Perhaps nowhere is the concept of a rapid change in the seismological record better demonstrated than with the advent of the International Seismological Centre (ISC) in 1964, after which we see a substantial increase in the volume of standardized seismological data. One such change that is basic knowledge to most scientists working in seismology, relates to the variety of scales used for recording earthquake magnitude and their evolution throughout the instrumental era. They can also be rapid, such as a systematic change in operating, recording and processing procedures. These changes can be gradual, such as improvements in location and magnitude estimation over time, as networks gradually increase or decrease in size and instrumentation improvements enhance the ratio of signal to noise in the seismological record. From the early days of instrumental seismology at the beginning of the twentieth century, seismological networks have undergone many changes that are reflected in the database of earthquake records in use today. The representation of the fundamental properties of the earthquake is affected by numerous biases and inconsistencies as one extends further back in time. Real earthquake catalogues, however, are usually inherently heterogeneous. In many cases, and in many parts of the world, they form the principal data set from which we interpret the earthquake process and model its statistical behaviour. Persistence, memory, correlations, clustering, Seismicity and tectonics, Statistical seismology, Africa 1 INTRODUCTIONĬatalogues of instrumental and historical earthquakes form one of the most fundamental building blocks upon which we base our understanding of the physical processes in the Earth. This extended catalogue, while not an appropriate substitute for a locally calibrated analysis, can help in studying global patterns in seismicity and hazard, and is therefore released with the accompanying software. Several existing high-quality earthquake databases, such as the ISC-GEM and the ISC Reviewed Bulletins, are harmonized into moment magnitude to form a catalogue of more than 562 840 events. In the second application the tools are used on a global scale for the purpose of creating an extended magnitude-homogeneous global earthquake catalogue. The first is a simple application in the Sub-Saharan Africa region where the spatial coverage and magnitude scales for different local recording networks are compared, and their relation to global magnitude scales explored. These tools are described and their application illustrated in two different contexts. New open-source tools are developed that can utilize this, or any other compiled database, to explore the relations between earthquake solutions provided by different recording networks, and to build and apply empirical models in order to harmonize magnitude scales for the purpose of creating magnitude-homogeneous earthquake catalogues. The database of the International Seismological Center (ISC) provides the most exhaustive compilation of records from local bulletins, in addition to its reviewed global bulletin. The process of homogenizing multiple catalogues of earthquakes into a single unified catalogue typically requires careful appraisal of available bulletins, identification of common events within multiple bulletins and the development and application of empirical models to convert from each catalogue's native scale into the required target. The creation of a magnitude-homogenized catalogue is often one of the most fundamental steps in seismic hazard analysis.
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