geochemical characterization and origin of granitoids from the south bohemian batholith in lower austria major and 31 minor elements have been determined in 39 large samples of variscan granitoids from 6 plutons or intrusions from the south bohemian batholith rastenberg weinsberg mauthausen schrems eisgarn and gebharts the granitoids are mainly granites but also diorites tonalites trondhjemites granodiorites average concentrations of ba th u la ce pb nd sr and k in the weinsberg mauthausen and schrems granites exceed those in average felsic i and s type granites by factors ranging between 2 1 and 1 3 the granites melts formed at waterundersaturated conditions and intruded at 10 to 15 km depth during late tectonic and post tectonic phases of the variscan orogeny about 330 to 300 ma ago hydrothermal or low temperature alteration is excluded for the majority of samples from a study of oxygen isotopes the thickness of the plutons is estimated at about 6 km from heat balance constraints by analogy with experimental partial melting three different sources of the granitoids can be identified and chemically characterized 1 the trondhjemites tonalites and diorites in the early rastenberg pluton are products of 15 to 40 melting respectively of a mafic partly amphibolitic lower crust redwitzites from the west bohemian massif which are comparable in age partly resemble the rastenberg rocks the mafic sources of the rastenberg granitoids and redwitzites are crustally contaminated as reflected in their sr nd isotopes 2 the very large syn tectonic weinsberg pluton was formed from about 30 partial melting of a tonalitic lower crust at 800 to 850 c its low proportion of ca 10 restite has a ferrodioritic composition the post tectonic fine grained mauthausen and schrems granites which tend to a granodioritic mode are very low in restite and are also products of melting of a tonalitic source 3 the youngest leuco granite the eisgarn pluton high in si p li rb cs u 87sr 86sr and low in ca sr ba reflects a pelitic source the change from mafic to tonalitic to pelitic source composition for the granitoid sequence may indicate that the depth of melt formation decreased with time the concentration of heavy rare earth elements decreased from weinsberg to eisgarn granites which indicates an increasing proportion of garnet in the source the orogenic heat conformable with a heat flow of about 100 mwm 2 was provided by mafic intrusions an alternative would be a drastic increase of the crustal thickness which cannot be recognized by barometry of the associated metamorphic rocks exposed metamorphic country rocks occur in higher amphibolite facies indicating about 5 kbar pressure mafic intrusions contain gabbros kleinzwettl or have formed quartz diorites gebharts the latter being contaminated by granitic melts from partial melting of the wall rocks mash process largescale contamination by crustal materials can be observed in 18o and in sr nd isotopes the major mafic activity was probably caused by depression of solidus temperatures in the mantle wedge above a subduction zone where water was available from dehydration of subducted ocean crust this water initiated partial melting of ultramafic rocks and metasomatism in the uppermost mantle above the level of melting the water also mobilized highly incompatible elements ba th u la ce pb nd sr and k from the uppermost mantle and transported them into the lower crust indicators of a nearby subduction or collision zone of late variscan age in addition to the specific association of granitoidal rocks are abundant upper mantle tectonites an alternate or additional source of metasomatic fluids may have been dehydration of lower crustal rocks during variscan high grade metamorphism

o h c isotope study of rocks from the ktb pilot hole crustal profile and constraints on fluid evolution the pilot hole of the continental deep borehole ktb drilling project is located in the bavarian oberpfalz at the western margin of the bohemian massif the 4 km deep borehole penetrated various paragneisses and minor orthogneisses with intercalations of amphibolites and metagabbros the different lithologies have systematically different whole rock oxygen isotope values and give little evidence for large scale water rock interaction minor fluid interaction is well documented during retrograde metamorphism by non equilibrium fractionations between refractory minerals quartz garnet and hornblende and altered minerals chlorite biolite and feldspar ubiquitous vein mineralisation indicates fluid induced retrogression at temperatures between 150 c and 400 c the d values of hydroxylbearing minerals are very uniform in all lithologic units the calculated hydrogen isotope composition of the fluid in equilibrium with matrix and vein minerals increases from 45 for metabasic rocks to 20 for gneisses to about 5 for vein minerals the oxygen isotope composition of the fluid has been buffered by the rock and decreases with decreasing temperature because of increasing fractionations at low temperatures and low water rock ratios modern fluids sampled from open cavities within the borehole have isotopic compositions that suggest a continuous fluid evolution during retrogression in a closed system the 13c values of calcite and graphite also indicate closed system mixing processes

energy release and heat generation during the 1999 ms7 6 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan integrating observed and inversed results of source parameters the fracture energy eg and frictional energy ef on the fault and its northern and southern segments are estimated together with given values of strain energy e and seismic radiation energy es the seismic efficiency i e es e and the radiation efficiency i e r es es eg are evaluated the average fracture energy per unit area g is also calculated from eg the frictional heat caused by dynamic frictional stress is calculated from ef results show a marked difference in source properties between the two segments the average frictional and ambient stress levels on the two segments are estimated the total energy budget of and heat generated by the earthquake are elucidated based on a two dimensional faulting model with frictional heat both observed and calculated results suggest the possible existence of fluids which produced suprahydrostatic gradients on the fault during faulting lubrication and thermal fluid pressurization might play a significant role on rupture

saline minewaters of the keweenaw peninsula northern michigan their nature origin and relation to similar deep waters in precambrian crystalline rocks of the canadian shield

a dynamic study of frictional and viscous effects on earthquake rupture a case study of the 1999 chi chi taiwan earthquake friction is commonly considered an important factor in controlling earthquake rupture in this work it is assumed that viscosity is also a significant factor a strike slip type two body spring slider model in the presence of both friction and viscosity is applied to approximate the rupture processes of an earthquake along the fault striking direction results show that in addition to friction viscosity is also an important factor in controlling rupture the m s 7 6 chi chi earthquake which struck central taiwan on 20 september 1999 ruptured a 100 km long east dipping transpressive fault the chelungpu fault measured and inferred results show that there are differences in physical properties between the northern and southern segments of the fault simulation results from a two body model can explain the differences in displacement velocity acceleration and predominant period between the two fault segments

saline groundwaters in the canadian shield a first overview abstract the chemical and isotopic compositions of saline groundwaters and brines in the canadian shield are described the occurrence of such waters is very widespread not related to any specific rock type or mineralization and generally can be expected at depths below 1 km the most saline brines have salinities exceeding 200 g l 1 dissolved solids and their chemistries tend to suggest that in the past saline waters penetrated the canadian shield the original chemistry of these solutions was subsequently modified through strong rock water interactions and it appears that their final chemical compositions are independent of the original chemistries stable isotope analyses indicate that these waters are not simple evaporated seawater sedimentary basin brines hydrothermal solutions or residual ore forming fluids although any of these could be a precursor of the brines secondary isotope exchange reactions and the hydration of primary silicates accompanied by the formation of clay minerals could have modified not only the primary isotopic composition but may have also profoundly influenced the chemistries of these brines to be effective these processes would have had to occur in closed systems

the importance of the dynamic source effects on strong ground motion during the 1999 chi chi taiwan earthquake brief interpretation of the damage distribution on buildings the 1999 chi chi taiwan earthquake that originated on a low angle reverse fault showed complexity and uncommon characteristics the records show that the hanging wall side is characterized by larger particle motions than the foot wall and the ground motion is stronger in the northern part than in the southern part of the causative fault although the strongest ground motion occurred near the north ern part of the trace structural damage was heavier in the southern part in order to get a better understanding of the complex damage distribution caused by this earth quake the dynamic rupture process was numerically simulated because of the dif ferences between the observed features of the rupture process in the northern and southern parts of the fault each part was modeled independently by using a 2d discrete element model dem the principal results of the simulation show that the velocity ground motions in the northern part in the frequency range of 0 5 2 hz natural frequency range of standard structures are small near the surface break thus light structural damage might be predicted near the surface rupture moreover in the northern part the fault rupture propagation reaches the surface with a very slow velocity about 1 2 km sec however in the southern part the rupture propa gation reaches the surface with higher velocity about 3 0 km sec these differences between the models could explain why the ground motion near the surface rupture in the northern part caused less damage in structures than the ground motion in the southern part

the mechanics of lubricated faults insights from 3 d numerical models 1 the weakening mechanisms occurring during an earthquake failure are of prominent importance in determining the resulting energy release and the seismic waves excitation in this paper we consider the fully dynamic response of a seismogenic structure where lubrication processes take place in particular we numerically model the spontaneous propagation of a 3 d rupture in a fault zone where the frictional resistance is controlled by the properties of a low viscosity slurry formed by gouge particles and fluids this model allows for the description of the fault motion in the extreme case of vanishing effective normal stress by considering a viscous fault response and therefore without the need to invoke in the framework of coulomb friction the generation of the tensile mode of fracture we explore the effects of the parameters controlling the resulting governing law for such a lubricated fault the viscosity of the slurry the roughness of the fault surfaces and the thickness of the slurry film our results indicate that lubricated faults produce a nearly complete stress drop i e a very low residual friction coefficient 0 01 a high fracture energy density eg few 10s of mj m2 and significant slip velocities vpeak few 10s of m s the resulting values of the equivalent characteristic slip weakening distance d0eq 0 1 0 8 m depending on the adopted parameters are compatible with the seismological inferences moreover in the framework of our model we found that supershear ruptures are highly favored in the case of enlarging gap height we can have the healing of slip or even the inhibition of the rupture quantitative comparisons with different weakening mechanisms previously proposed in the literature such as the exponential weakening and the frictional melting are also discussed

temperature estimates of coseismic heating in clay rich fault gouges the chelungpu fault zones taiwan abstract to investigate the coseismic frictional temperature in seismogenic fault zones we examine the characteristics of clays in the chelungpu fault zones with isothermal heating experiments scanning electron microscope coupled to an energy dispersive spectrometer sem edx and thermogravimetry analysis tga in the tcdp case taiwan chelungpu fault drilling project three fault zones of the chelungpu fault system were identified at the depth of 1111 m 1153 m and 1222 m described as fz1111 fz1153 and fz1222 hereafter respectively the clay mineral assemblages of fz1111 show evidence of melting and the temperature in a 2 cm band within the black gouge zone is estimated to be from 900 c to 1100 c by comparing the sem images of in situ natural samples with those of heated materials and the finding of no recrystallization of kaolinite amorphous aluminosilicates spinel in the fault samples the clay mineral assemblages of fz1153 suggested that kaolinite has been broken down by the thermal decomposition dehydroxylation but chlorite has not the clay characteristics and results of sem edx and tga constrain the faulting temperature from 500 c to 900 c with a spatial distribution up to 1 3 m the clay characteristics of fz1222 indicated that clays were changed by experiencing high temperature acid fluids instead of thermal decomposition dehydroxylation processes and that the temperature is localized in 2 cm and ranges from 350 c to 500 c the lowest temperature among three fault zones the estimates of temperature ranges and thermal anomaly intervals among three fault zones provide important information and constraints on the physical and chemical processes coseismic dynamic weakening mechanism and earthquake energy budget in the future

the rupture mode of the shallow large slip surge of the tohoku oki earthquake abstract the remarkable feature of the m w 9 1 tohoku oki earthquake of 2011 was a late shallow surge that propagated from about 12 km depth all the way to the trench this surge had very large slip and was depleted in high frequency radiation it was followed by normal faulting in the outer wedge this requires that the postsurge basal shear stress be close to zero explanations for the surge propagating through the velocity strengthening region by a thermal weakening mechanism fail to produce the near total stress drop required by the postseismic extension the surge propagated in a region of material contrast across the plate interface the combination of a strong nucleation pulse from down dip velocity strengthening and the bimaterial effect satisfies the conditions for wrinkle pulse propagation a wrinkle pulse rupture mode can produce an instability by overcoming velocity strengthening with the normal stress reduction produced by the bimaterial effect it also leads to total stress drop satisfying the extension constraint and explaining the prodigious slip amplitude of the surge because the surfaces are detached in wrinkle pulse mode asperity contact is reduced which explains the dearth of high frequency radiation during the surge this behavior appears to be a common feature of many of the greatest subduction earthquakes

coseismic slip on shallow decollement megathrusts implications for seismic and tsunami hazard abstract for years many studies of subduction zones and on land fold and thrust belts have assumed that the frontal portions of accretionary prisms are too weak to rupture coseismically and must therefore be fully creeping we present a series of examples both on land and offshore demonstrating that in many cases shallow decollements are capable of large coseismic slip events that rupture to the toes of the fault systems some of these events are associated with ruptures that initiate down dip while others appear to be limited to the frontal shallow portion of the wedge we suggest that this behavior is not limited to the examples described here but rather is common to many perhaps most accretionary wedges and fold and thrust belts around the world indeed there may be many other examples of similar earthquakes where existing data cannot constrain slip at the toe we do not characterize the regions and events described here as unusual as they encompass a wide range of settings this study indicates that there is an urgent need to reevaluate seismic and tsunami hazard in fold and thrust belts and subduction zones around the world allowing for the possibility of shallow decollement rupture

a stable isotope study of retrograde alteration in sw connemara ireland dalradian metamorphic rocks lower ordovician meta igneous rocks mgs and caledonian granites of the connemara complex in sw connemara all show intense retrograde alteration alteration primarily involves sericitization and saussuritization of plagioclase the alteration of biotite and hornblende to chlorite and the formation of secondary epidote the alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs and was the result of a phase of fluid influx into these rocks in hand specimen k feldspar becomes progressively reddened with increasing alteration mineralogical alteration in the mgs and caledonian granites took place at temperatures 275 15 c and in the mgs pfluid is estimated to be 1 5 kbar during alteration the d values of alteration phases are 18 to 29 fluid inclusions 47 to 61 chlorites and 11 to 31 epidotes chlorite 18o values are 0 2 to 4 3 while 18o values for quartz k feldspar pairs show both positively sloped mgs and highly unusual negatively sloped caledonian granites arrays diverging from the normal magmatic field on a plot the stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200 140 c the retrograde fluid had d 20 to 30 in all lithologies but the fluid 18o varied both spatially and temporally within the range 4 to 7 the fo2 of the fluid that deposited the epidotes in the mgs varied with its 18o value with the most 18o depleted fluid being the most oxidizing the d values together with low 0 18o values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin this meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration the variation in retrograde fluid 18o values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid rock interaction infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the galway granite soon after intrusion at 400 ma however convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later

the 2010 mw 8 8 chile earthquake triggering on multiple segments and frequency dependent rupture behavior 1 multi frequency back projection results of the february 27 2010 mw 8 8 chile earthquake reveal that this earthquake consists of distinct subevents with different slip characteristics the subevent south of the epicenter releases its energy at low frequencies 0 05 0 1 hz implying slow slip and has a rupture speed around 0 8 km s two subevents north of the epicenter are characterized by high frequency energy 1 5 hz release the first of these subevents appears to trigger slip on the second segment to the north which has higher amplitude energy release and a fast propagation speed of about 2 9 km s in addition to these rupture details high frequency energy release is observed at the rupture front followed by lower frequency energy release this observation suggests that the rupture of large earthquakes involves dynamic weakening of faults and hence their rupture properties may not be related easily to those of small earthquakes these distinct slip behaviors point out the need to consider data from a wide range of frequencies to fully assess the rupture process and associated hazards of giant earthquakes

nonlinear effects of temperature fluid pressure and inelastic porosity on dynamic fault slip and fault tip propagation emergence of slip strengthening and pulse like fault slip 1 we theoretically study dynamic faulting taking account of thermoporoelastic effects including inelastic porosity change the porosity is assumed to increase with increasing fault slip we first derive the analytical solutions for the changes of fluid pressure temperature and fault slip assuming 1 d fault model as found in our previous study the evolution of these quantities is controlled by a single nondimensional parameter su a quantity proportional to the rate of increase in inelastic porosity multiplied by the thickness of shear heating zone if we assume that temperature elevation remains below the melting temperature of fault rocks su is found be close to zero or greater than unity our 2 d simulation shows that pulse like slip appears when su is greater than unity which is a necessary consequence of the emergence of slip strengthening while slip weakening caused by thermal pressurization arises when su is close to zero the applied shear stress is entirely released when su is close to zero while it is released only partially when su is greater than unity so that the latter will be more reasonable according to seismological observations the fault tip stress increases significantly with the fault extension in classical singular fault model in contrast the fault tip stress is only weakly dependent on the size of extending fault in our model when su is greater than unity so that the fault growth is more vulnerable to spatial perturbation of model parameters our present study indicates the importance of slip strengthening for the understanding of dynamic faulting

elastohydrodynamic lubrication of faults the heat flow paradox provides evidence that a dynamic weakening mechanism may be important in understanding fault friction and rupture we present here a specific model for dynamic velocity weakening that uses the mechanics of well studied industrial bearings to explain fault zone processes an elevated fluid pressure is generated in a thin film of viscous fluid that is sheared between nearly parallel surface this lubrication pressure supports part of the load therefore reducing the normal stress and associated friction across the gap the pressure also elastically deforms the wall rock the model is parameterized using the sommerfeld number which is a measure of the lubrication pressure normalized by the lithostatic load for typical values of the material properties slip distance and velocity the sommerfeld number suggests that lubrication is an important process if the lubrication length scales as the slip distance in an earthquake the frictional stress during dynamically lubricated large earthquakes is 30 less than the friction with only hydrostatic pore pressure elastohydrodynamic lubrication also predicts a decrease in high frequency 1 hz radiation above a critical slip distance of a few meters this prediction is well matched by the strong motion data from the 1999 taiwan earthquake the observed 2 orders of magnitude variation in scaled radiated energy between small m w 6 is also predicted by the lubrication model

clay clast aggregates in gouges new textural evidence for seismic faulting 1 spherical aggregates named clay clast aggregates ccas have been reported from recent investigations on retrieved clay bearing fault gouges from shallow depth seismogenic faults and rotary shear experiments conducted on clay bearing gouge at seismic slip rates the formation of ccas appears to be related to the shearing of a smectite rich granular material that expands and becomes fluidized we have conducted additional high velocity rotary shear experiments and low velocity double shear experiments we demonstrate that a critical temperature depending on dynamic pressure temperature conditions is needed for the formation of ccas this temperature corresponds to the phase transition of pore water from liquid to vapor or to critical which induced gouge pore fluid expansion and therefore a thermal pressurization of the fault a detailed examination by energy dispersive x ray spectrometry edx sem element mapping sem and transmission electron microscopy tem shows strong similar characteristics of experimental and natural ccas with a concentric well organized fabric of the cortex and reveals that their development may result from the combination of electrostatic and capillary forces in a critical reactive medium during the dynamic slip weakening accordingly the occurrence of ccas in natural clay rich fault gouges constitutes new unequivocal textural evidence for shallow depth thermal pressurization and consequently for past seismic faulting

static stress drop inferred from near fault parameters for the 1999 chi chi earthquake in taiwan abstract in 2001 a special issue of the bulletin of the seismological society of america bssa featured seismological research for the 1999 chi chi taiwan earthquake this study uses source parameters suggested by the first author in this special issue to estimate static stress drop associated with the chi chi earthquake the waveform simulation method was used to carefully examine these source parameters the simulation results indicate that source parameters inferred from near fault observations are well determined according to the rupture area and slip the static stress drops s obtained were distributed between a small value of 47 bars near the epicentral region and a much larger value 200 bars to the north similar trends in dynamic stress drop d were also recognized by the first author in his paper published in 2001 bssa special issue comparing the s with d satisfies the relation s d 1 this relation suggests that fault motion is mostly spent releasing seismic wave energy during the rupture process of the chi chi earthquake the consistency between static and dynamic stress drops thus provides a measure of energy moment es m0 ratios which range from 9 0 10 5 to 6 5 10 4 the average es m0 ratio estimated for the northern portions of the fault is 3 4 10 4 which is about 3 times that of the south such a high es m0 ratio can be interpreted as having low strength in the rupture for the northern portions of the fault where the fault would release less energy per unit rupture surface to create the new rupture

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

euclidean and fractal models for the description of rock surface roughness accurate description of the topography of rock surfaces is essential because surface roughness affects frictional strength the flow of fluids in joints and fractures the seismic behavior of faults and the formation of gouge and breccia in fault zones real rock surfaces can be described using self similar and self affine fractal models of surface roughness if a surface is self similar a small portion of the surface when magnified isotropically will appear statistically identical to the entire surface if a surface is self affine a magnified portion of the surface will only appear statistically identical to the entire surface if different magnifications are used for the directions parallel and perpendicular to the surface at least two parameters are required to describe a fractal model one parameter typically describes how roughness changes with scale while the other specifies the variance or surface slope at a reference scale the divider method and the spectral method are in common use to determine the best fit fractal model from surface profile data power spectra from self similar surfaces have slopes of 3 on log log plots of power spectral density versus spatial frequency while spectra from self affine surfaces have slopes other than 3 power spectra can be interpreted with greater facility if dimensionless amplitude to wavelength ratios are contoured on plots of power spectral density versus frequency the topography of many natural rock surfaces including both fractures and faults is approximately self similar within the 6 5 order of magnitude wide wavelength band of 10 m to 40 m within smaller wavelength bands natural rock surfaces may exhibit self affine behavior

high magnetic susceptibility of fault gouge within taiwan chelungpu fault nondestructive continuous measurements of physical and chemical properties in fault rocks recovered from hole b tcdp 1 the taiwan chelungpu fault drilling project tcdp was undertaken in 2002 to investigate the faulting mechanism of the 1999 taiwan chi chi earthquake hole b penetrated the chelungpu fault and recovered core samples from between 948 42 m and 1352 60 m depth three zones marked 1136mfz 1194mfz and 1243mfz were recognized in the core samples as active fault zones within the chelungpu fault multi sensor core logger measurements revealed lower densities and higher magnetic susceptibilities within the black gouge zones in all three fault zones even though the fault zone that slipped during the 1999 earthquake has not been identified higher magnetic susceptibilities indicate that frictional heating has taken place in the chelungpu fault

investigation of the records of earthquake slip in carbonaceous materials from the taiwan chelungpu fault by means of infrared and raman spectroscopies this research was supported by a grant in aid for young scientists a from the japan ministry of education science sports and culture 23684039 2013

