Dynamic Upwelling Beneath the Salton Trough Imaged With Teleseismic Attenuation Tomography
Dynamic Upwelling Beneath the Salton Trough Imaged With Teleseismic Attenuation Tomography
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DOI：
10.1029/2020jb020347
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发表时间：
2020-06
期刊：
影响因子：
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通讯作者：
J. Byrnes;M. Bezada
中科院分区：
文献类型：
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作者：
J. Byrnes;M. Bezada
索尔顿海槽是地球上少数几个断裂是陆上而不是海底的地区之一。我们使用索尔顿海槽地震成像项目记录的相对衰减的P-MeeP相位来研究在伸展过程中形成的岩石圈和软流圈结构。地图视图分析显示，索尔顿海槽内的衰减比邻近省份更强。然后，我们构造层析模型的地震衰减随深度的变化，区分地壳和地幔信号与阻尼最小二乘法和贝叶斯方法。合成测试表明，阻尼最小二乘模型显着低估了衰减的强度，不能分离地壳和地幔信号，即使层析成像模型被允许在岩石圈-软流圈边界（LAB）是不连续的。我们表明，贝叶斯方法克服了这些问题时，反转相同的合成数据集，浅和深的信号更清楚地分离时，施加不连续性。在大于95%的置信度下，结果显示：第一，衰减主要发生在LAB下方;第二，衰减区域的宽度比120 km深度的裂谷窄;第三，衰减的强度要求衰减特征代表类似于大洋中脊下的熔融柱。在无挥发物固相线以下的熔融柱的狭窄宽度与被动上升流的模型不一致，其中流动仅由裂谷驱动。相反，我们认为早期洋壳的产生是由于地幔上涌集中在一个狭窄的底辟中。
The Salton Trough is one of the few regions on Earth where rifting is subaerial instead of submarine. We use the relative attenuation of teleseismic P phases recorded by the Salton Trough Seismic Imaging Project to investigate lithospheric and asthenospheric structures that form during extension. Map‐view analysis reveals stronger attenuation within the Salton Trough than in the adjacent provinces. We then construct tomographic models for variations in seismic attenuation with depth to discriminate between crustal and mantle signals with a damped least squares approach and a Bayesian approach. Synthetic tests show that models from damped least squares significantly underestimate the strength of attenuation and cannot separate crustal and mantle signals even if the tomographic models are allowed to be discontinuous at the lithosphere‐asthenosphere boundary (LAB). We show that a Bayesian approach overcomes these problems when inverting the same synthetic data sets and that shallow and deep signals are more clearly separated when imposing a discontinuity. With greater than 95% confidence, the results reveal first, that attenuation occurs primarily beneath the LAB; second, that the width of the attenuative region is narrower than the rift at 120 km depth; and third, that the strength of attenuation requires that the attenuative feature represents a melting‐column similar to those beneath mid‐ocean ridges. The narrow width of the melting column below the volatile‐free solidus is inconsistent with models for passive upwelling, where flow is driven only by rifting. Instead, we attribute the generation of incipient oceanic crust to mantle upwelling focused by buoyancy into a narrow diapir.