towards the reconstruction of the shallow plumbing system of the barombi mbo maar cameroon implications for diatreme growth processes of a polygenetic maar volcano abstract understanding the mechanisms involved in the formation of maars and their diatreme growth processes has been a subject of contention while there is no direct evidence of the presence of diatremes beneath most of the young maars their existence is inferred based on the amount and type of country rocks excavated at different depths and deposited as pyroclastic ejecta around their craters properly tracing fragmented country rocks in ejecta to interpret their depths of origin and thus the depths of phreatomagmatic explosions require good and detailed information on the substrate geology that is generally lacking at many maars as an alternative this paper explores the role of juvenile components in deposits of a maar for understanding the cratering and growth of diatremes during maar forming eruptions based on field investigations pyroclast distribution componentry and grain morphology examinations this study reports on the eruptive mechanisms that led to the formation of the barombi mbo maar bmm a polygenetic maar volcano in cameroon the bmm consists of three diatremes that formed during distinct eruptive events and coalesced to produce an amalgamated maar diatreme two end member types of eruption styles from the dry magmatic to the wet phreatomagmatic explosions governed the formation of the maar in total a minimum of 0 0658 km 3 of magma dense rock equivalent corrected was ejected based on calculation by applying interpolation techniques on digital elevation models obtained from srtm30m data corrected by rock textural data collected from the field the distribution of juvenile clasts throughout the stratigraphic sequence suggests a complex subsurface eruptive process which originated probably within the uppermost part of the diatreme from the distribution and morphology of juvenile clasts in the deposits it is inferred that cratering and country rock excavation during the growth of each of the small diatremes developed mainly from shallow level explosions sometimes with lateral and vertical variations in the position of the explosion loci a prospective juvenile based conceptual model is proposed for the formation of the bmm the model suggests that during maar forming eruptions explosions taking place at a deeper position might entrain extensive amount of lithics from the mostly lithic dominated upper crater infill to deposit juvenile poor 90 vol

unbedded diatreme deposits reveal maar diatreme forming eruptive processes standing rocks west hopi buttes navajo nation usa diatremes provide partial records of how dyke delivered magma periodically interacting with water produces the largest known cylindrical conduit structures of any volcano type we address how pre eruptive country rock is disrupted and redistributed to form the diatreme structure during an eruption by establishing the internal architecture of the unbedded diatreme at standing rocks west and the volumes and sources of wall rock within the diatreme and in a complementary tephra ring at teshim both in the hopi buttes volcanic field the unbedded diatreme is dominantly exposed as a massif comprising multiple subvertical columns interpreted as ephemeral conduit deposits of well mixed poorly sorted composite and juvenile pyroclast rich deposits that truncate marginal layered deposits plus a peripheral heterolithic country rock breccia wall rock clasts are scarce in the massif and were mainly sourced from 75 to 245 m depth below the paleosurface by contrast the tephra ring has abundant wall rock fragments dominantly from the upper 75 m of the pre eruptive sedimentary sequence the diatreme structure is interpreted to have been formed by many small volume explosions fed by a low flux of basaltic magma late stage explosive activity was rooted mostly within pyroclastic debris at shallow to intermediate depths within the diatreme structure this resulted in damped and shifting intra diatreme explosions and jets that facilitated gradual mixing recycling and remobilization of debris in the diatreme with incremental addition of juvenile material and possibly a local rise in the crater floor

cenozoic seismic stratigraphy and tectonic evolution of the algarve margin offshore portugal southwestern iberian peninsula the cenozoic seismic stratigraphy and tectonic evolution of the algarve margin southwestern border of the iberian peninsula are documented from multichannel seismic reflection data isochron and time structure maps six seismic units b to g bounded by unconformities and probably ranging in age from campanian to holocene are identified their ages are derived from 1 oil exploration wells drilled in the margin 2 geometrical relationship with the guadalquivir allochthonous unit 3 correlation with the onshore stratigraphic record of the algarve basin and 4 lateral correlation with unconformities dated in adjacent basins and related to tectonic events that affected iberia during the cenozoic three main tectonic domains bounded by major fault zones that segment the algarve margin are characterised a western central domain bounded to the west by the n s portimao monchique fault zone and to the east by the n s albufeira fault zone an eastern central domain bounded to the east by the n140 sao marcos quarteira fault zone and an eastern domain located east of this latter structure the cenozoic evolution of the algarve basin results from both hercynian basement reactivation and thin skinned contraction above a relative thick evaporitic unit probably upper triassic hettangian that acted as the main decollement controlling synchronous extensional and thrust detachments and generating both salt structures and salt withdrawal sub basins a persistent halokinesis is identified with two climax phases during the deposition of unit c lutetian to oligocene and at unit e upper tortonian to messinian the increasing flexure of the algarve margin is mainly expressed by spatial and temporal variations of the subsidence the overall tectonic regime is considered to be compressive and the close juxtaposition of compressed and extended areas is related to the orientation and geometry of preexisting basement tectonic structures and to the syncline evolution of the guadalquivir foredeep basin in response to the westward migration of the gibraltar arc

eruption processes and deposit characteristics at the monogenetic mt gambier volcanic complex se australia implications for alternating magmatic and phreatomagmatic activity the 5 ka mt gambier volcanic complex in the newer volcanics province australia is an extremely complex monogenetic volcanic system that preserves at least 14 eruption points aligned along a fissure system the complex stratigraphy can be subdivided into six main facies that record alternations between magmatic and phreatomagmatic eruption styles in a random manner the facies are 1 coherent to vesicular fragmental alkali basalt effusive hawaiian spatter and lava flows 2 massive scoriaceous fine lapilli with coarse ash strombolian fallout 3 bedded scoriaceous fine lapilli tuff violent strombolian fallout 4 thin medium bedded undulating very fine lapilli in coarse ash dry phreatomagmatic surge modified fallout 5 palagonite altered cross bedded medium lapilli to fine ash wet phreatomagmatic base surges and 6 massive palagonite altered very poorly sorted tuff breccia and lapilli tuff phreato vulcanian pyroclastic flows since most deposits are lithified to quantify the grain size distributions gsds image analysis was performed the facies are distinct based on their gsds and the fine ash to coarse fine ash ratios these provide insights into the fragmentation intensities and water magma interaction efficiencies for each facies the eruption chronology indicates a random spatial and temporal sequence of occurrence of eruption styles except for a magmatic horizon of effusive activity occurring at both ends of the volcanic complex simultaneously the eruption foci are located along nw se trending lineaments indicating that the complex was fed by multiple dykes following the subsurface structures related to the tartwaup fault system possible factors causing vent migration along these dykes and changes in eruption styles include differences in magma ascent rates viscosity crystallinity degassing and magma discharge rate as well as hydrological parameters

importance of small earthquakes for stress transfers and earthquake triggering 1 we estimate the relative importance of small and large earthquakes for static stress changes and for earthquake triggering assuming that earthquakes are triggered by static stress changes and that earthquakes are located on a fractal network of dimension d this model predicts that both the number of events triggered by an earthquake of magnitude m and the stress change induced by this earthquake at the location of other earthquakes increase with m as similar to 10 dm 2 the stronger the spatial clustering the larger the influence of small earthquakes on stress changes at the location of a future event as well as earthquake triggering if earthquake magnitudes follow the gutenberg richter law with b d 2 small earthquakes collectively dominate stress transfer and earthquake triggering because their greater frequency overcomes their smaller individual triggering potential using a southern california catalog we observe that the rate of seismicity triggered by an earthquake of magnitude m increases with m as 10 alpha m where alpha 1 05 0 05 we also find that the magnitude distribution of triggered earthquakes is independent of the triggering earthquake s magnitude m when alpha approximate to b small earthquakes are roughly as important to earthquake triggering as larger ones we evaluate the fractal correlation dimension d of hypocenters using two relocated catalogs for southern california the value of d measured for distances 0 1 r 5 km is d 1 54 for the shearer et al catalog and d 1 73 for the hauksson et al catalog the value of d reflects both the structure of the fault network and the nature of earthquake interactions by considering only those earthquake pairs with interevent times larger than 1000 days we can largely remove the effects of short term clustering then d approximate to 2 close to the value d 2 alpha 2 1 predicted by assuming that earthquake triggering is due to static stress the value d approximate to 2b implies that small earthquakes are as important as larger ones for stress transfers between earthquakes and that considering stress changes induced by small earthquakes should improve models of earthquake interactions

layered and laterally constrained 2d inversion of resistivity data in a sedimentary environment quasi layered models often can represent the actual geology more accurately than smooth minimum structure models we present a 2d inversion scheme with lateral constraints and sharp boundaries lci for continuous resistivity data all data and models are inverted as one system producing layered solutions with laterally smooth transitions the models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers a priori information used to resolve ambiguities and to add for example geological information can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites similarly information from areas with well resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result a simple synthetic model proves the need for a quasilayered 2d inversion when compared with a traditional 2d minimum structure inversion a 2d minimum structure inversion produces models with spatially smooth resistivity transitions making identification of layer boundaries difficult a continuous vertical electrical sounding field example from sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example a till layer on top of the bedrock hidden in the traditional inversion result is identified using the 2d lci scheme furthermore the depth to the bedrock surface is easily identified for most of the profile with the 2d lci model which is not the case with the model from the traditional minimumstructure inversion

self similar earthquake triggering bath s law and foreshock aftershock magnitudes simulations theory and results for southern california 1 bath s law the observation that the largest aftershock is on average 1 2 magnitudes smaller than its main shock independent of main shock size suggests some degree of self similarity in earthquake triggering this behavior can largely be explained with triggering models in which the increased triggering caused by larger magnitude events is exactly compensated for by their decreased numbers and these models can account for many features of real seismicity catalogs the bath s law magnitude difference of 1 2 places a useful constraint on aftershock productivity in these models a more general test of triggering self similarity is to plot foreshock and aftershock rates as a function of magnitude m relative to the main shock magnitude mmax of the largest event in the sequence both computer simulations and theory show that these dn dm curves should be nearly coincident regardless of main shock magnitude the aftershock dn dm curves have the same gutenberg richter b value as the underlying distribution but the foreshock dn dm curves have the same b value only for foreshock magnitudes less than about mmax 3 for larger foreshock values the dn dm curve flattens and converges with the aftershock dn dm curve at m mmax this effect can explain observations of anomalously low b values in some foreshock sequences and the decrease in apparent aftershock to foreshock ratios for small magnitude main shocks observed apparent foreshock and aftershock dn dm curves for events close in space and time to m 2 5 to 5 5 main shocks in southern california appear roughly self similar but differ from triggering simulations is several key respects 1 the aftershock b values are significantly lower than that of the complete catalog 2 the number of aftershocks is too large to be consistent with bath s law and 3 the foreshock to aftershock ratio is too large to be consistent with bath s law these observations indicate for southern california that triggering self similarity is not obeyed for these small main shocks or that the space time clustering is not primarily caused by earthquake to earthquake triggering

