Retrieval of crustal structure and thickness of Mars is among the main goals of InSight. Here we investigate which constraints on the crust at the landing site can be provided by apparent P-wave incidence angles derived from P-receiver functions. We consider receiver functions for six different Mars models, calculated from synthetic seismograms generated via Instaseis from the Green’s function databases of the Marsquake Service, in detail. To allow for a larger range of crustal thicknesses and structures, we additionally analyze data from five broad-band stations across Central Europe. We find that the likely usable epicentral distance range for P-wave receiver functions on Mars lies between 35∘$35^{\circ}$ and the core shadow, and can be extended to more than 150∘$150^{\circ}$ by also using the PP-phase. Comparison to models for the spatial distribution of Martian seismicity indicates that sufficient seismicity should occur within the P-wave distance range around InSight within the nominal mission duration to allow for the application of our method. Apparent P-wave incidence angles are derived from the amplitudes of vertical and radial receiver functions at the P-wave onset within a range of period bands, up to 120 s. The apparent incidence angles are directly related to apparent S-wave velocities, which are inverted for the subsurface S-wave velocity structure via a grid search. The veracity of the forward calculated receiver functions and apparent S-wave velocities is ensured by benchmarking various algorithms against the Instaseis synthetics. Results indicate that apparent S-wave velocity curves provide valuable constraints on crustal thickness and structure, even without any additional constraints, and considering the location uncertainty and limited data quantity of InSight. S-wave velocities in the upper half of the crust are constrained best, but if reliable measurements at long periods are available, the curves also provide constraints down to the uppermost mantle. Besides, it is demonstrated that the apparent velocity curves can differentiate between crustal velocity models that are indistinguishable by other methods.

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从表观入射角看地壳 S 波速度：准备洞察力的案例研究

检索火星的地​​壳结构和厚度是洞察号的主要目标之一。在这里，我们研究了从 P 接收器函数导出的表观 P 波入射角可以提供对着陆点地壳的哪些约束。我们详细考虑了六个不同火星模型的接收器函数，这些模型是通过 Instaseis 从火星地震服务的格林函数数据库生成的合成地震图计算得出的，详细信息。为了考虑更大范围的地壳厚度和结构，我们还分析了来自中欧五个宽带站的数据。我们发现火星上 P 波接收函数可能可用的震中距离范围在 35∘$35^{\circ}$ 和核心阴影之间，并且可以扩展到超过 150∘$150^{\circ}$也使用PP相。与火星地震活动空间分布模型的比较表明，在标称任务持续时间内，在 InSight 周围的 P 波距离范围内应该发生足够的地震活动，以允许应用我们的方法。视在 P 波入射角是从 P 波开始时的垂直和径向接收器函数的幅度推导出来的，在一个周期范围内，长达 120 秒。视入射角与视 S 波速度直接相关，通过网格搜索将其反演为地下 S 波速度结构。通过针对 Instaseis 合成物对各种算法进行基准测试，确保了前向计算的接收器函数和表观 S 波速度的准确性。结果表明，视 S 波速度曲线为地壳厚度和结构提供了有价值的约束，即使没有任何额外的约束，并考虑了 InSight 的位置不确定性和有限的数据量。地壳上半部的 S 波速度受到最好的约束，但如果有长期可靠的测量结果，这些曲线也提供了向下到最上地幔的约束。此外，还证明了表观速度曲线可以区分其他方法无法区分的地壳速度模型。曲线还提供了向下到最上地幔的约束。此外，还证明了表观速度曲线可以区分其他方法无法区分的地壳速度模型。曲线还提供了向下到最上地幔的约束。此外，还证明了表观速度曲线可以区分其他方法无法区分的地壳速度模型。