active deformation to the north of the altyn tagh fault constraints on the northward growth of the northern tibetan plateau abstract sinistral transpressive deformation occurs in the region north of the altyn tagh fault due to the indo eurasian collision in this region several late cenozoic faults have developed and the sanweishan fault is the key feature with clear landforms in this study slip rate measurements combined with several dating methods imply that the sanweishan fault has been active with sinistral strike slip rates of 0 33 0 04 mm a since 14 ka bp and 0 28 0 03 mm a since 20 ka bp which are more than an order of magnitude smaller than that of the atf to the south the horizontal displacements are 1 7 5 5 m in the eastern segment and 25 0 76 0 m in the middle and western segments of the sanweishan fault the increment of horizontal displacement along the main sanweishan fault is 3 0 4 0 m between paleoearthquakes and the magnitude of the latest paleoearthquake on the middle and eastern segments of the fault is up to m 7 2 7 5 the whole length of the sanweishan fault is 360 km or longer which include active faults in the yangguan and danghe reservoirs in the west more components of thrusting occur on the western and eastern segments of the sanweishan fault the growth of the sanweishan fault is similar to that of the atf but the former fault is younger and its slip rate is much smaller the differential slip rates on the sanweishan fault and atf may result in the clockwise rotation and eastward movement of the intervening block which compresses regions to the northeast

serial ruptures of the san andreas fault carrizo plain california revealed by three dimensional excavations 1 it is poorly known if fault slip repeats regularly through many earthquake cycles well documented measurements of successive slips rarely span more than three earthquake cycles in this paper we present evidence of six sequential offsets across the san andreas fault at a site in the carrizo plain using stream channels as piercing lines we opened a latticework of trenches across the offset channels on both sides of the fault to expose their subsurface stratigraphy we can correlate the channels across the fault on the basis of their elevations shapes stratigraphy and ages the three dimensional excavations allow us to locate accurately the offset channel pairs and to determine the amounts of motion for each pair we find that the dextral slips associated with the six events in the last millennium are from oldest to youngest 5 4 0 6 8 0 0 5 1 4 0 5 5 2 0 6 7 6 0 4 and 7 9 0 1 m in this series three and possibly four of the six offset values are between 7 and 8 m the common occurrence of 7 8 m offsets suggests remarkably regular but not strictly uniform slip behavior age constraints for these events at our site combined with previous paleoseismic investigations within a few kilometers allow a construction of offset history and a preliminary evaluation of slip and time predictable models the average slip rate over the span of the past five events between a d 1210 and a d 1857 has been 34 mm yr not resolvably different from the previously determined late holocene slip rate and the modern geodetic strain accumulation rate we find that the slip predictable model is a better fit than the time predictable model in general earthquake slip is positively correlated with the time interval preceding the event smaller offsets coincide with shorter prior intervals and larger offset with longer prior intervals

a mass failure model for the initial degradation of fault scarps with application to the 1959 scarps at hebgen lake montana abstract calculation of earthquake scarp ages from scarp morphology usually assumes that scarp materials reach their angle of repose immediately after a rupture however observations of the 1959 hebgen lake montana earthquake scarp and similar features worldwide confirm that scarps require a finite period of mass failure to reach the initial conditions for hillslope diffusion so the age of features less than 1000 yr old cannot be accurately estimated with methods based only on the linear diffusion equation we apply a numerical model of this interval of mass failure degradation to vertical initial angle scarps from the 1959 rupture at hebgen lake montana the mass failure rate coefficient r m ranges from 1 0 10 2 to 1 2 10 1 m yr 1 for young scarps at hebgen lake and nine other locations and has little or no dependence on climate conditions such as annual temperature range or average rainfall including an interval of mass failure gives more accurate age estimates where a scarp age is of the same order as the characteristic mass failure relaxation time of 10 1000 yr

stress slip and earthquakes in models of complex single fault systems incorporating brittle and creep deformations numerical simulations of slip evolution along a cellular vertical strike slip fault in an elastic half space are performed for several models representing discrete fault systems embedded in three dimensional elastic continua the geometry and imposed boundary conditions correspond approximately to the central san andreas fault the simulations incorporate brittle and creep deformations in series the net fault zone deformation rate is the sum of creep rate and frictional slip rate brittle fault properties are given by various distributions of earthquake stress drops on failing segments numerical cells the assumed distributions represent two idealized situations corresponding to different extreme states along an evolutionary path of a fault 1 a strongly disordered state characterized by a wide range of size scales representing immature fault zones and extended spatial domains and 2 a relatively regular state having a narrow range of size scales representing mature highly slipped faults the assumed creep properties are identical in all cases these are prescribed in terms of coefficients characterizing a power law dependency of creep slip rate on stress the combined brittle creep process and employed parameters lead to an overall pine tree stress depth profile with a brittle ductile transition depth of about 12 5 km and variable stress along strike profiles with brittle creep transition around 65 km nw of the 1857 rupture the spatial patterns of simulated hypocenters are statistically similar to observed data the results indicate that the range of size scales characterizing strong fault zone heterogeneities has important manifestations on the seismic response of a fault system a narrow range of size scales leads to frequency size statistics of earthquakes resembling the characteristic earthquake distribution and quasi periodic temporal distribution of large events as in the seismic gap hypothesis on the other hand a wide range of size scales leads to gutenberg richter power law frequency size statistics and random or clustered temporal distribution of large events the simulations demonstrate that treatment of the various observed forms of frequency size and temporal statistics of earthquakes can be unified through the concept of range of size scales characterizing fault zone heterogeneities this has a clear physical interpretation in terms of structural properties of a given fault zone or broad lithospheric domain and is supported by observed earthquake and fault data in some simulated cases the frequency size statistics of small earthquakes fall sharply below the self similar gutenberg richter line the results indicate that small earthquakes prepare the fault for the occurrence of a large event by smoothing during gradual tectonic loading the long wavelength components of stress on the fault this is done through short wavelength stress roughening associated with the numerous ruptures of the small events the above pattern of smoothing roughening of long short wavelengths of stress on the fault is reversed during large scale ruptures of the big events

open and almost shut case for explosive eruptions vent processes determined by so2 emission rates at karymsky volcano kamchatka vent processes were examined at karymsky volcano kamchatka by measuring so2 emissions using a correlation spectrometer cospec continuous high sensitivity cospec measurements and physical observations were collected on 11 and 12 september 1999 when karymsky was producing small ashy eruptions every 5 20 min each eruptive event began with an explosion and audible rumbling lasting 30 s followed in some cases by audible chugging lasting to 2 min gas plumes accompanied each event and almost without exception the plumes dissipated and became invisible despite significant so2 emissions variations in so2 output show distinctive patterns that correlate with eruption activity maximum so2 output occurred following each explosion and then declined rapidly to low but detectable levels in contrast a second type of event often associated with audible chugging was characterized by high so2 output long after the initial ash blast variations in degassing at karymsky can be explained by secondary boiling gas pressure accumulation and vent resealing we developed a new application of the cospec technique to study the dynamic vent processes of erupting volcanoes this application provides insights into the processes that occur at the otherwise inaccessible vents of erupting volcanoes particularly when a volcano changes from passive degassing and small explosions to degassing patterns that may precede a larger and more dangerous eruption

deformation processes adjacent to active faults examples from eastern california 1 major seismogenic faults are embedded within narrow zones of inelastic off fault deformation ofd where both distributed displacement and modification of rock properties occur active distributed displacement may affect slip rate estimates seismic energy radiation and geodynamic models this study addresses the role of ofd in the displacement history and mechanical behavior of seismogenic faults by multisite study of deformed geologic features adjacent to 30 60 km long active strike slip faults of 10 km of dextral displacement in the mojave desert eastern california we find that distributed displacement accommodates 0 to 25 of the total displacement over zones of one to two kilometers width displacement occurs mostly within 100 200 m of faults and decreases nonlinearly away from the main fault we show evidence for distributed displacement through simple shear in the form of parallel secondary faults and progressive deformation of linear markers adjacent to the calico fault we also find evidence for shear via rotation and progressive fragmentation adjacent to the harper lake fault analysis of block dimensions show that blocks tend to decrease in size toward faults and that cumulative length of secondary faults is longer than the main fault by at least a factor of 10 based on crosscutting relationships and the relationship of ofd to geophysically imaged compliant zones around active faults we argue that distributed displacement is an active process and suggest that zones of diminished rigidity near faults may be at least in part driven by secondary faulting during the rupture propagation along the main fault

characteristic slip for five great earthquakes along the fuyun fault in china the seismic hazard associated with an individual fault can be assessed from the distributions of slip and recurrence times of earthquakes however seismic cycle models 1 that aim to predict rupture lengths and fault displacements of successive earthquakes on one fault remain poorly validated it is therefore unknown whether individual fault segments rupture independently producing earthquakes with a diverse range of magnitudes and recurrence times or slip by characteristic amounts with characteristic magnitudes here we use highresolution satellite data to document the horizontal offsets of stream channels and terraces created by strike slip motion on the fuyun fault xinjiang china during five historical earthquakes we find that the ms 7 9 11 august 1931 earthquake produced a surface rupture with a length of 160 km dispersed over three different fault segments the 290 measured stream channel and terrace offsets record an average slip of 6 3 m we use the degree of preservation of geomorphological markers to assign relative ages to individual fault offsets and identify at least four distinct older earthquakes we find that these older earthquakes also produced fault offsets with a similar distribution to the 1931 earthquake as the slip distributions during five successive earthquakes were so similar we conclude that ruptures on the fuyun fault obey a characteristic slip model very few large earthquakes are known to have ruptured the same fault segment twice in historical or instrumental time 1 the

