A STUDY OF THE RELATIONSHIP BETWEEN SEISMICITY AND MINING ACTIVITY IN EASTERN ARIZONA

In order to understand how mining may affect the local stress field and seismicity, we looked at seismic activity near the Morenci copper mine in eastern Arizona to determine whether there is any relationship between a M 5.3 earthquake in Duncan, Arizona and the Morenci mining activity. In this case the earthquake was located approximately 55 km south of the mine. We used the earthquake catalog from IRIS to analyze spatial and temporal variations in the patterns of seismicity to determine whether the earthquakes near Morenci could be triggered by mining operations or are strictly tectonic in origin. We developed a 3D Finite Element Model (FEM) to calculate how the principal stress changes due to removal of rock mass to determine whether such a change could trigger an earthquake, and, if so, determine the size of the area that could be affected by the change of stress. Our research suggests that mining likely played a role in the Duncan earthquake. However, it does not appear to be directly related to blasting or removal of material from the mine shortly before the earthquake occurred. Rather, we suggest the M 5.3 earthquake occurred more than 10 years after a period of major mining activity that activated a trend of seismicity connecting the epicenter to the mine. The triggering mechanism has not yet been determined but it could include long term changes in the stress field or fluid migration over time.