What does the main frequency of earthquakes mean?

The period with the highest probability of random vibration. It is often used to describe earthquake vibration or site characteristics. The period of excellence was put forward a long time ago. Its original meaning is that a certain seismic wave or a harmonic component of a certain type of seismic wave causes the most significant vibration of the construction site, which is related to the thickness of the site covering soil and the shear wave velocity of the soil. For the same site, different types of seismic waves will get different dominant periods, so there are contradictions in concept. Now the earthquake engineering community has completely abandoned this formulation; At present, the characteristic period of the site is used to determine the seismic influence coefficient. That is to say, firstly, the site classification of buildings is determined according to the thickness of covering soil and the shear wave velocity of soil, and then the site characteristic period is obtained by looking up the table. Finally, the seismic influence coefficient used in seismic design is determined by the design seismic grouping and site characteristic period. When an earthquake occurs, the seismic wave emitted by the source propagates to the surface rock and soil, forcing it to vibrate. Because the surface rock and soil can selectively amplify the seismic waves of different periods, a rock and soil is always amplified with the waves of a certain period, which makes more and better waves recorded on the seismic map. This period is the characteristic period of rock and soil, also known as the excellent period. Thick sediment layer composed of multi-layers of soil will be reflected many times when the shear wave from the deep part propagates to the ground, and will be enhanced by the superposition of waves, making the long-period wave particularly prominent. The essence of optimal period is the * * * vibration of wave, that is, when the vibration period of local seismic wave is the same as the natural vibration period of surface rock and soil, the surface vibration is strengthened by * * * vibration. Long-distance earthquake with low acceleration on extremely thick alluvium will cause long natural vibration period of high-rise buildings.