the modi taung nankwe gold district slate belt central myanmar mesothermal veins in a mesozoic orogen abstract the recently discovered quartz gold veins comprising the modi taung nankwe gold district in central myanmar are largely hosted by mudstones of the late palaeozoic slate belt mesozoic rocks of the paunglaung mawchi zone separate the slate belt from the shan scarp and shan plateau to the east at modi taung 5 km of exploration adits indicate that the veins within steeply dipping oblique reverse slip shear zones are displaced by movements along the shears intruded by late jurassic calc alkaline dykes and offset on conjugate cross faults drill intercepts show that mineralization extends vertically for more than 500 m coarse visible gold book and ribbon texture and stylolitic laminations and trace metal values are consistent with mineralization at mesothermal depths of several kilometres in the brittle ductile regime our field observations suggest that mineralization took place in the early jurassic following collision of myanmar on the passive western margin of a greater shan thai continental block with an oceanic arc on the overriding plate to the west collision generated intra continental thrusting in and east of the paunglaung mawchi zone metamorphism of plateau rocks thrust west beneath the slate belt to form the mogok metamorphics and ascent of mineralizing fluids expelled from dehydrating underthrust rocks reversal in orogenic polarity initiated late jurassic eastward subduction of oceanic crust beneath myanmar and generation of a magmatic arc with dykes cutting the quartz gold veins renewed east directed thrusting translated the slate belt over arc clastics and probably resulted in exhumation of the mogok metamorphics and offsets of the veins on conjugate faults young k ar rb 87 sr 86 and ar 40 ar 39 ages on the mogok metamorphic belt imply renewed tertiary uplift and possibly intrusion of mid tertiary or palaeogene granites

the influence of pore pressure and confining pressure on dynamic elastic properties of berea sandstone compressional and shear wave velocities of watersaturated berea sandstone have been measured as functions of confining and pore pressures to 2 kbar the velocities measured by the pulse transmission technique were obtained at selected pressures for the purpose of evaluating the relative importance of confining pressure and pore pressure on elastic wave velocities and derived dynamic elastic constants changes in berea sandstone velocities resulting from changes in confining pressure are not exactly canceled by equivalent changes in pore pressure for properties that involve significant bulk compression compressional wave velocities and bulk modulus an incremental change in pore pressure does not entirely cancel a similar change in confining pressure on the other hand it is shown that a pore pressure increment more than cancels an equivalent change in confining pressure for properties that depend significantly on rigidity shear wave velocity and poisson s ratio this behavior as well as observed

control of rupture by fault geometry during the 1966 parkfield earthquake a reanalysis of the available data for the 1966 parkfleld california earthquake mr 5 suggests that although the ground breakage and aftershocks extended about 40 km along the san andreas fault the initial dynamic rupture was only 20 to 25 km in length the foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault detailed analysis of the p wave first motions from these events at the gold hill station 20 km southeast indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at parkfield analysis of the strong motion records suggests that the rupture stopped at another discontinuity in the fault plane an en echeion offset near gold hill that lies at the boundary on the san andreas fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred foreshocks to the 1857 earthquake occurred in this area sieh 1978 and the epicenter of the main shock may have coincided with the offset zone if it did a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do

the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

true tracks undertracks and eroded tracks experimental work with tetrapod tracks in laboratory and field abstract to be able to distinguish between true tracks undertracks and tracks altered by erosion is of great importance in tetrapod track ichnotaxonomy this paper reports three experimental approaches to the study of undertracks using the footprints of an emu dromaius novaehollandiae experiment 1 describes successive horizontal sections down through a plaster cast of an emu footprint emplaced in soft mud revealing a steady downward decrease in the area of the track particularly the length this is the result of the movements of the trackmaking limb during impact forward swing of the body and final kick off experiments 2 and 3 describe vertical sections cut through footprints emplaced in packages of layered coloured cement admixed with water to produce different consistencies firm and semi fluid after hardening the cement block was serial sectioned vertically and removal of a lightly cemented layer gave access to two undertrack bedding plane views successive undertracks downward show an increase in horizontal dimensions and decrease in vertical topography of the structure representing gradual degradation of the track anatomy with depth in experiment 3 the true track at the tracking surface was deformed by collapse and flow of the substrate after withdrawal of the foot in this case the undertracks that were formed in layers subjacent to the foot reproduced the morphology of the foot more faithfully than did the true track

joint inversion for vp vs and vp vs at safod parkfield california we refined the three dimensional 3 d vp vs and vp vs models around the san andreas fault observatory at depth safod site using a new double difference dd seismic tomography code tomoddps that simultaneously solves for earthquake locations and all three velocity models using both absolute and differential p s and s p times this new method is able to provide a more robust vp vs model than that from the original dd tomography code tomodd obtained simply by dividing vp by vs for the new inversion waveform cross correlation times for earthquakes from 2001 to 2002 were also used in addition to arrival times from earthquakes and explosions in the region the vp values extracted from the model along the safod trajectory match well with the borehole log data providing in situ confirmation of our results similar to previous tomographic studies the 3 d structure around parkfield is dominated by the velocity contrast across the san andreas fault saf in both the vp and vs models there is a clear low velocity zone as deep as 7 km along the saf trace compatible with the findings from fault zone guided waves there is a high vp vs anomaly zone on the southwest side of the saf trace that is about 1 2 km wide and extends as deep as 4 km which is interpreted to be due to fluids and fractures in the package of sedimentary rocks abutting the salinian basement rock to the southwest the relocated earthquakes align beneath the northeast edge of this high vp vs zone we carried out a 2 d correlation analysis for an existing resistivity model and the corresponding profiles through our model yielding a classification that distinguishes several major lithologies

3 d p wave velocity structure in western greece determined from tomography using earthquake data recorded at the university of patras seismic network patnet the 3 d p wave velocity structure of the upper crust in the region of western greece is investigated by inversion of about 1500 residuals of p wave arrival times from local earthquake data recorded in the year 1996 by the newly established university of patras seismic network patnet the resulting velocity structure shows strong horizontal variations due to the complicated structure and the variation of crustal thickness relatively low velocity contours are observed in the area defined by cephallonia zakynthos islands and northwestern peloponnesos this is in addition to some well localized peaks of relatively higher values of p wave velocity may be related to the zone of triassic evaporites in the region and correspond to diapirism that breaks through to the uppermost layer finally a low p velocity deeping zone extending from zakynthos to the gulf of patras is correlated with bouguer anomaly map and onshore and offshore borehole drillings which indicate that thick sediments overly the evaporites which exist there at depth greater than 2 km

deep burial of asian continental crust beneath the pamir imaged with local earthquake tomography an inclined zone of intermediate depth seismicity beneath the pamir orogen in central asia has been interpreted as southward subduction of a slab of asian lithosphere however it is not known whether asian lithosphere subducts intact or only partially we used arrival times of shallow and intermediate depth earthquakes recorded with a temporary 2008 2010 seismic network in this region to invert for 3d models of seismic velocities in an attempt to answer this question with local seismicity reaching depths of up to 240 km the deep structure of the pamir could be illuminated with high resolution the resulting velocity models show a north south contrast in crustal seismic velocities in the pamir with very low p velocities 5 7 5 9 km s at 15 30 km depth coupled with relatively low vp vsvp vs 1 70 at mid crustal levels in the southern part of the orogen at sub moho depths we image an arcuate high velocity 8 2 8 6 km s slab dipping south in the eastern pamir and east in the pamir s southwest underlying the intermediate depth earthquakes on top of the high velocity slab and just above the onset of deep seismicity between a depth of 60 to 100 km very low compressional wavespeeds around 7 1 km s and high vp vsvp vs ratios 1 80 attest to subducted crustal rocks additionally we carried out 2d numerical thermomechanical modeling of the continental collision in the pamir focusing on the fate of the crust and mantle lithosphere of the asian and indian plates seismic velocities were computed from the modeling results and the resulting images were compared with the velocity distributions obtained from seismic traveltimes combining tomography and modeling results we infer that a substantial amount of crustal material is pulled down beneath the pamir by cold mantle lithosphere to depths of at least 80 100 km from there on only lower crust and mantle lithosphere continue their subduction and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions the buoyant asian upper and middle crust does not penetrate deeper into the mantle but pools at this depth level from where it might eventually exhume or relaminate

