The high-resolution imaging (HRI) portable array; a seismic (and Internet) network dedicated to kilometric-scale seismic imaging

The geophysical characterization of geological structures remains a major task in natural hazard mitigation. Answering questions regarding the dynamics of physical processes related to natural hazards (e.g., landslides, seismic or volcanic hazards) often requires constraining the geometry and the spatial distribution of some physical parameters to map the location of temporal changes in the structures. A high-resolution probing tool is needed to address such problems as mapping an object's geometry (e.g., fault gouge), mapping a surface of physical discontinuity (e.g., water circulation, sliding surface), or mapping a spatial and temporal distribution of physical properties (e.g., feeder conduits). Although the term "high resolution" may be used for very different imaging scales (from subsurface shallow imaging to 3D oil exploration imaging, for instance), it has a common implication in all experiments: high-resolution imaging implies a high density of measurement points. A great effort has been made these past 20 years to develop portable networks throughout the world and increase the number of available seismographs. For example, the Incorporated Research Institutes for Seismology (IRIS) PASSCAL program in the United States (Fowler and Pavlis 1994) provides a pool of more than 1,000 portable seismographs. The Geophysical Instrument Pool (GIPP) at GeoForschungsZentrum (GFZ) Potsdam, Germany, is yet another important initiative that offers hundreds of seismographs. We cannot be exhaustive in listing portable networks, but we wish to emphasize that while many networks are devoted to crustal or lithospheric studies, others also offer equipment to perform shallower imaging, for example, SEIS-UK in the United Kingdom (Brisbourne et al. 2004) PASSCAL/single-channel Texans recorders, and volcanic imaging (Morita and Hamaguchi 1996). This paper provides a technical overview of the high-resolution imaging (HRI) array of portable seismic stations with an emphasis on its communication capabilities. This tool has been designed to provide a flexible and efficient instrument in 3D seismic imaging experiments conducted on targets with a typical size from several hundred meters to a few kilometers.