an ensemble approach for improved short to intermediate term seismic potential evaluation pattern informatics pi load unload response ratio lurr state vector sv and accelerating moment release amr are four previously unrelated subjects which are sensitive in varying ways to the earthquake s source previous studies have indicated that the spatial extent of the stress perturbation caused by an earthquake scales with the moment of the event allowing us to combine these methods for seismic hazard evaluation the long range earthquake forecasting method pi is applied to search for the seismic hotspots and identify the areas where large earthquake could be expected and the lurr and sv methods are adopted to assess short to intermediate term seismic potential in each of the critical regions derived from the pi hotspots while the amr method is used to provide us with asymptotic estimates of time and magnitude of the potential earthquakes this new approach by combining the lurr sv and amr methods with the choice of identified area of pi hotspots is devised to augment current techniques for seismic hazard estimation using the approach we tested the strong earthquakes occurred in yunnan sichuan region china between january 1 2013 and december 31 2014 we found that most of the large earthquakes especially the earthquakes with magnitude greater than 6 0 occurred in the seismic hazard regions predicted similar results have been obtained in the prediction of annual earthquake tendency in chinese mainland in 2014 and 2015 the studies evidenced that the ensemble approach could be a useful tool to detect short to intermediate term precursory information of future large earthquakes

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

aftershock triggering by complete coulomb stress changes 1 we examine the correlation between seismicity rate change following the 1992 m7 3 landers california earthquake and characteristics of the complete coulomb failure stress cfs changes cfs t that this earthquake generated at close distances the time varying dynamic portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement the permanent static portion cfs depends only on the final coseismic displacement cfs diminishes much more rapidly with distance than the transient dynamic stress changes a common interpretation of the strong correlation between cfs and aftershocks is that load changes can advance or delay failure stress changes may also promote failure by physically altering properties of the fault or its environs because it is transient cfs t can alter the failure rate only by the latter means we calculate both cfs and the maximum positive value of cfs t peak cfs t using a reflectivity program input parameters are constrained by modeling landers displacement seismograms we quantify the correlation between maps of seismicity rate changes and maps of modeled cfs and peak cfs t and find agreement for both models however rupture directivity which does not affect cfs creates larger peak cfs t values northwest of the main shock this asymmetry is also observed in seismicity rate changes but not in cfs this result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed

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

transport and mixing dynamics from explosions in debris filled volcanic conduits numerical results and implications for maar diatreme volcanoes abstract most volcanoes experience some degree of phreatomagmatism during their lifetime however the current understanding of such processes remains limited relative to their magmatic counterparts maar diatremes are a common volcano type that form primarily from phreatomagmatic explosions and are an ideal candidate to further our knowledge of deposits and processes resulting from explosive magma water interaction due to their abundance as well as their variable levels of field exposure which allows for detailed mapping and componentry two conceptual models of maar diatreme volcanoes explain the growth and evolution of the crater maar and subsurface vent diatreme through repeated explosions caused by the interaction of magma and groundwater one model predicts progressively deepening explosions as water is used up by phreatomagmatic explosions while the other allows for explosions at any level in the diatreme provided adequate hydrologic conditions are present in the former deep seated lithics in the diatreme are directly ejected and their presence in tephra rings is often taken as a proxy for the depth at which that particular explosion occurred in the latter deep seated lithics are incrementally transported toward the surface via upward directed debris jets here we present a novel application of multiphase numerical modeling to assess the controls on length scales of debris jets and their role in upward transport of intra diatreme material to determine the validity of the two models the volume of gas generated during a phreatomagmatic explosion is a first order control on the vertical distance a debris jet travels unless extremely large amounts of magma and water are involved it is unlikely that most explosions deeper than 250 m breach the surface other factors such as pressure and temperature have lesser effects on the length scales assuming they are within realistic ranges redistribution of material within a diatreme is primarily driven by subsidence following debris jet passage natural debris jet deposits often contain wall rock material that originated above the explosion site likely this material was first transported downward by subsidence associated with preceding explosions and debris jets the length scales of debris jets decrease with increasing depth all other factors staying equal the characteristics of the domains formed from just one explosion along with the difficulty of erupting deep seated material indicate that erupted material at maar diatreme volcanoes has a complex history before it is erupted and is mostly sourced from the upper most part of the diatreme

facies distribution of ejecta in analog tephra rings from experiments with single and multiple subsurface explosions the volume grain size and depositional facies of material deposited outside an explosion crater ejecta are sensitive to the depth of the explosion the explosion energy and the presence or absence of a crater before the explosion we detonate buried chemical explosives as an analog for discrete volcanic explosions in experiments to identify unique characteristics of proximal medial and distal ejecta facies and their distribution from a range of scaled depths in undisturbed and cratered ground ejecta are here discussed in terms of three facies 1 proximal ejecta which form a constructional landform around a crater 2 medial ejecta which form a continuous sheet deposit that thins much more gradually with distance and 3 distal ejecta that are deposited as isolated clasts the extent of proximal ejecta away from the crater relative to crater size is not sensitive to scaled depth but the volume proportion of proximal ejecta to the total ejecta deposit is sensitive to the presence of a crater and scaled depth medial ejecta distribution and volume contributions are both sensitive to the presence of a crater and to scaled depth distal ejecta distance is dependent on scaled depth and the presence of a crater while the volume proportion of distal ejecta is less sensitive to scaled depth or presence of a crater experimental facies and deposit structures inferred from observations of jet dynamics are used to suggest facies associations anticipated from eruptions dominated by explosions of different scaled depth configurations we emphasize that significant differences in tephra ring deposits can result from the effects of scaled depth and preexisting craters on ejecta dynamics and are not necessarily related to fundamental differences in explosion mechanisms or degree of magma fragmentation

seismicity rate changes in association with the evolution of the stress field in northern aegean sea greece summary seismicity rate changes in northern aegean area were studied by applying the dieterich 1994 rate state formulation the study area was divided into four smaller ones that exhibit seismotectonic homogeneity and accommodate strong events with similar to identical focal mechanisms seismicity rate evaluation concerns the study period between 1981 december 19 and 2010 august 31 whereas the reference seismicity rate was estimated for the learning period lasting from 1970 january 1 to 1981 december 19 the coseismic slip of the strongest events mw 5 8 that occurred during the study period was considered to contribute to the stress field evolution along with the continuous tectonic loading stress changes were calculated just before and after each strong event and their influence was then examined in connection with the occurrence rate of the smaller magnitude events above the individually determined magnitude of completeness in each subarea and for the respective time intervals after defining the probability density function of seismicity distribution a rate state model was used to combine static coulomb stress changes cff with seismicity rates and to compare the observed with the expected rates of earthquake production for each time period and subarea different parameter values combinations were tested to evaluate the model sensitivity qualitative and quantitative correlations were performed for each one of the selected study periods the modelling approach resulted to satisfactory correlation between real and synthetic seismicity rates and is expected to constitute a useful mean for the time dependent seismic hazard assessment

development of a combination approach for seismic hazard evaluation we developed a synth esis approach to augment current techniques for seismic hazard evaluation by combining four previously unrelated subjects the pattern informatics pi load unload response ratio lurr state vector sv and accelerating moment release amr methods since the pi is proposed in the premise that the change in the seismicity rate is a proxy for the change in the tectonic stress this method is used to quantify localized changes surrounding the epicenters of large earthquakes to objectively quantify the anomalous areas hot spots of the upcoming events on the short to intermediate term estimation we apply the lurr sv and amr methods to examine the hazard regions derived from the pi hot spots a predictive study of the 2014 earthquake tendency in chinese mainland using the seismic data from 1970 01 01 to 2014 10 01 shows that during jan 01 to oct 31 2014 most of the m 5 0 earthquakes especially the feb 12 m7 3 yutian may 30 m6 1 yingjiang aug 03 m6 5 ludian and oct 07 m6 6 earthquakes occurred in the seismic hazard regions predicted comparing the predictions produced by the pi and combination approaches it is clear that by using the combination approach we can screen out the false alarm regions from the pi estimation without reducing the hit rate and therefore effectively augment the predictive power of current techniques this provided evidence that the multi method combination approach may be a useful tool to detect precursory information of future large earthquakes

