Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone

International audienceFault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging‐wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP‐2). We present observational evidence for extensive fracturing and high hanging‐wall hydraulic conductivity (∼10−9 to 10−7 m/s, corresponding to permeability of ∼10−16 to 10−14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP‐2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging‐wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off‐fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation

Geophysical characterisation of the Alpine Fault at Haast, Turnbull and Whataroa, New Zealand

The geometry of the upper-crustal portion of the Alpine Fault, the Australian-Pacific plate boundary on the South Island of New Zealand, is poorly constrained by geophysical studies where it cuts through the young sedimentary units of the coastal plain. Excellent accessibility on the vast mainly flat coastal floodplain at Haast, Turnbull and Whataroa region provides rare opportunity to undertake geophysical surveys along the Alpine Fault of New Zealand. In 2009, two seismic reflection lines were collected to better image the upper km or so of the Alpine Fault in the vicinity of the surface scarps of the most recent, but still prehistoric, ruptures south of the Haast River. Both profiles were running perpendicular to the fault extend to 2.5 km in length along the Turnbull River and 3.3 km at Haast. Analysis of these lines suggests that multiple strands of the fault have been active during the Holocene. The fault strands cut across sub-parallel strata, interpreted to represent at least seven regionally identifiable sequences that correspond to the accumulation of Holocene sediments following the last glacial retreat. Total combined vertical throw on the fault strands is consistent with expected uplift rates on the fault. Dip on the fault strands is interpreted to be between 53 and 74° SE. The WhataDUSIE-2D seismic profile was collected in early 2011. The project led by researchers from the University of Otago, TU Bergakademie Freiberg (Germany) and the University of Alberta (Canada), provided relatively high-resolution coverage (4-8 m geophone spacing, 25-100 m shot spacing) along a ~5.1 km long profile across the Alpine Fault in the Whataroa Valley. Several technical difficulties arose during data collection and data processing. However, combination of CMP stacking and ray-theoretical travel time inversion methods provided detailed insight of a dynamic and complex geological setting. High-resolution seismic data imaged the uppermost part (~2-3 km) of the hanging wall of the Alpine Fault and show the bedrock topography eroded by glacial processes from the Last Glacial Maximum, which went through a rapid deposition process and filled with 200-400 m thick post-glacial sediments and outwash gravels. Several dipping reflectors, which likely associate to the Alpine Fault damage zone have been modelled dipping to ~40 – 42° SE in 600 m wide zone at depths of 1500 – ~2500 m. Two additional phases were modelled against dipping reflectors distributed in a ~1000-m-wide area dipping ~16° SE at the SE end of the transect. These features are likely positioned oblique to the 2D profile, therefore projecting the exact location of the reflectors is not possible by the data. These reflectors may indicate a potentially wide fractured damage zone

Geophysical characterisation of the Alpine Fault at Haast, Turnbull and Whataroa, New Zealand

The geometry of the upper-crustal portion of the Alpine Fault, the Australian-Pacific plate boundary on the South Island of New Zealand, is poorly constrained by geophysical studies where it cuts through the young sedimentary units of the coastal plain. Excellent accessibility on the vast mainly flat coastal floodplain at Haast, Turnbull and Whataroa region provides rare opportunity to undertake geophysical surveys along the Alpine Fault of New Zealand. In 2009, two seismic reflection lines were collected to better image the upper km or so of the Alpine Fault in the vicinity of the surface scarps of the most recent, but still prehistoric, ruptures south of the Haast River. Both profiles were running perpendicular to the fault extend to 2.5 km in length along the Turnbull River and 3.3 km at Haast. Analysis of these lines suggests that multiple strands of the fault have been active during the Holocene. The fault strands cut across sub-parallel strata, interpreted to represent at least seven regionally identifiable sequences that correspond to the accumulation of Holocene sediments following the last glacial retreat. Total combined vertical throw on the fault strands is consistent with expected uplift rates on the fault. Dip on the fault strands is interpreted to be between 53 and 74° SE. The WhataDUSIE-2D seismic profile was collected in early 2011. The project led by researchers from the University of Otago, TU Bergakademie Freiberg (Germany) and the University of Alberta (Canada), provided relatively high-resolution coverage (4-8 m geophone spacing, 25-100 m shot spacing) along a ~5.1 km long profile across the Alpine Fault in the Whataroa Valley. Several technical difficulties arose during data collection and data processing. However, combination of CMP stacking and ray-theoretical travel time inversion methods provided detailed insight of a dynamic and complex geological setting. High-resolution seismic data imaged the uppermost part (~2-3 km) of the hanging wall of the Alpine Fault and show the bedrock topography eroded by glacial processes from the Last Glacial Maximum, which went through a rapid deposition process and filled with 200-400 m thick post-glacial sediments and outwash gravels. Several dipping reflectors, which likely associate to the Alpine Fault damage zone have been modelled dipping to ~40 – 42° SE in 600 m wide zone at depths of 1500 – ~2500 m. Two additional phases were modelled against dipping reflectors distributed in a ~1000-m-wide area dipping ~16° SE at the SE end of the transect. These features are likely positioned oblique to the 2D profile, therefore projecting the exact location of the reflectors is not possible by the data. These reflectors may indicate a potentially wide fractured damage zone

