V. A. Saltykov

Precursors of large Kamchatka earthquakes based on monitoring of seismic noise

This paper presents results from a monitoring study in high frequency seismic noise in Kamchatka during 1992–2006 and reports their use for predicting large regional earthquakes (M ≥ 6.0) in an epicentral distance range Δ within 400 km. The prediction is based on an original method using earth tides as the standard external excitation to study patterns of seismic emission. The method as used at present is described in detail. Guidelines are delineated for future refinement of the prediction method.

Deep structure of the North Vent Area, Great Tolbachik Fissure Eruption of 1975–1976, Kamchatka: Evidence from low-frequency microseismic sounding

Studies were conducted to improve our knowledge of the deep structure of the magmatic system and the plumbing system for the North Vent, Great Tolbachik Fissure Eruption of 1975–1976 based on recordings of background microseismic emission by broadband digital instruments along two parallel lines running through eruptive centers of various ages across the main magma-conducting fault. The method of low-frequency microseismic sounding was used for constructing deep sections down to a depth of 20 km, showing the shear-velocity distributions along these lines. Elements of the magmatic system were revealed beneath both vents in the form of low-velocity anomalies. We identified regions of magma chambers at different depths together with the channelways that connect these. It was found that magma might come to shallow chambers from different deep-seated sources along spatially isolated magma conduits, which is one of the possible causes of the variation in the basalt composition during the eruptions. For the zone of areal volcanism we are the first to demonstrate a change in magma-conducting conduits in the transition from the crystalline basement to the volcanogenic sedimentary rock sequence, with subvertical channels being replaced by inclined forms. It was shown that the elements of the magmatic system beneath both eruptive centers studied here are similar. It is hypothesized that there is a regularity in the configuration of plumbing systems in the middle part of the Tolbachik regional zone of areal volcanism.

A statistical estimate of seismicity level: The method and results of application to Kamchatka

We present a technique for a unified estimate of seismicity level in specified space-time regions. The use of the distribution function of released seismic energy permits the formalization of qualitative description of seismicity intensity. We propose a seismicity scale that contains five main grades and three additional ones.

An analysis of precursory phenomena for the 2012–2013 Tolbachik Fissure Eruption: Seismicity parameters and crustal strain as inferred from data supplied by the system of multidisciplinary monitoring of volcanic activity in Kamchatka

Abstract—This paper is concerned with ground deformation and seismicity prior to the Tolbachik Fissure Eruption, which began in Kamchatka on November 27, 2012. Seismic and GPS data were analyzed to reveal synchronous precursory anomalies in crustal deformation and seismicity that lasted approximately 4 months (August to November 2012). The seismic anomaly was a statistically significant increase of seismicity with low energy (mostly KS = 4–6) beneath the Ploskii Tolbachik Volcano edifice at depths of less than 5 km. The rates of seismicity and seismic energy release were exceeded by factors of approximately 40 compared with the 2000–2011 mean values during the 2 to 3 weeks immediately before the eruption. The strain anomalies were observed as movements in the middle of the Klyuchevskoy volcanic group: a radial (relative to the eruption) compression and an extension in the tangential direction. The strain had reached ~ 10–7 by the beginning of the eruption. The durations of the seismic and strain anomalies were comparable in value (~ 4 months before the eruption), thus providing evidence of a common origin. We can classify them as belonging to the same time scale of precursors (the intermediate-term in the accepted terminology).

