Fig. 4 Injection and earthquakes in three additional study areas with fewer earthquakes and less SWD. In contrast to those in Fig. 3, here are three comparable areas with comparatively few earthquakes. Injection and earthquakes in three additional study areas with fewer earthquakes and less SWD. In contrast to those in Fig. 3, here are three comparable areas with comparatively few earthquakes. The vertical scales in the Enid and Oklahoma City study areas are the same as in Fig. 3. The Ardmore area has a different vertical axis because of the very large volumes of EOR injection. F. Rall Walsh III, and Mark D. Zoback Sci Adv 2015;1:e1500195 Copyright © 2015, The Authors