xkcd uploaded a short describing how magnitude 0 earthquakes exist and how they can go lower than that. That’s because the magnitudes are calculated using the logarithm of the maximum displacement of the earthquake’s signal according to a seismogram (ML = log10(A) – log10(A₀) if you want to see the Richter magnitude equation).
And it’s also Charles F. Richter and his Richter scale to thank for setting the “zero point” as an earthquake at a distance of 100 km making a maximum horizontal displacement of 1 micrometre (0.00004 in.) and anything smaller than that goes into the negative! I guess that confirms cats as animals of seismic chaos.
Filed under: Earth earthquakes logarithm video