Protection du droit à la vie privée et du droit à la protection des données des salariés sur les réseaux sociaux en ligne : en particulier en France et en Hongrie

Les sites de réseaux sociaux en ligne ont acquis une importance considérable dans la vie quotidienne. Leur utilisation conduit à une circulation sans précédent de données personnelles : des individus du monde entier partagent des données à caractère personnel dans une qualité et une quantité jamais vues auparavant. Parmi les utilisateurs de ces réseaux sociaux en ligne se trouvent des salariés et des candidats à l’embauche. Cela pose des problèmes spécifiques dans le contexte de l'emploi en ce qui concerne la vie privée et la protection des données. Bien que les moyens « traditionnels » de surveillance des salariés, tels que la surveillance CCTV ou encore la surveillance de l'utilisation d'internet et du courrier électronique, soient déjà réglementés à la fois au niveau international et au niveau national (français et hongrois), la réglementation complète des réseaux sociaux en ce qui concerne le contexte de l'emploi nécessite encore une élaboration. Les sites de réseaux sociaux ont fondamentalement influencé les conceptions de la vie privée et de la protection des données, ce qui a pour conséquence une dilution des limites entre vie professionnelle et vie personnelle, tant pendant qu'au-delà des heures de travail. Or, le traitement des données personnelles des réseaux sociaux pose de plus en plus la question de la protection des droits des salariés, et notamment la protection du droit au respect de la vie privée et du droit à la protection des données. Ces droits doivent être mis en balance avec les pouvoirs de l'employeur, qui découlent du droit de l'employeur à la propriété (s'assurer que l'équipement fourni par l'employeur est utilisé conformément à la finalité de la relation de travail), du droit de protéger son intérêt économique (par exemple en assurant la productivité, la protection de la réputation) ou encore de la sécurité et la santé au travail (ce qui confère des obligations à l'employeur). Ainsi, la thèse examine comment les règles existantes du droit du travail et du droit de la protection des données en France et en Hongrie peuvent être appliquées aux sites de réseaux sociaux et quels sont les principaux défis qu'ils posent, notamment dans la phase de recrutement et en ce qui concerne l'utilisation des réseaux sociaux pendant et en dehors des heures de travail. La principale question à laquelle la thèse répond est la suivante : à la lumière des frontières de plus en plus floues entre vies privée et professionnelle, où trouver un équilibre entre les droits des salariés et ceux de l'employeur en matière d’usage des réseaux sociaux numériques et des données qui y sont produites ?Online social network sites have gained considerable importance in everyday life. Their use results in the unprecedented share of personal data : individuals from all over the globe share personal information in a quality and quantity never seen before. Employees and prospective employees are amongst users as well, which raises privacy and data protection issues specific to the context of employment. Although the “traditional” ways of employee monitoring, such as CCTV surveillance, monitoring of the use of Internet and e-mail, etc. are already regulated both at the international and at the national (French and Hungarian) level, the comprehensive regulation of social network sites with regard to the context of employment is yet to be elaborated. Social network sites have fundamentally influenced conceptions of privacy and data protection, resulting in the boundaries of work and personal life becoming increasingly blurred, both within and outside working hours. Yet, the processing of personal data obtained from social network sites increasingly raises the question of the protection of employees’ rights – particularly the protection of the right to privacy and the right to data protection. These rights must be balanced notably against the employer’s right to control and monitor, which ensue from the employer’s right to property (ensuring the equipment provided by the employer is used in accordance with the purpose of the employment