Bibliographical search for reliable seismic moments of large earthquakes during 1900–1979 to compute MW in the ISC-GEM Global Instrumental Reference Earthquake Catalogue

Abstract

Moment magnitude (MW) determinations from the online GCMT Catalogue of seismic moment tensor solutions (GCMT Catalog, 2011) have provided the bulk of MW values in the ISC-GEM Global Instrumental Reference Earthquake Catalogue (1900–2009) for almost all moderate-to-large earthquakes occurring after 1975. This paper describes an effort to determine MW of large earthquakes that occurred prior to the start of the digital seismograph era, based on credible assessments of thousands of seismic moment (M0) values published in the scientific literature by hundreds of individual authors. MW computed from the published M0 values (for a time period more than twice that of the digital era) are preferable to proxy MW values, especially for earthquakes with MW greater than about 8.5, for which MS is known to be underestimated or “saturated”.After examining 1,123 papers, we compile a database of seismic moments and related information for 1,003 earthquakes with published M0 values, of which 967 were included in the ISC-GEM Catalogue. The remaining 36 earthquakes were not included in the Catalogue due to difficulties in their relocation because of inadequate arrival time information. However, 5 of these earthquakes with bibliographic M0 (and thus MW) are included in the Catalogue’s Appendix. A search for reliable seismic moments was not successful for earthquakes prior to 1904. For each of the 967 earthquakes a “preferred” seismic moment value (if there is more than one) was selected and its uncertainty was estimated according to the data and method used.We used the IASPEI formula (IASPEI, 2005) to compute direct moment magnitudes (MW[M0]) based on the seismic moments (M0), and assigned their errors based on the uncertainties of M0. From 1900 to 1979, there are 129 great or near great earthquakes (MW ⩾7.75) – the bibliographic search provided direct MW values for 86 of these events (or 67%), the GCMT Catalog provided direct MW values for 8 events (or 6%), and the remaining 35 (or 27%) earthquakes have empirically determined proxy MW estimates. An electronic supplementary file is included with this paper in order to provide our M0/MW catalogue of earthquakes (1904–1978) from the published literature, and a reference list of the 1,123 papers that we examined.