a reappraisal of the 2005 kashmir mw 7 6 earthquake and its aftershocks seismotectonics of nw himalaya abstract we study the source properties of the 2005 kashmir earthquake and its aftershocks to unravel the seismotectonics of the nw himalayan syntaxis the mainshock and larger aftershocks have been simultaneously relocated using phase data we use back projection of high frequency energy from multiple teleseismic arrays to model the spatio temporal evolution of the mainshock rupture our analysis reveal a bilateral rupture which initially propagated se and then nw of the epicenter with an average rupture velocity of 2 km s 1 the area of maximum energy release is parallel to and bound by the surface rupture incorporating rupture propagation and velocity we model the mainshock as a line source using p and sh waveform inversion our result confirms that the mainshock occurred on a ne dipping 35 fault plane with centroid depth of 10 km integrated source time function show that majority of the energy was released in the first 20 s and was confined above the hypocenter from waveform inverted fault dimension and seismic moment we argue that the mainshock had an additional 25 km blind rupture beyond the nw himalayan syntaxis combining this with findings from previous studies we conjecture that the blind rupture propagated nw of the syntaxis underneath a weak detachment overlain by infra cambrian salt layer and terminated in a wedge thrust all moderate to large aftershocks nw of the mainshock rupture are concentrated at the edge of the blind rupture termination source modeling of these aftershocks reveal thrust mechanism with centroid depths of 2 10 km and fault planes oriented sub parallel to the mainshock rupture to study the influence of mainshock rupture on aftershock occurrence we compute coulomb failure stress on aftershock faults all these aftershocks lie in the positive coulomb stress change region this suggest that the aftershocks have been triggered by either co seismic or post seismic slip on the mainshock fault

the architecture eruptive history and evolution of the table rock complex oregon from a surtseyan to an energetic maar eruption abstract the table rock complex trc pliocene pleistocene first documented and described by heiken heiken g h 1971 tuff rings examples from the fort rock christmas lake valley basin south central oregon j geophy res 76 5615 5626 is a large and well exposed mafic phreatomagmatic complex in the fort rock christmas lake valley basin south central oregon it spans an area of approximately 40 km2 and consists of a large tuff cone in the south trc1 and a large tuff ring in the northeast trc2 at least seven additional smaller explosion craters were formed along the flanks of the complex in the time between the two main eruptions the first period of activity trc1 initiated with a surtseyan style eruption through a 60 70 m deep lake the trc1 deposits are dominated by multiple 1 2 m thick fining upward sequences of massive to diffusely stratified lapilli tuff with intermittent zones of reverse grading followed by a finely laminated cap of fine grained sediment the massive deposits are interpreted as the result of eruption fed subaqueous turbidity current deposits whereas the finely laminated cap likely resulted from fallout of suspended fine grained material through a water column other common features are erosive channel scour and fill deposits massive tuff breccias and abundant soft sediment deformation due to rapid sediment loading subaerial trc1 deposits are exposed only proximal to the edifice and consist of cross stratified base surge deposits the eruption built a large tuff cone above the lake surface ending with an effusive stage which produced a lava lake in the crater 365 m above the lake floor a significant repose period occurred between the trc1 and trc2 eruptions evidenced by up to 50 cm of diatomitic lake sediments at the contact between the two tuff sequences the trc2 eruption was the last and most energetic in the complex general edifice morphology and a high percentage of accidental material suggest eruption through saturated trc1 deposits and or playa lake sediments trc2 deposits are dominated by three dimensional dune features with wavelengths 200 500 m perpendicular to the flow and 20 200 m parallel to the direction of flow depending on distance from source large u shaped channels 10 32 m deep run up features over obstacles tens of meters high and a large 13 m chute and pool feature are also identified the trc2 deposits are interpreted as the products of multiple erosive highly inflated pyroclastic surges resulting from collapse of an unusually high eruption column relative to previously documented mafic phreatomagmatic eruptions

a model of tectonic stress state and rate using the 1994 northridge earthquake sequence a model of the spatial and temporal distribution of seismicity both before and after the northridge california earthquake has been used to estimate the background stress state loading rate and some parameters relating to fault friction a detailed source model was used to calculate the stress change field from the northridge mainshock which was fit to the spatial distribution of seismicity agreement between the best fitting background stress state from seismicity modeling and the background stress state inferred from focal mechanisms was found to be 99 significant showing that the spatial distribution of seismicity contains information about the stress state the stress rate found for the northridge area 1 2 pa day 0 004 bar a is approximately a factor of 9 less than the stress rate expected from observed strain rates which implies that aseismic deformation is reducing seismic hazard in the los angeles basin the resulting estimate of the friction parameter a d 0 008 is similar to laboratory values if an effective normal stress much smaller than the overburden and similar to background stress magnitudes 70 mpa from the seismicity modeling is assumed to apply estimates of the magnitude of background stress gradient of stress with depth and effective coefficient of friction are quite uncertain

rhyolitic phreatomagmatism explored tepexitl tuff ring eastern mexican volcanic belt abstract rhyolitic tepexitl tuff ring in the serdan oriental basin of the eastern trans mexican volcanic belt is a young well preserved circular crater a simple morphology that belies a more complex eruptive history field observations ash studies granulometry componentry and morphology and volatile data loi and xrf allow the broad division of the tepexitl deposits into two sequences a lower sequence characterized by fine grained deposits with abundant bomb and lapilli sags and an upper sequence of coarse grained deposits that show little to no deformation the early eruptions at tepexitl are interpreted to have been dominated by discrete highly efficient phreatomagmatic blasts which caused a progressive deepening of the eruptive center lower sequence followed by a transition to dominantly magmatic behavior in the upper sequence dome growth occurred at the end of the eruption but subsequent retrogressive explosions triggered by external water destroyed all trace of the original dome morphology molten fuel coolant interaction mfci is commonly thought to cause the repetitive water magma interaction in phreatomagmatic eruptions but a process by which magma and viscous felsic magmas can mingle prior to explosive interaction has not been described a viable mechanism for rhyolitic mfci based upon field work at tepexitl and laboratory experiments requires that fluidized sediments intrude marginal fractures in the rhyolite magma creating enough interfacial surface area to initiate phreatomagmatic explosions from within the interior of a rising plug or dome

miocene phreatomagmatic volcanism at tihany pannonian basin hungary abstract a late miocene 7 56 ma maar volcanic complex tihany maar volcanic complex tmvc is preserved in the pannonian basin and is part of the bakony balaton highland volcanic field base surge and fallout deposits were formed around maars by phreatomagmatic explosions caused by interactions between water saturated sediments and alkali basalt magma carrying peridotite lherzolite xenoliths as well as pyroxene and olivine megacrysts subsequently nested maars functioned as a sediment trap where deposition built up gilbert type delta sequences at the onset of eruption magma began to interact with a moderate amount of groundwater in the water saturated sand as eruption continued phreatomagmatic blasts excavated downward into limestones providing access to abundant karst water and deeper to sandstones and schist both providing large amount of fracture filling water at the surface this wet eruption led to the emplacement of massive tuff breccias by fall surge mudflow and gravity flow deposition the nature of the tmvc maar eruptions and their deposits appears to depend on the hydrological condition of the karst and or fracture filling aquifer which varies seasonally with rainfall and spring runoff the west and east maar volcanoes of tmvc are interpreted to represent low water input from the karst and or fracture filling aquifer summer vent whereas the east maar is interpreted to have formed when abundant karst and or fracture filling water was available spring vent

quantitative earthquake forecasts resulting from static stress triggering 1 in recent years the triggering of earthquakes has been discussed controversially with respect to the underlying mechanisms and the capability to evaluate the resulting seismic hazard apart from static stress interactions other mechanisms including dynamic stress transfer have been proposed to be part of a complex triggering process exploiting the theoretical relation between long term earthquake rates and stressing rate we demonstrate that static stress changes resulting from an earthquake rupture allow us to predict quantitatively the aftershock activity without tuning specific model parameters these forecasts are found to be in excellent agreement with all first order characteristics of aftershocks in particular 1 the total number 2 the power law distance decay 3 the scaling of the productivity with the main shock magnitude 4 the foreshock probability and 5 the empirical bath law providing the maximum aftershock magnitude which supports the conclusion that static stress transfer is the major mechanism of earthquake triggering

a study of the coulomb stress and seismicity rate changes induced by the 2008 m w 7 9 wenchuan earthquake sw china abstract correlations between the calculated coulomb stress changes and observed seismicity rate changes after the wenchuan earthquake are investigated in this article three improvements are made in the calculation of static stress change including employing a dislocation method with triangular elements rather than traditional rectangular elements setting up a more realistic source slip model and a more complete receiver fault model and resolving stress changes on assumed receiver faults with spatially variable focal mechanisms based on well determined focal mechanisms at different calculation points the recorded aftershocks are mapped for comparison with the spatial distribution of stress changes the results indicate that the wenchuan earthquake encourages not only three major fault systems the east kunlun south of xianshuihe and west of qinling southern frontal but also several other regions including tazang north of min jiang north of pingwu qingchuan and west of chongqing in particular the eastern segment of longriba is shown to be quite dangerous with dramatic stress increase the influence of depth and frictional coefficient is analyzed the depth of calculation beyond the depth range of the source model will make a significant difference to the stress change map and thus cannot be neglected many aftershocks occurring in the stress shadow zone near the main rupture can be attributed to dynamic stress triggering and the fractal structure of the main fault the observed seismicity rate changes are compared with the static stress changes the results show that high background seismicity rates will amplify the effect of stress change the observed seismicity rate changes support the forecast rate of 10 year seismicity after the wenchuan earthquake based on the rate and state dependent friction model coulomb stresses increase on the focal mechanisms away from the main rupture which demonstrates the influence of the wenchuan earthquake over a wide range especially the focal mechanism for lushan earthquake undergoes a stress increase by more than 2 0 bars which suggests that the lushan earthquake has been effectively promoted by the wenchuan earthquake

