modelling shoreface profile evolution current knowledge of hydro sediment and morpho dynamics in the shoreface environment is insufficient to undertake shoreface profile evolution modelling on the basis of first physical principles we propose a simple panel type model to map observed behaviour the internal dynamics are determined by slope dependent wave induced cross shoreface transports while the external driving factors are lateral sediment supply and sea level rise this model concept is tested with reasonable success against the observed behaviour of the central holland coast considering two hindcast periods one covering the evolution over the last century the other the subboreal subatlantic evolution a limitation of this model is that the cross shoreface dynamics are solely steered by the variations of shoaling short waves since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment transport formula this limits the accuracy of the coefficients as used and our findings should be considered as an order of magnitude estimate only indeed behaviour oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward yet we expect that some of the conclusions are more generally applicable this concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing a worthwhile observation from the holland coast application is that the bottom slope effect on the transport is only important at geological time scales the profile evolution at the engineering time scales say 10 to 100 years is effectively quasi static in that there is no feedback between the long term averaged transport and the state of the profile this implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance this does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution it is only unimportant if a highly aggregated model like this is applied at relatively short time scales

earthquake recurrence on the southern san andreas modulated by fault normal stress earthquake recurrence data from the pallett creek and wrightwood paleoseismic sites on the san andreas fault appear to show temporal variations in repeat interval these sites are located near cajon pass southern california where detailed mapping has revealed geomorphically and structurally expressed domains of alternating extension and contraction respectively associated with releasing and restraining bends of the san andreas fault we investigate the interaction between strike slip faults and auxiliary reverse and normal faults as a physical mechanism capable of producing such variations under the assumption that fault strength is a function of fault normal stress e g byerlee s law failure of an auxiliary fault modifies the strength of the strike slip fault thereby modulating the recurrence interval for earthquakes in our finite element model auxiliary faults are driven by stress accumulation near restraining and releasing bends of a strike slip fault earthquakes occur when fault strength is exceeded and are incorporated as a stress drop which is dependent on fault normal stress the model is driven by a velocity boundary condition over many earthquake cycles resulting synthetic strike slip earthquake recurrence data display temporal variations similar to observed paleoseismic data within time windows surrounding auxiliary fault failures although observed recurrence data for the two paleoseismic sites are too short to be definitive about the temporal variations or the physical mechanism responsible for it our simple model supports the idea that interaction between a strike slip fault and auxiliary reverse or normal faults can modulate the recurrence interval of events on the strike slip fault possibly producing short term variations in earthquake recurrence interval

strain accumulation in western united states this review is principally concerned with recent geodetic strain measure ments in western united states undertaken by the us geological survey as part of the earthquake studies program and as a consequence is heavily biased toward the author s own publications most of the publications reporting crustal strain measurements in western united states prior to about 1968 have been compiled in one volume national geodetic survey 1973 and more recent work with complete bibliographies is summarized in three successive quadrennial reports to the international union of geodesy and geophysics meade 1971 savage 1975 thatcher 1979b the following conventions are employed in this paper strain a dimensionless quantity is reported in units of 10 6 extension is taken as positive to distinguish between engineering and tensor shear strain we denote the former by y and quote the units as j lrad whereas the latter is denoted by e and given the units of j lstrain uncertainties in all cases are quoted as one standard deviation at the present time geodetic techniques furnish the only reliable measure of strain accumulation in the seismic regions of the world the superiority of geodetic techniques derives principally from the long baseline of the measurements difficulties in coupling fiducial marks to the earth have generally made short baseline measurements of strain accumulation questionable wyatt 1982 however long baselines introduce the dis advantage that the measured strain is not closely localized the current technique of measuring strain accumulation involves the

stressing of locked patches along a creeping fault an analysis is presented of the stressing of locked patches along a fault zone which is creeping elsewhere the model consists of strike slip faulted elastic lithospheric plates loaded in a manner equivalent to imposition of a remotely uniform tectonic shear stress the fault zone has an inhomogeneous strength distribution both depth wise and along strike it is modeled as being composed of locked patches and freely slipping parts treated as cracks the solution is given with the use of the line spring model which analyzes the problem by thickness averaged plane stress theory for lithospheric plates which slip along a discontinuity cut at the plate boundary as a boundary condition thickness averaged stress and slip at each local section along the cut was related to one another by the result of an antiplane strain analysis of slip for the crack or crack pair which describes the slipping and locked depth ranges at that section the analysis indicates that the slip distribution along creeping parts of the fault as well as the stress distribution along locked patches depends strongly on the geometry of these zones the model is used to examine stress concentrations associated with a slip deficient seismic gap along strike and to study the effect of local irregularities in the margin of a locked region it is also used to simulate slip and stressing processes associated with the creeping portion of the san andreas fault in central california between the presently locked zones of the great 1906 and 1857 ruptures and to constrain the nature of an apparently locked zone at the southeastern end which ruptures in characteristic parkfield earthquakes near fault creep and broadscale displacement data along the fault since the 1966 parkfield earthquake and inferences from seismicity distributions are used limitations of the modeling procedure at short spatial wavelengths prohibit an accurate description of the parkfield locked patch but results suggest that it may be localized and occupy a small fraction of area of the normal seismogenic zone an effective remote stressing rate of order 0 3 10 6 shear modulus yr is inferred together with a less well constrained 30 to 40 km lithospheric thickness for consistency with the displacement data results enable estimates of stress accumulation along the locked 1857 rupture zone and the build up of fracture energy release capability of order 107 j m2 in 150 yr at its lower margin

prediction of cross shore sediment transport at different spatial and temporal scales abstract coastal sediment transport and associated morphological change can be examined at many spatial and temporal scales these scales range from instantaneous movement of single grains on a time scale of the local turbulence to seasonal and long term movement of large sand bodies such as longshore bars and tidal deltas researchers have begun to recognize that a first principles microscale approach to calculating long term and large scale megascale coastal change may not be possible or even adequate therefore new approaches are being sought to advance quantitative understanding and prediction of large scale coastal behavior the present paper opens with a discussion of compatible spatial and temporal scales for calculating sediment transport and morphology change motivation is given for the need to calculate morphologic change at scales greater than the typical one of microscale example calculations are made at different scales showing the assumptions and approximations of each the main conclusion is that calculations at different scales can be related and reconciled if limitations in prediction of initial and boundary conditions and in the fluid forcing are recognized

dated evidence of the interaction between humans and megafauna in the late pleistocene of sergipe state northeastern brazil abstract we present a radiocarbon date 12 742 12 562 cal bp for an eremotherium laurillardi tooth found in sergipe state northeastern brazil which shows anthropogenic marks our result provides additional information and reinforces the hypothesis that humans was present in south america earlier than accepted currently and interacted with megafauna during the late pleistocene in this region

