Dynamics of multifractal and correlation characteristics of the spatio-temporal distribution of regional seismicity before the strong earthquakes

International audienceInvestigations of the distribution of regional seismicity and the results of numerical simulations of the seismic process show the increase of inhomogenity in spatio-temporal distribution of the seismicity prior to large earthquakes and formation of inhomogeneous clusters in a wide range of scales. Since that, the multifractal approach is appropriate to investigate the details of such dynamics. Here we analyze the dynamics of the seismicity distribution before a number of strong earthquakes occurred in two seismically active regions of the world: Japan and Southern California. In order to study the evolution of spatial inhomogeneity of the seismicity distribution, we consider variations of two multifractal characteristics: information entropy of multifractal measure generation process and the higher-order generalized fractal dimension of the continuum of the earthquake epicenters. Also we studied the dynamics of the level of spatio-temporal correlations in the seismicity distribution. It is found that two aforementioned multifractal characteristics tend to decrease and the level of spatio-temporal correlations tends to increase before the majority of considered strong earthquakes. Such a tendency can be considered as an earthquake precursory signature. Therefore, the results obtained show the possibility to use multifractal and correlation characteristics of the spatio-temporal distribution of regional seismicity for seismic hazard risk evaluation

Cessation of activity in red nucleus neurons during stimulation of the medial medulla in decerebrate rats

The pontine oral reticular nucleus, gigantocellular reticular nucleus (Gi) and dorsal paragigantocellular nucleus (DPGi) of the medulla are key elements of a brainstem-reticulospinal inhibitory system that participates in rapid eye movement (REM) sleep atonia. Our recent study has shown that excitation of these brainstem nuclei in decerebrate rats inhibits locus coeruleus cells and the midbrain locomotor region neurons related to muscle tone facilitation. In the present study we have examined the influences of electrical and chemical stimulation of Gi and DPGi inhibitory sites on the activity of neurons located in the magnocellular part of the red nucleus (RMC), a cell group that participates in both the tonic and phasic regulation of motor output. A total of 192 RMC neurons were recorded in precollicular-premammillary decerebrate rats with muscle rigidity and induced locomotion. Thirty-three RMC neurons were identified antidromically as rubrospinal (RMC-spinal) cells by stimulation of the contralateral dorsolateral funiculus at the L2 level. A total of 141 RMC neurons (88.7 %) and all RMC-spinal neurons were inhibited during electrical stimulation of Gi and DPGi inhibitory sites. This cessation of activity was correlated with bilateral muscle atonia or blockage of locomotion. Six RMC cells (3.8 %) were excited (224 ± 50 %, n = 6, minimum = 98, maximum = 410, P < 0.05) and 11 cells (7 %) gave no response to Gi and DPGi stimulation. Microinjections of kainic acid (100 μm, 0.2 μl) into Gi and DPGi inhibitory sites, previously identified by electrical stimulation, produced a short-latency (35 ± 3.5 s, n = 11) decrease of rigid hindlimb muscle tone and inhibition of all tested RMC (n = 7) and RMC-spinal (n = 5) neurons. These results, combined with our recent published data, suggest that inhibition of motor function during activation of the brainstem inhibitory system is related to both the descending inhibition of spinal motoneurons and suppression of activity in supraspinal motor facilitatory systems. These two mechanisms acting synergistically may cause generalized motor inhibition during REM sleep and cataplexy