Extension of the ISC-GEM Global Earthquake

Instrumental Catalogue, an update

D. Di Giacomo, Bob Engdhal, D.A. Storchak, A. Villaseñor and J. Harris

IUGG 2015 Prague, Session S01

Background

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 110 years of instrumental seismology.

It is available as CSV file (both main and supplementary catalogues) and also as KMZ (see Download & Legal).

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www.isc.ac.uk/iscgem/ or

http://colossus.iris.washington.edu/iscgem/

Background

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:

1) Data collection

2) Relocation

3) Magnitude re-assessment4) Bibliographic search of reliable seismic moments for events before 1976 (i.e., pre-GCMT)

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www.isc.ac.uk/iscgem/ or

http://colossus.iris.washington.edu/iscgem/

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Major Sources of Phase Data:

• Gutenberg Notepads (1904-1917) and BAAS (1913-1917)

• ISS Bulletins (1918-1963)

Phase and Amplitude Data Collection

~1,000,000~10,000

1960-19701918-19591900-1917

Body/Surface Wave

Amplitudes

Body Wave Arrival Times

Period

DIGITALLY AVAILABLE, ISC database

Quality station bulletins

1971-2009

DIGITALLY NOT AVAILABLE BEFORE THIS PROJECT

Adding amplitudes from historical

seismological bulletin

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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

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• 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

Location improvements

7More details in Bondár et al., PEPI 2015

Improvements in magnitude, especially Ms

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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.

9~19,000 earthquakes were listed in the catalogue first release

Modified from Di Giacomo et al. (2015b)

Extension plan

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•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

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Number of ISS events in the 1950sYear Number of earthquakes relocated1950 4381951 4691952 5601953 3521954 3161955 2991956 3111957 3551958 5301959 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

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Timeline of the 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

First year extension: earthquakes without re-computed magnitude in the 1950s

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Timeline of the relocated events in the 1950s without magnitude (listed in the Supplementary Catalogue)

Spatial distribution of the relocated events in the 1950s without magnitude (listed in the Supplementary Catalogue)

Summary

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Before extension started With extension in the 1950s, 2010-2011

All ISC-GEM work is possible thanks to the support of

and 62 ISC Members from 45 countries