Abstract
We examine the relationship between observed tsunami water levels and tsunami currents in Humboldt Bay, California at different locations and events (27 February 2010; 11 March 2011; 29 July 2021; 15 January 2022). Water levels and currents were highly correlated for all four Humboldt Bay locations/events and dominated by oscillations with a period of roughly 57 min, consistent with previous analysis of water levels. Phase lags between water level and current were generally small (typically 0-30°). Tsunami current time series were shifted in time relative to tsunami water level time series, based on the observed lag; strong linear relationships were observed across all datasets. These results suggest that, in Humboldt Bay, tsunamis act more like propagating, dissipative waves (i.e., currents in phase with water level) rather than as purely reflecting/standing waves in a semi-enclosed basin (i.e., currents 90° out of phase with water levels). We hypothesize that the large regions of mudflats provide significant damping, so reflections are weak. We also examined available data for the 30 July 2025 Kamchatka event, developing proxy current estimates from the observed water levels. Model results for currents at Chevron Dock for this tsunami are generally of a similar range as the observations for this event; at Hookton Channel, the modeled currents were larger than the proxy estimates (by up to a factor of 1.7). We conclude that, for some estuarine geometries at least, it is possible to estimate tsunami currents directly from water level measurements using a simple linear relation.