Study on magnitude scaling relationship using Pn waves for the Korean earthquake early warning system

In recent, studies on the developing an Earthquake Early Warning (EEW) for protecting the human life and property attracts attention in world widely. An EEW rapidly transmits the information about location and magnitude of earthquake, which are estimated by using initial P waves, before strong ground shaking arrival.

A magnitude of an event in EEW can be measured from peak displacement (Pd) and maximum predominant period (τ_p^max) of P waves. However, τ_p^max is not preferred to estimate magnitude because it shows more variation and, thus, magnitude of P waves is usually estimated by the Pd of Pg waves observed within epicentral distances less than 100 km. Therefore, in order to issue the occurrence of large offshore earthquakes, it is necessary to develop a magnitude scaling relationship for Pn waves.

The Korean Earthquake Early Warning System has been operated by the Korea Meteorological Administration since January 2015. For developing the scaling relationships between the Pd of Pg or Pn waves and earthquake magnitude, we used observed Pds at epicentral distances of 20 to 400 km. The Pds were selected from earthquakes with magnitude greater than 3.0 that occurred from the July 2015 to the April 2018 in the Korean Peninsula. Magnitude scaling relationship is obtained from a regression analysis based on amplitudes of Pg and Pn waves. It is expected that the scaling relationship will enable us to issue the warning of large offshore earthquakes.