3D Seismic Reflection Imaging with Uncontrolled Sources using Large N Arrays
Reflection seismology with controlled sources often provides the highest resolution of structure of any seismic technique. However, the application of the reflection method to probe all but the shallowest of structures is often inhibited by the substantial cost of artificial sources as well as logistical barriers to their deployment. Here we describe how reflection processing can be applied to recordings of ambient energy sources, particularly microearthquakes, to produce reflection imagery that approaches the quality of conventional controlled source (CMP) surveys. Such “passive” seismic reflection imaging has only recently become practical with the advent of large N nodal technology that can simultaneously record spatially dense arrays for substantial lengths of time. Two distinct approaches will be described: seismic interferometry to re-datum microearthquakes into virtual surface sources and reverse VSP imaging of microearthquakes. Examples from Iceland, the eastern US and Alaska suggest that these methods represent a transformative approach to imaging deep structure and monitoring active processes in areas illuminated by transient or ongoing microseismicity.
Prof. Brown is the Sidney Kaufman Professor in Geophysics in the Department of Earth and Environmental Sciences. He receive his BS in Physics from Georgia Tech in 1973 and his PhD from Cornell in geophysics in 1976. He has been on the faculty at Cornell since 1977. Prof. Brown's research specialty is high resolution imaging of the lithosphere using seismic reflection techniques. Prof. Brown was a Principal Investigator for the COCORP (Consortium for Continental Reflection Profiling) program which pioneered the application of oil exploration seismic techniques to the study of deep crustal structure in the U.S. He has subsequently been PI for the URSEIS initiative across the Urals for central Russia and the INDEPTH initiative across Tibet. He has also directed field work to seismically image deep structure across Taiwan, the Andes mountains and on an active Caribbean volcano. His current work is focused on using ambient seismic sources (e.g. earthquakes, cultural noise) to image deep structure in both 3D and 4D using reflection techniques, especially structure associated with earthquake and volcanic processes. Of particular interest is the use of large N, high density seismic arrays for imaging of active subsurface processes using both artificial and natural sources, an approach with great potential for monitoring of, and imaging with, microearthquakes associated with aftershock sequences, magma movement, geothermal production and hydraulic fracturing.
Dr. Donald I Siegel, Syracuse University
“The Dismissal of Facts in Water-Related Decision Making: Root Causes and What to do About It”.
Water scientists no longer can assume that societal decisions on water, ranging from contamination to resource allocation, will be based on preponderance of scientific fact. Regional and social tribalism, single issues tied to ethics, and a fragmented digital media lead to bipartisan repudiation of science and the scientific method. Opposing sides of water (and other) scientific issues use identical play books to reduce the value of scientific facts; “cherry picking” data, smearing bearers of unwelcome scientific news, promoting obstructionist rhetoric, and not expressing true concerns. The scientific debate over methane concentrations in drinking water serves as a case in point. A possible way for scientists in water quality or quantity debates to ameliorate this sad state of affairs is to publicly respect and take the time understand the opposition to sound water science, thereby offering a chance for compromise in the future.
Dr. Esteban Gazel, Associate Professor Department of Earth and Atmospheric Sciences Cornell University.
"The rocks that joined the Americas: Is there a connection with climate and evolution of life?"
Earth’s crust is the life-sustaining interface between our planet’s deep interior and surface. Basaltic crusts similar to Earth’s oceanic crust characterize terrestrial planets in the solar system while the continental masses, areas of buoyant, thick silicic crust, are a unique characteristic of Earth. The continental crust is also enriched in incompatible elements (elements that separate from the mantle during partial melting) and although it is a volumetrically minor layer it plays a major role in the fractionation and storage of those elements. Therefore, understanding the processes responsible for the formation of continents is fundamental to reconstructing the evolution of our planet. Analyzing modern analogues where “juvenile” continental crust is forming can provide a better understanding of the formation of continental crust in the past. The evolution of the Central American Land-Bridge (CALB, Costa Rica and Panama) was used as a natural laboratory to answer this fundamental question. Geochemical and geophysical data support the evolution of the CALB into a young continent as a result of the interaction of Galapagos Hotspot tracks with this subduction system. A global survey of intra-oceanic arcs was conducted with the goal of identifying where magmas with continental crust signatures have been produced and what processes control the composition of the volcanic output. Finally, a new geochemical continental index was developed to quantitatively correlate geochemical composition with available average arc P-wave velocity, resulting in a strong correlation (r2=0.87) between those two parameters. Our work suggests that although the origin and evolution of continents may require many processes, melting of enriched oceanic crust and reaction of these melts with the mantle wedge in a subduction system will result in juvenile continental crust production, a process that was probably more common in the Archean than today. In Central America the production of “juvenile” continental crust culminated with the closure of the Panama Seaway ~15 to 3 Ma. This closure resulted in global change of ocean circulation, separated marine species, and allowed the exchange of fauna between the Americas, making the evolution of the CALB not only relevant to the understanding of geologic processes, but also had considerable impacts on evolution of life and climate on the planet.