scholarly journals Creepex-analysis of processes in focal zones of large earthquakes by means of GIS-ENDDB

2021 ◽  
Vol 3 (4) ◽  
pp. 7-17
Author(s):  
Anna Mikheeva ◽  
Igor Kalinnikov
Keyword(s):  
High Frequency ◽  
Main Shock ◽  
Temporal Dynamics ◽  
Kashmir Earthquake ◽  
Plate Convergence ◽  
Thermodynamic Effect ◽  
Abrupt Changes ◽  
Explosion Parameter ◽  
Large Earthquakes ◽  
Frequency Radiation

The creepex (creep & explosion) parameter provides information on the relation between low- and high-frequency radiation components in the earthquake source and has become a physically meaningful tool for analyzing various aspects of seismogenesis, in particular, the diagnostics of the preparation processes and the its aftershocks activity of a strong event. This paper investigates the spatial-temporal dynamics of creepex in the focal zones of a number of the major earthquakes from the plate convergence regions, including continental Kashmir earthquake (08.10.2005, MS=7.6) and continental-oceanic Tohoku (11.03.2011, Mw=8.7). One of the goals of this work is to demonstrate the capabilities of the method in studying physically grounded patterns of focal zones development at the first hours after the main shock. Because of this study, the following regularities of the source relaxation process were revealed: the partiality of the aftershock process, positive values of the creepex at its first hours (explained by the influence of the dilatancy process), and abrupt changes in the creepex during deep transitions (explained by the thermodynamic effect and by the increase in pressure with depth).

Seismicity and waveforms of the microearthquakes before and after the Shizuoka-Seibu earthquake, central Japan

1984 ◽  
Vol 74 (2) ◽  
pp. 605-620
Author(s):  
Mizuho Ishida ◽  
Masakazu Ohtake
Keyword(s):  
High Frequency ◽  
Main Shock ◽  
Amplitude Ratio ◽  
High Stress ◽  
Aftershock Sequence ◽  
Central Japan ◽  
Before And After ◽  
Asperity Model ◽  
Source Dimension ◽  
Large Earthquakes

Abstract Investigating the foreshock-main shock-aftershock sequence of the Shizuoka-Seibu earthquake (M = 2.8, 16 January 1981), central Japan, we found evidence that suggests high stress conditions for the foreshock period. The source dimension of the main shock was roughly estimated to be about 0.5 × 0.2 km2. The m value of the Ishimoto-lida's formula was 1.87 for foreshocks and 2.37 for aftershocks. Waveforms of the foreshocks, main shock, and aftershocks were similar to each other. However, the amplitude ratio of the low (0.9 to 0.8 Hz) to high (3.5 to 10 Hz) frequency band was different between the foreshocks and aftershocks. The ratio for the foreshocks was lower than that for the aftershocks, indicating that the foreshocks contain more high-frequency energy than the aftershocks. The Shizuoka-Seibu sequence included a larger number of foreshocks (70) compared to aftershocks (43). This characteristic, in contrast with large earthquakes, was found common to small-sized earthquakes occurring in the neighborhood areas. These observations can be interpreted based on the asperity model.

scholarly journals Electrophysiological aftereffects of high-frequency transcranial random noise stimulation (hf-tRNS): an EEG investigation

2021 ◽  
Author(s):  
Filippo Ghin ◽  
Louise O’Hare ◽  
Andrea Pavan
Keyword(s):  
High Frequency ◽  
Discrimination Task ◽  
Temporal Dynamics ◽  
Random Noise ◽  
Decomposition Analysis ◽  
Oscillatory Activity ◽  
Motion Direction ◽  
Time Frequency ◽  
Direction Discrimination ◽  
Transcranial Random Noise Stimulation

AbstractThere is evidence that high-frequency transcranial random noise stimulation (hf-tRNS) is effective in improving behavioural performance in several visual tasks. However, so far there has been limited research into the spatial and temporal characteristics of hf-tRNS-induced facilitatory effects. In the present study, electroencephalogram (EEG) was used to investigate the spatial and temporal dynamics of cortical activity modulated by offline hf-tRNS on performance on a motion direction discrimination task. We used EEG to measure the amplitude of motion-related VEPs over the parieto-occipital cortex, as well as oscillatory power spectral density (PSD) at rest. A time–frequency decomposition analysis was also performed to investigate the shift in event-related spectral perturbation (ERSP) in response to the motion stimuli between the pre- and post-stimulation period. The results showed that the accuracy of the motion direction discrimination task was not modulated by offline hf-tRNS. Although the motion task was able to elicit motion-dependent VEP components (P1, N2, and P2), none of them showed any significant change between pre- and post-stimulation. We also found a time-dependent increase of the PSD in alpha and beta bands regardless of the stimulation protocol. Finally, time–frequency analysis showed a modulation of ERSP power in the hf-tRNS condition for gamma activity when compared to pre-stimulation periods and Sham stimulation. Overall, these results show that offline hf-tRNS may induce moderate aftereffects in brain oscillatory activity.

