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A magnitude scale for local earthquakes in South Australia

DEPARTMENT OF ECONOMIC GEOLOGY UNIVERSITY OF ADELAIDE, SOUTH AUSTRALIA

Abstract

To minimize dispersion in local magnitude estimates due to different instrumental bandwidths, a scale has been established to allow for the average source spectrum, geometrical attenuation, and frequency-dependent absorption. The data used to derive the scale parameters were from S waves recorded in South Australia from 1967 through 1970, in the frequency range 1 to 10 Hz, and for epicentral distances up to 5°. The magnitudes were mainly in the range 1.5 to 3.5. The local scale M_N is given by

where A_g mm is the ground amplitude at f Hz at km epicentral distance, and c is a station correction.

The dispersion in observations of magnitude has probably been reduced by use of the scale to near the theoretical limits, allowing for possible source radiation patterns. The relationship of the scale to other measures of magnitude is uncertain, but M_N may be approximately equivalent to the local Richter magnitude M_L for the magnitude range (1.5 < M_L < 3.5) commonly observed in South Australia.

The scle is limited in use to data in the ranges given above, for local earthquakes in South Australia. Modification is necessary before such a magnitude scale can be applied elsewhere or to different data ranges.

Footnotes

^* Present address: Department of Physics, Memorial University, St. John's, Newfoundland, Canada.

This article has been cited by other articles:

				S. A. GREENHALGH and R. SINGH A revised magnitude scale for South Australian earthquakes Bulletin of the Seismological Society of America, June 1, 1986; 76(3): 757 - 769. [Abstract] [PDF]