Complex Propagation Patterns Research Articles

Rupture Process During the 2015 Illapel, Chile Earthquake: Zigzag-Along-Dip Rupture Episodes

We constructed a seismic source model for the 2015 MW 8.3 Illapel, Chile earthquake, which was carried out with the kinematic waveform inversion method adopting a novel inversion formulation that takes into account the uncertainty in the Green’s function, together with the hybrid backprojection method enabling us to track the spatiotemporal distribution of high-frequency (0.3–2.0 Hz) sources at high resolution by using globally observed teleseismic P-waveforms. A maximum slip amounted to 10.4 m in the shallow part of the seismic source region centered 72 km northwest of the epicenter and generated a following tsunami inundated along the coast. In a gross sense, the rupture front propagated almost unilaterally to northward from the hypocenter at <2 km/s, however, in detail the spatiotemporal slip distribution also showed a complex rupture propagation pattern: two up-dip rupture propagation episodes, and a secondary rupture episode may have been triggered by the strong high-frequency radiation event at the down-dip edge of the seismic source region. High-frequency sources tends to be distributed at deeper parts of the slip area, a pattern also documented in other subduction zone megathrust earthquakes that may reflect the heterogeneous distribution of fracture energy or stress drop along the fault. The weak excitation of high-frequency radiation at the termination of rupture may represent the gradual deceleration of rupture velocity at the transition zone of frictional property or stress state between the megathrust rupture zone and the swarm area.

Wavelet analysis of polar vortex variability over the twentieth century

AbstractRecent increases in extreme weather events in the Northern Hemisphere have been linked to amplified planetary waves. Changes in planetary wave properties are linked to changes in climate; hence, finding a mechanism that links the planetary wave variability under climatic forcing and midlatitude blocking events has engendered a great deal of interest. In this study, wavelet analysis is applied to time series of planetary wave phase speeds at high latitudes as a first step to assessing the potential for identifying these mechanisms in the observational record. A circumpolar multiannual cycle increase is found but signals also demonstrate a complex westward propagation pattern with periods of intense wave variability. Significant correlations between wavelet power at all time scales and albedo, snow cover, atmospheric ozone levels, and surface air temperature are demonstrated.

Detection and Location of Low‐Frequency Earthquakes Using Cross‐Station Correlation

Source geometry and simple propagation of S waves generated by low‐frequency earthquakes (LFEs) in northern Cascadia results in strong waveform coherence on horizontal channels for stations at smaller epicentral distances. As recognized by previous workers, this cross‐station similarity can be exploited for detection of LFEs in tremor. We develop a cross‐station correlation approach based on waveform coherence and travel‐time consistency that exploits a full complement of network stations, and we demonstrate its application to separate arrays on Vancouver Island and Washington state. Our approach yields thousands of impulsive LFE detections per slow‐slip episode and hundreds of events between episodes. LFE epicentral distributions reveal the presence of well‐defined regions of high asperity density with those regions farther downdip that are active during interepisodic tremor and slow‐slip periods. The LFE epicenters also display pronounced spatiotemporal clustering that compares favorably with independent tremor and LFE template catalogs and that defines rapid tremor reversals with complex propagation patterns. The LFE source depths can be estimated for some detections in which P waves are identified on the vertical channel through correlation with the horizontal‐component S waveforms. LFE hypocenters cluster between two recently developed plate interface models below southern Vancouver Island. Our approach enables the identification of high signal‐to‐noise‐ratio impulsive LFE detections from targeted regions on the plate boundary for generation of LFE templates to be used in studies of structure and seismogenesis in Cascadia. Online Material: Additional maps of station density for southern Vancouver Island, epicenter locations for northern Washington, and additional time–distance plots for southern Vancouver Island.

Correlation-based imaging technique using ultrasonic transmit–receive array for Non-Destructive Evaluation

This paper describes a novel array post-processing method for Non-Destructive Evaluation (NDE) using phased-array ultrasonic probes. The approach uses the capture and processing of the full matrix of all transmit–receive time-domain signals from a transducer array as in the case of the Total Focusing Method (TFM), referred as the standard of imaging algorithms. The proposed technique is based on correlation of measured signals with theoretical propagated signals computed over a given grid of points. In that case, real-time imaging can be simply implemented using discrete signal product. The advantage of the present technique is to take into account transducer directivity, dynamics and complex propagation patterns, such that the number of required array elements for a given imaging performance can be greatly reduced. Numerical and experimental application to contact inspection of isotropic structure is presented and real-time implementation issues are discussed.

