emergence of a band limited power law in the aftershock decay rate of a slider block model 1 in order to elucidate how structural heterogeneities affect the aftershock decay rate we examine the aftershock sequences produced by a slider block model of seismicity in this model the geometry of the seismic zone is the only free parameter and all aspects of the system are known the power law aftershock decay rate holds only for smooth faults a band limited power law emerges at intermediate fault complexity for rough faults only a transient regime toward an exponential decay is observed in all fault geometries examined a band limited power law model fits the synthetic aftershock decay rate better than the modified omori law then as the connected seismic elements form a simpler localised surface we show that the power law aftershock decay rate extends over longer time and that the power law exponent increases these results support the inference that the correlation time of the power law aftershock decay rate increases as the deformation localises along dominant major faults

fractal structure of spatial distribution of microfracturing in rock summary a constant stress fracture experiment of oshima granite was carried out at the confining pressure of 40mpa hypocentres of 2064 acoustic emissions were located during the experiment using the correlation integral we found that the spatial distribution of hypocentres of acoustic emission is a fractal and that the fractal dimension decreases with the evolution of rock fracturing the spatial distribution of earthquake s hypocentres reveals fractals ranging from regional to worldwide distribution if we extrapolate from laboratory measurements it is possible to predict the occurrence of large earthquakes by the decrease in the fractal dimension

strain rate and temperature dependence of omori law scaling constants of ae data implications for earthquake foreshock aftershock sequences 1 little is known about the temperature and strain rate dependence of acoustic emission ae activity ae hence we carried out a preliminary series of flow through triaxial compression tests on porous sandstones at different temperatures and strain rates the ae data exhibits clear foreshock and aftershock sequences with respect to the dynamic failure of the test specimen significant ae activity starts less than 5 min before sample failure irrespective of the strain rate the increase in the ae event rate is steeper and the foreshock exponent p is smaller in the slow strain rate tests it could be the reason why there are no easily recognisable foreshock sequences for most individual earthquakes the aftershock decay parameter p is a linear function of test temperature as it has also been inferred for natural seismicity the seismic b value decreases systematically with increasing deformation rate suggesting a greater proportion of small cracks in the slow strain rate tests hence the ae activity is a function of both strain rate and temperature

stochastic synthesis of earthquake catalogs a model of earthquake occurrence is proposed that is based on results of statistical studies of earthquake catalogs we assume that each earthquake generates additional a probability that depends on time as t 1 this assumption together with one regarding the independence of branching events on adjacent branches of the event tree is sufficient to permit the generation of complete catalogs of earthquakes that have the same time magnitude statistical properties as real earthquake catalogs if is about 0 5 the process generates sequences that have statistical properties similar to those for shallow earthquakes many well known relations are reproduced including the magnitude frequency law omori s law of the rate of aftershock and foreshock occurrence the duration of a recorded seismic event versus its magnitude the self similarity or lack of scale of rate of earthquake occurrence in different magnitude ranges etc a value of closer to 0 8 or 0 9 seems to simulate the statistical properties of intermediate and deep shocks a formula for seismic risk prediction is proposed and the implications of the model for risk evaluation are outlined the possibilities of the determination of long term risk from real or synthetic catalogs that have the property of self similarity are dim

effect of sliding rate on the activity of acoustic emission during stable sliding the mechanical and statistical characteristics of acoustic emission ae events during stable sliding are investigated through a laboratory experiment using a granite specimen with a pre cut fault numerous ae events are found to be generated on the pre cut fault indicating that microscopically unstable fracture occurs during macroscopically stable sliding the composite focal mechanism solution of ae events is determined from the first motion directions of p waves the determined mechanism is consistent with the double couple one expected for the slip on the pre cut fault the source radii of large ae events are estimated to be about 10 mm from the widths of the first p wave pulses these indicate that the ae events are generated by shear fracture whose faulting area is a part of the pre cut fault plane the occurrence of ae events as a stochastic process approximately obeys the poisson process if the effect of mutually dependent events consti tuting clusters is corrected the observed amplitude frequency relation of ae events approximately follows a power law for a limited amplitude range as the macroscopic sliding rate increases the number of ae events per unit sliding distance decreases this rate dependence of the ae activity is qualitatively consistent with the observation that the real area of contact between sliding surfaces decreases with an increase in the sliding rate as reported in the literature

preliminary analysis of observations of the pinatubo volcanic plume with a polarization sensitive lidar a dual polarization lidar aboard the nasa electra aircraft was used in july 1991 to survey the stratospheric plume from the recent mt pinatubo eruption both depolarizing and non depolarizing volcanic layers were observed ranging from 17 to 26 km in altitude differences in the depolarization signatures of the layers indicates differences in the composition or physical state of the particles in the layers

three dimensional volcanic aerosol dispersal a comparison between multiangle imaging spectroradiometer misr data and numerical simulations 1 the three dimensional reconstruction of volcanic plumes is a central goal to enhance our understanding on dispersal processes in this paper we use data from the multiangle imaging spectroradiometer misr on board nasa s terra spacecraft combined with a stereo matching retrieval procedure we show the potential of misr in capturing important features of volcanic plumes like column height optical depth type and shape of the finest particles of two highly explosive eruptions occurring on mount etna in 2001 and 2002 this work tests how tephra dispersal models reconstruct the 3 d shape of volcanic clouds we compare misr data with fall3d an eulerian model for the transport and deposition of volcanic ash and aerosols coupled with the weather research and forecasting mesoscale meteorological model agreement between simulations and misr data is good regarding both events although it could be improved by increasing the accuracy of the meteorological data a better constraint on volcanological input parameters like the height of the eruptive column and improving our understanding of processes such as aggregation phenomena and volcanic cloud microphysics