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

stress transfer during three sequential moderate earthquakes along the central calaveras fault california seismic and geodetic information on three sequential moderate earthquakes the 1979 m5 9 coyote lake the 1984 m6 2 morgan hill and the 1988 m5 1 alum rock along the central calaveras fault is used to examine how tractions on fault segments are transferred from one fault segment to the other geodetic data obtained before and after each earthquake are inverted for slip at depth the perturbed stress field induced by each earthquake is calculated using 3 d elastic dislocation theory although only long wavelength features of the slip distributions are well resolved the model suggests that the distribution of slip is nonuniform the largest slips tend to occur in regions having relatively few aftershocks or near the hypocenter according to the model the coyote lake earthquake induced 0 1 1 bar 0 01 0 1 mpa shear stress across the northern part of the morgan hill segment and only about 0 1 bar at the hypocenter of the morgan hill mainshock a shear stress of 0 5 bar was induced by the morgan hill earthquake at the hypocenter of the alum rock mainshock the average stress drops for the coyote lake morgan hill and alum rock earthquakes are estimated to be 30 25 and 15 bars respectively thus the earthquake induced shear stress of 0 1 0 5 bar at the hypocenter of the next earthquake is only a few percent of the total stress drop and cannot be solely responsible for the occurrence of the sequential earthquakes however the induced shear stress can trigger the adjacent earthquakes in the sense that adjacent earthquakes would have occurred at a later time if there was no such coseismic stress transfer it is inferred that fault geometry may influence the local stress field thereby initiation and termination of the rupture but not the regional stress accumulation

systematic search for repeating earthquakes along the haiyuan fault system in northeastern tibet repeating earthquakes have been found at many faults around the world and they provide valuable information on diverse faulting behavior at seismogenic depth the haiyuan fault is a major left lat

analysis of beach morphodynamics on the bragantinian mangrove peninsula para north brazil as prerequisite for coastal zone management recommendations a beach profile monitoring programme was initiated in 1997 as a contribution to the development of recommendations for an integrated coastal zone management scheme of the mangrove peninsula of braganca state of para north brazil it was the first scientific investigation on the coastal morphodynamics in a mangrove environment which was opened for human use only since the mid 1970s the observations were carried out on five sections for 4 years on a fortnightly basis whenever possible temporal evolution of the beach morphology was assessed using time series of beach height changes in profile shape sediment transport calculations and photographs this unique data set for new settlement areas in this mangrove dominated coastal zone illuminates the role of the interaction between human activities and natural coastal dynamics four coastal cells were identified as coastal management units each with specific dynamic behaviour and utilisation by humans the cells are rather small with dimensions in the order of 1 3 km only one of the units cell 1 had a stable coastline during the 4 years of observation while all others are eroding clearing of vegetation is the principal reason for the enhancement of the natural chronic erosion at these sites in the wake of increasing tourism housing was erected on the first dune ridge cell 2 with much damage to the natural vegetation in this unit erosion is predominantly targeted on the dunes in cell 3 the most important reason for the increased erosion is clearing of the adjacent fringing mangroves this is also true for cell 4 but additionally the construction of large fishing traps which artificially entrap sand and create sandbanks and thereby increase velocities in the tidal channel tend to enhance erosion at the shoreline only for cell 1 can protection measures for the still available vegetation be recommended while a planned retreat of many tourism facilities and fishermen s housings should be included in management recommendations

stress diffusion along rupturing plate boundaries an analysis is made of viscoelastic lithosphere asthenosphere coupling in the time dependent redistribution of stress along plate boundaries or other seismic lineaments following great earthquakes the study is based on a generalization by rice of elsasser s model of stress diffusion in which general elastic plane stress deformations are allowed in lithospheric plates which are coupled in an elementary way to a maxwellian viscoelastic asthenosphere solutions are developed which describe the large scale quasistatic distribution of thickness averaged in the lithosphere at or near stationary or travelling rupture zones modeled here by either crack like zones of fixed stress drop or dislocation type slip zones sudden ruptures shed load onto the asthenosphere which is gradually transferred back to the lithosphere by a slow relaxation process the spatial and temporal characteristics of the predicted stress alterations suggest a significant role of lithosphere asthenosphere coupling effects in triggering interactions of great earthquakes patterns of prolonged aftershock activity and the breaking of barriers or gaps by time dependent stressing

a probability method for predicting time dependent long term shoreline erosion this paper describes a practical procedure for predicting the probability distributions of long term shoreline erosion it treats the dynamical response of the shoreline over time as that of a time dependent stochastic system the input to the system are the long term wave climate and shoreline properties while the output of the system are the probability distributions of the maximum shoreline recession within any prescribed time period the procedure enables the combined effect of the longshore and cross shore sediment transport processes on the shoreline erosion to be taken into account as both processes are generally responsible for the maximum shoreline recession a series of simulations using idealised long term wave distributions which have relatively narrow directional spread was carried out to evaluate the capability of the method based on these simulations it was found that both the distributions and variability of wave climates have significant influence on the predicted shoreline erosion probability distributions while the chronology effect is less significant especially for long simulation time

moho orientation beneath central california from regional earthquake travel times table al is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 011 2 50 payment must accompany order analysis of relative pn travel times recorded by 238 stations of the u s geological survey central california seismic network calnet from 77 regional earthquakes and explosions shows that arrivals are progressively delayed to the northeast in both the coast ranges and sierra nevada foothills by dividing the calnet into 10 subarrays and assuming laterally uniform velocities for a crust over an upper mantle half space the orientation of a planar moho beneath each subarray is calculated by inversion of relative pn arrival times the results show that the moho dips to the northeast between 3 and 6 beneath the coast ranges and 8 17 beneath the great valley and is horizontal beneath the foothills pn residuals west of the san andreas fault are relatively early by 0 35 s but are interpreted as resulting from a lateral velocity contrast across the fault rather than variations in crustal thickness unexplained pn travel time variance improves by approximately 60 after correction for the travel time due to dip and mean pn residual at each station the pn data corrected for the travel time due to a dipping moho indicate an isotropic upper mantle velocity of 7 97 0 05 km s beneath the coast ranges great valley and foothills evidence of upper mantle velocity anisotropy in the azimuthal variation in pn apparent velocity corrected for dip is only marginally significant at the 5 level however large azimuthal variations in corrected apparent velocity do exist and may be attributed to velocity heterogeneities in the crust unmodeled higher order mantle structure and gradients in upper mantle velocity arrival times of cape mendocino earthquakes recorded in the coast ranges south of san francisco bay indicate lateral variations in upper mantle velocity the 7 4 km s apparent velocity estimate from travel times of the oroville earthquake recorded in the coast ranges out to distances greater than 400 km is anomalous in that pn is normally observed at distances greater than 200 km these arrivals may originate from updip propagation along a 6 9 km s layer in the lower crust of the coast ranges subparallel to the moho

postseismic deformation induced by brittle rock damage of aftershocks 1 large earthquakes are commonly followed by abundant aftershocks that are densely located around the coseismic rupture zone laboratory experiments indicate that microscopic brittle rock failures acoustic emission are associated collectively with a macroscopic damage related inelastic relaxation utilizing basic relations between local brittle failures and gradual inelastic strain in a viscoelastic damage rheology model we develop connections between aftershock decay rates and the aftershocks induced component of geodetic deformation the discussed mechanism is relevant for postseismic relaxation produced by sources located within the seismogenic zone and especially in regions that overlap locations of high aftershocks activity assuming the omori utsu decay rate for aftershocks we find that the temporal decay of the damage related postseismic relaxation follows a generalized power law relation with the standard omori utsu law as a limit case the results provide a way for estimating the separate contributions to observed postseismic displacements that stem from brittle failures in the seismogenic zone aftershocks and other aseismic processes using the obtained theoretical expectations we analyze postseismic displacements measured by gps stations around the north anatolian fault 3 months following the 1999 m7 4 izmit earthquake we find that the observed postseismic displacements decay slower than the aftershock seismicity based on our theoretical results we conclude that up to 50 of the measured surface displacements at near fault sites can be attributed to aftershock induced inelastic deformation in the seismogenic zone the remainder postseismic deformation can generally be explained by relaxation in the deeper ductile substrate

