Field trips in the Stratigraphy, Structure, Tectonics (SST) course transitioned to a virtual format in Fall 2020, due to the COVID pandemic. Virtual field experiences (VFEs) were developed in web Google Earth and were evaluated in comparison with on-location field trips via an online survey. Students recognized the value of VFEs for revisiting outcrops and noted improved accessibility for students with disabilities. Potential benefits of hybrid field experiences were also indicated.
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Fluid flow through rock occurs in many geological settings on different scales, at different temperature conditions and with different flow velocities. Fluid is eitherin local thermal equilibrium with the host rock or not. We explore the parameters of porous flow and give scaling laws. These allow to decide whether porous flows are in thermal equilibrium or not. Applied to magmatic systems moving melts in channels or dyke moderately to strongly deviate from thermal equilibrium, respectively.
We use the Minerve virtual reality software to bring undergraduate students to an unusual field trip at 1200 m below sea level in the Lesser Antilles area. This region is located above an active subduction zone responsible for intense volcanic and seismic activity. In particular, we focus on the Roseau submarine fault that ruptured during the Mw 6.3 Les Saintes earthquake and presented a fresh scarp that the students can analyze and map in VR. They compile their results in a GIS project.
Roman V. Sidorov, Mikhail K. Kaban, Anatoly A. Soloviev, Alexei G. Petrunin, Alexei D. Gvishiani, Alexei A. Oshchenko, Anton B. Popov, and Roman I. Krasnoperov
In the present study, the structure of sedimentary basins in the eastern Asia Arctic zone is analysed by employing the approach based on decompensative gravity anomalies. Two obtained models of thickness and density of sediments in the study area display significant changes in the thickness and distribution of sedimentary rocks revealed for some particular basins. The new results improve our knowledge about the region, providing a better understanding of the evolution of the sedimentary basins.
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Earthquake extent prediction is limited by our poor understanding of slip deficit patterns. From a mechanical analysis applied along the Chilean margin, we show that earthquakes are bounded by extensive plate interface deformation. This deformation promotes stress build-up leading to earthquake nucleation, earthquakes then propagate along smoothed fault planes, and are stopped by heterogeneously distributed deformation. Slip deficit patterns reflect the spatial distribution of this deformation.
Amir Kalifi, Philippe Hervé Leloup, Philippe Sorrel, Albert Galy, François Demory, Vincenzo Spina, Bastien Huet, Frédéric Quillévéré, Frédéric Ricciardi, Daniel Michoux, Kilian Lecacheur, Romain Grime, Bernard Pittet, and Jean-Loup Rubino
Molasse deposits, deposited and deformed at the western Alpine front during the Miocene (23 to 5.6 Ma), record the chronology of that deformation. We combine the first precise chronostratigraphy (precision of ∼0.5 Ma) of the Miocene molasse, the reappraisal of the regional structure, and the analysis of growth deformation structures in order to document three tectonic phases and the precise chronology of thrust westward propagation during the second one involving the Belledonne basal thrust.
One of the present-day challenges for geoscientists is tackling the big data revolution. An ever-growing amount of data needs to be processed and data are subjectively handled before using them to make inferences on the Earth’s interior. But imposing subjective decisions on the data might have strong influences on the final outputs. Here we present a totally novel and automatic application for screening the data and for defining data volumes that are consistent with physical hypotheses.
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Glacial Isostatic Adjustment is considered as a major process of seismicity in intraplate regions such as Scandinavia and eastern North America. We show that GIA associated with the alpine icecap induces a present-day response in vertical motion and horizontal deformation seen in GNSS strain rate field. We show that GIA induced stress is opposite to strain rate, with the paradoxical consequence that postglacial rebound in the Western Alps can explain the strain rate field but not the seismicity.
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In passive seismic measurement, all noise sources from environment, such as traffic, vibrations caused by distant excavation and explosive work from underground mine are utilized. In the Kylylahti experiment, receivers were recording ambient noise (AN) sources for 30 days. These recordings were subjected to data analysis and processing using novel methodology developed in our study and used for imaging of the subsurface geology of the Kylylahti mine area.
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Several alternative gravity modelling techniques and associated numerical codes with their own advantages and limitations are available for the Solid Earth community. With the upcoming state-of-the-art lithosphere density models and accurate global gravity field data sets it is vital to understand the differences of the various approaches. In this paper, we discuss the four widely used techniques: spherical harmonics, tesseroid integration, triangle integration, and hexahedral integration.