integrated satellite observations of the 2001 eruption of mt cleveland alaska abstract satellite data were the primary source of information for the eruption of mt cleveland alaska on 19 february and 11 and 19 march 2001 multiple data sets were used pre syn and post eruption to mitigate the hazard and determine an eruption chronology the 19 february eruption was the largest of the three resulting in a volcanic cloud that formed an arc over 1000 km long moved to the ne across alaska and was tracked using satellite data over more than a 50 h period the volcanic cloud was concurrently detected on the goes avhrr and modis data at various times and their respective signals compared all three sensors detected a cloud that had a very similar shape and position but there were differences in their areal extent and internal structural detail goes data showed the largest volcanic cloud in terms of area probably due to its oblique geometry modis bands 31 and 32 which are comparable to goes and avhrr thermal infrared wavelengths were the least effective single channels at detecting the volcanic cloud of those investigated modis bands 28 29 31 and 32 modis bands 28 and 29 detected the largest volcanic clouds that could easily be distinguished from weather clouds of the split window data modis bands 29 minus band 32 detected the largest cloud but the band 31 minus band 32 data showed the volcanic cloud with the most internal structural detail the puff tracking model accurately tracked the movement and predicted the extent and shape of this complex cloud even into areas beyond satellite detection numerous thermal anomalies were also observed during the eruption on the twice daily avhrr data and the high spatial resolution landsat data the high resolution radarsat data showed that the avhrr thermal anomalies were due to lava and debris flow features and a newly formed fan along the west coast of the island field observations and images from a hand held forward looking infrared radiometer flir showed that the flow features were a a lava debris flows and a warm debris fan along the west coast real time satellite data were the primary tool used to monitor the eruption track changes and to mitigate hazards high resolution data even though coverage is infrequent were critical in helping to identify volcanic processes and to compile an eruption chronology

puff a high resolution volcanic ash tracking model this paper presents a volcanic ash tracking model referred to as puff the model was developed to simulate the movement of airborne ash in near real time following an eruption for the purposes of hazard warning the model tracks particles through a lagrangian formulation of advection fallout and turbulent diffusion using a random walk technique three recent eruption events are simulated using archived data avhrr images from these events are used for comparison and to validate model results

can damage mechanics explain temporal scaling laws in brittle fracture and seismicity time delays associated with processes leading to a failure or stress relaxation in materials and earthquakes are studied in terms of continuum damage mechanics damage mechanics is a quasi empirical approach that describes inelastic irreversible phenomena in the deformation of solids when a rock sample is loaded there is generally a time delay before the rock fails this period is characterized by the occurrence and coalescence of microcracks which radiate acoustic signals of broad amplitudes these acoustic emission events have been shown to exhibit power law scaling as they increase in intensity prior to a rupture in case of seismogenic processes in the earth s brittle crust all earthquakes are followed by an aftershock sequence a universal feature of aftershocks is that their rate decays in time according to the modified omori s law a power law decay in this paper a model of continuum damage mechanics in which damage microcracking starts to develop when the applied stress exceeds a prescribed yield stress a material parameter is introduced to explain both laboratory experiments and systematic temporal variations in seismicity

estimating tectonic stress rate and state with landers aftershocks a new method of analyzing the location and timing of aftershocks that makes possible estimates of the rate at which faults in the area are being loaded with stress has been developed this new method is an application of a theory of aftershocks proposed by dieterich 1994 the stress step from the mainshock triggers the aftershocks which release energy stored by tectonic loading and the mainshock and the tectonic stressing rate is responsible for the background activity thus a comparison of the number of aftershocks with the rate of background activity as a function of stress step can provide an estimate of tectonic stress rate this method requires analysis of a catalog which includes background activity as well as aftershocks the method has been applied to the aftershocks of the 1992 landers california earthquake the tectonic stress rate estimated for the mojave block is 1 2 pa d which corresponds to a repeat time for large events of 14 000 years and suggests that much of the observed strain in the mojave is anelastic the southern san andreas fault system is found to have a stress fate of 100 pa d which corresponds to a repeat time of 270 years and is consistent with primarily elastic strain accommodation inversions for the best fitting background stress state are consistent with fits of focal mechanisms and support an effective friction coefficient near 0 6 fits to the aftershock decay provide estimates of the dieterich friction parameter ad ranging from 0 02 if lithostatic pore fluids are present to 0 0003 if they are not