New data on the deep structure of the Northern Vent of the Great Tolbachik Fissure Eruption (1975–1976)

In order to restore the deep structure in the region of the Northern Vent (NV) of the Great Tolbachik Fissure Eruption (GTFE) (1975–1976), low-frequency microseismic sounding was applied. For this purpose accumulation of spectra of the microseismic field was performed in a wide frequency band in 29 points along a linear profile 14 km in length embedded transversely to the fissure eruption. A deep cross section of the Earth’s crust was constructed up to 20 km, reflecting the distribution of relative velocities of transverse seismic waves. The revealed structural heterogeneities were interpreted with consideration of previously known results of complex studies of the eruption. The existence of an abnormal structure at the depths of 2–3 and 7–8 km under the NV GTFE was confirmed, which could be low-depth magma chambers. Deep subvertical low-velocity structures were revealed and spatially registered, which probably feed the conduits of the eruption. It was demonstrated that the ways of possible magma supply to the peripheral chamber at the depth of 2–3 km could be various. For the first time for the zone of areal volcanism, variation of the character of magmatic intrusions was demonstrated at the transition from a crystalline basement to the near-surface depth: subvertical forms are replaced with a system of sills and interesting injections.

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.

A Comprehensive Analysis of Kamchatka Seismicity for the Period 2005-2007 Using the Regional Catalog

We characterize the Kamchatka seismicity for the period 2005–2007. Regional catalogs of Kamchatka earthquakes were used to develop 2D distributions of parameters of background seismicity. The characteristics we consider include the activity A10, the slope of the recurrence curve γ, the parameters involved in the methods RTL, ΔS, and the “Z-function”, as well as the control of earthquake clustering. We have detected the space-time agreement between the anomalies exhibited by several parameters.

A Parametric Representation of Kamchatka Seismicity over Time

This paper presents a set of seismicity parameters that are estimated at the Kamchatka Branch of the Geophysical Service, Russian Academy of Sciences based on the regional catalog data with the purpose of routine monitoring of the current seismic situation in the region. The focus is on the identification of changes in the seismic regime (seismic quiescences and seismicity increases) in earth volumes adjacent to the maturing rupture zone of a large earthquake. The techniques we use include estimation of the seismicity level for the region using the SOUS’09 scale; calculation of the variations in the slope of the recurrence relation, identification of statistically significant anomalies in the slope using the Z test, and calculation of the seismic activity A10; monitoring the RTL parameter and variations in the area of seismogenic ruptures; using the Z test to detect areas of statistically significant decreases in the rate of seismicity; and identification of earthquake clusters. We furnish examples of such anomalies in these seismicity parameters prior to large earthquakes in Kamchatka.

Modulation of high-frequency seismic noise by tidal deformations: The features of the phenomenon before strong earthquakes and a probable physical mechanism

A probable physical mechanism of tidal modulation of intensity of the endogenous seismic noise is proposed. The mechanism associates this phenomenon with modulation of the size of the region over which the recorded noise is acquired due to nonhysteresis amplitude-dependent absorption in the Earth’s rocks. The two most important cases, namely dry and fluid-saturated rocks, are considered. In both cases, internal elongated strip-like contacts (even in minor quantities) are found to be of fundamental importance. The proposed mechanism provides an explanation for a variety of features of high-frequency seismic noise modulated by tides, which were revealed in the long-term observations on the Kamchatka Peninsula: (i) the modulation depth on the order of the first few percent; (ii) stabilization of the modulation phase before a strong earthquake; (iii) a frequently observed near jump-like change in the phase to the opposite-sign phase after the earthquake; (iv) the subsequent period of a relatively unstable phase; and (v) temporary predominance of the modulation component on the second harmonic of the fundamental tidal frequency in the vicinity of the time when the earthquake occurred.

The precursory phenomena before the Karymskii seismovolcanic crisis in parameters of seismicity in a wide range of energy

We report extensive anomalies identified in seismicity parameters at different energy levels which were observed during the precursory process of the Karymskii seismovolcanic crisis of January 1–2, 1996. The seismicity of different energies includes earthquakes contained in the Kamchatka regional catalog and seismic noise (amplitudes of 10−9–10−12 m, frequencies of a few tens of hertz), which is a manifestation of the seismic process in the lowest energy range. The parameters of background seismicity are considered in retrospect using techniques for analyzing the dynamics of the seismic process: RTL and the Z function. Microseismicity is examined using these authors’ own method based on monitoring the response of high frequency seismic noise to tidal excitation