Frequently Asked Questions (FAQ)

How do you measure earthquake magnitude?

Today, geoscientists use different magnitude scales to describe the strength of an earthquake. The Richter scale measures the actual size (amplitude) of seismic waves recorded by a seismograph and provides a quantitative comparison between seismic events.
Source: Newton’s Apple
This is an indirect measure of the amount of energy released by the earthquake. A one-point increase on the Richter scale equals a tenfold amplitude of wave increase, which equals approximately 31 times more earthquake energy. A second type of scale, the modified Mercalli intensity scale, measures the amount and type of damage that earthquakes do to buildings and other structures, and their effects on humans. Because of these differences in measurements, an earthquake with a low Richter magnitude reading that occurs in a densely populated area like Los Angeles can actually have a higher Mercalli value or intensity than a high-magnitude quake in a desolate region like Antarctica. [Source: Newton's Apple (ericir.syr.edu)]Answers to other Frequently Asked Questions regarding earthquakes can be found at USGS Earthquake FAQs.

What is Richter Magnitude?

The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology. It is a logarithmic scale used to compare the size of earthquakes based on the amplitude of seismic waves recorded by seismographs.
Source: United States Geological Survey (USGS)

What is Local Magnitude?

In South Africa, the National Seismograph Network operated by the Council for Geoscience calculates local magnitude from recorded ground motion using the Hutton and Boore (1987) relationship: Magnitude is derived from the maximum recorded amplitude and the hypocentral distance to the seismic event. This approach is commonly applied to regional and mining-related seismicity.

What is South Africa’s mine magnitude?

The magnitude scale most commonly used on South African mines is based on seismic energy (En) and seismic moment (Mo), both estimated from seismic waveforms. This mine-specific magnitude scale ensures consistency, allowing large mining-induced seismic events to receive comparable magnitude values whether recorded by mine seismic networks or the national seismic network.
After: Stankiewicz, 2005

What is the purpose of seismic monitoring?

Modern seismic monitoring systems are designed to meet defined monitoring objectives using state-of-the-art technology with improved sensitivity, location accuracy, and data throughput. Accurate event location and rapid reporting of seismic activity assists mine management in:
  • Emergency response and rescue operations
  • Hazard identification and risk management
  • Proactive decision-making following intermediate to large seismic events
After: Handbook for Rock Engineering Practice for Tabular Hard Rock Mines, SIMRAC, 1999

Can earthquakes be predicted?

Earthquake prediction is generally defined as determining the probability that an earthquake will occur within a specified:
  • Time interval
  • Spatial area
  • Magnitude range
Rather than exact prediction, modern seismology focuses on probabilistic assessment and risk-based decision-making.
Leon Knopoff, University of California, 1995

Are there legal requirements for seismic hazard monitoring?

Yes. At mines where a significant risk of rockfalls or rockbursts exists, legislation requires employers to engage competent persons to manage seismic and geotechnical risk. These responsibilities include, but are not limited to:
  • Proactively identifying hazardous conditions and implementing remedial actions
  • Participating in mine planning activities influenced by rockfall and rockburst risk
  • Evaluating face layouts for seismic and geotechnical hazards
  • Reviewing and recommending systems, procedures, and control measures
  • Establishing monitoring, recording, and reporting systems for seismic activity
  • Approving mining sequences to minimise seismic risk and ensure excavation stability
  • Advising on the development and implementation of the mine’s Code of Practice (COP)
  • Conducting detailed analysis of pillar and remnant mining strategies
  • Monitoring, interpreting, and analysing seismicity with appropriate expertise
  • Inspecting major rockbursts and significant falls of ground and reporting findings
  • Providing input into rock-related risk assessments
For full legislative requirements, refer to the mandatory Code of Practice to Combat Rockfalls and Rockburst Accidents.
Source: Department of Minerals and Energy (DME 7/4/118 AB1 of 2001)
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