effects of explosion energy and depth to the formation of blast wave and crater field explosion experiment for the understanding of volcanic explosion we made field explosion experiments as an analogue of volcanic explosion to understand the relationship between the explosion condition and the resultant surface phenomena the main parameters we employed were explosion depth and explosion energy through the experiments we confirmed that scaled depth which is the depth divided by cube root of energy is the main parameter determining the properties of explosive volcanism the energy assigned to blast wave decreased exponentially against the scaled depth the scaled crater diameter became maximum when the scaled depth was about 4 10 3 m j scaled crater diameters by nuclear chemical subsurface and some volcanic explosions were almost the same from the scaling law the overpressure at crater rim was estimated to be several mpa which corresponded to typical rock strength probably the ground forming materials were broken inside the area where overpressure exceeded their strength

how did the 2013 lushan earthquake ms 7 0 trigger its aftershocks insights from static coulomb stress change calculations the lushan earthquake ms7 0 occurred at 08 02 beijing time 00 02 utc on 20 april 2013 located on the eastern margin of the tibetan plateau where the 2008 ms8 0 wenchuan earthquake took place the other strong shock following the wenchuan earthquake occurred on the longmen shan thrust fault a large number of aftershocks were recorded after the mainshock to investigate how the aftershocks were triggered we firstly relocated the 6 month aftershock sequence by the double difference algorithm next we calculated coulomb failure stress changes imparted by the lushan mainshock both on the optimally oriented plane and on the aftershock nodal planes then we examined the correspondence between the coulomb failure stress changes and the spatial distribution of the aftershocks the computed results show that most of the aftershock hypocenters did not occur on the region with the positive coulomb stress changes caused by the lushan mainshock moreover the majority of aftershock nodal planes were brought away from failure by coseismic coulomb stresses this implies that coseismic static coulomb stress changes may not be the governing process for aftershock genesis in contrast postseismic stress transfer by processes of afterslip and pore fluid flow are assumed to play an important part in aftershock triggering based upon the spatiotemporal distribution of the aftershocks

phreatomagmatic eruptive and depositional processes during the 1949 eruption on la palma canary islands abstract in 1949 a 5 week long magmatic and phreatomagmatic eruption took place along the active volcanic ridge of la palma canary islands two vents duraznero and hoyo negro produced significant pyroclastic deposits the eruption began from duraznero vent which produced a series of deposits with an upward decrease in accidental fragments and increase in fluidal ash and spatter together inferred to indicate decreasing phreatomagmatic interaction hoyo negro erupted over a 2 week period producing a variety of pyroclastic density currents and ballistic blocks and bombs hoyo negro erupted within and modified an older crater having high walls on the northern to southeastern edges southwestern to western margins of the crater lay 50 to 100 m lower strongly contrasting deposits in the different sectors n se vs sw w were formed as a result of interaction between topography weak eruptive columns and stratified pyroclastic density currents tephra ring deposits are thicker and coarser grained than upper rim deposits formed along the higher edges of the crater and beyond the crater margin valley confined deposits are thicker than more thinly bedded mantling deposits on higher topography these differences indicate that the impact zone for the bulk of the collapsing tephra laden column lay within the crater and that the high crater walls inhibited escape of pyroclastic density currents to the north and east the impact zone lay outside the low sw w rims however thus allowing stratified pyroclastic density currents to move freely away from the crater in those directions depositing thin sections

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

evidence for the relative depths and energies of phreatomagmatic explosions recorded in tephra rings experimental work and field observations have inspired the revision of conceptual models of how maar diatreme eruptions progress and the effects of variable energy depth and lateral position of explosions during an eruption sequence this study reevaluates natural tephra ring deposits to test these new models against the depositional record two incised tephra rings in the hopi buttes volcanic field are revisited and published tephra ring stratigraphic studies are compared to identify trends within tephra rings five major facies were recognized and interpreted as the result of different transportation and depositional processes and found to be common at these volcanoes tephra rings often contain evidence of repeated discrete phreatomagmatic explosions in the form of couplets of two facies 1 massive lapilli tuffs and tuff breccias and 2 overlying thinly stratified to cross stratified tuffs and lapilli tuffs the occurrence of repeating layers of either facies and the occurrence of couplets are used to interpret major trends in the relative depth of phreatomagmatic explosions that contribute to these eruptions for deposits related to near optimal scaled depth explosions estimates of the mass of ejected material and initial ejection velocity can be used to approximate the explosion energy the 19 stratigraphic sections compared indicate that near optimal scaled depth explosions are common and that the explosion locations can migrate both upward and downward during an eruption suggesting a complex interplay between water availability and magma flux reverse to normal coarse tail graded tuff breccias inferred to be the product of closely timed phreatomagmatic explosions and deposits of magmatic gas driven explosions were observed interspersed with discrete explosion deposits this study not only provides a framework for more detailed interpretations of eruption sequences from tephra rings but also highlights the gap in our understanding of syn eruptive hydrology and variations in magma flux that enables phreatomagmatic explosions

triggering of seismicity at short timescales following californian earthquakes 1 a method for measuring seismicity rate changes caused by the occurrence of major earthquakes in the surrounding crust is proposed it is based on a nonstationary poisson modeling of earthquake activity an estimate of the seismicity rate change and a probability measure of seismicity triggering following a large shock are derived and the removal of the influence of independent aftershock sequences of other nearby previous earthquakes is attempted without using more traditional declustering techniques the seismicity rate change estimator is corrected for its natural bias in favor of positive changes at short timescales that has so far strongly hindered measures of seismicity quiescences three californian earthquakes are examined using this method the 1989 m7 1 loma prieta the 1992 m7 3 landers and the 1994 m6 7 northridge earthquakes positive triggering is very commonly observed as expected but quiescence is however more seldomly obtained for timescales up to 100 days after the main shock this relative absence of quiescence as compared to typical predictions of coulomb modeling for example is also independently observed through direct correlation analyses of californian seismicity the possibility that the stresses caused by the main shock are spatially highly variable may explain these observations

sensitivity of coulomb stress change to the parameters of the coulomb failure model a case study using the 2008 mw 7 9 wenchuan earthquake the coulomb stress change has been widely employed to interpret mainshock mainshock and mainshock aftershock triggering as well as interactions amongst earthquake faults and volcanoes this quantitative index is computed based on the coulomb failure criterion and is a function of fault parameters including the source and receiver fault geometries the friction coefficient on the receiver fault and skempton s coefficient of the host rock thus for the robust determination of the coulomb stress change the sensitivity of the coulomb stress change to these model parameters should be thoroughly assessed however notwithstanding numerous case studies almost no systematic investigation of the sensitivity of the coulomb stress change has been performed here we present an error estimator for the coulomb stress change and then quantitatively investigate the sensitivity of the coulomb stress change to the fault model parameters for the 2008 mw 7 9 wenchuan earthquake our results indicate that for this case the coulomb stress change is the most sensitive to the uncertainty in the dip angle of the receiver fault while the influences of the uncertainties in the slip model of the source fault the strike and rake angles of the receiver fault and the friction and skempton s coefficients cannot be neglected accordingly it is crucial to perform a realistic estimate of the uncertainty in the coulomb stress change by performing such calculation future coulomb stress analyses such as the stress triggering of earthquake sequence and the likelihoods of potential earthquakes could be based on more robust coulomb stress change maps

did the 2008 mw 7 9 wenchuan earthquake trigger the occurrence of the 2017 mw 6 5 jiuzhaigou earthquake in sichuan china

