technical paper flumo a mobile fluid chemical monitoring unit for geothermal plants a versatile fluid chemical monitoring unit has been developed in the framework of the geothermal research platform gros schonebeck germany it enables selective online and in situ measurements of various physico chemical parameters at different surface locations of a geothermal fluid loop sensors are provided for pressure temperature volumetric flow rate density ph value redox potential oxygen content and electrical conductivity in addition the apparatus features two fluid samplers to manually collect fluid under in situ conditions and ultimately analyze the solution composition all devices are mounted on a rack allowing easy transfer of the apparatus to other geothermal plants the maximum operating pressure and temperature of the unit are 15 bar and 150 c respectively the scientific and technical purpose of the system is to monitor a compositional variability of the produced fluid and chemical processes potentially occurring within the plant these may result from reactions between the fluid and the surrounding materials e g corrosion also mineral precipitation as a consequence of temperature and or pressure decrease or oxygen contamination may occur this information is of paramount importance as so induced reactions might lead to failure of plant components or may damage the geothermal reservoir upon fluid reinjection and thus decrease injectivity

in situ thermal conductivity of gas hydrate bearing sediments of the mallik 5l 38 well 1 detailed knowledge about thermal properties of rocks containing gas hydrate is required in order to quantify processes involving gas hydrate formation and decomposition in nature in the framework of the mallik 2002 program three wells penetrating a continental gas hydrate occurrence under permafrost were successfully equipped with permanent fiber optic distributed temperature sensing cables temperature data were collected over a 21 month period after completing the wells thermal conductivity profiles were calculated from the geothermal data as well as from a petrophysical model derived from the available logging data and application of mixing law models results indicate that thermal conductivity variations are mainly lithologically controlled with a minor influence from hydrate saturation average thermal conductivity values of the hydrate bearing sediments range between 2 35 and 2 77 w m 1 k 1 maximum gas hydrate saturations can reach up to about 90 at an average porosity of 0 3

palaeoearthquake surface rupture in a transition zone from strike slip to oblique normal slip and its implications to seismic hazard north island fault system new zealand

on the variation of slip direction during earthquake rupture supporting and conflicting evidence from the 1989 loma prieta earthquake abstract the direction of the slip can change during a rupture episode as a function of time and or of the position on the fault plane in this work we focus on the spatial variations of slip direction during an earthquake theoretically the spatial variations of rake are caused by changes in the direction of the static and dynamic traction the 1989 loma prieta earthquake provides one of the most striking examples of slip direction rotation during the coseismic rupture all the source models obtained by using different inversion procedures show strong spatial partitioning of slip into strike slip motion se of the epicenter and dip slip motion in the nw section in this study we perform both forward waveform modeling and waveform inversion tests to check if the previously observed variations of rake are constrained by seismological data we use the isochrone approach and a tomographic back projection algorithm to solve the forward modeling and the inverse problem respectively results show that observed ground velocities can be well reproduced by source models having spatial slip distribution similar to the beroza9s 1991 inversion solution but having constant rake synthetic inversion tests point out that the inversion procedure does not constrain the slip direction we have analyzed the s wave polarization in order to constrain the direction of slip along the fault this analysis confirms that a predominant strike component rake 160 characterizes the slip direction in the southeastern section while an increase of the reverse component in the northwest section of the fault allows one to explain the observed polarization well an oblique mechanism is consistent with the fault plane solution confirming a spatial variation of the slip direction during the earthquake if the rake actually varied then a nonuniform prestress condition due to a change in fault geometry or to a redistribution of static stress or a spatially inhomogeneous stress release should be proposed in order to explain the observed changes of slip direction we conclude that a nonuniform prestress is a likely explanation for the inferred rake rotations these variations of the direction of slip involve a low value of the initial stress

application of optical fiber temperature logging an example in a sedimentary environment continuous temperature depth logs especially when recorded in boreholes under thermal equilibrium conditions provide detailed information of the subsurface thermal structure which is necessary for the determination of reliable heat flow and rock thermal properties in conjunction with independent thermal conductivity determinations thermal logging data also allow the separation of heat conduction effects from thermal convection effects by fluid flow driven by various pressure differences such as pore fluid pressure the earth s thermal field is related intimately to geothermal resources and hydrocarbon resources therefore the characterization of temperature in the subsurface and its relationship to lithology is of critical importance

thermal mechanical and chemical influences on the performance of optical fibres for distributed temperature sensing in a hot geothermal well structural well bore integrity is an important issue for sustainable provision of geothermal energy raman scattering based fibre optic distributed temperature sensing dts can help to monitor the status of a well and therefore help to optimize expensive work over activities this study reports on the installation of a fibre optic cable in the cemented annulus behind the anchor casing in the high temperature geothermal well he 53 hellishei i geothermal field sw iceland although the cable has been damaged during the installation temperature data could be acquired during the entire length of installation down to 261 3 m temperature measurements were performed during the installation in spring 2009 during the onset of a flow test in summer 2009 and after a 8 5 month shut in period in summer 2010 during the flow test maximum temperatures of 230 c were measured after 2 weeks fluid production using optical time domain reflectometry otdr attenuation measurements at 850 and 1 300 nm enabled to identify mechanical thermal and chemical degradation along the optical fibre the observed degradation led to erroneous temperature readings and limits due to the optical budget of the dts system the accessible length of the fibre the characteristics and the influence of the different degradation mechanisms on the accuracy of the dts measurements are discussed and recommendations for an optimized installation are given

dynamic rupture propagation during the 1891 nobi central japan earthquake a possible extension to the branched faults the dynamic rupture process of the 1891 nobi japan earthquake was closely reinvestigated by using a boundary integral equation method based on currently available observations we discussed mainly a possibility of the rupture propagation on branched faults including a buried fault called the gifu ichinomiya line several numerical simulations were made incorporating the information on the fault geometry based on the active fault traces on the ground surface and the maximum principal strain direction observed by the triangular surveys for the past 100 years the results suggest that the rupture should propagate along the buried fault during the nobi earthquake if a weak geological discontinuity exists along the gifu ichinomiya line and is connected to the neodani fault which is one of the major surface faults appearing during the nobi earthquake

effect of mechanical interaction on the development of strike slip faults with echelon patterns abstract the overlapping geometry of echelon strike slip faults is well known we have quantified this observation by measuring the amount of overlap and separation and plotting them against each other for over 120 examples although there is large scatter the data show a linear trend suggesting that the overlap increases proportionally with separation up to a limiting value we have analyzed this conspicuous relationship in terms of fault interaction by using a numerical model based on displacement discontinuity the results show that fault interaction is in fact an important factor in contributing to the overlapping geometry of echelon strike slip faults

monitoring of vertical deformation response to water draining recharging conditions using bofda based distributed optical fiber sensors land subsidence is a geological disaster which has a variety of inducements this paper presents the results on the investigation of the soil deformation in land subsidence with a combination of laboratory and field experiments using the distributed fiber optics sensing dfos technology the laboratory experiment was mainly carried out to study the soil deformation in draining recharging cycles based on brillouin optical frequency domain analysis bofda in the field experiment the bofda technology and some grating sensors were applied in a borehole in the yangtze river delta region to monitor the pore pressure in certain specific strata and the change in strata parameter of the full borehole with the data that monitored 2 years the result of the laboratory experiment demonstrated that the soil structures changed in the draining recharging cycles the soil gradually tends toward elastic deformation the field experiment results show that the main deformation occurs at the aquitards adjacent to the pumping aquifer the compression amount in the vertical distribution is not uniform which is related to the distance from the pumping aquifer and the soil properties the compressive deformation of each layer is closely related to the change in groundwater level the result proposes that the bofda technology is suitable for monitoring land subsidence caused by seasonal water level fluctuations and dewatering projects it is also of great significance to investigate land subsidence mechanisms