late cretaceous ornithopod dominated theropod and pterosaur track assemblages from the nanxiong basin china new discoveries ichnotaxonomy and paleoecology re examination of the late cretaceous yangmeikeng tracksite in the zhutian formation nanxiong group near nanxiong guangdong province china has led to the documentation of over 30 vertebrate tracks the track assemblage is dominated by large and small ornithopod tracks the larger ornithopod tracks have been assigned to hadrosauropodus nanxiongensis and hadrosauropodus isp indet the smaller ornithopod tracks are consistently incomplete showing only three pes digit traces without heel or manus impressions for this reason the smaller tracks probably represent pes tracks penetrating from a higher layer and therefore have not been assigned to any particular ichnotaxon previous photography at yangmeikeng site confirms the presence of at least one small wupus like theropod track and a pteraichnus like pterosaur pes track large enigmatic didactyl tracks could be of deinonychosaurian affinity but are more likely the poorly preserved prints of a tridactyl theropod trackmaker the nanxiong dinosaur tracks and skeleton records represent the most important and diverse ichnofauna from upper cretaceous strata of south china and can be compared with the shandong and heilongjiang late cretaceous faunas the composition of the ichnofauna is significant because it reflects a diverse tetrapod community with hadrosaurs avian theropods non avian theropods and pterosaurs a co occurrence not evident from the skeletal record of this region from a global perspective this assemblage permits a unique insight into archosaur communities and interaction of animals in a typical late cretaceous lakeshore environment non avian theropods may have been attracted by the other groups that were considered as a potential prey

new didactyl dinosaur footprints dromaeosauripus hamanensis ichnogen et ichnosp nov from the early cretaceous haman formation south coast of korea abstract didactyl dinosaur footprints in fine grained sandstone of the early cretaceous haman formation namhae area korea are herein described the tracks are 15 cm long and 9 0 cm wide and consist only of impressions of digits iii and iv which show well developed pad impressions digit impressions are narrow about 2 0 cm and terminate in sharp claw traces trackway width is very narrow about 10 0 cm step length is about 92 cm and stride is about 185 cm pace angulation is about 180 i e consecutive tracks are nearly in a straight line the tracks are thought to have been made by a dromaeosaurid characterized by a strongly recurved pes digit ii that did not register on the substrate the didactyl trackway is attributed to a small dromaeosaurid deinonychosauria running bipedally with a speed of 17 5 km h on a lake margin the didactyl tracks described herein as dromaeosauripus hamanensis ichnogen et ichnosp nov represent only the fourth convincing record of didactyl tracks attributable to a member of the deinonychosauria in the world and the first in korea the report also provides significant information about the hip height body size foot morphology walking or running speed paleoecology and paleogeography of dromaeosaurids that flourished during the early cretaceous in northeast asia

detecting hazardous new zealand faults at depth using seismic velocity gradients abstract many large damaging earthquakes occur along previously unmapped faults because it is difficult to locate active faults that have slow average slip rates long recurrence intervals and weak surface expression we use recently collected seismic wave velocity data from new zealand to test whether there is a strong correlation between seismic velocity gradients deep in the earth s crust known active faults and large shallow historical earthquakes the correlation with active faults is significant at the 99 confidence level suggesting that seismic velocity gradients at depth can pinpoint active and in some cases unmapped faults that may reactivate and rupture in infrequent earthquakes in addition all eight of the post 1840 m w 7 upper crustal earthquakes in new zealand within the region of good tomographic coverage are spatially correlated with mid crustal seismic velocity gradients and ruptured faults that intersect them many of the seismic velocity gradients coincide with the faulted edges of strong blocks within basement rocks consistent with these marking preferred sites for fault reactivation owing to inherited strength contrasts we propose that seismic velocity gradients provide a means to map potentially hazardous undiscovered faults at mid crustal depths in advance of their activation in future damaging earthquakes

fault damage zones of the m7 1 darfield and m6 3 christchurch earthquakes characterized by fault zone trapped waves abstract to characterize the subsurface structure of the damage zones caused by the 2010 2011 canterbury earthquake sequence in new zealand s south island we installed two short linear seismic arrays array 1 across the greendale fault gf surface rupture and array 2 over the surface projection of the blind port hills fault phf that ruptured in the 2010 m7 1 darfield and 2011 m6 3 christchurch earthquakes respectively we recorded 853 aftershocks for 4 months after the christchurch earthquake fault zone trapped waves fztws identified at array 1 for aftershocks occurring on both the gf and the phf show that the post s durations of these fztws increase as focal depths and epicentral distances from the array increase suggesting an effective low velocity waveguide formed by severely damaged rocks existing along the gf and phf at seismogenic depths locations of aftershocks generating prominent fztws delineates the subsurface gf rupture extending eastward as bifurcating blind fault segments an additional 5 8 km beyond the mapped 30 km surface rupture into a zone with comparably lower seismic moment release west of the phf rupture which extends westward to within 5 3 1 km of the subsurface gf the propagation of fztw through the intervening gap indicates moderate gf phf structural connectivity we interpret this zone as a fracture mesh reflecting the interplay between basement faults and stress aligned microcracks that enable the propagation of phf sourced fztws into the gf damage zone simulations of observed fztws suggest that the gf rupture zone is 200 250 m wide consistent with the surface deformation width velocities within the zone are reduced by 35 55 with the maximum reduction in the 100 m wide damage core zone corresponding with surface and shallow subsurface evidence for discrete fracturing the damage zone extends down to depths of 8 km or deeper consistent with hypocentral locations and geodetically derived fault models

local high resolution passive seismic tomography and kohonen neural networks application at the rio antirio strait central greece a high resolution passive seismic investigation was performed in a 150 km 2 area around the rio antirio strait in centralgreeceusingnaturalmicroearthquakesrecordedduringthreemonthsbyadense temporaryseismicnetworkconsisting of 70 three component surface stations this work was part of the investigation for a planned underwater rail tunnel and it gives us the opportunity to investigate the potential of this methodology first 150 well located earthquake events were selected to compute a minimum 1d velocity model for the region next the 1d model served as the initialmodelfornonlinearinversionfora3dp ands velocity crustal structure by iteratively solving the coupled hypocenter velocity problem using a least squares method the retrieved vp and vp vs images were used as an input to kohonen self organizing maps soms to identify systematicallyandobjectively theprominentlithologiesintheregion soms are unsupervised artificial neural networks that map the input space into clusters in a topological form whose organization is related to trends in the input data this analysis revealed the existence of five major clusters one of which may be related to the existence of an evaporite body not shown in the conventional seismic tomography velocity volumes the survey results provide for the first time a 3d model of the subsurface in and around the rio antirio strait it is thefirst time that passive seismic tomography is used together with som methodologies at this scale thus revealing themethod spotential

estimation of effective anisotropy simultaneously with locations of microseismic events passive seismic tomography in which the event locations and the velocity model are inferred simultaneously is seldom used to process microseismic surveys acquired in the oil and gas industry we discuss advantages of applying tomographic ideas to typical microseismic data recorded in a single nearly vertical well to monitor hydraulic stimulation of a shale gas reservoir microseismic events are conventionally located in the energy industry applications using a velocity model derived from sonic logs and perforation shots instead of fixing the model as is normally done we alter it while locating the events this added flexibility not only makes it possible to accurately predict traveltimes of the recorded p and s waves but also provides a convincing evidence for anisotropy of the examined shale formation while we find that velocity heterogeneity does not need to be introduced to explain the data acquired at each stage of hydraulic fracturing the obtained models are suggestive of possible time laps

historic surface slip along the san andreas fault near parkfield california the parkfield earthquake prediction experiment is focusing close attention on the 44 km long section of the san andreas fault that last ruptured seismically in 1966 ms 6 0 the 20 km long central segment of the 1966 parkfield rupture extending from the mainshock epicenter at middle mountain southeastward to gold hill forms a 1 to 2 km salient northeastward away from the dominant n40 w strike following the 1966 earthquake afterslip aseismic slip has been nearly constant moderate parkfield earthquakes have recurred on average every 21 years since 1857 when a great earthquake m 8 ruptured at least as far north as the southern parkfield segment many measurements of slip have been made near parkfield since 1966 nevertheless much of the history of surface slip remained uncertain especially the total amount associated with the 1966 event in 1985 we measured accumulated slip on the four oldest cultural features offset by the fault along the 1966 parkfield rupture segment we interpret net slip on each feature as a sum of event slip sum of coseismic and rapid preseismic and postseismic slip from parkfield earthquakes and steady interseismic slip as measured over the last 20 years on nearby alinement arrays creep meters and trilateration lines we assumed for each site that event slip was identical for the 1922 1934 and 1966 parkfield events and that long term average rate of interseismic slip was constant between all events two fences on the southern segment southeast of gold hill indicate event slip of 13 and 15 cm and interseismic slip rate of 0 36 and 0 30 cm yr since 1959 and 1908 respectively at these sites redundant independent data support our assumption that both event and interseismic slip occur uniformly on the central segment near parkfield both the 1934 and the 1966 ruptures offset a bridge built in 1932 interseismic slip rate near the bridge has been about 1 1 cm yr since 1966 thus we deduce an average event slip of 31 cm for the 1934 and 1966 earthquakes on a parallel fault trace 1 km to the southwest slip was about 8 cm in 1966 thus total event slip summed across the entire fault zone near parkfield was nearly 40 cm on middle mountain 4 km north of the 1966 mainshock epicenter an offset fence indicates 17 cm of slip in 1966 and a 2 26 cm yr interseismic slip rate since circa 1946 thus the central segment of the 1966 rupture is characterized by much larger event slip 40 cm than both distal segments 15 cm this amount of surface slip per event is about twice what had been previously assumed larger 1966 surface slip in the central part of the rupture is geodetically compatible with a coseismic slip of 65 10 cm slip on a narrow buried asperity between middle mountain and gold hill that has been inferred from the depth distribution of early aftershocks assuming our characteristic surface slip model one can further deduce a deficit in slip since the great 1857 earthquake taking the long term slip rate as 3 3 cm yr the surface slip deficit is 3 0 2 m south of gold hill but only 0 3 0 3 m northward from parkfield

