The ISC-GEM Global Instrumental Earthquake Catalogue: an update D. Di Giacomo, Bob Engdhal, D.A. Storchak and J. Harris ESC 2016, Trieste, Session 16 1

Background www.isc.ac.uk/iscgem/ The ISC and a Team of International Experts released in January 2013 the ISC-GEM catalogue (1900-2009), which provides basic earthquake parameters (location, moment magnitude, and, if available, moment tensor) along with corresponding uncertainties. This product is unique since it lists parameters obtained using the same techniques (to the largest extent possible) throughout the last 100+ years of instrumental seismology. It is available as CSV file (both main and supplementary catalogues) and also as KMZ (see Download & Legal). www.isc.ac.uk/iscgem/ or http://isc-mirror.iris.washington.edu/iscgem/

Background www.isc.ac.uk/iscgem/ In 2013 a short paper was published on SRL to announce the release of the ISC-GEM Catalogue, whereas in a PEPI special volume we describe in detail the various tasks accomplished to produce the catalogue: Data collection Relocation Magnitude re-assessment Bibliographic search of reliable seismic moments for events before 1976 (i.e., pre-GCMT) www.isc.ac.uk/iscgem/ or http://isc-mirror.iris.washington.edu/iscgem/

Phase and Amplitude Data Collection Body/Surface Wave Amplitudes Body Wave Arrival Times Period 1900-1917 1918-1959 1960-1970 1971-2009 ~10,000 ~1,000,000 Quality station bulletins DIGITALLY NOT AVAILABLE BEFORE THIS PROJECT DIGITALLY AVAILABLE, ISC database Major Sources of Phase Data: Gutenberg Notepads (1904-1917) and BAAS (1913-1917) ISS Bulletins (1918-1963) 4

Adding amplitudes from historical seismological bulletin 1906 San Francisco earthquake report from Göttingen (Germany) station bulletin. The same report stored in digital format in the ISC database. Period and amplitude data finally available for magnitude recomputation.

Data Collection before extension started In order to produce the ISC-GEM catalogue, we digitized a multitude of sources of parametric seismological data to facilitate location and magnitude re-computation for earthquakes before 1960. The parametric data collected in this project will be useful for any future study for earthquakes occurred before 1964 Scans of the processed bulletins are available in PDF at SISMOS website: http://storing.rm.ingv.it/bulletins/ISC-GEM/ Di Giacomo et al., PEPI 2015a Add bullet on the data collection, stress more all of them

Location improvements More details in Bondár et al., PEPI 2015

Improvements in magnitude, especially Ms ISC-GEM recomputed Ms Ms from Abe’s catalogue More details in Di Giacomo et al., PEPI 2015b

Summary of the ISC-GEM catalogue before extension started Given the time and resources in the project we processed only selected earthquakes using time-variable cut-off magnitudes: M ≥ 7.5 up to 1917 (plus significant quakes in continental regions with M ≥ 6.5); M ≥ 6.25 between 1918 and 1959; M > 5.5 from 1960 onwards. ~19,000 earthquakes were listed in the catalogue first release Modified from Di Giacomo et al. (2015b)

Extension project The work is planned for 4 years; Large number of earthquakes below ~6.2 is to be added before 1960; Also current years (post 2009) to be added. Data for recent years is taken from the ISC Bulletin, whereas for earthquakes before 1960 we need to digitise the relevant data for relocation and magnitude re-computation

First year extension: 1950-1959 Number of ISS events in the 1950s Year Number of earthquakes relocated 1950 438 1951 469 1952 560 1953 352 1954 316 1955 299 1956 311 1957 355 1958 530 1959 526 Totals 4156 Box-and-whisker plot of the location differences before and after the ISC-GEM relocations in each year. Box-and-whisker plot of the depth differences before and after the ISC-GEM relocations in each year.

First year extension: events with re-computed MS in the 1950s Many ISS earthquakes in the 1950s fall below the ISC-GEM cut-off magnitude of 5.5, but rather than excluding completely those events we list them in the Supplementary Catalogue Timeline of the re-computed MS in the 1950s

Second year extension: 1935-1949 Number of ISS events in between 1935 and 1949 Year Number of earthquakes relocated 1935 253 1936 260 1937 246 1938 302 1939 235 1940 233 1941 204 1942 184 1943 287 1944 228 1945 295 1946 388 1947 387 1948 441 1949 460 Totals 4403 ~2800 ISS pages have been edited and proof-read during this year… All ISS data now digitized!! Box-and-whisker plot of the location differences before and after the ISC-GEM relocations in each year. Box-and-whisker plot of the depth differences before and after the ISC-GEM relocations in each year.

Second year extension: events with re-computed MS during 1935-1949 Many ISS earthquakes during 1935-1949 fall below the ISC-GEM cut-off magnitude of 5.5, but rather than excluding completely those events we list them in the Supplementary Catalogue Timeline of the re-computed MS during 1935-1949

More “amplitude” stations added in the extension project Thanks to additional bulletins collected from BGS, Uni-Strasbourg, GFU Prague, Ambraseys personal collection, RAS Obninsk and others we have been able to add many more stations compared to the first catalogue release.

Earthquakes already processed now with more MS stations Maps of the “amplitude” stations added during the second year extension. The data added does not regard only earthquakes not processed before but also the ones already ion the ISC-GEM catalogue The increase in the NSTA contributing to the event MS is quite significant: whilst 42% of the original MS was obtained from NSTA ≤ 5, for the revised MS this percentage drops to ~5%. In addition, the added amplitude data also allowed us to gain 36 more MS values.

Summary after the second year extension Before extension started With extension during 1935-1959, 2010-2012 Add bullet on the data collection, stress more all of them ESC 2016, Trieste, Session 16

ISC Members and Sponsors 67 Institutions in 49 countries make annual membership subscriptions. 12 international, public or commercial entities sponsor individual ISC projects: ISC-GEM Catalogue CTBTO Link to ISC database ISC Event Bibliography Aon Benfield, Lloyd’s, Guy Carpenter, Catlin. International Station Registry