Omori Analysis Tools
Introduction
The Omori Analysis app provides several windows each dedicated to specific tasks. The window provides the ability to select a blast or blasts from the blast database for which the ‘Omori chart’ is provided for the events within a specified volume around the blast(s) and a specified time after the blast(s). If more than one blasts is selected the individual and the stacked cumulative event distribution is provided.
Another window is dedicated to performing a best-fit of the Modified Omori Law to the events associated with a selected blast. The chosen volume and time window and the parameters for the MOL is saved. Another window dedicated to the analysis of these results is provided. The statistical and spatial distributions of the MOL parameters are assessed based on the saved parameters from the MOL best-fit.
The spatial and statistical distributions of the MOL parameters provide input to the re-entry analysis which is provided in another window. The re-entry assessment is based on the work by Vallejos and McKinnon (2010) and can be used in real time assessment of re-entry or for the back analysis of historical data to develop re-entry protocols.
References
This app is largely based on the PhD by Javier Vallejos. The PhD can be downloaded here. The paper below is a summary of the re-entry methodology. There are two more papers below about the implementation and effectiveness of the method.
Vallejos, J.A. and McKinnon, S.D. (2010), 'Temporal evolution of aftershock sequences for re-entry protocol development in seismically active mines'. In: Van Sint, J.M. and Potvin, Y. (eds). 5th International Seminar on Deep and High Stress Mining, 2010 Santiago, Chile. Australian Centre for Geomechanics, pp. 199-214.
Morkel, IG & Rossi-Rivera, P 2017, ‘The implementation and quantification of the Vallejos and McKinnon re-entry methodology’, in, Proceedings of the Eighth International Conference on Deep and High Stress Mining, 2017, Australian Centre for Geomechanics.
Tierney, S & Morkel, IG 2017, ‘The optimisation and comparison of re-entry assessment methodologies for use in seismically active mines’, in, Proceedings of the Eighth International Conference on Deep and High Stress Mining, 2017, Australian Centre for Geomechanics.
Blasting
Blast Editor
You will need blast data to use this app. This video shows you how to manage your blast information.
Response to Blasting
The response to blasting window lets you quickly plot the seismic response over time and space for selected blasts.
MOL
MOL (Analysis)
The MOL analysis window lets you fit responses to blasting with the Modified Omori Law.
MOL (Results)
The MOL results window shows the distribution of MOL parameters for fitted blast responses.
Re-Entry
Re-entry Analysis
The re-entry analysis window utilises the methods described by Vallejos and McKinnon (2010) to compare the selected responses with the database of modelled responses. This can be used to identify abnormal responses.
Learning Exercises
- Open the blast editor
- Is the blast database up-to-date? If not, update it!
- If it is, try adding a pretend blast and deleting it again.
- Open the Response to Blasting window
- Plot blasts in 3D and colour by the number of events, is there a pattern?
- Plot the Omori charts for the five blasts with the highest event counts.
- Note the difference between the normalised, stacked and individual charts
- Go through the top five blasts one-by-one and adjust the spheroid and time filters to capture the main response events
- Is there a pattern in the typical spatial distribution of events?
- Open the MOL Analysis window
- How many blasts have MOL parameters assigned (p, K, c)?
- Find a blast with more than 20 events that hasn’t been modelled yet and fit the MOL
- Try to do at least 5 fits
- Open the MOL Results window
- Plot the all blasts with a modelled MOL in 3D
- Colour by p-value, is there a pattern in space?
- Colour by K-value, is there a pattern in space? Does it seem higher where you have good system sensitivity?
- Tick just your three most recent blasts with a modelled MOL, where do they sit on the overall distributions of p and K? About average? Towards the top? Towards the bottom?
- Open the Re-entry Analysis window
- Tick a recent blast
- When did it start to move horizontally through the percentile curves?
- When did it drop below the Tmc line?
- When did it drop below the Background line?
FAQ
Where is the cumulative energy line on the Omori chart?
In early versions of MS-RAP, the Omori chart included the cumulative energy as a function of time after blasting. You won't find that line anymore in the default Omori Analysis Tools app.
Although the total energy released has a value, the shape of the cumulative energy graph inherently has no meaning. The accumulation of a logarithmic parameter is dominated by the largest events and results in a curve with a somewhat arbitrary, random shape. The total energy released is included in the blast table in the Omori Analysis Tools app but the cumulative energy line has no diagnostic value (in fact, it could be misleading) and does not represent the underlying stochastic process.
To illustrate further, the video below shows a repeated generation of synthetic seismic data where each sample has the same number of events, the same b-value, and the same Omori relationship.