crustal structure in the area of the 2002 molise earthquake clues for the evolution of the southern apennines the apennines is a mountain belt with paired extension and compression that are explained by the subduction and delamination of the ionian adria lithosphere during the belt formation the adria crust is flexed downward and then incorporated into the wedge after peeling off along some weak level whose origin is still discussed in southern apennines this process seems to have stopped at about 0 7 ma by the development of a tear in the subducting lithosphere and consequent extension that spread along the mountain range seismological data acquired after the 2002 mw 6 0 molise strike slip earthquake yield modeling the structure of the adria crust as congealed close to the leading edge of the belt tomography images show inverted normal faults within the sedimentary cover apulian units fault inversion incomplete close to the compressional front testifies for a final squeezing of the entire previously flexed apulian continental margin pronounced high vp and low vp vs anomalies are observed at depth greater than 12 km and undoubtfully attributed to heterogeneities of the basement solving the long lasting contention on the nature of similar high speed bodies observed beneath the apennines beneath these bodies we observe a strong reflectivity suggesting the presence of a fluid filled layer in the middle lower crust that may act as a decoupling level in the apennines tectonics the deep fluids are also favoring the rupture of strike slip earthquakes like those that occurred in 2002 and the intermediate depth seismicity diffused in the apulian region

nucleation of rupture under slip dependent friction law simple models of fault zone the initiation of frictional instability is investigated for simple models of fault zone using a linearized perturbation analysis the fault interface is assumed to obey a linear slip weakening law the fault is initially prestressed uniformly at the sliding threshold in the case of antiplane shear between two homogeneous linearly elastic media space time and spectral solutions are obtained and shown to be consistent the nucleation is characterized by 1 a long wavelength unstable spectrum bounded by a critical wave number 2 an exponential growth of the unstable modes and 3 an induced off fault deformation that remains trapped within a bounded zone in the vicinity of the fault these phenomena are characterized in terms of the elastic parameters of the surrounding medium and a nucleation length that results from the coupling between the frictional interface and the bulk elasticity these results are extended to other geometries within the same formalism and implications for three dimensional rupture are discussed finally internal fault structures are investigated in terms of a fault parallel damaged zone spectral solutions are obtained for both a smooth and a layered distribution of damage for natural faults the nucleation is shown to depend strongly on the existence of a internal damaged layer this nucleation can be described in terms of an effective homogeneous model in all cases frictional trapping of the deformation out of the fault can lead to the property that arbitrarily long wavelengths remain sensitive to the existence of a fault zone

a detailed seismicity study of the middle mountain zone at parkfield california in order to better understand the preparation zone of the predicted parkfield earthquake a detailed study of the seismicity at middle mountain in the parkfield california area was made using 71 digitally recorded earthquakes that located within or close to the middle mountain alert box these earthquakes were retimed on an interactive graphics system based on these new arrival times new station corrections were developed however the data did not support changing the velocity model developed from refraction and 1966 aftershock data the process of retiming the earthquakes and using the new station corrections reduced the rms travel time residuals by 70 per cent to 0 025 sec halved the location errors and clustered the earthquakes closer to the surface trace of the san andreas fault the seismicity can be approximated by a plane on the scale of several kilometers but at finer scales two clusters were discovered that show demonstrable width to the seismogenic zone previous workers had proposed a 5 bend in the fault at the hypocenter of the 1966 main shock on the basis of patterns in the first motion data in the 1966 aftershocks we find that this pattern also exists in the first motion data from 1969 to 1987 but the 5 bend was not evident in the hypocentral distribution this suggests that a more complicated explanation is needed to explain the first motion data fault plane solutions were determined for the 71 events and 69 of these were compatible with strike slip motion on a vertical san andreas fault an event located in the north end of the study area co locates with the strike slip solutions and may be a thrust or oblique solution the other earthquake located 2 kilometers northeast of the fault has a thrust or nne ssw striking right lateral solution but can not be explained by a san andreas style mechanism both possible solutions can be explained by structures observed in the geology

crustal heterogeneity and subduction processes 3 d vp vp vs and q in the southern north island new zealand summary along the southern hikurangi subduction zone in the southern north island new zealand the subduction zone changes from volcanic with moderately weak interseismic coupling to non volcanic with strong coupling in wellington to investigate how material heterogeneity relates to subduction processes we compute 3 d seismic properties using 342 earthquakes and 2 shots recorded by a 165 station seismic array the time base for some telemetered temporary stations was not stable which required revising the inversion code to allow an additional origin time related to the telemetered stations progressive inversions from 2 d to fine 3 d were carried out for vp vp vs and qp combined interpretation of these three seismic properties highlights features of the subduction zone the subducted slab is imaged as a high velocity high q feature in the overlying crust from southeast to northwest there is low velocity in the accretionary wedge high velocity in the axial ranges and low velocity in the wanganui basin high vp vs and low qp characterize the crust east of the north island dextral fault belt high vp vs is imaged above the subducted slab to 40 km depth in the northern half of the study area low qp is also prominent above the slab particularly trenchwards of the volcanic region in marked contrast to the high vp vs the low qp above the slab extends as a continuous feature up to the low qp in the shallow crust underlying the volcanic region the low qp and high vp vs are correlated with the region of weaker coupling and are consistent with significant subducted sediments with associated fluid release vp vs is particularly sensitive to overpressured fluid in the compressional forearc whereas qp also images the hydrostatically pressured fluid transport in the more permeable extensional volcanic region the rheology of the lower crust of the overlying plate is a factor in large scale subduction coupling as evidenced by the terrane boundaries and haast schist in the section near wellington the changing rheology of the lower crust of the overlying plate in the southern north island also provides a possible explanation for the southward cessation of volcanism

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

high resolution passive seismic tomography for 3d velocity poisson s ratio ν and p wave quality qp in the delvina hydrocarbon field southern albania we have studied using traveltimes of p and s waves and initial seismic pulse rise time measurements from natural microearthquakes to derive 3d p wave velocity vp information mostly structural as well as p and s wave velocity vp vs and p wave quality factor qp information mostly lithologic in a known hydrocarbon field in southern albania during a 12 month monitoring period 1860 microearthquakes were located at a 50 station seismic network and were used to obtain the above parameters the data set included earthquakes with magnitudes ranging from 0 1 to 3 0 r richter scale and focal depths typically occurring between 2 and 10 km kohonen neural networks were implemented to facilitate the lithological classification of the passive seismic tomography pst results the obtained results which agreed with data from nearby wells helped delineate the structure of the reservoir two subregions of the investigated area one corresponding to an oil field and one to a gas field were correlated with the

intrusive mechanism of the 2008 2009 mt etna eruption constraints by tomographic images and stress tensor analysis abstract since january 2008 several geophysical parameters have evidenced a recharging phase at mt etna volcano culminating with an effusive eruption that began on may 13 2008 seismic activity recorded at mt etna from january 2007 to may 2008 was analyzed in order to provide seismological constraints to the volcano dynamics leading to the eruption a total of 336 selected earthquakes with m l 1 5 were used as data source for this study specifically we calculated 3d velocity and attenuation tomography including a 3d relocation of the events and we computed 53 selected fault plane solutions fpss that were used for stress tensor inversion the most important result obtained from the joint analysis of v p v p v s and p wave attenuation is an anomalous zone with normal to high v p values between 3 5 and 4 5 km s and low v p v s values 1 64 which partially overlaps with a low q p values 50 volume located along a ns trending channel beneath the central crater this can be interpreted as a shallow volume characterized by high temperature where the magma is located with the presence of supercritical fluids the analysis of seismic stress tensor evidenced an extensional regime in the depth range 3 13 km with a vertically oriented 1 this finding may suggest an extensional stress regime probably related to the kinematic response of the volcanic edifice to both a deep magmatic intrusion and a condition of decreased regional compressive stress facilitated by sliding processes of the eastern flank of the volcano

