Catalogue Overview, Version 5.0, 27 February 2018

On the 27 of February 2018, the version 5.0 of the ISC-GEM catalogue was publicly released. The release marked the end of the fourth year of the Extension Project. During this year we added to the catalogue a) 1110 earthquakes that occurred between 1904 and 1919 (i.e., earthquakes not included in the catalogue’s previous versions); b) 521 earthquakes with magnitude 5.5 and above that occurred in 2014.
To process earthquakes during 1904-1919 we digitized body wave arrival times as well as amplitudes and periods for various phases using a multitude of sources to allow relocation and magnitude re-computation (for this time period only MS) using the same approaches described in Di Giacomo et al. (2015a). Compared to the first catalogue’s release, for this version we were able to add amplitudes from printed station bulletins that were not available in the original ISC collection. The additional station bulletins were kindly provided from the personal collection of Prof. N. Ambraseys, British Geological Survey (BGS) collection, bulletins from the Geophysical Institute of the Czech Academy of Sciences in Prague, the Geophysical Survey of the Russian Academy of Science in Obninsk and the University of Strasbourg (France). Such an enriched bulletin collection allowed us to add important surface wave amplitudes from different stations and to obtain for the first time MS for many historical earthquakes and to improve the MS for large earthquakes (MS>6.0) for earthquakes that were already listed in previous versions of the ISC-GEM catalogue.

Fig. 1 shows the ISC-GEM locations with symbols according to Agnew (2014) as obtained from the procedure described in Bondár et al. (2015). One feature that makes the ISC-GEM catalogue a unique product is that the locations (after 1903) are achieved by the same location technique and velocity model (ak135) and comes with uncertainties for each focal parameter.

Fig.1: map showing the earthquakes listed in the version 5.0 of the ISC-GEM catalogue (more than 28,000 earthquakes, see Fig.2). The symbols are plotted according to Agnew (2014) and colour coded according to the ISC-GEM depth.

Fig. 2 shows the current time-magnitude distribution of the ISC-GEM Catalogue (1904-2014).

Fig. 2: Top: cumulative annual number of earthquakes with Mw ≥ 5.5 (red), ≥ 6.5 (blue) and ≥ 7.5 (yellow); Bottom: time-magnitude distribution color-coded in cells of 0.1 units of Mw for each year of the ISC-GEM main catalogue. The earthquakes processed in 2014 exhibit the same distribution we can observe in recent years and add significant earthquakes to the catalogue. The biggest difference with previous versions occurs during 1904-1919, where, in the past versions, nearly no earthquake below Mw 7.5 was included. Both the time-frequency distribution and the annual number of events per year above 5.5 show, however, that in the 1904-1919 the ISC-GEM catalogue is not as complete as in the more recent decades. The shaded light grey areas highlight the years extended or added. For comparison with the original version, see Fig. 20 in Di Giacomo et al. (2015b).