ISC-GEM Global Reference Earthquake Instrumental Catalogue (1900-2009)

ISC-GEM Global Reference Earthquake Instrumental Catalogue (1900-2009)D. Di Giacomo, I. Bondr, E.R. Engdahl, D.A. Storchak, W.H.K. Lee, A. Villaseor, J. Harris, P. BormannESC 2012, Moscow

MotivationSeismic 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. *ESC 2012, Moscow

GEM: 3-4 Dec 2011, San Francisco

Project in a nutshellCollecting, digitising and processing data from a multitude of historical sources for earthquakes occurred up to 1970;110 years of relocated earthquake hypocenters;recomputed MS and mb values for relocated events using uniform procedures;MW values (with uncertainty) based on:seismic moment from GCMT (mainly 1976-2009);seismic moments from the literature search for earthquakes up to 1979;proxy values based on recomputed MS and mb in other cases using appropriate empirical relationships.*This Catalogue is unique because it contains homogeneous locations and magnitude estimates with the estimates of uncertainty for the entire period 1900-2009 done using the same tools and techniques to the extent possible.Cut-off magnitudes:1900-1917: MS7.5 worldwide + smaller shallow events in stable continental areas1918-1959: MS61960-2009: MS5.5ESC 2012, Moscow


*Major Sources of Phase Data:Gutenberg Notepads (1904-1917) and BAAS (1913-1917)ISS Bulletins (1918-1963)Phase and Amplitude Data Collection

~730,000

~100001960-19701918-19591900-1917DIGITALLY NOT AVAILABLE BEFORE THIS PROJECTDIGITALLY AVAILABLE, ISC databaseQuality station bulletins1971-2009


Processing historical seismological bulletin*ESC 2012, Moscow15,257 individual seismic bulletins from 293 institutions over the period 1904 1970 were recovered from ISC storage


Amplitude Data from Quality Station Bulletins** ~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


Earthquake Location Procedure*Location method:Determine event depth using the EHB style of processing (Engdahl, van der Hilst and Buland, 1998): comprehensive analysis of near-event surface reflections off the earth surface inland and ocean bottom or water surface in the oceans;Station patch corrections;

Use the new ISC location algorithm (Bondr and Storchak, 2011) with earthquake depths fixed to those from EHB analysis:more accurate epicentre locations due to correlated error structure taken into account (removes bias from uneven geometrical positioning of stations)independent depth confirmation using depth phase stacking;ESC 2012, Moscow


*ESC 2012, MoscowBefore relocationEarthquake Relocation results


Earthquake Relocation results*ESC 2012, Moscow.after relocation.


Earthquake Relocation results*ESC 2012, MoscowBeforeAfterEarthquake Relocation results


ESC 2012, MoscowMS and mb recomputation*The recomputed MS and mb 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 ( = 20%) of the single station magnitudes (no network magnitude based on one station only).


Mw from GCMT and literature search*MW from GCMT is available from 1976 (plus some deep earthquakes between 1962 and 1975).

For 970 relocated earthquakes direct measurements of M0 were compiled from the literature.

For the remaining relocated earthquakes, proxy MW values are obtained from the recomputed MS and mb using new empirical relationships


ESC 2012, MoscowMW proxy based on recomputed MS* Data population strongly dominated by earthquakes with magnitude below 6;

The relationship between MS and MW 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, MoscowMW proxy based on recomputed MS*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 MW vs true MW (=10% of the original population not used for deriving the model).


ESC 2012, MoscowMW proxy based on recomputed mb* The exponential model follows well the median values curve close to the saturation level of mb.


ESC 2012, MoscowMagnitude composition of the ISC-GEM catalogue*Direct MW per yearProxy MW per year


ESC 2012, MoscowMagnitude composition: Centennial vs ISC-GEM catalogue*Centennial catalogueISC-GEM catalogue


ESC 2012, MoscowMagnitude distribution of the ISC-GEM catalogue*


ESC 2012, MoscowFrequency-Magnitude distributions* Seismicity rates for large (M>7.5-7.6) 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


ConclusionsWe 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 MS and mb using uniform procedures, and new non-linear relationships are used to obtain MW proxies when direct computation of M0 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 (www.isc.ac.uk).*ESC 2012, Moscow


THANK YOU*ESC 2012, Moscow


Appendix*ESC 2012, Moscow


A Brief Time Line in Seismology*ESC 2012, Moscow


ISS bulletins (1918-1963)(predecessor of the ISC, phase data only!)**Converted into digital form by scanning the bulletin pages and applying an optical character recognition (OCR) procedure (Engdahl and Villaseor, 2002)Biggest source of earthquake data from 1918 to 1963.


Earthquake Relocation results*ESC 2012, MoscowAfterBefore


ESC 2012, MoscowMW proxy based on recomputed MS* The relationship between MS and MW is not linear; Authors normally perform bi-linear regression splitting the dataset at MS = 6.1; This separation, however, is arbitrary because slope change occurs in a transition zone between MS ~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, MoscowMW proxy based on recomputed MS*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, MoscowMagnitude composition of the ISC-GEM catalogue*


ESC 2012, MoscowMW proxy based on recomputed mb*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 mb. Proxy MW vs true MW (=10% of the original population not used for deriving the models), show how EXP model works better than GOR models, especially for MW < 6.


*ESC 2012, MoscowRegional Frequency-Magnitude distributions


*ESC 2012, MoscowRegional Frequency-Magnitude distributions (1)


*ESC 2012, MoscowRegional Frequency-Magnitude distributions (2)


*Add bullet on the data collection, stress more all of themKeep only the histograms, rearrange the before and after situation

ISC-GEM Global Reference Earthquake Instrumental Catalogue (1900-2009)

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