Faculty of Sciences

We present the results of a multidisciplinary study of the Ms = 6.2, 1995, June 15, Aigion earthquake (Gulf of Corinth, Greece). In order to constrain the rupture geometry, we used all available data from seismology (local, regional and teleseismic records of the mainshock and of aftershocks), geodesy (GPS and SAR interferometry), and tectonics. Part of these data were obtained during a postseismic field study consisting of the surveying of 24 GPS points, the temporary installation of 20 digital seismometers, and a detailed field investigation for surface fault break. The Aigion fault was the only fault onland which showed detectable breaks (< 4 cm). We relocated the mainshock hypocenter at 10 km in depth, 38 ° 21.7 ′ N, 22 ° 12.0 ′ E, about 15 km NNE to the damaged city of Aigion. The modeling of teleseismic P and SH waves provides a seismic moment Mo = 3.4 1018 N.m, a well constrained focal mechanism (strike 277 °, dip 33 °, rake − 77°), at a centroidal depth of 7.2 km, consistent with the NEIC and the revised Harvard determinations. It thus involved almost pure normal faulting in agreement with the tectonics of the Gulf. The horizontal GPS displacements corrected for the opening of the gulf (1.5 cm/year) show a well-resolved 7 cm northward motion above the hypocenter, which eliminates the possibility of a steep, south-dipping fault plane. Fitting the S-wave polarization at SERG, 10 km from the epicenter, with a 33° northward dipping plane implies a hypocentral depth greater than 10 km. The north dipping fault plane provides a poor fit to the GPS data at the southern points when a homogeneous elastic half-space is considered: the best fit geodetic model is obtained for a fault shallower by 2 km, assuming the same dip. We show with a two-dimensional model that this depth difference is probably due to the distorting effect of the shallow, low-rigidity sediments of the gulf and of its edges. The best-fit fault model, with dimensions 9 km E–W and 15 km along dip, and a 0.87 m uniform slip, fits InSAR data covering the time of the earthquake. The fault is located about 10 km east-northeast to the Aigion fault, whose surface breaks thus appears as secondary features. The rupture lasted 4 to 5 s, propagating southward and upward on a fault probably outcropping offshore, near the southern edge of the gulf. In the shallowest 4 km, the slip – if any – has not exceeded about 30 cm. This geometry implies a large directivity effect in Aigion, in agreement with the accelerogram aig which shows a short duration (2 s) and a large amplitude (0.5 g) of the direct S acceleration. This unusual low-angle normal faulting may have been favoured by a low-friction, high pore pressure fault zone, or by a rotation of the stress directions due to the possible dip towards the south of the brittle-ductile transition zone. This fault cannot be responsible for the long term topography of the rift, which is controlled by larger normal faults with larger dip angles, implying either a seldom, or a more recently started activity of such low angle faults in the central part of the rift.

Based on new multibeam bathymetric data, seismic-reflection profiles and side-scan sonar images, a great number of submarine failures of various types and sizes was identified along the northern margin of the Ligurian Basin and characterized with 3 distinct end-members concerning their location on the margin, sedimentary processes and possible triggering mechanisms. They include superficial landslides mainly located in the vicinity of the main mountain-supplied rivers and on the inner walls of canyons (typically smaller that 108 m3 in volume: Type 1), deep scars 100–500 m high along the base of the continental slope (Type 2), and large-scale scars and Mass Transport Deposits (MTDs) affecting the upper part of the slope (Type 3 failures). The MTDs are located in different environmental contexts of the margin, including the deep Var Sedimentary Ridge (VSR) and the upper part of the continental slope in the Gulf of Genova (Finale Slide and Portofino Slide), with volumes of missing sediment reaching up to 1.5 × 109 m3. High sedimentation rates related to hyperpycnal flows, faults and earthquake activity, together with sea-level fluctuations are the main factors invoked to explain the distribution and sizes of these different failure types.

