCS 422

Impact is a unique, short-time, high-energy geological process. The importance of impact cratering on terrestrial planets (Mercury, Venus, Mars), our Moon, and the satellites of the outer planets is obvious from the abundance of craters on their surfaces. On most bodies of the solar system that have a solid surface, impact cratering is the most important surface-modifying process even today. On Earth, active geological processes rapidly obliterate the cratering record. To date only about 170 impact structures have been recognized on the Earth’s surface. They come in various forms, shapes and sizes, from 300 km to less than 100 m in diameter, from Recent to 2 billion years in age. Mineralogical, petrographic, and geochemical criteria are used to identify the impact origin of such structures or related ejecta layers. The two most important criteria are the presence of shock metamorphic effects in mineral and rock inclusions in breccias and melt rocks, as well as the demonstration, by geochemical techniques, that these rocks contain a minor extraterrestrial component. In impact studies there is now a trend towards the use of interdisciplinary and multi-technique approaches to solve open questions. In this lecture we will take a look at impact craters on the Earth (and some other planets), and discuss how they formed and how they can be recognized. An aspect of impact cratering that may be underestimated is the influence of impacts on the geological and biological evolution of our own planet. Even the impact of relatively small asteroids or comets can have disastrous consequences for our civilization. There is a 1 in 10,000 chance that a large asteroid or comet 2 km in diameter (corresponding to a crater of about 25-50 km in diameter) may collide with the Earth during the next century, severely disrupting the ecosphere and annihilating a large percentage of the Earth's population. The biological evolution of our planets is punctuated by mass extinction events, of which the one 65 million years ago, which marks the Cretaceous-Tertiary boundary, is probably the best known one. Abundant impact debris marks this boundary, providing a clear link with a major impact event. The Chicxulub impact structure in Mexico, about 200 km in diameter, which resulted from the impact of an about 10-km-diameter asteroidal body, has been identified as the culprit. Understanding of impact structures, their formation processes, and their consequences should be of interest not only to earth and planetary scientists, but also to society in general.


Christian Koeberl is a professor at the Department of Geological Sciences at the University of Vienna, Austria, whose main research interest is the interdisciplinary study of meteorite impact craters, including shock petrography and the geochemistry of impactites, and also works on meteorites. He was the chairman of the European Science Foundation (ESF) “IMPACT” program (1998-2003), and is a member of the International Continental Scientific Drilling Program (ICDP) Science Advisory Group. He has published over 300 peer-reviewed research papers and has written or edited 12 books.

SEMINAR - Anne Sheehan

Seeing Beneath Mount Everest:
Probing a Breeding Ground of Destructive Earthquakes

IRIS/SSA Distinguished Lectureship
Dr. Anne Sheehan
University of Colorado, Boulder

Wednesday, November 28th, 1:00pm GMCS 422

The Himalaya mountains are the product of the largest continental collision in the world today, and are home to large and deadly earthquakes, such as the Pakistan earthquake of October 8, 2005. To understand how the mountains were created and to help quantify the earthquake hazards of this vulnerable region, Dr. Sheehan led a National Science Foundation funded project that included placement of ground motion recorders (seismometers) throughout eastern Nepal and southern Tibet. The seismic stations were installed in areas that are remote and logistically difficult, with challenges including the mountains, weather, scorpions, cobras, and political unrest and guerrilla warfare in Nepal. Much like a medical CT scan, ground motion recordings from earthquakes provide a detailed image of the Earth beneath the seismic stations. The earthquake recordings collected in Nepal and Tibet produce a first-ever glimpse of the earthquake faults beneath the Himalayan mountains, and can be used to determine details of the earthquake faulting processes.

About Dr. Sheehan
Education
Ph.D., Massachusetts Institute of Technology, 1991B.S., University of Kansas, 1984
Positions Held
Professor, University of Colorado, Boulder 2006-presentAssociate Professor, University of Colorado, Boulder 2001-2006Assistant Professor, University of Colorado, Boulder 1993- 2000Fellow, Cooperative Institute for Research in Environmental Sciences 1993-PresentResearch Assistant Professor, University of Nevada, Reno 1992-1993Postdoctoral Fellow, Lamont-Doherty Geological Observatory, Columbia University, 1991- 1992
Honors and Awards
NSF CAREER Award, 1995

Dr. Anne Sheehan joined the faculty at the University of Colorado at Boulder in 1993 and is currently a Professor of Geological Sciences and Fellow of the Cooperative Institute for Research in the Environmental Sciences. Sheehan's research interests include the study of crust and upper mantle structure of the Earth and its relation to tectonic deformation, particularly beneath mountains and plate boundaries. Much of her work includes the deployment of portable seismometers that record both distant and local earthquakes. She has led recent seismic experiments in the Himalaya, New Zealand, and the Rocky Mountains.

