Abstract: We use the endpoint suppression Hilbert-Huang transform to analyse the Indonesia M8.6 earthquake strain seismic waves recorded by four-component borehole strain meters located at Datong and Qingyuan in time and frequency domain. The result shows that different phases of the strain seismic wave of both the M8.6 main event and M8.2 aftershock eventshows different significant time-frequency features.Before the waveforms arrive, instantaneous frequency is low and instantaneous amplitude is small. At P wave first arrival, high frequency components appear of a sudden increase, at S wave arrival, lower frequency and amplitude rise sharply. When surface wave arrives, the amplitude further rises and reachesthe greatest value of the entire sequence. Coda amplitude decreases gradually, but the frequency is still high compared to the noise portion. The amplitude is still much larger. Although strain seismic wave and seismic wave have a correlation coefficient of up to 0.93, through the Hilbert-Huang transformation, the marginal spectrum shows that strain seismic wave andseismic wave are remarkably different. Strain seismic records have relatively more low frequency component. Hilbert spectrum is helpful in understanding the detailed characterof non-stationary signal. For transient signals of strain seismic wave, Hilbert-Huang transform is an effective time-frequency analysis tool.

Key words: Strain seismic wave, Hilbert-Huang transform, Empirical mode decomposition, Marginal spectrum