The Peille earthquake (Mw=3.4) occurred on 1st November 1999, 15 km to the north of the cities of Nice, Monaco and Menton. This event was very well recorded by 20 seismological stations located between 6 and 50 km from the epicenter. We used a non-linear location method and showed that the earthquake occurred at shallow depth (3±1.5 km) close to the Peille–Laghet fault trace. Moreover the computed focal mechanism is consistent with the left lateral strike slip movement of this fault. An empirical Green's function deconvolution showed that the rupture occurred on a fault portion smaller than 600 m long. This earthquake was also the occasion to point out remarkable site effect amplifications in some areas of the city of Nice.Le séisme de Peille (Mw=3,4) s'est produit le 1er novembre 1999, à 15 km au nord des villes de Nice, Monaco et Menton. Ce petit séisme a été très bien enregistré par 20 stations sismologiques, situées entre 6 et 50 km de l'épicentre. Nous avons utilisé une méthode de localisation non linéaire, qui montre que ce séisme a eu lieu à faible profondeur (3±1,5 km), près du tracé de la faille de Peille–Laghet. De plus, le mécanisme au foyer de ce séisme est cohérent avec le mouvement de décrochement sénestre le long de cette faille. En utilisant une méthode de déconvolution par fonctions de Green empiriques, nous montrons que la rupture a eu lieu sur une portion de la faille d'une longueur inférieure à 600 m. Ce séisme a également produit des effets de site remarquables, caractérisés par une amplification du signal sismique dans certains quartiers de la ville de Nice.

We focus on the northern Ligurian margin, at the geological junction of the subalpine domain and the Ligurian oceanic basin, in order (1) to identify the location of the southern limit of the Alpine compressive domain during the Cenozoic, and (2) to study the influence of a compressive environment on the tectonic and sedimentary evolution of a passive margin.Based on published onshore and offshore data, we first propose a chronology of the main extensional and compressional regional tectonic events.High-resolution seismic data image the margin structure down to ∼3 km below seafloor. These data support that past rifting processes control the present-day margin structure, and that 2800–4000 m of synrift sediment was deposited on this segment of the margin in two steps. First, sub-parallel reflectors indicate sediment deposition within a subsident basin showing a low amount of extension. Then, a fan-shaped sequence indicates block tilting and a higher amount of extension. We do not show any influence of the Miocene Alpine compression on the present-day margin structure at our scale of investigation, despite the southern subalpine relief formed in the close hinterland at that time. The southern front of the Miocene Alps was thus located upslope from the continental margin.Finally, a comparison with the Gulf of Lions margin suggests that the tectonic influence of the Alpine compression on the rifting processes is restrited to an increase of the subsidence related to flexure ahead of the Alpine front, explaining abnormally high synrift thicknesses in the study area. The Alpine environment, however, has probably controlled the sedimentary evolution of the margin since the rifting. Indeed, sediment supply and distribution would be mainly controlled by the permanent building of relief in the hinterland and by the steep basin morphology, rather than by sea-level fluctuations, even during the Messinian sea-level low-stand.► Tectonic and sedimentary effects of a compressive environment on the rifting processes. ► Abnormally thick synrift sediment in the Liguro-Provençal basin off the Alpine domain. ► Southern limit of the Western Alps. ► Chronology of compressional and extensional tectonics at the junction between the Alpine domain and the Liguro-Provençal basin.

For two months, ground motions induced by natural seismicity were recorded by 4 dense arrays, each of them including 9 seismological receivers. The target zone is a 400 km2 area and displays a characteristic topographic organization. The sites correspond to flat valleys filled with surficial soft sediments. The data recorded during this experiment will be used to characterize the wavefields through the different valleys (main energetic azimuthal contributions, apparent velocities) in the aim to quantify site effects.Durant deux mois, les vibrations du sol induites par la sismicité naturelle ont été enregistrées par 4 réseaux denses, comprenant chacun 9 stations sismologiques. La zone choisie couvre une superficie de 400 km2 et présente une topographie avec des orientations bien marquées. Les sites correspondent à des fonds de vallées plans et remplis de sédiments récents peu consolidés. Les données acquises lors de cette expérience serviront à caractériser les trains d'ondes traversant ces différentes vallées (azimuts des contributions énergétiques principales, vitesses apparentes) dans le but de quantifier les effets de site.

1] A seismic swarm occurred in the south-east of France in December 2000, about 15 km north of the densely populated cities of the French-Riviera. More than 300 events were located by a dense temporary seismic network that had been installed in the epicentral region one month before. We evidence an alignment of the seismicity that we interpret as an unknown active fault. On the basis of regional tectonics, we propose that this fault results from basement faulting cutting through the detached overlying sedimentary cover.

