Normally, loads for wind turbines are controlled by forces imposed on them by the wind. The recent strong magnitude 6.4 and 7.1 seismic events near Ridgecrest, California, which were felt in the wind power plant regions of Southern California, remind us that earthquakes induced loads must also be considered for wind turbines.
The shaking in Tehachapi and Palms Springs was relatively low, with a peak ground acceleration of 0.03 g and 0.016 g, respectively. With such low ground accelerations, no damage is expected to the wind power plant regions and none has been reported to date. However, many renewable energy projects lie near active faults and could be impacted by an earthquake at any time.
In past events where shaking was stronger, wind turbines have fared very well in comparison to other structures. The only known damage of wind turbines due to a tremor was in the 1986 North Palm Springs earthquake. A small number of turbines suffered damage, primarily consisting of buckling of some of the segmented tower walls which resulted in tilting of the structures, but no overturning and collapse of the towers was reported. These early turbines are considerably different than modern turbines and no catastrophic loss of a wind turbine has been recorded in any earthquake since 1986. The closest event where seismic activity was reported to impact a wind turbine is when the ground surrounding a wind turbine foundation liquefied during the 2011 Tōhoku earthquake resulting in minor tilt of the foundation. Generally, associated infrastructure such as substations have shown to be more fragile. It is important that wind turbines continue to be properly designed for earthquakes to continue good performance as wind energy become more widespread.
DNV is a world leader in earthquake engineering for renewable energy projects, and can provide hazard assessments, earthquake damage assessments, and assist in characterizing a project and providing recommendations so that seismic events will have less impact on continued operation and power generation.