crustal structure evolution and volcanic unrest of the alban hills central italy the alban hills a quaternary volcanic center lying west of the central apennines 15 25 km southeast of rome last erupted 19 ka and has produced approximately 290 km3 of eruptive deposits since the inception of volcanism at 580 ka earthquakes of moderate intensity have been generated there at least since the roman age modern observations show that intermittent periods of swarm activity originate primarily beneath the youngest features the phreatomagmatic craters on the west side of the volcano results from seismic tomography allow identification of a low velocity region perhaps still hot or partially molten more than 6 km beneath the youngest craters and a high velocity region probably a solidified magma body beneath the older central volcanic construct thirty centimeters of uplift measured by releveling supports the contention that high levels of seismicity during the 1980s and 1990s resulted from accumulation of magma beneath these craters the volume of magma accumulation and the amount of maximum uplift was probably at least 40 106 m3 and 40 cm respectively comparison of newer levelings with those completed in 1891 and 1927 suggests earlier episodes of uplift the magma chamber beneath the western alban hills is probably responsible for much of the past 200 ka of eruptive activity is still receiving intermittent batches of magma and is therefore continuing to generate modest levels of volcanic unrest bending of overburden is the most likely cause of the persistent earthquakes which generally have hypocenters above the 6 km deep top of the magma reservoir in this view the most recent uplift and seismicity are probably characteristic and not precursors of more intense activity

stress sensitivity of fault seismicity a comparison between limited offset oblique and major strike slip faults we present a new three dimensional inventory of the southern san francisco bay area faults and use it to calculate stress applied principally by the 1989 m 7 1 loma prieta earthquake and to compare fault seismicity rates before and after 1989 the major high angle right lateral faults exhibit a different response to the stress change than do minor oblique right lateral thrust faults seismicity on oblique slip faults in the southern santa clara valley thrust belt increased where the faults were unclamped the strong dependence of seismicity change on normal stress change implies a high coefficient of static friction in contrast we observe that faults with significant offset 50 100 km behave differently microseismicity on the hayward fault diminished where right lateral shear stress was reduced and where it was unclamped by the loma prieta earthquake we observe a similar response on the san andreas fault zone in southern california after the landers earthquake sequence additionally the offshore san gregorio fault shows a seismicity rate increase where right lateral oblique shear stress was increased by the loma prieta earthquake despite also being clamped by it these responses are consistent with either a low coefficient of static friction or high pore fluid pressures within the fault zones we can explain the different behavior of the two styles of faults if those with large cumulative offset become impermeable through gouge buildup coseismically pressurized pore fluids could be trapped and negate imposed normal stress changes whereas in more limited offset faults fluids could rapidly escape the difference in behavior between minor and major faults may explain why frictional failure criteria that apply intermediate coefficients of static friction can be effective in describing the broad distributions of aftershocks that follow large earthquakes since many of these events occur both inside and outside major fault zones

aggradation surfaces and implications for displacement rates along the wairarapa fault southern north island new zealand abstract three last glaciation aggradation surfaces waiohine 11 1ka rata c30 ka and porewa c60 ka are displaced by the wairarapa fault wairarapa valley southern part of the north island of new zealand dextral displacements of125 5m waiohine 385 5m rata and c770 800 m porewa indicate an average uniform dextral slip rate along the wairarapa fault of 11 5 mm yr during at least the last 60 ka this rate accounts for a third of the total oblique convergence rate of 33 mm yr for the australian and pacific plates along the hikurangi trough to the east of the north island vertical displacement rates along the wairarapa fault are variable and range from 0 1 to 1 9 mm yr where the wairarapa fault cuts aggradation gravels on greywacke basement this variation is controlled by growing bulges developed on the upthrown nw side as a result of left sidesteps of the fault trace where the fault cuts gravels overlying tertiary rocks it is sometimes upthrown to the se and at one locality the aggradation surfaces indicate the possibility of two reversals of vertical movement within the last 60 ka reversals in throw may be related to differential movement on fault clusters at depth that are located near or on growing anticlines in tertiary strata above upbulged greywacke undermass the pattern of long term

viscoelastic coupling model of the san andreas fault along the big bend southern california the big bend segment of the san andreas fault is the 300 km long segment in southern california that strikes about n65 w roughly 25 counterclockwise from the local tangent to the small circle about the pacific north america pole of rotation the broad distribution of deformation of trilateration networks along this segment implies a locking depth of at least 25 km as interpreted by the conventional model of strain accumulation continuous slip on the fault below the locking depth at the rate of relative plate motion whereas the observed seismicity and laboratory data on fault strength suggest that the locking depth should be no greater than 10 to 15 km the discrepancy is explained by the viscoelastic coupling model which accounts for the viscoelastic response of the lower crust thus the broad distribution of deformation observed across the big bend segment can be largely associated with the san andreas fault itself not subsidiary faults distributed throughout the region the working group on california earthquake probabilities 1995 in using geodetic data to estimate the seismic risk in southern california has assumed that strain accumulated off the san andreas fault is released by earthquakes located off the san andreas fault thus they count the san andreas contribution to total seismic moment accumulation more than once leading to an overestimate of the seismicity for magnitude 6 and greater earthquakes in their type c zones

