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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

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

Václav Vavryčuk1, Daniela Kühn2

1 Institute of Geophysics, Prague

2 NORSAR, Kjeller

motivation
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

moment tensor inversions
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

pyh salmi ore mine finland
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.

slide5

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

slide6

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

slide7

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

moment tensor inversions1
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

full waveform mt inversions
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

goal of the study
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)

moment tensor inversion time frequency approach

Moment tensor inversion: time-frequency approach

Motivation

Waveform modelling

MTI

strategy

Synthetic tests

Application to real data

Summary

moment tensor inversion scheme
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

full waveform mt inversions1
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

tests using synthetic data

Tests using synthetic data

Motivation

Waveform modelling

MTI

strategy

Synthetic tests

Application to real data

Summary

synthetic tests
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
double couple source iso
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

explosive source iso
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

application to real data

Application to real data

Motivation

Waveform modelling

MTI

strategy

Synthetic tests

Application to real data

Summary

mining blast iso
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

slide20

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

slide21

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

slide22

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

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