Forecasting Seismic Signatures of Stellar Magnetic Activity

For the Sun, a tight correlation between various activity measures and oscillation frequencies is well documented. For other stars, we have abundant data on magnetic activity and its changes but not yet on its seismic signature. A prediction of the activity induced frequency changes in stars based on scaling the solar relations is presented. This seismic signature of the activity should be measurable in the data expected within few years.Comment: 8 pages, 3 figures, to appear in proceedings of "Unsolved Problems in Stellar Physics" conference (Cambridge, UK, July 2007

Fluid-driven seismicity in a stable tectonic context: The Remiremont fault zone, Vosges, France

Some relocated seismic events, which have small magnitudes (ML < 4.8), are found to align along a 40 km-long fault zone flanking the southern Vosges Massif to the west. It joins to the south with the epicentral area of the historical 1682 earthquake (Io = VIII MSK). The Remiremont cluster was preceded by a period of seismic coalescence and triggered outward of bilateral seismic migration. The 1984 seismic crisis developed along a well defined 3 km-long vertical plane. In both cases, migration rates of the order of 5–10 km/yr over 30 km-long distances are determined. This pattern requires some mechanism of stress interaction which must act over distances of the order of 1 to 20 km within years. Given the low tectonic activity and the magnitudes of the events the stress transfer cannot result from co-seismic elastic loading or from transient strain at depth. We suggest that the seismic activity reflect rupture of asperities driven by fluid-flow in a zone of relatively high permeability

Icequakes coupled with surface displacements for predicting glacier break-off

A hanging glacier at the east face of Weisshorn (Switzerland) broke off in 2005. We were able to monitor and measure surface motion and icequake activity for 25 days up to three days prior to the break-off. The analysis of seismic waves generated by the glacier during the rupture maturation process revealed four types of precursory signals of the imminent catastrophic rupture: (i) an increase in seismic activity within the glacier, (ii) a decrease in the waiting time between two successive icequakes, (iii) a change in the size-frequency distribution of icequake energy, and (iv) a modification in the structure of the waiting time distributions between two successive icequakes. Morevover, it was possible to demonstrate the existence of a correlation between the seismic activity and the log-periodic oscillations of the surface velocities superimposed on the global acceleration of the glacier during the rupture maturation. Analysis of the seismic activity led us to the identification of two regimes: a stable phase with diffuse damage, and an unstable and dangerous phase characterized by a hierarchical cascade of rupture instabilities where large icequakes are triggered.Comment: 16 pages, 7 figure

Strong earthquakes, novae and cosmic ray environment

Observations about the relationship between seismic activity and astronomical phenomena are discussed. First, after investigating the seismic data (magnitude 7.0 and over) with the method of superposed epochs it is found that world seismicity evidently increased after the occurring of novae with apparent magnitude brighter than 2.2. Second, a great many earthquakes of magnitude 7.0 and over occurred in the 13th month after two of the largest ground level solar cosmic ray events (GLEs). The causes of three high level phenomena of global seismic activity in 1918-1965 can be related to these, and it is suggested that according to the information of large GLE or bright nova predictions of the times of global intense seismic activity can be made

Hierarchical Clustering of Seismic Activity Local Territories Globe

In article, the interrelation between energy parameters of Globe moving in a system Sun-Earth-Moon has been established. It includes features of a seasonal energy condition of an internal core of Earth and the key energy parameters of tectonic activity of seismically dangerous local territories of the planet. These parameters have been systematized by means of a clustering method hierarchical. The mechanism of energy influence of core Earth fluctuations on variations of axial rotation speed of the Globe and level of seismic activity has been grounded. The phenomenon of a periodic oscillation of planet condition seismic and effect of asymmetric distribution of the emergency situations (ES) of tectonic origin on the Earth's surface has been established. For the first time, ranging of the seismically fissile local territories of the Globe in the parameters determining the level of seismic activity and ranges of magnitudes was carried out. Based on these results the effect of division of the seismically fissile local territories into three main clusters that characterized by rather high, average and low degrees of seismic activity was established. Join of the ranged seismically fissile local territories of the Globe permit to establish zones with various degree of seismic activity along the section of various geophysical plates.The results received in article are a basis for further carrying out complex assessment of interrelations between key parameters of moving Globe in a system Sun-Earth-Moon and key parameters of tectonic danger of the seismically fissile local territories of Earth. It is base for further increase in effectiveness of monitoring of origin tectonic emergency by development of neural network prognostic models

Photospheric and chromospheric magnetic activity of seismic solar analogs. Observational inputs on the solar/stellar connection from Kepler and Hermes

We identify a set of 18 solar analogs among the seismic sample of solar-like stars observed by the Kepler satellite rotating between 10 and 40 days. This set is constructed using the asteroseismic stellar properties derived using either the global oscillation properties or the individual acoustic frequencies. We measure the magnetic activity properties of these stars using observations collected by the photometric Kepler satellite and by the ground-based, high-resolution Hermes spectrograph mounted on the Mercator telescope. The photospheric (Sph) and chromospheric (S index) magnetic activity levels of these seismic solar analogs are estimated and compared in relation to the solar activity. We show that the activity of the Sun is comparable to the activity of the seismic solar analogs, within the maximum-to-minimum temporal variations of the 11-year solar activity cycle 23. In agreement with previous studies, the youngest stars and fastest rotators in our sample are actually the most active. The activity of stars older than the Sun seems to not evolve much with age. Furthermore, the comparison of the photospheric, Sph, with the well-established chromospheric, S index, indicates that the Sph index can be used to provide a suitable magnetic activity proxy which can be easily estimated for a large number of stars from space photometric observations.Comment: Accepted for publication in A&

Delayed dynamic triggering of earthquakes: Evidences from a statistical model of seismicity

I study a recently proposed statistical model of earthquake dynamics that incorporates aging as a fundamental ingredient. The model is known to generate earthquake sequences that quantitatively reproduce the spatial and temporal clustering of events observed in actual seismic patterns. The aim of the present work is to investigate if this model can give support to the empirical evidence that earthquakes can be triggered by transient small perturbations, particularly by the passing of seismic waves originated in events occurring in far geographical locations. The effect of seismic waves is incorporated into the model by assuming that they produce instantaneous small modifications in the dynamical state of the system at the time they are applied. This change in the dynamical state has two main effects. On one side, it induces earthquakes that occur right at the application of the perturbation. These are called immediate events. On the other side, after the application of the perturbation there is a delayed effect: the seismic activity increases abruptly after the perturbation, then falls down below the level of background activity, and eventually recovers to the background value. The time scale of these variations depends on the internal dynamics of the system, and is totally independent of the duration of the perturbation. The number of delayed events in excess of the background activity is typically observed to be around a factor of twenty larger than the number of immediate events. The origin of the enhanced activity period following the perturbation is associated to the existence of aging relaxation, and it does not occur if relaxation is absent. These findings give support to the experimental evidence that earthquake can be remotely triggered by small transient perturbations as those produced by seismic waves.Comment: 6 pages, 3 figures, comments welcom