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This dataset contains geological data from the Western Afar Margin (WAM) in East Africa. These in-clude (reprocessed) earthquake data from previously published surveys and publically accessible databases (Keir et al. 2006, 2009; Ebinger et al 2008; Belachew et al. 2011; Illsley-Kemp et al. 2018a, b and the GCMT Project 2019), which form the basis for Seismic Moment Release (SMR) mapping as well as and tectonic stress analysis, revealing the location and intensity of ongoing deformation, as well as the direction of current extension, respectively. In addition, we present various large-scale maps of the WAM, depicting faults, dikes and sedimentary basins as interpreted from topographic indicators.Field data (GPS locations, fault measurements, field book), acquired during two field campaigns in Ethiopia and Eritrea are included, as well as the kinematic interpretation of the field data using Wintensor software (Delvaux & Sperner 2003). These results are combined with previously published kinematic data from Eritrea and Ethiopia (i.e. the northernmost and southern segments of the WAM, studied by Chorowicz et al. 1999 and Sani et al. 2017), yielding the first coherent overview of (current) tectonic deformation covering the whole margin. Note that we also provide a field book with detailed descriptions of every outcrop, including photographs. Finally, we include unique borehole data from the Kobo graben area, based on well logs from irrigation projects kindly provided to us by local geologists during the Ethiopian field campaign (see section 2.5 and the acknowledgements) .Applications and interpretation of the data provided in this dataset can be found in Zwaan et al. (in review). For more description please refer to the data description. This data publication consists of 90 files: (digital) maps, GPS locations, tables, text and Wintensor files. A detailed overview of all files within this dataset is given in the List of Files.
This dataset provides rheometric data of three viscous materials used for centrifuge experiments at the Tectonic Modelling Laboratory of CNR-IGG at the Earth Sciences Department of the University of Florence (Italy). The first material, PP45, is a mixture of a silicone (Polydimethylsiloxane or PDMS SGM36) and plasticine (Giotto Pongo). The PDMS is produced by Dow Corning and its characteristics are described by e.g. Rudolf et al. 2016a,b). Giotto Pongo is produced by FILA (Italy). Both components are mixed following a weight ratio of 100:45, and the final mixture has a density of 1520 kg m3. The second material, SCA705 is a mixture of Dow Corning 3179 putty, mixed with fine corundum sand and oleic acid with a weight ratio of 100:70:05 and a resulting density of 1660 kg m3. The final material, SCA7020 consists of the same components as SCA705, but with a slightly higher oleic acid content reflected in the weight ratio of 100:70:20. The mixture’s density is 1620 kg m3. The material samples have been analyzed in the Helmholtz Laboratory for Tectonic Modelling (HelTec) at GFZ German Research Centre for Geosciences in Potsdam using an Anton Paar Physica MCR 301 rheometer in a plate-plate configuration at room temperature (20˚C). Rotational (controlled shear rate) tests with shear rates varying from 10-4 to 1 s-1 were performed. Additional temperature tests were run with shear rates between 10-2 to 10-1 s-1 for a temperature range between 15 and 30˚C. According to our rheometric analysis, the materials all exhibit shear thinning behavior, with high power law exponents (n-number) for strain rates below 10-2s-1, while power law exponents are lower above that threshold.For PP45, the respective n-numbers are 4.8 and 2.6, for SCA705 6.7 and 1.5, and for SCA7020 9.1 and 2.0. The temperature tests show decreasing viscosities with increasing temperatures with rates of -3.8, -1.4 and -1.9% per ˚K for PP45, SCA705 and SCA7020, respectively. An application of the materials tested can be found in Zwaan et al. (2020).
The largest magnitude earthquakes nucleate at depths near the base of the seismogenic zone, near the transition from velocity weakening frictional slip to velocity strengthening ductile flow. However, the mechanisms controlling this transition, and relevant to earthquake nucleation, remain poorly understood. Here we present data from experiments investigating the effect of slip rate on the mechanical properties and microstructure development of simulated calcite fault gouge sheared at ~550°C, close to the transition from (unstable) velocity weakening to (stable) velocity strengthening behaviour, reported by Verberne et al. (2015).We conducted experiments at a constant effective normal stress (σneff) of 50 MPa, as well as σneff-stepping tests employing 20 MPa ≤ σneff ≤ 140 MPa, at constant sliding velocities (v) of 0.1, 1, 10, or 100 µm/s. Samples sheared at v ≥ 1 µm/s showed a microstructure characterized by a single, 30 to 40 μm wide boundary shear, as well as a linear correlation of shear strength (τ) with σneff. Remarkably, electron backscatter diffraction mapping of polygonal shear band grains demonstrated a crystallographic preferred orientation. By contrast, samples sheared at 0.1 µm/s showed a microstructure characterized by homogeneous deformation and plastic flow, as well as a flattening-off of the τ-σneff curve. Our results point to a strain rate dependent frictional-to-viscous transition in simulated calcite fault gouge, and have important implications for the processes controlling earthquake nucleation at the base of the seismogenic zone.
