Person:

Langstaff, Meredith Avery

The India-Asia collision zone accommodates the relative motion between India and Eurasia through both shortening and pervasive strike-slip faulting. To gain a mechanical understanding of how fault slip rates are driven across the Tibetan plateau, we develop a two-dimensional, linear elastic, two-stage, deformable microplate model for the upper crust based on the behavior of an idealized earthquake cycle. We use this approach to develop a suite of simple India-Asia collision zone models, differing only in boundary conditions, to determine which combination of edge forces and displacements are consistent with both the slip rate measurements along major Tibetan faults as well as the geodetically observed extrusion of crustal material toward Southeast Asia. Model predictions for the Altyn Tagh (1–14 mm/yr), Kunlun (3–10 mm/yr), Karakorum (5–12 mm/yr), and Haiyuan (3–5 mm/yr) faults are in agreement with geologically and geodetically inferred slip rates. Further, models that accurately reproduce observed slip rate gradients along the Altyn Tagh and Kunlun faults feature two critical boundary conditions: (1) oblique compressive displacement along the Himalayan range front west of the Shillong plateau, and (2) forcing in Southeast Asia. Additionally, the ratio of internal-block potency rate to the total potency rate for each microplate ranges from 28% to 79%, suggesting a hybrid view of deformation in Tibet as simultaneously localized on major faults and distributed at length scales <500 km.

We first describe the methodology for a two-dimensional, elastic deformable microplate modeling approach for continental plate boundaries. Deformable microplate models combine discrete slip on microplate boundaries (faults) with continuous deformation in block interiors. Two idealized models simulating continental collision are presented, one with two microplates and one with four microplates.