A search for a correlation between Earth-tides and seismicity in Colombia-first results

As a contribution to the knowledge of the sismic phenomenon and the study of earth tides, the possible connection between earthquakes and tides using seismic data for Colombia since 1993 should be analized. The purpose of this work is to study how much influence tides can have in the seismic activity of Colombia (NW South America), a country with a highly complex tectonic setting, where three tectonic plates and several independent blocks are converging. A set of nearly 138000 earthquakes from de database of the National Seismological Network of Colombia (RSNC from the Spanish “Red Sismologica Nacional de Colombia) from 1993 to 2015 was taken for analysis. We filtered out the  aftershocks using the Rasenberg algorithm to obtain a new set of 88395 declustered  events. For a first approximation, only the Earth tides were calculated and the time series of tides around each seismic event were calculated using the Eterna34 software. We determined de phase of the seismic events in relation to the components of Earth tides, such as vertical displacement and vertical strain; we looked for a possible correlation between the origin time of earthquakes and the semidiurnal, diurnal, fortnightly and monthly phases of the earth tides. For the statistical analysis, we use the Schuster test and calculate the log(p)-value. This value is used to reject the null hypothesis that events occur randomly. If log (p) <3 we can talk about a correlation.

Because the amount of data and time required for the routines, the tQuakes interactive tool was developed to allow for more efficient runs, calculations of time series and plotting of the results. We present the first results of the study applied to the total and declustered dataset, and for two special regions of Colombia that were taken as a case study: the Pacific Coast and the Bucaramanga Seismic Nest. Taking into account that the database is not homogeneous due to network densification, a data analysis was also conducted since 2009 (when the network became denser), with a total of 36150 events. The results for the overall log (p)-value both for the complete dataset and the events since 2009, are promising. Very low values of log (p) were obtained for events in the diurnal phase, suggesting that in fact there is a role of the earth tides in the earthquake generation in Colombia.