#### How do you measure earthquake magnitude?

Today, geologists use two different scales to measure how strong an earthquake is. The Richter scale measures the actual size (or amplitude) of the wave generated by a particular earthquake on a seismograph. [Source: Newton's Apple (ericir.syr.edu)]

#### What is Richter Magnitude?

The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. [Source: US Geological Survey]

#### What is Local Magnitude?

The SA National Seismograph Network operated by the Council for Geoscience in Pretoria calculates magnitude from recorded ground motion (Hutton & Boore, 1987):

where A is the the recorded max. amplitude in nano metres and D ist the hypo-central distance in km.

#### What is South Africa’s mine magnitude?

The magnitude scale most commonly used on SA mines is based on seismic energy (En) and seismic moment (Mo). Both are estimated from waveforms:

This scale ensures that the largest mine tremors receive similar magnitude values, whether they are recorded by mine networks or by the national seismic network (This email address is being protected from spambots. You need JavaScript enabled to view it., 2005).

#### What is the purpose of seismic monitoring?

A number of standard monitoring objectives have been formulated that make use of modern, state-of-the-art seismic systems with increased location accuracy, sensitivity, and data throughput. The accurate LOCATION of seismic events and the immediate reporting to management of event coordinates can assist in rescue operations after intermediate to large seismic events.
[After: A handbook for rock engineering practice for tabular hard rock mines, SIMRAC 1999]

#### Can earthquakes be predicted?

The issue of prediction has always been one of the establishment of the probability that an earthquake will occur within a specified time interval, a specified space interval, and a specified magnitude range.
[Leon Knopoff, Dep. of Physics and Inst. of Geophysics and Planetary Physics, Univ. of California, CA, in Proc.Natl.Aca.Sci., USA 1995]

#### Are there legal requirements in terms of seismic hazard monitoring?

At every mine where a significant risk of rockbursts or rock falls exist, the employer must engage the services of competent persons who...

• Proactively identify dangerous situations and take remedial action before persons are injured or workings are damaged.

• Participate in any relevant planning activities that need to take account of, could influence or be influenced by, the risk of rockfalls or rockbursts.