ammonium concentration and nitrogen isotope composition in metasedimentary rocks from different tectonometamorphic units of the european variscan belt the content and isotopic composition of ammonium nh4 were measured by using kjeldahl distillation for 63 samples of predominantly metasedimentary rocks from two different geological settings of the european variscides i e the erzgebirge and the zone of erbendorf vohenstrauss in germany the studied erzgebirge schists represent an early paleozoic passive margin sequence that reappears in different deep subducted metamorphic units this allows an efficient examination of nitrogen loss and isotope fractionation during prograde metamorphism ammonium is found to be progressively depleted accompanied by a shift in 15n from the low grade units 2 kbar 300 c with 638 124 ppm and 15n 2 2 0 6 to the garnet phyllite unit 9 kbar 470 c with 621 190 ppm and 15n 3 5 0 9 the mica schist eclogite unit 12 kbar 550 c with 394 113 ppm and 15n 3 9 0 8 and to the gneiss eclogite unit 12 kbar 730 c with 99 32 ppm and 15n 7 7 2 0 using equilibrium models for rayleigh distillation and batch volatilization suggest that the nitrogen depletion took place by ammonia release only for the mica schists this isotope fractionation can be explained by the loss of molecular nitrogen in comparison with the early paleozoic schists the proterozoic ortho and paragneisses of the erzgebirge gneiss unit 6 8 kbar 650 c contain significantly lower amounts of ammonium 70 ppm and reach relatively low 15n values 2 5 to 3 6 the paragneisses from the zone of erbendorf vohenstrauss zev sampled from the ktb pilot hole represents a separate tectonometamorphic unit that has undergone polyphase metamorphic conditions with the major imprint being amphibolite facies 7 kbar 650 700 c the metagraywackes have nh4 contents of 80 ppm and 15n of approximately 6 gneisses in the vicinity of a late cataclastic shear zone at 2000 m depth are characterized by a shift in nh4 250 ppm and 15n up to 12 which suggest late fluid rock interactions with a nitrogen and 15n enriched fluid

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

can observations of earthquake scaling constrain slip weakening summary we use observations of earthquake source parameters over a wide magnitude range m w 0 7 to place constraints on constitutive fault weakening the data suggest a scale dependence of apparent stress and stress drop both may increase slightly with earthquake size we show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes we select 30 earthquakes well recorded at 2 5 km depth at cajon pass california we use individual and empirical green s function spectral analysis to improve the resolution of source parameters including static stress drop and total slip s we also measure radiated energy e s w ecompare the cajon pass results with those from larger california earthquakes including aftershocks of the 1994 northridge earthquake and confirm the results of abercrombie 1995 e s m 0 where rigidity and both e s m 0 and increase as m 0 and s increases uncertainties remain large due to model assumptions and variations between possible models and earthquake scale independence is possible within the resolution assuming that the average trends are real we define a quantity g 2 es m 0 s 2w hich is the total energy dissipation in friction and fracture minus 1 s w here 1 is the final static stress if 1 d the dynamic shear strength during the last increments of seismic slip then g g the fracture energy in a slip weakening interpretation of dissipation

subsurface structure physical properties fault zone characteristics and stress state in scientific drill holes of taiwan chelungpu fault drilling project continuous cores and a suite of geophysical measurements were collected in two scientific drill holes to under stand physical mechanisms involved in large displacements during the 1999 chi chi earthquake physical properties obtained from wire line logs including p and s wave sonic velocity gamma ray electrical resistivity density and temperature are primarily dependent on parameters such as lithology depth and fault zones the average dip of bedding identified from cores and fmi or fms logs is about 30 degrees towards se nevertheless local azimuthal variations and increasing or decreasing bedding dips appear across fault zones a prominent increase of structural dip to 60 80 below 1856 m could be due to deformation associated with propagation of the sanyi fault a total of twelve fault zones identified in hole a are located in the plio pleistocene cholan formation pliocene chinshui shale and miocene kueichulin formation the shallowest fault zone occurs at 1111 m depth fza1111 it is a 1 m gouge zone including 12 cm of thick indurate black material we interpreted this zone as the slip zone during the chi chi earthquake fza1111 was characterized by 1 beddingparallel thrust fault with 30 dip 2 the lowest resistivity 3 low density vp and vs 4 high vp vs ratio and poisson s ratio 5 low energy and velocity anisotropy and low permeability within the homogeneous gouge zone 6 increasing gas co2 and ch4 emissions and 7 richness in smectite within the primary slip zone in situ stresses at the drill site were inferred from leak off tests borehole breakouts and drilling induced tensile fractures from borehole fms fmi logs and shear seismic wave anisotropy from dsi logs the dominant fast shear wave polarization direction is in good agreement with regional maximum horizontal stress axis particularly within the strongly anisotropic kueichulin formation a drastic change in orientation of fast shear polarization across the sanyi thrust fault at 1712 m depth reflects the change of stratigraphy physical properties and structural geometry

pyrite alteration and neoformed magnetic minerals in the fault zone of the chi chi earthquake mw7 6 1999 evidence for frictional heating and co seismic fluids 1 during an earthquake physical and chemical transformations lead to alteration and formation of minerals in the gouge layer altered and neoformed minerals can be used as tracers of some earthquake processes in this study we investigate pyrite and magnetic minerals within the host chinshui siltstone and the 16 cm thick gouge this gouge hosts the principal slip zone of chi chi earthquake mw7 6 1999 in the chinshui siltstone pyrite framboids of various sizes and euhedral pyrite are observed the magnetic mineral assemblage comprises stoichiometric magnetite greigite and fine grained pyrrhotite the pyrite content is generally reduced in the gouge compared to the wall rock the magnetic mineral assemblage in the gouge consists of goethite pyrrhotite and partially oxidized magnetite the pyrrhotite goethite and some magnetite are neoformed pyrrhotite likely formed from high temperature decomposition of pyrite 500 c generated during co seismic slip of repeated earthquakes goethite is inferred to have formed from hot aqueous co seismic fluid 350 c in association with the 1999 chi chi event elevated fluid temperatures can also explain the partial alteration of magnetite and the retrograde alteration of some pyrrhotite to pyrite we suggest that characterization of neoformed magnetic minerals can provide important information for studying earthquake slip zones in sediment derived fault gouge

structural geology of a classic thrust belt earthquake the 1999 chi chi earthquake taiwan mw 7 6 abstract we document the structural context of the 1999 chi chi earthquake m w 7 6 in western taiwan which is one of the best instrumented thrust belt earthquakes the main surface break and large slip 3 10 m is on two segments of the shallow otherwise aseismic bedding parallel chelungpu sanyi thrust system which shows nearly classic ramp flat geometry with shallow detachments 1 6 km in the pliocene chinshui shale and mio pliocene kueichulin tungkeng formations however rupture is complex involving at least six faults including a previously unknown deeper thrust 8 10 km on which the rupture began we compare the coseismic displacements with a new 3d map of the chelungpu sanyi system the displacements are spatially and temporally heterogeneous and well correlated with discrete geometric segments of the 3d shape of the fault system geodetic displacement vectors are statistically parallel to the nearest adjacent fault segment and are parallel to large scale oblique fault corrugations the displacement magnitudes are heterogeneous at several scales which requires in the long term other non chi chi events or significant aseismic deformation the chelungpu thrust has a total displacement of 14 km but the area of largest chi chi slip 10 m is on a newly propagated north chelungpu chinshui detachment 0 3 km total slip which shows abnormally smooth rupture dynamics

quantitative modeling of the newly formed magnetic minerals in the fault gouge of 1999 chi chi earthquake mw 7 6 taiwan when an earthquake occurs magnetic minerals are formed in the gouge under the combined action of frictional heating and fluid generally the gouge is altered and a detailed analysis of neoformed minerals is difficult the taiwan chelungpu fault drilling project provided continuous records of the active chelungpu fault gouges by analyzing the magnetic parameters along the 16 cm thick gouge which houses the principal slip zone of the 1999 chi chi earthquake mw 7 6 we observed a 4 cm shift between the maximum of magnetic susceptibility and the maximum of remanence the maximum magnetic susceptibility is localized along the principal slip zone the main identified magnetic minerals are magnetite and goethite which have very different magnetic parameters we propose that the maximum of the concentration of magnetite and goethite corresponds to the maximum of magnetic susceptibility and remanence respectively by modeling the concentration of these two magnetic minerals we explain satisfactorily the profiles of magnetic susceptibility and remanence this quantitative modeling indicates that 200 ppmv of magnetite formed in the principal slip zone and its main contact area similarly 1 of goethite is formed in the center of the gouge where the fluids are more enriched in iron we propose that the magnetite and goethite are formed and altered during seismic cycles key points investigate the magnetic mineral assemblage in the chi chi fault gougeclarify the distribution of goethite and magnetite in the gougepropose a model for goethite and magnetite distributions within the gouge

rupture behavior of the 1999 chi chi taiwan earthquake slips on a curved fault in response to the regional plate convergence abstract simple kinematic modeling of particle motion along a curved fault similar to the ruptured chelungpu fault taiwan indicates a unique spatial slip pattern specifically we find that the large convergent slip on the curve is a result of the minimum deformation scenario of the fault geometry and regional northwestern movement of the philippine sea plate psp the modeled deformation regime portrays an accumulation of deformation in the curved region which coincides very well with a long term observed nw se trending seismogenic zone in the central taiwan this consistence suggests that the chelungpu fault is a preexisting curved fault this is further evidenced by geological and geophysical observations because the spatial slip pattern is locally and regionally tectonically controlled it indicates that the rupture behavior of the chi chi earthquake is repeatable better knowledge of the fault geometry and the regional plate motion may help us to predict the possible spatial slip distribution of large earthquakes this discovery is important for avoiding large buildings and constructions near predicted large slip regions

a multiple time window rupture model for the 1999 chi chi earthquake from a combined inversion of teleseismic surface wave strong motion and gps data 1 we present the results of a comprehensive analysis of the rupture process of the 1999 chi chi taiwan earthquake using a broad array of seismic as well as geodetic data spanning a very wide frequency band our results indicate that the rupture was quite smooth with the slip concentrated in a wide arcuate region north of the epicenter with very little slip to the east or south we found a moment of 3 3 1027 dyn cm which is consistent with the long period determinations for this earthquake the rupture velocity is approximately 2 25 km s and is quite uniform across the fault we have tested both a single fault plane model as well as a composite fault model with a second e w striking plane to the north of the rupture to improve the fit of the geodetic data overall the differences in slip distribution between the two models are negligible but the fit to the gps data is significantly better for the composite model which is thus our preferred solution this model is similar to other rupture models as far as the large scale features are concerned but differs for the smaller asperities that are present in other models but not as much in ours these are usually poorly constrained and with the use of the geodetic data we believe that there is little evidence for a significant amount of slip away from our main slip concentration

