velocity structure of the kapuskasing uplift northern ontario from seismic refraction studies a crustal scale seismic refraction experiment was conducted over the kapuskasing structural zone northern ontario in 1984 the zone cuts obliquely across the east west structural grain of the superior province in the canadian shield and has been proposed as a cross section of archean crust exposed by thrust faulting along the ivanhoe lake cataclastic zone during early proterozoic time five seismic refraction lines of 360 450 km were shot over the area there were 18 profile shots and two fan shots with a recorder spacing of 2 5 km we have modeled the travel times and amplitudes of the data from the profile lines and analyzed reflections from the crust mantle boundary on the fan shots we have imaged a low velocity zone under the abitibi greenstone belt ranging from 4 5 to 9 12 km depth that is underlain by a highly reflective zone there is a considerable deepening of the moho from 40 43 km to 50 53 km under and to the west of the southern end of the kapuskasing structural zone a high velocity anomaly of 6 6 6 7 km s has been imaged in the upper crust down to 20 km depth beneath the kapuskasing structure with a suggested dip of 15 2 to the west this corresponds well to the proposed location of a granulite zone thrust up from the middle or lower crust in the early proterozoic

pulse like ruptures induced by low velocity fault zones low velocity fault zones lvfzs are found in most mature faults they are usually 100 400 m wide and have 20 60 wave velocity reductions relative to the country rock to study the effect of lvfzs on earthquake rupture and the radiated wavefield we conducted two dimensional 2 d simulations of dynamic rupture on faults that bisect a lvfz considering a range of velocity reductions and widths most earthquakes apparently have slip rise times much shorter than their overall rupture duration a number of dynamic mechanisms for such pulse like ruptures have been proposed including frictional self healing fault strength heterogeneities and bimaterial effects we find that ruptures in lvfzs with strong enough wave velocity contrast behave as pulses these pulses are generated by fault locking induced by waves reflected from the boundaries of the lvfz this mechanism of pulse generation is robust to variations of initial stress smoothness of the lvfz structure rupture mode and exclusion of frictional healing moreover we find that lvfzs can generate complex rupture patterns lvfzs with low velocity reduction induce multiple rupture fronts involving coexisting pulses and cracks lvfzs with certain widths can accelerate the transition to supershear rupture speed these additional effects of lvfzs on dynamic rupture can contribute to the complexity of high frequency ground motions

temporal changes of shallow seismic velocity around the karadere duzce branch of the north anatolian fault and strong ground motion we analyze temporal variations of seismic velocity along the karadere duzce branch of the north anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 mw7 4 izmit and mw7 1 duzce earthquakes the analysis employs 36 sets of highly repeating earthquakes each containing 4 18 events the events in each cluster are relocated by detailed multi step analysis and are likely to rupture approximately the same fault patch at different times the decay rates of the repeating events in individual clusters are compatible with the omori s law for the decay rate of regional aftershocks a sliding window waveform cross correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events we find clear step like delays in the direct s and early s coda waves sharp seismic velocity reduction immediately after the duzce main shock followed by gradual logarithmic type recoveries a gradual increase of seismic velocities is also observed before the duzce main shock probably reflecting post seismic recovery from the earlier izmit main shock the temporal behavior is similar at each station for clusters at various source locations indicating that the temporal changes of material properties occur in the top most portion of the crust the effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones and generally decrease with normal distance from the fault a strong correlation between the co seismic delays and intensities of the strong ground motion generated by the duzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material

modeling of sh wave propagation in an irregularly layered medium application to seismic profiles near a dome campillo m 1987 modeling of sh wave propagation in an irregularly layered medium application to seismic profiles near a dome geophysical prospecting 35 236249 an approach that relies on a discrete representation of seismic wavefields allows the computation of synthetic sh seismograms in a laterally varying medium with plane and curved interfaces in the two dimensional 2 d case the diffracting interfa is represented by an array of body forces located along the interfa at equal spacing the numerical treatment is limited to the irregular boundary while the propagation in fiat layered zones is obtained by the refiection transmission matrix method as an example we have studied the case of a dome in a stratified medium the solutions obtained verify the reciprocity theorem with good accuracy the computation of vertical profiles and of surface refiection profiles illustra tes the effects of diffraction and the importance of lateral propagation in such a structure

the tectonic evolution of the irtysh tectonic belt new zircon u pb ages of arc related and collisional granitoids in the kalaxiangar tectonic belt nw china abstract precise geochronological constraints of the irtysh tectonic belt situated between the saur island arc and the altay terrane are crucial to a better understanding of the tectonic evolution of the central asian orogenic belt caob recently we discovered repeatedly deformed arc related and collisional granitoids in the kalaxiangar tectonic belt ktb which is located in the eastern part of the irtysh tectonic belt in this study we report new whole rock geochemical zircon u pb and hf isotopic data of the arc related and collisional granitoids our data reveal that 1 arc related granodioritic porphyries formed at ca 382 374 ma recrystallized zircon grains from a ultra mylonitic granodiorite of the laoshankou zone in the southern ktb display a u pb age of ca 360 ma 2 syn collisional granodioritic porphyries which distribute along faults and parallel to the cleavage were emplaced at ca 367 356 ma with e hf t values varying from 7 8 to 14 2 and hf model ages from 873 to 459 ma 3 a post collisional a type granodioritic porphyry which crosscuts the nw nnw trending schistosity of the metasedimentary country rocks at a low angle has an age of ca 324 320 ma while the e hf t values range from 7 6 to 14 4 with hf model ages from 850 to 416 ma 4 post collisional strike slip a type granite dykes exposed along strike slip faults gave ages between 287 and 279 ma whereas the e hf t values range from 4 9 to 12 7 and the hf model ages from 995 to 500 ma and 5 a type biotite granite dykes which intruded along conjugate tension joints have ages of 274 271 ma and e hf t values from 1 5 to 13 2 with hf model ages from 1196 to 454 ma consequently we propose that the collision between the saur island arc and the altay terrane occurred in the early carboniferous ca 367 356 ma and the subsequent post collisional tectonic process continued to the late carboniferous ca 324 320 ma it is further suggested that the irtysh tectonic belt underwent large scale strike slip deformation during the mid permian between 287 and 279 ma the termination of the irtysh tectonic belt orogeny is thought to have also occurred during the mid permian between 274 and 271 ma

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

amplification of ground motion in fault and fracture zones observations from the tremestieri fault mt etna italy abstract a series of ambient noise measurements have been performed to evaluate their use in detecting the possible influence of tectonic structures on local amplification of seismic waves the area studied is located on the southeastern flank of mt etna a few kilometres north of the town of catania using a mobile station data were collected along three profiles which cross both a fault and an eruptive fracture in addition ambient noise was sampled at two permanent stations installed in close proximity to the fault and at another station located within the city limits of catania and considered to be a reference site analysis using spectral ratio techniques shows there is a tendency towards amplification at the sites located near the fault in h v spectral ratios such amplification is observed in the frequency range 4 0 8 0 hz and the amplitudes of the dominant spectral peaks decrease rapidly over the first few tens of meters from the discontinuity a similar tendency was observed for the sites located on the eruptive fracture zone dominant spectral peaks at 1 8 hz are also common in the study area the theoretical transfer function obtained through 1 d modelling indicates that such peaks can be related to the local stratigraphy the mean h h standard spectral ratio of microtremor evaluated at the permanent station located on the fault also shows an amplification peak at 4 0 hz azimuthal analysis shows that the resonance at 4 0 hz is directional with the maximum in the azimuth range n30 e n80 e

fault zone amplified waves as a possible seismic hazard along the calaveras fault in central california the calaveras fault lies within a low velocity zone lvz 1 2 km wide near gilroy california accelerographs g06 located in the lvz 1 2 km from the calaveras fault and g07 4 km from g06 recorded both the m 6 2 1984 morgan hill and the m 6 9 1989 loma prieta earthquakes comparison of the ground motions shows that a large 0 6 1 0 hz velocity pulse observed at g06 during the morgan hill event may be amplified by focussing caused by the lvz such amplified waves might be a mappable seismic hazard and the zone of increased hazard can extend as much as 1 2 km from the surface trace of the fault finite difference simulations of ground motions in a simplified lvz model show a zone of amplified motion similar to the observations

modeling the effect of san andreas fault structure on receiver functions using elastic 3d finite difference abstract teleseismic p wave data collected at the san andreas observatory sao seismic station show strong frequency dependent nonrectilinear particle motions consisting of off azimuth horizontal displacements that are sometimes larger than the vertical displacements the azimuthal dependence of the horizontal components amplitude is directly related to the symmetry of the fault zone a 3d finite difference program frankel and vidale 1992 is used to examine the response of the san andreas fault zone velocity structure to incident teleseismic p waves synthetic seismograms are formed using a 3d representation of an assumed 2d fault zone structure the fault zone velocity model produces large amplitude phases that contain combinations of refracted and internally reflected p to s converted phases diffractions and possible p to rayleigh converted phases the largest amplitude phases observed in the data are nondispersive and have complicated particle motions confined to the vertical plane perpendicular to the fault zone the data are fit best by synthetic receiver functions for field points similar to the location of sao relative to the san andreas fault zone since the velocity model used in the computations is nonunique sensitivity studies were performed by modifying the structure synthetics match the timing and nature of the observed phases at sao showing that assumption of plane layered structure is invalid in the area of this station

