Paleoseismic Investigation of the Aksay Restraining Double Bend, Altyn Tagh Fault, and Its Implication for Barrier‐Breaching Ruptures

Abstract

AbstractFault geometry is recognized as an important control on earthquake rupture extent, magnitude, and recurrence behavior. However, multicycle earthquake rupture simulations indicate that geometrical barriers do not always stop rupture propagation. Stress buildup over multiple prior earthquakes may promote an occasional breach of a barrier, producing a significantly larger rupture. Here we present paleoseismic data from the Aksay restraining double bend of the Altyn Tagh fault, which supports such breaching. The Aksay bend consists of two main strands, which bend together in a broad transpressional configuration. We investigate the paleo‐earthquake histories of both strands to assess the correlation of events within and beyond the bend. The south strand exhibits four very likely paleo‐earthquakes with an average interval of 1,433 ± 57 years and a coefficient of variation (COV) of ~ 0.5. The north strand records four highest‐quality events after 3650 Before Common Era with an average interval of ~1,326 ± 179 years and a COV of ~0.3. The varying recurrence intervals and relatively high COVs indicate that faults within the Aksay bend have only quasi‐periodic rupture recurrence. Comparing the event sequences also suggests a complex rupture history. The penultimate event appears to correlate across the bend, as well as to previously published paleoseismic chronologies both to the east and to the west, which supports it being a barrier‐breaching event. The event histories reported here indicate that multiple earthquakes must terminate within the bend, over several earthquake cycles, in order to arrive at a stress condition suitable for a breaching earthquake rupture.