fmnear determination of focal mechanism and first estimate of rupture directivity using near source records and a linear distribution of point sources abstract the fmnear method is based on both the waveform inversion of near source seismic records and on a linear finite source model the primary source parameters that are determined are the moment magnitude m w the double couple focal mechanism strike dip and rake and the distribution of seismic moment along strike which provides a first order estimate of rupture length and directivity source depth is also explored an advantage of the approach is the use of the finite source model directly within the search of the focal mechanism this strategy allows the inclusion of strong motion records at short distances for moderate to very large earthquakes m w 5 5 however for moderate to small earthquakes m w m w 4 5 to 9 0 test cases incorporate continental events recorded by a large number of well distributed stations and less favorable cases in its present form the fmnear approach is very well adapted to continental earthquakes surrounded by seismic stations but it can also give informative results in more difficult configurations the fmnear method is now ready for fully automated determinations and is already implemented in near real time online material details on inversion parameters flow charts of the fmnear method figures of waveform modeling and sensitivity for selected events and table of velocity models

frequency dependent effects of rupture for the 2004 parkfield main shock results from upsar the frequency dependent effects of rupture propagation of the parkfield california earthquake 28 september 2004 m6 to the northwest along the san andreas fault can be seen in acceleration records at upsar usgs parkfield seismic array in at least two ways first we can see the effects of directivity in the acceleration traces at upsar which is about 11 5 km from the epicenter directivity or the seismic equivalent of a doppler shift has been documented in many cases by comparing short duration high amplitude pulses p or s in the forward direction with longer duration body waves in the backward direction in this case we detect a change from a relatively large amplitude coherent high frequency signal at the start of rupture to a low amplitude low coherent low frequency signal at about the time the rupture front transfers from the forward azimuth to the back azimuth at about 34 36 s time is utc and is the seconds after day 272 and 17 h and 15 min s arrival is just after 30 s for rays leaving the fault and propagating to upsar the frequency change is obvious in the band about 5 to 30 hz which is significantly above the corner frequency of the earthquake about 0 11 hz from kinematic source models the duration of faulting is about 9 2 s and the change in frequency is during faulting as the rupture extends to the northwest understanding the systematic change in frequency and amplitude of seismic waves in relation to the propagation of the rupture front is important for predicting strong ground motion second we can filter the acceleration records from the array to determine if the low frequency energy emerges from the same part of the fault as the high frequency signal e g has the same back azimuth and apparent velocity at upsar an important clue to the dynamics of rupture analysis of sources of strong motion characterized by relatively high frequencies compared to kinematic slip models relatively low frequency for the 11 march 2011 tohoku earthquake as well as maule 27 february 2010 and chi chi 20 september 1999 earthquakes show that high and low frequency sources do not have the same locations on the fault in this paper we filter the accelerograms from upsar for the 2004 main shock in various passbands and then recompute the cross correlations to determine the vector slowness of the incoming waves at parkfield it appears that for seismic waves with frequencies above 1 hz there is no discernible frequency dependent difference in source position up to 8 hz based on estimates of back azimuth and apparent velocity however at lower frequencies sources appear to be from shallower depths and trail the high frequencies as the rupture proceeds down the fault this result is greater than one standard deviation of an estimate of error based on a new method of estimating error that is a measure of how broad the peak in correlation is and an estimate of the variance of the correlation values these observations can be understood in terms of a rupture front that is more energetic and coherent near the front of rupture radiating higher frequencies and less coherent and less energetic radiating in a lower frequency band behind the initial rupture front this result is a qualitative assessment of changes in azimuth and apparent velocity with frequency and time and does not include corrections to find the source location on the fault

fault structure control on fault slip and ground motion during the 1999 rupture of the chelungpu fault taiwan the chelungpu fault taiwan ruptured in a mw 7 6 earthquake on 21 september 1999 producing a 90 km long surface rupture analysis of core from two holes drilled through the fault zone combined with geologic mapping and detailed investigation from three outcrops define the fault geometry and physical properties of the chelungpu fault in its northern and southern regions in the northern region the fault dips 45 60 east parallel to bedding in both the hanging wall and footwall and consists of a narrow 1 20 cm core of dark gray sheared clay gouge the gouge is located at the base of a 30 to 50 m zone of increased fracture density confined asymmetrically to the hanging wall microstructural analysis of the fault gouge in dicates the presence of extremely narrow clay zones 50 300 lm thick that are interpreted as the fault rupture surfaces few shear indicators are observed outside of the fault gouge implying that slip was localized within the gouge zone slip localization along a bed parallel surface resulted in a narrow gouge zone that pro duced less high frequency ground motion and larger displacements average 8 m during the earthquake than in the southern region displacement in the southern region averaged only 2 m but ground shaking consisted of large amounts of high frequency ground motion the fault in the southern region dips 20 30 at the surface and consists of a wide 20 70 m thick zone of sheared foliated shale with numerous gouge zones these data demonstrate a potential correlation between fault structure i e gouge width geometry and earthquake characteristics such as displacement and ground motion i e acceleration

high magnetic susceptibility produced by thermal decomposition of core samples from the chelungpu fault in taiwan abstract we carried out thermomagnetic susceptibility analyses of fault rocks from core samples from hole b of the taiwan chelungpu fault drilling project tcdp to investigate the cause of high magnetic susceptibilities in the fault core test samples were thermally and mechanically treated by heating to different maximum temperatures of up to 900 c and by high velocity frictional tests before magnetic analyses thermomagnetic susceptibility analyses of natural fault rocks revealed that magnetization increased at maximum heating temperatures above 400 c in the heating cycle and showed three step increases at 600 to 550 c and at 300 c during the cooling cycle these behaviors are consistent with the presence of pyrite siderite and chlorite suggesting that tcdp gouge originally included these minerals which contributed to the generation the magnetic susceptibility by thermomechanical reactions the change in magnetic susceptibility due to heating of siderite was 20 times that obtained by heating pyrite and chlorite so that only a small fraction of siderite decomposition is enough to cause the slight increase of the susceptibility observed in the fault core color measurement results indicate that thermal decomposition by frictional heating took place under low oxygen conditions at depth which prevented the minerals from oxidizing to reddish hematite this finding supports the inference that a mechanically driven chemical reaction partly accounts for the high magnetic susceptibility a kinetic model analysis confirmed that frictional heating can cause thermal decomposition of siderite and pyrite our results show that decomposition of pyrite to pyrrhotite siderite and to some extent chlorite to magnetite is the probable mechanism explaining the magnetic anomaly within the chelungpu fault zone

estimated dynamic shear stress and frictional heat during the 1999 taiwan chi chi earthquake a chemical kinetics approach with isothermal heating experiments abstract we performed isothermal heating experiments on samples from a breccia zone adjacent to the slip zone of the taiwan chelungpu fault that slipped during the 1999 chi chi earthquake to determine the chemical kinetics function and parameters for thermal decomposition of carbonate minerals in the fault zone we found that a zero order reaction was the most likely reaction mechanism for thermal decomposition of these samples and determined an activation energy for the reaction of 137 kj mol 1 and a pre exponential term of 1 15 10 4 s 1 we applied these parameters in chemical kinetics calculations taking into account the temperature change over time caused by frictional heating and heat conduction energy conservation and energy taken up by the endothermic reaction to estimate the dynamic shear stress and maximum temperature reached in the slip zone and found them to be 6 62 mpa and 1079 c respectively

seismogenic structures of the 1999 mw 7 6 chi chi taiwan earthquake and its aftershocks abstract high resolution 3 d vp and vs velocity models around the source region of the mw7 6 chi chi taiwan earthquake show significant lateral and vertical variations the mainshock occurred within a narrow low velocity zone along the chelungpu fault a sudden increase of velocity and seismicity took place across the shuilikeng fault to the east most aftershocks were located in areas of high vp and vs a sharp east dipping zone extending from the shuilikeng fault on the surface to a depth of about 15 km separates the low velocity region in the west from the high velocity region in the east an apparent high angle west dipping seismic zone lies at depths of 15 30 km beneath the western central range numerous aftershocks with normal faulting were located west of the middle segment of the chelungpu fault

volume self diffusion of oxygen in biotite muscovite and phlogopite micas the kinetics of oxygen self diffusion have been measured in natural samples of biotite muscovite and phlogopite micas under hydrothermal conditions using both bulk exchange and profiling analyses all experiments were run at 1000 bars 100 mpa water pressure except those designed to measure water pressure dependence which ranged from 200 to 2000 bars the arrhenius relations obtained for layer parallel diffusive transport in the three micas by bulk exchange experiments fit to an infinite cylinder model are mineral biotite muscovite phlogopite 34 2 39 5 42 3 9 1 10 6 7 7 10 5 1 4 10 4 t c 500 800 512 700 600 900 the results of ion microprobe sims depth profiling perpendicular to the layers parallel to c axis yield diffusion coefficients 3 to 4 orders of magnitude lower than for transport parallel to the layers a single layer parallel step profiling experiment yields a diffusion coefficient identical within uncertainty to those obtained from bulk exchange experiments a slight dependence of diffusion rate on water pressure may obtain in phlogopite however the difference is approximately within the uncertainty of the measurement diffusion rates are similar within about a half an order of magnitude for a range of biotite composition from annite4 to annite63 as well as for muscovite comparison of oxygen diffusion rates in biotite from this study with ar k and rb diffusion from published data supports the idea that water is the oxygen bearing species in hydrothermal diffusion experiments the implication of these results for natural systems is that the micas especially biotite will continue to exchange oxygen isotopes via volume diffusion down to temperatures as low as 300 c the rapid diffusion kinetics may explain biotite oxygen isotope disequilibrium which is commonly observed even in rocks where other mineral phases preserve equilibrium compositions full size table table options view in workspace download as csv

fault rupture process of the 20 september 1999 chi chi taiwan earthquake we modeled the source rupture process of the 20 september 1999 chi chi taiwan earthquake mw 7 6 using an integrated dataset of near field strong ground motion and global positioning system observations this large inland thrust earthquake produced a surface break more than 80 km long along the chelungpu fault the event triggered over 700 strong motion instruments on the island of tai wan this large ground motion dataset provides the best opportunity to date to un derstand earthquake source processes in a major earthquake first we develop a 3d curved fault model consistent with the surface rupture data and aftershock distribu tion the subsurface fault plane has an average dip of 30 to the east and measures 96 km along strike and 40 km down dip next we applied a genetic algorithm to reconstruct the source rupture process the inversion results indicate a complex slip distribution with a generally broad triangular shaped slip zone that points down dip most of the displacement occurred over a 15 km depth range in the northern segment of the fault with the maximum slip exceeding 20 m the average slip is 3 8 m and the average rupture velocity is 2 6 km sec the mainshock slip distribution clearly complements the aftershock location distribution slip rise times range from 8 to 6 sec over most of the primary slip area and decrease slightly as rupture propagates south to north this relatively long rise time resulted in a low dynamic stress drop and low peak ground accelerations observed at surface stations the rake angle rotates across the rupture plane from predominantly dip slip in the southern segment to mostly left lateral oblique slip in the north we find that geometrical irregularities over the fault plane played an important role in controlling the temporal rupture behavior at fault bends rupture tends to decelerate the rake angle rotates to a near dip slip orientation and the shear stress increases as rupture tries to overcome the bending barriers the total seismic moment from our inversion is 2 9 10 27 dyne cm in good agreement with the harvard and the u s geological survey moment estimation