calculation of synthetic seismograms in a laterally varying medium by the boundary element discrete wavenumber method abstract we investigate the propagation of lg waves in laterally varying crustal structures by numerical simulation the method of calculation is formulated in terms of boundary integral equations where the green9s functions are evaluated by wavenumber summation the approach is well suited to study the propagation of seismic waves in a layered medium where the interfaces are flat in some regions and irregular in others we investigate the effect of a crustal fault with vertical offset and study the case of a lateral change in crustal thickness the results show that the lg wave amplitude is only slightly affected by the presence of these heterogeneities they confirm the robustness of lg wave propagation in presence of lateral heterogeneities observed in other numerical simulations they show that large scale geometric features of the crust cannot account alone for the strong attenuation of lg waves observed in many regions the results also suggest a possible relation between the level of lg wave coda and the degree of roughness of the moho they further indicate the importance of backscattering and suggest a possible use of the backscattered wave field to map strong crustal heterogeneities

a shallow fault zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian fault western turkey summary we discuss the subsurface structure of the karadere duzce branch of the north anatolian fault based on analysis of a large seismic data set recorded by a local passcal network in the 6 months following the mw 7 4 1999 izmit earthquake seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long period oscillations in both p and s wave trains that do not exist in nearby off fault stations examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone the anomalous features in fault zone seismograms produced by events not necessarily in the fault may be referred to generally as fault zone related site effects the oscillatory shear wave trains after the direct s arrival in these seismograms are analysed as trapped waves propagating in a low velocity fault zone layer the time difference between the s arrival and trapped waves group does not grow systematically with increasing source receiver separation along the fault these observations imply that the trapping of seismic energy in the karadere duzce rupture zone is generated by a shallow fault zone layer traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3 4 km the synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m a velocity decrease relative to the surrounding rock of approximately 50 per cent and an s wave quality factor of 10 15 the results are supported by large 2 d and 3 d parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones the inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower type structure the motion amplification associated with fault zone related site effects increases the seismic shaking hazard near fault zone structures the effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large

seismic scattering near the earth s surface the seismic coda is usually thought to be composed of waves scattered from the heterogeneities in the earth three classes of scattering mechanisms have been recognized repeated specular reflection of primary waves in a uniformly layered structure volume scattering of primary waves from localized volume heterogeneities and scattering of primary waves from irregularities in an otherwise generally layered structure the presence of the earth s surface complicates the description of all these scattering phenomena whenever the scattering obstacles are near or at the surface in this paper i review work which demonstrates the effects of scattering near the earth s surface emphasizing three general areas of investigation scattering of body waves from an irregular free surface scattering of body waves in irregular layers and propagation of surface waves across irregular topography or in irregular wave guides most of the effects of importance have been recognized in model studies of idealized geometries observational evidence in support of the model studies exists but is often inferred few controlled experiments to measure scattering have been performed

numerical simulation of fault zone guided waves accuracy and 3 d effects fault zones are thought to consist of regions with reduced seismic velocity when sources are located in or close to these low velocity zones guided seismic head and trapped waves are generated which may be indicative of the structure of fault zones at depth observations above several fault zones suggest that they are common features of near fault radiation yet their interpretation may be highly ambiguous analytical methods have been developed to calculate synthetic seismograms for sources in fault zones as well as at the material discontinuities these solutions can be used for accurate modeling of wave propagation in plane parallel layered fault zone structures however at present it is not clear how modest deviations from such simplified geometries affect the generation efficiency and observations of trapped wave motion as more complicated models cannot be solved by analytical means numerical methods must be employed in this paper we discuss 3 d finite difference calculations of waves in modestly irregular fault zone structures we investigate the accuracy of the numerical solutions for sources at material interfaces and discuss some dominant effects of 3 d structures we also show that simple mathematical operations on 2 d solutions generated with line sources allow accurate modeling of 3 d wave propagation produced by point sources the discussed simulations indicate that structural discontinuities of the fault zone e g fault offsets larger than the fault zone width affect significantly the trapping efficiency while vertical properly gradients fault zone narrowing with depth small scale structures and moderate geometrical variations do not the results also show that sources located with appropriate orientations outside and below a shallow fault zone layer can produce considerable guided wave energy in the overlying fault zone layer

geochemical and geochronological studies of granitoid rocks from the western tianshan orogen implications for continental growth in the southwestern central asian orogenic belt abstract the western tianshan orogen in northwestern china is part of the southwestern margin of the central asian orogenic belt caob which represents the largest tectonic assembly of accretionary complexes and the most significant area of phanerozoic continental growth in the world granitoid rocks have a widespread occurrence and occupy about 30 of the whole exposure of the orogen ages obtained for the granitoids vary from 896 ma to 247 ma while initial 87 sr 86 sr ratios vary from 0 70329 to 0 72070 and e nd values from 14 1 to 7 3 the occurrence of neoproterozoic granitic gneisses implies the presence of precambrian basement in this area during oceanic subduction continental growth occurred as a result of several combined processes i e by addition of oceanic crustal melts adakites the intrusion of basaltic magmas derived by partial melting of the metasomatized depleted mantle wedge and the upwelling of granitic magma derived from a mixed source of basaltic magmas and old continental basement however during the post collisional period vertical accretion of underplated juvenile mantle material may have been accomplished during slab breakoff delamination this study suggests a two stage model of continental growth of syn subduction lateral accretion of arc complexes and post collisional vertical accretion of underplated mantle material which may also be relevant for the western segment of the caob in the phanerozoic the reworking and involvement of old crust are more obvious in the western tianshan orogen compared to other parts of the caob comprising the western junggar eastern junggar alataw and altay terranes

properties of seismic fault zone waves and their utility for imaging low velocity structures a two dimensional solution for the scalar wave equation in a model of two vertical layers between two quarter spaces is used to study properties of seismic waves in a laterally heterogeneous low velocity structure the waves referred to as seismic fault zone waves include head waves internal fault zone reflections and trapped waves the analysis aims to clarify the dependency of the waves on media velocities media attenuation coefficients layer widths and source receiver geometry additional calculations with extreme low velocity layers provide examples that may be relevant for volcanic and geothermal domains the interference patterns controlling seismic fault zone waves change with the number of internal reflections in the low velocity structure this number increases with propagation distance along the structure decreases with fault zone width and increases for given length scales with the velocity contrast the relative lateral position of the source within the low velocity layer modifies die length scales associated with internal reflections and influences the resulting interference pattern low values of q affect considerably the dominant period and overall duration of the waves thus there are significant tradeoffs between propagation distance along the structure fault zone width velocity contrast source location within the fault zone and q the lateral and depth receiver coordinates determine the particular point where the interference pattern is sampled and observed motion is a strong function of both coordinates the zone connecting sources generating fault zone waves and observation points with appreciable wave amplitude can be over an order of magnitude larger than the fault zone width calculations for cases with layer p wave velocity of 200 m s 1 modeling a vertical dike or crack with fluid and gas show conspicuous persisting oscillations the results resemble aspects of seismic data in volcanic domains if these waves exist in observed records their explicit recognition and modeling will help to separate source and structural effects and aid in the interpretation of volcano seismology signals although the tradeoffs in parameters governing seismic fault zone waves are significant each variable has its own signature and the parameters may be constrained by additional geophysical data simultaneous modeling of many waveforms with an appropriate solution can resolve the various parameters and provide a high resolution structural image

calculation of strong ground motion due to an extended earthquake source in a laterally varying structure abstract lateral heterogeneity of the crust combined with the complexity of an extended earthquake source may account for observations of strong ground motion not easily explained by simplified source models in a laterally homogeneous medium both the effects of an extended source and lateral heterogeneity can be examined using a forward modeling technique that combines distributed nonuniform slip on a fault plane with dynamic ray tracing in a three dimensional medium using this technique velocity seismograms are calculated at ranges less than 10 km for a finite source which occurs in a wedge shaped zone of low velocity this structure is chosen to approximate the structure of fault zones found in reflection and refraction surveys across active faults in california iterative paraxial ray tracing is used to solve the two point ray tracing problem the low velocity zone surrounding the fault causes arrivals in the laterally varying structure to be delayed and rays to leave the fault more closely to the fault normal at most locations examined the effect of the three dimensional structure on isochrone velocity is small compared to the effects on geometric spreading and radiation pattern because rays are bent substantially in the near source region the seismograms calculated for the laterally varying structure vary substantially in amplitude and polarity from seismograms calculated for the laterally homogeneous structure

large amplitude variations recorded by an on fault seismological station during the l aquila earthquakes evidence for a complex fault induced site effect 1 a station fagn installed on a segment of the fault system that generated the april 2009 l aquila earthquakes shows larger ground motions compared to nearby stations spectral ratios using 304 earthquakes result in a station amplification significantly varying event by event in the frequency band 1 8 hz the resulting pattern of amplitude dependence on causative earthquake location reveals that the strongest up to a factor of 10 amplifications occur for tightly clustered aftershocks aligned with the fault dip beneath fagn thus indicating a fault guided effect fault models are investigated in a grid search approach by varying velocity q width and depth of the fault zone although the problem solution is not unique and there are strong trade offs among the model parameters constraints from observations yield a deep trapping structure model where the most likely values of velocity reduction q and damage zone width are 25 20 and 280 m respectively

