ALBERT

Description: 〈b〉Seismic Hazard of L'Aquila downtown (central Italy): new insights for 3D geological model based on high-resolution seismic reflection profile and borehole stratigraphy〈/b〉〈br〉 Marco Tallini, Marco Spadi, Domenico Cosentino, Marco Nocentini, Luca Macerola, Giuseppe Cavuoto, and Vincenzo Di Fiore〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-25,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 The interpretation of a 1 km-long high-resolution seismic reflection profile integrated with borehole stratigraphy was useful to reconstruct the geological subsoil model of L'Aquila downtown which was struck by the 6/4/2009 Mw 6.1 earthquake, and thus to provide indication on the seismic site effects and the faults activity. This information was essential to design urban masterplan able to mitigate the Seismic Hazard of cultural heritage cities of central Italy, such as the case study site.

Description: 〈b〉Precision of continuous GPS velocities from statistical analysis of synthetic time series〈/b〉〈br〉 Christine Masson, Stephane Mazzotti, and Philippe Vernant〈br〉 Solid Earth, 10, 329-342, https://doi.org/10.5194/se-10-329-2019, 2019〈br〉 We use statistical analyses of synthetic position time series to estimate the potential precision of GPS velocities. Regression tree analyses show that the main factors controlling the velocity precision are the duration of the series, the presence of offsets, and the noise. Our analysis allows us to propose guidelines which can be applied to actual GPS data that constrain the velocity accuracies.

Description: 〈b〉Deformation mechanisms in mafic amphibolites and granulites: record from the Semail metamorphic sole during subduction infancy〈/b〉〈br〉 Mathieu Soret, Philippe Agard, Benoît Ildefonse, Benoît Dubacq, Cécile Prigent, and Claudio Rosenberg〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-28,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 This study sheds light on the mineral-scale mechanisms controlling the progressive deformation of sheared amphibolites from the Oman metamorphic sole during subduction initiation, and unravels how strain is localized and accommodated in (hydrated) mafic rocks at high temperature conditions. Our results indicate how metamorphic reactions and pore-fluid pressures driven by changes in pressure–temperature conditions and/or water activity control the rheology of mafic rocks.

Description: 〈b〉Event couple spectral ratio 〈i〉Q〈/i〉 method for earthquake clusters: application to northwest Bohemia〈/b〉〈br〉 Marius Kriegerowski, Simone Cesca, Matthias Ohrnberger, Torsten Dahm, and Frank Krüger〈br〉 Solid Earth, 10, 317-328, https://doi.org/10.5194/se-10-317-2019, 2019〈br〉 We developed a method that allows to estimate the acoustic attenuation of seismic waves within regions with high earthquake source densities. Attenuation is of high interest as it allows to draw conclusions on the origin of seismic activity. We apply our method to north-west Bohemia, which is regularly affected by earthquake swarms during which thousands of earthquakes are registered within a few days. We find reduced attenuation within the active volume, which may indicate high fluid content.

Description: 〈b〉Granite microporosity changes due to fracturing and alteration: secondary mineral phases as proxies for porosity and permeability estimation〈/b〉〈br〉 Martin Staněk and Yves Géraud〈br〉 Solid Earth, 10, 251-274, https://doi.org/10.5194/se-10-251-2019, 2019〈br〉 Granite is suitable to host geothermal wells or disposals of hazardous waste and in these cases the rock porosity and permeability are critical. Our detailed porosity and permeability data on variously deformed Lipnice granite yield a span of 5 orders of magnitude in permeability between the least and the most deformed facies. To facilitate the estimation of porosity and permeability in similar settings, we provide optical and chemical data on the characteristic minerals of each facies.

Description: 〈b〉Slab Break-offs in the Alpine Subduction Zone〈/b〉〈br〉 Emanuel D. Kästle, Claudio Rosenberg, Lapo Boschi, Nicolas Bellahsen, Thomas Meier, and Amr El-Sharkawy〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-17,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 We provide an extensive comparison of high-resolution subsurface models of the Alpine subduction zone. The imaged slab geometries are discussed in relation to the geodynamic evolution of the Alpine region. In the eastern Alps, we compare the models to three scenarios from the literature and propose a fourth one which best fits the tomographic images and the geological constraints. We find that the European slab is broken off below the entire Alpine arc, at variable depth levels.

Description: 〈b〉Structural expression of a fading rift front: a case study from the Oligo-Miocene Irbid rift of northwest Arabia〈/b〉〈br〉 Reli Wald, Amit Segev, Zvi Ben-Avraham, and Uri Schattner〈br〉 Solid Earth, 10, 225-250, https://doi.org/10.5194/se-10-225-2019, 2019〈br〉 Plate-scale rifting is frequently expressed by the subsidence of structural basins along an axis, but postdating tectonic and magmatic activity mostly obscures them. A 3-D subsurface imaging and facies analysis down to 1 km reveals uniquely preserved Galilean basins subsiding along a failing rift front in two main stages. Rifting within a large releasing jog (20–9 Ma), followed by localized grabenization off the Dead Sea fault plate boundary (9–5 Ma), prevents them from dying out peacefully.

Description: 〈b〉Distinct Element geomechanical modelling of the formation of sinkhole cluster within large-scale karstic depressions〈/b〉〈br〉 Djamil Al-Halbouni, Eoghan P. Holohan, Abbas Taheri, Robert A. Watson, Ulrich Polom, Martin P. J. Schöpfer, Sacha Emam, and Torsten Dahm〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-20,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 A 2D numerical modelling approach to simulate the mechanical formation of sinkhole cluster inside large-scale karstic depressions is presented. Different multiple cavity growth scenarios at depth are compared regarding the mechanical process and collapse style. The outcomes of the models are compared to results from remote sensing and geophysics for an active sinkhole area at the Dead Sea region.

Description: 〈b〉Integration of geoscientific uncertainty into geophysical inversion by means of local gradient regularization〈/b〉〈br〉 Jeremie Giraud, Mark Lindsay, Vitaliy Ogarko, Mark Jessell, Roland Martin, and Evren Pakyuz-Charrier〈br〉 Solid Earth, 10, 193-210, https://doi.org/10.5194/se-10-193-2019, 2019〈br〉 We propose the quantitative integration of geology and geophysics in an algorithm integrating the probability of observation of rocks with gravity data to improve subsurface imaging. This allows geophysical modelling to adjust models preferentially in the least certain areas while honouring geological information and geophysical data. We validate our algorithm using an idealized case and apply it to the Yerrida Basin (Australia), where we can recover the geometry of buried greenstone belts.

Description: 〈b〉Experimental grain growth of quartz aggregates under wet conditions and its application to deformation in nature〈/b〉〈br〉 Junichi Fukuda, Hugues Raimbourg, Ichiko Shimizu, Kai Neufeld, and Holger Stünitz〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-13,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉The grain growth of quartz was investigated using two samples of quartz (powder and quartzite) with water under pressure and temperature conditions of 1.0–2.5 GPa and 800–1100 °C. The compacted powder preserved a large porosity, which caused a slower grain growth than in the dense quartzite. We assumed a grain-growth law of 〈i〉d〈sup〉n〈/sup〉〈/i〉-〈i〉d〈sub〉0〈/sub〉〈sup〉n〈/sup〉〈/i〉 = 〈i〉k〈/i〉〈sub〉0〈/sub〉 〈i〉f〈/i〉〈sub〉H〈sub〉2〈/sub〉O〈/sub〉〈sup〉〈i〉r〈/i〉〈/sup〉 exp⁡(−〈i〉Q〈/i〉/〈i〉RT〈/i〉)〈i〉t〈/i〉 with grain size 〈i〉d〈/i〉 (µm) at time 〈i〉t〈/i〉 (second), initial grain size 〈i〉d〈sub〉0〈/sub〉〈/i〉 (µm), growth exponent 〈i〉n〈/i〉, a constant 〈i〉k〈sub〉0〈/sub〉〈/i〉 (µm〈sup〉〈i〉n〈/i〉〈/sup〉 MPa〈sup〉−〈i〉r〈/i〉〈/sup〉 s〈sup〉−1〈/sup〉), water fugacity 〈i〉f〈/i〉〈sub〉H〈sub〉2〈/sub〉O〈/sub〉 (MPa) with the exponent 〈i〉r〈/i〉, activation energy 〈i〉Q〈/i〉 (kJ/mol), gas constant 〈i〉R〈/i〉, and temperature 〈i〉T〈/i〉 in Kelvin. The parameters we obtained were 〈i〉n〈/i〉 = 2.5 ± 0.4, 〈i〉k〈/i〉〈sub〉0〈/sub〉 = 10〈sup〉−8.8 ± 1.4〈/sup〉, 〈i〉r〈/i〉 = 2.3 ± 0.3, and 〈i〉Q〈/i〉 = 48 ± 34 for the powder, and 〈i〉n〈/i〉 = 2.9 ± 0.4, 〈i〉k〈/i〉〈sub〉0〈/sub〉 = 10〈sup〉−5.8 ± 2.0〈/sup〉, 〈i〉r〈/i〉 = 1.9 ± 0.3, and 〈i〉Q〈/i〉 = 60 ± 49 for the quartzite. The grain-growth parameters obtained for the powder may be of limited use because of the high porosity of the powder with respect to crystalline rocks, even if the differences between powder and quartzite vanish when grain sizes reach ~ 70 µm. Extrapolation of the grain-growth laws to natural conditions indicates that the contribution of grain growth to plastic deformation in the middle crust may be small. However, grain growth might become important for deformation in the lower crust when the strain rate is −12/s.〈/p〉

Description: 〈b〉The building, shaping, and filling of an Upper Slope Terrace: the Rio Grande Terrace, SW Atlantic〈/b〉〈br〉 Michel Michaelovitch de Mahiques, Javier Alcántara-Carrió, Francisco José Lobo, Uri Schattner, Rosangela Felício dos Santos, Samara Cazzoli y Goya, Raissa Basti Ramos, José Gustavo Natorf de Abreu, Luiz Antonio Pereira de Souza, Rubens Cesar Lopes Figueira, and Marcia Caruso Bícego〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-140,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 This paper is a contribution to the knowledge of the geological processes on the SW Atlantic. We tried to integrate data from different time-scales, such as the geological evolution (millions of years) to the hydrodynamic processes (days to years). The results allowed us to recognize the importance of the geological inheritance to the present morphology of submerged areas.

Description: 〈b〉Improving quality of empirical Greens functions, obtained by cross-correlation of high-frequency ambient seismic noise〈/b〉〈br〉 Nikita Afonin, Elena Kozlovskaya, Jouni Nevalainen, and Janne Narkilahti〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-29,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Studying the uppermost structure of the subsurface is a necessary part for solving many practical problems (exploration of minerals, groundwater studies, geoengineering, etc.). Practical application of active seismic methods is not always possible because of different reasons, such as logistical difficulties, high cost of work, high level of seismic and acoustic noise, etc. That is why developing and improving of passive seismic methods for these purposes is one of the important problems in applied geophysics. In our study, we describe the way of improving quality of Empirical Green’s Functions (EGFs), evaluated from high-frequency ambient seismic noise, by using of advanced technique of cross-correlation functions stacking in the time domain (in this paper we use term “high-frequency” for the frequencies higher than 1 Hz). In compare to existing techniques, based on weight-stacking, our proposed technique makes it possible to more significantly increase the signal-to-noise ratio and, therefore quality of the EGF. The technique is based on both iterative and global optimization algorithms, where the optimized parameter is a signal-to-noise ratio of an EGF, retrieved for each iteration. The technique has been tested with the field data acquired in an area with high level of industrial noise (Pyhäsalmi Mine, Finland) and in an area with low level of anthropogenic noise (Kuusamo Greenstone Belt, Finland). The results show that the our proposed technique can be used for extraction of EGFs from high-frequency seismic noise in practical problems of mapping of the shallow subsurface in areas with high and low level of high-frequency seismic noise.〈/p〉

Description: 〈b〉Uniaxial compression of calcite single crystals at room temperature: insights into twinning activation and development〈/b〉〈br〉 Camille Parlangeau, Alexandre Dimanov, Olivier Lacombe, Simon Hallais, and Jean-Marc Daniel〈br〉 Solid Earth, 10, 307-316, https://doi.org/10.5194/se-10-307-2019, 2019〈br〉 Calcite twinning is a common deformation mechanism that mainly occurs at low temperatures. Twinning activation appears at a critical strength value, which is poorly documented and still debated. Temperature is known to influence twin thickness and shape; however, few studies have been conducted on calcite deformation at low temperatures. The goal of this work is to determine if thickness is mainly due to high temperatures and to establish the validity of a threshold twinning activation value.

Description: 〈b〉Subsurface structures of a quick-clay sliding prone area revealed using land-river reflection seismic data and hydrogeological modelling〈/b〉〈br〉 Silvia Salas-Romero, Alireza Malehmir, Ian Snowball, and Benoît Dessirier〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-22,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Land-river reflection seismic, hydrogeological modelling, and magnetic investigations in an area prone to quick-clay landslides in SW Sweden provide a detailed description of the subsurface structures, such as undulating fractured bedrock, and a sedimentary sequence of intercalating leached and unleached clay, and coarse-grained deposits. Hydrological properties of the coarse-grained layer help understanding its role in the leaching process that leads to the formation of quick clays in the area.

Description: 〈b〉Impact of terrestrial reference frame realizations on altimetry satellite orbit quality and global and regional sea level trends: a switch from ITRF2008 to ITRF2014〈/b〉〈br〉 Sergei Rudenko, Saskia Esselborn, Tilo Schöne, and Denise Dettmering〈br〉 Solid Earth, 10, 293-305, https://doi.org/10.5194/se-10-293-2019, 2019〈br〉 A terrestrial reference frame (TRF) realization is a basis for precise orbit determination of Earth-orbiting artificial satellites and sea level studies. We investigate the impact of a switch from an older TRF realization (ITRF2008) to a new one (ITRF2014) on the quality of orbits of three altimetry satellites (TOPEX/Poseidon, Jason-1, and Jason-2) for 1992–2015, but especially from 2009 onwards, and on altimetry products computed using the satellite orbits derived using ITRF2014.

