subsurface failure in spherical bodies a formation scenario for linear troughs on vesta s surface abstract many asteroids in the solar system exhibit unusual linear features on their surface the dawn mission recently observed two sets of linear features on the surface of the asteroid 4 vesta geologic observations indicate that these features are related to the two large impact basins at the south pole of vesta though no specific mechanism of origin has been determined further the orientation of the features is offset from the center of the basins experimental and numerical results reveal that the offset angle is a natural consequence of oblique impacts into a spherical target here we demonstrate that a set of shear planes develops in the subsurface of the body opposite to the point of first contact these subsurface failure zones then propagate to the surface under combined tensile shear stress fields after the impact to create sets of approximately linear faults on the surface comparison between the orientation of damage structures in the laboratory and failure regions within vesta can be used to constrain impact parameters e g the approximate impact point and likely impact trajectory

wenlock ludlow and pridoli graptolites from yulin guangxi china late wenlock and ludlow transition graptolites are better developed and more diverse in the yulin region of guangxl province south china than elsewhere in china the upper homerian upper wenlock graptolites while moderately diverse are not amenable to a zonal subdivision because key species such as colonograptus praedeubeli colotmgraptus deubeli and colonograptus kudensis are found to completely overlap in their occurrences lndlow graptolites all probably assignable to the lowest ludlow nilssoni colonus biozone include lobograptus progenitor colonogrcrptus colonus colonogruptus gerhurdi and bohernogr ptus botwmicus sensu lato the single occurrence of monograptus cf rectijhnis prhyl is the only species suggestive of pridoli age strata the overall faunal assemblages are composed predominately of cosmopolitan species but two species colonograptus gerhczrdi and it4onogruptu s cf rectijhnis provide minor support for the suggestion that the yunkai block in which the yulin region is situated was originally part of gondwanaland

hirnantian ordovician through wenlock silurian conodont biostratigraphy bioevents and integration with graptolite biozones cape phillips formation slope facies cornwallis island canadian arctic islands cornwallis island in the canadian arctic archipelago provides one of the world s best areas for establishing an integrated graptolite conodont biozonation for the late ordovician silurian given the well exposed interfingering relationship of the basinal shale and carbonate platform facies building on earlier graptolite work 180 samples were collected from nine sections of the cape phillips formation of which 118 yielded approximately 7600 conodont elements representing 54 species in 25 genera including one new genus and species mayrodus melchini the conodonts are well preserved with minimal thermal alteration colour alteration index cai 1 nine conodont zones are recognized and defined for this region namely the amorphognathus ordovicicus distomodus kentuckyensis aspelundia expansa as fluegeli and pterospathodus celloni interval zones pt a amorphognathoides taxon range zone pt pennatus procerus and kockelella ranuliformis highest occurrence zones and k ortus absidata taxon range zone an integration of graptolite and conodont zones is documented earlier paleontological and isotope geochemical studies have demonstrated the dynamic nature of the silurian ocean climate system and identified major faunal turnovers or events five of these are recognized in the cornwallis fauna and related to oceanographic and climate changes in part referring to recent oxygen isotope data from conodonts from the cornwallis collections hirnantian extinction event sandvika event late aeronian llandovery snipklint primo episode early telychian llandovery ireviken event late telychian llandovery sheinwoodian wenlock and mulde event early homerian wenlock

independence of geostatic stress from overconsolidation in some beaufort sea clays reply since 1982 extensive use has been made of the self bored pressuremeter in arctic offshore site investigations one finding of this work is that the in situ geostatic stress ratio k0 of beaufort sea clays is apparently unrelated to the overconsolidation ratio ocr the procedures and data to support this finding are documented and the finding is discussed in light of the present geological understanding for the area it is concluded that the independence of k0 from ocr may be quite widespread a finding that contradicts the widely held tenet regarding the existence of a single valued function relating k0 and ocr if k0 is regarded as important then it should be measured in situ key words self bored pressuremeter geostatic stress ratio k0 beaufort shelf geologic history overconsolidation ratio

wenlock ludlow graptolite biostratigraphy and extinction a reassessment from the southwestern iberian peninsula spain and portugal a detailed reexamination of a key wenlock ludlow transition section in the valle syncline region spain and the incorportation of data from a coeval section in the barrancos area portugal both within the ossa morena zone reveal seven biostratigraphic units these are monograptus belophorus and cyrtograptus lundgreni monograptus testis biozones representing the upper sheinwoodian and the preextinction lower homerian faunas respectively the pristiograptus dubius parvus gothograptus nassa concurrent range biozone colonograptus praedeubeli colonograptus deubeli biozone and colonograptus ludensis biozone representing the upper homerian postextinction faunas and the ludlow neodiversograptus nilssoni and saetograptus fritschi linearis biozones the extinction beds between the lower homerian lundgreni testis biozone and the lowest upper homerian dubius parvus nassa interval biozone make up a several centimetre thick soft orange weathered almost barren volcanic bed

aftershock asymmetry on a bimaterial interface to better understand the asymmetric distribution of microearthquake aftershocks along the central san andreas fault we study dynamic models of slip weakening ruptures on an interface separating differing elastic half spaces subshear ruptures grow as slightly asymmetric bilateral cracks with larger propagation velocities slip velocities and normal stress changes at the rupture front moving in the direction of slip of the medium with the lower shear wave speed the southeast front in the context of the san andreas when the se front encounters a stress barrier the tensile stress perturbation behind the rupture front continues forward and for a wide range of barrier strengths nucleates a dying slip pulse this slip pulse smooths the stress field and reduces the static stress change beyond the se front furthermore because the tensile stress that carried the slip pulse into the barrier is a purely dynamic phenomenon the se rupture front can be left far below the failure threshold while the nw front remains quite close to failure both mechanisms could contribute to the observed aftershock asymmetry formation of a robust slip pulse requires a peak tensile stress perturbation that approaches the nominal strength drop of the slip weakening law to achieve this while minimizing off fault damage requires either substantial velocity contrasts or small reductions in friction the simulations also show a pronounced asymmetry in the timescales over which barriers to the se and nw experience increasing stresses a result that has implications for the asymmetric distribution of subevents in compound earthquakes

pulse like and crack like ruptures in experiments mimicking crustal earthquakes theoretical studies have shown that the issue of rupture modes has important implications for fault constitutive laws stress conditions on faults energy partition and heat generation during earthquakes scaling laws and spatiotemporal complexity of fault slip early theoretical models treated earthquakes as crack like ruptures but seismic inversions indicate that earthquake ruptures may propagate in a self healing pulse like mode a number of explanations for the existence of slip pulses have been proposed and continue to be vigorously debated this study presents experimental observations of spontaneous pulse like ruptures in a homogeneous linear elastic setting that mimics crustal earthquakes reveals how different rupture modes are selected based on the level of fault prestress demonstrates that both rupture modes can transition to supershear speeds and advocates based on comparison with theoretical studies the importance of velocity weakening friction for earthquake dynamics

the north anatolian fault in the sea of marmara 1 using the detailed geometry and tectonics of the main marmara fault that connects the gulf of izmit fault with the ganos fault established by le pichon et al 2001 and the new gps data set recently analyzed by meade et al 2002 we confirm the existence of a marmara block delimited to the north by the northern branch of the north anatolian fault the marmara branch and to the south by the southern branch the kinematics of this block indicate that the marmara branch that crosses the sea of marmara is close to pure dextral strike slip at a rate of 23 mm yr on its whole length the short cinarcik section is the only one where a significant extensional component is predicted a simple kinematic model accounts for slip partitioning there with 8 10 mm yr of extension to the south of the basin and 23 mm yr of dextral strike slip along the northern cinarcik margin the new gps data demonstrate the existence of important asymmetric elastic loading along the main marmara fault that may have significant implications for the seismotectonics of the area the expected future large earthquake may rupture the whole main marmara fault the partitioning in the cinarcik basin may produce magnitude 7 normal faulting earthquakes if their repetition time is about 250 years the 1896 earthquake may have been one of these normal fault earthquakes the marmara block is less than 1 ma prior to its formation it was part of the anatolian block at this time the ganos fault was already a dextral strike slip fault but the fault system in the sea of marmara would have been affected by an extensional component increasing toward the east that accounts for the increasing size of the sedimentary basins eastward

the effect of asymmetric damage on dynamic shear rupture propagation ii with mismatch in bulk elasticity high speed digital photography was used to study rupture propagation on the interface between transparent damaged and undamaged photoelastic plates bilateral ruptures were nucleated on pre machined faults at an angle to the uniaxial loading axis stress concentration at the crack tips produced fringes in polarized laser light that allowed their positions to be measured in successive photos we found that fracture damage introduces a strong asymmetry in propagation speed different from that expected due to the lower elastic stiffness in the damaged material alone when the tensile lobe of a rupture tip propagated through the damaged material the velocity of that rupture was reduced or stopped by contrast when the compressive lobe of a rupture tip passed through the damage the velocity of that rupture was unaffected by the damage a physical interpretation is that passage of a tensile lobe through the damage expends energy by lowering the normal stress on pre existing cracks thus allowing frictional sliding along the crack surfaces when the compressive lobe of the rupture passes through the damage compressive stresses prevent sliding only minor energy is dissipated and the damage has almost no effect on the velocity this effect can produce asymmetric propagation for earthquake ruptures on slip surfaces near the edge of a highly damaged fault zone