depth dependent structure of the landers fault zone from trapped waves generated by aftershocks we delineate the internal structure of the johnson valley and kickapoo faults landers southern rupture at seismogenic depth using fault zone trapped waves generated by aftershocks trapped waves recorded at the dense linear seismic arrays deployed across and along the surface breaks of the 1992 m7 5 landers earthquake show large amplitudes and dispersive wave trains following the s waves group velocities of trapped waves measured from multiple band pass filtered seismograms for aftershocks occurring at different depths between 1 8 km and 8 2 km show an increase in velocity with depth velocities range from 1 9 km s at 4 hz to 2 6 km s at 1 hz for shallow events while for deep events velocities range from 2 3 km s at 4 hz to 3 1 km s at 1 hz coda normalized amplitude spectra of trapped waves peak in amplitudes at 3 4 hz for stations located close to the fault trace the amplitude decays rapidly with the station offset from the fault zone normalized amplitudes also decrease with distance along the fault giving an apparent q of 30 for shallow events and 50 for deep events we evaluated depth dependent fault zone structure and its uncertainty from these measurements plus our previous results from near surface explosion excited trapped waves li et al 1999 in a systematic model parameter searching procedure using a three dimensional 3 d finite difference computer code graves 1996 our best model of the landers fault zone is 250 m wide at the surface tapering to 100 150 m at 8 2 km depth the shear velocity within the fault zone increases from 1 0 to 2 5 km s and q increases from 20 to 60 in this depth range fault zone shear velocities are reduced by 35 to 45 from those of the surrounding rock and also vary along the fault zone with an increase of 10 near ends of the southern rupture zone

fault zone trapped seismic waves two instances of fault zone trapped seismic waves have been observed at an active normal fault in crystalline rock near oroville in northern california trapped waves were excited with a surface source and recorded at five near fault borehole depths with an oriented three component borehole seismic sonde at parkfield california a borehole seismometer at middle mountain recorded at least two instances of the fundamental and first higher mode seismic waves of the san andreas fault zone at oroville recorded particle motions indicate the presence of both love and rayleigh normal modes the love wave dispersion relation derived for an idealized wave guide with velocity structure determined by body wave travel time inversion yields seismograms of the fundamental mode that are consistent with the observed love wave amplitude and frequency applying a similar velocity model to the parkfield observations we obtain a good fit to the trapped wavefield amplitude frequency dispersion and mode time separation for an asymmetric san andreas fault zone structure a high velocity half space to the southwest a low velocity fault zone a transition zone containing the borehole seismometer and an intermediate velocity half space to the northeast in the parkfield borehole seismic data set the locations depth and offset normal to fault plane of natural seismic events which do or do not excite trapped waves are roughly consistent with our model of the low velocity zone we conclude that it is feasible to obtain near surface borehole records of fault zone trapped waves because trapped modes are excited only by events close to the fault zone proper thereby fixing these events in space relative to the fault a wider investigation of possible trapped mode waveforms recorded by a borehole seismic network could lead to a much refined body wave tomographic velocity model of the fault and to a weighting of events as a function of offset from the fault plane it is an open question whether near surface sensors exist in a stable enough seismic environment to use trapped modes as an earth monitoring device

changes in source and site effects compared to coda q 1 temporal variations using microearthquakes doublets in california we analyse spectral ratio of the coda of doublets of microearthquakes our purpose is to find evidence for temporal changes of the attenuation in the crust before a large magnitude earthquake a moving window cross spectral analysis of the coda of doublets gives a plot of the spectral ratio as a function of lapse time along the seismogram for several frequency bands sr t f plot from a certain pattern in thesr t f plot we should infer a temporal change in coda attenuation several doublets recorded in central california by the usgs network are analysed

seismic radiation from an sh line source in a laterally heterogeneous planar fault zone a solution to the class of problems in which an sh line source is operating in a medium consisting of two quarter spaces with an arbitrary number of semi infinite vertical layers in between is given in a frequency wavenumber domain the general result is applied to a model with a single vertical layer and synthetic seismograms are calculated for a source specified as an sh line dislocation at the interface between the vertical layer and the faster quarter space the numerical examples demonstrate that moderate fault normal material heterogeneity can have significant effects on the seismic response of a medium the overall distribution of travel times amplitudes and motion polarities in the presence of fault zone material heterogeneity is different from a corresponding distribution in a homogeneous half space the effects are most prominent near the fault zone where head waves surface waves and trapped modes result in waveform complexities large amplifications over an order of magnitude in the fault zone itself and first motion polarities which are reversed from homogeneous medium predictions the results imply that material heterogeneity should be included in fault zone models which are used for the interpretation of observed seismic data and theoretical calculations of near fault responses such models can be utilized to obtain important fault zone and earthquake source parameters

shallow seismic trapping structure in the san jacinto fault zone near anza california summary we analyse fault zone trapped waves generated by 500 small earthquakes for high resolution imaging of the subsurface structure of the coyote creek clark valley and buck ridge branches of the san jacinto fault zone near anza california based on a small number of selected trapped waves within this data set a previous study concluded on the existence of a lowvelocity waveguide that is continuous to a depth of 15 20 km in contrast our systematic analysis of the larger data set indicates a shallow trapping structure that extends only to a depth of 3 5 km this is based on the following lines of evidence 1 earthquakes clearly outside these fault branches generate fault zone trapped waves that are recorded by stations within the fault zones 2 a traveltime analysis of the difference between the direct s arrivals and trapped wave groups shows no systematic increase moveout with increasing hypocentral distance or event depth estimates based on the observed average moveout values indicate that the propagation distances within the low velocity fault zone layers are 3 5 km 3 quantitative waveform inversions of trapped wave data indicate similar short propagation distances within the low velocity fault zone layers the results are compatible with recent inferences on shallow trapping structures along several other faults and rupture zones the waveform inversions also indicate that the shallow trapping structures are offset to the northeast from the surface trace of each fault branch this may result from a preferred propagation direction of large earthquake ruptures on the san jacinto fault

late carboniferous bimodal volcanic rocks and coeval a type granite in the suman khad area southwest mongolia implications for the tectonic evolution abstract the volcanic rocks in the suman khad area in southwest mongolia form a bimodal suite consisting mainly of peralkaline rhyolites with subordinate basalts the rhyolite sample collected from the bimodal suite yielded a shrimp zircon u pb age of 314 5 ma mswd 1 41 n 12 which was interpreted to represent formation time of the bimodal volcanic suite the basalts were characterized by enrichment in lile and lree and depletion in hfse indicating their formation was related to subduction processes these features together with their positive end t values 6 3 6 7 suggest that the basalts were likely derived from a depleted mantle source metasomatized by subduction related fluids in various tectonic discrimination diagrams the basalts exhibited a transition from true arc basalts to intraplate basalts and thus were suggested to from in a back arc tectonic setting the rhyolites show a close affinity to a type granites with enrichment in lile and lree depletion in nb ta and ti and positive end t values 6 0 6 4 considering the observed distinct compositional gap between the endmembers of the bimodal suite the rhyolites are proposed to originate from partial melting of juvenile basaltic crustal rocks rather than fractional crystallization of basaltic melt the granite associated with the bimodal volcanic rocks yielded a shrimp zircon u pb ages of 312 5 ma mswd 0 75 n 13 indicating that the granite is contemporaneous with the bimodal volcanic suite the granite samples showed typical a type granitic geochemical affinities and are considered to have been formed by partial melting of crustal rocks in a within plate tectonic setting based on a combination of the available data we suggest that the late carboniferous bimodal volcanic suite together with the coeval a type granites in the suman khad region probably document a back arc basin extensional environment which probably related to the roll back of the paleo asian oceanic plate during the northward subduction under the central mongolia microcontinent

accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield kroner a windley b f badarch g tomurtogoo o hegner e jahn b m gruschka s khain e v demoux a and wingate m t d 2007 accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield in hatcher r d jr carlson m p mcbride j h and martinez catalan j r eds 4 d framework of continental crust geological society of america memoir 200 p 181 209 doi 10 1130 2007 1200 11 for permission to copy contact editing geosociety org 2007 the geological society of america all rights reserved kroner kroener mail uni mainz de windley brian windley btinternet com tomurtogoo igmr magicnet mn hegner hegner lmu de jahn jahn earth sinica edu tw khain khain ginras ru demoux demoux uni mainz de wingate mwingate tsrc uwa edu au

a seismic refraction study of the santa clara valley and southern santa cruz mountains west central california abstract two seismic refraction profiles were recorded in the santa clara valley region of central california to determine the upper crustal seismic velocity structure a reversed 8 km long profile was recorded across the valley near gilroy and an unreversed 38 km long profile was recorded in the southern santa cruz mountains the data indicate that the valley is wedge shaped in cross section with the basement dipping 10 to the east the alluvial fill of the valley has a maximum thickness of 1 5 km and has an average compressional wave velocity of 2 3 km sec the top of the basement has a velocity of 4 3 km sec the velocity reaches 6 0 km sec at a depth of 2 km the calaveras fault zone located due east of the valley was crossed by a short unreversed profile it appears to be characterized by a low velocity v p 2 7 km sec to a depth of 2 5 km the southern santa cruz mountain profile indicates a 4 6 km sec near surface refractor and a layer with a velocity of 6 1 km sec at 2 km depth thus considered together the similarity in velocity structure determined from the two profiles indicates that the franciscan rocks of the santa cruz mountains continue beneath the valley the presence of high compressional wave velocities 6 0 km sec at 2 km depth in this franciscan terrain can best be explained by an abundance of metabasalts greenstones at that depth these seismic observations indicate that an area of at least 120 km 2 is underlain by this high velocity basaltic material therefore the upper crustal structure in the study area differs dramatically from the franciscan terrain of the diablo range where greywackies and metagreywackies v p 5 4 km sec dominate in the uppermost crust

