Recent Submissions

  • DYNAMIC TRANSITION APPROACHING JETTING SINGULARITY DURING THE COLLAPSE OF DROP-IMPACT CRATERS

    Yang, Zi Qiang; Tian, Yuan Si; Thoroddsen, Sigurdur T (ICTAM 2020+1, 2021-08-22) [Presentation]
  • The multiple ways of making perovskite/silicon tandem solar cells: Which way to go?

    Aydin, Erkan; De Wolf, Stefaan; Subbiah, Anand Selvin; Liu, Jiang; Ugur, Esma; Azmi, Randi; Allen, Thomas; de Bastiani, Michele; Babics, Maxime; Isikgor, Furkan Halis; Chen, Bin; Hou, Yi; Laquai, Frédéric; Sargent, Edward H.; Rehman, Atteq Ur (Fundació Scito, 2021-05-11) [Presentation]
    Monolithic perovskite/silicon tandem solar cells are of interest in the photovoltaic community thanks to their potential to combine high power conversion efficiency (PCE) with affordable cost. In the last decade, significant advancements have been reported towards this goal. However, to make perovskite/silicon tandems fully industry-relevant, exclusively scalable fabrication methods and materials need to be employed. Vacuum-based processing techniques can provide a conformal coverage on the pyramidal texture, typical for single-junction silicon solar cells. For such tandems, we reported 25% certified PCE with record current densities of 19.8 mA cm-2. Specifically, we used the vacuum/solution hybrid technique for the perovskite layer, combined with nanocrystalline recombination junctions to keep possible electrical micro shunts localized.[1] Solution-based techniques, specifically one-step perovskite spin-casting, have shown rapid advancements for single-junction perovskite solar cells. However, fully covering perovskite films on micron-scale textured interfaces with this technique requires process sophistication. To achieve end-to-end coverage, we reduced the pyramid size to 1-2 mm and adjusted the perovskite precursor solution concentration. Combining this with 1-butanethiol surface passivation enabled a certified PCE of 25.7% with negligible losses after 400 hours of operation.[2] Next, to translate the solution-based method to large-scale deposition, we adopted slot-die-coated perovskite top cells on textured surfaces since it offers significant advantages in throughput and material utilization. With this approach, we reported 23.7% PCE for the first proof-of-concept device.[3] Beyond the requirement towards the use of industry-compatible silicon bottom cells (avoiding mirror-polished surfaces), which dictates appropriate perovskite processing techniques, the best choice for the device polarity is still to be settled as well. The initial perovskite/silicon tandems were in the n-i-p configuration but were limited by a high parasitic absorption in the hole-collecting contact stacks at the front (as well as the non-ideal optical design of the bottom cells, using double-side polished wafers). Global tandem research refocused, therefore, onto the p-i-n configuration. However, as a result, perovskite/silicon tandem research no longer stood to benefit from impressive progress made for efficient n-i-p perovskite single-junction solar cells. Nevertheless, adopting these advancements to tandem solar cells may be key towards perovskite/silicon tandems with PCEs well over 30%. Therefore, in this contribution, we will also discuss the existing challenges and our recent advancement on the n-i-p configuration tandems. Overall, this talk will give insight into the future directions to be taken to push the PCE of the perovskite/silicon tandem solar cells beyond 30%.
  • Computation of Electromagnetic Fields Scattered From Dielectric Objects of Uncertain Shapes Using MLMC

    Litvinenko, A.; C. Yucel, A.; Bagci, H.; Oppelstrup, J.; Michielssen, E.; Tempone, R. (2021-03-16) [Presentation]
  • CubeSats deliver daily crop water use at 3 m resolution

    Aragon Solorio, Bruno Jose Luis; Ziliani, Matteo G.; McCabe, Matthew (Copernicus GmbH, 2021-03-04) [Presentation]
    Precision agriculture needs accurate information on crop water use (via evaporation) at high spatiotemporal resolutions. Conventional satellite missions have traditionally required a compromise between having high spatial resolution retrievals occasionally; or coarse resolution captures regularly. The development of CubeSats is relaxing the need for such a compromise by monitoring the Earth at high spatiotemporal resolutions. Here, we show the results of using Planet’s daily CubeSat imagery to derive evaporation at 3 m spatial resolution over three agricultural fields in Nebraska USA. Our results indicate that the derived evaporation estimates can provide accurate information on crop water use when evaluated against eddy covariance measurements (r2 of 0.86-0.89; mean absolute error between 0.06-0.08mm/h) and deliver new insights to enhance water security efforts and in-field decision making.
  • Quantifying Uncertainty through 3D Geological Modeling for Carbon Capture Utilization and Storage in the Unayzah Formation in Saudi Arabia

    Mantilla Salas, Sofia; Corrales, Miguel; Hoteit, Hussein; Alafifi, Abdulkader Musa; Tasianas, Alexandros (Copernicus GmbH, 2021-03-04) [Presentation]
    The development of Carbon Capture Utilization and Storage (CCUS) technology paired with existing energy systems will facilitate a successful transition to a carbon-neutral economy that offers efficient and sustainable energy. It will also enable the survival of multiple and vital economic sectors of high-energy industries that possess few other options to decarbonize. Nowadays, just about one-ten-thousandth of the global annual emissions are being captured and geologically-stored, and therefore with today’s emission panorama, CCS large-scale deployment is more pressing than ever. In this study, a 3D model that represents the key reservoir uncertainties for a CCUS pilot was constructed to investigate the feasibility of CO2 storage in the Unayzah Formation in Saudi Arabia. The study site covers the area of the city of Riyadh and the Hawtah and Nuayyim Trends, which contain one of the most prolific petroleum-producing systems in the country. The Unayzah reservoir is highly stratified and it is subdivided into three compartments: the Unayzah C (Ghazal Member), the Unayzah B (Jawb Member), and the Unayzah A (Wudayhi and Tinat Members). This formation was deposited under a variety of environments, such as glaciofluvial, fluvial, eolian, and coastal plain. Facies probability trend maps and well log data were used to generate a facies model that accounted for the architecture, facies distribution, and lateral and vertical heterogeneity of this high complexity reservoir. Porosity and predicted permeability logs were used with Sequential Gaussian Simulation and co-kriging methods to construct the porosity and permeability models. The static model was then used for CO2 injection simulation purposes to understand the impact of the flow conduits, barriers, and baffles in CO2 flow in all dimensions. Similarly, the CO2 simulations allowed us to better understand the CO2 entrapment process and to estimate a more realistic and reliable CO2 storage capacity of the Unayzah reservoir in the area. To test the robustness of the model predictions, geological uncertainty quantification and a sensitivity analysis were run. Parameters such as porosity, permeability, pay thickness, anisotropy, and connectivity were analyzed as well as how various combinations between them affected the CO2 storage capacity, injectivity, and containment. This approach could improve the storage efficiency of CO2 exceeding 60%. The analyzed reservoir was found to be a promising storage site. The proposed workflow and findings of the static and dynamic modeling described in this publication could serve as a guideline methodology to test the feasibility of the imminent upcoming pilots and facilitate the large-scale deployment of this very promising technology.
  • A model for off-fault plastic poroelastic deformation and its effects on permeability

    Yalcin, Bora; Zielke, Olaf; Mai, Paul Martin (Copernicus GmbH, 2021-03-04) [Presentation]
    Fractured reservoirs comprise finite or discrete fracture networks; if these are conductive, they<br>form heterogeneously distributed high-permeability streaks. These are generally referred as<br>fracture corridors. Unless they occur as joint swarms, fracture corridors are simply seismic or sub-<br>seismic fault zones with connected fractures in the near-fault damage zone. Several studies<br>document the decrease in rock-matrix permeability adjacent to the fault surface, within the<br>damage zone. Although the damage zone creates fracture connectivity and high permeability<br>anisotropy for reservoirs, the matrix fracture feeding mechanism is related to matrix permeability<br>generally described by a transfer function. This transfer function accounts for fracture properties<br>(i.e. fracture density, length and connectivity), relative fluid mobilities, imbibition and reservoir<br>properties (i.e. matrix permeability). Commonly, the matrix permeability for all transfer functions<br>is considered in terms of a representative rock type permeability. However, observational<br>evidence and our numerical model show that slip induced deformation causes significant strain on<br>matrix in vicinity to the fault surface causing a permeability decrease in the matrix.</p><p>In this study, we present a new approach to model strain in a porous medium and related<br>permeability changes due to stress perturbation from slip around pure strike slip faults. The fault<br>length is used to scale the amount fault slip. For given/computed dislocation (slip) the off-fault<br>strain is then calculated to derive porosity and permeability changes. In our study we propose an<br>off-fault plastic-poroelastic deformation model for any known fault length and known rock<br>mechanical and petrophysical properties of the surrounding material. Our modeling technique will<br>help to better quantify fault transmissivity in geo-reservoirs.
  • Analysis of correlation between structural response and ground motion intensity measures.

    Aquib, Tariq Anwar; Sivasubramonian, Jayalakshmi; Mai, Paul Martin (Copernicus GmbH, 2021-03-04) [Presentation]
    Loss estimation for buildings that experienced earthquake shaking is an important step in Performance Based Earthquake Engineering (PBEE), comprising four major components &#8211; seismic hazard, building response, probability of damage, and the costs incurred in losses and repair works. The implementation of PBEE strongly depends on the ability to predict Engineering Demand Parameters (EDPs) that are usually defined in terms of maximum story drifts, plastic hinge rotations, and floor accelerations.</p><p>In this study, we compute building responses for large sets of recorded ground motions considering frames with different natural periods (0.1-1.5s). The ground motion data used in our analysis comprise near field records from moderate-to-large earthquakes; these may generate shaking levels high enough to be of concern for the design and safety of buildings. We select the frames by varying the number of storys and bays to obtain a wide range of natural building periods. We compute ground motion intensity measures (IM) from the recorded dataset and extract engineering demand parameters (EDP) from building response analyses. Our results indicate that the inter-story drift correlates strongly with spectral measures of ground motion intensity (correlation coefficient above 0.85). We also investigate the effect of natural period on the estimated correlations. We find that the correlations with spectral intensity measures do not strongly depend on Vs30 and epicentral distance. Our results are useful in the context of applied performance-based design of structures, especially if uncertainties in seismological parameters due to limited knowledge of source, site or path effects play an important role in earthquake ground motions.
  • Spatial Variability of Near-field Ground Motions from Pseudo-Dynamic Rupture Simulations

    Sivasubramonian, Jayalakshmi; Mai, Paul Martin (Copernicus GmbH, 2021-03-04) [Presentation]
    We analyze the effect of earthquake source parameters on ground-motion variability based on near-field wavefield simulations for large earthquakes. We quantify residuals in simulated ground motion intensities with respect to observed records, the associated variabilities are then quantified with respect to source-to-site distance and azimuth. Additionally, we compute the variabilities due to complexities in rupture models by considering variations in hypocenter location and slip distribution that are implemented a new Pseudo-Dynamic (PD) source parameterization.</p><p>In this study, we consider two past events &#8211; the Mw 6.9 Iwate Miyagi Earthquake (2008), Japan, and the Mw 6.5 Imperial Valley Earthquake, California (1979). Assuming for each case a 1D velocity structure, we first generate ensembles of rupture models using the pseudo-dynamic approach of Guatteri et.al (2004), by assuming different hypocenter and asperities locations (Mai and Beroza, 2002, Mai et al., 2005; Thingbaijam and Mai, 2016). In order to efficiently include variations in high-frequency radiation, we adopt a PD parameterization for rupture velocity and rise time distribution in our rupture model generator. Overall, we generate a database of rupture models with 50 scenarios for each source parameterization. Synthetic near-field waveforms (0.1-2.5Hz) are computed out to Joyner-Boore distances Rjb ~ 150km using a discrete-wavenumber finite-element method (Olson et al., 1984). Our results show that ground-motion variability is most sensitive to hypocenter locations on the fault plane. We also find that locations of asperities do not alter waveforms significantly for a given hypocenter, rupture velocity and rise time distribution. We compare the scenario-event simulated ground motions with simulations that use the rupture models from the SRCMOD database (Mai and Thingbaijam, 2014), and find that the PD method is capable of reducing the ground motion variability at high frequencies. The PD models are calibrated by comparing the mean residuals with the residuals from SRCMOD models. We present the variability due to each source parameterization as a function of Joyner-Boore distance and azimuth at different natural period.
  • High-frequency ground-motion variability for rough-fault ruptures

    Vyas, Jagdish Chandra; Galis, Martin; Mai, Paul Martin (Copernicus GmbH, 2021-03-04) [Presentation]
    Geological observations show variations in fault-surface topography not only at large scale (segmentation) but also at small scale (roughness). These geometrical complexities strongly affect the stress distribution and frictional strength of the fault, and therefore control the earthquake rupture process and resulting ground-shaking. Previous studies examined fault-segmentation effects on ground-shaking, but our understanding of fault-roughness effects on seismic wavefield radiation and earthquake ground-motion is still limited. In this study we examine the effects of fault roughness on ground-shaking variability as a function of distance based on 3D dynamic rupture simulations. We consider linear slip-weakening friction, variations of fault-roughness parametrizations, and alternative nucleation positions (unilateral and bilateral ruptures). We use generalized finite difference method to compute synthetic waveforms (max. resolved frequency 5.75 Hz) at numerous surface sites&#160; to carry out statistical analysis. Our simulations reveal that ground-motion variability from unilateral ruptures is almost independent of distance from the fault, with comparable or higher values than estimates from ground-motion prediction equations (e.g., Boore and Atkinson, 2008; Campbell and Bozornia, 2008). However, ground-motion variability from bilateral ruptures decreases with increasing distance, in contrast to previous studies (e.g., Imtiaz et. al., 2015) who observe an increasing trend with distance. Ground-shaking variability from unilateral ruptures is higher than for bilateral ruptures, a feature due to intricate seismic radiation patterns related to fault roughness and hypocenter location. Moreover, ground-shaking variability for rougher faults is lower than for smoother faults. As fault roughness increases the difference in ground-shaking variabilities between unilateral and bilateral ruptures increases. In summary, our simulations help develop a fundamental understanding of ground-motion variability at high frequencies (~ 6 Hz) due small-scale geometrical fault-surface variations.
  • Target food security: assimilating ultra-high resolution satellite images into a crop-yield forecasting model

    Ziliani, Matteo G.; Aragon Solorio, Bruno Jose Luis; Franz, Trenton; Hoteit, Ibrahim; Sheffield, Justin; McCabe, Matthew (Copernicus GmbH, 2021-03-04) [Presentation]
    Assimilating biophysical metrics from remote sensing platforms into crop-yield forecasting models can increase overall model performance. Recent advances in remote sensing technologies provide an unprecedented resource for Earth observation that has both, spatial and temporal resolutions appropriate for precision agriculture applications. Furthermore, computationally efficient assimilation techniques can integrate these new satellite-derived products into modeling frameworks. To date, such modeling approaches work at the regional scale, with comparatively few studies examining the integration of remote sensing and crop-yield modeling at intra-field resolutions. In this study, we investigate the potential of assimilating daily, 3 m satellite-derived leaf area index (LAI) into the Agricultural Production Systems sIMulator (APSIM) for crop yield estimation in a rainfed corn field located in Nebraska. The impact of the number of satellite images and the definition of homogeneous spatial units required to re-initialize input parameters was also evaluated. Results show that the observed spatial variability of LAI within the maize field can effectively drive the crop simulation model and enhance yield forecasting that takes into account intra-field variability. The detection of intra-field biophysical metrics is particularly valuable since it may be employed to infer inefficiency problems at different stages of the season, and hence drive specific and localized management decisions for improving the final crop yield.
  • Earthquake rupture properties in presence of thermal -pressurization of pore fluids

    Mai, Paul Martin; Vyas, Jagdish Chandra; Gabriel, Alice-Agnes; Ulrich, Thomas (Copernicus GmbH, 2021-03-04) [Presentation]
    Frictional heat generated in the fault core during earthquake rupture can raise the fluid pressure in the slip zone. Such increase of fluid pressure decreases the effective normal stress and thereby lowers the frictional strength of the fault. Therefore, thermal pressurization (TP) of pore fluid affects earthquake rupture processes including nucleation, propagation, and arrest. While the effects of pore pressure and fluid flow rate on dynamic weakening of faults are qualitatively understood, a detailed analysis of how TP affects earthquake rupture parameters is needed to further deepen our understanding. In this study, we investigate the role of two key TP parameters -- hydraulic diffusivity and shear-zone half-width -- earthquake dynamics and kinematic source properties (slip, peak slip-rate, rupture speed and rise time). We conduct a suite of 3D dynamic rupture simulations applying a rate-and-state dependent friction law (with strong velocity weakening) coupled with thermal-pressurization of pore fluids. Simulations are carried out with the open source software SeisSol (www.seissol.org). The temporal evolution of rupture parameters over ~1’000 randomly distributed on-fault receivers is statistically analyzed in terms of mean variations of rupture parameters and correlations among rupture parameters. Our simulations reveal that mean slip decreases with increasing hydraulic diffusivity, whereas mean peak slip-rate and rupture speed remain nearly constant. On the other hand, we observe only a slight decrease of mean slip with increasing shear-zone half-width, whereas mean peak slip-rate and rupture speed show clear decrease. The faster diffusion of pore pressure as hydraulic diffusivity increases promotes faster increase of the effective normal stress (and fault strength) behind the main rupture front, reducing the rise time and, therefore also affecting mean slip. An increase in shear-zone half- width represents a heat source distributed over larger fault normal distance causing a second-order effect on mean slip. Additionally, our simulations reveal correlations among rupture parameters: 1) slip has weak negative correlation with peak slip-rate and negligible correlation with rupture speed, but a positive correlation with rise time, 2) peak slip-rate has a strong positive correlation with rupture speed, but a strong negative correlation with rise time, 3) rupture speed has strong negative correlation with rise time. We observe little or negligible effects of variations of hydraulic diffusivity and shear-zone half- width on the correlations between rupture parameters. Overall, our study builds a fundamental understanding on how thermal pressurization of pore fluids affects dynamic and thereby kinematic earthquake rupture properties. Our findings are thus important for the earthquake source modeling community, and particularly, for assessing seismic hazard due to induced events in geo-reservoirs.
  • Cascading earthquakes on a fracture network in a geo-energy reservoir

    Palgunadi, Kadek Hendrawan; Gabriel, Alice-Agnes; Garagash, Dimitry; Mai, Paul Martin (Copernicus GmbH, 2021-03-04) [Presentation]
    he increasing rate of induced seismicity in subsurface reservoirs, exceeding occasionally moment magnitude 5, has generated significant attention among earthquake scientists and regulators over the last decade. Fluid injection activity during the operation stage often produces a significant, sometimes even destructive, earthquake. Many approaches have been proposed to monitor, model, and predict the injection-related seismicity to avoid an earthquake larger than a threshold set by the regulator (e.g., Mw 2.0). However, unexpected higher magnitude events occur exceeding what is predicted by empirical models, theoretical relations, or computer simulations. Current models do not consider that subsurface reservoirs consist of complex fracture networks characterized by connected and unconnected individual fracture planes, often comprising a larger but inactive fault (unfavorably oriented with respect to regional stress). Fluid injection may then perturb stress conditions and trigger an initial rupture on fractures close to the injection well; this initial event may then dynamically trigger other fractures and potentially generate a large earthquake. We inspect conditions leading to induced earthquakes taking into account the complex fracture network intersected to an inactive fault using dynamic earthquake rupture simulations. We generate the fracture network using a nearest-neighbor method following statistical parameters (power-law distribution of fracture length and fracture density) based on field data. There are 134 fractures consisting of 95 connected fractures, 3 fractures connected with at least one fracture, and 38 unconnected fractures. We focus on two fracture populations oriented in strike N110E ± 10° and N210E ± 10°, respectively. The main fault has a depth-dependent dip orientation which results in a listric fault geometry. For our dynamic rupture simulations, we use the open-source software SeisSol (https://github.com/SeisSol/SeisSol), apply a laboratory-based rate-and-state with rapid velocity weakening friction law, and assign source radius-dependent characteristic length (L parameter) to the fractures. We vary stress conditions (maximum horizontal orientation, static-pore pressure, and prestress ratio) and conduct an initial static Mohr-Coulomb analysis before running the expensive dynamic rupture simulation. We choose conditions that lead to cascading rupture with (case 1) and without (case 2) the involvement of the main fault. Case 1 has higher artificial overstress within the nucleation area than case 2. Our simulation shows intricate rupture progression over small fractures via rupture branching with the parallel and orthogonal connected fractures. The rupture can also transfer to the unconnected fractures through dynamic triggering from the closest neighboring fracture. Case 1 produces a moment magnitude of Mw 6.36 that is equivalent to case 2. Our preliminary result reveals that connected fractures can generate a significant and potentially large induced earthquake if all fractures are favorable to the stress condition.
  • Fracture network analysis for carbon mineralization in basalts of the Oligocene Jizan volcanics, Saudi Arabia

    Al Malallah, Murtadha; Fedorik, Jakub; Losi, Giacomo; Panara, Yuri; Menegoni, Niccolo; Alafifi, Abdulkader Musa; Hoteit, Hussein (Copernicus GmbH, 2021-03-04) [Presentation]
    This study aims to characterize fracture permeability in altered Oligocene-Early Miocene basalts of the Jizan Group, which accumulated in half grabens during the continental rift stage of Red Sea evolution. Unlike fresh basalts, the Jizan Group was affected by low temperature hydrothermal metamorphism, which plugged the original matrix porosity in vesicles, breccias, and interflow layers with alteration minerals. On the other hand, the basalts are pervasively shattered by open closely spaced fractures in several directions. Characterization of these fractures is essential to reducing the fracture permeability uncertainty for mineral carbonation by the dissolved CO2 process such as Carbfix. Conventional measurements of fracture orientations and densities were initially taken at outcrops of the Jizan Group to characterize the fracture network. Photogrammetry of drone images covering larger areas were then used to create 3D models of the outcrops using Agisoft Metashape, which were analyzed for fracture geometries using Cloud Compare. The automated analysis of fracture orientations and densities compared well with conventional manual measurements. This gives confidence in semi-automated dronebased fracture characterization techniques in 3D, which are faster and less labor intensive, especially for characterization of large and difficult to reach outcrops. Our fracture characterization will be used to construct 3D fracture permeability models of the Jizan Group for combined physical and chemical simulation of injection of dissolved CO2 from industrial sources into basalts. This will provide essential parameters to mitigate geological risks and to determine depth, spacing, and injection rates in CO2 disposal wells.
  • Ground motion simulations for finite-fault earthquake scenarios on the Húsavík-Flatey Fault, North Iceland

    Abril, Claudia; Mai, Paul Martin; Halldórsson, Benedikt; Li, Bo; Gabriel, Alice-Agnes; Ulrich, Thomas (Copernicus GmbH, 2021-03-04) [Presentation]
    The Tjörnes Fracture Zone (TFZ) in North Iceland is the largest and most complex zone of transform faulting in Iceland, formed due to a ridge-jump between two spreading centers of the Mid-Atlantic Ridge, the Northern Volcanic Zone and Kolbeinsey Ridge in North Iceland. Strong earthquakes (Ms>6) have repeatedly occurred in the TFZ and affected the North Icelandic population. In particular the large historical earthquakes of 1755 (Ms 7.0) and 1872 (doublet, Ms 6.5), have been associated with the Húsavı́k-Flatey Fault (HFF), which is the largest linear strike-slip transform fault in the TFZ, and in Iceland. We simulate fault rupture on the HFF and the corresponding near-fault ground motion for several potential earthquake scenarios, including scenario events that replicate the large 1755 and 1872 events. Such simulations are relevant for the town of Húsavı́k in particular, as it is located on top of the HFF and is therefore subject to the highest seismic hazard in the country. Due to the mostly offshore location of the HFF, its precise geometry has only recently been studied in more detail. We compile updated seismological and geophysical information in the area, such as a recently derived three-dimensional velocity model for P and S waves. Seismicity relocations using this velocity model, together with bathymetric and geodetic data, provide detailed information to constrain the fault geometry. In addition, we use this 3D velocity model to simulate seismic wave propagation. For this purpose, we generate a variety of kinematic earthquake-rupture scenarios, and apply a 3D finite-difference method (SORD) to propagate the radiated seismic waves through Earth structure. Slip distributions for the different scenarios are computed using a von Karman autocorrelation function whose parameters are calibrated with slip distributions available for a few recent Icelandic earthquakes. Simulated scenarios provide synthetic ground motion and time histories and estimates of peak ground motion parameters (PGA and PGV) at low frequencies (<2 Hz) for Húsavík and other main towns in North Iceland along with maps of ground shaking for the entire region [130 km x 110 km]. Ground motion estimates are compared with those provided by empirical ground motion models calibrated to Icelandic earthquakes and dynamic fault-rupture simulations for the HFF. Directivity effects towards or away from the coastal areas are analyzed to estimate the expected range of shaking. Thick sedimentary deposits (up to ∼4 km thick) located offshore on top of the HFF (reported by seismic, gravity anomaly and tomographic studies) may affect the effective depth of the fault's top boundary and the surface rupture potential. The results of this study showcase the extent of expected ground motions from significant and likely earthquake scenarios on the HFF. Finite fault earthquake simulations complement the currently available information on seismic hazard for North Iceland, and are a first step towards a systematic and large-scale earthquake scenario database on the HFF, and for the entire fault system of the TFZ, that will enable comprehensive and physics-based hazard assessment in the region.
  • The influence of depth-varying elastic properties in controlling the dynamic rupture of megathrust earthquakes and upper-plate coseismic deformation

    Prada, Manel; Galvez, Percy; Sanchez-Linares, Carlos; Ampuero, Jean-Paul; Sallarès, Valentí; Macias, Jorge; Peter, Daniel (Copernicus GmbH, 2021-03-03) [Presentation]
    It has been recently proposed that the depth-varying rupture properties of megathrust earthquakes can be explained by the depth distribution of elastic properties of the rocks overlying the megathrust fault. Here we demonstrate that such relationship is mechanically viable by using 3D dynamic rupture simulations. We compare results from two subduction zone scenarios with different depth-distribution of elastic properties to explore the influence of realistic upper-plate elasticity on rupture characteristics such as slip, rupture duration, and frequency content.</p><p>The first scenario has a homogeneous distribution of elastic properties, with values of Vp, Vs, and density typical of rocks overlying the megathrust fault at 25 km depth. The second scenario includes the typical depth distribution of elastic properties overlying the megathrust fault inferred from worldwide tomographic models of the upper plate. For both scenarios, we simulate three cases with ruptures confined to the shallow domain (0-5 km depth), transitional domain (5-10 km depth), and regular domain (10-25 km depth), respectively. We assume the same friction properties for both scenarios.</p><p>Results show that the realistic distribution of elastic properties accounts for increasing slip and decreasing high frequency content trenchwards, and that slip may be 8 times larger and corner frequency 2 times lower in the shallow domain than in the regular domain. Rupture times along depth shows that the rupture through a realistic elastic model may be 2.5-3 times slower in the shallow domain than in the regular domain. Depth-variations of slip, frequency content, and rupture time quantitatively agree with previous predictions, confirming that depletion of high frequency content and slow rupture are inherent of ruptures propagating through the shallow domain, where elastic properties variations drop more rapidly than in the regular and transitional domains.</p><p>Depth-dependent elastic properties also affect the dynamics of slip rate. Peak slip rate values in the heterogeneous model anticorrelate with rigidity variations and are 3-4 times higher than those observed in the homogeneous model in the shallow domain. Increasing peak slip-rate difference trenchwards correlates with increasing local ground motion differences between models. We also find important differences on permanent coseismic deformation of the upper plate. We show that coseismic deformation is significantly larger in the shallow domain in the heterogeneous models, where uplift ratios may be up to 2 times larger and along-dip displacement of the seafloor may be >6 times larger than displacement values from the homogeneous model. We use the permanent uplift seafloor deformation from both models to model the corresponding tsunamis with Tsunami-HySEA software. The results show that, at the coast, the maximum amplitude of the tsunami generated by the heterogeneous model may be up to 25% larger than that excited by the homogeneous model.</p><p>This study demonstrate the relevant role of upper-plate elasticity in controlling not only rupture characteristics, but also coseismic upper plate deformation, and tsunamigenesis. Neglecting the distribution of these properties may result in important underestimation of slip, rupture time, and local ground motion, as well as on seafloor coseismic deformation of the shallow domain, which in turn may lead to underestimations of tsunami size.
  • The role of multi-sensor remote sensing for drought characterization: challenges and opportunities

    Wang, Lixin; Jiao, Wenzhe; McCabe, Matthew (Copernicus GmbH, 2021-03-03) [Presentation]
    Satellite based remote sensing plays important role in studying regional to continental scale drought. One of the unique elements of remote sensing platforms is their multi-sensor capabilities, which enhance the capacity for characterizing drought from a variety of aspects. However, multi-sensor integrated drought evaluation is in its infancy. To advocate and encourage on-going exploration and integration of multi-sensor remote sensing for drought studies, we provide an overview of the role of multi-sensor remote sensing for addressing knowledge gaps and driving advances in drought studies. We first present a comprehensive summary of large-scale drought-related remote sensing datasets that can be used for multi-sensor drought studies. Then we provide a detailed review of how the integrated multi-sensor remote sensing could enhance our analysis in multiple important drought related phenomena and mechanisms such as drought-induced tree mortality, drought-related ecosystem fires, post-drought recovery and legacy effects, flash drought, and drought trends under climate change. We also provide a summary of recent modeling advances towards developing integrated multi-sensor remote sensing drought indices. We highlight that leveraging multi-sensor remote sensing provides unique benefits for regional to global drought studies, particularly in: 1) revealing the complex drought impact mechanisms on various ecosystem components; 2) providing continuous long-term drought related information at large scales; 3) presenting real-time drought information with high spatiotemporal resolution; 4) providing multiple lines of evidence of drought monitoring to improve modeling and prediction robustness; and 5) improving the accuracy of drought monitoring and assessment efforts.
  • Parallel Hierarchical Matrix Technique to Approximate Large Covariance Matrices, Likelihood Functions and Parameter Identi fication