dynamic modeling of the 2004 mw 6 0 parkfield california earthquake 1 we present two spontaneous rupture models of the 2004 mw 6 0 parkfield earthquake constrained by near source ground motions we start with a stress drop distribution calculated from a kinematic slip distribution using a linear slip weakening friction law we utilize trial and error to obtain both the stress conditions and frictional parameters on the fault that produce synthetics consistent with records the material contrast across the san andreas fault is incorporated using different one dimensional velocity structures on each side of the fault an approximately constant s parameter of 0 3 and a uniform slip weakening distance of 0 15 m are used in the dynamic models in our preferred dynamic model consistent with the ground motion and gps the slip is bounded by seismicity streaks at 5 and 10 km depths confirming a locked zone at depth the stress drop is approximately 10 mpa in the hypocentral region and about 2 mpa elsewhere the material contrast across the fault causes significant normal stress variations 1 mpa leading to a larger strength drop to the southeast than to the northwest the main rupture front propagates at nearly a constant subshear rupture velocity 3 km s in both directions the total radiated energy determined from the preferred dynamic model is 1 1 1013 j seismic moment is 1 0 1018 nm and fracture energy is 3 0 1013 j the limited number of aftershocks in the slipped area suggests the important role of stress on the distribution of seismicity in the locked zone

sei whale sounds recorded in the antarctic sei whales are the least well known acoustically of all the rorquals with only two brief descriptions of their calls previously reported recordings of low frequency tonal and frequency swept calls were made near a group of four or five sei whales in waters west of the antarctic peninsula on 19 february 2003 these whales also produced broadband sounds which can be described as growls or whooshes many of the tonal and frequency swept calls 30 out of 68 consist of multiple parts with a frequency step between the two parts this being the most unique characteristic of the calls allowing them to be distinguished from the calls of other whale species the average duration of the tonal calls is 0 45 0 3s and the average frequency is 433 192hz using a calibrated seafloor recorder to determine the absolute calibration of a sonobuoy system the maximum source level of the tonal calls was 156 3 6db re 1 pa at 1m each call had different character and there was no temporal pattern in the calling

coseismic temporal changes of slip direction the effect of absolute stress on dynamic rupture abstract we investigate the dynamics of rupture at low stress level we show that one main difference between the dynamics of high and low stress events is the amount of coseismic temporal rake rotation occurring at given points on the fault curved striations on exposed fault surfaces and earthquake dislocation models derived from ground motion inversion indicate that the slip direction may change with time at a point on the fault during dynamic rupture we use a 3d boundary integral method to model temporal rake variations during dynamic rupture propagation assuming a slip weakening friction law and isotropic friction the points at which the slip rotates most are characterized by an initial shear stress direction substantially different from the average stress direction over the fault plane we show that for a given value of stress drop the level of initial shear stress i e the fractional stress drop determines the amount of rotation in slip direction we infer that seismic events that show evidence of temporal rake rotations are characterized by a low initial shear stress level with spatially variable direction on the fault possibly due to changes in fault surface geometry and an almost complete stress drop our models motivate a new interpretation of curved and cross cutting striations and put new constraints on their analysis the initial rake is in general collinear with the initial stress at the hypocentral zone supporting the assumptions made in stress tensor inversion from first motion analysis at other points on the fault especially away from the hypocenter the initial slip rake may not be collinear with the initial shear stress contradicting a common assumption of structural geology on the other hand the later part of slip in our models is systematically more aligned with the average stress direction than the early slip our modeling suggests that the length of the straight part of curved striations is usually an upper bound of the slip weakening distance if this parameter is uniform over the fault plane and the direction of the late part of slip of curved striations should have more weight in the estimate of initial stress direction

deep sound channel noise from high latitude winds the contribution to underwater ambient noise from the persistent winds which blow at high latitude is discussed and estimated energy is ducted into low loss paths in the deep sound channel by favorable horizontal sound speed gradients a concept of wind noise lanes is developed into a simple model which is used to predict the resulting underwater ambient noise levels as a function of season and latitude three main oceans are considered the pacific atlantic and indian oceans in general terms predicted omnidirectional levels at 50 hz lie between 65 and 75 db re 1 pa2 hz and are comparable to those generally associated with light to moderate ship traffic the spectral shape of high latitude wind noise is also similar to that associated with ships high latitude wind noise arrives within 15 of horizontal and the predicted magnitude of this low angle component also matches measurements well it is concluded that the component of noise associated with high latitude winds can be significant at low

the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data abstract a new inverse technique is presented here to separate stresses from heterogeneous fault slip data without a priori information on the stresses or on the classification of faults according to the stresses four parameters are determined by the inversion one for the shape of the stress ellipsoid and three for the direction of the stress axes accordingly the inversion is equivalent to the projection of the fault slip data to a point in four dimensional parameter space the data are divided into k element subsets to which the inverse technique is applied where k 4 or 5 is the optimal choice for the stability of solutions and for the reduction of computation significant solutions are identified as clusters in parameter space the technique is demonstrated first by simulated fault slip data as an example field data obtained from miocene fore arc sediments in western japan were processed by the method

the effects of fault stepovers on ground motion abstract using 3d dynamic models we investigate the effect of fault stepovers on near source ground motion we use the finite element method to model the rupture slip and ground motion of two parallel strike slip faults with an unlinked overlapping stepover of variable width we model this system as both an extensional and a compressional stepover and compare the results to those of single planar faults we find that overall the presence of a stepover along the fault trace reduces the maximum ground motion when compared to the long planar fault whether the compressional or extensional stepover exhibits higher ground motion overall depends on the width of the separation between the faults there is a region of reduced ground motion at the end of the first fault segment when the faults are embedded in a homogeneous material we also experiment with stress fields leading to supershear and subshear rupture velocities and with different stress drops within those conditions we find that subshear rupture produces stronger motions than supershear rupture but supershear ruptures produce that maximum over a larger area than subshear areas even though the overall area that experiences any shaking at all is not drastically different between the two cases lastly we experiment with placing realistic materials along and around the faults such as a sedimentary basin in an extensional stepover a damage zone around the fault and a soft rock layer on top of bedrock through the entire model area these configurations alter the pattern of ground motion from the homogeneous case the peaks in ground motion for the bimaterial cases depend on the materials in question the results may have implications for ground motion prediction in future earthquakes on geometrically complex faults online material mpeg 4 movies of models of dynamic rupture of fault stepovers embedded in heterogeneous material settings

the 1989 loma prieta earthquake imaged from inversion of geodetic data we invert geodetic measurements of coseismic deformation from the 1989 ms7 1 loma prieta earthquake to determine the geometry of the fault and the distribution of slip on the fault plane the data include electronic distance measurements global positioning system and very long baseline interferometry vectors and elevation changes derived from spirit leveling the fault is modeled as a rectangular dislocation surface in a homogeneous elastic half space first we assume that the slip on the fault is uniform and estimate the position orientation and size of the fault plane using a nonlinear quasi newton algorithm the best fitting dislocation strikes n48 4 w and dips 76 9 sw consistent with the trend of the aftershock zone and moment tensor solutions bootstrap resampling of the data is used to graphically illustrate the uncertainty in the location of the rupture plane the 95 confidence envelope overlaps the aftershock zone arguing that there is not a significant discrepancy between the geodetic data and the aftershock locations second we estimate the slip distribution using the best fitting uniform slip fault orientation but increase the fault length to 40 km and the downdip width to 18 km the fault is divided into 162 subfaults 18 along strike and 9 along dip each subfault is allowed to have constant right lateral and reverse components of slip we then solve for the slip on each subfault that minimizes a linear combination of the norm of the weighted data residual and the roughness of the slip distribution the smoothing parameter which determines the relative weight put on fitting the data versus smoothing the slip distribution is chosen by cross validation simulations indicate that cross validation estimates of the smoothing parameter are nearly optimal the preferred slip distribution is very heterogeneous with maximum strike slip and dip slip of about 5 and 8 m respectively located roughly 10 km north of the hypocenter there is insignificant dip slip in the southeastern most part of the fault causing the rake to vary from nearly pure right lateral in the southeast to oblique right reverse in the northwest the change in rake is consistent with a uniform stress field if the fault dip increases by about 10 toward the southeast as indicated by the aftershock locations there was little slip above 4 km depth consistent with the observation that there was little if any surface rupture

