CORROBORATING DYNAMIC SIMULATIONS OF FAULT INTERACTION WITH THE PALEOSEISMIC RECORD OF A RESTRAINING DOUBLE-BEND

Multi-cycle numerical models of dynamic earthquake rupture simulate realistic coseismic stress changes and naturally predict both rupture extents and nucleation locations. The spontaneous propagation and termination of rupture in dynamic rupture models reveal where stress perturbations form and how they inhibit or induce rupture. Despite their use in scenario earthquake simulations, the predictions of such models have not yet been rigorously compared to actual earthquake records derived from paleoseismology and geomorphology. We couple geologic investigation of earthquake occurrence with numerical finite element modeling of dynamic ruptures over multiple earthquake cycles along two parallel fault strands at the Aksay restraining bend and stepover of the Altyn Tagh fault to test the hypothesis that great (M≈8) earthquakes terminate at this bend. The two fault strands lie within 5 to 15 km of one another through the bend, but only one extends beyond the bend in either direction: the southern strand continues westward and the northern strand continues eastward. We conducted a 2D multi-cycle rupture simulation of this fault system using a procedure developed by Duan and Oglesby (2006), which implements slip-weakening friction laws for dynamic rupture and Maxwell viscoelastic behavior for interseismic relaxation and secular loading. Our preliminary models show that great earthquakes initiate outside the bend and lose energy along the less optimally oriented fault segments within the bend, terminating shortly thereafter. Smaller events occur locally where terminations of prior ruptures have increased and reoriented stresses. Thus the modeled cumulative slip after multiple earthquakes decreases into the bend along each strand, while event frequency increases. This result is consistent with our field observations of fault zone morphology in the stepover, which support higher slip rates on the principal fault strands where they enter the bend. Our paleoseismic investigations reveal that even the theoretically less active tail ends of both faults exhibit multiple Quaternary events. These preliminary results suggest that where these two faults overlap, the Aksay bend and stepover may terminate infrequent great earthquakes, but may host smaller, more frequent surface rupturing events.