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

simulation of collision zone segmentation in the central mediterranean abstract collision processes between the african and european plates in the ionian sea offshore calabria and in sicily take place in several ways to the east normal subduction of oceanic crust underlying the ionian sea occurs underneath the calabrian arc whereas to the west continental collision between the pelagian block and the calabrian arc which extends from calabria to the northeastern tip of sicily and offshore of the island to the north gives rise to the maghrebian thrust belt on mainland sicily this belt consists mostly of stacked basinal and platform carbonates of mesozoic early tertiary age deposited along the africa passive margin no clear subduction characterizes the area north of the hybleandashmalta plateau where it collides with the maghrebian chain the origin of the hybleandashmalta plateau is unclear geophysical data indicate however that its crustal structure is different from that of the surrounding pelagian foreland crustal structure variations at the edge of the subducted african plate may thus cause the observed segmentation of the collisional arc system a computer model of the region was created to learn about the deformation and faulting processes in the region the simulation starts prior to the collision of the pelagian block with the calabrian arc with time the hybleandashmalta plateau collides with the northern crustal block and as a result a new simulated topography a new distribution of velocities and most important a new distribution of fracture zones are created a shear fracture zone is formed east of the hybleandashmalta plateau malta escarpment extending to the subduction zone at the calabrian arc a less active strike slip fracture zone is created west of the hybleandashmalta plateau an additional e w trending active fracture zone is creating in the southern part of the simulated area this feature may correspond to a fault zone which runs from the strait of sicily to the ionian sea

seismicity and geometry of a 110 km long blind thrust fault 2 synthesis of the 1982 1985 california earthquake sequence during 1982 1985 three 5 4 mw 6 5 earthquakes migrated 65 km along the north half of a string of quaternary folds at the east front of the california coast ranges there is no surface fault associated with these earthquakes but the fold chain oriented parallel to the san andreas fault 30 km to the west takes up contraction normal to the san andreas fault identification of active blind thrust faults is hindered by the absence of a fault trace but may be revealed by the presence of growing folds at the surface and by earthquakes at depth because of excellent seismic geodetic and geologic data this earthquake sequence illuminates the geometry of the blind faults and enables us to probe their mechanics we relocate seismicity and compute focal mechanisms in a three dimensional velocity space and model the vertical deformation associated with the 1983 m 6 5 coalinga earthquake the aftershock zones abut at echelon offsets in the fold axes and the mainshocks display reverse slip perpendicular to the axes suggesting that the folds conceal a contiguous segmented thrust fault background seismicity concentrates at bends and breaks in the fold chain sites that may correspond to tears and ramps in the thrust fault at depth seismic reflection profiles reveal thrust and reverse faults dipping toward the san andreas fault at depths of 5 10 km with several kilometers of cumulative slip and high angle reverse faults in the anticlines with several hundred meters cumulative slip coseismic fold uplift accompanied the coalinga and kettleman hills north dome earthquakes suggesting that fold growth is episodic and coupled closely to repeated earthquakes on the underlying thrusts the north half of the fold chain has been the site of several 6 m 6 5 earthquakes since 1885 thus kettleman hills middle dome the next fold segment to the south has an elevated seismic potential the aftershock zones of the three main shocks are diffuse and occupy a region much larger than the site of seismic slip aftershocks occur 5 7 km from the fault regions where on the basis of a boundary element model the shear strain increase caused by the fault slip exceeds 20 ppm equivalent to about 0 7 mpa we argue that the broad aftershock zone is a product of high sustained off fault stress caused by repeated displacement on faults that do not cut the earth s surface the fault tip stresses lead to the formation of secondary faults which can become sites of aftershocks and postseismic creep

earthquake depths and the relation to strain accumulation and stress near strike slip faults in southern california earthquakes in the major fault zones are predominantly deep earthquakes in the crustal blocks bounding the fault zones are predominantly shallow in the san jacinto fault zone maximum earthquake depths correlate with surface heat flow these relations together with focal mechanisms geodetic strain measurements and fault zone models are consistent with the following ideas 1 interseismic plate motion is accommodated by aseismic slip along an extension of the major fault zone below a brittle zone that is locked between large earthquakes 2 the aseismic slip in a narrow fault zone in the brittle plastic transition region concentrates strain at the base of the brittle fault zone 3 deep earthquakes occur in thelower part of the brittle fault zone due to stick slip failure of highly stressed patches 4 background earhtquakes and aftershocks that occur several kilometers deeper than large earthquake hypocenters suggest that a zone of mixed slip behavior may exist between the stable sliding deep and stick slip shallow regions of the fault zone furthermore the difference in seismicity between the san jacinto and southern san andreas faults suggests that the nature of this mixed zone may evolve as total displacement in the fault zone increases 5 shear stress may be lessmore in the crustal blocks than in the deep brittle fault zones and generally at a level sufficient to cause brittle failure only shallow in the crustal blocks 6 in the stress field produced by plate motion and slip in the deep fault zone the upper brittle fault zone is not oriented favorably for shear failure lack of shallow earthquakes in the fault zones and the predominance of shallow earthquakes on favorably oriented fractures in the adjacent crustal blocks suggest that either stress in the upper brittle fault zone is relatively low or the upper fault zone is effectively strong due to its orientation less

long term creep rate changes and their causes 1 we discuss measurements of the long term creep rate from the san juan bautista section of the san andreas fault these observations of aseismic slip span a period of approximately half a century making it the longest creep record ever measured along an active fault zone the records show systematic changes in creep rate over time scales of tens of years and we address potential causes of these changes in principle they may be caused either by changes in resistive forces within the fault zone or by variations in plate tectonic driving forces such driving force variations have recently been suggested to have occurred in the same area western north america and within the same time window these should give rise to observable effects in the creep data but we find no evidence for temporal changes in plate tectonic forcing at these time scales a natural explanation for the observed long term changes is elastic reloading of adjacent locked portions of the san andreas fault after large earthquakes and possibly aseismic strain release that occurs before the earthquakes

implications of an elastic analysis of in situ stress measurements near the san andreas fault twenty nine measurements of in situ stress obtained with the hydraulic fracturing technique near palmdale california are the basis of an elastic analysis of the state of stress in the mojave desert adjacent to the san andreas fault the measurements were made at depths extending from 80 to 849 m and at distances from the fault between 2 and 34 km the elastic solution indicates a state of deviatoric stress typical for continents in that the inferred depth gradient of the maximum shear stress is about 7 9 mpa km extrapolation yields an average shear stress in the upper 14 km of the crust of about 56 mpa a result that is higher than estimates of the average shear stress on the san andreas fault based on the analysis of heat flow data this finding is consistent however with estimates of fault strength based on laboratory determinations of the coefficient of friction for samples of san andreas fault gouge if the regional state of deviatoric stress is limited by the strength of the fault zone if so then the coefficient of friction of the san andreas fault zone inferred from the stress field results is about 0 45 the state of stress does not appear to vary systematically with distance from the san andreas fault although considerable localized variation is observed the observations suggest an upper bound of about 0 1 mpa km for the horizontal gradient of the maximum shear stress in the direction perpendicular to the san andreas fault a result that implies a corresponding limit of about 1 4 mpa on the shear traction applied to the base of the seismogenic layer finally we demonstrate the potential application of in situ stress data to the direct assessment of accumulated slip which could be released in a large earthquake we show that on the basis of a model involving a locked fault extending to about 22 km the total fault slip below the locked portion is less than 13 m a more comprehensive set of stress data could permit the estimation of an even lower bound

response of the san andreas fault to the 1983 coalinga nunez earthquakes an application of interaction based probabilities for parkfield 1 the parkfield cholame section of the san andreas fault site of an unfulfilled earthquake forecast in 1985 is the best monitored section of the world s most closely watched fault in 1983 the m 6 5 coalinga and m 6 0 nunez events struck 25 km northeast of parkfield seismicity rates climbed for 18 months along the creeping section of the san andreas north of parkfield and dropped for 6 years along the locked section to the south right lateral creep also slowed or reversed from parkfield south here we calculate that the coalinga sequence increased the shear and coulomb stress on the creeping section causing the rate of small shocks to rise until the added stress was shed by additional slip however the 1983 events decreased the shear and coulomb stress on the parkfield segment causing surface creep and seismicity rates to drop we use these observations to cast the likelihood of a parkfield earthquake into an interaction based probability which includes both the renewal of stress following the 1966 parkfield earthquake and the stress transfer from the 1983 coalinga events we calculate that the 1983 shocks dropped the 10 year probability of a m 6 parkfield earthquake by 22 from 54 22 to 42 23 and that the probability did not recover until about 1991 when seismicity and creep resumed our analysis may thus explain why the parkfield earthquake did not strike in the 1980s but not why it was absent in the 1990s we calculate a 58 17 probability of a m 6 parkfield earthquake during 2001 2011 index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 7260 seismology theory and modeling keywords coalinga earthquake parkfield stress change earthquake probability seismicity rate

