KNIPAS - Knipovich Ridge passive seismic experimentStudying active mid-ocean ridge spreading processes and lithospheric structure on segment scale

KNIPAS是迄今为止在大洋中脊（MOR）进行的最大的被动地震实验。沿着尼波维奇山脊160公里长的一段，28个海底地震仪（OBS）记录了一年中发生的地震。MORs的地震可以让我们了解活跃的传播过程，但只有最大的地震才能被陆地上的地震仪或水声阵列捕捉到，而且它们的震中位置和震源深度仍然不确定。小规模OBS研究提供了较小震级的传播过程的更详细图像。近年来的海底地震仪研究表明，Knipovich脊所属的超低速扩展MOR与快速扩展脊表现出明显不同的地震活动性模式，因此其扩展机制也不同。超低速摩尔的大间距火山在地震上可能非常活跃。相比之下，岩浆脊剖面只会产生弱地震，并显示出一个厚厚的岩石圈，在上地幔中有地震带，这可能表明蛇纹岩作用的深度远比以前所知的要深。然而，尚不清楚这些局部研究的扩散过程在整个脊段的尺度上是否相关。KNIPAS缩小了小规模海底地震仪和远震研究之间的差距。预计将有9000次震级为M - 1-3的良好定位地震，我们将研究岩石圈的热状态、厚度和结构以及沿整个脊段的普遍变形模式。我们将研究岩石圈底部的地形是否足以保证熔体沿着整个板块向上流动，流向岩浆产出远远超过当地熔体产出的火山中心。此外，我们将研究火山之间岩浆区域的扩张是如何起作用的，以及上地幔潜在的深层蛇纹石化在多大程度上影响了变形模式。此外，目前尚不清楚上地幔的成分和物理性质是否存在变化，这些变化可能决定了岩浆和岩浆脊剖面中超低扩展摩尔比的长寿命分段。由于其大的空间范围和预期的地壳和岩石圈厚度和结构的显著差异，KNIPAS进一步形成了一个理想的数据集，以测试和优化被动地震方法，直到最近才被引入海洋地震学。接收函数和远震地震和环境噪声的面波反演将用于研究沿山脊的地震速度和上地幔结构的变化。我们计划进一步发展这些方法用于OBS网络的常规应用，并严格检查它们的分辨率潜力。

KNIPAS belongs to the largest passive seismic experiments that have ever been conducted at a mid-ocean ridge (MOR). Along a 160 km long section of Knipovich Ridge, 28 Ocean Bottom Seismometers (OBS) recorded earthquakes over a period of one year. Earthquakes at MORs give insight into the active spreading processes but only the largest earthquakes can be captured by seismometers on land or by hydroacoustic arrays and their epicentre locations and source depths remain uncertain. Small-scale OBS studies give a more detailed image of spreading processes at smaller magnitudes. Recent OBS studies showed that ultraslow spreading MOR, to which Knipovich Ridge belongs, display distinctively different seismicity pattern than faster spreading ridges and therefore different spreading mechanisms. The widely spaced volcanoes of ultraslow MOR may seismically be very active. Amagmatic ridge sections, in contrast, produce only weak earthquakes and show a thick lithosphere with aseismic regions in the upper mantle that may point to serpentinisation reaching far deeper than previously known. It remains however unknown how relevant these locally studied spreading processes are on the scale of entire ridge segments.KNIPAS closes the gap between small-scale OBS and teleseismic studies. With an expected 9000 well-located earthquakes of magnitudes M 1-3 we will examine the thermal regime of the lithosphere, its thickness and structure and the prevalent deformation mode along an entire ridge segment. We will investigate if the topography of the base of the lithosphere is sufficient to warrant an upward flow of melts along an entire segment towards the volcanic centres where magma output exceeds by far the local melt production. In addition, we will examine how spreading works in the magmatic regions between the volcanoes and to what extent a potentially deep-reaching serpentinisation of the upper mantle influences the deformation mode. Furthermore it is currently not known if there are variations in the composition and physical properties of the upper mantle that may govern the long-lived segmentation of ultraslow spreading MOR in magmatic and amagmatic ridge sections.Due to its large spatial extent and the expected pronounced differences in crustal and lithospheric thickness and structure, KNIPAS furthermore forms an ideal data set to test and optimize passive seismic methods that only recently have been introduced in marine seismology. Receiver functions and the inversion of surface waves from teleseismic earthquakes and ambient noise will be used to study variations in seismic velocity and structure of the upper mantle along the ridge. We plan to further develop these methods for routine application to OBS networks and critically examine their resolution potential.