No 1 (2019)

We present results from a study of lateral Earth’s surface deformation and vertical movements in the area of the Mount Etna active volcano (Sicily, Italy) based on observations by global satellite navigation systems in 2011–2017 at time intervals of 24 hours at sparse stations of the regional geodetic network. The study of Mount Etna is especially important because (1) the volcano stands in a densely populated area, (2) the eruptions are nearly continuous, and (3) the location of the volcano is inconsistent with plate tectonic concepts. Subregional trends have been identified in the deformation of the area of study. Extension was recorded, not only around the summit crater, but also far from it, in the Ionian Sea. This circumstance suggests the existence of an extensive plumbing system at depth whose sources are far from the active summit crater. We discuss geological and geophysical survey results of the coastal area and the sea area in the region. It is shown that Earth’s surface deformation should be studied from observations of the existing networks that are sparse, but cover a large area.

A revised earthquake catalog has been compiled for the White Sea region for the period between 2005 and 2016. The earthquake parameters were revised using a single velocity model (BARENTS), a single methodological approach (Generalized Beamforming), and all available raw data and bulletins of Russian and foreign seismic stations. The location of two nuclear explosions detonated on July 18, 1985 and September 6, 1988 in northern European Russia for civilian purposes showed that the algorithm for calculating hypocenter parameters combined with the BARENTS velocity model is an effective tool. The resulting earthquake catalog enabled us to reveal the leading patterns in the distribution of recent seismicity in the White Sea region.

The issue of whether tidal forces really affect seismicity has been raised many times in the literature. Nevertheless, even though there seems to be a kind of consensus that such effects do exist, no quantitative estimates are available to relate tide parameters to changes in the level of seismic activity. Such estimation for aftershocks of large earthquakes near Kamchatka is the goal of the present study. We consider the influence on seismicity due to ocean tides only, because their effects are stronger than those of solid earth tides. Accordingly, we only consider earthquakes that occurred in the ocean. One important feature that distinguishes the present study from most other such research consists in the fact that we study the height of ocean tides and its derivative rather than tidal phases as the decisive factors. We considered 16 aftershock sequences of earthquakes near Kamchatka with magnitudes of 6 or greater. We also examined shallow background earthquakes along the coast of Kamchatka. Our basic model of aftershock rate was the Omori–Utsu law. The background seismicity distribution was assumed to be uniform over time. In both of these cases we used the actual distributions in space. The heights of ocean tides were estimated using the FES 2004 model (Lyard et al., 2006). The variation in activity from what the basic model assumes in relation to tidal wave height and its time derivative was estimated by the method of differential probability gain. The main practical result of this study consists in estimates of averaged differential probability gain functions for aftershock rate with respect to both of theconsidered factors. These estimates can be used for earthquake hazard assessment from aftershocks with ocean tides incorporated. The results of our analysis show a persistent tendency of aftershock rate increasing during periods when the ocean tide decreased at a high rate. For the background events, we found a typical tendency of event rate increasing when the ocean tide decreased with high tidal amplitudes. The difference in the main factors that affect aftershocks and background seismicity suggest the inference that the effects of tides on aftershocks are more likely to be direct dynamic initiation of events during high strain rates, while the effects on the backgroundevents were static in character.