the effect of sea breeze on beach morphology surf zone hydrodynamics and sediment resuspension abstract beach morphodynamic processes were investigated over part of a sea breeze cycle on a microtidal low wave energy sandy beach in southwestern australia prior to the onset of the sea breeze offshore winds with speeds less than 5 m s prevailed during the sea breeze alongshore winds with speeds higher than 10 m s were experienced the sea breeze induced pronounced changes to the nearshore morphodynamics which were similar to that of a storm event 1 root mean square wave height increased from 0 3 to 0 5 m 2 zero upcrossing wave period decreased from 8 to 4 s 3 mean cross shore flows reached velocities of 0 2 m s directed offshore and 4 the longshore current increased in strength from 0 05 to 1 0 m s before the sea breeze sediment resuspension typically occurred during isolated high wave events associated with the passage of wave groups flux coupling between the wave oscillatory currents and the suspended sediment jaffe b e sternberg r w sallenger a h 1984 the role of suspended sediment in shore normal beach profile changes proc 19th int conf coastal engineering asce pp 1983 1996 induced net onshore suspended sediment transport resulting in beachface accretion and a steepening of the foreshore profile in contrast during the sea breeze sediment resuspension was almost continuous the suspended sediment load increased six fold and as a consequence the longshore suspended sediment transport rate increased by a factor of 100 during the sea breeze cross shore transport was directed offshore and primarily associated with mean offshore flows this resulted in erosion of the beachface and deposition in the surf zone and consequently a flattening of the beach profile the suspended sediment load was strongly related to the shields parameter defined for the combined action of waves and currents investigation of the suspended sediment profiles indicated that the degree of vertical mixing parameterised by the sediment diffusion coefficient increased with distance from the bed in addition the sediment diffusion coefficient exhibited a large temporal variation ranging between 0 005 and 0 018 m2 s the variability in the sediment diffusion coefficient is possibly due to changes in the sea bed morphology

reconstructing habitats in central amazonia using megafauna sedimentology radiocarbon and isotope analyses abstract a paleomegafauna site from central amazonia with exceptional preservation of mastodons and ground sloths allows for the first time a precise age control based on 14 c analysis which together with sedimentological and 13 c isotope data provided the basis to discuss habitat evolution within the context of climate change during the past 15 000 yr the fossil bearing deposits trapped within a depression in the paleozoic basement record three episodes of sedimentation formed on floodplains with an intermediate unit recording a catastrophic deposition through debris flows probably favored during fast floodings the integrated approach presented herein supports a change in humidity in central amazonia through the past 15 000 yr with a shift from drier to arboreal savanna at 11 340 50 14 c yr b p and then to a dense forest like we see today at 4620 60 14 c yr b p

studies on holocene mangrove ecosystem dynamics of the braganca peninsula in north eastern para brazil abstract three sediment cores from the braganca peninsula located in the coastal region in the north eastern portion of para state have been studied by pollen analysis to reconstruct holocene environmental changes and dynamics of the mangrove ecosystem the cores were taken from an avicennia forest bosque de avicennia bda a salt marsh area campo salgado cs and a rhizophora dominated area furo do chato pollen traps were installed in five different areas of the peninsula to study modern pollen deposition nine accelerator mass spectrometry radiocarbon dates provide time control and show that sediment deposits accumulated relatively undisturbed mangrove vegetation started to develop at different times at the three sites at 5120 14c yr bp at the cs site at 2170 14c yr bp at the bda site and at 1440 14c yr bp at the fdc site since mid holocene times the mangroves covered even the most elevated area on the peninsula which is today a salt marsh suggesting somewhat higher relative sea levels the pollen concentration in relatively undisturbed deposits seems to be an indicator for the frequency of inundation the tidal inundation frequency decreased probably related to lower sea levels during the late holocene around 1770 14c yr bp at bda around 910 14c yr bp at fdc and around 750 14c yr bp at cs the change from a mangrove ecosystem to a salt marsh on the higher elevation around 420 14c yr bp is probably natural and not due to an anthropogenic impact modern pollen rain from different mangrove types show different ratios between rhizophora and avicennia pollen which can be used to reconstruct past composition of the mangrove in spite of bioturbation and especially tidal inundation which change the local pollen deposition within the mangrove zone past mangrove dynamics can be reconstructed the pollen record for bda indicates a mixed rhizophora avicennia mangrove vegetation between 2170 and 1770 14c yr bp later rhizophora trees became more frequent and since ca 200 14c yr bp avicennia dominated in the forest

forecast model for moderate earthquakes near parkfield california earthquake instability models have possible application to earthquake forecasting because the models simulate both preseismic and coseismic changes of fault slip and ground deformation in the forecast procedure proposed here repeated measurements of preseismic fault slip and ground deformation constrain the values of model parameters the early part of the model simulation corresponds to the available field data and the subsequent part constitutes an estimate of future faulting and ground deformation in particular the time location and size of unstable faulting are estimates of the pending earthquake parameters the forecast accuracy depends on the model realism and parameter resolution the forecast procedure is applied to fault creep and trilateration data measured near parkfield california where at least five magnitude 5 5 to 6 earthquakes have occurred regularly since 1881 the last in 1966 the quasi static model consists of a flat vertical plane embedded in an elastic half space spacially variable fault slip of strike slip sense is driven by an increasing regional shear stress but is impeded by a relatively strong patch of brittle strain softening fault the field data are consistent with these approximate values of patch parameters radius of 3 km patch center 5 km deep and 8 km southeast of the 1966 epicenter and maximum brittle strength of 26 bars fluctuations in the available field data prevent estimating the earthquake time with any more precision than use of the 21 8 year recurrence interval however the model may later give a more precise estimate of the earthquake time if the fault slip rate near the inferred patch increases before the earthquake as predicted by the model

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

engineering geomorphology on the coast lessons from west dorset the central aim of this paper is to describe the general context in which an applied geomorphological investigation for a management project on a heritage coast will be set we attempt to show how the decisions may be affected by historical legacies and public or administrative attitudes modern attitudes to the coast in great britain are summarized in the light of recent studies by the department of the environment and the ministry of agriculture fisheries and food the dorset coast in southwest england is used to illustrate the main points the paper describes the coastal features explains the historical legacy of use and examines problems of contemporary coastal management the paper concludes with a consideration of the natural geomorphological principles of landscape design which might be employed as part of the guiding concepts

