Rayleigh-wave phase-velocity tomography of southern Sweden is presented using ambient seismic noise at 36 stations (630 station pairs) of the Swedish National Seismic Network. We analyse 1 yr (2012) of continuous recordings to get the first crustal image based on the ambient-noise method in the area. Time-domain cross-correlations of the vertical component between the stations are computed. Phase-velocity dispersion curves are measured in the frequency domain by matching zero crossings of the real spectra of cross-correlations to the zero crossings of the zeroth-order Bessel function of the first kind. We analyse the effect of uneven source distributions on the phase-velocity dispersion curves and correct for the estimated velocity bias before tomography. To estimate the azimuthal source distribution to determine the bias, we perform inversions of amplitudes of cross-correlation envelopes in a number of period ranges. Then, we invert the measured and bias-corrected dispersion curves for phase-velocity maps at periods between 3 and 30 s. In addition, we investigate the effects of phase-velocity bias corrections on the inverted tomographic maps. The difference between bias-corrected and -uncorrected phase-velocity maps is small (<1.2 per cent), but the correction significantly reduces the residual data variance at long periods where the bias is biggest. To obtain a shear velocity model, we invert for a 1-D velocity profile at each geographical node. The results show some correlation with surface geology, regional seismicity and gravity anomalies in the upper crust. Below the upper crust, the results agree well with results from other seismological methods.

中文翻译：

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从环境噪声数据的精确相速度测量中得出的瑞典南部的剪切波结构

瑞典南部的瑞利波相速度层析成像是利用瑞典国家地震台网的36个站（630个站对）的环境地震噪声来进行的。我们分析了1年（2012年）的连续记录，以基于该区域的环境噪声方法获得了第一张地壳图像。计算站点之间垂直分量的时域互相关。通过将互相关的实谱的零交叉与第一种零阶贝塞尔函数的零交叉进行匹配，可以在频域中测量相速度色散曲线。我们分析了不均匀源分布对相速度色散曲线的影响，并校正了层析成像之前估计的速度偏差。要估算方位角源分布以确定偏差，我们在多个周期范围内执行互相关包络幅度的反转。然后，我们在3到30 s的时间段内倒置相速度图的实测色散曲线和经偏差校正的色散曲线。此外，我们调查了反相层析成像图上的相速度偏差校正的影响。偏差校正后的相位速度图和未经校正的相速度图之间的差异很小（<1.2％），但是在偏差最大的长时间段内，校正显着减小了残留数据方差。为了获得剪切速度模型，我们在每个地理节点上求一维速度剖面。结果表明与上地壳的地表地质，区域地震活动和重力异常有关。在上地壳以下，该结果与其他地震方法的结果非常吻合。