Analysis of interaction between waves and cliff along the Adriatic coast of Polignano (Apulia, Italy)

Abstract

The aim of this study is the analysis of the dynamic behavior of rocky cliff located below the old urban center of Polignano (Apulia, Southern Italy). In order to characterize the behavior of the cliff under the impulse generated by sea waves, two types of measures were carried out on the rocky mass: (1) environmental vibrations and (2) accelerometer records. The first type of measures, which may be executed in a short time with a high spatial density, has provided a recognition of the different types of dynamic behavior of the cliff. The accelerometer records, carried out during heavy storms in December 2009 and January 2010, have been allowed to confirm the results of previous measures and to evaluate the energy transfer from waves to cliff, in terms of maximum values and temporal distribution. In order to facilitate a correct interpretation of measures, geological surveys for studying fracturation of rocky mass were carried out. The main results were the following: 1. The cliff shows a subdivision into two zones: (a) with stable behavior and without amplification of wave impulse, characteristic of limestones, (b) with amplification of wave impulse along several preferential directions, some of which are substantially coincident with the directions of main systems of fractures, while others coincide with local orientation of the rocky cliff. 2. The accelerometer measures confirm the different behavior. The most stable and less fractured zone is crossed by the energy transmitted from waves to cliff without giving its own contributions, the other zone filters this energy with its own frequencies. 3. The accelerations recorded (with maximum value of about 0.02 g) on the cliff during storms show a regular distribution of observed values; this distribution can be correlated with the wave height offshore.