Discrete Element Modeling of a Subduction Zone

1. Discrete Element Modeling of a Subduction Zone Ben Valentino1, Eduardo Toledo2, Eduardo Nobre2, Luciana Vieira2, Diogo Cintura2 1Department of Earth Sciences, SUNY Oswego 2Department of Civil Engineering, Federal University of Alagoas (UFAL) Introduction Objective Subduction is the process that occurs when the convergence of adjacent tectonic plates results in one plate overriding the other. This occurs only at oceanic-oceanic and oceanic-continental plate boundaries. This process has been studied extensively, but the process of subduction initiation remains a controversial topic (Geyra, 2011). The objective of this study was to successfully model a continental-oceanic subduction zone using the discrete element method (DEM) and conjointly to provide insight into the initiation process. Subduction is a very complex process, hence, modifications to the modeling software were necessary. Therefore it is an equally important objective to develop software capable of modeling a subduction zone using DEM. Theory and Methods The discrete element method utilizes particles which interact with each other under the laws of Newtonian physics. The program PreDEM was used to construct the models. The model is constructed by defining zones, called materials, which are filled with particles. For each material, a spring defines the interaction properties of the particles. A contact model, which controls the stiffness of the spring, is defined for each of the materials. In this study a Kelvin contact model was used. This model controls the tensile and compressional stiffness of the spring in addition to the damping coefficients. Once a model is constructed, the data for the simulation is produced in the program DEMOOP parallel, and the results of the simulation are observed in Demview. Template and dat files were used to implement a BPM to the model in order to strengthen the oceanic and continental crust and to prevent bunching of the oceanic crust. The driving mechanism behind tectonic plate movement is mantle convection. This is the same mechanism which drives subduction. The primary cause for subduction initiation is gravitational differences of the oceanic and cont crust, but there are other factors which play a role in the initiation process (Geyra, 2011). Once initiation has been achieved, the colder, less buoyant oceanic crust is forced under the hotter, more buoyant cont. crust. Image from the Pacific Northwest Seismic Network Results Conclusion References Acknowledgements Of the variables influencing subduction in these models, material density had the most significant impact on subduction of the oceanic crust. Drastic exaggeration of the oceanic crust density lead to the best subduction results, but they are unrealistic. Future modeling will incorporate implementation of a pressure/temperature gradient which varies elasticity with depth and will include thermal differences in the mantle wedges and oceanic/cont. crust. Optimally, these modifications will lead to a lower value for the cont. crust density and cause the oceanic layer to subduct further into the mantle. Once this is achieved, we can begin meaningful investigations of the initiation process of a subduction zone at a cont. margin. Geyra, Taras. Future directions in subduction modeling: Journal of Geodynamics V. 52 pp 344-378 The Pacific Northwest Seismic Network, PNSN http://old.pnsn.org/HAZARDS/CASCADIA/cascadia_zone.html