Complex Propagation Patterns Characterize Human Cortical Activity during Slow-Wave Sleep

Cortical electrical activity during nonrapid eye movement (non-REM) sleep is dominated by slow-wave activity (SWA). At larger spatial scales (∼2-30 cm), investigated by scalp EEG recordings, SWA has been shown to propagate globally over wide cortical regions as traveling waves, which has been proposed to serve as a temporal framework for neural plasticity. However, whether SWA dynamics at finer spatial scales also reflects the orderly propagation has not previously been investigated in humans. To reveal the local, finer spatial scale (∼1-6 cm) patterns of SWA propagation during non-REM sleep, electrocorticographic (ECoG) recordings were conducted from subdurally implanted electrode grids and a nonlinear correlation technique [mutual information (MI)] was implemented. MI analysis revealed spatial maps of correlations between cortical areas demonstrating SWA propagation directions, speed, and association strength. Highest correlations, indicating significant coupling, were detected during the initial positive-going deflection of slow waves. SWA propagated predominantly between adjacent cortical areas, albeit spatial noncontinuities were also frequently observed. MI analysis further uncovered significant convergence and divergence patterns. Areas receiving the most convergent activity were similar to those with high divergence rate, while reciprocal and circular propagation of SWA was also frequent. We hypothesize that SWA is characterized by distinct attributes depending on the spatial scale observed. At larger spatial scales, the orderly SWA propagation dominates; at the finer scale of the ECoG recordings, non-REM sleep is characterized by complex SWA propagation patterns.

Orthogonal wave propagation of epileptiform activity in the planar mouse hippocampus in vitro

In vitro brain preparations have been used extensively to study the generation and propagation of epileptiform activity. Transverse and longitudinal slices of the rodent hippocampus have revealed various patterns of propagation. Yet intact connections between the transverse and longitudinal pathways should generate orthogonal (both transverse and longitudinal) propagation of seizures involving the entire hippocampus. This study utilizes the planar unfolded mouse hippocampus preparation to reveal simultaneous orthogonal epileptiform propagation and to test a method of arresting propagation. This study utilized an unfolded mouse hippocampus preparation. It was chosen due to its preservation of longitudinal neuronal processes, which are thought to play an important role in epileptiform hyperexcitability. 4-Aminopyridine (4-AP), microelectrodes, and voltage-sensitive dye imaging were employed to investigate tissue excitability. In 50-μm 4-AP, stimulation of the stratum radiatum induced transverse activation of CA3 cells but also induced a longitudinal wave of activity propagating along the CA3 region at a speed of 0.09 m/s. Without stimulation, a wave originated at the temporal CA3 and propagated in a temporal-septal direction could be suppressed with glutamatergic receptor antagonists. Orthogonal propagation traveled longitudinally along the CA3 pathway, secondarily invading the CA1 region at a velocity of 0.22 ± 0.024 m/s. Moreover, a local lesion restricted to the CA3 region could arrest wave propagation. These results reveal a complex two-dimensional epileptiform wave propagation pattern in the hippocampus that is generated by a combination of synaptic transmission and axonal propagation in the CA3 recurrent network. Epileptiform propagation block via a transverse selective CA3 lesion suggests a potential surgical technique for the treatment of temporal lobe epilepsy.

Stochastic characteristics of seismic excitations at a non-uniform (rock and soil) site

This study analyzes data recorded at the dense array in the Parkway Valley, Wainuiomata, New Zealand, a small alluvial valley surrounded by graywacke outcrops. The array consisted of stations on both the sediment basin and the surrounding soft rock, with station separation distances pertinent for earthquake engineering applications. The array's configuration renders itself uniquely for the study of the spatial variation of seismic ground motions at sites with irregular topography for bridge response evaluations: the locations of the soft-rock stations surrounding the valley may be viewed as the locations of the bridge's abutments, and the locations of the stations in the basin as those of the bridge's intermediate piers. A further-away station, north-east of the valley, provided information on firm-rock data. The analysis suggested that the motions in the valley were dominated by surface waves and considered two time windows for the evaluation of the stochastic characteristics (power spectral densities and lagged coherencies) of the data. During the first time window, at the onset of the excitation, the motions in the valley exhibited both low and high frequency energy that propagated down the valley. During the second window, high-amplitude, low-frequency, surface-wave energy controlled the horizontal motions in the valley. Very significant variabilities were observed in the amplitudes of the power spectra of the motions throughout the array during both windows indicating a complex wave propagation pattern affecting not only the valley but also the soft rock that surrounds the valley. Significant correlations in the motions appeared in the form of “hills” in the lagged coherency estimates when the energy of the power spectra of the station pairs peaked at similar or close-by frequency ranges, irrespective of whether the station pairs were located on the same or different ground types. The valley data indicated significant correlations in the dominant frequency ranges of the surface waves that control the motions during the two windows analyzed. Interestingly, motions at the soft-rock and soil stations, as well as those at the soft-rock stations and the firm-rock station, are significantly correlated at the onset of the excitation. This result may or may not depend on the event analyzed, as the spectra of its motions at the firm-rock, soft-rock and basin stations during this window peak at similar frequency ranges, and, in addition, the motions at the soft-rock and basin stations appear to be controlled by similar surface-wave energy at higher frequencies. On the other hand, during the later windows, there is tremendous amplification of the motions in the valley, whereas the spectral amplitudes of the soft-rock data are, comparatively, very low. The differences result from the fact that the seismic excitations within the valley have a significantly longer duration than the seismic ground motions recorded at the rock stations due to the formation of additional, low-frequency surface waves. This observation may have significant implications for the design of bridges supported at variable site conditions. Whereas the motions at rock (or excitations at the bridge abutments) have essentially ceased, the motions in the valley (or excitations at the bridge piers) undergo the severe part of the earthquake excitation. This scenario of seismic excitations is not currently considered in bridge response evaluations, but can adversely affect the structure's response. The analysis provides insight into the stochastic characteristics of seismic excitations at sites with irregular subsurface topography.