Sheehan is an experienced public speaker and has given talks about her research to many school and community groups. Sheehan was the 2005-2006 Science Advisor to CU Science Explorers. This program offers hands-on workshops throughout the state of Colorado on science topics to teams of middle school teachers and students. Sheehan worked with Science Explorers staff to develop a curriculum on Natural Hazards, including earthquakes and tsunamis, avalanches, and forest fires. Sheehan teaches introductory geology at the University of Colorado to a class of 180 students, and consistently receives high marks for her teaching. She also teaches advanced undergraduate level and graduate level courses in geophysics and seismology.
Sheehan is married and has two school-age children. She enjoys coaching youth sports and participating in triathlons and bicycling events. Sheehan is a breast cancer survivor and is active with Rocky Mountain Team Survivor.

Books
Burger, H. R., A. F. Sheehan, and C. H. Jones, Introduction to Applied Geophysics: Exploring the Shallow Subsurface, W. W. Norton Publishers, 2006.

Selected Recent Publications
Schulte-Pelkum, V., G. Monsalve, A. F. Sheehan, M. Pandey, S. Sapkota, R. Bilham, and F. Wu, Imaging the Indian subcontinent beneath the Himalaya, Nature, v. 435, pp. 1222-1225, 30 June 2005doi:10.1038/nature03678, 2005.De la Torre, T., and A. F. Sheehan, Broadband seismic noise analysis of Himalayan Nepal Tibet Seismic Experiment, Bull. Seismol. Soc. Am., v. 95, 1202-1208, doi:10.1785/0120040098, 2005.Sheehan, A. F., V. Schulte-Pelkum, O. Boyd, and C. Wilson, Passive source seismology of the Rocky Mountain region, in The Rocky Mountain Region: An Evolving Lithosphere, Geophysical Monograph Series 154, 10.1029/154GM23, p. 309-315, 2005.
Boyd, O. S., C. H. Jones, and A. F. Sheehan, Foundering lithosphere imaged beneath the Southern Sierra Nevada, California, Science, v. 305, 660-662, 2004.
Gilbert, H. J., and A. F. Sheehan, Images of crustal variations in the intermountain west, Journal of Geophysical Research, v. 109, B03306, doi:10:1029/2003JB002730, 2004.
Blume, F., and A. F. Sheehan, Quantifying seismic hazard in the Southern Rocky Mountains through GPS measurements of crustal deformation, in Engineering Geology in Colorado: Contributions, Trends, and Case Histories, eds. D. Boyer, P. Santi, and W. Rogers, Association of Engineering Geologists Special Publication No. 15, Colorado Geological Survey Special Publication 55, 2003.Lastowka, L. A., A. F. Sheehan, and J. M. Schneider, Seismic evidence for partial delamination model for Colorado Plateau uplift, Geophys. Res. Lett.,v. 28, 1319-1322, 2001.
Sheehan, A. F., Microearthquake study of the Colorado Front Range: Combining research and teaching in seismology, Seismol. Res. Lett., v. 71, 175-179, 2000.Savage, M. K., and A. F. Sheehan, Seismic anisotropy and mantle flow from the Great Basin to the Great Plains, western United States, Journal of Geophysical Research, v, 105, 13715-13734, 2000.Sheehan, A. F., P. M. Shearer, H. Gilbert, and K. G. Dueker, Seismic migration processing of P-SV converted phases for mantle discontinuity structure beneath the Snake River Plain, western United States, Journal of Geophysical Research, v. 105, p. 19055-19065, 2000.Shen, Y., A. Sheehan, K. Dueker, C. de Groot-Hedlin, and H. Gilbert, Mantle discontinuity structure beneath the southern East Pacific Rise (MELT experiment region) from P-to-S converted phases, Science, v. 280, 1232-1235, 1998.Dueker, K. G., and A. F. Sheehan, Mantle discontinuity structure from mid-point stacks of converted P to S waves across the Yellowstone hotspot track, Journal of Geophysical Research, v. 102, 8313-8327,1997.

2007 Science Sampler

Science Sampler

Sunday, November 18, 2007

A Science Experience on for San Diego Area High School Students Given by SDSU School of Sciences Departments

The Menu:
Oriented toward San Diego County High School Students. A series of short presentations, experiments and labs Hands on, interactive activities demonstrating scientific principles. A sampler of the best of selected science fields. Visitor participation includes a write-up and proof of attendance certificate.

Purpose for High School Students:
Expose High School students to neat science stuff. Experience science in action and take part in experimental science.

Purpose for High School Science Teachers who are welcome:
Support local High School Science Teachers: Provide a local field trip and meet Selected State of California Science Standards

Science Areas:
SDSU School of Sciences Departments Instructions: Students can come by themselves or with others. Suggested arrival at SDSU before 1 :30 PM. for pre-show tour. Go to Geology, Mathematics, Computer Science (GMCS) building Room 333 at SDSU

Campus Directions and Parking Information GMCS Map