predominance of unilateral rupture for a global catalog of large earthquakes the manner in which an earthquake rupture propagates across a fault reflects both the initial properties of the fault and the dynamical stresses produced by the rupture we quantify the propagation of an earthquake rupture using the second moments of the earthquake space time distribution in particular the second moments provide a simple way to differentiate between approximately bilateral and predominantly unilateral ruptures we determined the second moments for a catalog of m w 7 earthquakes that have occurred since 1994 the results show that approximately 80 of large shallow ruptures are predominantly unilateral our result agrees well with strong motion inversions from previous studies on moderate and large earthquakes the predominance of unilateral propagation in large earthquakes is explained by a simple characteristic earthquake model in which large events rupture an entire structurally defined fault segment and nucleation points are uniformly distributed along the fault the predominance of unilateral rupture may also be enhanced by the dynamic stress field produced by contrasts in the elastic properties between the two sides of plate boundary faults manuscript received 16 november 2001

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

graptoloid evolutionary rates track ordovician silurian global climate change graptoloid evolutionary dynamics show a marked contrast from the ordovician to the silurian subdued extinction and origination rates during the ordovician give way during the late katian to rates that were highly volatile and of higher mean value through the silurian reflecting the significantly shorter lifespan of silurian species these patterns are revealed in high resolution rate curves derived from the conop constrained optimization scaled and calibrated global composite sequence of 2094 graptoloid species the end ordovician mass depletion was driven primarily by an elevated extinction rate which lasted for c 1 2 ma with two main spikes during the hirnantian the early silurian recovery although initiated by a peak in origination rate was maintained by a complex interplay of origination and extinction rates with both rates rising and falling sharply the global 13 c curve echoes the graptoloid evolutionary rates pattern the prominent and well known positive isotope excursions during the late ordovician and silurian lie on or close to times of sharp decline in graptoloid species richness commonly associated with extinction rate spikes the graptoloid and isotope data point to a relatively steady marine environment in the ordovician with mainly background extinction rates changing during the katian to a more volatile climatic regime that prevailed through the silurian with several sharp extinction episodes triggered by environmental crises the correlation of graptoloid species diversity with isotopic ratios was positive in the ordovician and negative in the silurian suggesting different causal linkages throughout the history of the graptoloid clade all major depletions in species richness except for one were caused by elevated extinction rate rather than decreased origination rate

some late wenlock and ludlow monograptid graptolites cornwallis island arctic canada seven species of uncompressed latest wenlock and ludlow monograptid graptolites isolated from calcareous concretions are described and illustrated the biostratigraphically important species pristiograptus ludensis of latest wenlock age and saetograptus fritschi linearis and monograptus ceratus of mid ludlow age are illustrated in uncompressed form for the first time the remaining species described include bohemograptus bohemicus tenuis colonograptus colonus saetograptus ex gr chimaera and pristiograptus dalejensis all of ludlow age the last named species is the most common but is biostratigraphically long ranging

the aftershock signature of supershear earthquakes recent studies show that earthquake faults may rupture at speeds exceeding the shear wave velocity of rocks this supershear rupture produces in the ground a seismic shock wave similar to the sonic boom produced by a supersonic airplane this shock wave may increase the destruction caused by the earthquake we report that supershear earthquakes are characterized by a specific pattern of aftershocks the fault plane itself is remarkably quiet whereas aftershocks cluster off the fault on secondary structures that are activated by the supershear rupture the post earthquake quiescence of the fault shows that friction is relatively uniform over supershear segments whereas the activation of off fault structures is explained by the shock wave radiation which produces high stresses over a wide zone surrounding the fault

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

u pb zircon age constraints on the timing and duration of wenlock silurian paleocommunity collapse and recovery during the big crisis high precision isotope dilution u pb zircon dating was conducted on three volcanic ash fall bentonite samples from the swedish island of gotland and on a fourth bentonite from the west midlands england zircons from the ireviken grotlingbo djupvik gotland and wren s nest hill 15 west midlands bentonites yielded weighted mean pb 206 u 238 ages of 431 83 0 23 0 67 ma 428 45 035 0 73 ma 428 06 0 2110 66 ma and 427 86 032 0 71 ma respectively analytical total uncertainties these biostratigraphically well controlled age dates effectively bracket the wenlock epoch of the silurian period and provide control for the duration of one of the major paleozoic biotic events and associated perturbations to the global carbon cycle the big crisis or lundgreni event graptolites the niulde event conodonts the mulde excursion carbon isotopes these new data suggest an older and shorter duration for the recalibration of the wenlock series and demonstrate that the cascade of biological and chemical events that took place during the big crisis happened on time scales of tens to hundreds of thousands of years less

earth pressure at rest of sovind marl a highly overconsolidated eocene clay abstract the present study evaluated the earth pressure at rest k 0 of sovind marl a highly overconsolidated eocene clay this clay exhibits extremely high plasticity indices of up to 300 a highly fissured structure and preconsolidation stresses up to 6800 kpa continuous loading oedometer clo tests at a constant rate of strain were performed in the danish clo apparatus this apparatus applies test water at 200 kpa and measures total horizontal stresses via pressure gauges placed in a stiff oedometer ring horizontal and vertical stresses were measured from in situ stresses to various stress levels to estimate continuous k 0 development in the clay normally consolidated earth pressures at rest were 0 42 and 0 68 for sovind marl at two different ages overconsolidated k 0 k 0 oc reached values as high as 6 to 8 in the in situ stress range the correlation between k 0 oc and the overconsolidation ratio ocr reported by meyerhof in 1976 was inconsistent with the k 0 oc development of sovind marl however the development of ocr in the laboratory under the previously applied test stresses ocr lab as an alternative to preconsolidation stresses showed congruent results regardless of sample age when an value of 1 05 was used

the late aeronian graptolite sedgwickii event associated positive carbon isotope excursion and facies changes in the prague synform barrandian area bohemia study of the lower silurian black shale succession of the prague synform has enabled detailed insight into graptolite faunal dynamics and diversity trends from the mid aeronian diversity maximum through to the late aeronian crisis graptolite diversity decreased from 33 taxa in the lituigraptus convolutus biozone to 17 taxa in the upper part of the stimulograptus sedgwickii biozone and newly erected lituigraptus rastrum biozone the graptolite assemblages of the latter biozones exhibit low species richness along with high dominance many graptolite species that became extinct in the early part of the sedgwickii zone were promptly replaced by new forms in the later part of the sedgwickii zone however replacement of extinct species by new forms considerably decelerated the increased rate of graptolite extinction recorded in the convolutus sedgwickii biozone boundary beds coincided with subtle changes in black shale lithologies and a positive shift in 13 c org of 2 2 compared to baseline values sea level drawdown can be inferred from siltstones and or temporary nondeposition in the middle sedgwickii zone this level also sees total organic carbon toc fluctuations and a strong positive 13 c org excursion with a peak shift of at least 7 the sedgwickii event exhibits substantial reorganization of the graptolite fauna its taxonomic impoverishment and concomitant increase in species dominance rather than a sudden collapse of the pre extinction assemblage associated changes in lithology toc and the pronounced 13 c org excursion suggest a relatively extended and probably multi phase period of stressed conditions that affected the pelagic realm inhabited by graptolites in the course of the late aeronian interval

