A method for seismic exploration using conversions between electromagnetic
and seismic energy, with particular attention to the electromagnetic
source waveform used. According to the invention, source waveforms are
correlated with reference waveforms selected to minimize correlation side
lobes. Line power at 60 Hz may be used to provide a waveform element
which may be sequenced by a binary code to generate an extended source
waveform segment with minimal correlation side lobes. Preferred binary
codes include Golay complementary pairs and maximal length shift-register
sequences.