characterization of slip zone associated with the 1999 taiwan chi chi earthquake x ray ct image analyses and microstructural observations of the taiwan chelungpu fault abstract to characterize the fault related rocks within the chelungpu fault we performed x ray computed tomography ct image analyses and microstructural observations of hole b core samples from the taiwan chelungpu fault drilling project we identified the slip zone associated with the 1999 chi chi earthquake within the black gouge zone in the shallowest major fault zone by comparison with previous reports the slip zone was characterized by low ct number cataclastic or ultracataclastic texture and high possibility to have experienced a mechanically fluidized state taking these characteristics and previous reports of frictional heating in the slip zone into consideration we suggested that thermal pressurization was the most likely dynamic weakening mechanism during the earthquake

gravity anomalies and flexure of the lithosphere at the middle amazon basin brazil the middle amazon basin is a large paleozoic sedimentary basin on the amazonian craton in south america it contains up to 7 km of mainly shallow water sediments a chain of bouguer gravity highs of approximately 40 to 90 mgals transects the basin roughly coincident with the axis of maximum thickness of sediment the gravity highs are flanked on either side by gravity lows of approximately 40 mgals the observed gravity anomalies can be explained by a steeply sided zone of high density in the lower crust varying in width from 100 to 200 km wide within this region the continental crust has been intruded replaced by more dense material to more than half its original thickness of 45 50 km the much wider sedimentary basin results from regional compensation of the subsurface load and the subsequent load of accumulated sediments by flexure of the lithosphere the observed geometry of the basin is consistent with an elastic lithosphere model with a mechanical thickness of 15 20 kin although this value is lower than expected for a stable cratonic region of early proterozoic age it is within the accepted range of effective elastic thicknesses for the earth rapid subsidence during the late paleozoic may be evidence of a second tectonic event or lithospheric relaxation which could lower the effective mechanical thickness of the lithosphere the high density zone in the lower crust as delineated by gravity and flexural modeling has a complex sinuous geometry which is narrow and south of the axis of maximum sediment thickness on the east and west margins and wide and offset to the north in the center of the basin the linear trough geometry of the basin itself is a result of smoothing by regional compensation of the load in the lower crust

anomalous streamflow and groundwater level changes before the 1999 m7 6 chi chi earthquake in taiwan possible mechanisms streamflow recorded by a stream gauge located 4 km from the epicenter of the 1999 m7 6 chi chi earthquake in central taiwan showed a large and rapid anomalous increase of 124 m3 s starting 4 days before the earthquake this increase was followed by a comparable co seismic drop to below the background level for 8 months in addition groundwater levels recorded at a well 1 5 km east of the seismogenic fault showed an anomalous rise 2 days before the earthquake and then a unique 4 cm drop beginning 3 h before the earthquake the anomalous streamflow increase is attributed to gravity driven groundwater discharge into the creek through the openings of existing fractures in the steep creek banks crossed by the upstream shueilikun fault zone as a result of pre earthquake crustal buckling the continued tectonic movement and buckling together with the downward flow of water in the crust may have triggered the occurrence of some shallow slow slip events in the shueilikun and other nearby fault zones when these events propagate down dip to decollement where the faults merges with the seismogenic chelungpu fault they may have triggered other slow slip events propagating toward the asperity at the hypocenter and the chelungpu fault these events may then have caused the observed groundwater level anomaly and helped to trigger the earthquake

magnetic properties of fault rocks from the yingxiu beichuan fault constraints on temperature rise within the shallow slip zone during the 2008 wenchuan earthquake and their implications abstract rock magnetic measurements were conducted on fault rocks from the dagou village outcrop at shuiguan town pingwu county sichuan province china which is located on the yingxiu beichuan fault the main fault ruptured in the 2008 wenchuan m s 8 0 earthquake results revealed that magnetic behavior of fault gouge is possibly dominated by paramagnetic siderite and lepidocrocite as well as pyrrhotite thermomagnetic analysis indicated that these fe bearing minerals are readily decomposed once temperature over 250 400 c and form newly ferrimagnetic magnetite maghemite that would increase the magnetization of fault rocks consequently the paramagnetic nature and relatively low magnetization of fresh fault gouge suggest that the shallow fault plane has not been subjected to thermal event over 250 400 c during the wenchuan earthquake this inference can be confirmed by a kinetic model analysis these findings proposed that thermal pressurization was not likely to occur during the wenchuan earthquake at least at the shallow part of slip zone onset of an elastohydrodynamic lubrication mechanism was alternatively discussed using a model in which fault zone containing viscous gouge results indicated that the lubrication pressure could reach up to 30 2 mpa which can widen the gap between the fault surfaces and reduce the area of asperity contact this prediction well matches the reported injection veins within the coseismic shear zone and the largest ground motions associated with lower predominant frequencies and large stress drop during the wenchuan earthquake

spatial and temporal distribution of slip for the 1999 chi chi taiwan earthquake we investigated the rupture process of the 1999 chi chi taiwan earth quake using high quality near source strong motion records broadband teleseismic displacement waveforms and well distributed global positioning system gps data the near source strong motion displacement waveforms recorded significant static offsets of up to 8 m the teleseismic displacement records show a significant pulse with duration of about 18 to 20 sec taking into account the surface displacements observed along the chelungpu fault we considered two fault geometries a single planar fault and a two segment fault with a northeast striking section near the north ern end using the finite fault model with variable slip vectors we derived two models of the temporal and spatial slip distribution of the earthquake the gps data provided good surface displacement constraints for the slip distribution determina tion the spatial slip distribution is generally consistent with field observations the results for the simple fault model show a large asperity located in the region about 25 to 55 km north of the hypocenter with maximum slip of about 15 m when we use the two segment model the asperity further extends to the region where the fault bends toward the northeast with a maximum slip of up to 20 m a large amount of right lateral slip beneath station tcu068 is necessary to explain its observed large west movement it implies a local converging slip at the corner where the fault bends to the northeast the slip amplitude near the hypocenter is about 3 to 6 m the seismic moments determined from the various data sets are within the range of 2 to 4 10 27 dyne cm most of the slip concentrated at shallow depths less than 10 km the total rupture duration is about 28 sec and the rupture velocity is 75 to 80 of the shear wave velocity the slip vector shows a clockwise rotation during the fault rupture the static stress drop of the large asperity region is comparable with the dynamic stress drop as observed directly from the slip velocity at the station near the large slip region

oxygen diffusion in quartz diffusional oxygen exchange between quartz and water was studied by determining 18o profiles in the quartz using an ion microprobe inverse error function plots of the data are linear as required for a diffusion mechanism one natural and two synthetic samples were used and although they had different impurity concentrations oh na and al per 106 si atoms are 7 4000 35 835 and 67 127 respectively the d values were the same within experimental uncertainty diffusion parallel to c is about 2 orders of magnitude faster than that normal to c at 700 c and diffusion normal to the rhombohedron is intermediate the data indicate a change in slope on an arrhenius plot at the boundary at 100 mpa 1 kbar water pressure the preexponential factors do in square centimeters per second and activation energies q in kilojoules per mole for quartz 500 550 c are as follows do 190 and q 284 parallel to c and do 8 10 2 and q 238 normal to the rhombohedron for quartz 600 800 c do 4 10 7 and q 142 parallel to c do 9 10 7 and q 155 normal to the rhombohedron and do 1 10 4 and q 234 normal to c d increases with ph 2 o and between 25 and 350 mpa log d versus log h 2 o has a slope of approximately 1 1 these d values are all several orders of magnitude larger than previously reported values for oxygen diffusion in water free systems

simulation of co seismic secondary fracture displacements for different earthquake rupture scenarios at the proposed nuclear waste repository site in forsmark simulation of co seismic secondary fracture displacements for different earthquake rupture scenarios at the proposed nuclear waste repository site in forsmark

nondestructive continuous physical property measurements of core samples recovered from hole b taiwan chelungpu fault drilling project 1 the taiwan chelungpu fault drilling project was undertaken in 2002 to investigate the faulting mechanism of the 1999 mw 7 6 taiwan chi chi earthquake hole b penetrated the chelungpu fault and core samples were recovered from between 948 42 and 1352 60 m depth three major zones designated fzb1136 fault zone at 1136 m depth in hole b fzb1194 and fzb1243 were recognized in the core samples as active fault zones within the chelungpu fault nondestructive continuous physical property measurements conducted on all core samples revealed that the three major fault zones were characterized by low gamma ray attenuation gra densities and high magnetic susceptibilities extensive fracturing and cracks within the fault zones and or loss of atoms with high atomic number but not a measurement artifact might have caused the low gra densities whereas the high magnetic susceptibility values might have resulted from the formation of magnetic minerals from paramagnetic minerals by frictional heating minor fault zones were characterized by low gra densities and no change in magnetic susceptibility and the latter may indicate that these minor zones experienced relatively low frictional heating magnetic susceptibility in a fault zone may be key to the determination that frictional heating occurred during an earthquake on the fault

structure of the 1999 chi chi earthquake rupture and interaction of thrust faults in the active fold belt of western taiwan abstract we summarize the structural characteristics of the surface ruptures of the 1999 mw 7 6 chi chi earthquake in western taiwan and discuss the geological interaction of the chelungpu fault with adjacent faults based on geological investigations seismological analyses and gps measurements of surface co seismic displacements we describe the regional 3 d fault plane and slip distribution of the chi chi earthquake and compare these to the geological features of the chelungpu fault we find that one key feature of the chelungpu fault is the stratigraphy controlled slip surface at the level of the uppermost few kilometers the chelungpu fault slip plane generally follows the bedding plane of the pliocene chinshui shale the second key feature of the chelungpu fault is the difference in structurally geometric configuration between its northern and southern segments the northern fengyuan segment shows a bedding parallel thrust fault within east dipping strata in both footwall and hanging wall in contrast the southern tsaotun segment exhibits east dipping strata are overthrust onto flat lying recent alluvial deposits these two features not only explain a hinterland imbricate thrusting on the hanging wall of the fengyuan segment but also explain the change in strike of the chi chi surface ruptures at the northern end the southern end of the 1999 chi chi rupture is interpreted to be linked to a series of nw trending strike slip faults in particular we propose that the luliao strike slip fault served as the lateral ramp of the chelungpu fault and the gukeng strike slip fault acted as a barrier to end the southern propagation of the 1999 rupture geomorphic features and paleoseismological data indicate that the range front chelungpu fault has generated large earthquakes during the last several thousand years alternatively in the miaoli area to the north and the chiayi area to south historical earthquakes as well as active geomorphic features are not restricted on the range front thrust faults instead more complicated structures including tightly spaced folds duplex structures and strike slip faults are involved in seismogenic processes a more detailed investigation of regional structural characteristics is needed for mitigation against the seismic hazards in the 300 km long active fold belt in western taiwan where several damaging large earthquakes have been documented during the last century

coseismic fluid rock interactions at high temperatures in the chelungpu fault chemical and isotopic variations in crushed material along the chelungpu fault in taiwan are suggestive of interactions at high temperatures with coseismically generated aqueous fluids high fluid pressures along the fault zone during the magnitude 7 6 chi chi earthquake in 1999 could have reduced friction and fault strength aqueous fluids are thought to have an essential role in faulting and the dynamic propagation of earthquake rupture fluid overpressure can affect earthquake nucleation1 2 and in a process termed thermal pressurization pore fluid pressure produced by frictional heating can reduce the effective normal stress acting on the fault surface3 4 5 this may lead to a marked reduction in fault strength during slip however the coseismic presence of fluids within slip zones and the role of fluids in dynamic fault weakening is still a matter of debate here we present compositions of major and trace elements as well as isotope ratios of core samples representing relatively undamaged as well as very fine grained deformed material from three active zones of the chelungpu fault taiwan depth profiles across the most intensely sheared bands that range in thickness from 2 15 cm exhibit sharp compositional peaks of fluid mobile elements and of strontium isotopes we suggest that high temperature fluids 350 c derived from heating of sediment pore fluids during the earthquake interacted with material within the fault zone and mobilized the elements the coseismic presence of high temperature fluids under conditions of low hydraulic diffusivity6 within the fault zone is favourable for thermal pressurization this effect may have caused a dynamic decrease of friction along the chelungpu fault during the 1999 magnitude 7 6 chi chi earthquake

frictional heat from faulting of the 1999 chi chi taiwan earthquake 1 the frictional heat generated during an earthquake is thought to be a major portion of the total energy release however there have been no direct measurements of the heat generated by a large earthquake we present an estimate of the frictional heat produced by the 1999 chi chi taiwan earthquake mw 7 6 from temperature anomaly that is measured in a borehole penetrating a large slip region 10 m of the fault a local increase in the temperature profile across the fault is interpreted to be the residual heat generated during the earthquake analyses of this temperature anomaly lead to a low estimate of the dynamic shear stress 0 5 to 0 9 mpa and the heat produced in the large slip region of the fault 0 68 to 1 32 1017 j the total frictional energy is estimated as 2 4 to 6 1 1017 j indicating that seismic efficiency is 1 to 3

