Constraints on the core-mantle boundary topography from P4KP-PcP differential travel times
Constraints on the core-mantle boundary topography from P4KP-PcP differential travel times
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DOI：
10.1029/2009jb006563
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发表时间：
2010-04
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通讯作者：
S. Tanaka
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作者：
S. Tanaka
研究了P4KP - PcP差分走时来推断核-幔边界（CMB）地形。共测量了362次P4KP - PcP，测量误差为0.5 s。利用P波层析模型校正了地球静力流体椭圆性和地幔非均质性的行程时间。模型参数化采用4次球面调和展开。然后在地幔最下方150 km处估计P波速度非均质性，以克服全球三维P波地幔模型中对地幔底部速度摄动估计不足的问题。随后，利用上述过程的残差推断出CMB的地形。由于CMB地形的奇度分量对P4KP - PcP次数不敏感，因此只求解了2度和4度分量。结果表明，CMB地形的最大振幅不超过±2 km，不确定度小于0.5 km。数值试验结果表明，在幅度恢复较小的情况下，4度模式更可靠。得到的4度模式显示振幅小于±1 km，表明在环太平洋、中太平洋和南非存在低气压。
P4KP‐PcP differential travel times are examined to infer the core‐mantle boundary (CMB) topography. A total of 362 P4KP‐PcP times are measured with a measurement error of 0.5 s. The travel times are corrected for the Earth's hydrostatic ellipticity and mantle heterogeneity using a P‐wave tomographic model. Spherical harmonic expansion up to degree 4 is adopted for model parameterization. The P‐wave velocity heterogeneity is then estimated in the lowermost 150 km of the mantle to overcome the problem of underestimation of the velocity perturbation at the base of the mantle in the global 3‐D P‐wave mantle model. Subsequently, the CMB topography is inferred using the residues of the above processes. Since the odd‐degree components of the CMB topography are insensitive to the P4KP‐PcP times, only the components of degrees 2 and 4 are solved for. The resultant features indicate that the maximum amplitude of the CMB topography does not exceed ±2 km, with an uncertainty of less than 0.5 km. A numerical test confirms that the pattern of degree 4 is more reliable with less amplitude recovery. The obtained degree 4 pattern shows an amplitude of less than ±1 km and indicates the presence of depressions under the circum‐Pacific, the central Pacific, and South Africa.