Upper Crustal Vp / Vs Ratios at the Endeavour Segment, Juan de Fuca Ridge, From Joint Inversion of P and S Traveltimes: Implications for Hydrothermal Circulation
Upper Crustal Vp / Vs Ratios at the Endeavour Segment, Juan de Fuca Ridge, From Joint Inversion of P and S Traveltimes: Implications for Hydrothermal Circulation
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胡安德富卡海岭奋进段的上地壳 Vp / Vs 比率，来自 P 和 S 走时的联合反演：对热液循环的影响
DOI：
10.1029/2018gc007921
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Kim, Young Hee
中科院分区：
文献类型：
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作者：
Kim, Eunyoung;Toomey, Douglas R.;Hooft, Emilie E. E.;Wilcock, William S. D.;Weekly, Robert T.;Lee, Sang‐Mook;Kim, Young Hee
胡安德富卡海岭的奋进段是大洋中脊系统中最活跃、最长寿的热液区之一。然而，在 High Rise、Main Endeavour 和 Mothra 油田等成熟油田中引起长期泄放的渗透性结构尚不完全清楚。在这里，我们使用 P 耦合约束在 Endeavor 段进行的地震折射实验中联合反演 Pg 和 Sg 旅行时间。然后，我们将微分有效介质理论应用于地震速度，计算作为裂缝纵横比函数的孔隙率和裂缝密度。在 1.4 公里深度处，与山脊轴相比，离轴约 5 公里的平均 Vp 增加约 0.4 公里/秒。脊轴上的平均 Vp/V 最小值为约 1.75，离轴时最大为约 1.84。推断的孔隙率和裂纹密度分布表明，厚裂纹与薄裂纹的比例从脊轴到侧面减小，因为理论模型表明 Vp/V 从厚裂纹到薄裂纹增加（纵横比从 0.1 减小到 0.01）。轴上主要存在的厚裂缝可能为高温热液循环中的上流提供长期管道，可能形成喷口场。侧面薄裂缝比例的增加，加上地震速度的增加，表明由于热液循环下流带中的矿物沉淀可能导致厚裂缝逐渐堵塞，导致渗透率下降。
The Endeavour segment of the Juan de Fuca Ridge is one of the most active and long‐lived hydrothermal areas of the mid‐ocean ridge system. However, the permeability structure that gives rise to long‐term venting at well‐established fields, such as the High Rise, Main Endeavour, and Mothra fields, is not fully understood. Here we jointly invertPgandSgtraveltimes from a seismic refraction experiment conducted at the Endeavour segment usingP‐to‐Scoupling constraints. We then calculate porosity and crack density as a function of crack aspect ratio by applying the differential effective medium theory to the seismic velocities. At 1.4‐km depth, averageVp~5 km off axis increases by ~0.4 km/s compared to the ridge axis. The averageVp/Vshas a minimum of ~1.75 on the ridge axis and increases to a maximum of ~1.84 off axis. The inferred porosity and crack density distributions show that the proportion of thick versus thin cracks decreases from the ridge axis to the flanks, since theoretical models indicate thatVp/Vsincreases going from thick to thin cracks (aspect ratio decreasing from 0.1 to 0.01). The dominant presence of thick cracks on the axis may provide long‐term conduits for upflow in high‐temperature hydrothermal circulation potentially forming the vent fields. The increased proportion of thin cracks on the flanks, coupled with the increased seismic velocity, indicates a decrease in permeability caused by progressive clogging of thick cracks due to mineral precipitation likely in the downflow zone of hydrothermal circulation.