Abstracted/indexed

This contribution shows that soft and coal-rich sedimentary rocks in central Spitsbergen absorbed most of the (Eurekan) contractional deformation that occurred in the early Cenozoic using seismic data and fieldwork, thus suggesting that no contractional deformation event is needed in the Late Devonian to explain the deformation differences among late Paleozoic sedimentary rocks. It also shows that the Billefjorden Fault Zone, a major crack in the Earth crust in Svalbard, is probably segmented.

In NW Iberia a low grade unit separates the unrooted accretionary prism from the autochthon. It was divided in Upper (pre-orogenic) and Lower (syn-orogenic) around the Morais Complex. A review on the sedimentary sequences characteristics, supported by U-Pb ages in 17 new samples of syn-orogenic sediments and volcanic olistoliths, allows to propose this model is general for the Galicia – Trás-os-Montes Zone forming a tectonic carpet exposed in most of the Parautochthon-Autochthon limit.

The low-relief, mean-elevation BaimaXueshan massif experienced slow exhumation at a rate of 0.01 km/Myr since at least 22 Ma, then regional rock uplift at a rate of 0.25 km/Myr since ~ 10 Ma. The high-relief, high-elevation Kawagebo massif shows much stronger local rock uplift related to the motion along a west-dipping thrust fault, at a rate of 0.45 km/Myr since at least 10 Ma, accelerating to 1.86 km/Myr since 1.6 Ma. Mekong River incision plays a minor role in total exhumation in both massifs.

We performed a seismic survey in two 4.3 km deep geothermal research wells using the novel method of distributed acoustic sensing and wireline cables. The characteristics of the acquired data, methods for data processing and quality improvement, and interpretations on the geometry and structure of the sedimentary and volcanic reservoir rocks are presented. The method enables measurements at high temperatures and reduced cost compared to conventional sensors.

The Albstadt Shear Zone, SW Germany, is an active rupture zone with sometimes damaging earthquakes but no visible surface structure. To identify its segmentations, geometry, faulting pattern and extension, we analyze the continuous earthquake activity 2011–2018. We find a segmented N-S oriented fault zone with mainly horizontal and minor vertical movement along preferably NNE and some NNW oriented rupture planes. The main horizontal stress is oriented NW and due to Alpine-related loading.

In this paper we test a simplified numerical model for pyroclastic density currents or PDCs (mixtures of hot gas, lapilli and ash moving across the landscape under the effect of gravity). The aim is quantifying the differences between real and modelled deposits of some PDCs of the AD 79 eruption of Vesuvius, Italy. This step is important because in the paper it is demostrated that this simplified model is useful for constraining input parameters for more computationally expensive models.

The last lava dome eruption of Mount Unzen (Japan) ended in 1995, but ongoing instability means much of the area remains an exclusion zone. The rocks in the lava dome impact its stability; heterogeneity (contrasting properties) and anisotropy (orientation-specific properties) can channel fluids and localise deformation, enhancing the risk of lava dome collapse. We recommend using measured material properties to interpret geophysical signals and to model volcanic systems.

Using plate tectonic reconstructions and geodynamic modelling, we show that the former Piemont-Liguria Ocean, which separated Europe from Africa-Adria in the Jurassic, opened as an arm of the Central Atlantic and reached only 250 km width between Europe and Adria. Moreover, at least 65 % of the lithosphere subducted into the mantle and/or incorporated into the Alpine mountain belt during convergence in Cretaceous and Cenozoic times was highly thinned continental, while only 35 % was truly oceanic.

Vertical incidence seismic profiling on the Iberian Massif images a mid-crustal scale discontinuity at the top of the reflective lower crust. This feature shows that upper and lower crustal reflections merge into it, thus suggesting that it has often behaved as a detachment. The orogen scale extension of this discontinuity, present in Gondwanan and Avalonian affinity terranes into the Iberian Massif demonstrates its relevance, leading us to interprete it as the Conrad Discontinuity.

We identified several problems in the Urbani et al. (2020) study, showing that their model does not conform to the age and location of faulting, identification and delimitation of uplifted areas and apical depressions, temperature and lithological wells log, and stratigraphic and radiometric data. Published data indicate that the pressurization of the LHVC magmatic/hydrothermal system driving resurgence faulting occurs at greater depth.

The Auckland Volcanic Field is monitored by a seismic network. The lockdown measures to combat COVID-19 in New Zealand proved an opportunity to evaluate the performance of the seismic stations in the network, and to search for small(er) local earthquakes, potentially hidden in the noise during normal times.

