ISC-GEM Global Reference Earthquake Instrumental Catalogue ( ) D. Di Giacomo, I. Bondár, E.R. Engdahl, D.A. Storchak, W.H.K. Lee, A. Villaseñor, J. Harris, P. Bormann ESC 2012, Moscow

Motivation Seismic hazard studies need accurate knowledge of the spatial distribution of seismicity and the magnitude-frequency relation. Existing catalogues for past 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. 2ESC 2012, Moscow

Project in a nutshell Collecting, digitising and processing data from a multitude of historical sources for earthquakes 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 magnitude estimates with the estimates of uncertainty for the entire period done using the same tools and techniques to the extent possible. This Catalogue is unique because it contains homogeneous locations and magnitude estimates with the estimates of uncertainty for the entire period done using the same tools and techniques to the extent possible. Cut-off magnitudes: : M S ≥7.5 worldwide + smaller shallow events in stable continental areas : M S ≥6¼ : M S ≥5.5 Cut-off magnitudes: : M S ≥7.5 worldwide + smaller shallow events in stable continental areas : M S ≥6¼ : M S ≥5.5 ESC 2012, Moscow

4 Major Sources of Phase Data: Gutenberg Notepads ( ) and BAAS ( ) ISS Bulletins ( ) Phase and Amplitude Data Collection ~730,000~ Body/Surface Wave Amplitudes Body Wave Arrival Times Period DIGITALLY NOT AVAILABLE BEFORE THIS PROJECT DIGITALLY AVAILABLE, ISC database Quality station bulletins

Processing historical seismological bulletin 5ESC 2012, Moscow 1906 San Francisco earthquake from station bulletin Göttingen, Germany The same report stored in digital format in the ISC database. Period and amplitude data finally available for magnitude recomputation. 15,257 individual seismic bulletins from 293 institutions over the period 1904 – 1970 were recovered from ISC storage

Amplitude Data from Quality Station Bulletins 66 ~300,000 “ brand new ” amplitudes up to 1970 now available in the ISC database Effort equivalent to ~70 person-months Time Coverage: UPP, RIV, and LPZ nearly continuous, gaps for other stations Station timeline

Earthquake Location Procedure 7 Location method : 1.Determine event depth using the EHB style of processing (Engdahl, van der Hilst and Buland, 1998) : a)comprehensive analysis of near-event surface reflections off the earth surface inland and ocean bottom or water surface in the oceans; b)Station patch corrections; 2.Use the new ISC location algorithm (Bondár and Storchak, 2011) with earthquake depths fixed to those from EHB analysis: a)more accurate epicentre locations due to correlated error structure taken into account (removes bias from uneven geometrical positioning of stations) b)independent depth confirmation using depth phase stacking; ESC 2012, Moscow

8 Before relocation… Earthquake Relocation results

9ESC 2012, Moscow ….after relocation.

Earthquake Relocation results 10ESC 2012, Moscow Before After Earthquake Relocation results

ESC 2012, Moscow M S and m b recomputation 11 The recomputed M S and m b benefit from: 1) amplitude data added up to 1970; 2) station magnitudes consistent with newly computed hypocentre solutions; 3) homogeneous magnitude calculations following the IASPEI standards; 4) network magnitudes based on several station measurements using alpha-trimmed median (α = 20%) of the single station magnitudes (no network magnitude based on one station only).

M w from GCMT and literature search 12 M W from GCMT is available from 1976 (plus some deep earthquakes between 1962 and 1975). For 970 relocated earthquakes direct measurements of M 0 were compiled from the literature. For the remaining relocated earthquakes, proxy M W values are obtained from the recomputed M S and m b using new empirical relationships…

ESC 2012, Moscow M W proxy based on recomputed M S 13 Data population strongly dominated by earthquakes with magnitude below 6; The relationship between M S and M W is not linear over the entire distribution; Median values for separated bins (dashed black line) suggest that a non-linear model could fit well the data. Num=17472

ESC 2012, Moscow M W proxy based on recomputed M S 14 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).

ESC 2012, Moscow M W proxy based on recomputed m b 15 The exponential model follows well the median values curve close to the saturation level of m b.

ESC 2012, Moscow Magnitude composition of the ISC-GEM catalogue 16 Direct M W per year Proxy M W per year

ESC 2012, Moscow Magnitude composition: Centennial vs ISC-GEM catalogue 17 Centennial catalogueISC-GEM catalogue

ESC 2012, Moscow Magnitude distribution of the ISC-GEM catalogue 18

ESC 2012, Moscow Frequency-Magnitude distributions 19 Mc =6.4 Mc =5.6 Seismicity rates for large (M> ) earthquakes better assessed considering a long time window (violet) For moderate earthquakes the modern period (red) is a better basis for magnitude- frequency studies, whereas for strong to major shallow earthquakes the entire ISC-GEM catalogue may be used

Conclusions We collected, digitised and processed an unprecedented amount of phase and amplitude data for earthquakes occurred before 1970; In the 110 years covered by the ISC-GEM catalogue, the relocation provided significant improvements especially in the first part of past century; We recomputed M S and m b using uniform procedures, and new non-linear relationships are used to obtain M W proxies when direct computation of M 0 from GCMT or literature is not available; The ISC-GEM Global Instrumental Earthquake Catalogue represents the final product of one of the ten global components in the GEM program, and will be available to researchers at the ISC website ( 20ESC 2012, Moscow

THANK YOU 21ESC 2012, Moscow

Appendix 22ESC 2012, Moscow

A Brief Time Line in Seismology 23ESC 2012, Moscow

ISS bulletins ( ) (predecessor of the ISC, phase data only!) 24 Converted into digital form by scanning the bulletin pages and applying an optical character recognition (OCR) procedure (Engdahl and Villaseñor, 2002) Biggest source of earthquake data from 1918 to Over 1.1 million phases (~1000 seismic stations between 1918 and 1963) from ISS have been used in the relocation process; over 730,000 have been inserted into the ISC database during this project for earthquakes occurred between 1918 and Over 5000 phases (from ~160 seismic stations) have been added before 1918 (mostly from BAAS and G&R notepads).

Earthquake Relocation results 25ESC 2012, Moscow After Before

ESC 2012, Moscow M W proxy based on recomputed M S 26 The relationship between M S and M W is not linear; Authors normally perform bi-linear regression splitting the dataset at M S = 6.1; This separation, however, is arbitrary because slope change occurs in a transition zone between M S ~6 and ~6.7. Data population strongly dominated by earthquakes with magnitude below 6; Median values for separated bins (dashed black line) suggest that a non-linear model could fit well the data over the entire distribution.

ESC 2012, Moscow M W proxy based on recomputed M S 27 The histogram equalization defines magnitude bins varying width so that each bin contains the same number of data points. For each bin a randomly chosen 10% of the data is assigned to the validation dataset, while the 90% to the training dataset used to obtain the regression model.

ESC 2012, Moscow Magnitude composition of the ISC-GEM catalogue 28

ESC 2012, Moscow M W proxy based on recomputed m b 29 We applied both the GOR (green) and 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 close to the saturation level of m b. Proxy M W vs true M W (=10% of the original population not used for deriving the models), show how EXP model works better than GOR models, especially for M W < 6.

30ESC 2012, Moscow Regional Frequency-Magnitude distributions

31ESC 2012, Moscow Regional Frequency-Magnitude distributions (1)

32ESC 2012, Moscow Regional Frequency-Magnitude distributions (2)