Kamchatka as the northern link of Kuril-Kamchatka insular arch is the classic region of young Paleogen-neogenic and recent volcanism concentrated in so-called Eastern Kamchatka volcanic belt. Being located in the zone where Asia continent bounds with Pacific Ocean Kamchatka is remarkable for powerful manifestations of tectonic-magmatic, volcanic and seismo-tectonic processes.
One more important structural-geological piculiarity of the region should be pointed out. This is the joint of two deep-sea grooves: Kuril-Kamchatsky and Aleutsky. Possibly, the result of such structural position is the fact that the most powerful volcanic centre consisting of 12 volcanoes (5 from which are active ones) is confined to the northern area of Eastern Kamchatka volcanic belt.
In this volcanic centre there is the highest Euroasiatic active volcano Kluchevskoy which is about 5000 m high and the volcano with giant volume of volcanic material - Shiveluch.
Shiveluch volcano is one of the world's biggest active volcanoes. Its structure is of somma-conical type. Catastrophic eruptions of Shiveluch volcano when there was destroyed most part of the cone and discharged from 1 to 6 km3 of stone material took place in 1854 and 1964 years. An extrusive eruption was observed on April 4, 1993. It was accompanied by a series of volcanic earthquakes and continued till January 1995. There were observed pyroclastic flows which caused powerful lahars which passed along valleys of dry rivers at the distance of 28 km from the volcano.
On September 3, 1998 at 16:21 local time the next weak eruption of this volcano took place. Gaseous-ashy column rose up to 5 km above the crater. At 16:44 local time there were observed directed explosions in south-western direction. Onto the south-western slope of the volcano there fell out volcanic sand spreaded to the distance of 5 km from the crater.
Erupted material was of dacite composition. There constantly acted fumarols with temperature from 90 up to 310°C.
Kluchevskoy volcano is the classic strato-volcano with numerous lateral craters on its slopes. It is located on the right bank of Kamchatka river within 35 km from Kluchi town. The volcano's age is about 7000 years. In 1994 its absolute height was 4822 m, but after a paroxysmal eruption the cone part was destroyed. Apical crater diameter is about 700 m. Repeated activations with discharges of ash which is as a rule taken in the direction of the ocean are characteristic for this volcano. Great volumes of liquid basalt lava flow out during lateral outbursts and paroxysmal eruptions of the apical crater.
Beginning from 1697 - the year of Kamchatka discovery - there have been noted 41 apical eruptions from Kluchevskoy volcano, 7 of them were very powerful, paroxysmal with destruction of the construction part. The last weak activation of the volcano took place on September 2, this year, at 22:25 local time when gaseous-ashy column rose up to the height of 1 km and ashy cloud rose up above the crater to the height of 8 km. Gaseoous-ashy outbursts stopped by the evening of September 2.
Bezymyanny volcano is located 10 km to the south-west from Kluchevskoy volcano. After the explosion a lava dome began to grow in the crater. Having the foot of 600-650 m in diameter it reached the height of 320 m even in four months. The dome's squeezing out continued. On the 8th of May, 1997 there again occured a short-lived eruption of the volcano. Ashy cloud rose up to the height of 14 km, fell out in Kluchi town. On December 5, 1997 there again was explosive eruption. Eruptive column rose up to 10 km. High-temperature fumarols with temperature up to 500°C are constantly acting on the dome.
Karymsky is the most active volcano here. Its age is about 7700 years. The most powerful eruptions according to tephrochronology data (materials of O.A.Braitseva, I.V.Melekestsev and V.U.Kiryanov) took place 5000, 4200 and 2800 years ago. Then there were 2300 years of calmness and about 500 years ago the volcano again activated. During the last 200 years more than 20 eruptions of this volcano were registered. Up to 60 million tons of magmatic material are thrown to the surface with each eruption.
