seismicity and eruptive activity at fuego volcano guatemala february 1975 january 1977 abstract we examine seismic and eruptive activity at fuego volcano 14 29 n 90 53 w a 3800 m high stratovolcano located in the active volcanic arc of guatemala eruptions at fuego are typically short lived vulcanian eruptions producing ash falls and ash flows of high alumina basalt from february 1975 to december 1976 five weak ash eruptions occurred accompanied by small earthquake swarms between 0 and 140 average 10 a type or high frequency seismic events per day with m 0 5 were recorded during this period estimated thermal energies for each eruption are greater by a factor of 10 6 than cumulative seismic energies a larger ratio than that reported for other volcanoes over 4000 a type events were recorded january 3 7 1977 cumulative seismic energy 10 9 joules yet no eruption occurred five 2 hour long pulses of intense seismicity separated by 6 hour intervals of quiescence accounted for the majority of events maximum likelihood estimates of b values range from 0 7 0 2 to 2 1 0 4 with systematically lower values corresponding to the five intense pulses the low values suggest higher stress conditions during the 1977 swarm a tiltmeter located 6 km southeast of fuego recorded a 14 3 microradian tilt event down to sw this value is too large to represent a simple change in the elastic strain field due to the earthquake swarm we speculate that the earthquake swarm and tilt are indicative of subsurface magma movement

seismic slip deficit in the southwestern forearc of the hellenic subduction zone abstract the seismic coupling and the spatiotemporal distribution of seismicity on the presumed rupture surface of the 365 a d m w 8 3 0 2 crete event at the shallow plate contact of the hellenic subduction zone hsz southwest of crete is investigated the maximum cumulative average seismic slip u seis on the rupture surface is estimated for different time periods using historic and instrumental seismicity catalogs and utilizing a formula that incorporates empirical relations linking rupture area and average slip of an event to its moment magnitude m w events above the completeness magnitude of the catalog are incorporated by summation while events below are taken account of by integrating over the extrapolated frequency magnitude distribution using a truncated gutenberg richter relation estimates of u seis for the time intervals 0 1999 1500 1999 and 1964 2006 using historic and instrumental catalogs suggest a considerable seismic slip deficit when compared with the total slip expected from the temporal extrapolation of geodetic measurements this suggests a recent weakly coupled plate contact and a total slip predominantly accommodated aseismically despite the 365 a d event high seismic activity up to magnitudes of about m w 6 is found accompanying the aseismic slip at the plate contact investigations of the seismicity distribution hint at a spatial variability of the seismic energy release in the western forearc of the hsz activity in the proximity of the 365 a d epicenter is observed to be an order of magnitude larger than toward the northwest between crete and peloponnese this spatiotemporal variability of the seismic energy release and seismic coupling suggests that subregions of the plate contact undergo alternating periods of locking followed by intermediate magnitude events and aseismic sliding thus the behavior of significant portions of the plate contact southwest of crete may be described as conditionally stable

physical links between crustal deformation seismic moment and seismic hazard for regions of varying seismicity summary seismic moment release rates m0 inferred from a weibull frequency magnitude distribution and its extreme value equivalent are compared with observation the seismotectonically diverse regions studied all exhibit the curvature of a log linear frequency magnitude plot associated with applying a maximum magnitude to earthquake recurrence statistics the inferred seismic moment release rates are consistent with available crustal deformation data within uncertainties resulting from the line fit and in magnitude determination the uncertainties for the regions studied southern california the new madrid seismic zone the central and eastern mediterranean and mainland uk vary from at worst an order of magnitude down to a factor of 2 or 3 this agreement can be used to justify the extrapolation of frequency magnitude statistics beyond the historical and instrumental era in seismic hazard studies as a test of the stationarity of short term statistics against long term effects a striking example of a bimodal seismicity distribution is observed in the new madrid zone this can be interpreted as being due to the superposition of two distinct seismogenic source types observed in the area a quantitative analysis of the separate orders of seismicity observed in the frequency magnitude statistics comparing the different maximum magnitudes and inferred seismic moment release rates with those observed supports this hypothesis superposition of many such seismogenic sources can explain the linearity observed in global frequency versus seismic moment magnitude statistics

scaling invariance of crack surfaces the morphology of fractured rock surfaces is studied in terms of their scaling invariance fresh brittle fractures of granite and gneiss were sampled with a mechanical laboratory profilometer and 1 1 dimensional parallel profiles were added to build actual maps of the surfaces a first step in the scaling invariance description is a self affine analysis using three independent methods the root mean square and the maximum minimum difference of the height are shown to follow a power law with the sample length the return probability and the fourier spectrum are also computed all these approaches converge to a unique self affine exponent 0 80 analysis over a broad statistical set provides a reproducibility error of 0 05 no significant differences between the isotropic granite and the markedly anisotropic gneiss appear for the scaling exponents an analysis of the profilometer shows that the two main drawbacks of the setup are not significant in these analyses the systematic errors of the scaling analysis are estimated for the different methods isotropy of the scaling invariance within the mean fracture plane is shown either with the result obtained from different fracture orientations or with the two dimensional fourier spectrum of the surface topography itself the analysis is brought further into the multifractal framework the structure functions are shown to have power law behavior and their scaling exponent varies nonlinearly with the moment order finally the corresponding conserved process belongs to a universal multifractal class with 1 5 for the levy index and c1 0 3 for the fractal codimension of the mean singularities the three indices and c1 completely characterize the scale invariance the multifractal behavior is significant for physical properties which depend on high order moments like contact according to this study and that of other groups the self affine exponent is constant over a large range of scales and for different fracture modes and various materials this opens the possibility that there exists a form of universality in the cracking process it appears that only the prefactor of the roughness is dependent on material and mode

large scale patterns associated with tropical cyclogenesis in the western pacific abstract five characteristic low level large scale dynamical patterns associated with tropical cyclogenesis in the western north pacific basin are examined along with their capacity to generate the type of mesoscale convective systems that precede genesis an 8 yr analysis set for the region is used to identify and create composites for the five characteristic patterns of monsoon shear line monsoon confluence region monsoon gyre easterly waves and rossby energy dispersion this brings out the common processes that contribute to tropical cyclogenesis within that pattern which are described in detail a 3 yr set of satellite data is then used to analyze the mesoscale convective system activity for all cases of genesis in that period and to stratify based on the above large scale patterns it is found that mesoscale convective systems develop in all cases of genesis except one seventy percent of cases developed mesoscale convective systems at more than one time during the genesis period and 44 of

idealized simulations of the intertropical convergence zone and its multilevel flows abstract a mesoscale numerical model with an idealized tropical channel environment is used to study the dynamics of intertropical convergence zones itczs and the recently identified shallow return flow srf and midlevel inflow mli four idealized sea surface temperature sst distributions are used a meridionally symmetric sst profile with a sharply peaked sst maximum at the equator a similar profile with the maximum sst shifted off the equator a cosine shaped sst profile with zero gradient at the equator and an idealized sst profile modeled after the observed sst of the eastern pacific the simulations show that both the srf and the mli are robust features of the itcz the prior result that the srf is a sea breeze like response to surface temperature gradients is further supported whereas the mli is caused by the upper level maxima in diabatic heating and vertical motion simulations with the sst maximum at the equator generate long lasting convectively coupled kelvin waves when the sst maxi

temporal change in coda q before the tangshan earthquake of 1976 and the haicheng earthquake of 1975 a new earthquake precursor called coda q is demonstrated for the tangshan earthquake of 1976 and for the haicheng earthquake of 1975 the precursor is based on the measurement of coda decay rate for small local earthquakes in the general area that is preparing for a major earthquake during the 3 year period preceding the tangshan earthquake the coda q was about 3 times lower than it was before or after this period a comparable change also occured at the time of the haicheng earthquake the observed change cannot be due to the change in the source parameters such as the focal depth or the source spectrum the coda q precursor appears to detect the same physical process detected by other precursors such as b value quiescence radon water quality vp vs and animal behavior but has advantages over them in its clearer physical mechanism easier sampling and better defined anomalous region