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

lateral variations in the long term slip rate of the chelungpu fault central taiwan from the analysis of deformed fluvial terraces the chelungpu fault ruptured during the september 1999 mw 7 6 chi chi earthquake in central taiwan this event was characterized by coseismic displacements increasing along strike and updip from south to north previous studies suggested that such lateral variations also existed in the long term fault slip rate but this has not yet been clearly documented to address this we investigate deformed fluvial terraces along the choushui and tatu wu rivers in the southern and central segments of the thrust fault optical ages of 13 ka to 38 ka obtained for these terraces enable estimation of fault slip rates of 5 8 2 0 and 10 3 1 6 3 0 mm yr for the southern and central segments respectively we combine these findings with the fault slip rate determined by other authors for the northern segment statistical analysis of the data suggests lateral variations in the long term fault slip rate with values increasing toward the north this pattern in the slip rate averaged over approximately tens of thousand years is similar to that observed for coseismic displacements during the chi chi earthquake the similarities in the deformation pattern observed for one earthquake or cumulated over several events suggest that the chi chi earthquake could be characteristic of the earthquakes breaking the chelungpu fault with respect to slip distribution our results also allow for discussing the plausible evolution of major rivers draining the foothills of central taiwan over the last 40 60 kyr

analyses of pseudotachylyte from hole b of taiwan chelungpu fault drilling project tcdp their implications for seismic slip behaviors during the 1999 chi chi earthquake abstract the seismic slip behavior during the 1999 chi chi taiwan earthquake m w 7 6 was contrastive between the northern and southern segments of the activated chelungpu fault large fast and smooth slips with large stress drop in the north while smaller slower and irregular slips with smaller stress drop in the south we analyzed the pseudotachylyte samples recovered from 1194 m 1243 m and 1314 m depths of hole b of taiwan chelungpu fault drilling project tcdp to reveal the spatial difference in friction mechanism all pseudotachylyte layers are thin 0 7 2 8 cm the volume fraction of protoliths is very large more than 63 and the estimated temperature distribution is very heterogeneous from ca 750 1750 c these observations suggest that these pseudotachylyte melts were in the partial melting regime of montgomery montgomery r s 1976 friction and wear at high sliding speeds wear 36 275 298 where friction coefficient is abnormally large similar pseudotachylyte was found already in the core sample from 175 m depth of the nanto borehole penetrating the southern fault since both pseudotachylyte samples from the two boreholes are older than the 1999 chi chi event and have been uplifted from depths farther down dip of their current locations it is likely that recent seismic ruptures also would have encountered these mechanical barriers of viscous melt patches at deeper parts in the north than in the south elastohydrodynamic lubrication of clayey gouge worked effectively at the shallower parts of the northern segment however there is no evidence that it played an important role in the south these differences are the plausible causes of the contrastive local slip behaviors during the chi chi earthquake

thermal history estimation of the taiwan chelungpu fault using rock magnetic methods 1 to investigate the cause of high magnetic susceptibility in disk shaped black materials bm disks within core samples of hole b the taiwan chelungpu fault drilling project we carried out magnetic analyses of samples from the bm disks and surrounding gouge zones frequency dependence of low temperature magnetic susceptibility and thermal demagnetization of low temperature remanent magnetization revealed lower amounts of superparamagnetic grains in the bm disks than in the surrounding gouges magnetic grain size reduction by shearing is therefore not a plausible explanation for the high magnetic susceptibility of the bm disks thermomagnetic analyses of the gouge samples showed that above 400 c magnetization could be increased by thermal decomposition of paramagnetic minerals whereas analyses of the bm disks showed a much smaller increase in magnetization thus formation of ferrimagnetic magnetite or maghemite by thermal decomposition of paramagnetic minerals was inferred to be the cause of the high magnetic susceptibility of the bm disks indicating that the bm disks but not the gouges have experienced temperatures of at least 400 c

the contribution of structural geology experimental rock deformation and numerical modelling to an improved understanding of the seismic cycle preface to the special volume physico chemical processes in seismic faults

moment tensor inversions using strong motion waveforms of taiwan tsmip data 1993 2009 abstract earthquake source parameters are important for earthquake studies and seismic hazard assessment moment tensors are among the most important earthquake source parameters and are now routinely derived using modern broadband seismic networks around the world similar waveform inversion techniques can also apply to other available data including strong motion seismograms strong motion waveforms are also broadband and recorded in many regions since the 1980s thus strong motion data can be used to augment moment tensor catalogs with a much larger dataset than that available from the high gain broadband seismic networks however a systematic comparison between the moment tensors derived from strong motion waveforms and high gain broadband waveforms has not been available in this study we inverted the source mechanisms of taiwan earthquakes between 1993 and 2009 by using the regional moment tensor inversion method using digital data from several hundred stations in the taiwan strong motion instrumentation program tsmip by testing different velocity models and filter passbands we were able to successfully derive moment tensor solutions for 107 earthquakes of m w 4 8 the solutions for large events agree well with other available moment tensor catalogs derived from local and global broadband networks however for m w 5 0 or smaller events we consistently over estimated the moment magnitudes by 0 5 to 1 0 we have tested accelerograms and velocity waveforms integrated from accelerograms for the inversions and found the results are similar in addition we used part of the catalogs to study important seismogenic structures in the area near meishan taiwan which was the site of a very damaging earthquake a century ago and found that the structures were dominated by events with complex right lateral strike slip faulting during the recent decade the procedures developed from this study may be applied to other strong motion datasets to compliment or fill gaps in catalogs from regional broadband networks and teleseismic networks

isotropic events observed with a borehole array in the chelungpu fault zone taiwan shear failure is the dominant mode of earthquake causing rock failure along faults high fluid pressure can also potentially induce rock failure by opening cavities and cracks but an active example of this process has not been directly observed in a fault zone using borehole array data collected along the low stress chelungpu fault zone taiwan we observed several small seismic events i type events in a fluid rich permeable zone directly below the impermeable slip zone of the 1999 moment magnitude 7 6 chi chi earthquake modeling of the events suggests an isotropic nonshear source mechanism likely associated with natural hydraulic fractures these seismic events may be associated with the formation of veins and other fluid features often observed in rocks surrounding fault zones and may be similar to artificially induced hydraulic fracturing

have steering flows in the western north pacific and the south china sea changed over the last 50 years 1 long term trends in steering flows over the western north pacific wnp and the south china sea scs are examined during the peak typhoon season a nonparametric and robust trend detection method is employed both the ncep and era reanalysis data sets suggest a statistically significant decreasing trend in steering flows in the subtropical region of the western wnp between 120 e or near taiwan and 145 e and the northern scs during 1958 2001 over this period the decrease in the wnp is quite large with a magnitude of 1 1 m s 1 given that the background mean steering flow is only 3 26 m s 1 this decrease corresponds approximately to one third of the mean flow when the data are extended from 1958 to 2009 the long term decrease in steering flows in the aforementioned subtropical region are still significant although more modest at a rate of 0 7 m s 1 time series of translational speeds averaged over the same subtropical region also exhibit a slow down of storms motion over the last 52 years this is consistent with the weakening of easterly steering flows analyzed from independent data sets results of this study imply a longer life span for tropical cyclones and a greater tendency for storms along prevailing typhoon tracks to recurve

a chemical kinetic approach to estimate dynamic shear stress during the 1999 taiwan chi chi earthquake 1 estimation of the dynamic shear stress on a fault during an earthquake is important for understanding the earthquake itself using a chemical kinetic approach we examined the thermal decomposition of carbonate minerals to estimate the shear stress on the taiwan chelungpu fault which slipped during the 1999 chi chi earthquake the reaction rate of the decomposition was related to temperature by using the arrhenius equation and the chemical kinetics taking into account the temperature change over time caused by frictional heating and heat conduction was solved by the finite difference method the dynamic shear stress during the chi chi earthquake was deduced to be 1 31 mpa and the frictional coefficient to be 0 04 0 05 this estimated value agrees with the hypothesis that friction along the chelungpu fault was low

evidence for fault lubrication during the 1999 chi chi taiwan earthquake mw7 6 the ground motion data of the 1999 chi chi taiwan earthquake exhibit a striking difference in frequency content between the north and south portions of the rupture zone in the north the ground motion is dominated by large low frequency displacements with relatively small high frequency accelerations the pattern is opposite in the south with smaller displacements and larger accelerations we analyze the fault dynamics in light of a fault lubrication mechanism using near field seismograms and a detailed rupture model the fault zone contains viscous material e g gouge in which pressure increases following the reynolds lubrication equation when the displacement exceeds a threshold lubrication pressure becomes high enough to widen the gap thereby reducing the area of asperity contact with less asperity contact the fault slips more smoothly suppressing high frequency radiation

a rupture model for the 1999 chi chi earthquake from inversion of teleseismic data using the hybrid homomorphic deconvolution method this study investigates the kinematics of the rupture process of the ml 7 3 chi chi taiwan earthquake on september 21 1999 by applying the proposed hybrid homomorphic deconvolution method to deconvolve teleseismic broadband p wave displacement recordings of the earthquake this study derives the apparent source time functions astfs at ten stations located around the epicenter to further characterize the fault the kinematic history of the rupture was inverted from astfs using a genetic algorithm coupled with nonlinear iterative technique the calculated asfts reveal that the total rupture event lasted for approximately 27 s static slip distribution images indicate that most slip occurred at shallower portions of the fault plane especially 20 55 km north of the epicenter the maximum slip reached 20 m at 45 km north of the epicenter and the average slip throughout the observed rupture area was approximately 2 m large asperities on the fault appeared at 25 35 km and 40 50 km north of the hypocenter and coincided with relatively high rupture velocity this suggests that the earthquake s energy may have been released quickly the rupture velocity decreased upon encountering an asperity and increased again after passing the asperity this implies that the rupture required more time to overcome the resistances of the asperities the maximum rupture velocity was 3 8 km s while the average rupture velocity was approximately 2 2 km s the rise time distribution suggests that larger slip amplitudes generally correspond to shorter rise times on the subfaults

