Numerical simulations of impact crater formation with dilatancy
Numerical simulations of impact crater formation with dilatancy
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DOI：
10.1002/2014je004708
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发表时间：
2014-12-01
影响因子：
4.8
通讯作者：
Collins, G. S.
中科院分区：
文献类型：
--
作者：
Collins, G. S.
撞击引起的断裂产生了孔隙，这是造成撞击坑地球物理特征的许多方面的原因。本文描述了一个简单的剪切地质材料孔隙度产生模型及其在iSALE冲击物理程序中的实现。该模型被用来研究地球上简单和复杂的陨石坑形成过程中撞击引起的不稳定性。简单的火山口形成的模拟产生的孔隙度分布与观察一致。适合于低质量岩体的膨胀模型参数与观测结果最吻合;更强烈的膨胀行为需要大量的冲击后孔隙度降低。岩石在高压下剪切时膨胀较小的趋势是该模型的一个重要性质。压力抑制了撞击引起的不稳定性：在冲击波中，在陨石坑底部以下的深度，以及在形成中央隆起的会聚的陨石坑下流动中。因此，地下孔隙度分布是火山口大小的强函数，这反映在推断的重力异常中。小于25公里的模拟陨石坑的布格重力异常是一个广泛的低与大小成比例的陨石坑半径;较大的陨石坑表现出一个中心重力高的抑制重力低。月球上的地壳压力相对于地球较低，这意味着在最初无孔的目标中，对于相同大小的撞击，撞击引起的磁共振在月球上比在地球上更有效。这种差异可能会因月球地壳中存在的孔隙而减轻。
Impact-induced fracturing creates porosity that is responsible for many aspects of the geophysical signature of an impact crater. This paper describes a simple model of dilatancythe creation of porosity in a shearing geological materialand its implementation in the iSALE shock physics code. The model is used to investigate impact-induced dilatancy during simple and complex crater formation on Earth. Simulations of simple crater formation produce porosity distributions consistent with observations. Dilatancy model parameters appropriate for low-quality rock masses give the best agreement with observation; more strongly dilatant behavior would require substantial postimpact porosity reduction. The tendency for rock to dilate less when shearing under high pressure is an important property of the model. Pressure suppresses impact-induced dilatancy: in the shock wave, at depth beneath the crater floor, and in the convergent subcrater flow that forms the central uplift. Consequently, subsurface porosity distribution is a strong function of crater size, which is reflected in the inferred gravity anomaly. The Bouguer gravity anomaly for simulated craters smaller than 25 km is a broad low with a magnitude proportional to the crater radius; larger craters exhibit a central gravity high within a suppressed gravity low. Lower crustal pressures on the Moon relative to Earth imply that impact-induced dilatancy is more effective on the Moon than Earth for the same size impact in an initially nonporous target. This difference may be mitigated by the presence of porosity in the lunar crust.