relationship), the right to protect his/her economic interest (e.g. through ensuring productivity, the protection of reputation) and occupational safety and health (which confers obligations on the employer). Thus, the dissertation examines how the existing rules of labour law and of data protection law in France and in Hungary can be applied to social network sites and what the main challenge posed by them are, particularly in the phase of recruitment and during the use of social networks during and outside working hours. The main question to be answered by the dissertation is: in the light of the increasingly blurred boundaries, where should the balance be struck between the employees’ and the employer’s rights?Az online közösségi oldalak jelentős szerepet játszanak a mindennapi életben. Használatuk során az egyének soha nem látott minőségben és mennyiségben osztják meg személyes adataikat, szerte az egész világon. A munkavállalók és a leendő munkavállalók szintén a felhasználók közé tartoznak, ami a foglalkoztatás kontextusában specifikus kérdéseket vet fel a magánélet és a személyes adatok védelme terén. Bár a munkavállalók megfigyelésének „hagyományos” módszereit, mint például a kamerás megfigyelést, az internet és az e-mail használatának megfigyelését, már mind nemzetközi, mind tagállami (francia és magyar) szinten szabályozzák, a közösségi oldalak foglalkoztatással összefüggő kimerítő szabályozása még kidolgozás alatt áll. A közösségi hálózati oldalak alapjaiban hatnak a magánéletre és a személyes adatok védelmére, aminek eredményeként a munka és magánélet határai egyre inkább elmosódnak, mind a munkaidőn belül, mind azon kívül. Ugyanakkor a közösségi oldalakról származó személyes adatok kezelése fokozottan felveti a munkavállalók jogainak védelmének kérdését – különös tekintettel a magánélet védelmére és a személyes adatok védelméhez való jogra. Ezeket a jogokat össze kell vetni különösen a munkáltató ellenőrzési és felügyeleti jogával, amely a munkáltató tulajdonhoz fűződő jogából (pl.: annak biztosítása, hogy a munkáltató által biztosított felszerelést a munkavállaló a munkaviszony céljának megfelelően használja), valamint a jogos gazdasági érdekeinek védelméből. (pl. produktivitás biztosítása, jó hírnév védelme) és a munkahelyi biztonság és egészségvédelemből (amely kötelezettségeket ró a munkáltatóra) következik. Következésképp, a disszertáció azt vizsgálja, hogy a Franciaországban és Magyarországon már létező munkajogi és adatvédelmi rendelkezések miként alkalmazhatók a közösségi oldalakra, és melyek az általuk felvetett legfőbb kihívások, különösen a munkaerőfelvétel, valamint a közösségi oldalak munkaidőben és azon kívül történő használata terén. A disszertáció által megválaszolandó fő kérdés az, hogy a fokozottan elmosódó határok fényében hol kell megtalálni az egyensúlyt a munkavállalók és a munkáltatók jogai között

Extreme hydrothermal conditions at an active plate-bounding fault

Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre. At temperatures above 300-450 degrees Celsius, usually found at depths greater than 10-15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional-mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults

Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone

Fault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging-wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP-2). We present observational evidence for extensive fracturing and high hanging-wall hydraulic conductivity (∼10−9 to 10−7 m/s, corresponding to permeability of ∼10−16 to 10−14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP-2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging-wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off-fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation

Extreme hydrothermal conditions at an active plate-bounding fault

Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes1. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre2,3. At temperatures above 300–450 degrees Celsius, usually found at depths greater than 10–15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional–mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades4,5. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults