MAGNITUDE THRESHOLDS TO EVALUATE THE DAMAGE FROM INDUCED-SEISMICITY EARTHQUAKES TO EARTH DYKE STRUCTURES

Jorge Macedo^1*Norman Abrahamson²

• ¹Georgia Institute of Technology, Atlanta, United States
• ²University of California Berkeley, Berkeley, United States

In seismic hazard analysis, it is common to consider only earthquakes with magnitudes greater than 5, assuming that smaller events cannot damage engineered structures. However, this assumption may not hold for induced seismicity, where earthquakes often occur at very shallow depths and rupture distances of only a few kilometers. The steep attenuation of ground motion within the first 10 km for small-magnitude events can yield median short-period accelerations that exceed those predicted by conventional ground-motion models. The combination of higher ground-motion amplitudes and elevated earthquake rates challenges the assumption that earthquakes smaller than magnitude 5 cannot cause damage to earth structures. This study evaluates the damage potential of small-to-moderate (Magnitudes 3 to 5) induced earthquakes occurring at shallow depths on the seismic performance of earth canal dykes. The earthquake scenarios and ground motions selected for the assessments represent features expected from induced seismicity associated with wastewater injection. For dykes with a yield acceleration of 0.1g, results indicate that significant deformations (>10 cm) may occur for earthquakes with magnitudes between 3.0 and 4.0 at a rupture distance of 3 km. The methodology presented also provides a framework for assessing minimum-magnitude thresholds for other engineered systems in regions affected by induced seismicity.