What do the hazard isos mean?

Overview

The grid-based hazard calculations in the Hazard Assessment app were discussed in a previous post. The Iso View describes the hazard at all locations within the mine but when you are considering the seismic risk for a particular work area, large events and strong ground motions may come from multiple sources. The Excavation View estimates the seismic hazard associated with working areas (minode locations) in a few different ways as described below.

Mine Geometry Model Minode Generator is a new utility app which enables you to generate your own new minodes from a mine geometry model. If you're not sure what minodes are or why you would want to generate them, see What are minodes? If you're not sure what mine geometry models are, see Mine Geometry Models Application.

Probabilistic seismic hazard calculations are dependent on the number of events (N) and the b-value. But which has more effect on the hazard result? The chart below shows how seismic hazard varies with b-value for N = 1,000, N = 10,000 and N = 100,000.

A new window has been added to the Hazard Assessment app (Figure 1). The sensitivity analysis aims to quantify the effect of the variation of the input parameters on the hazard. These analyses can also help the user to determine the optimal settings to use for many of the parameters. This window allows the user to vary only one parameter at the time.

A stochastic declustering algorithm has been implemented in mXrap to separate events into 'clustered' and 'background' components. It can be useful when designing seismic exclusions and re-entry procedures to separate seismicity that occurs in short bursts from seismicity that has low variability in space and time. Short-term exclusions cannot be used to manage the risk associated with background seismicity, since the hazard inside a potential exclusion would be the same as outside the exclusion. Efficient exclusion and re-entry procedures target areas where seismicity is most clustered and where the seismic hazard to which people are exposed can be reduced with a short disruption to production.

The strong ground motion (SGM) relationship is used to calculate the peak particle velocity (PPV) generated by a seismic event. You may also hear this referred to as a ground motion prediction equation (GMPE), but only the maximum velocity is estimated, i.e. the strong ground motion, rather than the full, complex wave motion.

That is the question. An explainer on seismic hazard measurement.

A few new features have been added to the Hazard Assessment application, aiming to improve usability, understanding and investigation. The first addition is a chart in the hazard setup window to indicate the current date range settings. Usually the date range for calculating b-value will be a lot longer than for calculating event rate. Hopefully the chart will be a handy visual aid to help you keep your bearings when setting the hazard analysis periods.