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

genesis of zeolites in the neapolitan yellow tuff geological volcanological and mineralogical evidence the study proposes a model by which a thick succession of volcanic tuffs can be zeolitized by alteration of pyroclastic material in the presence of sufficient eruptive water and at temperatures close to water vapour condensation in the case of phreatomagmatic products the model simplifies interpretation of problematic deposits that exhibit pronounced vertical and lateral variation in lithification grade a major feature of the model is that thick zeolitized tuffs can be formed during emplacement of pyroclastic products in marked contrast to later alteration in an open hydrologic system geological volcanological and mineralogical data for the neapolitan yellow tuff a widespread trachytic pyroclastic deposit outcropping around campi flegrei southern italy have been used to infer the physico chemical conditions that determined mineral genesis this tuff shows a reduction in lithification grade towards the base top and with distance from the vent and very variable zeolitization within the lithified portion we suggest that during initial emplacement the erupted products chilled against the ground inhibiting zeolite crystallization during rapid deposition of the thick wet succession thermal insulation allowed the persistence of elevated temperatures for a time sufficient for enhancement of hydration dissolution processes in the volcanic glass the highly reactive alkali trachytic glass quickly buffered the acid ph of the system favouring phillipsite crystallization followed by chabazite nucleation the variable zeolite content reflects fluctuating emplacement conditions e g changes in water content and temperature cooling of the upper and relatively thin distal deposits inhibited the zeolitization process thereby preserving the primary unlithified deposit

a 3 d viscoelastoplastic model for simulating long term slip on non planar faults summary the geometrical complexity of non planar faults is known to affect not only fault slip rates but also crustal deformation and seismicity in the surrounding region but implementing non planar faults in numerical models has been challenging we have developed a 3 d viscoelastoplastic finite element model to simulate long term steady state fault slip along conceptual restraining bends and crustal deformation around them by incorporating plastic yielding in both fault zones and the surrounding crust this model can predict the quasi steady state stress field and strain partitioning while avoiding pathological stress build up encountered in traditional viscoelastic models here we detail the formulation of this model and explore major model parameters the model results show that restraining bends tend to impede fault slip increase shear stress in the surrounding crust and localize strain in a pair of belts off the fault zone these effects are enhanced by high viscosity in the lower crust and upper mantle high aspect ratio of bend width over fault length fast relative motion of fault blocks and high fault friction these model results may help explain the diffuse deformation surrounding the big bend of the san andreas fault and the more confined deformation around the lebanon bend of the dead sea fault

forecast experiment do temporal and spatial b value variations along the calaveras fault portend m 4 0 earthquakes 1 the power law distribution of earthquake magnitudes and frequencies is a fundamental scaling relationship used for forecasting however can its slope b value be used on individual faults as a stress indicator some have concluded that b values drop just before large shocks others suggested that temporally stable low b value zones identify future large earthquake locations this study assesses the frequency of b value anomalies portending m 4 0 shocks versus how often they do not i investigated m 4 0 calaveras fault earthquakes because there have been 25 over the 37 year duration of the instrumental catalog on the most active southern half of the fault with that relatively large sample i conducted retrospective time and space earthquake forecasts i calculated temporal b value changes in 5 km radius cylindrical volumes of crust that were significant at 90 confidence but these changes were poor forecasters of m 4 0 earthquakes m 4 0 events were as likely to happen at times of high b values as they were at low ones however i could not rule out a hypothesis that spatial b value anomalies portend m 4 0 events of 20 m 4 shocks that could be studied 6 to 8 depending on calculation method occurred where b values were significantly less than the spatial mean 1 to 2 happened above the mean and 10 to 13 occurred within 90 confidence intervals of the mean and were thus inconclusive thus spatial b value variation might be a useful forecast tool but resolution is poor even on seismically active faults

factors controlling normal fault offset in an ideal brittle layer we study the physical processes controlling the development and evolution of normal faults by analyzing numerical experiments of extension of an ideal two dimensional elastic plastic brittle layer floating on an inviscid fluid the yield stress of the layer is the sum of the layer cohesion and its frictional stress faults are initiated by a small plastic flaw in the layer we get finite fault offset when we make fault cohesion decrease with strain even in this highly idealized system we vary six physical parameters the initial cohesion of the layer the thickness of the layer the rate of cohesion reduction with plastic strain the friction coefficient the flaw size and the fault width we obtain two main types of faulting behavior 1 multiple major faults with small offset and 2 single major fault that can develop very large offset we show that only two parameters control these different types of faulting patterns 1 the brittle layer thickness for a given cohesion and 2 the rate of cohesion reduction with strain for a large brittle layer thickness 22 km with 44 mpa of cohesion extension always leads to multiple faults distributed over the width of the layer for a smaller brittle layer thickness the fault pattern is dependent on the rate of fault weakening a very slow rate of weakening leads to a very large offset fault and a fast rate of weakening leads to an asymmetric graben and eventually to a very large offset fault when the offset is very large the model produces major features of the pattern of topography and faulting seen in some metamorphic core complexes

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

magnetic fabric and implications for pyroclastic flow and lahar emplacement albano maar italy 1 the albano polygenetic maar is the youngest eruptive center of the quiescent colli albani volcano located near the city of rome the most recent activity of the albano maar extends from 23 ka into the holocene and produced the small volume basic phreatomagmatic peperino albano pa ignimbrite and more recently phreatomagmatic surge and lahar deposits related to the overspill of the albano maar lake we have performed an anisotropy of magnetic susceptibility ams study in order to define the relationships between the magnetic fabric and the flow mechanisms of the pa and of the phreatomagmatic deposits and lahars ams results indicate different transport and or depositional systems for the veneer and valley pond facies in the pa ignimbrite and for the lahar deposits ams also demonstrates that flow directions are mainly controlled by the paleotopography the paleotopographic control has been interpreted in terms of talweg sedimentation even at proximal locations where deposition occurs from dilute pyroclastic flows furthermore ams results clearly evidence a southward provenance for holocene post pa ignimbrite units cropping out in the ciampino plain and confirm their origin from albano maar lake overspill we demonstrate that ams is a reliable marker to determine paleoflow directions also in small volume phreatomagmatic ignimbrites and in syneruptive lahar deposits and can be successfully used to define their depositional systems

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

major constraints on the use of radiocarbon dating for tephrochronology it is well recognised that radiocarbon dating is a powerful tool capable of providing a detailed chronostratigraphy for areas that have been subjected to recurrent volcanic activity during late pleistocene and holocene time in such geological contexts carbon bearing materials suitable for 14c dating are for the most part refractory components of pedosphere e g paleosol humic matter and organic detritus e g charred uncharred remains of higher plants which occur within the tephra suites since such materials derive initially from atmospheric carbon dioxide as well as record significant lapses in volcanic activity it is then often assumed that these conditions comply ideally with the fundamental requirements of the radiocarbon dating theory however two recent 14c dating programmes based on materials from the volcanic districts of the phlegrean fields and the island of procida campania southern italy yielded evidence to the contrary and in turn gave rise to concern over the validity of the 14c dating method when applied in volcanic regions in particular it has been found that the conventional radiocarbon ages recorded by modern tree leaves from the caldera of solfatara volcano range from modern to ca 5000 yr bp furthermore the magnitude of the age anomaly is determined by the pattern of localised dilution of the mean atmospheric 14c concentration by juvenile 14c free and 13c enriched carbon dioxide issuing from nearby volcanic vents in the case of paleosols a series of 14c measurements on different chemical fractions isolated from the humic matter in a suite of four paleosol horizons entrained in tephra deposits at procida island yielded for each paleosol horizon a systematic ca 2000 yr scatter of 14c ages it is shown that such intra soil age differences which reflect the origin and history of humic constituents can be used to afford a better definition of the true paleosol age

the albano maar lake colli albani volcano italy recent volcanic activity and evidence of pre roman age catastrophic lahar events abstract the evaluation of volcanic hazard in the roman hinterland related to the quiescent colli albani volcano has recently been the subject of renewed attention and several interpretations by many authors however very little was known of the recent history of the volcano making such interpretations rather speculative the most recent activity of colli albani volcano originated from the albano polygenetic maar lake which erupted several phreatomagmatic units the most recent of which the peperino albano ignimbrite has been dated at around 25 ka an area of several square kilometers centered around albano lake is presently the site of shallow and frequent seismic activity and gaseous emission as well as hydrothermal activity and is therefore considered the most prone to geologic hazards this paper presents new stratigraphic and geomorphologic data as well as age determinations that allow rejuvenation of the most recent activity of the colli albani volcano and particularly the albano maar lake to the holocene this study allows for the first time to identify a potential hazard related to the albano maar lake withdrawal interpreted to be related to endogenous causes namely co 2 emission the main results of the study are 1 the peperino albano is not as is generally believed the last phreatomagmatic eruption from the colli albani volcano a previously unrecognized phreatomagmatic surge deposit has been identified overlying the paleosol at the top of the peperino albano and related lahar deposits 2 two lahar deposits separated by paleosols top the stratigraphic succession and are dispersed only to the nw corresponding to the lowest point of the maar rim indicating that catastrophic hydrologic events occurred at the albano lake in recent times rapid and substantial lake level variations and lake withdrawal are reported by roman historians and recorded by the stratigraphy of the albano lake lacustrine sediments 3 microfracturing related to seismic energy release is linked to sudden variation of co 2 flow and upwelling of hydrothermal fluids these occurrences across the lake are the likely causes that triggered during holocene several episodes of lake withdrawal rising the water table and probably triggering convective rollover of the lake water

