A method of seismic investigation using the swept impact seismic technique involves measuring the response of a site to be investigated to a series of controlled impact sequences applied at different points of the site, each sequence using impacts generating pulses of energy at 100-2500 Hz., the impacts of the sequence having a repetition frequency swept between frequencies in the range of 10 to 500 Hz., the end frequencies having a ratio of at least 1.5 to 1, and the number of impacts in the sequence being at least 100 (and preferably at least 500). The invention also extends to apparatus for implementing such a method, comprising an electrically-actuated hammer having an impact frequency variable through a range of at least 1.5:1 within the range 10 to 500 Hz., and generating impacts characterized by substantial energy within a frequency range of 100-5000 Hz., a drive circuit for energizing the hammer to deliver a sequence of at least 100 (and preferably at least 500) impacts having a repetition frequency swept through a ratio of at least 1.5 to 1, and means for repositioning the hammer between sequences.
展开▼
