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A Two-Step Time-Frequency Moment Tensor Inversion: Application to Mining Data

A Two-Step Time-Frequency Moment Tensor Inversion: Application to Mining Data. V áclav Vavry č uk 1 , Daniela Kühn 2 1 Institute of Geophysics, Prague 2 NORSAR, Kjeller. Motivation. Motivation. Waveform modelling. MTI strategy. Synthetic tests. Application to real data. Summary.

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A Two-Step Time-Frequency Moment Tensor Inversion: Application to Mining Data

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  1. A Two-Step Time-Frequency Moment Tensor Inversion:Application to Mining Data Václav Vavryčuk1, Daniela Kühn2 1 Institute of Geophysics, Prague 2 NORSAR, Kjeller

  2. Motivation Motivation Waveform modelling MTI strategy Synthetic tests Application to real data Summary To be able to invert for focal mechanisms and moment tensors: accurate robust and stable Difficulties: complex mining environment complex source-time function non-double-couple moment tensors

  3. Moment tensor inversions Motivation Waveform modelling wave amplitudes (Vavryčuk et al. 2008; Fojtíková et al. 2010; Godano et al. 2011) amplitude ratios (Miller et al. 1998; Hardebeck & Shearer 2003; Jechumtálová & Šílený 2005) full waveforms (Šílený et al. 1992 Cesca et al. 2006; Cesca & Dahm 2008; Sokos & Zahradník 2009) MTI strategy Synthetic tests Application to real data • applicable to simple • media • linear • fast • applicable to simple • media • insensitive to • amplifications • non-linear • applicable to complex • media • linear • more time consuming Summary

  4. Pyhäsalmi ore mine, Finland • microseismic monitoring: • since January 2003 • safety of the underground personnel • optimisation of mining process • network: • 12 1-C geophones • + 6 3-C geophones (ISS) • 3-D geometry • sampling rate: < 3000 Hz • events: • 1500 events /months (including blasting) • -2 < Mw < 1.5 Motivation Waveform modelling MTI strategy Synthetic tests Application to real data Summary owned by Inmet Mining Co., installation of seismometer network by the ISS Int. Ltd.

  5. Velocity model • Strongly heterogeneous velocity model • ore body: vp = 6.3 km/s • host rock: vp = 6.0 km/s • excavation area: vp = 0.3 km/s Motivation Waveform modelling MTI strategy U Synthetic tests W E D Application to real data Summary

  6. Waveform modelling: 2D • E3D: viscoelastic 3-D FD code (Larsen and Grieger, 1998) • strong interaction with mining cavities: reflection, scattering, conversion Motivation 620 m Waveform modelling MTI strategy Synthetic tests Application to real data Summary

  7. Waveformmodelling synthetic seismograms Motivation • - complex waveforms • long, strong coda • complex secondary arrivals • difficult to interpret P-wave • polarities • difficult to identify S-wave • arrivals Waveform modelling MTI strategy Synthetic tests Application to real data Summary observed seismograms

  8. Moment tensor inversions Motivation Waveform modelling wave amplitudes (Vavryčuk et al. 2008; Fojtíková et al. 2010; Godano et al. 2011) amplitude ratios (Miller et al. 1998; Hardebeck & Shearer 2003; Jechumtálová & Šílený 2005) full waveforms (Šílený et al. 1992 Cesca et al. 2006; Cesca & Dahm 2008; Sokos & Zahradník 2009) MTI strategy Synthetic tests Application to real data • applicable to simple • media • linear • fast • applicable to simple • media • insensitive to sensor • amplifications • non-linear • applicable to complex • media • linear • more time consuming Summary

  9. Full waveform MT inversions time-domain inversion frequency-domain inversion Motivation Waveform modelling MTI strategy simplified approach (Sokos & Zahradník 2009) Adamová et al. 2009) amplitude spectra (Cesca et al., 2006; Cesca & Dahm, 2008) complex spectra (Vavryčuk, 2011a,b) Synthetic tests • polarity of waves • is considered • insensitive to time • shifts • linear • simple source-time • function • polarity of waves • is neglected • insensitive to time • shifts • non-linear • complex source-time • function • polarity of waves • is considered • sensitive to time • shifts • non-linear • complex source-time • function    Application to real data       Summary   

  10. Goal of the study Motivation Waveform modelling MTI strategy Synthetic tests Application to real data Summary To develop a moment tensor inversion: combination of time and frequency approaches keeps advantages of all approaches (accurate, robust and stable)

  11. Moment tensor inversion: time-frequency approach Motivation Waveform modelling MTI strategy Synthetic tests Application to real data Summary

  12. Moment tensor inversion scheme Frequency-domain MTI using complex spectra 1. step: Motivation Waveform modelling Moment tensor + MTI strategy Source-time function Synthetic tests 2. step: Time-domain MTI Application to real data Summary Final moment tensor

  13. Full waveform MT inversions Motivation time-domain inversion time-frequency inversion Waveform modelling MTI strategy • polarity of waves • is considered • insensitive to time • shifts • linear • simple source-time • function • polarity of waves • is considered • insensitive to time • shifts • linear • complex source-time • function   Synthetic tests     Application to real data   Summary

  14. Tests using synthetic data Motivation Waveform modelling MTI strategy Synthetic tests Application to real data Summary

  15. Synthetic tests Motivation Waveform modelling MTI strategy two distinct maxima Synthetic tests Application to real data Summary • source mechanism: DC and explosion • source time function: • noise: in amplitudes and in time shifts • amplitude noise; 0-100% in 5% steps • time shift noise:0-0.01 s in steps of 0.005 s • repeating inversions: 100 inversions

  16. Double-couple source: ISO % Mean value Standard deviation time-domain Inversion ISO = 3% Motivation Waveform modelling MTI strategy frequency-domain Inversion ISO = 0% Synthetic tests Application to real data time-frequency Inversion ISO = 0% Summary

  17. Explosive source: ISO % Mean value Standard deviation time-domain Inversion ISO = 95% Motivation Waveform modelling MTI strategy frequency-domain Inversion ISO = 100% Synthetic tests Application to real data time-frequency Inversion ISO = 100% Summary

  18. Application to real data Motivation Waveform modelling MTI strategy Synthetic tests Application to real data Summary

  19. Mining blast: ISO % Mean value Standard deviation time-domain Inversion ISO = 66% Motivation Waveform modelling MTI strategy frequency-domain Inversion ISO= 71% Synthetic tests Application to real data time-frequency Inversion ISO = 68% Summary

  20. Mining blast: DC, waveforms P time-domain inversion Motivation T Waveform modelling MTI strategy frequency-domain inversion Synthetic tests P T Application to real data Summary time-frequency inversion P T

  21. Summary I structural model in mines usually is very complex large and abrupt changes in velocity at cavities the model varies in time Motivation Waveform modelling MTI strategy earthquake source is complex (single forces, non-DC components, complex source history) Synthetic tests Application to real data radiated wave field is complex (reflected, converted, scattered waves, head waves) Summary

  22. Summary II Motivation Waveform modelling MTI strategy Synthetic tests Application to real data Summary the most promising approach: full waveform MTI simplified time-domain MTI is robust and stable two-step time-frequency MTI improves the performance by considering more complex source-time function inversion of blasts reveals some stable DC part

  23. Thank you!

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