Tectonophysics Research
The tectonophysics group is internationally recognized for effectively combining experimental, theoretical, and field studies to determine physical processes operative in the Earth's crust and mantle. Their research is interdisciplinary, and thus well suited to students with strong backgrounds in geology, physics, mathematics and/or engineering.
Seismology/Geodynamics
In the past few years at Brown, the effort to understand flow in the Earth's mantle has included several oceanographic research cruises to the Pacific, Indian, and Atlantic Oceans, the deployment of arrays of seismometers across eastern and central North America and the East Pacific Rise, and the development of sophisticated numerical simulations of three-dimensional flow and wave propagation. One particular focus has been the generation of melt by upwelling beneath mid-ocean ridges and its subsequent migration to the surface at the ridge axis to form new seafloor. Seismic experiments, gravity measurements, side-scan sonar, and multi-beam bathymetry all provide observational constraints for the attempt to develop theoretical models that explain the segmentation of the ridge system, the thickness and composition of the oceanic crust, and the formation of median valleys and axial, topographic highs.
Another important focus is the use of seismic velocity anomalies and anisotropy to help map flow in the mantle. Seismic anisotropy in the upper mantle is likely caused by shearing due to plate motions and convection, with additional influence from partial melt in certain regions. With the aid of theoretical models of convection and wave propagation, we are studying mantle structure and flow near subduction zones and mid-ocean ridges, beneath continents, and at the core-mantle boundary. Unique data sets of seismic waveforms have been acquired in the TUCAN, GLIMPSE, MELT, MOMA (Missouri to Massachusetts), NOMAD and FLED (Florida to Edmonton) Experiments. These examples show how integration of theory and observation is fundamental to the philosophy of our group. Our mode of research emphasizes collaboration. Students typically work with more than one of our faculty, and we enjoy an interactive environment that includes seminars, informal research talks and lots of discussion.
Our mode of research emphasizes collaboration. Students typically work with more than one of our faculty, and we enjoy an interactive environment that includes seminars, informal research talks and lots of discussion.
Structural Geology
Structural Geology at Brown involves experimental, theoretical and field work. Emphasis is on obtaining an understanding of deformational processes over a range of scales from the sub-microscopic to the global. The use of continuum mechanics figures strongly in the theoretical work. Students with a strong undergraduate background in geology, physics, or engineering are well suited for study in structural geology. Coursework is individually tailored to match the background and interests of incoming graduate students. Courses are usually selected from many available in the Department of Geological Sciences, the Division of Engineering and the Applied Math Department. An important difference between undergraduate and graduate education is that original research plays an important role in graduate school. Students get involved in an individual research program in their first year. The importance of research compared to courses increases every year, as formal course work is completed and students become more experienced and able to conduct their research projects independently. Students normally undertake more than one research project in order to gain a variety of experience and background that will help them obtain the type of employment they each desire.
The structure group has built one of the best-equipped rock deformation labs in the country. Constitutive laws for frictional sliding of important rock types as well as the processes responsible for observed behavior can be determined in experiments on faulting and friction mechanics performed in a rotary shear gas apparatus. Field studies of faults help guide the laboratory experiments and test their applicability to nature. Theoretical modeling currently underway for Parkfield and Loma Prieta sections of the San Andreas investigates the reasons for earthquake instabilities to determine ways to attempt earthquake prediction. Experimental studies to determine grain-scale deformation mechanisms, microstructures, and flow laws operative in crustal rocks are conducted in 3 piston-cylinder apparatus capable of applying a wide range of temperatures, pressures, and strain rates. Specific studies concern the nature of the brittle-ductile transition, formation of mylonites and ductile shear zones, and the role of fluids in deformation. Collaborative studies with Prof. Emeritus Yund (mineralogy) investigate the interaction of chemical and mechanical processes in deforming metamorphic rocks. Field and theoretical studies of the tectonic history of New England involve collaboration with Prof. L. Peter Gromet (geochemistry).
Environmental Geophysics and Hydrology
Environmental geophysics applies ground penetrating radar, seismic, gravity, magnetic, electromagnetic, and resistivity techniques to characterize the Earth's subsurface for groundwater studies and engineering applications (see also Environmental Science).
Environmental geophysics and hydrology is a relatively new initiative at Brown University, and involves the application of geophysical methods and computer modeling to environmental investigations of groundwater flow, watershed dynamics, subsurface hazardous waste assessment and contaminant migration. We use computer modeling and field research — as well as the broad resources of interdisciplinary activity throughout the University — to follow the precept, "Think globally, but act locally," to investigate environmental problems that, while of local community importance, are paradigms of analogous concerns on the national and international scale.
Facilities
Brown is unusually well equipped for experimental studies. The high pressure, high-temperature experimental rock deformation laboratory has three Griggs-type piston-cylinder apparatus designed for conducting experiments at temperatures up to 1200ƒC, pressures up to 1500 MPa, and time durations up to several months. This allows study of the deformation mechanisms and rheology of rock samples at conditions including those of the entire crust and upper mantle.
The lab also has a unique high-pressure rotary-shear apparatus capable of doing rock friction experiments to arbitrarily high displacements and torsion of solid samples to arbitrarily high shear strains. This machine uses gas as the confining medium, has a flow-through pore-pressure system, features internal measurement of displacement, torque, and axial load, and is interfaced to a UNIX computer for digital data acquisition and control. Consequently it can measure the mechanical properties of rocks and minerals with unusually high precision.
The laboratory also has facilities for coring, sawing and grinding of experimental samples and for petrographic examination of the deformed samples. The Department has a thin-section lab and technician, a machine shop and machinist. A nearby central facility houses modern scanning and transmission electron microscopes.
Brown is also well equipped for theoretical and field studies. Computer facilities include Sun SPARCstations, IBM RS/6000 workstations, DECstations, new MacIntosh computers, two color postscript printers and several black and white printers. All the computers are networked; the UNIX machines are on ethernet. The network allows high speed access via internet to computers all over the world. This network is used for computing on supercomputers at several of the supercomputer centers across the country.
Equipment for field studies includes surveying equipment and both a portable rock saw with diamond blade and a portable diamond core drill.