Compiling an earthquake catalogue for the Arabian Plate, Western Asia

The ISC-GEM Earthquake Catalogue (1904–2014): status after the Extension Project

“…Such variations reflect the cut-off magnitudes adopted for selecting earthquakes in different time periods: 7.5 and above before 1918 (plus significant continental earthquakes 6.5 and above); 6.25 between 1918 and 1959; 5.5 from 1960 onwards (see Di Giacomo et al, 2015b, for more details on the V1 earthquake selection criteria). It is worth remembering here that the cut-off magnitudes are simply thresholds set for selection purposes (not all pre-1960 events have known or reliable magnitudes) and should not be interpreted as completeness levels (variations of the completeness over different time periods for V1 were briefly outlined by Di Giacomo et al, 2015a, and investigated in more detail by Michael, 2014).…”

“…The catalogue is distributed in CSV format and is composed of two parts (the Main catalogue, also available as a KMZ file for use with Google Earth, and the Supplementary catalogue, the latter including events with either poor location and/or magnitude quality; see Storchak et al, 2015). Location parameters and magnitudes (either direct or proxy moment magnitude M w ; Di Giacomo et al, 2015a) come with formal uncertainties and quality flags (from A to D, denoting well and poorly constrained parameters, respectively), fol-lowed, if available, by the solution of the Global Centroid Moment Tensor (GCMT; http://www.globalcmt.org, last access: 10 October 2018, Dziewonski et al, 1981;Ekström et al, 2012). The criteria to assign the quality flags for location, depth and magnitude are summarised in Table 1.…”

“…For the depth quality flag we consider the availability of very close stations (within 10 km, NSTA10) and in the local distance range (within 150 km, NSTAlocal), the depth constrained by depth-phases (if available, depdp in Table 1) and the location accuracy (GTCAND). For the magnitude quality flag we consider the author (GCMT or literature; Lee and Engdahl, 2015) for direct M w values, whereas for the M w proxy based on our recomputed M S or m b (Di Giacomo et al, 2015a), the quality flag depends on combinations of the magnitude value, type (M S or m b ), uncertainty, number of stations used and the uncertainty of M w proxy.…”

“…Although such catalogues proved to be important resources for many years, they cover different time periods and, more importantly, are often characterised by either large heterogeneities in their parameters and/or produced with undocumented or mixed procedures and/or underlying data (e.g. Di Giacomo et al, 2015a). For example, the Centennial Catalogue lists both locations from various catalogues (including the ones mentioned above) and recomputed ones (from 1964 onwards and only for selected large earthquakes between 1918 and 1964) using the Engdahl et al (1998) methodology (normally referred to as EHB), whereas magnitudes are not recomputed but compiled from several different sources/authors (see Di Giacomo et al, 2015a).…”

“…Di Giacomo et al, 2015a). For example, the Centennial Catalogue lists both locations from various catalogues (including the ones mentioned above) and recomputed ones (from 1964 onwards and only for selected large earthquakes between 1918 and 1964) using the Engdahl et al (1998) methodology (normally referred to as EHB), whereas magnitudes are not recomputed but compiled from several different sources/authors (see Di Giacomo et al, 2015a). Very similar considerations also apply to PAGER-CAT, which is based on the Centennial Catalogue up to 1973 (Allen et al, 2009).…”