HVSR prospecting in multi-layered environments: An example from the Tyrnavos Basin (Greece)

The Tyrnavos Basin (Central Greece) is an E-W trending graben bordered by two major antithetic sets of right-stepping dip-slip normal faults that began forming during Middle Pleistocene as a consequence of the N-S extension which affected the whole Aegean Region. This Quaternary structure is superimposed on the Pliocene-Early Pleistocene NW-SE trending Larissa Basin, approximately 700–800 m deep. Seismic activity is instrumentally well documented within and surrounding the investigated area. Based on structural, morphotectonic and palaeoseismological data, several structures previously characterised as active faults have been investigated by applying the HVSR method. This method is commonly used to map the thickness of sedimentary layers in a basin based on the variation of the fundamental 1-D frequency. The polyphased structural evolution and the consequently complex geological setting do not allow for the contouring of a unique continuous surface. We therefore developed a new interpretation technique for statistically significant HVSR peaks, in order to obtain 2-D sections that can be interpreted in a seismic-like fashion. We applied this technique across the major active faults bordering the basin. The results confirm their occurrence at depth and document the important vertical component of displacement.     

晚太古代Sanukite（赞岐岩）与地球早期演化

Shirey and Hanson(1984)将某些太古代的高镁闪长岩套称为sanukite(赞岐岩),类似于日本中新世(11～15Ma)Setouchi火山岩带的高镁安山岩。Sanukitoids由闪长岩-二长闪长岩-花岗闪长岩组成,不同于TTC岩套(奥长花岗岩-英云闪长岩-花岗闪长岩)。Sanukitoids具有下列地球化学特征:富Mg,Mg~#>0.60,Ni和Cr>100μg/g,Sr和Ba>500μg/g,LREE富集(大于球粒陨石100倍),无Eu异常。高镁安山岩在太古代很少见,而其相应的侵入岩高镁闪长岩或sanukitoids,虽然数量也很少,但却是各地晚太古代地体中随处可见的。Sanukitoids的原始岩浆是交代的地幔楔部分熔融形成的,随后可能经历了广泛的分离结晶作用。TTC和sanukitoids岩套可以相伴产出,二者均与板片熔融有关,TTG与其直接有关,sanukitoids可能与其间接有关。全球Sanukitoids主要集中在晚太古代时期,可能暗示板块的消减作用在～3.0Ga以后才起了重要的作用。     

Overburden deformation associated with halokinesis in the Southern North Sea: implications for the origin of the Silverpit Crater

Gravitational collapse in response to the creation of salt swells and diapirs is a common phenomenon within regions such as the Southern North Sea. Although collapse faulting and slumping of linear salt swell flanks has previously been documented, the existence of concentric collapse structures surrounding diapirs and isolated salt lows is a recently recognised feature. 3-D seismic data from the Southern North Sea demonstrates that concentric collapse faulting around both diapirs and subcircular salt lows is common. The recognition of concentric collapse structures formed in response to salt withdrawal, and adjacent inflation, provides an alternative mechanism for the origin of the proposed Silverpit impact crater.     

Fold-Thrust-Belt Structure of the Proterozoic Eastern Ghats Mobile Belt: A Proposed Correlation Between India and Antarctica in Gondwana

The Proterozoic Eastern Ghats Mobile Belt along the east coast of India shares a thrusted lower contact with the surrounding cratons. The thrust, known as the Terrane Boundary shear zone, is associated with two large lateral ramps resulting in a curved outline on the northwestern corner of the mobile belt. The Eastern Ghats Mobile Belt is divided into two lithotectonic units, the Lathore Group and the Turekela Group, based on their lithological assemblages and deformational history. On the basis of published data from a Deep Seismic Sounding (DSS) profile of the Eastern Ghats crust, the Terrane Boundary Shear Zone is considered to be listric in nature and acts as the sole thrust between craton and mobile belt. The Lathore and Turekela Groups are nappes. With this structural configuration the NW part is described as a fold thrust belt. However, the thrusting postdates folding and granulite metamorphism that occurred in the Eastern Ghats, as in the Caledonide type of fold thrust belt of NW Scotland. The Terrane Boundary Shear Zone is interpreted to be contiguous with the Rayner-Napier boundary of the Enderby Land in a Gondwana assembly.     