frequency characteristics of acoustic emission in rocks under uniaxial compression and its relation to the fracturing process to failure acoustic emission generated during the uniaxial compression of brittle rocks were counted after band pass filtering throughout the whole process from application of load to failure the count rate monitored through a low pass window was compared statistically with the monitored through a high passs window the emission rate monitored through a low pas window increases more rapidly than that monitored through a high pass window as rock approaches failure two possible explanations for this effect are 1 generation of larger cracks or coalescence of cracks into larger sizes and 2 the relative attenuation of higher frequency wave components this finding is consistent with past observations i e the relative number of large amplitude events increases i e a decrease in b value as rock approaches failure we suggest that larger cracks tend to generate events with larger amplitudes and containing lower frequency components the frequency characteristics of acoustic emissions are used to characterize the microfracturing processes leading to failure the beginning of a sequence of acoustic emission activity is discussed in relation to the stress strain curve and the onset of dilatancy the present observations may be utilized in understanding structural instability of a region where rockbursts or earthquakes can potentially occur if a sizable microseismicmore population is observed through sensors placed near the fault then a potential exists for predicting major earthquakes less

transient pulse test and morphological analysis of single rock fractures abstract transient pulse tests were performed on single rock fractures at different confining pressures a new data analysis method based on polynomial fitting was introduced to investigate the relationship between flow velocity and hydraulic gradient 3d laser scanning was used to quantify the morphological changes of the fracture surface after the transient pulse test or under the hydro mechanical coupling effect the results show that the flow velocity versus hydraulic gradient data gradient shows a nonlinear relationship at very low hydraulic possibly due to strong solid water interaction but becomes approximately linear after the hydraulic gradient is high enough the permeability of a single fracture is sensitive to the confining pressure as the confining pressure increases the permeability first remarkably decreases when the confining pressure is lower than a certain value and then decreases at a much lower speed when the confining pressure is higher than that value both mechanical and hydraulic apertures decrease at a decreasing rate with the increase in confining pressure the effect of fracture roughness on the permeability is related to the magnitude of the confining pressure rougher fractures have lower permeability at low confining pressures but the opposite can be true when the confining pressure is high enough roughness is no longer critical to permeability when the confining pressure is over a certain value

rock fracture as a precursor to lava dome eruptions at mount st helens from june 1980 to october 1986 following its plinian eruption on 18 may 1980 mount st helens washington state usa entered a period of intermittent lava dome extrusion until 1986 renewed extrusion was frequently preceded by accelerating rates of seismicity with more precursory seismicity observed prior to eruptions later in the sequence here the failure forecasting method ffm is used to investigate changes in the observed rate of volcano tectonic vt seismicity the analysis indicates that 1 all vt crises resulted in an eruption within 3 weeks usually less than 10 days 2 the majority of eruptions had vt precursors and 3 patterns of precursory seismicity showed fluctuations about the ideal model trend thus although these seismic events could be used to warn of an impending eruption specific forecasts were subject to an uncertainty of weeks or more it is proposed that 1 increased seismicity prior to later eruptions is a result of a larger and more solidified dome acting as a greater impediment to magma ascent 2 the consistency of seismic swarms resulting in an eruption indicates that stresses high enough to initiate fracturing in the country rock and lava dome carapace were only achieved once the approach to an eruption had already begun and 3 discrepancies between models of accelerating rock fracture and the observed seismicity may arise due to a significant amount of the rocks deforming through ductile mechanisms rather than seismogenic fracture

genesis of tropical storm eugene 2005 from merging vortices associated with itcz breakdowns part i observational and modeling analyses abstract although tropical cyclogenesis occurs over all tropical warm ocean basins the eastern pacific appears to have the highest frequency of tropical cyclogenesis events per unit area in this study tropical cyclogenesis from merging mesoscale convective vortices mcvs associated with breakdowns of the intertropical convergence zone itcz is examined this is achieved through a case study of the processes leading to the genesis of tropical storm eugene 2005 over the eastern pacific using the national centers for environmental prediction reanalysis satellite data and 4 day multinested cloud resolving simulations with the weather research and forecast wrf model at the finest grid size of 1 33 km observational analyses reveal the initiations of two mcvs on the eastern ends of the itcz breakdowns that occurred more than 2 days and 1000 km apart the wrf model reproduces their different movements intensity and size changes and vortex vortex interaction at nearly the right timing and location at

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

source mechanism of volcanic tremor low frequency 10 hz volcanic earthquakes originate at a wide range of depths and occur before during and after magmatic eruptions the characteristics of these earthquakes suggest that they are not typical tectonic events physically analogous processes occur in hydraulic fracturing of rock formations low frequency icequakes in temperate glaciers and autoresonance in hydroelectric power stations we propose that unsteady fluid flow in volcanic conduits is the common source mechanism of low frequency volcanic earthquakes tremor the fluid dynamic source mechanism explains low frequency earthquakes of arbitrary duration magnitude and depth of origin as unsteady flow is independent of physical properties of the fluid and conduit fluid transients occur in both low viscosity gases and high viscosity liquids a fluid transient analysis can be formulated as generally as is warranted by knowledge of the composition and physical properties of the fluid material properties geometry and roughness of the conduit and boundary conditions to demonstrate the analytical potential of the fluid dynamic theory we consider a single phase fluid a melt of mount hood andesite at 1250 c in which significant pressure and velocity variations occur only in the longitudinal direction further simplification of the conservation of mass and momentum equations presents an eigenvalue problem that is solved to determine the natural frequencies and associated damping of flow and pressure oscillations for a simple constant pressure reservoir conduit orifice fluid system a change in orifice size can cause the source signal duration due to a single disturbance to change from several seconds to in excess of an hour fluid kinematic viscosity 0 412 m2 s is both included and neglected in the analysis to illustrate its effect upon system damping tremor magnitude is related to the magnitude of the conduit wall motion occurring in response to oscillating fluid pressures the entire volcanic fluid system does not generally experience a transient flow condition at a given time closed end and constant pressure fluid system boundaries reflect pressure waves and isolate components of the fluid system total fluid movement may not be accurately monitored by tremor data alone since steady state and slowly changing flows are aseismic

quantitative relations of seismic source parameters and a classification of earthquakes abstract relations between earthquake parameters moment m0 fault area s fault length l and width w stress drop time characteristics and magnitudes and faulting type dip slip ds and strike slip ss are quantitatively analyzed using a dataset of 240 events m 5 the analysis is carried further toward an earthquake systematization by introducing earthquake classes the results are 1 1 l w 2 1 for ds l w 2 30 for ss and l w 3 7 for giant m0 1029 dyne cm earthquakes respectively 2 2 log m0 1 5 log s 22 2 s in km2 and tentatively log m0 2 45 log s 17 49 for ds and ss and giant earthquakes respectively 3 3 the large scatter of data in m0 s dependences is the result of the combined effect of the variation in and l w 4 4 the concept of constant is replaced by variable to explain the large variations in relations between m0 s l and w for both ds and ss earthquakes and partly between body and surface wave magnitudes low intermediate and high stress drop gd 30 30 60 and 60 bar respectively earthquakes are defined 5 5 a relation of reciprocity exists between seismic slip fault length and width and stress drop 6 6 a saturation of s for some very large earthquakes is suggested from the interpretation of actual data on m0 s l w etc 7 7 the total source duration tsd increases with m0 in relation with earthquake type and tentatively log m0 2 16 log tsd 24 50 holds for ds earthquakes 8 8 log m0 1 5 mm 16 1 holds for mm brune engen mantle wave magnitude 8 5 8 75 9 9 more magnitudes of shorter or longer period on both body and surface wave basis are useful in constraining significant earthquake features 10 10 low and high frequency earthquakes can be distinguished using the gutenberg richter relation ms mb as a reference relation or a relation between ms and mmaxb 11 11 aki s similarity conditions are extended by adding two more conditions as to express more specifically four basic features geometry deformation frequency and time of the earthquake source 12 12 a reference earthquake is defined by criteria consistent with the similarity conditions 13 13 on this basis and in view of nonsimilarity of earthquakes in their totality a scheme for earthquake classification is proposed

testing self organized criticality by induced seismicity we examine the hypothesis proposed in recent years by several authors that the crust is in a self organized critical soc state this hypothesis has been suggested on the basis of the observation of power law distributions such as the gutenberg richter law for earthquakes and the fault length distribution and of the fractal geometry of sets of earthquake epicenters and of fault patterns these self similar properties are shared by simplified models of the crust exhibiting a spontaneous organization toward a critical point characterized by similar scale invariant properties the term critical is here used in the sense of phase transitions such as the curie point in magnetism the usefulness of a hypothesis is measured by its predictive and explanatory power outside the range of observations that have helped defined it we thus explore how the soc concept can help in understanding the observed earthquake clustering on relatively narrow fault domains and the phenomenon of induced seismicity we review the major reported cases of induced seismicity in various parts of the world and find that both pore pressure changes p and mass transfers m leading to incremental deviatoric stresses of 1 mpa are sufficient to trigger seismic instabilities in the uppermost crust with magnitude ranging up to 7 0 in otherwise historically aseismic areas once triggered stress variations of at least 1 order of magnitude less but still larger than the 0 01 mpa tidal stress are enough to sustain seismic activity we argue that these observations are in accord with the soc hypothesis as they show that a significant fraction of the crust is not far from instability and can thus be made unstable by minute perturbations this property is shared by simplified models of soc not all perturbations however trigger seismic activity this is also compatible with the soc hypothesis which embodies naturally the existence of large heterogeneities in the stress field the induced seismicity is found to obey generally the gutenberg richter law up to a magnitude cutoff which correlates well with the width of the local seismogenic bed ranging in size from that of mine pillars for mining induced seismicity to the thickness of brittle sedimentary beds in the vicinity of dams or depleted hydrocarbon reservoirs in conclusion the properties of induced seismicity and their rationalization in terms of the soc concept provide further evidence that potential seismic hazards extend over a much larger area than that where earthquakes are frequent

on the interaction of tropical cyclone scale vortices i observations a detailed analysis is made of the observed behaviour in interaction tropical cyclone scale vortices in the western north pacific region it is found that all multiple vortex interactions can be broken down into a common model of binary interaction the classical fujiwhara model of converging cyclonic rotation about a centroid followed by merger is rarely followed capture tends to occur rapidly within several hours and is followed by a period of relatively stable cyclonic orbit cyclone merger occurs by one vortex experiencing a loss of convective organization followed by horizontal shearing and incorporation into the outer circulation of the other vortex however a substantial proportion of interacting cyclones escape from the interaction and the changeover from a stable orbiting configuration occurs rapidly a model of binary interaction is presented cases where swarms of mesoscale vortices are formed in convectively active regions without tropical cyclones are also documented these vortices have a much narrower range of influence a few hundred kilometres then that observed for tropical cyclones when groups of vortices come within this range they are observed to conform to the same interaction model as observed for tropical cyclones

the role of vortical hot towers in the formation of tropical cyclone diana 1984 abstract a high resolution 3 km horizontal grid spacing near cloud resolving numerical simulation of the formation of hurricane diana 1984 is used to examine the contribution of deep convective processes to tropical cyclone formation this study is focused on the 3 km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle the numerical simulation reveals the presence of vortical hot towers or cores of deep cumulonimbus convection possessing strong vertical vorticity that arise from buoyancy induced stretching of local absolute vertical vorticity in a vorticity rich prehurricane environment at near cloud resolving scales these vortical hot towers are the preferred mode of convection they are demonstrated to be the most important influence to the formation of the tropical storm via a two stage evolutionary process i preconditioning of the local environment via diabatic production of mul

possible structural control on the 2011 eruption of puyehue cordon caulle volcanic complex southern chile determined by insar gps and seismicity

mesoscale interactions in tropical cyclone genesis with the multitude of cloud clusters over tropical oceans it has been perplexing that so few develop into tropical cyclones the authors postulate that a major obstacle has been the complexity of scale interactions particularly those on the mesoscale which have only recently been observable while there are well known climatological requirements these are by no means sufficient a major reason for this rarity is the essentially stochastic nature of the mesoscale interactions that precede and contribute to cyclone development observations exist for only a few forming cases in these the moist convection in the preformation environment is organized into mesoscale convective systems each of which have associated mesoscale potential vortices in the midlevels interactions between these systems may lead to merger growth to the surface and development of both the nascent eye and inner rainbands of a tropical cyclone the process is essentially stochastic but the degree of stochasticity can be reduced by the continued interaction of the mesoscale systems or by environmental influences for example a monsoon trough provides a region of reduced deformation radius which substantially improves the efficiency of mesoscale vortex interactions and the amplitude of the merged vortices further a strong monsoon trough provides a vertical wind shear that enables long lived midlevel mesoscale vortices that are able to maintain or even redevelop the associated convective system the authors develop this hypothesis by use of a detailed case study of the formation of tropical cyclone oliver observed during toga coare 1993 in this case two dominant mesoscale vortices interacted with a monsoon trough to separately produce a nascent eye and a major rainband the eye developed on the edge of the major convective system and the associated atmospheric warming was provided almost entirely by moist processes in the upper atmosphere and by a combination of latent heating and adiabatic subsidence in the lower and middle atmosphere the importance of mesoscale interactions is illustrated further by brief reference to the development of two typhoons in the western north pacific

the polymodal frequency magnitude relationship of earthquakes earthquake frequency magnitude relationships can be well described as a polymodal composite of normal distributions a pattern consistent with varying causal mechanisms in different tectonic settings and or magnitude ranges but a pattern also in conflict with the assumption of self similarity or the fractal nature of earthquakes from the giardini catalog 4660 deep 350 km worldwide earthquakes presumably homogeneous with respect to causal mechanism are well described as a single normally distributed population analysis of 10 341 earthquakes ranging in magnitude from 2 0 to 8 2 from the 1989 to 1991 national earthquake information center quick epicenter determination catalogue yields three populations each of whose magnitude frequency is expressed in terms of probability some nonsimilar frequency magnitude distributions for low magnitudes are also explicable as the result of one or more normally distributed populations in our model b is a measure of the dispersion of the population

variations in the frequency magnitude distribution with depth in two volcanic areas mount st helens washington and mt spurr alaska the frequency magnitude distribution of earthquakes characterized using the b value is examined as a function of space beneath mount st helens 1988 1996 and mt spurr 1991 1995 at mount st helens two volumes of anomalously high b b 1 3 can be observed at depths of 2 6 3 6 km below the crater floor and below 6 4 km these anomalies coincide with 1 the depth of vesiculation of ascending magma and 2 the suggested location of a magma chamber at mount st helens study of mt spurr reveals an area of high b value b 1 3 at a depth of about 2 3 4 5 km below the crater floor of the active vent crater peak we propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b value at shallow depths alternatively interaction of magma with groundwater may have increased pore pressure and lowered the effective stress the deeper anomaly at mount st helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber our results indicate that detailed mapping of the frequency magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers

earthquake recurrence of a particular type the recurrence relation for turkish earthquakes expressed as the single frequency versus magnitude dependence exhibits significant maxima and minima reflecting true physical conditions various mathematical formulations are developed to fit the observed data for the single or the cumulative frequency and are compared with each other as regards their accuracy and simplicity the results may be applicable to regions with high seismicity

fracturing of volcanic systems experimental insights into pre eruptive conditions conditions for fracturing are a primary control on the behaviour of volcanic systems especially during the approach to eruption we here present the results of deformation experiments under simulated volcanic conditions on a porhyritic andesite from ancestral mount shasta andesite was chosen as a representative material because it is common at subduction zone volcanoes among both erupted products and country rock we deformed the lava in tension and triaxial compression tests at strain rates of 10 5 s 1 confining pressures from 0 to 50 mpa and temperatures up to 900 degrees c we also concurrently recorded acoustic emissions ae in order to monitor cracking activity the results show that deformation behaviour changes significantly in the temperature range 600 750 degrees c thus as temperatures increased across this interval the tensile fracture toughness increased from 2 5 0 5 mpa m 1 2 to 3 5 1 mpa m 1 2 the compressive strength decreased from 110 30 mpa to 55 35 mpa at 900 degrees c and the corresponding young s modulus decreased from 20 4 gpa to 6 4 gpa the changes occur when the deformation of the sample changes from elastic brittle to brittle ductile behaviour which we attribute to the blunting of crack tips due to melting of the glass phase and enhanced crystal plasticity at high temperature ae activity was observed in all experiments indicating that earthquakes can be generated not only in country rock but also in hot magma such as may be found in lava domes and at the margins of magma conduits in addition the trends in accelerating ae event rates before sample failure were comparable to those seen in earthquakes before some volcanic eruptions and a minimum in the seismic b value coincided with sample failure applied to volcanic systems the results suggest that 1 andesite strength and elasticity will not be affected by temperature or pressure beyond similar to 10 100 m from active magma 2 before eruptions fractures propagate preferentially through weaker horizons in a mechanically heterogeneous volcano and 3 volcanic rocks have characteristic seismic b values that are perturbed during the approach to bulk failure each of these conditions provides quantitative constraints on models for seismic precursors to eruption or intrusion c 2009 elsevier b v all rights reserved

