Ambient Noise Recorded by a Dense Broadband Seismic Deployment in Western Iberia
Ambient Noise Recorded by a Dense Broadband Seismic Deployment in Western Iberia
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伊比利亚西部密集宽带地震部署记录的环境噪声
DOI：
10.1785/0120140079
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发表时间：
2014
影响因子：
3
通讯作者：
C. Haberland
中科院分区：
文献类型：
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作者：
S. Custódio;N. Dias;B. Caldeira;F. Carrilho;S. Carvalho;C. Corela;Jordi Díaz;J. Narciso;Guilherme Madureira;L. Matias;C. Haberland
摘要西伊比利亚岩石圈和软流圈结构（WILAS）项目在葡萄牙密集部署了2年的宽带地震台站，本文概述了该项目的部署情况，并描述了网络环境噪声及其来源。在解释了包括传感器方向评估在内的质量控制之后，我们描述了短周期（SP）、微震和长周期（LP）波段的背景噪声。我们观察与人类活动有关的SP噪声的日变化。临时和永久监测站在所有时间段的噪音水平非常相似，但在水平LP处，临时监测站录得的噪音水平较高。我们发现，中值噪声水平是非常均匀的整个网络中的微震带（3-20秒），但在此范围外变化很大。微震噪声的振幅显示出强烈的季节性变化。季节性主要是由非常长周期的双频微震（8 s），可能与冬季风暴有关。环境噪声振幅的叠加表明，在整个地震动频谱中，从0.3到100 s，可以看到一些微震噪声峰值。微震振幅增加的时期通常与葡萄牙近海的海洋条件相关。一些地震记录显示了一个有趣的12小时周期的LP（100-s）噪声，这可能与大气潮汐有关。最后，我们使用功率谱密度与时间的关系图来监测LP仪器响应的变化。该方法允许识别LP响应变化发生的确切时间，这是为了提高对该仪器伪影的理解并最终校正数据。在线资料：说明地震噪声幅度随传感器类型、时间和土壤类型变化的图形和电影。
Abstract The West Iberia Lithosphere and Asthenosphere Structure (WILAS) project densely covered Portugal with broadband seismic stations for 2 yrs. Here we provide an overview of the deployment, and we characterize the network ambient noise and its sources. After explaining quality control, which includes the assessment of sensor orientation, we characterize the background noise in the short‐period (SP), microseismic, and long‐period (LP) bands. We observe daily variations of SP noise associated with anthropogenic activity. Temporary and permanent stations present very similar noise levels at all periods, except at horizontal LPs, where temporary stations record higher noise levels. We find that median noise levels are extremely homogeneous across the network in the microseismic band (3–20 s) but vary widely outside this range. The amplitudes of microseismic noise display a strong seasonal variation. The seasonality is dominated by very‐long‐period double‐frequency microseisms (8 s), probably associated with winter storms. Stacks of ambient noise amplitudes show that some microseismic noise peaks are visible across the whole ground‐motion spectrum, from 0.3 to 100 s. Periods of increased microseismic amplitudes generally correlate with ocean conditions offshore of Portugal. Some seismic records display an interesting 12 hr cycle of LP (100‐s) noise, which might be related to atmospheric tides. Finally, we use plots of power spectral density versus time to monitor changes in LP instrumental response. The method allows the identification of the exact times at which LP response changes occur, which is required to improve the understanding of this instrumental artifact and to eventually correct data. Online Material: Figures and movie illustrating the variation of seismic noise amplitudes with sensor type, time, and soil type.