construction of the north head maungauika tuff cone a product of surtseyan volcanism rare in the auckland volcanic field new zealand the auckland volcanic field avf comprises at least 52 monogenetic eruption centres dispersed over 360 km2 eruptions have occurred sporadically since 250 ka predominantly when glacio eustatic sea levels were lower than today now that around 35 of the field is covered by shallow water up to 30 m depth any eruption occurring in the present or near future within this area may display surtseyan dynamics the north head tuff cone evidences eruptive dynamics caused by magma interaction with seawater the first stages of the eruption comprise a phreatomagmatic phase that built a 48 m high tuff cone north head tuff deposits contain few lithic fragments 10 vol and are characterized by deposits from collapsing tephra jets and fall from relatively wet tephra columns the conditions needed for this eruption existed between 128 and 116 ka when the sea level in the auckland area was at least 10 12 m above the pre eruptive surface the hazards associated with this type of eruption pose a risk to the densely populated coastal residential zones and the activities of one of the busiest harbours in new zealand

response of the san andreas fault to the 1983 coalinga nunez earthquakes an application of interaction based probabilities for parkfield 1 the parkfield cholame section of the san andreas fault site of an unfulfilled earthquake forecast in 1985 is the best monitored section of the world s most closely watched fault in 1983 the m 6 5 coalinga and m 6 0 nunez events struck 25 km northeast of parkfield seismicity rates climbed for 18 months along the creeping section of the san andreas north of parkfield and dropped for 6 years along the locked section to the south right lateral creep also slowed or reversed from parkfield south here we calculate that the coalinga sequence increased the shear and coulomb stress on the creeping section causing the rate of small shocks to rise until the added stress was shed by additional slip however the 1983 events decreased the shear and coulomb stress on the parkfield segment causing surface creep and seismicity rates to drop we use these observations to cast the likelihood of a parkfield earthquake into an interaction based probability which includes both the renewal of stress following the 1966 parkfield earthquake and the stress transfer from the 1983 coalinga events we calculate that the 1983 shocks dropped the 10 year probability of a m 6 parkfield earthquake by 22 from 54 22 to 42 23 and that the probability did not recover until about 1991 when seismicity and creep resumed our analysis may thus explain why the parkfield earthquake did not strike in the 1980s but not why it was absent in the 1990s we calculate a 58 17 probability of a m 6 parkfield earthquake during 2001 2011 index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 7260 seismology theory and modeling keywords coalinga earthquake parkfield stress change earthquake probability seismicity rate

a spatial random field model to characterize complexity in earthquake slip 1 finite fault source inversions reveal the spatial complexity of earthquake slip over the fault plane we develop a stochastic characterization of earthquake slip complexity based on published finite source rupture models in which we model the distribution of slip as a spatial random field the model most consistent with the data follows a von karman autocorrelation function acf for which the correlation lengths a increase with source dimension for earthquakes with large fault aspect ratios we observe substantial differences of the correlation length in the along strike a x and downdip a z directions increasing correlation length with increasing magnitude can be understood using concepts of dynamic rupture propagation the power spectrum of the slip distribution can also be well described with a power law decay i e a fractal distribution in which the fractal dimension d remains scale invariant with a median value d 2 29 0 23 while the comer wave number k c which is inversely proportional to source size decreases with earthquake magnitude accounting for larger slip patches for large magnitude events our stochastic slip model can be used to generate realizations of scenario earthquakes for near source ground motion simulations

depositional processes of the suwolbong tuff ring cheju island korea the suwolbong pyroclastic sequence in the western part of cheju island korea comprises partly preserved rim beds of a quaternary basaltic tuff ring whose vent lies about 1 km seaward of the present shoreline the sequence consists of breccia lapillistone lapilli tuff and tuff eighteen sedimentary facies are established and organized into six lateral facies sequences lfs and seven vertical facies sequences vfs the lfs 1 4 and 5 begin with massive lapilli tuff which transforms downcurrent into either planar bedded lfs 1 undulatory bedded lfs 4 or climbing dune bedded lfs 5 lapilli tuff units they are representative of relatively dry base surge whose particle concentration decreases downcurrent with a progressive increase in both tractional processes and sorting the lfs 2 begins with disorganized and massive lapilli tuff and transforms into crudely stratified units downcurrent it results from relatively wet base surge in which sorting is poor due to the cohesion of damp ash the lfs 3 comprises well sorted lapilli tuff and stratified tuff further downcurrent suggestive of deposition from combined fall and surge of relatively dry hydroclastic eruption all seven vertical facies sequences generally comprise two facies units of coarse grained fines depleted lapilli tuff and an overlying fine grained tuff these sequences are suggestive of deposition from base surge that consists of a turbulent head and a low concentration tail depositional processes in the suwolbong tuff ring were dominated by a relatively dry base surge the base surge comprises turbulent and high concentration suspension near the vent whose deposits are generally unstratified due to the lack of tractional transport as the base surge becomes diluted downcurrent through fallout of clasts and mixing of ambient air it develops large scale turbulent eddies and is segregated into coarse grained bedload and overlying fine grained suspension forming thinly stratified units further downcurrent the base surge may be either cooled and deflated or pushed up into the air depending on its temperature the suwolbong tuff ring comprises an overall wet to dry cycle with several dry to wet cycles in it suggestive of overall decrease in abundance of external water and fluctuation in the rate of magma rise

modeling seismicity rate changes during the 1997 umbria marche sequence central italy through a rate and state dependent model 1 we model the spatial and temporal pattern of seismicity during a sequence of moderate magnitude normal faulting earthquakes which struck in 1997 the umbria marche sector of northern apennines italy by applying the dieterich 1994 rate and state dependent constitutive approach the goal is to investigate the rate of earthquake production caused by repeated coseismic stress changes computed through a 3 d elastic dislocation model in a homogeneous half space the reference seismicity rate is assumed time independent and it is estimated by smoothing the seismicity that occurred in the previous decade without declustering we propose an analytical relation for deriving the stressing rate directly from the reference seismicity rate this allows us to perform a tuning of the constitutive parameter a where a accounts for the direct effect of friction in the rate and state dependent model and is the effective normal stress into the dieterich model through a maximum likelihood method which yields for this seismic sequence a best fitting value equal to 0 04 mpa our computations show that although seven out of eight main shocks are located in areas of increased rate of earthquake production numerous aftershocks are located in seismicity shadows our simulations point out that the adopted value of a strongly affects the pattern of both seismicity shadow and areas of enhanced rate of earthquake production we conclude that solely accounting for static stress changes caused by the main shocks of this seismic sequence is not sufficient to forecast the complex spatial and temporal evolution of seismicity

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

directed blasts and blast generated pyroclastic density currents a comparison of the bezymianny 1956 mount st helens 1980 and soufriere hills montserrat 1997 eruptions and deposits we compare eruptive dynamics effects and deposits of the bezymianny 1956 bz mount st helens 1980 msh and soufriere hills volcano montserrat 1997 shv eruptions the key events of which included powerful directed blasts each blast subsequently generated a high energy stratified pyroclastic density current pdc with a high speed at onset the blasts were triggered by rapid unloading of an extruding or intruding shallow magma body lava dome and or cryptodome of andesitic or dacitic composition the unloading was caused by sector failures of the volcanic edifices with respective volumes for bz msh and shv c 0 5 2 5 and 0 05 km3 the blasts devastated approximately elliptical areas axial directions of which coincided with the directions of sector failures we separate the transient directed blast phenomenon into three main parts the burst phase the collapse phase and the pdc phase in the burst phase the pressurized mixture is driven by initial kinetic energy and expands rapidly into the atmosphere with much of the expansion having an initially lateral component the erupted material fails to mix with sufficient air to form a buoyant column but in the collapse phase falls beyond the source as an inclined fountain and thereafter generates a pdc moving parallel to the ground surface it is possible for the burst phase to comprise an overpressured jet which requires injection of momentum from an orifice however some exploding sources may have different geometry and a jet is not necessarily formed a major unresolved question is whether the preponderance of strong damage observed in the volcanic blasts should be attributed to shock waves within an overpressured jet or alternatively to dynamic pressures and shocks within the energetic collapse and pdc phases internal shock structures related to unsteady flow and compressibility effects can occur in each phase we withhold judgment about published shock models as a primary explanation for the damage sustained at msh until modern 3d numerical modeling is accomplished but argue that much of the damage observed in directed blasts can be reasonably interpreted to have been caused by high dynamic pressures and clast impact loading by an inclined collapsing fountain and stratified pdc this view is reinforced by recent modeling cited for shv in distal and peripheral regions solids concentration maximum particle size current speed and dynamic pressure are diminished resulting in lesser damage and enhanced influence by local topography on the pdc despite the different scales of the blasts devastated areas were respectively 500 600 and 10 km2 for bz msh and shv and some complexity involving retrogressive slide blocks and clusters of explosions their pyroclastic deposits demonstrate strong similarity juvenile material composes 50 of the deposits implying for the blasts a dominantly magmatic mechanism although hydrothermal explosions also occurred the character of the magma fragmented by explosions highly viscous phenocryst rich variable microlite content determined the bimodal distributions of juvenile clast density and vesicularity thickness of the deposits fluctuates in proximal areas but in general decreases with distance from the crater and laterally from the axial region the proximal stratigraphy of the blast deposits comprises four layers named a b c d from bottom to top layer a is represented by very poorly sorted debris with admixtures of vegetation and soil with a strongly erosive ground contact its appearance varies at different sites due to different ground conditions at the time of the blasts the layer reflects intense turbulent boundary shear between the basal part of the energetic head of the pdc and the substrate layer b exhibits relatively well sorted fines depleted debris with some charred plant fragments its deposition occurred by rapid suspension sedimentation in rapidly waning high concentration conditions layer c is mainly a poorly sorted massive layer enriched by fines with its uppermost part laminated created by rapid sedimentation under moderate concentration weakly tractive conditions with the uppermost laminated part reflecting a dilute depositional regime with grain by grain traction deposition by analogy to laboratory experiments mixing at the flow head of the pdc created a turbulent dilute wake above the body of a gravity current with layer b deposited by the flow body and layer c by the wake the uppermost layer d of fines and accretionary lapilli is an ash fallout deposit of the finest particles from the high rising buoyant thermal plume derived from the sediment depleted pyroclastic density current the strong similarity among these eruptions and their deposits suggests that these cases represent similar source transport and depositional phenomena