formation of high grade ignimbrites part ii a pyroclastic suspension current model with implications also for low grade ignimbrites analogue experiments in part i led to the conclusion that pyroclastic flows depositing very high grade ignimbrite move as dilute suspension currents in the thermo fluid dynamical model developed the degree of cooling of expanded turbulent pyroclastic flows dynamically evolves in response to entrainment of air and mass loss to sedimentation initial conditions of the currents are derived from column collapse modeling for magmas with an initial h2o content of 1 3 wt erupting through circular vents and caldera ring fissures the flows spread either longitudinally or radially from source up to a runout distance that increases with higher mass flux but decreases with higher gas content temperature bottom slope and coarser initial grain size progressive dilution by entrainment and sedimentation causes pyroclastic currents to transform into buoyant ash plumes at the runout distance the ash plumes reach stratospheric heights and distribute 30 80 of the erupted material as widespread co ignimbrite ash pyroclastic suspension currents with initial mass fluxes of 107 1012 kg s can spread for tens of kilometers with only limited cooling although they move as supercritical strongly entraining currents for the eruption conditions considered here with increasing eruption mass flux cooling during passage through the fountain diminishes while cooling during flow transport increases the net effect is that eruption temperature exerts the prime control on emplacement temperature pyroclastic suspension currents can form welded ignimbrite across their entire extent if eruption temperature is to 1 3 tmw the minimum welding temperature high eruption rates a large fraction of fine ash and a ring fissure vent favor the formation of extensive high grade ignimbrite for very hot eruptions producing sticky partially molten pyroclasts analysis of particle aggregation systematics shows that factors favoring longer runout also favor more efficient aggregation which reduces runout as a result very high grade ignimbrites cannot spread more than a few tens of kilometers from their source in cooler pyroclastic currents particles do not aggregate and the sedimentation process may involve re entrainment of particles which potentially leads to more extensive cooling and longer runout such effects however are only significant when net erosion of substrate occurs model results can be employed to estimate mass flux and duration of ignimbrite eruptions from measured ignimbrite masses and aspect ratios the model also provides an alternative explanation of the observed decrease in h lratios with ignimbrite mass

effect of climate change on sea water intrusion in coastal aquifers there is increasing debate these days on climate change and its possible consequences much of this debate has focused in the context of surface water systems in many arid areas of the world rainfall is scarce and so is surface runoff these areas rely heavily on groundwater the consequences of climate change on groundwater are long term and can be far reaching one of the more apparent consequences is the increased migration of salt water inland in coastal aquifers using two coastal aquifers one in egypt and the other in india this study investigates the effect of likely climate change on sea water intrusion three realistic scenarios mimicking climate change are considered under these scenarios the nile delta aquifer is found to be more vulnerable to climate change and sea level rise copyright 1999 john wiley sons ltd

on the use of combined geophysical methods to assess water content and water conductivity of near surface formations abstract we propose to deepen the interpretation of combined geophysical methods georadar seismic and electric to assess physical properties characterizing the near surface porous formations especially the influence of water velocity analysis of multioffset georadar data are used together with seismic methods to estimate lateral and vertical ground water fluctuations this enables us to identify transitions from non saturated to fully saturated porous layers with certainty furthermore the accurate knowledge of seismic velocities helps to estimate the porosity of the ground water formations finally we show how the radar technique may be useful in solving the problem of trade off between bulk resistivity which is deduced from electrical measurements and that of water ionic conductivity and water content these theoretical considerations are illustrated using various measurements conducted at the same test site our interpretation is compared with a few laboratory measurements on water and soil samples this study displays the impact of combined geophysical approaches for providing models of water and ionic transfers down to a depth of several metres

nontrivial decay of aftershock density with distance in southern california the decay of the aftershock density with distance plays an important role in the discussion of the dominant underlying cause of earthquake triggering here we provide evidence that its form is more complicated than typically assumed and that in particular a transition in the power law decay occurs at length scales comparable to the thickness of the crust this is supported by an analysis of a very recent high resolution catalog for southern california sc and surrogate catalogs generated by the epidemic type aftershock sequence etas model which take into account inhomogeneous background activity short term aftershock incompleteness anisotropic triggering and variations in the observational magnitude threshold our findings indicate specifically that the asymptotic decay in the aftershock density with distance is characterized by an exponent larger than 2 which is much bigger than the observed exponent of approximately 1 35 observed for shorter distances ranging from the main shock rupture length up to a length scale comparable to the thickness of the crust this has also important consequences for time dependent seismic hazard assessment based on the etas model

deposition of rheomorphic ignimbrite d mogan formation gran canaria canary islands spain rheomorphic ignimbrite d 13 4 ma upper mogan formation on gran canaria a multiple flow single cooling unit is divided into four major structural zones that differ in fabric and finite strain of deformed pyroclasts their structural characteristics indicate contrasting deformation mechanisms during rheomorphic flow the zones are a a basal zone vitrophyre with pure uniaxial flattening perpendicular to the foliation b an overlying shear zone characterized by asymmetric fabrics and a significantly higher finite strain with an ellipsoid geometry similar to stretched oblate bodies c a central zone with a finite strain geometry similar to that of the underlying shear zone but without evidence of a rotational strain component and d a slightly deformed to non deformed top zone where the almost random orientation of subspherical pyroclasts suggests preservation of original syn depositional clast shapes rheomorphic flow in d is the result of syn to post depositional remobilization of a hot pyroclastic flow as shown by kinematic modeling based on a the overall vertical structural zonation suggested by finite strain and fabric analysis b the relation of shear sense to topography c the interrelationship of the calculated vertical cooling progression at the base of the flow formation of vitrophyre and the related vertical changes in strain geometry d the complex lithification history and e the consequent mechanisms of deformational flow rheomorphic flow was caused by load pressure due to an increase in the vertical accumulation of pyroclastic material on a slope of generally 6 8 we suggest that every level of newly deposited pyroclastic flow material of d first passed through a welding process that was dominated by compaction pure flattening before rheomorphic deformation started

earthquake monitoring in southern california for seventy seven years 1932 2008 the southern california seismic network scsn has produced the scsn earthquake catalog from 1932 to the present a period of more than 77 yrs this catalog consists of phase picks hypocenters and magnitudes we present the history of the scsn and the evolution of the catalog to facilitate user understanding of its limitations and strengths hypocenters and magnitudes have improved in quality with time as the number of stations has increased gradually from 7 to 400 and the data acquisition and measuring procedures have become more sophisticated the magnitude of completeness m c of the network has improved from m c 3 25 in the early years to m c 1 8 at present or better in the most densely instrumented areas mainshock aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470 000 events the earthquake frequency size distribution has an average b value of 1 0 with m 6 0 events occurring approximately every 3 yrs the three largest earthquakes recorded were 1952 m w 7 5 kern county 1992 m w 7 3 landers and 1999 m w 7 1 hector mine sequences and the three most damaging earthquakes were the 1933 m w 6 4 long beach 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes all of these events ruptured slow slipping faults located away from the main plate boundary fault the san andreas fault their aftershock sequences constitute about a third of the events in the catalog the fast slipping southern san andreas fault is relatively quiet at the microseismic level and has not had an m 6 earthquake since 1932 in contrast the slower san jacinto fault has the highest level of seismicity including several m 6 events thus the spatial and temporal seismicity patterns exhibit a complex relationship with the plate tectonic crustal deformation

seismicity rate immediately before and after main shock rupture from high frequency waveforms in japan 1 we analyze seismicity rate immediately before and after 82 main shocks with the magnitudes ranging from 3 to 5 using waveforms recorded by the hi net borehole array in japan by scrutinizing high frequency signals we detect 5 times as many aftershocks in the first 200 s as in the japan meteorological agency catalogue after correcting for the changing completeness level immediately after the main shock the aftershock rate shows a crossover from a slower decay with an omori s law exponent p 0 58 0 08 between 20 and 900 s after the main shock to a faster decay with p 0 92 0 04 after 900 s the foreshock seismicity rate follows an inverse omori s law with p 0 73 0 08 from several tens of days up to several hundred seconds before the main shock the seismicity rate in the 200 s immediately before the main shock appears steady with p 0 35 0 50 these observations can be explained by the epidemic type aftershock sequence etas model and the rate and state model for a heterogeneous stress field on the main shock rupture plane alternatively nonseismic stress changes near the source region such as episodic aseismic slip or pore fluid pressure fluctuations may be invoked to explain the observation of small p values immediately before and after the main shock

statistical analysis of bubble and crystal size distributions application to colorado plateau basalts abstract a new analytical technique for the statistical analysis of bubble populations in volcanic rocks proussevitch a a sahagian d l and tsentalovich e p 2007 this issue statistical analysis of bubble and crystal size distributions formulations and procedures j volc geotherm res has been applied to a collection of colorado plateau basalts 96 samples a variety of mono and polymodal distributions has been found in the samples all of which belong to the logarithmic family of statistical functions most samples have bimodal log normal distributions while the others are represented by mono or bimodal log logistic and weibull distributions we have grouped the observed distributions into 11 groups depending on distribution types mode location and intensity the nature of the curves within these groups can be interpreted as evolution of vesiculation processes we conclude that within bimodal log normal distributions the mode of smaller bubbles is the result of a second nucleation and growth event in a lava flow after eruption in the case of log logistic distributions the larger mode results from coalescence of bubbles coalescence processes are reflected in growth of a larger mode and decreasing bubble number density another style of population evolution leads to a monomodal weibull or exponential distribution as a result of superposition of multiple log normal distributions in which the modes are comparable in size and intensity these various population distribution styles can be interpreted with an understanding of vesiculation processes that can be gained through appropriate numerical models of coalescence and population evolution the applicable vesiculation processes include a a single nucleation growth event b continuous multiple nucleation growth events c coalescence and d ostwald ripening

assembling an ignimbrite mechanical and thermal building blocks in the bishop tuff california abstract the building blocks that control ignimbrite physical characteristics are here defined as mechanical flow units and flow packages and thermal cooling units ignimbrite construction from these mechanical and thermal building blocks is illustrated by a longitudinal profile of the bishop tuff in the owens river gorge california in the bishop ignimbrite flow unit boundaries can be defined only locally but known or inferred multiple flow units combine to form eruptive packages showing imbricate offlapping relationships such that each package is thickest successively farther from the source in these packages the presence or absence of flow unit boundaries does not necessarily reflect directly the presence or absence respectively of time breaks thus massive ignimbrite need not be the product of continuous accumulation progressive aggradation the intrinsic thermal properties of each package or parts thereof have combined with local thicknesses of accumulated material to control the weld

