At the end of 2017 we have finished the work on the Extension project that ended with public release of Version 5 of the ISC-GEM catalogue in February 2018. As a result of the Extension project, we have considerably improved the magnitude cut-off thresholds during the early instrumental period and updated the catalogue with recent earthquakes during 2010-2014 (Fig. 1).

We plan the following work packages:

Over the last seven years we digitised and included the arrival time and body/surface wave amplitude and period information from a very large volume of individual station and network bulletins in order to re-compute the location and magnitude of each earthquake (Di Giacomo et al., 2015a). For each earthquake, at least three different station reports were required to compute a reliable estimate of MS magnitude to be then converted to M_W where the latter is not independently available. The absence of three consistent measurements has stopped many earthquakes from being included into the Main ISC-GEM catalogue (Fig. 2). Such earthquakes remained part of the Supplementary catalogue of earthquakes with highly uncertain determinations of magnitude and/or location.

Determination of the uniform M_W magnitude throughout the ISC-GEM catalogue is based on either GCMT or the M_S/M_W and mb/M_W magnitude regression curves developed during the project (Di Giacomo et al., 2015b). However, the initial selection of earthquakes from the ISC Bulletin though was not based on these regressions, as they were not available at the time.

We shall review the initial earthquake selection during 1960-1990 and add a number of previously excluded moderate earthquakes in order to improve the magnitude completeness of the ISC-GEM catalogue during this period.

It would help regional studies of seismic hazard if we supplemented the ISC-GEM catalogue with smaller yet still damaging earthquakes, such as the mb 5.2 Dulce, New Mexico 1966 earthquake (Fig.4) or the M_W 5.1 Lorca 2011 earthquake in Spain. This work would also assist calibration of local catalogues and magnitudes in individual regions where the ISC-GEM catalogue can be used as a reference.

It is a common knowledge that recording of earthquakes at the beginning of the 20^th century was often made by station networks with quite poor geometrical configuration with respect to the earthquake sources. This resulted in low station azimuthal coverage and large uncertainties in the earthquake location. We would like to try working together with the macroseismic community to review parameters of large felt and damaging earthquakes during the 1900-1920 period where addition of macroseismic information may lead to better-constrained hypocentre solutions.

At the time of major data entry work for the ISC-GEM catalogue, we have chosen to mainly use the printed volumes of the International Seismological Summaries (ISS) and the ISC’s collection of individual station and network bulletins because those contained well-formatted comprehensive information in a tabulated form and have already been partly scanned and sometimes even digitised. Now we would like to complement these data with the data from Bureau Central International Seismologique (BCIS). For considerable periods of time, ISS in England and BCIS in France have been running global bulletin operations in parallel with an element of apparent duplication in their missions. The original sources of data coming to ISS and BCIS varied.

We shall concentrate on recovering additional station arrival times for earthquakes already in ISC-GEM in order to improve the station azimuthal coverage and hence the accuracy of locations. We shall also look out for earthquakes that may have been missed by the ISS in those time periods when funding shortages dictated unfortunate rise in earthquake magnitude cut-off thresholds.

We plan to monitor recent publications (Fig. 5) in several tens of journals for new and updated determinations of historical earthquake sources, magnitudes and moment tensor parameters based on analogue or digital seismogram records and update the ISC-GEM catalogue accordingly.

We shall make a concerted effort to link earthquakes in the ISC-GEM catalogue to known bibliographical references to scientific articles describing these earthquakes.

We have already searched through scientific literature for accurate direct determination of scalar moment and moment magnitude of certain earthquakes studied by individual scientists or groups of scientists. We have never attempted to include determinations of fault plane / moment tensor solutions into the catalogue. These are usually derived by individual scientists from various techniques and data sources such as digitized waveform inversions, visible surface rupture, direction of body wave first motions, configuration of the aftershock zones etc (Fig. 6). It would be of considerable value for consequent seismic hazard studies, if the fault planes were also included into the ISC-GEM catalogue, especially for the years before 1976 when the Global CMT project has begun.

We are currently updating the ISC Bulletin (1964 onwards) with the recomputed ISC hypocentres based on the new location program, ak135 velocity model and robust magnitude calculation scheme (Bondár & Storchak, 2011). As part of this project, we bring numerous data of both permanent and temporary (experimental and aftershock) deployments that were missing from the ISC Bulletin.

We shall update the ISC-GEM catalogue in the modern instrumental period based on the previously unavailable datasets that may help to improve the accuracy of ISC-GEM parameter determinations.

At the same time, together with University of Colorado Boulder, we are working on another project to review and improve the ISC-EHB dataset of well-recorded seismic events ordinarily used for tomographic studies. This dataset benefits from more precise event depth determination. Some earthquakes are common to both the ISC-GEM and the ISC-EHB.

We shall review the relevant outcomes from the ISC-EHB project to see which ISC-GEM earthquakes may require an update.

We shall continue the update of the ISC-GEM catalogue with earthquakes of recent years beyond 2014 as and when each new data year of the reviewed ISC Bulletin becomes available. We shall implement the same earthquake selection, location and magnitude determination procedure to keep the ISC-GEM catalogue as homogeneous as possible.

We shall incrementally improve the ISC-GEM catalogue. An upgraded version of the catalogue will be made publicly available at the beginning of March of each following year, giving lead time to Project Sponsors.

Bondar, I. and D. Storchak, 2011. Improved location procedures at the International Seismological Centre, Geophys. J. Int., 186, 1220-1244, doi: 10.1111/j.1365-246X.2011.05107.x.

Di Giacomo, D., J. Harris, A. Villaseñor , D.A. Storchak, E.R. Engdahl, W.H.K. Lee and the Data Entry Team, 2015. ISC-GEM: Global Instrumental Earthquake Catalogue (1900-2009), I. Data collection from early instrumental seismological bulletins, Phys. Earth Planet. Int., 239, 14-24, doi: 10.1016/j.pepi.2014.06.003.

Di Giacomo, D., I. Bondár, D.A. Storchak, E.R. Engdahl, P. Bormann and J. Harris, 2015. ISC-GEM: Global Instrumental Earthquake Catalogue (1900-2009): III. Re-computed MS and mb, proxy MW, final magnitude composition and completeness assessment, Phys. Earth Planet. Int., 239, 33-47, doi: 10.1016/j.pepi.2014.06.005.

Doser, D., 1990. Source characteristics of earthquakes along the Southern San Jacinto and Imperial fault zones (1937 to 1954), Bull. Seism. Soc. Am., 80, 1099-1117.

Hoffman, J.P. and Northrop, S.A., 1977. The Dulce, New Mexico earthquake, January 23, 1966, Seismol. Res. Lett., 49, 3-20.

Storchak, D.A., D. Di Giacomo, E.R. Engdahl, J. Harris, I. Bondár, W.H.K. Lee, P. Bormann and A. Villaseñor, 2015. The ISC-GEM Global Instrumental Earthquake Catalogue (1900-2009): Introduction, Phys. Earth Planet. Int., 239, 48-63, doi: 10.1016/j.pepi.2014.06.009.