While a traditional seismograph records the variations of displacement with time at a point,a tensor strainmeter monitors the variations of the spacial gradient of displacement.An YRY-4 borehole strainmeter at Guza,Sichuan province,recorded three local seismic events at the sampling rate of 100 sps for the first time.At this high sampling rate,the data of the YRY-4 demonstrated a satisfying degree of self-consistency and sufficiently high credibility.The observation shows that P wave strain contains areal strain components as well as shear strain component.It gives direct evidence for the property of P wave.According to the theory of seismology,P wave is clarified to have no rotation,but it has volumetric strain and shear strains.