2,350 research outputs found
Antarctic Ice Shelf Aquifers:Characteristics and Potential Contributions to Ice Shelf Loss
No full textEGU General Assembly 2022, Vienna, Austria, 23–27 May 2022https://meetingorganizer.copernicus.org/EGU22/EGU22-820.htm
Tectonic and climate induced mass changes - competing signals in long term gravity signals
No full textSeveral mountain ranges as Alps, Himalaya and Tibet are presently subject to uplift, as documented by GNSSvertical movement rates. Uplift occurs in response to climatic mass loss (deglaciation or hydrologic mass loss)or due to the dynamic forces (crustal compression or mantle inflow below uplifting crust). The uplift generates amass change, which produces a time variation of the gravity field. The deglaciation and changes in the subsurfacehydrologic budget, also generate a mass change, which sums to the tectonic change. Satellite remote sensingis useful in determining the shrinking outlines of glaciers, using both multispectral imaging as well as Radarobservations, thus allowing to determine the surface geometry change. The essential value for climate change andestimate of the hydrologic budget is though the total volume budget estimate, which requires also the thicknessvariation. Remote sensing catches the surface height changes, but these must be corrected for the crustal uplift. Thegeodetic measurements of the crustal dynamics of the Alpine and Himalayan mountain ranges in terms of heightand gravity changes, are therefore in close relation to the estimate of the climatic changes inducing glacier andhydrologic budget changes. We estimate the hydrologic and glacier signal for the Alps and Himalaya-Tibet, usingresults from remote sensing and subsurface hydrologic observations, where available (for the methodologicalrationale see Chen et al. 2018). We estimate the contribution of the dynamic uplift by direct observations ofGNSS. We find that the hydrologic and glacier gravity signal calculated at satellite heights of GRACE andGOCE are superposed to the tectonic signal, and discuss to which amount the signals can be resolved by gravitymeasurements. We compare the predicted signals with the satellite observations of GRACE and GOCE, findingthat the tectonic uplift signal is small relative to the expected glacier/hydrologic signals, but that it cannot beneglected. We define the requirements to future gravity satellites in order to make a significante contribution to thedetection of hydro-glacial mass changes and the separation of the tectonic signal.Reference:Chen W., Braitenberg, C., Serpelloni, E. (2018) Interference of tectonic signals in subsurface hydrologic monitor-ing through gravity and GPS due to mountain building, Global and Planetary Change, Volume 167, August 2018,Pages 148-159
Depositional processes of mass flows beyond the base-of-slope area and changes in slope failures in the SW Ulleung Basin (East Sea, Korea)
No full text17 AMS 14C ages reveals spatial and temporal variations in depositional style of mass-flow lobes in the Ulleung Basin. On MR1 sonar image, eight N􀀀S elongated mass-flow lobes are identified in the western basin plain (>2100 m). Lobes 1􀀀4, deposited retrogressively, have large dimensions (>27 km long and 15􀀀25 km wide) and occupy in the lower stratigraphic position. On the other hand, lobes 5􀀀8, deposited in the more proximal area,have small dimensions (8.8􀀀31.5 km long and 1.2􀀀12 km wide) and occur in the upper stratigraphic position. Lobes 1 and 2 are characterized by relatively strong back-scattering intensity with smooth surfaces on MR1 image,and show flat, sharp bottom echo and several distinct to diffuse internal reflectors in chirp profiles. Sediments near their edges consist of fine-grained (muddy) turbidites with minor massive clay-rich sand. However, they change to coarse-grained debrites and turbidites with the overlying fine-grained turbidites toward the proximal part. Lobes 1 and 2 deposited between ca. 20 and 18 cal. ka B.P. Lobes 3 and 4, overlying lobe 2, show weak to medium back-scattering intensity on MR1 image with slightly irregular to hummocky surfaces corresponding to small-scale (27 km long and 15􀀀25 km wide) and occupy in the lower stratigraphic position. On the other hand, lobes 5􀀀8, deposited in the more proximal area,have small dimensions (8.8􀀀31.5 km long and 1.2􀀀12 km wide) and occur in the upper stratigraphic position. Lobes 1 and 2 are characterized by relatively strong back-scattering intensity with smooth surfaces on MR1 image,and show flat, sharp bottom echo and several distinct to diffuse internal refl1
Terrestrial Laser Scanning (TLS) over volcanic areas: experiments on Vesuvius, Stromboli and Vulcano (Italy)
No full textGeomorphological changes of areas affected by crustal deformation, eruptive events, gravitative instabilities, land-
slide and glacier evolution, and other phenomena, can be detected and quantified using high-accuracy digital sur-
face models. The comparison between multitemporal models provides a space-time description of geophysical
processes, and can be used to estimate deformation patterns, displacements, surface variations, volumes involved
in mass movements, and other physical features. Several techniques, including GPS kinematic methodology, digi-
tal aerial and terrestrial photogrammetry, airborne and terrestrial laser scanning, satellite-based and ground-based
interferometric radar and optical satellite imagery systems, are suitable surveying methods that provide appropriate
spatial resolution.