Description: 〈b〉Power spectra of random heterogeneities in the solid earth〈/b〉〈br〉 Haruo Sato〈br〉 Solid Earth, 10, 275-292, https://doi.org/10.5194/se-10-275-2019, 2019〈br〉 Recent seismological observations clarified that the velocity structure of the crust and upper mantle is randomly heterogeneous. I compile reported power spectral density functions of random velocity fluctuations based on various types of measurements. Their spectral envelope is approximated by the third power of wavenumber. It is interesting to study what kinds of geophysical processes created such a power-law spectral envelope at different scales and in different geological environments.

Description: 〈b〉Constraining metamorphic dome exhumation and fault activity through hydrothermal monazite-(Ce)〈/b〉〈br〉 Christian A. Bergemann, Edwin Gnos, Alfons Berger, Emilie Janots, and Martin J. Whitehouse〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-10,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Zoned monazite-(Ce) from Alpine fissures/clefts is used to gain new insights into the exhumation history of the Central Alpine Lepontine metamorphic dome, and timing of deformation along the Rhone-Simplon fault zone on the dome's western termination. These hydrothermal monazites-(Ce) directly date deformation and changes in physiochemical conditions through crystallization ages, in contrast to commonly employed cooling-based methods. The 480 SIMS measurement ages from 20 individual crystals record ages over a time interval between ~ 19 and 5 Ma, with individual grains recording ages over a lifetime of 2 to 7.5 Ma. The age range combined with age distribution and internal crystal structure help to distinguish between areas whose deformational history was dominated by distinct tectonic events or continuous exhumation. The combination of this age data with geometrical considerations and spatial distribution give a more precise exhumation/cooling history for the area. In the east and south of the study region, the units underwent monazite-(Ce) growth at 19–12.5 and 16.5–10.5 Ma, followed by a central group of monazite-(Ce) ages at 15–10 Ma and the movements and related cleft monazites-(Ce) are youngest at the western border with 13–7 Ma. A last phase around 8–7 Ma is limited to clefts of the Simplon normal fault and related strike slip faults as the Rhone and Rhine-Rhone faults. The large data-set spread over significant metamorphic structures shows that the opening of clefts, fluid flow and monazite-(Ce) stability is direct linked to the geodynamic evolution in space and time.

Description: 〈b〉The Geodynamic World Builder: a solution for complex initial conditions in numerical modelling〈/b〉〈br〉 Menno Fraters, Cedric Thieulot, Arie van den Berg, and Wim Spakman〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-24,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Three-dimensional numerical modelling of geodynamic processes may benefit strongly from using realistic 3D starting models that approximate e.g. natural subduction settings in the geological past or at present. To this end we developed the Geodynamic World Builder (GWB) which enables relatively straight-forward parameterization of complex 3D geometric structures associated with geodynamic processes. The GWB is an open source community code designed to easily interface with geodynamic codes.

Description: 〈b〉On the link between Earth tides and volcanic degassing〈/b〉〈br〉 Florian Dinger, Stefan Bredemeyer, Santiago Arellano, Nicole Bobrowski, Ulrich Platt, and Thomas Wagner〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-14,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Evidences for tidal impacts on volcanism have been gathered by numerous empirical studies. This paper elucidates whether a causal link from the tidal forces to a variation in the volcanic degassing can be traced analytically. We model the response of a simplified magmatic system to the local tidal gravity variations, find that the tide-induced dynamics may significantly alter the bubble coalescence rate, and discuss the consequences for the volcanic degassing behaviour.

Description: 〈b〉Petrographic and Petrophysical Characteristics of Lower Cretaceous Sandstones from northern Israel, determined by micro-CT imaging and analytical techniques〈/b〉〈br〉 Peleg Haruzi, Regina Katsman, Baruch Spiro, Matthias Halisch, and Nicolas Waldmann〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-21,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 We studied petrophysical characteristics of three consecutive sandstone layers of the Lower Cretaceous Hatira Formation from Israel. Evaluated micro- and macro-scale petrophysical properties predetermined the permeability of the layers, measured in turn in the lab and upscaled from pore-scale velocities. Two scales of porosity variations were found: at 300 μm scale due to pores size variability, and at 2 mm scale due to high and low porosity occlusions, suggested to control the permeability.

Description: 〈b〉Fault-controlled dolomitization in the Montagna dei Fiori Anticline (Central Apennines, Italy): Record of a dominantly pre-orogenic fluid migration〈/b〉〈br〉 Mahtab Mozafari, Rudy Swennen, Fabrizio Balsamo, Hamdy El Desouky, Fabrizio Storti, and Conxita Taberner〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-136,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 The dolomitized intervals of the Lower Jurassic deposits exposed in the Montagna dei Fiori Anticline (Central Apennines, Italy) have been investigated. Accordingly, two fault-related dolomitization events were recognised and interpreted as occurred before and during the Apenninic orogeny, respectively. The analyses suggest significant involvement of evaporitic fluids in both events, most likely derived from the underlying Upper Triassic Burano Formation in the detachment level.

Description: 〈b〉Induced seismicity in geologic carbon storage〈/b〉〈br〉 Víctor Vilarrasa, Jesus Carrera, Sebastià Olivella, Jonny Rutqvist, and Lyesse Laloui〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-129,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 To meet the goal of the Paris Agreement to limit temperature increase below 2 ºC, Geologic Carbon Storage (GCS) will be necessary at the gigatone scale. But to successfully deploy GCS, seismicity induced by CO〈sub〉2〈/sub〉 injection should be controlled and maintained below a threshold that does not generate nuisances to the population. We conclude that felt induced seismicity can be minimized provided that a proper site characterization, monitoring and pressure management are performed.

Description: 〈b〉Moment magnitude estimates for Central Anatolian earthquakes using coda waves〈/b〉〈br〉 Tuna Eken〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-8,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Proper magnitude estimates for earthquakes can give an insight into the seismic energy released at earthquake source. This is, in fact, essential for better seismic hazard assessments in tectonically active regions. In the present work, I examine local earthquakes in central Anatolia to estimate their moment magnitudes. The main outcome of this study is an empirical relation that can provide a direct physical quantity of seismic energy in the study region.

Description: 〈b〉3-D seismic travel-time tomography validation of a detailed subsurface model: a case study of the Záncara river basin (Cuenca, Spain)〈/b〉〈br〉 David Marti, Ignacio Marzan, Jana Sachsenhausen, Joaquina Alvarez-Marrón, Mario Ruiz, Montse Torne, Manuela Mendes, and Ramon Carbonell〈br〉 Solid Earth, 10, 177-192, https://doi.org/10.5194/se-10-177-2019, 2019〈br〉 A detailed knowledge of the very shallow subsurface has become of crucial interest for modern society, especially if it hosts critical surface infrastructures such as temporary waste storage sites. The use of indirect methods to characterize the internal structure of the subsurface has been successfully applied, based on the 3-D distribution of seismic velocities and well-log data, which are of great interest for civil engineering companies.

Description: 〈b〉Fluid-mediated, brittle-ductile deformation at seismogenic depth: Part I – Fluid record and deformation history of fault-veins in a nuclear waste repository (Olkiluoto Island, Finland)〈/b〉〈br〉 Barbara Marchesini, Paolo Stefano Garofalo, Luca Menegon, Jussi Mattila, and Giulio Viola〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-5,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 1 comment)〈br〉 The influence of fluids on the initiation and evolution of faults at the brittle ductile transition is still underdocumented. We studied the rocks of a deeply exhumed fault characterized by mixed brittle-ductile deformation. The chemistry of synkinematic fluids trapped in the crystals and thermobarometic estimates highlighted several cycles of fluid pressure and stress fluctuations that caused the initial faulting and its following structural evolution.

Description: 〈b〉Correlation between tectonic stress regimes and methane seepage on the western Svalbard margin〈/b〉〈br〉 Andreia Plaza-Faverola and Marie Keiding〈br〉 Solid Earth, 10, 79-94, https://doi.org/10.5194/se-10-79-2019, 2019〈br〉 Vast amounts of methane are released to the oceans at continental margins (seepage). The mechanisms controlling when and how much methane is released are not fully understood. In the Fram Strait seepage may be affected by complex tectonic processes. We modelled the stress generated on the sediments exclusively due to the opening of the mid-ocean ridges and found that changes in the stress field may be controlling when and where seepage occurs, which has implications for seepage reconstruction.

Description: 〈b〉A multi-technology analysis of the 2017 North Korean nuclear test〈/b〉〈br〉 Peter Gaebler, Lars Ceranna, Nima Nooshiri, Andreas Barth, Simone Cesca, Michaela Frei, Ilona Grünberg, Gernot Hartmann, Karl Koch, Christoph Pilger, J. Ole Ross, and Torsten Dahm〈br〉 Solid Earth, 10, 59-78, https://doi.org/10.5194/se-10-59-2019, 2019〈br〉 On 3 September 2017 official channels of the Democratic People’s Republic of Korea announced the successful test of a nuclear device. This study provides a multi-technology analysis of the 2017 North Korean event and its aftermath using a wide array of geophysical methods (seismology, infrasound, remote sensing, radionuclide monitoring, and atmospheric transport modeling). Our results clearly indicate that the September 2017 North Korean event was in fact a nuclear test.

Description: 〈b〉Bayesian geological and geophysical data fusion for the construction and uncertainty quantification of 3D geological models〈/b〉〈br〉 Hugo K. H. Olierook, Richard Scalzo, David Kohn, Rohitash Chandra, Ehsan Farahbakhsh, Gregory Houseman, Chris Clark, Steven M. Reddy, and R. Dietmar Müller〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-4,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Traditional approaches to develop 3D geological models employ a mix of quantitative and qualitative scientific techniques, which do not fully provide quantification of uncertainty in the constructed models and fail to optimally weight geological field observations against constraints from geophysical data. Here, we demonstrate a Bayesian methodology to fuse geological field observations with aeromagnetic and gravity data to build robust 3D models in a 13.5 × 13.5 km region of the Gascoyne Province, Western Australia. Our approach is validated by comparing model results to independently-constrained geological maps and cross-sections produced by the Geological Survey of Western Australia. By fusing geological field data with magnetics and gravity surveys, we show that at 89 % of the modelled region has 〉 95 % certainty. The boundaries between geological units are characterized by narrow regions with 〈/p〉

Description: 〈b〉ER3D: a structural and geophysical 3D model of central Emilia-Romagna (Northern Italy) for numerical simulation of earthquake ground motion〈/b〉〈br〉 Peter Klin, Giovanna Laurenzano, M. Adelaide Romano, Enrico Priolo, and Luca Martelli〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-1,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Using geological and geophysical data we set-up a 3D digital description of the underground structure in the central part of the Po alluvial plain. By means of computer simulated propagation of seismic waves we were able to identify the structural features that caused the unexpected elongation and amplification of the earthquake ground motion that was observed in the area during the 2012 seismic crisis. The study permits a deeper understanding of the seismic hazard in alluvial basins.

Description: 〈b〉A semi-automated algorithm to quantify scarp morphology (SPARTA): application to normal faults in southern Malawi〈/b〉〈br〉 Michael Hodge, Juliet Biggs, Åke Fagereng, Austin Elliott, Hassan Mdala, and Felix Mphepo〈br〉 Solid Earth, 10, 27-57, https://doi.org/10.5194/se-10-27-2019, 2019〈br〉 This work attempts to create a semi-automated algorithm (called SPARTA) to calculate height, width and slope of surface breaks produced by earthquakes on faults. We developed the Python algorithm using synthetic catalogues, which can include noise features such as vegetation, hills and ditches, which mimic natural environments. We then apply the algorithm to four fault scarps in southern Malawi, at the southern end of the East African Rift system, to understand their earthquake potential.

Description: 〈b〉Improving subduction interface implementation in dynamic numerical models〈/b〉〈br〉 Dan Sandiford and Louis Moresi〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-11,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉This study focuses on methodological issues related to dynamic subduction zone modelling. Numerical models often employ an entrained weak layer (WL approach) to facilitate decoupling between the subducting and overriding plates. In such a setup, the kinematics of the flow lead to width variations in the subduction interface. When a uniform-width interface is prescribed, a transient evolution of the interface thickness occurs, during which the volmetric flux along the interface profile establishes equilibrium. Width variations can exceed 4× during this stage, which may impact the effective strength of the interface, both through physical effects if the rheology is linear, and numerical effects if the fault becomes poorly resolved. This transient process induces strong sensitivity to model resolution, and may present a significant challenge to reproducibility. Developing more robust ways to model the subduction interface will enable fully dynamic models to address sensitive subduction-zone processes, such as metamorphism near the slab top. In this study we discuss a simple strategy aimed at improving the standard WL approach. By prescribing a variable thickness weak layer at the outset of the model, and by controlling the limits of the layer thickness during the model evolution, we find improved stability and resolution convergence of the models.〈/p〉

Description: 〈b〉Geochronological and thermometric evidence of unusually hot fluids in an Alpine fissure of Lauzière granite (Belledonne, Western Alps)〈/b〉〈br〉 Emilie Janots, Alexis Grand'Homme, Matthias Bernet, Damien Guillaume, Edwin Gnos, Marie-Christine Boiron, Magali Rossi, Anne-Magali Seydoux-Guillaume, and Roger De Ascenção Guedes〈br〉 Solid Earth, 10, 211-223, https://doi.org/10.5194/se-10-211-2019, 2019〈br〉 This geochronological and thermometric study reveals unusually hot fluids in an Alpine-type fissure of granite from the external crystalline massif (Western Alps). The fluid is estimated to be 150-250 °C hotter than the host rock and requires a dynamic fluid pathway at mid-crustal conditions in the ductile regime. This fluid circulation resets the zircon fission track thermochronometer, but only at the fissure contact. Thermal disturbances due to advective heating appear to be localized.

Description: 〈b〉Electrical Formation Factor of Clean Sand from Laboratory Measurements and Digital Rock Physics〈/b〉〈br〉 Mohammed Ali Garba, Stephanie Vialle, Mahyar Madadi, Boris Gurevich, and Maxim Lebedev〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-133,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 1 comment)〈br〉 〈p〉Electrical properties of rocks are important parameters for well-log and reservoir interpretation. Laboratory measurements of such properties are time-consuming, difficult, and are impossible in some cases. Being able to compute them from 3-D images of small samples will allow generating massive data in a short time, opening new avenues in applied and fundamental science. To become a reliable method, the accuracy of this technology needs to be tested. In this study, we developed a comprehensive and robust workflow with clean sand from two beaches. Electrical conductivities at 1 kHz were first carefully measured in the laboratory. A range of porosities spanning from a minimum of 0.26 to 0.33 to a maximum of 0.39 to 0.44, depending on the samples. Such range was achieved by compacting the samples in a way that reproduces natural packing of sand. Characteristic electrical formation factor versus porosity relationships were then obtain for each sand type. 3-D micro-computed tomography images of each sand sample from the experimental sand pack were acquired at different resolutions. Image processing was done using global thresholding method and up to 96 sub-samples of sizes from (200)〈sup〉3〈/sup〉 to (700)〈sup〉3〈/sup〉 voxels. After segmentation, the images were used to compute the effective electrical conductivity of the sub-cubes using a Finite Element electrostatic modelling. For the samples, a good agreement between laboratory measurements and computation from digital cores was found, if the sub-cube size REV is reached that is between (1300 μm)〈sup〉3〈/sup〉 and (1820 μm)〈sup〉3〈/sup〉, which, with an average grain size of 160 μm, is between 8 and 11 grains. Computed digital rock images of the clean sands have opened a way forward in getting the formation factor within a shortest possible time; laboratory calculations take five (5) to thirty-five (35) days as in the case of clean and shaly sands respectively, whereas, the digital tomography takes just three (3) to five (5) hours.〈/p〉

Description: 〈b〉Tectono-thermal evolution of Oman's Mesozoic passive continental margin under the obducting Semail Ophiolite: a case study of Jebel Akhdar, Oman〈/b〉〈br〉 Arne Grobe, Christoph von Hagke, Ralf Littke, István Dunkl, Franziska Wübbeler, Philippe Muchez, and Janos L. Urai〈br〉 Solid Earth, 10, 149-175, https://doi.org/10.5194/se-10-149-2019, 2019〈br〉 The Mesozoic sequences of the Oman mountains experienced only weak post-obduction overprint and deformation, and thus they offer a unique natural laboratory to study obduction. We present a study of pressure and temperature evolution in the passive continental margin under the Oman Ophiolite using numerical basin models calibrated with thermal maturity data, fluid-inclusion thermometry, and low-temperature thermochronology.

Description: 〈b〉Monitoring induced distributed double-couple sources using Marchenko-based virtual receivers〈/b〉〈br〉 Joeri Brackenhoff, Jan Thorbecke, and Kees Wapenaar〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-142,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Earthquakes in the subsurface are hard to monitor due to their complicated signals. We aim to make the monitoring of the subsurface possible by redatuming the sources and the receivers from the surface of the Earth to the subsurface to monitor earthquakes originating from small faults in the subsurface. By using several sources together, we create complex earthquake signals for large scale faults sources.

Description: 〈b〉Deformation of feldspar at greenschist facies conditions – the record of mylonitic pegmatites from the Pfunderer Mountains, Eastern Alps〈/b〉〈br〉 Felix Hentschel, Claudia A. Trepmann, and Emilie Janots〈br〉 Solid Earth, 10, 95-116, https://doi.org/10.5194/se-10-95-2019, 2019〈br〉 We used microscopy and electron backscatter diffraction to analyse the deformation behaviour of feldspar at greenschist facies conditions in mylonitic pegmatites of the Austroalpine basement. There are strong uncertainties about feldspar deformation, mainly because of the varying contributions of different deformation processes. We observed that deformation is mainly the result of coupled fracturing and dislocation glide, followed by growth and granular flow.

Description: 〈b〉Green's theorem in seismic imaging across the scales〈/b〉〈br〉 Kees Wapenaar, Joeri Brackenhoff, and Jan Thorbecke〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-141,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 The solid earth and exploration communities independently developed a variety of seismic imaging methods for passive- and active-source data. Despite the seemingly different approaches and underlying principles, many of those methods are based in some way or another on the same mathematical theorem. Starting with this theorem, we discuss a variety of classical and recent seismic imaging methods in a systematic way and explain their similarities and differences.

Description: 〈b〉Topographic changes due to the 2004 Chuetsu thrusting earthquake in low mountain region〈/b〉〈br〉 Zhikun Ren, Takashi Oguchi, Peizhen Zhang, and Shoichiro Uchiyama〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-3,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 This research might be the first time to study the topographic changes due to strong earthquakes in region of low relief. We use high-resolution pre- and post-earthquake DEMs to detect the topographic changes caused by the Wenchuan earthquake. However, the topographic changes caused by the Chuetsu earthquake is different. Our findings might indicate that the earthquake mainly acts as roughening and driving the topographic growth in region of low relief.

Description: 〈b〉Anticlockwise metamorphic pressure–temperature paths and nappe stacking in the Reisa Nappe Complex in the Scandinavian Caledonides, northern Norway: evidence for weakening of lower continental crust before and during continental collision〈/b〉〈br〉 Carly Faber, Holger Stünitz, Deta Gasser, Petr Jeřábek, Katrin Kraus, Fernando Corfu, Erling K. Ravna, and Jiří Konopásek〈br〉 Solid Earth, 10, 117-148, https://doi.org/10.5194/se-10-117-2019, 2019〈br〉 The Caledonian mountains formed when Baltica and Laurentia collided around 450–400 million years ago. This work describes the history of the rocks and the dynamics of that continental collision through space and time using field mapping, estimated pressures and temperatures, and age dating on rocks from northern Norway. The rocks preserve continental collision between 440–430 million years ago, and an unusual pressure–temperature evolution suggests unusual tectonic activity prior to collision.

Description: 〈b〉Mechanisms of destructing translational domains in passive margin salt basins: Insights from analogue modelling〈/b〉〈br〉 Zhiyuan Ge, Matthias Rosenau, Michael Warsitzka, and Rob L. Gawthorpe〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2019-2,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Salt basins are important as they bear abundant hydrocarbon resource and record the geological evolution. However, current understanding does not fully reconcile with natural examples. Using state-of-the-art analogue modelling technique, we study how an undefromed area occurs in the experiment and gets destroyed later. The results suggest the natural systems work quite differently as we currently know. This study can help us to better explore natural resources in the salt basins.

Description: 〈b〉Spatio-temporal dynamics of sediment transfer systems in landslide-prone alpine catchments〈/b〉〈br〉 François Clapuyt, Veerle Vanacker, Fritz Schlunegger, Marcus Christl, and Kristof Van Oost〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-139,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 In mountainous environments, landslides act as stochastic but discrete sediment sources in the landscape and randomly affect these catchments. Our study highlights that at the regional scale, one single landslide has not necessarily an impact on landscape evolution. It is the integrated effect of multiple sediment pulses providing sediments to the river network at the decadal scale, which are subsequently attenuated by sediment transport that may regulate sediment fluxes at the regional scale.

Description: 〈b〉The imprints of contemporary mass redistribution on regional sea level and vertical land motion observations〈/b〉〈br〉 Thomas Frederikse, Felix W. Landerer, and Lambert Caron〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-128,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Due to ice sheets and glaciers losing mass, and because continents get wetter and drier, a lot of water is redistributed over the earth's surface. The earth is not completely rigid, but deforms under these changes in the load on top. This deformation affects sea-level observations. With the GRACE satellite mission, we can measure this redistribution of water, and compute the resulting deformation. We use this computed deformation to improve the accuracy of sea-level observations.

Description: 〈b〉High-precision U–Pb ages in the early Tithonian to early Berriasian and implications for the numerical age of the Jurassic–Cretaceous boundary〈/b〉〈br〉 Luis Lena, Rafael López-Martínez, Marina Lescano, Beatriz Aguire-Urreta, Andrea Concheyro, Verónica Vennari, Maximiliano Naipauer, Elias Samankassou, Márcio Pimentel, Victor A. Ramos, and Urs Schaltegger〈br〉 Solid Earth, 10, 1-14, https://doi.org/10.5194/se-10-1-2019, 2019〈br〉 This paper investigates the numerical age of the J–K boundary that remains one of the last main Phanerozoic system boundaries without an adequate constraint by adequate radioisotopic ages. Here we find that there is potentially 4 Myr of difference between the current age of the J–K boundary and our data.

Description: 〈b〉The impact of earthquake cycle variability on neotectonic and paleoseismic slip rate estimates〈/b〉〈br〉 Richard Styron〈br〉 Solid Earth, 10, 15-25, https://doi.org/10.5194/se-10-15-2019, 2019〈br〉 Successive earthquakes on a single fault are not perfectly periodic in time. There is some natural random variability. This leads to variations in estimated fault slip rates over short timescales though the longer-term mean slip rate stays constant, which may cause problems when comparing slip rates at different timescales. This paper is the first to quantify these effects, demonstrating substantial variation in slip rates over a few to tens of earthquakes, but much less at longer timescales.

Description: 〈b〉How do we see fractures? Quantifying subjective bias in fracture data collection〈/b〉〈br〉 Billy J. Andrews, Jennifer J. Roberts, Zoe K. Shipton, Sabina Bigi, Maria C. Tartarello, and Gareth O. Johnson〈br〉 Solid Earth Discuss., https//doi.org/10.5194/se-2018-135,2019〈br〉 〈b〉Manuscript under review for SE〈/b〉 (discussion: open, 0 comments)〈br〉 Rocks often contain fracture networks, which can strongly impact sub-surface fluid flow and the strength of a rock mass. We examine how participants interpret the same fracture network, both in the field and using field photographs. Considerable variability between participant's resulted in significant differences in derived fracture statistics, which are often used as inputs for geological models. We suggest protocols to recognise, understand and limit this effect on fracture data collection.

Description: The Lower Jurassic platform and basinal deposits exposed in the Montagna dei Fiori Anticline (Central Apennines, Italy) are pervasively affected by dolomitization. Based on the integration of field work, petrography, and geochemistry, two fault-related dolomitization events were recognized and interpreted as occurred before and during the Apenninic orogeny, respectively. Fluid inclusion analysis indicates moderate to elevated salinity values of 3.5 to 20.5 and 12.8 to 18.6 eq. wt. % NaCl, in the first and the second event, respectively. The estimated salinities, in combination with δ18O values and 87Sr/86Sr ratios, suggest significant involvement of evaporitic fluids in both events, most likely derived from the underlying Upper Triassic Burano Formation. In addition, the 87Sr/86Sr ratios up to 0.70963 suggest the circulation of deep-sourced fluids that interacted with siliciclastics and/or the crystalline basement during the dolomitization events. The first dolomitization event which is also considered as the most pervasive one started prior to the significant burial conditions, as reflected in homogenization temperatures of their fluid inclusions being mostly below about 40–50 °C. Two major dolomite types (D1 and D2) were recognized as pertaining to this event, both postdated by high amplitude bed-parallel stylolites. This relationship supports a syn-burial, pre layer-parallel shortening dolomitization, interpreted as controlled by the extensional fault pattern affecting the carbonate succession before its involvement in the Apenninic thrust wedge. A possible geodynamic framework for this dolomitization event is Early to Late Jurassic rift-related extensional tectonism. The second dolomitization event initiated with a dolomite type (D3) characterized by a slight temperature upturn (up to 73 °C), followed by a second type (D4) with markedly higher homogenization temperatures (up to 105 °C), interpreted as associated with the inflow of hydrothermal fluids, possibly related to major changes in the permeability architecture of faults during early- to syn-thrusting and folding activity. Eventually, D4 was overprinted by a late generation of dolomite veins (D5) interpreted as associated with late orogenic extensional faulting in the backlimb of the Montagna dei Fiori Anticline. Based on the timing of deformation in the Montagna dei Fiori Anticline, D3 to D5 dolomitization likely occurred in Late Miocene to Pliocene times. The findings regarding characteristics and timing of dolomitization here illustrates the long-term controlling role of the eveporitic detachments in dolomitization process. Our data shows the Mg-rich fluids most likely derived from these evaporites may prime the tectonically involved successions for repeated dolomitization, and formation of potential reservoirs in sequential tectonic modifications (extensional vs. compressional).

Description: We derive trends and monthly anomalies in global and regional sea-level and solid-earth deformation that result from mass redistribution observed by GRACE and an ensemble of GIA models. With this ensemble, we do not only compute mean changes, but we also derive uncertainty estimates of all quantities. We find that over the GRACE era, the trend in land mass change has led to a sea-level trend of 1.28–1.82 mm/yr, which is driven by ice mass loss, while terrestrial water storage has increased over the GRACE period, causing a sea-level drop of 0.11–0.47 mm/yr. This redistribution of mass causes sea-level and deformation patterns that do not only vary in space, but also in time. The temporal variations affect GNSS-derived vertical land motion (VLM) observations, which are now commonly used to correct tide-gauge observations. We find that for many GNSS stations, including GNSS stations in coastal locations, solid-earth deformation resulting from present-day mass redistribution causes trends in the order of 1 mm/yr or higher. Since GNSS records often only span a few years, these trends are generally not representative for the tide-gauge records, which often span multiple decades, and extrapolating them backwards in time could cause substantial biases. To avoid this possible bias, we computed trends and associated uncertainties for 8228 GNSS stations after removing deformation due to GIA and present-day mass redistribution. With this separation, we are able to explain a large fraction of the discrepancy between observed sea-level trends at multiple long tide-gauge records and the reconstructed global-mean sea-level trend from recent reconstructions.

Description: Progresses in understanding the sedimentary dynamic of the Western Alboran Basin lead us to propose a model of evolution of its tectonic inversion since the Pliocene to present-time. Extensive and strike-slip structures accommodate the Miocene back-arc extension of the Alboran Basin, but undergo progressive tectonic inversion since the Tortonian. Across the Alboran Basin, the Alboran Ridge becomes a transpressive structure accommodating the shortening. We map its southwestern termination: a Pliocene rhombic structure exhibiting series of folds and thrusts. A younger structure, the Al-Idrissi fault zone (AIF), is Pleistocene to present-day active strike-slip fault zone. This fault zone crosses the Alboran Ridge and connects southward to the transtensive Nekor Basin and the Nekor fault. In the Moroccan shelf and at the edge of a submerged volcano, we date the inception of the local shelf subsidence from the 1.81–1.12 Ma. It marks the propagation of the AIF toward the Nekor Basin. Pliocene thrusts and folds and Quaternary transtension appear at first sight as different tectonic periods but reflects the long-term evolution of a transpressive system. Despite a constant direction of Africa/Eurasia convergence since 5 Ma at the scale of the southern margin of Alboran Basin, the Pliocene-Quaternary inversion evolves from transpressive to transtensive on the AIF and the Nekor Basin. This system reflects the expected evolution of the deformation of the Alboran Basin under the indentation of the African lithosphere.

