Multiplet-Clustering Analysis Reveals Structural Details within the Seismic Cloud at the Soultz Geothermal Field, France

Multiplet-clustering analysis is a method for precise determination of microseismic event locations and is used to identify subsurface fractures and fracture networks. A multiplet is a group of microseismic events with very similar waveforms, despite different origin times, and it is likely the expression of stress release on the same structure. The relative source locations of similar events can be determined with high resolution and accuracy by using the moving-window cross-spectrum analysis technique. Deduced seismic clusters, called multiplet clusters, are indicative of seismically activated structures, and the orientations of these structures can be estimated using the seismic clusters even though the absolute locations of the multiplet clusters cannot themselves be determined. We examine methods of determining the relative locations of multiplet clusters and introduce the concept of clustering analysis. The clustering analysis method is used to estimate the relative location of multiplet clusters by detecting phase differences between similar stacked events. We describe the procedure for multiplet-clustering analysis, estimate relative locations of multiplet clusters, and apply the method to induced microseismic data from the Soultz Hot Dry Rock field, France. We show that a fracture network can be delineated through multiplet-clustering analysis, whereas it is difficult to identify detailed structures on the basis of source locations estimated by the joint hypocenter determination method. Manuscript received 1 March 2002.

[1]  Gregory C. Beroza,et al.  Detailed observations of California foreshock sequences: Implications for the earthquake initiation process , 1996 .

[2]  Leigh House,et al.  Detailed joint structure in a geothermal reservoir from studies of induced microearthquake clusters , 1997 .

[3]  J. Fréchet,et al.  Application of the cross-spectral moving-window technique (CSMWT) to the seismic monitoring of forced fluid migration in a rock mass , 1990 .

[4]  B. E. Shaw,et al.  Postseismic response of repeating aftershocks , 1998 .

[5]  Leigh House,et al.  Determining planes along which earthquakes occur: Method and application to earthquakes accompanying hydraulic fracturing , 1987 .

[6]  R. H. Jones,et al.  A method for determining significant structures in a cloud of earthquakes , 1997 .

[7]  Jonathan M. Lees,et al.  Multiplet analysis at Coso geothermal , 1998, Bulletin of the Seismological Society of America.

[8]  Stephen D. Malone,et al.  High precision relative locations of earthquakes at Mount St. Helens, Washington , 1987 .

[9]  W Foxall,et al.  Clustering and Periodic Recurrence of Microearthquakes on the San Andreas Fault at Parkfield, California , 1995, Science.

[10]  K. J. Chang,et al.  Int. J. Rock Mech. Min. Sci. & Geomech. Abstr.: Reply to the Discussion by W. G. Pariseau of the paper by K. J. Chang and T.-W. Yang, “A constitutive model for the mechanical properties of rock”. 19, 123–134 (1982) , 1983 .

[11]  Gregory C. Beroza,et al.  Foreshock sequence of the 1992 Landers, California, earthquake and its implications for earthquake nucleation , 1995 .

[12]  Hiroaki Niitsuma,et al.  Detailed Fracture System of the Soultz-sous-Forêts HDR Field Evaluated Using Microseismic Multiplet Analysis , 2002 .

[13]  William Scott Phillips,et al.  Using Automated, High-precision Repicking to Improve Delineation of Microseismic Structures at the Soultz Geothermal Reservoir , 2002 .

[14]  Hiroaki Niitsuma,et al.  Stress estimated using microseismic clusters and its relationship to the fracture system of the Hiji , 2000 .

[15]  F. Waldhauser,et al.  A Double-Difference Earthquake Location Algorithm: Method and Application to the Northern Hayward Fault, California , 2000 .

[16]  H. Kaieda,et al.  Current status of seismic and borehole measurements for HDR/HWR development , 1999 .

[17]  Christopher John Young,et al.  An Automatic, Adaptive Algorithm for Refining Phase Picks in Large Seismic Data Sets , 2002 .

[18]  Allan M. Rubin,et al.  Highly concentrated seismicity caused by deformation of Kilauea's deep magma system , 1996, Nature.

[19]  A. Rubin,et al.  Streaks of microearthquakes along creeping faults , 1999, Nature.

[20]  J. E. Vidale,et al.  Variations in rupture process with recurrence interval in a repeated small earthquake , 1994, Nature.

[21]  E. A. Flinn.  Signal analysis using rectilinearity and direction of particle motion , 1965 .

[22]  Reinhard Jung,et al.  European HDR research programme at Soultz-sous-Forêts (France) 1987–1996 , 1999 .

[23]  W. Scott Phillips,et al.  Precise Microearthquake Locations and Fluid Flow in the Geothermal Reservoir at Soultz-sous-Forêts, France , 2000 .

[24]  William L. Ellsworth,et al.  Monitoring velocity variations in the crust using earthquake doublets: An application to the Calaveras Fault, California , 1984 .

[25]  Nicholas Deichmann,et al.  Rupture geometry from high-precision relative hypocentre locations of microearthquake clusters , 1992 .

[26]  H. Moriya,et al.  Precise source location of AE doublets by spectral matrix analysis of triaxial hodogram , 1994 .

[27]  D. P. Schwartz,et al.  Fault behavior and characteristic earthquakes: Examples from the Wasatch and San Andreas Fault Zones , 1984 .

[28]  M. Nafi Toksöz,et al.  Seismic monitoring of the growth of a hydraulic fracture zone at Fenton Hill, New Mexico , 1998 .