Terrestrial Laser Scanning (TLS) allows an accurate and cost-effective representation of the topographical details
of the observed surface. For this reason, TLS is currently used in geologic survey, engineering practice, cultural
heritage, and mobile mapping. Besides the geometric data, the point cloud provided by a TLS observation con-
tains radiometric information, i.e. the intensity of the received pulses, that can be used for classification purposes.
Moreover, some instruments are equipped with a calibrated camera to add RGB color data to the intensity data.
Since a TLS survey, including the corresponding data processing and analysis, can be carried out in relatively short
time, an operational procedure can be planned and executed. The TLS and other remote sensing techniques, like
digital photogrammetry, can be integrated to profit from the strength of each single technique and overcome the
corresponding weakness, leading to a better modeling of the observed system.
We show the results of observations on three Italian volcanoes by using a TLS recently implemented in the moni-
toring system of the INGV. The most complete set has been acquired on Mt. Vesuvius crater in May 2005, October
2006 and June 2009. The whole crater was measured with several overlapped scans and the corresponding digital
surface models were generated and registered into the UTM-WGS84 reference frame. The comparison between
the models leads to an evaluation of the occurred changes. The deformation maps showed a progressive mass loss
due to rock-falls in an area of about 5000 m2 with a corresponding accumulation at the bottom of the crater. The
volume loss which occurred from 2005 to 2009, was computed by subtraction of volumes defined with respect
to reference planes parallel to the caldera walls and was estimated to be 20300 m3. Some results were also in-
terpreted on the basis of micro-seismic and meteorological data in order to plan a monitoring technique where
seismic signals related to rock-fall and/or signals of intense rainfalls are used as alarms for fast TLS surveys able
to characterize the corresponding changes of the caldera walls. The proposed methodology, in particular the simple
but effective approach used in the estimation of volume uncertainties, can be applied to each rock slope instability
phenomenon, regardless to the particular environment.
Two measurements were carried out at Vulcano in April 2009, by surveying the whole “La Fossa” crater and
the “La Forgia” unstable slope, and in April 2010, by re-surveying again the “La Forgia” slope. All measurements
were acquired with several overlapped scans. The comparison between the two measurements at “La Forgia” shows
small change in the morphology that will be further investigated by new measurements; new measures will also be
carried out to image again the “La Fossa” crater.
Measurements at Stromboli were aimed at testing the capability of the technique in very difficult surveying con-
ditions: the 2007 lava fan in the Sciara del Fuoco, an inaccessible and unstable area of the Stromboli volcano. In
such a condition, TLS observes the fan only with high incidence angles and from distances longer than La Fossa
case. In addition, the lava fan consists in black porous lavas, characterized by a bad reflectivity.PublishedVienna, Austria 3–8 April 20111.3. TTC - Sorveglianza geodetica delle aree vulcaniche attiveope
Terrestrial Laser Scanning (TLS) over volcanic areas: experiments on Vesuvius, Stromboli and Vulcano (Italy)
No full textGeomorphological changes of areas affected by crustal deformation, eruptive events, gravitative instabilities, land-
slide and glacier evolution, and other phenomena, can be detected and quantified using high-accuracy digital sur-
face models. The comparison between multitemporal models provides a space-time description of geophysical
processes, and can be used to estimate deformation patterns, displacements, surface variations, volumes involved
in mass movements, and other physical features. Several techniques, including GPS kinematic methodology, digi-
tal aerial and terrestrial photogrammetry, airborne and terrestrial laser scanning, satellite-based and ground-based
interferometric radar and optical satellite imagery systems, are suitable surveying methods that provide appropriate
spatial resolution.