Description: Oxygen isotope geochemistry is a powerful tool for investigating rocks that interacted with fluids, to assess fluid sources and quantify the conditions of fluid-rock interaction. We present an integrated modelling approach and the computer program PTLOOP that combine thermodynamic and oxygen isotope fractionation modelling for multi-rock open systems. The strategy involves a robust petrological model performing on-the-fly Gibbs energy minimizations coupled to an oxygen fractionation model both based on internally consistent databases. This approach is applied to subduction zone metamorphism to predict the possible range of δ18O values for stable phases and aqueous fluids at various pressure-temperature (P-T) conditions in the subducting slab. The modelled system is composed by a sequence of oceanic crust (mafic) with sedimentary cover of known initial chemical composition and bulk δ18O. The evolution of mineral assemblage and δ18O values of each phase is calculated along a defined P-T path. Fluid-rock interactions may occur as consequence of (1) infiltration of an external fluid into the mafic rocks or (2) transfer of the fluid liberated by dehydration reactions occurring in the mafic rocks into the sedimentary rocks. The effects of interaction with externally-derived fluids on the mineral and bulk δ18O of each rock are quantified for two typical compositions of metabasalts and metasediments with external fluid influx from serpentinite. The dehydration reactions, fluid loss and mineral fractionation produce minor to negligible variations in bulk δ18O values, i.e. within 1 ‰. By contrast, the interaction with external fluids may lead to shifts in δ18O up to one order of magnitude larger. Such variations can be detected by analysing in-situ oxygen isotope in key metamorphic minerals such as garnet, white mica and quartz. The simulations show that, when the water released by the slab infiltrates the forearc mantle wedge, it can cause extensive serpentinization within fractions of a Myr and significant oxygen isotope variation at the interface. This technique opens new perspectives to track fluid pathways in subduction zones, to distinguish porous from channelized fluid flows, and to determine the P-T conditions and the extent of fluid/rock interaction.

Description: Anelasticity may decrease the shear modulus of the asthenosphere by 8–10 % at semi-diurnal tidal periods compared with the reference 1 s period of seismological Earth models. We show that such anelastic effects are likely to be significant for ocean tide loading displacement at the M2 tidal period around the East China Sea. By comparison with tide gauge observations, we establish that NAO99Jb is the most accurate numerical ocean tide model in this region, and that related errors in the predicted M2 vertical ocean tide loading displacements will be 0.2–0.5 mm. In contrast, GPS observations on the Ryukyu Islands (Japan), with uncertainty 0.2–0.3 mm, show discrepancies of over 1.5 mm with respect to ocean tide loading displacements predicted using the purely elastic radial Preliminary Reference Earth Model. We show that the use of an anelastic PREM-based Earth model reduces these discrepancies to no more than 0.8 mm, which is of the same order as the sum of the remaining errors due to uncertainties in the ocean tide model and the GPS observations. Use of a regional Earth model based on the laterally-varying S362ANI, with or without further empirical tuning, results in minor additional improvements in fit.

Description: Soil position in the landscape reveals its history of formation and genesis. Therefore, the landscape is the combination of features of the surface of the earth with subsurface components (parent material), while the soil is a three-dimensional, dynamic natural body inserted in the landscape. This research aimed to study the soil-landscape relationship in a sandstone-gneiss topolithosequence in Amazonas, Brazil. The study was carried out along a 9.253-meter transect from the top downwards the softer slope. Soil profiles were selected in five landscape compartments (top, upper third, lower third, transport foothill, and deposition foothill). Morphological, mineralogical, physical, chemical, and ray diffraction characterizations were performed. Soils had different morphological, physical, chemical, and mineralogical attributes due to the variations of the geological substrate and landscape position. The mineralogy of the clay fraction is composed of kaolinite, goethite, hematite, and gibbsite, with goethite being the predominant iron oxide. A sand fraction dominance was observed in relation to the other fractions in all the profiles, being related to the alluvial nature of the parent material, with the highest values occurring in the lower third. The separation of the landscape into geomorphic surfaces and identification of the parent material were effective for understanding the variation of soil attributes along the landscape.

Description: Nappe assembly in the Köli Nappe Complex, Jämtland, Sweden, has been associated with in- and out-of-sequence thrusting. Kinematic data from shear zones bounding the Köli Nappe Complex are compatible with this model, but direct evidence from fault zones internally subdividing the nappe complex does not exist. We studied a series of pseudotachylyte exposures in these fault zones for deciphering the role seismic faulting played in the assembly of the Caledonian nappe pile. To constrain the fault kinematics, microstructural and magnetic fabrics of pseudotachylyte in foliation-parallel fault veins have been investigated. Because the pseudotachylyte veins are thin, we focused on small (c. 0.2 cm3) samples for measuring the anisotropy of magnetic susceptibility. The results show inverse proportionality between specimen size and anisotropy of magnetic susceptibility degree, which is most likely an analytical artifact related to instrument sensitivity and small sample dimensions. This finding implies magnetic anisotropy results acquired from small specimens demand cautious interpretation. However, analysis of structural and magnetic fabric data indicates that seismic faulting occurred during exhumation into the upper crust but yield no kinematic in-formation. Structural field data suggest that seismic faulting was postdated by brittle E–W extensional deformation along steep normal faults. Therefore, it is likely that the pseudotachylytes formed late during out-of-sequence thrusting of the Köli Nappe Complex over the Seve Nappe Complex.

Description: Residual pressure can be preserved in mineral inclusions, e.g. quartz-in-garnet, after exhumation due to differential expansion between inclusion and host crystals. Raman spectroscopy has been applied to infer the residual pressure and provides information on the entrapment temperature and pressure conditions. However, the amount of residual pressure relaxation cannot be directly measured. An underestimation of pressure relaxation may lead to significant errors between calculated and actual entrapment pressure. This study focuses on three mechanisms responsible for the residual-pressure relaxation: 1) viscous creep; 2) plastic yield; 3) proximity of inclusion to thin-section surface. Criteria are provided to quantify how much of the expected residual pressure is relaxed due to these three mechanisms. An analytical solution is introduced to demonstrate the effect of inclusion depth on the residual pressure field when the inclusion is close to thin-section surface. It is shown that for quartz-in-garnet system, the distance between thin-section surface and inclusion centre needs to be at least two times the inclusion radius to avoid pressure relaxation. In terms of viscous creep, representative case studies on quartz-in-garnet system show that viscous relaxation may occur from temperatures as low as 600∼700 °C depending on the particular P-T path and various garnet compositions. For quartz entrapped along the prograde P-T path and subject to viscous resetting at peak T above 600∼700 °C, its residual pressure after exhumation may be higher than predicted from its true entrapment conditions. Moreover, such a viscous resetting effect may introduce apparent overstepping of garnet nucleation that is not related to reaction affinity.

Description: Modern geodetic and seismic monitoring tools are enabling the study of moderate-sized earthquake sequences in unprecedented detail. Here we use a variety of methods to examine surface deformation caused by a sequence of earthquakes near Lake Muir in southwest Western Australia in 2018. A shallow MW 5.3 earthquake on the 16th of September 2018 was followed on the 8th of November 2018 by a MW 5.2 event in the same region. Focal mechanisms for the events suggest reverse and strike-slip rupture, respectively. Interferometric Synthetic Aperture Radar (InSAR) analysis of the events suggests that the ruptures are in part spatially coincident. Field mapping, guided by the InSAR results, reveals that the first event produced an approximately 3 km long and up to 0.5 m high west-facing surface rupture, consistent with slip on a moderately east-dipping fault. Double difference hypocentre relocation of aftershocks using data from rapidly deployed seismic instrumentation confirms an east-dipping rupture plane for the first event, and shows a concentration located at the northern end of the rupture where the InSAR suggests greatest vertical displacement. The November event resulted from rupture on a northeast-trending strike-slip fault. UAV-derived digital terrain models (differenced with pre-event LiDAR) reveal a surface deformation envelope consistent with the InSAR for the first event, but could not discern deformation unique to the second event. New rupture length versus magnitude scaling relationships developed for non-extended cratonic regions as part of this study allow for the distinction between “visible†surface rupture lengths (VSRL) from field-mapping and “detectable†surface rupture lengths (DSRL) from remote sensing techniques such as InSAR, and suggest longer ruptures for a given magnitude than implied by commonly used scaling relationships.

Description: Geologic carbon storage, as well as other geo-energy applications, such as geothermal energy, seasonal natural gas storage and subsurface energy storage, imply fluid injection/extraction that causes changes in the effective stress field and induces (micro)seismicity. If felt, seismicity has a negative effect on public perception and may jeopardize wellbore stability and damage infrastructure. Thus, induced earthquakes should be minimized to successfully deploy geo-energies. However, the processes that trigger induced seismicity are not fully understood, which translates into a limited forecast ability of current predictive models. We aim at understanding the triggering mechanisms of induced seismicity and to develop methodologies to minimize its occurrence through dimensional and numerical analysis. We find that the properties of the injected fluid, e.g., water or CO2, have a significant effect on pressure buildup evolution and thus, on fracture/fault stability. In addition to pressure changes, the injected fluid usually reaches the injection formation at a lower temperature than that of the rock, inducing rock contraction, thermal stress reduction and stress redistribution around the cooled region. If low-permeable faults cross the injection formation, local stress changes are induced around them which may reduce their stability and eventually cause fault reactivation. To minimize the risk of inducing felt seismicity, we have developed characterization techniques to reduce the uncertainty on rock properties and subsurface heterogeneity both for the screening of injection sites and for the operation of projects. Overall, we contend that felt induced seismicity can be minimized provided that a proper site characterization, monitoring and pressure management are performed.

Description: Current gravitational tectonics models illustrating the structural style of passive margin salt basins typically have domains of upslope extension and corresponding downslope contraction, separated by a domain of rather undeformed mid-slope translation. However, such a translational domain is rarely observed in natural systems where extensional and contractional structures may interfere in the mid-slope area. In this study, we use sandbox analogue modelling analyzed by 4D digital image correlation (DIC) to investigate how the pre-kinematic layer thickness, differential sediment loading and sedimentation rate control the structural evolution of translational domains. As in nature, experimental deformation is driven by slowly increasing gravitational forces associated with continuous basal tilting. The results show that a translational domain persists throughout the basin evolution when the pre-kinematic layer is evenly distributed, although a thin (1 mm in the experiment, 100 m in nature) pre-kinematic layer can render the translational domain relatively narrow when comparing to settings with a thicker (5 mm) pre-kinematic layer. In contrast, early differential sedimentary loading in the mid-slope area creates minibasins intervened by salt diapirs overprinting the translational domain. Similarly, very low sedimentation rate (1 mm per day in the experiment, equates to

Description: Traditional approaches to develop 3D geological models employ a mix of quantitative and qualitative scientific techniques, which do not fully provide quantification of uncertainty in the constructed models and fail to optimally weight geological field observations against constraints from geophysical data. Here, we demonstrate a Bayesian methodology to fuse geological field observations with aeromagnetic and gravity data to build robust 3D models in a 13.5 × 13.5 km region of the Gascoyne Province, Western Australia. Our approach is validated by comparing model results to independently-constrained geological maps and cross-sections produced by the Geological Survey of Western Australia. By fusing geological field data with magnetics and gravity surveys, we show that at 89 % of the modelled region has 〉 95 % certainty. The boundaries between geological units are characterized by narrow regions with

Description: We aim to monitor and characterize signals in the subsurface by combining these passive signals with recorded reflection data at the surface of the Earth. To achieve this, we propose a method to create virtual receivers from reflection data using the Marchenko method. By applying homogeneous Green’s function retrieval, these virtual receivers are then used to monitor the responses from subsurface sources. We consider monopole point sources with a symmetric source signal, where the full wavefield without artefacts in the subsurface can be obtained. Responses from more complex source mechanisms, such as double-couple sources, can also be used and provide results with comparable quality as the monopole responses. If the source signal is not symmetric in time, our technique that is based on homogeneous Green’s function retrieval provides an incomplete signal, with additional artefacts. The duration of these artefacts is limited and they are only present when the source of the signal is located above the virtual receiver. For sources along a fault rupture, this limitation is also present and more severe due to the source activating over a longer period of time. Part of the correct signal is still retrieved, as well as the source location of the signal. These aretefacts do not occur in another method which creates virtual sources as well as receivers from reflection data at the surface. This second method can be used to forecast responses to possible future induced seismicity sources (monopoles, double-couple sources and fault ruptures). This method is applied to field data, where similar results to synthetic data are achieved, which shows the potential for the application on real data signals.

Description: Electrical properties of rocks are important parameters for well-log and reservoir interpretation. Laboratory measurements of such properties are time-consuming, difficult, and are impossible in some cases. Being able to compute them from 3-D images of small samples will allow generating massive data in a short time, opening new avenues in applied and fundamental science. To become a reliable method, the accuracy of this technology needs to be tested. In this study, we developed a comprehensive and robust workflow with clean sand from two beaches. Electrical conductivities at 1 kHz were first carefully measured in the laboratory. A range of porosities spanning from a minimum of 0.26 to 0.33 to a maximum of 0.39 to 0.44, depending on the samples. Such range was achieved by compacting the samples in a way that reproduces natural packing of sand. Characteristic electrical formation factor versus porosity relationships were then obtain for each sand type. 3-D micro-computed tomography images of each sand sample from the experimental sand pack were acquired at different resolutions. Image processing was done using global thresholding method and up to 96 sub-samples of sizes from (200)3 to (700)3 voxels. After segmentation, the images were used to compute the effective electrical conductivity of the sub-cubes using a Finite Element electrostatic modelling. For the samples, a good agreement between laboratory measurements and computation from digital cores was found, if the sub-cube size REV is reached that is between (1300 μm)3 and (1820 μm)3, which, with an average grain size of 160 μm, is between 8 and 11 grains. Computed digital rock images of the clean sands have opened a way forward in getting the formation factor within a shortest possible time; laboratory calculations take five (5) to thirty-five (35) days as in the case of clean and shaly sands respectively, whereas, the digital tomography takes just three (3) to five (5) hours.