indicators of critical point behavior prior to rock failure inferred from pre failure damage abstract to investigate possible indicators of critical point behavior prior to rock failure the statistical properties of pre failure damage were analyzed based on acoustic emission events ae recorded during the catastrophic fracture of typical rock samples under differential compression aes were monitored using a high speed 32 channel waveform recording system time dependent statistics including the energy release rate b value of the magnitude frequency distribution fractal dimension and spatial correlation length scl of the ae hypocenters were calculated for each data set each parameter is a function of the time to failure and thus can be treated as an indicator of the critical point it is clear that the pre failure damage evolution prior to catastrophic failures in several common rock types is generally characterized by 1 accelerated energy release 2 a decrease in fractal dimension and scl with a subsequent precursory increase and 3 a decrease in b value from 1 5 to 0 5 for hard rocks and from 1 1 to 0 8 for soft rocks such s c cataclasite however each parameter also reveals more complicated temporal evolution due to either the heterogeneity of the rock mass or the micro mechanics of shear fracturing this confirms the potential importance of integrated analysis of two or more parameters for successfully predicting the critical point the decreasing b value and increasing energy release may prove meaningful for intermediate term prediction while the precursory increase in fractal dimension and scl may facilitate short term prediction

fractal dimension of fault systems in japan fractal structure in rock fracture geometry at various scales based on fault maps whether or not the fracture geometry of rocks is self similar was examined by using a box counting algorithm the statistical self similarity fractal structure of the fault fracture systems holds well at the scale of about 2 to 20 km the fractal dimension in japan varied from 1 05 to 1 60 the fractal dimension is about 1 5 1 6 at the central part of the japan arc and decreases with distance from the center at a smaller scale the fractal structure also holds well in the rock fracture geometry the fractal dimension of the north izu peninsula fault system branching faults is 1 49 at the scale of 0 625 to 10 km the fractal dimension of rock fracture geometry at the scale order of 10 1 to 10 2 meters is about 1 49 1 61 the upper limit of the fractal dimension of rock fracture geometry is about 1 6 judging from the estimation of fractal dimension on actual fracture geometry of rocks this value may impose a restraint on modeling of faulting and the fracture process of rocks

earthquakes as self organized critical phenomena a cellular automation model with threshold elements previously proposed by bak et al 1988 which generates 1 f noise and self organizes into a critical state is studied as a model for earthquake occurrence the model explains some of fractal features of earthquakes such as the power law distribution of the size of the earthquake the model is modified so that every earthquake may trigger aftershocks the modified trigger model explains other fractal features of earthquakes such as the power law decay of aftershock frequency and the power law decay of aftershock frequency and the power law correlation of the hypocenter distribution

volcanic ash plume identification using polarization lidar augustine eruption alaska 1 during mid january to early february 2006 a series of explosive eruptions occurred at the augustine volcanic island off the southern coast of alaska by early february a plume of volcanic ash was transported northward into the interior of alaska satellite imagery and puff volcanic ash transport model predictions confirm that the aerosol plume passed over a polarization lidar 0 694 m wavelength site at the arctic facility for atmospheric remote sensing at the university of alaska fairbanks for the first time lidar linear depolarization ratios of 0 10 0 15 were measured in a fresh tropospheric volcanic plume demonstrating that the nonspherical glass and mineral particles typical of volcanic eruptions generate strong laser depolarization thus polarization lidars can identify the volcanic ash plumes that pose a threat to jet air traffic from the ground aircraft or potentially from earth orbit

collapsing minerals crackling noise of sandstone and coal and the predictability of mining accidents mining accidents are sometimes preceded by high levels of crackling noise which follow universal rules for the collapse of minerals the archetypal test cases are sandstone and coal their collapse mechanism is almost identical to earthquakes the crackling noise in large porous samples follows a power law gutenberg richter distribution p e e with energy exponents e for near critical stresses of e 1 55 for dry and wet sandstone and e 1 32 for coal the exponents of early stages are slightly increased 1 7 sandstone and 1 5 coal and appear to represent the collapse of isolated uncorrelated cavities a significant increase of the acoustic emission ae activity was observed close to the final failure event which acts as warning signal for the impending major collapse waiting times between events also follow power law distributions with exponents 2 between 2 and 2 4 aftershocks occur with probabilities described by omori coefficients p between 0 84 sandstone and 1 coal the bath s law predicts that the ratio between the magnitude of the main event and the largest aftershock is 1 2 our experimental findings confirm this conjecture our results imply that acoustic warning methods are often possible within the context of mining safety measures although it is not only the increase of crackling noise that can be used as early warning signal but also the change of the energy distribution of the crackling events

theoretical study on volcanic plume hbox so _ 2 and ash retrievals using ground tir camera sensitivity analysis and retrieval procedure developments in this paper a sensitivity analysis and procedure development for volcanic plume sulfur dioxide and ash retrievals using ground thermal infrared camera have been carried out the semiconductor device camera considered as a reference has a spectral range of 8 14 m with noise equivalent temperature difference that is better than 100 mk at 300 k the camera will be used to monitor and assess the hazards of mt etna volcano to mitigate the risk and impact of volcanic eruptions on the civil society and transports a minimum number of filters have been selected for sulfur dioxide so2 and volcanic ash retrievals the sensitivity study has been carried out to determine the so2 and volcanic ash minimum concentration detectable by the system varying the camera geometry and the atmospheric profiles results show a meaningful sensitivity increase considering high instrument altitudes and low camera elevation angles for all geometry configurations and monthly profiles the sensitivity limit varies between 0 5 and 2 g m 2 for so2 columnar abundance and between 0 02 and 1 for ash optical depth two procedures to detect so2 and ash based on the least square fit method and on the brightness temperature difference btd algorithm respectively have also been proposed results show that high concentration of atmospheric water vapor columnar content significantly reduces the ash plume effect on the btd a water vapor correction procedure introduced improves the ash retrievals and the cloud discrimination in every season considering all the camera geometries

