EXPLORING THRESHOLD CONDITIONS FOR SLIP PARTITIONING UNDER OBLIQUE CONTRACTION

Slip partitioned systems that have different slip rake on two or more faults (e.g. strike-slip on one and oblique slip on the other) are well documented in fault zones characterized by oblique contraction or extension. Despite their prevalence, little is known on how these systems evolve. Using scaled physical experiments in wet kaolin clay, we explore how convergence direction and accumulated strain control the degree of slip partitioning. Modeling slip-partitioned systems with wet kaolin offers benefits over dry sand in that the clay produces long-lived fault structures that easily reactivate. The wet kaolin is placed over rigid blocks that have a dipping contact (dips from 15˚ to 45˚). This contact slips obliquely as the motorized plates converge oblique to the strike of the contact and drives fault development within the overlying wet kaolin. We precut a vertical fault above the block contact. As with previous experiments in dry sand, greater convergence angle (measured from fault trace) suppresses strike-slip. Within the wet kaolin we observe two convergence angle thresholds for strike-slip. Below the lower threshold, strikes-slip persists throughout the experiment and along with the dipping oblique-slip fault, comprise a full slip partitioned system. Between the two convergence thresholds, the fault system is slip partitioned at the start of the experiment but the strike-slip fault does not persist. Above the upper threshold convergence angle, no strike-slip develops and the fault system is not slip partitioned. We explore the affect of block contact dip on these thresholds. Analysis of the partitioning evolution is facilitated with digital image correlation (horizontal strains) and stereovision (uplift). These state of the art methods provide complete slip vectors for the faults and constrain fault dip. The evolution and maintenance of slip partitioning within oblique convergence margins may depend on loading and configuration of the system.