ALBERT

Description: SUMMARY Seven years after the beginning of a massive wastewater injection project in eastern Colombia, local earthquake activity increased significantly. The field operator and the Colombian Geological Survey immediately reinforced the monitoring of the area. Our analysis of the temporal evolution of the seismic and injection data together with our knowledge of the geological parameters of the region indicate that the surge of seismicity is being induced by the re-injection of produced water into the same three producing reservoirs. Earthquake activity began on known faults once disposal rates had reached a threshold of ∼2 × 106 m3 of water per month. The average reservoir pressure had remained constant at 7.6 MPa after several years of production, sustained by a large, active aquifer. Surface injection pressures in the seismically active areas remain below 8.3 MPa, a value large enough to activate some of the faults. Since faults are mapped throughout the region and many do not have seismicity on them, we conclude that the existence of known faults is not the only control on whether earthquakes are generated. Stress conditions of these faults are open to future studies. Earthquakes are primarily found in four clusters, located near faults mapped by the operator. The hypocentres reveal vertical planes with orientations consistent with focal mechanisms of these events. Stress inversion of the focal mechanisms gives a maximum compression in the direction ENE-WSW, which is in agreement with borehole breakout measurements. Since the focal mechanisms of the earthquakes are consistent with the tectonic stress regime, we can conclude that the seismicity is resulting from the activation of critically stressed faults. Slip was progressive and seismic activity reached a peak before declining to few events per month. The decline in seismicity suggests that most of the stress has been relieved on the main faults. The magnitude of a large majority of the recorded earthquakes was lower than 4, as the pore pressure disturbance did not reach the mapped large faults whose activation might have resulted in larger magnitude earthquakes. Our study shows that a good knowledge of the local fault network and conditions of stress is of paramount importance when planning a massive water disposal program. These earthquakes indicate that while faults provide an opportunity to dispose produced water at an economically attractive volume–pressure ratio, the possibility of induced seismicity must also be considered.

Description: Mining, water-reservoir impoundment, underground gas storage, geothermal energy exploitation and hydrocarbon extraction have the potential to cause rock deformation and earthquakes, which may be hazardous for people, infrastructure and the environment. Restricted access to data constitutes a barrier to assessing and mitigating the associated hazards. Thematic Core Service Anthropogenic Hazards (TCS AH) of the European Plate Observing System (EPOS) provides a novel e-research infrastructure. The core of this infrastructure, the IS-EPOS Platform (tcs.ah-epos.eu) connected to international data storage nodes offers open access to large grouped datasets (here termed episodes), comprising geoscientific and associated data from industrial activity along with a large set of embedded applications for their efficient data processing, analysis and visualization. The novel team-working features of the IS-EPOS Platform facilitate collaborative and interdisciplinary scientific research, public understanding of science, citizen science applications, knowledge dissemination, data-informed policy-making and the teaching of anthropogenic hazards related to georesource exploitation. TCS AH is one of 10 thematic core services forming EPOS, a solid earth science European Research Infrastructure Consortium (ERIC) (www.epos-ip.org).