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

coseismic strike slip at a point during the last four earthquakes on the wellington fault near wellington new zealand 1 we analyze progressively displaced late quaternary 12 ka fluvial terraces along the wellington fault near wellington new zealand optically stimulated luminescence dating indicates that degradational terraces were produced at a rate of about one terrace per 1000 years similar to the rate of earthquake surface rupturing along the hutt river near te marua we measured the strike slip of 15 terrace risers and paleochannels on the lowest 8 of these terraces of holocene age the river after earthquakes was generally capable of smoothing its faulted riverbanks the dextral offsets appear to fall into several groupings that record slip accumulation during the last four earthquakes we calculate a mean single event slip of 5 0 0 24 m 95 confidence with an rms scatter 1 of slips about the mean of 1 5 m the coefficient of variation cv of single event slip is thus 0 30 this cv is slightly less than a recently compiled global average for point measurements on strike slip faults suggesting that the southernmost wellington fault has behaved in a more nearly characteristic way we speculate that recent large earthquake ruptures have been bounded on their southern end by the wellington fault s offshore fault termination and perhaps on their northern end by a 2 km wide releasing step over such persistent sources of rupture arrest might have led to a relative uniformity of rupture dimensions and slip amounts we infer a late holocene dextral slip rate of 4 5 0 4 mm yr 1 and 8 2 mm yr and a mean earthquake recurrence interval of 610 1100 years

past and future earthquakes on the san andreas fault the san andreas fault in calfornia is one of the best studied earthquake generating faults in the world in their perspective weldon et al discuss recent efforts to construct rupture scenarios that is possible histories of the date location and length of fault rupture of past earthquakes on the fault existing knowledge of the locations and dates of past earthquakes can be explained by different scenarios but the authors argue that the evidence favors the hypothesis that the fault breaks in relatively infrequent large earthquakes they caution that the current 148 year hiatus since the last big earthquake is likely to end within the next 50 years with a large rupture or sequence of ruptures spanning a substantial part of the fault

seismic source mechanism of degassing bursts at kilauea volcano hawaii results from waveform inversion in the 10 50 s band the current march 2008 to february 2009 summit eruptive activity at kilauea volcano is characterized by explosive degassing bursts accompanied by very long period vlp seismic signals we model the source mechanisms of vlp signals in the 10 50 s band using data recorded for 15 bursts with a 10 station broadband network deployed in the summit caldera to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account the vlp signals associated with the bursts originate in a source region 1 km below the eastern perimeter of halemaumau pit crater the observed waveforms are well explained by the combination of a volumetric component and a vertical single force component for the volumetric component several source geometries are obtained which equally explain the observed waveforms these geometries include 1 a pipe dipping 64 to the northeast 2 two intersecting cracks including an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east 3 a pipe dipping 58 to the northeast intersecting a crack dipping 48 to the west southwest and 4 a pipe dipping 57 to the northeast intersecting a pipe dipping 58 to the west southwest using the dual crack model as reference the largest volume change obtained among the 15 bursts is 24 400 m3 and the maximum amplitude peak to peak of the force is 20 gn each burst is marked by a similar sequence of deflation and inflation trailed by decaying oscillations of the volumetric source the vertical force is initially upward synchronous with source deflation then downward synchronous with source reinflation followed by oscillations with polarity opposite to the volumetric oscillations this combination of force and volume change is attributed to pressure and momentum changes induced during a fluid dynamic source mechanism involving the ascent expansion and burst of a large slug of gas within the upper 150 m of the magma conduit as the slug expands upon approach to the surface and more liquid becomes wall supported by viscous shear forces the pressure below the slug decreases inducing conduit deflation and an upward force on the earth the final rapid slug expansion and burst stimulate vlp and lp oscillations of the conduit system which slowly decay due to viscous dissipation and elastic radiation consideration of the fluid dynamic arguments leads us to prefer the dual crack vlp source model as it is the only candidate model capable of producing plausible values of length scales and pressure changes the magnitudes of the vertical forces observed in the 15 bursts appear consistent with slug masses of 104 to 106 kg

modeling repeated coseismic slip to identify and characterize individual earthquakes from geomorphic offsets on strike slip faults abstract coseismic slip distributions of repeated earthquakes are important data used to forecast magnitude and recurrence characteristics of future earthquakes many studies infer coseismic slip of past individual paleoearthquakes from frequency histograms of geomorphic offsets such histograms often expressed as a copd cumulative offset probability distribution commonly show multiple peaks with similar displacements which are interpreted to be incremental slip associated with successive paleoearthquakes however assumptions in linking copd peaks to individual earthquakes have not been fully explored here we combine statistical modeling with global historical coseismic surface rupture data to evaluate the conditions required for the approach the results show that only coseismic slip with low variability allow more than one event identification for example even low covs coefficient of offset variation of 0 25 and 0 35 permit identification of only 2 to 3 events in contrast the mean cov value for all historical ruptures is 0 58 to 0 66 furthermore interpreting the first copd peak as a single event slip distribution could result in artificially low variation and flatter distribution of offset than observed in historical earthquakes this study cautions that robust copd interpretation on large strike slip faults requires low offset variability a sufficient number of offset measurements and additional constraints like historical coseismic slip data or paleoseismic event sequence data

multiparameter quantification of gas release during weak strombolian eruptions at pacaya volcano guatemala 1 activity at pacaya volcano guatemala is characterized by persistent degassing coupled at times with lava effusion and or coincident strombolian style explosions we used 0 25 hz sample rate sulfur dioxide emission data from a uv camera and coincident infrasound recordings to investigate the link between varied emission rates and infrasound events degassing rates varied on two scales during this study smaller more rapid variations on the scale of 1 to 3 minutes are superimposed on larger slower changes over 30 minutes to 1 hour the acoustic record was dominated by repeated n shaped events characteristic of strombolian explosions because of the high resolution of the gas measurements we were able to calculate gas masses for individual explosions from both datasets and find the two estimates agree within an order of magnitude the infrasound explosion records correlate with small pulses in degassing but the longer term degassing trends may represent a deeper process

variability in eruption style and associated very long period events at fuego volcano guatemala 1 repeated short term deployments of seismic infrasound video and gas emission instruments at fuego volcano guatemala have revealed three types of very long period vlp events associated with conduit sealing pressure accumulation and release in 2008 ash rich explosions issued from a vent on the western flank and produced one type of vlp type 1 impulsive bomb rich explosions from the summit vent in 2009 produced a shorter period vlp type 2 but also generated ash release type 3 vlp events occurred during ash free exhalations from the summit in 2008 and had waveform shapes similar to type 2 events weak infrasound records for type 1 explosions compared to type 2 suggest lower pressures and higher magma porosity for type 1 type 3 events correlate with spikes in so2 emission rate and are driven by partial sealing and rapid release of ash free gas at the summit vent variations in the vlp period may provide a new tool for monitoring conditions within the conduit

volcanic gas emissions from soufriere hills volcano montserrat 1995 2009 with implications for mafic magma supply and degassing volcanic gas emissions illustrate a complex volatile budget for soufriere hills volcano montserrat fluxes of sulphur dioxide carbon dioxide hydrogen sulphide and hydrogen chloride and probably water are substantial from this arc volcano additional sources of volatiles in addition to the erupting andesite are required to satisfy the mass balance defined by gas emissions and petrological constraints mafic magma is intruded at depths of 10 km supplying volatiles by quenching crystallising and vesiculating at the andesite mafic magma interface sulphur carbon dioxide and other volatiles supplied to the system migrate to the surface and their fluxes remain high while mafic recharge at depth is sustained decompression degassing of porphyritic andesite supplies chlorine and water to the gas plume chlorine partitions into vapour from the melt during periods of active extrusion making the hcl so2 ratio of volcanic gases a reliable indicator of the onset of eruptive activity studies of this volatile budget highlight the role of deep degassing and vapour production at arc volcanoes which are important mechanisms for driving the eruption due to its effects on magma buoyancy and the advection of heat through the system

three dimensional investigation of a 5 m deflected swale along the san andreas fault in the carrizo plain topographic maps produced from light detection and ranging lidar data are useful for paleoseismic and neotectonic research because they pro vide submeter representation of faulting related surface features offset measurements of geomorphic features made in the field or on a remotely sensed imagery commonly assume a straight or smooth i e undeflected pre earthquake geometry here we present results from investigation of an 20 cm deep and 5 m wide swale with a sharp bend along the san andreas fault saf at the bidart fan site in the carrizo plain california from analysis of lidar topography images and field measure ments the swale was initially interpreted as a channel tectonically offset 4 7 m our observations from exposures in four backhoe excavations and 25 hand dug trenchettes show that even though a sharp bend in the swale coincides with the trace of the a d 1857 fault rupture the swale formed after the 1857 earthquake and was not tectonically offset subtle fractures observed within a surficial gravel unit overlying the 1857 rupture trace are similar to fractures previously documented at the phelan fan and ly4 paleoseismic sites 3 and 35 km northwest of bidart fan respectively collectively the fractures suggest that a post 1857 moderate magnitude earthquake caused ground cracking in the carrizo and cholame stretches of the saf our obser vations emphasize the importance of excavation at key locations to validate remote and ground based measurements and we advocate more geomorphic characterization for each site if excavation is not possible online material figures of trench logs

