Formation of Complex Craters in Layered Targets With Material Anisotropy. Issue 2 (9th February 2019)

• Record Type: Journal Article
• Authors: Hopkins, Ryan T.; Osinski, Gordon R.; Collins, Gareth S.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 2(2019)
• Page Start: 349
• Page End: 373
• Publication Date: 2019-02-09
• Subjects: impact cratering -- anisotropy -- complex craters -- shock‐physics code; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2018JE005819
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Meteorite impacts often occur in layered targets, where the strength of the target varies as a function of depth, but this complexity is often not represented in numerical impact simulations because of the high computational cost of resolving thin layers. To address this limitation, we developed a method to approximate the effect of multiple thin weak layers within a sedimentary sequence using a single material layer to represent the entire sequence. Our approach, implemented in the iSALE (impact‐Simplified Arbitrary Lagrangian Eulerian) shock physics code, combines an anisotropic yield criterion with a cell‐based method to track the orientation of layers. To demonstrate the efficacy of the method and constrain parameters of the anisotropic strength model required to replicate the effects of thin, weak layers, we compare results of simulations of an ~20‐ to 25‐km diameter complex crater on Earth using the new method to those from simulations that explicitly resolve multiple thin weak layers. We show that our approach allows for a reduction in computational cost, negating the need for an increase in spatial resolution to resolve thin layers in the target, while replicating crater formation and final morphology from the high‐resolution models. In keeping with field observations, we also find that anisotropic layers may be responsible for a lack of central uplift expression observed at many craters formed in targets with thick sedimentary layers (e.g., the Haughton and Ries impact structures). Plain Language Summary: In computer simulations of meteorite impacts, the target is often simplified by removing details such as layering that may be present. Planetary bodies, such as Earth, the Moon, and Mars, are rarely so simple. We introduce an efficient method of simulating the inclusion of layers within the target. This new method, which treats the target as an anisotropic material (i.e., the strength of the target can be defined separately for different directions), accurately simulates the inclusion of weak layers in the target without the need to explicitly define these layers. Since the minimum thickness of target layers is dependent on the resolution of the models, the inclusion of an anisotropic model to replace these layers can significantly reduce the computational burden required to model layered targets. Using this new model, we address some of outstanding questions regarding complex crater (i.e., large craters, >5‐km diameter on Earth) formation in targets with thick sedimentary layers; specifically, we examine the apparent suppression that an increase in the anisotropy parameters causes on the uplift of the crater floor, known as the central uplift. Key Points: An anisotropic strength model can be used to simulate the inclusion of weak layers within the target when modeling an impact event The parameters used in the anisotropic strength model can be set to simulate both thick and thin weak layers within the target Increasing parameters in the anisotropic strength model results in suppression of structural uplift and central peak formation