Complementing regional moment magnitudes to GCMT: a perspective from the rebuilt International Seismological Centre Bulletin

• Main Authors: D. Di Giacomo, J. Harris, D. A. Storchak
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-05-01
• Series: Earth System Science Data
• Online Access: https://essd.copernicus.org/articles/13/1957/2021/essd-13-1957-2021.pdf

<p>Seismologists and geoscientists often need earthquake catalogues for various types of research. This input usually contains basic earthquake parameters such as location (longitude, latitude, depth, and origin time), as well as magnitude information. For the latter, the moment magnitude <span class="inline-formula"><i>M</i>_w</span> has become the most sought after magnitude scale in the seismological community to characterize the size of an earthquake. In this contribution we provide an informative account of the <span class="inline-formula"><i>M</i>_w</span> content for the newly rebuilt Bulletin of the International Seismological Centre (ISC, <span class="uri">http://www.isc.ac.uk</span>, last access: May 2021), which is regarded as the most comprehensive record of the Earth's seismicity. From this data, we extracted a list of hypocentres with <span class="inline-formula"><i>M</i>_w</span> from a multitude of agencies reporting data to the ISC. We first summarize the main temporal and spatial features of the <span class="inline-formula"><i>M</i>_w</span> provided by global (i.e. providing results for moderate to great earthquakes worldwide) and regional agencies (i.e. also providing results for small earthquakes in a specific area). Following this, we discuss their comparisons, by considering not only <span class="inline-formula"><i>M</i>_w</span> but also the surface wave magnitude <span class="inline-formula"><i>M</i>_S</span> and short-period body wave magnitude <span class="inline-formula"><i>m</i>_b</span>. By using the Global Centroid Moment Tensor solutions as an authoritative global agency, we identify regional agencies that best complement it and show examples of frequency–magnitude distributions in different areas obtained both from the Global Centroid Moment Tensor alone and complemented by <span class="inline-formula"><i>M</i>_w</span> from regional agencies. The work done by the regional agencies in terms of <span class="inline-formula"><i>M</i>_w</span> is fundamental to improve our understanding of the seismicity of an area, and we call for the implementation of procedures to compute <span class="inline-formula"><i>M</i>_w</span> in a systematic way in areas currently not well covered in this respect, such as vast parts of continental Asia and Africa. In addition, more studies are needed to clarify the causes of the apparent overestimation of global <span class="inline-formula"><i>M</i>_w</span> estimations compared to regional <span class="inline-formula"><i>M</i>_w</span>. Such difference is also observed in the comparisons of <span class="inline-formula"><i>M</i>_w</span> with <span class="inline-formula"><i>M</i>_S</span> and <span class="inline-formula"><i>m</i>_b</span>. The results presented here are obtained from the dataset <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx16">Di Giacomo and Harris</a>, <a href="#bib1.bibx16">2020</a>, <a href="https://doi.org/10.31905/J2W2M64S">https://doi.org/10.31905/J2W2M64S</a>)</span> stored at the ISC Dataset Repository (<span class="uri">http://www.isc.ac.uk/dataset_repository/</span>, last access: May 2021).</p>