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Petropavlovsk-Kamchatskiy, Russia

Gusev A.A.,Institute of Volcanology and Seismology
Pure and Applied Geophysics | Year: 2010

A wavetrain of high-frequency (HF) P waves from a large earthquake, when recorded at a distant station, looks like a segment of modulated noise, with its duration close to the duration of rupture. These wavetrains, with their bursts and fadings, look much more intermittent than a segment of common stationary random noise. We try to describe quantitatively this bursty behavior. To this end, variogram and spectral analyses are applied to time histories of P-wave envelopes (squared-amplitude or instant-power signals) in six HF bands of 1-Hz width. Nine M w = 7.6-9.2 earthquakes were examined, using, in total, 232 records and 992 single-band traces. Variograms of integrated instant power are approximately linear on a log-log scale, indicating that the correlation structure of the instant-power signal is approximately self-similar. Also, estimates of the power spectrum of the instant-power signal look approximately linear on a log-log scale. Log-log slopes of the variograms and spectra deliver estimates of the Hurst exponent H that are mostly in the range 0.6-0.9, markedly above the value H = 0.5 of uncorrelated (white-noise) signals. The preferred estimate over the entire data set is H = 0.83, still, this estimate may include some bias, and must be treated as preliminary. The inter-event scatter of H estimates is about 0.04, reflecting individual event-to-event variations of H. Many of the average log-log spectral plots show slight concavity that perturbs the approximately linear slope; this is a secondary effect that seems to be mostly related to the limited bandwidth of the data. Evidence is given in support of the idea that the observed approximately selfsimilar correlation structure of the P-wave envelope originates in a similar structure of the body wave instant-power signal radiated by the source, so that the propagation-related distortions can be regarded as limited. The facts presented suggest that the space-time organization of the earthquake rupture process is multiscaled and bears significant fractal features; it deviates from the brittlecrack model with its two well-separated characteristic scales. Phenomenologically, the high-frequency body-wave radiation from an earthquake source can be thought of as a product of stationary noise and the square root of a positive random envelope function with a power-law spectrum. From the viewpoint of applications, the self-similarity of body wave envelopes provides a useful constraint for earthquake source models used to simulate strong ground motions. © 2010 Birkhäuser / Springer Basel AG. Source

Girina O.A.,Institute of Volcanology and Seismology
Journal of Volcanology and Seismology | Year: 2012

Kamchatka is one of the most active volcanic regions on the planet. Large explosive volcanic eruptions, in which the ash elevates up to 8-15 km above sea level, occur here every 1. 5 years. Study of eruptions precursors in order to reduce a volcanic risk for the population is an urgent problem of Volcanology. The available precursor of strong explosive eruptions of volcanoes, identified from satellite data (thermal anomaly), as well as examples of successful prediction of eruptions using this precursor, are represented in this paper. © 2012 Pleiades Publishing, Ltd. Source

Kiryukhin A.,Institute of Volcanology and Seismology
Journal of Volcanology and Geothermal Research | Year: 2016

This study reports and interprets observational data of geyser cycling in the Valley of Geysers and Uzon hydrothermal systems between 2007 and 2015. The monitoring of the Velikan and Bolshoy Geysers after the catastrophic landslide on 3.06.2007 (which dammed and created Podprudnoe Lake, drowning some geysers) and before a mudflow on 3.01.2014 (which destroyed the dam and almost completely drained Podprudnoe Lake) shows that the interval between eruptions (IBE) of the Bolshoy Geyser decreased from 108 to 63 min and that the IBE of the Velikan Geyser slowly declined over three years from 379 min to 335 min. The seasonal hydrological cycle of the Velikan Geyser shows an increase in the IBE during winter (average of 41 min). The dilution of the chloride deep components of the Bolshoy (-23%) and Velikan Geysers (-12%) is also observed. A local TOUGH2 model of the Velikan Geyser is developed. This model is used to describe the transient thermal hydrodynamic and CO2 changes in a Velikan Geyser conduit during the entire cycling process by using cyclic, time-dependent boundary mass flow conditions (major eruption discharge and sub-cyclically assigned CO2 mass flow recharge into the base of the geyser conduit and water recharge at the mid-height of the geyser conduit) and a constant mass flow of water into the geyser at depth. This model also indicates a seepage element at the conduit's top to allow pre-eruptive discharge and a buffering isothermal reservoir below to compensate for pressure declines from major eruptions at earlier times. A local TOUGH2 model is successfully calibrated against temperature observations at both the mid-height and base of the conduit of the Velikan Geyser, which shows the essential role of the above parameters in describing the functionality of the geyser. A reservoir model of shallow production geysers is also developed. This 2D model is used to describe changes in the thermal hydrodynamic state and evolving chloride concentrations in the areas of most prominent discharge, both at steady state and when perturbed by cold water injection from Podprudnoe Lake and other cold water sources (after 3.06.2007). A "well on deliverability" option is used to model the geyser discharge features in the model. The modeled increases in geyser discharge that is caused by an increase in the reservoir pressure from cold water injection reasonably matches observations of IBE decreases in the Bolshoy (~58%) and Velikan Geysers (~9%). The modeling also shows the possibility of chloride dilution in the Velikan Geyser but no dilution in the Bolshoy Geyser. The latter observation is attributed to the presence of direct cold water inflow into the Bolshoy Geyser conduit. © 2016 Elsevier B.V. Source

Girina O.A.,Institute of Volcanology and Seismology
Journal of Volcanology and Geothermal Research | Year: 2013

Bezymianny Volcano is one of the most active volcanoes in the world. In 1955, for the first time in history, Bezymianny started to erupt and after six months produced a catastrophic eruption with a total volume of eruptive products of more than 3km3. Following explosive eruption, a lava dome began to grow in the resulting caldera. Lava dome growth continued intermittently for the next 57years and continues today. During this extended period of lava dome growth, 44 Vulcanian-type strong explosive eruptions occurred between 1965 and 2012. This paper presents a summary of activity at Bezymianny Volcano from 1956 to 2010 with a focus on descriptive details for each event. © 2013 Elsevier B.V. Source

Katsumata A.,Institute of Volcanology and Seismology
Journal of Geophysical Research: Solid Earth | Year: 2010

The crustal structure beneath the Japanese islands, including depth distributions of the Conrad and Moho discontinuities, was estimated using a tomographic inversion of regional body wave arrival times. Depth distributions of the bottom of the surface layer, the Conrad, and the Moho were modeled with two-dimensional B spline functions, while velocity distributions in layers were expressed by three-dimensional B spline functions. The depth of the discontinuities and the velocity in the layers were estimated simultaneously by the least squares method. The velocity structure was sequentially estimated from shallower parts to deeper parts to avoid correlation between them. This sequential analysis provided improved depth resolution. The deepest region of the Moho discontinuity was located in central Honshu, reaching about 40 km. The Moho discontinuity was generally deep in the central part of the islands, whereas it was relatively shallow in the Kanto, southwestern Chubu, and Chugoku districts in Honshu and in northern Kyushu. Some of the shallow Moho regions would be related to graben formation due to tensile tectonic stress since the Miocene. The results were compared with those of seismic refraction surveys and receiver function analyses, and it was found that the obtained model was consistent with many of these studies. © 2010 by the American Geophysical Union. Source

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