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

deformation of rock a pressure sensitive dilatant material permanent plastic deformation of rock materials in the brittle regime cataclastic flow is modelled here in terms of mohr coulomb behaviour in which all three of the parameters cohesion friction angle and dilation angle follow hardening or softening evolution laws with both plastic straining and increases in confining pressure the physical basis for such behaviour is provided by a sequence of uniaxial shortening experiments performed byedmond andpaterson 1972 at confining pressures up to 800 mpa on a variety of materials including gosford sandstone and carrara marble these triaxial compression experiments are important for the large range of confining pressures covered and for the careful recording of data during deformation particularly volume change of the specimens both materials are pressure sensitive and dilatant it is therefore possible to derive from these experiments a set of material parameters which allow a preliminary description of the deformation behaviour in terms of a non associated mohr coulomb constitutive model thus providing the first constitutive modelling of geological materials in the brittle ductile regime these parameters are used as input to a finite difference numerical code flac with the aim of investigating how closely this numerical model simulates real material behaviour upon breakdown of homogeneous deformation the mechanical and macrostructural behaviour exhibited by the numerical model is in close agreement with the physical results in that the stress strain curves are duplicated together with localization behaviour the results of the modelling illustrate how the strength of the upper crust may be described by two different but still pressure dependent models the linear shear stress normal stress relationship of amontons that is byerlee s law and a non linear mohr coulomb constitutive model both include parameters of friction and both describe brittle deformation behaviour consideration of the non linear bulk material model allows investigation of the geologic regimes which favour localization of the deformation over a continuing homogeneous deformation more complex models are required to describe the deformation of rock with increasing depth and temperature as the behaviour becomes increasingly temperature sensitive and rate dependent

initiation of the san jacinto fault and its interaction with the san andreas fault insights from geodynamic modeling the san andreas fault saf is the pacific north american plate boundary yet in southern california a significant portion of the relative plate motion is accommodated by the san jacinto fault sjf here we investigate the initiation of the sjf and its interaction with the saf in a three dimensional visco elasto plastic finite element model the model results show that the restraining bend of the southern saf causes strain localization along the sjf thus may have contributed to its initiation slip on the sjf tends to reduce slip rate on the saf and enhance deformation in the eastern california shear zone the initiation of the sjf and its interaction with the saf reflect the evolving plate boundary zone as it continuously seeks the most efficient way to accommodate the relative plate motion

identifying geomorphic features using landsat 5 tm data processing techniques on lesvos greece in order to delineate the geomorphic features of the island of lesvos greece fieldwork and digital satellite landsat 5 tm data analysis were combined the main image analysis techniques involved in this study were 1 principal component analysis pca and 2 false color composite fcc these techniques led to the creation of enhanced satellite images with respect to the topographic and geomorphologic characteristics of the island the final digitally enhanced landsat 5 tm images have been used to interpret and map the geomorphic features of lesvos ground truthing of image data led to the identification of the following geomorphic units dissected metamorphic terrains lava plateaus colluvial foothills alluvial plains including coastal and fluvial and eroded regions underlain by ignimbrite and welded tuff lineaments detected in this study were coincident with 1 mapped contacts or faults 2 extensions of previously mapped faults or 3 previously undetected geologic features including faults tectonic contacts or formational contacts

facies associations of rain generated versus crater lake withdrawal lahar deposits from quaternary volcanoes central italy abstract two syneruption lahar deposit successions from quaternary italian volcanoes are presented displaying different facies associations interpreted to reflect different water sources the lahar deposits associated with the white trachytic tuff cupa wttc ignimbrites from the quaternary roccamonfina volcano located 150 km to the southeast of rome have been interpreted in terms of rain generated lahars the wttc ignimbrites are made of more than 1 km 3 of loose pumice and lava lithic debris emplaced along the hyperbolic slope of the volcano at ca 300 ka during an interglacial period characterised by mild and wet climate the lahar deposits are organised in a coarsening upward aggradational and back stepping succession of medium to thick bedded progressively juvenile poorer non cohesive debris flow to fluvial deposits box shaped channels cut the wttc ignimbrites along the steep upper slopes channels are filled with lava lithic rich fluvial to hyperconcentrated flow sand and conglomerate which are interpreted as lag deposits related to processes of bulking due to the removal of light pumice and ash debris from the upper slope along the lower slopes of the volcano and in the surrounding ring plains where the average slope inclination decreases to few degrees lahars emplaced an aggradational succession of bedded ash rich hyperconcentrated flow deposits entirely derived from wttc components the succession coarsens upward with increasing presence of lava rich conglomerate lenses fluvial in origin interpreted to record the progressive restoration through time of the drainage network the succession is cut by incised gullies filled with polygenetic fluvial deposits which indicate the restoration of intererruption condition by contrast the ca 23 ka small volume peperino albano phreatomagmatic eruption from colli albani volcano located 30 km to the southeast of rome emplaced a valley ponded block and ash ignimbrite which along the western slope of the volcano grades laterally into a single far reaching thick lahar deposit the lahar deposit coarsens upward from coarse ash hyperconcentrated flow deposit into a lithic block rich debris flow deposit this lahar deposit has been interpreted to be directly derived from a pyroclastic flow and particularly related to the entrance of the pyroclastic flow into a pre existing maar crater lake along the pyroclastic flow path the basal sand size hyperconcentrated flow deposit is interpreted to represent early deposition from the fast frontal flood wave whereas the coarse lithic rich debris flow deposit at the top may represent the rear of the lahar the separation of the two facies can be related to processes of hydraulic sieving operated by the lake water which couples with ash particles leaving behind the coarser fraction

inception of the eastern california shear zone and evolution of the pacific north american plate boundary from kinematics to geodynamics 1 the san andreas fault saf is the transform boundary between the pacific and the north american plates yet up to 25 of the relative plate motion is now accommodated by the eastern california shear zone ecsz here we investigate the inception of the ecsz and its geodynamic interactions with the saf using a 3 d viscoelastoplastic finite element model for a given fault configuration of the plate boundary zone the model simulates long term slip on the faults and plastic strain outside the faults our results show that the formation of the big bend of the saf around 5 12 ma impeded fault slip and localized strain along the ecsz causing its inception development of the ecsz was further enhanced by the activation of the garlock fault gf and lithospheric weakening caused by the encroachment of the basin and range extension similarly the san jacinto fault sjf in southern california developed along a belt of localized strain which resulted from the formation of the restraining bend along the san bernardino mountains segment of the saf 2 myr ago once activated the sjf reduced slip on both the southern saf and the ecsz across the mojave desert these results indicate causative relationship between the saf and the ecsz the inception of the ecsz and other young faults is the consequence of the evolving saf plate boundary zone that continuously adjusts itself to accommodate the relative plate motion

numeric modeling of the strain accumulation and release of the 2008 wenchuan sichuan china earthquake abstract as one of the most devastating earthquakes the 2008 wenchuan earthquake occurred on imbricate high angle listric reverse faults the faults dip 70 above 15 km depth become 30 to 40 below 15 km depth and presumably root into a subhorizontal brittle ductile transition zone below about 22 2 km depth in this paper we use the viscoelastic finite element method to simulate coseismic deformation and stress change and recurrence of major earthquakes associated with the high angle listric reverse fault our modeling shows that changes of coseismic equivalent stress mainly occur in the vicinity of the seismogenic fault especially the hanging wall of the fault in the depth range above 12 km modeled coseismic slip distribution and modeled average recurrent interval corroborate with geological geodetic and seismological observations we modeled 250 000 yr slip history of the fault slip the result shows that minor slips which obey slip predictable model take place on 30 40 dipping fault plane at depth below 15 km when the isotropic stress accumulation on the gentle fault reaches the critical level the entire gently dipping fault ruptures to form a large slip the large slips on the gently dipping fault comply with a time predictable model of recurrences these larger slips on the gently dipping fault occur simultaneously with slips on the steeply dipping fault and might have triggered slips on the steeply dipping fault to form great events such as the 2008 wenchuan earthquake

evolution of stress in southern california for the past 200 years from coseismic postseismic and interseismic stress changes summary the seismicity of southern california results from stresses that arise from the relative motion of the pacific and north american plates being accommodated along the san andreas fault saf system and the eastern california shear zone ecsz here we calculate how the stress field in southern california has evolved over the past two centuries due to interseismic loading as inferred from current gps observations of surface velocities from redistributions of static stress induced by large m w 6 5 earthquakes since the 1812 wrightwood quake and postseismic viscoelastic relaxation associated with these events that serves to transfer coseismic stresses from the deep warm lower crust and upper mantle to the overlying seismogenic upper crust we calculate coulomb stress changes on vertical strike slip faults striking parallel to the saf and at the hypocenters on the rupture planes of all m w 6 events over the past two centuries our results suggest that the 1857 m w 8 2 fort tejon earthquake by far the largest event to have occurred in the region over the past two centuries had a profound influence on the state of stress in southern california during the 19th century inducing significant stress increases to the north parkfield region and adjoining creeping saf and south southern saf and san jacinto fault and stress relief across the southern ecsz these stress changes were then greatly magnified by postseismic relaxation through the early part of the 20th century slow interseismic build up of stress further loads all major strike slip faults and works to reload the areas of the ecsz where stress was relieved by the 1857 quake our calculations suggest that only 56 of hypocenters were pushed closer to failure by preceding coseismic stress changes suggesting that the occurrence of large earthquakes is not strongly determined by coseismic coulomb stress changes this percentage rises to 70 when postseismic stress changes are also considered our calculations demonstrate the importance of postseismic viscoelastic relaxation in the redistribution of stress following large earthquakes we find however that postseismic processes associated with events more than about a decade old are near completion and thus do not significantly influence the regional velocity field presently observed in southern california

a three dimensional semianalytic viscoelastic model for time dependent analyses of the earthquake cycle 1 exploring the earthquake cycle for large complex tectonic boundaries that deform over thousands of years requires the development of sophisticated and efficient models in this paper we introduce a semianalytic three dimensional 3 d linear viscoelastic maxwell model that is developed in the fourier domain to exploit the computational advantages of the convolution theorem a new aspect of this model is an analytic solution for the surface loading of an elastic plate overlying a viscoelastic half space when fully implemented the model simulates 1 interseismic stress accumulation on the upper locked portion of faults 2 repeated earthquakes on prescribed fault segments and 3 the viscoelastic response of the asthenosphere beneath the plate following episodic ruptures we verify both the analytic solution and computer code through a variety of 2 d and 3 d tests and examples on the basis of the methodology presented here it is now possible to explore thousands of years of the earthquake cycle along geometrically complex 3 d fault systems