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

tephra ring interpretation in light of evolving maar diatreme concepts stracciacappa maar central italy abstract maar diatreme volcanoes in their simplest form are thought to result primarily from discrete subsurface phreatomagmatic explosions tephra ring deposits around maar craters are commonly interpreted in terms of a framework wherein explosions begin at shallow levels and migrate downward ejecting progressively deeper seated lithic clasts that contribute to the tephra rings additionally variations in grain size of the deposits are sometimes inferred to record different degrees of fragmentation which are in turn related to variations in magma water ratios at the explosion sites recent detailed studies of diatremes and of maar tephra rings suggest a different conceptual model wherein explosions can happen at various vertical and lateral locations within a diatreme during its eruptive lifetime rather than being limited to simple downward migration experiments numerical modeling and field data indicate that most explosions deeper than about 200 250 m will not vent to the surface but instead contribute to mixing within the diatremes arrival of deep seated lithics at the surface is related to this mixing process experiments also indicate that explosion phenomena can result in a range of emplacement mechanisms and grain sizes in tephra rings even in the absence of variations in explosion mechanisms fragmentation efficiency here we document the tephra ring of stracciacappa maar central italy and interpret its eruption and emplacement history in terms of evolving conceptual models along with a comparison to more traditional interpretations because most elements of both conceptual models are viable the work points to an important need to develop criteria to distinguish between the various inferred mechanisms

premixing of magma and water in mfci experiments experimental studies have been performed to evaluate pre explosive water melt mixes with respect to explosive volcanic molten fuel coolant interaction mfci i e phreatomagmatic explosion remolten ultrabasic volcanic rock was used as a magma simulant measurement of the explosion intensity was used to determine optimal premixing conditions a well defined optimal range was found for the hydrodynamic mixing energy differential flow speed of 4 2 m s as well as for the water melt mass ratio 0 03 to 0 04 under experimental conditions the mass flux of water had a minor influence on the explosion intensity additionally transparent mixing experiments with silicon oil and inked water were carried out they indicate a direct dependence of the pre explosive water melt interface area on the explosion intensity the experimental results show that the contact conditions of water and melt required for explosive mfci may easily be established in natural volcanic systems thus explosive mfci is a probable mechanism of explosive volcanism

the sensitivity of the loa unload response ratio and critical region selection before large earthquakes occurrence of a large earthquake could be predicted by anomalous temporal increase of the load unload response ratio lurr previous studies have indicated that the stress field that existed before a large earthquake may have a strong influence on the evaluation of lurr in this paper we replace the circular region usually adopted in lurr practice with an area within which the tectonic stress change would mostly affect the coulomb stress on a potential seismogenic fault of a future event this algorithm is devised to increase the sensitivity of lurr to measure criticality of stress accumulation before a large earthquake in the algorithm we assess the stress change and identify the areas with increased coulomb stress before an earthquake using a simple back slip dislocation model of the event retrospective tests of this algorithm on some disastrous earthquakes that occurred in the chinese mainland in recent years show remarkable enhancement of the lurr precursory anomalies by using the hypothetical faults for the large earthquake prediction we further illustrate that the new algorithm is more sensitive to detect future earthquake of a particular magnitude range and location than the circular region algorithm hence where sufficient information of the regional fault tectonics is given the coulomb stress algorithm can be used to augment current lurr technique for seismic hazard estimation

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

modeling of kashmir aftershock decay based on static coulomb stress changes and laboratory derived rate and state dependent friction law we model the spatial and temporal evolution of october 8 2005 kashmir earthquake s aftershock activity using the rate and state dependent friction model incorporating uncertainties in computed coseismic stress perturbations we estimated the best possible value for frictional resistance a n background seismicity rate r and coefficient of stress variation cv using maximum log likelihood method for the whole kashmir earthquake sequence we measure a frictional resistance a n 0 0185 mpa r 20 m3 7 events year and cv 0 94 0 01 the spatial and temporal forecasted seismicity rate of modeled aftershocks fits well with the spatial and temporal distribution of observed aftershocks that occurred in the regions with positive static stress changes as well as in the apparent stress shadow region to quantify the effect of secondary aftershock triggering we have re run the estimations for 100 stochastically declustered catalogs showing that the effect of aftershock induced secondary stress changes is obviously minor compared to the overall uncertainties and that the stress variability related to uncertain slip model inversions and receiver mechanisms remains the major factor to provide a reasonable data fit

a new estimation of the decay of aftershock density with distance to the mainshock we investigate how aftershocks are spatially distributed relative to the mainshock compared to previous studies ours focuses on earthquakes causally related to the mainshock rather than on aftershocks of previous aftershocks we show that this distinction can be made objectively but becomes uncertain at long time scales and large distances analyzing a regional earthquake data set it is found that at time t following a mainshock of magnitude m the probability of finding an aftershock at distance r relative to the mainshock fault decays as r where is typically between 1 7 and 2 1 for 3 m 6 and is independent of m for r less than 10 to 20 km and t less than 1 day uncertainties on this probability at larger r and t do not allow for a correct estimation of this spatial decay we further show that a static stress model coupled with a rate and state friction model predicts a similar decay with an exponent 2 2 in the same space and time intervals this suggests that static stress changes could explain the repartition of aftershocks around the mainshock even at distances larger than 10 times the rupture length

aftershock modeling based on uncertain stress calculations 1 we discuss the impact of uncertainties in computed coseismic stress perturbations on the seismicity rate changes forecasted through a rate and state dependent frictional model we aim to understand how the variability of coulomb stress changes affects the correlation between predicted and observed changes in the rate of earthquake production we use the aftershock activity following the 1992 m7 3 landers california earthquake as a case study to accomplish these tasks we first analyze the variability of stress changes resulting from the use of different published slip distributions we find that the standard deviation of the uncertainty is of the same size as the absolute stress change and that their ratio the coefficient of variation cv is approximately constant in space this uncertainty has a strong impact on the forecasted aftershock activity if a rate and state frictional model is considered we use the early aftershocks to invert for friction parameters and the coefficient of variation by means of the maximum likelihood method we show that when the uncertainties are properly taken into account the inversion yields stable results which fit the spatiotemporal aftershock sequence the analysis of the 1992 landers sequence demonstrates that accounting for realistic uncertainties in stress changes strongly improves the correlation between modeled and observed seismicity rate changes for this sequence we measure a friction parameter asn 0 017 mpa and a coefficient of stress variation cv 0 95

maar diatreme phreatomagmatism at hopi buttes navajo nation arizona usa remnants of an extensive maar diatreme volcanic field are magnificently exposed at various depths of erosion in the hopi buttes volcanic field of northeastern arizona field and petrographic studies of both the maar and diatreme elements of a selection of volcanoes within the field show that 1 lower sections of the maar rim sequences are typically rich in sandy mudrock derived from the pre eruptive mio pliocene bidahochi formation and the muddy bidahochi sediment was soft and wet at the time of maar eruptions 2 beds higher within the rims contain generally increased proportions of sandstone clasts from the triassic wingate formation in the diatremes late emplaced breccia has deeper seated lithics than more marginal breccia emplaced earlier and 3 many vents are topped by megacryst enriched scoria and spatter and deep seated xenoliths are known only from upper diatreme and craterfilling tephra these observations show that 1 eruptions at hopi buttes involved interaction of magma with unconsolidated mudrock at shallow levels and the phreatomagmatic processes that provided the bulk of the energy involved in the violent eruptions were driven by the interaction of magma and wet sediment 2 the locus of explosive activity migrated downward as eruptions progressed and 3 the closing stage of many eruptions was characterized by rapid magma rise and relative depletion of water