crystallization of mount st helens 1980 1986 dacite a quantitative textural approach quantitative measurements of crystal size distributions csds have been used to obtain kinetic information on crystallization of industrial compounds randolph and larson 1971 and more recently on hawaiian basalts cashman and marsh 1988 the technique is based on a population balance resulting in a differential equation relating the population densityn of crystals to crystal sizel i e at steady staten no exp l itg whereno is nucleation density g is the average crystal growth rate is the average growth time and the nucleation ratej nog csd inn vsl plots of plagioclase phenocrysts in 12 samples of mount st helens blast dacite and 14 samples of dacite from the 1980 1986 mount st helens dome are similar and averageg 9 6 1 1 10 3 cm andno 1 2 106 cm 4 reproducibility of the measurements was tested by measuring csds of 12 sections cut from a single sample in three mutually perpendicular directions precision of the size distributions is good in terms of relative but not necessarily absolute values 10 growth and nucleation rates for plagioclase have been calculated from these measurements using time brackets of 30 150 years growth ratesg are 3 10 10 12cm s and nucleation ratesj are 5 21 10 6 cm3 s g andj for fe ti oxides calculated from csd data areg 2 13 10 13 cm sec andj 7 33 10 5 cm3 s respectively the higher nucleation rate and lower growth rate of oxides resulted in a smaller average crystal size than for plagioclase sizes of plagioclase microlites 0 01 mm in the blast dacite groundmass have been measured from backscatter sem photographs nucleation of these microlites was probably triggered by intrusion of material into the cone of mount st helens in spring 1980 this residence time of 52 days gives minimum crystallization estimates ofg 1 3 10 11 cm s andj 9 16 1o3 cm3 s the skeletal form of the microlites provides evidence for nucleation and growth at high values of undercooling t relative to the phenocrysts a comparison of nucleation and growth rates for the two crystal populations phenocrysts vs microlites suggests that while growth rate seems to be only slightly affected by changes in t nucleation rate is a very strong function of undercooling a comparison of plagioclase nucleation and growth rates measured in the mount st helens dacite and in basalt from makaopuhi lava lake in hawaii suggests that plagioclase nucleation rates are not as dependent on composition groundmass textures suggest that plagioclase microphenocrysts crystallized at depth rather than in the conduit in the dome or after extrusion onto the surface most of this crystallization appears to be in the form of crystal growth coarsening of groundmass microphenocrysts at small degrees of undercooling rather than extensive nucleation of new crystals this continuous crystallization in a shallow magmatic reservoir may provide the overpressurization needed to drive the continuing periodic domebuilding extrusions which have been the pattern of activity at mount st helens since december 1980

application of transient electromagnetic and audio magnetotelluric methods for imaging the monte real aquifer in portugal fifty transient electromagnetic tem and 15 audio magnetotelluric amt soundings were carried out in the west central part of portugal over an area of approximately 40 km2 to characterize the geological formations associated with the monte real aquifer in order to 1 assess the spatial extent of the aquifer 2 detect the zones of higher water productivity and 3 evaluate the aquifer salinization risk the dimensionality and strike direction of the amt profiles were studied using phase tensor analysis and the amt data was inverted using a two dimensional 2d nonlinear conjugate gradient algorithm in addition the tem soundings were inverted using a one dimensional 1d levenberg marquardt technique in order to obtain 1d layered earth resistivity models the tem results reveal that the aquifer is not uniform in the study area a more resistive zone is evident in the north and northeast of the investigated area where we expect to have higher productivity on the other hand the amt models suggest that the aquifer basement is probably located at a depth of more than 800 m based on the results of this investigation no traces of saltwater intrusion were found for the monte real aquifer therefore we assume that the risk of saltwater intrusion is small in the study area

reply to comment by s hainzl on self similar earthquake triggering bath s law and foreshock aftershock magnitudes simulations theory and results for southern california 1 increasedcatalogincompleteness followingmainshocks can indeed result in artificially low b value estimates for aftershock sequences in their early stages hanizl 2013 nicely documents how this effect could explain the low b values seen for aftershocks of m 2 5 to 5 5 mainshocks in southern california documented in shearer 2012a however catalog incompleteness is most clearly seen following large earthquakes where it is generally attributed to network and or analyst overload and the overlapping codas of the main shock and its larger aftershocks e g kagan 2 004 peng et al 2007 these effects will be less important for smaller main shocks which have shorter codas and individually produce many fewer aftershocks above any threshold magnitude thus it is not clear if a relative lack of smaller aftershocks inthe 12hoursfollowingm2 5to5 5 mainshocks insouthern california is an artifact of catalog incompleteness or a real property of the earth resolving this issue may require new observational studies to search for the missing aftershocks that the catalog incompleteness model predicts should exist 2 one diagnostic property of catalog incompleteness is a flattening in the magnitude versus frequency curve at smaller magnitudes this can be seen in the concave down curvature of the synthetic aftershock dn dm curves in figures 1 and 2b of hanizl 2013 however the curvature is fairly subtle and comparisons to the corresponding data curves are inconclusive some amount of curvature is visible in the data plotted in hainzl s figure 3b but interestingly does not appear in the corresponding data curves plotted in figure 8 of shearer 2012a further study is warranted but resolving the exact shape of the dn dm curves may be difficult given the small differences that need to be resolved 3 i agree with hanizl 2013 that bath s law is subject to some uncertainty with respect to the space time windows used for its computation and that models with higher triggering productivities than those nominally consistent with baths law should be explored comparisons between the absolute numbers of aftershocks seen in the data versus those predicted by triggering simulations should ideally use the same time space windowing method for both data and synthetics thus it is potentially misleading to compare synthetic aftershock sequences with spatially windowed catalog aftershocks as is done in figure 3 of hanizl 2013 i attempted to take these data windowing effects into account in shearer 2012a which concludes that observed aftershock numbers for 2 5 m 5 5 main shocks are too large to be compatible with bath s law in a follow up paper shearer 2012b more completely explores the space time clustering of california earthquakes and reaches a similar conclusion that at least some of the temporal clustering of seismicity observed at short scales 0 5 5km does not appear to be caused by local earthquake triggering but instead reflects an underlying physical process that temporarily increases the seismicity rate such as is often hypothesized to drive earthquake swarms this conclusion is based on comparisons between data and synthetic triggering models over a wide range of scales which identify a number of models versus data differences but perhaps the strongest evidence supporting the conclusion is the anomalously high foreshock to aftershock ratio seen for the smaller earthquakes whichisa point ofagreement withhanizl 2013 4 additional tests of earthquake to earthquake triggering models versus seismic observations are warranted at a range of magnitudes and time distance scales it is important to understand where current models work and where they fail because their limitations provide clues about the underlying physical changes that drive earthquake activity

modeling tephra dispersal in absence of wind insights from the climactic phase of the 2450 bp plinian eruption of pululagua volcano ecuador the determination of eruptive parameters is crucial in volcanology not only to document past eruptions but also for tephra fallout hazard assessments in most tephra fallout studies eruptive parameters have been determined either by empirical techniques or analytical models but the uncertainty of such parameters is usually not well described we have applied both empirical and analytical models to characterize the climactic phase of the 2450 bp plinian eruption of pululagua bf2 layer and explore the variations in the total erupted mass column height and total grain size distribution both approaches yield comparable results in the total mass of tephra erupted 4 5 1 5 1011 kg while they show some discrepancies for the determination of the column height 36 20 km from empirical techniques and 30 20 km from analytical techniques the total grain size distribution of the bf2 layers varies with the different techniques used for the calculation and significantly affects the outputs of analytical models furthermore the determination of the total grain size distribution depends strongly on the number and spatial distribution of the sample location inverting tephra fallout deposits on the total accumulation or thickness gives a good constraint on the total mass erupted but not on the column height however inverting on individual grain size classes better constrains the possible range of column heights but cannot resolve particle release height results from the inversion on individual grain size classes show that large diffusion coefficients are necessary to model the bf2 layer and might be required to model proximal tephra deposits in order not to overestimate the total erupted mass additionally we used a statistical method smoothed bootstrap approach to quantify the uncertainty in eruptive parameters such as column height and total erupted mass our uncertainty analysis yields a mean total erupted mass of 4 5 0 3 1011 kg and a mean column height of 30 3 km results from the uncertainty analysis compare well with results from other approaches finally although the climactic phase of the 2450 bp plinian eruption of pululagua occurred in relatively calm atmospheric conditions our results show that the dispersion of the bf2 layer was influenced by slight northeasterly wind conditions

fiamme textures in volcanic successions flaming issues of definition and interpretation abstract fiamme are aligned flame like lenses found in welded ignimbrite fiamme also occur in welded pyroclastic fall deposits secondary welded pumice rich facies diagenetically altered and compacted non welded pumiceous volcaniclastic facies and lavas fiamme can be formed in a variety of ways the common genetic use of the term fiamme for pumice clasts that have undergone welding compaction is too narrow fiamme is best used as a descriptive term for elongate lenses or domains of the same mineralogy texture and composition which define a pre tectonic foliation and are separated by domains of different mineralogy texture or composition this descriptive term can be used regardless of the origin of the texture and remains appropriate for flattened pumice clasts in welded ignimbrite

statistical features of foreshocks in instrumental and etas catalogs we study the spatial distribution of earthquakes in temporal intervals before and after the occurrence of large shocks mainshocks in the magnitude range m in 2 5 for four different regional catalogs we find that the spatial organization of pre shock seismicity depends on the mainshock magnitude and is independent of the lower magnitude threshold these properties are found to be a stable feature of regional catalogs and cannot be reproduced by epidemic type aftershock sequence models our findings suggest that the area fractured during the mainshock is encoded in the foreshock spatial organization and therefore enhance the prognostic value of foreshocks

bimodal grain size distribution of chinese loess and its palaeoclimatic implications grain size analysis indicates that chinese loess generally shows a bimodal distribution with a coarse and a fine component the coarse component comprising the main part of the loess has pronounced kurtosis and is well sorted which is interpreted to be the product of dust storms generated by low altitude northwesterly winds its grain size reflects the strength of the low altitude circulation in the dust seasons of the year and its percentage provides an indicator of the source area aridity and the frequency of dust storms conversely the fine component has a wide grain size range and is poorly sorted sedimentary illustrations based on the grain size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high altitude westerly airstreams its grain size provides an estimate of the westerly air stream intensity the coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain size data and this procedure constitutes an approach for reconstructing the palaeowind system of northern china c 2003 elsevier b v all rights reserved

submarine deposits from pumiceous pyroclastic density currents traveling over water an outstanding example from offshore montserrat iodp 340 pyroclastic density currents have been observed to both enter the sea and to travel over water for tens of kilometers here we identified a 1 2 m thick stratified pumice lapilli ash cored at site u1396 offshore montserrat integrated ocean drilling program iodp expedition 340 as being the first deposit to provide evidence that it was formed by submarine deposition from pumice rich pyroclastic density currents that traveled above the water surface the age of the submarine deposit is ca 4 ma and its magma source is similar to those for much younger soufriere hills deposits indicating that the island experienced large magnitude subaerial caldera forming explosive eruptions much earlier than recorded in land deposits the deposit s combined sedimentological characteristics are incompatible with deposition from a submarine eruption pyroclastic fall over water or a submarine seafloor hugging turbidity current derived from a subaerial pyroclastic density current that entered water at the shoreline the stratified pumice lapilli ash unit can be subdivided into at least three depositional units with the lowermost one being clast supported the unit contains grains in five separate size modes and has a 12 phi range particles are chiefly subrounded pumice clasts lithic clasts crystal fragments and glass shards pumice clasts are very poorly segregated from other particle types and lithic clasts occur throughout the deposit fine particles are weakly density graded we interpret the unit to record multiple closely spaced 2 d hot pyroclastic density currents that flowed over the ocean releasing pyroclasts onto the water surface and settling of the various pyroclasts into the water column our settling and hot and cold flotation experiments show that waterlogging of pumice clasts at the water surface would have been immediate the overall poor hydraulic sorting of the deposit resulted from mixing of particles from multiple pulses of vertical settling in the water column attesting to complex sedimentation slow settling particles were deposited on the seafloor together with faster descending particles that were delivered at the water surface by subsequent pyroclastic flows the final sediment pulses were eventually deflected upon their arrival on the seafloor and were deposited in laterally continuous facies this study emphasizes the interaction between products of explosive volcanism and the ocean and discusses sedimentological complexities and hydrodynamics associated with particle delivery to water

