100+ years of recomputed surface wave magnitude of shallow earthquakes

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.

Application of minimum phase wavelet for generation of synthetic seismic signals

Seismic signals are analyzed by using different wavelet transforms to evaluate the magnitude of the signal. Through experimentation, it is reported that surface wave magnitude is greater than equals to three, it would affect the environment. In this paper, an attempt is made to apply minimum phase wavelet technique to analyze the seismic signals through minimum phase wavelets using CREWES data.

A New Empirical Relation between Surface Wave Magnitude and Rupture Length for Turkey Earthquakes

<p>Many practical problems encountered in quantitative oriented disciplines entail finding the best approximate solution to an over determined system of linear equations. In this study, it is investigated the usage of different regression methods as a theoretical, practical and correct estimation tool in order to obtain the best empirical relationship between surface wave magnitude and rupture length for Turkey earthquakes. For this purpose, a detailed comparison is made among four different regression norms: (1) Least Squares, (2) Least Sum of Absolute Deviations, (3) Total Least Squares or Orthogonal and, (4) Robust Regressions. In order to assess the quality of the fit in a linear regression and to select the best empirical relationship for data sets, the correlation coefficient as a quite simple and very practicable tool is used.</p><p>A list of all earthquakes where the surface wave magnitude (<em>Ms</em>) and surface rupture length (<em>L</em>) are available is compiled. In order to estimate the empirical relationships between these parameters for Turkey earthquakes, log-linear fit is used and following equations are derived from different norms:</p><p>for <em>L</em>₂Norm regression (<em>R</em>²=0.71),</p><p>for <em>L</em>₁Norm regression (<em>R</em>²=0.92),</p><p>for Robust regression (<em>R</em>²=0.75),</p><p>for Orthogonal regression (<em>R</em>²=0.68), </p><p>Consequently, the empirical equation given by the Least Sum of Absolute Deviations regression as with a strong correlation coefficient (<em>R</em>²=0.92) can be thought as more suitable and more reliable for Turkey earthquakes. Also, local differences in rupture length for a given magnitude can be interpreted in terms of local variation in geologic and seismic efficiencies. Furthermore, this result suggests that seismic efficiency in a region is dependent on rupture length or magnitude. </p><p> </p><p><strong>Resumen</strong></p><p>Muchos problemas prácticos encontrados en las disciplinas de orientación cuantitativa implican encontrar la mejor solución aproximada para un sistema determinado de ecuaciones lineales. En este estudio se investiga el uso de diferentes métodos de regresión tanto teóricos como prácticos y la herramienta de estimación correcta con el fin de obtener la mejor relación empírica entre la magnitud de onda superficial y la ruptura de longitud para los terremotos en Turquía. Para este propósito se hace una comparación detallada a partir de cuatro normas diferentes de regresión: (1) mínimos cuadrados, (2) mínimas desviaciones absolutas, (3) mínimos cuadrados totales y (4) regresiones robustas. Con el fin de evaluar la regresión lineal adecuada y seleccionar la mejor relación empírica de grupos de datos empíricos, la correlación de coeficiente es una herramienta simple y muy práctica. Se compiló una lista de todos los terremotos donde se cuenta con la magnitud de onda superficial (Ms) y la ruptura de longitud superficial (L). Con el fin de determinar las relaciones empíricas entre estos parámetros para los terremotos de Turquía, se utiliza la regresión lineal adecuada y las siguientes ecuaciones se derivan de diferentes reglas.</p><p><strong>Ms = 1.02* LogL + 5.18</strong>, para la regresión normal L₂ (R²=0.71),</p><p><strong>Ms = 1.15* LogL + 4.98</strong>, para la regresión normal L₁ (R²=0.92),</p><p><strong>Ms = 1.04* LogL + 5.15</strong>, para la regresión robusta (R²=0.75),</p><p><strong>Ms = 1.25* LogL + 4.86</strong>, para la regresión ortogonal (R²=0.68).</p><p>Por consiguiente, la ecuación empírica dada por la regresión de desviaciones mínimas absolutas es con un fuerte coeficiente de correlación (R²=0.92) que sería más apropiado y más confiable para los terremotos de Turquía. También, las diferencias locales en la ruptura de longitud para una magnitud dada puede ser interpretada en términos de eficiencia sísmica y geológica en la variación local. Además, el resultado sugiere que la eficiencia sísmicaen una región depende de la ruptura de longitud o de la magnitud.</p>