1] We studied the patterns, rates and evolution of 9 fluvial terraces and fault system during the building 10 process of an intracontinental transpressional mountain 11 in the Gobi-Altay (Mongolia). By analyzing incisions 12 and offsets of fluvial terraces and alluvial fans, we show 13 that the massif has grown by outward migration of 14 thrust faults through time. On the northern flank, the 15 present bounding thrust fault began its activity $600 ka 16 ago, while a more internal sub-parallel fault was still 17 active until $200-100 ka. Vertical offset of an alluvial 18 fan abandoned $100 ka ago allows an estimate of 19 0.1 mm/yr Upper Pleistocene -Holocene uplift rate. 20 The morphology of the catchment-piedmont system 21 strongly suggests a periodical formation of the alluvial 22 45 1986; Bayasgalan et al., 1999; Cunningham et al., 2003], 46 but few examples have provided chronological data allow-47 ing to understand and quantify the growing process over 48 tens of thousand years in details. For example, it is not clear 49 whether the deformation in a restraining bend occurs on the 50 most external faults alone or whether it is distributed on 51 several faults, or if pre-existing structures control the 52 location of the active faulting during the mountain widen-53 ing. Establishing the chronology of fault activity should 54 help to better understand the mechanical behavior of a pre-55 structured lithosphere in a transpressive context. Moreover, 56 such a chronology has broad implications concerning the 57 seismic potential of faults within a restraining bend. The 58 studied restraining bend, the Ih Bogd massif, is located 59 along the Bogd fault system in the Gobi-Altay range in 60 Mongolia (Figure 1). It has been the focus of several 61 morphotectonic studies, because the geomorphic markers 62 are exceptionally preserved in this region, and because a 63 8.3 Mw earthquake occurred on the Bogd fault in 1957 [i.e., 64 Ritz et al., 1995; Bayasgalan et al., 1999; Carretier et 65 al., 2002; Ritz et al., 2003; Vassallo et al., 2005; Ritz et al., 66 2006]. 67 [3] In order to document the evolution of faults pattern 68 and rates, we analyze how faults have disturbed the geo-69 morphology at a regional scale, and at fault scarp scale. In 70 particular, we map the faults and the geology in the massif, 71 and we map the fluvial terraces and alluvial fans in a 72 selected catchment-piedmont system. Our basic geomorphic 73 reference surfaces for analyzing incision and fault slip rates 74 are the terrace strath levels and the top of the alluvial fan 75 surfaces, respectively. 76 [4] The Bitut catchment-piedmont system is the largest of 77 the massif and displays the best-preserved levels of fluvial 78 terraces (Figure 2). Terraces and fans are affected by 79 different faults parallel to the mountain front, and to the 80 main left-lateral strike-slip fault (the Bogd fault). We 81 measure incisions and offsets of these markers using precise 82 topographic GPS leveling and we date them using 10 Be 83 exposure dating. This approach allows us to establish the 84 timing of the activity on the different faults in the Bitut 85 valley and fans. 86 [5] Moreover, the fluvial terraces are preserved enough to 87 reconstruct paleo-river profiles correlated with alluvial fans 88 in the apron. The fluvial terraces are likely the product of a 89 cyclic climate with period of 100 ka, characterized by the 90 alternation of long-dry glacial periods and short-wet inter-

Several hundred earthquakes of small and moderate magnitude occur each year at the southwestern Alps–Ligurian basin junction. In addition, the historical seismicity data attests for earthquakes of magnitude close to 6.5. Despite the seismic hazard and the vulnerability of this region, the present-day driving mechanism of deformation and the major structures accommodating these deformations remain unclear. This littoral area presents a strong topographic gradient from 3000 masl on the Argentera alpine massif to 2500 m.u.s.l. in the Ligurian basin and a strong structural inheritage resulting from 50 My geological evolution combining different processes such as continental collision and ocean basin opening.We present new results about the kinematics of the Corsica–Sardinia continental block with respect to the western alpine belt. From 7 years of continuous GPS measurements we show that a small part of the Nubia–Eurasia convergence is certainly transferred northward of the Maghrebides deformation belts to the Corsica–Sardinia block. In the southwesternmost Alps from Torino to the Mediterranean coast, the baselines reveal differential motions of lengthening between the Po plain and the Argentera and shortening between the Argentera and the Ligurian domain.In a region where few focal solutions are available we determine seven new focal mechanisms located in the Argentera massif. These new data underline a quaternary change from compression to extension in that part of the western alpine belt. The focal mechanisms calculated attest for extensional faulting at shallow level between 1 and 11 km depth. We add 7 focal mechanisms from the literature to calculate the stress tensor: a homogeneous solution indicates a direction of extension broadly perpendicular to the topographic axis culmination of the Argentera. In contrast, the earthquakes recorded below 15 km at the northwestern margin of the Po plain testify reverse faulting and a compressional state of stress in the deep crust. Thus, we point out that the stress field is vertically heterogeneous in the crust of the Argentera area.The Ligurian domain is mainly characterized by reverse and strike-slip faulting. The major earthquakes are located in the northern margin and at the ocean–continent transition. These earthquakes are assumed to result from the reactivation, in a compressional state of stress, of the structures formed during the Oligo-Miocene opening of the Ligurian basin.Finally, we propose three hypotheses to explain the current deformation at the Alps–Ligurian basin junction, taking into account the far-field kinematics between the Nubia and the Eurasia plates, the topographic gradient between the Argentera massif and the Ligurian oceanic floor and the distribution of the deformations.