comprehensive hydro geophysical prospecting to delineate fresh water zone in the coastal aquifer south india abstract the integrated hydrogeophysical surveys were used to discriminate between fresh and saline groundwater in the coastal aquifer zones of lower vellar river basin south india which is considered to be the main source of groundwater in the basin geologically the basin consists of tertiary and quaternary formation in order to delineate the freshwater aquifer zone sixty nine 69 ves locations were surveyed by schlumberger electrode arrangement and eight 8 scanning surveys were conducted by multi electrode scanning method the ves results reflect that the overall resistivity ranges from 0 01 to 12 670 m and thickness varies from 0 49 to 49 9 m with a maximum of four subsurface layers the dominant curve types are h and qh followed by kh 8 and k 6 the pseudo sections prepared to understand the variations of subsurface characteristics and to delineate potential fresh saline water aquifer zones in the basin whereas the scanning surveys results showed resistivity ranges from 1 to 500 m the resistivity 20 60 m was considered as freshwater aquifer zone and observed at six locations at varying depths the both the ves and scanning results were correlated with existing borewell lithology and it showed reliable matching the results of this survey identified the freshwater aquifer zones 20 60 m in central and south central part of the basin with high potential aquifer thickness and optimum yield this integrated hydrogeophysical methods proved to be an excellent solution for delineation of fresh water aquifer zone and could be applied to any other basins with similar lithological conditions

use of vertical electrical soundings to delineate seawater intrusion in a coastal area of byunsan korea to delineate spatial extent of seawater intrusion in a small experimental watershed in the coastal area of byunsan korea electrical resistivity surveys with some evaluation core drillings and chemical analysis of groundwaters were conducted the vertical electrical sounding ves method was applied which is useful to identify variations in electrical characteristics of layered aquifers the drilling logs identified a three layered subsurface including reclamation soil weathered layer and relatively fresh sedimentary bedrock the upper two layers are the main water bearing units in this area a total of 30 electrical sounding curves corresponded mostly to the h type and they were further divided into three classes highly conductive intermediate and low conductive according to the observed resistivity values of the most conductive weathered layer in addition groundwater samples from 15 shallow monitoring wells were analyzed and thus grouped into two types based on hco3 cl and ca na molar ratios with tds levels which differentiated groundwaters affected by seawater intrusion from those not or less affected according to relationships between the three classes of the sounding curves and groundwater chemistry locations of the monitoring wells with low hco3 cl and ca na ionic ratios coincided with the area showing the highly conductive type curve while those with the high ratios corresponded to the area showing low conductive curve type both the low electrical resistivity and the low ionic ratios indicated effects of seawater intrusion from this study it was demonstrated that the ves would be useful to delineate seawater intrusion in coastal areas

evidence for mogi doughnut behavior in seismicity preceding small earthquakes in southern california 1 we examine the average space time behavior of seismicity preceding m 2 5 earthquakes in southern california from 1981 to 2005 using a high resolution catalog and identify regions of enhanced activity in a 1 day period preceding larger earthquakes at distances comparable to their predicted source radii the difference in precursory behavior between large and small earthquakes is subtle but statistically significant when averaged over many earthquakes and it has similarities to the mogi doughnut seismicity pattern observed to occur prior to some m 6 and larger earthquakes these results indicate that many standard earthquake triggering models do not account for all of the processes involved in earthquake occurrence

applying a three dimensional velocity model waveform cross correlation and cluster analysis to locate southern california seismicity from 1981 to 2005 we compute high precision earthquake locations using southern california pick and waveform data from 1981 to 2005 our latest results are significantly improved compared to our previous catalog by the following 1 we locate events with respect to a new crustal p and s velocity model using three dimensional ray tracing 2 we examine six more years of waveform data and compute cross correlation results for many more pairs than our last analysis and 3 we compute locations within similar event clusters using a new method that applies a robust fitting method to obtain the best locations satisfying all the differential time constraints from the waveform cross correlation these results build on the relocated catalogs of hauksson and shearer 2005 and shearer et al 2005 and provide additional insight regarding the fine scale fault structure in southern california and the relationship between the san andreas fault saf and nearby seismicity in particular we present results for two regions in which the seismicity near the southern saf seems to align on dipping faults

simple relative space time scaling of electrical and electromagnetic depth sounding arrays implications for electrical static shift removal and joint dc tem data inversion with the most squares criterion a simple scaling relationship is shown to facilitate comparison correlation and integration of data recorded using the common experimental configurations in electrical and electromagnetic depth sounding applications of the scheme to field data from typical geological and landfill environments show that it is robust and where transient electromagnetic tem data are available enables easy identification and quantification of electrical static shift galvanic distortion in magnetotelluric and direct current dc sounding curves tem based procedures are suggested for both the direct removal of static shift in dc sounding curves and effective joint data inversion with the most squares criterion in the presence of static shift a case study of aquifer characterization using sounding data from borehole sites in the vale of york in england shows that static shift is a common problem in this glacial covered terrain and demonstrates the effectiveness of the proposed joint dc tem inversion strategy in handling distorted soundings

estimating depth of investigation in dc resistivity and ip surveys in this paper the term depth of investigation refers generically to the depth below which surface data are insensitive to the value of the physical property of the earth estimates of this depth for dc resistivity and induced polarization ip surveys are essential when interpreting models obtained from any inversion because structure beneath that depth should not be interpreted geologically we advocate carrying out a limited exploration of model space to generate a few models that have minimum structure and that differ substantially from the final model used for interpretation visual assessment of these models often provides answers about existence of deeper structures differences between the models can be quantified into a depth of investigation doi index that can be displayed with the model used for interpretation an explicit algorithm for evaluating the doi is presented the doi curves are somewhat dependent upon the parameters used to generate the different models but the results are robust

grain size distribution of volcaniclastic rocks 2 characterizing grain size and hydraulic sorting quantification of the grain size distribution of sediments allows interpretation of processes of transport and deposition jutzeler et al 2012 developed a technique to determine grain size distribution of consolidated clastic rocks using functional stereology allowing direct comparison between unconsolidated sediments and rocks here we develop this technique to characterize hydraulic sorting and infer transport and deposition processes we compare computed grain size and sorting of volcaniclastic rocks with field based characteristics of volcaniclastic facies for which transport and depositional mechanisms have been inferred we studied pumice rich subaqueous facies of volcaniclastic rocks from the oligocene ohanapecosh formation ancestral cascades washington usa pliocene dogashima formation izu peninsula honshu japan miocene manukau subgroup northland new zealand and the quaternary sierra la primavera caldera jalisco state mexico these sequences differ in bed thickness grading and abundance of matrix we propose to evaluate grain size and sorting of volcaniclastic deposits by values of their modes matrix proportion 2 mm f 1 and d16 instead of median diameter d50 and standard deviation parameters f 1 and d16 can be uniformly used to characterize and compare sieving and functional stereology data volcaniclastic deposits typically consist of mixtures of particles that vary greatly in density and porosity hydraulic sorting ratios can be used to test whether inferred density of mixed clast populations of pumice and dense clasts are hydraulically sorted with each other considering various types of transport under water evaluation of this ratio for our samples shows that most studied volcaniclastic facies are deposited by settling from density currents and that basal dense clast breccia are emplaced by shear rolling these hydraulic sorting ratios can be applied to any type of clastic rocks and indifferently on consolidated and unconsolidated samples

ranking welding intensity in pyroclastic deposits welding of pyroclastic deposits involves flattening of glassy pyroclasts under a compactional load at temperatures above the glass transition temperature progressive welding is recorded by changes in the petrographic e g fabric and physical e g density properties of the deposits mapping the intensity of welding can be integral to studies of pyroclastic deposits but making systematic comparisons between deposits can be problematical here we develop a scheme for ranking welding intensity in pyroclastic deposits on the basis of petrographic textural observations e g oblateness of pumice lapilli and micro fabric orientation and measurements of physical properties including density porosity point load strength and uniaxial compressive strength our dataset comprises measurements on 100 samples collected from a single cooling unit of the bandelier tuff and parallel measurements on 8 samples of more densely welded deposits the proposed classification comprises six ranks of welding intensity ranging from unconsolidated rank i to obsidian like vitrophyre rank vi and should allow for reproducible mapping of subtle variations in welding intensity between different deposits the application of the ranking scheme is demonstrated by using published physical property data on welded pyroclastic deposits to map the total accumulated strain and to reconstruct their pre welding thicknesses

combined time domain electromagnetic soundings and gravimetry to determine marine intrusion in a detrital coastal aquifer southern spain summary marine intrusion is undoubtedly the most serious problem facing coastal aquifers that are exploited for use it is also an excellent indicator of the state of the aquifers resources this work proposes the combined application of two complementary geophysical techniques as an effective method for locating the saline wedge on one hand time domain electromagnetic soundings are the most reliable geophysical method for determining low resistivity zones that usually correspond to the presence of seawater although in some cases low resistivities may be due to the properties of the substrate on the other hand gravimetry allows a precise determination of the depth of the aquifer basement thus resolving the above uncertainty information provided by the lithological columns from boreholes has also allowed great precision in the calibration of the results from both techniques this methodology has been applied to the motril salobrena detrital coastal aquifer which has had no problems of marine intrusion to date nonetheless changes in soil use brought about by housing developments golf courses and a proliferation of hothouse agriculture comprise significant shifts in aquifer use in addition the construction of a dam which is drastically reducing the main recharge of the aquifer the guadalfeo river makes it likely there will be profound hydrogeological changes delimiting the extent of the saline wedge is therefore a fundamental step towards quantifying the effects of both the dam and the changes in soil use seawater saturated zones have a resistivity ranging from 0 5 to 5 m detrital sediments 8 400 m carbonates 80 300 m and schists from 2 to 60 m the current position of the saline wedge has been located at 100 200 m from the coastline indicating a healthy state for the aquifer areas with wide and narrow mixing zones have been noted and related to differences in the hydrogeological characteristics of the aquifer

facies architecture of a continental below wave base volcaniclastic basin the ohanapecosh formation ancestral cascades arc washington usa the 800 m thick oligocene ohanapecosh formation records voluminous sedimentation of volcanic clasts in the ancestral cascades arc washington state usa most volcaniclastic beds are dominated by angular pumice clasts and fiamme of andesitic composition now entirely devitrified and altered all beds are laterally continuous and have uniform thickness fine sandstone and mudstone beds have features typical of deposits from low density turbidity currents and suspension settling erosion surfaces cross beds and evidence of bi directional oscillatory currents i e wave ripples and swaley and hummocky cross stratification are almost entirely absent we infer that the setting was subaqueous and below wave base the abundance of angular pumice clasts crystals and dense volcanic clasts and the extreme thickness of several facies suggest they were derived from magmatic volatile driven explosive eruptions the extremely thick beds are ungraded or weakly graded and lack evidence of hot emplacement suggesting deposition from subaqueous water supported high concentration volcaniclastic density currents some of the thickest beds contain coarse rounded dense clasts at their base and are interbedded with accretionary lapilli bearing mudstone these beds are interpreted to be deposits from subaqueous density currents fed by subaerial pyroclastic flows that crossed the shoreline shallow basaltic intrusions and mafic volcanic breccia composed of scoria lapilli indicate the presence of intra basinal scoria cones that may have been partly subaerial the range in facies in the ohanapecosh formation is typical of below wave base continental lacustrine basins that form in proximity to active volcanic arcs and includes eruption fed and resedimented facies extreme instantaneous aggradation rates are related directly to explosive eruptions and sediment pathways reflect the locations of active volcanoes in contrast to conventional sedimentation processes acting in non volcanic environments

multifractal omori law for earthquake triggering new tests on the california japan and worldwide catalogues summary the multifractal stress activated model is a statistical model of triggered seismicity based on mechanical and thermodynamic principles it predicts that above a triggering magnitude cut off m 0 the exponent p of the omori law for the time decay of the rate of aftershocks is a linear increasing function p m a 0 m b0 of the main shock magnitude m we previously reported empirical support for this prediction using the southern california earthquake center scec catalogue here we confirm this observation using an updated longer version of the same catalogue as well as new methods to estimate p one of this methods is the newly defined scaling function analysis sfa adapted from the wavelet transform this method is able to measure a mathematical singularity hence a p value erasing the possible regular part of a time series the sfa also proves particularly efficient to reveal the coexistence and superposition of several types of relaxation laws typical omori sequences and short lived swarms sequences which can be mixed within the same catalogue another new method consists in monitoring the largest aftershock magnitude observed in successive time intervals and thus shortcuts the problem of missing events with small magnitudes in aftershock catalogues the same methods are used on data from the worldwide harvard centroid moment tensor cmt catalogue and show results compatible with those of southern california for the japan meteorological agency jma catalogue we still observe a linear dependence of p on m b ut with a smaller slope the sfa shows however that results for this catalogue may be biased by numerous swarm sequences despite our efforts to remove them before the analysis

predictability in the epidemic type aftershock sequence model of interacting triggered seismicity 1 as part of an effort to develop a systematic methodology for earthquake forecasting we use a simple model of seismicity on the basis of interacting events which may trigger a cascade of earthquakes known as the epidemic type aftershock sequence model etas the etas model is constructed on a bare unrenormalized omori law the gutenberg richter law and the idea that large events trigger more numerous aftershocks for simplicity we do not use the information on the spatial location of earthquakes and work only in the time domain we demonstrate the essential role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source we offer an analytical approach to account for the yet unobserved triggered seismicity adapted to the problem of forecasting future seismic rates at varying horizons from the present tests presented on synthetic catalogs validate strongly the importance of taking into account all the cascades of still unobserved triggered events in order to predict correctly the future level of seismicity beyond a few minutes we find a strong predictability if one accepts to predict only a small fraction of the large magnitude targets specifically we find a prediction gain defined as the ratio of the fraction of predicted events over the fraction of time in alarms equal to 21 for a fraction of alarm of 1 a target magnitude m 6 an update time of 0 5 days between two predictions and for realistic parameters of the etas model however the probability gains degrade fast when one attempts to predict a larger fraction of the targets this is because a significant fraction of events remain uncorrelated from past seismicity this delineates the fundamental limits underlying forecasting skills stemming from an intrinsic stochastic component in these interacting triggered seismicity models quantitatively the fundamental limits of predictability found here are only lower bounds of the true values corresponding to the full information on the spatial location of earthquakes

geoelectrical and hydrogeochemical studies for delineating seawater intrusion in the outlet of wadi ham uae the quaternary aquifer of wadi ham uae has been overexploited during the last two decades to meet the increasing water demands as a result the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated in this paper a 2d earth resistivity survey was conducted in wadi ham in the area between fujairah and kalba to delineate the seawater intrusion existing monitoring wells were used to measure the horizontal and vertical variations in water salinity and thus to improve the interpretation of earth resistivity imaging data results of vertical electrical soundings and chemical analyses of collected water samples were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids this relationship was used along with the true resistivity sections resulting from the inversion of 2d resistivity data to identify three zones of water bearing formation fresh brackish and salt water zones along the four 2d resistivity profiles the depth to the fresh brackish interface exceeded 50 m at the western part of the area and was in the order of 10 m or less in the eastern side near the shoreline depth to the brackish saline water interface reached about 70 m in the western side and was in the order of 20 m in the eastern side the thickness of the fresh water zone decreases considerably in the farming areas toward kalba and thus the degree of seawater intrusion increases

constraints on the size of the smallest triggering earthquake from the epidemic type aftershock sequence model bath s law and observed aftershock sequences 1 the physics of earthquake triggering together with simple assumptions of self similarity imply the existence of a minimum magnitude m0 below which earthquakes do not trigger other earthquakes noting that the magnitude md of completeness of a seismic catalog is not in general the same as the magnitude m0 of the smallest triggering earthquake we compare observed aftershock sequence parameters with the predictions made by the epidemic type aftershock sequence model to constrain the value of m0 in particular we use quantitative fits to observed aftershock sequences from three previous studies as well as bath s law to obtain four estimates of m0 we show that the branching ratio n average number of triggered earthquakes per earthquake also equal to the fraction of aftershocks in a seismic catalog is the key parameter controlling the estimate of the minimum triggering magnitude m0 conversely physical upper bounds for m0 estimated from rate and state friction indicate that at the very least 55 of all earthquakes are aftershocks

grain size distribution of volcaniclastic rocks 1 a new technique based on functional stereology the power of explosive volcanic eruptions is reflected in the grain size distribution and dispersal of their pyroclastic deposits grain size also forms part of lithofacies characteristics that are necessary to determine transport and depositional mechanisms responsible for producing pyroclastic deposits however the common process of welding and rock lithification prevents quantification of grain size by traditional sieving methods for deposits in the rock record here we show that functional stereology can be used to obtain actual 3d volume fractions of clast populations from 2d cross sectional images tests made on artificially consolidated rocks demonstrate successful correlations with traditional sieving method we show that the true grain size distribution is finer grained than its representation on a random 2d section our method allows the original size of vesicular pumice clasts to be estimated from their compacted shapes we anticipate that the original grain size distribution of welded ignimbrites can also be characterized by this method our method using functional stereology can be universally applied to any type of consolidated weakly to non deformed clastic material regardless of grain size or age and therefore has a wide application in geology

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

quasi 2d inversion of dcr and tdem data for shallow investigations joint or sequential inversion of direct current resistivity dcr and time domain electromagnetic tdem data commonly are performed for individual soundings assuming layered earth models dcr and tdem have different and complementary sensitivity to resistive and conductive structures making them suitable methods for the application of joint inversion techniques this potential joint inversion of dcr and tdem methods has been used by several authors to reduce the ambiguities of the models calculated from each method separately a new approach for joint inversion of these data sets based on a laterally constrained algorithm was found the method was developed for the interpretation of soundings collected along a line over a 1d or 2d geology the inversion algorithm was tested on two synthetic data sets as well as on field data from saudi arabia the results show that the algorithm is efficient and stable in producing quasi 2d models from dcr and tdem data acquired in relatively complex environments

3d particle size distributions from 2d observations stereology for natural applications abstract we have developed a general formulation for stereological analysis of particle distributions which is applicable to any particle size or size distribution not limited to log normal unimodal etc we have applied numerical techniques to define intersection probability distributions for any shapes previously only known for spheres and quantified the errors involved in using spherical coefficients for various non spherical particles this stereological technique is based on knowing the probability distribution of random cross sections through various particles so that small circle cross sections can be subtracted from an observed population to provide the 3d size distribution of particles the results indicate that the most important parameter controlling calculated size distribution is particle aspect ratio for a distribution of particles with a specific aspect ratio or range of aspect ratios variations of particle form spherical vs cubic rectangular vs elliptical do not alter the results so the technique can be applied to a range of particle shapes applications can be made in a petrology volcanology and other fields only a few of which can also be treated using expensive x ray techniques

space time clustering of seismicity in california and the distance dependence of earthquake triggering 1 using two recent high resolution earthquake catalogs i examine clustering in california seismicity by plotting the average rate of earthquakes as a function of both space and time from target events of m 2 to 5 comparisons between pre and post target event activity can be used to resolve earthquake to earthquake triggering associated with target events of different magnitudes the results are more complicated than predicted by computer simulations of earthquake triggering that begin with background events occurring at random times in particular at least some of the temporal clustering of seismicity at short scales 0 1 to 5 km does not appear to be caused by local earthquake triggering but instead reflects an underlying physical process that temporarily increases the seismicity rate such as is often hypothesized to drive earthquake swarms earthquake triggering for m 4 5 earthquakes is only resolvable in average seismicity rates at times less than about one day and to distances of less than about 10 km and its linear density decreases as r 1 5 to r 2 5 significantly steeper than some previous studies have found

salt water intrusion mapping by geoelectrical imaging surveys the geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore water salinity a new field survey technique that can be used for environmental and geotechnical investigations has been developed this study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt water intrusion boundary in yan state of kedah northwest malaysia the technique was incorporated into these surveys and it has proved to be a robust method for accurately mapping the fresh water saline water boundary the resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the geological survey of malaysia at those sites

quantitative 3d petrography using x ray tomography application to bishop tuff pumice clasts abstract textures are traditionally studied using the petrographic microscope which limits observations to 2d sections of 3d objects given the difficulty in retrieving information on shapes sizes and spatial distribution of objects in 3d from random sections a method that can yield observations in 3d is highly desirable x ray tomography yields a 3d map of the linear x ray attenuation coefficient which is a function of the atomic number and density of the material and the x ray energy used based on the compositional contrasts between different phases various phases can be identified in a rock pumice clasts characterized by isolated crystals surrounded by a low density matrix are ideal for the application of this technique we present our first results obtained using x ray tomography for pumice clasts from the bishop tuff samples studied are from units f7 and f8 and are representative of the variability in density and crystal contents observed in the early erupted bishop tuff data were collected on the geosoilenvironcars beamline at the advanced photon source argonne national laboratory using a 22 kev monochromatic x ray beam image analysis was performed using the software blob3d brightness contrasts in the resulting images allow the separation of magnetite sanidine quartz including minor plagioclase glass and vesicles crystals smaller than 5 voxels in diameter cannot be quantified properly mostly due to noise in the images this constrains the spatial resolution of the resulting images such that there is a trade off between sample size and spatial resolution we employed two runs with samples of varying sizes 5 and 10 mm to obtain adequate resolution voxel sizes ca 8 and 17 m we have previously studied quartz size distributions in bishop pumice clasts using a crushing sieving and winnowing procedure the agreement between our new and previous results is excellent quartz size distributions obtained using the tomography data are concave upward on population density vs size plots and resemble the size distributions for all quartz crystals including both whole crystals and fragments these size distributions were probably generated by fragmentation through which large crystals were converted in a larger number of small crystals petrographic observations suggest fragmentation occurred mostly under magmatic conditions sanidine size distributions are similar to those observed for quartz magnetite size distributions are typically linear indicating a simple magmatic history in contrast with the tektosilicates