detailed analysis of acoustic emission activity during catastrophic fracture of faults in rock abstract the detailed time space distribution of acoustic emission ae events during the catastrophic fracture of rock samples containing a pre existing joint or potential fracture plane is obtained under triaxial compression using a high speed 32 channel waveform recording system and the results are discussed with respect to the prediction and characterization of catastrophic fault failure ae activity is modeled quantitatively in terms of the seismic b value of the magnitude frequency relation the self excitation strength of the ae time series and the fractal dimension of ae hypocenters consistent with previous studies on rock samples containing a fracture plane with several asperities the present analyses reveal three long term phases of ae activity associated with damage creation on heterogeneous faults each clearly identifiable based on the above parameters a long term decreasing trend and short term fluctuation of the b value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass a homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity

monitoring etna volcanic plumes using a scanning lidar in this paper we use data obtained from lidar measurements during an ash emission event on 15 november 2010 at mt etna in italy in order to evaluate the spatial distribution of volcanic ash in the atmosphere a scanning lidar system located at 7 km distance from the summit craters was directed toward the volcanic vents and moved in azimuth and elevation to analyse different volcanic plume sections during the measurements ash emission from the north east crater and high degassing from the bocca nuova crater were clearly visible from our analysis we were able to 1 evaluate the region affected by the volcanic plume presence 2 distinguish volcanic plumes containing spherical aerosols from those having non spherical ones and 3 estimate the frequency of volcanic ash emissions moreover the spatial distribution of ash mass concentration was evaluated with an uncertainty of about 50 we found that even during ash emission episodes characterised by low intensity like the 15 november 2010 event the region in proximity of the summit craters should be avoided by air traffic operations the ash concentration being greater than 4 10 3 g m3 the use of a scanning permanent lidar station may usefully monitor the volcanic activity and help to drastically reduce the risks to aviation operations during the frequent etna eruptions

review of the physical basis of laboratory derived relations for brittle failure and their implications for earthquake occurrence and earthquake nucleation a laboratory derived crack growth based constitutive relation for brittle faulting is developed the relation consists of two rheologic components a nonlinear arrhenius dependence of strain rate on temperature and stress corresponding to subcritical crack growth and a linear slip weakening behavior associated with dilatancy crack coalescence and supercritical crack growth the implications of this general behavior for the onset of rapid slip earthquake nucleation are considered laboratory observations of static fatigue and time dependent failure from rock fracture and rock friction experiments are consistent with this simple constitutive description as are the predictions of rate and state dependent equations for the onset of rapid frictional slip between bare rock surfaces i argue that crack growth is the physical process that controls time dependent rock fracture and the time dependent onset of unstable frictional sliding some similar and related arguments made in the past 1 2 century in the fields of rock mechanics and earthquake seismology are reviewed for stressing rates appropriate for the san andreas fault system the simple constitutive relation with lab derived constants predicts a minimum time for nucleation of 1 yr general predictions are a minimum nucleation patch radius of 0 06 to 0 2 m and a minimum earthquake moment of 8 5 x 107nm

improved prediction and tracking of volcanic ash clouds abstract during the past 30 years more than 100 airplanes have inadvertently flown through clouds of volcanic ash from erupting volcanoes such encounters have caused millions of dollars in damage to the aircraft and have endangered the lives of tens of thousands of passengers in a few severe cases total engine failure resulted when ash was ingested into turbines and coating turbine blades these incidents have prompted the establishment of cooperative efforts by the international civil aviation organization and the volcanological community to provide rapid notification of eruptive activity and to monitor and forecast the trajectories of ash clouds so that they can be avoided by air traffic ash cloud properties such as plume height ash concentration and three dimensional ash distribution have been monitored through non conventional remote sensing techniques that are under active development forecasting the trajectories of ash clouds has required the development of volcanic ash transport and dispersion models that can calculate the path of an ash cloud over the scale of a continent or a hemisphere volcanological inputs to these models such as plume height mass eruption rate eruption duration ash distribution with altitude and grain size distribution must be assigned in real time during an event often with limited observations databases and protocols are currently being developed that allow for rapid assignment of such source parameters in this paper we summarize how an interdisciplinary working group on eruption source parameters has been instigating research to improve upon the current understanding of volcanic ash cloud characterization and predictions improved predictions of ash cloud movement and air fall will aid in making better hazard assessments for aviation and for public health and air quality

the activity of vesuvius in the next millennium abstract the time distribution of the historical eruptions of vesuvius allows the forecasting of the activity of the volcano for the next millennium according to three independent models the next event with volcanic explosivity index vei 4 is likely to occur during the next few decades followed by a decreasing number of smaller eruptions in the successive few centuries and by a very long period of quiescence up to the beginning of the following fourth millennium when the next plinian event vei 5 might occur

neural network dynamic modelling of rock microfracturing sequences under triaxial compressive stress conditions abstract rock fracturing processes are very complicated nonlinear dynamic systems distributions of acoustic emission ae events in the time dimension during microfracturing processes of rock under triaxial compressive stress conditions have fractal structures that proceed as c t td where the fractal dimension d is 0 43 d