dynamic earthquake ruptures in the presence of lithostatic normal stresses implications for friction models and heat production we simulate dynamic ruptures on a strike slip fault in homogeneous and layered half spaces and on a thrust fault in a layered half space with traditional friction models sliding friction exceeds 50 of the fault normal compressive stress and unless the pore pressures approach the lithostatic stress the rupture characteristics depend strongly on the depth and sliding generates large amounts of heat under application of reasonable stress distributions with depth variation of the effective coefficient of friction with the square root of the shear modulus and the inverse of the depth creates distributions of stress drop and fracture energy that produce realistic rupture behavior this ad hoc friction model results in 1 low sliding friction at all depths and 2 fracture energy that is relatively independent of depth additionally friction models with rate weakening behavior which form pulselike ruptures appear to generate heterogeneity in the distributions of final slip and shear stress more effectively than those without such behavior which form cracklike ruptures for surface rupture on a thrust fault the simple slip weakening friction model which lacks rate weakening behavior accentuates the dynamic interactions between the seismic waves and the rupture and leads to excessively large ground motions on the hanging wall waveforms below the center of the fault which are associated with waves radiated to teleseismic distances indicate that source inversions of thrust events may slightly underestimate the slip at shallow depths

induced thermal compaction in cohesive sediments around a borehole heat exchanger laboratory tests on the effect of pore water salinity in closed loop geothermal systems the operation of a borehole heat exchanger bhe affects the thermal equilibrium of the surrounding subsoil this study was part of a large laboratory program undertaken to understand how the cyclic thermal stress induced by a bhe in the subsoil can change sediments mechanical properties if the bhe works in extreme running conditions which induce both freeze thaw cycles and heating processes in the ground this paper presents the results from an experimental laboratory investigation on the effects of different pore water salinity concentrations on the vertical strain induced in a thermally loaded silty clay the considered study case is the historical center of venice italy which provides an example of typical conditions of densely urbanized areas inserted in coastal or transitional environments with abundance of cohesive layers and brackish conditions in the subsoil results show that the irreversible compaction effect induced on sediments increases with higher salinity concentration despite the fact that increasing salt content lowers the sediment freezing point thereby protecting the soil from freezing processes

3d simulations of multi segment thrust fault rupture thrust faults such as those that underlie the los angeles basin are typically segmented by tear faults that offset the thrust fault segments we perform 3d finite difference simulations of earthquake rupture to evaluate the effectiveness of these offsets in retarding rupture the simulations include orthogonal intersecting faults to model the interaction of the thrust fault segments with the tear fault for reasonable assumptions for fault segment length strength and stress drop rupture can jump offsets of up to 2 km if a tear fault is present consistent with observations of well studied thrust earthquakes absent a tear fault the maximum offset that can be breached is an order of magnitude smaller

vertical line array measurements of ambient noise in the north pacific shipping noise and wind are the dominant sources of ocean noise in the frequency band between 20 and 500 hz this paper analyzes noise in that band using data from the spicex experiment which took place in the north pacific in 2004 2005 and compares the results with other north pacific experiments spicex included vertical arrays with sensors above and below the surface conjugate depth facilitating an analysis of the depth dependence of ambient noise the paper includes several key results first the 2004 05 noise levels at 50 hz measured in spicex had not increased relative to levels measured by morris 1978 j acoust soc am 64 581 590 at a nearby north pacific site three decades earlier but rather were comparable to those levels second at 50 hz the noise below the conjugate depth decreases at a rate of 9 9 db km which is similar to the rate measured by morris and much less than the rate measured by gaul knobles shooter and wittenborn 2007 ieee j ocean eng 32 497 512 for the

surficial slip and rupture geometry on the beichuan fault near hongkou during the mw 7 9 wenchuan earthquake chinasurficial slip and rupture geometry on beichuan fault near hongkou during the wenchuan earthquake

inversion of field data in fault tectonics to obtain the regional stress i single phase fault populations a new method of computing the stress tensor summary we attempt a general definition of the inverse problem of computing the components of the regional stress tensor from a set of field data including the measurements of the strike and dip of several faults and the directions and senses of relative motion along these faults as indicated by slickenslides in previous treatments of this problem no experimental errors could be taken into account except those in measuring the pitch of slickenslides thus errors in the orientation of the fault strike and dip which have considerable practical importance were neglected in our work all experimental errors in the field measurements are taken into account so that the agreement between the computed stress tensor and the set of field measurements can be rigorously checked

finite source modeling of the 1999 taiwan chi chi earthquake derived from a dense strong motion network the 1999 chi chi earthquake m w 7 6 20 september 1999 17 47 15 9 utc located at 23 853 n 120 816 e and depth of 7 5 km inicted severe re gional scale damage to taiwan the strong motion waveeld was captured by a dense network of stations with average station spacing of 5 km which represents the most complete strong motion dataset to date to use to study the kinematic source process of an earthquake we inverted velocity waveforms recorded by 21 stations for the spatial variation in slip on a planar fault model composed of 416 subfaults each with a dimension of 3 5 km by 3 5 km the planar model has a strike of n5 e and a dip of 30 e and the inversion solves for the direction and magnitude of the slip to account for possible temporal source complexity we allowed each subfault to slip within 10 overlapping time windows each with a duration of 3 sec the results show that the source is composed primarily of three major asperities the rst of which is mainly dip slip extending from the hypocenter to the northern end of the surface rupture in this asperity slip occurred in two pulses separated in time by 5 sec the dislocation rise time for each pulse is short 3n4 sec yielding an approximate av erage slip velocity of 80 cm sec the second asperity is located at shallow depth near the northern end of the rupture where very large ground velocities were observed this asperity is on average oblique and shows a temporal rake rotation from pure dip slip to strike slip the rotating rake suggests a low initial shear stress on the northern end of the fault slip in this asperity is dominated by a large pulse with a dislocation rise time of 8 sec a station near the northern end of the surface rupture recorded a peak velocity of 390 cm sec which we nd to be due to the constructive interference of energy radiated from the rst two asperities the third asperity is located south of the epicenter the total moment from the three asperities is 4 1 10 27 dyne cm which was released over a period of 30n35 sec within an area of 900 km 2 synthetics calculated from the three asperity model explain 85 of the data and represent 98 of the total variance reduction our results indicate that slip is conned to the shallow region of the fault deep slip patches are less constrained and that the slip distribution may be representative of fault segmentation along the chelungpu fault system

surface fault ruptures and slip distributions of the mw 6 6 11 april 2011 hamadoori fukushima prefecture northeast japan earthquake the 11 april 2011 hamadoori fukushima prefecture northeast japan earthquake occurred in a seismically active area one month after the 11 march 2011 off the pacific coast of tohoku earthquake the hamadoori earthquake resulted in a 14 km long down to the west normal slip rupture on the north northwest south southeast striking itozawa fault as well as a 16 km long down to the south normal slip rupture on the west northwest east southeast striking yunodake fault the slip along the itozawa fault increases abruptly from the southern end to the central part of the fault where the measured maximum displacement is close to 2 m the slip decreases gradually from the central section to the northwestern end of the fault the yunodake fault also has an asymmetric slip distribution with a peak of about 0 9 m near the northwestern section of the fault considering the direction of rupture propagation along the two faults it is apparent that the measured surface offset is asymmetric along the strike with the largest offsets observed nearer the end of the fault where the rupture began and showing a gradual decrease in the direction of rupture termination the surface observations of the slip distribution and the epicenter location are consistent with the general features of earthquake ruptures derived from slip inversion models on more than 60 of the rupture length of the hamadoori earthquake faults as well as on other historic normal fault earthquakes slip displacements are less than or equal to 30 of the maximum slip the moment magnitude m w of the earthquake estimated from ruptures length maximum and average displacements is between 6 5 and 6 8 in accordance with the seismologically determined value of 6 6 online material supplementary data of the surface slip distributions of the 11 april 2011 hamadoori earthquake along the itozawa and yunodake faults