joint inversion of geophysical data summary by jointly inverting several different kinds of geophysical measurements at a site we avoid some of the ambiguity inherent in the individual methods we show how this can be done for the combination of dc resistivity and magnetotelluric measurements on a layered medium by considering a simple 3 layer model the combination resolves the resistivity of the thin resistive second layer even though neither of the two methods can do so alone the method is then applied to field data from a shallow sedimentary basin a blind zone occurs beneath a thick near surface conductive shale by a study of the eigenvalue structure of the model it can be seen that resolution in this zone would be slightly enhanced by higher frequency magnetotelluric data but additional dc data at larger spacing would yield no improvement

dynamics and deposits generated by the kos plateau tuff eruption controls of basal particle loss on pyroclastic flow transport the explosive eruption of voluminous silicic magmas often produces widespread and massive deposits formed from pyroclastic density currents while these punctuated events dramatically alter the landscape and have potential climate altering impact our understanding of the internal structure and transport dynamics of these eruptions is hampered by a lack of direct observations we utilize the natural boundary conditions encountered by the eruption of the kos plateau tuff to probe its internal structure as well as constrain the neotectonic activity in the region and eruption duration of this moderate to large 60 km3 event at the time of the eruption 161 ka the lower sea level in the mediterranean may have resulted in flows that traversed mostly land to the north of the eruptive vent while flows to the south may have encountered an expanse of water steep topography and overwater transport can impede the transport of the dense basal portions of the flow where particles make multiple or sustained contact with the bed we use an eulerian eulerian lagrangian computational approach coupled with overwater and overland boundary conditions including topography to determine the role of bed load versus suspended load in the transport of these flows we find that a ring vent structure and eruptive fluxes greater than 2 106 m3 s are required for the spatial distribution of the kpt the maximum grain size and deposit locations of the first voluminous ignimbrite unit d can be explained by suspended flow to the south consistent with overwater transport and bed load and suspended load transport to the north consistent with overland transport however the maximum lithic size for the largest and last ignimbrite unit e requires some bed load transport in all directions we propose that the boundary conditions were significantly altered during the course of the eruption through either the in filling of a shallow sea to the south or the development of a thick pumice raft to aid saltation on the basis of the inferred eruptive flux we estimate that the duration of the eruption climax in which most of the material was erupted likely only lasted from a few hours to a day

the spatial density of foreshocks 1 aftershocks follow a well defined spatial decay pattern in the intermediate field here i investigate the same pattern for foreshocks foreshock linear density decays as r 1 5 0 1 over distances r of 0 1 30 km for 15 minutes before magnitude 3 4 mainshocks this trend is the same as that of the aftershocks within the error of the measurement this consistency of spatial decay can be explained by the clustering inherent in earthquake interactions no additional preparatory process beyond earthquake triggering is necessary to explain the spatial decay

identifying seawater intrusion in coastal areas by means of 1d and quasi 2d joint inversion of tdem and ves data abstract seawater intrusion is an increasingly widespread problem in coastal aquifers caused by climate changes sea level rise extreme phenomena like flooding and droughts and groundwater depletion near to the coastline to evaluate and mitigate the environmental risks of this phenomenon it is necessary to characterize the coastal aquifer and the salt intrusion geophysical methods are the most appropriate tool to address these researches among all geophysical techniques electrical methods are able to detect seawater intrusions due to the high resistivity contrast between saltwater freshwater and geological layers the combination of two or more geophysical methods is recommended and they are more efficient when both data are inverted jointly because the final model encompasses the physical properties measured for each methods in this investigation joint inversion of vertical electric and time domain soundings has been performed to examine seawater intrusion in an area within the ferragudo albufeira aquifer system algarve south of portugal for this purpose two profiles combining electrical resistivity tomography ert and time domain electromagnetic tdem methods were measured and the results were compared with the information obtained from exploration drilling three different inversions have been carried out single inversion of the ert and tdem data 1d joint inversion and quasi 2d joint inversion single inversion results identify seawater intrusion although the sedimentary layers detected in exploration drilling were not well differentiated the models obtained with 1d joint inversion improve the previous inversion due to better detection of sedimentary layer and the seawater intrusion appear to be better defined finally the quasi 2d joint inversion reveals a more realistic shape of the seawater intrusion and it is able to distinguish more sedimentary layers recognised in the exploration drilling this study demonstrates that the quasi 2d joint inversion improves the previous inversions methods making it a powerful tool applicable to different research areas

vesiculation and fragmentation history in a submarine scoria cone forming eruption an example from nishiizu izu peninsula japan an uplifted 50 m thick half dissected submarine emplaced below wave base scoria cone occurs as dipping beds in coastal outcrops at nishiizu on the izu peninsula in japan concentrically outward dipping weakly stratified ungraded framework supported thin to very thick beds consist of brown coarse tuff to scoria lapilli tuff with outsized fluidal bombs throughout accessory lithic clasts chiefly occur in the lowermost visible beds scoria bombs have quenched margins weak bread crust textures and their vesicle number densities decrease inward which is indicative of fast surface cooling composite textures in the scoria bombs indicate recycling and agglutination of quenched and semi molten pyroclasts at the submarine vent in contrast to weak concentric gradations in vesicle size distribution in the bombs lapilli have asymmetrical gradients in vesicle size distribution indicating that they are fragments of coarser quenched lumps three grain size modes characterise the nishiizu brown scoria with coarse magma lumps ejected during magmatic fragmentation and quench jointed upon contact with seawater to be subsequently fragmented into lapilli and coarse ash by various styles of fragmentation where seawater plays a critical role the cone was constructed by slow moving fallout fed granular flow creep fed directly by suspension settling focused at the crater rim but extending onto the cone flanks with only minor resedimentation by granular flows nishiizu deposits yield an exceptional record of eruption and sedimentation dynamics during submarine cone building activity and in this study we compare their vesiculation and fragmentation mechanisms with those of potential subaerial analogues

piecewise 1d laterally constrained inversion of resistivity data in a sedimentary environment layered models are often capable of representing the actual geology more accurately than smooth minimum structure models furthermore interval thicknesses and resistivities are often the parameters to which non geophysicist experts can relate and base decisions on when using them in waste site remediation groundwater modelling and physical planning we present a laterally constrained inversion scheme for continuous resistivity data based on a layered earth model 1d all 1d data sets and models are inverted as one system producing layered sections with lateral smooth transitions the models are regularized through laterally equal constraints that tie interface depths and resistivities of adjacent layers prior information e g originating from electric logs migrates through the lateral constraints to the adjacent models making resolution of equivalences possible to some extent information from areas with well resolved parameters will migrate through the constraints in a similar way to help resolve the poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result examples from synthetic 2d models show that the model recognition of a sublayered 2d wedge model is improved using the laterally constrained inversion approach when compared with a section of combined 1d models and when compared with a 2d minimum structure inversion case histories with data from two different continuous dc systems support the conclusions drawn from the synthetic example

hydrogeophysical exploration of three dimensional salinity anomalies with the time domain electromagnetic method tdem summary the time domain electromagnetic method tdem is widely used in groundwater exploration and geological mapping applications tdem measures subsurface electrical conductivity which is strongly correlated with groundwater salinity tdem offers a cheap and non invasive option for mapping saltwater intrusion and groundwater salinization traditionally tdem data is interpreted using one dimensional layered earth models of the subsurface however most saltwater intrusion and groundwater salinization phenomena are characterized by three dimensional anomalies to fully exploit the information content of tdem data in this context three dimensional modeling of the tdem response is required we present a finite element solution for three dimensional forward modeling of tdem responses from arbitrary subsurface electrical conductivity distributions the solution is benchmarked against standard layered earth models and previously published three dimensional forward tdem modeling results concentration outputs from a groundwater flow and salinity transport model are converted to subsurface electrical conductivity using standard petrophysical relationships tdem responses over the resulting subsurface electrical conductivity distribution are generated using the three dimensional tdem forward model the parameters of the hydrodynamic model are constrained by matching observed and simulated tdem responses as an application example a field dataset of ground based tdem data from an island in the okavango delta is presented evaporative salt enrichment causes a strong salinity anomaly under the island we show that the tdem field data cannot be interpreted in terms of standard one dimensional layered earth tdem models because of the strongly three dimensional nature of the salinity anomaly three dimensional interpretation of the field data allows for detailed and consistent mapping of this anomaly and makes better use of the information contained in the tdem field dataset

omori utsu law c values associated with recent moderate earthquakes in japan we investigate the early aftershock activity associated with four moderate earthquakes m w 6 6 6 7 that occurred recently in japan for each aftershock sequence we examine continuous high pass filtered seismograms recorded at seismic stations nearby the main fault to identify as many early events as possible the magnitude of these events is calibrated using aftershocks that are listed in the earthquake catalog of japan meteorological agency jma the analysis of the aftershock decay rates reveals a power law time dependence with a scaling exponent close to 1 0 that starts from about one minute from the mainshock our results demonstrate that the c value of the omori utsu law is very small although a lower bound is not established due to completeness problems in the first minute after the mainshock and statistical fluctuations

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

image analysis and circular statistics for shape fabric analysis applications to lithified ignimbrites computer assisted image analysis can be successfully used to derive quantitative textural data on pyroclastic rock samples this method provides a large number of different measurements such as grain size particle shape and 2d orientation of particle main axes directional or shape fabric automatically and in a relatively short time orientation data reduction requires specific statistical tests mainly devoted to defining the kind of particle distribution pattern the possible occurrence of preferred particle orientation the confidence interval of the mean direction and the degree of randomness with respect to pre assigned theoretical frequency distributions data obtained from image analysis of seven lithified ignimbrite samples from the vulsini volcanic district central italy are used to test different statistics and to provide insight about directional fabrics first the possible occurrence of a significant deviation from a theoretical circular uniform distribution was evaluated by using the rayleigh and tukey 2 tests then the kuiper test was performed to evaluate whether or not the observation fits with a unimodal von mises like theoretical frequency distribution finally the confidence interval of mean direction was calculated with the exception of one sample fpd10 which showed a well developed bimodality all the analysed samples display significant anisotropic and unimodal distributions the minimum number of measurements necessary to obtain reasonable variabilities of the calculated statistics and mean directions was evaluated by repeating random collections of the measured particles at increments of 100 particles for each sample although the observed variabilities depend largely on the pattern of distribution and an absolute minimum number cannot be stated approximately 1500 2000 measurements are required in order to get meaningful mean directions for the analysed samples

geologic history of martian regolith breccia northwest africa 7034 evidence for hydrothermal activity and lithologic diversity in the martian crust the timing and mode of deposition for martian regolith breccia northwest africa nwa 7034 were determined by combining petrography shape analysis and thermochronology nwa 7034 is composed of igneous impact and brecciated clasts within a thermally annealed submicron matrix of pulverized crustal rocks and devitrified impact volcanic glass the brecciated clasts are likely lithified portions of martian regolith with some evidence of past hydrothermal activity represented lithologies are primarily ancient crustal materials with crystallization ages as old as 4 4 ga one ancient zircon was hosted by an alkali rich basalt clast confirming that alkalic volcanism occurred on mars very early nwa 7034 is composed of fragmented particles that do not exhibit evidence of having undergone bed load transport by wind or water the clast size distribution is similar to terrestrial pyroclastic deposits we infer that the clasts were deposited by atmospheric rainout subsequent to a pyroclastic eruption s and or impact event s although the ancient ages of igneous components favor mobilization by impact s despite ancient components the breccia has undergone a single pervasive thermal event at 500 800 c evident by groundmass texture and concordance of 1 5 ga dates for bulk rock k ar u pb in apatite and u pb in metamict zircons the 1 5 ga age is likely a thermal event that coincides with rainout breccia lithification we infer that the episodic process of regolith lithification dominated sedimentary processes during the amazonian epoch the absence of pre amazonian high temperature metamorphic events recorded in ancient zircons indicates source domains of static southern highland crust punctuated by episodic impact modification

