Abstract

In this study, a new local magnitude (ML) scale is developed for New Zealand and adjacent offshore regions. SeisComP3 (SC3) has been in use for earthquake analysis in New Zealand since September 2012 with the original Richter (1935) logA0 attenuation relationship for calculating ML. The attenuation characteristics of New Zealand differ significantly from southern California, where ML was originally defined, and therefore result in ML that is consistently high when compared with moment magnitude (Mw). Using Mw from 528 regional moment tensor solutions along with peak observed amplitudes, a new logA0 curve is derived, along with station correction factors that define a revised ML scale for New Zealand earthquakes that is more consistent with Mw. The new logA0 curve is similar to the original Richter (1935) definition at hypocentral distances of ∼100–200  km but differs significantly at closer and farther distances. The new ML is more consistent with Mw across New Zealand, including crustal earthquakes and earthquakes below the crust. The California Institute of Technology (Caltech)–U.S. Geological Survey seismic processer (CUSP) system was used for earthquake analysis prior to SC3, and previous studies have derived regression relationships relating CUSP ML with Mw. After applying the regression relationships to CUSP ML, we found very good agreement between CUSP ML and the new SC3 ML, which is important for developing a consistent ML between different catalogs.

Online Material: Table of station corrections for the New Zealand seismograph network.

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