source process of the chi chi earthquake a joint inversion of strong motion data and global positioning system data with a multifault model the chi chi taiwan earthquake of 21 september 1999 was a large thrust earthquake that caused disastrous damage the surface fracture trace runs along the chelungpu fault which strikes n5 e along most of the faulting area but turns to the northeast while approaching its northern end it finally presents a horsetaillike faulting system and bends to an east northeast direction at the northern end both strong motion and global positioning system gps data recorded large displace ments in the northern part in this study we use a multifault model to simulate the observed large strong motion and gps data the results of the joint inversion reveal that in the southern part slip occurred mainly in the shallow portion reaching a maximum about 20 m on the ene fault where the rupture propagated to the deep part of the fault there was obviously slip vector rotation from south to north such that the slip on the branched fault plane was almost purely reverse faulting the seismic moment a total of 2 7 10 20 n m was released in less than 40 sec during the mainshock aftershocks occurred mainly in areas where little or no slip occurred slip vector rotation can be explained by the complexity of regional tectonic stress changes in tectonic stress at the northern end of the fault inhibited the northward propagation of the rupture and favored the rupturing of the ene fault

experimental evidence that thrust earthquake ruptures might open faults many of earth s great earthquakes occur on thrust faults these earthquakes predominantly occur within subduction zones such as the 2011 moment magnitude 9 0 eathquake in tohoku oki japan or along large collision zones such as the 1999 moment magnitude 7 7 earthquake in chi chi taiwan notably these two earthquakes had a maximum slip that was very close to the surface this contributed to the destructive tsunami that occurred during the tohoku oki event and to the large amount of structural damage caused by the chi chi event the mechanism that results in such large slip near the surface is poorly understood as shallow parts of thrust faults are considered to be frictionally stable here we use earthquake rupture experiments to reveal the existence of a torquing mechanism of thrust fault ruptures near the free surface that causes them to unclamp and slip large distances complementary numerical modelling of the experiments confirms that the hanging wall wedge undergoes pronounced rotation in one direction as the earthquake rupture approaches the free surface and this torque is released as soon as the rupture breaks the free surface resulting in the unclamping and violent flapping of the hanging wall wedge our results imply that the shallow extent of the seismogenic zone of a subducting interface is not fixed and can extend up to the trench during great earthquakes through a torquing mechanism

fossil fluid reservoir beneath a duplex fault structure within the central range of taiwan implications for fluid leakage and lubrication during earthquake rupturing process in order to understand the kinematics which likely facilitated the speedy rupturing process of the 1999 mw 7 6 taiwan chichi earthquake we examined exposed rocks in the taiwan slate belt where the pressure and temperature conditions most resembled the hypocentre of the chi chi earthquake i e subgreenschist facies field observations and composition analyses of the silicified vein rich zones beneath the duplex structure suggest that impermeable slate layers may serve as cap rocks for confining deep seated fluids these fluids most likely come from the taiwan metamorphic complex at deeper depths by the dehydration and decarbonation reactions or partial melting in addition the gouge zone of a link fault above the detachment also indicates the presence of overpressured fluids during faulting it is probable that episodic leakage of the confined fluid reservoirs may provide essential fluids for fault lubrication during earthquake ruptures

dynamic wedge failure reveals anomalous energy radiation of shallow subduction earthquakes abstract dynamically induced coulomb failure in the overriding wedge significantly affects energy radiation of shallow subduction earthquakes for a wedge on the verge of failure extensive fluid assisted coseismic failure due to updip rupture causes significant seafloor uplift above a shallow dipping basal fault the large inelastic uplift greatly enhanced by the presence of free surface significantly dilates the fault behind the rupture front during the rupture propagation which reduces the effective normal stress and sliding friction on the fault and increases the dynamic stress drop and slip velocity as a result slip velocity time histories in the shallow section of the fault tend to have a snail like shape leading to depletion of high frequencies in the slip velocity field and the resultant source time function we also show that the failure in the wedge acts as a large energy sink while contributing to seismic moment giving rise to distributed heat generation i e small heat flow anomaly across the fault low moment scaled radiated energy slow rupture velocity and small directivity which provides a unifying interpretation for nearly all anomalous observations documented for shallow subduction earthquakes

eclogite facies relics and a multistage breakdown in metabasites of the ktb pilot hole ne bavaria implications for the variscan tectonometamorphic evolution of the nw bohemian massif complex reaction textures in coronitic metagabbros and retrograded eclogites of the ktb pilot and an adjacent drilling provide evidence for a multistage metamorphic history in the variscan basement of the nw bohemian massif the eclogites show complete metamorphic recrystallization leaving no textural or mineral relics of their igneous precursors in contrast textural relics of the igneous protolith are still preserved in the metagabbros where the metamorphic overprint under high pressure conditions achieved only partial replacement of the initial assemblage plagioclase augite amphibole olivine or orthopyroxene ilmenite to form the eclogite facies assemblage garnet omphacite kyanite zoisite quartz rutile the garnets in the metagabbros occur in the typical necklace fashion at the borders between the original plagioclase and mafic phase domains in the same rocks omphacite formed by a topotactic reaction mechanism replacing igneous augite as well as in smaller grains at the margins of the texturally igneous clinopyroxene where it occurs without fixed orientation with respect to the relict phase both eclogites and metagabbros show a partial breakdown under high pressure granulite transitional to high pressure amphibolite facies conditions during which omphacite broke down to vermicular symplectites of diopside plagioclase a later pervasive medium pressure metamorphism under amphibolite facies conditions led to the development of assemblages dominated by hornblende plagioclase titanite phases prevailing in the overwhelming majority of the surrounding metabasites subsequent vein associated retrogression produced minerals typical of the greenschist to zeolite facies all metamorphic stages may be represented in a single thin section but although the overall reaction sequence is apparent the obvious disequilibrium in the rocks makes the use of conventional geothermobarometry difficult however calculations made by assuming an approach to domainal equilibrium show that both the eclogite facies and early breakdown occurred above 10 kb as the metamorphic unit hosting these particular metabasites is generally characterized by pressures below 10 kb these results have important implications for understanding the tectonometamorphic evolution of the region the relationship between the studied rocks and other units in the nw bohemian massif exhibiting a multistage metamorphic evolution is discussed and possible tectonic models evaluated

simulating earthquake rupture and off fault fracture response application to the safety assessment of the swedish nuclear waste repository abstract to assess the long term safety of a deep repository of spent nuclear fuel upper bound estimates of seismically induced secondary fracture shear displacements are needed for this purpose we analyze a model including an earthquake fault which is surrounded by a number of smaller discontinuities representing fractures on which secondary displacements may be induced initial stresses are applied and a rupture is initiated at a predefined hypocenter and propagated at a specified rupture speed during rupture we monitor shear displacements taking place on the nearby fracture planes in response to static as well as dynamic effects as a numerical tool we use the 3dimensional distinct element code 3dec because it has the capability to handle numerous discontinuities with different orientations and at different locations simultaneously in tests performed to benchmark the capability of our method to generate and propagate seismic waves 3dec generates results in good agreement with results from both stokes solution and the compsyn code package in a preliminary application of our method to the nuclear waste repository site at forsmark southern sweden we assume end glacial stress conditions and rupture on a shallow gently dipping highly prestressed fault with low residual strength the rupture generates nearly complete stress drop and an m w 5 6 event on the 12 km 2 rupture area of the 1584 secondary fractures 150 m radius with a wide range of orientations and locations relative to the fault a majority move less than 5 mm the maximum shear displacement is some tens of millimeters at 200 m fault fracture distance

diffusion effects on oxygen isotope temperatures of slowly cooled igneous and metamorphic rocks recently obtained data on oxygen diffusion in feldspars quartz and hornblende permit the prediction of the apparent18o16o temperatures that would be measured in a rock that consisted only of those three minerals and cooled slowly from high temperature the computed temperatures would be based on the differences in the18o16o ratios between coexisting pairs of minerals the present calculation takes into account the diffusion rates for oxygen as a function of temperature the cooling rate of the rock the mineral grain sizes and the mode of the rock for mineral grains 1 mm in radius and a cooling rate of 10 c m y the minimum difference in apparent temperature between quartz feldspar and feldspar hornblende pairs will be 115 c despite the assumption of a normal uneventful slow cooling history to room temperature further the apparent quartz hornblende temperature will range over 30 c 590 620 c depending on the mode of the rock for a cooling rate of 1000 c m y the apparent difference in temperature can be as much as 400 c consequently consistency in temperatures obtained by oxygen isotope analysis should not be expected in most high grade metamorphic rocks or igneous rocks which are cooled slowly departures from the pattern of temperatures obtained in this model would imply a very rapid quench from high temperature or a complex history for the rock for some minerals including hornblende the relation between temperature and the equilibrium fractionation of oxygen isotopes between coexisting phases has been derived from observed relations in natural specimens the choice of the specimens used for such calibrations needs to be re evaluated in light of these findings this may result in a change in the equilibrium equation constants an example from the literature the san jose tonalite baja california mexico was modelled and yields 18o concentrations in the minerals that correspond closely with the measured values this suggests that the model used is appropriate that the rock has had a simple thermal history and that it cooled at 100 200 c m y over the temperature range 800 500 c the set of paleotemperatures obtained for a rock will in general yield neither the mineral closure temperatures nor the formation or crystallization temperatures on the other hand the cooling rate of the rock may be derived from the data this in turn may have important tectonic implications with regard to denudation and uplift rates

fault zone geology lessons from drilling through the nojima and chelungpu faults several drilling projects have been conducted through active faults with the aim of learning about the geology of the fault zones and tentatively correlating the structure and mineralogy of the fault zones with their seismological behaviour during recent earthquakes here we present the major results obtained from structural and mineralogical studies of core samples retrieved from the dextral reverse strike slip nojima fault japan within granitic rocks following the kobe earthquake 1995 and from the chelungpu thrust fault taiwan within alternating silts and shales following the chi chi earthquake 1999 we show how these projects despite not fullfilling all their objectives have still contributed to a better geological knowledge of the fault zones to a better characterization of the slip zones related to the recent earthquakes particularly of their thickness microstructures and deformation mechanisms and to a better understanding of the nature and role of fluids within the fault zone they have also led to new questions and to new approaches for studying fault rock samples for all of these reasons they have stimulated international scientific research into fault zone geology