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

tetrapod track assemblages from lower cretaceous desert facies in the ordos basin shaanxi province china and their implications for mesozoic paleoecology tetrapod ichnofaunas are reported from desert playa lake facies in the lower cretaceous luohe formation at baodaoshili shaanxi province china which represent the first asian example of an ichnnofauna typical of the chelichnus ichnofacies brasilichnium sub ichnofacies characteristic of desert habitats the mammaliomorph tracks assigned to brasilichnium represent the first report of this ichnogenus from asia the assemblages also contain three different theropod trackway morphotypes one very wide magnoavipes like morphotype one relatively wide broad toed small eubrontes like form with short steps and strides and wide straddle and an elongate morphotype sarmientichnus with longer steps and narrower straddle representing a didactyl trackmaker the latter being the first example of the enigmatic ichnogenus found outside its type area in argentina the sarmientichnus occurrence the first in asia has important implications demonstrating that the trackmaker was not monodactyl but didactyl with probable affinities to deinonychosaurians which are ichnologically well represented in the lower cretaceous of asia although morphologically distinctive sarmientichnus should be recognized as a form ichnotaxon compromised by suboptimal preservation the combination of brasilichnium isp sarmientichnus isp and tridactyl theropod tracks indicates mammaliomoprhs and small theropods and is comparable to ichnofaunas from similar desert facies on other continents thus cretaceous desert ichnofaunas from china are consistent with global ichnofacies predictions

a three dimensional crustal velocity model of the southwestern alps from local earthquake tomography a temporary network of 65 short period seismological stations was installed in the southwestern alps during the second half of 1996 it complemented the permanent monitoring networks obtaining an average interstation distance of 10 km travel time data from 446 local earthquakes and 104 quarry blasts were inverted simultaneously for hypocenter parameters and three dimensional velocity structure the p wave velocity model displays strong lateral contrasts both at shallow and deeper levels a low velocity anomaly stands out at shallow depths beneath the digne and castellane nappes in the southwestern part of the investigated area farther east the monviso ophiolitic massif appears to have a much larger extension at depth than previously assumed the largest and strongest anomaly is located under the dora maira massif and the westernmost po plain it correlates with the well known ivrea body which is classically interpreted as a wedge of adriatic upper mantle at the best resolved depths 10 and 15 km it appears as a rather thin 10 to 15 km north south elongated high velocity 7 4 to 7 7 km s 1 anomaly with very sharp edges extending to the south as far as 10 km north of the surface trace of the frontal penninic thrust special care was taken with regard to the quantitative estimation of the resolution for the main anomalies using the inversion of synthetic travel time data

the southern tyrrhenian subduction zone deep geometry magmatism and plio pleistocene evolution abstract we report on a high resolution vp vp vs and qp model of the southern tyrrhenian subduction zone obtained by the inversion of p and s wave arrival times and t values from intraslab seismicity the arcuate shape of the southern apennines calabrian arc sicilian maghrebides is perfectly mirrored by two rather continuous low and high vp bands lying beneath the belt system at ca 25 and 100 km respectively between 100 and 300 km two independent high vp slabs lie beneath the neapolitan region and the southern tyrrhenian sea separated by unperturbed mantle we suggest that the ca 150 km wide slab window beneath the southern apennines opened after a tear occurring within a composite subduction system formed by the apulian continental lithosphere and the ionian oceanic slab the abrupt slab rupture induced ultrafast southeastward retreat of the ionian slab and the 19 cm yr spreading of the back arc oceanic marsili basin between ca 2 1 and 1 6 ma ago the 25 km low vp zone beneath the arc denotes continental upper crustal rocks below the chain its striking continuity requires a unique orogenic wedge at 25 km depth below the southern apennines the calabrian arc and the sicilian maghrebides the alternative explanation would imply the ubiquitous occurrence of autochthonous lower plate rocks at 25 km depth i e a puzzling autochthonous continental calabria the ionian slab beneath calabria shows high vp high qp and low vp vs anomalies typical of old oceanic lithosphere intermediate depth seismicity is concentrated within its thin oceanic crust suggesting the occurrence of vigorous metamorphism the slab dehydration promotes the melting of the overlying mantle as testified by high vp vs and low qp anomalies between the slab and the aeolian magmatic arc

a new species of troodontid theropod dinosauria maniraptora from the horseshoe canyon formation maastrichtian of alberta canada troodontid material from the maastrichtian of north america is extremely rare beyond isolated teeth from microvertebrate sites here we describe troodontid frontals from the early maastrichtian horseshoe canyon formation horsethief member the most complete specimen tmp 1993 105 0001 is notably foreshortened and robust when compared with numerous specimens referred to troodon from the dinosaur park formation and exhibits several characteristics that distinguish it from other late cretaceous troodontids morphometric analyses reinforce shape differences between tmp 1993 105 0001 and other north american troodontids and show that proportional differences are independent of size we therefore erect a new taxon albertavenator curriei gen et sp nov which is diagnosed by the following autapomorphies 1 primary supraciliary foramen is truncated anteriorly by the lacrimal contact 2 superficial ectocranial surface of the frontal proportionally shorter than all known troodontids with a length to

intrinsic qp seismic attenuation from the rise time of microearthquakes a local scale application at rio antirrio western greece we determine the attenuation structure of a three dimensional medium based on first pulse width measurements from microearthquake data ninety five microearthquakes from a seventy stations local network were considered in this study measurements of the first half cycle of the wave the so called rise time r were carried out on high quality velocity seismograms and inverted to estimate the p waves intrinsic quality factor q p the results of this investigation indicate that first pulse width data from a local microearthquake network permit retrieval with sufficient accuracy of the heterogeneous q p structure the inferred attenuation variability corresponds to the known geological formations in the region

strategy for automated analysis of passive microseismic data based on s transform otsu s thresholding and higher order statistics small magnitude seismic events either natural or induced microearthquakes have increasingly been used in exploration seismology with applications ranging from hydrocarbon and geothermal reservoir exploration to high resolution passive seismic tomography surveys we developed an automated methodology for processing and analyzing continuously recorded single channel seismic data this method comprised a chi squared based statistical test for microseismic event detection and denoising filtering in the stransform domain based on the otsu thresholding method an automatic p phase picker based on higher order statistics criteria was used the method was used with data from a surface seismic station the performance of the method was tested and evaluated on synthetic and real data from a microseismic network used in a high resolution pst survey and revealed a high level of consistency

seismic evidence for rock damage and healing on the san andreas fault associated with the 2004 m 6 0 parkfield earthquake we deployed a dense linear array of 45 seismometers across and along the san andreas fault near parkfield a week after the m 6 0 parkfield earthquake on 28 september 2004 to record fault zone seismic waves generated by aftershocks and explosions seismic stations and explosions were co sited with our previous exper iment conducted in 2002 the data from repeated shots detonated in the fall of 2002 and 3 months after the 2004 m 6 0 mainshock show 1 0 1 5 decreases in seismic wave velocity within an 200 m wide zone along the fault strike and smaller changes 0 2 0 5 beyond this zone most likely due to the coseismic damage of rocks during dynamic rupture in the 2004 m 6 0 earthquake the width of the damage zone characterized by larger velocity changes is consistent with the low velocity waveguide model on the san andreas fault near parkfield that we derived from fault zone trapped waves li et al 2004 the damage zone is not symmetric but extends farther on the southwest side of the main fault trace waveform cross correlations for repeated aftershocks in 21 clusters with a total of 130 events located at different depths and distances from the array site show 0 7 1 1 increases in s wave velocity within the fault zone in 3 months starting a week after the earthquake the velocity recovery indicates that the damaged rock has been healing and regaining the strength through rigidity recovery with time most likely due to the closure of cracks opened during the mainshock we estimate that the net decrease in seismic velocities within the fault zone was at least 2 5 caused by the 2004 m 6 0 parkfield earthquake the healing rate was largest in the earlier stage of the postmainshock healing process the magnitude of fault healing varies along the rupture zone being slightly larger for the healing beneath middle mountain correlating well with an area of large mapped slip the fault healing is most promi nent at depths above 7 km

prominent hill a hematite dominated iron oxide copper gold system the discovery of iron oxide copper gold iocg mineralization at prominent hill in the mount woods inlier south australia by minotaur resources ltd in november 2001 was based on an empirical exploration model that focused specifically on the hematite end member of the iocg ore deposit model type copper and gold bearing hematite rich breccias formed by repetitive hydrothermal brecciation milling and explosive venting within a volcanic setting high pressure spalling chemical corrosion of breccia clasts and compositional layering within the breccias are distinctive features iron oxide sericite silica alteration is pervasive within and marginal to the main breccias and is surrounded by a wider zone of less intense alteration iron copper gold barium fluorine uranium cerium and lanthanum are strongly correlated and associated with a relatively low temperature hydrothermal system mineralization was synchronous with volcanism and sedimentation within a narrow east west trending graben that developed at 1585 ma

stratigraphy of the danek bonebed upper cretaceous horseshoe canyon formation central alberta and correlations with strata in the drumheller and grande prairie regions although considerable work has been conducted on the stratigraphy and dinosaur assemblages of the horseshoe canyon formation of southern alberta equivalent strata and assemblages in central alberta remain poorly understood data from the danek bonebed edmonton alberta are beginning to fill this gap the bonebed occurs 4 m above the 9 big island coal seam this stratigraphic position lies just below the middle of the horseshoe canyon formation in the edmonton region and also lies below a thick stratigraphically significant non coaly interval that is expressed throughout central and southern alberta the stratigraphic position of the danek bonebed equates best with the uppermost horsethief member of the horseshoe canyon formation in the drumheller region and the upper part of unit 4 of the wapiti formation in the grande prairie region in both drumheller and grande prairie the correlated position of the bonebed underlies a zone of marine transgression drumheller marine tongue which in turn incl

thrust top basin formation along a suture zone cantwell basin alaska range implications for development of the denali fault system the cantwell formation consists of a lower sedimentary sequence as much as 4000 m thick and an upper volcanic sequence with a maximum thickness of 3750 m that was deposited in the cantwell basin south central alaska previous to this study the cantwell basin was interpreted as a paleogene nonmarine mainly fluvial pull apart basin that formed in response to dextral strike slip displacement on the denali fault system this study proposes that the cantwell basin formed as part of the mesozoic accretionary phase of deformation prior to the development of the cenozoic postaccretionary denali fault system our reinterpretation is based on several new lines of data 1 age new data based on palynologic analyses of 135 fine grained samples indicate that the lower cantwell formation was deposited during the late campanian and early maastrichtian on the basis of previous regional tectonic studies and this new age constraint the formation of the cantwell basin was coeval with regional late cretaceous shortening associated with accretionary tectonics in southern alaska 2 depositional systems our analysis of the cantwell formation demonstrates that sedimentation occurred mainly in stream dominated alluvial fan axial braided stream and lacustrine settings these depositional systems were strongly influenced by a southward dipping asymmetric basin floor the presence of abundant terrestrially derived organic material together with palynological assemblages that include marine dinoflagellates and the associated presence of oncolites may be suggestive of a time of marginal marine influence during the deposition of the upper part of the lower cantwell formation the late campanian to early maastrichtian timing of this possible marine influence is within the range of the bearpaw transgressive event of the cordilleran foreland basin and allows for regional stratigraphic correlation of the cantwell basin with other sedimentary basins in northwestern north america 3 structural controls on basin formation mapping of intraformational angular unconformities and progressively tilted strata along the southern margin of the cantwell basin provides direct evidence that thrust fault deformation and lower cantwell formation sedimentation were synchronous distinctive cantwell formation conglomerate clasts derived from the uplifted hanging walls of nearby thrust sheets adjacent to the southern basin margin also support a syndepositional thrusting interpretation provenance data and the concentration of proximal alluvial fan deposits along the northwestern basin margin adjacent to the hines creek fault indicate that it too was active during deposition of the cantwell formation on the basis of the new data the cantwell basin is interpreted to have formed as a thrust top basin i e piggyback basin along the late cretaceous suture zone between the accreting wrangellia composite terrane and the north american continental margin in contrast to previous studies this reinterpretation of the formation of the cantwell basin implies that the lower cantwell formation is not a synorogenic deposit directly associated with strike slip displacement along the denali fault system therefore the cantwell basin cannot be used to constrain the timing for the early development of the denali fault system

geophysical properties within the san andreas fault zone at the san andreas fault observatory at depth and their relationships to rock properties and fault zone structure 1 we examine the relationships between borehole geophysical data and physical properties of fault related rocks within the san andreas fault as determined from data from the san andreas fault observatory at depth borehole geophysical logs cuttings data and drilling data from the region 3 to 4 km measured depth of the borehole encompass the active part of the san andreas fault the fault zone lies in a sequence of deformed sandstones siltstone shale serpentinite bearing block in matrix rocks and sheared phyllitic siltstone the borehole geophysical logs reveal the presence of a low velocity zone from 3190 to 3410 m measured depth with vp and vs values 10 30 lower than the surrounding rocks and a 1 2 m thick zone of active shearing at 3301 3303 m measured depth seven low velocity excursions with increased porosity decreased density and mud gas kick signatures are present in the fault zone geologic data on grain scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data in places vp and vs increase with grain scale deformation and alteration and decrease with porosity in the fault zone the low velocity zone is associated with a significant lithologic and structural transition to low velocity rocks dominated by phyllosilicates and penetratively foliated sheared rocks the zone of active shearing and the regions of low sonic velocity appear to be associated with clay rich rocks that exhibit fine scale foliation and higher porosities that may be a consequence of the fault related shearing of foliated and fine grained sedimentary rocks

a three dimensional qp imaging of the shallowest subsurface of campi flegrei offshore caldera southern italy to improve the knowledge of the shallowest subsurface of campi flegrei caldera a 3 d p wave attenuation tomography of the area was performed we analyzed about 18 000 active seismic traces which provided a dataset of 11 873 t measurements e g the differential traveltimes to quality factor ratios these were inverted through an adapted tomographic inversion procedure the 3 d tomographic images reveal an average qp about 70 interpreted as water saturated volcanic and marine sediments an arc like low qp structure at 0 5 1 km depths was interpreted as a densely fractured fluid saturated rock volume well matching the buried rim of campi flegrei caldera the spatial distribution of high and low qp bodies in the inner caldera is correlated with low vp values and may reflect either the differences in the percentage of fluid saturation of sediments or the presence of vapor state fluids beneath fumaroles manifestations

three dimensional attenuation model of the shallow hikurangi subduction zone in the raukumara peninsula new zealand 1 the material properties of the shallow subduction zone are imaged with data from a passive seismic deployment in the raukumara peninsula attenuation images are obtained using t values measured from 2848 spectra of p wave arrivals the t values are inverted for frequency independent three dimensional 3 d qp using a 3 d velocity model linked nodes in a preliminary 2 d inversion are used to obtain the most reliable initial model for 3 d inversions the results show the benefits of obtaining 3 d q in addition to 3 d vp and vp vs q is related to localized permeability and heterogeneity and thus 3 d q is an important tool for interpreting active tectonic regions qp in the shallow overlying plate generally corresponds to the mapped geology two high qp features 600 represent subducted seamounts or cretaceous volcanics within the overlying plate the gradient above the subducting plate is the strongest feature in the qp model with the slab having high qp 600 900 below 20 km depth and above the plate interface there is a zone of 50 decrease in qp and high vp vs about 10 km thick which represents actively subducting sediment and has distributed microearthquake activity associated with active underplating

velocity structure and seismicity of southeastern tennessee the seismic zone in southeastern tennessee is at the confluence of major crustal features which have been interpreted largely from potential data and their relation to seismicity could help us understand why major earthquakes sometimes occur in the eastern united states in this paper we solve for the previously unknown velocity structure of the upper crust by an inversion of travel time residuals from relocated earthquakes the gravity anomalies are included by using a linear relation between average anomalous density and average anomalous velocity the velocity model demonstrates that the seismicity is concentrated in areas of average to below average velocity and does not appear to be associated with one of the previously identified major crustal features the high velocity zones mark areas that are generally lacking in seismicity the association of earthquake hypocenters with regions of low velocity crustal rocks is consistent with other intraplate seismic zones and this association supports the conjecture that intraplate earthquakes occur in crust that may have been weakened the velocity anomalies at midcrustal depths do not support the new york alabama ny al lineament as a linear feature extending through southeastern tennessee and parallel to contours in gravity anomalies as originally proposed a continuation of the ny al lineament to the southwest requires either a 15 degree southwestward change in direction or a displacement to be consistent with the velocity anomalies the seismically active areas in southeastern tennessee do not appear to be constrained by the major crustal features but instead the seismicity is characterized by the distribution of hypocenters and their association with low velocity regions at midcrustal depths

northern california seismic attenuation 3d qp and qs models the geological complexity of northern california and its accreted terranes produces pronounced regional variations in the attenuation 1 q of earthquake waves using local earthquakes 3d q p and q s models have been obtained for this region that includes the san andreas fault system the great valley the sierra nevada batholith and the gorda subduction volcanic system path attenuation t values were determined from p and s spectra of 959 spatially distributed earthquakes magnitude 2 5 6 0 using 1254 stations from northern california earthquake data center networks and mendocino and sierra nevada temporary arrays the t data were used in q inversions using existing 3d velocity models and basic 10 km node spacing uneven data coverage was accommodated with linking nodes into larger areas for useful q images across the 3d volume results at shallow depth show very low q in the sacramento delta the eureka area and parts of the san francisco bay area in the brittle crust low q tends to be associated with regions of fault zones and microearthquakes in the ductile lower crust low q is observed below fault zones with large cumulative displacement and inferred grain size reduction with apparent broad ductile shear zones across the fault system in the coast ranges underlying active arc volcanoes low q features are apparent below 20 km depth under the long valley caldera two distinct partial melt features at 3 and 15 km depth are inferred moderately high q is associated with sierra nevada and salinian igneous rocks whereas the franciscan subduction complex shows moderately low q prominent high q relates to the great valley ophiolite the pattern of path specific attenuation rate from 3d q is generally similar to the pattern of psuedospectral acceleration residuals for the south napa earthquake indicating that it may be beneficial to incorporate 3d q models into future ground motion prediction equations for northern california online material figures of q p and q s resolution and station delays for t and table of q p v p q s and v s

