楚科奇海-阿拉斯加内陆地区环境地震噪声差异研究

Ambient seismic noise difference between Chukchi Sea and Interior Alaska

  • 摘要: 基于北极海冰消退与阿拉斯加近海勘探活动增多的背景,探讨楚科奇海与阿拉斯加内陆环境地震噪声特征的海陆差异。本文利用第九次北极科学考察获取的楚科奇海OBS观测数据及阿拉斯加地震台站连续波形数据,采用功率谱密度与概率密度函数方法分析噪声的时间与频段分布特征,并结合海冰密集度、海浪、河流与人类活动信息对噪声来源进行识别与归因。在微地震带,楚科奇海在有冰期与无冰期的环境地震噪声强度差异明显:海冰覆盖抑制双频微震能量,而无冰期海浪活动增强使微震噪声显著上升。阿拉斯加内陆台站的双频微震峰值季节性变化与远源北冰洋风暴相关,在夏、秋季峰值周期略有缩短。短周期范围内,楚科奇海OBS记录到海浪与浮冰碰撞产生的间歇性高能量噪声,内陆台站则易受到河流湍流及人类活动的综合影响,表现出明显的季节性和日变化规律。长周期范围内,楚科奇海环境地震噪声强度较高,与海底洋流有关,而内陆台站此周期范围噪声整体较低且平稳。

     

    Abstract: Based on the background of receding Arctic sea ice and increasing exploration activities offshore Alaska, we explored the sea-land differences in seismic noise characteristics between the Chukchi Sea and the inland of Alaska, for which the Chukchi Sea OBS data obtained from the Ninth Arctic Scientific Expedition and the continuous waveform data from Alaska seismic stations were used, the temporal and frequency distribution characteristics of the noise were analyzed using the power spectral density and probability density function methods, and the sources of the noise were identified and described from the information on sea-ice density, ocean waves, river flow, and human activities. Result shows that in the microseismic zone, the ambient seismic noise intensity in the Chukchi Sea varies significantly between ice and ice-free periods: sea ice cover suppressed the dual-frequency microseismic energy, whereas the enhanced wave activity in the ice-free period significantly increased the microseismic noise. Seasonal variations in double-frequency microseismic peaks were revealed in the inland Alaskan stations and correlated with distant-source Arctic Ocean storms, showing a slight shortening of the peak period in summer and autumn. On the short-period scale, the Chukchi Sea OBS (Ocean Bottom Seismometer) records intermittent high-energy noise from wave–ice-floe collisions, while the inland stations are susceptible to a combination of river turbulence and human activities, and show clear seasonal and diurnal variation patterns. The higher ambient seismic noise intensity in the Chukchi Sea over a long period is related to submarine currents, whereas that in the inland stations is generally low and stable.

     

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