interaction of the san andreas fault creeping segment with adjacent great rupture zones and earthquake recurrence at parkfield three dimensional finite element calculations are employed to study interactions in space and time between the creeping segment of the san andreas fault in central california and the adjacent currently locked zones of the 1857 and 1906 great earthquakes vertically the model consists of an elastic upper crust over a maxwell viscoelastic region representing the entire lower crust or a narrower horizontal detachment layer and a stiffer and more viscous upper mantle the crust has a single vertical fault extending to the top of the mantle at 25 km depth in zones along strike corresponding to the 1857 and 1906 events the top 12 5 km of the fault is locked against slip except in great earthquakes below the locked zones and everywhere along the creeping region between them the fault is freely slipping the model parameters are compatible with seismological and geological observations and with a ratio of maxwell relaxation time to the relaxing layer thickness in the range 1 to 2 yr km as established by li and rice 1987 and fares and rice 1988 based on fits to geodetic data along the san andreas fault an imposed constant far field shear motion and periodic 1857 and 1906 type earthquakes generate slip rates along the creeping fault segment that evolve in time throughout the entire earthquake cycle shortly after an adjacent great earthquake slip rates in the creeping zone are higher than the far field velocity while later in the cycle they are lower hence time dependency should be accounted for when measurements of fault slip are used to estimate the plate motion if parkfield earthquakes are a response to a time dependent loading of the type simulated here their recurrence interval would tend to lengthen with time since the 1857 event thus the hypothesis of characteristic periodic earthquakes at parkfield may not provide the best estimate of the occurrence time of the next event using for example the statistics of past events and assuming that parkfield earthquakes are a response to a slip deficit near middle mountain and that the elastic crustal layer is 17 5 km thick we find that the next event is predicted for about 1992 9 years if the lower crust is a 7 5 km thick layer having a material relaxation time of 15 years and 1995 11 years if the 7 5 km thick lower crust is characterized by a relaxation time of 7 5 years these values may be compared to the 1988 7 years estimate based on periodicity in time the modeling results also indicate that the interaction between the 1857 and 1906 rupture zones is small

change of apparent segmentation of the san andreas fault around parkfield from space geodetic observations across multiple periods sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by coseismic and postseismic phases of stress release because the recurrence time of large earthquakes is often greater than the available span of space geodetic data it has been challenging to monitor the evolution of interseismic loading in its entire duration here we analyze large data sets of surface deformation at different key episodes around the cholame parkfield and creeping segments of the san andreas fault that show evidence of significant deceleration of fault slip during the interseismic period we compare the average fault slip rates before and after the 2004 mw6 parkfield earthquake in the 1986 2004 and 2006 2012 periods respectively avoiding 2 years of postseismic deformation after 2004 using a combination of gps data from the plate boundary observatory the southern california earthquake center crustal motion map and the bay area velocity unification networks and interferometric synthetic aperture radar from the advanced land observing satellite alos and envisat satellites we show that the area of coupling at the transition between the parkfield and cholame segments appears larger later in the interseismic period than it does earlier on while strong plate coupling is uniform across the parkfield and cholame segments in the 1986 2004 period creep occurs south of the 2004 epicenter after 2006 making segmentation of the san andreas fault south of parkfield more clearly apparent these observations indicate that analyses of surface deformation late in the earthquake cycle may overestimate the area of plate coupling a fault surface creeping much below plate rate may in some case be a region that does not promote earthquake nucleation but rather just be at a slower stage of its evolution our analysis also shows signs of large variation of slip velocity above and below plate rate in the creeping segment indicating that cycles of weakening and hardening can also be at play in dominantly aseismic areas

models of recurrent strike slip earthquake cycles and the state of crustal stress numerical models of the strike slip earthquake cycle assuming a viscoelastic asthenosphere coupling model are examined the time dependent simulations incorporate a stress driven fault which leads to tectonic stress fields and earthquake recurrence histories that are mutually consistent single fault simulations with constant far field plate motion lead to a nearly periodic earthquake cycle and a distinctive spatial distribution of crustal shear stress the predicted stress distribution includes a local minimum in stress at depths less than typical seismogenic depths the width of this stress trough depends on the magnitude of crustal stress relative to asthenospheric drag stresses the models further predict a local near fault stress maximum at greater depths sustained by the cyclic transfer of strain from the elastic crust to the ductile asthenosphere models incorporating both low stress and high stress fault strength assumptions are examined under newtonian and non newtonian rheology assumptions model results suggest a preference for low stress a shear stress level of about 10 mpa fault models in agreement with previous estimates based on heat flow measurements and other stress indicators

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

municipal initiatives for managing dunes in coastal residential areas a case study of avalon new jersey usa abstract the characteristics of foredunes created in a municipal management program on a developed barrier island are evaluated to identify how landforms used as protection structures can be natural in appearance and function yet compatible with human values shoreline management zones include a naturally evolving undeveloped segment a noneroding developed segment eroding and noneroding segments of an improved beach where dunes have been built by artificial nourishment and a privately built artificially nourished dune on the shoreline of an inlet a disastrous storm in 1962 resulted in an aggressive program for building dunes using sand fences vegetation plantings purchase of undeveloped lots and sediment backpassing to maintain beach widths and dune elevations the present nourished and shaped foredune in the improved beach is higher wider and closer to the berm crest than the natural dune restricted inputs of aeolian sand keep the surface flat and poorly vegetated a stable section of this engineered shore has a wider beach and sand fences have created a higher foredune with greater topographic diversity the cross shore zonation of vegetation here is more typical of natural dunes but the environmental gradient is much narrower the privately built dune is low narrow and located where it could not be created naturally foreshore and aeolian sediments in the undeveloped segment and the improved beach are similar in mean grain size 0 16 0 21 mm and sorting 0 31 0 39 but sediment on the surface of the nourished dune is coarser 28 1 gravel with a more poorly sorted sand fraction 1 30 representing lag elements on the deflation surface willingness to enhance beaches and dunes for protection has reduced insurance premiums and allowed the municipality to qualify for funds from the federal emergency management agency fema to replace lost sediment thus placing an economic value on dunes success of the management program is attributed to i timing property purchase and dune building programs to periods immediately after storms causing residents to accept high dunes that restrict access or views ii instituting a vigorous education program reminding residents of hazards during nonstorm periods iii maintaining control over local sediment supplies to keep pace with erosion and create new shoreline environments iv investing private and municipal economic resources in landforms qualifying them for external funds for replacement and v maintaining augmenting or simply tolerating biodiversity and natural processes retaining a natural heritage

slip deficit on the san andreas fault at parkfield california as revealed by inversion of geodetic data a network of geodetic lines spanning the san andreas fault near the rupture zone of the 1966 parkfield california earthquake magnitude m 6 has been repeatedly surveyed since 1959 in the study reported here the average rates of line length change since 1966 were inverted to determine the distribution of interseismic slip rate on the fault these results indicate that the parkfield rupture surface has not slipped significantly since 1966 comparison of the geodetically determined seismic moment of the 1966 earthquake with the interseismic slip deficit rate suggests that the strain released by the latest shock will most likely be restored between 1984 and 1989 although this may not occur until 1995 these results lend independent support to the earlier forecast of an m 6 earthquake near parkfield within 5 years of 1988

seismic gap hypothesis ten years after the seismic gap hypothesis states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries one of the earliest and clearest applications of the seismic gap theory to earthquake forecasting was by mccann et al 1979 who postulated zones of high medium and low seismic potential around the pacific rim in the 10 years since there have been over 40 large m 7 0 earthquakes enough to test statistically the earlier forecast we also analyze another forecast of long term earthquake risk that by kelleher et al 1973 the hypothesis of increased earthquake potential after a long quiet period can be rejected with a large confidence the data suggest that contrary to these forecasts places of recent earthquake activity have larger than usual seismic hazard whereas the segments of the circum pacific belt with no large earthquakes in recent decades have remained relatively quiet the clustering of earthquake times does not contradict the plate tectonic model which constrains only the long term average slip rate not the regularity of earthquakes

long term fault creep observations in central california the u s geological survey usgs has been monitoring aseismic fault slip in central california for more than 10 years as part of an earthquake prediction experiment since 1968 the usgs creep network has grown from one creep meter at the cienega winery south of hollister to a 44 station network that stretches from hayward east of san francisco bay to palmdale in southern california in general the long term slip pattern is most variable on sections of the faults where several magnitude 4 and larger earthquakes occurred during the recording period e g calaveras fault near hollister and san andreas fault between san juan bautista and bear valley these fault sections are the most difficult to characterize with a single long term slip rate in contrast sections of the faults that are seismically relatively quiet e g san andreas fault between bear valley and parkfield produce the steadiest creep records and are easiest to fit with a single long term slip rate appendix is available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington d c 20009 document j82 004 1 00 payment must accompany order