spatio temporal seismicity patterns using mutual information application to southern iberian peninsula spain earthquakes abstract a quantitative method to characterize the spatio temporal evolution of the seismic activity of a region for a given time interval is proposed in this paper the epicentral region is divided in equal area parallelograms that we call cells a probability p i is assign to every cell depending on its seismic activity level the evolution of the mutual information based on these probabilities allows us to fit the optimal value for p i s the analysis results show that is possible to monitor the change of seismic activity quantitatively we show that a propagation model based on cross template model ct model give us a criteria whether or not an area whose size is determined by the model mathematically is going to be considered seismically activated in a period of time whose value is also the result of the application of the method our method is applied to the data of southern iberian peninsula seismicity including more than 10 000 earthquakes data available from the andalusian seismic network is used from 1985 to 1995

predicting regions susceptible to high concentrations of airborne volcanic ash in the north pacific region abstract airborne ash probability distribution aapd maps have been generated to show the distribution of airborne volcanic ash in the north pacific nopac region by simulating volcanic eruption clouds from 22 of the 100 most historically active volcanoes in the region the puff ash dispersion model was run daily using archived wind field data between 1994 1995 and 1997 2001 for low and high aircraft flight levels subsequent statistics are generated representing the distribution of simulated airborne ash at 6 and 24 h intervals defining the regions most likely to contain airborne ash and the direction and distance a volcanic ash cloud may propagate from a given volcano the aapd maps show the extent of ash from a given volcano can encompass all of alaska most of the north pacific ocean portions of northwestern north america regions as far south as 35 n regions over the western arctic ocean and portions of eastern russia in general low altitude atmospheric regions 3 8 km asl are more susceptible to airborne volcanic ash when compared to regions above 8 km asl due to the eruption characteristics of volcanoes in the north pacific and the region s atmospheric profile the results indicate that the paths of many nopac air traffic routes coincide with airborne ash distribution probability maxima the upper atmospheric region most likely to contain airborne ash is located off the eastern coast of the kamchatkan peninsula and is generally centered over the heavy air traffic flight corridor of the nopac although this paper focuses on the nopac region the technique can be directly applied to other regions characterized by active volcanism

the instantaneous rate dependence in low temperature laboratory rock friction and rock deformation experiments 1 earthquake occurrence probabilities that account for stress transfer and time dependent failure depend on the product of the effective normal stress and a lab derived dimensionless coefficient a this coefficient describes the instantaneous dependence of fault strength on deformation rate and determines the duration of precursory slip although an instantaneous rate dependence is observed for fracture friction crack growth and low temperature plasticity in laboratory experiments the physical origin of this effect during earthquake faulting is obscure we examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by tullis and weeks 1987 we compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher temperature dislocation glide experiments the same normalization scheme is used to compare rate dependence in friction to rock fracture and to low temperature crack growth tests for particular weak phyllosilicate minerals the instantaneous friction rate dependence is consistent with dislocation glide in intact rock failure tests for each rock type considered the instantaneous rate dependence is the same size as for friction suggesting a common physical origin during subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible the instantaneous rate dependence measured during failure or creep tests at high stress has long been thought to be due to crack growth however direct comparison between crack growth and friction tests shows poor agreement the crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered

spatio temporal evolution of rockfall activity from 2007 to 2011 at the piton de la fournaise volcano inferred from seismic data abstract seismic data have been used to catalog the location and volume of most of the rockfalls that occurred at the piton de la fournaise volcano from may 2007 just after the major collapse of the dolomieu summit crater floor to may 2011 this catalog made it possible to compare the evolution of the number and volume of rockfalls at a high temporal resolution and to investigate their links with eruptions seismicity deformations and rainfalls affecting the piton de la fournaise volcano results show that the purge of unstable areas created by the dolomieu crater floor collapse occurred in two phases a first phase lasting three months during which the intense rockfall activity immediately following the collapse decreased abruptly and a second phase lasting more than two years during which the daily volume of the rockfalls slowly decreased before reaching a steady state a detailed study of 4 time periods including 3 eruptive cycles indicates that strong seismicity can increase the number of rockfalls furthermore when a dike reaches the surface at the summit of the central cone giving birth to an eruption the associated local forcing can in some cases increase the volume of rockfalls possibly by creating or expanding weak zones in most cases this is not observed for dike intrusions that do not reach the surface the newly created weak zones are most often far from the eruptive fissures of the ongoing eruption but close to the location of the next eruption this suggests that these distant zones are also weakened at depth thus creating preferred paths for future dikes propagating toward the surface the impact of rainfall on rockfall activity was also studied given that la reunion island is subject to very intense rainfall events our results show that rainfall can in some cases trigger rockfalls rapidly with response times of less than a day but not systematically and no triggering rainfall threshold was found