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

the coefficient of earth pressure at rest laboratory experiments on undisturbed specimens of a large number of soft clay deposits as well as previous measurements on clays and granular soils were used to examine and explain the magnitude and behavior of the coefficient of earth pressure at rest k0 i after sedimentation primary consolidation ii during secondary compression aging iii after active or passive preshearing away from the laterally constrained condition iv during a decrease in effective vertical stress and v during an increase in effective vertical stress in the recompression or compression range in terms of the slope of the effective horizontal versus effective vertical stress path the behavior of k0 is explained using the concept of mobilized angle of friction in laterally constrained deformation condition the jaky equation provides in terms of the angle of internal friction a good estimate of k0 of sedimented normally consolidated young clays and granular soils as well as of of presheared clays and sands

multi fault rupture and successive triggering during the 2012 mw 8 6 sumatra offshore earthquake 1 on april 11 2012 a mw 8 6 strike slip earthquake struck the northern sumatra offshore region and became the largest intraplate event ever recorded there preliminary study results show a remarkably complex rupture pattern on a fault system manifested by north south trending paleo transform faults and east west striking abyssal hill fabric to image the rupture pattern of the earthquake we back projected teleseismic p wave recordings observed at three regional seismic networks eu au and f net our results indicate that the earthquake ruptured on a conjugate fault system composed of two subparallel wnw ese trending faults and a nne ssw striking fault in between for a duration of at least 120 s the rupture started at the wnw end of the first wnw ese trending fault located at the east of the conjugate fault system and propagated toward ese it then jumped to the second nne ssw trending fault located west of the first fault and first extended sswward and 15 s later nneward after its end on the second fault the rupture jumped onto the third wnw ese trending fault and continued wnwward the static coulomb stress changes calculated from the rupture of the first and then the second faults based on simplified uniform slip models suggest that initiation of the rupture on the second fault could be statically and dynamically triggered by the first fault however the third fault was primarily dynamically triggered by s or even love waves radiated from the southern branch of the second fault

planktic foraminiferal turnover and δ13c isotopes across the paleocene eocene transition at caravaca and zumaya spain abstract biostratigraphic and faunal analysis of planktic foraminifera and benthic foraminiferal isotopes at zumaya and caravaca sections in spain indicate that zumaya has a continuous record with high sediment accumulation rates across the paleocene eocene transition whereas caravaca has a hiatus with the uppermost zone p4 zone p5 and the lower part of zone p6 missing both sections contain nearly continuous and expanded records of the global 13c excursion at zumaya and caravaca respectively the 13c excursion is associated with dark grey shale deposition in a dysaerobic benthic environment this 13c event is associated with a major planktic foraminiferal turnover marked by the gradual extinction and evolution of 33 and 18 of the species respectively a rapid change in the relative abundances of these taxa occurs at the 13c excursion coincident with the extinction of 50 of the small benthic foraminiferal taxa the entire water column was affected by this faunal turnover surface intermediate deep dwellers but in contrast to benthic foraminifera there was no net loss of habitats since species extinctions of planktic foraminifera were largely replaced by originations

early silurian wenlockian δ13c profiles from the cape phillips formation arctic canada and their relation to biotic events geochemical data from the cape phillips formation arctic canada are examined in association with three silurian biotic crises in the graptolite community the early wenlockian ireviken mid wenlockian cyrtograptus lundgreni and end wenlockian colonograptus ludensis extinction events positive 13corg excursions are associated with the ireviken and c lundgreni events but not the co ludensis event the ireviken and c lundgreni excursions are recognized worldwide and are herein interpreted to be the result of carbonate weathering in response to eustatic sea level drop the c lundgreni excursion is of greater magnitude in the more proximal basin margin section at abbott river cornwallis island and is explained by the amplification of a more strongly positive 13c signature in shallower parts of an epeiric basin during increased exposure and weathering of the carbonate shelf excursion c5 within the c praedeubeli c deubeli zone is also of regional significance as it occurs in both the abbott r

upper silurian and lower devonian graptolites and graptolite biostratigraphy northern yukon canada upper silurian and lower devonian graptolite biostratigraphy of the northern canadian cordillera is revised in the light of new data the zones listed in order of oldest to youngest are lobograptus progenitor saetograptus fritschi linearis and bohemograptus bohemicus tenuis ludlow monograptus formosus pristiograptus ultimus pristiograptus chelmiensis monograptus bouceki and pristiograptus transgrediens praecipuus pridoli monograptus uniformis and m hercynicus lochkov and monograptus falcarius m fanicus m thomasi and m yukonensis prag the following taxa inclusive of new species are described pristiograptus separabilis teller pseudomonoclimacis tetlitensis n sp p richardsonensis n sp p bispinosus n sp monograptus ceratus n sp m aequabilis bardoensis porebska m cf anerosus koren m fanicus koren m hercynicus hercynicus perner m uniformis parangustidens jackson and lenz saetograptus fritschi linearis boucek and abiesgraptus sp

photo acoustic study of subshear and supershear ruptures in the laboratory abstract we report supershear ruptures observed in spontaneously nucleating laboratory microearthquakes and describe the signature of the associated mach wavefront radiation transducers detect the wavefield both close and at a distance from the fault the rupture velocities are inferred from either photoelastic high speed imaging or using the acoustic recordings both methods yield compatible estimates of sufficient accuracy to discriminate between sub shear and supershear ruptures the acoustic records allow to characterize the mach wavefront radiated from the supershear rupture front in particular its amplitude and decay velocity functions recovered by integrating high frequency accelerometer signals in the case of supershear ruptures consist in a double pulse function a first pulse traveling at supershear velocity followed by a second pulse traveling at the rayleigh wave velocity conversely the sub shear event is characterized by a single pulse finally we perform numerical simulations of our experiment using a prescribed supershear rupture velocity the synthetic waveforms obtained from these simulations including the mach wave amplitude and phase yield a satisfactory fit to the experimental results

a new gorstian radiolarian fauna from the upper silurian of the cape phillips formation cornwallis and bathurst islands canadian arctic this study provides a taxonomic treatment and comparison of lower gorstian silurian radiolarians recovered from two sections of the cape phillips formation in the canadian arctic that accumulated in two different paleoenvironmental settings twilight creek is more basinal located 100 km from the paleo shelf margin whereas snowblind creek is located within 1 km of the paleo shelf break on cornwallis island the fauna like other material from the cape phillips formation is extremely well preserved and was recovered from four samples at two localities all from the lobograptus progenitor graptolite zone an interval that has few published studies regarding radiolarians a total of 28 species are recognized of which two are new and described herein fusalfanus bilateralis n sp and pseudospongoprunum parvispina n sp belonging to the haplotaeniatidae inaniguttidae sponguridae ceratoikiscidae entactiniidae palaeoscenidiidae and secuicollactidae based on these new data the stratigraphic r

uppermost wenlock and ludlow graptolites from southern yunnan china a diverse late homerian and ludlow graptolite fauna including 38 species is recognized from shales and claystones of shuiqingliangzi section in mojiang county southern yunnan china two wenlock and three ludlow graptolite biozones are recognized which in ascending order are colonograptus praedeubeli biozone colonograptus ludensis biozone lobograptus progenitor biozone lobograptus scanicus biozone and saetograptus fritschi linearis biozone the 20 species described in the present paper comprise plectograptus macilentus tornquist plectograptus sp agastograptus clathrospinosus eisenack agastograptus sp 1 agastograptus sp 2 gothograptus nassa holm neogothograptus sp colonograptus praedeubeli jaeger colonograptus ludensis murchison pseudomonoclimacis dalejensis boucek monograptus ex gr uncinatus tullberg monograptus sp saetograptus chimaera barrande saetograptus fritschi linearis boucek saetograptus leintwardinensis hopkinson lobograptus progenitor urbanek lobog

earthquake fault superhighways abstract motivated by the observation that the rare earthquakes which propagated for significant distances at supershear speeds occurred on very long straight segments of faults we examine every known major active strike slip fault system on land worldwide and identify those with long 100 km straight portions capable not only of sustained supershear rupture speeds but having the potential to reach compressional wave speeds over significant distances and call them fault superhighways the criteria used for identifying these are discussed these superhighways include portions of the 1000 km long red river fault in china and vietnam passing through hanoi the 1050 km long san andreas fault in california passing close to los angeles santa barbara and san francisco the 1100 km long chaman fault system in pakistan north of karachi the 700 km long sagaing fault connecting the first and second cities of burma rangoon and mandalay the 1600 km great sumatra fault and the 1000 km dead sea fault of the 11 faults so classified nine are in asia and two in north america with seven located near areas of very dense populations based on the current population distribution within 50 km of each fault superhighway we find that more than 60 million people today have increased seismic hazards due to them

rupture dynamics with energy loss outside the slip zone 1 energy loss in a fault damage zone outside the slip zone contributes to the fracture energy that determines rupture velocity of an earthquake a nonelastic two dimensional dynamic calculation is done in which the slip zone is modeled as a fault plane and material off the fault is subject to a coulomb yield condition in a mode 2 crack like solution in which an abrupt uniform drop of shear traction on the fault spreads from a point coulomb yielding occurs on the extensional side of the fault plastic strain is distributed with uniform magnitude along the fault and it has a thickness normal to the fault proportional to propagation distance energy loss off the fault is also proportional to propagation distance and it can become much larger than energy loss on the fault specified by the fault constitutive relation the slip velocity function could be produced in an equivalent elastic problem by a slip weakening friction law with breakdown slip dc increasing with distance fracture energy g and equivalent dc will be different in ruptures with different initiation points and stress drops so they are not constitutive properties they are determined by the dynamic solution that arrives at a particular point peak slip velocity is however a property of a fault location nonelastic response can be mimicked by imposing a limit on slip velocity on a fault in an elastic medium