regional variation of coastal morphology in southwestern australia a synthesis abstract the morphology of landforms on the south coast of western australia is determined predominantly by wave refraction around discrete headlands and islands wherever offshore structures protect the shore from the direct effects of swell sheltered sandy beaches have developed in association with cuspate forelands and tombolos in contrast to this open coast setting the nearshore waters of the west coast are protected by semi continuous reef systems which significantly modify the morphology of large scale accretionary landforms beaches and foredune sequences on the south coast foredune plains occur primarily as fill in sheltered embayments and storm built ridges do not occur foredunes on the west coast include washover ridges and low aeolian dunes on the backshore of embayment and inset beaches the form of high wave energy beaches of the south coast fluctuates between reflective and dissipative morphodynamic states and most commonly between transitional and dissipative states sediments are mainly fine grained siliceous sands in contrast the low energy west coast beaches are composed of medium to coarse grained calcareous sands the beaches are planar in section characterised by lines of debris deposited by tidal and longer term fluctuations in sea level and their form does not alter with short term changes in the wave regime despite the very low energy micro tidal conditions experienced by the coasts of southwestern australia systematic variation in the morphology of coastal landforms does occur as protection to the coast increases from the open fetch south coast environment to the reef protected west coast setting swell energy decreases there is an increase in the relative importance of locally generated wind waves wave set up and tidal forcing of currents and forelands become increasingly asymmetric due to the strength of longshore sediment transport

comments on an anthropogenic modification in an eremotherium tooth from northeastern brazil over150yearsago peterw lundproposedthatlatequaternaryextinct megafauna henceforth just megafauna and homo sapienscoexisted in brazil lund 1844 but only recently his hypothesiswas supported by direct radiocarbon dating on megafauna bones neves and pilo 2003 hubbe et al 2007 2009 2011 these datesshowed that in some brazilian regions at least some speciessurvived until the beginning of the holocene and became extinctafter the arrival of the rst human groups besides the chronolog ical evidence which indicates that humans and megafauna lived inthe same region at the same time there are also claims that theymayhaveinteractedmoreactivelybasedonthe ndingofsingle orvery few bones or bone fragments associated with human occu pation levels near archeological material or showing marks thatsuggest their usage by humans however based on the meticulousrevision provided by prous 2002 it is possible to rule out most ofthese cases due to theircontroversial nature in fact few of those ifany can be held as solid evidence of this close interaction notconsidering scavengingon bones from a long ago deceased animal prous and fogaca 1999 recently dantas et al in press reported the nding of a singletooth fragment of the ground sloth eremotherium in sergipe state northeastern brazil that according to the authors presentsanthropogenic marks that favor the coexistence of this species andh sapiens however in our opinion their work does not providesolid evidence of an interaction of this nature and therefore theaim of this comment is to discuss the validity of their nding asreliable evidence of megafauna more speci cally eremotherium and humans coexistence in sergipe the coexistence and notablythe close interaction between the former and the later may haveimportant implications to the understanding of the initial humanoccupation of south america hence this kind of nding should notbe taken as granted but rather should be analyzed with rigorouscriteria in the following comments we question the interpretationof the marks seen in the tooth as human made cutmarks based on1 thenatureandlocationofthecutmarksand2 thearchaeologicalandpaleontologicalcontextof the nding furthermore wediscussreasons why the conclusions based on this nding could beseverely distorted dantas et al in press 1 described the marks found on thereported tooth as an effort to build a triangular object based onthe material the location of the marks and the scant informationprovided e g it is notclear if morebones fromeremotheriumwerefound if there are more bones from other species with marks whichother species were found it is hardtoaccept that the marksobserved are the result of human intervention on the tooth themarks are described by dantas et al in press 1 as being humanbecause they have parallel grooved striations narrower anddeeper which follow the curvature of the tooth along apical andlateral borders unfortunately these characteristics are unclear tous in the pictures presented by the authors fig 2f shows onlystriations fig 2g appear to show microwear striations when thescaleofthephoto 0 1mm istakenintoaccount andfig 2hshowsa network of shallow striations that crisscross the surface in everydirection in summary it is not possible to see the diagnosticfeatures in the pictures presented by the authors to justify theirconclusions of an anthropogenic origin for them added to the diagnostic dif culties of the marks in this tooth their occurrence is not in accordance to the standard patternsobserved for food processing in ethnographic and archaeologicalcontexts e g walker 1978 lupo 2002 lyman 2005 martinez 2009 thus diminishing the possibility of butchering marks onthis tooth indeed dantas et al in press never claimed thesemarks were the result of butchering however it is very hard to

geomorphology and the urban tropics building an interface between research and usage abstract the developing countries located almost entirely within the tropics are currently undergoing urbanization at a rapid pace many of these cities are not more than a few centuries old having been established to function as regional trading posts or administrative centers by either colonial or regional powers it is doubtful that the site conditions were taken into consideration and consequently many of these cities were established in hazardous or environmentally sensitive areas as these cities developed over time they spread across a wide range of terrain conditions much of which are unsuitable such as floodplains coastal swamps steep slopes or sand dunes for a number of these cities which are located near active plate margins and tropical cyclone belts such problems are magnified increased demand for water has required subsurface extraction leading to problems of subsidence and quality we examine the range of these cities with reference to 1 their site related problems 2 the nature of geomorphological information required for specific ameliorating actions and 3 the level of management required for city maintenance management requires interfacing geomorphology with engineering practices and urban planning we present case studies of cities ranging from those with limited problems and possible engineering and land zoning solutions singapore to cities where the hazards either natural or anthropogenic are so acute and widespread that a practical solution is difficult to achieve kingston bangkok precise geomorphological and geological information and long term data sets are not available for most of the cities furthermore it is necessary to present the information in formats appreciated by the engineering and planning communities often a set of specialized maps are extremely useful we complete the discussion with several examples and suggestions for collection of geomorphological information and inventory preparation for communicating geomorphological data to city engineers and planners

insights into holocene megafauna survival and extinction in southeastern brazil from new ams 14 c dates abstract the extinction of late quaternary megafauna in south america has been extensively debated in past decades the majority of the hypotheses explaining this phenomenon argue that the extinction was the result of human activities environmental changes or even synergism between the two although still limited a good chronological framework is imperative to discuss the plausibility of the available hypotheses here we present six new direct ams 14 c radiocarbon dates from the state of sao paulo brazil to further characterize the chronological distribution of extinct fauna in this part of south america the new dates make evident that ground sloths toxodonts and saber toothed cats lived in the region around the pleistocene holocene transition and in agreement with previous studies also suggest an early holocene survival for the ground sloth catonyx cuvieri taken together with local paleoclimatic and archaeological data the new dates do not support hunting or indirect human activities as a major cause for megafauna extinction although more data are required parsimony suggests that climatic changes played a major role in this extinction event

u series dating and taphonomy of quaternary vertebrates from brazilian caves abstract the geochronology and taphonomy of internationally important fossil bearing cave deposits were studied both in the semi arid northern bahia area and the subtropical southeastern lagoa santa area of brazil taphonomic analysis suggests that the processes responsible for bone accumulation in the brazilian caves vary between sites and taphonomic bias can therefore be significant in causing differences in faunal composition in the toca da boa vista caves the presence of single articulated skeletons and the entrance related distribution indicate that random penetration of animals is the main mechanism of fossil accumulation a process that biases the assemblage to smaller species and takes place over extended time periods in nearby toca dos ossos cave transport by runoff in the cave river is predominant and biases the fauna remains to larger more robust bones and species deposition probably also occurred only at times of enhanced runoff giving a more contemporaneous assemblage similar processes were responsible for emplacement of the copious fossil remains in the more humid lagoa santa area where terrigenous fossil deposits are found intercalated by massive speleothem calcite layers in this area runoff under a drier climate probably accounts for the sediment emplacement inside caves in both areas the mode of emplacement implies bias in the fossil record resulting in fossil assemblages that do not mirror surface faunas limiting palaeoenvironmental reconstruction mass spectrometric u series analysis of speleothem calcite overlaying fossil remains gives minimum ages for fossil deposition these ages confirm the previous view that many of the deposits derive from the late glacial but also show that much older material some 350 000 yr is also present the habitat requirements of critical fossil species such as bats and monkeys strongly suggest that they derive from much wetter periods when forest cover was present in the currently semi arid northern bahia area taphonomy exerts a major control on the diversity and mode of emplacement of cave fossil deposits in eastern brazil and thus detailed sedimentological and hydrological studies coupled with a sound geochronological approach are essential in quantifying the relative importance of each taphonomic processes before faunal and palaeoecological interpretations can be attempted

