International Seismological Centre: The Global Authority on Earthquake Data
In the complex field of seismology, accuracy is paramount. The International Seismological Centre (ISC) serves as the world's premier non-governmental, nonprofit organization dedicated to the final collection, definitive analysis, and publication of global seismicity. Established in 1964, the ISC operates independently of national governments, providing a centralized and authoritative repository for earthquake data that scientists and agencies worldwide rely upon.
The organization was formed to continue the vital work of the International Seismological Summary and to manage the massive influx of data from the World-Wide Standard Seismograph Network (WWSSN). Today, the ISC's primary mission is to collect and re-analyze all available seismic data to produce the most complete and definitive records of earthquake parameters.
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Key Facts
- Founded: 1964
- Status: Independent, non-governmental, nonprofit organization
- Core Mission: Definitive collection and re-analysis of global earthquake seismic data
- Data Volume: Processes over 200,000 station readings per month
- Primary Output: The ISC Bulletin, considered the definitive record of Earth's seismicity
Scientific Methodology and Data Processing
The ISC's scientific goal is the definitive compilation of earthquake information and the specific readings that support them. This process involves not only analyzing seismic waves but also collecting reports on earthquake effects to recompute the location and occurrence time of events worldwide.
While seismic locations were determined manually using large globes prior to 1957, the modern ISC utilizes a sophisticated network of workstations. These systems access a relational database containing nearly 50 Gbytes of online data. The analysis is conducted in monthly batches, typically beginning after an 18-month period to ensure the maximum amount of information is available for a complete review.
The workflow combines advanced computing with human expertise. A suite of computer programs first groups origin estimates from various agencies and associates individual station readings with the most likely event. In a typical month, the system analyzes more than 200,000 station readings to identify an average of 10,000 events. To ensure accuracy, seismologists manually review approximately 4,000 of these events to rectify misassociations and ensure no unreported earthquakes are missed.
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Specialized Data Products
The ISC transforms raw seismic data into several highly specialized products used for research, hazard modeling, and calibration.
The ISC Bulletin
The On-line Bulletin is the primary collection of ISC data, organized by event. After approximately two years, all data for an event is reviewed, and the hypocenters (the actual point of origin of an earthquake within the Earth) and magnitudes are recalculated. This "Reviewed Bulletin" is regarded as the definitive record of global seismicity.
ISC-EHB Bulletin
The ISC-EHB Bulletin is an extension of the catalog that utilizes a specific location algorithm developed by Engdahl, van der Hilst, and Buland (1998). This product extends the catalog's reach to include data up to 2013.
ISC-GEM Catalogue
Prepared for the GEM Foundation, the ISC-GEM Global Instrumental Earthquake Catalogue (1900-2013) focuses on earthquakes with a magnitude of 5.5 or greater. This catalog is specifically designed for modeling and assessing seismic hazard and risk. It uses a consistent velocity model to recalculate epicentral locations and hypocentral depths, expressing magnitudes on the moment magnitude scale (Mw).
IASPEI Ground Truth (GT) Reference Events
This database contains 9,280 earthquakes and explosions with hypocenters located within 10 km of accuracy. Often verified through on-site studies, these "ground truth" events are used to calibrate seismic networks and better understand the Earth's internal structure.
Event Bibliography
To assist researchers, the ISC maintains an Event Bibliography. This catalog tracks scientific papers discussing over 14,000 specific seismic events, providing a reliable way to find literature without the errors common in standard search engines regarding place names or spellings.
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Summary of ISC Data Products
| Product Name | Primary Focus | Key Feature |
|---|---|---|
| ISC Bulletin | Definitive global seismicity | Reviewed after ~2 years for maximum accuracy |
| ISC-EHB Bulletin | Extended catalog | Uses Engdahl, van der Hilst & Buland algorithm |
| ISC-GEM Catalogue | Seismic hazard and risk | Covers M5.5+ events from 1900-2013 |
| IASPEI GT Events | Network calibration | High-precision hypocenter locations (<10km) |
| Event Bibliography | Scientific literature | Catalog of 14,000+ specific event papers |
Frequently Asked Questions
What makes the ISC catalog authoritative?
The ISC catalog is considered authoritative because it involves a rigorous re-analysis of all available data. Unlike preliminary reports, the ISC performs a definitive review of events—often after an 18-month delay—to ensure that hypocenters and magnitudes are recalculated using the most complete information possible.
How does the ISC ensure the accuracy of its earthquake locations?
The ISC uses a combination of large-scale computer processing and manual scrutiny. While programs group station readings and identify potential events, professional seismologists manually review thousands of events each month to correct misassociations and verify the output.
What is the difference between the On-line Bulletin and the Reviewed Bulletin?
The On-line Bulletin is the main collection of data organized by event. The Reviewed Bulletin is the version produced after approximately two years of data collection, at which point the hypocenters and magnitudes have been recalculated for definitive accuracy.
What is the purpose of the ISC-GEM Catalogue?
The ISC-GEM Catalogue is specifically designed to assist in modeling and assessing seismic hazard and risk. It catalogs earthquakes of magnitude 5.5 or greater from 1900 to 2013, using a consistent velocity model for all calculations.
Why does the ISC wait 18 months before final analysis?
The 18-month period allows the maximum amount of seismic data and information regarding earthquake effects to become available, ensuring the final re-analysis is as comprehensive and accurate as possible.