Pocket beach management: the use of ambient noise to estimate beach sedimentary thickness

Pocket beaches, otherwise known as embayed beaches are beaches whose existence are traceable to human activity or natural occurrence. These beaches are found to be confined within the base of geological structures or artificially designed set up such as groin, hence, pocket beaches are always subject to various attacks via anthropogenic or natural forces. These attacks in many cases reflects in the thickness of the beach sediments and therefore determine the extent to which it can survive when hit by unfriendly environmental impact. Estimation of the sedimentary thickness of the beach is a vital tool in a successful geomorphological investigation geared towards the effective execution of coastal area management. This study aims to estimate the sedimentary thickness in several pocket beaches located in Malta using the passive seismic survey method of Horizontal-to-Vertical spectral ratio (H/V). This geophysical survey method employs seismic noise to estimate the depth or thickness of a sedimentary layer over a bedrock with higher shear wave velocity.  Although in recent years, this methodology has increased in popularity in geological investigations, however, there are few examples of the application of this approach to marine sandy beaches in the scientific literature, making this study a novel contribution to the field. The results of the study revealed clear H/V peaks on the beaches studied, with frequency variations corresponding to the expected sediment thickness variations. The latter was also computed by modelling of the H/V curves as well as the use of known data. The application of the H/V technique to the Maltese pocket beach system has demonstrated its effectiveness in providing valuable information for the effective use in the management of the coastal environments. This study has been supported by the SIPOBED project financed by the Malta Council of Science and Technology (MCST) - Space Reearch Funds