On January 2, 1996 after 14 years of calmness Karymsky volcano began to act. During first days of the eruption ashy-gaseous material was thrown out in pulsing eruptive regime up to the height of 1,0-1,5 km. Ash discharge was evaluated as 3 t/s. Ashy train can be traced at the distance of 40 km. On January 14, 1996 clumpy lava flow of andesite-dacite composition appeared from the crater. This eruption is still going on. Lava flow has already reached the absolute mark - 850 m. At present explosions and ashy-gaseous material outbursts take place with the interval 6-10 minutes. Taking into consideration the erupted material volume and the volcano action regime it can be assumed that it will act for not less than 6-7 months more.
Avacha volcano is being constantly observed. Fumarol occurences with temperature up to 300°C are met at the volcano flat summit along radial fissures.
Not great activation with ash outburst was observed in spring 1998 in Ebeko volcano (Paramushir island) which, fortunately, had no negative ecological consequences.
At present a crater lake with acid water was formed in one of Gorely volcano craters.
This year intensive movement of a glacier is observed in Mutnovsky volcano crater. It has already practically overlapped Donnoe thermal field. A huge lake was formed there. Many sulphur towers and solfataras disappeared under water. Fumarols in Aktivnaya funnel are acting as before.
Periodic degassing explosions occur on scales of minutes to tens of minutes and are common at many basaltic and andesitic active volcanoes worldwide. In the past year, we recorded seismic and acoustic signals generated at two volcanoes with 'Strombolian-type' activity. We have determined geologically plausible models for explosion periodicity and interpreted seismic and acoustic waveforms generated by the active volcanoes.
Despite variations in explosion frequency (6 per hour at Karymsky as opposed to 2 per hour at Sangay), the nature of the explosions is remarkably similar at these two, diverse field sites.
In all explosions, gas emission begins rapidly and is correlated with an impulsive acoustic pressure pulse. Seismic signals are emergent and precede acoustic energy by ~4 s at vent distances of 1.5 km (indicating first arrival seismic velocities of 2000 to 3000 m/s, assuming concurrent seismo-acoustic sources). We classify events at the two volcanoes as either short-duration (less than 1 minute) simple impulses or long-duration (up to 5 mintues) tremor events. Many of the tremor events are harmonic and correspond to regular 1 seconds acoustic pulses which are often audible and sound like chugging from a steam engine.
We argue that the minute-long periodicity between explosions could be explained by a high-viscosity, volatile-depleted section of the upper conduit which acts as a plug and traps rising gases until a threshold pressure is reached. The one-second-long periodicity (chugs) have been attributed to sources as varied as fluid body resonance or gas release through a close-able nozzle.
Volcanic tremor at Stromboli (Aeolian islands, Italy) is correlated to small infrasonic transients which repeat almost rythmically in time in a range between 0.8 to 1.2 s. We demonstrated that infrasonic transient are associated to small gas bursting which are producing no transients in the seismic signals. Coherent fluctuations of energy in the timescale of 30 s shows that infrasonic and seismic signals are linked to the same dynamical process.
In the short timescale, time shift of ˜1 s evidenciated by cross-correlation analysis indicates that infrasonic and seismic signals are produced by two distinctive processes acting at different time. We suggest that the possible physical model is acting in two step: first gas coalescence and then gas bursting. In our model seismic signal is related to the coalescence of a gas bubble from a layer of small bubbles. While, the infrasonic signal is linked to the bursting of the bubble when it reaches the magma surface. In this dynamical process the time delay between infrasonic pulses should reflect the gas nucleation interval of 1-2 s of basaltic magma. We propose that the source function for the shallow volcanic tremor at Stromboli could be the viscoelastic reaction of the magma to the pressure decrease induced by gas bubble growth rate under constant depressurization.
The spectrum of the first derivative of our source function is controlled by the time duration of the pressure pulse which represents the viscoelastic relaxation time of the magma. The predicted asymptotic decays of the frequency contents fits the spectral behaviour of the ground displacement of the vocanic tremor recorded at Stromboli. We show that the same spectral behaviour can be found in the ground displacement spectra of volcanic tremor recorded on different volcanoes.
