Will InSight be able to accomplish the task to image Mars interior?
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摘要: 本文聚焦于“洞察”号（InSight）的SEIS项目，介绍它的主要科研目标，以及已有的初步探测与解释成果. 作者试图就“洞察”号能在什么程度上实现对火星内部结构探测的科研目标作出评论. 评论从三个方面展开：即它能够基本回答的问题，部分回答的问题，及基本上不可能回答的问题. 基于到目前为止的观测事实，可以说SEIS的数据分析结果对“洞察”号着陆点附近的浅地表结构会有精细的描述；对火星壳层的局部结构会有相当的了解. 有可能会对火星上部幔层结构提供一些比以前更为严密的约束. 但是，到目前为止SEIS数据对人类加深对于火星核结构了解的贡献应该是相对有限的. 主要原因是缺乏能量足够大的震源来产生传播于整个火星的波动场.Abstract: In this review, I briefly summarize the scientific objects of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) program and the major findings so far on Mars internal structure. The focus is on InSight's SEIS (Seismic Experiment for Internal Structure) project. Based on the observation up to date, it appears that SEIS is able to provide relatively precise depth profile of the physical properties of the regolith and bedrock underneath the InSight landing site. It is also able to provide certain constraints on Mars crust at the local to regional range. It may also place some constraints on properties of Martian upper mantle. However, it has been unable to provide meaningful constraints on the property of the core so far. The main reason is the lack of strong sources (large Marsquake or impact) that can generate seismic waves propagating in the entire planet.
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Key words:
- Mars /
- planet internal structure /
- InSight /
- Marsquake /
- dust devil /
- meteoroid impact
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图 1 基于单台、多个单震数据反演火星结构的流程图（修改自Khan et al., 2016）
Figure 1. Joint seismic event-location and structure-inversion scheme based on single station，multiple single-event (modified from Khan et al., 2016)
图 2 经过半径归一化后的层状火星模型（修改自Brennan et al., 2020）（红色曲线）与层状地球模型（修改自Dziewonski and Anderson, 1981）（蓝色曲线）. 点线为密度；实线为P波速度；断线为S波速度
Figure 2. The layered modelsof density (dotted line), P-wave velocity VP (solid line) and S-wave velocity Vs (broken line) for Mars (modified from Brennan et al., 2020) (red) and the Earth (modified from Dziewonski and Anderson, 1981) (blue)
图 3 火星震P波与S波速度深度剖面模型切片图（修改自Brennan et al., 2020）
Figure 3. The layered model of P-wave velocity VP and S-wave velocity VS of the Mars expressed as the cross-section through a great circle (modified from Brennan et al., 2020)
图 4 由位于θ=180°的径向撞击源造成的3个时刻（1 000s，左列；10 000s，中列；20 000s，右列）的模拟波场（上行：体应变；下行：剪应变）在火星内部的分布. 波场色标各异，以突出波场特征
Figure 4. The synthetic wave field caused by the impact source at θ=180°. Volumetric strain: top row; shear strain: bottom row; t=1 000 s, left column, t=10 000 s, central column; t=20 000 s, right column. The color scales are varying for individual plot to highlight the tempo-spatial variation of the wave fields
图 5 由位于θ=180°的垂直撞击源造成的在震中距为0°～180°内6个小时的合成记录图 （左列：表面压强P；中列：径向震动速度Vr；右列：环向震动速度Vθ）
Figure 5. The 6-h synthetic seismogram caused by a vertical impact source at θ=180°; left: surface pressure P; middle: radial particle velocity Vr; right: tangential particle velocity Vθ
图 6 位于撞击源对顶点（震中距Δ=180°）的合成记录图
Figure 6. The single station synthetic seismogram recorded at epicenter distance Δ=180°
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