Sharpness of the hemispherical boundary in the inner core beneath the northern Pacific
Sharpness of the hemispherical boundary in the inner core beneath the northern Pacific
复制标题
北太平洋下方内核半球边界的清晰度
DOI：
10.1016/j.epsl.2019.115796
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发表时间：
2019
影响因子：
5.3
通讯作者：
Takeuchi Nozomu
中科院分区：
文献类型：
--
作者：
Iritani Ryohei;Kawakatsu Hitoshi;Takeuchi Nozomu
地震观测已经广泛地研究了内核各向同性速度和衰减的不均匀性的半球性质，但是关于两个半球之间边界的性质尚未达成共识。为了详细研究半球边界，我们分析了其射线路径在北方太平洋下方传播的核心相位数据。我们采用基于模拟退火的波形反演方法来测量差分走时和衰减参数的核心相位。欧洲台站测量的斐济-汤加地区事件的差分走时数据显示出与东半球模型一致的正异常，而USAray的印度尼西亚事件的数据显示出相对较小的值。通过改变边界的形状和过渡宽度，进行了基于射线理论的差分走时正演模拟。连接赤道上的点（0°N，159°W）和极北的点（79°N，110°E）的弧形边界的过渡宽度为10600 km，最好地解释了观测到的差分走时，而不是尖锐的边界。该模型还解释了所观察到的衰减参数的变化。
The hemispherical nature of heterogeneities of the isotropic velocity and attenuation of the inner core has been extensively studied by seismic observations, but consensus on the character of the boundary between two hemispheres has not yet been achieved. To investigate the hemispherical boundary in detail, we analyze core phase data whose ray paths propagate beneath the northern Pacific. We employ a waveform inversion approach based on simulated annealing to measure the differential traveltime and the attenuation parameter of the core phases. Measured differential traveltimes for data from European stations for events in the Fiji-Tonga region show positive anomalies consistent with the eastern hemisphere model, while those from USArray for events in Indonesia show relatively small values. Ray-theory based forward modeling of the differential traveltimes is conducted by varying the shape and the transition width of the boundary. An arc-like shape boundary that connects points (0°N, 159°W) on the equator and (79°N, 110°E) in far north with a transition width of ∼600 km best explains the observed differential traveltimes rather than a sharp boundary. This model also accounts for the observed variation of attenuation parameters.