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

sand dynamics at the mouth of a rock bound tide dominated estuary abstract the lowermost kennebec river is a relatively narrow deep bedrock cut estuary situated along the highly indented central coast of maine a large tidal prism and strong tidal currents control bedload sediment transport at the estuary mouth riverine sediment is introduced to the estuary during spring freshets when freshwater discharge may increase by an order of magnitude during the same time some of the existing estuarine sediment is exported to the nearshore a barrier adjacent to the estuary is the product of an abundant riverine sand supply and numerous bedrock ridges which anchor this sand deposit a variety of sedimentologic geomorphic and hydraulic data collected over a 14 year period document a clockwise sand circulation cell that involves the exchange of bedload among the entrance channel to the estuary adjacent beaches nearshore and offshore region tidal currents transport sand from the estuary through a subsidiary channel bordered on both sides by bedrock islands to an offshore subtidal bar northeast storm waves breaking along this outer bar move sand westward and landward toward the beach leading to the development of large bar complexes the welding of a bar complex to the western end of hunnewell beach occurs every 6 9 years and adds 2 300 000 m3 of sand to the shoreline sediment transport calculations along the outer bar are consistent with this volume of sand the sediment gyre is completed as beach sands are moved eastward along the beach and dumped into the estuarine channel this movement of sand is produced by wave action and tidal currents that enter the estuary peripherally during the flooding tide during the ebb cycle strong tidal currents flowing seaward through the subsidiary channel advect water from along the beach which enhances sand transport into the estuary thirteen years of beach profile surveys demonstrate a good correspondence between bar welding events and short term 1 4 years accretionary shoreline changes however the volumetric changes of hunnewell beach cannot be accounted for by bar welding alone the apparent movement of sand between hunnewell beach and other sand is further evidenced by the 135 year record of historical shoreline changes that reveal up to 200 m of shoreline excursions over a 26 year period these data suggest that erosional depositional trends along hunnewell beach are complex and the result of the exchange of sand among the adjacent beaches nearshore zone fox and wood island tombolos kennebec river channel and offshore region the effects of major spring floods and strong bedrock influences produce patterns of sedimentation and a distribution of sand bodies at the mouth of kennebec river that differ markedly from accepted estuarine models that are based on the relative importance of wave and tidal energy this study demonstrates the need to consider structural controls when using these models

a shear strain anomaly following the loma prieta earthquake borehole tensor strain instruments deployed along the san andreas fault for the past ten years have provided sufficient resolution and stability to sample regional tectonic processes potentially enhancing earthquake prediction capability data obtained from the instrument at san juan bautista in the near field region of the 17 october 1989 loma prieta earthquake ms 7 1 provide the first opportunity to observe shear strain processes associated with a large earthquake we previously reported1 a prominent shear strain anomaly in those data for more than a year before the earthquake this anomaly ceased immediately after the earthquake but as we report here a new and higher rate of fault parallel shear accumulation 2 microstrain per year was established about four months later and has continued to the present associated changes in creep rate are apparent at a number of sites on the surface trace of the fault within 30 km of the strain meter we propose that the observed strain accumulation results from increased slip around a nearby locked section of the fault this slip arising from loading by the failed loma prieta source region to the north this model is consistent with suggestions of an increased probability of a moderate earthquake near san juan bautista9 10 and with evidence12 that interactions between fault regions are important in earthquake processes

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

crustal deformation in great california earthquake cycles periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model a depth l h extending downward from the earth s surface at a transform boundary between uniform elastic lithospheric plates of thickness h is locked between earthquakes it slips an amount consistent with remote plate velocity vpl after each lapse of earthquake cycle time tcy lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress the plates are coupled at their base to a maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions compatible with plate velocity are transmitted to the surface plates the coupling is described approximately through a generalized elsasser model we argue that the model gives a more realistic physical description of tectonic loading including the time dependence of deep slip and crustal stress buildup throughout the earthquake cycle than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone parameters of the model are chosen to fit seismic and geologic constraints and the apparent time dependence of surface strain rates along presently locked traces of the 1857 and 1906 san andreas ruptures we fix vpl 35 mm yr tcy 160 years and l 9 11 km based on earthquake nucleation depths the geodetic data are then found to be described reasonably within the context of a model that is locally uniform along strike and symmetric about a single san andreas fault strand by lithosphere thickness h 20 30 km and elsasser relaxation time tr 10 16 years we therefore suggest that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps crust mantle transition zone and has an effective viscosity between about 2 1018 and 1019 pa s depending on the thickness assigned to the asthenospheric layer predictions based on the chosen set of parameters are also consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces although the fit is degraded by asymmetry relative to the fault and by slip on adjacent fault strands

nonlinear strain buildup and the earthquake cycle on the san andreas fault two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault accompanied by a progressive broadening of the zone of deformation adjacent to it in the thin lithosphere model transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere for an earth model with a thick elastic lithosphere plate thickness depth of seismic slip transient motions are due to postearthquake aseisrnic slip below the coseismic fault plane data from the san andreas fault indicate a long term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle observations support a cycle long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar if so the usually lower strain rates and broader deformation zone currently observed on the southern san andreas represent a later evolutionary stage of the northern locked section where a great earthquake is a more recent occurrence although the data allow some extreme models to be discarded no sufficiently strong constraints exist to decide between the thin and thick lithosphere models regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause significant departures from recurrence estimates based on linear strain accumulation and the time predictable model

assessment of stress coupling among the inter co and post seismic phases related to the 2004 m6 parkfield earthquake due to large uncertainties and non uniqueness in fault slip inversion the investigation of stress coupling based on the direct comparison of independent slip inversions for example between the coseismic slip distribution and the interseismic slip deficit may lead to ambiguous conclusions in this study we therefore adopt the stress constrained joint inversion in the bayesian approach of wang et al and implement the physical hypothesis of stress coupling as a prior we test the hypothesis that interseismic locking is coupled with the coseismic rupture and the early post seismic deformation is a stress relaxation process in response to the coseismic stress perturbation we characterize the role of stress coupling in the seismic cycle by evaluating the efficiency of the model to explain the available data taking the 2004 m6 parkfield earthquake as a study case we find that the stress coupling hypothesis is in agreement with the data the coseismic rupture zone is found to be strongly locked during the interseismic phase and the post seismic slip zone is indicated to be weakly creeping the post seismic deformation plays an important role to rebuild stress in the coseismic rupture zone based on our results for the stress accumulation during both inter and post seismic phase in the coseismic rupture zone together with the coseismic stress drop we estimate a recurrence time of m6 earthquake in parkfield around 23 41 yr suggesting that the duration of 38 yr between the two recent m6 events in parkfield is not a surprise