linearized inversion for fault rupture behavior application to the 1984 morgan hill california earthquake we present a technique to infer the rupture history of an earthquake from near source records of ground motion unlike most previous studies each point on the fault is assumed to slip only once when the rupture front passes with a spatially variable slip intensity in this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture time we perform a linearized inversion for slip intensity and rupture time by iteratively perturbing an assumed starting model the inverse problem for the model perturbation is solved using a tomographic back projection technique smoothing and inequality constraints are applied to ensure that the resulting solution is stable and feasible asymptotic ray theory is used to calculate theoretical seismograms and partial derivatives with respect to model parameters in test cases with noisy synthetic data sets we found that it is possible to distinguish between rupture models having variable slip amplitude and models having variable rupture velocity provided the station coverage is adequate we apply the technique to recordings of the april 24 1984 morgan hill earthquake the results indicate that slip amplitude on the fault plane was extremely variable and that the rupture front did not propagate uniformly away from the hypocenter in particular rupture was delayed on a 12 km2 section of the fault approximately 14 km to the southeast of the hypocenter the rupture front surrounded the region which subsequently failed with a component of rupture propagation back toward the hypocenter similar behavior has been observed in dynamic rupture models with stress or strength inhomogeneities this segment of the fault ruptured with a large slip amplitude releasing 12 of the total seismic moment from 4 of the total area of the aftershock zone the surface trace of this section of the fault is characterized by a complex left step that could act to increase the normal stress acting across the fault however the distribution of aftershocks suggests that the fault at depth is simpler and that it may bend to the right in either case our rupture model suggests that this segment of the fault represents an asperity which initially resisted rupture but eventually ruptured massively we estimate the shear fracture energy for this earthquake to be 2 106 j m2

zircon u pb ages and hf isotopes of paleozoic metasedimentary rocks from the habahe group in the qinghe area chinese altai and their tectonic implications abstract as one of the largest accretionary orogens in earth s history the central asian orogenic belt has attracted much attention in the past two decades but there are still many unresolved issues regarding its tectonic nature and evolution this is the case with the chinese altai whose tectonic provenance remains controversial especially for the paleozoic era as the most widely exposed meta sedimentary rocks in the chinese altai the habahe group was previously considered as representing a component of precambrian micro continent forming at a passive continental margin our new u pb data for detrital zircons from the habahe group in the qinghe region of the eastern chinese altai indicate that the strata were deposited from the late silurian to early devonian 427 405 ma and experienced regional metamorphism in the middle devonian 383 9 ma as constrained by the age of youngest detrital zircons 427 13 ma the age 405 3 ma of the tonalite that intrudes the habahe group and the metamorphic age of 383 9 ma additionally the majority of zircons from the habahe group have positive ehf t values 0 22 15 02 these data combined with geochemical features and maturity of the sedimentary rocks indicate an immature provenance for the habahe group with the source materials mainly derived from a juvenile crust with some old continental components the juvenile crust was most likely formed in a subduction zone developing in the chinese altai during early middle paleozoic time new geochemical data presented in this study suggest that the chinese altai was a transitional arc during early paleozoic time similar to the japan type arc with involvements of old continental components therefore it is proposed that the chinese altai was likely rifted from the south margin of the siberia craton probably related to the break up of the rodinia supercontinent and then experienced accretion and reworking with the subduction of the paleo asian ocean during early paleozoic time

crack location in granitic samples submitted to heating low confining pressure and axial loading summary until now observations of mechanically and thermally induced microcracks in rocks could only be carried out by indirect measurements or destructive observations on samples brought back to atmospheric pressure conditions a special triaxial test cell was designed in order to perform direct observations during loading the use of a cell in tomography apparatus involves new devices 1 a movable horizontal load frame around a scanner and 2 a test cell transparent to x rays able to withstand up to 28 mpa maximum confining pressure and temperatures of up to 180 c volumetric strains are compared with radiological density measurements the first processed x ray images locating microcracks during propagation are also presented mineralogical evects on the crack location can be demonstrated strain inferred from ct density measurement is clearly correlated with the strain usually measured by a strain gauge diverent phases of mechanical behaviour are described contracted phase and failure by macrocrack formation the principal results obtained with this tool are the description of the porosity formation and macrocracking results show two principal factors localizing the porosity first the divused porosity volume is controlled by mineralogical parameters quartz and plagioclase grains and boundaries of biotite grains during the thermal and mechanical loading second macrocracking begins at the perimeter of the central section of core and grows towards the sample piston interface it seems that the first macrocracking is not located in the high porosity zone formed during the loading phase but in a relatively low porosity zone

san jacinto fault zone guided waves a discrimination for recently active fault strands near anza california we deployed three 350 m long eight element linear seismic arrays in the san jacinto fault zone sjfz near anza california to record microearthquakes starting in august through december 1995 two arrays were deployed 18 km northwest of anza across the casa loma fault clf and the hot springs fault hsf strands of the sjfz the third array was deployed across the san jacinto fault sjf in the anza slip gap we observed fault zone guided waves characterized by low frequency large amplitudes following s waves at the clf array and the sjf array for earthquakes occurring within the fault zone however we did not observe guided waves at the hsf array for any events the amplitude spectra of these guided waves showed peaks at 4 hz at the clf and 6 hz at the sjf which decreased sharply with the distance from the fault trace in contrast no spectral peaks at frequency lower than 6 hz were registered at the hsf array we used a finite difference method to simulate these guided modes as 5 waves trapped in a low velocity waveguide sandwiched between high velocity wall rocks the guided mode data are adequately fit by a waveguide on the clf with the average width of 120 m and s velocity of 2 5 km s about 25 reduced from the s velocity of the surrounding rock this waveguide becomes 40 to 60 m wide with the 5 velocity of 2 8 km s in the anza slip gap on the other hand there is not a continuous waveguide on the hsf at depth locations of the events with guided modes suggest that the fault plane waveguide extends along the clf between the towns of san jacinto and anza dipping northeastward at 75 80 to a depth of about 18 km it becomes nearly vertical in the anza gap we speculate that the existence of a continuous low velocity waveguide on the clf can be caused by the rupture of the magnitude 6 9 earthquake on april 21 1918 occurring near the towns of san jacinto and hemet further the lack of a clear waveguide on the hsf suggests that it was not ruptured in this event

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

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

the response of two joined quarter spaces to sh line sources located at the material discontinuity interface summary exact analytical solutions to problems of sh line force and line dislocation operating at the interface between two quarter spaces are derived and discussed it is shown that the resulting fields differ from that of a homogeneous half space in the distribution of travel times wave amplitudes and polarity of first motions these effects are documented in the literature it is therefore suggested that when constructing theoretical seismic displacement fields from source path and site effects it is important to use response functions that account for material heterogeneity in the source region an extension of the formulation used in the case of sh line dislocation leads to a 3 d representation theorem which gives the displacement field in terms of the displacement discontinuities along the rupture area the resulting overall sue scaling parameter is the potency which does not suffer from an ambiguity associated with seismic moment in the case of heterogeneous source region

focusing and defocusing of teleseismic p waves by known three dimensional structure beneath pahute mesa nevada test site the focusing and defocusing of teleseismic p waves predicted by a known three dimensional structure beneath the nevada test site is calculated by dynamic raytracing and superposition of gaussian beams the 20 to 100 km scale lengths of this model having velocity fluctuations of several per cent account for a factor of 3 fluctuation in the azimuthal pattern of p amplitudes since similar sized scale lengths and intensities of velocity fluctuation are commonly resolved in three dimensional inversions of mantle structure in other regions focusing and defocusing of teleseismic p waves is likely to be a ubiquitous feature of every test site hence network averages of mb that weight azimuthal windows in which p energy is either focused or defocused will tend to either over or underestimate the yields of underground tests the results obtained with a known nevada test site structure suggest that structural inversions having similar structural resolution may be capable of reducing 25 per cent of the variance in amplitudes due to the focusing and defocusing of upper mantle structure near the source assuming that scattering processes are concentrated in the crust and upper most mantle beneath the source and receiver the integrated energy in the p coda should be more stable than direct p because it tends to homogenize the effect of focusing defocusing structure near the source for scattering into direct p near the source for direct p scattering near the receiver however even the late coda is not capable of completely removing the effects of focusing defocusing near the source

continuity of the west napa franklin fault zone inferred from guided waves generated by earthquakes following the 24 august 2014 mw 6 0 south napa earthquake we measure peak ground velocities from fault zone guided waves fzgws generated by on fault earthquakes associated with the 24 august 2014 m w 6 0 south napa earthquake the data were recorded on three arrays deployed across north and south of the 2014 surface rupture the observed fzgws indicate that the west napa fault zone wnfz and the franklin fault ff are continuous in the subsurface for at least 75 km previously published potential field data indicate that the wnfz extends northward to the maacama fault mf and previous geologic mapping indicates that the ff extends southward to the calaveras fault cf this suggests a total length of at least 110 km for the wnfz ff because the wnfz ff appears contiguous with the mf and cf these faults apparently form a continuous calaveras franklin wnfz maacama cfwm fault that is second only in length 300 km to the san andreas fault in the san francisco bay area the long distances over which we observe fzgws coupled with their high amplitudes 2 10 times the s waves suggest that strong shaking from large earthquakes on any part of the cfwm fault may cause far field amplified fault zone shaking we interpret guided waves and seismicity cross sections to indicate multiple upper crustal splays of the wnfz ff including a northward extension of the southhampton fault which may cause strong shaking in the napa valley and the vallejo area based on travel times from each earthquake to each recording array we estimate average p s and guided wave velocities within the wnfz ff 4 8 5 7 2 2 3 2 and 1 1 2 8 km s respectively with fzgw velocities ranging from 58 to 93 of the average s wave velocities