shear test results for cohesion and friction coefficients for different granular materials scaling implications for their usage in analogue modelling abstract laboratory tests have been carried out on dry granular materials such as quartz sand glass microspheres and sugar with different grain size rounding and sphericity the measurements have been made with a simple shear test machine for different values of normal stress 50 900 pa shear stress has been plotted against normal stress in order to determine the cohesion and coefficient of internal friction for the investigated materials resulting values of cohesion and coefficient of internal friction are mainly dependent on rounding and sphericity while grain size has a less significant influence further the behaviour of the materials for very small normal stresses 0 400 pa is more complex than previously assumed the fracture envelopes for all materials investigated are convex outward for this small range and converge towards a straight failure envelope with increasing normal stress finally in extensional faulting experiments there is no significant change in fault dip with increasing depth therefore the non linear behaviour for small normal stresses is best described as a dependence of the cohesion on the normal stress and not as a dependence of the coefficient of internal friction on the normal stress values for cohesion increase from 0 pa 15 pa at zero normal stress to 137 247 pa 15 pa for normal stresses greater than 250 400 pa the results show that well rounded spherical material is better suited to model brittle behaviour of rocks in crustal and lithospheric scale analogue models than less well rounded material since it has a smaller cohesion and a coefficient of internal friction which is closer to values of natural rocks

rollover in volcanic crater lakes a possible cause for lake nyos type disasters abstract seemingly stably stratified fluids that is a heavier layer of fluid underlying an upper layer of lighter fluid can overturn if there is a heat flux through the system such events are termed rollover in the engineering literature occurring for instance in liquid natural gas tanks they take place as well in lakes and ponds in all such cases the stratification starts off with the heavier more dense fluid underlying lighter convection driven mixing at the stratification interface due to the heat flux as well as other processes serves to minimize with time the stabilizing density differences which may eventually cause the stratification to invert if gas has been contained under pressure in the lower layer this gas may explosively vent from the fluid as it suddenly rises to the top such as occurs in liquid natural gas tanks where rollover is a hazard these processes are quantifiable and are applied here to various scenarios that might refer to volcanic crater lakes whose lower layers are charged with volatiles provided herein are some examples of calculated conditions and calculated time of evolution leading to rollover with attendant release of gases from supersaturated ascending fluids these calculations suggest rollover could occur in volcanic lakes the august 1986 gas release at lake nyos is employed as an example these estimates were made taking note that water is commonly supersaturated in co2

viscoelastic shear zone model of a strike slip earthquake cycle i examine the behavior of a two dimensional 2 d strike slip fault system embedded in a 1 d elastic layer schizosphere overlying a uniform viscoelastic half space plastosphere and within the boundaries of a finite width shear zone the viscoelastic coupling model of savage and prescott 1978 considers the viscoelastic response of this system in the absence of the shear zone boundaries to an earthquake occurring within the upper elastic layer steady slip beneath a prescribed depth and the superposition of the responses of multiple earthquakes with characteristic slip occurring at regular intervals so formulated the viscoelastic coupling model predicts that sufficiently long after initiation of the system 1 average fault parallel velocity at any point is the average slip rate of that side of the fault and 2 far field velocities equal the same constant rate because of the sensitivity to the mechanical properties of the schizosphere plastosphere system i e elastic layer thickness plastosphere viscosity this model has been used to infer such properties from measurements of interseismic velocity such inferences exploit the predicted behavior at a known time within the earthquake cycle by modifying the viscoelastic coupling model to satisfy the additional constraint that the absolute velocity at prescribed shear zone boundaries is constant i find that even though the time averaged behavior remains the same the spatiotemporal pattern of surface deformation particularly its temporal variation within an earthquake cycle is markedly different from that predicted by the conventional viscoelastic coupling model these differences are magnified as plastosphere viscosity is reduced or as the recurrence interval of periodic earthquakes is lengthened application to the interseismic velocity field along the mojave section of the san andreas fault suggests that the region behaves mechanically like a 600 km wide shear zone accommodating 50 mrn yr fault parallel motion distributed between the san andreas fault system and eastern california shear zone in the viscoelastic coupling model savage and prescott 1978 time dependent deformation around a strike slip fault zone is realized by loading subsequent rupture and relaxation of a fault present in a schizosphere elastic upper crust overlying a ductile plastosphere assuming a two dimensional 2 d geometry periodic rupture of the fault and identical slip interseismic deformation is obtained as the superposition of viscoelastic relaxation of the plastosphere summed over the infinity of past periodic earthquakes this model yields far field interseismic motions equal to 1 2 of the average slip rate v0 imposed on the fault thus even when no external mechanism is invoked to load the fault i e when the locked portion of the fault penetrates the entire schizosphere the model satisfies the expectation of rigid plate like behavior in the far field in addition when periodic coseismic offsets are factored in the model predicts that the time averaged fault parallel velocity of each point is vol2 depending on location

