Seismological Research Letters (SRL) announces a Focus Section on nonexplosive active source monitoring and imaging. In recent years, there have been many efforts worldwide to image crustal structure and monitor subtle subsurface velocity changes with nonexplosive active seismic sources, for example, air‐guns, vibroseis, electric sources, accurately controlled routine‐operated seismic sources (ACROSS), and piezoelectric sources. These types of active sources are environmentally green compared to chemical explosives that were widely used in continental‐scale seismic exploration studies. They have also been used to image fine structures of the Earth’s interior at various length scales and to monitor the subsurface structural...

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