Abstract: In the emergency response to large earthquakes, semi-quantitative estimates play a very important role.This article introduces a few examples of such “Fermian approaches” with their physical significance and underlying physical problems, including the kinematic function (KF) of intensity distribution,the estimate of source time function (STF) of large earthquakes using the high-frequency energy envelope of teleseismic seismograms, polarization analysis for the fast retrieval of the rupture process of large earthquakes,and the magnitude estimate for earthquake early warning (EEW).