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SBRG group researching the tectonic base frequencies in Venezia Giulia, Italy

Tag: archaeoacoustics, archaeo-acoustics, low frequency, infrasound, transducers, Grotta Gigante, tectonic noise, geological fault, SBRG, SB Research Group 

After beginning the archaeoacoustic study of Bugomili’s Dolina and other archaeological sites in Venezia-Giulia (Italy), SBRG group needed a yardstick with which to compare the tectonic base noise in this area, with that of sacred sites in the region.

The Grotta Gigante cave is nestled deep in the Karsic area and located only a few kilometers away from Bugomili’s Dolina, making it an ideal candidate for this acoustic study. Its main cavern is the largest in Europe and second in the world (measuring 98,50 metres high,  76,30  metres wide and 167,60 metres long). Inside are a number of geological instruments (including a seismograph and geodetic pendulum) used to measure the tectonic plate (earth tides) on which lies this territory.

The study of the noises present in this area are not the only one reported for comparison to that recorded in  Bogumili’s Dolina (of which we have already reported here), but also to what is reported to the Mithraeum, one of the few still existing although violently destroyed in the fifth century AD, which is located nearby too we looked at recently, but for now that does not seem to be accompanied by a resonance phenomenon inside.


Fig. 1 – The remains of the ancient Mithraeum located in the vicinity of the mouth of Timavo river, famous for its long underground water course before ending in the sea


The Mithraeum is located in a cave overlooking the mouth of the Timavo river, possibly frequented since the Neolithic period. Which could explain why a Roman temple dedicated to the god Mithras, is there, as is the tradition of placing a temple in a natural cave near a source of water. This reaffirms the bond of the deity with the heavenly world, deduced from sacred images carved on two stones inside the Mithraeum.


Fig. 2 – Some of the stone plates inside the natural cave depicting the god Mithra photographed with an infrared camera


Back to Grotta Gigante (translation from Italian language: giant cave) in collaboration with the Julian Alpine Society (section of C.A.I, Club Alpino italiano) we obtained the authorization to place the microphones in the cave (outside visiting hours) to record any sounds present for a whole night. These files are still be analyised (about 12 hours).


Fig. 3 – The building for the reception of tourists at the entrance and the stairs leading to the cave


In the cave two huge geodetic pendulums are located in the center of the main chamber by the Institute of Geophysics of the University of Trieste. This measures the slope of the tectonic plate on which the Venezia Giulia area rests and there is a very sensitive seismograph that can record earthquakes thousands of miles away which is placed on the bottom of the same chamber.


Fig. 4 - The access to the main chamber with the huge pendulums which hangs from the top of the cavern until the ground


With the help of Fulvio Forti, the guide of Julian Alpine Society, the microphones were initially placed on the bottom of the cave, approximately 500 steps in a location away from water, but partially disturbed by the noise of the fans of seismograph placed at some distance.


Fig. 5 - The place where the microphones were placed in the bottom of the cave not far from the seismograph, locked in a small shack in cement


The results were however amazing. We recorded all night long until the cave was opened to the public in the morning. There was an incredible amount of noise recorded in the dark and silent environment. The sounds of breaking rocks from the rubbing of tectonic layers of hard rocks resulting from the phenomena of attraction of celestial bodies, the sun and the moon in particular, expressing the constant noise coming from the movements of the geological fault inside the cave. This owes its rise to a cataclysm that occurred about 12,000 years ago, the exact dating of which was determined by measuring the incremental lines of the growing stalactites that broke in the cataclysm.

Here is an example of a piece of original unaltered recording of less than a minute in mp3 format (the original recording has a significant size in 24 bit wav format) in which (ignoring the noise from the electronic fan cooling equipment of the seismograph) you can hear the cracking of the rocks that are moving, clearly distinguishable from the drops of falling water. We recommend listening to the file with a high fidelity headset.



Fig. 6 – A very evident fracture passes transversely through the entire thickness of the walls of the cave


 Fig. 7 - Part of the research team: on the left Fulvio Forti, guide of the Julian Alpine Society, and on the right our assistant / photographer, Chiara Chiandotto


At the end of August, we will take more measurements, placing the microphones in different locations. For now however, it does not appear that the low frequency sounds present in the sacred sites of the region are caused by the movement of underground water.



Fig. 8 – The graph of the data collected at the bottom of the cave. Low frequencies or infrasound are not present, only high frequencies from the noise of the drops, or the breaking of rocks in the fault line that runs through the cave transversely (the peak of ultrasound at around 70kHz is an effect due to the sensitivity of the microphones, but it is not real)


The range of grinding noise from the rock fracture within the geological fault, although surprising, do not look like the frequencies detected in other archaeological sacred sites previously studied by SBRG group.

Paolo Debertolis – August 2, 2014



We thank the Julian Alpine Society (Società Alpina delle Giulie) for their willingness to cooperate with this investigation, providing its facilities. A sincere thanks in particular to the Director of the Grotta Gigante, arch. Alessio Fabbricatore, and the guide Fulvio Forti.




Translated by Nina Earl


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