- © 2014 by the Seismological Society of America
Online Material: Table of event parameters and magnitudes.
Since the introduction of the concept of magnitude to seismology by Richter (1935), many different magnitude scales have been proposed. The United States Geological Survey National Earthquake Information Center (NEIC) routinely uses many of these, including moment magnitude, Mw (Hanks and Kanamori, 1979); energy magnitude, Me (Choy and Boatwright, 1995); surface‐wave magnitude, Ms (International Association of Seismology and Physics of the Earth’s Interior, IASPEI); short‐period teleseismic P‐wave magnitude, mb (Gutenberg and Richter, 1956); local magnitude, ML (Richter, 1935; Hutton and Boore, 1987); surface‐wave magnitude for variable periods and maximum amplitudes, Ms(Vmax) (Bonner et al., 2006; Russell, 2006); and the focus of this study, (Nuttli, 1973, 1986).
Nuttli (1973) developed a magnitude scale for use in the eastern United States that accounted for regional attenuation of the Lg phase observed on the short‐period (SP) Worldwide Standard Seismograph Network (WWSSN) photographic seismograms. To avoid fluctuations in event magnitude due to the use of the largest recorded amplitude, he used the third‐largest zero‐to‐peak amplitude. He called this magnitude to emphasize that it was a short‐period magnitude based on the prominently observed Lg phase calibrated to teleseismic mb for some central United States earthquakes. Nuttli (1986) generalized the original definition to account for regional variations in the attenuation of the Lg phase.
The IASPEI Commission on Seismological Observation and Interpretation (CoSOI) Working Group on Magnitudes formula for , described online at http://www.iaspei.org/commissions/CSOI/Summary_WG_recommendations_20130327.pdf (last accessed March 2014), is based on the Nuttli (1986) formulation and procedures. The NEIC has used this definition since at least 2010.
Within the NEIC, Mw is the preferred magnitude for earthquake source characterization. Moment magnitude, either directly measured or estimated through empirical relations with other magnitude …