The Campi Flegrei caldera, located near the city of Naples, Italy,
has shown signs of unrest, characterized by large ground deformation,
seismic activity, and changes in the hydrothermal system since 1970.
Any attempt to model the processes giving rise to these phenomena
requires some knowledge of the subsurface structure and of the physical
properties of the rocks at depth. In this study we report the results
of laboratory measurements of ultrasonic compressional and shear
wave velocities in rock samples cored in 4 different geothermal wells
reaching a maximun depth of 3 km. The wells are located in the San
Vito (SV) and Mofete (MF) areas, at about 3 km north and 4 km west,
respectively, from the center of the caldera. We selected 10 core
samples, 7 from the SV wells and 3 from the MF wells, the attention
being focused on the most important rock formations underneath Campi
Flegrei and on the lower sections of the wells where data had been
lacking. The measurements involved the transmission of ultrasonic
waves along three orthogonal directions through dry and water-saturated
rocks at room conditions. The samples are only moderately anisotropic
(13\% for one SV sample and <8\% for all the other samples). Wave
velocities generally increase with the depth of the sample. The range
of velocities is 3-5.4 km/s for P waves and 1.5-2.9 km/s for S waves.
For the SV samples, water saturation generally implies slightly larger
(<10\%) Vp values and smaller (<20\%) Vs values as compared with
'dry' velocities. For the MF samples, water saturation implies both
higher VP and VS velocities (up to 35\% and 18\%, respectively).
These results may be explained by the different type of porosity
of the SV samples (vesicular) and the MF samples (fissurai). The
ultrasonic measurements on water-saturated samples are slightly higher
than the available in situ VP sonic measurements (25\% for one SV
sample and <15\% for all the other samples). These differences can
be explained by velocity dispersion between ultrasonic and sonic
frequencies and by the different pressure-temperature conditions
existing at depth.
%0 Journal Article
%1 zamora_etal:1994
%A Zamora, M.
%A Sartoris, G.
%A Chelini, W.
%D 1994
%J Journal of Geophysical Research
%K geophysics seismics
%N B7
%P 13553--13562
%R 10.1029/94JB00121
%T Laboratory measurements of ultrasonic wave velocities in rocks from
the Campi Flegrei volcanic system and their relation to other field
data
%U http://dx.doi.org/10.1029/94JB00121
%V 99
%X The Campi Flegrei caldera, located near the city of Naples, Italy,
has shown signs of unrest, characterized by large ground deformation,
seismic activity, and changes in the hydrothermal system since 1970.
Any attempt to model the processes giving rise to these phenomena
requires some knowledge of the subsurface structure and of the physical
properties of the rocks at depth. In this study we report the results
of laboratory measurements of ultrasonic compressional and shear
wave velocities in rock samples cored in 4 different geothermal wells
reaching a maximun depth of 3 km. The wells are located in the San
Vito (SV) and Mofete (MF) areas, at about 3 km north and 4 km west,
respectively, from the center of the caldera. We selected 10 core
samples, 7 from the SV wells and 3 from the MF wells, the attention
being focused on the most important rock formations underneath Campi
Flegrei and on the lower sections of the wells where data had been
lacking. The measurements involved the transmission of ultrasonic
waves along three orthogonal directions through dry and water-saturated
rocks at room conditions. The samples are only moderately anisotropic
(13\% for one SV sample and <8\% for all the other samples). Wave
velocities generally increase with the depth of the sample. The range
of velocities is 3-5.4 km/s for P waves and 1.5-2.9 km/s for S waves.
For the SV samples, water saturation generally implies slightly larger
(<10\%) Vp values and smaller (<20\%) Vs values as compared with
'dry' velocities. For the MF samples, water saturation implies both
higher VP and VS velocities (up to 35\% and 18\%, respectively).
These results may be explained by the different type of porosity
of the SV samples (vesicular) and the MF samples (fissurai). The
ultrasonic measurements on water-saturated samples are slightly higher
than the available in situ VP sonic measurements (25\% for one SV
sample and <15\% for all the other samples). These differences can
be explained by velocity dispersion between ultrasonic and sonic
frequencies and by the different pressure-temperature conditions
existing at depth.
@article{zamora_etal:1994,
abstract = {The Campi Flegrei caldera, located near the city of Naples, Italy,
has shown signs of unrest, characterized by large ground deformation,
seismic activity, and changes in the hydrothermal system since 1970.
Any attempt to model the processes giving rise to these phenomena
requires some knowledge of the subsurface structure and of the physical
properties of the rocks at depth. In this study we report the results
of laboratory measurements of ultrasonic compressional and shear
wave velocities in rock samples cored in 4 different geothermal wells
reaching a maximun depth of 3 km. The wells are located in the San
Vito (SV) and Mofete (MF) areas, at about 3 km north and 4 km west,
respectively, from the center of the caldera. We selected 10 core
samples, 7 from the SV wells and 3 from the MF wells, the attention
being focused on the most important rock formations underneath Campi
Flegrei and on the lower sections of the wells where data had been
lacking. The measurements involved the transmission of ultrasonic
waves along three orthogonal directions through dry and water-saturated
rocks at room conditions. The samples are only moderately anisotropic
(13\% for one SV sample and <8\% for all the other samples). Wave
velocities generally increase with the depth of the sample. The range
of velocities is 3-5.4 km/s for P waves and 1.5-2.9 km/s for S waves.
For the SV samples, water saturation generally implies slightly larger
(<10\%) Vp values and smaller (<20\%) Vs values as compared with
'dry' velocities. For the MF samples, water saturation implies both
higher VP and VS velocities (up to 35\% and 18\%, respectively).
These results may be explained by the different type of porosity
of the SV samples (vesicular) and the MF samples (fissurai). The
ultrasonic measurements on water-saturated samples are slightly higher
than the available in situ VP sonic measurements (25\% for one SV
sample and <15\% for all the other samples). These differences can
be explained by velocity dispersion between ultrasonic and sonic
frequencies and by the different pressure-temperature conditions
existing at depth.},
added-at = {2012-09-01T13:08:21.000+0200},
author = {Zamora, M. and Sartoris, G. and Chelini, W.},
biburl = {https://www.bibsonomy.org/bibtex/25a8a58c1900b3461fc13dcd691936685/nilsma},
doi = {10.1029/94JB00121},
interhash = {71bd26915dac8d95bccb87e6f336cf96},
intrahash = {5a8a58c1900b3461fc13dcd691936685},
issn = {0148-0227},
journal = {Journal of Geophysical Research},
keywords = {geophysics seismics},
month = jul,
number = {B7},
pages = {13553--13562},
timestamp = {2021-02-09T13:26:58.000+0100},
title = {Laboratory measurements of ultrasonic wave velocities in rocks from
the Campi Flegrei volcanic system and their relation to other field
data},
url = {http://dx.doi.org/10.1029/94JB00121},
volume = 99,
year = 1994
}