fault slip and earthquake recurrence along strike slip faults contributions of high resolution geomorphic data article i nfo understanding earthquake eq recurrence relies on information about the timing and size of past eq ruptures along a given fault knowledge of a fault s rupture history provides valuable information on its potential future behavior enabling seismic hazard estimates and loss mitigation stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing eqs analysis of the latter data sets culminated during the mid 1980s in the formulation of now classical eq recurrence models now routinely used to assess seismic hazard within the last decade light detection and ranging lidar surveying technology and other high resolution data sets became increasingly available to tectono geomorphic studies promising to contribute to better informed models of eq recurrence and slip accumulation patterns after reviewing motivation and background we outline requirements to successfully reconstruct a fault s offset accumulation pattern from geomorphic evidence we address sources of uncertainty affecting offset measure ment and advocate approaches to minimize them a number of recent studies focus on single eq slip distribu tions and along fault slip accumulation patterns we put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation cv for eq inter event time and slip per event and find that a single event offsets vary over a wide range of length scales and the sources for offset variability differ with length scale b at fault segment length scales single event offsets are essentially constant c along fault offset accumulation as resolved in the geomorphic record is dominated by essentially same size large offset in crements and d there is generally no one to one correlation between the offset accumulation pattern constrained in the geomorphic record and eq occurrence as identified in the stratigraphic record revealing the higher resolution and preservation potential of the latter while slip accumulation along a fault segment may be dominated by repetition of large nearly constant offset increments timing of surface rupture is less regular

quantification of the gas mass emitted during single explosions on stromboli with the so2 imaging camera we performed measurements using an so2 imaging camera of the so2 gas mass emitted during five discrete explosive events on stromboli volcano on 3 october 2006 the so2 gas mass released during discrete explosions was 15 40 kg per explosion producing 3 8 of the total daily so2 gas emission demonstrating that in terms of gas flux strombolian explosions are a second order phenomenon compared with quiescent degassing using the typical gas composition measured with op ftir allows us to determine the total gas mass released during an explosion as 360 960 kg with a volume of 1500 4100 m 3 at 1 bar at the probable source pressure of gas slug formation of 75 mpa this gas amount would occupy a volume equivalent to a sphere with a radius of 0 8 1 m comparable with estimates of stromboli s conduit geometry c 2009 elsevier b v all rights reserved

stratigraphic evidence for seven meters of dextral slip on the san andreas fault during the 1857 earthquake in the carrizo plain the smallest geomorphic offsets along a 35 km section of the san andreas fault in the carrizo plain vary from 7 to 10 m our three dimensional excavation of alluvial deposits a few km southeast of wallace creek confirms that at least 6 6 to 6 9 m of dextral slip occurred there during the latest large earthquake in 1857 dates on detrital charcoal suggest that the last event prior to the 1857 earthquake occurred before a date within the range a d 1305 to 1623 the 3 m range in smallest offsets along this portion of the fault may reflect either a 3 m variation in slip along the san andreas in 1857 or 2 to 3 m of slip during an event prior to 1857 observations made after the recent landers earthquake are compatible with the hypothesis of large local variations in slip during a single earthquake but do not explain the cause of such variations off fault dextral rotations would be one plausible explanation however paleoseismic data in the carrizo plain are too sparse to allow rejection of the alternative hypothesis that slip in the event prior to 1857 was only 2 to 3 m an amount of slip which would be several times too small to fit a time predictable model

influence of lithosphere viscosity structure on estimates of fault slip rate in the mojave region of the san andreas fault system 1 it is well known that slip rate estimates from geodetic data are nonunique because they depend on model assumptions and parameters that are often not known a priori estimates of fault slip rate on the mojave segment of the san andreas fault system derived from elastic block models and gps data are significantly lower than estimates from geologic data to determine the extent to which the slip rate discrepancy might be due to the oversimplified models of the rheology of the lithosphere we develop a two dimensional linear maxwell viscoelastic earthquake cycle model and simultaneously estimate fault slip rates and lithosphere viscosity structure in the mojave region the model consists of episodic earthquakes in an elastic crust overlying layers with different viscosities that represent the lower crust uppermost mantle and upper mantle we use gps measurements of postseismic relaxation following the 1992 landers earthquake triangulation measurements spanning 1932 1977 gps measurements of the contemporary velocity field and paleoseismic data along the san andreas fault we infer lower crustal 15 30 km depth viscosity of 1019 10 20 pa s uppermost mantle 30 60 km viscosity of 10 20 22 pa s and underlying upper mantle viscosity of 10 18 10 19 pa s consistent with inferences from laboratory experiments of relatively high viscosity lithospheric mantle and lower viscosity lower crust and underlying asthenospheric mantle we infer a 20 30 mm yr slip rate on the san andreas fault in agreement with the lower end of geologic estimates inversions of geodetic data with models that do not incorporate layered viscosity structure may significantly misestimate slip rates

modes of extension at oceanic spreading centers evidence from the solea graben troodos ophiolite cyprus abstract the solea graben in the troodos ophiolite cyprus represents a preserved cretaceous age axial valley formed during a brief period of amagmatic seafloor spreading structural analysis of all crustal levels of the graben reveals two periods of deformation an extensive early phase of extensional deformation associated with seafloor spreading and a later phase of minor deformation associated with obduction and doming of the complex during the tertiary recent amagmatic extensional deformation produced networks of normal faults that dip toward the graben axis and sole into a regional detachment fault located at the sheeted dike plutonic contact and oriented subparallel to ophiolite pseudostratigraphy individual fault segments are essentially planar but link to approximate listric geometries locally bulk structural rotation of fault blocks bounding the graben occurred about a nnw trending axis parallel to the present graben trend average dips in the sheeted complex within the central portions of the graben suggest 40 50 of structural rotation although this is a minimum figure because present dike dips are not a simple function of rotation magnitude tensor analysis of fault populations associated with extensional deformation shows that 3 was oriented approximately perpendicular to the graben axis late near axis extensional deformation segmented the detachment fault along nnw trending normal faults obduction related uplift and doming of the troodos ophiolite is expressed in the solea graben by minor thrust reverse and strike slip faults principally developed during reactivation of pre existing low angle fault zones formed during seafloor deformation tensor analysis of this later phase of faulting shows that 1 was oriented approximately n s and that 2 and 3 alternated position during the deformation the style of deformation documented in the solea graben supports recent speculation for basin and range style detachment faulting at slow spreading ridge crests with low magma budgets such as parts of the mid atlantic ridge near large offset transform faults natural cross sectional exposure of the solea graben shows how extensional structures might link at depth beneath such slow spreading ridge segments and demonstrates the importance of extensive brittle deformation of the crust prior to establishment of large scale ore forming hydrothermal circulation cells

changes to the volcanic outgassing mechanism and very long period seismicity from 2007 to 2011 at mt asama japan abstract volcanic gases can provide significant information on the state of magma which is important for interpreting and predicting volcanic activity we present a study of the seismicity and volcanic gases from mt asama japan from 2007 to 2011 to elucidate the change in the mechanism of volcanic gas supply for very long period vlp seismic events two types of degassing occur at mt asama persistent degassing and a gas burst ash free eruption following a vlp seismic event we used the linear relationship between the seismic moment and sulfur dioxide so 2 emissions and seismic records to estimate the quantity of so 2 gas in the ash free eruption which causes the vlp seismic events the amount of so 2 and volcanic gas composition data were used to calculate the amount of volcanic gases including h 2 o co 2 and other species we compared the volcanic gas emission rates of ash free eruptions eruptive gas emission rates and total volcanic gas emission rates including the persistent degassing the ratio of the eruptive gas emission rate to the total gas emission rate eruptive total gas ratios showed a drastic change with eruption an increase occurred immediately before the 2008 and after the 2009 eruptions the vlp seismic events are likely caused by sudden outgassing at a shallow depth that is induced by the propagation of the gas phase expansion and rupture we suggest that the rates of sudden outgassing are controlled by the distribution of gas phases in the conduit the variability of the eruptive gas emission rates suggests changes in the gas phase distribution in the conduit

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

earthquake slip distribution a statistical model 1 the purpose of this paper is to interpret slip statistics in a framework of extended earthquake sources we first discuss deformation pattern of the earth s surface from earthquakes and suggest that continuum versus block motion controversy can be reconciled by a model of the fractal distribution of seismic sources we consider earthquake slip statistical distributions as they can be inferred from seismic moment frequency relations and geometrical scaling for earthquakes using various assumptions on temporal earthquake occurrence these distributions are synthesized to evaluate the accuracy of geologic fault slip determinations and to estimate uncertainties in long term earthquake patterns based on paleoseismic data because the seismic moment distribution is a power law pareto a major part of the total seismic moment is released by major earthquakes m 10 19 5 n m moment magnitude m 7 for these large earthquakes the rupture is confined to the upper brittle crust layer we review the various moment frequency and earthquake scaling relationships and apply them to infer the slip distribution at area and site specific regions simulating the seismic moment and strain accumulation process demonstrates that some synthetics can be interpreted as examples of a quasiperiodic sequence we demonstrate the application of the derived slip statistical relations by analyzing the slip distribution and history of the san andreas fault at wrightwood california