2D high-resolution seismic profiles are acquired in north and south of the Chibougamau area, Quebec, Canada located at north-east of the Abitibi Greenstone belt. The Chibougamau area mostly includes volcanic rocks and both profiles cross over several fault zones. The seismic method is acquired to image subsurface down to depth of 12 km. The main target of this study is to image major faults and geological formation in connection to those faults to investigate metal endowment in the area.

In this work, we combined different imaging and experimental measuring methods for analysis of cross-scale effects which reduce permeability of tight reservoir rocks. Simulated permeability of digital images of rocks is often overestimated which is caused by non-resolvable clay content within the pores of a rock. By combining FIB-SEM with micro-XCT imaging, we were able to simulate the true clay mineral abundance to match experimental measured permeability with simulated permeability.

This paper presents a trans-disciplinary approach bridging the gap between observations of instabilities from the molecular scale to the very large scale. We show that all scales communicate via propagation of volumetric deformation waves. Similar phenomena are encountered in quantum optics where wave collisions can release sporadic bursts of light. Ocean waves show a similar phenomenon of rogue waves that seem to come from nowhere. This mechanism is proposed to be the trigger for earthquakes.

Earthquakes cause rapid deformation that have long-term effects on the Earth's crust. We studied the most abundant mineral, feldspar, in the vicinity of an earthquake to unravel its deformation history. With microscopy we found internal nm-scale structures that indicate a history of high stress and destruction of the feldspar atomic makeup. This was quickly followed by high temperature and rapid healing of the damage. Our findings illustrate the intense conditions imposed on rocks by earthquake.

Distributed Acoustic Sensing (DAS) is an emerging technology that measures stretching of an optical-fibre cable. This technology can be used to record the ground shaking of earthquakes, which offers a cost-efficient alternative to conventional seismometers. Since DAS is relatively new, we need to verify that existing seismological methods can be applied to this new data type. In this study, we reveal several issues by comparing DAS with conventional seismometer data for earthquake localisation.

During the COVID-19 pandemic, most countries put in place social interventions, aimed at restricting human mobility, which caused a decrease in the seismic noise, generated by human activities and called anthropogenic seismic noise. In particular, in the densely populated Eastern Sicily, we observed a decrease in the seismic amplitude reaching 50 %. We also found an impressive similarity between the patterns of this seismic noise and human mobility, as quantified by the mobile phone-derived data.

Constraining the conditions at which rocks form is crucial for understanding geologic processes. For years, the conditions under which rocks from Syros, Greece formed, have remained enigmatic; yet, these rocks are fundamental for understanding processes occurring at the interface between colliding tectonic plates (subduction zones). Here, we constrain conditions under which these rocks formed, and show they were transported to the surface adjacent to the down-going (subducting) tectonic plate.

In the Pitoa-Figuil area (Northern Cameroon), an interpretation of aeromagnetic data was conducted with an aim of investigating lineaments hidden under geological formations and proposing subsurface structures through a 2.75D modelling. A multiscale analysis combines with the 2.75D modelling has lead to put in evidence 18 faults and some intrusive bodies. According to Euler's solutions, anomaly sources go up to a depth of 5.3 km.

As a result of the collision between the European and Apulian plates, the Alps have experienced several evolutionary stages. The Penninic Frontal Thrust (PFT) (major thrust) was associated to compression and now seismic studies show ongoing extensional activity. Calcite mineralisations associated to extension and compresionnal strucures were sampled. Last deformation stage is dated by U-Pb at 4.9–2.3 Ma and isotopes analysis evidence deep crustal fluid's mobilisation.

Dynamic change of aeolian landforms and desertification under global warming is a typical problem of climate change and landscape response. In the past half century, the warming and humidification of local climate caused a potential trend of anti-desertification in the Hexi Corridor, indicating a control of climate change but not human activities. However, restriction of the decline of groundwater is the only key to preventing desertification in oasis areas of arid environment, but not climate.

We have analysed the role of deep salt layers during tectonic shortening of a group of sedimentary basins buried below the North Sea. Due to the ability of salt to flow over geological timescales, the salt layers are much weaker than the surrounding rocks during tectonic deformation. Therefore, complex structures formed mainly where salt was present in our study area. Our results align with findings from other basins and experiments, underlining the importance of salt tectonics.

Serpentinite, generated by the hydration of ultramafic rocks, is thought to be related to slow earthquakes in the mantle wedge, although its mechanism is not fully understood yet. We conducted friction experiments on brucite, one of the main minerals of serpentinite, and found that brucite exhibits low and unstable friction under the low effective normal stress condition. This result suggests that brucite can be a key for slow earthquakes in the hydrated mantle wedge.