Extreme sea-level events occur across a range of temporal and spatial scales, including high-frequency oscillations (periods T < 2 h). However, most research uses hourly or daily data and neglects higher-frequency processes such as seiches and meteotsunamis. This study investigates the characteristics of high-frequency (HF) sea-level extremes along the North Sea coast. Long-term (1993–2025) measurements were analysed from 29 tide gauges. After quality control, the astronomical tide was removed to isolate residuals, which were decomposed into low-frequency (T > 2 h) and high-frequency (T < 2 h) components. Next, extremes were extracted from the HF signal alone (HF extremes) and from the residual (residual extremes). Clustering techniques (K-medoids with Dynamic-Time-Warping and Euclidean distances) were applied to HF extremes to classify event types and identify regional patterns. HF extremes were grouped into six event types, and selected stations yielded five spatial clusters. Each event type was characterised by period, intensity, and its relationship to residual extremes. HF extremes were generally low compared with tidal ranges, and compound events (i.e., events in which an HF extreme coincided with a residual extreme) were infrequent (12.2% of HF extremes on average). Nevertheless, during compound events, alignment of HF and residual peaks substantially amplified sea levels. Spatial patterns highlighted the most intense events along the Dutch coast (IJmuiden Buitenhaven, Scheveningen, Brouwershavensche Gat, and Terschelling). These results were influenced by differences in local environmental conditions and sampling. Therefore, this study advances understanding of HF sea-level variability and compound events along the North Sea coast, supporting improved coastal hazard assessments.

On February 6, 2023, two strong earthquakes with magnitudes Mw 7.8 and Mw 7.5 struck southeastern Turkiye, causing widespread structural damage and loss of life. An unexpected tsunami was observed in the Eastern Mediterranean following the first earthquake, despite the rupture occurring onshore. This study investigates the tsunami source mechanism, hypothesizing submarine landslides generated the waves recorded at five tide gauges. We integrate field survey observations, sea level analysis and numerical simulations to estimate the location, dimensions and orientation of the tsunami source(s). Surveys along the Gulf of Iskenderun revealed pronounced sea level fluctuations, including a 0.55 m tsunami run-up and ∼65 m inundation in Samandag-Cevlik. Our findings suggest a submarine landslide source ∼20 km × 14 km in size, with ±1.0 m initial amplitude and an estimated volume of 0.163 km³. The numerical simulations successfully reproduce observed tsunami amplitudes and survey data, confirming that a submarine landslide is a plausible cause. Furthermore, our analysis highlights the strong sensitivity to landslide orientation and a nearly linear relationship between initial amplitude and maximum sea level response. Our findings contribute to improved tsunami early warning systems by incorporating atypical tsunami sources, enhancing hazard mitigation, and guiding future undersea investigations in the region.