resistivity structure of unzen volcano derived from time domain electromagnetic tdem survey abstract time domain electromagnetic tdem surveys were carried out around unzen volcano shimabara peninsula south west japan in 2001 and 2002 in the eastern part of the peninsula the surveys were a completion of the previously interpreted tdem data collected from surveys in 1995 in the western part of the peninsula interpretation of the recorded transient magnetic fields resulted in a general feature of the resistivity structure which are composed of three main layers a resistive surface layer a conductive layer below 10 m from about sea level to 2 5 km below the surface and a third resistive layer the conductive layer is considered to be a complex of water saturated and altered layers which spreads widely beneath shimabara peninsula the spatial conductance distribution shows a w e trending pattern of high conductance from tachibana bay to the summit of unzen fugen dake this evidence indicates that volcanic gas was supplied to shallow layer in the western part of the peninsula which is in accordance with the path of magma migration derived from seismic and deformation studies another high conductance zone was also found near mayu yama in the eastern part of shimabara peninsula indicating magma degassing process due to the possibility of the presence of a magma system beneath it

mainshocks are aftershocks of conditional foreshocks how do foreshock statistical properties emerge from aftershock laws 1 the inverse omori law for foreshocks discovered in the 1970s states that the rate of earthquakes prior to a mainshock increases on average as a power law 1 tc t p of the time to the mainshock occurring at tc here we show that this law results from the direct omori law for aftershocks describing the power law decay 1 t tc p of seismicity after an earthquake provided that any earthquake can trigger its suit of aftershocks in this picture the seismic activity at any time is the sum of the spontaneous tectonic loading and of the activity triggered by all preceding events weighted by their corresponding omori law the inverse omori law then emerges as the expected in a statistical sense trajectory of seismicity conditioned on the fact that it leads to the burst of seismic activity accompanying the mainshock in particular we predict and verify by numerical simulations on the epidemic type aftershock sequence etas model that p is always smaller than or equal to p and a function of p of the b value of the gutenberg richter law gr and of a parameter quantifying the number of direct aftershocks as a function of the magnitude of the mainshock the often documented apparent decrease of the b value of the gr law at the approach to the mainshock results straightforwardly from the conditioning of the path of seismic activity culminating at the mainshock however we predict that the gr law is not modified simply by a change of b value but that a more accurate statement is that the gr law gets an additive or deviatoric power law contribution with exponent smaller than b and with an amplitude growing as a power law of the time to the mainshock in the space domain we predict that the phenomenon of aftershock diffusion must have its mirror process reflected into an inward migration of foreshocks toward the mainshock in this model foreshock sequences are special aftershock sequences which are modified by the condition to end up in a burst of seismicity associated with the mainshock foreshocks are not just statistical creatures but are genuine forerunners of large shocks as shown by the large prediction gains obtained using several of their qualifiers

seismicity analysis through point process modeling a review the occurrence times of earthquakes can be considered to be a point process and suitable modeling of the conditional intensity function of a point process is useful for the investigation of various statistical features of seismic activity this manuscript summarizes likelihood based methods of analysis of point processes and reviews useful models for particular analyses of seismicity most of the analyses can be implemented by the computer programs published by the author and collaborators

submarine eruption fed and resedimented pumice rich facies the dogashima formation izu peninsula japan in the izu peninsula japan the pliocene pumice rich dogashima formation 4 55 0 87 ma displays exceptional preservation of volcaniclastic facies that were erupted and deposited in a below wave base marine setting it includes high concentration density current deposits that contain clasts that were emplaced hot indicating an eruption fed origin the lower part of the dogashima 2 unit consists of a very thick sequence 1 m pumice and ash rich bed overlying the breccias may be derived from delayed settling of pyroclasts from suspension in dogashima 1 and 2 thick cross and planar bedded facies composed of sub rounded pumice clasts are intercalated with eruption fed facies implying inter eruptive mass wasting on the flank of a submarine volcano and reworking and resedimentation by high energy tractional currents in a below wave base environment

particle sizes of andesitic ash fallout from vertical eruptions and co pyroclastic flow clouds volcan de colima mexico we report particle size distributions for andesitic ash fall from vertical eruptions and clouds above block and ash fl ows at volcan de colima mexico during 2004 2006 we analyzed 17 samples using laser diffraction 11 from vertical eruptions and 6 from block and ash fl ows copyroclastic fl ow ash vertical eruptions produce well sorted fall deposits whereas co pyroclastic fall deposits are poorly sorted with high proportions of very fi ne grained ash 30 m statistical analysis shows particle size distributions of vertical eruptions are more leptokurtic peaked than co pyroclastic samples deconvolution of grain size histograms shows that copyroclastic samples have at least one subpopulation with a mode of 8 3 8 7 2 4 3 1 m estimates of the number of particles in different size ranges show that co pyroclastic samples contain much greater numbers of very fi ne particles than vertical eruption samples our results provide no direct evidence that milling or comminution produces hazardous fi ne ash particles in pyroclastic fl ows but are consistent with that interpretation

crystal size distributions csd in three dimensions insights from the 3d reconstruction of a highly porphyritic rhyolite growth histories and residence times of crystals in magmatic systems can be revealed by studying crystal sizes size distributions and shapes in this contribution serial sectioning has been employed on a sample of porphyritic rhyolite from a permo carboniferous laccolith from the halle volcanic complex germany to reconstruct the distribution of felsic phenocrysts in three dimensions in order to determine their true shapes sizes and three dimensional size distributions a model of all three phenocryst phases quartz plagioclase k feldspar with 217 crystals and a larger model containing 1599 k feldspar crystals was reconstructed in three dimensions the first model revealed a non touching framework of crystals in three dimensions suggesting that individual crystals grew freely in the melt prior to quenching of the texture however crystal shapes are complex and show large variation on a zingg diagram intermediate over long axis plotted against short over intermediate axis they often do not resemble the crystallographic shapes expected for phenocrysts growing unhindered from a melt indicating complex growth histories in contrast the three dimensional size distribution is a simple straight line with a negative slope stereologically corrected size distributions from individual sections compare well with stereologically corrected size distributions obtained previously from the same sample however crystal size distribution csd data from individual sections scatter considerably it is shown that csds can be robustly reproduced with a sampling size of greater than 200 crystals the kind of shape assumed in stereological correction of csds however has a large influence on the calculation and estimation of crystal residence times

textural studies of vesicles in volcanic rocks an integrated methodology abstract vesicles in volcanic rocks are frozen records of degassing processes in magmas for this reason their sizes spatial arrangements numbers and shapes can be linked to physical processes that drive magma ascent and eruption although numerous techniques have been derived to describe vesicle textures there is no standard approach for collecting analyzing and interpreting vesicular samples here we describe a methodology for techniques that encompass the entire data acquisition process from sample collection to quantitative analysis of vesicle size and number carefully chosen samples from the lower mean and higher density vesicularity endmembers are characterized using image nesting strategies we show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes a new program foams was designed to perform the quantification stage from vesicle measurement to distribution plots altogether this approach allows substantial reduction of image acquisition and processing time while preserving enough user control to ensure the validity of obtained results we present three cameo investigations on basaltic lava flows scoria deposits and pumice layers to show that this methodology can be used to quantify a wide range of vesicle textures which preserve information on a wide range of eruptive conditions

short term properties of earthquake catalogs and models of earthquake source i review the short term properties of earthquake catalogs in particular the time and size distributions and the completeness of the early part of aftershock sequences for strong shallow earthquakes i determine the parameters of the omori and gutenberg richter laws for aftershocks close in time to a mainshock aftershock sequences of large earthquakes in southern california 1952 kern county 1992 joshua tree landers big bear sequence 1994 northridge and 1999 hector mine recorded in the caltech catalog are analyzed to demonstrate that at the beginning of these series many small earthquakes are absent from the catalog the number of missing earthquakes increases with the magnitude range of a catalog and for some data sets exceeds the number of aftershocks close to a mainshock listed in a catalog comparing global earthquake catalogs harvard centroid moment tensor and preliminary determination of epicenter with local data sets indicates that the catalogs based on longer period waves miss many early aftershocks even when their magnitudes are well above the stated magnitude threshold such short term incompleteness may introduce significant biases to the statistical analysis of the seismicity pattern in particular for branching models of earthquake occurrence incorporating the omori law for such models the likelihood function strongly depends on close aftershocks i review the techniques to alleviate this problem analyzing the source rupture process of several recent large earthquakes suggests that rupture propagation is highly inhomogeneous in space time and focal mechanism these random variations in the rupture process can be viewed as an extension of the aftershock stochastic generating mechanism toward the origin time of a mainshock i review various models of the earthquake rupture process and suggest that fractal distributions of microevents in time space and focal mechanism constitute the development of an earthquake the final identification of an individual earthquake depends on both objective and subjective factors manuscript received 21 may 2003

quasi 3d modeling of airborne tem data by spatially constrained inversion we present a new methodology spatially constrained inversion sci that produces quasi 3d conductivity modeling of electromagnetic em data using a 1d forward solution spatial constraints are set between the model parameters of nearest neighboring soundings data sets models and spatial constraints are inverted as one system the constraints are built using delaunay triangulation which ensures automatic adaptation to data density variations model parameter information migrates horizontally through spatial constraints increasing the resolution of layers that would be poorly resolved locally sci produces laterally smooth results with sharp layer boundaries that respect the 3d geological variations of sedimentary settings sci also suppresses the elongated artifacts commonly seen in interpretation results of profile oriented data sets in this study sci is applied to airborne time domain em data but it can also be implemented with other ground based or airborne data types

application of geophysical methods for the investigation of the large gravitational mass movement of sechilienne france several geophysical techniques electromagnetic profiling electrical tomography seismic refraction tomogra phy and spontaneous potential and seismic noise measurement were applied in the investigation of the large gravita tional mass movement of sechilienne france the aim of this study was to test the ability of these methods to characterize and delineate the rock mass affected by this complex movement in mica schists whose lateral and vertical limits are still uncertain a major observation of this study is that all the zones strongly deformed previously and at present by the movement are characterized by high electrical resistivity values 3 k m in contrast to the undis turbed mass which exhibits resistivity values between a few hundred and 1 k m as shown by the surface observa tions and the seismic results this resistivity increase is due to a high degree of fracturing associated with the creation of air filled voids inside the mass other geophysical techniques were tested along a horizontal transect through the movement and an outstanding coherency appeared between the geophysical anomalies and the displacement rate curve these preliminary results illustrate the benefits of combined geophysical techniques for characterizing the rock mass in volved in the movement results also suggest that monitoring the evolution of the rock mass movement with time lapse geophysical surveys could be beneficial resume plusieurs techniques geophysiques profil electromagnetique tomographie electrique tomographie sismique et potentiel spontane et bruit de fond sismique ont ete appliquees pour la reconnaissance du grand mouvement de ter rain de sechilienne france situe dans des micaschistes l objectif de cette etude etait de tester ces methodes geophy siques afin de caracteriser et de delimiter la masse de roche affectee par ce mouvement complexe dont la limite laterale reste incertaine l etude a montre que toutes les zones tres deformees encore actuellement et dans le passe par le mouvement sont caracterisees par de fortes valeurs de resistivite electrique superieur ea3k m tandis que dans la zone non perturbee les valeurs de resistivite sont de quelques centaines de m a1k m comme le montrent les observations de surface et les profils de tomographie sismique cette augmentation de resistivite est due a une frac turation importante associee a la creation de vides remplis d air au sein du massif les techniques electromagnetiques ps et de mesure de bruit ont ete testees le long d un profil transversal recoupant le mouvement une correlation remar quable est obtenue entre les anomalies geophysiques et le taux de deplacement ces resultats preliminaires soulignent l interet de combiner les methodes geophysiques pour caracteriser la masse de roche impliquee dans le mouvement et pour determiner l evolution du mouvement par un suivi temporel des parametres geophysiques mots cles mouvement gravitaire methodes geophysiques sechilienne meric et al 1115

