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In the present study, synthetic seismograms on the Moon are generated for a shallow moonquake event that occurred on 3 January 1975, of M w -4.1 using the spectral element method.The spectral element seismograms for this event are also compared against the MI-NEOS normal mode solutions.Moreover, the influence of the low-velocity layer, surface topography, crustal thickness, and medium heterogeneity on the synthetic lunar seismograms has been studied.In addition, the comparisons between the recorded and synthetic seismograms for M w -4.1 event showed that the implemented model was able to reproduce the lunar characteristics that are observed in the lunar seismic data.

地外天体的内部结构是了解其自身演化奥秘的钥匙,能够为人们深入认识地球自身的演化规律提供重要参考。地外天体内部结构探测是光学、遥感、采样返回等深空探测任务的重要补充和拓展。阿波罗时代的月震仪为揭示月球内部的奥秘做出了卓越贡献,然而,受到当时硬件水平的限制,有关月球内部圈层结构的探测结果至今仍然存在很大争议,严重制约了月球科学的发展。我国嫦娥七号任务拟对月球南极进行探测,随后逐步建立月球科研站,期间将布设我国第一台月震仪,以探测月球内部圈层结构及状态。本文阐述了月球内部结构探测的重要意义,列举了月震仪研制和布设可能面临的困难,分析了潜在问题的应对措施,提出了后续科学研究需要关注的问题,并给出了系列建议。本文旨在激发更多学者关注和从事月球及行星内部结构探测事业,以促进我国在相关研究领域的稳步前进,争列国际学术前沿。

We perform the analysis of both long and short period data for 40 large meteoroid impacts eventgathered by the Apollo lunar seismic network. We extract the linear momentum released by the impactand the cutoff frequency of the recorded seismic spectrum, related to the radiation process of the shockwave generated by the impact. By using a proxy to the local porosity, based on the density of surfacecraters and well correlated to the most recent GRAIL observations, we demonstrate that the seismic cutofffrequencies for 40 selected impacts correlate with this proxy and therefore likely with the porosity at theimpacted areas. Our finding shows that lunar seismic records of meteoroid impacts represent uniquegeophysical data documenting medium to high-energy (0.1-1 kt TNT yield) impact processes, includingthe interaction of shock waves with porous media. This work can be applied to the analysis of the seismicdata to be obtained by the InSight mission in 2016 and the investigation of the lateral variations in theMartian regolith.

时至今日，尽管阿波罗任务已经结束超过40年，阿波罗任务所接收到的月震数据仍是人类获取与月震相关信息的唯一来源。随着航空航天，仪器技术等一系列科学的发展，人们对类地行星探测也越来越感兴趣。洞察号已经开始接收火震数据，多个国家也将在月球布设地球物理台网作为目标计划。因此阿波罗月震数据识别到的震相的准确性不仅对研究讨论月球内部结构构造，约束月球速度密度模型，精确月震位置至关重要，更决定了未来探索月球任务的目标和重点。在以前的大部分研究中，主要用到了阿波罗月震记录的到时信息，而波形信息通常被忽略。宽频带波形信息在震源机制反演和精细速度结构成像中起到了关键作用。然而精确高质量的波形数据的获取一方面受制于月震仪受到的长期漂移、倾斜、信号畸变等问题，另一方面也受制于月震仪本身仪器响应的不稳定。 在本论文中，我们重点关注了长周期月震仪观测模式中的平坦模式，其对应仪器响应平坦的频段为0.1-1Hz，然而月震仪仪器响应是随时间变化的。因此正确获得仪器响应参数随时间变化的规律，是获得精确的宽频带月震波形信号的基础。我们通过拟合随时间变化的脉冲校准信号，反演获得了平坦模式下仪器响应参数的时变特征。在此基础上，我们对月震事件数据进行去仪器响应，并进一步压制和校正月震数据中受到仪器变化影响产生的噪声或畸变。在建立阿波罗月震处理流程的基础上，我们重点选择和研究了具有重复波形，被归类到不同月震“巢”的深源月震。月震“巢”中的数据天然具有可叠加性，我们进一步通过一系列互相关对同一月震“巢”中的月震事件进行时间对齐和质量筛选，对比线性叠加，主成分分析叠加(PCA)和相位加权叠加(PWS)结果，分析叠加信号的可信度。最后我们筛选出质量较好的20个月震“巢”叠加宽频波形数据，并对包括P波和S波的到时和波形进行了初步约束和讨论，并给出了利用本文处理流程的月震数据的研究前景。

地外天体的内部结构是了解其自身演化奥秘的钥匙,能够为人们深入认识地球自身的演化规律提供重要参考。地外天体内部结构探测是光学、遥感、采样返回等深空探测任务的重要补充和拓展。阿波罗时代的月震仪为揭示月球内部的奥秘做出了卓越贡献,然而,受到当时硬件水平的限制,有关月球内部圈层结构的探测结果至今仍然存在很大争议,严重制约了月球科学的发展。我国嫦娥七号任务拟对月球南极进行探测,随后逐步建立月球科研站,期间将布设我国第一台月震仪,以探测月球内部圈层结构及状态。本文阐述了月球内部结构探测的重要意义,列举了月震仪研制和布设可能面临的困难,分析了潜在问题的应对措施,提出了后续科学研究需要关注的问题,并给出了系列建议。本文旨在激发更多学者关注和从事月球及行星内部结构探测事业,以促进我国在相关研究领域的稳步前进,争列国际学术前沿。

