Upper-mantle structure in southern Norway from beamforming of Rayleigh wave data presenting multipathing
Upper-mantle structure in southern Norway from beamforming of Rayleigh wave data presenting multipathing
复制标题
挪威南部的上地幔结构，来自呈现多路径的瑞利波数据的波束形成
DOI：
10.1111/j.1365-246x.2011.04989.x
复制
发表时间：
2011
影响因子：
2.8
通讯作者：
V. Maupin
中科院分区：
文献类型：
--
作者：
V. Maupin
总结
通过对挪威南部地区瑞利波基模的平均相速度进行深度反演，得到了该地区上地幔SV波速度模型。平均频散曲线的周期范围为22-200秒，由MAGNUS网络，一个临时的区域网络的41个宽带站记录的190瑞利波的波束形成。利用Lucy-Richardson算法从阵列响应函数中对原始波束进行去卷积，提高了波束形成过程的分辨率。除了平均相速度之外，波束形成还为我们提供了关于入射波场性质的一些信息。我们检测到的波动传播方向的偏差，从大圆路径，通常达到10°，在一个周期为25秒的地震事件。正如预期的那样，偏差的幅度随着周期的增加和震中距离的减小而减小。通过波束形成测量的相速度与偏离大圆路径没有显示出任何相关性，这表明偏离不会使相速度测量偏置。我们还检测到显着的多路径，其特征随频率迅速变化。所获得的SV波速度剖面清楚地表明，挪威南部是由上地幔的低速区，并没有盾状特征，尽管它的位置在波罗的海盾。这些发现支持了挪威南部的高地形是由异常的上地幔物质维持的假设。
SUMMARY
A model for the upper mantle SV-wave velocity under southern Norway is obtained by depth inversion of the average phase velocity of the Rayleigh wave fundamental mode in the area. The average dispersion curve is obtained in the period range 22–200 s by beamforming of 190 Rayleigh waves recorded by the MAGNUS network, a temporary regional network of 41 broad-band stations. Resolution of the beamforming procedure is increased by deconvolving the original beams from the array response function using the Lucy–Richardson algorithm. In addition to an average phase velocity, beamforming gives us some information concerning the nature of the incoming wavefield. We detect deviations of the wave propagation direction from the great-circle paths which commonly reach 10° at a period of 25 s for the teleseismic events. The amplitude of the deviations decreases with increasing period and with decreasing epicentral distance, as expected. The phase velocity measured by beamforming does not show any correlation with the deviation from great circle path, suggesting that deviation does not bias phase velocity measurements. We detect also significant multipathing with characteristics that vary rapidly with frequency. The obtained SV-wave velocity profile clearly shows that southern Norway is underlain by a low-velocity zone in the upper mantle and does not have shield-like characteristics, despite its location in the Baltic shield. These findings support the hypothesis that the high topography of southern Norway is sustained by anomalous upper-mantle material.