Terrestrial Laser Scanning (TLS) allows an accurate and cost-effective representation of the topographical details
of the observed surface. For this reason, TLS is currently used in geologic survey, engineering practice, cultural
heritage, and mobile mapping. Besides the geometric data, the point cloud provided by a TLS observation con-
tains radiometric information, i.e. the intensity of the received pulses, that can be used for classification purposes.
Moreover, some instruments are equipped with a calibrated camera to add RGB color data to the intensity data.
Since a TLS survey, including the corresponding data processing and analysis, can be carried out in relatively short
time, an operational procedure can be planned and executed. The TLS and other remote sensing techniques, like
digital photogrammetry, can be integrated to profit from the strength of each single technique and overcome the
corresponding weakness, leading to a better modeling of the observed system.
We show the results of observations on three Italian volcanoes by using a TLS recently implemented in the moni-
toring system of the INGV. The most complete set has been acquired on Mt. Vesuvius crater in May 2005, October
2006 and June 2009. The whole crater was measured with several overlapped scans and the corresponding digital
surface models were generated and registered into the UTM-WGS84 reference frame. The comparison between
the models leads to an evaluation of the occurred changes. The deformation maps showed a progressive mass loss
due to rock-falls in an area of about 5000 m2 with a corresponding accumulation at the bottom of the crater. The
volume loss which occurred from 2005 to 2009, was computed by subtraction of volumes defined with respect
to reference planes parallel to the caldera walls and was estimated to be 20300 m3. Some results were also in-
terpreted on the basis of micro-seismic and meteorological data in order to plan a monitoring technique where
seismic signals related to rock-fall and/or signals of intense rainfalls are used as alarms for fast TLS surveys able
to characterize the corresponding changes of the caldera walls. The proposed methodology, in particular the simple
but effective approach used in the estimation of volume uncertainties, can be applied to each rock slope instability
phenomenon, regardless to the particular environment.
Two measurements were carried out at Vulcano in April 2009, by surveying the whole “La Fossa” crater and
the “La Forgia” unstable slope, and in April 2010, by re-surveying again the “La Forgia” slope. All measurements
were acquired with several overlapped scans. The comparison between the two measurements at “La Forgia” shows
small change in the morphology that will be further investigated by new measurements; new measures will also be
carried out to image again the “La Fossa” crater.
Measurements at Stromboli were aimed at testing the capability of the technique in very difficult surveying con-
ditions: the 2007 lava fan in the Sciara del Fuoco, an inaccessible and unstable area of the Stromboli volcano. In
such a condition, TLS observes the fan only with high incidence angles and from distances longer than La Fossa
case. In addition, the lava fan consists in black porous lavas, characterized by a bad reflectivity.PublishedVienna, Austria 3–8 April 20111.3. TTC - Sorveglianza geodetica delle aree vulcaniche attiveope
Recurrent fault - valve behaviour detected by strain measurements in N - Adria
No full textWe analysed the data recorded by the NE-Italy tilt/strain gauges network in the time interval 1976-1996 (Braitenberg et al., 2006; 2019) at the light of the results of the analyses of Rossi et al. (2016; 2017; 2018) of the cGNSS at the northern tip of the Adria microplate. We considered the longest tiltmeter time series, in which long-term oscillations were previously observed (Rossi and Zadro, 1996). A transient oscillation appears to be present in the recordings of four tiltmeter sites, revealing a tilting along the tectonic features in the period 1984-1987. By using the same tomographic approach and the model of Rossi al. (2016; 2017), we located the transient’s source as originated in correspondence of the South Alpine thrust front, near its intersection with the Idrija fault, in western Slovenia, not far from the source identified by Rossi et al. (2016) for the 2006-2009 transient. The velocity field is compatibel with a fluid diffusion, confirmed by the results of the hydraulic tomographic inversion. The area, hence, would be confirmed as a source of fluid diffusion. The various thrusts and transpressive structures, involving formations with variable permeability, can act as barriers, generating overpressure conditions, and, from time to time, enable fluid diffusion in the surroundings. We calculated the fluid influx and the total discharge