stress orientation profile to 3 5 km depth near the san andreas fault at cajon pass california a detailed profile of the orientation of the apparent maximum horizontal compressive stress was constructed over the depth interval 1 75 3 46 km in the cajon pass drill hole located 4 2 km from the san andreas fault in southern california the profile is based on the analysis of stress induced well bore breakouts and consists of 32 616 orientation determinations at a basic sampling interval of 4 cm the azimuth of the apparent maximum horizontal compressive stress around the borehole is 057 s d 19 depth dependent variations in breakout azimuths from a few degrees to as much as 100 occur over depth intervals of several centimeters to hundreds of meters in the borehole with wavelengths showing a self similar distribution over a range of depth intervals the variations in breakout orientation at depth seem to reflect stress fluctuations associated with active faults penetrated by the drill hole assuming linear elastic behavior perturbations in stress magnitude and orientation were computed for predrilling slip on these faults fault stress drops limited to the ambient shear stress i e up to total stress drop along with occasional local extreme stress drops and geometrical complications can explain the variations in breakout orientations in the drill hole the penetrative stress inhomogeneity may suggest that the average orientation of borehole breakouts in cajon pass which indicates left lateral shear on planes parallel to the san andreas fault may not be representative of the state of stress near the fault at depth in this region rather the stress orientation profile indicates the superposition of numerous local stress perturbations on an average stress field which is characterized by an absence of appreciable right lateral shear on planes parallel to the san andreas combining these observations with the highly variable stress state in shallow boreholes in the western mojave desert it is suggested that the heterogeneous stress field in this region representing a spectrum of seismic events may extend over substantial distances across and along the san andreas fault zone if the average measured breakout orientation in cajon pass is representative of the state of stress near the san andreas in this region then substantial left lateral shear stress is resolved on planes parallel to the fault in contradiction to the sense of its long term motion we use an elastic dislocation model to compute the net stress change near the cajon pass drill site since just prior to the large 1812 earthquake taking into account coseismic slip in major earthquakes and aseismic accumulation of slip on the san andreas and san jacinto faults the model suggests that the net change in fault parallel shear stress during the current earthquake cycle in the cajon pass area is nearly negligible the difference between the measured and computed results requires that additional left lateral shear stress be superimposed on a generally fault normal maximum horizontal compressive stress the results suggest that during the great fort tejon earthquake of 1857 left lateral shear stress parallel to the san andreas fault in the region of cajon pass may have played a role in terminating the southeastward extent of the rupture propagation

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

single link cluster analysis of earthquake aftershocks decay laws and regional variations using single link cluster analysis the authors investigate how various properties of aftershock sequences depend on their tectonic regime and focal depth for international seismological centre earthquakes of m sub b ge 4 8 they find that earthquakes deeper than 70 km have the fewest and smallest aftershock sequences even after accounting for differences in detectability and maximum magnitude they find that ridge transform earthquakes have smaller aftershock sequences that shallow subduction zone earthquakes among different subduction zones they find that zones with high moment release rates possess larger aftershock sequences comparing ridge transform zones they find those with slower spreading rates possess larger aftershock sequences by transposing origin times of several different aftershock sequences as if all had main shocks occurring at time zero they are able to study the properties of aftershock sequences which individually have too few aftershocks to study by other means secondary events determined by single link cluster analysis follow a modified omori s power law decay for time separations of 0 1 day to 20 days from the parent event with p values ranging from 0 539 plus minus 0 022 intermediate and deep focus earthquakes to 0 928 plus minus 0 024 ridge transform earthquakes they find that earthquake foreshocks and multiplets also follow a modified omori s law atmore greater times from the main shock the decay is steeper than a power law decay more like an exponential decay aftershocks in the adak catalog m sub b ge 2 0 show a marked decrease in activity between 40 and 50 km depth they speculate that the observed differences in number of aftershocks and p values may be caused by variations in fault heterogeneity or in fluid pressures less

spatio temporal analysis of stress diffusion in a mining induced seismicity system the spatio temporal correlation of micro earthquakes occuring in a mining induced seismic system creighton mine ontario canada is investigated it is shown that when considering only the after events correlated to a main event i e not accounting for the uncorrelated regime of background activity the spatial distribution of these after events occuring at t after the main event change with t this change takes the form of an expanding pattern characterized by a typical scale l c t varying as l c t similar to t h h being estimated to 0 18 this diffusion exponent is found to increase when considering only a subset of the most energetic events as mainshocks we interpret this result as the indication of a stress sub diffusion mechanism involving propagation on the heterogeneous fractal fault network