high frequency spectral falloff of earthquakes fractal dimension of complex rupture b value and the scaling of strength on faults the high frequency falloff omega sup minus gamma of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones the author assumes that the high frequency energy of a main shock is produced by a self similar distribution of subevents where the number of subevents with radii greated than r is proportional to r sup minus d d being the fractal dimension in this model an earthquake is composed of a hierarchical set of smaller earthquakes the static stress drop is parameterized to be proportional to r sup eta and strength is assumed to be proportional to static stress drop he finds that a distribution of subevents with d 2 and stress drop independent of seismic moment eta 0 produces a main shock with an omega sup minus 2 falloff if the subevent areas fill the rupture area of the main shock by equating subevents to islands of high stress of a random self similar stress field on a fault he relates d to the scaling of strength on a fault such that d 2 minus eta thus d 2 corresponds to constant stress drop scaling eta 0 and scale invariant fault strength amore self similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value the size distribution of aftershock rupture zones and the scaling of strength on a fault the b value for aftershock sequences on a fault is found to equal 3 minus 1 5 eta 3 eta therefore this model indicates that the typically observed spectral falloffs of omega sup minus 2 and b values of 1 can be entirely caused by scale invariant strength eta 0 along fault zones less

the phase relations among atmospheric co2 content temperature and global ice volume over the past 420 ka the phase relations leads lags among atmospheric co 2 content temperature and global ice volume are key to understanding the causes of glacial interglacial g ig climate transitions comparing the co 2 record with other proxy variables from the vostok ice core and stacked marine oxygen isotope records allows the phase relations among these variables over the last four g ig cycles to be estimated lagged generalized least squares regression provides an e cient and precise technique for this estimation bootstrap resampling allows account to be taken of measurement and timescale errors over the full 420 ka of the vostok record co 2 variations lag behind atmospheric temperature changes in the southern hemisphere by 1 3 1 0 ka and lead over global ice volume variations by 2 7 1 3 ka however signi cant short term changes in the lag of co 2 relative to temperature subsequent to terminations ii and iii are also detected 2001 elsevier science ltd all rights reserved

facies variation of eruption units produced by the passage of single pyroclastic surge currents hopi buttes volcanic field usa abstract base surges are a significant volcanic hazard associated with phreatomagmatism but their transport and depositional dynamics are incompletely understood stratigraphic analysis and lateral tracing of surge eruption units produced by the passage of single base surges from haskie tuff ring hopi buttes volcanic field usa extend to 1 km from the vent and show similar downcurrent changes in lithofacies within 200 m of the vent eruption units are primarily disorganized lapilli tuff that is rich in juvenile pyroclasts at distances 200 m from the vent eruption units transform into a couplet of juvenile rich lapilli that grades upward into bedform bearing ash tuff at distances 900 m upper and lower beds of the eruption unit couplet transform into planar stratified beds at distances 1100 m couplets composing different eruption units are almost entirely composed of planar beds and amalgamate to form almost identical planar bedded ash tuff the collapse of dense eruption columns following explosive magma wet sediment interaction generated turbulent surge currents as the surges traveled away from the haskie vent they expanded and partitioned into a basal juvenile rich traction carpet and overlying accidental rich ash cloud surge near the limit of their runout the surges cooled and lost their pyroclastic load leaving planar beds of accidental rich ash the deposition of multiple surge eruption units with similar lateral and vertical facies transitions and a paucity of interbedded fallout suggests an eruption characterized by recurring phreatomagmatic explosions of similar size and the generation of surges with similar flow characteristics

sensitivity of static stress calculations to the earthquake slip distribution 1 the apparent strong correlation between coulomb stress changes and the spatial distribution of aftershocks suggests the possibility of making near real time estimations of areas at risk of experiencing off fault aftershocks in order to do this in practice a number of issues must first be addressed including the extent to which the main shock slip must be known in detail before a meaningful stress map can be constructed here we investigate this issue by constructing a time ordered sequence of slip solutions for the landers earthquake computing coulomb stress changes for each solution and quantitatively comparing the stress field with the observed aftershocks by 1 resolving the coulomb stress change onto the aftershock nodal planes and calculating the percentage of events consistent with triggering and 2 constructing a two dimensional map of coulomb stress and computing the correlation coefficient between the positive and negative areas and the locations of the aftershocks we find that slip solutions based on empirical relations and either focal mechanism or moment tensor data produce stress fields inconsistent with the observed spatial distribution of aftershocks whereas slip solutions incorporating the correct rupture geometry but greatly simplified slip produce stress fields consistent with the aftershock distribution when very near fault events are excluded we further find that resolving stress perturbations onto earthquake nodal planes and computing the percentage of events experiencing positive coulomb stress provides a poor measure of success because of the limited range of structures on which events occur and the compatibility of the main shock stress field with these structures our results support the hypothesis that coulomb stress changes affect the spatial distribution of aftershocks and suggest that meaningful calculations of coulomb stress can be made as soon as an earthquake s rupture geometry is well constrained

amplified hazard of small volume monogenetic eruptions due to environmental controls orakei basin auckland volcanic field new zealand orakei maar and tuff ring in the auckland volcanic field is an example of a basaltic volcano in which the style and impacts of the eruption of a small volume of magma were modulated by a fine balance between magma flux and groundwater availability these conditions were optimised by the pre 85 ka eruption being hosted in a zone of fractured and variably permeable plio pleistocene mudstones and sandstones orakei maar represents an end member in the spectrum of short lived basaltic volcanoes where substrate conditions rather than the magmatic volatile content was the dominant factor controlling explosivity and eruption styles the eruption excavated a crater 80 m deep that was subsequently filled by slumped crater wall material followed by lacustrine and marine sediments the explosion crater may have been less than 800 m in diameter but wall collapse and wave erosion has left a 1 000 m diameter roughly circular basin a tuff ring around part of the maar comprises dominantly base surge deposits along with subordinate fall units grain size texture and shape characteristics indicate a strong influence of magma water and magma mud interactions that controlled explosivity throughout the eruption but also an ongoing secondary role of magmatic gas driven expansion and fragmentation the tuff contains 70 of material recycled from the underlying plio pliestocene sediments which is strongly predominant in the 2 fraction the magmatic clasts are evolved alkali basalt consistent with the eruption of a very small batch of magma the environmental impact of this eruption was disproportionally large when considering the low volume of magma involved dre 0 003 km3 hence this eruption exemplifies one of the worst case scenarios for an eruption within the densely populated auckland city destroying an area of 3 km2 by crater formation and base surge impact an equivalent scenario for the same magma conditions without groundwater interaction would yield a scoria spatter cone with a diameter of 400 550 m destroying less than a tenth of the area affected by the orakei event

nanoseismicity and picoseismicity rate changes from static stress triggering caused by a mw 2 2 earthquake in mponeng gold mine south africa static stress changes following large earthquakes are known to affect the rate and distribution of aftershocks yet this process has not been thoroughly investigated for nanoseismicity and picoseismicity at centimeter length scales here we utilize a unique data set of m 3 4 earthquakes following a mw 2 2 earthquake in mponeng gold mine south africa that was recorded during a quiet interval in the mine to investigate if rate and state based modeling is valid for shallow mining induced seismicity we use dieterich s 1994 rate and state dependent formulation for earthquake productivity which requires estimation of four parameters 1 coulomb stress changes due to the main shock 2 the reference seismicity rate 3 frictional resistance parameter and 4 the duration of aftershock relaxation time comparisons of the modeled spatiotemporal patterns of seismicity based on two different source models with the observed distribution show that while the spatial patterns match well the rate of modeled aftershocks is lower than the observed rate to test our model we used three metrics of the goodness of fit evaluation the null hypothesis of no significant difference between modeled and observed seismicity rates was only rejected in the depth interval containing the main shock results show that mining induced earthquakes may be followed by a stress relaxation expressed through aftershocks located on the rupture plane and in regions of positive coulomb stress change furthermore we demonstrate that the main features of the temporal and spatial distributions of very small mining induced earthquakes can be successfully determined using rate and state based stress modeling

