A SEISMODYNAMICAL MODEL OF LITHOSPHERE DEFORMATION - DEVELOPMENT OF CONTINENTAL AND OCEANIC RIFT NETWORKS

Seismicity and lithosphere extension on the scale of a tectonic plate are investigated in two horizontal dimensions and time using a dynamic al model for a thin plate overlying a viscoelastic channel, The plate consists of two layers, a brittle elastic-plastic crust that deforms a s a result of earthquakes along faults and a strong viscoelastic layer representing the aseismic, creeping lower lithosphere. Numerical expe riments of lithosphere rifting are performed for one- and two-layer li thosphere models using two different rupture criteria, In all the calc ulations, earthquakes and faults of various sizes may form anywhere in the numerical domain as a result of the constitutive formulation. The differences between the one-and two-layer model results suggest a mec hanical explanation for the difference between continental and oceanic rifting. When the lower lithosphere is absent, a small number of faul ts dominate the deformation, and a relatively simple, narrow rift zone develops corresponding to oceanic rifting. When a highly viscous lowe r Lithosphere is included a complex, distributed network of faults dev elops, similar to continental rifting, The complexity of the fault sys tem also depends on the yield criterion in the crystal layer. In our s imulations, complexity is greater for a yield criterion with strong sh ear stress dependence than for one with. mainly extensional stress dep endence, Whether a result of lower lithosphere stretching, crustal het erogeneity, or the yield criterion, higher complexity increases the ti mescale for fault development, increases self-similarity in fault syst em geometry and stress and strain time series, and results in power la w moment-frequency earthquake size scaling.