The study of low-frequency sea-level oscillations: case of Algiers harbor (Algeria)

Abstract

Sea-level rise induced by global warming is increasingly threatening coastal populations, especially those living on low-lying coasts. However, coastal flooding can also be observed on a short scale but over larger areas. This sudden sea-level rise can be induced by meteorological or seismic phenomena and can cause disasters on the coast. Our work aims to study low-frequency sea-level oscillations induced by meteorological events. As a case study, sea-level disturbance events of June–July 2002 observed at Algiers harbor are examined by spectral analysis applied to the original sea-level signal measured from a tide gauge with a frequency sampling of 0.003 Hz. The original sea-level signal is filtered using cutoff frequencies of a band-pass filter to extract the meteorological oscillations. Results of the spectral analysis show periods of 16, 20, and 30 min that correspond to the frequency ranges of tsunamis, meteotsunamis, and seiches. The absence of a seismic event during this period suggests that these signals are related to the seiche phenomena that are very frequent in the Bay of Algiers. The main period of 20 min observed is similar to some main frequencies observed in Balearic Islands during the tsunami event of the 2003 Zemmouri earthquake. On the other hand, it is important to notice that the frequency sampling of 0.003 Hz is relatively low because it does not allow detection of infragravity waves and wind waves/swells. Indeed, these signals could help to better understand meteotsunamis, seiches, and harbor oscillations.