We present a quantitative analysis of the oscillations of a household pressure cooker and relate the model to physical parameters in exploding volcanos at Karymsky Volcano (Kamchatka, Russia) and Sangay Volcano (Ecuador).
Degassing of volcanos with viscous plugs produce several levels of periodicity, as does a pressure cooker held in a state of unstable equilibrium balance between the constraining weight and the internal pressure of the main cooking chamber. Acoustic and seismic signals, recorded on exploding volcanos, exhibit similar patterns and can be compared directly to the physical processes observed in the kitchen.
We present differential equations relating the evolution of pressure in each stage of the model, and show how our model predicts periodic behavior in signals recorded on volcanos.
Based on the character of the crustal seismicity under Klyuchevskoy volcano during 1971-1997 four seismoactive areas ( or zones ) were distinguished. The depths intervals from up to down are following: -4 3 km, 3 11 km, 11- 20 km, 20 40 km.
The seismicity of these zones reflects the modern magmatic activity of Klyuchevskoy volcano. Geometric dimensions, frequency and summary seismic energy of earthquakes in each of these zones were estimated. Earthquakes occurred at the distinguished depth intervals differ with seismogram features, spectral and other dynamic parameters, and the character of the relationship with volcanic activity.
In zone 4 (depths of 20 40 km ) there is observed the velocity inversion and maximum density of number of earthquakes which summary seismic energy is about two orders smaller than in zone 1. Maximum energy class of these earthquakes is limited by 6.5-7.0 ( M = 1.3 1.6 ), b-value of the Gutenberg-Richter low is anomalously high, all earthquakes have a similar shape records and more long period of seismic waves, than the other ones at the upperlaying horizons in the crust under volcano or the earthquakes with the same focal depths from adjacent regions.
There is made the conclusion that the medium beneath Klyuchevskoy volcano at depths of 20-40 km differs with it's physical properties from the surrounding medium at more high depths in the crust and from the crust-mantle transition layer one. According to preliminary estimation viscosity of this medium is considerably ( at least about several orders ) lower than viscosity of the astenosphere. Deep long-period ( DLP ) earthquakes have different nature than ordinary volcano-tectonic ( VT ) earthquakes occurring in elastic-deformed medium around magmatic channels and/or magmatic chambers under influence changing stress field.
As a rule frequency increasing of DLP- earthquakes takes place before ( ascendant flow of seismic energy ) or just after ( descendant flow of seismic energy ) some noticeable volcanic events ( the beginning of summit or lateral eruptions, increasing of explosive or effusive activity during the development of eruption, forestalling from some days to 2-3 months occurrence of predicted swarms of shallow (SVT )-earthquakes. Different models of DLP-earthquakes sources are discussed.
A seismic experiment was conducted at Unzen Volcano using artificial explosion sources on November 30, 1995. About 290 geophones were deployed along two main profiles (N-S and E-W). The E-W and N-S profiles are about 26.5 and 12.5 km long in the WNW-ESE and NNE-SSW directions, respectively.
These profiles cross on the western flank of the volcano. Six shots of 200-250 kg dynamite were fired on the profiles, and the seismic signals were recorded on a compact data-logger with precise GPS clock at each geophone site.
The preliminary results from the travel-time analysis using ray tracing are
as follows:
(1) The subsurface structure of Unzen Volcano consists of materials with P wave velocities of 1-1.9, 2.1-3.5, 4-4.5 and 6-6.1 km/s, layered from the top.
(2) The layers of 4-4.5 km/s and 6-6.1 km/s rise toward the western flank of the volcano. Beneath this swelling, pressure sources (magma chambers) derived from geodetic measurements are located with depth of 4-5 and 7-10 km
(3) It is considered that the N-S profile is crossing the graben in which Unzen Volcano is formed. However, we can not recognize the apparent subsidence of layers corresponding to the graben structure. The graben structure is probably restricted at extremely shallow part of the crust in the Unzen volcanic area.
