Major research frontiers, grand challenges, and thorny problems in geophysics & tectonics

How does the near-surface environment affect natural hazards and resources?

• How can the National Seismic Hazard Maps be improved using advanced physics-based understanding of earthquake ruptures, sub-surface properties, and strong ground motions?
• How can time-dependent properties of shallow aquifers best be characterized to monitor water and contaminant transport?
• Can potential ground failures from landslides and karst be robustly assessed and monitored?
• Can nuclear testing be monitored with confidence levels necessary for the Comprehensive Test Ban Treaty?
• What is the resolution of seismological techniques to identify and locate unexploded ordinance, tunnels, buried landfills, and other human-made subsurface hazards?

How do faults slip?

• How do earthquakes start and stop?
• How do fault geometry, rheology, and history combine to determine the propagation, size, and location of earthquakes?
• What is the fundamental nature of high-stress asperities (areas of high-slip in an earthquake)?
• What is the fundamental nature of episodic fault tremor and slip and how are they related to occurrence of large earthquakes?
• Can we forecast the spatial and temporal occurrence of earthquakes and accurately predict their effects on ground motions and on the built environment?
• How quickly can the size of an earthquake be determined and reliable shaking and tsunami warnings issued?

What is the relationship between stress and strain in the lithosphere?

• What is the state of stress on active faults and how does it vary in space and time?
• What are the stress-strain laws of faults and the surrounding crust that give rise to slow and fast slip?
• How are new faults initiated and reactivated throughout Earth history?
• What is the stress distribution in the lithosphere, and does this stress accumulate, get transferred through the lithosphere, and get released during the earthquake cycle?
• How much deformation occurs between seismic events, during an event, and shortly after an earthquake?

How do processes in the ocean and atmosphere interact with the solid Earth?

• How do ocean wave and other seismic background noise variations track climate change?
• Are models of thermohaline circulation consistent with seismic images of oceanic internal structure?
• How can bounds be placed on the energy budgets and other physical properties of bolide impacts, glacial calving, volcanic eruptions, tornado touchdowns, and other sources jointly observed by seismic and atmospheric monitoring?
• How is glacier activity changing and can we monitor rapid changes like ice-sheet collapses in advance?
• What is the nature of sub-glacial friction and what is the role of fluids at the base of glaciers?

How is Earth's habitable surface a consequence of the planet's interior?

• How does water cycle through Earth's interior and how does it affect mantle rheology and melting temperatures?
• How can we efficiently and inexpensively quantify and monitor the extraction and replenishment of groundwater resources using seismological techniques?
• What is the potential for sequestration of large volumes of carbon dioxide in underground reservoirs?
• How can we image time-dependent changes in fracture systems, including the migration of fluids?
• How do aqueous and carbon-rich fluids behave at depth, how do fluids and rocks interact, and how do they cycle with surface systems?

How do magmas ascend and erupt?

• What is the physical state of volcano plumbing systems in different tectonic regimes,?
• Where is melt stored within the crust before erupting, and how does this alter the crust?
• How do volcanoes and earthquakes interact? How does the release or storage of aqueous fluids affect the rupture process?
• How have volatiles partitioned by partial melting/solidification among various regions of the crust and mantle over Earth's history?

What is the lithosphere-asthenosphere boundary?

• Were the processes that formed the early continental crust and mantle different from those acting today? How much of today's continental crust formed early in Earth's history?
• How deep do boundaries associated with accreted terrains extend?
• How do preexisting structures such as ancient faults or sutures affect modern-day deformation, magmatism, seismicity, and other processes?
• What is the 3D rheology of the lithosphere and asthenosphere and how does it relate to earthquake cycle deformation, the development of anisotropic fabric, and the long-term deformation of the continent?
• What is the asthenosphere and what controls the lithosphere-asthenosphere boundary?
• To what extent is the present deformation of the crust coupled to active deformation in the mantle?