Description: This study focuses on methodological issues related to dynamic subduction zone modelling. Numerical models often employ an entrained weak layer (WL approach) to facilitate decoupling between the subducting and overriding plates. In such a setup, the kinematics of the flow lead to width variations in the subduction interface. When a uniform-width interface is prescribed, a transient evolution of the interface thickness occurs, during which the volmetric flux along the interface profile establishes equilibrium. Width variations can exceed 4× during this stage, which may impact the effective strength of the interface, both through physical effects if the rheology is linear, and numerical effects if the fault becomes poorly resolved. This transient process induces strong sensitivity to model resolution, and may present a significant challenge to reproducibility. Developing more robust ways to model the subduction interface will enable fully dynamic models to address sensitive subduction-zone processes, such as metamorphism near the slab top. In this study we discuss a simple strategy aimed at improving the standard WL approach. By prescribing a variable thickness weak layer at the outset of the model, and by controlling the limits of the layer thickness during the model evolution, we find improved stability and resolution convergence of the models.

Description: The grain growth of quartz was investigated using two samples of quartz (powder and quartzite) with water under pressure and temperature conditions of 1.0–2.5 GPa and 800–1100 °C. The compacted powder preserved a large porosity, which caused a slower grain growth than in the dense quartzite. We assumed a grain-growth law of dn-d0n = k0 fH2Or exp⁡(−Q/RT)t with grain size d (µm) at time t (second), initial grain size d0 (µm), growth exponent n, a constant k0 (µmn MPa−r s−1), water fugacity fH2O (MPa) with the exponent r, activation energy Q (kJ/mol), gas constant R, and temperature T in Kelvin. The parameters we obtained were n = 2.5 ± 0.4, k0 = 10−8.8 ± 1.4, r = 2.3 ± 0.3, and Q = 48 ± 34 for the powder, and n = 2.9 ± 0.4, k0 = 10−5.8 ± 2.0, r = 1.9 ± 0.3, and Q = 60 ± 49 for the quartzite. The grain-growth parameters obtained for the powder may be of limited use because of the high porosity of the powder with respect to crystalline rocks, even if the differences between powder and quartzite vanish when grain sizes reach ~ 70 µm. Extrapolation of the grain-growth laws to natural conditions indicates that the contribution of grain growth to plastic deformation in the middle crust may be small. However, grain growth might become important for deformation in the lower crust when the strain rate is

Description: After the onset of plate collision in the Alps, tectonic processes are inferred to have changed dramatically in the Alps: European plate break-offs in various places of the Alpine arc, as well as a subduction polarity reversal in the eastern Alps have been proposed. We review body-wave tomographic studies, compare them to our surface-wave-derived model, and interpret them in terms of slab geometries. We infer that the shallow subducting portion of the European plate is likely detached under both the western and eastern (but not the central) Alps. The Alps-Dinarides transition may be explained by a combination of European and Adriatic subduction. This implies that the deep high-velocity anomaly (〉 200 km depth) mapped by tomographers under the eastern Alps is a detached segment of the European plate. The shallower fast anomaly (100–200 km depth) can be ascribed to European or Adriatic subduction, or both. These findings are compared to previously proposed models for the eastern Alps in terms of slab geometry, but also integrated in a a new, alternative geodynamic scenario that best fits both tomographic images and geological constraints.

Description: Zoned monazite-(Ce) from Alpine fissures/clefts is used to gain new insights into the exhumation history of the Central Alpine Lepontine metamorphic dome, and timing of deformation along the Rhone-Simplon fault zone on the dome's western termination. These hydrothermal monazites-(Ce) directly date deformation and changes in physiochemical conditions through crystallization ages, in contrast to commonly employed cooling-based methods. The 480 SIMS measurement ages from 20 individual crystals record ages over a time interval between ~ 19 and 5 Ma, with individual grains recording ages over a lifetime of 2 to 7.5 Ma. The age range combined with age distribution and internal crystal structure help to distinguish between areas whose deformational history was dominated by distinct tectonic events or continuous exhumation. The combination of this age data with geometrical considerations and spatial distribution give a more precise exhumation/cooling history for the area. In the east and south of the study region, the units underwent monazite-(Ce) growth at 19–12.5 and 16.5–10.5 Ma, followed by a central group of monazite-(Ce) ages at 15–10 Ma and the movements and related cleft monazites-(Ce) are youngest at the western border with 13–7 Ma. A last phase around 8–7 Ma is limited to clefts of the Simplon normal fault and related strike slip faults as the Rhone and Rhine-Rhone faults. The large data-set spread over significant metamorphic structures shows that the opening of clefts, fluid flow and monazite-(Ce) stability is direct linked to the geodynamic evolution in space and time.

Description: Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identifying coarse-grained materials associated to the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Göta River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with the radio magnetotelluric and traveltime tomography models. The morphology of the river bottom and riverbanks, as e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits is clearly revealed. An extensive coarse-grained layer exists in the sedimentary sequence and is interpreted and modelled in a regional context. Individual fractures and fracture zones are identified within bedrock and sediments. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops. The groundwater flow in the coarse-grained layer promotes leaching of marine salts from the overlying clays by slow infiltration and/or diffusion, which helps in the formation of potential quick clays. Magnetic data show coarse-grained materials at the landslide scar located in the study area, which may have acted as a sliding surface together with quick clays.

Description: Studying the uppermost structure of the subsurface is a necessary part for solving many practical problems (exploration of minerals, groundwater studies, geoengineering, etc.). Practical application of active seismic methods is not always possible because of different reasons, such as logistical difficulties, high cost of work, high level of seismic and acoustic noise, etc. That is why developing and improving of passive seismic methods for these purposes is one of the important problems in applied geophysics. In our study, we describe the way of improving quality of Empirical Green’s Functions (EGFs), evaluated from high-frequency ambient seismic noise, by using of advanced technique of cross-correlation functions stacking in the time domain (in this paper we use term “high-frequency” for the frequencies higher than 1 Hz). In compare to existing techniques, based on weight-stacking, our proposed technique makes it possible to more significantly increase the signal-to-noise ratio and, therefore quality of the EGF. The technique is based on both iterative and global optimization algorithms, where the optimized parameter is a signal-to-noise ratio of an EGF, retrieved for each iteration. The technique has been tested with the field data acquired in an area with high level of industrial noise (Pyhäsalmi Mine, Finland) and in an area with low level of anthropogenic noise (Kuusamo Greenstone Belt, Finland). The results show that the our proposed technique can be used for extraction of EGFs from high-frequency seismic noise in practical problems of mapping of the shallow subsurface in areas with high and low level of high-frequency seismic noise.

Description: During the 2012 seismic sequence of Emilia region (Northern Italy), the earthquake ground motion in the epicentral area featured longer duration and higher velocity than those estimated by empirical-based prediction equations typically adopted in Italy. In order to explain these anomalies, we (1) build up a structural and geophysical 3D digital model of the crustal sector involved in the sequence, (2) reproduce the earthquake ground motion at some seismological stations through physics-based numerical simulations and (3) compare the observed recordings with the simulated ones. In this way we investigate how the earthquake ground motion in the epicentral area is influenced by local stratigraphy and geological structure buried under the Po Plain alluvium. Our study area covers approximately 5000 km2 and extends from the Po river right bank to the Northern Apennines morphological margin in N-S direction, and between the two chief towns of Reggio Emilia and Ferrara in W-E direction, involving a crustal volume with 20 km of thickness. We set up the 3D model by using already published geological and geophysical data, with a detail corresponding to a map at scale 1:250 000. The model depicts the stratigraphic and tectonic relationships of the main geological formations, the known faults and the spatial pattern of the seismic properties. Being a digital vector structure, the 3D model can be easily modified or refined locally for future improvements or applications. We exploited high performance computing to perform numerical simulations of the seismic wave propagation in the frequency range up to 2 Hz. In order to get rid of the finite source effects and validate the model response, we choose to reproduce the ground motion related to two moderate-size aftershocks of the 2012 Emilia sequence that were recorded by a large number of stations. The obtained solutions compare very well to the recordings available at about 30 stations, in terms of peak ground velocity and signal duration. Snapshots of the simulated wavefield allow us to explain the exceptional length of the observed ground motion as due to surface waves overtones that are excited in the alluvial basin by the buried ridge of the Mirandola anticline. Physics-based simulations using realistic 3D geo-models show eventually to be effective for assessing the local seismic response and the seismic hazard in geologically complex areas.

Description: The 2D Distinct Element Method (DEM) code (PFC2D_V5) is here used to simulate the evolution of subsidence-related karst landforms, such as single and clustered sinkholes, and associated larger-scale depressions. Subsurface material in the DEM model is removed by a feedback loop to produce an array of cavities; this simulates a network of subsurface groundwater conduits growing by chemical/mechanical erosion. The growth of the cavity array is coupled mechanically to the surroundings such that cavities can grow also in part by material failure at their margins, which in the limit can produce individual collapse sinkholes. Two end-member growth scenarios of the cavity array and their impact on surface subsidence were examined in the models: (1) cavity growth at the same level and at the same individual growth rate; (2) cavity growth at progressively deepening levels with varying individual growth rates. These growth scenarios are characterised by differing stress patterns across the cavity array and its overburden, which are in turn an important factor for the formation of sinkholes and uvala-like depressions. For growth scenario (1), a stable compression arch is established around the cavity array, hindering sinkhole collapse into individual cavities and favouring block-wise subsidence across the whole cavity array. In contrast, for growth scenario (2), the stress system is more heterogeneous, such that local stress concentrations exist around individual cavities leading to stress interaction. Consequently, sinkhole collapses into individual cavities occurs by shear or tensile failure of the overburden, and these sinkholes lie within a larger scale depression linked to the cavity array as a whole. The results from models with growth scenario (2), which also account for variations in mechanical properties of the overburden, are in close agreement with surface morphological and subsurface geophysical observations from a karst area on the eastern shore of the Dead Sea.

Description: In this study petrophysical characteristics of three consecutive sandstone layers of the Lower Cretaceous Hatira Formation from northern Israel were comprehensively investigated and analysed. The methods used were: experimental petrographic and petrophysical methods, 3D micro-CT imaging and pore-scale single-phase flow modelling, conducted in parallel. All three studied sandstone layers show features indicative of high textural and mineralogical maturity in agreement with those reported from the Kurnub Group in other localities in the Levant. The occurrence of cross-bedding in layers enriched in silt and clay, between the quartz arenite rich beds, may suggest a deposition in a fluvial environment. A higher degree of Fe-ox cementation was observed in the top layer contrasting with a low extent of Fe-ox cementation in the bottom layer. Both quartz-arenite layers are located above and below the intermediate 20 cm thick least permeable quartz wacke sandstone layer. The latter presumably prevented the supply of the iron-rich meteoric water to the bottom layer. Evaluated micro-scale geometrical rocks properties (pore size distribution, pore throat size, characteristic (pore-throat) length, pore throat length of maximal conductance, specific surface area, grain roughness) and macro-scale petrophysical properties (porosity and tortuosity) predetermined the permeability of the studied layers. Large-scale laboratory porosity and permeability measurements show low variability in the quartz arenite (top and bottom) layers, and high variability in the quartz wacke (intermediate) layer. These degrees of variability are confirmed also by anisotropy and homogeneity analyses conducted in the μCT-imaged geometry. Qualitative evaluation of anisotropy (based on statistical distribution of pore space) and connectivity (using Euler Characteristic) were correlated with mineralogy and grain surface characteristics, clay matrix and preferential location of cementation. Two scales of porosity variations were found with variogram analysis of the upper quartz arenite layer: fluctuations at 300 μm scale due to pores size variability, and at 2 mm scale due to the appearance of high and low porosity occlusion by ferruginous bands showing iron oxide cementation. We suggest that this cementation is a result of iron solutes transported by infiltrating water through preferential permeable paths in zones having large grains and pores. Fe-ox precipitated as a result of reaction with oxygen in a partly-saturating realm at the large surface area localities adjacent to the preferential conducting paths. The core part of the study is the investigation of macroscopic permeability, upscaled from pore-scale velocity field, simulated by free-flow in real μCT-scanned geometry on mm-scale sample. The results show an agreement with lab petrophysical estimates on cm-scale sample for the top and bottom layers. Estimated permeability anisotropy correlates with the presence of beddings with 2 mm scale variability in the top layer. The results show that this kind of anisotropy rather than a variability at the pore-scale controls the macroscopic rock permeability. Therefore, we suggest that in order to upscale reliably to the lab permeability, a sufficiently large modelling domain is required to capture the textural features that appear at a scale larger than the pore scale. We also discuss imaging and modelling practices able to preserve the characteristics of the pore network during the entire computational workflow procedure, applicable to studies in the fields of hydrology, petroleum geology, or sedimentary ore deposits.

Description: Long-term measurements of volcanic gas emissions conducted during the recent decade suggest that under certain conditions the magnitude or chemical composition of volcanic emissions exhibits periodic variations with a period of about two weeks. A possible cause of such a periodicity can be attributed to the Earth tidal potential. The phenomenology of such a link has been debated for long, but no quantitative model has yet been proposed. The aim of this paper is to elucidate whether a causal link from the tidal forcing to variation in the volcanic degassing can be traced analytically. We model the response of a simplified magmatic system to the local tidal gravity variations and derive a periodical vertical magma displacement in the conduit with an amplitude of 0.1–1 m, depending on geometry and physical state of the magmatic system. We find that while the tide-induced vertical magma displacement has presumably no significant direct effect on the volatile solubility, the differential magma flow across the radial conduit profile may result in a significant increase of the bubble coalescence rate in a depth of several kilometres by up to several ten percent. Because bubble coalescence facilitates separation of gas from magma and thus enhances volatile degassing, we argue that the derived tidal variation may propagate to a manifestation of varying volcanic degassing behaviour. The presented model provides a first basic framework which establishes an analytical understanding of the link between the Earth tides and volcanic degassing.

