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

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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

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

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

- 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

- 1500 events /months

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.

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

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

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

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

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

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

Motivation

Waveform modelling

MTI

strategy

Synthetic tests

Application to real data

Summary

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

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

Motivation

Waveform modelling

MTI

strategy

Synthetic tests

Application to real data

Summary

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

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

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

Motivation

Waveform modelling

MTI

strategy

Synthetic tests

Application to real data

Summary

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

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

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

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

Thank you!