estimation of the refractive index of volcanic ash from satellite infrared sounder data abstract we investigated the spectral refractive indices ris of volcanic ash materials in the wavenumber range of 700 1100 cm 1 using satellite infrared sounder measurements and radiative transfer calculations the ash ris of 10 ash clouds from eight volcanoes were evaluated bezymianny on 2 september 2012 chaiten on 3 may 2008 kelut on 14 february 2014 kirishimayama on 27 january 2011 kliuchevskoi on 30 june 2007 and 18 october 2013 puyehue cordon caulle on 5 june 2011 sangeang api on 31 may 2014 and sheveluch on 28 october 2010 and 18 september 2012 we elaborated on a dataset of volcanic ash measurements made by the atmospheric infrared sounder airs onboard the aqua satellite the measured brightness temperatures in the ash cloud data revealed silicate absorption features at around 10 m by applying atmospheric profiles from results of a global data assimilation system and using ash cloud properties ash optical depth effective radius and ash cloud height as parameters for radiative transfer calculations least squares analyses for the observed and calculated brightness temperatures were conducted using airs channels in the wavenumber range of 700 1100 cm 1 except for the o3 absorption channels in the range of 980 1070 cm 1 using the ris for typical volcanic rocks in the ascending order of sio2 content basalt andesite and rhyolite a mixture of basalt and rhyolite and a mixture of andesite and rhyolite for the ash material were considered the volume fraction of the mixture was used as a retrieval parameter and as the ash cloud parameter using the estimated ash cloud parameters as fixed values and under the assumption that the ri from the estimated volume fraction had some accuracy in the wavenumber ranges of 850 980 cm 1 and 1070 1100 cm 1 the ri imaginary part of each eruptive ash cloud captured by airs was then determined from iterative calculations at wavenumbers between 750 cm 1 and 980 cm 1 in the wavenumber range of 850 980 cm 1 the observed brightness temperatures could be approximately simulated using the reported ris from pollack toon and khare 1973 for andesite basalt and rhyolite and their combinations furthermore some estimated ris were consistent with the reported rock types of the volcanoes which had been previously classified by compositional analyses in the literature our analysis also identified weak absorptions around 750 850 cm 1 which could not be reproduced by the reported ris these weak absorptions were likely due to si o and or al o vibrations which have been proposed in reports from previous laboratory experiments for some silicate glass samples our results suggest that the detailed ri of volcanic ash can be determined from an analysis of satellite infrared sounder data the ri of the ash material estimated from satellite infrared sounder data can be used to improve the ash retrieval algorithms of other satellite measurements furthermore an ri retrieved by sounder measurements may provide diagnostic information regarding volcanic activity from comparisons with the ash ris from past eruptions

a self exciting process of acoustic emission occurrence in steady creep of granite under uniaxial stress clustering of acoustic emissions ae in space and time was found in a laboratory experiment to investigate the stochastic process of ae occurrence event times of ae were measured during steady creep phases under different stress levels oshima granite was continuously subjected to constant uniaxial stress of different intensity the occurrence time of ae event was analyzed as a combination of a poisson process and a self exciting part in the latter events are excited by preceding events the self exciting character was more enhanced under higher crack density in accordance with a stronger concentration in hypocenter distribution at higher stress

omori s power law aftershock sequences of microfracturing in rock fracture experiment a time series of acoustic emissions ae in basalt was measured under constant uniaxial compression some bursts of ae events considered to be the main shock and aftershock sequences were observed two models describing the aftershock sequences the exponential decay model n t k exp pt and the omori s power law model n t k c t p where n t denotes the occurrence rate of aftershocks at time t were examined with the progress of the fracturing process the bursts changed from the exponential decay type to omori s power law type and the p value of omori s power law aftershock sequences decreased these results indicate that microfracturing gains a longer tail with the evolution of the fracture process the reproduction of omori s power law aftershock sequences of ae events suggests that the self similarity of rock fracturing holds good over a range from microfracturing to large earthquakes

a renormalization group approach to the stick slip behavior of faults we treat a fault as an array of asperities with a prescribed statistical distribution of strengths when an asperity fails the stress on the failed asperity is transferred to one or more adjacent asperities for a linear array the stress is transferred to a single adjacent asperity and for a two dimensional array to three adjacent asperities using a renormalization group rg method we investigate the properties of a scale invariant hierarchical model for the stochastic growth of fault breaks through induced failure by stress transfer an extrapolation to arbitrarily large scales shows the existence of a critical applied stress at which the solutions bifurcate at stresses less than the critical stress virtually no asperities fail on a large scale and the fault is locked above the critical stress asperity failure cascades away from the nucleus of failure we interpret this catastrophic failure as an earthquake and it corresponds to the transition from stick to slip behavior on the fault thus the stick slip behavior of most faults can be attributed to the distribution of asperities on the fault we propose our stochastic mechanism as an alternative to the traditional hypotheses for the stick slip behavior of faults a major advantage of our approach is the inclusion of scale invariance thus the observed frequency magnitude relation for seismicity is a natural consequence of our basic hypothesis

seismicity response to stress perturbations analysed for a world wide catalogue summary a statistical analysis of the relative distance and time delay separating pairs of earthquakes is performed to determine how a seismicity system evolves dynamically following a stress perturbation earthquake we analyse the space time correlations of a worldwide seismicity data set cnss catalogue 1963 1998 m 5 depth 70 km and show that seismic activity diffuses away from an earthquake as the time delay increases following its occurrence two regimes are observed a slow diffusion at short timescales up to 10 days during which the mean distance r t between the initial earthquake and the subsequent earthquakes grows as r t t h with h 0 19 and a second regime at longer timescales with h 0 4 the growth exponent h in the first regime increases systematically with the size of the initial earthquake but no such dependence is observed for the second regime associating the latter with the viscous diffusion of stress in the upper mantle we obtain an estimate of about 10 17 pa s for the asthenospheric lateral viscosity this diffusion indicates that the relaxation response of the crust to a stress step depends non linearly in respect of both its intensity and general form on the perturbation a positive correlation between the regional heat flow and diffusion exponent is found suggesting a strong thermal control on the diffusion the overall autodecorrelation and this diffusion process are the two major mechanisms by which seismicity systems relax stress concentrations by redistributing them in space and in time both processes exhibit typical power law behaviours supporting the notion of space time scale invariance of stress exchanges between seismically active faults