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

fault interaction near hollister california a numerical model is used to study fault stress slip near hollister california the geometrically complex system of interacting faults including the san andreas calaveras sargent and busch faults is approximated with a two dimensional distribution of short planar fault segments in an elastic medium the steady stress and slip rate are simulated by specifying frictional strength and stepping the remote stress ahead in time the resulting computed fault stress is roughly proportional to the observed spatial density of small earthquakes suggesting that the distinction between segments characterized by earthquakes and those with aseismic creep results in part from geometry a nonsteady simulation is made by introducing in addition stress drops for individual moderate earthquakes a close fit of observed creep with calculated slip on the calaveras and san andreas faults suggests that many changes in creep rate averaged over several months are caused by local moderate earthquakes in particular a 3 year creep lag preceding the august 6 1979 coyote lake earthquake on the calaveras fault seems to have been a direct result of the november 28 1974 thanksgiving day earthquake on the busch fault computed lags in slip rate preceding some other moderate earthquakes in the area are also duemore to earlier earthquakes although the response of the upper 1 km of the fault zone may cause some individual creep events and introduce delays in others the long term rate appears to reflect deep slip less

dynamic rupture simulations with heterogeneous initial stresses inversed from a given slip distribution a case study of the 2017 mw 6 5 jiuzhaigou earthquake abstract heterogeneous initial stresses are extremely important in understanding the physics of earthquake rupture processes we propose a method to estimate heterogeneous initial stresses by comparing the slip from dynamic rupture simulations and the input joint inversion result and apply it to the 2017 mw 6 5 jiuzhaigou earthquake which occurred in the intersection area of the minjiang tazang and huya faults in sichuan province china with the slip distributed on two distinct left lateral strike slip faults as shown in previous geodetic and seismic joint inversion we use the seismic efficiency empirical relation to infer the average stress and the average stress drop is estimated using the static stress drop with the angle of the maximum principal stress and the nucleation fault determined from the relocated aftershocks different principal stresses are calculated with different combinations of average stress and average stress drop the initial normal and residual stresses can be determined using the projection of the principal stresses the initial shear stresses are generated by adding the residual stress and the heterogeneous stress drop which is generated by a set of gaussian random numbers with a given mean and the variance and mapped one by one with the given slip on the fault so that the area with a large slip has a large stress drop by comparing the slip from dynamic rupture simulations and the input joint inversion result we show that the case with a 36 mpa average stress and 2 1 mpa average stress drop provides the best fitting slip snapshots the dynamic coulomb stress change shows that the 2017 mw 6 5 jiuzhaigou earthquake could bring the southeast of the tazang fault and the middle of the minjiang fault closer to failure this work provides a new insight to understand the initial stresses of nature earthquakes

thermal hydraulic measurements and modelling of the brine circuit in a geothermal well wellhead temperature and pressure are critical parameters of a geothermal well their prediction requires knowledge of the geofluid properties and detailed thermal modelling of the well and formation high salinity and gas content complicate the task this article presents a comprehensive thermal hydraulic wellbore model which is parameterized and validated with data from the gross schoenebeck site and used for a long term prognosis geofluid properties are calculated based on the specific gas and salt contents by determining the vapour liquid equilibrium

rare dynamic triggering of remote m 5 5 earthquakes from global catalog analysis probing the effects of a transient stress on the timing of an earthquake occurrence is necessary for understanding the remote interaction of large magnitude events global catalog data containing 35 years of m 5 5 earthquakes allow us to explore for periods of enhanced or suppressed seismic activity we consider 113 m 7 5 main shocks between 1977 and 2012 and focus on seismic activity on time scales from seconds to days following these main shocks we search for evidence of dynamic triggering of large magnitude events similar to the previously observed global increase during the first few days following the 2012 m8 6 indian ocean main shock we restrict the analysis to regions of elevated strain during the passage of surface waves using a threshold of 0 1 microstrain 3 kpa and a temporal window of 1 year we stack daily seismicity rate curves using the exclusion zone declustered m 5 5 catalog events in order to resolve deviations from the background rate our results do not indicate a significant change in activity for at least 10 days when considering the collective set of 113 main shocks and subsets at m8 0 and m8 5 thresholds the results also do not indicate immediate triggering of m 5 5 events we do find two instances of increased seismicity in the elevated strain region within 10 days these increases are subsequent to two main shocks the 1977 m8 3 and 2012 m8 6 both located in the indian ocean we conclude that a global change in m 5 5 earthquake rates following a transient stress from distant earthquakes is a rare occurrence

near source modeling of the loma prieta earthquake evidence for heterogeneous slip and implications for earthquake hazard i have analyzed records from 20 strong motion instruments that recorded the 1989 loma prieta earthquake ml 6 9 to determine the spatial and temporal distribution of slip using a tomographic back projection technique i find that the earthquake ruptured bilaterally at approximately 80 of the local shear wave velocity over a distance of slightly more than 30 km from 13 km northwest to 20 km southeast of the hypocenter slip within the rupture zone was highly variable both in magnitude and direction slip at the hypocenter and immediately up dip was relatively low about 1 m there were two main areas of concentrated slip one centered 7 km northwest of the hypocenter at a depth of 14 km and the other centered 6 km southeast of the hypocenter at a depth of 12 km peak slip amplitude on these high slip patches exceeded 4 5 m a surprising aspect of the rupture model is that rake varies from being predominately strike slip to the southeast of the hypocenter to being predominately reverse slip to the northwest despite this variation in rake the average rake determined from the strong motion data is in agreement with that determined teleseismically there is a correlation between areas of high slip and areas of low aftershock activity a simple model to explain this observation is that the areas of high slip are also areas of high strength which slip only during infrequent large mainshocks other areas of the fault are weaker and may slip both seismically and aseismically most of the slip in the loma prieta earthquake occurred between 9 and 16 km depth on a structure that dips to the southwest and runs underneath the surface trace of the san andreas fault at a depth of 8 to 10 km this observation complicates the assessment of seismic hazard on the southern santa cruz mountains segment of the san andreas fault