This dataset provides results from rheological tests of glucose syrup from two suppliers tested within the EPOS Multi-scale Laboratories (MSL) trans-national access (TNA) program 2019 at the Laboratory of Experimental Tectonics (LET), Univ. Roma TRE, Italy. Syrups Glucowheat 45/81 (GW45) and Glucowheat 60/79 (GW60) are produced by Blattmann Schweiz AG, Switzerland (2019 batch). Syrups GlucoSweet 44 (GS44) and GlucoSweet 62 (GS62) are produced by ADEA (Amidi Destrini ed Affini), Italy (2019 batch) . The four tested glucose syrups are labeled according to their DE value (dextrose equivalent value). For tested products from Blattmann Schweiz AG, the second number refers to the weight percentage of dry substance. Glucose syrup GS44 is used in full lithospheric scale analogue experiments at the Tectonic Modelling Lab (TecLab) at the University of Bern, Switzerland as a low-viscosity material simulating the asthenospheric mantle lithosphere to provide isostatic equilibration. The materials have been analyzed using a MCR301 Rheometer (Anton Paar) equipped with parallel plates geometry and rotational regime . To prevent the evaporation of the samples during the measurements, an external water-lock device has been used.
This data set provides two series of experiments from ring-shear tests (RST) on glass beads that are in use at the Helmholtz Laboratory for Tectonic Modelling (HelTec) at the GFZ German Research Centre for Geosciences in Potsdam. The main experimental series contains shear experiments to analyse the slip behaviour of the granular material under analogue experiment conditions. Additionally, a series of slide-hold-slide (SHS) tests was used to determine the rate and state friction properties. A basic characterisation and average friction coefficients of the glass beads are found in Pohlenz et al. (2020). The glass beads show a slip behaviour that is depending on loading rate, normal stress and apparatus stiffness which were varied systematically for this study. The apparatus was modified with springs resulting in 4 different stiffnesses. For each stiffness a set of 4 experiments with different normal stresses (5, 10, 15 and 20 kPa) were performed. During each experiment loading rate was decreased from 0.02 to 0.0008 mm/s resulting in 9 subsets of constant velocity for each experiment. We observe a large variety of slip modes that ranges from pure stick-slip to steady state creep. The main characteristics of these slip modes are the slip velocity and the ratio of slip event duration compared to no slip phases. We find that high loading rates promote stable slip, while low loading rates lead to stick-slip cycles. Lowering the normal stress leads to a larger amount of creep which changes the overall shape of a stick-slip curve and extends the time between slip events. Changing stiffness leads to an overall change in slip behaviour switching from simple stick-slip to more complex patterns of slip modes including oscillations and bimodal slip events with large and small events. The SHS tests were done at maximum stiffness and higher loading rates (>0.05 mm/s) but at the same normal stress intervals as the main series. Using various techniques, we estimate the rate-and-state constitutive parameters. The peak stress after a certain amount of holding increases with a healing rate of b=0.0057±0.0005. From the increase in peak stress compared to the loading rate in slide-hold-slide tests we compute a direct effect a=-0.0076±0.0005 which leads to (a-b)=-0.0130±0.0006. Using a specific subset of the SHS tests, which have an equal ratio of hold time to reloading rate, we estimate (a-b)=-0.0087±0.0029. Both approaches show that the material is velocity weakening with a reduction in friction of 1.30 to 0.87 % per e-fold increase in loading rate. Additionally, the critical slip distance Dc is estimated to be in the range of 200 µm. With these parameters the theoretical critical stiffness kc is estimated and applied to the slip modes found in the main series. We find that the changes in slip mode are in good agreement with the estimated critical stiffness and thus confirm the findings from the SHS tests.
The data set contains stress-strain data of Carrara marble experimentally deformed in triaxial compression at temperatures of 20 – 800°C, confining pressures of 30 – 300 MPa, and strain rates between 10-3 and 10-6 s-1. This range covers conditions, at witch marble deforms in the semi-brittle regime, i.e., strength depends on all parameters, but with different sensitivity. Semi-brittle deformation behavior is expected to be important in the mid continental crust. The experiments were conducted in the Experimental Rock Deformation Laboratory of the GFZ German Research Centre for Geosciences in Potsdam, Germany. The data are separated into 91 individual ASCII files, one for each sample. The corresponding temperature, pressure and strain rate conditions are listed in Tab. 1. of the data description and in the associated work by Rybacki et al. (submitted).
This data set includes overviews depicting the surface evolution (time-lapse photography, topography analysis, digital image correlation [DIC] analysis), as well as and progressive physical cross-section analysis of 18 laboratory experiments (analogue models) testing the influence of rheologically weak layers (i.e. layers with [a component of] viscous behaviour) and basal fault kinematics on deformation in the weak layer’s overburden. This model set-up was inspired by the geological situation in the Swiss Alpine Foreland. All experiments were performed at the Tectonic Modelling Laboratory of the University of Bern (UB). Detailed descriptions of the model set-up preparation and results, as well as the monitoring techniques can be found in Zwaan et al. (in review).