geochemistry and intrusive directions in sheeted dikes in the troodos ophiolite implications for mid ocean ridge spreading centers 1 sheeted dikes at mid ocean ridge volcanoes represent the link between deep magma production and storage processes and shallow processes such as volcanism and hydrothermal activity as such they are crucial for the interpretation of many observations at mid ocean ridges or other volcanoes with pronounced rift zones including topography hydrothermal systems petrology and geochemistry we carried out a structural magnetic and chemical investigation of a 4 10 km sheeted dike section in the troodos ophiolite cyprus on the basis of major and trace element geochemistry we distinguish dikes that may be correlated with the basal high ti series hts lavas from those of the overlying low ti series lts lavas all dikes studied are nearly parallel to each other with vertical or steeply dipping planes whose strike likely indicates the orientation of the spreading center anisotropy of magnetic susceptibility measurements suggests that the hts and lts dikes intrude in fundamentally different ways hts dikes reflect the intrusive behavior of dikes in the vicinity of a magma supply system and define ridge parallel intrusive sheets that radiate out from the magma chamber lts dikes show a bimodal orthogonal set of intrusive directions one shallow and one near vertical near lateral propagating dikes provide a means for delivery of magma into distant portions of a rift system and near vertical dike propagation directions are probably associated with feeder dikes to down rift surface flows our study suggests that the types of dike intrusive behavior in the troodos ophiolite may also be typical for normal mid ocean ridges or other major shield volcanoes with well developed rift zones

strain accumulation across strike slip faults investigation of the influence of laterally varying lithospheric properties 1 we use boundary element methods to develop antiplane strike slip earthquake cycle models consisting of faulting in an elastic plate with possibly different thickness and stiffness on either side of the fault overlying a linear maxwell viscoelastic substrate we show that isolated plate models that neglect the coupling of the plate to the underlying substrate might significantly overpredict the asymmetry in deformation across the fault we also show that flow in a low viscosity channel in the lower crust could significantly contribute to the asymmetry through a fully probabilistic scheme we invert geodetic data across three strike slip fault systems for effective elastic thickness and elastic stiffness on both sides of the fault using geological and geophysical constraints for the renun segment of the great sumatra fault inversion results show the elastic layer on the east side is stiffer than the west side but the effective elastic thicknesses are not resolvable for the carrizo segment of the san andreas fault the inversion results slightly favor a thicker elastic layer on the east side 2 2 times but stiffer layer on west side 1 2 times however uniform effective elastic thickness and stiffness cannot be ruled out for the aksay segment of the altyn tagh fault in northern tibet inversion results show the effective elastic crust of the tarim basin must be stiffer and thicker than the effective elastic crust of the tibetan plateau to the south but the viscosity of a hypothesized mid crustal tibetan channel is not resolvable

estimating surface rupture length and magnitude of paleoearthquakes from point measurements of rupture displacement we present a method to estimate paleomagnitude and rupture extent from measurements of displacement at a single point on a fault the variability of historic ruptures is summarized in a histogram of normalized slip then scaled to give the probability of finding a given displacement within a rupture for any magnitude considered the histogram can be inverted assuming any magnitude earthquake is as likely as another yielding probability density functions of magnitude and rupture length for any given displacement measurement to improve these distributions we include a term to account for the probability that the earthquake would cause ground rupture and two alternative distributions of earthquake magnitude the gutenberg richter magnitude distribution predicts shorter rupture lengths and smaller magnitudes than does a uniform distribution where any magnitude earthquake is considered equally likely longer ruptures and larger magnitudes than the uniform model are predicted by an alternative magnitude distribution designed to return site average displacement this model is a generalization of the characteristic earthquake model and reasonably describes paleoseismic findings on the southern san andreas fault where slip is accommodated by average displacements of a few meters and earthquake recurrence times of 100 250 years our results should increase the value of paleoseismic displacement measurements for hazard assessment in particular they quantify probability estimates of earthquake magnitude and rupture length where point observations of rupture displacement are available and so can contribute to probabilistic seismic hazard analyses online material rupture profiles used to sample rupture variability

slip complexity in earthquake fault models we summarize studies of earthquake fault models that give rise to slip complexities like those in natural earthquakes for models of smooth faults between elastically deformable continua it is critical that the friction laws involve a characteristic distance for slip weakening or evolution of surface state that results in a finite nucleation size or coherent slip patch size h models of smooth faults using numerical cell size properly small compared to h show periodic response or complex and apparently chaotic histories of large events but have not been found to show small event complexity like the self similar power law gutenberg richter frequency size statistics this conclusion is supported in the present paper by fully inertial elastodynamic modeling of earthquake sequences in contrast some models of locally heterogeneous faults with quasi independent fault segments represented approximately by simulations with cell size larger than h so that the model becomes inherently discrete do show small event complexity of the gutenberg richter type models based on classical friction laws without a weakening length scale or for which the numerical procedure imposes an abrupt strength drop at the onset of slip have h 0 and hence always fall into the inherently discrete class we suggest that the small event complexity that some such models show will not survive regularization of the constitutive description by inclusion of an appropriate length scale leading to a finite h and a corresponding reduction of numerical grid size

direct geological evidence for prior earthquakes on the 1981 corinth fault central greece we present the preliminary results of geomorphic and trench investigations at the eastern end of a scarp produced by the 1981 corinth earthquake sequence at this site the 1981 rupture produced average vertical displacements of 0 6 0 7 m maximum 1 3 m that in part occurred along a cumulative scarp which displaces the fan surface by up to 5 m based on this cumulative scarp displacing the holocene fan surface we estimate a vertical slip rate of 1 mm yr that translates to 1 mm yr n s extension we found evidence for two individual pre 1981 earthquakes which occurred on the basis of preliminary radiocarbon dating on two paleosols shortly after a d 590 and a d 1295 each of these events produced a vertical displacement ranging between 0 5 and 1 2 m hence comparable to the 1981 scarp height this suggests that coseismic slip may have been characteristic at this location over the past three seismic cycles following this hypothesis and assuming a periodic strain release a maximum recurrence interval of 700 yr is calculated these results indicate that the 1981 surface breaking faults accommodate only part of the regional extension deduced from the geodetic measurements

evidence for an earthquake barrier model from mw 7 8 kokoxili tibet earthquake slip distribution abstract the slip distribution of the mw 7 8 kokoxili tibet 2001 earthquake has been measured at high resolution using optical correlation of satellite images and provides both the parallel and perpendicular components of the horizontal co seismic slip this reveals a variation of the horizontal slip at a scale of 20 km along strike anti correlation of slip parallel and perpendicular to the fault indicates transfer of slip from the horizontal to the vertical component at the ends of segments these features suggest a rupture model with segments separated by strong persistent geometric barriers the unexpected ending of the rupture south of the main fault can be explain by such a structure but bears important implications for the initiation and rupture directivity of the next earthquake

revised dates of large earthquakes along the carrizo section of the san andreas fault california since a d 1310 30 1 precise knowledge of the age and magnitude of past earthquakes is essential for characterizing models of earthquake recurrence and key to forecasting future earthquakes we present 28 new radiocarbon analyses that refine the chronology of the last five earthquakes at the bidart fan site along the carrizo section of the south central san andreas fault which last ruptured during the fort tejon earthquake in a d 1857 the new data show that the penultimate earthquake in the carrizo plain occurred not earlier than a d 1640 and the modeled 95th percentile ranges of the three earlier earthquakes and their mean are a d 1540 1630 1585 a d 1360 1425 1393 and a d 1280 1340 1310 indicating an average time interval of 137 44 years between large earthquakes since a d 1310 30 a robust earthquake recurrence model of the carrizo section will require even more well dated earthquakes for thorough characterization however these new data imply that since a d 1310 30 the carrizo section has failed more regularly and more often than previously thought

variability of displacement at a point implications for earthquake size distribution and rupture hazard on faults abstract to investigate the nature of earthquake magnitude distributions on faults we compare the interevent variability of surface displacement at a point on a fault from a composite global data set of paleoseismic observations with the variability expected from two prevailing magnitude frequency distributions the truncated exponential model and the characteristic earthquake model we use forward modeling to predict the coefficient of variation cv for the alternative earthquake distributions incorporating factors that would effect observations of displacement at a site the characteristic earthquake model with a characteristic magnitude range of 0 25 produces cv values consistent with the data cv 0 5 only if the variability for a given earthquake magnitude is small this condition implies that rupture patterns on a fault are stable in keeping with the concept behind the model this constraint also bears upon fault rupture hazard analysis which for lack of point specific information has used global scaling relations to infer variability in average displacement for a given size earthquake exponential distributions of earthquakes from m 5 to the maximum magnitude give rise to cv values that are significantly larger than the empirical constraint a version of the model truncated at m 7 however yields values consistent with a larger cv 0 6 determined for small displacement sites although this result allows for a difference in the magnitude distribution of smaller surface rupturing earthquakes it may reflect in part less stability in the displacement profile of smaller ruptures and or the tails of larger ruptures online material global surface displacement data and identified sources of uncertainty

stratigraphic architecture and fault offsets of alluvial terraces at te marua wellington fault new zealand revealed by pseudo 3d gpr investigation 1 past earthquake slips on faults are commonly determined by measuring morphological offsets at current ground surface because those offsets might not always be well preserved we examine whether the first 10 m below ground surface contains relevant information to complement them we focus on the te marua site new zealand where 11 alluvial terraces have been dextrally offset by the wellington fault we investigated the site using pseudo 3d ground penetrating radar and also produced a high resolution digital elevation model dem of the zone to constrain the surface slip record the gpr data reveal additional information 1 they image the 3d stratigraphic architecture of the seven youngest terraces and show that they are strath terraces carved into graywacke bedrock each strath surface is overlain by 3 5 m of horizontally bedded gravel sheets including two pronounced and traceable reflectors 2 thanks to the multilayer architecture terrace risers and channels are imaged at three depths and their lateral offsets can be measured three to four times constraining respective offsets and their uncertainties more reliably and 3 the offsets are better preserved in the subsurface than at the ground surface likely due to subsequent erosion deposition on the latter from surface and subsurface data we infer that te marua has recorded six cumulative offsets of 2 9 7 6 18 23 2 26 and 31 m 1 2 m large earthquakes on southern wellington fault might produce 3 5 m of slip slightly less than previously proposed pseudo 3d gpr thus provides a novel paleoseismological tool to complement and refine surface investigations