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

poroelastic rebound along the landers 1992 earthquake surface rupture maps of surface displacement following the 1992 landers california earthquake generated by interferometric processing of ers 1 synthetic aperture radar sar images reveal effects of various postseismic deformation processes along the 1992 surface rupture the large scale pattern of the postseismic displacement field includes large lobes mostly visible on the west side of the fault comparable in shape with the lobes observed in the coseismic displacement field this pattern and the steep displacement gradient observed near the emerson camp rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture models show that horizontal slip occurring on a buried dislocation in a poisson s material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10 20 km from the fault yet this pattern is not observed in the postseismic interferograms as previously proposed to explain local strain in the fault step overs peltzer et al 1996b we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault compensating the vertical ground shift produced by fault afterslip such a rebound is explained by the gradual change of the crustal rocks poisson s ratio value from undrained coseismic to drained postseismic conditions as pore pressure gradients produced by the earthquake dissipate using the poisson s ratio values of 0 27 and 0 31 for the drained and undrained crustal rocks respectively elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the sar data and the horizontal displacement measured at global positioning system gps sites along a 60 km long transect across the emerson fault savage and svarc 1997 using a detailed surface slip distribution on the homestead valley kickapoo and johnson valley faults we modeled the poroelastic rebound in the homestead valley pull apart a poisson s ratio value of 0 35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3 5 years following the earthquake this large value implies a seismic velocity ratio vp vs of 2 1 consistent with the observed low vs values of fault zone guided waves at shallow depth li et al 1997 the sar data also reveal postseismic creep along shallow patches of the eureka peak and burnt mountain faults with a characteristic decay time of 0 8 years coseismic dilatant hardening locking process followed by post seismic pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault

three dimensional imaging of steeply dipping structure near the san andreas fault parkfield california shot gathers from the parkfield california deep crustal seismic reflection line recorded in 1977 by cocorp reveal coherent events having horizontal to reverse moveouts these events were migrated using a multioffset three dimensional kirchhoff summation method this method is a ray equation back projection inversion of the acoustic wave field which is valid under the born wkbj and far field assumptions migration of full wave acoustic synthetics having the same limitations in geometric coverage as the cocorp survey demonstrates the utility of the imaging process the images obtained from back projection of the survey data suggest that the gold hill fault carries ultramafic rocks from the surface to 3 km depth at a dip greater than 45 degrees where it joins the san andreas fault which may cut through more homogeneous materials at shallow depths to the southwest a 2 km tertiary sedimentary section appears to terminate against a near vertical fault the zone between this fault and the san andreas may be floored at 3 km by flat lying ultramafics lateral velocity inhomogeneities are not accounted for in the migration but in this case do not seriously hinder the reconstruction of reflectors

first high precision u pb ca id tims age for the battle formation upper cretaceous red deer river valley alberta canada implications for ages correlations and dinosaur biostratigraphy of the scollard frenchman and hell creek formations the battle formation bfm is a widespread upper cretaceous marker horizon in western canada that records a time of low sediment input and marks the boundary between the edmontonian and lancian lan

microearthquake imaging of the parkfield asperity microearthquake data from a downhole seismometer network on the san andreas fault appear to outline two aseismic asperities that may correspond to the locations of the foreshocks and main shocks of the parkfield characteristic earthquakes the source parameters of the microearthquakes show that a few of the earthquakes have significantly higher stress drops than most furthermore the magnitude frequency statistics suggest that at local magnitude 0 6 the cumulative number of small events begins to fall off the usual gutenberg richter b 1 relation in which the number of events increases exponentially with decreasing magnitude the downhole seismometer data establish a baseline from which the evolution of the earthquake process at parkfield can be monitored and suggest that different mechanical conditions than those that lead to the typical gutenberg richter relation may be operating for the smallest of parkfield microearthquakes

three dimensional velocity structure in northern california coast ranges from inversion of local earthquake arrival times abstract the three dimensional p wave velocity structure in the upper crust in the northern california coast ranges from santa rosa to ukiah is obtained by simultaneous inversion of local earthquake and refraction travel time data for velocity and hypocentral parameters in this region where there are lateral heterogeneities the three dimensional inversion provides important results not found in two dimensional refraction studies the medium is parameterized with velocities at the intersections gridpoints of a nonuniform three dimensional grid travel times are calculated with approximate ray tracing along arcuate paths which are reasonable for lateral distances less than 45 km inversions with 5 to 10 and 2 to 3 km gridspacing achieved 80 per cent decreases in data variance the inversion with 2 to 3 km gridspacing reduced the rms residual level to approximately the level of timing error anomalously low velocities to at least 6 km depth are found along the maacama and healdsburg rodgers creek hrc fault zones the low velocity region is widest at the en echelon junction of the maacama and hrc fault zones low velocities are associated with the clear lake basin where there is a thick sequence of volcanics interbedded with sedimentary deposits there is a high velocity body located southeast of the geysers between the maacama and collayomi fault zones which may be associated with igneous intrusives or high grade metamorphism related to an underlying inferred partial melt body modeled in previous teleseismic travel time studies there is some indication in the vapor dominated geothermal reservoir of lower velocities relative to surrounding water saturated rock as has been shown in some laboratory experiments hypocenter locations obtained in the inversion show little variation from hypocenters obtained through inversion for one dimensional velocity model and station corrections for the inversion with 2 to 3 km gridspacing however some groups of events become more tightly clustered

tomographic inversion of local earthquake data from the hengill grensdalur central volcano complex iceland parameters is generally low however a quantitative analysis of resolution provides an unambiguous assessment of well resolved volumes within the better resolved regions of the model the averaging volumes are 1 2 km and 2 4 km in vertical and horizontal extent respectively results of tomographic inversion image three distinct bodies of anomalously high velocity two of these extend from near the surface to a depth of about 3 km these high velocity volumes are located directly beneath the surface expressions of the extinct grensdalur volcano and the extinct husmuli basalt shield the third high velocity structure occurs in the depth range of 3 4 km but does not extend to the surface these three high velocity bodies are interpreted to be solidified magmatic intrusions relatively low velocities underlay limited portions of the trace of the present accretionary axis and a low velocity body is imaged in the roots of the active hengill volcano the volume of lower velocities located beneath the surface expression of the hengill volcano is interpreted to be a region of partial melt

microearthquake s wave observations from 0 to 1 km in the varian well at parkfield california abstract high gain three component seismometers from 0 to 1 km deep along the varian a 1 well at parkfield california were used to record the waveforms of nearby microearthquakes despite being in the thick tertiary sediments of the parkfield syncline the s wave amplification at this site is only about a factor of 3 the spectral content and spectral ratios of s waves along the well show that the average qs in the top 1 km at this site is 37 with the qs in different subintervals varying between 8 and 65 based on initial s wave polarizations a complex s wave velocity structure must exist at and below the varian site this structure appears to include position dependent anisotropy as well as steep lateral velocity gradients at a depth of 1 km s wave splitting parallel and normal to the san andreas fault zone is consistently observed this splitting scales at roughly 0 01 sec km subsequent to the split s waves the particle motion seems to be controlled by event focal mechanism above 1 km the upgoing s waves attenuate and change directions of polarization with a new splitting rate of 0 1 sec km uniquely for some events on the san andreas fault immediately below the varian site large post s wave signals with normal dispersion are present we propose that these phases are fault zone guided waves channeled from the san andreas fault to the varian site along the gold hill fault

pore pressure and oceanic crustal seismic structure summary marine refraction studies during the past decade have found considerable lateral variability in the seismic properties of the upper basaltic regions of the oceanic crust in many localities compressional and shear wave velocities are quite low at the top of the basalt section and velocities increase rapidly with depth it is concluded that pore pressure may be at least in part responsible for the low upper crustal velocities and contribute significantly to the lateral variability this is supported by compressional and shear wave velocity measurements as functions of confining pressure and pore pressure for basalt from the juan de fuca ridge and dolerite from the samail ophiolite oman within the oceanic crust regions of overpressure and underpressure will possess anomalous velocities the magnitude of which will depend upon the porosity and the deviation of the pore pressure from hydrostatic the influence of pore pressure on velocities is expected to diminish with depth and is unlikely to be significant at lower crustal depths where porosity is extremely low of significance poisson s ratio is shown to be dependent on pore pressure as well as confining pressure at constant confining pressure poisson s ratio increases with increasing pore pressure thus overpressured regions within the upper oceanic crust are likely to have relatively high poisson s ratios as well as low compressional and shear wave velocities

