Evidencing the relationship between injected volume of water and maximum expected magnitude during the Puerto Gaitán (Colombia) earthquake sequence from 2013 to 2015

ABSTRACT Since 2013 to date more than 1000 seismic events have been recorded by the Servicio Geologico Colombiano (Colombian Geological Survey, SGC) in the municipality of Puerto Gaitán (Colombia). A total of 14 earthquakes are moment magnitude Mw > 4.0. The largest event ever recorded in the area occurred in November 2015 with Mw 4.8. It seems like the case of Puerto Gaitán is associated with the deep injection of coproduced wastewater from oil and gas extraction. The data presented in this work suggests a close relationship in space and time between injection operations and seismicity. An analysis of temporality between both data sets resulted in a time lag equivalent to about 218 d. For this paper, we computed the input and output energy during injection operations from 2013 to 2015 in order to estimate the fraction of total input energy that is radiated as seismic waves. Our results suggest that the seismic energy is only a small fraction of the total energy into the system. Although Puerto Gaitan is one of the places with the most significant volume of wastewater injected among the ones reported in the literature, the energy efficiency of the system is the lowest reported to date in comparison with other applied technologies. The low efficiency seems to be associated to the aseismic deformation of the reservoir rocks. The observed clustering of earthquakes is delimited by the basement crystalline depth. From an operational point of view, we determine that, like most cases associated with fluid injection, volume of fluid is the variable that determines change in the seismic moment released. Furthermore, the sequence of events in Puerto Gaitán may not fit into a well-known correlation between the volume of fluid injected and the maximum expected magnitude. The observed magnitudes in Puerto Gaitan are well bellow compared to those reported in the literature for similar volumes of injected fluid.

A study of the Koyna earthquake of December 10, 1967

abstract Data now available on the Koyna earthquake have been studied in detail. Different origin times and epicenters given by India Meteorological Department and Central Water and Power Research Station, field evidences and nature of the seismograms for this earthquake suggest a multiple event. A fault plane solution has been obtained by using the sense of first motions. Seismicity in Koyna region has been found to increase with the increase of water level in the reservoir and vice-versa with a certain time lag. The two major earthquakes of this region have similar foreshock-aftershock pattern, corresponding to type 2 of Mogi's (1963) models. Aftershocks of this earthquake are related by a function Log N = a + bM, value of b being −0.8. Possibility of predicting maximum expected magnitude at a certain seismic activity level of Koyna region has been also pointed out.