We present here a detailed analysis of a seismic data set recorded by a dense seismological network installed over 6 months in the southeast of France. This experiment was set-up at the boundary between the Ligurian basin and the southern subalpine thrust belt (the Nice arc), which is a complex tectonic region that undergoes low to moderate seismicity. We recorded more than 500 microearthquakes, among which 348 occurred exactly in the centre of the network during a very active seismic sequence that lasted mainly over 2 months.

The Tunka basin was initiated during Oligocene, under transtensional regime (normal-sinistral) as shown by large-scale structures and geomorphology. Nevertheless, a preliminary analysis of the most recent deformations allows us to evidence transpression on several sites within the basin. These tectonic features together with focal mechanisms and preliminary GPS data, suggest that the kinematics of the Tunka basin has undergone a very recent change, which could be due to the northward propagation of the India–Eurasia collisional strain field.Le bassin de Tunka s'est développé depuis l'Oligocène dans un régime transtensif (normal sénestre) associé à l'ouverture du rift Baı̈kal. Cependant, une analyse morphotectonique sur le terrain nous permet de caractériser un régime tectonique actuel transpressif dans plusieurs secteurs. L'examen de la déformation quaternaire suggère ainsi un changement récent de la cinématique des failles qui bordent le bassin de Tunka. Ce changement, qui va dans le sens d'une inversion des failles normales initiales, pourrait être lié à la propagation vers le nord du champ de déformation produit par la collision Inde–Eurasie.

We used satellite imagery and field data to investigate the south-westernmost Baikal rift zone. We focus our study in the Mondy and Ikhe Ukhgun valleys, site of an Mw ¼ 6.9 seismic event in 1950. Surface deformations are observed along the E-W-trending Mondy strike-slip fault and along the Ikhe Ukhgun thrust. The Mondy fault system is 80 km long and is composed of four segments 10-15 km long. These segments are characterized by subvertical planes with left-lateral movements. The Ikhe Ukhgun thrust is 20 km long, dips 40°to the south and shows reverse movement with a left-lateral compo-nent. These observations are consistent with the present-day regional NNE-SSW compression and with the focal mechanism of the 1950 Mondy earthquake that was recently re-evaluated. These features, like those observed in the Tunka basin, demonstrate a recent change of regional strain regime from transtension to transpression that we place before the Late Pleistocene.

The Sicilian accretionary prism shows a large, southward imbricated system of thrust sheets. The frontal part of the belt has been tectonically emplaced in Plio-Pleistocene times. Major décollement surfaces and sole thrusts at the base of and inside the prism consist of mélanges with a “blocks in matrix” fabric. In the frontal part, two superposed décollement levels are recognized, the upper one located at the base of the Paleogene-Neogene sedimentary series, and the basal one at the base of duplexes (Triassic-Miocene sedimentary series). Syntectonic dewatering of the sedimentary sections occurred along décollements and thrust faults, involving hydrofracture and mineralized vein development.Inside the deep sole thrusts (rooted in the basal décollement); hydrofractured blocks show different generations of syntectonic quartz and calcite extensional veins, while in the upper décollement only calcite veins have been observed. Both quartz and calcite veins show aqueous primary fluid inclusions of low salinity, with low trapping temperature for fluids in the upper décollement (< 60°C) and high trapping temperature for fluids in the deep sole thrusts (up to 235°C in calcite, for a pressure near 0.8–1.0 kbar).If we assume that, at the time of deformation, the main heat source was the regional conductive geothermal gradient, the trapping temperatures of the fluids inside veins of the deep sole thrusts are higher than those predicted by the Pilo-Pleistocene gradient for this subduction zone and correspond to a thermal anomaly. We suggest that the frontal Sicilian prism supported localized transient fluid flow of deep freshwater sourced from two different origins: a shallow one for fluids now trapped in the upper décollement, and a deep internal origin (6–10 km minimum depth) for the hot fluids channelized along the basal décollement and now trapped inside the sole thrust of the Mt. Scalpello duplex area.

We present results of three sand-box experiments that model the association between tectonic accretion and sedimentation in a forearc basin. Experimental sedimentation occurs step by step in the forearc basin during shortening of the sand wedge.In each experiment, the development of the accretionary wedge leads to the formation of a major backthrust zone. This major deformation zone accounts for the thickening in the rear part of the wedge. In natural settings this tectonic bulge dams sediments that are transported toward the trench from mountainous terrain behind the forearc.We test the variation of friction along the déollement and note the following: (1) shortening of a low-friction wedge involves a mechanical balance between forethrusts and backthrust propagation and this balance is recorded by the sedimentary sequence trapped in the forearc basin. Indeed, if most of the movement occurs along the backthrust, the deepening of the basin will be larger and consequently the thickness of the sedimentary sequence will be greater. (2) Such balance does not exist in the case of a high-friction wedge. (3) Variation of friction along the décollement during shortening of the sand wedge leads to modification in the forearc basin filling. Thus, for similar increments of convergence, the sequence deposited in the forearc basin shows relatively larger thickness when the wedge is shortened above a high-friction décollement.We suggest that contraction and thickening in the rear part of the wedge is an efficient mechanism to, initiate and develop a forearc basin. Thus, this kind of basin occurs in convergent settings, without collapse related to local extension or tectonic erosion. They represent a sedimentary trap on a passive basement, bounded by a tectonic bulge.The Quaternary Hikurangi forearc basin, southeast of the North Island of New Zealand, is bounded by two actively uplifting ridges. Thus, this basin is considered to be a possible example of the basins modelled in our experiments, and we suggest that the limit between the basin and the wedge could be a complex backthrust zone.

The dating of the uplift onset of the Mongolian mountain ranges, the northernmost relief associated with the India-Eurasia convergence, is a fundamental issue to better understand the mechanisms of propagation of the Cenozoic transpressive deformation in Central Asia. Using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the Gurvan Bogd system, in the Gobi-Altay, since the Middle Mesozoic to the Late Cenozoic. The region was firstly affected by a Lower-Middle Jurassic tectonic phase, characterized by a vertical crustal movement larger than 2 km. Then followed a protracted period without major crustal vertical movements until the last uplift phase. The peneplanation of the Jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 Ma. This same surface corresponds to the present summit plateaux of the massifs, standing about 2000 m above the surrounding region, which corresponds to the vertical movement produced by the ongoing uplift. Modelling of fission track data from the massifs of Ih Bogd and Baga Bogd shows that this uplift phase probably started at 5 ± 3 Ma. The Gobi-Altay mountain range appears therefore as one of the youngest mountain ranges in Central Asia, which is consistent with the idea of a northward propagation of the transpressional deformation from the Himalayan front to the Siberian craton. The Cenozoic uplift rate of the massifs is estimated to be between 0.25 and 1 mm/yr, which is slightly higher than the upper Pleistocene vertical slip rates of the bordering faults. This suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries.

ABSTRACT The precise nature of the transition between the present-day compressional tectonics in central Mongolia and extensional deformation in the central Baikal rift has still to be determined. For that purpose we have built a comprehensive earthquake focal mechanism data base for the Mongolia – southern Siberia area, from which we map the variations of the stress field. We focus our detailed investigations on the largest seismic event in the transition zone, the 1950 (Mw 6.9) Mondy earthquake, for which several discordant focal mechanisms have been proposed. Using a new approach in source inversion, we resolve the focal mechanism (left-lateral strike slip type on a steep south-dipping fault) and depth (14 ± 3 km) of the Mondy earthquake with a satisfactory accuracy. This seismological information, combined with the geological observations, allows us to decipher the connections between the 1950 mainshock, the local stress tensor and the active faults, which strongly suggest a partitioning of the deformation between two faults, namely the Mondy and Ikhe–Ukghun faults.

We analyze observed three-component seismograms recorded by a dense array of 21 short-period receivers (f>2 Hz) installed on a homogeneous Quaternary plain with 1.5×3.5 km2 horizontal dimensions. The experiment was conducted in the district of Caille, in SE France for 3 months. The observed waveform data are related to diffraction and refraction of the direct wavefield by different geological structures and topographic morphologies surrounding the array. The origin of the coda energy following the energetic Pg or Sg arrivals is either influenced by heterogeneities close to and inside of the valley, for instance thrust of Jurassic limestones over Cretaceous marls in the northern and southern limits of the valley, or by heterogeneities located outside of the valley such as the interface unconformity between crystalline basement and sedimentary cover in the northern border of the Maures–Tanneron ranges. The main energetic arrivals of the seismograms arrive at the array with a definite range of azimuths that is not correlated with the event back-azimuth. Moreover, these arrivals do not appear with azimuths related to the characteristic NS and EW valley orientations, and thus may be related to heterogeneities located outside of the valley.

