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Nagy, Ildikò
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Nagy, Ildikò
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- PublicationOpen AccessTerrain uplift due to natural hydrologic overpressure in karstic conduits(2019-01)
; ; ; ; ; ; ; ; ; ; ; Water supply from karst sources is a worldwide natural resource and the exploitation is tied to the knowledge of the positions of the hydrologic channels. We show that surface deformation induced by flood events in karst conduits is observable, and consists in uplift and outward movement from the hydraulic channel. Precipitation events produce the natural occurrence of subsurface hydraulic overpressure up to 1 MPa. Numerical modeling shows that the stresses are so strong to uplift and dislocate the surface by several mm and induce tilts in the order of microradians. The naturally induced deformation is compatible with a transient internal pressure loading of a channel. The results can be used to find new channels with dense GNSS networks. Sea water incursion and channels accessed for tourism could be monitored. Seismicity has been shown to have a seasonal variation in some areas, which could be explained by the subsurface stresses induced by the natural subsurface overpressure. The pressure induced deformation is expected to be observed in all karstic systems worldwide.162 129 - PublicationOpen AccessLA STAZIONE GEOFISICA IPOGEA DELLA GROTTA GIGANTE (CARSO TRIESTINO)(2012-10-26)
; ; ; ; ; ; ; ; ; ; ; ;Braitenberg, Carla; Dipartimento di Geoscienze, Università di Trieste (DIGeo, ex DST) ;Zadro, Maria; Dipartimento di Geoscienze, Università di Trieste (DIGeo, ex DST) ;Nagy, Ildikò; Dipartimento di Geoscienze, Università di Trieste (DIGeo, ex DST) ;Grillo, Barbara; Dipartimento di Geoscienze, Università di Trieste (DIGeo, ex DST) ;Tenze, Daniele; Dipartimento di Geoscienze, Università di Trieste (DIGeo, ex DST) ;Mariani, Patrizia; Dipartimento di Geoscienze, Università di Trieste (DIGeo, ex DST) ;Zidarich, Sergio Zidarich; Dipartimento di Geoscienze, Università di Trieste (DIGeo, ex DST) ;Romeo, Giovanni; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Taccetti, Quintilio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia ;Spinelli, Giuseppe; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Benedetti, Paolo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; ; ; ; ; ; aggiornamento sul dispositivo di calibrazione dell’acquisizione digitale dati dei pendoli della Grotta Gigante.308 331 - PublicationRestrictedCansiglio Karst Plateau: 10 Years of Geodetic–Hydrological Observations in Seismically Active Northeast ItalyTen years’ geodetic observations (2006–2016) in a natural cave of the Cansiglio Plateau (Bus de la Genziana), a limestone karstic area in northeastern Italy, are discussed. The area is of medium–high seismic risk: a strong earthquake in 1936 below the plateau (Mm = 6.2) and the 1976 disastrous Friuli earthquake (Mm = 6.5) are recent events. At the foothills of the karstic massif, three springs emerge, with average flow from 5 to 10 m3/s, and which are the sources of a river. The tiltmeter station is set in a natural cavity that is part of a karstic system. From March 2013, a multiparametric logger (temperature, stage, electrical conductivity) was installed in the siphon at the bottom of the cave to discover the underground hydrodynamics. The tilt records include signals induced by hydrologic and tectonic effects. The tiltmeter signals have a clear correlation to the rainfall, the discharge series of the river and the data recorded by multiparametric loggers. Addition- ally, the data of a permanent GPS station located on the southern slopes of the Cansiglio Massif (CANV) show also a clear corre- spondence with the river level. The fast water infiltration into the epikarst, closely related to daily rainfall, is distinguished in the tilt records from the characteristic time evolution of the karstic springs, which have an impulsive level increase with successive exponential decay. It demonstrates the usefulness of geodetic measurements to reveal the hydrological response of the karst. One outcome of the work is that the tiltmeters can be used as proxies for the presence of flow channels and the pressure that builds up due to the water flow. With 10 years of data, a new multidisciplinary frontier was opened between the geodetic studies and the karstic hydrogeology to obtain a more complete geologic description of the karst plateau.
