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G. Kwiatek and JAGUARS Research Group

To understand earthquake rupture process in picoscale : Two years of high-frequency seismic monitoring at the Mponeng g old mine in South Africa. G. Kwiatek and JAGUARS Research Group. Aims of JAGUARS project. Investigate the self similarity of earthquake rupture process

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G. Kwiatek and JAGUARS Research Group

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  1. To understand earthquake rupture process in picoscale: Two years of high-frequency seismic monitoring at the Mponeng gold mine in South Africa G. Kwiatek and JAGUARS Research Group

  2. AIM Workshop, Prague, 29-30 September 2011

  3. Aims of JAGUARS project • Investigate the self similarity of earthquake rupture process • Link laboratory studies and nano-picoseismicity recorded in-situ cm-scale m-scale km-scale Courtesy of E. Charalampidou; W.D. Ortlepp, RaSiM5 proceedings; Wikipedia AIM Workshop, Prague, 29-30 September 2011

  4. Mponeng „Look with pride” deep gold mine JAGUARS materials, google maps, Anglogold Ashanti materials AIM Workshop, Prague, 29-30 September 2011

  5. B A N JAGUARS in-situ geomechanical laboratory • Depth 3540m; vicinity of a dyke and active mining (exploitation level ~90m above the network). Small area (300x300x300m) monitored. AIM Workshop, Prague, 29-30 September 2011

  6. AE-sensor JAGUARS materials (M. Nakatani) AIM Workshop, Prague, 29-30 September 2011

  7. Network • 8 Acoustic emission (AE) sensors (1kHz-170kHz) • One 3C, high frequency accelerometer (0.05-25kHz) • Located in boreholes • Triggering mode • In-situ location and acquisition • Sampling frequency 500kHz AIM Workshop, Prague, 29-30 September 2011

  8. Accelerometer (ACC) • Developed by ISS (now IMS) • 3-component and 1-component sensors • Sensitivity between 50Hz-25000Hz JAGUARS materials AIM Workshop, Prague, 29-30 September 2011

  9. Acoustic emission (AE) sensors • Developed by Gesellschaft für Materialprüfung und Geophysik (GMuG mbH) • Installation & coupling issues JAGUARS materials (M. Nakatani) AIM Workshop, Prague, 29-30 September 2011

  10. Network sensitivity • System capable of recording MW -4.5 (source size of few cm) @ ~80m • Significant damping & scattering due to local engineering structures • Strong variations in magnitude of completeness (Plenkers, Schorlemmer, Kwiatek, 2011, Bull. Seism. Soc. Am. 101 (6), in press) AIM Workshop, Prague, 29-30 September 2011

  11. Seismic data | Aftershock sequence • MW1.9 30m from the network, followed by 25,000 aftershocks • No accelerating activity (immediate foreshocks) before the main event After mainshock Before mainshock Madariaga! (Naoi et al., 2011, Bull Seism. Soc. Am. 101 (5); Focal mechanism calculated by M. Boettcher, Univ. New Hampshire AIM Workshop, Prague, 29-30 September 2011

  12. Seismic data | Aftershock sequence • Aftershock activity follows Gutenberg-Richter scaling relation • b=1.26, Mc=-4.30 for the fault plane (F) MC=-4.30 b=1.26 (Kwiatek et al., 2010, Bull. Seism. Soc. Am.100) AIM Workshop, Prague, 29-30 September 2011

  13. Seismic data | Post-blasting activity • Post-blasting activity starts right after blasting (~6-7pm). The Omori decay is visible even 12 hours after blasting. (Plenkers & Kwiatek, 2010, Seismological Research Letters 81) AIM Workshop, Prague, 29-30 September 2011

  14. Seismic data | Post-blasting activity • Post-blasting also follows scaling relations with b=1.16 (Kwiatek et al., 2010, Bull. Seism. Soc. Am.100) AIM Workshop, Prague, 29-30 September 2011

  15. Extensive scaling relation study • Gutenberg-Richter scaling relation • Static and dynamic scaling relations (stress drop vs seismic moment, apparent stress vs seismic moment) • Magnitude clustering and interevent time clustering Selection for source parameters: Post-blasting activity, aftershocks located far away Analysis: Spectral fitting + spectral ratio (Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press) AIM Workshop, Prague, 29-30 September 2011

  16. Scaling relations (stress drop) ►Constant static stress drop scaling relation observed between MW -0.8 and -4.1 • Frequency range 500-17kHz (source radius 4m-5cm) • Rupture proces self-similar (Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press) AIM Workshop, Prague, 29-30 September 2011

  17. Scaling relations (apparent stress) • Uniform energy release per unit slip and unit area • Rupture process self-similar • Second-order disturbances identified as originating from limited frequency band (Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press) AIM Workshop, Prague, 29-30 September 2011

  18. Tired of self-similarity and scaling relations? • We found no evidence for time-dependent magnitude clustering both for aftershock sequence of MW1.9 event and post-blasting activity. • Assumption of time-independent magnitudes is justified • Existence of magnitude correlations is an artificact related to catalog incompleteness • Important for statistical models e.g. PSHA or ETAS-related • We found no evidence for correlation between subsequent interevent times both for foreshocks of MW1.9 event and natural seismic activity (Davidsen & Kwiatek, 2011a, Phys. Res. Lett., submitted) (Davidsen & Kwiatek, 2011b, Phys. Res. Lett., in preparation) AIM Workshop, Prague, 29-30 September 2011

  19. Evidences for slow ruptures • Low corner frequency fP/fS ratio observed • Rupture governed by rupture time (low rupture velocity preferred) Low radiation efficiency observed ▶ Suggest low rupture velocity This ratio you typically observe ▶ Influences stress drop/apparent stress values!!! (Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press) AIM Workshop, Prague, 29-30 September 2011

  20. Non-double-couple components • Low ES/EP ratio observed in the whole magnitude range • Many events possibly display a non-DC behavior • Work in progress (co-op with Y. Ben-Zion) Tensile Shear (Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press) AIM Workshop, Prague, 29-30 September 2011

  21. Variations in stress drop and apparent stress • Depends on geological setup (cracked/isotropic) • Various rupture velocities? (Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press) AIM Workshop, Prague, 29-30 September 2011

  22. Summary • The combined AE-ACC network allowed to bridge the gap between laboratory experiments on rock samples and induced seismicity. • Earthquake rupture process is governed by similar physics over a range of magnitudes between laboratory experiments and small earthquake. This is supported by G-R relation, dynamic and static source parameters and time-dependent statistical analysis of magnitude clustering and event-time interval • Local variations in stress drop and apparent stress clearly depend on geological setup. Rupture velocity must be addressed in future works on scaling relations (Brodsky & Kanamori, AGU Monograph). • We reached the frequency limit of the recording system calibrated in an absolute sense that allows to calculate reliably the source parameters. AIM Workshop, Prague, 29-30 September 2011

  23. Thank you for your attention! Acknowledgments The Rock Engineering and Geology departments (R. Carstens, C. Miller, M. Pienaar and G. Flitton) at Mponeng gold mine (AngloGold Ashanti), ISS Carletonville, ISS Stellenbosch and CSIR Johannesburg are acknowledged for providing us with many useful information and electronic materials.We would like to thank R. Barth,O. Germer, L. Vasquez and M. Wieprich for helping us with the manual preparation of the dataset. Y. Ben-Zion is acknowledged for many valuable discussions. AIM Workshop, Prague, 29-30 September 2011

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