Parallel computing of multi-scale continental deformation in the Western United States: Preliminary resultsIntroductionMulti-scale tectonics in the western USParallel computing of lithospheric dynamics: a new approachModeling active tectonics in the western USEffects of gravitational potential energyEffects of plate boundary forcesEffects of basal shearShort-term versus long-term deformationModeling multi-timescale slips along the San Andreas FaultA 3D visco-elasto-plastic modelLong-term fault slip rates and strain localizationMulti-timescale fault behavior: from ruptures to earthquake cyclesDiscussionConclusionsAcknowledgementsReferencesPhysics of the Earth and Planetary Interiors 163 (2007) 35–51Parallel computing of multi-scale continental deformationin the Western United States: Preliminary resultsMian Liua, Youqing Yanga,∗, Qingsong Lib, Huai Zhanga,caDepartment of Geological Sciences, University of Missouri-Columbia, Columbia, MO 65211, USAbLunar and Planetary Institute, Houston 77058, USAcComputational Geodynamics Lab, Graduate University of Chinese Academy of Sciences, Beijing, ChinaReceived 18 January 2007; received in revised form 16 June 2007; accepted 16 June 2007AbstractLithospheric deformation in the western United States is one of the best examples of diffuse continental tectonics that deviate fromthe plate tectonics paradigm. Conceptually, diffuse continental deformation is known to result from (1) weak and heterogeneousrheology of continents and (2) driving forces that arise from plate boundaries as well as within the continental lithosphere. However,the dynamic interplay of continental rheology and driving forces, hence the geodynamics of continental tectonics, remains poorlyunderstood. The heterogeneous rheology and multiple driving forces cause continents to deform over different spatiotemporal scaleswith different physical processes, yet most geodynamic models for continental tectonic avoid dealing with such multiphysics partlybecause of (1) the limited observational constraints of lithospheric structure and deformation, and (2) high demands on computingalgorithms and resources. These constraints, however, have relaxed significantly in recent years to permit exploration of some ofthe multi-scale physics governing continental tectonics. Here we present preliminary results of modeling multi-scale tectonics inthe western United States using parallel finite element computation. In a 3D subcontinental-scale model, we used fine numericalmeshes to incorporate all major tectonic boundaries and rheological heterogeneities in the model to explore their interplay withtectonic driving forces in controlling active tectonics in the western US. In another model for the entire San Andreas Fault system,we explored strain localization and simulated fault behavior at multi-timescales ranging from rupture in seconds to secular faultcreep in tens of thousands of years. These models can help to integrate data grids with distributed high-performance computingresources in the emerging geosciences cyberinfrastructure.© 2007 Elsevier B.V. All rights reserved.Keywords: Parallel computing; Continental tectonics; Finite elements; San Andreas Fault; Western US; Cyberinfrastructure1. IntroductionIn the plate tectonics paradigm, the outer shell of theEarth consists of a dozen or so rigid plates that moverelative to each other. The relative motion between apair of plates can be entirely determined by a simple∗Corresponding author.E-mail address: [email protected] (Y. Yang).Euler vector (DeMets et al., 1990, 1994), and deforma-tion of the plates is limited to narrowly defined plateboundaries. Although the rigid-plate approximation issatisfactory in explaining many geological observations,broadly diffuse deformation away from plate boundaries,and significant deformation in plate interior, are common(Gordon and Stein, 1992; Molnar and Tapponnier, 1975).Such non-plate behavior is particularly conspicuous incontinents; examples include the broad crustal deforma-tion in the Tibetan plateau and central Asia, and diffuse0031-9201/$ – see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.pepi.2007.06.00836 M. Liu et al. / Physics of the Earth and Planetary Interiors 163 (2007) 35–51continental deformation in the western United States.The diffuse continental tectonics have helped propellingmodern geosciences research to advance from rigid-platekinematics toward a more holistic understanding of litho-spheric deformation in the context of the Earth’s dynamicsystems (Molnar, 1988).The cause of diffuse continental deformation isconceptually clear: the relatively weak and laterally het-erogeneous rheology of the continental lithosphere, andthe driving forces that arise not only from plate bound-aries but also from within and at the base of continentallithosphere (Artyushkov, 1973; Forsyth and Uyeda,1975; Molnar, 1988). However, the dynamic interplaybetween lithospheric rheology and driving forces, hencethe geodynamics of continental tectonics, remain poorlyunderstood, partly because numerical modeling of conti-nental tectonics is difficult. One of the major challengesis that continental deformation varies at different spatialand temporal scales. For example, present crustal defor-mation measured by the Global Positioning Systems(GPS) and other space-based geodetic techniques reflectmainly short-term deformation. Given the knowledgeof timescale-dependent lithospheric rheology (Jeanlozand Morris, 1986; Liu et al., 2000; Pollitz, 1997, 2003a;Ranalli, 1995), and the fact that tectonic processes andboundary conditions can change significantly throughgeological history, it is not surprising that short-termdeformation derived from space-geodesy often differsignificantly from long-term crustal deformation indi-cated by geological records (Dixon et al., 2003; Friedrichet al., 2003; He et al., 2003; Liu et al., 2000; Pollitz,2003a; Shen et al., 1999). Continental deformationalso varies strongly with spatial scales. At continentalscales, most geological discontinuities, including faultsand structural boundaries, may be ignored in first-orderapproximations (Bird, 1999; England and McKenzie,1982). However, at smaller scales these features oftendominate the tectonic processes.Current numerical models are usually limited to cer-tain spatial and temporal scales. Whereas there are soundscientific rationales for doing so, this practice oftenrepresents a compromise to two major obstacles: