scholarly journals Development of fully Bayesian multiple-time-window source inversion

2016 ◽  
Vol 204 (3) ◽  
pp. 1601-1619 ◽  
Author(s):  
Hisahiko Kubo ◽  
Kimiyuki Asano ◽  
Tomotaka Iwata ◽  
Shin Aoi
Keyword(s):  
Time Window ◽  
Multiple Time ◽  
Source Inversion ◽  
Fully Bayesian

3-D joint geodetic and strong-motion finite fault inversion of the 2008 May 12, Wenchuan, China Earthquake

2020 ◽  
Vol 222 (2) ◽  
pp. 1390-1404
Author(s):  
Leonardo Ramirez-Guzman ◽  
Stephen Hartzell
Keyword(s):  
Time Window ◽  
Joint Inversion ◽  
Strong Motion ◽  
Multiple Time ◽  
Source Inversion ◽  
Geodetic Inversion ◽  
Finite Fault Inversion ◽  
Finite Fault ◽  
China Earthquake ◽  
The Moment

SUMMARY We present a source inversion of the 2008 Wenchuan, China earthquake, using strong-motion waveforms and geodetic offsets together with 3-D synthetic ground motions. We applied the linear multiple time window technique considering geodetic and dynamic Green's functions computed with the finite-element method and the reciprocity and Strain Green's Tensor formalism. All ground motion estimates, valid up to 1 Hz, accounted for 3-D effects, including the topography and the geometry of the Beichuan and Pengguan faults. Our joint inversion has a higher moment (M0) than a purely geodetic inversion and the slip distribution presents differences when compared to 1-D model source inversions. The moment is estimated to be M0 = 1.2 × 1021 N·m, slightly larger than other works. Our results show that considering a complex 3-D structure reduces the size of large areas of 10 m slip or greater by distributing it in wider zones, with reduced slips, in the central portion of the Beichuan and the Pengguan faults. Finally, we compare our source with a relocated aftershock catalogue and conclude that the 4–5 m slip contours approximately bound the absence or presence of aftershocks.

scholarly journals RETRACTED ARTICLE: Estimation of the source process and forward simulation of long-period ground motion of the 2018 Hokkaido Eastern Iburi, Japan, earthquake

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Hisahiko Kubo ◽  
Asako Iwaki ◽  
Wataru Suzuki ◽  
Shin Aoi ◽  
Haruko Sekiguchi
Keyword(s):  
Ground Motion ◽  
Velocity Structure ◽  
Time Window ◽  
Waveform Inversion ◽  
Strong Motion ◽  
Source Model ◽  
Multiple Time ◽  
Velocity Models ◽  
Long Period ◽  
Slip Area

Abstract In this study, we investigate the source rupture process of the 2018 Hokkaido Eastern Iburi earthquake in Japan (MJMA 6.7) and how the ground motion can be reproduced using available source and velocity models. First, we conduct a multiple-time-window kinematic waveform inversion using strong-motion waveforms, which indicates that a large-slip area located at a depth of 25–30 km in the up-dip direction from the hypocenter was caused by a rupture propagating upward 6–12 s after its initiation. Moreover, the high-seismicity area of aftershocks did not overlap with the large-slip area. Subsequently, using the obtained source model and a three-dimensional velocity structure model, we conduct a forward long-period (< 0.5 Hz) ground-motion simulation. The simulation was able to reproduce the overall ground-motion characteristics in the sedimentary layers of the Ishikari Lowland.

scholarly journals Multi-UAV Reconnaissance Task Assignment for Heterogeneous Targets Based on Modified Symbiotic Organisms Search Algorithm

Sensors ◽  
2019 ◽  
Vol 19 (3) ◽  
pp. 734 ◽  
Author(s):  
Hao-Xiang Chen ◽  
Ying Nan ◽  
Yi Yang
Keyword(s):  
Assignment Problem ◽  
Time Window ◽  
Search Algorithm ◽  
Task Assignment ◽  
Multiple Time ◽  
Nsga Ii ◽  
Symbiotic Organisms Search ◽  
Simulation Results ◽  
Symbiotic Organisms ◽  
Task Assignment Problem

This paper considers a reconnaissance task assignment problem for multiple unmanned aerial vehicles (UAVs) with different sensor capacities. A modified Multi-Objective Symbiotic Organisms Search algorithm (MOSOS) is adopted to optimize UAVs’ task sequence. A time-window based task model is built for heterogeneous targets. Then, the basic task assignment problem is formulated as a Multiple Time-Window based Dubins Travelling Salesmen Problem (MTWDTSP). Double-chain encoding rules and several criteria are established for the task assignment problem under logical and physical constraints. Pareto dominance determination and global adaptive scaling factors is introduced to improve the performance of original MOSOS. Numerical simulation and Monte-Carlo simulation results for the task assignment problem are also presented in this paper, whereas comparisons with non-dominated sorting genetic algorithm (NSGA-II) and original MOSOS are made to verify the superiority of the proposed method. The simulation results demonstrate that modified SOS outperforms the original MOSOS and NSGA-II in terms of optimality and efficiency of the assignment results in MTWDTSP.

Effect of inaccurate specification of time-correlated model error in an Ensemble Smoother

2020 ◽  
Author(s):  
Haonan Ren ◽  
Peter Jan Van Leeuwen ◽  
Javier Amezcua
Keyword(s):  
Data Assimilation ◽  
Time Scale ◽  
Correlation Time ◽  
Time Window ◽  
Model Error ◽  
Multiple Time ◽  
Model Errors ◽  
Time Step ◽  
Single Observation ◽  
Kalman Smoother

&lt;p&gt;Data assimilation has been often performed under the perfect model assumption known as the strong-constraint setting. There is an increasing number of researches accounting for the model errors, the weak-constrain setting, but often with different degrees of approximation or simplification without knowing their impact on the data assimilation results. We investigate what effect inaccurate model errors, in particular, the an inaccurate time correlation, can have on data assimilation results, with a Kalman Smoother and the Ensemble Kalman Smoother.&lt;br&gt;We choose a linear auto-regressive model for the experiment. We assume the true state of the system has the correct and fixed correlation time-scale&amp;#160;&amp;#969;&lt;sub&gt;r&lt;/sub&gt; in the model errors, and the prior or the background generated by the model contains the model error with the fixed, guessed time-scale &amp;#969;&lt;sub&gt;g&lt;/sub&gt; which differs from the correct one and is also used in the data assimilation process. There are 10 variables in the system and we separate the simulation period into multiple time-windows. And we use a fairly large ensemble size (up to 200 ensemble members) to improve the accuracy of the data assimilation results. In order to evaluate the performance of the EnKS with auto-correlated model errors, we calculate the ratio of root-mean-square error over the spread of all ensemble members.&lt;br&gt;The results with a single observation at the end of the simulation time-window show that, using an underestimated correlation time-scale leads to overestimated spread of the ensemble, and with an overestimated time-scale, the results show underestimation in the ensemble spread. However, with very dense observation frequency, observing every time-step for instance, the results are completely opposite to the results with a single observation. In order to understand the results, we derive the expression for the true posterior state covariance and the posterior covariance using the incorrect decorrelation time-scale. We do this for a Kalman Smoother to avoid the sampling uncertainties. The results are richer than expected and highly dependent on the observation frequency. From the analytical solution of the analysis, we find that the RMSE is a function of both &amp;#969;&lt;sub&gt;r&lt;/sub&gt;&lt;sub&gt;&amp;#160;&lt;/sub&gt;and &amp;#969;&lt;sub&gt;g&lt;/sub&gt;, and the spread or the variance only depends on &amp;#969;&lt;sub&gt;g&lt;/sub&gt;. We also find that the analyzed variance is not always a monotonically increasing function of &amp;#969;&lt;sub&gt;g&lt;/sub&gt;, and it also depends on the observation frequency. In general, the results show the effect of the correlated model error and the incorrect correlation time-scale on data assimilation result, which is also affected by the observation frequency.&lt;/p&gt;

Extraction and analysis of multiple time window features associated with muscle fatigue conditions using sEMG signals

2014 ◽  
Vol 41 (6) ◽  
pp. 2652-2659 ◽  
Author(s):  
G. Venugopal ◽  
M. Navaneethakrishna ◽  
S. Ramakrishnan
Keyword(s):  
Muscle Fatigue ◽  
Time Window ◽  
Multiple Time ◽  
Semg Signals

Geomorphological controls on seismic recordings in volcanic areas

2020 ◽  
Author(s):  
Simona Gabrielli ◽  
Luca De Siena ◽  
Matteo Spagnolo
Keyword(s):  
Time Window ◽  
Near Field ◽  
Debris Avalanche ◽  
Source Inversion ◽  
S Wave ◽  
Low Velocity ◽  
Lapse Time ◽  
Scattering Attenuation ◽  
Seismic Coda ◽  
Velocity Anomalies

&lt;p&gt;In volcanoes, topography, shallow heterogeneity, and even shallow morphology can substantially modify seismic coda signals. Coda waves are an essential tool to monitor eruption dynamics and model volcanic structures jointly and independently from velocity anomalies: it is thus fundamental to test their spatial sensitivity to seismic path effects. Here, we apply the Multiple Lapse Time Window Analysis (MLTWA) to measure the relative importance of scattering attenuation vs absorption at Mount St. Helens volcano (MSH) before its 2004 eruption. The results show the typical dominance of scattering attenuation in volcanoes at lower frequencies (3 - 6 Hz), while absorption is the primary attenuation mechanism at 12 Hz and 18 Hz. Still, the seismic albedo (measuring the ratio between seismic energy emitted and received from the area) is anomalously-high (0.95) at 3 Hz.&lt;/p&gt;&lt;p&gt;A radiative-transfer forward model of far- and near-field envelopes confirms this is due to strong near-receiver scattering enhancing anomalous phases in the intermediate and late coda across the 1980 debris avalanche and central crater. Only above this frequency and in the far-field, diffusion onsets at late lapse times.&amp;#160; We also implemented a layered model with a shallower layer with increased scattering properties to model late coda envelopes. While the broadening of late coda phases improves, this model cannot explain the phases of the intermediate coda with higher amplitude than the direct waves.&lt;/p&gt;&lt;p&gt;The scattering and absorption parameters derived from MLTWA are used as inputs to construct 2D frequency-dependent bulk sensitivity kernels for the S-wave coda in the multiple-scattering (using the Energy Transport Equations - ETE) and diffusive (AD, independent of MLTWA results) regimes. At 12 Hz, high coda-attenuation anomalies characterise the eastern side of the volcano using both kernels, in spatial correlation with low-velocity anomalies from literature. At 3 Hz, the anomalous albedo, the forward modelling, and the results of the tomographic imaging confirm that shallow heterogeneity beneath the extended 1980 debris-avalanche and crater enhance anomalous intermediate and late coda phases, mapping shallow geological contrasts.&lt;/p&gt;&lt;p&gt;The geomorphological map of MSH highlights extremely rough landforms (hummocky structures) of the already complex morphology of the debris avalanche. The comparison with the attenuation tomography reveals several matches, not only with the debris avalanche itself but also with other areas in the south flank of MSH, like the volcanoclastic plane, affected by intense eruptions in the past (e.g. Cougar stage, 28-18 ka).&lt;/p&gt;&lt;p&gt;We remark the effect those may have on coda-dependent source inversion and tomography, currently used across the world to image and monitor volcanoes.&lt;/p&gt;

scholarly journals Estimation of the Wenchuan Earthquake Rupture Sequence Utilizing Teleseismic Records and Coseismic Displacements

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Deyu Yin ◽  
Qifang Liu ◽  
Jingke Wu
Keyword(s):  
Wenchuan Earthquake ◽  
Time Window ◽  
Temporal Distribution ◽  
Field Investigation ◽  
Rupture Process ◽  
Least Square ◽  
Multiple Time ◽  
Finite Fault ◽  
Beichuan Fault ◽  
Dip Angle

For the 12 May 2008 Mw 7.9 Wenchuan earthquake, two imbricate faults, Beichuan fault and Pengguan fault, have ruptured simultaneously. Special attention should be paid to the point of 40 km northeast of the epicenter, in which the Xiaoyudong fault intersects the above two faults, creating a complex fault structure. Surface rupture data from field surveys and previous research of dynamics studies indicate that an important transformation may take place at the intersection. But, few studies about inversion of source rupture process have focused on this issue. We establish a multiple-segment, variable-slip, finite-fault model to reproduce the rupture process and distinguish rupture sequence. Based on the nonnegative least square method and multiple-time-window approach, the spatial and temporal distribution of slip for three rupture sequences are exhibited, using teleseismic records and coseismic displacements. The conformity between synthetic and observed teleseismic records as well as the slip value of the shallowest subfaults and the coseismic displacements is utilized to calibrate the model. The results are as follows: (1) The teleseismic records inversion alone could not distinguish different rupture sequences. However, in order to make the slip of the Hongkou and Yingxiu area coincide with the field investigation, only the Beichuan fault has a bilateral rupture on the point of intersection of Xiaoyudong fault. So the possible rupture sequence is that the earthquake started at the low dip angle part of southern Beichuan fault, and then it propagated to the Pengguan fault, which caused the rupture of Xiaoyudong fault. Then the southern part of Beichuan fault with high dip angle is triggered by the Xiaoyudong fault. (2) The coseismic displacements constraint can control the slip of subfaults near the surface and has little impact on the deeper subfaults. (3) The maximum slip on the fault is located near the Yingxiu and Beichuan area; moreover, the slip is mainly distributed at the shallow region rather than at the deep, which led to serious disasters. Meanwhile, majority of the aftershocks occur in the periphery of large slip.

On the link between Beamforming and Kernel-based Source Inversion

2020 ◽  
Author(s):  
Daniel Bowden ◽  
Korbinian Sager ◽  
Andreas Fichtner ◽  
Małgorzata Chmiel
Keyword(s):  
Prior Information ◽  
Time Window ◽  
Great Promise ◽  
Source Inversion ◽  
Finite Frequency ◽  
Noise Sources ◽  
Data Driven Approach ◽  
Gradient Based ◽  
Cross Correlations ◽  
A Current

&lt;p&gt;Beamforming and backprojection methods offer a data-driven approach to image noise sources, but provide no opportunity to account for prior information or iterate through an inversion framework. In contrast, recent methods have been developed to locate ambient noise sources based on cross-correlations between stations and the construction of finite-frequency kernels, allowing for inversions over multiple iterations (i.e., Tromp et al., 2010, Ermert et al. 2017, Sager et al. 2018). These kernel-based approaches show great promise, both in mathematical rigour and in results, but may remain difficult to understand or implement for the wider community. Here we show that these two different classes of methods, beamforming and kernel-based inversion, are achieving exactly the same result in certain circumstances. This means existing beamforming and backprojection methods can also incorporate prior information in a mathematically correct manner.&lt;/p&gt;&lt;p&gt;We start with a description of a relatively simple beamforming or backprojection algorithm, based on time-domain shifting and measurement of waveform coherence. Only by changing the order of steps, we begin to resemble the kernel-based approaches. By adding a physical model for the distribution of noise sources, and therefore synthetic correlation functions, we can extend backprojection to an iterative, gradient-based inversion scheme. Adjoint methods and a direct simulation of correlation wavefields can later be used to increase computational efficiency, but we stress that these are not needed to understand the approach.&lt;/p&gt;&lt;p&gt;Given the equivalence of these approaches between these two communities, both sides can benefit from bridging the gap. For example, for kernel-based inversion schemes, a current challenge lies in defining the misfit and time window over which a correlation will be scored; a windowing function based on beamform images offers a more intuitive way to identify significant contributions in the noise wavefield, exploiting more than just the direct surface-wave arrivals.&lt;/p&gt;

Understanding seismic path biases and magmatic activity at Mount St Helens volcano before its 2004 eruption

2020 ◽  
Vol 222 (1) ◽  
pp. 169-188 ◽  
Author(s):  
S Gabrielli ◽  
L De Siena ◽  
F Napolitano ◽  
E Del Pezzo
Keyword(s):  
Time Window ◽  
Debris Avalanche ◽  
Coda Waves ◽  
Source Inversion ◽  
Borehole Data ◽  
Lapse Time ◽  
Scattering Attenuation ◽  
Seismic Coda ◽  
Velocity Anomalies ◽  
Mount St Helens

SUMMARY In volcanoes, topography, shallow heterogeneity and even shallow morphology can substantially modify seismic coda signals. Coda waves are an essential tool to monitor eruption dynamics and model volcanic structures jointly and independently from velocity anomalies: it is thus fundamental to test their spatial sensitivity to seismic path effects. Here, we apply the Multiple Lapse Time Window Analysis (MLTWA) to measure the relative importance of scattering attenuation vs absorption at Mount St Helens volcano before its 2004 eruption. The results show the characteristic dominance of scattering attenuation in volcanoes at lower frequencies (3–6 Hz), while absorption is the primary attenuation mechanism at 12 and 18 Hz. Scattering attenuation is similar but seismic absorption is one order of magnitude lower than at open-conduit volcanoes, like Etna and Kilauea, a typical behaviour of a (relatively) cool magmatic plumbing system. Still, the seismic albedo (measuring the ratio between seismic energy emitted and received from the area) is anomalously high (0.95) at 3 Hz. A radiative-transfer forward model of far- and near-field envelopes confirms this is due to strong near-receiver scattering enhancing anomalous phases in the intermediate and late coda across the 1980 debris avalanche and central crater. Only above this frequency and in the far-field diffusion onsets at late lapse times. The scattering and absorption parameters derived from MLTWA are used as inputs to construct 2-D frequency-dependent bulk sensitivity kernels for the S-wave coda in the multiple-scattering (using the Energy Transport Equations—ETE) and diffusive (AD, independent of MLTWA results) regimes. At 12 Hz, high coda-attenuation anomalies characterize the eastern side of the volcano using both kernels, in spatial correlation with low-velocity anomalies from literature. At 3 Hz, the anomalous albedo, the forward modelling, and the results of the tomographic imaging confirm that shallow heterogeneity beneath the extended 1980 debris-avalanche and crater enhance anomalous intermediate and late coda phases, mapping shallow geological contrasts. We remark the effect this may have on coda-dependent source inversion and tomography, currently used across the world to image and monitor volcanoes. At Mount St Helens, higher frequencies and deep borehole data are necessary to reconstruct deep volcanic structures with coda waves.

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