from velocity and attenuation tomography to rock physical modeling inferences on fluid driven earthquake processes at the irpinia fault system in southern italy we retrieve 3 d attenuation images of the crustal volume embedding the fault system associated with the destructive ms 6 9 1980 irpinia earthquake by tomographic inversion of t measurements a high qp anomaly is found to be correlated with the 1980 fault geometry while the qs model shows regional scale variations related to the ne edge of the uplifted pre tertiary limestone an upscaling strategy is used to infer rock properties such as porosity consolidation type of fluid mixing and relative saturation percentage at 8 10 km fault depth we constrain the porosity and consolidation in the ranges 4 5 and 5 9 respectively with the possible fluid mixes being both brine co2 and ch4 co2 the consolidation parameter range indicates high pore pressures at the same depths these results support the evidence for a fracture system highly saturated in gases and a seismicity triggering mechanism at the fault zone which is strongly controlled by fluid induced pore pressure changes

troodontids theropoda from the dinosaur park formation alberta with a description of a unique new taxon implications for deinonychosaur diversity in north america troodontids are known from asia and north america with the most complete specimens from the jurassic of china and the cretaceous of mongolia north american troodontids are poorly known and specimens that have been described are isolated elements or partial skeletons with limited material a new troodontid from the upper dinosaur park formation upper campanian is based on partial skulls several vertebrae ribs gastralia chevrons a sacrum partial pelvis and partial fore and hind limbs it is the largest troodontid known with an estimated height of 180 cm and length of 350 cm like other troodontids it possesses an elongated ambiens process and has a horizontal ventral margin of the postacetabular process it differs from all other derived troodontids in that the slightly retroverted pubis has a shaft that curves anteroventrally some specimens from the dinosaur park formation previously assigned to troodon are reassigned to the new taxon including multiple partial crania an associated dentary

remote sensing for mineral exploration abstract remote sensing is the science of acquiring processing and interpreting images and related data acquired from aircraft and satellites that record the interaction between matter and electromagnetic energy remote sensing images are used for mineral exploration in two applications 1 map geology and the faults and fractures that localize ore deposits 2 recognize hydrothermally altered rocks by their spectral signatures landsat thematic mapper tm satellite images are widely used to interpret both structure and hydrothermal alteration digitally processed tm ratio images can identify two assemblages of hydrothermal alteration minerals iron minerals and clays plus alunite in northern chile tm ratio images defined the prospects that are now major copper deposits at collahuasi and ujina hyperspectral imaging systems can identify individual species of iron and clay minerals which can provide details of hydrothermal zoning silicification which is an important indicator of hydrothermal alteration is not recognizable on tm and hyperspectral images quartz has no diagnostic spectral features in the visible and reflected ir wavelengths recorded by these systems variations in silica content are recognizable in multispectral thermal ir images which is a promising topic for research

palaeomagnetic evidence for southward displacement of the chuan dian fragment of the yangtze block summary cretaceous red sandstones of the feitianshan formation and the xiaoba formation were sampled at 33 sites from the dadeli and mishi synclines of xichang 27 9 n 102 3 e the study area is a part of the chuan dian fragment bounded by the xianshuihe xiaojiang and the red river fault systems which in turn constitute the southwestern part of the yangtze block almost all the samples give a characteristic palaeomagnetic direction with unblocking temperatures up to 680 c the primary nature of magnetization is ascertained by a positive fold test with a 99 per cent confidence level for the dadeli syncline the tilt corrected overall mean direction of the 33 sites is d 3 7 i 41 5 95 3 4 with a corresponding palaeopole at 85 2 n 241 7 e a95 3 5 this pole occupies the near sided position with respect to the estimate of the cretaceous pole of the sichuan basin indicating that the xichang area experienced a significant southward displacement combined with earlier reported palaeomagnetic data from the chuan dian fragment a significant southward displacement of 6 7 3 5 in latitude is estimated for the whole fragment with respect to the sichuan basin since the late cretaceous extrusion dynamics in the asian continent due to its collision with india brought about the southward displacement of the chuan dian fragment declination data indicate that the southern part of the chuan dian fragment was subjected to clockwise sense rotation of up to 45 this significantly large tectonic rotation probably occurred during extrusion of this

three dimensional velocity structure seismicity and fault structure in the parkfield region central california this study examines the three dimensional velocity structure in a 60 by 80 km region containing the parkfield segment of the san andreas fault we use local earthquake and shot p arrival times in an iterative simultaneous inversion for velocity and hypocentral parameters using the three dimensional model we relocated 5251 events that occurred from 1969 to 1991 as well as the 1966 aftershocks and computed 664 fault plane solutions the san andreas fault saf characterized by a sharp across fault velocity gradient is the primary feature in the velocity solution there is a 5 20 lateral change in velocity over a 4 km width the contrast being sharper where there is better resolution the model also shows significant variations in the velocity and in the complexity of the velocity patterns along the saf the largest across fault velocity difference is below middle mountain where a large volume of low velocity material impinges on the saf from the northeast this material is inferred to be overpressured and may be key to understanding the unusual behavior in the parkfield preparation zone a 20 km long high velocity slice is imaged northeast of the saf near gold hill its along fault length corresponds to the length of the maximum slip in 1966 the relocated seismicity shows that the san andreas fault is a planar vertical fault zone at seismogenic depths ninety percent of the fault plane solutions that are on or near the saf were right lateral strike slip on subvertical fault planes that parallel the saf thus the surface fault complexities do not appear to extend to depth and therefore do not explain the rupture character at parkfield at parkfield variations in material properties play a key role in fault segmentation and deformation style our observations suggest that there may be a general relation between increasing velocity and increasing ability of the rocks to store strain energy and release it as brittle failure

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

defining the morphological quality of fossil footprints problems and principles of preservation in tetrapod ichnology with examples from the palaeozoic to the present abstract the morphology of fossil footprints is the basis of vertebrate footprint ichnology however the processes acting during and after trace fossil registration which are responsible for the final morphology have never been precisely defined resulting in a dearth of nomenclature therefore we discuss the concepts of ichnotaphonomy ichnostratinomy taphonomy biostratinomy registration and diagenesis and describe the processes acting on footprint morphology in order to evaluate the morphological quality of tetrapod footprints we introduce the concept of morphological preservation which is related to the morphological quality of footprints m preservation acronym mp and distinguish it from physical preservation p preservation acronym pp which characterizes whether or not a track is eliminated by taphonomic and diagenetic processes m preservation includes all the morphological features produced during and after track registration prior to its study and may be divided into substages ichnostratinomic registrational taphonomic stratinomic diagenetic moreover we propose an updated numerical preservation scale for m preservation it ranges from 0 0 worst preservation to 3 0 best preservation intermediate values may be used and specific features may be indicated by letters in vertebrate footprint ichnotaxonomy we regard the anatomy consistent morphology and to a lesser extent the trackway pattern as the only acceptable ichnotaxobases only footprints showing a good morphological preservation grade 2 0 3 0 are useful in ichnotaxonomy whereas ichnotaxa based on poor morphological preservation grade 0 0 1 5 are considered ichnotaphotaxa nomina dubia characterized by extramorphologies we applied the preservation scale on examples from the palaeozoic to the present time including three ichnotaphotaxa and 18 anatomy consistent ichnotaxa morphotypes attributed to several vertebrate footprint producers results indicate the utility feasibility and suitability of this method for the entire vertebrate footprint record in any lithofacies strongly recommending its use in future ichnotaxonomic studies

taphonomy age and paleoecological implication of a new pachyrhinosaurus dinosauria ceratopsidae bonebed from the upper cretaceous campanian wapiti formation of alberta canada the grande prairie region alberta canada includes some of the richest cretaceous fossil sites in north america including the recently described bonebed of pachyrhinosaurus lakustai at the pipes

high precision u pb ca id tims dating and chronostratigraphy of the dinosaur rich horseshoe canyon formation upper cretaceous campanian maastrichtian red deer river valley alberta canada the non marine horseshoe canyon formation hcfm southern alberta yields taxonomically diverse late campanian to middle maastrichtian dinosaur assemblages that play a central role in documenting