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

fem simulation of interseismic and coseismic deformation associated with the 2008 wenchuan earthquake abstract we make use of two step modeling to simulate inter and coseismic deformation within one seismic cycle by means of visco elastic finite element method fem the first step is to perform inversion to find the optimum modeling parameters by fitting the observed interseismic deformation then the model continues to produce a major seismic event to simulate the wenchuan earthquake the model results show that in order to fit the observed interseismic deformation it needs a soft lower crust and upper mantle beneath the eastern tibet and a very strong lithosphere of the sichuan basin the computed interseismic strain accumulation in the lower crust beneath the eastern tibet is much faster than that in the other regions especially the elastic strain energy density rate esed accumulates very rapidly in and around the longmen shan fault in the depth above 30 km that may explain why the great wenchuan earthquake occurs in the region of such a slow surface deformation rate simulations of coseismic processes reveal relationships among slip acceleration normal stress and shear stress changes on surface of the seismogenic fault coseismic slip appears to initiate in the gently dipping section of the fault but primary slips coseismic rupture on both gently dipping and steeply dipping sections take place simultaneously minor fault slip accelerations decrease normal stress on fault surface to reduce frictional strength of fault and in general increase shear stress on fault surface to enhance tectonic stress on the fault to drive the fault further slips both processes facilitate major slip or rupture on the listric reverse fault coseismic slip distribution also suggest that an important role of high angle listric reverse faulting is to transfer overwhelming horizontal deformation of the eastern tibet into significant vertical displacement in the longmen shan during the 2008 wenchuan earthquake

seismic cycle and rheological effects on estimation of present day slip rates for the agua blanca and san miguel vallecitos faults northern baja california mexico 1 geodesy can be used to infer long term fault slip rates assuming a model for crust and upper mantle rheology we examine the sensitivity of fault slip rate estimates to assumed rheology for the agua blanca and san miguel vallecitos faults in northern baja california mexico part of the pacific north america plate boundary zone the agua blanca fault is seismically quiet but offset alluvial fans indicate young activity current seismicity is confined to the nearby san miguel vallecitos fault a small offset fault better aligned with plate motion gps measurements between 1993 and 1998 suggest that both faults are active with a combined slip rate of 4 8 mm yr 1 regardless of rheological model however slip rate estimates for the individual faults are sensitive to assumed rheology elastic half space models yield 2 3 mm yr 1 for the agua blanca fault and somewhat faster rates for the san miguel vallecitos fault 2 4 mm yr 1 with uncertainties of about 1 mm yr 1 models incorporating viscoelastic rheology and seismic cycle effects suggest a faster slip rate for the agua blanca fault 6 1 mm yr 1 and a slower rate for the san miguel vallecitos fault 1 1 mm yr 1 in better agreement with geological data but these rates are sensitive to assumed rheology numerical simulations with a finite element model suggest that for similar rheological and friction conditions slip on the san miguel vallecitos fault should be favored due to better alignment with plate motion long term faulting processes in the larger offset agua blanca fault may have lowered slip resistance allowing accommodation of motion despite misalignment with plate motion index terms 1206 geodesy and gravity crustal movements interplate 8155 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 8107 tectonophysics continental neotectonics keywords fault slip rates and the seismic cycle northern baja california

geodetic estimates of fault slip rates in the san francisco bay area bourne et al 1998 have suggested that the interseismic velocity profile at the surface across a transform plate boundary is a replica of the secular velocity profile at depth in the plastosphere on the other hand in the viscoelastic coupling model the shape of the interseismic surface velocity profile is a consequence of plastosphere relaxation following the previous rupture of the faults that make up the plate boundary and is not directly related to the secular flow in the plastosphere the two models appear to be incompatible if the plate boundary is composed of several subparallel faults and the interseismic surface velocity profile across the boundary known each model predicts the secular slip rates on the faults which make up the boundary as suggested by bourne et al the models can then be tested by comparing the predicted secular slip rates to those estimated from long term offsets inferred from geology here we apply that test to the secular slip rates predicted for the principal faults san andreas san gregorio hayward calaveras rodgers creek green valley and greenville faults in the san andreas fault system in the san francisco bay area the estimates from the two models generally agree with one another and to a lesser extent with the geologic estimate because the viscoelastic coupling model has been equally successful in estimating secular slip rates on the various fault strands at a diffuse plate boundary the success of the model of bourne et al 1998 in doing the same thing should not be taken as proof that the interseismic velocity profile across the plate boundary at the surface is a replica of the velocity profile at depth in the plastosphere

isotopic and chemical assessment of geothermal potential of the colli albani area latium region italy abstract the chemical and isotopic compositions of low temperature mineral waters discharged over the colli albani region south of rome italy are those of highly immature waters of essentially meteoric origin formed through absorption of gases emanating from greater depth followed by cation leaching of country rock at shallow levels the composition of the gases discharged points to the presence at depth of a co2 producing high temperature system in its waning stage low h2 and unsaturated hydrocarbon contents as well as relative he ar and n2 contents indicate long residence time for the rising gas phase of the order of 1 ma on the basis of these findings temperatures higher than 120 c appear unlikely to exist at shallow depth

