PRECISE SOURCE LOCATION OF AE DOUBLETS BY SPECTRAL MATRIX ANALYSIS OFTRIAXIAL HODOGRAM

We have developed a precise relative source location technique using a coustic emission doublets (AE doublets) in the triaxial hodogram metho d to evaluate the direction and distance of subsurface extension crack s. An AE doublet is a pair of acoustic emissions with similar waveform s and adjacent locations on the same crack but which occur at differen t times. The relative source location is estimated by an analysis in t he frequency domain. The relative distance between two AE sources is d etermined from the difference of P-S arrival time delays by cross-spec trum analysis. The relative direction is derived using a spectral matr ix from the difference in P-wave polarization directions. We also prop ose a method to optimize the estimated relative location by using a gr oup of AE doublets. The accuracy of the estimated source location was confirmed by performing field experiments. The relative locations of a rtificial wave sources about 150 m from a triaxial detector can be est imated with distance errors of less than 1 m, and direction errors of less than 3.8 degrees in both azimuth and inclination. Results of the application of this analysis on AE doublets in a geothermal field demo nstrate its ability to evaluate deeper subsurface fractures.