138 1 - PublicationRestrictedThe study of karstic aquifers by geodetic measurements in bus de la genziana station – cansiglio plateau (northeastern Italy)(2011)
; ; ; ; ;Grillo, B.; Dept. Geosciences, University of Trieste ;Braitenberg, C.; Dept. Geosciences, University of Trieste ;Devoti, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Nagy, I.; Dept. Geosciences, University of Trieste; ; ; using tiltmeters and GPS observations. The study region is located in northeastern Italy, in the seismic area of the Cansiglio Plateau. The Zöllner type Marussi tiltmeters are installed in a natural cavity (Bus de la Genziana) that is part of an interesting karstic area of particular hydrogeologic importance. The Livenza river forms from a number of springs at the foothills of the karstic massif and flows through the Friuli-Veneto plain into the Adriatic Sea. Comparing the tiltmeter signal recorded at the Genziana station with the local pluviometrical series and the hydrometric series of the Livenza river, a clear correlation is recognized. Moreover, the data of a permanent GPS station located on the southern slopes of the Cansiglio Massif (CANV) show also a clear correspondence with the water runoff. Here we present the hydrologic induced deformations as observed by tiltmeter and GPS. After heavy rain events we record rapid deformations both by tiltmeters and GPS corresponding to the rainfall duration. In the following days a slow geodetic motion recovers the accumulated deformation with a distinctive pattern both in tilt and GPS data, which correlates with the runoff of the karstic aquifer. The purpose of this research is to open a new multidisciplinary frontier between geodetic and karstic systems studies to improve the knowledge of the underground fluid flow circulation in karstic areas. Furthermore a better characterization of the hydrologic effects on GPS and tilt observations will have the benefit that these signals can be corrected when the focus of the study is to recover the tectonic deformation.172 22 - PublicationRestrictedThe very-broad-band long-base tiltmeters of Grotta Gigante (Trieste,Italy): Secular term tilting and the great Sumatra-Andaman islands earthquake of December 26, 2004(2006)
; ; ; ; ;Braitemberg, C.; Dipartimento di Scienze della Terra, Universit`a di Trieste, ;Romeo, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Taccetti, Q.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia ;Nagy, I.; Dipartimento di Scienze della Terra, Universit`a di Trieste,; ; ; The horizontal pendulums of the Grotta Gigante (Giant Cave) in the Trieste Karst, are long-base tiltmeters with Z¨ollner type suspension. The instruments have been continuously recording tilt and shear in the Grotta Gigante since the date of their installation by Prof. Antonio Marussi in 1966. Their setup has been completely overhauled several times since installation, restricting the interruptions of the measurements though to a minimum. The continuous recordings, apart from some interruptions, cover thus almost 40 years of measurements, producing a very noticeable long-term tiltmeter record of crustal deformation. The original recording system, still in function, was photographic with a mechanical timing and paper-advancing system, which has never given any problems at all, as it is very stable and not vulnerable by external factors as high humidity, problems in power supply, lightning or similar. In December 2003 a new recording system was installed, based on a solid-state acquisition system intercepting a laser light reflected from a mirror mounted on the horizontal pendulum beam. The sampling rate is 30 Hz, which turns the longbase instrument to a very-broad-band tiltmeter, apt to record the tilt signal on a broad-band of frequencies, ranging from secular deformation rate through the earth tides to seismic waves. Here we describe the acquisition system and present two endline members of the instrumental observation, the up to date long-term recording, and the observation of the great Sumatra-Andaman Islands earthquake of December 26, 2004, seismic moment magnitude Mw = 9.1–9.3 [Lay, T., Kanamori, H., Ammon, C.J., Nettles, M., Ward, S.N., Aster, R.C., Beck, S.L., Bilek, S.L., Brudzinski, M.L., Butler, R., DeShon, H.R., Ekstr¨om, G., Satake, K., Sipkin, S., 2005. The Great Sumatra-Andaman Earthquake of 26 December 2004. Science. 308, 1127–1133.]. The secular-term observations indicate an average tilting over the last four decades towards NW of 23.4 nrad/year. We find evidences that this tilting is regional and has been going on since at least 125 ka. The recent earthquake of December 26, 2004 was well recorded by the pendulums.We show that the free oscillation modes were activated, including the lowest modes as e.g. 0T2, 0T3, 0T4, 0T5 and 2S1, 0S3, 0S4, 1S2.181 25