Earthquake System Science at USC

Earthquake system science seeks to understand how matter and energy interact within the lithosphere to produce emergent seismic phenomena by solving three basic geophysical problems: (a) the dynamics of fault systems—how forces evolve within a fault network over hours to centuries to generate a sequence of earthquakes; (b) the dynamics of fault rupture—how forces evolve over seconds to minutes when a fault breaks during an earthquake; and (c) the dynamics of ground motions—how seismic waves propagate from the rupture to shake sites on Earth’s surface. These system-level problems involve a hierarchy of multiscale interactions, coupled through the nonlinear processes of brittle and ductile deformation. The world’s largest collaboration in earthquake system science is the Southern California Earthquake Center (SCEC), which is based at USC.

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A snapshot of the ShakeOut animation (M7.8 earthquake on the San Andreas fault) that was made by Geoff Ely (USC postdoc) from the simulation published in R. Graves, B. Aagaard, K. Hudnut, L. Star, J. Stewart & T. H. Jordan, Broadband simulations for Mw 7.8 southern San Andreas earthquakes:  Ground motion sensitivity to rupture speed, Geophys. Res. Lett., 35, L22302, doi: 10.1029/2008GL035750, 2008




What is a Geosystem?

Geosystem is the generic term for an interacting set of physical, chemical, and biological processes that governs a natural system of terrestrial scale. More precisely, it is a highly simplified, though internally consistent, representation of nature designed to model and so predict specific behaviors observed in the Earth environment. The behavior of interest defines the geosystem: at USC, current quantitative geosystems research focuses on the numerical modeling of earthquake, mantle and climate systems, which are all interrelated.


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from Grotzinger & Jordan, "Understanding  Earth" (6th ed., 2009)


Climate System Science at USC

Climate system behavior emerges from the non-linear interaction of various near-surface Earth systems, mainly the atmosphere, oceans, cryosphere, biosphere and lithosphere.

Climate system dynamics at USC focuses on the long-term interactions between the tropical oceans and atmosphere. Through sophisticated statistical tools, we seek to reconstruct key climate fields like tropical Pacific sea-surface temperature over the past 2000 years from an array of proxy data. Through simplified climate-proxy models, we seek to characterize the geochemical fingerprint of climate processes and forcings in the geological record. The ultimate goal of this approach is to bridge the gap between models and data over timescales of relevance to the societal adaption to climate change.

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Contours in this figure display oxygen isotope ratios as simulated by an isotope-enabled atmospheric general circulation model, regressed onto the NINO3 index of El Niño activity. Symbols are collocated with existing proxy records of tropical climate over the past 500 years : corals (circles), speleothems (diamonds), ice cores (asterisks), sediment cores (squares). The image illustrates how proxy records can be used to capture the geochemical fingerprint of dynamical systems like El Niño.





Mantle System Science at USC
Mantle system dynamics at USC focuses on the interactions between mantle convection, tectonic deformation, and Earth's thermal evolution.
We strive to integrate a broad array of data with computer and analog experiments in order to construct quantitative models of plate tectonics, from grain-scale deformation to plate-scale flow. Recent research projects focused on seismic anisotropy, mantle heat transport, subduction dynamics, and fault slip-rates and crustal stress.

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Snapshot of a spherical convection computation that strives to consistently generate, plate-tectonics like surface motions and mantle heterogeneity structure. (Foley & Becker, G-Cubed, 2009)