近日，英国布里斯托尔大学
研究人员在火星上探测到的两个远地端地震事件中，观测到了地震阶段SKS的核心转移，并测量了SKS的相对于地幔穿过体波的传播时间。SKS以压缩波的形式穿过核心，提供了体积模量和密度的信息。研究人员使用对核心敏感的相对传播时间以及总地球物理数据和来自其他更接近的地震事件进行概率反演，以寻求描述液态铁合金核心最佳的状态参数方程。反演限制了火星核心的速度，并被用于开发第一个基于地震的对其成分的预估。
研究人员表明，与以前相比，SKS数据提供的模型更倾向于较小(核心半径中值= 1,780-1,810km)和密度(核心密度= 6.2 - 6.3g/cm3)的核心，核心-地幔边界的P波速度为4.9-5.0 km / s，地幔的组成和结构是不确定性的主要来源。当考虑硫、氧、碳和氢时，从模型中推断，火星的核心含有20-22 wt %的轻合金元素。这些数据可以用来为行星吸积、组成和演化的模型提供信息。
据介绍，研究小组首次观察地震波在火星核心传播。使用洞察地球物理任务收集的地震数据进行观察，使研究人员能够为火星内核的弹性属性构建第一个地震约束模型。
附：英文原文
Title: First observations of core-transiting seismic phases on Mars
Author: Irving, Jessica C. E., Leki, Vedran, Durán, Cecilia, Drilleau, Mélanie, Kim, Doyeon, Rivoldini, Attilio, Khan, Amir, Samuel, Henri, Antonangeli, Daniele, Banerdt, William Bruce, Beghein, Caroline, Bozda, Ebru, Ceylan, Savas, Charalambous, Constantinos, Clinton, John, Davis, Paul, Garcia, Raphal, null, Domenico Giardini, Horleston, Anna Catherine, Huang, Quancheng, Hurst, Kenneth J., Kawamura, Taichi, King, Scott D., Knapmeyer, Martin, Li, Jiaqi, Lognonné, Philippe, Maguire, Ross, Panning, Mark P., Plesa, Ana-Catalina, Schimmel, Martin, Schmerr, Nicholas C., Sthler, Simon C., Stutzmann, Eleonore, Xu, Zongbo
Issue&Volume: 2023-4-24
Abstract: We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars’ core. We observe core-transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-alloy core. Our inversions provide constraints on the velocities in Mars’ core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core–mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars’ core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution.
DOI: 10.1073/pnas.2217090120
Source: https://www.pnas.org/doi/10.1073/pnas.2217090120