scholarly journals Pulse-like partial ruptures and high-frequency radiation at creeping-locked transition during megathrust earthquakes

2017 ◽  
Vol 44 (16) ◽  
pp. 8345-8351 ◽  
Author(s):  
Sylvain Michel ◽  
Jean-Philippe Avouac ◽  
Nadia Lapusta ◽  
Junle Jiang
Keyword(s):  
High Frequency ◽  
Megathrust Earthquakes ◽  
Frequency Radiation ◽  
High Frequency Radiation

scholarly journals A new asymptotic method for the modeling of near-field accelerograms

1984 ◽  
Vol 74 (2) ◽  
pp. 539-557
Author(s):  
P. Bernard ◽  
R. Madariaga
Keyword(s):  
High Frequency ◽  
Near Field ◽  
Dislocation Model ◽  
Rupture Propagation ◽  
Time Step ◽  
Change Of Variables ◽  
High Frequency Waves ◽  
Stopping Phases ◽  
Simple Integration ◽  
Frequency Radiation

Abstract We study high-frequency radiation from a dislocation model of rupture propagation at the earthquake source. We demonstrate that in this case all the radiation emanates from the rupture front and, by a change of variables, that at any instant of time the high-frequency waves reaching an observer come from a line on the fault plane that we call isochrone. An asymptotic approximation to near-source velocity and acceleration is obtained that involves a simple integration along the isochrones for every time step. It is shown that wave front discontinuities (critical or stopping phases) are radiated every time an isochrone becomes tangent to a barrier. This leads to what we call the critical ray approximation which is given in a closed form. The previous results are compared with discrete wavenumber synthetics obtained by Bouchon (1982) for the Gilroy 6 recording of the Coyote Lake earthquake of 1980. The fit between the asymptotic and full numerical method is extremely good. The critical ray approximation permits the identification of different phases in Bouchon's synthetics and the prediction of the behavior of the signal in the vicinity of their arrival time.

scholarly journals High-frequency monitoring reveals nutrient sources and transport processes in an agriculture-dominated lowland water system

2016 ◽  
Vol 20 (5) ◽  
pp. 1851-1868 ◽  
Author(s):  
Bas van der Grift ◽  
Hans Peter Broers ◽  
Wilbert Berendrecht ◽  
Joachim Rozemeijer ◽  
Leonard Osté ◽  
...  
Keyword(s):  
Water Quality ◽  
High Frequency ◽  
Preferential Flow ◽  
Temporal Dynamics ◽  
Water Systems ◽  
Transport Processes ◽  
Rainfall Events ◽  
Nutrient Sources ◽  
Pumping Station ◽  
Frequency Monitoring

Abstract. Many agriculture-dominated lowland water systems worldwide suffer from eutrophication caused by high nutrient loads. Insight in the hydrochemical functioning of embanked polder catchments is highly relevant for improving the water quality in such areas or for reducing export loads to downstream water bodies. This paper introduces new insights in nutrient sources and transport processes in a polder in the Netherlands situated below sea level using high-frequency monitoring technology at the outlet, where the water is pumped into a higher situated lake, combined with a low-frequency water quality monitoring programme at six locations within the drainage area. Seasonal trends and short-scale temporal dynamics in concentrations indicated that the NO3 concentration at the pumping station originated from N loss from agricultural lands. The NO3 loads appear as losses via tube drains after intensive rainfall events during the winter months due to preferential flow through the cracked clay soil. Transfer function-noise modelling of hourly NO3 concentrations reveals that a large part of the dynamics in NO3 concentrations during the winter months can be related to rainfall. The total phosphorus (TP) concentration and turbidity almost doubled during operation of the pumping station, which points to resuspension of particulate P from channel bed sediments induced by changes in water flow due to pumping. Rainfall events that caused peaks in NO3 concentrations did not results in TP concentration peaks. The rainfall induced and NO3 enriched quick interflow, may also be enriched in TP but retention of TP due to sedimentation of particulate P then results in the absence of rainfall induced TP concentration peaks. Increased TP concentrations associated with run-off events is only observed during a rainfall event at the end of a freeze–thaw cycle. All these observations suggest that the P retention potential of polder water systems is primarily due to the artificial pumping regime that buffers high flows. As the TP concentration is affected by operation of the pumping station, timing of sampling relative to the operating hours of the pumping station should be accounted for when calculating P export loads, determining trends in water quality, or when judging water quality status of polder water systems.

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