diagnosis of the mjo modulation of tropical cyclogenesis using an empirical index the modulation of tropical cyclone activity by the madden julian oscillation mjo is explored using an empirical genesis potential gp index composite anomalies of the genesis index associated with the different mjo phases are consistent with the composite anomalies in tc genesis frequency that occur in the same phases indicating that the index captures the changes in the environment that are at least in part responsible for the genesis frequency changes of the four environmental variables that enter the genesis potential index the midlevel relative humidity makes the largest contribution to the mjo composite gp anomalies the second largest contribution comes from the low level absolute vorticity and only very minor contributions come from the vertical wind shear and potential intensity when basin integrated mjo composite anomalies of the gp index are regressed against basin integrated composite anomalies of tc genesis frequency the results differ quantitatively from those obtained from the analogous calculation performed on the annual climatologies in the two quantities the gp index captures the mjo modulation of tc genesis to a lesser degree than the climatological annual cycle of genesis to which it was originally tuned this may be due to weaknesses of the reanalysis or indicative of the importance of precursor disturbances not well captured in the gp index computed from weekly data to the intraseasonal tc genesis frequency fluctuations

genesis of tropical storm eugene 2005 from merging vortices associated with itcz breakdowns part ii roles of vortex merger and ambient potential vorticity abstract in this study the roles of merging midlevel mesoscale convective vortices mcvs and convectively generated potential vorticity pv patches embedded in the intertropical convergence zone itcz in determining tropical cyclogenesis are examined by calculating pv and absolute vorticity budgets with a cloud resolving simulation of tropical storm eugene 2005 results show that the vortex merger occurs as the gradual capture of small scale pv patches within a slow drifting mcv by another fast moving mcv thus concentrating high pv near the merger s circulation center with its peak amplitude located slightly above the melting level the merging phase is characterized by sharp increases in surface heat fluxes low level convergence latent heat release and upward motion lower tropospheric pv surface pressure falls and growth of cyclonic vorticity from the bottom upward melting and freezing appear to affect markedly the vertical structures of diabatic heating convergence absolute vorticity

earthquake clustering on volcanic and tectonic structures abstract temporal clustering of seismic shocks is investigated using the generalized poisson process and assuming that grouped events are distributed according to riemann statistics the e parameter inversely proportional to the clustering level has been calculated for both volcanic and tectonic earthquakes listed in the catalogues of the aeolian island local network southern italy e values from other investigations have also been used in order to extend the analysis clustering is generally higher for volcanic earthquakes than for tectonic earthquakes in volcanic regions the tendency of shocks to group in time increases during eruptive phases with respect to quiescent periods a similar relationship between earthquake clustering and the activity state of seismogenetic structures may be preliminarily hypothesized in tectonic environments these findings reveal an interesting analogy between seismic clustering 1 e and the coefficient b of the gutenberg richter relationship which controls the earthquake distribution in the magnitude domain a possible explanation of the behaviour of the e and b parameters is proposed advancing some hypotheses on the role both of rock fracturing level and stress intensity and on the combined effect of these factors on the statistical properties of earthquake sequences

oceanic cyclogenesis as induced by a mesoscale convective system moving offshore part i a 90 h real data simulation abstract recent observations have revealed that some mesoscale convective systems mcss could undergo multiple cycles of convective development and dissipation and under certain environments they appeared to be responsible for barotropic oceanic or tropical cyclogenesis in this study oceanic cyclogenesis as induced by an mcs moving offshore and then driven by deep convection in a near barotropic environment is investigated by extending to 90 h the previously documented 18 h simulation of the mcss that were responsible for the july 1977 johnstown flash flood it is demonstrated that the mesoscale model can reproduce very well much of the meso scale structures and evolution of the long lived mcs out to 90 h these include the development and dissipation of the continental mcss as well as the associated surface and tropospheric perturbations the timing and location in the initiation of a new mcs after 36 h and in the genesis of a surface mesolow over the warm gulf stream water after 60 h integra

temporal variations in seismic event rate and b values from stress corrosion constitutive laws abstract main i g meredith p g and sammonds p r 1992 temporal variations in seismic event rate and b values from stress corrosion constitutive laws in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 233 246 a model is developed to characterise the state of damage for a fractal population of cracks in terms of a mean energy release rate g which depends on the stress the event rate n and the seismic b value n is assumed to be proportional to the total number of potentially active cracks and b to be proportional to the exponent d of the crack length distribution g is then positively correlated with n and negatively correlated with b consistent with experimental observation based on stress intensity as a constitutive variable the model predicts that higher b values are associated either with lower stress intensity or greater material heterogeneity both experiment and theory predict intermediate term seismic quiescence of similar magnitude to that observed in the field 45 90 for only a small simultaneous reduction in stress and stress intensity 2 7 or the equivalent mean energy release rate the theoretical model predicts three different types of quiescence associated with increasing constant or decreasing b value the first two are associated with stable intermediate term quiescence due to a reduction in g and the third is associated with unstable short term quiescence associated with constant or increasing g the theory can be used to infer relative changes in g from acoustic emissions in the laboratory experiments to date show that quiescence of the order 10 can be seen in the laboratory at strain rates of 10 5 s 1 but that this has the characteristics of short term rather than intermediate term quiescence

convective contribution to the genesis of hurricane ophelia 2005 abstract the convection occurring in the tropical depression that became hurricane ophelia 2005 was investigated just prior to tropical storm formation doppler radar showed a deep wide intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail the updraft of the cell was 10 km wide 17 km deep had updrafts of 10 20 m s 1 throughout its mid to upper levels and contained a cyclonic vorticity maximum the massive convective updraft was maintained by strong positive buoyancy which was maximum at about the 10 km level probably aided by latent heat of freezing evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft the convective updraft was fed by a layer of strong inflow that was several kilometers deep wind induced turbulence just above the ocean surface enriched the equi

stress changes focal mechanisms and earthquake scaling laws for the 2000 dike at miyakejima japan faulting processes in volcanic areas result from a complex interaction of pressurized fluid filled cracks and conduits with the host rock and local and regional tectonic setting often volcanic seismicity is difficult to decipher in terms of the physical processes involved and there is a need for models relating the mechanics of volcanic sources to observations here we use focal mechanism data of the energetic swarm induced by the 2000 dike intrusion at miyakejima izu archipelago japan to study the relation between the 3 d dike induced stresses and the characteristics of the seismicity we perform a clustering analysis on the focal mechanism fm solutions and relate them to the dike stress field and to the scaling relationships of the earthquakes we find that the strike and rake angles of the fms are strongly correlated and cluster on bands in a strike rake plot we suggest that this is consistent with optimally oriented faults according to the expected pattern of coulomb stress changes we calculate the frequency size distribution of the clustered sets finding that focal mechanisms with a large strike slip component are consistent with the gutenberg richter relation with a b value of about 1 conversely events with large normal faulting components deviate from the gutenberg richter distribution with a marked roll off on its right hand tail suggesting a lack of large magnitude events mw 5 5 this may result from the interplay of the limited thickness and lower rock strength of the layer of rock above the dike where normal faulting is expected and lower stress levels linked to the faulting style and low confining pressure

response of the hadley circulation to convective forcing in the itcz abstract through the use of a zonal balance model we investigate the response of the mean meridional circulation to a specified diabatic forcing for both resting and nonresting zonal flows the use of a potential latitude coordinate and transformed meridional circulation components results in a simplified meridional circulation equation in which the variable coefficients are the normalized potential vorticity and inertial stability solutions of this equation illustrate how latent heat release away from the equator forces a winter hemisphere hadley cell that is more intense than the summer hemisphere cell this asymmetric response is due primarily to the anisotropy associated with the spatial variation of the inertial stability field despite the sensitivity of the meridional circulation to the location and breadth of the forcing the low latitude thermodynamic response is for the most part insensitive as long as the total latent heat release remains the same numerical solutions of the zonal balance mode

itcz breakdown in three dimensional flows the intertropical convergence zone itcz is observed to undulate and at times break down into a series of tropical disturbances in several days some of these disturbances may develop into tropical cyclones and move to higher latitudes while others dissipate and the itcz may reform in the original region it has been proposed that the itcz may break down because of its heating induced potential vorticity pv anomalies here this process is examined in three dimensional simulations using a primitive equation model a simulation of the itcz in a background state of rest is compared to simulations in different background flows the effect of different vertical structures of the prescribed heating is also examined deep heating induces a positive pv anomaly in the lower troposphere leading to a reversal of the pv gradient on the poleward side of the heating while the induced pv anomaly at upper levels is negative leading to a reversal of the pv gradient on the equatorward side of the heating the response at upper levels leads to a weaker pv gradient change but the response is greater in areal extent than the lowertropospheric response for shallow heating the lower tropospheric pv response is greater than that for deep heating and there is no upper tropospheric pv response the itcz lasts longer before breaking in this case than in the deep heating case effects of the background flow are mainly felt in the deep heating cases when the background flow enforces the pv induced wind field itcz breakdown occurs more rapidly whereas when the background flow is opposite to the pv induced flow itcz breakdown takes longer and the itcz may dissipate before breakdown

observations of volcanic tremor at mount st helens in april and may 1980 abstract high amplitude nearly monochromatic volcanic tremor was observed before during and after the 18 may 1980 eruption of mount st helens the tremor often remained stationary for periods of several minutes or more for the period before and immediately following the main eruption spectra calculated from three component seismograms contained a nearly constant dominant frequency of 1 1 to 1 5 hz this contrasts with a dominant frequency of 1 7 to 2 1 hz calculated for the tremor associated with the 25 may eruption amplitude decay with distance obeys the form a r n where a is the tremor amplitude and r is the observation distance from the source the exponent n was determined in a least squares sense to be 1 5 0 4 1 5 0 3 and 1 7 0 3 before and shortly after the main eruption on 18 may 1980 and 24 may 1980 respectively the exponent for low frequency volcanic earthquakes before the main eruption was 1 6 0 3 a value similar to that of the volcanic tremor and suggests that the source of the volcanic tremor is shallow as is the source of the low frequency earthquakes the spectra of the tremor periods are very similar to those of the low frequency volcanic earthquakes there are cases where volcanic tremor appears as a continuation of a low frequency earthquake these observations suggest that the volcanic tremor and the low frequency volcanic earthquakes are strongly interconnected and indeed may well share a common source mechanism based on both signal stationarity and spectral amplitude decay consistency we suggest in common with others that the monochromatic nature of volcanic tremor is mainly due to a source effect while the path and station effects are relatively minor the tremor amplitude changes as a result of variations in the source driving force the frequency shift for the 24 may 1980 tremor may be due to a source dimension change

the itcz in the central and eastern pacific on synoptic time scales the itcz in the central and eastern pacific on synoptic time scales is highly dynamic the active season extends roughly from may through october during the active season the itcz continuously breaks down and re forms and produces a series of tropical disturbances the life span of the itcz varies from several days to 3 weeks sixty five cases of itcz breakdown have been visually identified over five active seasons 1999 2003 in three independent datasets itcz breakdown can be triggered by two mechanisms 1 interaction with westward propagating disturbances wpds and 2 the vortex rollup vr mechanism results show that the frequency of occurrence of itcz breakdown from these two mechanisms is the same the vr mechanism may have been neglected because the produced disturbances are rather weak and they may dissipate quickly the itcz shows a strong tendency to re form within 1 2 days in the same location the itcz may break down via the vr mechanism without any other support and thus it may continuously generate numerous tropical disturbances throughout the season there are two main differences between the two mechanisms 1 the wpds induced itcz breakdown tends to create one or two vortices that may be of tropical depression strength the vr induced itcz breakdown generates several nearly equal sized weak disturbances 2 the wpds tend to disturb the itcz in the eastern pacific only disturbances generally move along the mexican coast after shedding off from the itcz and do not further disturb the itcz in the central pacific therefore the vr mechanism is observed more clearly and is the dominating mechanism for itcz breakdown in the central pacific

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

seismic signals preceding the explosive eruption of mount st helens washington on 18 may 1980 abstract the intense seismic activity which preceded the 18 may 1980 eruption of mount st helens washington released 2 to 3 10 18 ergs day in earthquakes that did not correlate temporally with phreatic eruptions which occurred during the same period although the b value and amplitude ratios long period short period of the earthquakes vary with time there are no definitive precursors to the 18 may earthquake and eruption a mogi type ii frequency magnitude relation with critical magnitude mc 4 6 constrains the characteristic dimension of the highly stressed region under mount st helens to approximately 3 km preceding the eruption a major increase in seismic energy release and a decrease in b value around 1 april 1980 may indicate the first major influx of magma into the upper portion of the volcano seismic waves from low frequency volcanic earthquake have large periods at all epicentral distances recordings of volcanic earthquakes from 2 to 4 april 1980 at sites 4 to 9 km from mount st helens show two predominant periods of 0 55 and 1 0 sec we speculate that seismic signals from the low frequency volcanic earthquakes have a tectonic origin but may be modified by pressure oscillations in nearby magma

a random field model for surface roughness and aperture of rock fractures present constitutive models for rock fracture behaviour require information concerning the fracture geometry on which the mechanical and hydraulic properties of the rock mass are greatly dependent in this paper measurements of rock fracture surfaces and aperture using a 3 d laser scanning technique are reported in order to check the validity of a fractal model for fracture geometry this formulation incorporates fractal descriptions of roughness angularity and aperture fractal patterns can be persistent if an increasing increment implies an increase in the next increment or anti persistent if increasing increments follows decreasing increments persistence and anti persistence are recognised as descriptors of the geometrical complexity of roughness and aperture the analysis of the data also shows that the fractal models apply until stationarity occurs for sufficiently large samples which behave as random variables these sample sizes are defined as stationarity thresholds of roughness and aperture moreover the study of the cross correlation between the asperity height and aperture provides the link between fracture roughness and aperture geometry a theoretical model of fracture aperture during shearing is developed and successfully compared with experimental and numerical studies reported in the literature

spatio temporal microseismicity clustering in the cretan region abstract spatio temporal clustering of microseismicity in the central forearc of the hellenic subduction zone in the area of crete is investigated data for this study were gathered by temporary short period networks which were installed on the islands of crete and gavdos between 1996 and 2004 the similarity of waveforms is quantified systematically to identify clusters of microseismicity waveform similarities are calculated using an adaptive time window containing both the p and s wave onsets the cluster detection is performed by applying a single linkage approach clusters are found in the interplate seismicity as well as in the intraplate seismicity of the continental crust in the region of the transtensional ptolemy structure the majority of the clusters are off the southern coast of crete in a region of elevated intraplate microseismic activity within the aegean plate clusters in the gavdos region are located at depths compatible with the plate interface while cluster activity in the region of the ptolemy trench is distributed along a nearly vertical structure throughout the crust extending down to the plate interface most clusters show swarm like behaviour with seismic activity confined to only a few hours or days without a dominant earthquake and with a power law distribution of the interevent times for the largest cluster precise relocations of the events using travel time differences of p and s waves derived from waveform cross correlations reveal migration of the hypocenters this cluster is located in the region of the ptolemy trench and migration occurs along the strike of the trench at 500 m day relocated hypocenters as well as subtle differences in the waveforms suggest an offset between the hypocenters and thus the activation of distinct patches on the rupture surface the observed microseismicity patterns may be related to fluids being transported along the plate interface and escaping towards the surface in zones of crustal weakness ptolemy structure triggering swarm like cluster activity along its way

potential vorticity modeling of the itcz and the hadley circulation abstract a simple zonally symmetric balanced model of the hadley circulation is presented the model is based on potential vorticity arguments and consists of a predictive equation for the potential pseudodensity and an invertibility principle to diagnose the associated balanced wind and mass fields when the theory is formulated in the potential latitude coordinate the meridional advection is implicit in the coordinate transformation which makes the prediction equation for potential pseudodensity analytically solvable for convective heating patterns that simulate the itcz the model produces upper and lower tropospheric potential vorticity anomalies of opposite sign the associated winds are easterly at low levels and westerly aloft except between the equator and the itcz where there are low level westerlies and upper level easterlies since the potential vorticity anomalies develop within a background state that has potential vorticity increasing to the north reversed poleward gradients of potenti

breakdown and reformation of the intertropical convergence zone in a moist atmosphere abstract the effects of moisture on the intertropical convergence zone itcz over the eastern pacific on the synoptic time scale are investigated using an intermediate complexity atmospheric circulation model the quasi equilibrium tropical circulation model qtcm1 on an aquaplanet the dry simulation shows results consistent with those of simple dynamic models except that a slightly stronger heating rate is needed owing to different model designs in the moist simulations the most important result is the formation of a tail southwest of a vortex during and after the itcz breakdown this tail may extend zonally more than 60 longitude and last for more than two weeks in an idealized simulation in the eastern north pacific this phenomenon is often observed in cases that involve easterly waves in a sense the formation of the tail suggests a possible mechanism that forms an itcz efficiently this study shows that the surface convergent flow induced by a disturbance initializes a positive wind evapor

the contact between opposing fault surfaces at dixie valley nevada and implications for fault mechanics well exposed normal fault surfaces from dixie valley nevada provide a unique opportunity to study the contact properties of fault surfaces because it is possible to examine both the hanging wall and footwall surfaces of a fault zone which was once seismically active the topography of the individual surfaces as well as the aperture or gap between the two surfaces was measured using surface profiling instruments and a resin replication technique these measurements enable frictional parameters of the surfaces most notably the characteristic decay distance dc to be calculated using contact theory although the individual surfaces are approximately self similar and fractal the aperture between the opposing surfaces is a stationary quantity because the surfaces are well correlated at dimensions larger than approximately 2 mm consequently contact theory can be used to calculate an average size for contact spots between the surfaces and by inference a characteristic decay distance dc for frictional slip between the surfaces direct inspection of resin replicas of the aperture allows an independent estimate of average contact spot size both approaches give contact spot diameters of 0 16 mm and dc of 0 01 0 1 mm because the individual surfaces of the fault are fractal and approximately self similar correlation between the surfaces should decrease significantly during slip events particularly if slip rates are high seismic events decreased correlation between the surfaces should lead to larger contact spot sizes and hence larger dc thus critical slip distances for natural faults should evolve concurrently with seismic fault slip

barotropic aspects of itcz breakdown abstract in satellite images the itcz intertropical convergence zone is sometimes observed to undulate and break down into a series of tropical disturbances tropical cyclones may later develop within these disturbances and move into higher latitudes allowing the itcz to reform it has been proposed that itcz breakdown results from a convectively modified form of combined barotropic and baroclinic instability of the mean flow an unstable mean flow can be produced by itcz convection in just a couple of days in this sense the itcz produces favorable conditions for its own instability and breakdown in this study a nonlinear shallow water model on the sphere is used to simulate barotropic aspects of itcz breakdown in the shallow water model the itcz is simulated by a prescribed zonally elongated mass sink near the equator the mass sink produces a cyclonic potential vorticity pv anomaly that has a reversed meridional pv gradient on its poleward side according to the ripa theorem a flow that has a

a characteristic earthquake model of the seismicity preceding the eruption of mount st helens on 18 may 1980 abstract the two classes of earthquakes which preceded the explosive eruption of mount st helens washington on 18 may 1980 can be related to two different forms of energy release this is manifest both in the predominant periods of the two classes of seismic energy release at 1 0 and 0 55 s and in the ratio of their source dimensions in the range 2 1 to 6 1 inferred from characteristic magnitudes of the two possible classes of earthquakes apparent in the discrete frequency magnitude distribution the observed increase in the ratio of long to short period amplitudes of surface waves recorded on mso a local wwssn station can be numerically related to the growth of a magma chamber or conduit within which are generated the transient oscillations thought to be responsible for volcanic tremor these calculations predict an increase in the chamber s diameter at a rate of 2 7 m day 1 at depth in the 2 months preceding the eruption and this is consistent with an observed growth rate of 2 m day 1 of the precursory bulge which appeared at the surface on the mountain s north flank at the time the frequency magnitude distribution is analysed in two parts corresponding to a power law at low magnitudes and a gaussian distribution of typical fault lengths at high magnitudes an extension of the characteristic earthquake model first developed for individual fault zones the power law can in general have a non integer exponent which can be equated to a fractal self similarity dimension d temporal changes in d which is proportional to the seismic b value are proposed as an alternative and complementary description of the way seismic energy is released to the more commonly used viewpoints of changes in stress and heterogeneity despite a reassessment of the completeness of the magnitude catalogue no clear seismic precursor to the explosive eruption is observed in the b value although an earlier phase of phreatic eruptions was strongly associated with a b value anomaly

earthquake magnitude recent research and current trends abstract the magnitude recommendations adopted by the iaspei assembly at zurich in 1967 have had both a stabilizing and a stimulating effect on magnitude determinations and related research from 1967 onwards one magnitude research paper has appeared on the average almost every week thus making this parameter the most studied one in seismology new facilities and more accurate methods e g concerning instrumental equipment and interpretation techniques have made it possible to improve earlier achievements the application of magnitude scales has been extended in all respects e g with regard to epicentral distances focal depths wave types and wave periods magnitude frequency relations have become the most investigated equations within seismology observationally as well as theoretically they have wide applications e g for estimating the maximum magnitudes of future earthquakes an important item in earthquake prediction the magnitudes provide significant information on other source parameters such as wave energy fault length seismic moment relations between different types of magnitude yield valuable information on source properties for instance relations between magnitudes based on body and surface waves are used for efficient discrimination between earthquakes and underground explosions it is our purpose to review the magnitude development in the post zurich period 1967 1980 partly for geologists tectonophysicists and engineers who need an overview partly for seismologists who need an introduction to an overwhelmingly comprehensive literature

the b value as an earthquake precursor a systematic study of b values in new zealand has shown that within the vicinity of forthcoming large earthquakes there is initially an increase in b and then a return to normal the caracas and san fernando earthquakes show the same phenomenon which is related to that of seismic gaps

are volcanic seismic b values high and if so when abstract the gutenberg richter exponent b is a measure of the relative proportion of large and small earthquakes it is commonly used to infer material properties such as heterogeneity or mechanical properties such as the state of stress from earthquake populations it is well known that the b value tends to be high or very high for volcanic earthquake populations relative to b 1 for those of tectonic earthquakes and that b varies significantly with time during periods of unrest we first review the supporting evidence from 34 case studies and identify weaknesses in this argument due predominantly to small sample size the narrow bandwidth of magnitude scales available variability in the methods used to assess the minimum or cutoff magnitude m c and to infer b informed by this we use synthetic realisations to quantify the effect of choice of the cutoff magnitude on maximum likelihood estimates of b and suggest a new work flow for this choice we present the first quantitative estimate of the error in b introduced by uncertainties in estimating m c as a function of the number of events and the b value itself this error can significantly exceed the commonly quoted statistical error in the estimated b value especially for the case that the underlying b value is high we apply the new methods to data sets from recent periods of unrest in el hierro and mount etna for el hierro we confirm significantly high b values of 1 5 2 5 prior to the 10 october 2011 eruption for mount etna the b values are indistinguishable from b 1 within error except during the flank eruptions at mount etna in 2001 2003 when 1 5 b b 1 our results confirm that these volcano tectonic earthquake populations can have systematically high b values especially when associated with eruptions at other times they can be indistinguishable from those of tectonic earthquakes within the total error the results have significant implications for operational forecasting informed by b value variability in particular in assessing the significance of b value variations identified by sample sizes with fewer than 200 events above the completeness threshold