A digital broadband seismic network has been installed around Soufriere Hills Volcano on Montserrat. While several distinctive types of seismic events with frequencies ranging from 0.5Hz to 30Hz could be identified, the emphasis is on two types of low-frequency events which indicate the involvement of a fluid phase in the source mechanism: the so-called long-period events and the hybrid events. The latter occur in swarms with distinct periodicities of 4 to 12 hours and preceed major dome collapses and explosions. The swarms correlate very well with the tilt observed at the flanks of the volcanic edifice and, hence, can be linked to the pressurization of the magmatic system.
Occasionally separate hybrid events merge and form harmonic tremor, which sometimes has a shifting spectral content. This reveals temporary changes in the source parameters. Low-frequency seismic signals on Montserrat are considered to be key parameters for the monitoring of the internal dynamics of the volcano. A model is presented to explain the low-frequency observation including the frequency-shift of the tremor signal.
Assessments of the probability and the consequences of future volcanic activity are critical aspects when evaluating the safety of populated areas. A stochastic model has been developed for the forecasting of volcanic hazards that allows the creation of hazard maps related to different volcanic scenarios.
This new type of model, based on a Cox process and a hazard function, enables observed temporal and spatial correlations of volcanic eruptions to be taken account of. The number of future eruptions and the probabilities related to the different scenarios are obtained using a Monte Carlo approach.
The model has been applied to data recorded at Stromboli volcano. In this case the situation is very different from other volcanoes, in that several (moderate) eruptions are recorded each hour. This activity is usually not dangerous for the population of the island and not even for the tourists on the summit. However, some more energetic (and therefore potentially dangerous) explosions are occasionally recorded.
The availability of a time series of the number of events, sampled daily over a 2.5 year period, offers a unique opportunity both to test the stochastic model and to study the time evolution of Stromboli volcanic activity. This work has allowed the detection of an exceptional time correlation in the series; the memory of the volcanic system exceeds two months. Based on this result, Monte Carlo simulations have been performed which enable the forecasting of the number of eruptions for the next few days together with the uncertainty.
Seismic data recorded in the vicinity of the active vent of the 1995 Fogo eruption is used to constrain the associated stress field and deformation. Using the frequency content of the seismograms to distinguish between brittle fracture of cold host rock and deformation in the vicinity of the intruding magma, a vertical dyke with 060 strike is identified as the feeder of the eruption, and delineated down to a depth of about 5 Km.
The local stress field during the eruption is estimated from composite focal mechanisms. Besides the expected sigma 3 direction normal to the dyke, a group of focal solutions point to a stress-field with nearly dyke-parallel sigma 3, which is interpreted as a gravity-controlled readjustment of the edifice. This effect may have increased the instability of the steep eastern flank of the island, since focal mechanisms computed for the late phases of the monitoring are compatible with predominantly dip-slip motion on east-dipping surfaces.
In 1976, during the Large Tolbachik Fissure Eruption, observations were conducted over the discharge of lava flow from the active crater in comparison with the planetary geomagnetic disturbance, solar activity, and other geophysical factors.
Lava discharge had proven to be in correlation with a geomagnetic index at a delay of 4 days, and with Wolf's numbers at a delay of 20 days. When comparing the Avachinsky volcano's microseismicity in 1984 with the planetary geomagnetic index and other geophysical parameters, it has been shown that changes of everyday values of slight volcanic earthquakes of K=3-6 energetic class during two turns of the Sun repeat the variations of geomagnetic field of the Earth with a distinct delay of 21-22 days. These and several other results serve as a basis for a suggestion that the development of seismic and volcanic processes at the active volcanoes of Kamchatka is to a significant extent caused by an impact of electromagnetic energy of the changing solar corpuscular flow upon the geomagnetic field of the Earth.
In our opinion, degassing processes are also related to the acoustic and seismic emission of processes of mountain rock destruction occurring at different levels of the lithosphere. Closed magma and hydrothermal systems are good natural volumetric deformographs, where changes of thermodynamic conditions will lead to the alteration of partial pressures of dissolved gases. Such systems will react to both tidal and non-tidal impacts.