age and depositional environment of the dinosaur graveyard at las aguilas southern coahuila ne mexico abstract here we provide a detailed description of the upper campanian sediment succession at las aguilas southern coahuila northeastern mexico including the first absolute age dating for this interval paleoenvironmental reconstructions and taphonomic observations on the abundant dinosaur remains at the locality stratigraphic investigations of the dinosaur bearing succession at the las aguilas vertebrate fossil area near porvenir de jalpa reveal a diverse vertebrate assemblage including dinosaurs crocodilians and turtles new findings in adjacent sites include eusuchian crocodylomorphs four different kinds of turtles dromaeosaurids lambeosaurines pterosaurs and elasmosaurid plesiosaurs strontium isotope measurements on fossil oyster shells provide an absolute age of 73 1 ma for the lower part of the las aguilas section the locality is thus of late campanian age the vertebrate invertebrate and plant materials as well as the sediment structures observed in a 50 m thick predominantly siliciclastic succession of the cerro del pueblo formation suggest deposition in an extensive delta plain environment the facies succession indicates a short termed cyclicity of limnic brackish and shallow marine environments during the late campanian early maastrichtian cerro del pueblo formation with numerous layers containing dinosaur fossil remains resumen aqui damos una descripcion detallada de la sucesion de sedimentos del campaniano superior en las aguilas sur de coahuila noreste de mexico incluyendo la primera datacion absoluta para este intervalo reconstrucciones paleoambientales y observaciones taxonomicas sobre la abundancia de restos de dinosaurios en la localidad investigaciones estratigraficas de los estratos con dinosaurios en el area fosilifera de las aguilas cerca de porvenir de jalpa revelan un ensamblaje vertebrado diverso incluyendo dinosaurios cocodrilos y tortugas nuevos descubrimientos en sitios adyacentes incluyen crocodylomorfos eusuquios cuatro diferentes tipos de tortugas dromaeosauridos lambeosaurinos pterosaurios y plesiosaurios elasmosauridos mediciones de isotopos de estroncio en conchas de ostiones fosiles proveen una edad absoluta de 73 1 millones de anos para la parte inferior de la seccion de las aguilas la localidad es por lo tanto de edad campaniana tardia el material de vertebrados invertebrados y de plantas asi como las estructuras sedimentarias observadas en una sucesion predominantemente siliciclastica de 50 m de la formacion cerro del pueblo sugieren una depositacion en un ambiente de una extensa planicie deltaica la sucesion de facies indica una ciclicidad de periodo corto de ambientes limnicos estuarinos y marinos someros durante el campaniano tardio maastrichtiano temprano de la formacion cerro del pueblo con numerosos estratos conteniendo fosiles de dinosaurios palabras clave las aguilas sucesion de dinosaurios campaniano superior ambientes deposicionales formacion cerro del pueblo coahuila

velocity structure of the pamir hindu kush region possible evidence of subducted crust the arrival times of compressional p and shear s waves from approximately 580 microearthquakes recorded by a temporary array in the pamir hindu kush region in central asia are used to deduce one and three dimensional velocity structures of this region the results for one dimensional structures imply that the moho is at 70 5 depth also there is a velocity reversal near 160 km depth which is inferred to be the beginning of the low velocity zone this reversal continues to depths of approximately 230 km below 230 km velocities are somewhat higher than those of normal mantle at similar depths 9 3 km s versus 8 4 km s for p waves the outstanding feature of the results for three dimensional velocity structures is a broad 40 km centrally located region with 8 to 10 lower velocities than those in the surrounding regions this low velocity region envelopes the seismic zone at depths between 70 and 150 km the region may actually extend beyond these depths but the results for shallower and deeper structure lack sufficient resolution to decide several tests using both hypothetical and real data were performed to estimate the reliability of the three dimensional solutions the results of these tests suggest that the inferred velocities are reasonably accurate representations of the average velocities in the blocks although one must be cautious of the effects of averaging in interpreting the solution the low velocity region is inferred to be a manifestation of substantial quantities of subducted continental crust therefore while subduction has occurred in the pamir hindu kush the results of the three dimensional inversions suggest that continental rather than only oceanic lithosphere has been subducted to depths of at least 150 km appendices are available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 013 1 00 payment must accompany order

geological methods in mineral exploration and mining second edition roger marjoribanks pp 238 2010 springer heidelberg isbn 978 3 540 74370 5 price us 129 00 marjoribanks has updated one of the handiest and most readable books ever written for the exploration community exploration managers should be handing copies of it to all their new hires and aspiring explorationists should be reading it before their first interview let alone camp job geared to the entry levels of the profession it s also a handy reference for old hands it covers the basics of the full gamut of modern exploration methods and techniques ranging from mapping through sampling and drilling into geophysics and geochemistry and thence to image analysis and gis examples drawn from real life are very well chosen and the book is larded with designs for handy field apparatus that can significantly streamline cumbersome tasks in the bush marjoribanks focus always seems to be on how to wring as much information out of your exploration activities and data as possible the book starts by examining the underlying philosophy of how one explores and what techniques work when and why and passes on to consideration of

differential analysis of coda q using similar microearthquakes in seismic gaps part 2 application to seismograms recorded by the parkfield high resolution seismic network abstract nearly two thirds of the microseismicity occurring at parkfield california consists of repeating clusters of closely located events exhibiting waveform cross correlation values exceeding 0 95 this observation coupled with a high probability for an m 6 earthquake within the next decade working group on california earthquake probabilities 1988 make this segment of the san andreas fault system a prime location to search for temporal variations in coda q associated with crustal changes that may occur during the earthquake cycle the coda comparison analysis method described in part 1 of this study aster et al 1996 is applied to data from four borehole stations of the parkfield high resolution seismic network hrsn for the period january 1987 through february 1994 we examine 21 of the nearly 300 repeating clusters observed to date the restriction of the data set to only the most highly similar sources is observed to be critical small differences in the source process even for event pairs with centroid locations within approximately 20 m significantly increase the spurious noise level in the parameter estimates absolute 68 confidence bound estimates obtained on the repeatability of coda q for all microearthquake pairs are 10 for frequencies below 20 hz tighter constraints are obtainable by reconstructing the temporal history of coda q from the first difference measurements between microearthquake pairs these functional reconstructions show that the mean value of coda q has not varied by more than approximately 5 from 3 to 30 hz at the 1 level during the study period however other observables such as an increased level of microseismicity suggest that a preparatory stage for the next parkfield earthquake has begun indicating that coda q is so far showing no sign of sensitivity to preparatory processes at parkfield

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

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

reanalysis of the cocorp deep seismic reflection profile across the san andreas fault parkfield california in 1977 cocorp recorded a short seismic reflection test line across the san andreas fault through parkfield california where the salinian crustal block is juxtaposed against a contrasting terrane of franciscan and overlying material although analysis of this seismic line has been limited by crooked geometry lack of cross lines complex terrain possible recording noise and perhaps most of all its short length gross crustal features are discernible after extensive reprocessing and reanalysis the salinian block southwest of the san andreas consists of a maximum of 2 km of relatively underformed sediments overlying a reflective and inhomogeneous basement which exhibits deep subhorizontal layering at 8 to 10 km depth density and amplitude of reflections markedly decay perhaps corresponding to the base of a salinian granitic crust which overlies franciscan or other contrasting material northeast of the san andreas subhorizontal reflections suggest that franciscan material may extend as deeply as 13 km below which is a nonreflective zone which might represent relict oceanic crust reflections from moho depths differ across the san andreas fault beneath the salinian block is a thick zone of reflections beginning at about 22 km depth while less layered and weaker reflections seem to define the moho discontinuity at 29 km beneath the franciscan terrane the san andreas fault zone appears to be traceable as a distinct feature on the reflection section throughout the entire crust forming a near vertical zone about 3 km wide in the seismogenic upper crust down to 15 km the fault zone is marked by sharp structural truncations and short reflection or diffraction segments at depth it seems to be distinguished by a nonreflective column this vertical change in reflection character may correspond to the transition from a brittle to a ductile deformation regime

seismological studies at parkfield i simultaneous inversion for velocity structure and hypocenters using cubic b splines parameterization a model for the 3d p and s wave velocity structure at parkfield has been developed by the systematic inversion of arrival times for microearthquakes and surface vibroseis sources recorded by nearby calnet stations and by the local borehole installed 10 station high resolution seismic network there a modification of the linear b splines model parameterization method of thurber 1983 to a cubic b splines formulation through tests inverting synthetic data sets for the parkfield configuration is found to produce smooth velocity distributions that still retain some small scale features application of the method to 953 p wave and 288 s wave arrivals from 111 microearthquakes and 8 vibroseis locations throughout the study area yields a velocity structure having variable resolution a low velocity zone appears to coincide with the creeping segment of the san andreas fault zone northwest of the 1966 parkfield earthquake epicenter an increase of about 15 per cent in seismic velocities is seen from the northeast to southwest across this segment of the fault zone the higher velocities to the southwest apparently correspond to the granitic basement the contrast across the fault is subdued to the southeast along the 1966 rupture zone a high vp vs ratio of 1 9 is seen in a 2 km wide volume near the location of the 1966 main shock hypocenter presumably the nucleation zone for the expected m 6 parkfield earthquake