oceanic cyclogenesis as induced by a mesoscale convective system moving offshore part ii genesis and thermodynamic transformation abstract the genesis of intense cyclonic vorticity in the boundary layer and the transformation of a low level cold pool to a warm core anomaly associated with the long lived mesoscale convective systems mcss which produced the july 1977 johnstown flash flood and later developed into a tropical storm are examined using a 90 h real data simulation of the evolution from a continental mcs vortex to an oceanic cyclone storm system it is shown that the midlevel vortex trough at the end of the continental mcs s life cycle is characterized by a warm anomaly above and a cold anomaly below the mesovortex as it drifts toward the warm gulf stream water plays an important role in initiating and organizing a new mcs and a cyclonic shear vorticity band at the southern periphery of the previously dissipated mcs it is found from the vorticity budget that the vorticity band is amplified through stretching of absolute vorticity as it is wrapped around in a slantwise manner toward the cyclone center then the as

the genesis of hurricane guillermo texmex analyses and a modeling study abstract the transformation of a mesoscale convective system into hurricane guillermo was captured by aircraft and doppler wind data during the tropical experiment in mexico the early phase of the system evolves in a way very similar to previously documented mesoscale convective systems with a midlevel mesocyclone developing in the stratiform precipitation region more unusually the cyclone extends to low altitudes a weak cyclone is discernable even in the 300 m altitude wind field after another day of evolution a small surface based warm core cyclone is observed to develop within the relatively cold air associated with the mesocyclone aloft this mesocyclone develops into a hurricane over the subsequent day a nonhydrostatic axisymmetric numerical model is used to explore the evolution of the initially cold core midlevel vortex into a tropical cyclone a mesoscale midlevel showerhead is switched on in an initially quiescent tropical atmosphere overlying a warm ocean surface evaporation of t

variation ofb values before the etnean eruption of march 1981 a fissural eruption occurred from the northern flank of mt etna on march 17 1981 and the associated earthquake activity recorded by the seismic network operating on the volcano was carefully examined to detect possible variations ofb values according to the frequency magnitude relationship before the start of the eruption

the role of tropical waves in tropical cyclogenesis abstract this paper analyzes relationships between tropical wave activity and tropical cyclogenesis in all of the earth s major tropical cyclone basins twenty nine years of outgoing longwave radiation data and global reanalysis winds are filtered and analyzed to determine statistical relationships between wave activity in each basin and the corresponding cyclogenesis composite analyses relative to the storm genesis locations show the structures of the waves and their preferred phase relationships with genesis five wave types are examined in this study including mixed rossby gravity waves tropical depression type or easterly waves equatorial rossby waves kelvin waves and the madden julian oscillation the latter is not one of the classical tropical wave types but is a wavelike phenomenon known to have a strong impact on tropical cyclogenesis tropical cyclone formation is strongly related to enhanced activity in all of the wave filter bands except for the kelvin band in each basin the structure o

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

slip patterns and earthquake populations along different classes of faults in elastic solids numerical simulations of slip instabilities on a vertical strike slip fault in an elastic half space are performed for various models belonging to two different categories the first category consists of inherently discrete cellular fault models such are used to represent fault systems made of segments modeled by numerical cells that can fail independently of one another their quasi independence is assumed to provide an approximate representation of strong fault heterogeneity due to geometric or material property disorder that can arrest ruptures at segment boundaries the second category consists of models having a well defined continuum limit these involve a fault governed by rate and state dependent friction and are used to evaluate what types of property heterogeneity could lead to the quasi independent behavior of neighboring fault segments assumed in the first category the cases examined include models of a cellular fault subjected to various complex spatial distributions of static to kinetic strength drops and models incorporating rate and state dependent friction subjected to various spatial distributions of effective stress normal stress minus pore pressure the results indicate that gradual effective stress variations do not provide a sufficient mechanism for the generation of observed seismic response strong and abrupt fault heterogeneity as envisioned in the inherently discrete category is required for the generation of complex slip patterns and a wide spectrum of event sizes strong fault heterogeneity also facilitates the generation of rough rupture fronts capable of radiating high frequency seismic waves the large earthquakes in both categories of models occur on a quasi periodic basis the degree of periodicity increases with event size and decreases with model complexity however in all discrete segmented cases the models generate nonrepeating sequences of earthquakes and the nature of the large quasi periodic events is highly variable the results indicate that expectations for regular sequences of earthquakes and or simple repetitive precursory slip patterns are unrealistic the frequency size fs statistics of the small failure episodes simulated by the cellular fault models are approximately self similar with b 1 2 and ba 1 where b and ba are b values based on magnitude and rupture area respectively for failure episodes larger than a critical size however the simulated statistics are strongly enhanced with respect to self similar distributions defined by the small events this is due to the fact that the stress concentrated at the edge of a rupture expanding in an elastic solid grows with the rupture size when the fault properties e g geometric irregularities are characterized by a narrow range of size scales the scaling of stress concentrations with the size of the failure zone creates a critical rupture area terminating the self similar earthquake statistics in such systems events reaching the critical size become on the average unstoppable and they continue to grow to a size limited by a characteristic model dimension when however the system is characterized by a broad spectrum of size scales the above phenomena are suppressed and the range of apparent self similar fs statistics is broad and characterized by average b and ba values of about 1 the simulations indicate that power law extrapolations of low magnitude seismicity will often underestimate the rate of occurrence of moderate and large earthquakes the models establish connections between features of fs statistics of earthquakes range of self similar regimes local maxima and structural properties of faults dominant size scales of heterogeneities dimensions of coherent brittle zones the results suggest that observed fs statistics can be used to obtain information on crustal thickness and fault zone structure

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

earthquake failure sequences along a cellular fault zone in a three dimensional elastic solid containing asperity and nonasperity regions numerical simulations of earthquake failure sequences along a discrete cellular fault zone are performed for a three dimensional 3 d model representing approximately the central san andreas fault the model consists of an upper crust overlying a lower crust and mantle region together defining an elastic half space with a vertical half plane fault the fault contains a region where slip is calculated on a uniform grid of cells governed by a static kinetic friction law and regions where slip is prescribed so as to represent tectonic loading aseismic fault creep and adjacent great earthquakes the computational region models a 70 km long and 17 5 km deep section of the san andreas fault to the nw of the great 1857 rupture zone different distributions of stress drops on failing computational cells are used to model asperity parkfield asperity and nonasperity fault regions the model is inherently discrete and corresponds to a situation in which a characteristic size of geometric disorder within the fault i e cell size here a few hundreds of meters is much larger than the nucleation size of the order of tens of centimeters to tens of meters based on slip weakening or state evolution slip distances the computational grid is loaded by a constant plate motion imposed at the lower crust upper mantle and creeping fault regions and by a staircase slip history imposed at the 1857 and 1906 rupture zones stress transfer along and outside the fault due to the imposed loadings and failure episodes along the computational grid is calculated using 3 d elastic dislocation theory the resulting displacement field in the computational region is compatible with geodetic and seismological observations only when the asperity and nonasperity regions are characterized by significantly different average stress drops the frequency magnitude statistics of the simulated failure episodes are approximately self similar for small events with b 1 2 the b value of statistics based on rupture area ba is about 1 but are strongly enhanced with respect to self similarity for events larger than a critical size this is interpreted as a direct manifestation of our 3 d elastic stress transfer calculations beyond certain rupture area and potency seismic moment divided by rigidity release values the event is usually unstoppable and it continues to grow to a size limited by a characteristic model dimension this effect is not accounted for by cellular automata and block spring models in which the adopted simplified stress transfer laws fail to scale properly with increasing rupture size the simulations suggest that local maxima in observed frequency magnitude statistics correspond to dimensions of coherent brittle zones such as the width of the seismogenic layer or the length of a fault segment bounded by barriers the analysis indicates that a single cell size representing approximately a single scale of geometric disorder cannot induce self similarity in a 3 d elastic model over a broad range of magnitudes a representation of geometric disorder covering a range of scales may thus be required to generate a wide domain of self similar gutenberg richter statistics our simulations show a great diversity in the mode of failure of the parkfield asperity the earthquakes themselves define an irregular sequence of events the modeling like many other discrete fault models suggests that expectations for periodic parkfield earthquakes and or simple precursory patterns repeating from one event to the other are unrealistic

