木卫二的预期地震活动和地震噪声环境
Expected seismicity and the seismic noise environment of Europa
摘要：
如果我们在木卫二表面着陆仪器，地震数据将是木卫二内部结构的重要地球物理约束。从大的、可识别的信号和环境背景噪声两个方面量化木卫二上预期的地震活动，对于理解月球的动力学以及解释潜在的未来数据非常重要。地震能源可能包括冰壳的破裂和海洋中的湍流运动。我们定义了一系列的地震活动模型在木卫二的冰壳，假设每个模型遵循古腾堡-里希特关系与不同的参数。通过将潮汐耗散能量换算为地球月球上的构造事件来定义$10^{16}$和$10^{18}$ Nm/yr之间的累积地震矩释放范围。随机目录的产生和使用，以创建合成连续的噪音记录，通过数值波传播的内部结构的木卫二的自洽模型。通过确定合成记录的概率功率谱密度来计算噪声的谱特性。虽然地震活动性模型的范围内预测的噪声水平变化80分贝，我们表明，大多数噪声估计低于自噪声地板的高频地震检波器，但可能会记录更敏感的仪器。最大预期信号超过背景噪声$\sim$ 50 dB。噪声记录可以允许通过自相关对内部结构进行约束。由于地下海洋中的湍流运动，冰壳底部的压力变化所产生的地震噪声模型也可能产生可观察到的地震噪声。
英文摘要：
Seismic data will be a vital geophysical constraint on internal structure of Europa if we land instruments on the surface. Quantifying expected seismic activity on Europa both in terms of large, recognizable signals and ambient background noise is important for understanding dynamics of the moon, as well as interpretation of potential future data. Seismic energy sources will likely include cracking in the ice shell and turbulent motion in the oceans. We define a range of models of seismic activity in Europa's ice shell by assuming each model follows a Gutenberg-Richter relationship with varying parameters. A range of cumulative seismic moment release between $10^{16}$ and $10^{18}$ Nm/yr is defined by scaling tidal dissipation energy to tectonic events on the Earth's moon. Random catalogs are generated and used to create synthetic continuous noise records through numerical wave propagation in thermodynamically self-consistent models of the interior structure of Europa. Spectral characteristics of the noise are calculated by determining probabilistic power spectral densities of the synthetic records. While the range of seismicity models predicts noise levels that vary by 80 dB, we show that most noise estimates are below the self-noise floor of high-frequency geophones, but may be recorded by more sensitive instruments. The largest expected signals exceed background noise by $\sim$50 dB. Noise records may allow for constraints on interior structure through autocorrelation. Models of seismic noise generated by pressure variations at the base of the ice shell due to turbulent motions in the subsurface ocean may also generate observable seismic noise.
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