SUMMARY 
 
High-quality, weekly solutions for the coordinates of 45 permanent GPS stations spanning 1–6 years and covering the Alpine Mediterranean area are used to estimate a horizontal velocity field aligned with the ITRF2000 velocity datum. After subtracting model velocities for the Eurasian Plate, we show that the residual velocity field north of the Apennines, in the Adriatic/Dinaric region, describes a NNE-trending tectonic flow with a negative velocity gradient, from 6 mm yr−1 NE of the Apennines to virtually zero NE of the Dinarids. In the Calabria region we observe a divergent pattern, with NNW orientation, which turns to west as one moves north, towards Tuscany. Very small residual velocities are observed for stations in the Sardinia Corsica block, Spain, Southern France and north of the Alps. This regional pattern of velocities defines areas of intraplate strain. On the basis of good station coverage and of a strain rate value above a threshold, we define five provinces: Calabria, Central Apennines, both in the extensional regime, and North Adriatic, Eastern Alps and South Adriatic, under compression. We show that the orientations of the principal strain rate axes agree with the stress pattern that is inferred from local seismicity. A comparison of the geodetically determined strain rate with the strain rate associated with the seismic moment of earthquakes in the past 30 yr shows that each province may differ considerably from the others in the amount of seismic moment that is accommodated by surface strain. For example, the Umbria seismic sequence of 1997 seems to have released a seismic moment that was not exceptionally large, but concentrated over a short time interval, so that the equivalent coseismic strain rate was larger than the value observed geodetically. On average, depending on the assumptions on the seismogenic volume and time span, 70–100 per cent of the surface strain seems to be accommodated by the release of seismic moment in the upper Italian crust.

Average Strain Rate in the Italian Crust Inferred From a Permanent GPS Network

Deception Island has been interpreted variously as a classical ring fault caldera, as a tectonically controlled collapse caldera or as a tectonic depression. Review of previous studies combined with new fieldwork has allowed us to obtain a more precise model of the formation and internal structure of the Deception Island caldera. It formed as a result of the explosive eruption of basaltic-to-andesitic magmas, mostly as pyroclastic density currents representing in total a bulk volume of the order of 90 km3. Caldera collapse occurred rapidly along a polygonal structural network consisting of several pre-existing major normal faults. These faults, which originated as a result of regional tectonics, controlled pre- and post-caldera volcanism on the island. The formation of the caldera generated a very active geothermal system inside its depression, which is responsible for most of the present-day seismic activity and may also have a significant influence on the observed surface deformation. Our results do not support the hypothesis that there is a large but shallow, active magma chamber beneath the current caldera; instead we suggest that recent eruptions have been fed by small batches of deeper-sourced magmas. The intrusive remains of these eruptions and probably of other minor intrusions that have not reached the surface provide the main heat source that sustains the current geothermal system.

Origin and evolution of the Deception Island caldera (South Shetland Islands, Antarctica)

Deception Island is one of the most visited places in Antarctica. There are biological, geological, and archeological features that are major attractions within Port Foster, its horse shoe-shaped natural inner bay, and two scientific bases that are occupied during austral summers. Deception Island is an active volcano, however, and needs to be monitored in order to reduce risk to people on the island. Surface deformation in response to fluid pressure is one of the main volcanic activities to observe. Automated data acquisition and processing using the global navigation satellite systems allow measurements of surface deformation in near real time. Nevertheless, the positioning repeatability in sub-daily solutions is affected by geophysical influences such as ocean tidal loading, among others. Such periodic influences must be accurately modeled to achieve similar repeatability as daily solutions that average them. However, a single solution each 24 h will average out the deformation suffered during that period, and the position update waiting time can be a limitation for near real-time purposes. Throughout the last five austral summer campaigns in Deception, using simultaneous wireless communications between benchmarks, a processing strategy was developed to achieve millimeter-level half-hourly positioning solutions that have similar repeatability as those given by 24-h solutions. For these half-hourly solutions, a tidal analysis was performed to assess any mismodeling of ocean tide loading, and a discrete Kalman filter was designed and implemented to enhance the sub-daily positioning repeatability. With these solutions, the volcano-dynamic activity resulting in localized surface deformation for the last five austral summer campaigns is addressed. Although based on only three carefully located benchmarks, it is shown that Deception has been shortening and subsiding during these last 4 years. The method’s accuracy in baselines up to a few hundred kilometers assures its applicability to other volcanoes worldwide.