monitoring so2 emission at the soufriere hills volcano implications for changes in eruptive conditions correlation spectrometer measurements of sulfur dioxide so2 emission rates during the current eruption of the soufriere hills volcano montserrat have contributed towards identifying different phases of volcanic activity so2 emission rate has increased from 550 td 1 6 4 kgs 1 after july 1996 with the uncertainty associated with any individual measurement ca 30 significantly enhanced so2 emission rates have been identified in association with early phreatic eruptions 800 td 1 9 3 kgs 1 and episodes of vigorous dome collapse and pyroclastic flow generation 900 to 1500 td 1 10 4 to 17 4 kgs 1 so2 emission rate has proved a useful proxy measurement for magma production rate observed so2 emission rates are significantly higher than those inferred from analyses of glass inclusions in phenocrysts implying the existence of a s rich magmatic vapour phase

high resolution topography derived offsets along the 1857 fort tejon earthquake rupture trace san andreas fault the great fort tejon earthquake of 1857 with an 350 km long surface rupture was the most recent major earthquake along the south central san andreas fault saf prior reconstruction of its surface slip distribution and reconstruction of preceding earthquakes along the 1857 rupture trace have contributed to formulation of the characteristic earthquake cem and uniform slip models usm for earthquake recurrence that find wide application in seismic hazard assessment and earthquake forecasting we used the high resolution b4 light detection and ranging lidar topographic data set sufficient for depiction of meter scale tectonic landforms to reevaluate the distribution of surface displacement along the 1857 rupture trace we present 450 offset measurements with displacements below 60 m increasing observation density relative to previous studies by a factor of 2 our results show that the 1857 earthquake had overall an average displacement below 3 5 m with 4 6 m released along the northwestern half of the rupture its along fault slip distribution is smooth at 10 km length scales at 28 less than prior estimates assuming a 10 km rupture depth and a 30 gpa shear modulus reconstruction of pre 1857 earthquakes is impeded by an exponential decrease in observation density with increasing displacement amount offset observation density soon reaches a level where only tentative and nonunique reconstructions are permitted the results of this study question prior surface slipreconstructions of pre 1857 rupture s that were based on a distinctly lower number of offset observations challenging the applicability of the aforementioned earthquake recurrence models to explain saf rupture behavior online material catalog of offset measurements along the 1857 surface rupture trace as well as an annotated map 1 embed inline graphic 1 gif

paleoseismic evidence of characteristic slip on the western segment of the north anatolian fault turkey we have conducted a paleoseismic investigation of serial fault rupture at one site along the 110 km rupture of the north anatolian fault that produced the mw 7 4 earthquake of 17 august 1999 the benefit of using a recent rupture to compare serial ruptures lies in the fact that the location magnitude and slip vector of the most recent event are all very well documented we wished to determine whether or not the previous few ruptures of the fault were similar to the recent one we chose a site at a step over between two major strike slip traces where the principal fault is a normal fault our two excavations across the 1999 rupture reveal fluvial sands and gravels with two colluvial wedges related to previous earthquakes each wedge is about 0 8 m thick considering the processes of collapse and subsequent diffusion that are responsible for the formation of a colluvial wedge we suggest that the two paleoscarps were similar in height to the 1999 scarp this similarity supports the concept of characteristic slip at least for this location along the fault accelerator mass spectrometry ams radiocarbon dates of 16 charcoal samples are consistent with the interpretation that these two paleoscarps formed during large historical events in 1509 and 1719 if this is correct the most recent three ruptures at the site have occurred at 210 and 280 year intervals

the relationship between degassing and ground deformation at soufriere hills volcano montserrat we examine the correlations between so2 emission rate seismicity and ground deformation in the month prior to the 25 june 1997 dome collapse of the soufriere hills volcano montserrat during this period the volcano exhibited a pattern of cyclic inflation and deflation with an 8 14 h period we find that so 2 emission rates measured by cospec correlate with the amplitude of these tilt cycles and that higher rates of so 2 emission were associated with stronger ground deformation and enhanced hybrid seismicity within tilt cycles degassing peaks coincide with maximum deformation gradients increases in the amount of gas in the magma conduit feeding the dome probably due to increases in volatile content of ascending magma volume can account for the observed increases in tilt amplitude hybrid seismicity and so2 emission rate q 2000 elsevier science b v all rights reserved

reevaluation of surface rupture parameters and faulting segmentation of the 2001 kunlunshan earthquake mw7 8 northern tibetan plateau china the 14 november 2001 m w 7 8 kunlunshan earthquake ruptured the westernmost part of the kunlun fault northern tibetan plateau the main segment affected by this event was the kusaihu segment field investigations allowed us to constrain the length the width and the coseismic horizontal displacement distribution of the kunlunshan earthquake rupture zone the mapped surface rupture zone starts from 90 257 e in the west and ends at 94 795 e in the east with a total length of 426 km it consists of three main sections the western strike slip section the transtensional section and the eastern strike slip section the rupture zone is oriented n100 10 e on average the distribution of the coseismic horizontal displacements is characterized by multiple peaks departing clearly from a general bell shaped distribution reassessment of the maximum coseismic horizontal left lateral displacement yields a value of 7 6 0 4 m at the site 35 767 n 93 323 e consistent with independent measurements derived from interferometric synthetic aperture radar and seismology from this site the horizontal displacement decreases unevenly to both the west and east coseismic vertical reverse displacement is also noted at the eastern end of the rupture but it remains much smaller than the horizontal component the width of the rupture zone varies from site to site from several meters to few kilometers the maximum width measured reaches 8 km along the yuxi feng subsection where a large number of shaking related cracks were well developed

seismological evidence for three dimensional melt migration beneath the east pacific rise the extent to which crustal processes along mid ocean ridges are controlled by either the pattern of mantle upwelling or the mode of magma injection into the crust is not known models of mantle upwelling vary from two dimensional passive flow1 to three dimensional diapiric flow2 3 4 similarly beneath a ridge segment bounded by tectonic offsets crustal magma chambers may be replenished continuously along the ridge5 6 7 or at a central injection zone2 3 4 from which magma migrates towards the segment s ends here we present tomographic images that reveal the seismic structure and anisotropy of the uppermost mantle beneath the east pacific rise the anisotropy is consistent with two dimensional mantle flow diverging from the rise whereas the anomalous isotropic structure requires a three dimensional but continuous distribution of melt near the crust mantle interface our results indicate that crustal magma chambers are replenished at closely spaced intervals along axis and that crustal systems inherit characteristics of scale from melt transport processes originating in the mantle

correlations between so2 flux and long period seismicity at galeras volcano the 14 january 1993 eruption of galeras volcano in colombia which killed six scientists and three tourists1 was followed by a larger eruption on 23 march 19932 both eruptions were preceded by episodes of long period seismicity the source of long period seismic events has been modelled extensively3 8 as the resonance within a fluid filled crack induced by pressure transients in the fluid5 7 here we use the so2 flux from galeras volcano measured remotely to infer the degassing history during the episode of long period events preceding the 23 march eruption so2 flux and long period seismicity have been monitored separately elsewhere to forecast volcanic activity9 13 our results show how the combination and correlation of the two methods can be used to interpret the movement of gases from the magma body to the surface and to monitor the pressure buildup leading to an eruption at explosive volcanoes

finding the buried record of past earthquakes with gpr based palaeoseismology a case study on the hope fault new zealand in places where sedimentation and erosion compete at fast rates part of the record of past earthquakes on faults may be buried hence hidden in the first few metres below the surface we developed a novel form of palaeoseismology of geophysical type based on the use of a dense pseudo 3 d ground penetrating radar gpr survey to investigate such possible buried earthquake traces on a long fast slipping strike slip fault hope fault new zealand at a site terako where marked alluvial conditions prevail we first used lidar data to analyse the ground surface morphology of the 2 km2 site at the greatest resolution nineteen morphological markers were observed mainly alluvial terrace risers and small stream channels that are all dextrally offset by the fault by amounts ranging between 3 and 200 m the measurements document about 10 past earthquake slip events with a mean coseismic slip of 3 3 1 m with the most recent earthquake event having a slip of 3 0 5 m we then investigated a detailed area of the site 400 x 600 m2 with pseudo 3 d gpr we measured 56 similar to 400 m long 510 m spaced gpr profiles 250 mhz parallel to the fault and evenly distributed on either side the analysis revealed the existence of a palaeosurface buried at about 3 m depth corresponding to the top of alluvial terraces of different ages that buried surface is incised by a dense network of stream channels that are all dextrally offset by the fault we measured 48 lateral offsets in the buried channel network more than twice than at the surface these offsets range between 6 and 108 m as observed at the surface yet provide a more continuous record of the fault slip the similarity of the successive slip increments suggests a slip per event averaging 4 4 1 m fairly similar to that estimated from surface data from the total surface and buried 67 offset collection we infer that a minimum of 30 large earthquakes have broken the hope fault at the terako site in the last about 67 kyr with an average coseismic slip of 3 2 1 m a minimum average recurrence time of about 200 yr and a magnitude of at least mw 7 07 4 our study therefore confirms that part of the record of past earthquakes may indeed reside in the first few metres below the surface where it may be explored with geophysical gpr based palaeoseismology developing such a new palaeoseismological tool should provide rich information that may complement surface observations and help to document the past earthquakes on faults

