Comment on essd-2021-266

Emmanuel Scordilis

doi:10.5194/essd-2021-266-rc3

Abstract

Among the multitude of magnitude scales developed to measure the size of an earthquake, the surface wave magnitude MS is the only magnitude type that can be computed since the dawn of modern observational seismology (beginning of the 20th century) for most shallow earthquakes worldwide. This is possible thanks to the work of station operators, analysts and researchers that performed measurements of surface wave amplitudes and periods on analogue instruments well before the development of recent digital seismological practice. As a result of a monumental undertaking to digitize such pre-1971 measurements from printed bulletins and integrate them in parametric data form into the database of the International Seismo- logical Centre (ISC, www.isc.ac.uk, last access: August 2021), we are able to recompute MS using a large set of stations and obtain it for the first time for several hundred earthquakes. We summarize the work started at the ISC in 2010 which aims to provide the seismological and broader geoscience community with a revised MS dataset (i.e., catalogue as well as the underlying station data) starting from December 1904 up to the last complete year reviewed by the ISC (currently 2018). This MS dataset is available at the ISC Dataset Repository at https://doi.org/10.31905/0N4HOS2D.

Highlights

Since its introduction, the surface wave magnitude MS has been very popular and for a long period of time, before the moment magnitude Mw was introduced by Kanamori (1977) and Hanks and Kanamori (1979), it was considered the most reliable15 magnitude to estimate an earthquake size
Among the multitude of magnitude scales developed to measure the size of an earthquake, the surface wave magnitude MS is the only magnitude type that can be computed since the dawn of modern observational seismology for most shallow earthquakes worldwide
Its popularity originated due to: 1) as opposed to the magnitude concept introduced at a local scale by Richter (1935), MS allows seismologists to compute magnitudes for earthquakes worldwide, including those recorded at teleseismic distances, without relying on local recordings that were not available in most seismic zones; 2) thanks to the work of station operators, analysts and researchers at various observatories around the world that produced readings of surface wave data for shallow earthquakes since the beginning of the last century, MS can be computed

Summary

Introduction

The surface wave magnitude MS has been very popular and for a long period of time, before the moment magnitude Mw was introduced by Kanamori (1977) and Hanks and Kanamori (1979), it was considered the most reliable. ∆ is the distance in degrees of the seismic station from the earthquake epicentre (distance and period limits will be discussed ) This is the so-called Moscow-Prague formula and it was accepted as the standard for MS computation by the International Association of Seismology and Physics of the Earth’s Interior Since researchers have extend Abe’s catalogue beyond 1980 with MS solutions 35 from the International Seismological Centre (ISC, www.isc.ac.uk, last access: August 2021) and/or the National Earthquake Information Center of the USGS (https://earthquake.usgs.gov/earthquakes/search/, last access: August 2021) Such a composite MS catalogue was used as the magnitude basis for recent compilations such as the Centennial Catalogue (Engdahl and Villaseñor, 2002) and PAGER-CAT (Allen et al, 2009) as well as various types of research, from calibration purposes (Herak and Herak, 1993; Rezapour and Pearce, 1998) to patterns of the Earth’s seismicity (e.g., Pérez and Scholz, 1984; Ogata and 40 Abe, 1991; Pacheco and Sykes, 1992; Pérez, 1999). We briefly discuss the largest earthquakes ever recorded and outline further activities that could 50 improve this dataset in different time periods

Recomputing MS

Catalogue properties

On the MS saturation and large differences with Mw

Future developments

Findings

Conclusions