Description: Proper estimate of moment magnitude that is a physical measure of the energy released at earthquake source is essential for better seismic hazard assessments in tectonically active regions. Here a coda wave modeling approach that enables the source displacement spectrum modeling of examined event was used to estimate moment magnitude of central Anatolia earthquakes. To achieve this aim, three component waveforms of local earthquakes with magnitudes 2.0 ≤ ML ≤ 5.2 recorded at 72 seismic stations which have been operated between 2013 and 2015 within the framework of the CD-CAT passive seismic experiment. An inversion on the coda wave traces of each selected single event in our database was performed in five different frequency bands between 0.75 and 12 Hz. Our resultant moment magnitudes (MW-coda) exhibit a good agreement with routinely reported local magnitude (ML) estimates for study area. Finally, we present an empirical relation between MW-coda and ML for central Anatolian earthquakes.

Description: TheGeodynamic World Builder is an open source code library intended to set up initial conditions for computational geodynamic models in both Cartesian and Spherical geometries. The inputs for the JSON-style parameter file are not mathematical, but rather a structured nested list describing tectonic features, e.g. a continental, an oceanic or a subducting plate. Each of these tectonic features can be assigned a specific temperature profile (e.g. plate model) or composition label (e.g. uniform). For each point in space, the Geodynamic World Builder can return the composition and/or temperature. It is written in C++, but can be used in almost any language through its C and Fortran wrappers. Various examples of 2D and 3D subduction settings are presented. The World builder comes with an extensive online User Manual.

Description: The dynamic evolution of fault zones at the seismogenic brittle-ductile transition zone (BDTZ) expresses the delicate interplay of numerous physical and chemical processes that occur at the time of strain localization. Deformation and flow of aqueous fluids in these zones, in particular, are closely related and mutually dependent during cycles of repeating, transient frictional and viscous deformation. Despite numerous studies documenting in detail seismogenic faults exhumed from the BDTZ, uncertainties remain as to the role of fluids in facilitating deformation in this zone, particularly with regard to the mechanics of broadly coeval brittle and ductile deformation. We combine here structural analysis, fluid inclusion data and mineral chemistry data from synkinematic and authigenic minerals to reconstruct the temporal variations in P, T and bulk composition of the fluids that mediated deformation and steered strain localization in a strike-slip fault from the BDTZ. This is a fault formed within the Paleoproterozoic migmatitic basement of southwestern Finland, hosting in its core two laterally continuous quartz veins formed by two texturally distinct quartz types – Qtz I and Qtz II, where Qtz I is demonstrably older than Qtz II. Veins within the diffuse damage zone of the fault are infilled by Qtz I. Multi-scalar structural analysis indicates recurrent cycles of mutually overprinting brittle and ductile deformation. Fluid inclusion microthermometry and mineral pair geothermometry indicate that both quartz types precipitated from a fluid that was in a homogeneous state during the recurrent cycles of faulting, and whose bulk salinity was in the 0–5 wt % NaCleq range. The temperature of the fluid phase involved with the various episodes of initial strain localization and later reactivation changed with time, from c. 240 °C in the damage zone to c. 350 °C in the core during Qtz I precipitation to 〈 200 °C at the time of Qtz II crystallization. Fluid pressure estimates show an oscillation in pore pressure comprised between 160 and 10 MPa during the fault activity stages. Our results suggest significant variability in the overall physical conditions during the fault deformation history, possibly reflecting the interaction of several batches of compositionally similar fluids ingressing the dilatant fault zone at different stages of its evolution, each with specific T and P conditions. Initial, fluid-mediated embrittlement of the faulted rock volume generated a diffuse network of joint and/or hybrid/shear fractures in the damage zone, whereas progressive strain localization led to more localized deformation within the fault core. Localization was guided by cyclically increasing fluid pressure and transient embrittlement of a system that was otherwise at overall ductile conditions. Our analysis implies that fluid overpressure at the brittle-ductile transition can play a key role in the initial embrittlment of the metamorphic basement and strain localization mechanisms.

Description: The solid earth and exploration communities independently developed a variety of seismic imaging methods for passive- and active-source data. Despite the seemingly different approaches and underlying principles, many of those methods are based in some way or another on Green's theorem. The aim of this paper is to discuss a variety of imaging methods in a systematic way, using a specific form of Green's theorem (the homogeneous Green's function representation) as the common starting point. The imaging methods we cover are time-reversal acoustics, seismic interferometry, back propagation, source-receiver redatuming and imaging by double focusing. We review classical approaches and discuss recent developments that fully account for multiple scattering, using the Marchenko method. We briefly indicate new applications for monitoring and forecasting of responses to induced seismic sources, which are discussed in detail in a companion paper.

Description: On 6 April 2009, a Mw 6.1 earthquake struck the Plio-Quaternary intermontane L'Aquila Basin in central Italy, causing strong damages in L'Aquila historical downtown and surroundings, which were affected by notable site effects. Previous works have suggested that different site effects may be related to the complex subsurface geologic architecture, given by the variability of thickness and lithology of L'Aquila Basin clastic deposits, on which the city was built. To improve the 3D geological model of L'Aquila downtown for seismic site response evaluation and to estimate the Seismic Hazard of possible buried active normal faults, a multitask project has been carried out consisting mainly of the integration of subsurface dataset, including geological and geophysical surveys. Data have been interpreted with the aim to conceive and build a detailed model for the Plio-Quaternary cover of the continental basin and the buried morphology of the Meso-Cenozoic bedrock. We report the results concerning the interpretation of a 1 km-long high-resolution seismic reflection profile and refraction tomography integrated with the stratigraphy from deep and shallow boreholes. The results allowed us to reconstruct the Plio-Quaternary succession below L'Aquila downtown. The Plio-Quaternary depocentre corresponds to a minor NNW-SSE graben, which is developed within the main regional graben that borders L'Aquila Basin. Finally, data interpretation allowed to reconstruct the Plio-Quaternary tectono-stratigraphic evolution of the basin, to evidence the recent activity of several faults, and to define the subsoil geological model of the study area. All these data, which are functional to define the seismic site effects and to detect the activity of faults, are useful to mitigate the Seismic Hazard of cultural heritage cities of central Italy, such as the case study of L'Aquila downtown.

Description: Acoustic energy emitted by drill bit can be recorded by geophones on the surface and processed for an image of the subsurface using seismic interferometry methods. Pilot sensors record bit signal on the drill rig and play an important role in processing geophone traces for the image. When pilot traces are not available, traces of the nearest geophone to the rig may be used in deconvolution and crosscorrelation of data but extra signal processing efforts are required to reduce the effect of source signature on crosscorrelation results. In this study, we use seismic interferometry method to image the shallow subsurface beneath a 2D geophone array by converting geophones to virtual sources. As there is no pilot signal available for this survey, we use nearest geophone trace for pilot crosscorrelation and pilot deconvolution. We modify the spectrum of pilot crosscorrelation and deconvolution results so that the effect of source function on virtual data is minimized. We then migrate the virtual shots and compare the results of interferometric imaging with the available image from 3D (active source) survey and assess the efficiency of our approach. We show that drill bit noise data can be used to generate a reasonably accurate image of the subsurface even in the absence of pilot recordings but the results should be checked for appearance of virtual multiples and depth inconsistencies that are caused by errors in the migration velocity.

Description: In this work, we analyze the origin, evolution, and recent sedimentation of the Rio Grande Terrace (RGT), the most prominent upper slope terrace of the SW Atlantic. We gathered data from deep to shallow seismic, echo-sounding and surface sediments in order to recognize the role played by the geological inheritance, the sediment origin, and the present hydrodynamics, this last one defined by the action of the high speeds of the Brazil Current. The RGT is here interpreted as a unique geomorphological feature, which was developed over a pre-Aptian basement high. It presents a complex modern morphology, given by the erosional action of the Brazil Current and its present surface sediments show a high complexity in terms of origin and grain size.

Description: This study sheds light on the deformation mechanisms of subducted mafic rocks metamorphosed at amphibolite and granulite facies conditions, and on their importance for strain accommodation and localization at the top of the slab during subduction infancy. These rocks, namely metamorphic soles, are oceanic slivers stripped from the downgoing slab and plastered below the upper plate mantle wedge during the first million years of intra-oceanic subduction, when the subduction interface is still warm. Their formation and intense deformation (i.e. shear strain ≥ 5) attest to a systematic and transient coupling between the plates over a restricted time span of ~1 My and specific rheological conditions. Combining micro-structural analyses with mineral chemistry constrains grain-scale deformation mechanisms and the rheology of amphibole and amphibolites along the plate interface during early subduction dynamics, as well as the interplay between brittle and ductile deformation, water activity, mineral change, grain size reduction and phase mixing. Results indicate, in particular, that increasing pressure-temperature conditions and slab dehydration (from amphibolite to granulite facies) lead to the crystallization of mechanically strong phases (garnet, clinopyroxene and high-grade amphibole) and rock hardening. In contrast, during early exhumation and cooling (from ~850 down to ~700 °C – 0.7 GPa), the garnet-clinopyroxene-bearing amphibolite experiences pervasive retrogression (and fluid ingression) and significant strain weakening essentially accommodated by dissolution-precipitation and grain boundary sliding processes. Observations also indicate cyclic brittle deformation near peak conditions and throughout the early exhumation, which contributed to fluid channelization within the amphibolites, and possibly strain localization accompanying detachment from the slab. These mechanical transitions, coeval with detachment and early exhumation of the HT metamorphic soles, controlled mechanical coupling across the plate interface during subduction infancy, between the top of the slab and the peridotites above. Our findings may thus apply to other geodynamic environments where similar temperatures, lithologies, fluid circulation and mechanical coupling between mafic rocks and peridotites prevail, such as in mature warm subduction zones (e.g., Nankai, Cascapedia), in lower continental crust shear zones and oceanic detachments.

Description: In NE Poland, the Eastern European Craton (EEC) crust of the Fennoscandian affinity is concealed under a Phanerozoic platform cover and penetrated by the sparse deep research wells. Most of the inferences regarding its structure rely on geophysical data. Until recently, this area was covered only by the refraction/wide-angle reflection (WARR) profiles, which show a relatively simple crustal structure with a typical cratonic 3-layer crust. ION Geophysical PolandSPAN™ regional seismic program, acquired over the marginal part of the EEC in Poland, offered a unique opportunity to derive a detailed image of the deeper crust. Here, we apply extended correlation processing to a subset (~950 km) of the PolandSPAN™ dataset located in NE Poland, which enabled us to extend the nominal record length of the acquired data from 12 to 22 s (~60 km depth). Our new processing revealed reflectivity patterns, that we primarily associate with the Paleoproterozoic crust formation during the Svekofennian (Svekobaltic) orogeny and which are similar to what was observed along the BABEL and FIRE profiles in the Baltic Sea and Finland, respectively. We propose a mid- to lower-crustal lateral flow model to explain the occurrence of two sets of structures that can be collectively interpreted as kilometre-scale S-C' shear zones. The structures define a penetrative deformation fabric invoking ductile extension of hot orogenic crust. Localized reactivation of these structures provided conduits for subsequent emplacement of gabbroic magma that produced a Mesoproterozoic anorthosite-mangerite-charnockite-granite (AMCG) suite in NE Poland. Delamination of overthickened orogenic lithosphere may have accounted for magmatic underplating and fractionation into the AMCG plutons. We also found sub-Moho dipping mantle reflectivity, which we tentatively explain as a signature of the crustal accretion during the Svekofennian orogeny. Later tectonic phases (e.g. Ediacaran rifting, Caledonian orogeny) did not leave a clear signature in the deeper crust, however, some of the subhorizontal reflectors below the basement, observed in the vicinity of the AMCG Mazury complex, can be alternatively linked with lower Carboniferous magmatism.

Description: Interpretation of deep seismic data is challenging due to the lack of direct geological constraints from drilling and the more limited amount of data available from 2-D profiles in comparison to hydrocarbon exploration surveys. Thus other constraints that can be derived from the seismic data themselves can be of great value. Though the origin of most deep seismic reflections remains ambiguous, an association between seismic reflections and crustal strain, e.g. shear zones, underlies many interpretations. Estimates of the 3D orientation of reflectors may help associate specific reflections, or regions of the crust, with geological structures mapped at the surface whose orientation and tectonic history are known. In the case of crooked 2-D onshore seismic lines, the orientation of reflections can be estimated when the range of azimuths in a common midpoint gather is greater than approximately 20 degrees, but integration of these orientation attributes into an interpretation of migrated seismic data requires that they also be migrated. Here we present a simple approach to the 2-D migration of these orientation attributes that utilises that apparent the dip of reflections on the unmigrated stack, and maps reflector strike, for example, to a short linear segment depending on its original position and a migration velocity. This interpretation approach has been applied to a seismic line shot across the Younami Terrane of the Australian Yilgarn Craton, and indicates that the lower crust behaved differently from the overlying middle crust as the newly assembled crust collapsed during the Late Archean. Some structures related to approximately east-directed shortening are preserved in the middle crust, but the lower crust is characterized by reflectors that suggest N-NNE-oriented ductile flow. Deployment of off-line receivers during seismic acquisition allows the recording of a larger range of source-receiver azimuths, and should produce more reliable future estimates of reflector attributes.

Description: Imaging via Pre-Stack Depth Migration (PSDM) from reflection towed-streamer Multi-Channel Seismic (MCS) data at the scale of the whole crust is inherently difficult. This mainly results because the depth-penetration of the seismic wavefield is controlled, firstly (i) by the acquisition design, like streamer length and air-gun source configuration, and secondly (ii) by the complexity of the crustal structure. Indeed, the limited length of the streamer makes the estimation of velocities from deep targets challenging due to the velocity-depth ambiguity. The problem is even more pronounced when processing 2D seismic data, due to the lack of multi-azimuthal coverage. Therefore, in order to broaden our knowledge about the deep crust using seismic methods, one shall target the development of specific imaging workflows integrating different seismic data. Here we propose the combination of velocity model-building using (i) first-arrival traveltime tomography (FAT) and full-waveform inversion (FWI) of wide-angle/long-offset data collected by stationary Ocean Bottom Seismometers (OBS) and (ii) PSDM of short-spread towed-streamer MCS data for reflectivity imaging, using the former velocity model as background model. We present an application of such workflow to seismic data collected by Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER) in the eastern Nankai Trough (Tokai area) during the 2000/2001 SFJ experiment. We show that the FWI model, although derived from OBS data, provides yet an acceptable background velocity field for the PSDM of the MCS data. Furthermore, from the initial PSDM, we first refine the FWI background velocity model by minimizing the residual moveouts (RMO) picked in the prestack migrated volume through slope tomography (ST), from which we generate a better focused migrated image. Such integration of different seismic data sets and leading-edge imaging techniques led to optimal imaging results at different resolution levels. That is, the large-to-intermediate scale crustal units identified in the high-resolution FWI velocity model extensively complement the short-scale reflectivity inferred from the MCS data to better constrain the structural factors controlling the geodynamics of the Nankai Trough area.

