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.