Testing the sensitivity of new Australian empirical magnitude conversion equations on seismic hazard analyses

Because all modern ground motion prediction equations (GMPEs) are now calibrated to the moment magnitude scale MW, it is essential that earthquake rates are also expressed in terms of moment magnitudes for probabilistic seismic hazard analyses. However, MW is not routinely estimated for earthquakes in Australia because of the low-to-moderate level of seismicity, coupled with the relatively small number of seismic recording stations. As a result, the Australian seismic catalogue has magnitude measures mainly based on local magnitudes, ML. To homogenise the earthquake catalogue based on a uniform MW, a “reference catalogue” that includes earthquakes with available MW estimates was compiled. This catalogue consists of 240 earthquakes with original MW values between 2.0 and 6.58. This reference catalogue served as the basis for the development of magnitude conversion equations between MW and other magnitude scales: ML, body-wave magnitude mb, and surface-wave magnitude MS. The conversions were evaluated using general orthogonal regression (GOR), which accounts for measurement errors in the x and y variables, and provides a unique solution that can be used interchangeably between magnitude types. The impact of the derived magnitude conversion equations on seismic hazard is explored by generating synthetic earthquake catalogues and computing seismic hazard level at an arbitrary site. The results indicate that we may expect up to 20-40% reduction in PGA hazard, depending on the selection and application process of the magnitude conversion equations. Abstract submitted to and presented at the 2017 Australian Earthquake Engineering Society (AEES) Conference