L'accident du Toulourenc : une limite tectonique entre la plate-forme provençale et le Bassin vocontien à l'Aptien–Albien (SE France)

The WNW–ESE trending Toulourenc Fault Zone (TFZ) is the western segment of the major Ventoux–Lure Fault Zone, which separates the Provençal platform from the Baronnies Vocontian Basin. The TFZ was subject to polyphased Mid-Cretaceous movements, during the Early Aptian and Middle–Late Albian times. The latter faulting episode generated conglomerates and olistoliths resulting from dismantled faultscarps cutting Barremian–Bedoulian limestones. The deformation is related to compressional wrench faulting (NE–SW sinistral faults; dextral component for the TFZ). It induced the uplift of the northwestern corner of the platform, as indicated by a mid-Cretaceous hiatus (Early Aptian pro parte to Early Albian) narrowly delimited in space. The opening of submeridian grabens within the platform favoured the northward transit of channelised coarse-grained Albian sands originating from a southern area. To cite this article: C. Montenat et al., C. R. Geoscience 336 (2004).     

Coastal neotectonics in Southern Central Andes: uplift and deformation of marine terraces in Northern Chile (27°S)

Neotectonic observations allow a new interpretation of the recent tectonic behaviour of the outer fore arc in the Caldera area, northern Chile (27°S). Two periods of deformation are distinguished, based on large-scale Neogene to Quaternary features of the westernmost part of the Coastal Cordillera: Late Miocene to Early Pliocene deformations, characterized by a weak NE–SW to E–W extension is followed by uppermost Pliocene NW–SE to E–W compression. The Middle Pleistocene to Recent time is characterized by vertical uplift and NW–SE extension. These deformations provide clear indications of the occurrence of moderate to large earthquakes. Microseismic observations, however, indicate a lack of shallow crustal seismicity in coastal zone. We propose that both long-term brittle deformation and uplift are linked to the subduction seismic cycle.     

Origin of the salt valleys in the Canyonlands section of the Colorado Plateau: Evaporite-dissolution collapse versus tectonic subsidence

The salt valleys over the axis of the salt-cored anticlines in the Paradox fold and fault belt (Canyonlands, Utah and Colorado) are created by subsidence of the anticline crests. Traditionally, the collapse of the anticlinal crests was attributed to dissolution of the salt walls (diapirs) forming the anticline cores. Recent studies based on scaled physical models and field observations propose that the salt valleys are a result of regional extension and that salt dissolution had only a minor influence in the development of the axial depressions. This paper presents several arguments and lines of evidence that refute the tectonic model and support the salt dissolution subsidence interpretation.The development of contractional structures in salt dissolution experiments led the advocates of the tectonic interpretation to reject the dissolution-induced subsidence explanation. However, these salt dissolution models do not reproduce the karstification of salt walls in a realistic way, since their analog involves removal of salt from the base of the diapirs during the experiments. Additionally, numerous field examples and laboratory models conducted by other authors indicate that brittle subsidence in karst settings is commonly controlled by subvertical gravity faults.Field evidence against the regional extension model includes (1) a thick cap rock at the top of the salt walls, (2) the concentration of subsidence deformation structures along the crest of the anticlines (salt walls), (3) deformational structures not consistent with the proposed NNE extension, like crestal synforms and NE–SW grabens, (4) dissolution-induced subsidence structures controlled by ring faulting, revealing deep-seated dissolution, (5) large blocks foundered several hundred meters into the salt wall, (6) evidence of recent and active dissolution subsidence, and (7) the aseismic nature of the recently active collapse faults. Although underground salt dissolution seems to be the main cause for the generation of the salt valleys, this phenomenon may have been favored by regional extension tectonics that enhance the circulation of groundwater and salt dissolution.