straightening of the northern san jacinto fault california as seen in the fault structure evolution of the san jacinto valley stepover abstract we investigate a releasing stepover between the casa loma and claremont strands of the northern san jacinto fault zone to evaluate the late quaternary structural evolution of the fault zone and to assess the likelihood of a rupture jumping across the stepover our new cone penetration test cpt and trench observations along the claremont fault at mystic lake indicate that the main strand of the claremont fault has jumped nearly a half kilometer westward into the san jacinto releasing stepover during the late quaternary multiple faults are inferred from the cpt data within a small sag at the northeast side of the stepover that cuts through younger stratigraphy to the west of the basin bounding fault near mystic lake previous seismic reflection data also suggest the presence of a young fault that cuts basin strata beneath the middle of mystic lake farther west of our study area numerous tectono geomorphic features observed in satellite and light detection and ranging digital elevation model lidar dem imagery are interpreted to delineate the location of the currently active faults including a zone of faults that cut across the basin from the northern end of the casa loma fault to the claremont fault seismicity observations suggest the presence of many faults within the stepover zone finally new paleoseismic data from the mystic lake site suggest that some late holocene earthquakes may have jumped the stepover all of these observations suggest that the san jacinto stepover which has been used as the primary basis for segmenting the northern san jacinto fault zone is being bypassed and that the fault zone may now be capable of larger earthquakes than previously expected

three dimensional spontaneous rupture propagation and implications for the earthquake source mechanism summary we consider spontaneous cracks spreading out areally over a fault plane in an infinite medium as a realistic earthquake source model the boundary integral equation technique described in das is used to determine the displacements and stresses everywhere on the crack plane for faults spreading out symmetrically in all four quadrants over infinite planes of constant yield strength we find that the terminal rupture velocity viiicr in the direction of purely anti plane rupture is given by viiicr in the purely in plane direction of rupture propagation we find the terminal rupture velocity viicr to be given by viicr or viicr 0 5 depending on the yield strength we also find that crack propagation in the purely antiplane direction does not influence crack propagation in the purely in plane direction and vice versa for infinitely long shear cracks of finite width the slip at a point is found to grow more slowly after the arrival of a shear wave diffracted from the nearer crack edge the slip virtually ceases after the shear arrival from the further crack edge this implies that for such faults the slip is controlled by the fault width for a rectangular fault in an infinite medium our final dynamic solution is in closer agreement with the static elliptical crack solution of eshelby than with the static rectangular dislocation model solution of chinnery we find the relationship between the average slip and average dynamic stress drop e on such a rectangular fault of half width w to be e c w where c 0 7 the slip at an interior point is again controlled by the fault width for faults that are much longer than wide so that the slip may stop in the region where the fault initiated before the completion of the rupture process this implies that two rectangular faults of varying lengths but of the same width have the same slip for the same average stress drop a fact clearly contradicted by observations that fault slip increases with earthquake size for great earthquakes occurring along the same fault this contradiction is resolved if stress drops are also bigger for bigger earthquakes

growth linkage and termination processes of a 10 km long strike slip fault in jointed granite the gemini fault zone sierra nevada california abstract field based structural analysis of an exhumed 10 km long strike slip fault zone elucidates processes of growth linkage and termination along moderately sized strike slip fault zones in granitic rocks the gemini fault zone is a 9 3 km long left lateral fault system that was active at depths of 8 11 km within the transpressive late cretaceous sierran magmatic arc the fault zone cuts four granitic plutons and is composed of three steeply dipping northeast and southwest striking noncoplanar segments that nucleated and grew along preexisting cooling joints the fault core is bounded by subparallel fault planes that separate highly fractured epidote chlorite and quartz breccias from undeformed protolith the slip profile along the gemini fault zone shows that the fault zone consists of three 2 3 km long segments separated by two zones of local slip minima slip is highest 131 m on the western third of the fault zone and tapers to zero at the eastern termination slip vectors plunge shallowly west southwest and show significant variability along strike and across segment boundaries four types of microstructures reflect compositional changes in protolith along strike and show that deformation was concentrated on narrow slip surfaces at or below greenschist facies conditions taken together we interpret the fault zone to be a segmented linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and fault rock resulted in nonuniform slip orientations complex fault segment interactions and asymmetric slip distance profiles

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

aftershocks of the coyote lake california earthquake of august 6 1979 a detailed study aftershock hypocenters and focal mechanism solutions for the coyote lake california earthquake reveal a geometrically complex fault structure consisting of multiple slip surfaces the faulting surface principally consists of two right stepping en echelon northwest trending partially overlapping nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 parkfield california earthquake the overlap occurs near a prominent bend in the surface trace of the calaveras fault at san felipe lake slip during the main rupture as inferred from the distribution of early aftershocks appears to have been confined to a 14 km portion of the northeastern sheet between 4 and 10 km depth focal mechanisms and the hypocentral distribution of aftershocks suggest that the main rupture surface itself is geometrically complex with left stepping imbricate structure seismic shear displacement on the southwestern slip surface commenced some 5 hours after the mainshock aftershocks in this zone define a single vertical plane 8 km long between 3 and 7 km depth within the overlap zone between the two main slip surfaces the average strike of aftershock nodal planes is significantly rotated clockwise relative to the strike of the fault zone in close agreement with the stress perturbations predicted by crack interaction models aftershock activity in the overlap zone is not associated with a simple dislocation surface space and time clustering within the entire aftershock set suggest an alternation of seismic displacement between the component parts of the fault zone this alternation is consistent with local stress perturbations predicted by crack interaction models we conclude that the fault structure is geometrically complex and that the displacements that occur on its component surfaces during the aftershock process dynamically interact by generating perturbations in the local stress field which in turn control the displacements table 5 is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 006 1 00 payment must accompany order

rupture process of the wenchuan earthquake mw 7 9 from surface ruptures and fault striations characteristics abstract on 12 may 2008 the wenchuan earthquake mw 7 9 produced complicated thrust type co seismic surface rupture zones which encompass the dextral slip thrust of the yingxiu beichuan fault the approximately pure thrust of the guanxian anxian fault and the sinistral slip thrust of the xiaoyudong rupture zone located between the former two in order to understand the faulting mechanism we discuss the rupture process by examining the segmentation and kinematics of the surface rupture zones together with the co seismic fault striations at various sites based on the two along strike main displacement peaks 6 6 5 m and 11 12 m and on the different geometric and kinematic patterns for the southern and northern segments of the surface rupture zones we find that the wenchuan earthquake might have consisted of two rupture stages which is in agreement with seismic wave inversion results by comparing the kinematics of fault striations occurring in the bajiaomiao and beichuan areas it suggests that during the first stage thrusting along both the yingxiu beichuan fault and guanxian anxian fault produced the 80 100 km long yingxiu qingping surface rupture segment and the 80 km long guanxian anxian surface rupture zone respectively then faulting was triggered along the yingxiu beichuan fault by the first rupture process yielding the second rupture stage which was characterized by dextral strike slip or dextral oblique thrusting due to the overlap between the two rupture stages the southern segment yingxiu qingping of the yingxiu beichuan rupture zone comprises two different processes while the northern segment gaochuan beichuan shikan only suggests one rupture phase

constraining fault constitutive behavior with slip and stress heterogeneity 1 we study how enforcing self consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event we explore features of rupture dynamics that 1 lead to slip heterogeneity in earthquake ruptures and 2 maintain these conditions following rupture so that the stress field is compatible with the generation of aftershocks and facilitates heterogeneous slip in subsequent events our three dimensional finite element simulations of magnitude 7 events on a vertical planar strike slip fault show that the conditions that lead to slip heterogeneity remain in place after large events when the dynamic stress drop initial shear stress and breakdown work fracture energy are spatially heterogeneous in these models the breakdown work is on the order of mj m 2 which is comparable to the radiated energy these conditions producing slip heterogeneity also tend to produce narrower slip pulses independent of a slip rate dependence in the fault constitutive model an alternative mechanism for generating these confined slip pulses appears to be fault constitutive models that have a stronger rate dependence which also makes them difficult to implement in numerical models we hypothesize that self consistent ruptures could also be produced by very narrow slip pulses propagating in a self sustaining heterogeneous stress field with breakdown work comparable to fracture energy estimates of kj m 2

