3DSEM is a system using thousands of eight channel receivers recording seismic and magnetic field at fixed location for months. Vibroseis and EM transmitters will be moving around at the vicinity of the receivers. An intermediate or preliminary system before 3DSEM is the MTSeis, which is a multiple eight channel recorder for magneto-telluric and seismic.
A typical MT station layout. The stations can be anywhere from a quarter-mile to tens of miles apart, depending on the type of survey. The new system will have an additional 3C Geophone or MEMS accelerometer recording simultaneously.