short baseline variations in site response and wave propagation effects and their structural causes four examples in and around the santa clara valley california abstract ground motion records of local and regional events from a portable array are used to investigate the structural causes of variations in ground motion over distances of a few hundred meters to a few kilometers in the sedimentary basin environment of the santa clara valley california and its margins arrays of portable seismic stations are used to target four study areas with different ground motion patterns 1 an edge of the alluvial basin extending up onto a marginal ridge blossom hill 2 a cenozoic basin with a nearly flat bottom cupertino basin 3 a long narrow cenozoic basin with a steep v profile evergreen basin and 4 a line perpendicular to the trace of the hayward fault average peak velocities on blossom hill from local earthquakes are a factor of 2 5 times higher than nearby valley sites three dimensional 3d modeling is used to conclude that the majority of the amplification is due to lower shear wave velocities along a local fault zone shannon berrocal site amplification over the cupertino basin in the frequency band 0 5 4 hz is generally low less than 2 0 relative to a mesozoic rock site and spatially uniform this response is attributed to the shallow flat bottomed shape of the basin and the uniform flat laying sedimentary fill in contrast site amplification in the evergreen basin generally exceeds 3 0 and is attributed to the deep v shaped geometry of the basin and younger sedimentary fill 3d waveform modeling shows the elongated shape of the evergreen basin causes more efficient trapping of long period waves for sources along the long axis of the basin a low velocity zone is postulated along the hayward fault with a width between 100 and 200 m based on elevated site response along the fault trace and 4 5 hz fault zone guided waves on the horizontal components of stations near the fault

seismic site characterization of an urban sedimentary basin livermore valley california site response basin edge induced surface waves and 3d simulations thirty two accelerometers were deployed in the livermore valley california for approximately one year to study sedimentary basin effects many local and near regional earthquakes were recorded including the 24 august 2014 m w 6 0 napa california earthquake the resulting ground motion data set is used to quantify the seismic response of the livermore basin a major structural depression in the california coast range province bounded by active faults site response is calculated by two methods the reference site spectral ratio method and a source site spectral inversion method longer period 1 s amplification factors follow the same general pattern as bouguer gravity anomaly contours site response spectra are inverted for shallow shear wave velocity profiles which are consistent with independent information frequency wavenumber analysis is used to analyze plane wave propagation across the livermore valley and to identify basin edge induced surface waves with back azimuths different from the source back azimuth finite element simulations in a 3d velocity model of the region illustrate the generation of basin edge induced surface waves and point out strips of elevated ground velocities along the margins of the basin online material figures comparing 5 damped acceleration response spectra for data and synthetics

observations of guided waves from the pamir seismic zone provide additional evidence for the existence of subducted continental lower crust abstract as part of the tipage tien shan pamir geodynamic program project passive seismological observations were made along an approximately n s profile crossing the pamir seismic zone for about one year from these observations guided waves were recognized these guided waves occur as a single continuous secondary compressional p wave phase behind the first p wave arrivals an equivalent phase in the shear s wavefield is hardly recognizable modelling of the phase shows that an approximately 10 km thick low velocity zone lvz between the moho and about 160 km depth reproduces the guided waves as a single continuous phase much better than a 15 20 km thick lvz modelling of the arrival times of the guided waves reveals that a model with a p wave velocity of 6 3 km s above about 100 km depth and a velocity of 7 6 km s between this depth and the deep cluster of earthquakes at about 150 km depth provides the best fit to the observed travel time data one plausible way to explain the low velocity of 6 3 km s is to invoke the presence of melts in the lvz then taking a velocity of 6 9 km s for the lower crust being subducted about 10 13 melt is required to obtain a velocity of about 6 3 km s in the lvz between the moho and about 100 km depth this would be in keeping with the estimated burial depths from xenoliths of gondwana terrane affinity brought to the surface in the southeastern pamir around 11 million yr ago the present day lvz is interpreted to comprise continental lower crust although guided waves are known to exist associated with subducted oceanic crust or fault zones this is the first time to the knowledge of the authors that guided waves have been observed resulting from a lvz associated with subducted continental lower crust

a prototype earthquake warning system for strike slip earthquakes a prototype expert system has been developed to provide rapid warning of earthquakes while they are occurring warning times of up to 100 seconds will be possible in the complete system several accelerometers are distributed at intervals within a few kilometers of a known fault data are telemetered to a central computer which implements the expert system the expert system incorporates specific information about the type of fault to be monitored and includes simple rules for estimating the fault slip rupture length and seismic moment all in real time if the seismic moment exceeds a preset value an alarm may be issued the prototype is designed for deployment on near surface strike slip faults such as the san andreas and has been successfully tested with data from the 1979 imperial valley and 1984 morgan hill earthquakes crucial concepts have also been tested using synthetic data calculated for a model of the 1857 fort tejon earthquake parkfield california could be used as a test site

earthquake ground motions in this review we discuss some of the many phenomena that can determine the nature of strong ground motion some of these phenomena have been inferred from the study of existing ground motion records and others are inferred from theoretical models of earthquake sources and wave propagation

fault zone guided waves from explosions in the san andreas fault at parkfield and cienega valley california fault zone guided waves were successfully excited by near surface explosions in the san andreas fault zone both at parkfield and cienega valley central california the guided waves were observed on linear three component seismic arrays deployed across the fault trace these waves were not excited by explosions located outside the fault zone the amplitude spectra of guided waves show a maximum peak at 2 hz at parkfield and 3 hz at cienega valley the guided wave amplitude decays sharply with observation distance from the fault trace the explosion excited fault zone guided waves are similar to those generated by earthquakes at parkfield but have lower frequencies and travel more slowly these observations suggest that the fault zone wave guide has lower seismic velocities as it approaches the surface at parkfield we have modeled the waveforms as s waves trapped in a low velocity wave guide sandwiched between high velocity wall rocks resulting in love type fault zone guided waves while the results are nonunique the parkfield data are adequately fit by a shallow wave guide 170 m wide with an s velocity 0 85 km sec and an apparent q 30 to 40 at cienega valley the fault zone wave guide appears to be about 120 m wide with an s velocity 0 7 km sec and a q 30

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

depth extent of damage zones around the central calaveras fault from waveform analysis of repeating earthquakes summary we systematically investigate spatial variations of temporal changes and depth extent of damage zones along the calaveras fault that ruptured during the 1984 morgan hill earthquake by the waveform analysis of 333 sets of repeating earthquakes we use a sliding window waveform cross correlation technique to measure traveltime changes in waveforms generated by each repeating cluster we find clear traveltime delays in the s and early s coda waves for events immediately after the morgan hill main shock the amplitudes of the time delays decrease logarithmically with time since the main shock indicating a time dependent recovery healing process following the abrupt coseismic temporal changes the largest temporal changes are observed at station cco that is the closest to the rupture zone of the morgan hill main shock the time delays at this station are larger for clusters in the top 6 km and decrease systematically at larger depth in comparison the time delays observed at other five stations are much smaller and do not show clear relationship with hypocentral depth we suggest that the temporal changes at these five stations mostly occur in the top few hundred metres of the near surface layers while the temporal changes at station cco are likely associated with the damage zone around the calaveras fault that is well developed in the top few kilometres of the upper crust our results are consistent with the inference of a widespread damage and non linearity in the near surface layers associated with strong ground motions of nearby large earthquakes and localized damages and flower type structures around active faults based on previous studies of fault zone structures and recent 3 d numerical simulations

effects of a low velocity zone on a dynamic rupture dynamic crack earthquake simulations generally assume that the crustal material surrounding faults is laterally homogeneous tomographic and near fault seismic studies indicate that the crust near faults is instead comprised of rocks of varying material velocities we have tested the effects of adding material velocity variation to simulations of spontaneously propagating earthquakes we used two dimensional plane strain conditions coupled with a slip weakening fracture criterion and examined earthquakes on faults that bisect finite width low velocity zones embedded in country rock and earthquakes on faults that bound two different velocity materials when a fault bisects a low velocity zone the normal stress remains unchanged but both the rupture velocity and slip velocity pulse shape are perturbed the presence of the low velocity zone induces high frequency oscillations in the slip function near the rupture front when the fault is on the edge of the low velocity zone the oscillations are more pronounced and repeated sticking and slipping can occur near the rupture front for the slip weakening velocity independent friction model however the temporary sticking does not lead to permanent arrest of slip and slip duration is still controlled by the overall rupture dimension when an earthquake ruptures a fault juxtaposing a lower velocity material against a higher velocity material the normal stress across the fault near the crack tip is perturbed the sign of the normal stress perturbation depends on the direction of rupture leading in some cases to a directional dependence of rupture velocity when slip is accompanied by stress reduction a positive feedback develops between the normal and shear stress changes as previously noted by andrews and ben zion 1997 resulting in an apparently unavoidable grid size dependence in computation of stress change near the rupture front numerical experiments indicate however that the rupture velocity is insensitive to this zone size dependence which is highly localized immediately behind the crack tip the factors controlling the rupture velocity in the simulations including directional dependence are further elucidated by a new analytical solution for rupture of an asperity on a frictionless interface