slip distribution of the 1992 landers earthquake and its implications for earthquake source mechanics we use near source 10 to 164 km displacement seismograms to image the slip distribution and rupture history of the 28 june 1992 mw 7 3 landers california earthquake aftershock seismograms from similar distances are modeled to find the velocity model and frequency range 0 05 to 0 25 hz over which theoretical green s functions are most accurate and the measure of fit is used as an upper bound on theoretical error in the mainshock inversion we represent the rupture surface with three planar segments divided into 3 by 3 km elements extending from the surface to 18 km depth and solve for the slip distribution and the rupture time model that minimizes misfit to both recorded seismograms and mapped surface displacement in a least squares sense we investigate two faulting models one with a uniformly short 3 sec rise time everywhere on the fault surface and the other with a variable rise time 2 to 6 sec we perform sensitivity tests using synthetic data from a hypothetical earthquake to evaluate model resolution and solution stability in the sensitivity tests both fault models recover similar slip and rupture features but neither is capable of imaging details of the rise time for the landers earthquake we find an average rupture velocity of 2 5 km sec and use this average for a starting model in a linearized inversion for rupture time in our solutions of slip amplitude distribution the southernmost johnson valley fault segment has 20 of the total seismic moment 6 to 8 1019 n m with small displacements near the hypocenter the homestead valley segment contributes half of the moment with the largest slip amplitudes 25 to 35 km northwest of the hypocenter at 4 to 12 km depth and the camp rock emerson segment contributes the remaining moment with the largest slip amplitude 35 to 50 km northwest of the hypocenter in the shallow crust 9 km there is some evidence that the rupture front is delayed as it encounters high slip regions suggesting that prior to the mainshock these areas were further from failure owing either to greater strength or lower prestress

long range and long term fault interactions in southern california paleoseismological data suggest the occurrence of four bursts of seismic moment release in the los angeles region during the past 12 000 yr the historic period appears to be part of an ongoing lull that has persisted for about the past 1000 yr these periods of rapid seismic displacement in the los angeles region have occurred during the lulls between similar bursts of activity observed on the eastern california shear zone in the mojave desert which is now seismically active a kinematic model in which the faults of the greater san andreas system suppress activity on faults in the eastern california shear zone and vice versa can explain the apparent switching of activity between the two fault networks combined with the observation that short term geodetic and longer term geologic rates co vary on major southern california fault systems this suggests that either 1 a temporal cluster of seismic displacements on upper crustal faults increases ductile deformation on their downward extensions or 2 rapid ductile slip in the lower crust beneath faults loads the upper crust driving a seismic cluster we suggest that alternating periods of rapid seismic displacement may be the expected mode of seismicity when two fault systems accommodate the same plate boundary motion and slip on one system suppresses slip on the other

viscoelastic coupling model for the earthquake cycle driven from below in a linear system the earthquake cycle can be represented as the sum of a solution which reproduces the earthquake cycle itself viscoelastic coupling model and a solution that provides the driving force we consider two cases one in which the earthquake cycle is driven by stresses transmitted along the schizosphere and a second in which the cycle is driven from below by stresses transmitted along the upper mantle i e the schizosphere and upper mantle respectively act as stress guides in the lithosphere in both cases the driving stress is attributed to steady motion of the stress guide and the upper crust is assumed to be elastic the surface deformation that accumulates during the interseismic interval depends solely upon the earthquake cycle solution viscoelastic coupling model not upon the driving source solution thus geodetic observations of interseismic deformation are insensitive to the source of the driving forces in a linear system in particular the suggestion of bourne et al 1998 that the deformation that accumulates across a transform fault system in the interseismic interval is a replica of the deformation that accumulates in the upper mantle during the same interval does not appear to be correct for linear systems

valley pond and ignimbrite veneer deposits in the small volume phreatomagmatic peperino albano basic ignimbrite lago albano maar colli albani volcano italy influence of topography abstract the ca 23 ka small volume basic phreatomagmatic peperino albano ignimbrite from the polygenetic albano maar colli albani volcano central italy shows valley pond facies as well as veneer deposits along the maar rim and along topographic ridges valley pond facies is characterised mainly by massive structure and chaotic texture and can be up to 30 m thick veneer deposit facies is characterised by parallel to low angle cross stratified bedforms alternating fines depleted lapilli sized layers and massive matrix supported beds occurrence of uncharred wood remains and accretionary lapilli suggests temperature of emplacement comprised between 246 and 100 c we have interpreted the lateral facies variations in terms of temporal and spatial variations of the sediment supply from the transport system to the depositional system of the pyroclastic flow ignimbrite veneer facies at the maar rim may reflect pulsatory eruption dynamics whereas valley pond facies may reflect the bulking of the pyroclastic flow inside the valleys and consequent high sedimentation rates ignimbrite veneer facies at topographic ridges has been interpreted to reflect detachment processes of more concentrated undercurrents draining within valleys from the more dilute upper part of the pyroclastic flow that climbs the ridges the present interpretation suggests that processes of pyroclastic flow transformation downcurrent and induced by topography are not necessarily peculiar of hot high mobility pyroclastic density currents the more likely source of water interacting with magma is interpreted to be groundwater contained within the karstic aquifer located at approximately 1 km below the ground level this is inferred by both the large amount of limestone xenoliths present in the peperino albano and the absence of vesicular juvenile clasts the latter implying that magma water interaction occurred before gas exolution processes were significant

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