Measurement of seismometer orientation using the tangential P-wave receiver function based on harmonic decomposition
Measurement of seismometer orientation using the tangential P-wave receiver function based on harmonic decomposition
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DOI：
10.1093/gji/ggx515
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发表时间：
2018-03
影响因子：
2.8
通讯作者：
Hobin Lim;Younghee Kim;T. Song;Xuzhang Shen
中科院分区：
文献类型：
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作者：
Hobin Lim;Younghee Kim;T. Song;Xuzhang Shen
准确确定地震计的方位是地震研究的先决条件，包括但不限于地震各向异性。虽然陆地上的井下地震仪产生的地震波形数据在某种程度上没有人为噪声，但它们可能有一个缺点，即方向不确定。本文计算了远震接收函数的P相和PP相的调和分解，并通过最小化S附近和在0处的后方向切向接收函数的调和展开式中的常数项来确定地震计的方位。这种方法归一化了震源的影响，并确定了地震仪的方位，而不需要假定各向同性介质。与极小S附近和0的切向接收函数平均幅度的方法相比，该方法在震源的后方向覆盖不均匀和不完整的情况下(即使是在海底地震仪的情况下)也能得到更准确的定向。我们将这种方法应用于韩国地震台网(52个宽带速度地震仪，其中30个是井下传感器)的数据，以估计2005年−2016年期间的传感器方位。我们还通过切向接收器函数的极性和幅度的变化来跟踪传感器方向的时间变化。证实有6个钻孔台站在10年内经历了显著的方位变化(10°−180°)。我们通过估计海底传感器的方位来证明我们的方法的有效性，众所周知，海底传感器在相对较短的部署时间内具有高噪声水平。
Accurate determination of the seismometer orientation is a prerequisite for seismic studies including, but not limited to seismic anisotropy. While borehole seismometers on land produce seismic waveform data somewhat free of human-induced noise, they might have a drawback of an uncertain orientation. This study calculates a harmonic decomposition of teleseismic receiver functions from the P and PP phases and determines the orientation of a seismometer by minimizing a constant term in a harmonic expansion of tangential receiver functions in backazimuth near and at 0 s. This method normalizes the effect of seismic sources and determines the orientation of a seismometer without having to assume for an isotropic medium. Compared to the method of minimizing the amplitudes of a mean of the tangential receiver functions near and at 0 s, the method yields more accurate orientations in cases where the backazimuthal coverage of earthquake sources (even in the case of ocean bottom seismometers) is uneven and incomplete. We apply this method to data from the Korean seismic network (52 broad-band velocity seismometers, 30 of which are borehole sensors) to estimate the sensor orientation in the period of 2005−2016. We also track temporal changes in the sensor orientation through the change in the polarity and the amplitude of the tangential receiver function. Six borehole stations are confirmed to experience a significant orientation change (10°−180°) over the period of 10 yr. We demonstrate the usefulness of our method by estimating the orientation of ocean bottom sensors, which are known to have high noise level during the relatively short deployment period.