Monitoring of gas concentrations in such systems can be a basis for the study of the processes of effects of external influences and for diagnostics of the state of these systems. The measurements carried out at the Verkhne-Paratunskaya geothermal system can be an obvious case. Records of variations of hydrogen concentration from a deep well of the Karymshinsky structure have been obtained. A record from August 8th to 11th 1993 is the most remarkable one as, from the morphological point of view, it is similar to geomagnetic pulsations of the PC1-'pearl'-type being recorded in the magnite-telluric field of the Earth.
These observations can be considered as a confirmation of the said suggestions concerning the interrelation between magnetic disturbances of the magnetosphere and volcanic and tectonic processes.
Since 1978 the Institute volcanology will carry out thermal aeroshooting of active volcanoes and geothermal of regions of Kamchatka with the help of thermovision AGA-680. (2-5.6), also arranges by data of thermal aeroshootings executed with application of other systems (Autumn, Winter, TIMS). The objective of shootings execution was data retrieval about a structure of heat radiation of a surface in near infra-red area in windows of atmosphere transparency.
With use of experience of ground termo-balance works the obtained data allow to describe values thermal discharge of volcanoes not only on radiation component, but also by that part convective component, which corresponds disrtibuted discharge of heat.
In case of high powers of heat discharge, which are observed on geothermal manifestations and active volcanoes, the remote thermal shooting allows immediately to monitor namics of the process development. The characteristic examples are obtained at ground measurements from distance 50 and 30 kms for ash cloud of Klyuchevskoi Volcano and during eruption of Avachinsky, and also of Shiveluch Volcano at aeroshooting of the crater and of extrusive dome.
In the schedule of the predictionss of volcanoes eruptions, during preparation of eruptions the changes of a thermal mode in the Avacha Volcano crater, and in the Karymsky Volcano crater showing of origin new thermal anomalies at the bottom of these craters, new long before a beginning of eruptions are fixed. In connection with eruption of the Academy of Sciences Volcano (Karymskoe lake) is of interest and increased values of temperatures in northern part of lakes in April, 1993 is fixed.
The experience of application of thermal shooting in the schedule of the volcanic eruptions predictions and learning of dynamics of eruptions shows, that the instrument allowing of used systems should be not worse than 5 m. With such requirement it is necessary to approach and to possibilities of using of space observations data.
According the inductive frequency data (analog MELIS method), a conductive horizon existed about 0.5 km beneath the Avachinsky volcano during 1981-1984 years. It has been suggested about hydrothermal nature of the phenomena. Measurements in February 1991 showed the disappearrance of this structure. Then from August 1992, the high conductivity horizon occurred again at approximately constant depth at the same depth and was characterized by very high electroconductivity (? < 1 omm).
Geoelectric situation was relatively constant with low variations of the depth of the conducting surface. Since September 1996 significant variations of geoelectricity have appeared which can be explained by some changes above the Avacha magma body. The origin of these changes is not clear, but they can indicate the activation of the volcano.
The variations of geoelectricity under the Avachinsky volcano:
| Year, month | ,1981-1984 | ,1991 Feb | ,1992 Aug | ,1992 Oct | ,1993 Aug | ,1993 Sept | ,1994 Aug | ,1994 Sept | ,1994 Oct | ,1995 July | ,1995 Sept | 1996 Aug | ,1996 Sept | ,1996 Oct | ,1997 Aug | ,1997 Oct |
| h1, m | ,432 | ,>200 | ,507 | ,344 | ,485 | ,442 | ,320 | ,357 | ,390 | ,345 | 360 | 390 | 297 | 424 | 626 | 482 |
| r1, omm | ,5000 | ,5000 | ,5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 |
| h2, m | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | |||||||
| r2,omm | 280 | 8 | < 1 | < 1 | < 1 | < 1 | < 1 | < 1 | < 1 | 8 | 8 | 8 | 264 | 160 | 8 | 8 |
| h3, m | - | - | - | - | - | - | - | - | - | - | - | - | 8 | 8 | - | - |
| r3, omm | - | - | - | - | - | - | - | - | - | - | - | - | < 1 | 7000 | - | - |
All the basic characteristics of volcanic eruptions could be described by a simple model of erupting volcano system (EVS): voluminous chamber filled with magma with some excess pressure in it and connected with the day surface by strait vertical narrow conduit. It is isolated everywhere except the outlet of the conduit.
