mikroseismik

Mikroseismik, or microseism, refers to persistent, low-amplitude ground motions that are not caused by earthquakes but by natural environmental processes. In seismic recordings, mikroseismik forms a major part of the background noise at long periods and can be detected by standard seismometers distributed around the world.

The primary source of mikroseismik is the Earth’s oceans. There are two main classes: primary microseisms, generated by the direct pressure of moving ocean waves on the seabed, and secondary microseisms, produced by nonlinear interactions of opposing waves that create pressure fluctuations at the sea floor. Primary microseisms typically have long periods on the order of tens of seconds (roughly 0.05–0.1 Hz), while secondary microseisms have shorter periods of a few seconds to about ten seconds (roughly 0.1–0.3 Hz). The two types exhibit different spectral characteristics and contribute differently to the observed ground motion.

Geographically, mikroseismik are strongest near oceans, coastlines, and continental shelves, but they are detectable globally. Their amplitude correlates with wind, sea state, storm activity, fetch length, and water depth. The signals appear in all three components of ground motion, with secondary microseisms often showing a stronger presence on horizontal components.

Applications of mikroseismik include seismic interferometry and ambient-noise tomography, which exploit the continuous background signal to image Earth’s structure. They also aid in monitoring ocean-wave climates and validating models of ocean–atmosphere interaction. While not hazards themselves, mikroseismik must be distinguished from earthquakes in seismic data analysis. In summary, mikroseismik are ocean-driven, background seismic signals that play a useful role in Earth science.