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

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Presentation on theme: "A Two-Step Time-Frequency Moment Tensor Inversion: Application to Mining Data Václav Vavryčuk 1, Daniela Kühn 2 1 Institute of Geophysics, Prague 2 NORSAR,"— Presentation transcript:

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

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

3 Moment tensor inversions 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 Cesca et al. 2006; Cesca & Dahm 2008; Sokos & Zahradník 2009) applicable to simple media insensitive to amplifications non-linear applicable to simple media linear fast applicable to complex media linear more time consuming Motivation Waveform modelling MTI strategy Summary Synthetic tests Application to real data

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

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

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

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

8 Moment tensor inversions 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 Cesca et al. 2006; Cesca & Dahm 2008; Sokos & Zahradník 2009) applicable to simple media insensitive to sensor amplifications non-linear applicable to simple media linear fast applicable to complex media linear more time consuming Motivation Waveform modelling MTI strategy Summary Synthetic tests Application to real data

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

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

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

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

13 Full waveform MT inversions time-domain inversion 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 time-frequency inversion Motivation Waveform modelling MTI strategy Summary Synthetic tests Application to real data

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

15 Synthetic tests 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: s in steps of s repeating inversions: 100 inversions two distinct maxima Motivation Waveform modelling MTI strategy Summary Synthetic tests Application to real data

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

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

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

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

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

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

22 Summary II 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 Motivation Waveform modelling MTI strategy Summary Synthetic tests Application to real data

23 Thank you!


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