san andreas fault damage at safod viewed with fault guided waves 1 highly damaged rocks within the san andreas fault zone at parkfield form a low velocity waveguide for seismic waves giving rise to fault guided waves prominent fault guided waves have been observed at the san andreas fault observatory at depth safod site including a surface array across the fault zone and a borehole seismograph placed in the safod well at a depth of 2 7 km below ground the resulting observations are modeled here using 3 d finite difference methods to fit the amplitude frequency and travel time characteristics of the data the models require a downward tapering 30 40 m wide fault core embedded in a 100 200 m wide jacket compared with the intact wall rocks the core velocities are reduced by 40 and jacket velocities by 25 based on the depths of earthquakes generating guided waves we estimate that the low velocity waveguide along the fault at safod extends at least to depths of 7 km more than twice the depth reported in pervious studies

new upper homerian uppermost wenlock silurian monograptids from arctic canada five species of new or little known upper homerian uppermost wenlock graptolites are described from the arctic islands these are lobograptus sherrardae sherwin lobograptus aff sherrardae lobograptus claudiae koren lobograptus cf cornuatus lenz and pristiograptus schedidoneus n sp the first and last named species range through the pristiograptus praedeubeli and pristiograptus ludensis biozones that is through the entire upper homerian whereas the remaining three species appear to be confined to the older p praedeubeli biozone these species further document the rapid global evolution of the late homerian graptolites and this study records lobograptus claudiae koren from outside central asia for the first time

the lundgreni event in the silurian of the east european platform poland abstract the lundgreni event late wenlock silurian is here interpreted in terms of palaeontologic graptolites microphytoplankton benthos biostratigraphic and geochemical evidence derived from homerian deposits drilled in the bartoszyce well east european platform in poland the lundgreni event in the graptolite record of bartoszyce comprises extinction survival and recovery phases the graptolite extinction proceeded in three steps lundgreni testis and flemingii dubius the testis extinction eliminated the largest number of species only the long lasting pristiograptus dubius survived the combined extinctions and was joined during the survival phase by the opportunistic gothograptus nassa and pristiograptus parvus the graptolite recovery is expressed by the diachronous arrival of new species in association with p dubius all documented phytoplankton taxa survived the lundgreni event phytoplankton frequency and diversity patterns together with total organic carbon toc fluctuations indicate that oligotrophy productivity regime was unsteady during the testis and flemingii dubius extinctions and stable during the early graptolite survival there is no evidence for extinction within benthic fauna assemblages diversified benthos appeared in a great abundance during the early survival phase this records a redox related event of substrate colonization that took place simultaneously with local decline in primary productivity the last two phases of graptolite extinction and the onset of the survival correlate with strong positive anomalies of 18o 13corg and 13ccarb the anomalies coincide with the fall in local primary productivity and the enhanced storage of organic carbon in peri gondwanan upwelling zones sudeten thuringia the stepped graptolite extinction in bartoszyce occurred in an environment that was situated within the low latitude baltica shelf and was markedly stable in terms of bathymetry distance from land and oxic regime this local extinction was most likely caused by catastrophic fluctuations in nutrient supply breaking primary productivity the trophic perturbations on the baltica shelf were coeval with and related to eutrophication of the high latitude upwelling zones of the rheic ocean the postulated spatial fluctuations in the trophic resource continuum may reflect palaeooceanographic changes that accompanied the global late sea level highstand of that time

evaluating ko in champlain clays with hydraulic fracture tests hydraulic fracture tests using piezometer tips 10 500 mm long were performed in champlain clays at five different sites with overconsolidation ratios ocr varying from 1 6 to 4 8 before the test the piezometer fluid was replaced by a methylene blue solution 10 g l to dye the fissures resulting from the test after the hydraulic fracture the soil around the piezometer tips was recovered by means of a large diameter sampler for 300 and 500 mm long piezometers the fissure pattern was radial and vertical even in deposits with an ocr above unity confirming that hydraulic fracturing is related to the total stress acting on the cavity walls the results for the five sites define for the champlain clay deposits a ko ocr relationship that gives higher ko values than generally proposed in the literature key words hydraulic fracture piezometer tip sensitive clay fissure stress ratio ko overconsolidation

geological and geomorphologic asymmetry across the rupture zones of the 1943 and 1944 earthquakes on the north anatolian fault possible signals for preferred earthquake propagation direction summary the east and west rupture directions of the 1943 and 1944 earthquakes on the north anatolian fault naf are hypothesized to represent respectively long term preferred propagation directions on the corresponding sections of the naf fault sections with preferred rupture direction are expected to have an asymmetric damage structure with respect to the slipping zone to test the above hypothesis we study geological and geomorphologic manifestations of structural asymmetry with respect to the active trace of the naf along the 1943 and 1944 sections the following fault zone elements are mapped gouge fabric in the cm scale fault core structure in a metre scale and secondary faults and fault rocks in tens of metres scale mapping results at three sites on the 1943 rupture and one site on the 1944 rupture are consistent with accumulation of more rock damage on the south side of the 1943 section and on the north side of the 1944 section erosion patterns adjacent to the fault that are not correlated with the distribution of intrinsic and extrinsic erosion controlling variables e g rock type are interpreted as morphologic responses to the damage content of rocks and its impact on rock erodibility the valleys of 11 rivers are parallel to the studied fault sections about 75 per cent of the total river valleys length along the 1943 rupture is on the south side of the fault and about 89 per cent of the total river valleys length along the 1944 rupture is on the north side of the fault morphometric analysis of watersheds in two correlative terrains displaced along the 1944 rupture section shows that stream erosion is considerably more intense in the terrain north of the fault with drainage density values almost double in the north compare to the south badland topography at two sites along the 1943 rupture section is substantially more developed at the 100 m scale on the south side of fault our observations along the 1943 1944 rupture sections including various types of signals that span a large range of scales are systematically compatible with an opposite sense of damage asymmetry between the two fault sections these observations are consistent with opposite preferred direction of ruptures for the two sections similar to the propagation directions of the two recent earthquakes if those rupture directions are dictated by the velocity structure at depth we infer that the south side of the 1943 rupture has faster seismic velocity at seismogenic depth than the north side and that the sense of velocity contrast is reversed along the 1944 rupture zone

identifying the unique ground motion signatures of supershear earthquakes theory and experiments the near field ground motion signatures associated with sub rayleigh and supershear ruptures are investigated using the laboratory earthquake experiment originally developed by rosakis and co workers xia et al 2004 2005a lu et al 2007 rosakis et al 2007 heterodyne laser interferometers enable continuous high bandwidth measurements of fault normal fn fault parallel fp and vertical v particle velocity ground motion records at discrete locations on the surface of a homalite 100 test specimen as a sub rayleigh or a supershear rupture sweeps along the frictional fault photoelastic interference fringes acquired using high speed digital photography provide a synchronized spatially resolved whole field view of the advancing rupture tip and surrounding maximum shear stress field the first phase of experimental investigations examine and verify the ground motion signatures of supershear ruptures experimental results demonstrate that a shear mach front produced by a stable supershear rupture is characterized by a dominant fp velocity component the situation is shown to reverse in the sub rayleigh rupture speed regime whereby the fn particle velocity component dominates the ground motion record additional distinguishing particle velocity signatures consistent with theoretical and numerical predictions and repeatedly observed in experimental records are 1 a pronounced peak in the fp velocity record induced by the leading dilatational field which sweeps the measurement station in advance of the shear mach front and 2 a pronounced velocity swing in the fn record associated with the arrival of a trailing rayleigh sub rayleigh secondary rupture which follows the arrival of the shear mach front analysis of the particle velocity records also confirms 2d steady state theoretical predictions pertaining to the separation attenuation and radiation partitioning of the shear and dilatational portions of the rupture velocity field components the second phase of our experimental investigations re examine the 2002 mw7 9 denali fault earthquake and the remarkable set of near source ground motion records obtained at ps10 located approximately 85 km east of the epicenter and just 3 km north of the fault along the alaska pipeline motivated by the analysis and interpretation of these records by ellsworth et al 2004 dunham and archuleta 2004 2005 we attempt to mimic the denali strike slip rupture scenario and replicate the ps10 ground motion signatures using a laboratory earthquake experiment the experiments feature a left to right west to east propagating right lateral rupture within a homalite 100 test specimen with particle velocity data collected at a near field station situated just above north of the fault both sub rayleigh and supershear laboratory earthquake experiments are conducted using the denali ps10 configuration in order to compare and contrast the resulting particle velocity signatures supershear laboratory records capture all of the prominent features displayed within the ps10 ground motion records noted velocity signatures are correlated to the location of the rupture fronts and their noted arrival times in the synchronized photoelastic image sequence scaling relationships are also presented which transform the laboratory records through six orders of magnitude in time to match the scale of the ps10 ground motion records the strong correlation between the scaled experimental records and the actual ps10 ground motion records support the hypothesis that the denali strike slip fault exhibited a supershear burst finally we present a 2d steady state stress velocity formulation that relates the fp and fn particle velocity records measured close to the fault to the evolution of the stress tensor at the same location a locally steady state condition is assumed within a restricted time interval in order to invoke these relationships and estimate the dynamic stresses xx t and t at the near fault station dynamic stress measurements enable a new class of friction investigations using the laboratory earthquake configuration experimental findings are presented which capture the temporal and spatial distributions of xx and evolution of the dynamic friction coefficient and velocity weakening behavior of a supershear slip pulse