Description: Curie depth offers a valuable constraint on the thermal structure of the lithosphere, based on its interpretation as the depth to 580 °C, but current methods underestimate the range of uncertainty. We formulate the estimation of Curie depth within a Bayesian framework to quantify its uncertainty across the British Isles. Uncertainty increases exponentially with Curie depth but this can be moderated by increasing the size of the spatial window taken from the magnetic anomaly. The choice of window size needed to resolve the magnetic thickness is often ambiguous, but based on our chosen spectral method, we determine that significant gains in precision can be obtained with windows sizes 15–30 times larger than the deepest magnetic source. Our Curie depth map of the British Isles includes a combination of window sizes: smaller windows are used where the magnetic base is shallow to resolve small-scale features, and larger window sizes are used where the magnetic base is deep in order to improve precision. On average, the Curie depth increases from Laurentian crust (22.2 ± 5.3 km) to Avalonian crust (31.2 ± 9.2 km). The temperature distribution in the crust, and associated uncertainty, was simulated from the ensemble of Curie depth realisations assigned to a lower thermal boundary condition of a crustal model (sedimentary thickness, Moho depth, heat production, thermal conductivity), constructed from various geophysical and geochemical data sets. The uncertainty of the simulated heat flow field substantially increases from ± 10 mW m−2 for shallow Curie depths ~ 15 km to ± 80 mW m−2 for Curie depths 〉 40 km. Surface heat flow observations are concordant with the simulated heat flow field except in regions that contain igneous bodies. Heat flow data within large batholiths in the British Isles exceed the simulated heat flow by ∼ 25 mW m−2 as a result of their high rates of heat production (4–6 μW m−3). Conversely, heat refraction around thermally resistive mafic volcanics and thick sedimentary layers induce a negative heat flow misfit of a similar magnitude. A northward thinning of the lithosphere is supported by shallower Curie depths on the northern side of the Iapetus Suture, which separates Laurentian and Avalonian terranes. Cenozoic volcanism in Northern Britain and Ireland has previously been attributed to a lateral branch of the proto-Icelandic mantle plume. Our results show that high surface heat flow (〉 90 mW m−2) and shallow Curie depth (∼ 15 km) occur within the same region, which supports the hypothesis that lithospheric thinning occurred due to the influence of a mantle plume. That the uncertainty is only ± 3–8 km in this region, demonstrates that Curie depths are more reliable in hotter regions of the crust where the magnetic base is shallow.

Description: Subduction-Transform Edge Propagator (STEP) faults are the locus of continual lithospheric tearing at slab edges, resulting in sharp changes in the lithospheric and crustal thickness and triggering lateral and/or near-vertical mantle flow. However, the mechanisms at the lithospheric mantle scale are still poorly understood. Here, we present the microstructural study of olivine-rich lherzolite, harzburgite and wehrlite mantle xenoliths from the Oran volcanic field (Tell Atlas, NW Algeria). This alkali volcanic field occurs along a major STEP fault responsible for the Miocene westward slab retreat in the westernmost Mediterranean. Mantle xenoliths provide a unique opportunity to investigate the microstructures in the mantle section of a STEP fault system. The microstructures of mantle xenoliths show a variable grain size ranging from coarse granular to fine-grained equigranular textures uncorrelated with modal variations. The major element composition of the mantle peridotites provides temperature estimates in a wide range (790–1165 °C) but in general, the coarse-grained and fine-grained peridotites suggest deeper and shallower provenance depth, respectively. Olivine grain size in the fine-grained peridotites depends on the size and volume fraction of the pyroxene grains, which is consistent with pinning of olivine grain growth by pyroxenes as second phase particles. In the coarse-grained peridotites, well-developed olivine crystal preferred orientation (CPO) is characterized by orthorhombic and [100]-fiber symmetries, and orthopyroxene has a coherent CPO with that of olivine, suggesting their coeval deformation by dislocation creep at high-temperature. In the fine-grained microstructures, along with the weakening of the fabric strength, olivine CPO symmetry exhibits a shift towards [010]-fiber and the [010]- and [001]-axes of orthopyroxene are generally distributed subparallel to those of olivine. These data are consistent with deformation of olivine in the presence of low amounts of melts and the precipitation of orthopyroxenes from a melt phase. The bulk CPO of clinopyroxene mimics that of orthopyroxene via a topotaxial relationship of the two pyroxenes. This observation points to a melt-related origin of most clinopyroxenes in the Oran mantle xenoliths. The textural and geochemical record of the peridotites are consistent with interaction of a refractory harzburgite protolith with a high-Mg# melt at depth (resulting in the formation of coarse-grained clinopyroxene-rich lherzolite and wehrlite), and with a low-Mg# evolved melt in the shallow subcontinental lithospheric mantle (forming fine-grained harzburgite). We propose that pervasive melt-peridotite reaction – promoted by lateral and/or near-vertical mantle flow associated with lithospheric tearing – resulted in the synkinematic crystallization of secondary lherzolite and wehrlite and played a key effect on grain size reduction during the operation of the Rif-Tell STEP fault. Melt-rock reaction and secondary formation of lherzolite and wehrlite may be widespread in other STEP fault systems worldwide.

Description: The stratigraphic architecture of the Swiss Molasse basin reveals crucial information about the basin’s geometry, its evolution and the processes leading to the deposition of the clastic material. Nevertheless, the formation of the Upper Marine Molasse (OMM) and the controls on the related Burdigalian transgression are not fully understood yet. During these times, from c. 20 to 17 Ma, the Swiss Molasse basin was partly flooded by a peripheral shallow marine sea, striking SW – NE. We proceeded through detailed sedimentological and stratigraphic examinations of several sites across the entire Swiss Molasse basin in order to deconvolve the stratigraphic signals related surface and tectonic controls. Surface-related signals include stratigraphic responses to changes in eustatic sea level and sediment fluxes, while the focus on crustal-scale processes lies on the uplift of the Aar-massif at c. 20 Ma. Field examinations show, that the evolution of the Burdigalian seaway was characterized by (i) shifts in the depositional settings, (ii) changes in discharge directions, a deepening and widening of the basin, and (iv) phases of erosion and non-deposition. We relate these changes in the stratigraphic records to a combination of surface and tectonic controls at various scales. In particular, roll-back subduction of the European mantle lithosphere, delamination of crustal material and the associated rise of the Aar-massif most likely explain the widening of the basin particular at distal sites. In addition, the uplift of the Aar-massif was likely to have shifted the patterns of surface loads. These mechanisms could have caused a flexural adjustment of the foreland plate underneath the Molasse basin, which we use as mechanism to explain the establishment of distinct depositional environments and particularly the formation of subtidal-shoals where a lateral bulge is expected. In the Alpine hinterland, these processes occurred simultaneously with a period of fast tectonic exhumation accomplished through slip along the Simplon detachment fault, with the consequence that sediment flux to the basin decreased. It is possible that this reduction in sediment supply contributed to the establishment of marine conditions in the Swiss Molasse basin and thus amplified the effect related to the tectonically controlled widening of the basin. Because of the formation of shallow marine conditions, subtle changes in the eustatic sea level contributed to the occurrence several hiatus that chronicle periods of erosion and non-sedimentation. While these mechanisms are capable of explaining the establishment of the Burdigalian seaway and the formation of distinct sedimentological niches in the Swiss Molasse basin, the drainage reversal during OMM-times possibly requires a change in the tectonic processes at the slab scale. We conclude that sedimentological records can be used to decipher surface controls and lithospheric-scale processes in orogens from the stratigraphic record, provided that a detailed sedimentological and chronological database is available.

Description: The depth-dependent anisotropic structure of the lithosphere under the Borborema Province of northeast Brazil has been investigated through harmonic stripping of receiver functions developed at 39 stations in the region. This method retrieves the first (k = 1) and second (k = 2) degree harmonics of a receiver function dataset, which characterize seismic anisotropy beneath a seismic station. Anisotropic fabrics are in turn directly related to the deformation of the lithosphere from past and current tectonic processes. Our results reveal the presence of anisotropy within the crust and the lithospheric mantle throughout the entire Province, with the exception of a few stations in the continental interior that lack evidence for any anisotropic signatures. Most stations in the continental interior report consistent anisotropic orientations in the crust and lithospheric mantle, suggesting a dominant NE-SW pervasive deformation along lithospheric-scale shear zones developed during the Brasiliano-Pan African orogeny. The lack of anisotropy at a few stations along a NE-SW trend in the center on the Province is harder to explain, but might be related to heating of the lithosphere by an asthenospheric channel. Finally, several stations along the Atlantic coast reveal depth-dependent anisotropic orientations roughly (sub)perpendicular to the margin. These results suggest a more recent overprint, probably related to the presence of frozen anisotropy in the lithosphere due to stretching and rifting during the opening of the South Atlantic.

Description: The geochemical conditions conducive to dolomite formation in shallow evaporitic environments along the Triassic Tethyan margin are still poorly understood. Most of the Triassic dolomites in the Austroalpine and the South Alpine realm are affected by late diagenetic or hydrothermal overprinting, but recent studies from the Carnian Travenanzes Formation (South Alpine) provide evidence of primary dolomite. Here a petrographic and geochemical study of the dolomites intercalated in a 100-m-thick Carnian sequence of distal alluvial plain deposits is presented to gain better insight into the conditions and processes of dolomite formation. The dolomites occur as 10- to 50-cm-thick homogenous beds, mm-scale laminated beds and nodules associated with palaeosols. The dolomite is nearly stoichiometric with slightly attenuated c-reflections. Sedimentary structures indicate that the initial primary dolomite or precursor phase consisted largely of unlithified mud. Strontium isotope ratios (87Sr / 86Sr) of homogeneous and laminated dolomites reflect Triassic seawater, suggesting precipitation in evaporating seawater in a coastal ephemeral lake or sabkha system. However, the setting differed from modern sabkha or coastal ephemeral lake systems by seasonally wet conditions with a significant siliciclatic input and inhibition of significant lateral groundwater flow through impermeable clay deposits, thus representing a non-actualistic system in which dolomite formed along the ancient Tethyan margin.

Description: The Cheb Basin, a region of ongoing swarm earthquake activity in the western Czech Republic, is characterized by intense carbon dioxide degassing along two known fault zones – the N-S-striking Počatky-Plesná fault zone (PPZ) and the NW-SE-striking Mariánské Lázně fault zone (MLF). The fluid pathways for the ascending CO2 of mantle origin are subject of an International Continental Scientific Drilling Program (ICDP) project in which several geophysical surveys are currently carried out to image the near-surface geologic situation, as existing boreholes are not sufficiently deep to characterize the structures. As electrical resistivity is a sensitive parameter to the presence of low-resistivity rock fractions as liquid fluids, clay minerals and also metallic components, a large-scale dipole-dipole experiment using a special type of electric resistivity tomography (ERT) was carried out in June 2017 in order to image fluid-relevant structures. We used static remote-controlled data loggers in conjunction with high-power current sources for generating sufficiently strong signals that could be detected all along the 6.5 km long profile with 100 m and 150 m dipole spacings. Extensive processing of time series and apparent resistivity data lead to a full pseudosection and allowing interpretation depths of more than 1000 m. The subsurface resistivity image reveals the deposition and transition of the overlying Neogene Vildštejn and Cypris formations, but also shows a very conductive basement of phyllites and granites that can be attributed to high salinization or rock alteration by these fluids in the tectonically stressed basement. Distinct, narrow pathways for CO2 ascent are not observed with this kind of setup which hints at wide degassing structures over several kilometers within the crust instead. We also observed gravity/GPS data along this profile in order to constrain ERT results. Gravity clearly shows the deepest part of the Cheb Basin along the profile, its limitation by MLF at NE end, but also shallower basement with an assumed basic intrusion in SW part of profile. We propose a conceptual model in which certain lithological layers act as caps for the ascending fluids, based on stratigraphic records and our results from this experiment, providing a basis for future drills in the area aimed at studying and monitoring fluids.

Description: In the European region, the magnetic field at satellite altitudes (~ 350 km) is mainly defined by a long-wavelength magnetic-low called here the Central Europe Magnetic Low (CEML), located to the southwest of the Trans European Suture Zone (TESZ). We studied this area by a joint analysis of the magnetic and total gradient (∇T) anomaly maps, for a range of different altitudes of 5 km, 100 km and 350 km. Tests on synthetic models showed the usefulness of the joint analysis at various altitudes to identify reverse dipolar anomalies and to characterize areas in which magnetization is weak. By this way we identified areas where either reversely or normally magnetized sources are locally dominant. At a European scale these anomalies are sparse, with a low degree of coalescence effect. The ∇T map indeed presents generally small values within the CEML area, indicating that the Palaeozoic Platform is weakly magnetized. At 350 km altitude, the TESZ effect is largely dominant: with intense ∇T highs above the East European Craton (EEC) and very small values above the Palaeozoic Platform, this again denoting a weakly magnetized crust. Small coalescence effects are masked by the trend of the TESZ. Although we identified sparsely located reversely magnetized sources in the Palaeozoic Platform of the CEML, the joint analysis does not support a model of a generally reversely magnetized crust. Instead, our analysis strongly favors the hypothesis that the CEML anomaly is mainly caused by a sharp contrast between the magnetic properties of EEC and Palaeozoic Platform.