Enhancement of sub-daily positioning solutions for surface deformation monitoring at Deception volcano (South Shetland Islands, Antarctica)

Inter-satellite links for satellite autonomous integrity monitoring

Deception Island volcano (South Shetland Islands, Antarctica) has been monitored in summer surveys since 1994. We analyse the seismicity recorded from 1999–2011 with a local network and seismic arrays. It includes long-period (LP) events, volcanic tremor episodes and volcano-tectonic (VT) earthquakes. Long-period events are conspicuous, ranging from 58 (2007–08) to 2868 events (2003–04). The highest number of LP events in one day is 243 on 2 February 2001, and there are several discrete periods of intense LP activity. These variations may be related to alterations in the shallow hydrothermal system of Deception Island. The number of VT earthquakes recorded during the surveys range from 4 (2008–09) to 125 (2007–08). In some periods VT distributions are temporally and spatially homogeneous, with a generally low level of seismicity. In other periods we observe a peak of VT activity lasting a few days, concentrated in a particular area. These two patterns may respond to different processes, involving regional stresses and local tectonic destabilization induced by volcanic activity. Overall, this study indicates that over the period 1999–2011 the volcano presented a moderate level of seismicity, and suggests that there has been no significant reactivation of the volcano since the 1999 seismic crisis.

Results of seismic monitoring surveys of Deception Island volcano, Antarctica, from 1999–2011

Since 1987, Spain has been continuously developing several scientific projects, mainly based on Earth Sciences, in Geodesy, Geochemistry, Geology or Volcanology. The need of a geodetic reference frame when doing hydrographic and topographic mapping meant the organization of the earlier campaigns with the main goals of updating the existing cartography and of making new maps of the area. During this period of time, new techniques arose in Space Geodesy improving the classical methodology and making possible its applications to other different fields such as tectonic or volcanism. Spanish Antarctic Geodetic activities from the 1987–1988 to 2006–2007 campaigns are described as well as a geodetic and a levelling network are presented. The first network, RGAE, was designed and established to define a reference frame in the region formed by the South Shetlands Islands, the Bransfield Sea and the Antarctic Peninsula whereas the second one, REGID, was planned to control the volcanic activity in Deception Island. Finally, the horizontal and vertical deformation models are described too, as well as the strategy which has been followed when computing an experimental geoid.

Geodetic Research on Deception Island and its Environment (South Shetland Islands, Bransfield Sea and Antarctic Peninsula) During Spanish Antarctic Campaigns (1987–2007)

Deception Island (62.93oS, 60.57oW) is one of the few active volcanoes in the Antarctica, whose most recent eruptions took place in 1842, 1967, 1969 and 1970.

/pdf/horizontal-deformation-models-for-deception-island-south-2j5ck6czf8.pdf

Horizontal Deformation Models for Deception Island (South Shetland Islands, Antarctica)

We have applied wavelet techniques to analyze GPS time-series data from REGID geodetic network, deployed at Deception Island Volcano (South Shetland Islands, Antarctica). In the present analysis wavelets are used to detect periodic components and to filter the data. The high frequency components can be associated to the orbital period of the satellites and to local tidal effects, whereas the medium frequencies seem to be related to the weather cycle. The wavelet filtering procedure is based on the SURE estimator, and a considerable reduction in noise is achieved, particularly in the Up component, whose deviation is reduced down to the deviation of the horizontal components before the denoising. An estimation of the displacements in the network for the period 2001/02 – 2005/06 is also included.

/pdf/crustal-deformation-models-and-time-frequency-analysis-of-48ijtp7ko0.pdf

Crustal Deformation Models and Time-Frequency Analysis of GPS Data from Deception Island Volcano (South Shetland Islands, Antarctica)

The purpose of this paper is to develop a new methodology for analyzing astronomical data, in particular, one of the light curves obtained in the PHEMU campaign in 1997, where the mutual phenomena between Jupiter and its satellites were observed from the Earth due to the coincidence of the equatorial plane of Jupiter and the orbit plane of the Earth. The more specific aim of this study is to determine the times of the beginning and the end of the phenomena, and the moment when the recorded light flux was at a minimum. The techniques we applied were based on the wavelet theory, which allows us to study a signal from its approximations and details at different scales. Before applying the designed algorithm to our experimental data, we considered a synthetic light curve in order to check the reliability of our method. It should be mentioned that the results are not relevant from the astronomical point of view, since no corrections for albedo or illumination were applied to the recorded data.

/pdf/a-new-data-analysis-technique-in-the-study-of-mutual-event-2wtold6lam.pdf

M. E. Ramírez

Papers

Geodetic Research on Deception Island and its Environment (South Shetland Islands, Bransfield Sea and Antarctic Peninsula) During Spanish Antarctic Campaigns (1987–2007)

Horizontal Deformation Models for Deception Island (South Shetland Islands, Antarctica)

Crustal Deformation Models and Time-Frequency Analysis of GPS Data from Deception Island Volcano (South Shetland Islands, Antarctica)

A new data analysis technique in the study of mutual event lightcurves

Diseño, desarrollo, objetivos y estado actual de las redes geodésicas establecidas en la Antártida durante las campañas antárticas españolas