On March 2, 2009, the National Disaster Reduction Committee and the Ministry of Civil Affairs released news. With the approval of the State Council, since May 2009, May 12th is the national “Disaster Prevention and Mitigation Dayâ€.
On May 12, 2008, the National Seismological Bureau determined that the Wenchuan Earthquake was 7.8 on the Richter scale and was revised to 8.0 on the Richter scale at 18:50 on May 18.
What do these figures represent compared to the strongest 9.5-magnitude earthquake in Chile or the 9.0-magnitude earthquake in the northeast of Japan? How is the scale calculated?
The scale of the Richter earthquake (the scale of the Taiwanese translation of the earthquake, the Hong Kong translation of the special system), also known as the scale of the near earthquake, is the scale for recording the degree of earthquake.
In 1935, it was jointly developed by American seismologist Richter and Gutenberg at the California Institute of Technology. This scale was originally designed for the California area and 2,800 times the Woods-An Desheng Torsional Seismograph.
Rickett designed this scale to distinguish between the large number of small earthquakes and a small number of large-scale earthquakes that occurred in California at the time, and the inspiration came from the "stars" in astronomy that indicate the brightness of celestial bodies. But with this grading standard popular around the world, Richter is also famous.
The scale of the Richter scale is based on the amplitude of the seismic wave recorded by the seismograph. When the magnitude of the earthquake is fixed, the farther the source is, the smaller the amplitude of the seismic wave is. When the distance from the source is constant, the amplitude and magnitude of the seismic wave. The size is positively correlated. The specific values ​​are derived from the common logarithmic calculus of the total horizontal amplitude of the maximum displacement recorded by the seismograph.
Since the location of the seismograph is not at the center of the earthquake (the center of the earthquake), the logarithm of the amplitude of the magnitude 0 earthquake at the location of the seismometer should be subtracted. In order to make the result not negative, Richter chose an earthquake with a maximum horizontal displacement of 1 μm at an observation point 100 km away from the epicenter as a magnitude 0 earthquake. However, the scale of the Richter earthquake does not specify an upper or lower limit. Modern precision instruments often record earthquakes of negative magnitude.
Due to the limitation of the 2800 times Wude-An Desheng torsional seismograph used in designing the scale of the Richter scale, the magnitude of the near earthquake is greater than about 6.8 or the observation point is more than about 600 km from the epicenter. The researchers propose some improvements, with surface wave scale and solid wave scale being the most common.
The main drawback of the scale of the Richter scale is that it is not directly related to the physical characteristics of the seismic source, and it produces a magnitude saturation problem around 8.3-8.5, that is, after the earthquake scale exceeds 8.6, even though the surface appears longer. The rupture shows that the earthquake has a larger scale, but the measured surface wave magnitude Ms value is hard to increase.
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