frequency magnitude distribution of earthquakes in vrancea relevance for a discrete model a high resolution analysis of a homogeneous and complete data set of intermediate depth microearthquakes h 60 km extending over an interval of 9 3 years emphasizes a significant deviation at low magnitudes ml 4 in a linear frequency magnitude distribution it appears as a distinct change in the slope of the cumulative distribution and as a seismicity deficit followed by a relative enhancement in the corresponding noncumulative curve this is in agreement with the presence of two characteristic mechanisms and allows the identification of both the magnitude threshold of asperity like earthquakes and the transition zone ml 3 3 3 9 from crack like earthquakes background seismicity to asperity like events these features are better pointed out on well individualized active zones the background seismicity shows a tremendeous decrease in its b slope from 1 03 to 0 57 during a 6 year interval before the occurrence of a major earthquake in 1986 mw 7 3 followed by a fast recovery to 1 03 in 2 years after this event such a behavior could be correlated to the continuous growth of the shear stress free surface on the fault as in a percolation process followed by its sudden diminution due to the locking of the fault the above results provide relevance for the discrete character of faulting and enable a coherent modeling of the earthquake generation process from microearthquake to major event scale lengths

scale interactions during the formation of typhoon irving the development of typhoon irving is investigated using a variety of data including special research aircraft data from the tropical cyclone motion tcm 92 experiment objective analyses satellite data and traditional surface and sounding data the development process is treated as a dry adiabatic vortex dynamics problem and it is found that environmental and mesoscale dynamics mutually enhance each other in a cooperative interaction during cyclone formation synoptic scale interactions result in the evolution of the hostile environment toward more favorable conditions for storm development mesoscale interactions with the low level large scale circulations and with other midlevel mesoscale features result in development of vorticity in the midlevels and enhancement of the low level vorticity associated with the developing surface cyclone multiple developments of mesoscale convective systems after the storm reaches tropical depression strength suggests both an increase in low level confluence and a tendency toward recurrent development of associated mesoscale convective vortices this is observed in both aircraft data and satellite imagery where subsequent interactions including mergers with the low level tropical depression vortex are observed a contour dynamics experiment suggests that the movement of mesoscale convective systems in satellite imagery corresponds well to the movement of their associated midlevel vortices results from a simple baroclinic experiment show that the midlevel vortices affect the large scale low level circulation in two ways 1 initially interactions between midlevel vortices produce a combined vortex of greater depth 2 interaction between midlevel vortices and the low level circulation produces a development downward of the midlevel vorticity this strengthens the surface vortex and develops a more cohesive vortex that extends from the surface through the midtroposphere

description and classification of rock surfaces by means of laser profilometry and mathematical morphology the evaluation of surface roughness is crucial to the hydrochemical and mechanical description of fractured rock masses surface roughness contains information on rock strength deformability permeability etc recent years have witnessed a rapid development of new methods for measuring the surface of rock fracture using state of the art technologies currently available measuring instruments such as profilometers and confocal microscopes provide information about hundreds of thousands of even millions measurement points which represent the investigated surface the key problem therefore is to work out methods to adequately interpret such large packets of data this study attempts a thorough analysis of this type of data using image processing and mathematical morphology methods the paper presents the results received from morphological gradients analyses of the results obtained from the watershed as well as the analyses of variograms furthermore it proposes the application of morphological filtering for selecting the roughness component of a rock fracture these results have been used in classifying the investigated rock this classification was based on pattern recognition methods by the definition of the 6d features space and the definition of learning sets a successful classification of investigated rocks has been obtained with up to ca 95 correct recognitions

high resolution non destructive measurement and characterization of fracture apertures abstract we measure at high resolution the fracture aperture of several consolidated materials and statistically characterize the aperture distribution for future studies on single and multiphase flow and transport through fractured porous media the images of the real fractures in granite and sandstone rocks are obtained with a computer aided tomography cat x ray scanner the minimum pixel size is 0 27 0 27 mm but fractures as small as 35 m can be accurately measured using a calibration standard for the variation in ct number due to the missing rock mass in a given pixel the distribution of fracture apertures is best described by a lognormal function this was also corroborated by comparing the theoretical to actual ratio of geometric mean to arithmetic mean apertures the mechanical roughness of the fractures ranged from 0 17 to 1 5 the variability in fracture aperture displayed only short range structure with correlation lengths of 0 8 to 7 mm at maximum which is at most one tenth of the minimum dimension width of the fracture plane fracture aperture distribution is rather heterogeneous potential flow channels can be deduced from the fracture aperture distribution

maximum earthquake magnitudes in the aegean area constrained by tectonic moment release rates summary seismic moment release is usually dominated by the largest but rarest events making the estimation of seismic hazard inherently uncertain this uncertainty can be reduced by combining long term tectonic deformation rates with short term recurrence rates here we adopt this strategy to estimate recurrence rates and maximum magnitudes for tectonic zones in the aegean area we first form a merged catalogue for historical and instrumentally recorded earthquakes in the aegean based on a recently published catalogue for greece and surrounding areas covering the time period 550 bc 2000 ad at varying degrees of completeness the historical data are recalibrated to allow for changes in damping in seismic instruments around 1911 we divide the area up into zones that correspond to recent determinations of deformation rate from satellite data in all zones we find that the gutenberg richter gr law holds at low magnitudes we use akaike s information criterion to determine the best fitting distribution at high magnitudes and classify the resulting frequency magnitude distributions of the zones as critical gr law subcritical gamma density distribution or supercritical characteristic earthquake model where appropriate we determine the ratio of seismic to tectonic moment release rate low values of 1 0 the seismic and tectonic moment release rates are then combined to constrain recurrence rates and maximum credible magnitudes in the range 6 7 7 6 m w where the results are well constrained based on extrapolating the short term seismic data with current earthquake data many of the tectonic zones show a characteristic distribution that leads to an elevated probability of magnitudes around 7 but a reduced probability of larger magnitudes above this value when compared with the gr trend a modification of the generalized gamma distribution is suggested to account for this based on a finite statistical second moment for the seismic moment distribution

tropical cyclogenesis due to itcz breakdown idealized numerical experiments and a case study of the event in july 1988 abstractthe mechanism of tropical cyclogenesis due to the breakdown of the intertropical convergence zone itcz breakdown and the structure of associated vortices are studied by numerical experiments using a nonhydrostatic mesoscale model first an idealized numerical experiment in which a simple initial state without external disturbances is assumed is performed without cumulus parameterization a zonally uniform forcing of high sea surface temperature sst is imposed to generate an itcz like structure this itcz starts to undulate and eventually breaks down to form several tropical cyclones tcs these tcs merge and end up with a single tc the energy budget analysis shows that barotropic instability of the low level flow associated with the itcz is responsible for the genesis of vortices and tc scale buoyancy production soon takes over to contribute to the intensification of tcs conversion from the cumulus scale kinetic energy into the tc scale kinetic energy is found to be insignificant duri

genesis of tropical storm eugene 2005 from merging vortices associated with itcz breakdowns part iii sensitivity to various genesis parameters abstract in this study a series of sensitivity simulations is performed to examine the processes leading to the genesis of tropical storm eugene 2005 from merging vortices associated with the breakdowns of the intertropical convergence zone itcz over the eastern pacific this is achieved by removing or modifying one of the two vortices in the model initial conditions or one physical process during the model integration using the results presented in parts i and ii as a control run results reveal that while the itcz breakdowns and subsequent poleward rollup through a continuous potential vorticity supply provide favorable conditions for the genesis of eugene the vortex merger is the most effective process in transforming weak tropical disturbances into a tropical storm the sensitivity experiments confirm the authors previous conclusions that eugene would not reach its observed tropical storm intensity in the absence of the merger and would become much shorter lived without the potential vorticit

hurricane spiral bands abstract the spiral bands that occur in tropical cyclones can be conveniently divided into two classes outer bands and inner bands evidence is presented here that the outer bands form as the result of nonlinear effects during the breakdown of the intertropical convergence zone itcz through barotropic instability in this process a zonal strip of high potential vorticity the itcz shear zone or monsoon trough begins to distort in a varicose fashion with the potential vorticity pv becoming pooled in local regions that are connected by filaments of high pv as the pooled regions become more axisymmetric the filaments become thinner and begin to wrap around the pv centers it is argued that inner bands form in a different manner as a tropical cyclone intensifies due to latent heat release the pv field becomes nearly circular with the highest values of pv in the cyclone center the radial gradient of pv provides a state on which pv waves the generalization of rossby waves can propagate the nonline