Microgravimetric and ground penetrating radar geophysical methods to map the shallow karstic cavities network in a coastal area (Marina Di Capilungo, Lecce, Italy)

TLDR: In this paper, an accurate interpretation was obtained using small station spacing and accurate geophysical data processing, facilitated by combining the modelling of the data with the geological and topographic information for explored caves.

Abstract: The coastal area Marina di Capilungo located ~50km south-west of Lecce (Italy) is one of the sites at greatest geological risk in the Salento peninsula In the past few decades, Marina di Capilungo has been affected by a series of subsidenceevents,whichhaveledinsomecasestothepartialcollapse ofbuildingsandroadsurfacesTheseeventshadboth social repercussions, causing alarm and emergency situations, and economic ones in terms of the funds for restoration With the aim of mapping the subsurface karstic features, and so to assess the dimensions of the phenomena in order to preventand/orlimitthegroundsubsidenceevents,integratedgeophysicalsurveyswereundertakeninanareaof~70000m 2 at Marina di Capilungo Large volume voids such as karstic cavities are excellent targets for microgravity surveys The absent mass of the void creates a quantifiable disturbance in the earth's gravitational field, with the magnitude of the disturbance directlyproportionaltothevolumeofthevoidSmallershallowvoidscanbedetectedusingground-penetratingradar(GPR) Microgravimetric and GPR geophysical methods were therefore used An accurate interpretation was obtained using small station spacing and accurate geophysical data processing The interpretation was facilitated by combining the modelling of the data with the geological and topographic information for explored caves The GPR method can complement the microgravimetrictechniqueindeterminingcavitydepthsandinverifyingthepresenceofoff-linefeaturesandnumerousareas of small cavities, which may bedifficultto beresolved withonly microgravimetric data However, themicrogravimetric can complement GPR in delineating with accuracy the shallow cavities in a wide area where GPR measurements are difficult Furthermore, microgravity surveysin anurban environmentrequire effective and accurate consideration of the effects given by infrastructures, such as buildings, as well as those given by topography, near a gravity station The acquired negative anomaly in the residual Bouguer anomalies field suggested the presence of possible void features GPR and modelling data were used to estimate the depth and shape of the anomalous source