thermal and pore fluid pressure history on the chelungpu fault at a depth of 1111 m during the 1999 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan in 2005 the taiwan chelungpu fault drilling project was launched to drill two deep holes holes a and b cutting across the fault plane the heat strength 7 0 c m within a heated layer of 5 mm on the fault at hole a due to frictional faulting is evaluated from the values of shear stress and thermal and mechanical parameters measured from the core samples based on a 1 d heat conduction equation and 2 d faulting model with the values of thermal diffusivity evaluated within a representative temperature range the thermal and pore fluid pressure history at depths 1110 37 1111 34 m in hole a is constructed results show that the peak temperature at the center of the heated layer could have been higher than 1100 c during faulting and temperature rise decreased with increasing distance and time the possible relationships between the temperatures and chemical reactions of clay minerals are discussed in detail in the heated layer pseudotachylites have been formed and quartz plasticity might also have been operative during faulting outside this slip zone the temperature rise was low and thus clay minerals were stable during faulting the evaluated pore fluid pressure is 22 5 mpa this suggests the existence of a suprahydrostatic state in the fault zone during the earthquake indirect evidence of the existence of fluids in the fault zone during faulting is described additionally rock physics is applied to interpret the observations

exotic stable isotope compositions of saline waters and brines from the crystalline basement the overwhelming majority of groundwaters reported in literature show isotopic compositions that place them on or right of the meteoric water line mwl in a 2h vs 18o diagram a closer look to the steadily increasing data from the deeper crystalline basement reveals nevertheless that points left of the mwl are not so unusual as has been suggested during the last decades their supposed rareness seems to be due to a bias of sampling the concerned fluids develop only at greater depths and in low permeability environments which makes access to them so difficult paradoxically exotic stable isotope compositions may be the rule in a restricted depth zone in all crystalline basements with slow groundwater movements but not too high temperatures the present study takes stable isotope data on saline fluids from the deep french granitic basement as a starting point in order to situate the french data from the vienne region in a more general context a literature review has been undertaken assembling more than 1300 stable isotope analyses of waters and brines in crystalline rocks from stable cratons and mountain belts world wide the french fluids show some particular features with respect to the majority of other studies as their major ion composition close to seawater or a significant isotopic shift at relatively low salinities detailed knowledge on the hydrological and chemical history of the site allowed to develop a conceptual model of isotopic evolution by interaction of fracture fluids with fracture minerals this model considers interactions of the last fluids flushing the system marine water unaltered evaporated or diluted with previously precipitated mineral phases and the neoformation of the last generation of fracture minerals the model has been tested quantitatively for several combinations of dissolution precipitation reactions involving formation of carbonates clay minerals and fe hydroxides most of the modelled scenarios would leave the residual liquid phase depleted in 18o and either enriched or depleted in 2h and produce waters with isotopic signatures corresponding to the observed 2h vs 18o correlation it is therefore suggested that the general phenomenon of an isotopic shift in deep fissured silicate rocks which seems to be rather independent of lithology may result from a combination of different reaction mechanisms implying not solely the rock matrix but also the different generations of fracture minerals

dynamic simulation of the 1999 chi chi taiwan earthquake 1 we apply a modified three dimensional finite difference method to investigate the dynamics of the 1999 chi chi earthquake we determine the dynamic source rupture process and simulate the strong ground motions over a frequency range of 0 05 0 5 hz our dynamic source model reveals that the rupture process of the chi chi earthquake is much more complex than that described in the classical propagation rupture models the chi chi earthquake rupture process includes the jumping phenomenon the northern parts on the fault plane have a longer slip duration than the southern parts the motions on the hanging wall are larger than those on the footwall side which is a consequence of the asymmetry of the fault with respect to the free surface in general the synthetics calculated by the dynamic source model agree well with the observed data our dynamic source model reproduces distinctive velocity pulses at stations located in the forward rupture direction and at stations close to the fault surface breaks the apparent rupture directivity propagating from south to north then produces noticeably larger peak ground velocity to the north these results demonstrate that the dynamic rupture model reproduces the main features of long period ground motions these results may lead to improved understanding of rupture processes accompanying large earthquakes the dynamic modeling scheme may produce more reasonable and reliable strong ground motion predictions for assessment of seismic hazard

characteristics and implication of clay minerals in the northern and southern parts of the chelung pu fault taiwan abstract in this study we report the characteristics of clay minerals present in the chelung pu fault in taiwan in the 1999 chi chi earthquake different slip motions were recorded along the chelung pu fault in the northern and southern parts of the fault the characteristics of clay minerals present in the fault zones can be attributed to the differences in motion we analyzed the shallow drill core samples obtained from the northern and southern sites penetrating the fault the clay minerals identified in most of the samples from both the sites are smectite illite and chlorite there are illite smectite mixed layers with a high illite content and no chlorite smectite mixed layer in some samples no smectite is detected we also examined the iron content and symmetry of iron and magnesium in the silicate and hydroxide layers in chlorite at the northern site the total iron content in chlorite of gouge is larger than that of the host rocks on the other hand at the southern site the total iron content varies widely it is hypothesized that the smectite consumption and differences in the characteristics of chlorite may be controlled by the differences in the lithology fluid chemistry fluid temperature or fault activities heating or breakage between the northern and southern sites

co seismic frictional melting along an out of sequence thrust in the shimanto accretionary complex implications on the tsunamigenic potential of splay faults in modern subduction zones abstract out of sequence thrusts ost play an important role in the thickening of accretionary prisms formation of forearc basins and tsunami generation in subduction zones by detailed investigations of geological and paleogeothermal structures an ancient seismogenic ost is identified in the shimanto accretionary complex southwest japan this ost consists of a mappable en echelon fault system developed at a late stage of the accretionary process the estimated accumulated displacement of 2 5 8 5 km and formation depth of 2 5 5 5 km based on a thermal analysis indicates much higher fault activities sense of slip with a sinistral slip and the large displacement was distributed among multiple small faults each with a small offset most of the faults in the en echelon fault system recorded repeated brittle failure and one fault preserves pseudotachylyte a fault rock indicative of seismic faulting this is the first report of pseudotachylyte along an ost in an accretionary prism repeated fracturing in the same narrow shear zones each only a few millimeters thick suggests the osts perform as major shear localized zone in the accretionary prism shallow estimated formation depth and consequent low normal stress also support the hypothesis by a weak coupling along this fault zone these findings are in accord with a thrust activity in the shallow portion of the accretionary prism being associated with rupture propagation from the deep seismogenic region this ost showed high activity and repeated faulting in the shallow portion of the accretionary prism comparable to that of the submarine tsunamigenic ost in the present nankai trough

why does the co seismic slip of the 1999 chi chi taiwan earthquake increase progressively northwestward on the plane of rupture the chi chi 1999 earthquake ruptured the out of sequence chelungpu thrust fault ctf in the fold and thrust belt in western central taiwan an important feature of this rupture is that the calculated slip increases approximately linearly in the se nw convergence plate direction from very little at its deeper edge to a maximum near the surface we propose here a new explanation for this co seismic slip distribution based on the study of both stress and displacement over the long term as well as over a seismic cycle over the last 0 5 my the convergence rate in the mountain front belt is accommodated by the frontal changhua fault ch f the ctf and the shuangtung fault sh f based on previously published balanced cross sections we estimate that the long term slip of the ch f and of the ctf accommodate 5 30 and 30 55 of the convergence rate respectively this long term partitioning of the convergence rate and the modeling of inter seismic and post seismic displacements suggest that the peculiar linear co seismic slip distribution is accounted for by a combination of the effect of the obliquity of the ctf to the direction of inter seismic loading and of increasing aseismic creep on the deeper part of the ch f and ctf many previous interpretations of this slip distribution have been done including the effects of material properties lubrication site effect fault geometry and dynamic waves the importance of these processes with respect to the effects proposed here is still unknown taking into account the dip angle of the ctf asperity dynamic models have been proposed to explain the general features of coseismic slip distribution in particular recent works show the importance of heterogeneous spatial distribution of stress prior to the chi chi earthquake our analysis of seismicity shows that previous large historic earthquakes cannot explain the amplitude of this heterogeneity based onour approach we rather think that the highstress in the northern part ofthe ctf proposed by oglesby and day oglesby d d day s m 2001 fault geometry and the dynamics of the 1999 chi chi taiwan earthquake bull seismol soc am 91 1099 1111 reflects the latitudinal variation of inter seismic coupling due to the obliquity of the ctf d 2004 elsevier b v all rights reserved

what does control earthquake ruptures and dynamic faulting a review of different competing mechanisms the fault weakening occurring during an earthquake and the temporal evolution of the traction on a seismogenic fault depend on several physical mechanisms potentially concurrent and interacting recent laboratory experiments and geological field observations of natural faults revealed the presence and sometime the coexistence of thermally activated processes such as thermal pressurization of pore fluids melting of gouge and rocks material property changes thermally induced chemical environment evolution elasto dynamic lubrication porosity and permeability evolution gouge fragmentation and wear etc in this paper by reviewing in a unifying sketch all possible chemico physical mechanisms that can affect the traction evolution we suggest how they can be incorporated in a realistic fault governing equation we will also show that simplified theoretical models that idealistically neglect these phenomena appear to be inadequate to describe as realistically as possible the details of breakdown process i e the stress release and the consequent high frequency seismic wave radiation quantitative estimates show that in most cases the incorporation of such nonlinear phenomena has significant often dramatic effects on the fault weakening and on the dynamic rupture propagation the range of variability of the value of some parameters the uncertainties in the relative weight of the various competing mechanisms and the difference in their characteristic length and time scales sometime indicate that the formulation of a realistic governing law still requires joint efforts from theoretical models laboratory experiments and field observations

high magnetic susceptibility produced in high velocity frictional tests on core samples from the chelungpu fault in taiwan 1 we carried out high velocity frictional tests on crushed fault gouge from core samples from hole b of the taiwan chelungpu fault drilling project to investigate the cause of high magnetic susceptibilities in the fault core black ultracataclasite resembling that observed in hole b formed during the experiments even under low axial stress of 0 5 to 1 5 mpa the bulk magnetic susceptibility of the tested samples was proportional to the frictional work applied and increased as slip increased thermomagnetic analysis of the samples before frictional testing revealed that magnetization increased at temperatures above 400 c probably because of thermal decomposition of paramagnetic minerals both the thermally and mechanically induced formation of ferrimagnetic minerals by high velocity friction might have caused a magnetic susceptibility anomaly our experimental results support the assumption that heat generation of short duration even if it is below the melting point can increase magnetic susceptibility

detailed internal structure and along strike variability of the core of a plate boundary fault the highland boundary fault scotland the highland boundary fault near stonehaven ne scotland provides a rare opportunity to study the internal fault structure of a well exposed along strike section of an ancient plate boundary fault as in many plate boundaries serpentinite juxtaposes quartzo feldspathic crustal rocks of distinct terranes we report for the first time the complex internal structure of the highland boundary fault core comprised of four structurally and chemically distinct clay rich units that remain unmixed despite the evidence for internal strain relatively intact clasts of wall rock and microfossils are preserved within the clay the fault core clay minerology is consistent with a shallow low temperature authigenesis derived from shear enhanced chemical reactions between wall rocks of contrasting chemistry during sinistral strike slip the observed structure is comparable to those of other major weak cored plate boundaries e g the san andreas fault through detailed mapping we demonstrate that the internal structure of a plate boundary fault core can vary in thickness and composition along strike over centimetre to metre length scales earthquake rupture mechanics critically depend on the physical properties of fault rock assemblages therefore models that investigate rupture propagation at active plate boundaries should incorporate or else assess tolerance and sensitivity to variable fault core thickness and composition supplementary material further x ray diffraction xrd analytical data are available at https doi org 10 6084 m9 figshare c 4663640