Cuantificación de la relación frecuencia-magnitud (análisis de regresión) en el Borde Llanero: Huila-Meta-Cundinamarca-Boyacá-Casanare, a partir de datos de la RSNC

Abstract

By the middle of the nineteenth century the first modern seismograph was invented in Europe with the aim of recording the earthquakes; although the ancient Chinese had already tried for centuries to establish the direction from which came round this shake. Seismographs measure the movement produced by an earthquake through a record called seismogram, the seismogram is a graphical representation of seismic waves. Magnitude, one of two ways of measuring an earthquake, is a way of quantifying the energy released by an earthquake; the magnitude is calculated from seismic records (seismograms) and thus quantifies the energy released in the focus of an earthquake. Nowadays, it is known that the slow accumulation of energy along specific zones in the Earth's crust over time produces ruptures in the area under stress. The Gutenberg-Richter ratio (law G-R, 1954) represents the correlation between the magnitude of the earthquakes and its repetitiveness over a period of time, and it allows quantifying this relationship. The value b is the slope (in logarithmic scale) of the distribution of the G-R ratio; its estimate is directly related to the average stress in a seismic/seismogenic source. In this investigation, the b value will be determined. The value b - a constant approximately equal to 1.0 - is calculated as an initial part in the formulation of the source line threat model; its temporal variation (the variation of the b-value) allows describing the distribution of probabilities, the range of possible and probable magnitudes, and the rate of occurrence of the earthquakes of a specific seismic source. In the present work the regression analysis (and Maximum Likelihood Estimation, MLE) will be used to quantify the relationship between the number of earthquakes N and magnitude ML within the region called Borde Llanero: Huila -Meta-Cundinamarca-Boyacá-Casanare, and dominated by the East Frontal Fault System (EFFS). The quantification of the frequency-magnitude relationship will be made from data recorded since 1993, and until 2017, by the National Seismological Network of Colombia RSNC (for its acronym in Spanish).