Seismisk

Seismisk is an adjective used in several Scandinavian languages to describe things related to seismology or earthquakes. In English, the closest term is seismic. The word appears in references to seismisk activity, seismisk waves, and seismisk instrumentation, as well as in discussions of analysis methods and engineering applications connected to earthquake motion.

Earthquake waves are the core subject of seismisk study. The primary waves are P-waves (compressional) and S-waves (shear); surface waves travel along the Earth’s exterior. P-waves are typically the fastest and move through solids, liquids, and gases, while S-waves move only through solids and often cause more visible shaking. Seismometers and seismographs record ground motion, producing seismograms that enable seismologists to locate epicenters, determine focal mechanisms, and infer properties of the Earth's interior.

Magnitude and intensity are distinct but related concepts in seismisk analysis. Magnitude measures the energy released at the source, with modern practice emphasizing moment magnitude (Mw). Local magnitude (historically called the Richter scale) and other scales have been used in the past. Intensity describes shaking experienced at a location, often quantified by the Mercalli scale. Seismic data from multiple stations feed probabilistic seismic hazard analyses to estimate expected ground motions for regions.

Applications of seismisk knowledge include earthquake engineering and urban planning. Seismic design codes specify how buildings and critical infrastructure should respond to shaking, employing damping systems and base isolation. Retrofitting and site characterization help reduce risk. Related terms include seismology, seismometer, and earthquake engineering.