1999 Jiji earthquake The tremor measured 7.6 on the Moment magnitude scale, 7.3 on the Richter scale, and the focal depth was . The Central Weather Bureau recorded a total of 12,911 aftershocks in the month following the main tremor. The total energy released is estimated to be 2.1 × 10 J, approximately the same as the yield of the Tsar Bomba. The earthquake was in an unusual location for Taiwan, which experiences the majority of its earthquakes off the eastern coast, such quakes normally causing little damage. One of the aftershocks, on 26 September, was a strong earthquake in its own right,
Richter magnitude scale used by astronomers. Second, he wanted a magnitude of zero to be around the limit of human perceptibility. Third, he specified the Wood-Anderson seismograph as the standard instrument for producing seismograms. Magnitude was then defined as "the logarithm of the maximum trace amplitude, expressed in microns", measured at a distance of 100 km. The scale was calibrated by defining a magnitude 3 shock as one that produces (at a distance of 100 km) a maximum amplitude of 1 micron (1 µm, or 0.001 millimeters) on a seismogram recorded by a Wood-Anderson torsion seismograph. Finally, Richter calculated a table of distance