decay of aftershock density with distance does not indicate triggering by dynamic stress the most predictable earthquakes are aftershocks which invariably follow mainshocks so what triggers aftershocks it was recently argued controversially that the decay of aftershocks with distance from the main earthquake could only be explained by dynamic triggering keith richards dinger and colleagues have tested this hypothesis and conclude that the observed decay can be better explained by static triggering resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard it has recently been argued that the decay of aftershocks with distance from the main earthquake could be explained only by dynamic triggering this hypothesis has now been tested the conclusion being that the observed decay can be better explained by static triggering resolving whether static1 2 3 or dynamic4 5 6 7 8 stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard9 felzer and brodsky10 examined the distance distribution of earthquakes occurring in the first five minutes after 2 m 3 and 3 m 4 mainshocks and found that their magnitude m 2 aftershocks showed a uniform power law decay with slope 1 35 out to 50 km from the mainshocks from this they argued that the distance decay could be explained only by dynamic triggering here we propose an alternative explanation for the decay and subject their hypothesis to a series of tests none of which it passes at distances more than 300 m from the 2 m 3 mainshocks the seismicity decay 5 min before the mainshocks is indistinguishable from the decay five minutes afterwards indicating that the mainshocks have no effect at distances outside their static triggering range omori temporal decay the fundamental signature of aftershocks is absent at distances exceeding 10 km from the mainshocks finally the distance decay is found among aftershocks that occur before the arrival of the seismic wave front from the mainshock which violates causality we argue that felzer and brodsky10 implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second and that the first of two shocks in a creep or intrusion driven swarm triggers the second when this need not be the case

delineation of saltwater intrusion into the freshwater aquifer of lekki peninsula lagos nigeria recently the deterioration of water quality in the coastal zones of lekki peninsula area of lagos due to saltwater infiltration into the freshwater aquifer has become a major concern with the aim of providing valuable information on the hydrogeologic system of the aquifers the subsurface lithology and delineating the groundwater salinity vertical electrical resistivity ves sounding survey was carried out utilizing surface schlumberger electrode arrays and electrode spacing varying between 1 and 150m the dc resistivity surveys revealed significant variations in subsurface resistivity also the ves resistivity curves showed a dominant trend of decreasing resistivity with depth thus increasing salinity in general the presence of four distinct resistivity zones were delineated viz the unconsolidated dry sand a having resistivity values ranging between 125 and 1 028 m represent the first layer the fresh water saturated soil zone b having resistivity values which correspond to 32 256 m is the second layer the third layer zone c is interpreted as the mixing transition zone of fresh with brackish groundwater the resistivity of this layer ranges from 4 to 32 m while layer four zone d is characterized with resistivities values generally below 4 m reflecting an aquifer possibly containing brine the rock matrix salinity and water saturation are the major factors controlling the resistivity of the formation moreover this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface dc resistivity method

basalt vesicularity as a measure of atmospheric pressure and palaeoelevation the pressure in and thus the size of a bubble in a lava flow is determined by the atmospheric pressure and the hydrostatic pressure of the overlying lava if atmospheric sea level pressure is known or assumed vesicle size distributions in basalt flows can thus be used as an indicator of the palaeoelevation of emplacement1 here we show by analysis of the vesicle size distribution of basalt samples collected from the summit and base of mauna loa volcano in hawaii that the technique provides estimates of ambient pressure that are accurate to within 0 1 bar and thus estimates of elevation with a resolution of about 1 400m this palaeoaltimetric technique should find useful application in palaeogeographical reconstruction2 for times when sea level pressure was similar to the present value conversely if the elevation of emplacement is known our technique should be able to provide a measure of sea level palaeopressure unlike palaeo botanical methods for estimating elevations3 6 this method does not have to assume a relationship between temperature and altitude on the other hand its use is restricted to lava flows that have had a simple emplacement history

combined microgravity electrical resistivity tomography and induced polarization to detect deeply buried caves algaidilla cave southern spain abstract the suitability of the combined microgravity and electrical tomography to detect and characterize caves deeply buried in limestones is tested we have selected the buried algaidilla cave in the estepa range western betic cordillera which is partially submerged below the water table and which was intersected between 26 and 66 m in depth by two boreholes at that location microgravity electrical resistivity tomography ert and induced polarization ip data was collected along four profiles algaidilla cave is associated with a 0 5 mgal residual gravity anomaly minimum microgravity models reveal an approximately horizontal n s elongated shape with a maximum length of 150 m and a width of 40 m resistivity variations provide information on the cave sectors remaining above as well as below the water table forward modeling and depth of investigation doi support the suitability of ert to constrain the cave geometry the cave is identified as having an intermediate to low resistivity feature which approximately matches the 250 m contour line along its ceiling in addition induced polarization models show high chargeability anomalies probably associated with decalcification clays the location and approximately geometry of algaidilla cave estimated from geophysical modeling suggests that nearby overburden may develop cave ins and collapse sinkholes microgravity is proved as a powerful tool to detect caves at this depth but this method alone fails to estimate the geometry ert results delineate the cavity both above and below the water table although the deepest sectors of the models should be interpreted with caution since they are less constrained by the data below the water table the cavity shows great resistivity contrast with regard to the background carbonate in addition this study points out the usefulness of the ip method for detecting decalcification clays often present at the base of karstic caves

quantitative analysis of the joint variability of rock texture and composition in thin section the generalized griffiths descriptor and its application to sediment generation from granitoids abstract the general protocol for quantitative petrographic description of clastic sediments envisioned by j c griffiths approximately 60 years ago is built on specification of the following five statistically independent fundamental properties of aggregates modal composition spatial arrangement size distributions shape distributions and orientation distributions of the elements each element is represented by a grain falling into one of an exhaustive set of petrographic classes we introduce the so called generalized griffiths descriptor ggd which extends this protocol to igneous and metamorphic rocks statistical independence of the fundamental properties permits rigorous testing of petrogenetic hypotheses as well as simulation of rocks based on any conceivable combination of them the benefits of a unifying scheme for description of crystalline parent rocks and their weathering products are illustrated by exploratory analysis of a petrographic data set derived from five granodiorites from across north america comprising the parent rocks and three size fractions coarse medium and fine of their detritus compositional data analysis is used to estimate sediment generation and evolution sge trajectories for each of the plutons sampled the bulk mineral composition and the mineral composition of the rock fragment assemblage display a common trend of relative depletion of quartz and k feldspar with decreasing grain size compensated for by relative enrichment of biotite and accessory minerals the evolution of crystal interface composition suggests that the balance between chemical and mechanical weathering may be reflected in relative stabilities of crystal interfaces we propose a computationally efficient stereological inversion procedure for estimating the parameters of crystal size probability distributions in rocks based on the assumption of lognormality the lognormal distribution is an acceptable default model for crystal size in granitoids at the level of individual thin sections about 87 passes the tests for lognormality but less so at the level of entire plutons only 62 success ratio the current implementation of the ggd is not yet complete because it deals explicitly with the first three fundamental properties only as a consequence of adopting the simplifying assumption that all elements which make up a rock are spherical shape and orientation distributions may be included in future implementations of the ggd dedicated data sets comprising sediments generated from a single parent rock under different conditions will be needed to advance sge studies by shedding more light on the balance between chemical and mechanical weathering

comparison of short term and time independent earthquake forecast models for southern california we have initially developed a time independent forecast for southern california by smoothing the locations of magnitude 2 and larger earthquakes we show that using small m 2 earthquakes gives a reasonably good prediction of m 5 earthquakes our forecast outperforms other time independent models kagan and jackson 1994 frankel et al 1997 mostly because it has higher spatial resolution we have then developed a method to estimate daily earthquake probabilities in south ern california by using the epidemic type earthquake sequence model kagan and knopoff 1987 ogata 1988 kagan and jackson 2000 the forecasted seismicity rate is the sum of a constant background seismicity proportional to our time independent model and of the aftershocks of all past earthquakes each earthquake triggers aftershocks with a rate that increases exponentially with its magnitude and decreases with time following omori s law we use an isotropic kernel to model the spatial distribution of aftershocks for small m 5 5 mainshocks for larger events we smooth the density of early aftershocks to model the density of future aftershocks the model also assumes that all earthquake magnitudes follow the gutenberg richter law with a uniform b value we use a maximum likelihood method to estimate the model parameters and test the short term and time independent forecasts a retro spective test using a daily update of the forecasts between 1 january 1985 and 10 march 2004 shows that the short term model increases the average probability of an earthquake occurrence by a factor 11 5 compared with the time independent forecast

comment on self similar earthquake triggering bath s law and foreshock aftershock magnitudes simulations theory and results for southern california by p m shearer 1 shearer 2012 finds three differences of the seismicity clustering in southern california compared to self similar triggering models i a significantly lower b value for the aftershocks ii a too large aftershock number and iii a too large foreshock aftershock ratio to be consistent with the bath law based on these observations the author concluded that the observed seismicity is not in agreement with self similarity triggering and or the observed clustering is not primarily caused by earthquake to earthquake triggering however i show that the observed lower b value is likely related to incomplete recordings after mainshocks and that the apparently too large aftershock number does not disprove the self similarity thus only the enhanced foreshock to aftershock ratio seems to indicate some discrepancy to self similar triggering

foreshocks explained by cascades of triggered seismicity 1 the observation of foreshocks preceding large earthquakes and the suggestion that foreshocks have specific properties that may be used to distinguish them from other earthquakes have raised the hope that large earthquakes may be predictable among proposed anomalous properties are the larger proportion than normal of large versus small foreshocks the power law acceleration of seismicity rate as a function of time to the mainshock and the spatial migration of foreshocks toward the mainshock when averaging over many sequences using southern california seismicity we show that these properties and others arise naturally from the simple model that any earthquake may trigger other earthquakes without arbitrary distinction between foreshocks aftershocks and mainshocks we find that foreshock precursory properties are independent of the mainshock size this implies that earthquakes large or small are predictable to the same degree as seismicity rate is predictable from past seismicity by taking into account cascades of triggering the cascades of triggering give rise naturally to long range and long time interactions which can explain the observations of correlations in seismicity over surprisingly large length scales