High-rate GNSS detects the near- and far-field effects of displacements during the 2011 Tohoku Mw9.0 earthquake

Abstract

Although there are a great number of research and publications on empirical amplitude, distance and magnitude scaling laws, none of them have ever considered the near- and far-field effects of displacement functions of seismic waves. We use the GEONET GNSS data collected from the 2011 Tohoku Mw9.0 earthquake to resolve the inconsistency between empirical amplitude, distance and magnitude scaling laws and theoretical displacement functions. We find that the high-rate dynamical GNSS PPP displacements clearly detect the near- and far-field amplitude distance scaling effects during the 2011 Tohoku Mw9.0 earthquake. The GNSS PPP coseismic displacements decay much more rapidly than theoretically expected in the near field but likely more slowly in the far field. If the near-field effect of displacements is not correctly taken into account, the decay rate will be significantly underestimated, implying that magnitudes of earthquakes will be significantly underestimated from near-field data with profound negative impact in earthquake early warning and hazard assessment.