stream channel offset and late holocene slip rate of the san andreas fault at the van matre ranch site carrizo plain california sets of well preserved channels offset across the san andreas fault saf at the van matre ranch vmr site in the northwestern elkhorn hills area of the carrizo plain offer the opportunity to measure slip rate and examine geomorphic development of the channels the fault zone and offset channels were exposed by excavation in one fault perpendicular and five fault parallel trenches the geomor phology and stratigraphy in the channels reveal a record of filling by fluvial sedi mentation lateral colluviation and pedogenesis the buried thalweg of the currently active channel is offset 24 8 1 m while the geomorphic channel is offset approx imately 27 6 1 m seventeen samples were collected from channel margin deposits for 14 c dating an oxcal model of the radiocarbon dates with stratigraphic control suggests that the oldest date for channel incision was a d 1160 minimum and maximum slip rates ranging from 29 3 to 35 6 mm yr are derived from different assumptions about the timing of channel incision and offset the resulting slip rates at vmr agree well with the late holocene slip rate of 33 9 2 9 mm yr at wallace creek approximately 18 km to the northwest and imply that within measurement uncertainty the 30 37 mm yr velocity gradient across the saf from decadal time scale geodetic measurements is accommodated across the several meter wide saf zone at vmr over the last millennium

lateral offsets and revised dates of large prehistoric earthquakes at pallett creek southern california recent excavation and new radiocarbon dates of sediments at pallett creek are the basis for new conclusions regarding the late holocene history of the san andreas fault systematic dissection of a 50 m long 15 m wide 5 m deep volume of earth centered on the fault enables documentation in three dimensions of fault patterns lateral offsets and vertical deformation associated with large earthquakes of the past the excavations expose evidence for 12 earthquakes that occurred between about 260 and 1857 a d with an average recurrence interval of about 145 years prehistoric slip events that occurred in 1720 50 1550 70 1350 50 1080 65 and 845 75 a d have lateral offsets that are comparable to those of the most recent great earthquake of 1857 thus all of these events represent earthquakes of large magnitude the lateral offsets of two other events in 935 85 and 1015 100 a d are an order of magnitude smaller and may be interpreted in several ways with regard to the size of these events the new data constrain the average recurrence interval for large earthquakes at this site to between 145 and 200 years but suggest a monotonic decrease in individual intervals to below this range during the past 900 years on the basis of these data the probability of a large earthquake with surficial fault rupture at this site is between 0 2 and 5 during 1984 and 7 and 60 by the year 2000

overview of the eruption of soufriere hills volcano montserrat 18 july 1995 to december 1997 the onset of phreatic volcanic activity at the soufriere hills volcano montserrat on 18 july 1995 followed a three year period of heightened volcano seismic activity beneath the island phreatic explosions gave way to continuous eruption of juvenile andesitic magma in the form of a lava dome on or around 15 november 1995 magma production rate has varied leading to changes in eruptive style an explosive eruption on 17 september 1996 followed a period of enhanced dome growth and large scale gravitational collapses from its eastern flank increasing dome volume led to stressing and overtopping of the confining crater walls to the southwest north and west during early 1997 sustained high magma production rate since june 1997 has led to three periods of major gravitational dome collapses followed by vulcanian explosive eruptions dome growth re started immediately after the cessation of the latest of these explosive phases in october 1997 and continues as of december 1997

degassing processes during lava dome growth insights from santiaguito lava dome guatemala abstract eruptions of intermediate magma may be explosive or effusive the development of open system degassing has been proposed as a pre requisite for effusion of intermediate magma however processes leading to open system degassing are poorly understood to better understand degassing processes during lava dome extrusion we report high temporal resolution so2 emission rate measurements collected with an ultra violet imaging camera at santiaguito guatemala santiaguito is an ideal case study as the dome lava is compositionally very similar to products of the 1902 plinian eruption of the parental santa maria volcano we find that degassing is weak 0 4 1 kg s 1 but continuous and explosions are associated with small increases in emission rates up to 2 3 kg s 1 continuous repose degassing occurs through a shallow cap rock which likely represents a proto crust on the block lava flow which is extruded from the same vent the continual permeability of the upper conduit argues against a mechanism of explosion triggering in which gas pressure builds beneath a viscous cap rock or plug rather we consider degassing data better consistent with a model of shear fracturing at the conduit margins using field constraints we model the viscosity of santiaguito magma as a function of depth and show that conditions for shear fracturing are met from 150 600 m to the surface this is in line with independent estimates of explosion initiation depth we show that repose timescales are orders of magnitude longer than the timescale for shear fracture and suggest that explosions are triggered when a continuous network of smaller scale fractures develops at which point decompression occurs and an explosion is triggered fracture healing occurs by viscous relaxation however near to the surface where viscosity is highest an unconsolidated gouge layer may develop our model implies that the observed explosions are a by product of extrusion shear fracturing can drive open system degassing of crystal rich intermediate magma at shallow levels in the conduit as high magma viscosity is able to overcome the low strain rates associated with slow ascent of magma

coupled effect of magma degassing and rheology on silicic volcanism abstract explosive volcanism such as the 1991 mt pinatubo philippines and the 2008 mt chaiten chile eruptions is caused by violent vesiculation of hydrous magma however gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit this makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common here we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation x ray radiography and computed tomography we observed for the first time in situ that the shear localization caused magma fracturing and formed a slip plane and thus inhibited deformation and outgassing elsewhere we also observed the compaction of vesicular magma into a dense lava as a result of outgassing when shear localization did not occur in a natural setting shear localizes along the edges of a volcanic conduit where the strain rate is high causing a highly permeable fracturing layer to form at the conduit s edge and leaving less sheared and less outgassed magma at its center the less outgassed magma in the center may ascend rapidly and cause explosive volcanism non explosive lava effusion may occur only when shear localization does not occur effectively this new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity pyroclastic obsidian and highly vesiculated pumice

century long average time intervals between earthquake ruptures of the san andreas fault in the carrizo plain california paleoseismological data constrain the age location and associated magnitude of past surface rupturing earthquakes these are critical parameters for developing and testing fault behavior models and characterizing seismic hazard we present new earthquake evidence and radiocarbon analyses that refi ne the chronology of the six most recent earthquakes that ruptured the south central san andreas fault in the carrizo plain california united states at the bidart fan site modeled 95 percentile ranges of the earthquakes prior to the a d 1857 earthquake are a d 1631 1823 1580 1640 1510 1612 1450 1475 and 1360 1452 the average time interval between the last six earthquakes that ruptured the san andreas fault in the carrizo plain is 88 41 yr this is less than the time since the most recent a d 1857 earthquake less than all reported average intervals of prehistoric earthquakes along the entire san andreas fault and signifi cantly shorter than the 235 yr average used in recent seismic hazard evaluations the new chronological data combined with recent slip studies imply that the magnitudes of the earthquakes that ruptured the southern san andreas fault in the carrizo plain since ca a d 1360 were variable and suggest that the widely held view of rare but great surface rupturing earthquakes along this portion of the southern san andreas fault should be reevaluated 118

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

direct evidence from anisotropy of magnetic susceptibility for lateral melt migration at superfast spreading centers 1 rare fault bounded escarpments expose natural cross sections of ocean crust in several areas and provide an unparalleled opportunity to study the end products of tectonic and magmatic processes that operated at depth beneath oceanic spreading centers we mapped the geologic structure of ocean crust produced at the east pacific rise epr and now exposed along steep cliffs of the pito deep rift near the northern edge of the easter microplate the upper oceanic crust in this area is typified by basaltic lavas underlain by a sheeted dike complex comprising northeast striking moderately to steeply southeast dipping dikes paleomagnetic remanence of oriented blocks of dikes collected with both alvin and jason ii indicate clockwise rotation of 61 related to rotation of the microplate indicating structural coupling between the microplate and crust of the nazca plate to the north the consistent southeast dip of dikes formed as the result of tilting at the epr shortly after their injection anisotropy of magnetic susceptibility of dikes provides well defined magmatic flow directions that are dominantly dike parallel and shallowly plunging corrected to their original epr orientation magma flow is interpreted as near horizontal and parallel to the ridge axis these data provide the first direct evidence from sheeted dikes in ocean crust for along axis magma transport these results also suggest that lateral transport in dikes is important even at fast spreading ridges where a laterally continuous subaxial magma chamber is present

repeat times of large earthquakes implications for earthquake mechanics and long term prediction information on the time intervals between large earthquakes is now available for several fault segments along plate boundaries in japan alaska california cascadia and turkey when dates in a sequence are known historically as along much of the nankai trough they provide information on the natural intrinsic variability of the rupture process most sets of repeat times however are dominated by paleoseismic determinations of dates of older large earthquakes which contain measurement uncertainties in addition to intrinsic variability a bayesian technique along with prior information on measurement uncertainties is used to make maximum likelihood estimates of intrinsic repeat time and its normalized standard deviation the coefficient of variation cv it is these intrinsic parameters and their uncertainties that are most useful for understanding the mechanics of earthquakes and for prediction for timescales of a few decades our estimates of intrinsic cv are small 0 to 0 25 for several very active fault segments where deformation is relatively simple large events do not appear to be missing in historic and paleoseismic records and data are available at or near major asperities and away from the ends of rupture zones cv is larger for regions of multibranched faulting overlapping slip near the ends of rupture zones and for data from uplifted terraces at subduction zones a poisson process is an inferior characterization of all of the 11 segments we examined scenarios used by recent working groups that assume either poissonian behavior or renewal processes with cv of 0 5 0 2 for the most active fault segments in the san francisco bay area likely lead to incorrect 30 year probability estimates the hayward fault and perhaps the peninsular segment of the san andreas fault in the san francisco bay area appear to be advanced in their buildup of stress that will be released in future large earthquakes multibranched faulting may account for why the predicted tokai earthquake in japan has not occurred as of 2006 parkfield earthquakes from 1857 to 2004 were characterized by the largest uncertainty of the sequences we studied cv 0 37 which may account for the failure of past predictions the large cv for parkfield fits our hypothesis that relatively weak fault segments are characterized by more irregular earthquake recurrence paleoseismic data from coastal sites along the cascadia subduction zone are characterized by cvs of about 0 3