Description: The advent of cable-free nodal arrays for conventional seismic reflection and refraction experiments is changing the acquisition style for active source surveys. Instead of triggering short recording windows for each shot, the nodes are continuously recording over the entire acquisition period from the first to the last shot. The main benefit is a significant increase in geometrical and logistical flexibility. As a by-product, a significant amount of continuous data might also be collected. These data can be analysed with passive seismic methods and therefore offer the possibility to complement subsurface characterization at marginal additional cost. We present data and results from a 2.4 km long active source profile which has been recently acquired in Western Colorado (US) to characterize the structure and sedimentary infill of an over-deepened alpine valley. We show how the leftover passive data from the active source acquisition can be processed towards a shear wave velocity model with seismic interferometry. The shear wave velocity model supports the structural interpretation of the active P-wave data, and the P-to-S-wave velocity ratio provides new insights into the nature and hydrological properties of the sedimentary infill. We discuss the benefits and limitations of our workflow and conclude with recommendations for acquisition and processing of similar data sets.

Description: Few data exist that provide insight into processes affecting the long-term carbon cycle at shallow forearc depths. To better understand the mobilization of carbon in sediments and crust of the subducting slab, we investigated carbonate materials that originate from the subduction channel at the Mariana forearc (

Description: We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement until ~ 3 km depth obtained by full-waveform inversion of multichannel seismic data acquired with a 6 km-long streamer in the Alboran Sea (SE Iberia). The inherent non-linearity of the method, especially for short-offset, band-limited seismic data as this one, is circumvented by applying a data processing/modeling sequence consisting of three steps: (1) data re-datuming by back-propagation of the recorded seismograms to the seafloor; (2) joint refraction and reflection travel-time tomography combining the original and the re-datumed shot gathers; and (3) FWI of the original shot gathers using the model obtained by travel-time tomography as initial reference. The final velocity model shows a number of geological structures that cannot be identified in the travel-time tomography models or easily interpreted from seismic reflection images alone. A sharp strong velocity contrast accurately defines the geometry of the top of the basement. Several low-velocity zones that may correspond to the abrupt velocity change across steeply dipping normal faults are observed at the flanks of the basin. A 200–300 m thick, high-velocity layer embedded within lower velocity sediment may correspond to evaporites deposited during the Messinian crisis. The results confirm that the combination of data re-datuming and joint refraction and reflection travel-time inversion provides reference models that are accurate enough to apply full-waveform inversion to relatively short offset streamer data in deep water settings starting at field-data standard low frequency content of 6 Hz.

Description: We compare experimentally determined porosity with values derived from X-ray tomography for a suite of eight sandstone varieties covering a porosity range from about 3 to 25 %. In addition, we performed conventional stereological analysis of SEM images and examined thin sections. We investigated the sensitivity of segmentation, the conversion of the tomographic gray-value images representing the obtained X-ray attenuation coefficients into binary images, to (a) resolution of the digital images, (b) denoising filters, and (c) seven thresholding methods. Images of sandstones with porosities of 15 to 25 % exhibit a bimodal intensity distribution of the attenuation coefficients, enabling unambiguous segmentation that gives porosity values closely matching the laboratory values. For samples with lower porosities, pores and grains do not separate well in the skewed unimodal intensity histograms. For these samples, all tested thresholding methods tend to miscalculate porosity significantly. In addition to absolute porosity, the ratio between pore size and resolution, and mineralogical composition of the rocks affect the biases of the global segmentation methods.

Description: We present the implementation of Thomsen's weak anisotropy approximation for VTI media within TOMO3D, our code for 2-D and 3-D joint refraction and reflection traveltime tomographic inversion. In addition to the inversion of seismic P-wave velocity and reflector depth, the code can now retrieve models of the Thomsen's parameters δ and ε. Here we test this new implementation following four different strategies on a canonical synthetic experiment. First, we study the sensitivity of traveltimes to the presence of a 25 % anomaly in each of the parameters. Next, we invert for two combinations of parameters, (v, δ, ε) and (v, δ, v⟂), following two inversion strategies, simultaneous and sequential, and compare the results to study their performances and discuss their advantages and disadvantages. Simultaneous inversion is the preferred strategy and the parameter combination (v, δ, ε) produces the best overall results. The only advantage of the parameter combination (v, δ, v⟂) is a better recovery of the magnitude of v. In each case we derive the fourth parameter from the equation relating ε, v⟂ and v. Recovery of v, ε and v⟂ is satisfactory whereas δ proves to be impossible to recover even in the most favorable scenario. However, this does not hinder the recovery of the other parameters, and we show that it is still possible to obtain a rough approximation of δ distribution in the medium by sampling a reasonable range of homogeneous initial δ models and averaging the final δ models that are satisfactory in terms of data fit.

Description: By combining 3D boundary element model, frictional slip theory and fast computation method, we propose a new tool to improve fault slip analysis that allows to analyze a very large number of scenarios of stress and fault mechanical properties variations through space and time. Using both synthetic and real fault system geometries we analyze a very large number of numerical simulations (125,000) using fast iterative method to define for the first time macroscopic rupture envelopes for fault systems, referred to as “fault slip envelopes”. Fault slip envelopes are defined using variable friction, cohesion and stress state, and their shape is directly related to the fault system 3D geometry and the friction coefficient on fault surfaces. The obtained fault slip envelopes shows that very complex fault geometry implies low and isotropic strength of the fault system compared to geometry having limited fault orientations relative to the remote stresses, providing strong strength anisotropy. This technique is applied to the realistic geological conditions of the Olkiluoto high-level nuclear waste repository (Finland). The model results suggests that Olkiluoto fault system has a better probability to slip under the present day Andersonian thrust stress regime, than for the strike-slip and normal stress regimes expected in the future due to the probable presence of an ice sheet. This new tool allows to quantify the anisotropy of strength and probability of slip of 3D real fault networks as a function of a wide range of possible geological conditions an mechanical properties. This significantly helps to define the most conservative fault slip hazard case or to account for potential uncertainties in the input data for slip. This technique therefore applies to earthquakes hazard studies, geological storage, geothermal resources along faults and fault leaks/seals in geological reservoirs.

Description: Besides classical emplacement and accretion related nappe tectonics, the Oligocene to middle Miocene post-collisional evolution of the central European Alps was also characterized by pronounced vertically directed tectonics. These are expressed by backthrusting along the Insubric Line and the subsequent uplift of the External Crystalline Massifs (ECMs). During late Miocene times, the Central Alps experienced lateral growth when deformation propagated into the external parts of both the pro- and retro-side of the orogen. For the North Alpine foreland, pro-wedge propagation of deformation has been kinematically and spatially linked to the uplift and exhumation of the ECMs. In this paper, we investigate the young exhumation history of the North Alpine foreland. Based on low-temperature apatite (U-Th-Sm)/He thermochronometry, we constrain thrusting in the Subalpine Molasse between 12 Ma and 5 Ma, thus occurring coeval to the main deformation phase in the adjacent Jura fold-and-thrust belt (FTB) and late stage exhumation of the ECMs. However, this pattern of tectonic activity is not restricted to areas which are bordered by the ECMs, but is consistent along the entire front of the Central Alps, regardless of its hinterland architecture. The local-scale pattern of strain partitioning and style of deformation is governed by lateral variations in the sedimentary foreland basin architecture. We suggest that the large-scale constant tectonic signal is the response to a shift in tectonic forces caused by a deep-seated geodynamic process. This resulted in a change from dominantly vertical to orogen-scale horizontal tectonics and an associated orogen-perpendicular growth of crustal thickening. We constrain the onset of this major tectonic change to ca. 15 Ma in the Southern Alps and ca. 12 Ma in the North Alpine foreland, where it results in (re-)activation of thrusts in the Subalpine Molasse and folding in the Jura FTB.

Description: Considering poroelastic media containing aligned periodic fractures, we numerically quantify the effects that fractures with variable aperture distributions have on seismic wave attenuation and velocity dispersion due to fluid pressure diffusion (FPD). To achieve this, realistic models of fractures are generated with a stratified percolation algorithm which provides statistical control over geometrical fracture properties such as density and distribution of contact areas. The results are sensitive to both geometrical properties, showing that an increase in the density of contact areas as well as a decrease in their correlation length, reduce the effective seismic attenuation and the corresponding velocity dispersion. Moreover, no FPD effects are observed in addition to the one occurring between the fractures and the background, in the analysed frequency range, by considering realistic fracture models. We demonstrated that if appropriate equivalent physical properties accounting for the effects of contact areas are employed, a simple planar fracture can be used to emulate the seismic response of fractures with realistic aperture distributions. The excellent agreement between their seismic responses is demonstrated for all incidence angles and wave modes.

Description: Least-squares reverse-time migration (LSRTM) attempts to invert for the broadband-wavenumber reflectivity image by minimizing the residual between observed and predicted seismograms via linearized inversion. However, rugged topography poses a challenge in front of LSRTM. To tackle this issue, we present an unstructured mesh-based solution to topography LSRTM. As to the forward/adjoint modeling operators in LSRTM, we take a so-called unstructured mesh-based “grid method”. Before solving the two-way wave equation with the grid method, we prepare for it a velocity-adaptive unstructured mesh using a Delaunay Triangulation plus Centroidal Voronoi Tessellation (DT-CVT) algorithm. The rugged topography acts as constraint boundaries during mesh generation. Then, by using the adjoint method, we put the observed seismograms to the receivers on the topography for backward propagation to produce the gradient through the cross-correlation imaging condition. We seek the inverted image using the conjugate gradient method during linearized inversion to linearly reduce the data misfit function. Through the 2D SEG Foothill synthetic dataset, we see that our method can handle the LSRTM from rugged topography.

Description: Faults can act as barriers to fluid flow in sedimentary basins, hindering the migration of buoyant fluids in the subsurface, trapping them in reservoirs and facilitating the build-up of vertical fluid columns. The maximum height of these columns is reliant on the retention potential of the sealing fault with regards to the trapped fluid. Several different approaches for the calculation of maximum supported column height exist for hydrocarbon systems. Here, we translate these approaches to the trapping of carbon dioxide by faults and asses the impact of uncertainties in i) the wettability properties of the fault rock, ii) fault rock composition, and iii) reservoir depth, on retention potential. In similarity to hydrocarbon systems, uncertainties associated with the wettability of a CO2-brine-fault rock system for a given reservoir have less of an impact on column heights than uncertainties of fault rock composition. However, the wettability of the carbon dioxide system is highly sensitive to depth, with a large variation in possible column height predicted at 1000m and 2000m depth, the likely depth range for carbon storage sites. In contrast to hydrocarbon systems higher phyllosilicate entrainment into the fault rock may reduce the amount of carbon dioxide that can be securely retained. Our results show that if approaches developed for fault seal in hydrocarbon systems are translated, without modification, to carbon dioxide systems the capacity of carbon storage sites will be inaccurate, and the predicted security of storage sites erroneous.

Description: Layered evaporite sequences (LES) comprise interbedded weak layers (halite and, commonly, bittern salts) and strong layers (anhydrite and usually non-evaporite rocks such as carbonates and siliciclastics). This results in a strong rheological stratification, with a range of effective viscosity up to a factor of 105. We focus here on the deformation of competent intrasalt beds in different modes of salt tectonics using a combination of conceptual, numerical and analog models, and seismic data. In bedding-paralell extension, boudinage of the strong layers forms ruptured stringers, within a halite matrix, that become increasingly isolated with increasing strain. In bedding-parallel shortening, competent layers tend to maintain coherency while forming harmonic, disharmonic, and polyharmonic folds, with the rheological stratification leading to buckling and fold growth by bedding-parallel shear. In differential loading, extension and the resultant stringers dominate beneath suprasalt depocenters while folded competent beds characterize salt pillows. Finally, in tall passive diapirs, stringers generated by intrasalt extension are rotated to near vertical in tectonic melanges during upward flow of salt. In all cases, strong layers are progressively removed from areas of salt thinning and increasingly disrupted and folded in areas of salt growth as deformation intensifies. The varying styles of intrasalt deformation impact seismic imaging of LES and associated interpretations. Ruptured stringers are often visible where they have low dips, as in slightly extended salt layers or beneath depocenters, but are usually not imaged in tall passive diapirs due to steep dips. In contrast, areas of slightly to moderately shortened salt typically have well imaged, mostly continuous intrasalt reflectors, although seismic coherency decreases as deformation intensifies. Similarly, wells are most likely to penetrate strong layers in contractional structures and salt pillows, less likely in extended salt because they might drill between stringers, and unlikely in tall passive diapirs because the stringers are near-vertical. Thus, both seismic and well data may be interpreted to suggest that diapirs and other areas of more intense intrasalt deformation are more halite rich than is actually the case.

Description: Carbon capture and storage (CCS) is a potentially important technology for the mitigation of industrial CO2 emissions, however the majority of the subsurface storage capacity is in geological strata for which there is relatively little information, the so-called saline aquifers. Published estimates of the potential storage capacity of such formations, based on limited data, often give no indication of the uncertainty, despite there being substantial uncertainty associated with the data used to calculate such estimates. Using only publicly available data, a group of experts independently estimated the storage capacity of 7 regional saline aquifers. The experts produced a wide range of estimates for each aquifer due a combination of using different published values for some variables and differences in their judgements of the aquifer properties such as area and thickness. The range of storage estimates produced by the experts shows that there is significant uncertainty in such estimates, in particular the experts' range does not capture the highest possible capacity estimates, meaning that by not accounting for uncertainty, such regional estimates may underestimate the true storage capacity. The result is applicable to single values of storage capacity of regional potential, but not to detailed studies of a single storage site.

Description: Assessments of future climate warming-induced seafloor methane (CH4) release rarely include anaerobic oxidation of methane (AOM) within the sediments. Considering that more than 90 % of the CH4 produced in ocean sediments today is consumed by AOM, this may result in substantial overestimations of future seafloor CH4 release. Here we integrate a fully coupled AOM module with a numerical hydrate model to investigate under what conditions rapid release of CH4 can bypass AOM and result in significant fluxes to the ocean and atmosphere. The results presented in this study should be seen as a first step towards understanding AOM dynamics in relation to climate change and hydrate dissociation. Although the model is somewhat poorly constrained, our results indicate that vertical CH4 migration through hydraulic fractures can result in low AOM efficiencies. Fracture flow is the predicted mode of methane transport under warming-induced dissociation of hydrates on upper continental slopes. Therefore, in a future climate-warming scenario, AOM might not significantly reduce methane release from marine sediments.