empirical settlement predictions in overconsolidated champlain sea clays using settlement observations published for several embankments on marine clays of the champlain sea an empirical model is proposed to estimate long term settlements the effect of the overconsolidation ratio is taken into consideration within the model footing and raft type foundation cases are considered to give guidelines when using the model for these foundation types a specific embankment resting on a foundation of high water content clay with a high compressibility index demonstrates that a correction factor should be applied under these conditions key words settlement embankment champlain sea clay consolidation empirical model

rupture directivity of microearthquakes on the san andreas fault from spectral ratio inversion summary earthquakes often occur on faults separating materials with different elastic properties on theoretical grounds it is expected that earthquakes on such bimaterial interfaces might have a preferred rupture propagation direction that being the direction of motion of the more compliant material the goal of this paper is to determine whether a large sample of natural earthquakes on a bimaterial interface exhibits this tendency since the creeping section of san andreas fault has a large across fault velocity contrast and has produced thousands of microearthquakes over the last few decades the rupture directions of 3100 magnitude 0 5 3 0 earthquakes were studied using spectral ratio analysis the spectral ratios of all earthquake pairs in spatially defined clusters were fitted with synthetic spectral ratios at qualified stations the synthetics were computed from a simple moving point source model in which each modelled earthquake has four parameters two rupture lengths one to the se and one to the nw and their propagation velocities the resolution of rupture directivity increases with event size such that nearly 900 events mostly those larger than 70 m appear reasonably well resolved the inversion results suggest that 40 per cent of the well resolved events are roughly bilateral although more than 80 per cent of the 144 events classified as strongly unilateral rupture to the se consistent with the theoretical prediction for those rupture halves that were large enough for the propagation speed to be somewhat resolved that speed was greater by roughly 10 per cent for those halves propagating to the se qualitatively consistent with numerical and laboratory experiments we also found that events with nearby foreshocks within several hours tend to rupture away from those foreshocks whether to the nw or to the se indicating that asymmetry of prior stressing history can exert a stronger influence on rupture directivity than the material contrast

bimaterial effects in an earthquake cycle model using rate and state friction we have developed a computational framework to study earthquake cycles in 2 d plane strain and apply it to faults separating dissimilar material we consider a planar strike slip fault governed by rate and state friction where quasi dynamic events nucleate spontaneously due to remote tectonic loading we investigate the influence of material contrast over the course of many hundreds of years for the parameters we consider we find that the presence of bimaterial properties influences the earthquake nucleation site such that rupture in the preferred direction that is in the direction of particle motion of the side of the fault with lower shear wave velocity is favorable for large values of the critical slip distance dc events propagating in the preferred rupture direction occur for a wide range of material contrasts for smaller values of dc small events emerge even in the monomaterial case with material mismatch present some of these small events propagate in the nonpreferred direction made possible by a favorable stress distribution left on the fault from previous ruptures these results may shed light on our understanding of rupture directivity on large strike slip faults like the san andreas fault in california which occasionally host events rupturing in the nonpreferred direction

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

spatiotemporal properties of sub rayleigh and supershear ruptures inferred from full field dynamic imaging of laboratory experiments many earthquakes propagate at sub rayleigh speeds earthquakes propagating at supershear speeds though less common are by far more destructive hence it is important to quantify the motion characteristics associated with both types of earthquake ruptures here we report on the spatiotemporal properties of dynamic ruptures measured in our laboratory experiments using the dynamic digital image correlation technique earthquakes are mimicked by the frictional rupture propagating along the interface of two homalite plates digital images of the propagating ruptures are captured by an ultrahigh speed camera and processed with digital image correlation in order to produce sequences of evolving displacement and velocity maps our measurements reveal the full field structure of the velocity components bridge the gap between previous spatially sparse velocimeter measurements available only at two to three locations and enable us to quantify the attenuation patterns away from the interface

upper homerian wenlock silurian graptolites and graptolite biostratigraphy arctic archipelago canada integration of graptolite data obtained from isolated and flattened material from arctic canada permits the recognition of three upper homerian biostratigraphic zones these from oldest to youngest are the pristiograptus dubius gothograptus nassa interval biozone colonograptus praedeubeli colonograptus deubeli biozone and colonograptus ludensis biozone species of flattened graptolites described in this study include c deubeli c ludensis c praedeubeli colonograptus schedidoneus lobograptus angustus n sp lobograptus claudiae lobograptus sherrardae plectograptus macilentus agastograptus clathrospinosus and gothograptus nassa with only a few exceptions the zone by zone diversity of monograptid and plectograptine graptolites of the canadian arctic is remarkably similar to that elsewhere

large deformation finite element modelling of earthquake induced landslides considering strain softening behaviour of sensitive clay large scale landslides in sensitive clays cannot be explained properly using the traditional limit equilibrium or lagrangian based finite element fe methods in the present study dynamic fe anal

palaeocope ostracods from the silurian wenlock series of arctic canada silurian wenlock series deposits of the cape phillips formation on baillie hamilton island and cornwallis island arctic canada have yielded a silicified ostracod assemblage that spans the late sheinwoodian and homerian stages sixteen palaeocope ostracod species are recorded including the new species beyrichia beyrichia marssae gabrielsella copelandi and platybolbina abruptobolbina adraini the ostracod faunas can be linked into local trilobite microvertebrate and graptolite zonal schemes and a few of the ostracod species offer potential for local and perhaps wider biostratigraphical correlation the ostracods are mostly known only from the cape phillips formation but also include two taxa found in the wenlock series of the avalanche lake area northwest territories canada other ostracod species suggest links with silurian successions in northern canada and the baltic low diversity ostracod faunas characterize the level of a marked positive carbon isotope excursion and coeval mid homerian

laboratory earthquakes along inhomogeneous faults directionality and supershear we report on the experimental observation of spontaneously nucleated ruptures occurring on frictionally held bimaterial interfaces with small amounts of wave speed mismatch rupture is always found to be asymmetric bilateral in one direction rupture always propagates at the generalized rayleigh wave speed whereas in the opposite direction it is subshear or it transitions to supershear the lack of a preferred rupture direction and the conditions leading to supershear are discussed in relation to existing theory and to the earthquake sequence in parkfield california and in north anatolia

ludlow and pridoli upper silurian graptolite biostratigraphy of the central arctic islands a preliminary report a fauna comprising slightly more than 30 species of upper silurian graptolites has been recognized from the arctic islands the following preliminary biostratigraphic biozones are recognizable l

carbon isotope excursion near the wenlock ludlow silurian boundary in the anglo welsh area oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from several exposures that show the boundary between the wenlock and ludlow series in the classic silurian areas of wales the welsh borderland and the west midlands of england our data indicate a monotonic decline in 13 c from positive to negative values across the boundary between the much wenlock limestone formation wenlock series and the lower elton formation ludlow series and correlatives in all sites investigated a slightly earlier negative excursion is also present in the upper wenlock strata of two of these localities both negative 13 c excursions appear to be contemporaneous with episodes of increased ocean ventilation and eustatic sea level lowstand postulated by kemp at least one and possibly both of the late wenlock carbon isotope depletions can also be related to the decline in pelagic graptolite diversity the distribution of the carbon isotope depletion in both carbonate platform and off shelf facies implies that this trend is unlikely to have been caused by local diagenetic alteration isotope chemostratigraphy may also provide an extra correlation tool that can be integrated with traditional biostratigraphic methods for silurian strata

postseismic fault healing on the rupture zone of the 1999 m 7 1 hector mine california earthquake we probed the rupture zone of the october 1999 m 7 1 hector mine earthquake using repeated near surface explosions in october 2000 and november 2001 three dense linear seismic arrays were deployed across the north and south lavic lake faults llfs that broke to the surface in the mainshock and across the bullion fault bf that experienced minor slip in that event two explosions each year were detonated in the rupture zone one on the middle and one on the south llf we found that p and s velocities of fault zone rocks increased by 0 7 1 4 and 0 5 1 0 between 2000 and 2001 respectively in contrast the velocities for p and s waves in surrounding rocks increased much less this trend indicates that the hector mine rupture zone has been healing by strengthening after the main shock most likely due to the closure of cracks that opened during the 1999 earth quake the observed fault zone strength recovery is consistent with an apparent crack density decrease of 1 5 within the rupture zone the ratio of travel time decrease for p to s waves was 0 72 consistent with partially fluid filled cracks near the fault zone this restrengthening is similar to that observed after the 1992 m 7 4 landers earthquake which occurred 25 km to the west li and vidale 2001 we also find that the velocity increase with time varies from one fault segment to another at the hector mine rupture zone we see greater changes on the llfs than on the bf and the greatest change is on the middle llf at shallow depth we tentatively conclude that greater damage was inflicted and thus greater healing is observed in regions with larger slip in the mainshock

