2024年6月28日，英国伦敦帝国理工学院Saskia Goes的研究团队在《地质学》杂志发表论文，报道了向下持续的海底地震仪数据显示了成熟的海洋上地壳持续的热液演化。

据悉，热流测量表明，洋壳中的热液活动在形成后至少持续了65m.y.。热液活动逐渐用蚀变产物填满裂缝和孔隙，预计将导致地震速度随年龄增加的趋势。从海底地震仪(OBS)数据反演的地震—P波速度模型汇编未能探测到超过地壳年龄ca.10Ma的这种老化趋势。然而，在这些模型中，流体流动最集中的最上层地壳的速度分辨率很低。这是因为随着洋壳的成熟，OBS记录的第一批到达的热液隐藏在水波的尾波中。这可能导致地震速度的任何老化趋势被掩盖。

研究组首次展示了如何将向下延拓(DC)应用于横跨65 Ma海底的OBS数据分析中，从而显著改善了对上地幔P波速度的测量。新分析揭示了一个高度不均匀的上地壳，与脊平行的P波速度变化为25%，这意味着局部孔隙度值高达全球平均水平的两倍。研究新结果与其他最新的先进地震分析相结合，揭示了地震速度确实随着年龄的增长而变化，至少可以达到70 Ma，这证实了热液活动在成熟的海洋火山口继续存在。

附：英文原文

Title: Downward continued ocean bottom seismometer data show continued hydrothermal evolution of mature oceanic upper crust

Author: Lianjun Li, Jenny Collier, Tim Henstock, Saskia Goes

Issue&Volume: 2024-06-28

Abstract: Heat flow measurements indicate hydrothermal activity in oceanic crust continues at least for 65 m.y. after formation. Hydrothermal activity progressively fills cracks and pores with alteration products, which is expected to lead to a trend of increasing seismic velocities with age. Compilations of seismic-P-wave velocity models inverted from ocean bottom seismometer (OBS) data have failed to detect such an aging trend beyond crustal ages of ca. 10 Ma. However, in these models, the velocities of the uppermost crust, where fluid flow would be most concentrated, are poorly resolved. This is because as the oceanic crust matures, the first crustal arrivals on OBS records (which best resolve upper crustal velocities using tomographic inversion), become hidden in the coda of the water wave. This may lead to the masking of any aging trend in the seismic velocities. For the first time, we show how including downward continuation (DC) in the analysis of OBS data collected across 65 Ma seafloor significantly improves measurements of the P-wave velocities of the upper crust. Our new analysis reveals a highly heterogeneous upper crust, with ridge-parallel P-wave velocity variations of 25%, implying local porosity values that are up to double that of global averages. Our new results, combined with other most recent advanced seismic analyses, reveal that seismic velocities indeed evolve with age up to at least 70 Ma, confirming that hydrothermal activity continues in mature oceanic crust.

DOI: 10.1130/G52329.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G52329.1/645232/Downward-continued-ocean-bottom-seismometer-data