The Richter earthquake magnitude scale in South Australia |
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| Authors: | S A Greenhalgh R T Parham |
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| Institution: | 1. School of Earth Sciences , Flinders University of South Australia , Bedford Park, SA, 5042, Australia;2. Department of Physics , South Australian College of Advanced Education , Salisbury, SA, 5108, Australia |
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| Abstract: | Richter magnitudes ML have been determined for 718 well recorded South Australian earthquakes by converting amplitudes derived from existing seismograph stations to equivalent Wood‐Anderson amplitudes, and substituting in Richter's formula (Richter 1935), derived for such instruments and for Southern California. The magnitudes so determined were generally found to increase with distance A for each earthquake, at least for events at distances below a few hundred kilometres, reflecting lower attenuation of crustal S waves in South Australia. A distance‐dependent correction, which must be subtracted from Richter magnitudes, was obtained by integrating the weighted least squares fit to the (A, dML/dA) data. The correction increases to one‐half of a magnitude unit at a distance of 400 km, and thereafter decreases smoothly to 0.3 units at 600 km. Station corrections, due to local geological variations, have also been determined. Values range from ‐0.6 to + 0.2 units. Empirical relationships between the revised ML scale and the previously used local magnitude scales mL and MN (White 1968; Stewart 1975) and the body wave magnitude scale mb have been established. The latter yields results consistent with the well known Gutenberg‐Richter formula (Richter 1958) |
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