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

paleoseismic and postseismic observations of surface slip along the parkfield segment of the san andreas fault parkfield is considered a transitional segment along the san andreas fault saf between continuous fault creep to the northwest and segments to the southeast that last slipped in the great 1857 fort tejon earthquake historically creep and recurring m 6 0 earthquakes have been observed at parkfield california but the segment s relevance in great saf earthquakes has remained uncertain this paleoseismic study of the central parkfield segment provides a 2000 year record of tectonically deformed fluvial and sag stratigraphy two fault perpendicular excavations across a pressure ridge and a sag pond 200 m north of carr hill exposed five primary fault zones displaying apparent vertical offsets upward splaying clay shear bands and warped stratigraphy four of five fault zones extended into the uppermost stratigraphy suggesting recent surface offset and fault creep several antithetic fault splays and one primary fault zone displayed upward terminations but strong indicators of large magnitude earthquakes with meter scale surface offset and rupture such as filled fissures and colluvial scarp deposits were not observed the absence of evidence for large magnitude earthquakes does not preclude the possibility of 1857 style earthquakes extending into the parkfield segment however all deformation exposed within these trenches is consistent with repeated small ground rupture and fault creep the 2004 m 6 0 parkfield earthquake ruptured through the site and activated at least three of the five fault zones exposed in our excavations comparison between 2004 vertical offset and vertical offsets within the exposed stratigraphy suggests a recurrence interval between 8 and 188 years for m 6 0 earthquakes at parkfield online material supplemental unit descriptions unanalyzed radiocarbon samples and trench logs and photos

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

relation between single very long period pulses and volcanic gas emissions at mt asama japan 1 multiple volcanic observations conducted at mt asama japan provide evidence of a link between single very long period vlp seismic pulses and volcanic gas emissions so2 flux measurements were conducted on 2 june 2009 when mt asama was producing ash free eruptions with vlp pulses gas bursts from a vent at the crater bottom following the vlp pulses provided an excellent opportunity to examine the relation directly the so2 emission for each eruption was calculated by integrating high temporal so2 flux data obtained by the so2 imaging system and subtracting the contribution from quiescent degassing from fumaroles around the crater bottom a seismic moment of vlp pulse was estimated by the waveform inversion we observed seven eruptions and obtained the proportional relation between vlp pulse moment and so2 emission the relation determined is consistent with the vlp source model these observational results are the first report of a quantitative comparison between single vlp pulse moment and volcanic gas emission

pressure changes associated with the ascent and bursting of gas slugs in liquid filled vertical and inclined conduits at basaltic volcanoes the sources of long period and very long period seismicity and acoustic signals are frequently described in terms of fluid dynamic processes in particular the formation and ascent of gas slugs within the magma column and their bursting at the surface to investigate pressure changes associated with these processes two phase flow experiments have been carried out in vertical and inclined pipes with both single gas slugs and a continuously supplied gas phase the ascent of individual gas slugs is accompanied by strong dynamic pressure variations resulting from the flow of liquid around the slug these dynamic transients generate sub static pressures below the ascending slug in viscosity controlled systems and produce super static pressures when the slug reaches the surface and motion ceases in inertia dominated systems conduit inclination promotes a change of regime from bubbly to slug flow and favours an increase in size and velocity of the slugs at the expense of their frequency of occurrence during continuously supplied two phase flow the experimental pressure data support previous theoretical analyses of oscillatory sources in ascending slugs as the slugs approach the surface and burst pressure oscillations are also observed during the release of gas slugs and in their wake region

very long period pulses at asama volcano central japan inferred from dense seismic observations summary we observed seismic events consisting of several one sided velocity pulses with durations of 5 30 s hereafter called very long period or vlp pulses using up to 14 broad band seismometers installed near the summit area of asama volcano japan particle motions do not point to a single source location despite their rectilinearities suggesting a non isotropic source mechanism together with path effect we conducted moment tensor inversion analyses for these events using the green s functions of not only translational motions but also of tilt motions the best fitting source locations are located north of the crater centre at depths of 100 150 m below the crater bottom the principal value ratios of moment tensor solutions can be approximated as 5 3 2 which is indicative of a combination of a tensile crack and a cylinder with the strike and dip angle of the crack both being nearly 70 and symmetry axis of the cylinder being inclined by nearly 30 from the vertical the time histories of moment tensors are indicative of an initial sudden pressurization and subsequent gradual depressurization at the source region we sought to model vlp pulses at asama volcano by considering the inflow and outflow of gas at the source cavity compensated by boiling in another deeper reservoir

co seismic and cumulative offsets of the recent earthquakes along the karakax left lateral strike slip fault in western tibet abstract the 400 km long karakax left lateral strike slip fault is the westernmost segment of the altyn tagh fault it separates northwestern tibet to the south from the tarim basin to the north the western section of the karakax fault exhibits clear co seismic surface ruptures of past large earthquakes geomorphic offset measurements from the field and high resolution ikonos images along 1 5 km across the sanshiliyingfang fan and along 55 km of the fault range from 3 to 28 m with distinct clusters at 6 2 3 14 2 19 2 and 24 3 m the cluster of the smallest offsets around 6 m full range from 3 to 10 m distributed over a minimum length of 55 km is attributed to the last largest surface rupturing event that testifies of the occurrence of a magnitude mw 7 4 7 6 earthquake along the karakax fault we interpret the other offset clusters as the possible repetition of similarly sized events thus favoring a characteristic slip model for the karakax fault in a 3 m deep trench dug across the active trace of the fault we can identify the main rupture strands of the last and penultimate events the penultimate event horizon a silty sand layer has been radiocarbon dated at 975 1020 ad ams 14 c age it is proposed that large mw 7 4 7 6 events with co seismic slip of about 6 m rupture the karakax fault with a return time of about 900 years implying an average slip rate of about 6 7 mm years during the late holocene these results suggest that the karakax fault is the largest left lateral strike slip fault at the rim of northwestern tibet accommodating eastward movement of tibet due to the india eurasia collision

slip on the san andreas fault at parkfield california over two earthquake cycles and the implications for seismic hazard parkfield california which experienced m 6 0 earthquakes in 1934 1966 and 2004 is one of the few locales for which geodetic observations span multiple earthquake cycles we undertake a comprehensive study of deformation over the most recent earthquake cycle and explore the results in the context of geodetic data collected prior to the 1966 event through joint inversion of the variety of parkfield geodetic measurements trilateration two color laser and global positioning system including previously unpublished two color data we estimate the spatial distribution of slip and slip rate along the san andreas using a fault geometry based on precisely relocated seismicity although the three most recent parkfield earthquakes appear complementary in their along strike distributions of slip they do not produce uniform strain release along strike over multiple seismic cycles since the 1934 earthquake more than 1 m of slip deficit has accumulated on portions of the fault that slipped in the 1966 and 2004 earthquakes and an average of 2 m of slip deficit exists on the 33 km of the fault southeast of gold hill to be released in a future perhaps larger earthquake it appears that the fault is capable of partially releasing stored strain in moderate earthquakes maintaining a disequilibrium through multiple earthquake cycles this complicates the application of simple earthquake recurrence models that assume only the strain accumulated since the most recent event is relevant to the size or timing of an upcoming earthquake our findings further emphasize that accumulated slip deficit is not sufficient for earthquake nucleation online material model fault geometry fit to the data for the inversions and model resolution

six similar sequential ruptures of the san andreas fault carrizo plain california we document the precise sizes but not the dates of the six latest offsets across the san andreas fault at wallace creek california three and perhaps four of these including the latest in 1857 show dextral offset of 7 5 8 m the third and fourth offsets however are just 1 4 and 5 2 m the predominance of similar offsets for the latest six events suggests that the fundamental properties of the fault system that control slip size do not vary greatly from event to event the large offsets imply that ruptures involving this site are typically more than 200 km long

inference of multiple earthquake cycle relaxation timescales from irregular geodetic sampling of interseismic deformation abstract characterizing surface deformation throughout a full earthquake cycle is a challenge due to the lack of high resolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals 250 10 000 years here we approach this problem by comparing long term geologic slip rates with geodetically derived fault slip rates by sampling only a short fraction 0 001 0 1 of a complete earthquake cycle along 15 continental strike slip faults geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle the timing of the last earthquake on many of these faults is poorly known and may vary greatly from fault to fault assuming that the underlying mechanics of the seismic cycle are similar for all faults geodetic observations from different faults may be interpreted as samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record along any one fault alone as an ensemble we find that geologically and geodetically inferred slip rates agree well with a linear relation of 0 94 0 09 to simultaneously explain both the ensemble agreement between geologic and geodetic slip rate estimates with observations of rapid postseismic deformation we consider the predictions from simple two layer earthquake cycle models with both maxwell and burgers viscoelastic rheologies we find that a two layer burgers model with two relaxation timescales is consistent with observations of deformation throughout the earthquake cycle whereas the widely used two layer maxwell model with a single relaxation timescale is not suggesting that the earthquake cycle is effectively characterized by a largely stress recoverable rapid postseismic stage and a much more slowly varying interseismic stage

seismicity on volcanoes generated by gas slug ascent 1 very long period vlp signals provide a unique insight into the source process of seismic signals recorded on active or restless volcanoes this is due to the large wavelengths that may allow the structural heterogeneity to be ignored hence source inversions can be calculated the source process involved in such events is thought to be related to magma transport gas slug ascent or dike resonance initiated by a fluid driven process numerical modelling of gas slug ascent constrained by results from published laboratory experiments shows that this process is capable of generating long period and vlp like signals inputting the fluid dynamic derived forces into an elastic medium with volcano like topography vlp signals are reproduced a moment tensor inversion is performed on these synthetic vlp signals retrieving the correct input source mechanism a pipe structure