back propagating super shear rupture in the 2016 mw7 1 romanche transform fault earthquake how an earthquake rupture propagates strongly influences the potentially destructive ground shaking complex ruptures often involve slip along multiple faults which masks information on the frictional behaviour of fault zones geometrically smooth ocean transform fault plate boundaries offer a favourable environment to study fault dynamics because strain is accommodated along a single wide fault zone that offsets the homogeneous geology here we present an analysis of the 2016 mw 7 1 earthquake on the romanche fracture zone in the equatorial atlantic using data from both nearby seafloor seismometers and global seismic networks we show that this rupture had two phases 1 upward and eastward propagation towards a weaker region where the transform fault intersects the mid ocean ridge and then 2 an unusual back propagation westwards at a supershear speed towards the centre of the fault we suggest that deep rupture into weak fault segments facilitated greater seismic slip on shallow locked zones this highlights that even earthquakes along a single distinct fault zone can be highly dynamic observations of back propagating ruptures are sparse and the possibility of reverse propagation is largely absent in rupture simulations and unaccounted for in hazard assessments in one earthquake an oceanic transform fault ruptured in one direction and then backwards at a speed exceeding that of shear wave propagation according to an analysis of data recorded by nearby seafloor and global seismometers

how fast is rupture during an earthquake new insights from the 1999 turkey earthquakes we report that during the two devastating 1999 earthquakes in turkey rupture propagated over a large part of the nearly 200km long fault zone at supershear speed approaching 5km s we present observations and modeling which confirm the original inference of supershear rupture during the izmit earthquake and we show that supershear rupture also occurred during the duzce earthquake we show that the rupture velocity measured about 2 times the shear wave velocity is the value predicted by theoretical studies in fracture dynamics we look for clues to explain these observations

in situ evaluation of k0 in eastern canada clays an approximate value of the horizontal effective stress in an overconsolidated clay deposit is often determined from an estimate of the effective stress ratio k0 using the equation it is also generally considered that the parameter is approximately equal to sin for evaluating k0 in sensitive clays of eastern canada a testing program has been initiated on three different sites representing a large range of overconsolidation ratios three different in situ devices were used the cambridge self boring pressuremeter the flat dilatometer and hydraulic fracturing the results show that the different techniques give essentially the same k0 values they also give k0 values larger than those expected with an parameter typically between 0 75 and 1 15 key words clay dilatometer horizontal stress hydraulic fracturing in situ tests self boring pressuremeter

the graptolites pristiograptus praedeubeli jaeger and pristiograptus ludensis murchison uppermost wenlock silurian from arctic canada taxonomy and evolution isolated uncompressed specimens of pristiograptus dubius pristiograptus praedeubeli and pristiograptus ludensis are described from arctic canada pristiograptus dubius and early forms of p

graptolite biozonation of the wenlock series silurian of the builth wells district central wales the graptolite biozonation of the wenlock series in the builth wells district is reassessed the graptolite fauna is dominated by relatively few but variable species of monograptus s s pristiograptus and monoclimacis these species are mostly long ranging and are of limited biostratigraphical use biozonation is based largely on the relatively rare cyrtograptids the lower wenlock series of the district comprises the widely recognized centrifugus murchisoni and riccartonensis biozones the middle to upper wenlock biostratigraphy differs from that previously recognized in the uk above the riccartonensis biozone dubius rigidus and lundgreni biozones are distinguished separate flexilis and ellesae biozones are not recognized monograptus flexilis appears earlier than then largely co exists with cyrtograptus rigidus s l while cyrtograptus ellesae appears later than cyrtograptus lundgreni the uppermost wenlock nassa ludensis biozone is sparsely fossiliferous its subdivision has not proved possible this revised biostratigraphical scheme for the wenlock series of the builth wells district suggests that the sheinwoodian homerian boundary as defined in the welsh borderland might occur within rather than at the base of the lundgreni biozone however difficulties in correlation with other wenlock sequences particularly overseas suggest significant biofacies control with the wenlock seas of the builth wells district appearing to have been periodically inhospitable to graptolites

proprietes caracteristiques des argiles de l est du canada the compilation of numerous geotechnical data has allowed the definition of the main physical mechanical and hydraulic properties of marine and lacustrine clays of eastern canada as well as the establishment of correlations between some of these properties the possible uses of these correlations are described this study shows that the clays of eastern canada exhibit a behaviour similar to that of other clays but that they are characterized by a higher degree of structuration keywords physical properties mechanical properties hydraulic properties clays canada correlations journal translation

how well do surface slip measurements track slip at depth in large strike slip earthquakes the importance of fault structural maturity in controlling on fault slip versus off fault surface deformation abstract comparisons of observed surface displacements with geodetically inferred slip at depth in six large m w 7 1 strike slip earthquakes reveal a correlation between the structural maturity of the fault and the ratio of deep slip to surface slip that occurs on localized zones of surface rupture specifically structurally immature faults 25 km of total displacement manifest only 50 60 of total slip on narrow fault surface traces versus 85 95 for structurally mature faults 85 km total slip the same pattern holds when structurally simple parts of a surface rupture are analyzed separately from parts that exhibit obvious structural complexity e g discontinuous or multiple traces or significant dip slip these results imply that geologic measurements of surface slip along structurally immature faults are likely to significantly underestimate the true slip at depth in large earthquakes this observation has implications for a number of important problems including determination of fault slip rates which are based on surface offsets earthquake probability assessments which are based on geologic fault slip rates comparisons of geologic and geodetic rate data in the search for strain transients the structural evolution of fault zones estimation of paleo earthquake magnitudes based on geomorphic offsets analyses of the relative importance of faulting vs distributed deformation in accommodating relative plate motions in continental crust the design and construction of infrastructure built near active faults and possibly for the prediction of strong ground motions which may at least partially depend on the degree of slip localization to the surface

llandovery lower silurian graptolites from the sepon mine truong son terrane central laos and their palaeogeographical significance abstract graptolites are described from the llandovery of the sepon mine area central laos part of the truong son terrane the palaeobiogeographical affinities of the rhuddanian graptolites are with peri gondwanan europe and arabia rather than equatorial regions such as south china and laurentia arctic canada a review of previous palaeontological research on the middle palaeozoic of the indochina terranes reveals an often contradictory picture with vertebrates suggesting close proximity of south china to the truong son terrane in the devonian and invertebrates and radiolarians providing evidence for a palaeogeographical barrier between the two graptolites from the mojiang area yunnan are typical of low latitude silurian faunas and suggest that this area simao or loei terrane was separate from the truong son terrane

initial investigations of the soft clay test site at bothkennar this paper presents findings from a wide range of in situ tests and laboratory investigations of the soft silty clay at bothkennar many of which were undertaken prior to the purchase of the site the soft clays at bothkennar are unusual in being remarkably uniform compared to other similar deposits in the uk this is thought to result from their deposition under rather stable estuarine conditions during the period 8500 6000 years before present bp thus apart from the presence of a highly laminated zone in the south east corner the soft clay is generally consistent across the site with many engineering properties increasing linearly with depth in contrast with many other soft clays the bothkennar clay has high effective strength parameters and high undrained strength the site appears to be ideal for a wide range of research and the presence of the highly laminated zone only enhances its potential cet article presente les resultats d une grande variete d essais in situ et en laboratoire de l argile

material contrast does not predict earthquake rupture propagation direction 1 earthquakes often occur on faults that juxtapose different rocks the result is rupture behavior that differs from that of an earthquake occurring on a fault in a homogeneous material previous 2d numerical simulations have studied simple cases of earthquake rupture propagation where there is a material contrast across a fault and have come to two different conclusions 1 earthquake rupture propagation direction can be predicted from the material contrast and 2 earthquake rupture propagation direction cannot be predicted from the material contrast in this paper we provide observational evidence from 70 years of earthquakes at parkfield ca and new 3d numerical simulations both the observations and the numerical simulations demonstrate that earthquake rupture propagation direction is unlikely to be predictable on the basis of a material contrast