These data are supplementary to the GJI research article of Blanke et al. 2020, in which static stress drop estimates of laboratory acoustic emission (AE) waveform records were analyzed. Stick-slip experiments were conducted on two triaxial loaded Westerly Granite samples of different roughness: 1) a smooth saw-cut fault (sample S12) and 2) a rough fault (sample W5). Both experiments resulted in six stick-slip failures of which five were analyzed for each fault. A variant of the spectral ratio technique was applied to find the best fitting source parameters. Laboratory Experiments: Acoustic emission waveform data of two triaxial stick-slip experiments was recorded at room temperature on cylindrical oven-dried Westerly Granite samples of 105-107 mm height and 40-50 mm diameter. The experiments were conducted on a smooth saw-cut (sample S12) and a rough fault (sample W5). Both experiments were performed in a servo-controlled MTS loading frame equipped with a pressure vessel. The acoustic emission activity was monitored by 16 piezoceramic transducers with a resonance frequency of about 2 MHz. A transient recording system (DAX-Box, Prökel, Germany) recorded full waveform data in triggered mode at a sampling frequency of 10 MHz and an amplitude resolution of 16 bits. The rough fault W5 was first prepared with Teflon-filled saw-cut notches at 30° inclination to the vertical axis and then fractured at 75 MPa. Then, each sample, S12 and W5, was subjected to constant confining pressure of 133 MPa and 150 MPa and then loaded in axial compression using a strain rate of 3*10-4 mm/s and 3*10-6 mm/s, respectively. Data description: The tables 2020-008_Blanke-et-al_S1_S12.txt and 2020-008_Blanke-et-al_S2_W5.txt contain AE locations and occurrence, and source parameter estimates of the smooth fault S12 and the rough fault W5, respectively. Both column headers show coordinates of AE locations (X, Y, Z [mm]), temporal occurrence (t [sec]), seismic moment (M0 [Nm]), corner frequency (f0 [Hz]), source radius (r [mm]), static stress drop (stress drop [MPa]), and moment magnitude (MW). M0 and f0 were estimated from the amplitude spectra, using the spectral ratio technique. The source radii were calculated for S-waves using the dynamic circular source model of Madariaga (1976). Static stress drops were estimated following Eshelby (1957). Both tables are used and displayed in Blanke et al. (2020).
This data set includes the results of digital image correlation analysis applied to analogue modelling experiments (Table 1) on the effect of weakness during distributed crustal extension performed at the Helmholtz Laboratory for Tectonic Modelling (HelTec) of the GFZ German Research Centre for Geosciences in Potsdam. Ten generic analogue models made of a layer of Quartz sand (G12, Rosenau et al., 2018) including a weak silicone oil “seed” (PDMS G30M, Rudolf et al., 2016) to localize deformation have been extended on top of a basal foam block. A benchmark experiment (basal foam only) and a reference model (layer of sand without seed) are also reported. Detailed descriptions of the experiments can be found in Osagiede et al. (2021) to which this data set is supplement. The models have been monitored by means of digital image correlation (DIC) analysis (Adam et al., 2005). DIC analysis yields quantitative information about model surface deformation in 2D and 3D. The data presented here are visualized as finite strain and displacement maps as well as cumulative strain and displacement profiles.
Data supporting the publication Hornby, AJ, Kueppers U, Maurer BM, Poetsch C and Dingwell DB (2020) "Experimental constraints on volcanic ash generation and clast morphometrics in pyroclastic density currents and granular flows". In this study, fine ash is generated from lapilli-sized volcanic pumice and scoria in rotary tumbler experiments. We seek to explore ash production processes and clast attrition in natural PDCs, and gain insight into the controlling parameters for particle production efficiency with PDC transport distance. We vary the starting mass, apparatus size, and material properties and tumble clasts over multiple transport distance steps from 0.2-6 km. The data are provided in ASCII or image formats as one zipped folder (2020-025_Hornby-et-al_data.zip) and organised in the following sub-folder structure (for more information please consult the associated data description and Hornby et al (2020): (1) Experimental methods, apparatus and data collections (2) Ash generation data for tumbling experiments (3) Laser particle size distribution data for ash generated in tumbling experiments (4) Post-experimental lapilli size (generated via 3-axis caliper measurements), mass, bulk density and dense rock equivalent (DRE) porosity results (5) 2D image analysis morphology results (6) 2D image analysis size results (7) Cropped, scaled and thresholded images lapilli used for morphometric analysis (8) Image analysis macros and workflow for ImageJ (9) Integrated analysis of results This project has received funding from the European Union's Horizon 2020 research and innovation programme.
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