Long-term seismic noise investigations on Shikotan Island: First results

In 2003–2004, long-term seismic noise observations were launched on Shikotan Island (Lesser Kuril Range) based on the “Shikotan” dormant regional seismic station. The geological and geophysical data on the registration area are reported. Information about the equipment and its technical specifications is given. The precursors to the strongest local earthquakesthat occurred in the Shikotan Island region in January 2005–March 2007 are identified.     

Spatial relation between the tidal component of seismic noise and development zones of strong earthquakes (from long-term regular observations on the Kamchatka Peninsula)

The results of long-term studies of seismic noise before strong regional earthquakes on the Kamchatka Peninsula in 1992–2006 are presented. These results show that parameters of seismic noise variations caused by the tidal effect depend on the source position of the forthcoming earthquake. The reproducibility of the observed effects is demonstrated by the example of two strong deep (～200 km) subduction earthquakes with similar parameters that occurred on June 16, 2003 (M = 6.9), and on June 10, 2004 (M = 6.8). The physical mechanism of the synchronization of the tidal component extracted from high-frequency seismic noise with the wave of the gravitational tidal potential can be related to the possible development of near-surface dilatancy zones.     

Distribution of polymorphs of aluminum hydroxides in the allophane-gibbsite rocks of the Volga region

Distribution of polymorphs of aluminum hydroxides within an ore lode of allophone-gibbsite rocks of the Volga region has been studied and compared with the results of experimental research on the behavior of aluminum in diluted solutions. The XRD study of morphology and crystallinity of gibbsite confirmed trends noted by Ershova et al. (1979) for the lateritic-sedimentary bauxite series. In these rocks, bayerite and nordstrandite are typically secondary minerals with respect to gibbsite. In the rocks studied, bayerite and nordstrandite form at the early diagenetic stage that leads to decrease of gibbsite crystallinity. The crystallization model of minerals during the formation of the allophone-gibbsite rocks of the Volga region is proposed.     

Variations of Seismicity in the Avachinsky Gulf (Kamchatka, Russia)

Variations of seismic mode in the region of the Avachinsky Gulf (Kamchatka, Russia) are considered. Observed anomalies (seismic quiescence, the ring seismicity, reduction of the slope of the earthquake recurrence diagram) provide a basis to consider this region as a place of strong earthquake preparation. The Kamchatka regional catalogues of earthquakes between 1962–1995 were used in the analysis. A reduced seismicity rate is observed during 10 years in an area of 150 km × 60 km in size. During the last five years, in the vicinity of the area considered, earthquakes with M > 5 occurred three times more often than the average over thirty years. It is interpreted as ring seismicity. The block of 220 km × 220~km in size, including the quiescence zone, is characterized by a continuous decrease of the recurrence diagram slope, which has reached a minimum value for the last 33 years in this region.     

The Tolud Burst of Seismicity and the Earthquake of November 30, 2012 (<Emphasis Type="Italic">M</Emphasis><Subscript>C</Subscript> = 5.4, <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> = 4.8) that Accompanied the Start of the 2012‒2013 Tolbachik Eruption

This paper reports a study of the Tolud earthquake sequence; the sequence was a burst of shallow seismicity between November 28 and December 7, 2012; it accompanied the initial phase in the Tolbachik Fissure Eruption of 2012?2013. The largest earthquake (the Tolud earthquake of November 30, 2012, to be referred to as the Tolud Earthquake in what follows, with K_S = 11.3, M_L = 4.9, M_C = 5.4, and M_W = 4.8) is one of the five larger seismic events that have been recorded at depths shallower than 10 km beneath the entire Klyuchevskoi Volcanic Cluster in 1961?2015. It was found that the Tolud earthquake sequence was the foreshock–aftershock process of the Tolud Earthquake. This is one of the larger seismicity episodes ever to have occurred in the volcanic areas of Kamchatka. Data of the Kamchatka seismic stations were used to compute some parameters for the Tolud Earthquake and its largest (M_L = 4.3) aftershock; the parameters include the source parameters and mechanisms, and the moment magnitudes, since no information on these is available at the world seismological data centers. The focal mechanisms for the Tolud Earthquake and for its aftershock are consistent with seismic ruptures at a tension fault in the rift zone. Instrumental data were used to estimate the intensity of shaking due to the Tolud Earthquake. We discuss the sequence of events that was a signature of the time-dependent seismic and volcanic activity that took place in the Tolbachik zone in late November 2012 and terminated in the Tolud burst of seismicity. Based on the current ideas of the tectonics and magma sources for the Tolbachik volcanic zone, we discuss possible causes of these earthquakes.     

Deep Structure of the Zone of Tolbachik Fissure Eruptions (Kamchatka,Klyuchevskoy Volcano Group): Evidence from a Complex of Geological and Geophysical Data

With the use of the method of low-frequency microseismic sounding, the configuration of the magmatic feeding system of the Tolbachinsky Dol—a regional zone of areal basaltic volcanism in the southern part of the Klyuchevskoy volcano group in Kamchatka—is studied. The initial data are obtained by a stepby-step recording of the background microseismic noise in 2010–2015 within a thoroughly marked-out survey area covering the zones of fissure eruptions in 1975–1976 and 2012–2013 and, partly, the edifice of the Ploskii (flat) Tolbachik volcano. The depth sections reflecting the distributions of the relative velocities of seismic waves in the Earth’s crust are constructed. For a more reliable interpretation of the revealed deep anomalies, the results of independent geological and geophysical studies are used. The ascertained low-velocity structures are closely correlated to the manifestations of present-day volcanism. It is shown that the feeding structure of the Tolbachinsky Dol is spatially heterogeneous, incorporating subvertical and lateral pipeshaped magma conduits, closely spaced magma feeding channels, and shallow magma reservoirs. A longlived local transcrustal magma conducting zone is revealed, and regularities in the deep structure of the feeding systems of fissure eruptions are identified. The configuration of the established subvertical magma conduits permits basalts moving to rise to the surface by different paths, which, inter alia, explains the contrasting magma compositions observed during a single eruption. Thus, based on the instrumental data, it is shown that the magmatic feeding structure of the Tolbachinsky Dol has a number of specific peculiarities and is significantly more complicated than has been previously thought about the areal volcanic fields.     

On the possibility of using the tidal modulation of seismic waves for forecasting earthquakes

The earthquake forecasting technique based on the effect of the modulation of high frequency seismic noise (HFSN) by the Earth’s tides is discussed and the experience of its practical application in Kamchatka is described based on the extensive measurement data for 1996–2013. The empirical development of the lower magnitude threshold on the epicentral distance is refined. The reliability and validity of the precursor are assessed. The efficiency of the precursor is estimated in two ways. It is shown that the results of applying the prognostic procedure statistically significantly differ from a random guess. The presented estimates are based on the catalog containing 68 earthquakes of 1996–2013 in the predicted magnitude interval M ≥ 5.0 at the epicentral distances that are linked to the magnitude by functional dependence.