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

wenlock silurian graptolite biostratigraphy of the cape phillips formation canadian arctic islands the canadian arctic islands wenlock is represented by a diverse assemblage of graptolites from the cape phillips formation cyrtograptids are continuously present throughout all but the uppermost wenlock species of cyrtograptus constitute the main basis for biostratigraphic zonation supported to a much lesser degree by monograptus monoclimacis and pristiograptus through most of the series the uppermost wenlock is dominated by pristiograptus in association with rare gothograptus the following biostratigraphic zones and their correlations are proposed 1 cyrtograptus centrifugus cyrtograptus insectus zone earliest wenlock 2 cyrtograptus aff rigidus monograptus aff riccartonensis zone late early wenlock 3 cyrtograptus perneri monograptus cf munchi zone in which cyrtograptus multiramis is a particularly common element mid wenlock age 4 cyrtograptus lundgreni monograptus testis zone divisible into a lower monograptus testis n ssp and an upper monograptus testis testis subzon

the 1999 izmit turkey earthquake a 3d dynamic stress transfer model of intraearthquake triggering before the august 1999 izmit kocaeli turkey earthquake theoretical studies of earthquake ruptures and geological observations had provided estimates of how far an earthquake might jump to get to a neighboring fault both numerical simulations and geological observations suggested that 5 km might be the upper limit if there were no transfer faults the izmit earthquake appears to have followed these expectations it did not jump across any step over wider than 5 km and was instead stopped by a narrower step over at its eastern end and possibly by a stress shadow caused by a historic large earthquake at its western end our 3d spontaneous rupture simulations of the 1999 izmit earthquake provide two new insights 1 the west to east striking fault segments of this part of the north anatolian fault are oriented so as to be low stress faults and 2 the easternmost segment involved in the august 1999 rupture may be dipping an interesting feature of the izmit earthquake is that a 5 km long gap in surface rupture and an adjacent 25 restraining bend in the fault zone did not stop the earthquake the latter observation is a warning that significant fault bends in strike slip faults may not arrest future earthquakes manuscript received 30 august 2000

laboratory earthquakes the sub rayleigh to supershear rupture transition we report on the experimental observation of spontaneously nucleated supershear rupture and on the visualization of sub rayleigh to supershear rupture transitions in frictionally held interfaces the laboratory experiments mimic natural earthquakes the results suggest that under certain conditions supershear rupture propagation can be facilitated during large earthquake events

the mid homerian silurian biotic crisis in offshore settings of the prague synform czech republic integration of the graptolite fossil record with conodonts shelly fauna and carbon isotope data abstract the middle homerian biotic crisis resulted in the almost complete eradication of graptolites the shale dominated kosov quarry section central bohemia preserves the most complete graptolite record across the crisis in peri gondwanan europe the pre extinction graptolite assemblage of the upper lundgreni biozone composed of ten species vanished in three extinction phases recognized in an interval 1 6 m thick the crisis commenced with the increasing dominance of generalist taxa and subsequent extinction of several abundant species including cyrtograptus lundgreni the second phase coincided with the extinctions of genera cyrtograptus and testograptus whereas long ranging generalist monograptids prevailed before they became extinct as the crisis culminated in its third phase in the flemingii biozone the lower part of the overlying parvus biozone contains only pristiograptus parvus which became abundant in the upper part of the biozone together with incoming gothograptus nassa the recovery interval is marked by a moderate diversification of monograptids and retiolitids the extinction did not affect the diversity of pelagic cephalopods although their abundance was reduced a bivalve dominated benthic fauna disappeared throughout the extinction interval and re appeared not earlier than in the latest homerian it was temporarily replaced by a time specific fauna of anachronistic trilobites and brachiopods the extinction interval coincided with sea level fall indicated by limestone slump beds in a generally shaly succession the post extinction interval corresponds with a lowstand systems tract with deposition of condensed shelly limestone and burrowed shale a positive carbon isotope excursion started in the flemingii biozone and 13c values increased up to the lower parvus biozone above which the plateau of the first peak started the beginning of the graptolite extinction predated the early phase of the late homerian carbon isotope excursion the terminal phase of the extinction nevertheless coincided with the onset of the carbon isotope excursion and change in benthic fauna

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

in situ lateral stress coefficient k0 from shear wave velocity measurements in soils abstractthe at rest lateral stress coefficient k0 is an important soil parameter in geotechnical design problems and yet it is quite elusive in our ability to assess its value either by laboratory or in situ tests in this study an innovative geophysics approach toward the evaluation of the in situ k0 profile with depth is obtained by using small strain stiffness anisotropy ratio g0 hh g0 vh in soils the newly proposed k0 equation is derived from a database compiled from 12 test sites which have direct k0 measurements as procured from field tests either self boring pressuremeters sbp or total stress cells tsc and or laboratory triaxial tests instrumented consolidometers and or suction measurements the data show a strong relationship between the overconsolidation difference ocd p vo and stiffness anisotropy ratio thus enabling a k0 assessment in clays silts and sands

healing of the shallow fault zone from 1994 1998 after the 1992 m7 5 landers california earthquake we conducted seismic surveys at the johnson valley fault in 1994 1996 and 1998 we found that the shear velocity of the fault zone rock increased by 1 2 between 1994 and 1996 and increased further by 0 7 between 1996 and 1998 this trend indicates the landers rupture zone has been healing by strengthening after the mainshock most likely due to the closure of cracks that opened during the 1992 earthquake the observed fault zone strength recovery is consistent with a decrease of 0 03 in the apparent crack density within the fault zone the ratio of decrease in travel time for p to s waves changed from 0 75 in the earlier two years to 0 65 in the later two years between 1994 and 1998 suggesting that cracks near the fault zone are partially fluid filled and have became more fluid saturated with time

off fault plasticity and earthquake rupture dynamics 1 dry materials or neglect of fluid pressure changes 1 we analyze inelastic off fault response during earthquakes spontaneous crack like rupture with slip weakening is modeled in 2 d plane strain using an explicit dynamic finite element procedure a mohr coulomb type elastic plastic description describes the material bordering the fault we identify the factors which control the extent and distribution of off fault plasticity during dynamic rupture those include the angle with the fault of the maximum compressive prestress the seismic s ratio and the closeness of the initial stress state to mohr coulomb failure plastic response can significantly alter the rupture propagation velocity delaying or even preventing a transition to supershear rupture in some cases plastic straining also alters the residual stress field left near the fault in part 1 we consider dry materials bordering the fault or at least neglect pore pressure changes within them part 2 addresses the effects of fluid saturation showing that analysis procedures of this part can describe undrained fluid saturated response elastic plastic laws of the type used are prone to shear localization resulting in an inherent grid dependence in some numerical solutions nevertheless we show that in the problems addressed the overall sizes of plastic regions and the dynamics of rupture propagation seem little different from what are obtained when we increase the assumed plastic hardening modulus or dilatancy parameter above the theoretical threshold for localization obtaining a locally smooth numerical solution at the grid scale evidence for scaling of some localization features with a real nongrid length scale in the model is also presented

llandovery graptolite biostratigraphy and paleobiogeography cape phillips formation canadian arctic islands llandovery graptolites have been collected from 11 sections in the cape phillips formation of the canadian arctic archipelago melville bathurst truro cornwallis devon and ellesmere islands the cape phillips formation appears to have been deposited in a distinct subbasin here termed the cape phillips basin under deep shelf to shallow basin conditions intermediate in position between the arctic platform to the south and east and the deeper hazen trough to the northwest a total of 170 graptolite species and a further 25 subspecies have been identified their stratigraphic distribution allows the recognition of 11 graptolite zones the acuminatus atavus acinaces cyphus curtus convolutus minor turriculatus crispus griestoniensis and sakmaricus zones the curtus zone can be subdivided into the pectinatus and orbitus subzones the zones can be correlated with graptolite sequences worldwide the canadian arctic faunas show strong affinities with those of siberia china and the northern canadian

dynamic rupture propagation on fault planes with explicit representation of short branches abstract an active fault zone is home to a plethora of complex structural and geometric features that are expected to affect earthquake rupture nucleation propagation and arrest as well as interseismic deformation simulations of these complexities have been largely done using continuum plasticity or scalar damage theories in this paper we use a highly efficient novel hybrid finite element spectral boundary integral equation scheme to investigate the dynamics of fault zones with small scale pre existing branches as a first step towards explicit representation of anisotropic damage features in fault zones the hybrid computational scheme enables exact near field truncation of the elastodynamic field allowing us to use high resolution finite element discretization in a narrow region surrounding the fault zone that encompasses the small scale branches while remaining computationally efficient our results suggest that the small scale branches may influence the rupture in ways that may not be realizable in homogenized continuum models specifically we show that these short secondary branches significantly affect the post event stress state on the main fault leading to strong heterogeneities in both normal and shear stresses and also contribute to the enhanced generation of high frequency radiation the secondary branches also affect off fault plastic strain distribution and suggest that co seismic inelasticity is sensitive to pre existing damage features we discuss our results in the larger context of the need for modeling earthquake ruptures with high resolution fault zone physics