Bimodal septal and cortical triggering and complex propagation patterns of spontaneous waves of activity in the developing mouse cerebral cortex

Spontaneous waves of activity that propagate across large structures during specific developmental stages play central roles in CNS development. To understand the genesis and functions of these waves, it is critical to understand the spatial and temporal patterns of their propagation. We recently reported that spontaneous waves in the neonatal cerebral cortex originate from a ventrolateral pacemaker region. We have now analyzed a large number of spontaneous waves using calcium imaging over the entire area of coronal slices from E18-P1 mouse brains. In all waves, the first cortical region active is this ventrolateral pacemaker. In half of the waves, however, the cortical pacemaker activity is itself triggered by preceding activity in the septal nuclei. Most waves are restricted to the septum and/or ventral cortex, with only some invading the dorsal cortex or the contralateral hemisphere. Waves fail to propagate at very stereotyped locations at the boundary between ventral and dorsal cortex and at the dorsal midline. Waves that cross these boundaries pause at these same locations. Waves at these stages are blocked by both picrotoxin and CNQX, indicating that both GABA(A) and AMPA receptors are involved in spontaneous activity.

Strong local processing in human cortical slow wave propagation

Event Abstract Back to Event Strong local processing in human cortical slow wave propagation Balázs Hangya1*, Laszlo Entz2, Dániel Fabó2, Lóránd Eross2, Benedek Tihanyi1, Rita Jakus2, Viktor Varga1, Tamás Freund1 and István Ulbert2 1 Hungarian Academy of Sciences, Institute of Experimental Medicine, Hungary 2 Hungarian Academy of Sciences, National Institute of Neuroscience, Institute of Psychology, Hungary Cortical activity during deep stages of non rapid eye movement sleep (non-REM) is dominated by slow oscillations (SO). This type of activity has been proved to be crucial for memory consolidation via ensemble reactivation and synaptic downscaling. Based on the analysis of temporal lags between the troughs of SO waves recorded with high density scalp EEG, these waves were shown to linearly propagate over wide cortical areas appearing as traveling waves. Detailed spatio-temporal analysis of SO propagation dynamics would provide an important step in understanding sleep related cortical activity. Thus, we investigated convergence, divergence and non-continuities in the spread of slow wave activity. Instead of considering only the peak or trough of each wave, we correlated the whole waveforms of SO from human electrocorticography (ECoG) recordings using mutual information (MI). ECoG was obtained from patients having drug resistant epilepsy implanted with frontal grid electrodes during natural non-REM sleep. Using MI we were able to gain insight into detailed SO dynamics by constructing a time-dependent spatial map of connections between cortical areas revealing slow wave propagation directions, speed and strength. Waves of SO propagated predominantly to adjacent electrodes, albeit rapid non-continuities (jumps) to distant electrodes also occurred. MI analysis revealed significant convergence and divergence of SO. The electrodes receiving the most convergent information were similar to those with high divergence rate, probably constituting the hubs of cortical network. MI values were highest associated to the ascending segments of slow waves, showing that information between cortical areas might mostly be conveyed during this phase of the oscillatory cycle. Thus, information theoretical analysis uncovered complex propagation patterns of cortical slow waves that might shed new light on the traditional view of ‘travelling waves’. Conference: IBRO International Workshop 2010, Pécs, Hungary, 21 Jan - 23 Jan, 2010. Presentation Type: Poster Presentation Topic: Cognition and behavior Citation: Hangya B, Entz L, Fabó D, Eross L, Tihanyi B, Jakus R, Varga V, Freund T and Ulbert I (2010). Strong local processing in human cortical slow wave propagation. Front. Neurosci. Conference Abstract: IBRO International Workshop 2010. doi: 10.3389/conf.fnins.2010.10.00151 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 29 Apr 2010; Published Online: 29 Apr 2010. * Correspondence: Balázs Hangya, Hungarian Academy of Sciences, Institute of Experimental Medicine, Budapest, Hungary, hangyab@koki.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Balázs Hangya Laszlo Entz Dániel Fabó Lóránd Eross Benedek Tihanyi Rita Jakus Viktor Varga Tamás Freund István Ulbert Google Balázs Hangya Laszlo Entz Dániel Fabó Lóránd Eross Benedek Tihanyi Rita Jakus Viktor Varga Tamás Freund István Ulbert Google Scholar Balázs Hangya Laszlo Entz Dániel Fabó Lóránd Eross Benedek Tihanyi Rita Jakus Viktor Varga Tamás Freund István Ulbert PubMed Balázs Hangya Laszlo Entz Dániel Fabó Lóránd Eross Benedek Tihanyi Rita Jakus Viktor Varga Tamás Freund István Ulbert Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Spatial and temporal coupling between slow waves and pendular contractions