the dynamics of strike slip step overs with linking dip slip faults fault step overs with linking dip slip faults are common features on long strike slip fault systems worldwide it has been noted by various researchers that under some circumstances earthquakes can jump across fault step overs to cascade into large events while under other circumstances rupture is arrested at step overs there is also evidence that fault step overs may be preferential locations for earthquake nucleation the present work uses the 3d finite element method to model the dynamics of strike slip fault systems with step overs and linking dip slip faults i find that the presence of a linking normal or thrust fault greatly increases the ability of earthquake rupture to propagate across the step over leading to a larger event additionally dilational step overs with linking normal faults are more prone to through going rupture than compressional step overs with linking thrust faults this difference is due to the sign of the normal stress increment on the dip slip fault caused by slip on the strike slip segments slip on the strike slip segments causes a negative unclamping normal stress increment on the linking normal fault in a dilational step over whereas the opposite effect occurs on the linking thrust fault in a compressional step over even in cases for which both dilational and compressional step overs can experience through going rupture dilational step overs typically experience higher slip particularly on the linking normal fault in the compressional case rupture nucleation on the linking thrust fault may increase the likelihood of through going rupture compared to nucleation on one of the strike slip segments near the intersections between the fault segments the stress interaction between the fault segments also causes a significant rotation of rake away from that which would be inferred from the regional stress field the results help to emphasize the importance of two way interactions between nearby fault segments during the earthquake rupture process the results also may have implications for the probability of large earthquakes along geometrically complex strike slip fault systems and may help explain why step overs sometimes act as barriers and other times as nucleation locations for large earthquakes

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

dynamic transfer of rupture across differently oriented segments in a complex 3 d fault system 1 we simulate spontaneous dynamic propagation of rupture across two adjacent fault segments subject to a triaxial compressive stress regime these segments have different orientations and hence different focal mechanisms vertical strike slip and dipping thrust numerical simulations using a biem boundary integral equation method have revealed that under a typical triaxial homogeneous compressive stress regime where the magnitude of the intermediate principal stress lies halfway between those of the maximum and minimum ones ruptures of different focal mechanisms are not likely to occur simultaneously in a single rupture event propagation of rupture from a vertical strike slip fault segment to a pure dip slip normal reverse fault segment is possible only when the stress field is close to uniaxial compression or when the intermediate stress magnitude is close either to the minimum or the maximum one these findings are useful for evaluating possible earthquake scenarios along fault systems with complex 3d geometries

temporal slip change based on curved slickenlines on fault scarps along itozawa fault caused by 2011 iwaki earthquake northeast japan abstract we observed co seismic slickenlines caused by the 2011 mw 6 6 iwaki earthquake along the itozawa fault co seismic surface rupture zone the structures are characterized by co seismic curved slickenlines and slickenlines with cross cutting relationships on the fault scarps the curved slickenlines indicate that the direction of fault motion during the rupture of the 2011 iwaki earthquake shifted from normal faulting with a left lateral component to that with a right lateral component the angular misfits between the slip direction predicted from the nw se trending extensional stress before the 2011 iwaki earthquake and that predicted from each component of the curved slickenlines on the fault scarps are 33 to 65 and 2 to 17 respectively the misfit changes show that the co seismic slip direction discordant with the extensional stress shifted to normal faulting and is explained by the stress during the faulting these results suggest that co seismic rupture processes near the surface are a key in revealing the detailed dynamic processes of a seismic event

fault geometry and the dynamics of the 1999 chi chi taiwan earthquake the 1999 m 7 6 chi chi taiwan earthquake produced a data set of unparalleled size and quality particularly in the near source region where data have been previously quite scarce the large amount of near source data allows the verification of many predictions of thrust fault behavior for faults that intersect the surface of the earth through rigorous three dimensional dynamic models of the chi chi earthquake it can be shown that many aspects of the observed near source ground motion in this event are direct effects of the asymmetrical dipping fault geometry these effects include the hanging wall moving more than the footwall with strongly peaked velocities right at the fault trace and a transition from predominantly thrust motion in the south of the fault to largely left lateral motion in the north building on the work of oglesby and day 2001 the current work helps to delineate the effects of fault geometry nonuniform prestress and dynamic waves on the physics of the chi chi earthquake and dip slip faults in general in particular we find that a completely homogeneous prestress pattern still fits the gross features of the near source ground motion quite well additionally the strike slip component of motion near the fault trace is seen to be a combination of dynamic and static effects finally dynamic overshoot is seen to be much larger for dip slip faults than for otherwise identical vertical faults the results emphasize the necessity of rigorous models that correctly account for both the effects of fault geometry and dynamic waves in the rupture and slip processes manuscript received 31 july 2000

on the inference of absolute stress levels from seismic radiation abstract spudich p k p 1992 on the inference of absolute stress levels from seismic radiation in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 99 106 this paper determines the conditions under which it is possible to learn the absolute stress level at a subset of points on a fault from observation of the fault kinematics specifically the points on a rupturing fault can be divided into two groups those points at which the rake rotates during the rupture process and those points at which the rake does not rotate if it is true that sliding frictional traction is collinear with the instantaneous velocity of one side of a fault then at the former group of points having rotating rakes there is a unique absolute stress consistent with the motion while at the latter group of points having rakes that do not rotate the absolute stress is unspecified by the motion published dislocation solutions for the 1979 imperial valley 1986 north palm springs 1987 whittier narrows and 1989 loma prieta california earthquakes are examined for evidence of temporal rotations of rake at the hypocenters and largest asperities the 1986 north palm springs earthquake shows evidence of a possible rake rotation at the hypocenter this may imply a low absolute stress level

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock aftershock interaction the diverse aftershock sequence of the 1989 loma prieta earthquake is inconsistent with conventional models of mainshock aftershock interaction because the aftershocks do not accommodate mainshock induced stress changes instead the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane this orientation implies that i stress drop in the mainshock was nearly complete ii mainshock induced decreases of fault strength helped were important in controlling the occurrence of after shocks and iii mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip

use of fault striations and dislocation models to infer tectonic shear stress during the 1995 hyogo ken nanbu kobe earthquake dislocation models of the 1995 hyogo ken nanbu kobe earthquake derived by yoshida et al 1996 show substantial changes in direction of slip with time at specific points on the nojima and rokko fault systems as do striations we observed on exposures of the nojima fault surface on awaji island spudich 1992 showed that the initial stress that is the shear traction on the fault before the earthquake origin time can be derived at points on the fault where the slip rake rotates with time if slip velocity and stress change are known at these points from yoshida s slip model we calculated dynamic stress changes on the ruptured fault surfaces to estimate errors we compared the slip velocities and dynamic stress changes of several published models of the earthquake the differences between these models had an exponential distribution not gaussian we developed a bayesian method to estimate the probability density function pdf of initial stress from the striations and from yoshida s slip model striations near toshima and hirabayashi give initial stresses of about 13 and 7 mpa respectively we obtained initial stresses of about 7 to 17 mpa at depths of 2 to 10 km on a subset of points on the nojima and rokko fault systems our initial stresses and coseismic stress changes agree well with postearthquake stresses measured by hydrofracturing in deep boreholes near hirabayashi and ogura on awaji island our results indicate that the nojima fault slipped at very low shear stress and fractional stress drop was complete near the surface and about 32 below depths of 2 km our results at depth depend on the accuracy of the rake rotations in yoshida s model which are probably correct on the nojima fault but debatable on the rokko fault our results imply that curved or cross cutting fault striations can be formed in a single earthquake contradicting a common assumption of structural geology