Passive seismic imaging methods use natural earthquakes as seismic sources, while in active seismic imaging methods, artificial sources (e.g. explosives) are used to generate seismic waves. We imaged some structures related to a major fault plane through a passive seismic imaging approach using microearthquakes with magnitudes smaller than 0.9 (Mw). These structures have not been illuminated by a previously conducted 3D active seismic survey due to their large dip angles.
The Alpine mountain belt was formed by the collision of the Eurasian and African plates in the geological past, during which parts of the colliding plates sank into the earth's mantle. Using seismological data from distant earthquakes recorded by the AlpArray Seismic Network, we have derived an image of the current location of these subducted parts in the earth's mantle. Their quantity and spatial distribution is key information needed to understand how the Alpine orogen was formed.
New images from the multi-national AlpArray experiment illuminate the Alps from below. They indicate thick European mantle descending beneath the Alps and forming blobs that are mostly detached from the Alps above. In contrast, the Adriatic mantle in the Alps is much thinner. This difference helps explain the rugged mountains and the abundance of subducted and exhumed units at the core of the Alps. The blobs are stretched remnants of old ocean and its margins that reach down to at least 410 km.
Emilija Krsnik, Katharina Methner, Marion Campani, Svetlana Botsyun, Sebastian G. Mutz, Todd A. Ehlers, Oliver Kempf, Jens Fiebig, Fritz Schlunegger, and Andreas Mulch
Here we present new surface elevation constraints for the middle Miocene Central Alps based on stable and clumped isotope geochemical analyses. Our reconstructed paleoelevation estimate is supported by isotope-enabled paleoclimate simulations and indicates that the Miocene Central Alps were characterized by a heterogeneous and spatially transient topography with high elevations locally exceeding 4000 m.
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Underground energy and waste storage require re-purposing of existing oil and gas wells for gas storage; compressed air, hydrogen, methane and CO2 disposal, requiring an impermeable cap rock (e.g. shales) over the porous reservoir. We measured shale permeability over a range of burial pressures and gas pore pressures. Permeability decreases markedly as effective pressure on the rocks is increased. Knowing these relationships is essential to the safe design of engineered gas reservoirs.
Felix N. Wolf, Dietrich Lange, Anke Dannowski, Martin Thorwart, Wayne Crawford, Lars Wiesenberg, Ingo Grevemeyer, Heidrun Kopp, and the AlpArray Working Group
The Ligurian Sea opened ~30–15 Ma during SE migration of the Calabrian subduction zone. Using ambient seismic noise from stations on land and at the ocean bottom, we calculated a 3D shear-velocity model of the Ligurian Basin. In keeping with existing 2D studies, we find a shallow crust–mantle transition at the SW basin centre that deepens towards the northeast, Corsica, and the Liguro-Provençal coast. We observe a separation of SW and NE basins. We do not observe high crustal vP/vS ratios.
Past strong earthquakes can produce topographic deformations, often memorized in Quaternary sediments, which are typically studied by paleoseismologists through trenching. Using a ground-penetrating radar (GPR), we unveiled possible buried Quaternary faulting in the Mt. Pollino seismic gap region (southern Italy). We aim to contribute to seismic hazard assessment of an area potentially prone to destructive events as well as promote our workflow in similar contexts around the world.
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1. Based on observations of the CL images and chemical analysis, two zircon growth stages in a magmatism can be distinguished. 2. Melting of a high Sr/Y (and La/Yb) source is an important process for the generation of Yanshanian high Sr/Y rocks in the NCC. 3. The granite formed in a compressional environment related to subduction.
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We study time varying vertical deformation signals in the European Alps by analyzing GNSS position time series. We associate each deformation signal to geophysical forcing processes, finding that atmospheric and hydrological loading are by far the most important cause of seasonal displacements, together with temperature-related processes. Recognizing and filtering out non-tectonic signals allows us to improve the accuracy and precision of the vertical velocities.
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We demonstrate the applicability of vertical seismic profiling (VSP) acquired using wireline distributed acoustic sensing (DAS) technology for deep geothermal reservoir imaging and characterisation. Borehole DAS data provides critical input for seismic interpretation and helps assess small-scale geological structures. This case study can be used as a basis for detailed structural exploration of geothermal reservoir and provide insightful information for the geothermal exploration projects.