Magma is two-component and two-phase media and the dynamics of the eruption is the dynamics of two phase flow in the conduit. Types of eruptions are connected with the two phase flow structure at the exit of conduit. There could be only 3 types of such structure: The beginning and ceasing of plinian stage of catastrophic explosive eruptions correspond to such jumps of discharge rate. The characteristics of EVS which are necessary for the catastrophic jumps of intensity were found. The result is the possibility of prediction of such events. With the help of the model the effect of many external factors could be described ( first of them are trigger-effects such as the effect of volcanic edifice destruction), and possible amount of erupted products could be estimated.
1) barbotizing (bubbling with big bubbles going up much faster than liquid);
2) dispertion (gas-pyroclastic mixture);
3) partly destroyed foam (gas escapes through the labirinth of connected with each other pores in continuous slow-moving magma). Dispersion regime was described by the system of gydrodynamical equations, numerical analysis of wich have shown the existing of the region of instability and the possibility of nearly instantaneous increase or decrease of magma discharge rate on several orders of magnitude.
Since 1977 in Kamchatka systematic observations for the underground water regime are conducting. Observations are conducting for the reason to reveal a relationship between of seismic and hydrogeological regimes. The network of observations includes seven self-pour out wells and two low-temperature springs, which are situated in Petropavlovsk - Kamchatsky vicinities.
Of many years data show presence of the relationship between seismic and hydrogeological regimes. This is reflected in arising the anomalies in underground water regime before and after strong earthquakes. Established fact that earthquakes which have the power more than 4 (for the Petropavlovsk - Kamchatsky area) cause postseismic anomalies in regime of the springs. Earthquakes which have the power 5 and more, but more exactly processes of their preparation, are capable to cause forerunning anomalies in regime of the selfpour out wells. The particularities, in reactions of underground hydrosphere on processes of the preparation volcanotectonic event of the Karymsky volcano area, are discovered (earthquake 1.01.96, v. Karymsky and v. Academy of Sciences eruptions ).
The accumulated information, about the behaviour of the different parameters of regime before strong earthquakes, allows to value the current seismic situation for the Petropavlovsk - Kamchatsky area.
The Mutnovsky geothermal field, located in southeastern Kamchatka, is currently being studied for potential electric power development. Continuous high-resolution pressure monitoring has been carried out in an observation well since September 1995.
Several instances of quasi-periodic pressure excursions were observed that appear to correlate with seismic events at approximately 100 km distance from the field. This report briefly summarizes important characteristics of the Mutnovsky field and of the pressure monitoring system used, and presents pressure data recorded in the field. The likelihood that observed pressure excursions are indeed triggered by seismicity is discussed. Several hypothetical scenarios that could provide a coupling between regional seismicity and reservoir hydraulics are proposed and evaluated.
At the 10h 57m ,1st of January, 1996 in vicinity of Karymsky volcano occured big earthquake (M=7.0). Just after earthquake started eruption of Karymski volcano and new vent in Karymski Lake (the Academy Nauk caldera). The distance between Karymski volcano and new vent in the Karymski Lake is out 5 km. The relation between big earthquake (M=7.0) and the eruptions of the Karymsky volcano and the Academy Nauk caldera was revealed by the analysis of the previous and following seismicity.
The process of the eruptions and seismic activity was going by this way: 8 hours before big earthquake started microearthquakes in the depth 3 km under Karymsky volcano; 5 hours later the strong forshock swarm began in the future focal volume of the main shock; the Karymsky volcano eruption was started at the same time as big earthquake; the eruption in the Karymsky Lake was happened, next day about 14 hours later than the main earthquake.