Active tectonics in the Western Alps is revealed by a moderate level of seismic activity and geological evidences for Quaternary deformation. We present new geodetic determinations of the current strain rates in the southern part of the Western Alps, that complement existing results in Provence, the Jura, and the Subalpine and Belledone massifs around Grenoble. We combined first-and second-order triangulation data collected in 1948 with global positioning system (GPS) data collected in 1998. We estimate shear strain rates of 0.1-0.2 mrad yr−1 over distances on the order of 30 km, significantly different from zero in most of the network. We obtain NW-SE to N-S compressive shear strain directions over most of the area, in agreement with the seismological and geological data. These geodetic estimates correspond to long-term overall N-S to NW-SE shortening of 2-4 mm yr−1 over the study area, on the same order as the far-field shortening measured by continuous GPS on the Grasse-Torino baseline (−2.0±0.5 mm yr−1), that incorporates our geodetic network. These results provide new constraints on interseismic strain in the Western Alps.

Although numerous transfer zones of deformation have been observed in thrust wedges, their mechanisms and conditions of development are poorly understood. In this paper three basic questions are addressed: (1) what are the parameters controlling the genesis of transfer zones?(2) what are the kinematics of thrust propagation during transfer zone development?(3) which kinds of geological structure link the two compartments on either side of the transfer zone?We attempted to solve these problems using a 3-D experimental approach. Sand models were used to simulate the foreland, a rigid, but mobile, backstop was used to produced a thrust Coulomb wedge which was studied during the various stages of its formation. Shortening led to the development of transfer zones in the wedge, separating two domains of homogenous behaviour and connecting thrust planes in different domains.The experimental results show that the development of transfer zones is controlled by mechanical and/or geometrical parameters such as: (1) variations in the sedimentary thickness in the foreland.(2) the steepness of the backstop.(3) domains with different basal friction in the foreland.(4) kinked backstop geometry.The results of analogue modelling suggest that the development of transfer zones is directly linked to variations in the boundary conditions (mechanical and/or geometrical) between two adjacent parts of a thrust wedge.

The porosity and wettability properties of hydrogen ion treated poly(tetrafluoroethylene) (PTFE) materials are related using contact angle, scanning electron microscopy (SEM) and ellipsometry techniques. PTFE samples are irradiated using a low-energy hydrogen ion shower (LEHIS) produced by a Gas Discharge Ion Source (GDIS). The plasma discharge current (Id) is varied at intervals of 1 mA. Results show that treatment using lower Id improved the hydrophobic property of the PTFE material with water contact angle increasing from 102◦ to 119◦. It also becomes less porous as indicated by the increase in the index of refraction, decrease in optical transmittance, and increased fissures and striations in the SEM images. Opposite effects are observed for higher Id.

The wettability and optical transmittance properties of hydrogen ion treated polytetrafluoroethylene (PTFE) materials were evaluated using contact angle, laser irradiation, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) tests. The materials were processed using low energy hydrogen ion shower (LEHIS) produced by a Gas Discharge Ion Source (GDIS). The duration of treatment and ion shower energy were varied to determine their effects on the PTFE specimens. Mass spectrometry showed the ion shower constituents to be H+ and H2+ species. Within the bounds of the discharge conditions, flux density for the Hn+ beam measured a minimum of 0.06 A/m2 and a maximum of 0.25 A/m2. Both one- and two-way analysis of variance were employed to assist in the interpretation of the empirical data. Results showed that treatment using lower plasma discharge currents (Id) improved material hydrophobicity with contact angles measuring a high of 115o while higher Id resulted in enhanced hydrophilicity reducing contact angles down to 61o. Transmittance and wettability were found to correlate, i.e., a surface made more wettable became optically transmissive allowing as much as 99% signal transmittance. Conversely, a
surface made more hydrophobic reduced light leakage to as low as 60%. As the material showed increased surface striations, its optical transmittance, wettability, and surface
tension also increased. With no observable shifting of the IR-absorption peaks, the surface modification was essentially morphological in character.