formation of the kokchetav subduction collision zone northern kazakhstan insights from zircon u pb and lu hf isotope systematics abstract the kokchetav subduction collision zone is located in the western part of the ancestral central asian orogenic belt this zone is built up by the precambrian kokchetav microcontinent which includes a hp uhp metamorphic belt and the north kokchetav tectonic zone nktz which represents an accretionary complex between the kokchetav microcontinent and the adjacent stepnyak island arc the entire region is widely intruded by palaeozoic granitoids which were emplaced after the collision of the stepnyak island arc with the kokchetav microcontinent we present zircon u pb ages and lu hf systematics in zircon to better characterize the tectonic evolution of the kokchetav subduction collision zone the lu hf results indicate that the kokchetav basement rocks are derived from late neoarchaean early palaeoproterozoic 2 5 ga crust for the granite gneiss basement of the kokchetav microcontinent early mesoproterozoic grenville age 1 17 1 14 ga zircon u pb crystallization ages were obtained for the nktz two main age components were recognized 1 an oldest mesoproterozoic age component 1 20 1 05 ga similar as for the kokchetav microcontinental zircons and 2 a younger early cambrian 540 520 ma or late cambrian early ordovician 490 480 ma age component th u ratios 0 1 and are typical of a magmatic protolith the distinction between both zircon types is supported by characteristic cathodoluminescence images these results confirm previous observations indicating early palaeozoic high grade metamorphism 540 520 ma and collisional deformation 490 480 ma of the mesoproterozoic kokchetav zone as a result of subduction accretion and collision of the stepnyak island arc to the kokchetav microcontinent for two additional samples of the balkashin granitic complex early devonian 415 395 ma zircon crystallization ages magmatic th u ratios were obtained the occurrence of a mesozoic xenocryst within these leucogranites may indicate that they were emplaced in a continental arc setting

guided waves from sources outside faults an indication for shallow fault zone structure using 3 d numerical modeling of seismic wave propagation we investigate the possibility of generating fault zone fz trapped wave energy from sources well outside a fault the fz is represented by a o 200 m wide vertical low velocity layer in a half space we find that fz trapped waves can be excited from sources well outside the fault if 1 the low velocity structure extemds only to shallow depth and the source is located at greater depth or 2 the structure of the low velocity zone is such that only the shallow part of the fz traps energy fz trapped waves are not excited from sources well outside a fz continuous with depth the results support in conjunction with recent observational evidence a model for natural faults with shallow trapping structures rather than ones that span the entire seismogenic zone this may have implications for fault mechanics as well as for aspects of shaking hazard near faults

amplification of ground motion and waveform complexity in fault zones examples from the san andreas and calaveras faults summary p wave seismograms at ranges less than 10 km are synthesized by asymptotic ray theory and by summation of gaussian beams for point sources located in a low velocity wedge surrounding a fault the computations are performed using models of the wedge inferred from the analysis of reflection and refraction experiments across the san andreas and haywardcalaveras faults calculations in these models show that the 10 20hz vertical displacements of earthquakes located at 3 10 km depth are amplified by up to an order of magnitude in a 1 2 km wide region centred on the fault trace compared to displacements predicted by laterally homogeneous models of the crust this amplification is not cancelled by high attentuation in the fault zone and compensates for the reduction in amplitudes directly above the source predicted from the radiation pattern of a strike slip earthquake depending on the source depth of the earthquake and the structure and velocity contrast of the wedge multiple triplications in the travel time curve of direct p and s waves will occur at stations in the fault zone a wedge model successfully predicts the triplications observed in the p waveforms of aftershocks of the coyote lake earthquake recorded in the fault zone showing that body waves from microearthquakes can be used to determine the three dimensional velocity structure of the fault zone the amplification waveform complexity and distortion of ray paths introduced by the lowvelocity wedge suggest that its effects should be included in the interpretation of strong ground motions and travel times observed in the fault zone for realistic models of the wedge asymptotically approximate methods of calculating the body waveforms are strictly valid for frequencies greater than 20hz numerical methods may be necessary to calculate accurately the wavefield at lower frequencies

directional topographic site response at tarzana observed in aftershocks of the 1994 northridge california earthquake implications for mainshock motions abstract the northridge earthquake caused 1 78 g acceleration in the east west direction at a site in tarzana california located about 6 km south of the mainshock epicenter the accelerograph was located atop a hill about 15 m high 500 m long and 130 m wide striking about n78 e during the aftershock sequence a temporary array of 21 three component geophones was deployed in six radial lines centered on the accelerograph with an average sensor spacing of 35 m station c00 was located about 2 m from the accelerograph we inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion we identified a 3 2 hz resonance that is a transverse oscillation of the hill a directional topographic effect the top base amplification ratio at 3 2 hz is about 4 5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill this resonance is seen most strongly within 50 m of c00 other resonant frequencies were also observed a strong lateral variation in attenuation probably associated with a fault caused substantially lower motion at frequencies above 6 hz at the east end of the hill there may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill causing particle motions not spectral ratios at the top of the hill to be rotated about 20 away from the direction transverse to the hill the resonant frequency but not the amplitude of our observed topographic resonance agrees well with theory even for such a low hill comparisons of our observations with theoretical results indicate that the 3d shape of the hill and its internal structure are important factors affecting its response the strong transverse resonance of the hill does not account for the large east west mainshock motions assuming linear soil response mainshock east west motions at the tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill probable variations in surficial shear wave velocity do not account for the observed differences among mainshock acceleration observed at tarzana and at two different sites within 2 km of tarzana

effects of three dimensional crustal structure on the estimated slip history and ground motion of the loma prieta earthquake abstract the strong ground motion of the loma prieta earthquake is synthesized using a known three dimensional 3d crustal model of the region a rupture model determined under the assumption of laterally homogeneous structure and green9s functions computed by superposition of gaussian beams compared to results obtained assuming a laterally homogeneous crust stations within 30 km of the hypocenter and 5 km of the fault trace are predicted to be strongly focused by factors up to 10 or more while stations lying at the northeastern edge of the santa clara valley are predicted to be weakly defocused by factors of 0 5 the focusing is caused by low velocities lying between the zayante and san andreas faults and the defocusing is caused by a wedge of high velocity material between the san andreas and sargent faults the magnitude of amplitude variations resulting from known 3d structure is similar to that incorporated in site effects resulting from variations in surface impedance and shallow structure beneath receivers the existence of these effects add to the uncertainty in estimates of future strong ground motion the strong path dependence of the effects makes it possible to include them in estimates of future ground motions only by knowing both the 3d structure and the sites of localized high slip in future earthquakes to match observed waveforms with the structure model of eberhart phillips et al 1990 the slip model of beroza 1991 is modified by reducing the magnitude of the northwest maximum in slip by a factor of 0 7 and increasing the magnitude of the southeast maximum slip by a factor of 2 5 these modifications are in the range of variations in the estimated slip history published by investigators using different data sets and inversion procedures

magmatism and metallogeny associated with mantle upwelling zircon u pb and lu hf constraints from the gold mineralized jinchang granite ne china abstract the jinchang gold deposit is located in the easternmost portion of the central asian orogenic belt caob and represents one of the major gold districts in eastern jilin heilongjiang provinces of china the gold ore bodies are hosted mainly in altered mesozoic granitoids breccia pipes and ring and radial faults gold mineralization consists of alteration stockwork in hydrothermally altered granites breccia and quartz sulfide vein types alteration assemblages around the alteration style ore body show a vertical sequence of potassic phyllic and propylitic zones in this study we present u pb and lu hf isotope data on zircons derived from mineralized granophyric granite biotite monzogranite granodiorite and granite porphyry and sericite rb sr ages from the jinchang gold deposit the results show 206pb 238u ages of 201 3 ma mswd 1 1 203 4 ma mswd 1 4 201 5 ma mswd 2 1 and 110 3 ma mswd 1 6 respectively sericite from the gold mineralized phyllic altered granodiorite and granite porphyry returns rb sr isochron ages of 110 4 ma mswd 1 04 and 107 5 ma mswd 0 91 respectively our new data indicate that the gold mineralization at jinchang took place at ca 110 ma and was temporally related to intrusion of the granite porphyry zircon e hf 200 ma values of the ca 200 ma granites vary from 4 8 to 8 1 with tcdm model ages of 727 1535 ma reflecting their derivation mainly by partial melting of juvenile proterozoic crust the gold bearing 110 ma granite porphyry returns e hf 110 ma values in the range of 1 6 to 9 8 with tcdm model ages of 542 1069 ma suggesting partial melts of juvenile proterozoic crust with notable input of mantle components as compared to the ca 200 ma granites compiled oxygen 18osmow 0 7 10 1 and hydrogen dsmow 99 to 70 stable isotopic values of quartz from ores indicate that the ore forming fluids were predominantly exsolved from magmas with minor amount of meteoric water in quartz sulfide veins at the late stage the hf isotope data from the granite porphyry integrated with the results from previous data on s and pb isotopic composition of ores constrain the source of ore forming components as lower crust with discernible mantle inputs and wall rock assimilation our results have implications bearing on the widespread magmatism and metallogenic event during the early cretaceous time in east china and link them to mantle upwelling that contributed both heat and volatiles for crustal melting and scavenging of metals which in turn were concentrated in upper crustal levels through exsolution for the magmas

