Dynamics of a phase change at the base of the mantle consistent with seismological observations
Dynamics of a phase change at the base of the mantle consistent with seismological observations
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地幔底部相变动力学与地震观测一致
DOI：
10.1029/1999jb900065
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发表时间：
1999
影响因子：
--
通讯作者：
D. Helmberger
中科院分区：
文献类型：
--
作者：
I. Sidorin;M. Gurnis;D. Helmberger
通过对流模拟结果与地震观测结果的对比，检验了D″地震间断起源的相变模型。我们计算了一些全球动态模型，其中包括在地幔的底部具有不同特性的相变，并将由此产生的温度场和相位分布转换为地震速度。超过900个二维合成波形计算的S，ScS，和Scd相位从每个模型。这些阶段的相对振幅和差分走时残差的分布进行了统计比较，从四个很好的研究地区（北方西伯利亚，阿拉斯加，印度和中美洲）的数据的分布在搜索的相变，最好地匹配这些地震观测的特点。我们发现，在所考虑的模型中，最好的拟合是在绝热温度或127 GPa和2650 K（P，T）图上的克拉珀龙斜率为1.66 MPa K−1和核幔边界以上1.150 km的相变。动力学模型表明，Clapeyron斜率的值和相位之间的密度差可以有显着的影响动力学的羽流，但可能只有轻微的影响俯冲板的动力学。我们发现，俯冲板块的热结构可以是重要的，在引起地震三重化，在我们的模型中观察到的最强的Scd到达的俯冲区域。地幔底部板片的褶皱导致了与地震观测相一致的微分走时分布模式，并表明最大的不均匀性发生在D″层的顶部或其正上方。微分走时残差的空间自相关函数的分析表明，它们的特征峰反映了板片褶皱的模式，并可能提供对流变学的约束。地幔底部的板块
The phase change model for the origin of the D″ seismic discontinuity is tested by comparing the results of convection modeling with seismic observations. We compute a number of global dynamic models that incorporate a phase change at the base of the mantle with different characteristics and transform the resulting temperature field and the distribution of phases to seismic velocities. Over 900 two-dimensional synthetic waveforms are computed for each of the models from which S, ScS, and Scd phases are picked. The distribution of the relative amplitudes and differential travel time residuals for these phases are statistically compared with the distribution of data from four well studied regions (northern Siberia, Alaska, India, and Central America) in a search for the characteristics of a phase transition that best match these seismic observations. We find that the best fit among the models considered is obtained for phase transitions characterized by a Clapeyron slope of ∼6 MPa K−1 and an elevation above the core-mantle boundary of ∼150 km under adiabatic temperature or 127 GPa and 2650 K on a (P,T) diagram. Dynamic models demonstrate that the value of Clapeyron slope and the density difference between the phases can have significant influence on the dynamics of plumes but probably only a minor influence on the dynamics of subducted slabs. We find that the thermal structure of subducted slabs can be important in giving rise to the seismic triplication; the strongest Scd arrivals in our models are observed in the area of subduction. The folding of the slab at the base of the mantle leads to patterns in differential travel time distributions consistent with seismic observations and suggests that the largest heterogeneity occurs at the top of the D″ layer or just above it. Analysis of the spatial autocorrelation functions of the differential travel time residuals suggests that their characteristic peaks reflect the patterns of slab folding and may provide constraints on the rheology of slabs at the base of the mantle.