A Seiche Hazard Study for Lake Union, Seattle, Washington

Abstract

Abstract Large seismic waves can be a result of earthquakes on local, regional, or distant fault zones occasionally setting bodies of water into oscillation. Seismic seiching is a recurrent phenomenon in the state of Washington and elsewhere (e.g., Berninghausen, 1969; Barberopoulou et al. , 2004; Cassidy et al. , 2005; Barberopoulou et al. , 2006). To investigate and characterize wave motion in lakes during strong ground shaking, various scenarios of seiche generation are considered for Lake Union in Seattle, Washington, as subjected to a variety of ground motions. Both relatively simple harmonic and more complex earthquake excitation (synthetic and real data) are used in the modeling. To isolate any effects resulting from a predominantly east–west or north–south motion or the contribution from parts of the shoreline, ground motions are first separated into their horizontal components (motions along latitude or longitude) before they are combined. This approach shows that long linear shorelines are the largest contributors to water wave heights. Depending on the shape of the lake, enhanced wave heights can also be a result of focusing. The wave motion in the lake is found to be predominantly east–west even when the ground motions are in the north–south direction. The results of this study suggest that coastal structures can be vulnerable due to resonant excitation initiated from earthquakes on water bodies far from tsunamigenic sources.