How do plate boundary systems evolve?

• What controls the development of subduction zone features, including accretionary prisms, mantle wedge volcanism, and back-arc basins?
• What causes deep earthquakes and what are the stress and thermal conditions in deep slabs?
• What controls the localization and segmentation of extension in rift zones and at mid-ocean ridge spreading centers and how much lateral transport of melt is there along ridge segments and between ridges and hot spots?
• How is continental deformation in plate boundary zones accommodated at depth and role is played by small-scale convection in driving broad deformation zones around plate boundaries?
• To what extent do different types of basins (foreland, forearc/backarc, passive margin, cratonic, or pull-apart) reflect or affect deep crustal and mantle structure?

How do temperature and composition variations control mantle and core convection?

• What are the scales of heterogeneity in the global mantle convection system, what are their chemical, thermal, and mineralogical causes, and how do patterns of seismic velocity, anelasticity, and attenuation correlate with them?
• What is the form and amount of flux of material between the upper and lower mantle, and on what time scales does it occur?
• What forms do mantle plumes take and how are they related to surface hotspots? Are the two large, lowermost-mantle low-shear velocity provinces in the deep mantle megaplumes or megapiles?
• What are the melting and phase relations of mantle materials from the near surface to the core-mantle boundary, and what are the chemistries and physical properties of melts?
• What are the factors that drive outer core convection, and how does this convection generate the core geodynamo and Earth's magnetic field?
• How is the strong heterogeneity and anisotropy of the inner core related to its growth processes over Earth's history and to the geodynamo?

How are Earth's internal boundaries affected by dynamics?

• How sharp are internal mantle and core boundaries and what are their causes? Is the mantle chemically layered?
• What is the topography and lateral extent of mantle boundaries, including the core-mantle boundary, and what causes it?
• What are the effects of the transition zone boundaries on mass flux between the upper and lower mantle, and is the transition zone a large reservoir of water?
• Are there any other thermal boundary layers besides the D˝ layer that serve as sources of mantle plumes?
• How are mantle-core interactions related to the ultra-low velocity zone and D˝ anisotropy?
• How do lowermost mantle topography, temperature, and electrical conductivity constrain outer core flow and are there stable thermo-chemical boundary layers in the outermost outer and lowermost outer core?
• What is the likely age and growth rate of the inner core?

How do the structures and dynamics of other planetary bodies differ from Earth?

• What are the dominant tectonic mechanisms on other terrestrial planets and moons?
• How does the distribution of water and carbon dioxide within the terrestrial planets affect their tectonics?
• What is the impact history of planetary bodies and how has it affected their histories?
• To what degree are other planetary bodies differentiated and to what degree do they undergo convection?
• How do the differing compositions of the silicate mantles of other planets influence melting and crustal generation of these bodies?
• What are the parameters that control how magnetic fields are generated within different planetary bodies and can cause them to turn off?

Lay, T., R. Aster, D. Forsyth, B. Romanowicz, R. Allen, V. Cormier, J. Gomberg, J. Hole, G. Masters, D. Schutt, A. Sheehan, J. Tromp, and M. Wysession, Seismological Grand Challenges in Understanding Earth's Dynamic Systems, Incorporated Research Institutions for Seismology Report to the National Science Foundation, 74 pp., 2009

Trehu, A., R. Aster, C. Ebinger, B. Ellsworth, K. Fischer, J. Freymuller, J. Hole, S. Owen, T. Pavlis, A. Schultz, B. Tikoff, and M. Wysession, Unlocking the Secrets of the North American Continent: An Earthquake Science Plan for 2010-2020, 82 pp., 2010

Williams, Q., J. M. Brown, J. Tyburczy, J van Orman, P. Burnley, J. Parise, M. Rivers, R. Wentzcovitch, and R. Liebermann, Understanding the Building Blocks of the Planet, Long-Range Planning for High-Pressure Geosciences Workshop, 68 pp., 2010.