The average periodicity of Karymsky volcano eruption is 10-15 years. The big earthquake in this area has repeating time of many hundreds years. The extra pressure in magma chamber below Karymsky volcano was the trigger for the forshock swarm and for the big earthquake. The fault constructed by the big earthquake opened the new way for magma, which started eruption in the Karymsky Lake (the Academy Nauk caldera). The hypocenter's distribution of the earthquakes located since 1962; shows a big gap under Karymsky volcano, that can be interpreted as a magma chamber. The upper border of this magma chamber can be estimated from the distribution of hypocenters is 4-5 km deep.
The energy-rich geophysical medium possess property of microseismic activity. Seismic noise radiation is most conspicuous in zones of faults, contacts of earth crust blocks, hydroterms. In this investigation we use the method of noise seismotomography for reconstruction of microseismic emission field, that was observed by seismic array. The noise signals, considered earlier in seismology as an annoying hindrance only, now regards as a highly informative field, containing the information about a structure and a condition of environment.
For determination of coherent seismic radiation sources the parameter SEMBLANCE (S) was employed. This parameter reflects the proportion between useful signal and hindrance. Semblance estimation is found as a ratio between the energy of a signal summed over all sensors and the sum of signal energies at each sensor separately, and is calculated for each point of medium under the array. The elementary models, demonstrating capabilities of this method, are considered.
The microseismic fields registration was held on 2 specially organized places near Northern breakthrough of 1975-76 Large Tolbachik Fissure Eruption in Kamchatka. The continuing geotectonic and geochemical activity, as well as fragmentation and heterogeneity of this area, suggested the presence of high emission there, making the Northern vent a test site that could yield interesting results through the use of noise seismotomography. The scanned regions are in a narrow belt about 3 km wide, to which the volcanic activity of the past 2000 years was restricted.
The seismic array consist of 9 vertical seismometers. The configuration of the seismic group is the square 1 km x 1 km. The input data were filtered by digital filter in windows 3-6 and 6-12 Hz. The volume being scanned is 2 km x 2 km and 3000 m in depth. For the set of fixing depth S-distribution maps had been constructed.
It is shown by 1992 and 1996 registrations, that there are the areas with noise activity under III cone of Northern vent and under cone Alaid. The registration, carried out in 1994, has coincided with period of Kluchevskoy volcano activization. There is the medium activization under the influence of volcanic tremor: radiation sources under III cone and cone Alaid are observed very brightly for depth 1100-3000 m. The results of data processing, obtained in a various time, agree among themselves. This fact evidences that mapping images correspond to actual objects, fixed in researched environment.
By 1996 registration which was carried near I cone of Northern vent microseismic active area was connected with I cone position. On deeper horizons noise sources are displaced under a chain of cinder cones by wide strip.
What is the nature of found anomalies? Probably, they are connected with anomalies of temperature, lifting of gases on cracks, chemical processes, dikes systems under cones. But it is a problem of the geological interpretation, which is not considered in shown report.
Many volcanoes present permanent or at least long term activity, although this activity can show very different eruptive phases. A new approach to the modelling of this behaviour is that of using the theory of dynamical systems. The basic idea is to test the hypothesis of the existence of a deterministic dynamical system governing the evolution of the volcano.
Several methods exist trying to extract information from observed geophysical
time series in order to establish constraints on this underlying dynamical system. If signs of determinism are found in the experimental time series, the analysis of the long term time evolution of the estimates of the dynamical parameters can then offer new insights on the characterization of different eruptive phases of a volcano.
Volcano seismology often deals with rather shallow seismic sources and seismic stations deployed in their near-field. As most volcanoes have a pronounced topography the interference of the seismic wavefield with the stress-free surface results in severe waveform perturbations which affect seismic interpretation methods.
We derive a correction term for plane seismic waves and a plane free surface such that for smooth topographies the effect of the free surface can be totally removed. Seismo-volcanic sources radiate energy in a broad frequency range with a correspondingly wide range of different Fresnel zones. A 2-D boundary element method has been employed to study the seize of the Fresnel zone dependent on source depth, dominant wavelength and topography in order to estimate the limits of the plane wave approximation. This approximation remains valid if the dominant wavelength does not exceed twice the source depth.