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults

millennial recurrence of large earthquakes on the haiyuan fault near songshan gansu province china the haiyuan fault is a major active left lateral fault along the northeast edge of the tibet qinghai plateau studying this fault is important in understanding current deformation of the plateau and the mechanics of continental deformation in general previous studies have mostly focused on the slip rate of the fault paleo seismic investigations on the fault are sparse and have been targeted mostly at the stretch of the fault that ruptured in the 1920 m 8 6 earthquake in ningxia province to investigate the millennial seismic history of the western haiyuan fault we opened two trenches in a small pull apart basin near songshan in gansu province the excavation exposes sedimentary layers of alternating colors dark brown silty to clayey deposit and light yellowish brown layers of coarser grained sandy deposit the main fault zone is readily recognizable by the disruption and tilting of the layers six paleoseismic events are identified and named ss1 through ss6 from youngest to oldest charcoal is abundant yet generally tiny in the shallowest parts of the trench exposures thirteen samples were dated to constrain the ages of paleoseismic events all six events have occurred during the past 3500 3900 years the horizontal offsets associated with these events are poorly known however events ss3 to ss6 appear to be large ones judging from comparison of vertical separations and widths of fault zones the youngest event ss1 instead seems to be a minor one probably the 1990 mw 5 8 earthquake thus four large events in 3500 3900 years would imply a re currence interval of about 1000 years three events ss2 to ss4 prior to 1990 occurred sometime during 1440 1640 a d shortly after 890 1000 a d and 0 410 a d re spectively we tentatively associate them with the 1514 a d 1092 a d and 143 or 374 a d historical earthquakes taking 10 2 m of slip for large events ss3 and ss4 comparable to the 1920 m 8 haiyuan earthquake their occurrence times would be consistent with the long term 12 4 mm yr estimate of lasserre et al 1999 however a more realistic evaluation of slip rate and its possible change with time requires a more rigorous determination of coseismic slip amounts of past earth quakes

high resolution satellite imagery mapping of the surface rupture and slip distribution of the mw 7 8 14 november 2001 kokoxili earthquake kunlun fault northern tibet china the mw 7 8 kokoxili earthquake of 14 november 2001 which ruptured a 450 km long stretch of the sinistral kunlun strike slip fault at the northeastern edge of the tibet plateau china ranks as the largest strike slip event ever recorded instrumentally in asia newly available high resolution satellite hrs images pixel size 1 m acquired in the months following the earthquake proved a powerful tool to complement field investigations and to produce the most accurate map to date of the coseismic displacements along the central kusai hu segment of the rupture the coseismic rupture geometry south and west of buka daban feng near the earthquake epicenter was also investigated in detail along the kusai hu segment slip parti tioning is for the first time observed to occur simultaneously during a single event with two parallel strands 2 km apart localizing almost pure strike slip and normal faulting in all 83 new hrs coseismic offset measurements some of which calibrated by field work show large well constrained variations 100 of the slip function over distances of only25 km tension cracks opening ahead of the shear dislocation and later offset by the upward propagating strike slip rupture were observed dem onstrating that the rupture front propagated faster at depth than near the surface the triple junction between the central kusai hu segment the kunlun pass fault where the rupture ended and the xidatan dongdatan segment which could be the next segment to fail along the main kunlun fault acted as a strong barrier implying that direct triggering of earthquake rupture on the xidatan dongdatan segment by kokoxili type earthquakes may not be the rule

san andreas fault rupture scenarios from multiple paleoseismic records stringing pearls we present a new method to objectively combine paleoseismic event data from multiple sites into rupture scenarios and apply it to the southern san andreas fault ssaf of california first a pool is constructed of all ruptures between sites allowed by fault geometry and available event age probability distribution functions pdfs scenarios constructed by drawing from this pool are evaluated by the average quality of agreement event dating evidence by the degree of misfit of cumulative displacement over all ruptures compared to a prediction from the fault slip rate and elapsed time and by the number of events in the scenario three slip rate models from the 2008 working group on california earthquake probabilities wgcep were considered scenarios with full fault length ruptures tend to be inconsistent with low slip rates through the san bernardino and san gorgonio sections of the ssaf favorable scenarios tend to include 1857 like ruptures for three of the most recent five prehistoric ruptures in the northern half of the ssaf from carrizo to approximately wrightwood they also include one to two ruptures that involve the southern half of the ssaf but most earthquakes there appear shorter and exhibit less consistency from event to event by combining paleoseismic data into ensembles of scenarios and selecting viable scenarios using external constraints our method provides rupture histories useful for seismic hazard assessment without having to first settle which event at a site correlates with those at adjoining sites this opens a way for paleoseismic data to be used with greater power to understand the seismic hazard posed by faults like the southern san andreas

dogtails versus rainbows synthetic earthquake rupture models as an aid in interpreting geological data geologists have been collecting for decades information from historical and paleoearthquakes that could contribute to the formulation of a big picture of the earthquake engine observations of large earthquake ruptures unfortunately are always going to be spotty in space and time so the extent to which geological information succeeds in contributing to a grander view of earthquakes is going to be borne not only by the quantity and quality of data collected but also by the means by which it is interpreted this article tries to understand geological data more fully through carefully tailored computer simulations of fault ruptures dogtails and rainbows are two types of fault rupture terminations that can be recognized in the field and can be interpreted through these models rainbows are concave down ruptures that indicate complete stress drop and characteristic slip rainbow terminations usually coincide with fault ends or strong segment boundaries dogtails are concave up ruptures that indicate incomplete stress drop and noncharacteristic slip dogtail terminations can happen anywhere along a fault or fault segment the surface slip pattern of the magnitude 6 6 1979 imperial valley california earthquake shows both dogtail and rainbow terminations the rainbow confirms the presence of a strong fault segment boundary 6 km north of the international border that had been suggested by sieh 1996 the dogtail implies that the displacement observed in 1979 is not characteristic by combining paleoseismic information with the surface slip patterns from this event and the magnitude 7 1 1940 imperial valley earthquake i develop a quantitative imperial fault model with northern central and southern segments possessing 50 110 and 50 bar strength respectively both the 1940 and 1979 events caused 1 m amplitude dogtailed ruptures of the northern segment however characteristic slip of the segment is more likely to be about 3 m to illustrate the full spectrum of potential rupture modes models were run forward in time to generate a 2000 year rupture encyclopedia even with well constrained segmentation and strengths modest changes in two friction law parameters produce several plausible histories further discrimination awaits analysis of the extensive paleoseismic record that geologists believe exists in the shore deposits of the intermittent lakes of the salton trough

the repetition of large earthquake ruptures abstract this survey of well documented repeated fault rupture confirms that some faults have exhibited a characteristic behavior during repeated large earthquakes that is the magnitude distribution and style of slip on the fault has repeated during two or more consecutive events in two cases faults exhibit slip functions that vary little from earthquake to earthquake in one other well documented case however fault lengths contrast markedly for two consecutive ruptures but the amount of offset at individual sites was similar adjacent individual patches 10 km or more in length failed singly during one event and in tandem during the other more complex cases of repetition may also represent the failure of several distinct patches the faults of the 1992 landers earthquake provide an instructive example of such complexity together these examples suggest that large earthquakes commonly result from the failure of one or more patches each characterized by a slip function that is roughly invariant through consecutive earthquake cycles the persistence of these slip patches through two or more large earthquakes indicates that some quasi invariant physical property controls the pattern and magnitude of slip these data seem incompatible with theoretical models that produce slip distributions that are highly variable in consecutive large events

activity of the yoro fault system determined from coseismic subsidence events recorded in the holocene delta sequence of the nobi plain central japan the holocene delta sequence of the nobi plain central japan records coseismic subsidence in the western part of the plain caused during the past 6000 years by movement on the yoro fault we identified four episodes of upward fining deposition and increasing electrical conductivity in delta front deposits that occurred 600 200 1300 900 4200 3800 and 5600 4700 years ago suggesting that episodes of sea level rise interrupted progradation of the kiso river delta considering the general trend of relative sea level fall during the middle to late holocene under the influence of eustasy and hydroisostasy the temporal correspondence of rises of relative sea level with activity on the yoro fault suggests they reflect coseismic subsidence due to yoro fault activity the timing of the coseismic subsidence events identified in this study also corresponds with that of previously reported faulting events at the kuwana fault to the south of the yoro fault these results are consistent with the previous interpretation that the yoro and kuwana faults comprise a behavioral segment within the yoro fault system our off fault paleoseismic study shows that coseismic subsidence events detected in holocene delta sequences can provide further evidence of faulting events inferred from the on fault paleoseismic studies