Comparison between the seismic amplification values obtained from the Italian second-level microzonation (SM2) abacuses and numerical simulation
No full textThe Italian second level seismic Microzonation (SM2) aims to solve the uncertainties of the first level with new studies and gives a numeric estimate of seismic amplification through simplified methods. Seismic amplification occurs when the seismic waves reach a site composed at the top by a low velocity and loosened layer and, at the bottom, by a high velocity (Vs > 800 m/s) and rigid layer. SM2 is a simplified approach that can be applied only to 1D subsoil model (i.e., homogenous parallel layers). It consists of several tables of correspondences, called seismic abacuses, that allow to obtain two different seismic amplification factors (AF) values expected at the site: AFa and AFv. AFa corresponds to the low period amplification factor and is determined around the proper period for which there is the maximum acceleration response, whereas AFv corresponds to the amplification factor over long periods for which the maximum pseudo-speed response is obtained. These abacuses were obtained for specific lithologies of sediment cover (i.e., silt, that consists of all cohesive lithologies, sand and gravel), for established shear waves trend (i.e., constant, maximum or intermediate slope), for established peak ground acceleration at site (i.e., ag = 0.06 g, 0.18 g, 0.26 g) and for established range of seismic bedrock depth (5 m – 150 m) and for velocity of Vs30 or Vs equivalent (150 m/s – 700 m/s). Since the abacuses are thought to be applied for the whole national territory and are not site dependent, this study aims to understand if the seismic amplification factors obtained from these abacuses are representative of the actual values obtained from numerical simulation concerning the Friuli Venezia Giulia plain and if they under/overestimate the seismic hazard. Data has been collected from the Italian National Civil Protection repository and analyzed to obtain the necessary parameters to enter the abacuses. With the same data, several numerical simulations were carried out to obtain the site seismic amplification factors. The results were analysed from different perspectives: soil category obtained from Italian regulation, lithology cover soil, slope of the shear wave velocity - depth curve, and depth of the seismic bedrock. The AF obtained from seismic numerical simulations are higher with respect to the those from abacuses; the AF obtained from silt soils have the highest values; the AF from abacuses are greater than the AF obtained from simulations except for the sites where the slope of shear wave velocity - depth curve is considered maximum, i.e., where the seismic bedrock is shallow. Lastly, apart from some isolated values, the AFa ranges for sites characterized by a seismic bedrock depth lower than 30 m and higher than 30 m, are 1 to 3 and 2 to 5, respectively, while the AFv ranges are 1 to 2 and 1.25 to 4.5, respectively. In general, it is noted that abacuses underestimate the local seismic site effects except for the sites that have a shallow seismic bedrock. Moreover, there were identified no trends between abacuses AF and the ones from numerical simulations.
How to cite: Beltrame, C., Taverna, P., Peressi, G., Costa, G., and Pazzi, V.: Comparison between the seismic amplification values obtained from the Italian second-level microzonation (SM2) abacuses and numerical simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8329, https://doi.org/10.5194/egusphere-egu24-8329, 2024
Estimation of runup heights of the 2011 Tokohu tsunami based on 3D numerical simulations and 1D analytical runup theory
No full textA gigantic earthquake (M9.0) occurred at 14h46m (JST) 11th, March 2011 in the Pacific Ocean east off the Tohokudistrict north east part of the Honshu Island, Japan. It was accompanied by the huge tsunami. Measuredrunup heights of this tsunami are collected in several web sites and papers. In this study, we compare observedand computed runup heights. Numerical computations are performed in the framework of the 3D hydrodynamicequations matched with 1D theory of long wave runup near shoreline.is tsunami are collected in several web sites and papers. In this study, we compare observedand computed runup heights. Numerical computations are performed in the framework of the 3D hydrodynamicequations matched with 1D theory of long wave runup near shoreline.1
Precipitation over the Southern Ocean: comparison of several ship-based measurement techniques during the Antarctic Circumnavigation Expedition
No full textPublished in: Geophysical Research Abstracts. Vol. 21, EGU2019-15209, 2019 - EGU General Assembly 2019. © Author(s) 2019. CC Attribution 4.0 license.CRYOSLT
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