Martin Thorwart, Anke Dannowski, Ingo Grevemeyer, Dietrich Lange, Heidrun Kopp, Florian Petersen, Wayne C. Crawford, Anne Paul, and the AlpArray Working Group
We analyse broadband ocean bottom seismometer data of the AlpArray OBS network in the Ligurian Basin. Two earthquake clusters with thrust faulting focal mechanisms indicate compression of the rift basin. The locations of seismicity suggest reactivation of pre-existing rift structures and strengthening of crust and uppermost mantle during rifting-related extension. Slightly different striking directions of faults may mimic the anti-clockwise rotation of the Corsica–Sardinia block.
In this paper, we dated fault movements at geological timescales which uplifted the sedimentary successions of the Jura Mountains from below the sea level up to Earth's surface. To do so, we applied the novel technique of U–Pb geochronology on calcite mineralizations that precipitated on fault surfaces during times of tectonic activity. Our results document a time frame of the tectonic evolution of the Jura Mountains and provide new insight into the broad geological history of the Western Alps.
After an earthquake, the fault continues to slip for days to months. Yet, little is know about the very early part of this phase (i.e., minutes to hours). We have looked at what happens just after an earthquake in Chile from 2015. We find that the fault responds in two ways: south of the rupture zone it slips seismically in the form of aftershocks, while north of the rupture zone it slips slowly. Early inference of such bimodal behavior could prove to be useful for forecasting aftershocks.
Robert Jackisch, Björn Henning Heincke, Robert Zimmermann, Erik Vest Sørensen, Markku Pirttijärvi, Moritz Kirsch, Heikki Salmirinne, Stefanie Lode, Urpo Kuronen, and Richard Gloaguen
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We integrate UAS-based magnetic and remote sensing mineral exploration data with legacy exploration data of a Ni-Cu-PGE prospect on Disko Island, West Greenland. The basalt unit has a complex magnetization, and we use a 3D magnetic vector inversion on the UAS magnetics to estimate magnetic properties and spatial dimensions of the mineralized unit. Our 3D modelling reveals a horizontal sheet and a strong remanent magnetization component. We highlight the advantage of UAS in rugged terrain.
A large amount of new seismic data from the greater Alpine area have been obtained within the AlpArray and SWATH-D projects. S-to-P converted seismic phases from the Moho and from the mantle lithosphere have been processed with a newly developed method. Examples of new observations are a rapid change in Moho depth at 13° E below the Tauern Window from 60 km in the west to 40 km in the east and a second Moho trough along the boundary of the Bohemian Massif towards the Western Carpathians.
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The local topographic slope of an accretionary prism is often used to determine the effective friction on subduction megathrust. We investigate how the brittle-ductile and the smectite-illite transitions affect the topographic slope of an accretionary prism and its internal deformation to provide clues to determine the origin of observed low topographic slopes in subduction zones. We finally discuss their implications in terms of the fore-arc basin and fore-arc high genesis and nature.
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Novel methods for mineral exploration play an important role in future resource exploration. The methods have to be environmentally friendly, socially accepted, and cost effective by integrating multidisciplinary methodologies. We investigate the potential of passive, ambient noise tomography combined with 3D airborne electromagnetics for mineral exploration in Geyer, Germany. We show that the combination of both geophysical data sets has a promising potential for future mineral exploration.
As continental plates collide, mountain belts grow. This study investigated the provenance of rocks from the northwestern segment of the Zagros mountain belt to unravel the convergence history of the Arabian and Eurasian plates. Provenance data synthesis and field relationships suggest that the Zagros Mountains developed as a result of the oceanic crust emplacement on the Arabian continental plate, followed by the Arabia–Eurasia collision and later uplift of the broader region.
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We propose and apply a workflow to combine the modelling and interpretation of magnetic anomalies and resistivity anomalies to better image the basement. We test the method on a synthetic case study and apply it to real world data from the Cloncurry area (Queensland, Australia), which is prospective for economic minerals. Results suggest new interpretation about the composition and structure towards to east of the profile that we modelled.
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Sediments can play an important role in global volatile and tectonic cycles, yet their effect on subduction dynamics is poorly resolved. In this study, we investigate how sediment properties influence subduction dynamics, and obtain accretionary or erosive style margins. Results show that even a thin layer of sediments can exert a profound influence on the emergent regional-scale subduction dynamics.
The 2 June 1994 Java tsunami earthquake ruptured in a seismically quiet subduction zone and generated a larger-than-expected tsunami. Here, we re-process a seismic line across the rupture area. We show that a subducting seamount is located up-dip of the mainshock in a region that did not rupture during the earthquake. Seamount subduction modulates the topography of the marine forearc and acts as a seismic barrier in the 1994 earthquake rupture.