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Trends of Global Seismic Noise Properties in Connection to Irregularity of Earth's Rotation

机译：与地球旋转不规则有关的全球地震噪声特性的趋势

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摘要

The properties of continuous records of low-frequency seismic noise on a global network consisting of 229 broadband seismic stations located around the world are considered. Changes in the properties of seismic noise, estimated daily for the time interval from the beginning of 1997 to the end of February 2019, are investigated. We consider the generalized Hurst exponent, the singularity spectrum support width, the entropy of the wavelet coefficients, and wavelet-based Donoho-Johnstone index. For the centers of 50 clusters of seismic stations, the average values of these 4 statistics from the 5 nearest operational stations are calculated daily. As a result, 4 multidimensional time series with a dimension of 50 are obtained with a time step of 1 day for more than 22 years of measurements. Average daily values of the noise properties studied, calculated over all cluster centers, have piecewise linear trends, the break point of which is estimated by the principal component method as mid-2003. After the break point, the average values of generalized Hurst exponent, singularity spectrum support width and Donoho-Johnstone index the parameters decrease whereas the entropy increases. This is interpreted as a simplification of the noise structure which is typical for areas of high seismic hazard. Trends in average noise properties after 2003 are accompanied by a linear increase with imposed 3-years quasi-periodic fluctuations in the average value of pairwise correlation coefficients between the values in cluster centers when evaluated in a sliding time window with a length of 1 year. It is hypothesized that the simultaneous simplification of the structure of global seismic noise, an increase in its spatial correlation and an increase in the intensity of the strongest earthquakes in the world after the end of 2004 is a single process associated with the irregularity of the Earth's rotation. To confirm this hypothesis, a change in the coherence spectrum between the first principal component of the seismic noise properties and the time series of the length of day is estimated.
机译：考虑了由位于世界各地的229个宽带地震车站的全球网络上连续记录的持续记录。调查了地震噪声属性的变化，每年估计为1997年初到2019年2月底的时间间隔。我们考虑广泛的肿瘤指数，奇点谱支撑宽度，小波系数的熵，以及基于小波的Donoho-Johnstone指数。对于50个地震站的中心，每天计算来自5个最近的运营站的这4个统计数据的平均值。结果，使用尺寸为50的4个多维时间序列，其时间步长为1天超过22年的测量。所有集群中心计算的噪声属性的平均每日值具有分段线性趋势，其断点是由2003年中期的主要成分方法估算。断点后，广义肿瘤指数的平均值，奇异度谱支撑宽度和Donoho-Johnstone指数参数减少，而熵增加。这被解释为噪声结构的简化，这对于高地震危害的区域是典型的。 2003年后平均噪声属性的趋势伴随着线性增加，在群集中心的值与长度为1年的滑动时间窗口中评估时，在群集中心的值之间的平均值的平均值增加了3年的准周期性波动。假设全球地震噪声结构的同时简化，其空间相关性的增加和世界在2004年底之后的世界最强大的地震强度的增加，是与地球不规则相关的单一过程回转。为了确认这一假设，估计地震噪声特性的第一主成分与一段时间长度的时间序列之间的相干光谱的变化。

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