time and space variations in magmatic and phreatomagmatic eruptive processes at easy chair lunar crater volcanic field nevada usa the products of monogenetic volcanoes often record complex sequences of eruptive processes easy chair volcano lunar crater volcanic field nevada usa was formed by a monogenetic eruption along a 2 5 km long series of en echelon fissure vents hawaiian to strombolian fountains along the fissures dominated initial activity producing a series of agglomerate ramparts focusing of eruptive activity to two central vents and the formation of two overlapping scoria cones followed the early phase fountain fed lavas from those cones merged to form a channel that fed lava onto a flow field at the foot of the cones focusing of subsurface magma flow toward the central conduits may have reduced magma flux in the remaining fissures and the southern segment s entered a phase of phreatomagmatic explosions that destroyed the early agglomerate rampart and formed a maar and tephra ring composed of lapilli tuff rich in clasts derived from pre easy chair lavas and early agglomerates the eruption closed with a minor phase of magmatic activity that deposited scoria lapilli and bombs on top of the phreatomagmatic deposits the eruptive sequence indicates that relatively low hazard strombolian to hawaiian activity can be replaced by more hazardous phreatomagmatic explosions well into a monogenetic eruption

a seismicity burst following the 2010 m 6 4 jiashian earthquake implications for short term seismic hazards in southern taiwan abstract following the 4 march 2010 mw 6 4 jiashian earthquake the seismicity rate in southern taiwan was determined to be significantly higher than before the quake and aroused seismic hazard awareness in this work seismic hazards were investigated in terms of earthquake activity the coulomb stress change the rate and state friction model and short term seismic hazard assessments the significantly higher seismicity rate that followed the 2010 jiashian earthquake was found to mainly be attributed to aftershock decay in terms of the modified omori formula the results suggest that aftershock duration may continue until the end of 2012 the spatial migration of seismicity was modeled using the coulomb stress changes of large earthquakes most of the consequent events were distributed in the vicinity of large earthquakes the observations corresponded to a remarkable stress increase within the same area additionally large events were located within regions with stress increases promoted by previous earthquakes the results confirm interactive relationships between large events by considering time dependency the seismicity rate evolution was estimated using the rate and state friction model the results indicated that a high seismic rate will persist at least until the end of 2012 short term probabilistic seismic hazard assessments were also applied in terms of the probability of strong ground motion using this application a sudden jump in seismic hazards in southern taiwan was accompanied by each large earthquake at the end of 2012 it is expected that hazards will return to a background level our results may be valuable in the future to decision makers and public officials engaged in seismic hazard mitigation

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

afterslip and aftershocks in the rate and state friction law istituto nazionale di geofisica e vulcanologia italy ingv centre national de la recherche scientifique cnrs exxonmobil upstream research company

improving empirical aftershock modeling based on additional source information 1 several mechanisms are proposed to underlie earthquake triggering including static stress interactions and dynamic stress transfer significant differences of these mechanisms are particularly expected in the spatial distribution of aftershocks however testing the different hypotheses is challenging because it requires the consideration of the large uncertainties involved in stress calculations as well as the appropriate consideration of secondary aftershock triggering which is related to stress changes induced by smaller pre and aftershocks in order to evaluate the forecast capability of different mechanisms we take the effect of smaller magnitude earthquakes into account by using the epidemic type aftershock sequence etas model where the spatial probability distribution of direct aftershocks if available is correlated to alternative source information and mechanisms we test surface shaking rupture geometry and slip distributions as an approximation of the shaking level we use shakemap data which are available in near real time after a main shock and thus could be used for first order forecasts of the spatial aftershock distribution alternatively we test the use of empirical decay laws related to minimum fault distance and coulomb stress change calculations based on published and random slip models for comparison we analyze the likelihood values of the different model combinations in the case of several well known aftershock sequences 1992 landers 1999 hector mine 2004 parkfield our test shows that the fault geometry is the most valuable information for improving aftershock forecasts furthermore we find that static stress maps can additionally improve the forecasts of off fault aftershock locations while the integration of ground shaking data could not upgrade the results significantly

the effect of pre existing craters on the initial development of explosive volcanic eruptions an experimental investigation most volcanic eruptions occur in craters formed by previous activity the presence of a crater implies specific confinement geometries variably filled by loose fragmental deposits which are expected to exert a strong yet poorly studied control on the violent gas expansion that drives the eruption here we analyze patterns of ejection from buried explosions in analog experiments in order to investigate how the presence of a crater and changes in explosion depth and intensity may affect the formation of eruptive ejecta jets results show that scaled depth charge burial depth divided by the cubic root of charge energy controls the velocity and partly spread angle of eruptive jets independently of the presence of a pre existing crater conversely for a fixed scaled depth the presence of a pre existing crater limits the development of a laterally expanding annulus of the jet these results are directly applicable to interpretation of volcanic explosions key points analysis of ejection patterns from intra and extra crater buried explosions velocity and spread angle of ejecta jet are sensitive to explosion scaled depth radially expanding annulus of the jet is sensitive to pre existing crater

impact of the receiver fault distribution on aftershock activity 1 aftershock models are usually based either on purely empirical relations ignoring the physical mechanism or on deterministic calculations of stress changes on a predefined receiver fault orientation here we investigate the effect of considering more realistic fault systems in models based on static coulomb stress changes for that purpose we perform earthquake simulations with elastic half space stress interactions rate and state dependent frictional earthquake nucleation and extended ruptures with heterogeneous fractal slip distributions we find that the consideration of earthquake nucleation on multiple receiver fault orientations does not influence the shape of the temporal omori type aftershock decay but changes significantly the predicted spatial patterns and the total number of triggered events so called stress shadows with decreased activity almost vanish and activation decays continuously with increasing distance from the main shock rupture the total aftershock productivity which is shown to be almost independent of the assumed background rate increases significantly if multiple receiver fault planes exist the application to the 1992 m7 3 landers california aftershock sequence indicates a good agreement with the locations and the total productivity of the observed directly triggered aftershocks

cumulative coulomb stress triggering as an explanation for the canterbury new zealand aftershock sequence initial conditions are everything using 2 years of aftershock data and three fault plane solutions for each of the initial m7 1 darfield earthquake and the larger m 6 aftershocks we conduct a detailed examination of coulomb stress transfer in the canterbury 2010 2011 earthquake sequence moment tensor solutions exist for 283 of the events with m ge 3 6 while 713 other events of m ge 3 6 have only hypocentre and magnitude information available we look at various methods for deciding between the two possible mechanisms for the 283 events with moment tensor solutions including conformation to observed surface faulting and maximum delta cff transfer from the darfield main shock for the remaining events imputation methods for the mechanism including nearest neighbour kernel smoothing and optimal plane methods are considered fault length width and depth are arrived at via a suite of scaling relations a large 50 70 proportion of the faults considered were calculated to have initial loading in excess of the final stress drop the majority of faults that accumulated positive delta cff during the sequence were encouraged by the main shock failure but on the other hand of the faults that failed during the sequence more than 50 of faults appeared to have accumulated a negative delta cff from all preceding failures during the sequence these results were qualitatively insensitive to any of the factors considered we conclude that there is much unknown about how coulomb stress triggering works in practice

evolution and hydrological conditions of a maar volcano atexcac crater eastern mexico abstract the atexcac maar is located in the central part of the serdan oriental lacustrine playa basin in the eastern mexican volcanic belt it is part of a dispersed and isolated monogenetic field consisting of maar volcanoes basaltic cinder cones and rhyolitic domes atexac is a maar volcano excavated into pyroclastic deposits basaltic lava flows and the flanks of a cinder cone cluster which itself was built on a topographic high consisting of limestone it has an ene trending elliptical shape with beds mostly unconsolidated deposits that dip outward at 16 22 the atexcac crater was formed from vigorous phreatomagmatic explosions in which fluctuations in the availability of external water temporal migration of the locus of the explosion and periodic injection of new magma were important controls on the evolution of the maar crater variations in grain sizes and component proportions of correlated deposits from the different sections suggest a migration of the locus of explosions producing different eruptive conditions with fluctuating water magma interactions deposits rich in large intrusive and limestone blocks are associated with a matrix enriched in small andesitic lapilli this could suggest differential degrees of fragmentation due to inherited previously acquired fragmentation and or relative distance to the locus of explosions initial short lived phreatic explosions started at the southwest part of the crater and were followed by an ephemeral vertical column and the influx of external water that led to relatively shallow explosive interactions with the ascending basaltic magma drier explosions progressed downward and or laterally northward sampling subsurface rock types particularly intrusive limestone and andesitic zones as well as localized altered zones n ne caused by repetitive injection of basaltic magma a final explosive phase involved a new injection of magma and a new influx of external water producing wetter conditions at the end of the maar formation we infer the aquifer was formed by fractured rocks predominantly andesitic lava flows and limestone rocks andesitic accessory clasts dominate in all stratigraphic levels but these rocks are not exposed in the nearby area these local hydrogeological conditions contrast with those at nearby maar volcanoes where the water for the magma water interactions apparently mostly came from a dominantly unconsolidated tuffaceous aquifer producing tuff rings with a much lower profile than atexcac

