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通过叠加长周期水平分量地震图绘制了大尺度的410和660km地震波速度间断面的形貌图,数据由全球数字地震台网(GDSN)(1976～1996)、地震学联合研究协会-国际部署加速度仪(IRIS-IDA)(1988～1996)和地球透镜计划(Geoscope)台网(1988～1996)提供。来自这些间断界面的下底面反射波是SS震相的前驱波,可用它们的到时来获得各反射界面深度的全球变化。我们分析了13000多个地震记录,这些地震的震级m_o>5.5,震源深度<75km,震中距范围在110°到180°之间。我们拾取并校核SS震相,然后沿间断面反射波理论走时曲线对记录进行叠加,获得了416个半径为10°的等间距覆盖的叠加记录;几乎所有覆盖区的叠加记录都可以看到清晰的410和660km的反射面,而在大约一半的覆盖区可以看到520km的反射面。每个叠加记录上都可量取SS到时与前驱波的走时差,并使用模拟重采样方法获得其不确定性的估计。然后相对于40s周期的各向同性的初始地球参考模型(PREM)计算了间断面的深度,其中地表地形和地表厚度变化校正用Mooney等(1995)的CRUST5.0模型,上地幔S波速度的非均勻性校正用Masters等(1996)的S16B30模型。间断面形态的结果图象比之以前的研究具有更完整的覆盖;相邻覆盖之间观测深度高度相关,并且显示出大尺度的形态变化。660km间断面显示了约38km峰-峰起伏,其区域性的凹陷与环太平洋地区现今和过去的消减带地区密切相关。410km间断面的大尺度形态变化幅度小,与660km界面上的形态变化大不一致。过渡带厚度W_(TZ)按410和660km间断面之间的距离来计算,活动消减带地区(如千岛群岛、菲律宾群岛和汤加群岛)最厚,在南极洲和中太平洋的大部分地区都较薄。W_(TZ)的空间变化与洋-陆差异不相关,但大致与S16B30的过渡带速度相关,这同两种类型的共同热源相一致。小幅度起伏的520km反射界面更难分辨,但就优先观测到的具有大多数资料的那些反射点覆盖来看,它具有一定的全球性。
The topographic maps of large-scale seismic velocity discontinuities between 410 and 660 km are superimposed by long-period horizontal component seismograms. The data are provided by Global Digital Seismograph Network (GDSN) (1976 ~ 1996), Association of Seismological Research - International Deployment Acceleration (IRIS-IDA) (1988 ~ 1996) and Geoscope Network (1988 ~ 1996). The bottom-surface reflected waves from these discontinuous interfaces are precursors to the SS phase and can be used to obtain global variations in the depth of each reflection interface. We analyzed more than 13,000 seismograms with magnitudes m_o> 5.5, focal depth <75km and epicentral distances between 110 ° and 180 °. We picked up and checked the SS phase and then superimposed the records along the discontinuity reflected wave theoretical travel time curve to obtain 416 superimposed records with an equal interval covering 10 ° of radiance; the overlay recording of almost all of the covered areas can be seen Clear 410 and 660 km of reflector, while in about half of the coverage area can see the 520km reflector. The time lag between the SS arrival and the precursor wave can be measured on each superimposed record and an estimation of its uncertainty can be obtained using simulated resampling methods. The depth of the discontinuities is then calculated relative to the isotropic initial Earth Reference Model (PREM) over a period of 40 s, where the variation of surface topography and surface thickness is calculated using the CRUST 5.0 model of Mooney et al. (1995), the S-wave velocity of the upper mantle Non-uniformity correction Masters et al. (1996) S16B30 model. The resulting images of the cross-sectional morphology have more complete coverage than previous studies; the observed depths are highly correlated between adjacent covers and show large-scale morphological changes. The 660km section shows about 38km of peak-to-peak fluctuations, and its regional depression is closely related to present and past subtropical zones of the Pacific Rim. The large-scale morphological change of the 410 km section is small, which is inconsistent with the morphological change at the 660 km interface. The thickness of the transitional zone W_ (TZ) is calculated as the distance between the intercepts of 410 and 660 km. The areas of active depleted zone (such as the Thousand Islands, the Philippine Islands and the Tonga Islands) are the thickest and are thinner in most parts of Antarctica and the Central Pacific . The spatial variation of W_ (TZ) is not related to the ocean-continent divergence, but is roughly related to the transitional zone velocity of S16B30, consistent with both types of common heat sources. The small, fluctuating 520 km reflection interface is more difficult to discern, but it is somewhat global in view of the priority observed over those reflections with most of the data.