A new principle of recording earthquakes on magnetic tape by triggering is described. Utilizing the multiplex FM system, an ordinary tape recorder is run both as memory and as storage equipment. The recorder runs normally forward during a cycle of about 10 min. If no earthquake has triggered the system, the tape is rewound to its initial position; but if a seismic pulse surpasses the trigger level, the “rewind” function of the recorder is postponed, and every time this level is surpassed, a new period of postponement begins. Thus, a continuous and complete record of an earthquake is obtained.