Lithosphere-asthenosphere decoupling in the Central/Eastern Alps from seismic anisotropy beneath the dense SWATH-D network

2021 ◽  
Author(s):  
Frederik Link ◽  
Georg Rümpker
Keyword(s):  
Transverse Energy ◽  
Seismic Anisotropy ◽  
Lower Layer ◽  
Eastern Alps ◽  
Joint Analysis ◽  
Energy Tensor ◽  
Data Set ◽  
Axis Direction ◽  
Fast Axis ◽  
Best Fitting

<p>The Alpine orogeny is characterized by tectonic sequences of subduction and collision accompanied by break-off events and possibly preceded by a flip of subduction polarity. The tectonic evolution of the transition to the Eastern Alps has thus been under debate. The dense Swath-D seismic network as complementary experiment to the AlpArray network provides unprecedented lateral resolution to address this open discussion. We analyze shear wave splitting of this data set to get insights into the deformation at depth by studying seismic anisotropy. Previous studies indicate two-layer anisotropy in the Eastern Alps. This is supported by azimuthal pattern of the measured fast axis direction across all stations of the network. The temporary character of the deployment requires a joint analysis of multiple stations to increase the number of events adding complementary information of the anisotropic property of the mantle. We perform a cluster analysis based on a correlation of the remaining transverse energy between all stations. The energy tensor is calculated in the grid search for the best fitting two-layer splitting parameters to the ensemble of events at each station. This leads to two main groups of different two-layer properties separated at 12.5 degrees Longitude. We identify a layer with constant fast axis direction of 60° over the whole area, with a possible dip from West to East. The lower layer in the West shows N-S direction and upper layer in the East 115° alignment. We propose two likely scenarios, both accompanied by a slab break-off in the Eastern part. The continuous layer can either be interpreted as frozen-in anisotropy with lithospheric origin or an asthenospheric flow evading the retreat of the European slab that would precede the break-off event.  In both scenarios the upper layer in the East is result of a channel flow through the gap formed in the slab break-off. The N-S direction is interpreted as asthenospheric flow mainly driven by the subduction of the European plate below Adria.</p>

scholarly journals Resolving Seismic Anisotropy of the Lithosphere–Asthenosphere in the Central/Eastern Alps Beneath the SWATH-D Network

2021 ◽  
Vol 9 ◽  
Author(s):  
Frederik Link ◽  
Georg Rümpker
Keyword(s):  
Transverse Energy ◽  
Seismic Anisotropy ◽  
Lower Layer ◽  
Eastern Alps ◽  
Seismic Network ◽  
Joint Analysis ◽  
Data Set ◽  
Axis Direction ◽  
Fast Axis ◽  
Anisotropic Layers

The Alpine orogeny is characterized by tectonic sequences of subduction and collision accompanied by break-off events and possibly preceded by a flip of subduction polarity. The tectonic evolution of the transition to the Eastern Alps has thus been under debate. The dense SWATH-D seismic network as a complementary experiment to the AlpArray seismic network provides unprecedented lateral resolution to address this ongoing discussion. We analyze the shear-wave splitting of this data set including stations of the AlpArray backbone in the region to obtain new insights into the deformation at depth from seismic anisotropy. Previous studies indicate two-layer anisotropy in the Eastern Alps. This is supported by the azimuthal pattern of the measured fast axis direction across all analyzed stations. However, the temporary character of the deployment requires a joint analysis of multiple stations to increase the number of events adding complementary information of the anisotropic properties of the mantle. We, therefore, perform a cluster analysis based on a correlation of energy tensors between all stations. The energy tensors are assembled from the remaining transverse energy after the trial correction of the splitting effect from two consecutive anisotropic layers. This leads to two main groups of different two-layer properties, separated approximately at 13°E. We identify a layer with a constant fast axis direction (measured clockwise with respect to north) of about 60° over the whole area, with a possible dip from west to east. The lower layer in the west shows N–S fast direction and the upper layer in the east shows a fast axis of about 115°. We propose two likely scenarios, both accompanied by a slab break-off in the eastern part. The continuous layer can either be interpreted as frozen-in anisotropy with a lithospheric origin or as an asthenospheric flow evading the retreat of the European slab that would precede the break-off event. In both scenarios, the upper layer in the east is a result of a flow through the gap formed in the slab break-off. The N–S direction can be interpreted as an asthenospheric flow driven by the retreating European slab but might also result from a deep-reaching fault-related anisotropy.

scholarly journals Shear-wave splitting beneath Fennoscandia — evidence for dipping structures and laterally varying multilayer anisotropy

2020 ◽  
Vol 223 (3) ◽  
pp. 1525-1547
Author(s):  
Michael Grund ◽  
Joachim R R Ritter
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Seismic Stations ◽  
Axis Direction ◽  
Fast Axis ◽  
Source Regions ◽  
Wave Splitting ◽  
Data Coverage ◽  
Continental Growth

SUMMARY The geodynamic evolution of Fennoscandia in northern Europe (Finland, Sweden and Norway) is coined by ca. 3 Ga history of tectonic processes including continental growth in its central and eastern parts and Neogene uplift processes of the Scandinavian mountains (Scandes) located along its western edge. Many details are still under debate and we contribute with new findings from studying deep-seated seismic anisotropy. Using teleseismic waveforms of more than 260 recording stations (long-running permanent networks, previous temporary experiments and newly installed temporary stations) in the framework of the ScanArray experiment, we present the most comprehensive study to date on seismic anisotropy across Fennoscandia. The results are based on single and multi-event shear-wave splitting analysis of core refracted shear waves (SKS, SKKS, PKS and sSKS). The splitting measurements indicate partly complex, laterally varying multilayer anisotropy for individual areas. Consistent measurements at permanent and temporary recording stations over several years and for seismic events of specific source regions allow us to robustly constrain dipping anisotropic structures by adding systematic forward modelling. Although the data coverage is partly limited to only few source regions, our findings support concepts of continental growth due to individual episodes of (paleo-) subduction, each affecting a plunging of the anisotropic fast axis direction due to collisional deformation. Along the northern Scandes the fast axis direction (ϕ) is parallel to the mountain range (NE-SW), whereas an NNW-SSE trend dominates across the southern Scandes. In the south, across the Sorgenfrei–Tornquist Zone, a NW-SE trend of ϕ dominates which is parallel to this suture zone. The Oslo Graben is characterized by an NNE-SSW trend of ϕ. In northern Norway and Sweden (mainly Paleoproterozoic lithosphere), a dipping anisotropy with ϕ towards NE prevails. This stands in contrast to the Archean domain in the NE of our study region where ϕ is consistently oriented NNE-SSW. In the Finnish part of the Svecofennian domain, a complex two-layer anisotropy pattern is found which may be due to lateral variations around the seismic stations and which requires a higher data density than ours for a unique model building. Based on these findings our study demonstrates the importance of long recording periods (in the best case > 10 yr) to obtain a sufficient data coverage at seismic stations, especially to perform meaningful structural modelling based on shear-wave splitting observations.

Messages of Oscillatory Correlograms: A Spike Train Model

2008 ◽  
Vol 20 (5) ◽  
pp. 1211-1238 ◽  
Author(s):  
Gaby Schneider
Keyword(s):  
Spike Train ◽  
Null Model ◽  
Simulated Data ◽  
Joint Analysis ◽  
Data Set ◽  
Proposed Model ◽  
Peak Asymmetry ◽  
Millisecond Range ◽  
Temporal Interactions ◽  
Underlying Processes

Oscillatory correlograms are widely used to study neuronal activity that shows a joint periodic rhythm. In most cases, the statistical analysis of cross-correlation histograms (CCH) features is based on the null model of independent processes, and the resulting conclusions about the underlying processes remain qualitative. Therefore, we propose a spike train model for synchronous oscillatory firing activity that directly links characteristics of the CCH to parameters of the underlying processes. The model focuses particularly on asymmetric central peaks, which differ in slope and width on the two sides. Asymmetric peaks can be associated with phase offsets in the (sub-) millisecond range. These spatiotemporal firing patterns can be highly consistent across units yet invisible in the underlying processes. The proposed model includes a single temporal parameter that accounts for this peak asymmetry. The model provides approaches for the analysis of oscillatory correlograms, taking into account dependencies and nonstationarities in the underlying processes. In particular, the auto- and the cross-correlogram can be investigated in a joint analysis because they depend on the same spike train parameters. Particular temporal interactions such as the degree to which different units synchronize in a common oscillatory rhythm can also be investigated. The analysis is demonstrated by application to a simulated data set.

scholarly journals High-throughput inference of pairwise coalescence times identifies signals of selection and enriched disease heritability

2018 ◽  
Author(s):  
Pier Francesco Palamara ◽  
Jonathan Terhorst ◽  
Yun S. Song ◽  
Alkes L. Price
Keyword(s):  
Positive Selection ◽  
Snp Array ◽  
Complex Trait ◽  
Joint Analysis ◽  
Background Selection ◽  
Sequencing Data ◽  
Data Set ◽  
Coalescence Time ◽  
Recent Positive Selection ◽  
Coalescence Times

AbstractInterest in reconstructing demographic histories has motivated the development of methods to estimate locus-specific pairwise coalescence times from whole-genome sequence data. We developed a new method, ASMC, that can estimate coalescence times using only SNP array data, and is 2-4 orders of magnitude faster than previous methods when sequencing data are available. We were thus able to apply ASMC to 113,851 phased British samples from the UK Biobank, aiming to detect recent positive selection by identifying loci with unusually high density of very recent coalescence times. We detected 12 genome-wide significant signals, including 6 loci with previous evidence of positive selection and 6 novel loci, consistent with coalescent simulations showing that our approach is well-powered to detect recent positive selection. We also applied ASMC to sequencing data from 498 Dutch individuals (Genome of the Netherlands data set) to detect background selection at deeper time scales. We observed highly significant correlations between average coalescence time inferred by ASMC and other measures of background selection. We investigated whether this signal translated into an enrichment in disease and complex trait heritability by analyzing summary association statistics from 20 independent diseases and complex traits (average N=86k) using stratified LD score regression. Our background selection annotation based on average coalescence time was strongly enriched for heritability (p = 7×10−153) in a joint analysis conditioned on a broad set of functional annotations (including other background selection annotations), meta-analyzed across traits; SNPs in the top 20% of our annotation were 3.8x enriched for heritability compared to the bottom 20%. These results underscore the widespread effects of background selection on disease and complex trait heritability.

SUSPENSION OPTIMIZATION USING DESIGN OF EXPERIMENT (DOE) METHOD ON MSC/ADAMS-INSIGHT

2015 ◽  
Vol 75 (8) ◽  
Author(s):  
N. Ikhsan ◽  
R. Ramli ◽  
A. Alias
Keyword(s):  
Design Of Experiment ◽  
Suspension System ◽  
Optimization Process ◽  
Data Set ◽  
Pareto Chart ◽  
Axis Direction ◽  
Parallel Movement ◽  
Suspension Model ◽  
Vehicle Suspension System ◽  
Multi Body

In this paper, the optimum setting for suspension hard points was determined from a half vehicle suspension system. These optimized values were obtained by considering the Kinematic and Compliance (K&C) effects of a verified PROTON WRM 44 P0-34 suspension model developed using MSC/ADAMS/CAR. For optimization process, multi body dynamic software, MSC/ADAMS/INSIGHT and Design of Experiment (DoE) method was employed. There were total of 60 hard points (factors) in x, y and z axis-direction for both front and rear suspension while toe, camber and caster change were selected as the objective function (responses) to be minimized. The values of 5 mm, 10 mm and 15 mm were used as relative values of factor setting to determine the factor range during optimization process. The hard point axis-direction that has the most effects on the responses was identified using the Pareto chart to optimize while the rests were eliminated. As expected result, a new set of suspension system model with a selected of Kinematic and Compliance (K&C) data set were obtained, and compared with the verified simulation data when subjected to the vertical parallel movement simulation test to determine the best setting and optimum suspension hard points configuration.  

The 1998 Valhall microseismic data set: An integrated study of relocated sources, seismic multiplets, and S-wave splitting

Geophysics ◽  
2009 ◽  
Vol 74 (5) ◽  
pp. B183-B195 ◽  
Author(s):  
K. De Meersman ◽  
J.-M. Kendall ◽  
M. van der Baan
Keyword(s):  
Seismic Anisotropy ◽  
Amplitude Ratio ◽  
Temporal Variations ◽  
Oil Field ◽  
P Wave ◽  
Wave Form ◽  
S Wave ◽  
Data Set ◽  
Wave Splitting ◽  
Source Mechanisms

We relocate 303 microseismic events recorded in 1998 by sensors in a single borehole in the North Sea Valhall oil field. A semiautomated array analysis method repicks the P- and S-wave arrival times and P-wave polarizations, which are needed to locate these events. The relocated sources are confined predominantly to a [Formula: see text]-thick zone just above the reservoir, and location uncertainties are half those of previous efforts. Multiplet analysis identifies 40 multiplet groups, which include 208 of the 303 events. The largest group contains 24 events, and five groups contain 10 or more events. Within each multiplet group, we further improve arrival-time picking through crosscorrelation, which enhances the relative accuracy of the relocated events and reveals that more than 99% of the seismic activity lies spatially in three distinct clusters. The spatial distribution of events and wave-form similarities reveal two faultlike structures that match well with north-northwest–south-southeast-trending fault planes interpreted from 3D surface seismic data. Most waveform differences between multiplet groups located on these faults can be attributed to S-wave phase content and polarity or P-to-S amplitude ratio. The range in P-to-S amplitude ratios observed on the faults is explained best in terms of varying source mechanisms. We also find a correlation between multiplet groups and temporal variations in seismic anisotropy, as revealed by S-wave splitting analysis. We explain these findings in the context of a cyclic recharge and dissipation of cap-rock stresses in response to production-driven compaction of the underlying oil reservoir. The cyclic nature of this mechanism drives the short-term variations in seismic anisotropy and the reactivation of microseismic source mechanisms over time.

The inverse problem of resistivity sounding

Geophysics ◽  
1984 ◽  
Vol 49 (12) ◽  
pp. 2143-2158 ◽  
Author(s):  
Robert L. Parker
Keyword(s):  
Inverse Problem ◽  
Apparent Resistivity ◽  
Single Point ◽  
Quadratic Program ◽  
Data Set ◽  
Regularization Technique ◽  
Resistivity Sounding ◽  
Best Fitting ◽  
Electrical Data ◽  
Fitting Model

The electric potential due to a single point electrode at the surface of a layered conducting medium is calculated by means of a linear combination of the potentials associated with a set of two‐layer systems. This new representation is called the bilayer expansion for the Green’s function. It enables the forward problem of resistivity sounding to be solved very efficiently, even for complicated profiles. Also, the bilayer expansion facilitates the solution of the resistivity inverse problem: the coefficients in the expansion are linearly related to apparent resistivity as it is measured and they are readily mapped into parameters for a model. Specifically, I consider models comprising uniformly conducting layers of equal thickness; for a given finite data set a quadratic program can be used to find the best‐fitting model in this class for any specified thickness. As the thickness is reduced, models of this kind can approximate arbitrary profiles with unlimited accuracy. If there is a model that satisfies the data well, there are other models equally good or better whose variation takes place in an infinitesimally thin zone near the surface, below which there is a perfectly conducting region. This extraordinary class of solutions underscores the serious ambiguity in the interpretation of apparent resistivity data. It is evident that strong constraints from outside the electrical data set must be applied if reliable solutions are to be discovered. Previous work seems to have given a somewhat overly optimistic impression of the resolving abilities of this kind of data. I consider briefly a regularization technique designed to maximize the smoothness of models found with the bilayer inversion.

Implementation of the CMS-SUS-19-006 analysis in the MadAnalysis 5 framework (supersymmetry with large hadronic activity and missing transverse energy; 137 fb−1)

2020 ◽  
pp. 2141007
Author(s):  
Malte Mrowietz ◽  
Sam Bein ◽  
Jory Sonneveld
Keyword(s):  
Transverse Momentum ◽  
Transverse Energy ◽  
Final States ◽  
Missing Transverse Energy ◽  
Final State ◽  
Data Set ◽  
Proton Proton ◽  
Missing Transverse Momentum ◽  
Proton Data ◽  
Two Jets

We present the MadAnalysis 5 implementation and validation of the analysis Search for supersymmetry in proton-proton collisions at 13 TeV in final states with jets and missing transverse momentum (CMS-SUS-19-006). The search targets signatures with at least two jets and large missing transverse momentum in the all-hadronic final state. The analyzed luminosity is 137 fb[Formula: see text], corresponding to the Run 2 proton-proton data set recorded by the CMS detector at 13 TeV. This implementation has been validated in a variety of simplified models, by comparing derived cut flow tables and histograms with information provided by the CMS collaboration, using event samples that we simulated for the purpose of this re-implementation study. The validation is found to reproduce the signal acceptance in most cases.

An investigation of seismic anisotropy in the lowermost mantle beneath Iceland

2019 ◽  
Vol 219 (Supplement_1) ◽  
pp. S152-S166 ◽  
Author(s):  
Jonathan Wolf ◽  
Neala Creasy ◽  
Angelo Pisconti ◽  
Maureen D Long ◽  
Christine Thomas
Keyword(s):  
Seismic Anisotropy ◽  
Horizontal Flow ◽  
Mantle Flow ◽  
Small Data ◽  
Vertical Flow ◽  
Low Velocity ◽  
Data Set ◽  
Study Region ◽  
Deep Mantle ◽  
Lowermost Mantle

SUMMARY Iceland represents one of the most well-known examples of hotspot volcanism, but the details of how surface volcanism connects to geodynamic processes in the deep mantle remain poorly understood. Recent work has identified evidence for an ultra-low velocity zone in the lowermost mantle beneath Iceland and argued for a cylindrically symmetric upwelling at the base of a deep mantle plume. This scenario makes a specific prediction about flow and deformation in the lowermost mantle, which can potentially be tested with observations of seismic anisotropy. Here we present an investigation of seismic anisotropy in the lowermost mantle beneath Iceland, using differential shear wave splitting measurements of S–ScS and SKS–SKKS phases. We apply our techniques to waves propagating at multiple azimuths, with the goal of gaining good geographical and azimuthal coverage of the region. Practical limitations imposed by the suboptimal distribution of global seismicity at the relevant distance ranges resulted in a relatively small data set, particularly for S–ScS. Despite this, however, our measurements of ScS splitting due to lowermost mantle anisotropy clearly show a rotation of the fast splitting direction from nearly horizontal for two sets of paths that sample away from the low velocity region (implying VSH > VSV) to nearly vertical for a set of paths that sample directly beneath Iceland (implying VSV > VSH). We also find evidence for sporadic SKS–SKKS discrepancies beneath our study region; while the geographic distribution of discrepant pairs is scattered, those pairs that sample closest to the base of the Iceland plume tend to be discrepant. Our measurements do not uniquely constrain the pattern of mantle flow. However, we carried out simple ray-theoretical forward modelling for a suite of plausible anisotropy mechanisms, including those based on single-crystal elastic tensors, those obtained via effective medium modelling for partial melt scenarios, and those derived from global or regional models of flow and texture development in the deep mantle. These simplified models do not take into account details such as possible transitions in anisotropy mechanism or deformation regime, and test a simplified flow field (vertical flow beneath the plume and horizontal flow outside it) rather than more detailed flow scenarios. Nevertheless, our modelling results demonstrate that our ScS splitting observations are generally consistent with a flow scenario that invokes nearly vertical flow directly beneath the Iceland hotspot, with horizontal flow just outside this region.

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