Constraining the maximum depth of brittle deformation at slow- and ultraslow-spreading ridges using microseismicity
Constraining the maximum depth of brittle deformation at slow- and ultraslow-spreading ridges using microseismicity
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DOI：
10.1130/g46577.1
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发表时间：
2019-11-01
期刊：
影响因子：
5.8
通讯作者：
Dannowski, Anke
中科院分区：
文献类型：
--
作者：
Grevemeyer, Ingo;Hayman, Nicholas W.;Dannowski, Anke
沿着洋中脊的地震深度受到覆盖在热的上涌地幔上的相对薄而脆的岩石圈的限制。随着扩展速率的降低，地震可能发生在岩石圈的更深处，在更厚的脆性层内容纳应变。加勒比海中开曼群岛超低速扩张扩张中心的新数据表明，地震发生在海底以下10公里深处，因此比沿着大多数其他低速扩张海脊发生的地震更深。MCSC以15毫米/年的全速率传播，而西南印度洋脊（SWIR）的一个类似的研究良好的倾斜开口部分以更慢的速率传播，如果考虑到传播的连续性，大约为8毫米/年。SWIR以前曾被认为有地震发生在32公里深，但不浅于5公里。这些特征是由于蛇纹化地幔的稳定变形和极深的热边界层共同作用的结果。在我们的MCSC结果的背景下，我们重新分析了SWIR数据，发现地震活动的最大深度为17公里，与来自缓慢和超低扩展脊的扩展速率依赖性的汇编一致。总之，这里提出的新的MCSC数据和SWIR再分析支持这样的假设，即大洋中脊的深度-地震活动性关系是其热机械结构的函数，反映在其扩展速率中。
The depth of earthquakes along mid-ocean ridges is restricted by the relatively thin brittle lithosphere that overlies a hot, upwelling mantle. With decreasing spreading rate, earthquakes may occur deeper in the lithosphere, accommodating strain within a thicker brittle layer. New data from the ultraslow-spreading Mid-Cayman Spreading Center (MCSC) in the Caribbean Sea illustrate that earthquakes occur to 10 km depth below seafloor and, hence, occur deeper than along most other slow-spreading ridges. The MCSC spreads at 15 mm/yr full rate, while a similarly well-studied obliquely opening portion of the Southwest Indian Ridge (SWIR) spreads at an even slower rate of similar to 8 mm/yr if the obliquity of spreading is considered. The SWIR has previously been proposed to have earthquakes occurring as deep as 32 km, but no shallower than 5 km. These characteristics have been attributed to the combined effect of stable deformation of serpentinized mantle and an extremely deep thermal boundary layer. In the context of our MCSC results, we reanalyze the SWIR data and find a maximum depth of seismicity of 17 km, consistent with compilations of spreading-rate dependence derived from slow- and ultraslow-spreading ridges. Together, the new MCSC data and SWIR reanalysis presented here support the hypothesis that depth-seismicity relationships at mid-ocean ridges are a function of their thermal-mechanical structure as reflected in their spreading rate.