The discrete element method is anumerical approach to be generally used in large dynamic deformation. The approach permits mega-fault generationand evolution without pre-arranged initial settings. The results provideinsight into fault birth, propagation and rupture. We use this method in three different types ofdeformation from large-scale continental deformation, relatively small-scalevolcanic extrusion and short time scale fault rupture process.
First, we use the India-Asian collisionas an example, the Indiancollision has deformed the eastern Asian continent in a multifaceted way,uplifting Tibet and surrounding mountains, activating ≥ 1000 km-longstrike-slip faults, and opening Tertiary rifts and oceanic basins up to ≈ 3000km away from the Himalayas. We use Discrete Element Modelling to simulate andfurther understand the evolution of 3D strain across east Asia since the onsetof collision, ≈ 55 Ma ago. The planar, 50 million km2, 125 km-thickmodels, scaled for gravity corroborate that continental crustal thickeningalternated with the extrusion of large blocks that rifted apart in the farfield.
In volcanic silicic spine extrusion, seismicity involves recurrentexcitation of similar sources at stationary depth beneath the crater. We assessstress, strain and faulting in ascending magma which, although hot, behaves asa solid. Earthquake fault-plane solutions during the 09/2004-08/2005 eruptionsof Mount St. Helens imply shrinking of magma rising across a conduit“bottle-neck”. Constriction across the neck and vertical shear along theconduit walls thus predominate. Dynamic Discrete Element Modeling successfully reproduces repetitive nucleation of thrust faults within the neck. Furthermore,the pressure drop across the neck boosts crack opening and hence gas extraction(natural “fracking”).
During large earthquake fault rupture, seismic sources tendto split in several sub-events that rupture neighboring fault segments. Usingnumerical modelling, we demonstrate that when a pristine layer of brittlematerial is sheared, the first oblique Riedel fractures nucleate with regularspacing controlled by the thickness of that layer. During later localization,modelling results show that initial fractures control the spatial structurationof the entire fault system.