strong motion seismology strong motion seismology is concerned with earthquake ground motion in the amplitude range that poses the threat of human injury or property damage because the occurrence of strong motion cannot be predicted in advance and because the time between significant events at any one place may range from tens to thousands of years strong motion data is recorded on triggered instruments that typically must be maintained in readiness for years between periods of significant recording as a consequence the strong motion data set is sparse because of the engineering need for estimates of future ground motion the scope of the field of strong motion seismology encompasses seismic source theory and any other aspect of seismology that can provide insights helpful in making the best possible estimates given the limited data this relationship with the rest of seismology is a reciprocal one in that strong motion data gives perhaps the best information available on earthquake source processes

petrogenesis of late paleozoic diorites and a type granites in the central eastern tianshan nw china response to post collisional extension triggered by slab breakoff abstract geological evolution of the eastern tianshan in the late paleozoic is significant to understanding the multiple accretions and final formation of the southern central asian orogenic belt here we report new whole rock geochemical and sr nd isotopic data and in situ zircon u pb ages for three typical a type granitic intrusions syenogranite k feldspar granite and monzonitic granite and one dioritic pluton in the central eastern tianshan nw china in order to constrain their petrogenesis tectonic setting and geodynamic evolution zircon la icp ms u pb ages indicate that the syenogranites and k feldspar granites were both formed during a short time interval in the early permian 284 286 ma whereas the diorites were crystallized at 293 6 ma the monzonitic granites were generated at 307 3 ma earlier than the other two granitic intrusions the three kinds of granites syenogranite k feldspar granite and monzonitic granite have high hfse hree and y nb ratios 1 68 2 84 and remarkably low sr and ba contents with the absence of aluminium rich minerals and show metaluminous to weakly peraluminous natures indicating geochemical characteristics of aluminous a2 type granites these granites show negative end t 3 32 to 4 40 values and mesoproterozoic two stage nd model ages tdm2 1 36 to 1 43 ga which suggest a relatively old crustal source for these rocks the sr nd isotopic compositions imply that the mesoproterozoic metamorphic basement of the central tianshan block can be considered as a potential magmatic source for these aluminous a2 type granites in addition they have geochemical characteristics similar to the experimental melt that was derived from partial melting of crustal metaigneous rocks at the depth of middle to lower crust levels therefore the granites were most likely produced by partial melting of metaigneous rocks in a post collisional extensional setting the diorites have low sio2 and high mgo with uniform 87sr 86sr i values 0 7055 negative end t values 4 11 to 4 59 and mesoproterozoic two stage nd model ages tdm2 1 41 to 1 45 ga they have higher ti zr 42 8 46 7 and ti y 280 359 ratios than continental crust and show negative nb ta ti anomalies which can be explained by partial melting of a relatively fertile mantle modified by old crustal materials of the central tianshan block the formation of the dioritic pluton was induced by an upwelling asthenosphere in an extensional geodynamic setting based on the zircon saturation temperatures of these a type granites and the distribution of late carboniferous to early permian mantle derived intrusions a slab breakoff model is suggested to interpret the formation of the studied a type granites and diorites we infer that the slab breakoff was initiated in the late carboniferous and ended in the early permian

shallow seismic structure of kunlun fault zone in northern tibetan plateau china implications for the 2001 ms8 1 kunlun earthquake summary the shallow seismic velocity structure of the kunlun fault zone klfz was jointly deduced from seismic refraction profiling and the records of trapped waves that were excited by five explosions the data were collected after the 2001 kunlun ms8 1 earthquake in the northern tibetan plateau seismic phases for the in line record sections 26 records up to a distance of 15 km along the fault zone were analysed and 1 d p and s wave velocity models of shallow crust within the fault zone were determined by using the seismic refraction method sixteen seismic stations were deployed along the off line profile perpendicular to the fault zone fault zone trapped waves appear clearly on the record sections which were simulated with a 3 d finite difference algorithm quantitative analysis of the correlation coefficients of the synthetic and observed trapped waveforms indicates that the kunlun fault zone width is 300 m and s wave quality factor q within the fault zone is 15 significantly s wave velocities within the fault zone are reduced by 30 45 per cent from surrounding rocks to a depth of at least 1 2 km while p wave velocities are reduced by 7 20 per cent a fault zone with such pand s low velocities is an indication of high fluid pressure because vs is affected more than vp the low velocity and low q zone in the klfz model is the effect of multiple ruptures along the fault trace of the 2001 ms8 1 kunlun earthquake

late carboniferous high pressure metamorphism of the kassan metamorphic complex kyrgyz tianshan and assembly of the sw central asian orogenic belt abstract high pressure hp metamorphism of the kassan metamorphic complex kmc in the western kyrgyz tianshan has been related to either late ordovician or late carboniferous permian subduction processes we report sm nd ages for retrogressed eclogite samples and 40ar 39ar cooling ages for enclosing garnet muscovite samples from the kmc as new age constraints on hp metamorphism and rock exhumation these data will be used for an upgraded paleogeographic model for late paleozoic crustal consolidation in the southwestern central asian orogenic belt the retrogressed eclogite samples have transitional alkaline to tholeiitic affinity and trace element patterns consistent with protoliths derived from garnet bearing mantle sources at rifting plate margins geothermobarometric data for a retrogressed eclogite sample indicate peak metamorphic conditions of 540 30 c at 1 6 0 1 gpa samples from different lithotectonic units of the kmc provide coherent sm nd garnet whole rock ages of 317 4 ma and 316 3 ma 2 the prograde major element zoning in the mm sized garnets in combination with the moderate peak metamorphic temperature support our interpretation of the sm nd garnet ages as unambiguous evidence for late carboniferous hp metamorphism the sm nd garnet growth ages overlap within error with the 40ar 39ar mica cooling ages of 314 2 ma and 313 2 ma 2 indicating rapid uplift of the subduction complex after peak metamorphism the ca 317 313 ma hp exhumation event of the kmc is contemporaneous with those of the atbashi and akeyazi ca 500 km east in nw china hp complexes and implies similar collision histories at the south tianshan suture to the east and west of the talas fergana fault tff the exhumation of the kmc and atbashi hp complexes overlaps with the initiation of the tff rolland et al 2013 suggesting incipient separation of the chatkal and atbashi complexes during rock exhumation and early plate collision

shallow structure of the landers fault zone from explosion generated trapped waves with fault zone trapped waves generated by near surface explosions within the fault zone of the 1992 landers california earthquake and recorded by linear seismic arrays deployed along and across the fault we have delineated the shallow seismic structure near the 30 km long southern rupture on the johnson valley fault the explosion excited trapped waves with relatively large amplitude and long duration wave train after the s waves are similar to those generated by aftershocks li et al 1994a b but have lower frequencies and travel more slowly coda normalized amplitude spectra of explosion excited trapped waves show a maximum at 2 hz which decreases rapidly with the station offset from the fault trace on the cross fault profiles normalized amplitudes of trapped waves on the along fault profile also decreased with distance between the explosion and station giving an apparent q of 18 at 1 2 hz in the fault zone for the shot near the profile the dispersion of trapped waves from 0 6 to 2 5 hz recorded on this along fault profile implies a shear velocity of 1 0 km s for the fault zone and 1 8 km s for the wall rock while the data from the farther shot show an increase in velocity and q with depth measured group velocities and q values were used as constraints in the numerical modeling of trapped waves on cross fault and along fault profiles results reveal that the shallow johnson valley fault is marked by a zone 250 m wide where the shear velocity is 1 km s and q is 20 calculation of finite difference synthetics for a depth varying fault structure show that these model parameters apply to the depth of 1 km below which the fault zone shear velocity increases to 1 9 km s and q increases to 30