作为地球唯一的天然卫星,月球是人类探索宇宙迈出第一步的落脚点。月球不具有与地球类似的全球性内禀偶极磁场,无法形成大尺度磁层结构,且其半径和内部电导率(尤其是月壳电导率)远低于地球;当变化的行星际磁场掠过月球时,会在极短的时间内完全穿透月球。这种特性为研究行星际磁场与月球的相互作用提供了非常好的手段。 月球深部磁成像技术是我们提出的一种新的月球内部结构探测方法。它以地磁测深理论为基础,在月球表面进行高精度磁场矢量探测,特别是由行星际磁场跃变所产生的月球感应磁场三分量变化,进而反演月球深部的地质结构。这将有助于人们认知月球壳层电导率的分布特征,也有助于认知月壳的内部结构与非对称性等特征。 1969年,美国的Apollo 12和Explorer 35磁强计分别在月面和月球轨道上同时对数十个行星际阶跃磁场的扰动事件进行了观测,并记录了磁场三分量的变化;随后Apollo 14、15、16及前苏联的Lunokhod 2磁强计也分别在月表不同位置对固有磁场进行了单点探测,并推断出了月球内部的一维结构分布。 我国未来的探测可以在此基础上更进一步——在月表设置一个或多个磁强计阵列,并通过磁场联测的数据反演出各测点垂向厚度的差异和更高精度的月球内部结构。月球车和它携带的各种仪器可以提供技术支持,宇航员可通过实际操作完成这些科学实验。受到月球空间特殊电磁环境的影响和限制,在月表布设的测区面积不会太大,测点间距可能只相当于月球半径的几百分之一甚至几千分之一,这使得测区的曲率几乎可以忽略不计。 为保证数据的高质量和可靠性,对磁强计阵列位置的选取就非常重要。本研究针对均匀模型,利用球体电磁感应理论,计算了不同的模型参数下,行星际阶跃磁场在月表产生的感应磁场,并选取部分测点给出了其变化过程;对于二维偏心模型,还给出了相邻测点的磁场分量差值与垂向壳层厚度差值、测点间距的定量关系,希望能够对将来的磁强计阵列布置方案起到一定的参考作用

The Apollo astronauts deployed seismic experiments on the nearside of the Moon between 1969 and 1972. Five stations collected passive seismic data. Apollo 11 operated for around 20 days, and stations 12, 14, 15, and 16 operated nearly continuously from their installation until 1977. Seismic data were collected and digitized on the Moon and transmitted to Earth. The data were recorded on magnetic reel-to-reel tapes, with timestamps representing the signal reception time on Earth. The taped data have been widely used for many applications and have previously been shared in various formats. The data have slightly varying sampling rates, due to random f luctuations of the data sampler and also its sensitivity to the significant temperature variations on the Moon’s surface. Additionally, there were timing errors. Previously shared versions of the Apollo data were affected by these problems. We have reimported the passive data to SEED (Standard for the Exchange of Earthquake Data) format, and we make these data available via Incorporated Research Institutions for Seismology and the Planetary Data System. We have cleaned the timestamp series to reduce incorrectly recorded timestamps. The archive includes five tracks: three components of the mid-period seismometers, one short-period component, and a time track containing the timestamps. The seismic data are provided unprocessed in their raw format, and we provide instrument response files. We hope that the new archive will make it easier for a new generation of seismologists to use these data to learn more about the structure of the Moon.

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Observatory monthly means provide an excellent opportunity to study the temporal changes of the geomagnetic field at a given location. Unfortunately, determination of the global pattern of changes using observatory data is hampered by their uneven distribution. Satellite data provide excellent global coverage, but the spacecraft movement makes direct comparisons of satellite and observatory data difficult. To investigate short‐period secular variation in observatory and satellite data, we developed an approach to extract satellite monthly means for “virtual observatories” at 400 km altitude, using CHAMP magnetic measurements. Comparison of these virtual observatory monthly means with the corresponding ground values shows a remarkably well‐correlated signal at time‐scales of months to years, which is beyond the temporal resolution limit of recent global models. Here, we describe this newly developed approach, its validation, and discuss how it can be used to understand short‐period changes of the recent geomagnetic field.

A reanalysis of the Apollo lunar seismic data and the subsequent application of an inverse Monte Carlo method to P and S‐wave arrival times has resulted in a more detailed lunar velocity structure than previously obtainable. The velocity is seen to increase from the surface down to the base of the crust at 45±5 km depth. The results furthermore indicate a constant velocity upper mantle extending to 560±15 km km depth, separated from a more complex high velocity middle mantle by an increase in velocity of 1.0 km/s. In addition, the moonquake locations have been improved. The shallow moonquakes are found to be located in the depth range 50–220 km. The majority of deep moonquakes are concentrated in the depth range 850–1000 km with an apparently rather sharp lower boundary.