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| Passive Seismic Experiment | |
|---|---|
| Name | Passive Seismic Experiment |
| Type | Geophysical experiment |
| Field | Seismology |
| Location | Global |
Passive Seismic Experiment
Passive Seismic Experiment refers to observational studies that record natural and anthropogenic seismic vibrations without generating active sources, used to probe Earth's structure, monitor volcanic and tectonic activity, and explore subsurface resources. These experiments combine long-term field deployment, sensitive instrumentation, and computational analysis to extract signals from ambient noise and discrete events such as earthquakes, tremor, landslides, and meteor impacts. Passive approaches complement active surveys and remote sensing programs conducted by organizations such as United States Geological Survey, European Space Agency, Japan Meteorological Agency, British Geological Survey, and academic groups at institutions including California Institute of Technology, Massachusetts Institute of Technology, and Stanford University.
Passive seismic methods exploit vibrations recorded by networks of sensors to infer properties of the crust, mantle, ice sheets, and engineered structures. Projects range from global arrays coordinated by International Seismological Centre and Incorporated Research Institutions for Seismology to focused campaigns by universities and agencies like Scripps Institution of Oceanography, Columbia University, and ETH Zurich. They analyze signals from sources such as teleseisms cataloged by United States National Earthquake Information Center, regional seismicity tracked by Geological Survey of Canada, microseismicity associated with Induced seismicity monitored near Salton Sea Scientific Drilling Project, and ambient noise influenced by weather events recorded by observatories including Lamont–Doherty Earth Observatory.
Fundamental principles include seismic wave propagation theory developed within the context of work by Andrija Mohorovičić and Beno Gutenberg and scattering frameworks derived from studies by Harold Jeffreys and Kurtosis. Methods utilize waveform cross-correlation, ambient noise interferometry popularized in studies by Roel Snieder and Nicolas M. Shapiro, receiver function analysis advanced at Seismological Society of America meetings, and array processing techniques refined by researchers at Los Alamos National Laboratory and Lawrence Livermore National Laboratory. Modal decomposition, surface wave dispersion analysis, and coda wave interferometry are combined with tomography approaches inspired by global models such as PREM and regional inversions like USArray.
Typical instrumentation includes broadband seismometers from manufacturers used by IRIS consortium, short-period geophones employed in experiments coordinated with National Aeronautics and Space Administration, and ocean-bottom seismometers developed in collaboration with Woods Hole Oceanographic Institution and Institut Français de Recherche pour l'Exploitation de la Mer. Deployments use temporary arrays modeled after USArray Transportable Array, permanent networks such as Global Seismographic Network, and borehole installations influenced by protocols at Berkeley Seismological Laboratory and GFZ German Research Centre for Geosciences. Power systems, telemetry via satellites like Iridium (satellite constellation) and networks like GEONET, and instrument calibration standards set by International Union of Geodesy and Geophysics are integral to campaign planning.
Processing pipelines adapt algorithms from signal processing work at Bell Labs and statistical methods taught at Princeton University and University of Oxford. Tasks include quality control, instrument response removal following conventions from International Association of Seismology and Physics of the Earth's Interior, spectral analysis using multitaper methods popularized by Bronez and Thomson, and machine learning classification inspired by projects at Google DeepMind and Carnegie Mellon University. Tomographic inversions draw on regularization techniques from Cambridge University and computational frameworks implemented on supercomputers at Oak Ridge National Laboratory and National Energy Research Scientific Computing Center. Event detection leverages algorithms related to the STA/LTA approach and modern neural networks demonstrated by teams at Massachusetts Institute of Technology and Stanford University.
Applications span crustal imaging for geothermal exploration near Iceland and Yellowstone National Park, volcano monitoring at Mount St. Helens, Mount Etna, and Kīlauea, earthquake sequence analysis for events like the 1964 Alaska earthquake and 2011 Tōhoku earthquake and tsunami, hydrocarbon-induced microseismic monitoring in fields in North Sea and Permian Basin, and cryoseismology in Antarctica coordinated with British Antarctic Survey. Case studies include ambient noise tomography across California using USArray, tremor studies at Cascadia subduction zone carried out by Pacific Northwest Seismic Network, and ocean-bottom passive experiments revealing mantle anisotropy around Hawaii and Iceland.
Challenges include signal-to-noise limitations in urban settings such as Tokyo and New York City, site noise from infrastructure near Los Angeles International Airport, deployment logistics in remote regions like Greenland and Siberia, and instrument failure risks noted in Arctic campaigns by Alfred Wegener Institute. Ambiguities in source characterization persist as discussed in literature from Seismological Research Letters and Journal of Geophysical Research, and ethical, regulatory, and permitting issues arise in contexts involving Induced seismicity debated by authorities including Environmental Protection Agency and regional regulators.
Historical roots trace to passive observations by pioneers at Royal Observatory, Greenwich and early seismic catalogs assembled by Benjamin Hopkins and the Smithsonian Institution. Landmark experiments include global seismology advances following data syntheses by Beno Gutenberg and Charles Richter, ambient noise interferometry demonstrations by Nicolas M. Shapiro and Roel Snieder, the continental-scale USArray deployment enabling dense passive imaging, ocean-bottom experiments by Woods Hole Oceanographic Institution and Scripps Institution of Oceanography, and volcanic tremor monitoring breakthroughs at Montserrat and Eyjafjallajökull. Contemporary large-scale campaigns involve collaborations among IRIS, USGS, European Seismological Commission, and national research programs at CNRS and National Centre for Seismology.