more on mmax m max the maximum magnitude earthquake that a fault is likely to suffer plays an important role in earthquake hazard estimation although observational evidence summarized in plots of characteristic earthquake magnitude m char versus fault length indicate that smaller faults produce lower magnitude events an argument has been made that any fault regardless of its length should have m max near magnitude 8 the rationale for this argument charges that the contrary observational evidence stems from historical catalogs of limited extent and that it largely excludes nonconventional earthquakes in which several short and apparently disconnected fault segments fail simultaneously this article addresses m max using computer models of rupture on faults of various strengths and configurations computer models have advantages in that a m max earthquakes always can be generated by forcing complete stress drop on fully stressed faults thus avoiding the limitations of short historical catalogs and b the circumstances necessary for the failure of several segments to contribute to a large m max can be investigated quantitatively i find that for a strikeslip california environment it is physically unlikely for an m 8 event to break less than 300 to 400 km of fault were this m 8 rupture to occur on as few as five independent segments shear strength of the participating faults would have to be raised to implausible levels if the fault segments are not independent and their coseismic stress fields interact then amplifications in slip are possible without drastic increase in strength the range of fault geometries where strong interactions and amplifications of stress occur however is very restricted and discontinuous faults separated by even 5 of their length act more or less independently m max earthquakes breading realistic looking distributions of discontinuous faults rarely are more than 0 1 magnitude unit bigger than would be predicted from a moment summation based on the characteristic magnitude m char of each of the individual faults a prudent course in hazard analysis differentiates m max from m char allowing m max to be 0 2 to 0 3 units larger than m char but not automatically equal to 8

dynamic stress field of a kinematic earthquake source model with k squared slip distribution summary source models such as the k squared stochastic source model with k dependent rise time are able to reproduce source complexity commonly observed in earthquake slip inversions an analysis of the dynamic stress field associated with the slip history prescribed in these kinematic models can indicate possible inconsistencies with physics of faulting the static stress drop the strength excess the breakdown stress drop and critical slip weakening distance dc distributions are determined in this study for the kinematic k squared source model with k dependent rise time several studied k squared models are found to be consistent with the slip weakening friction law along a substantial part of the fault a new quantity the stress delay is introduced to map areas where the yielding criterion of the slip weakening friction is violated hisada s slip velocity function is found to be more consistent with the source dynamics than boxcar brune s and dirac s slip velocity functions constant rupture velocities close to the rayleigh velocity are inconsistent with the k squared model because they break the yielding criterion of the slip weakening friction law the bimodal character of dc dtot frequency magnitude distribution was found dc approaches the final slip dtot near the edge of both the fault and asperity we emphasize that both filtering and smoothing routinely applied in slip inversions may have a strong effect on the space time pattern of the inferred stress field leading potentially to an oversimplified view of earthquake source dynamics

erratum to surficial slip and rupture geometry on the beichuan fault near hongkou during the mw 7 9 wenchuan earthquake china worldwide occurrence and documentation of reverse type ruptures are sparse near hongkou the wenchuan rupture passes through the broad baisha river valley and provides excellent opportunities to trace the surface faulting in fine details for 13 km distance one of the longest continuous sections along the entire rupture in this paper we present the results of our mapping of the surface rupture in this reach based on the discontinuities in slip and geometry the rupture was divided into four sections for convenience from west to east the shenxi gou the miaoba the gaoyuan and the bajiao miao sections respectively the vertical offset is large in the shenxi gou and the bajiao miao sections locally reaching 5 6 m in maxima and generally low in the miaoba section 1 2 m or less in most places the slip gradient for vertical offset is generally 10 3 locally up to 10 1 similar to that in well documented strike slip ruptures near gaoyuan village the surface rupture con sists of two subparallel branches with the northern one exhibiting right lateral slip with minor southeast side up thrusting while the southern one is almost pure south east side up thrusting this pattern mimics the incomplete slip partitioning of oblique thrusting on parallel faults but at a local scale in addition the sense of vertical throw on these two strands is opposite to the general northwest side up thrusting of the wenchuan rupture we propose that it is likely due to the inheritance at shallow depth from the southeast dipping geological faults and that old fault zone structures can have a strong effect on the dynamic rupture by guiding the rupture propagation onto paths of preexisting though locally unfavorable dipping fault planes we also discuss the cross cutting slickenside striations observed near bajiao miao which indicated temporal rake rotation during dynamic rupture and their geological and seismological implications

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

dynamic stress drop and rupture dynamics of the october 15 1979 imperial valley california earthquake abstract a dynamic faulting model is constructed to determine the dynamic stress drop and relative strength distribution for the october 15 1989 imperial valley earthquake and to study the dynamics of rupture propagation for this event reproduction of the kinematic quantities of the strike slip rate strike slip final offset rupture time and rupture duration bu varying the dynamic parameters of dynamic stress drop and yield strength is attempted the fault plane is discretized in 1 5 km square grids the model incorporates first order corrections for the effect of the free surface and material property heterogeneity on the calculation of rupture at depth the strike slip particle velocities final offsets and rupture durations of the kinematic model are matched within about 40 everywhere below about 5 km except in the hypocentral region and in a high displacement region 20 km north of the epicenter the strike slip rate of the dynamic model is half and rupture duration double those of the kinematic model in the epicentral region the rupture durations and strike slip final offsets are two thirds those of the kinematic model in a high stress drop region beneath the el centro crossing array two slip concentrations correspond to stress drop concentrations one of about 80 bar at 20 km from the epicenter and at 8 km depth and the other of about 70 bar at 30 km from the epicenter and 10 km depth most of the dynamic stress drop occurs between the depths of 9 and 11 km averaging about 60 bar stress drops in the 7 9 km range vary between 25 and 35 bar while stress drops in the 5 7 km depth range vary between 10 and 15 bar this depth dependence of stress drop was a consistent feature across nearly 20 km of the fault stress drop appeared to be well correlated with rock type negative stress drop was found in the sediment regions and the regions at depth while positive stress drop was found in the metasediment regions between the depths of 5 and 11 km yield strength and rupture velocity are inversely related high yield strength is found in regions of low rupture velocity and vice versa rupture was found to terminate at the northern end of the fault by collision with a high strength barrier a region of supersonic rupture velocity was found to occur in a region of high stress drop and low fracture strength the kinematic rupture velocity at the northern end of the fault was found to be unreasonably low results show that this region reaches its peak stress before the kinematic break time yield strength increased with depth in the seismogenetic zone until the base of the zone was reached below which it tapered off slightly

inferring earthquake physics and chemistry using an integrated field and laboratory approach abstract earthquakes are the result of a combination of 1 physico chemical processes operating in fault zones which allow ruptures to nucleate and rock friction to decrease with increasing slip or slip rate and 2 of the geometrical complexity of fault zones in this review paper we summarize recent experimental findings from high velocity conducted at about 1 m s slip rate or typical seismic slip rates rock friction experiments with an emphasis on potential dynamic weakening mechanisms melt lubrication nanopowder lubrication etc and how these mechanisms might be recognized by means of microstructural and mineralogical studies in exhumed fault zones we discuss how earthquake source parameters coseismic fault strength weakening distances energy budgets etc might be derived from the field and laboratory experiments additionally we discuss what needs to be considered in terms of fault zone geometry and morphology focusing on fault surface roughness in order to develop models of realistic fault surfaces and present theoretical considerations for microphysical modeling of laboratory data at seismic slip rates with an emphasis on the case of melt lubrication all experimental data and in the case of melt lubrication microphysical models indicate that faults must be very weak

