Abstract:The sand bed stress instrument is a precursory observation instrument used to transmit crustal stress signals via particle media,which entails sensors buried in the sand underground to receive the stress generated by the sand movement surrounding the sensor.It is widely accepted that the collision between sand grains can lead to stress changes in the Earth's crust and may affect the direction and numerical value of the crustal stress.To demonstrate the manner in which data recorded by the sand bed stressstress observation instrument,among which the frequency at 1.1574x10-5 Hz was the strongest signal,followed by 2.314 8x10-5 Hz.These frequency components included in the sand bed stress data clearly show the periodic tidal variations of the solid Earth under the tidal forces of the sun and the moon.A tidal cycle consists mainly of one-day waves and half-day waves;the former have the greatest influence on periodic tidal variations.In addition,we compared the stress data of sand bed in Huai＇an with those in Xiji,Beijing,and Putian,Fujian province,to determine that despite the differences in geological environments,they exhibited the same trend of rise and fall in value,which obviously show a synchronous change and a consistent annual variation.The changes in stress data from the Huai＇an station create an effective model for studying seismic activity.Such changes reflect the entire processes of major earthquake seismogenic phenomena,which include loading,rallying,unloading,and rising,in addition to higher frequency signal loading or unloading prior to a major earthquake with a frequency between 0.3and 0.4.On the contrary,when a moderate earthquake occurs,the sand beds near seismic stations exhibit short stress seismogenic phenomena,which includes loading,unloading,and rising.Moreover,the sand bed stress data curve shows abnormal fluctuation changes in waveforms.
