Based on an updated model of the regolith’s elastic properties, we simulate the ambient vibrations background wavefield recorded by InSight’s Seismic Experiment for Interior Structure (SEIS) on Mars to characterise the influence of the regolith and invert SEIS data for shallow subsurface structure. By approximately scaling the synthetics based on seismic signals of a terrestrial dust devil, we find that the high-frequency atmospheric background wavefield should be above the self-noise of SEIS’s SP sensors, even if the signals are not produced within 100–200 m of the station. We compare horizontal-to-vertical spectral ratios and Rayleigh wave ellipticity curves for a surface-wave based simulation on the one hand with synthetics explicitly considering body waves on the other hand and do not find any striking differences. Inverting the data, we find that the results are insensitive to assumptions on density. By contrast, assumptions on the velocity range in the upper-most layer have a strong influence on the results also at larger depth. Wrong assumptions can lead to results far from the true model in this case. Additional information on the general shape of the curve, i.e. single or dual peak, could help to mitigate this effect, even if it cannot directly be included into the inversion. We find that the ellipticity curves can provide stronger constraints on the minimum thickness and velocity of the second layer of the model than on the maximum values. We also consider the effect of instrumentation resonances caused by the lander flexible modes, solar panels, and the SEIS levelling system. Both the levelling system resonances and the lander flexible modes occur at significantly higher frequencies than the expected structural response, i.e. above 35 Hz and 20 Hz, respectively. While the lander and solar panel resonances might be too weak in amplitude to be recorded by SEIS, the levelling system resonances will show up clearly in horizontal spectra, the H/V and ellipticity curves. They are not removed by trying to extract only Rayleigh-wave dominated parts of the data. However, they can be distinguished from any subsurface response by their exceptionally low damping ratios of 1% or less as determined by random decrement analysis. The same applies to lander-generated signals observed in actual data from a Moon analogue experiment, so we expect this analysis will be useful in identifying instrumentation resonances in SEIS data.

中文翻译：

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体波、仪器共振和先验假设对 InSight 着陆点浅层结构瑞利波椭圆度反演的影响

基于风化层弹性特性的更新模型，我们模拟了洞察号火星内部结构地震实验 (SEIS) 记录的环境振动背景波场，以表征风化层的影响并反演浅层地下结构的 SEIS 数据。通过对基于地面尘暴地震信号的合成信号进行近似缩放，我们发现高频大气背景波场应该高于 SEIS 的 SP 传感器的自噪声，即使信号不在 100-200 m 范围内产生。车站。我们一方面将基于表面波的模拟的水平垂直光谱比和瑞利波椭圆率曲线与另一方面明确考虑体波的合成物进行比较，但没有发现任何显着差异。反转数据，我们发现结果对密度假设不敏感。相比之下，对最上层速度范围的假设对更大深度的结果也有很大影响。在这种情况下，错误的假设可能导致结果与真实模型相去甚远。有关曲线一般形状的附加信息，即单峰或双峰，可以帮助减轻这种影响，即使它不能直接包含在反演中。我们发现椭圆率曲线可以对模型第二层的最小厚度和速度提供比最大值更强的约束。我们还考虑了着陆器柔性模式、太阳能电池板和 SEIS 调平系统引起的仪器共振的影响。调平系统共振和着陆器柔性模式都发生在明显高于预期结构响应的频率上，即分别高于 35 Hz 和 20 Hz。虽然着陆器和太阳能电池板共振的振幅可能太弱而无法被 SEIS 记录，但水平系统共振将在水平光谱、H/V 和椭圆率曲线中清楚地显示出来。尝试仅提取瑞利波主导的数据部分并不能去除它们。然而，它们可以通过随机减量分析确定的 1% 或更低的异常低阻尼比与任何地下响应区分开来。这同样适用于在月球模拟实验的实际数据中观察到的着陆器生成的信号，因此我们预计这种分析将有助于识别 SEIS 数据中的仪器共振。