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Evaluation of the NSHA23 Magnitude Conversion Equations Using a New Moment Magnitude Catalogue

Created 16/10/2025

Updated 16/10/2025

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An earthquake catalogue based on the moment magnitude scale (MW) is a prerequisite for global best practice seismic hazard analyses. The 2018 National Seismic Hazard Assessment (NSHA18) was the first national-scale seismic hazard assessment for Australia to apply magnitude conversions to express earthquake magnitudes uniformly in terms of MW. This approach led to the single-biggest change in seismic hazard estimates between Geoscience Australia-led national seismic-hazard models. Between the 2012 and 2018 assessments, the hazard reduced because of: 1) the general reduction in the number of earthquakes of magnitude 4.0 and larger due to the correction of local magnitudes (ML) and subsequent conversion to MW, and; 2) the increase in the Gutenberg-Richter b-value due to the non-linear conversion of local magnitudes ML to MW. Using a new continental-scale attenuation model, independent assessment of MW has been performed for over 300 earthquakes recorded between 1990 and September 2024. After recalculating ML for the same earthquakes using improved filtering and time-domain windowing criteria, the MW catalogue is used to test and validate the ML to MW conversion equations used in the 2023 National Seismic Hazard Assessment (NSHA23). The earthquakes are partitioned into their regional magnitude polygons as applied by Geoscience Australia in its real-time operations; notionally central and western Australia, South Australia (Mt Lofty and Flinders Ranges) and eastern Australia. The performance NSHA23 ML to MW conversion equation is then assessed for each of these magnitude regions. Overall, the NSHA23 ML to MW conversion performs very well relative to continental-scale earthquake dataset. The sensitivity of this conversion to an earthquake’s static stress drop is also assessed. There is evidence that minor adjustments could be applied to the NSHA23 ML–MW conversion equation for larger-magnitude events with high stress drops.

Presented at the Australian Earthquake Engineering Society (AEES) National Conference 2024

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Field Value
Title Evaluation of the NSHA23 Magnitude Conversion Equations Using a New Moment Magnitude Catalogue
Language eng
Licence Not Specified
Landing Page https://data.gov.au/data/en/dataset/3d7dc96a-aa03-4bc9-a08e-25f02bade98e
Contact Point
Geoscience Australia Data
clientservices@ga.gov.au
Reference Period 16/12/2024
Geospatial Coverage
Map data © OpenStreetMap contributors
{
  "coordinates": [
    [
      [
        112.0,
        -44.0
      ],
      [
        154.0,
        -44.0
      ],
      [
        154.0,
        -9.0
      ],
      [
        112.0,
        -9.0
      ],
      [
        112.0,
        -44.0
      ]
    ]
  ],
  "type": "Polygon"
}
Data Portal Geoscience Australia

Data Source

This dataset was originally found on Geoscience Australia "Evaluation of the NSHA23 Magnitude Conversion Equations Using a New Moment Magnitude Catalogue". Please visit the source to access the original metadata of the dataset:
https://ecat.ga.gov.au/geonetwork/srv/eng/csw/dataset/evaluation-of-the-nsha23-magnitude-conversion-equations-using-a-new-moment-magnitude-catalogue