ALBERT

Description: Global earthquake catalogs covering the early twentieth century differ in their listings of a large earthquake, or earthquakes, on 12 December 1908. Some catalogs list an M∼7 earthquake originating in northern Myanmar (Burma) at ∼12:55 UTC on that date. Other catalogs do not list the Myanmar origin but list an earthquake with magnitude 8.2 originating in or near Peru at 12:08 UTC on the date. Some catalogs list both origins, but sometimes with additional evidence suggesting that the 1908 M 8.2 Peru origin may be “mythical.” In a review of arrival times of phases reported in seismic bulletins of 1908, conducted specifically to identify data that might be consistent with the sometimes‐cataloged Peru origin, we do not find a coherent set of such data. Many bulletin arrival times reported for 12 December 1908, however, are mutually consistent with the cataloged Myanmar origin. Comparisons of seismograms recorded at the Seismological Observatory of Göttingen in Germany (station GTT) on 12 December 1908 with seismograms obtained on the same instruments for later large earthquakes that are reliably located in Myanmar and Peru, respectively, are consistent with the implication of the bulletin arrival‐time observations. We conclude that a major earthquake did indeed occur in or near northern Myanmar on 12 December 1908 but that there was not on that date a great earthquake near Peru that would correspond to the sometimes‐cataloged M 8.2 Peru origin.

Description: We outline the work done to extend and improve the ISC-GEM Global Instrumental Earthquake Catalogue, which was first released in 2013 (Storchak et al., 2013, 2015). Due to time and resource limitations, version 1 (V1) of the ISC-GEM Catalogue included global earthquakes selected according to time dependent cut-off magnitudes between 1900 and 2009: 7.5 and above before 1918 (plus significant 6.5 and above continental earthquakes); 6.25 between 1918 and 1959; 5.5 from 1960 onwards. With the Extension Project we added both pre-1960 events below the original cut-off magnitudes (if enough station data was available to perform relocation and magnitude re-computation) and added magnitude 5.5 and above events from 2010 to 2014. The project ran over a 4-year period where a new version of the ISC-GEM Catalogue was released each year via the ISC website (www.isc.ac.uk/iscgem/). For each year not only have we added new events to the catalogue for a given time range but also revised events already in V1 if additional data became available or location and/or magnitude reassessments were required. Here we recall the general background behind the production of the ISC-GEM Catalogue and describe the features of the different periods where the catalogue has been extended. Compared to the 2013 release, the new version (V5) of the ISC-GEM Catalogue now contains about 12,000 more events between 1904 and 1960 and ends in 2014 instead of 2009.We expect the ISC-GEM Catalogue to continue to be one of the most useful datasets for studies of the Earth’s global seismicity and an important benchmark for seismic hazard analyses, and, ultimately, an asset for the seismological community as well as other geoscience fields, education and outreach activities. The ISC-GEM Catalogue is freely available at http://doi.org/10.31905/D808B825.

Description: In this article we summarize the availability of earthquake source mechanisms in the Bulletin of the International Seismological Centre (ISC). The bulletin in its current status contains ∼81 000 seismic events with only one associated mechanism solution and ∼25 000 events with at least two associated source mechanisms. The main sources of earthquake mechanisms in the ISC Bulletin are reported solutions provided by data contributors and ISC-computed focal mechanisms based on first motion polarities. Given the importance of using pre-determined fault plane solutions in different types of studies, here we briefly discuss the methodologies adopted by major data providers to the ISC and investigate the intra-event variability of the source mechanisms. We conclude that the overall agreement among different earthquake mechanisms for the same event as reported by different sources can show a similarity coefficient as high as 80 %, based on the rotation angles of their best-fitting double couple solutions, for the majority of the cases. The earthquake source mechanisms discussed in this work are freely available within the ISC Bulletin websearch at http://doi.org/10.31905/D808B830.

Description: We outline the work done to extend and improve the ISC-GEM Global Instrumental Earthquake Catalogue, a dataset which was first released in 2013 (Storchak et al., 2013, 2015). In its first version (V1) the catalogue included global earthquakes selected according to time-dependent cut-off magnitudes: 7.5 and above between 1900 and 1918 (plus significant continental earthquakes 6.5 and above); 6.25 between 1918 and 1959; 5.5 between 1960 and 2009. Such selection criteria were dictated by time and resource limitations. With the Extension Project we added both pre-1960 events below the original cut-off magnitudes (if enough station data were available to perform relocation and magnitude recomputation) and added events with magnitude 5.5 and above from 2010 to 2014. The project ran over a 4-year period during which a new version of the ISC-GEM Catalogue was released each year via the ISC website (http://http://www.isc.ac.uk/iscgem/, last access: 10 October 2018). For each year, not only have we added new events to the catalogue for a given time range but also revised events already in V1 if additional data became available or location and/or magnitude reassessments were required. Here we recall the general background behind the production of the ISC-GEM Catalogue and describe the features of the different periods in which the catalogue has been extended. Compared to the 2013 release, we eliminated earthquakes during the first 4 years (1900–1903) of the catalogue (due to lack of reliable station data), added approximately 12 000 and 2500 earthquakes before 1960 and between 2010 and 2014, respectively, and improved the solution for approximately 2000 earthquakes already listed in previous versions. We expect the ISC-GEM Catalogue to continue to be one of the most useful datasets for studies of the Earth's global seismicity and an important benchmark for seismic hazard analyses, and, ultimately, an asset for the seismological community as well as other geoscience fields, education and outreach activities. The ISC-GEM Catalogue is freely available at https://doi.org/10.31905/D808B825.

Description: In this article we summarize the availability of earthquake source mechanisms in the Bulletin of the International Seismological Centre (ISC). The bulletin in its current status contains ∼ 81,000 seismic events with only one associated mechanism solution, and ∼ 22,000 events with at least two associated source mechanisms. The main sources of earthquake mechanisms in the ISC Bulletin are reported solutions provided by data contributors, and ISC computed focal mechanisms based on first motion polarities. Given the importance of using pre-determined fault plane solutions in different types of studies, here we focus only on the reported mechanisms and we briefly discuss the methodologies adopted by major data providers to the ISC and investigate the intra-event variability of the source mechanisms. We conclude that the overall agreement among different earthquake focal mechanisms for the same event as reported by different sources can be as high as 90% for the majority of the cases. The earthquake source mechanisms discussed in this work are freely available within the ISC Bulletin websearch at http://doi.org/10.31905/D808B830.