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

structural constraints on the spatial distribution of aftershocks 1 calculations of static stress changes due to large earthquakes have shown that the spatial distribution of aftershocks is predictable to first order with aftershocks primarily occurring in areas experiencing positive stress changes delineation of these areas relies on resolving the stress perturbation onto planes with known orientations common practice is to use poorly constrained regional stress information to compute optimally oriented failure planes assuming that they exist everywhere here we show that this assumption is not supported by observation but rather that aftershock failure planes are controlled by geological structure we argue that useful aftershock hazard estimates are better made by replacing information on regional stress with statistical measures of structural orientations

can coseismic stress variability suppress seismicity shadows insights from a rate and state friction model 1 the paucity of detectable seismicity shadows in the days months following a main shock has raised the question as to whether dynamic rather than static triggering could be the main mechanism driving the seismicity at these timescales the lack of correlation between the stress unloading of the main fault and the typically vigourous aftershock production taking place on it however suggests that the spatial heterogeneity of the coseismic stress change could also be a factor in the apparent suppression of seismicity shadows at least on the main fault here we study whether this stress variability can indeed be an important aspect in the stress modeling of earthquake sequences a rate and state friction model of seismicity is used in conjunction with realistic levels of stress heterogeneity at the earthquake nucleation scale 1 10 m as predicted from these friction laws based on scale invariant models of coseismic slip distribution in this model a relatively weak on fault quiescence is delayed by months to years because of the high stress heterogeneity delayed quiescences due to slip heterogeneity are similarly predicted at distances of up to about half the rupture length away from the fault we also postulate that off fault seismicity can be significantly controlled by stress variability that originates from small scale crustal heterogeneity and the complexity in fault geometries rather than mapping stress changes by providing a single stress value at every grid point these results suggest that an estimate of the likely stress variability acting at the nucleation scale is also needed especially when trying to account for the seismicity occurring at relatively short timescales

response of seismic activity in mines to the stress changes due to mining induced strong seismic events the influence of the static stress transfer due to two stronger seismic events from one mine section on subsequent seismicity linked to the same section is studied the first strong tremor was provoked by destressing blasting the static stress transfer caused by this tremor had apparently a triggering effect for the occurrence of the second strong event this second event occurred in less than three weeks after the first one and on the area of simultaneous enhancement of both shear and normal components of the coulomb stress change caused by the first event it appears also that in the next few months the cumulative stress change due to both the events influenced significantly the location and rate of smaller subsequent events interestingly contrary to the results of previous analyses the negative coulomb stress changes turn out to have a major role in this respect the coseismic stress change impact even seems to prevail over the influence of time varying stress alteration caused by advancement of the mining front

onto what planes should coulomb stress perturbations be resolved 1 coulomb stress maps are produced by computing the tensorial stress perturbation due to an earthquake rupture and resolving this tensor onto planes of a particular orientation it is often assumed that aftershock fault planes are optimally oriented in other words the regional stress and coseismic stress change are used to compute the orientation of planes most likely to fail and the coseismic stress is resolved onto these orientations this practice assumes that faults capable of sustaining aftershocks exist at all orientations an assumption contradicted by the observation that aftershock focal mechanisms have strong preferred orientations consistent with mapped structural trends here we systematically investigate the best planes onto which stress should be resolved for the landers hector mine loma prieta and northridge earthquakes by quantitatively comparing observed aftershock distributions with stress maps based on optimally oriented planes two and three dimensional main shock orientation and regional structural trend we find that the best model differs between different tectonic regions but that in all cases models that incorporate the regional stress field tend to produce stress maps that best fit the observed aftershock distributions although not all such models do so equally well our results suggest that when the regional stress field is poorly defined or in structurally complex areas the best model may be to fix the strike of the planes upon which the stress is to be resolved to that of the main shock but allow the dip and rake to vary

response of the san jacinto fault zone to static stress changes from the 1992 landers earthquake we perform an analysis of the seismicity response of the san jacinto fault zone to static coulomb stress changes from the 1992 landers earthquake sequence results show that in general stress changes forecast rate changes well we find a significant positive correlation between the change in rate and the magnitude of the coulomb stress change with a correlation coefficient of 0 76 equivalent to 5 6 when compared to a 0 null hypothesis furthermore although the correlations are less clear over negative than positive stress changes there is evidence of some coulomb stress dependent quiescence on stress shadows models that account for heterogeneity in reference seismicity show clear improvements in their predictions of spatial variability of aftershock rates compared to those that assume uniform reference we find also that better performance is obtained 1 using a time dependent coulomb rate state model compared to a time independent exponential model and 2 using structurally constrained rather than optimal target fault orientations these results are an important step in the validation of coulomb stress based methods for quantitative seismicity forecasting we conclude that the correspondence between the predictions of coulomb stress models for aftershock seismicity may be sensitive to strong heterogeneity in aftershock locations and orientations associated with the presence of large scale structure in aftershock study areas in these cases we suggest that where the regional structure is mapped incorporating it explicitly into coulomb stress models may improve the performance of quantitative coulomb stress based forecasts

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

a variety of aftershock decays in the rate and state friction model due to the effect of secondary aftershocks implications derived from an analysis of real aftershock sequences the model based on rate and state dependent friction law reproduces the temporal decay of an aftershock sequence with the p value of the omori utsu law equal to 1 if we simply assume a constant stress rate over time however because p values vary in real aftershock sequences this model requires some modification this study examined the effect of secondary aftershocks on the variety of the p value a large aftershock causes a stepwise stress increase in the aftershock area and the expected seismicity rate derived from the friction law also increases abruptly these multiple increases in the seismicity rate during its decay following a mainshock could cause variation in the apparent p value in this study a model incorporating this idea is applied to two aftershock sequences observed in japan and is shown to substantially modify the modeling of aftershock activity

extending earthquakes reach through cascading earthquakes whatever their size can trigger other earthquakes mainshocks cause aftershocks to occur which in turn activate their own local aftershock sequences resulting in a cascade of triggering that extends the reach of the initial mainshock a long lasting difficulty is to determine which earthquakes are connected either directly or indirectly here we show that this causal structure can be found probabilistically with no a priori model nor parameterization large regional earthquakes are found to have a short direct influence in comparison to the overall aftershock sequence duration relative to these large mainshocks small earthquakes collectively have a greater effect on triggering hence cascade triggering is a key component in earthquake interactions

the stress shadow induced by the 1975 1984 krafla rifting episode 1 it has been posited that the 1975 1984 krafla rifting episode in northern iceland was responsible for a significant drop in the rate of earthquakes along the husavik flatey fault hff a transform fault that had previously been the source of several magnitude 6 7 earthquakes this compelling case of the existence of a stress shadow has never been studied in detail and the implications of such a stress shadow remain an open question according to rate state models intense stress shadows cause tens of years of low seismicity rate followed by a faster recovery phase of rate increase here we compare the long term predictions from a coulomb stress model of the rifting episode with seismological observations from the sil catalog 1995 2011 in northern iceland in the analyzed time frame we find that the rift induced stress shadow coincides with the eastern half of the fault where the observed seismicity rates are found to be significantly lower than expected given the historical earthquake activity there we also find that the seismicity rates on the central part of the hff increased significantly in the last 17 years with the seismicity progressively recovering from west to east our observations confirm that rate state theory successfully describes the long term seismic rate variation during the reloading phase of a fault invested by a negative coulomb stress coincident with this recovery we find that the b value of the frequency magnitude distribution changed significantly over time we conclude that the rift induced stress shadow not only decreased the seismic rate on the eastern part of the hff but also temporarily modified how the system releases seismic energy with more large magnitude events in proportion to small ones this behavior is currently being overturned as rift induced locking is now being compensated by tectonic forcing

southern california hypocenter relocation with waveform cross correlation part 2 results using source specific station terms and cluster analysis we obtain precise relative relocations for more than 340 000 southern california earthquakes between 1984 and 2002 by applying the source specific station term ssst method to existing p and s phase picks and a differential lo cation method to about 208 000 events within similar event clusters identified with waveform cross correlation the entire catalog is first relocated by using existing phase picks a reference 1d velocity model and the ssst method of richards dinger and shearer 2000 we also perform separate relocations of imperial valley events by using a velocity model more suited to this region next we apply cluster analysis to the waveform cross correlation output to identify similar event clusters we re locate earthquakes within each similar event cluster by using the differential times alone keeping the cluster centroid fixed to its initial ssst location we estimate standard errors for the relative locations from the internal consistency of differential locations between individual event pairs these errors are often as small as tens of meters in many cases the relocated events within each similar event cluster align in planar features suggestive of faults we observe a surprising number of such faults at small scales that strike nearly perpendicular to the main seismicity trends in general the fine scale details of the seismicity reveal a great deal of structural com plexity in southern california fault systems