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

seismic channel waves in the accretionary prism of the middle america trench a visual examination of seismograms of earthquakes located near the middle america trench and recorded on vbb seismographs along the pacific coast of mexico when bandpass filtered between 6 and 30 s shows the presence of two types of waves the first is a short pulse and the second is a dispersed wavetrain the first type of wave is quickly attenuated while the second type propagates without significant attenuation we applied a frequency mime analysis to identify the nature of these waves a comparison of period group velocity diagrams for signals recorded on different stations shows that the first arrival is a rayleigh wave propagating in the continental plate while the second one propagates along the trench in the thickened sediment wedge of the accretionary prism we have also measured group velocities of rayleigh wave propagating in the cocos plate far from the coast at periods between 15 and 20 s the group velocities of the wave propagating along the trench are lower than the velocity of rayleigh waves propagating in adjacent continental and oceanic plates we conclude that the dispersed wavetrain observed near the coast is a wave trapped in a channel formed by low velocity sediments of the accretionary prism

three dimensional calculations of fault zone guided waves in various irregular structures summary the detailed structure of fault zones fzs plays an important role in problems related to fault mechanics earthquake rupture wave propagation and seismic hazard fzs are thought to consist of an o 10 100 m wide region of decreased seismic velocity but structural details such as their depth extent lateral and vertical variations etc are elusive the small spatial scales involved make such structures difficult to image with ray theoretical methods such as tomography however seismic energy trapped inside fz layers can provide dispersive wave trains that carry information on the fz structure these waves can travel many kilometres inside the fz before reaching the surface and are therefore strongly altered by its properties candidate trapped waves have been observed above several active faults inversion algorithms exist that can model these observations in terms of planar fault zone structures however at present it is not clear how reliable these estimates are as the effects of even small 3 d variations on trapped waves are not well understood the goal of this study is to distinguish 3 d structures that do and do not significantly affect fz waves to achieve this we perform numerical calculations of wave propagation in various fz geometries and analyse the waveforms spectra and envelopes of the synthetic seismograms the main results are that 1 moderate changes of the shape of fz or 2 small scale heterogeneities or 3 depth dependent properties do not strongly affect the observed fz waves in contrast strong effects are to be expected from 4 breaks in the continuity of fz structure e g offsets which may at some point allow imaging of such features at depth

rupture history of the 1984 morgan hill california earthquake from the inversion of strong motion records near source strong motion velocity records and teleseismic short period p waveforms are modeled to obtain the spatial and temporal distribution of slip for the 1984 morgan hill earthquake both forward modeling and constrained least squares inversion techniques are used to interpret the strong motion velocity waveforms in the frequency range of approximately 0 2 to 2 0 hz these data support a nearly unilateral rupture to the southeast with a rupture propagation velocity of nine tenths of the local s wave velocity the majority of the slip occurs over a fault length of 25 km and to a first approximation can be interpreted as two main source regions each with an extent of about 5 km with their centers separated by about 12 km however each of the sources has detailed structure of its own and a simple two point source model is not an accurate representation of the morgan hill earthquake the second source occurs about 4 5 sec after the first and is approximately 3 times larger the maximum dislocation on the fault plane is about 1 m the total moment of the earthquake is estimated to be 2 1 10 25 dyne cm the morgan hill earthquake offers convincing evidence for very inhomogeneous slip and stress distributions on shallow strike slip faults

3d eight order elastic finite difference modeling of refraction and strong motion data from the coyote lake region california abstract 3d elastic modeling of vertical component explosive source refraction data is performed to constrain the shallow part of a velocity model followed by 3d modeling of three component strong motion data from a spatially and temporally extended earthquake source in that model modeling is by eighth order finite differencing on a staggered grid which automatically generates all body and surface waves including multiples and conversions application is to the 1981 usgs refraction survey and the 6 august 1979 coyote lake event in central california 3d modeling was able to reproduce the main observed features in both the refraction and earthquake data for the refraction data the synthetics explain local variations in first arrival travel times reverberations in the near surface sediments and surface waves for the strong motion data the initial arrival times and amplitudes are determined by the position and orientation of the initial rupture the shapes of the trailing edges of the pulses are modified by the actual source distribution changes of source position of 1 to 2 km are easily resolvable through changes in the position of nodal planes discontinuities in material properties e g layering produce a coda of multiples and converted waves lateral variations in velocities especially in the upper few kilometers change the energy distribution among the trace components by 3d refraction and so shift the apparent source directivity and position as well as contributing to the coda remaining differences between the observed and synthetic data are attributed to local seismometer coupling effects very local site structures and phenomena such as anelasticity and anisotropy which are not explicitly modeled

modeling of short period surface wave propagation in southern california abstract for the 1992 landers mainshock the lateral heterogeneity of the lithosphere combined with an extended earthquake source may account for the complexity of the strong motion observations that cannot be easily interpreted by a simplified point source model in a laterally homogeneous medium both the effect of an extended source and that of lateral heterogeneity are examined using a forward modeling technique that combines distributed nonuniform slip on a fault plane in a 3d medium surface wave synthetics are constructed using surface wave gaussian beam method which allows for a mild degree of lateral heterogeneity we analyze the amplitude and waveform data of the landers strong motion recordings in southern california in order to identify the path effects and the effect of an extended source the overall source parameters of the landers earthquake are obtained by comparing synthetics with recordings at near source stations which lie within relatively homogeneous path structures this procedure yields a unilateral rupture propagating northwesterly over two distinct rupture segments with somewhat different focal mechanisms the surface wave phase velocity map is modified to fit the data recorded at larger hypocentral distances the final improved model generates a very good agreement between observations and synthetics in the presence of lateral heterogeneity the focusing defocusing and multipath interference are found to contribute significantly to the strong motion shaking in a 3d basin

seismic measurements of the internal properties of fault zones the internal properties within and adjacent to fault zones are reviewed principally on the basis of laboratory borehole and seismic refraction and reflection data the deformation of rocks by faulting ranges from intragrain microcracking to severe alteration saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity but from borehole measurements densely fractured rocks do show significantly reduced velocities the amount of reduction generally proportional to the fracture density highly fractured rock and thick fault gouge along the creeping portion of the san andreas fault are evidenced by a pronounced seismic low velocity zone lvz which is either very thin or absent along locked portions of the fault thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone high pore pressure within the pronounced lvz may be conductive to fault creep deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated seismically anisotropic mylonites

spatial variability and non linearity of strong ground motion near a fault summary we present observations of ground accelerations recorded at a small array close to the fault during the duzce earthquake and its early aftershocks the records show the strong spatial variability of ground acceleration over distances of only a few hundred metres during the main shock the peak horizontal acceleration values ranged from 0 3 to about 1 0 g at stations distant of 1 5 km only we attribute this spatial variability to a fault zone site effect as peak ground acceleration steadily increases as the distance to the fault trace decreases the spectral ratio between the ground motion recorded near the fault and the one outside the fault zone shows a shift of the spectral peak to lower frequencies with increasing peak accelerations such an observation suggests a non linear behaviour of the fault zone due to the strong ground shaking as much as a 45 per cent reduction in the shear wave velocity is necessary for the observed shifts the opening of pre existing cracks throughout the fault zone is the proposed mechanism to account for the observed shear wave reductions the observation that elastic fault zone properties are soon recovered following episodes of large strains shows that cracks and fissures close rapidly after the strong shaking is over

can seismic waves be trapped inside an inactive fault zone the case study of nocera umbra central italy in march 1998 a small aperture 350 m linear array of five broadband stations was installed across a pliocene strike slip fault crossing the town of nocera umbra central italy three component seismograms of local earthquakes recorded during the umbria marche seismic sequence have shown that the degradation of mechanical properties in damaged rock causes a significant amplification of ground motion within the fault zone marra et al 2000 during the operation of the array an m w 5 3 subcrustal earthquake occurred at a depth of 48 km and an epicentral distance of 10 km from nocera umbra the near vertical incidence of this event offers a unique opportunity for constraining the 2d geometry of the laterally heterogeneous low velocity structure responsible for the large amplification across the fault based on the observed symmetry of the amplification pattern a 2d wedge shaped model of the fault zone is used for the computation of antiplane sh synthetic waveforms to be compared with observations along the array two parameters of the wedge model can be constrained by independent geophysical and geological data 1 shear wave velocity in pristine rock outside the fault zone v s 2200 m sec and 2 the lateral extent of the damaged rock zone l 160 m the other two model parameters namely the wedge depth h and shear wave velocity of the fault zone v f s are varied computer simulations show that trapped waves which have been observed so far for earthquakes occurring inside the fault zone can develop inside a 2d wedge model when struck by external vertically incident seismic radiation results of numerical modeling indicate that in spite of its extreme simplicity such an idealized model is successful in reproducing many of the essential characters of ground motion within the fault zone of nocera umbra even though the best fit solution is not unique and the model parameters trade off each other a study of parameter sensitivity comparing synthetics with recorded data indicates that the variability of h and v f s can be restricted to a limited range of values the quality of fit is optimal when the shear velocity reduction lies in the range of 40 50 and the depth of the trapping zone is comprised between 1 and 2 km

ground motion modeling of the 1906 san francisco earthquake part i validation using the 1989 loma prieta earthquake we compute ground motions for the beroza 1991 and wald et al 1991 source models of the 1989 magnitude 6 9 loma prieta earthquake using four different wave propagation codes and recently developed 3d geologic and seismic velocity models in preparation for modeling the 1906 san francisco earthquake we use this well recorded earthquake to characterize how well our ground motion simulations reproduce the observed shaking intensities and amplitude and durations of recorded motions throughout the san francisco bay area all of the simulations generate ground motions consistent with the large scale spatial variations in shaking associated with rupture directivity and the geologic structure we attribute the small variations among the synthetics to the minimum shear wave speed permitted in the simulations and how they accommodate topography our long period simulations on average under predict shaking intensities by about one half modified mercalli inten sity mmi units 25 35 in peak velocity while our broadband simulations on average under predict the shaking intensities by one fourth mmi units 16 in peak velocity discrepancies with observations arise due to errors in the source models and geologic structure the consistency in the synthetic waveforms across the wave propagation codes for a given source model suggests the uncertainty in the source parameters tends to exceed the uncertainty in the seismic velocity structure in agree ment with earlier studies we find that a source model with slip more evenly distributed northwest and southeast of the hypocenter would be preferable to both the beroza and wald source models although the new 3d seismic velocity model improves upon previous velocity models we identify two areas needing improvement nevertheless we find that the seismic velocity model and the wave propagation codes are suitable for modeling the 1906 earthquake and scenario events in the san francisco bay area online material modified mercalli intensities and velocity waveforms and a movie of simulated wave propagation