[J03-3] Deformation of the lithosphere: Integrating seismology and geodesy through modelling III

[J03-3-01] Modeling lithospheric tectonics with space geodesy: the problem of timescales

^○Mian Liu¹ (1.University of Missouri, Columbia, USA, 2.The Computational Geodynamics Lab, Beijing, China)

Space-based geodesy has provided unprecedented details of crustal kinematics that have been widely used in models of lithospheric dynamics, but the results are sometimes unsatisfactory and confusing. The problem arises from the timescale-dependent lithospheric rheology. Space-based geodetic measurements, usually over a few years, take snapshots of the deforming crust that is often dominated by transient elastic or viscoelastic strain. The tectonic evolution of lithosphere, however, only leaves permanent (plastic) strain in geological records. Thus using space-based geodetic measurements in long-term lithospheric dynamic models requires consideration of all elastic, viscous, and plastic strains. I will illustrate this challenge in our studies of tectonic evolution in western US, the Andes, and the Tibetan Plateau. In the southwestern US, crustal kinematics delineated by the GPS measurements differs significantly from that reconstructed from the geological records, leading to different estimates of the driving forces. Our numerical model shows that the GPS data is dominated by the transient viscoelastic shear strain across the Pacific-North American plate boundary zone. The geological strain in the past few million years, on the other hand, reflects mainly the extensional strain driven by gravitational collapse of the Basin and Range Province. Across the Andean orogenic belt, the GPS-measured crustal shortening is largely elastic and tends to be restored by repeated trench earthquakes, whereas permanent strain accumulates in the subandes where the plastic strength of the crust is lower than that of the plate interface. Across the Himalayan-Tibetan orogen, deformation by the indentation of the Indian plate is largely limited to the Tibetan Plateau, whereas gravitational potential energy is chiefly responsible for the widespread crustal deformation measured by GPS in much of central and eastern Asia.