late wenlock ludlow silurian graptolite extinction evolution and biostratigraphy perspectives from arctic canada late wenlock early ludlow was a period of profound change in the graptolite world and two crises are evident the most important changeover occurred within the late wenlock homerian stage during which time cyrtograptus became extinct monograptids while severely reduced introduced new thecal and and sicular types and plectograptines underwent a striking diversification the second lesser change coincided with the wenlock ludlow boundary at which time monograptids reemerged as the dominant taxon group and plectograptines declined and shortly thereafter became extinct two species pristiograptus praedeubeli jaeger and lobograptus cornuatus n sp recovered in isolated and uncompressed form are described and illustrated the presence of the former species permits the subdivision of the upper homerian of the canadian arctic into two biozones the lower pristiograptus praedeubeli biozone and the upper pristiograptus ludensis pristiograptus sherrardae biozone both species exemplif

in situ and laboratory stress strain relationships the question of whether or not the end of primary consolidation curve from laboratory oedometer tests is representative of in situ behaviour has been the subject of much discussion the behaviour of the berthierville test embankment is described and in situ effective stress strain curves are defined for two well defined clay sublayers these compressibility curves are then compared with laboratory end of primary consolidation curves similar comparisons are also made for sublayers under three other well instrumented embankments all the results show that the laboratory end of primary consolidation curve strongly underestimates in situ settlements and thus that theory a is not valid on s est souvent demande si la courbe de la fin de consolidation primaire obtenue a partir d essais oedometriques en laboratoire represente effec tivement le comportement en place l article decrit le comportement du remblai experimental de berthierville et definit les courbes contrainte deformation effectives en place pour de

fault healing inferred from time dependent variations in source properties of repeating earthquakes we analyze two sets of repeating earthquakes on the calaveras fault to estimate in situ rates of fault strengthening healing earthquake recurrence intervals tr range from 3 to 803 days variations in relative moment and duration are combined to study changes in stress drop rupture dimension rupture veloc ity and particle velocity as a function of t healing rates and source variations are compared with predictions of laboratory derived friction laws two interpretations of event duration z are used one in which is given by the ratio of slip to particle ve locity and one in which it scales as rupture dimension divided by rupture velocity our data indicate that faults strengthen during the interseismic period we infer that source dimension de creases with t r due to aseismic creep within the region surround ing the repeating events stress drop increases 1 3mpa per dec ade increase in twhich represents an increase of a factor of 2 3 relative to events with tbetween 10 and 100 days this rate of fault healing is consistent with extrapolations of laboratory meas urements of healing rates if fault strength is high on order of 60mpa and stress drop is roughly 10 of this value

rupture dynamics on a bimaterial interface for dipping faults dip slip faulting may juxtapose different geologic materials with differ ent properties such that a strong material contrast will naturally tend to form both the material contrast across a fault and dip slip motion on a nonvertical fault lead to normal stress variations during earthquake rupture this normal stress variation will significantly affect dynamic rupture propagation to demonstrate this we model dynamic rupture propagation on two dimensional 2d reverse and normal faults 30 45 and 60 dipping with 20 material contrasts for predominantly up dip rupture propagation we find that normal stress variations due to the free surface and material contrast can either reinforce or counteract each other depending on the configuration for reverse faults we find a larger strength drop for a more com pliant hanging wall and a lower strength drop for a more compliant footwall for normal faults we find a larger strength drop for a more compliant footwall and a lower strength drop for a more compliant hanging wall for both reverse and normal faults ground motion will be more symmetric between the hanging wall and footwall with compliant material on the footwall and more asymmetric if more compliant materials are on the hanging wall our results have important implications for the dynamics of crustal and perhaps subduction zone earthquake faulting where strong bimaterial contrasts across dipping faults are possible in continental settings reverse faulting will tend to advect rigid materials from greater depth onto the hanging wall such that the effects of fault dip and material contrast will counteract one another in subduction zones the hanging wall is likely to be more compliant and hence the material and geometric effects may reinforce one another

assessing the coefficient of the earth pressure at rest from shear wave velocity and electrical resistivity measurements abstract determination of earth pressure coefficient k 0 in natural soil deposits is a significantly important issue in geotechnical engineering this paper evaluates the feasibility of predicting k 0 values from measurements of vertical and horizontal shear wave velocities v s vh v s hh and v s hv and vertical and horizontal electrical resistivities s v s h a series of seismic piezocone tests scptu improved crosshole ch tests and soil resistivity tests using a modified laboratory apparatus were carried out at two research sites in jiangsu province of china and results were used to develop two existing k 0 shear wave velocity correlations for prediction of k 0 the seismic and electrical resistivity test results showed that both the shear wave velocity ratios v s hh v s hv or v s hv v s vh and the horizontal to vertical electrical resistivity ratio s h s v may provide a good indicator of the inherent soil anisotropy at these sites the existing v s k 0 prediction framework largely requires determining c s hv c s hh ratio and a simple procedure for evaluating this ratio based on the measured horizontal and vertical electrical resistivities the k 0 values predicted by shear wave velocity at both sites are also compared with values determined by jaky s formula and mayne kulhwy s formula in normally consolidated nc soils the k 0 values predicted from these methods showed good agreement however for over consolidated oc soils at shallow depths certain variations between different methods are noted further investigations of the effects of overconsolidation ratio on k 0 predictions will lead to the correction factors for better prediction of k 0 for oc soils this paper has confirmed that reasonable predictions of k 0 for natural soil deposits can be made using the proposed methodology

ground motion signatures of supershear ruptures in the burridge andrews and free surface induced mechanisms abstract we analyze the ground motions of supershear ruptures in the burridge andrews bam and free surface induced fsi mechanisms bam supershear ruptures require higher initial shear stress than fsi supershear ruptures thus cause faster rupture speed the supershear slip pulse initiates at the free surface or upper boundary of a fault for fsi and at the hypocenter depth in the in plane direction for bam in homogeneous models both bam and fsi supershear ruptures can generate mach waves and the rayleigh wave field the bam and the faster fsi supershear ruptures can make stronger shear mach waves the shear mach waves show a larger amplitude of negative component for a faster fsi supershear rupture the fsi supershear ruptures make the strongest dilatational wave next to the fault while it is at a distance away from the fault for the bam supershear ruptures the different shapes of supershear rupture front locations of supershear triggered and the rupture speeds contribute to these contrasts and we find that the bam and the faster fsi supershear ruptures can trigger more high frequency radiation due to the sharper and stronger shear mach waves finally the comparisons between the simulated seismograms and the records of ps10 indicate that the 2002 denali earthquake may represent a supershear one with the fsi mechanism and a slow supershear rupture speed

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

earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod 1 arrival time data from 453 local earthquakes and 6 explosions at parkfield ca are inverted for earthquake locations and three dimensional vp and vp vs structure the structure is dominated by the velocity contrast across the saf with the southwest side about 20 25 faster consistent with previous studies nearly all the earthquakes occur almost directly beneath the fault trace we find high vp vs anomalies that correlate with low resistivity features in a magnetotelluric model that are interpreted to represent fluids we locate a magnitude 2 earthquake that is a potential target event for the final stage of safod drilling yielding a depth of 3 1 km below surface and an epicenter 100 m southwest of the fault trace nonlinear analyses indicate 95 confidence relative and absolute uncertainties on the order of 500 700 m vertically and 200 300 m horizontally for this target earthquake

the brachymetopid trilobite radnoria in the silurian wenlock of new york state and arctic canada radnoria bretti n sp from the wenlock sheinwoodian rochester formation of western new york state is the best preserved and most completely known member of its genus it provides the first definitive information on radnoria s hourglass shaped rostral plate the first known hypostome of a silurian member of the genus demonstrates that radnoria engaged in sphaeroidal enrollment and reveals that early holaspid individuals had tubercles on the posterior thoracic axes and pygidial axial rings that were effaced with maturity three new species from the wenlock of the cape phillips formation of nunavut are known from sparse material and are reported in open nomenclature together the species greatly increase knowledge of laurentian silurian brachymetopids which have until now been known from a single cranidium from the wenlock of arkansas

evaluating the in situ lateral stress coefficient k0 of soils via paired shear wave velocity modes abstractthe utilization of shear wave velocities toward the evaluation of the in situ geostatic horizontal stress state in soils is validated specifically the lateral stress coefficient k0 field shear wave velocities from paired sets of different directional and polarization modes are compiled from 16 well documented test sites involving a variety of geomaterials focus is particularly placed on shear wave velocities measured by downhole tests vsvh crosshole tests vshv and special rotary type crosshole tests vshh at these sites field k0 stress states have been quantified using one or more direct assessment techniques including self boring pressuremeter total stress cells and hydrofracture in field testing as well as suction measurements special consolidometers and or triaxial arrangements on undisturbed samples in the laboratory although the specific delineation of stress induced versus inherent or fabric anisotropy may be difficult it is shown that the ratio of horizontally polarized