In contrast to the mechanisms of segmental and peristaltic contractions in the small intestine, not much is known about the mechanism of pendular contractions. High-resolution electrical and mechanical recordings were performed from isolated segments of the rabbit ileum during pendular contractions. The electrical activities were recorded with 32 extracellular electrodes while motility was assessed simultaneously by video tracking the displacements of 20-40 serosal markers. The electrical activities consisted of slow waves, followed by spikes, that propagated in either the aboral or oral direction. The mechanical activity always followed the initial electrical activity, describing a contraction phase in one direction followed by a relaxation phase in the opposite direction. Pendular displacements were always in rhythm with the slow wave, whereas the direction of the displacements was dictated by the origin of the slow wave. If the slow wave propagated aborally, then the pendular displacement occurred in the oral direction, whereas if the slow wave propagated in the oral direction, then the displacement occurred in the aboral direction. In the case of more complex propagation patterns, such as in the area of pacemaking or collision, direction of displacements remained always opposite to the direction of the slow wave. In summary, the direction and pattern of propagation of the slow wave determine the rhythm and the direction of the pendular motility. The well-known variability in pendular movements is caused by the variability in the propagation of the underlying slow wave.

The anomalous amplification of M2 tide in the Taiwan Strait

The complex tidal wave propagation pattern in the Taiwan Strait invites parochialism. Along the eastern (Taiwan) boundary of the strait, the anomalous amplification of M2 tide in the middle often led to the parochial view that two tidal waves coming from both ends of the strait collide in the middle, creating wave resonance. Along the western (China) boundary, one sees a southward progressive tidal wave and hence no wave collision. To reconcile, we examine a few solutions of a numerical tidal model below. Both realistic bottom bathymetry and idealized bottom topographies are used to identify dominant mechanism leading to the complex tidal wave propagation. Our process of elimination identifies the wave reflection of southward propagating tidal wave by the deep trench in the southern strait as the true cause responsible for the complex wave propagation pattern.

Internal Waves on the Continental Shelf of the Gulf of Tehuantepec, Mexico

The continental shelf of the Gulf of Tehuantepec in the southern Mexican Pacific exhibits complex propagation patterns of internal waves. Both in situ data and satellite imagery are consistent with the interaction of internal wave groups and intense coastal flows. The passage of these waves is shown to contribute to the mixing of the upper ocean. The vertical temperature and dissolved oxygen distributions are modified by the combined effect of several internal wave groups.

Non-linear dynamics of cardiac excitation and impulse propagation.

Extremely complex frequency-dependent patterns of excitation and impulse propagation can be shown in cardiac tissues. Such complex behaviour can be analysed using methods derived from chaos theory, which is concerned with the non-linear dynamics of deterministic systems that have irregular periodicities as well as an exquisite sensitivity to the initial conditions. We report here that the general response patterns of non-oscillatory cardiac conducting tissues, when driven rhythmically by repetitive stimuli from their surroundings, are similar to those of other deterministic systems showing chaotic dynamics. Such patterns include phase locking, period-doubling bifurcation and irregular activity. We have used electrophysiological techniques and analytical arguments to explain this unforeseen behaviour and to provide some key information about its mechanisms. The study of these dynamics is of general application to the understanding of disordered phenomena in excitable media, and may provide new insight about the origin of fatal cardiac arrhythmias.