    Litvinenko, Alexander; Berikov, V.; Genton, Marc G.; Keyes, David E.; Kriemann, R.; Sun, Ying (2021-03-01) [Presentation]
    We develop the HLIBCov package, which is using parallel hierarchical (H-) matrices to: 1) Approximate large dense inhomogeneous covariance matrices with a log-linear computational cost and storage requirement. 2) Compute matrix-vector product, Cholesky factorization and inverse with a log-linear complexity. 3) Identify unknown parameters of the covariance function (variance, smoothness, and covariance length). These unknown parameters are estimated by maximizing the joint Gaussian log-likelihood function. To demonstrate the numerical performance, we identify three unknown parameters in an example with 2,000,000 locations on a PC-desktop.
  • Photoactive Layer Design Rules for Efficient and Stable Nonfullerene Solar Cells

    Baran, Derya (Fundació Scito, 2021-01-25) [Presentation]
    The efficiency of organic photovoltaics have seen a phenomenal increase in the last couple of years with the discovery of small molecule nonfullerene acceptors (NFAs). Molecular design strategies of the photoactive layer have boosted the performance with intelligent interface engineering beyond 18% so far. One way to boost the performance of the NFA devices is to add a third component in the photoactive layer, known as ternary approach. Most of the record efficiency devices have been reported adopting this strategy in the field of OPV. However, there is still a lack of understanding how to design a third component to achieve both efficient and stable devices with no burn-in at the first 100h of operation. In order to bring OPV technology into commercial applications in solar windows, building integrated PV, agrivoltaics or even in integrated circuits one would need not only efficient but also reliable devices. In this talk, I will focus on how to design the photoactive layer components and morphology so that we would have state-of-the-art performances along with improved photostability.
  • Ultrafast Energy Transfer Triggers Ionization Energy Offset Dependence of Quantum Efficiency in Low-bandgap Non-fullerene Acceptor Solar Cells

    Gorenflot, Julien; Laquai, Frédéric; Firdaus, Yuliar; De Castro, Catherine S. P.; Harrison, George; Khan, Jafar Iqbal; Markina, Anastasia; Balawi, Ahmed; Dela Peña, Top Archie; Liu, Wenlan; Liang, Ru-Ze; Sharma, Anirudh; Karuthedath, Safakath; Zhang, Weimin; Lin, Yuanbao; Alarousu, Erkki; Anjum, Dalaver H.; Beaujuge, Pierre; De Wolf, Stefaan; McCulloch, Iain; Anthopoulos, Thomas D.; Baran, Derya; Andrienko, Denis; Paleti, Sri Harish Kumar (Fundació Scito, 2021-01-25) [Presentation]
    In bulk heterojunction (BHJ) solar cells, the heterojunction interface between electron donor and acceptor drives the exciton-to-charge conversion, yet it also adds to energy and carrier losses. In principle, in low-bandgap non-fullerene acceptor (NFA) BHJs both electron affinity (EA) and ionization energy (IE) offsets should equally control the internal quantum efficiency (IQE). Allegedly, exciton-to-charge conversion is efficient even for close-to-zero offsets. Here, we rebut both notions and demonstrate that counterintuitively, the charge transfer from the exciton rather than the further charge separation is the limiting step controlled by the IE offset and secondly, that sizeable IE offsets are required to reach high exciton-to charge conversion efficiency. We find that efficient Förster Resonant Energy Transfer to the low bandgap acceptor precedes the charge transfer, which thus always occurs via hole transfer from the acceptor, hence the unimportance of the EA offset. We discuss the reasons for the threshold IE offset in terms of interface energetics and find that two physical parameters are sufficient to describe the evolution of the IQE with IE offset on a very large range of material systems. Our model also explain other experimental observations such as the difficulty of observing CT states emission and absorption in NFA based systems.

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