Further implications of this study concern the particle motion analysis to locate point sources, the deployment strategy of seismic instruments on volcanoes, as well as the direct interpretation of the broadband waveforms in terms of pressure fluctuations in the volcanic plumbing system.
Response of high-frequency seismic noise (HFSN, frequency - first tens of Hz, amplitudes - 10-9 - 10-12 m) to the Earth tides is investigated. The most conveniently to use the tidal wave O1, having period 25.82 hours. This wave will play a role of the reference action on medium. Continuous observation of the HFSN was conducted in one place on Southern Kamchatka (Russia) during six years. We use the envelope of the quasiharmonic noise signal for analysis.
There is shown, that the component of the HFSN envelope, having period of the wave O1, has a phase varying in time. These variations are connected with preparation of strong earthquakes. The seismicity in radius of 250 km from item of registration is considered. The stabilization of the phase on some level was observed (retrospectively) before 9 earthquakes with magnitude M>6.0. The duration of the stabilization is equal to some months. It possible, that the value of the level of stable phase is connected to position of the earthquake epicenter. After strong earthquake a phase of the HFSN envelope varies sharply. The average jump of a phase is equal to p.
The authors propose opportunity of use the HFSN monitoring for intermediate-term prediction of strong earthquakes. From analysis of the HFSN in June, 1996 warning about big earthquake (M>6.0) in three months in area with size 100 km by 100 km was made. This earthquake (June 21, 1996, Mw=7.0) occurred in three days after warning in area which was marked. The warning about next strong Kamchatkan earthquake was made 9 days ahead Kronotsky Earthquake (December 5, 1997, Mw=7.9).
Volcanic eruptions are notable for their great variety in both style and intensity, which produce a wide range of wave disturbances in the atmosphere: from long-wave, with a period of a few tens of minutes, to sound oscillations. A phenomenological classification of these disturbances was devised on the basis of spectral characteristics of signals and a wealth of experimental material.
(1) Aerodynamic noise (f=20-1000 Hz). During a continuous outflow of an ash-gas mixture from the crater (Plinian- and Vulcanian-type eruptions) a sound noise is generated by the aerodynamic impact of the flow on the environment. As the aerodynamic noise power is proportional to the eighth power of the outflow rate, one can clearly define variations in the outflow rate using the results of recording the aerodynamic noise.
(2) Nonsteady processes in the crater during eruptions trigger air-shock waves (f=1-20 Hz). During the Vulcanian and Plinian-type eruptions, supersonic jumps of an outflow of an ash-gas mixture at the crater rim, explosions of volcanic gases in the air may trigger them. During Strombolian activity, blisters swelling on the surface of low-viscous lava burst. As a result, weak air-shock waves (ASW) are also generated. In the near zone at some distances from the source, ASW, as a result of their evolution, turn into ordinary air wave impulses.
(3) Infrasound (f=0.003-1 Hz). During the origin and formation of
pyroclastic flows related to the destruction of extrusive domes at andesitic volcanoes, powerful turbulent convective flows arise in the atmosphere, and quasiharmonic ground vibrations (volcanic tremor) are recorded. Separate convective cells of the eruptive cloud are sources of wave oscillations in the infrasonic-range atmosphere. The power of acoustic emission depends on the intensity of heat release from the surface of pyroclastic flows, which is defined by temperature, area, gas saturation and character of deposit material. At the same time, the seismic source power is largely determined only by the flow rate, which suggests that the correlation of both emission types is an informative parameter of the nature of pyroclastic flow formation.
(4) Long-wave disturbances (f<0.003 Hz). Of special interest are strong explosive eruptions (Plinian-type eruption), during which the eruptive column rises the tropopause and higher. Acoustic emission during such eruptions is characterized by a wide frequency range and by high intensity; the intensity is determined by heat release in the source. As the main amount of heat during explosive eruptions is transported to the atmosphere by fine-disperse ash, then the amount of ejected ash can be defined from the value of heat release.