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

rates of aftershock decay and the fractal structure of active fault systems abstract aftershock activity on frequency decay against time is characterized by a power law the modified omori formula of an exponent p which differs with each aftershock sequence a theoretical study suggested that p which is a rate constant of aftershock decay is related to the fractal dimension of a pre existing fault system this has however never been checked aftershock activity on size distribution is also characterized by an exponential distribution against magnitude the gutenberg richter relation with a slope b although p is expected to be related to b which is related to the partitioning rate of earthquake energy the relationship has never been established here the relation between the p values and the fractal dimensions of the pre existing fault systems and that between the p values and the b values are explored using natural seismicity data and data of the observable fault systems the p and b values were estimated for fifteen aftershock sequences which occurred in japan in this paper aftershocks were identified on the basis of a phenomenological definition in the seismicity data the fractal capacity dimensions d0 are estimated for the pre existing active fault systems observed on the surface in the aftershock regions in the present paper the standard box counting method was adopted to get the d0 negative correlations between 1 p and d0 and 2 p and b were observed with some scattering observation 1 shows that the rate of aftershock decay p decreases systematically with increasing occupancy rate of the pre existing active fault system d0 and suggests that aftershock decay dynamics is constrained by the pre existing fracture field observation 2 shows that p certainly has a relation with b moreover we offer possible interpretation on these negative correlations and some scatters in both observations the scatters are interpreted as the scatter of the difference of two fractal dimensions between 3 d fracture construction in the crust and 2 d cross sectional surface observed active fault system supported by further tests this paper strongly suggests that the scaling for a natural fracture system is self affine with different fractal scalings in different directions rather than self similar which would be a manifestation of regional anisotropy of the fracture system and that the seismic parameters p and b depend on the 3 d construction of the fracture system in the crust

chaos hides and generates order an application to forecasting the next eruption of vesuvius abstract the poissonian and non fractal characters generally exhibited by the most intense natural events do not allow the application of the current exponential and power law long term hazard predictive models and have suggested searching for a new model this has been set up also taking into account that the random sequence representing disorder of these events is linked to the duration of the stationary small ones representing order the model proposed in terms of the orbit of a simple non linear hazard function simulates the large eruptions of vesuvius quite well and permits estimation of the next subplinian eruption to occur there around a d 2030 a short range forecasting model based on the tidal triggering is also provided and discussed when large tidally triggered m2 term in the earthquakes at vesuvius become significant at the 0 01 level the proposed long term hazard model will yield a more accurate estimate of the above prediction

towards a new view of earthquake phenomena recent advances in the theory of fracture and fragmentation are reviewed empirical laws in seismology are interpreted from a fractal perspective and earthquakes are viewed as a self organized critical phenomenon soc earthquakes occur as an energy dissipation process in the earth s crust to which the tectonic energy is continuously input the crust self organizes into the critical state and the temporal and spatial fractal structure emerges naturally power law relations known in seismology are the expression of the critical state of the crust an soc model for earthquakes which explains the gutenberg richter relation the omori s formula of aftershocks and the fractal distribution of hypocenters is presented a new view of earthquake phenomena shares a common standpoint with other disciplines to study natural complex phenomena with a unified theory

physical modeling of the formation and evolution of seismically active fault zones acoustic emission ae in rocks is studied as a model of natural seismicity a special technique for rock loading has been used to help study the processes that control the development of ae during brittle deformation this technique allows us to extend to hours fault growth which would normally occur very rapidly in this way the period of most intense interaction of acoustic events can be studied in detail characteristics of the acoustic regime ar include the gutenberg richter b value spatial distribution of hypocenters with characteristic fractal correlation dimension d hurst exponent h and crack concentration parameter pc the fractal structure of ar changes with the onset of the drop in differential stress during sample deformation the change results from the active interaction of microcracks this transition of the spatial distribution of ae hypocenters is accompanied by a corresponding change in the temporal correlation of events and in the distribution of event amplitudes as signified by a decrease of b value the characteristic structure that develops in the low energy background ae is similar to the sequence of the strongest microfracture events when the ar fractal structure develops the variations of d and b are synchronous and d 3b this relation which occurs once the fractal structure is formed only holds for average values of d and b time variations of d and b are anticorrelated the degree of temporal correlation of ar has time variations that are similar to d and b variations the observed variations in laboratory ae experiments are compared with natural seismicity parameters the close correspondence between laboratory scale observations and naturally occurring seismicity suggests a possible new approach for understanding the evolution of complex seismicity patterns in nature

premonitory transformation of steel fracturing and seismicity abstract transformation of microfracturing preceding the break up of steel and rock samples is similar to transformation of earthquakes flow prior to strong earthquakes in southern california the break up in a sample is preceded by transition from formation of new microcracks to coalescence or expansion of existing cracks this is reflected in the relation between the length and the number of the cracks similar transformation of seismicity precedes southern california earthquakes with magnitude m 6 6 1935 1994 specifically magnitude frequency relation bends downward for magnitudes from 3 to 4 5 and upward for magnitudes from about 4 5 to 6 in the usual notations the b value becomes larger in the first interval and smaller in the second one this transformation is accompanied by the increased share of aftershocks in the earthquakes flow in such a way the approach of a strong earthquake is reflected in both major traits of seismicity magnitude frequency relation and earthquake clustering imprecision of the earthquake catalog and reasonable variations in its analysis do not change our conclusions this phenomenon explains so far qualitatively a wide set of premonitory seismicity patterns we give it a formal definition allowing to test whether it takes place in other seismic regions