[Paper Review] Global characterization of seismic noise with broadband seismometers

Michael William Coughlin, J. Harms|arXiv (Cornell University)|Feb 22, 2012

Seismic Waves and Analysis12 references3 citations

TL;DR

This study presents a global analysis of seismic noise using 3-hourly power spectral densities from over 3,500 broadband seismometers across IRIS, F-net, and Orfeus networks from 2007–2011. It reveals that stations in Africa, Australia, and Antarctica record noise levels significantly below global low-noise models above 1 Hz, and identifies strong correlations between seismic noise and wind speeds above 0.1 Hz, urban proximity above 1 Hz, and earthquake activity near 80 mHz.

ABSTRACT

In this paper, we present an analysis of seismic spectra that were calculated from all broadband channels (BH?) made available through IRIS, NIED F-net and Orfeus servers covering the past five years and beyond. A general characterization of the data is given in terms of spectral histograms and data-availability plots. We show that the spectral information can easily be categorized in time and regions. Spectral histograms indicate that seismic stations exist in Africa, Australia and Antarctica that measure spectra significantly below the global low-noise models above 1 Hz. We investigate world-wide coherence between the seismic spectra and other data sets like proximity to cities, station elevation, earthquake frequency, and wind speeds. Elevation of seismic stations in the US is strongly anti-correlated with seismic noise near 0.2 Hz and again above 1.5 Hz. Urban settlements are shown to produce excess noise above 1 Hz, but correlation curves look very different depending on the region. It is shown that wind speeds can be strongly correlated with seismic noise above 0.1 Hz, whereas earthquakes produce seismic noise that shows most clearly in correlation around 80 mHz.

Motivation & Objective

• To systematically characterize global seismic noise using long-term, high-temporal-resolution spectral data from publicly available broadband networks.
• To identify spatial and temporal correlations between seismic noise and auxiliary geophysical data such as wind speed, population density, topography, and seismicity.
• To improve understanding of dominant noise sources across different frequency bands and regions, particularly in remote and low-noise areas.
• To provide a publicly accessible, long-term spectral dataset for future studies of seismic background variations and climate-seismicity links.

Proposed method

• Acquired continuous 3-hour power spectral density (PSD) data from BH? channels of broadband seismometers via IRIS, F-net, and Orfeus data servers.
• Processed data from over 3,500 stations across all continents, including calibration factor normalization and time-series segmentation into 3-hour intervals.
• Generated spectral histograms and data-availability plots to assess global station distribution and data coverage over time.
• Performed spatial and temporal cross-correlations between seismic noise spectra and external datasets: population density, wind speed, station elevation, and earthquake magnitudes.
• Used percentile-based grouping and regional subdivision (e.g., by continent) to analyze spectral behavior across different geophysical environments.
• Visualized results using interactive Google Earth files and MATLAB-based mapping tools to display diurnal and seasonal variations in microseismic amplitudes.

Experimental results

Research questions

• RQ1 Which regions exhibit seismic noise levels significantly below the global low-noise models, particularly above 1 Hz?
• RQ2 How do wind speeds correlate with seismic noise across different frequency bands, and where are these correlations strongest?
• RQ3 To what extent is urban proximity a driver of elevated seismic noise above 1 Hz, and how does this vary by region?
• RQ4 How does station elevation correlate with seismic noise levels at 0.2 Hz and above 1.5 Hz in the United States?
• RQ5 What is the temporal correlation between seismic noise and earthquake activity, particularly around 80 mHz?

Key findings

• Seismic stations in Africa, Australia, and Antarctica record noise levels significantly below the global low-noise models above 1 Hz, indicating the presence of exceptionally quiet seismic environments.
• Wind speeds show strong correlation with seismic noise above 0.1 Hz, with 10% of stations exhibiting coherence values above 0.5 at 1 Hz and 10 Hz, particularly at coastal locations.
• Urban settlements produce excess seismic noise above 1 Hz, but the correlation patterns differ significantly across regions, indicating regional variability in anthropogenic noise sources.
• In the United States, station elevation is strongly anti-correlated with seismic noise at 0.2 Hz and above 1.5 Hz, suggesting topographic shielding or site effects.
• Earthquake activity produces the clearest correlation with seismic noise around 80 mHz, indicating a dominant role of seismicity in this frequency band.
• Spectral coherence between wind and seismic noise is notably high in coastal regions, with some stations showing strong wind-driven noise across a broad frequency range above 0.1 Hz.