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

paleoseismic evidence for late holocene tectonic deformation along the saddle mountain fault zone southeastern olympic peninsula washington abstract trench and wetland coring studies show that northeast striking strands of the saddle mountain fault zone ruptured the ground about 1000 years ago generating prominent scarps three conspicuous subparallel fault scarps can be traced for 15 km on light detection and ranging lidar imagery traversing the foothills of the southeast olympic mountains the saddle mountain east fault the saddle mountain west fault and the newly identified sund creek fault uplift of the saddle mountain east fault scarp impounded stream flow forming price lake and submerging an existing forest thereby leaving drowned stumps still rooted in place stratigraphy mapped in two trenches one across the saddle mountain east fault and the other across the sund creek fault records one and two earthquakes respectively as faulting juxtaposed miocene age bedrock against glacial and postglacial deposits although the stratigraphy demonstrates that reverse motion generated the scarps slip indicators measured on fault surfaces suggest a component of left lateral slip from trench exposures we estimate the postglacial slip rate to be 0 2 mm yr and between 0 7 and 3 2 mm yr during the past 3000 years integrating radiocarbon data from this study with earlier saddle mountain fault studies into an oxcal bayesian statistical chronology model constrains the most recent paleoearthquake age of rupture across all three saddle mountain faults to 1170 970 calibrated years cal b p which overlaps with the nearby m w 7 5 1050 1020 cal b p seattle fault earthquake an earlier earthquake recorded in the sund creek trench exposure dates to around 3500 cal b p the geometry of the saddle mountain faults and their near synchronous rupture to nearby faults 1000 years ago suggest that the saddle mountain fault zone forms a western boundary fault along which the fore arc blocks migrate northward in response to margin parallel shortening across the puget lowland

on the origin of diverse aftershock mechanisms following the 1989 loma prieta earthquake summary we test the hypothesis that the origin at the diverse suite of aftershock mechanisms following the 1989 m 7 1 loma prieta california earthquake is related to the post main shock static stress field we use a 3 d boundary element algorithm to calculate static stresses combined with a coulomb failure criterion to calculate conjugate failure planes at aftershock locations the post main shock static stress field is taken as the of a sum of a pre existing stress field and changes in stress due to the heterogeneous slip across the loma prieta rupture plane the background stress field is assumed to be either a simple shear parallel to the regional trend of the san andreas fault or approximately fault normal compression a suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared allowing for uncertainties in both mechanism parameters and earthquake locations to well constrained mechanisms reported in the us geological survey northern california seismic network catalogue we also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes assuming either plane to be a likely rupture plane various permutations of the assumed background stress field fractional coefficients of aftershock fault planer methods of comparisons etc explain between 52 and 92 per cent of the aftershock mechanisms we can explain a similar proportion of mechanisms however by comparing a randomly reordered catalogue with the various suites of synthetic aftershocks the inability to duplicate aftershock mechanisms reliably on a one to one basis is probably a function of the combined uncertainties in models of main shock slip distribution the background stress field and aftershock locations in particular we show theoretically that any specific main shock slip distribution and a reasonable background stress field are able lo generate a highly variable suite of failure planes such that quite different aftershock mechanisms may be expected to occur within a kilometre of less of each other this scale of variability is less than the probable location error of aftershock earthquakes in the loma prieta region we successfully duplicate a measure of the variability in the mechanisms of the entire suite of aftershocks if static stress changes are responsible for the generation of aftershock mechanisms we are able to place quantitative constraints on the level of stress that must have existed in the upper crust prior to the loma prieta rupture this stress level appears to be too low to generate the average dip across the main shock rupture plane possible reasons for this result range from incorrect initial assumptions of homogeneity in the background stress field friction and fault geometry to driving stresses that arise from deeper in the crust or upper mantle alternatively aftershock focal mechanisms may be determined by processes other than or in addition to static stress changes such as pore pressure changes or dynamic stresses

evidence for a supershear transient during the 2002 denali fault earthquake elastodynamic considerations suggest that the acceleration of ruptures to supershear velocities is accompanied by the release of rayleigh waves along the fault from the stress breakdown zone these waves generate a secondary slip pulse trailing the rupture front but manifest almost entirely in ground motion perpendicular to the fault in the near source region we construct a spontaneously propagating rupture model exhibiting these features and use it to explain ground motions recorded during the 2002 denali fault earthquake at pump station 10 located 3 km from the fault we show that the initial pulses on both the fault normal and fault parallel components are due to the supershear stress release on the fault whereas the later arriving fault normal pulses result from the trailing subshear slip pulse on the fault online material mpeg movies of rupture history and ground motion

preliminary geological geochemical and numerical study on the first egs project in turkey geothermal energy is attracting more and more attention due to its large capacity and lack of dependency on the weather currently many countries have planned enhanced geothermal system egs projects in this paper the first egs project in turkey which is being implemented at the license area of sds energy inc in dikili of the izmir province is introduced extensive geological paleostress 279 fault slip data from 33 locations geophysical magnetotelluric and vertical electrical sounding at 80 and 129 locations respectively and geochemical studies as well as paleostress measurements have been conducted in this area within the scope of this project in the light of all these studies it has been determined that the dikili region is remarkable in terms of its high thermal gradient of about 7 c 100 m the geothermal reservoir formation the kozak granodiorite is a homogeneous crystalline volcanic rock mass with high radiogenic heat production and suitable for an egs application the analysis shows that the dominating fault system is normal and the corresponding primary stress regime is extensional based on the geological geophysical surveys and the estimated in situ stresses numerical studies were carried out to assess the results of the hydraulic fracturing and geothermal energy production using the numerical codes flac3dplus and tough2mp respectively in the area a of the dikili site the simulation results show that the stimulated reservoir volume and area could reach 44 5 million m3 and 1 km2 respectively with an injection volume of 122 931 m3 assuming the fractured zone has a height of 1000 m and a half length of 1200 m the distance between injection and production wells being 1000 m an average overall geothermal capacity of 83 7 mwth in 20 years could be reached with an injection rate of 250 l s the injection strategy and design parameters of the reservoir stimulation and geothermal production will be further optimized with the project running

natural and experimental evidence of melt lubrication of faults during earthquakes melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake here we estimate the dynamic shear resistance f in the presence of friction induced melts from both exhumed faults and high velocity 1 28 meters per second frictional experiments exhumed faults within granitoids tonalites indicate low f at 10 kilometers in depth friction experiments on tonalite samples show that f depends weakly on normal stress extrapolation of experimental data yields f values consistent with the field estimates and well below the byerlee strength we conclude that friction induced melts can lubricate faults at intermediate crustal depths

onshore to offshore ground surface and seabed rupture of the jordan kekerengu needles fault network during the 2016 mw 7 8 kaikōura earthquake new zealand

a microphysical model for strong velocity weakening in phyllosilicate bearing fault gouges 1 previous rotary shear experiments performed on a halite muscovite fault gouge analogue system have shown that the presence of phyllosilicates under conditions favoring the operation of cataclasis and pressure solution in the matrix phase can have major effects on the frictional behavior of gouges while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behavior the strength of mixtures containing 10 30 muscovite is both normal stress and sliding velocity dependent at high sliding velocities 1 m s 1 such mixtures show unusually marked velocity weakening along with the development of a structureless cataclastic microstructure in the present paper a micromechanical model is developed in an attempt to explain this behavior the model assumes a granular flow process involving competition between intergranular dilatation and compaction by pressure solution the predictions of the model agree favorably with the experimental results extension of the model to quartz mica systems implies that the presence of phyllosilicates plus the operation of pressure solution can strongly promote unstable velocity weakening behavior at rapid slip rates on natural faults under midcrustal conditions static stress drop predictions based on the model agree reasonably well with estimates from seismic observations our results may help explain the discrepancy between laboratory derived rate and state friction parameter values obtained for dry low strain and or single phase rock systems and the values for natural fault rocks inferred from seismological data