100+ years of instrumental seismology: the example of the ISC-GEM Global Earthquake Catalogue D.A. Storchak, D. Di Giacomo, and the International Team of Experts 1 1 E.R. Engdhal, I. Bondár, A. Villaseñor, W. Lee, P. Bormann, J. Harris

Motivation Seismic hazard studies need accurate knowledge of the spatial distribution of seismicity and of the magnitude-frequency relation. Existing catalogues for the 20 th century, however, are compilations of different sources covering different time periods, and therefore contain inhomogeneous locations and magnitudes. There is the need for an improved global instrumental catalogue for large earthquakes spanning the entire 100+ years period of instrumental seismology. 2

Project in a nutshell Collecting, digitising and processing data from a multitude of historical sources for earthquakes that occurred up to 1970; 110 years of relocated earthquake hypocenters; recomputed M S and m b values for relocated events using uniform procedures; M W values (with uncertainty) based on: 1.seismic moment from GCMT (mainly ); 2.seismic moments from the literature search for earthquakes up to 1979; 3.proxy values based on recomputed M S and m b in other cases using appropriate empirical relationships. 3 This Catalogue is unique because it contains homogeneous locations and magnitudes with estimates of uncertainty for the entire period done by using the same tools and techniques to the extent possible. This Catalogue is unique because it contains homogeneous locations and magnitudes with estimates of uncertainty for the entire period done by using the same tools and techniques to the extent possible. Cut-off magnitudes (before extension started) : : M S ≥7.5 worldwide + smaller shallow events in stable continental areas : M S ≥6¼ : M S ≥5.5 Cut-off magnitudes (before extension started) : : M S ≥7.5 worldwide + smaller shallow events in stable continental areas : M S ≥6¼ : M S ≥5.5

ISC-GEM Catalogue available from the ISC website The ISC and a Team of International Experts released in January 2013 the ISC-GEM catalogue ( ), which provides basic earthquake parameters (location, moment magnitude, and, if available, moment tensor) along with corresponding uncertainties. It is available as CSV file (both main and supplementary catalogues) and also as KMZ (see Download & Legal). 4 or

A timeline of instrumental seismology (from last century) 5 More details in Storchak et al., PEPI 2015

Putting together parametric data 6 The work on the ISC-GEM Catalogue required digitising of a large volume of data that has not been available electronically in the past (Di Giacomo et al., PEPI 2015a)

7 Major Sources of Phase Data: Gutenberg Notepads ( ) and BAAS ( ) ISS Bulletins ( ) Phase and Amplitude Data Collection ~1,000,000~10, Body/Surface Wave Amplitudes Body Wave Arrival Times Period DIGITALLY AVAILABLE, ISC database Quality station bulletins DIGITALLY NOT AVAILABLE BEFORE THIS PROJECT

Adding amplitudes from historical seismological bulletin 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 9 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 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: Di Giacomo et al., PEPI 2015a

Global Network Development: arrival times 10 More details in Storchak et al., PEPI 2015

Location improvements 11 More details in Bondár et al., PEPI 2015

Location improvements 12 Location maps and cross-sections in the Arica region. More details in Bondár et al., PEPI 2015 As a result of consistent relocation of hypocentres with the same technique (EHB+ISC) and velocity model ( ak135 ) we observe tighter clustering of earthquake hypocentres, better focusing, many regional tectonic features are illuminated

Global Network Development: MS 13 More details in Storchak et al., PEPI 2015

Improvements in magnitude, especially Ms 14 ISC-GEM recomputed MsMs from Abe’s catalogue More details in Di Giacomo et al., PEPI 2015b

M W proxy based on recomputed M S 15 We applied a non-linear regression using an exponential model of the form My = exp(a+b*Mx)+c (EXP, purple). The exponential model follows well the median values curve over the entire population. Proxy M W vs true M W (=10% of the original population not used for deriving the model).

Magnitude composition: Centennial vs ISC-GEM catalogue 16 Centennial catalogueISC-GEM catalogue

Summary 17 With extension in the 1950s, In order to produce the ISC-GEM Catalogue we collected, digitized and processed a multitude of parametric data sources encompassing 100+ years of instrumental seismology; Many developments occurred in this time period which regarded seismic instruments, seismological observational practice, physics of the earthquake source, Earth models and seismological organizations; With the ISC-GEM Catalogue we provide a seismic instrumental catalogue obtained with homogeneous techniques (to the largest extent possible) for large global earthquakes over a long time span