aseismic slip and fault normal strain along the central creeping section of the san andreas fault 1 we use gps data to measure the aseismic slip along the central san andreas fault csaf and the deformation across adjacent faults comparison of edm and gps data sets implies that except for small scale transients the fault motion has been steady over the last 40 years we add 42 new gps velocities along the csaf to constrain the regional strain distribution shear strain rates are less than 0 083 0 010 strain yr adjacent to the creeping saf with 1 4 5 mm yr of contraction across the coast ranges dislocation modeling of the data gives a deep long term slip rate of 31 35 mm yr and a shallow 0 12 km creep rate of 28 mm yr along the central portion of the csaf consistent with surface creep measurements the lower shallow slip rate may be due to the effect of partial locking along the csaf or reflect reduced creep rates late in the earthquake cycle of the adjoining saf rupture zones

long term afterslip of the 2004 m 6 0 parkfield california earthquake implications for forecasting amount and duration of afterslip on other major creeping faults abstract we present the longest record of surface afterslip on a continental strike slip fault for the 2004 m 6 0 parkfield california earthquake from which we can derive critical information about the duration and predictability of afterslip relevant to urban displacement hazard applications surface slip associated with this event occurred entirely postseismically along the interseismically creeping 0 6 1 5 cm yr main trace of the san andreas fault using the first year of afterslip data the program after correctly predicted the cumulative surface afterslip maximum 35 cm eventually attained by 1 yr postearthquake observed afterslip had accumulated to only 74 of its modeled final value u f in units of length the 6 yr data suggested final slip would be reached everywhere by 6 12 yrs parkfield s afterslip lasted much longer 6 12 yrs than afterslip following a 2014 m 6 0 event in napa california where no interseismic creep was known and its afterslip neared completion 97 of u f by 1 yr the uncertainty in u f for the napa event fell to 2 cm in only three months versus in 2 yrs for the parkfield event mostly because duration of the power law stage of afterslip at parkfield is much longer 1000 493 1666 days versus 100 35 421 days for napa because the urban hayward fault near san francisco california like the parkfield section exhibits interseismic creep in a similar geological regime significant afterslip might last for up to a decade following an anticipated m 6 7 earthquake potentially delaying postearthquake recovery electronic supplement tables of afterslip observations and coefficients for computing afterslip

archaeology of the pleistocene holocene boundary in brazil abstract after a short history of brazilian research about pleistocene peopling the late pleistocene early holocene changes of climate and resources are discussed claims for a very ancient presence of man before 13 000 bp itaborai toca da esperanca pedra furada and lapa vermelha sites are polemic because putative structures and artifacts could have been made by natural processes in central and northeastern brazil some sites dated between 14 000 and 10 000 bp provide clear evidence of human activities and coexistence with huge pleistocene mammals in a synthesis of our present knowledge about the 12 000 8000 bp period biological aspects of the lagoa santa people and their subsistence are discussed the main regional traditions are umbu with bifacial projectile points and humaita with heavy implements in the southern part of brazil in the central and northeastern regions the itaparica tradition is characterized by typical retouched flakes and limaces although projectile points are generally thought to be absent in the earliest levels of this tradition some have been found in boquete cave in amazonia some cultural aspects seem to have been the same as in central brazil

a new multilayered visco elasto plastic experimental model to study strike slip fault seismic cycle nowadays technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle however the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years to overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters we have developed a new experimental approach allowing for the simulation of strike slip fault earthquakes and analyze in detail hundreds of successive seismic cycle model rheology is made of multilayered visco elasto plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle ductile coupling postseismic deformation phase and far field stress transfers the kinematic evolution of the model surface is monitored using an optical system based on subpixel spectral correlation of high resolution digital images first results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory these results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth along the fault plane our analog modeling approach appears then as an efficient complementary approach to investigate earthquake dynamics

slip patterns and earthquake populations along different classes of faults in elastic solids numerical simulations of slip instabilities on a vertical strike slip fault in an elastic half space are performed for various models belonging to two different categories the first category consists of inherently discrete cellular fault models such are used to represent fault systems made of segments modeled by numerical cells that can fail independently of one another their quasi independence is assumed to provide an approximate representation of strong fault heterogeneity due to geometric or material property disorder that can arrest ruptures at segment boundaries the second category consists of models having a well defined continuum limit these involve a fault governed by rate and state dependent friction and are used to evaluate what types of property heterogeneity could lead to the quasi independent behavior of neighboring fault segments assumed in the first category the cases examined include models of a cellular fault subjected to various complex spatial distributions of static to kinetic strength drops and models incorporating rate and state dependent friction subjected to various spatial distributions of effective stress normal stress minus pore pressure the results indicate that gradual effective stress variations do not provide a sufficient mechanism for the generation of observed seismic response strong and abrupt fault heterogeneity as envisioned in the inherently discrete category is required for the generation of complex slip patterns and a wide spectrum of event sizes strong fault heterogeneity also facilitates the generation of rough rupture fronts capable of radiating high frequency seismic waves the large earthquakes in both categories of models occur on a quasi periodic basis the degree of periodicity increases with event size and decreases with model complexity however in all discrete segmented cases the models generate nonrepeating sequences of earthquakes and the nature of the large quasi periodic events is highly variable the results indicate that expectations for regular sequences of earthquakes and or simple repetitive precursory slip patterns are unrealistic the frequency size fs statistics of the small failure episodes simulated by the cellular fault models are approximately self similar with b 1 2 and ba 1 where b and ba are b values based on magnitude and rupture area respectively for failure episodes larger than a critical size however the simulated statistics are strongly enhanced with respect to self similar distributions defined by the small events this is due to the fact that the stress concentrated at the edge of a rupture expanding in an elastic solid grows with the rupture size when the fault properties e g geometric irregularities are characterized by a narrow range of size scales the scaling of stress concentrations with the size of the failure zone creates a critical rupture area terminating the self similar earthquake statistics in such systems events reaching the critical size become on the average unstoppable and they continue to grow to a size limited by a characteristic model dimension when however the system is characterized by a broad spectrum of size scales the above phenomena are suppressed and the range of apparent self similar fs statistics is broad and characterized by average b and ba values of about 1 the simulations indicate that power law extrapolations of low magnitude seismicity will often underestimate the rate of occurrence of moderate and large earthquakes the models establish connections between features of fs statistics of earthquakes range of self similar regimes local maxima and structural properties of faults dominant size scales of heterogeneities dimensions of coherent brittle zones the results suggest that observed fs statistics can be used to obtain information on crustal thickness and fault zone structure

earthquake failure sequences along a cellular fault zone in a three dimensional elastic solid containing asperity and nonasperity regions numerical simulations of earthquake failure sequences along a discrete cellular fault zone are performed for a three dimensional 3 d model representing approximately the central san andreas fault the model consists of an upper crust overlying a lower crust and mantle region together defining an elastic half space with a vertical half plane fault the fault contains a region where slip is calculated on a uniform grid of cells governed by a static kinetic friction law and regions where slip is prescribed so as to represent tectonic loading aseismic fault creep and adjacent great earthquakes the computational region models a 70 km long and 17 5 km deep section of the san andreas fault to the nw of the great 1857 rupture zone different distributions of stress drops on failing computational cells are used to model asperity parkfield asperity and nonasperity fault regions the model is inherently discrete and corresponds to a situation in which a characteristic size of geometric disorder within the fault i e cell size here a few hundreds of meters is much larger than the nucleation size of the order of tens of centimeters to tens of meters based on slip weakening or state evolution slip distances the computational grid is loaded by a constant plate motion imposed at the lower crust upper mantle and creeping fault regions and by a staircase slip history imposed at the 1857 and 1906 rupture zones stress transfer along and outside the fault due to the imposed loadings and failure episodes along the computational grid is calculated using 3 d elastic dislocation theory the resulting displacement field in the computational region is compatible with geodetic and seismological observations only when the asperity and nonasperity regions are characterized by significantly different average stress drops the frequency magnitude statistics of the simulated failure episodes are approximately self similar for small events with b 1 2 the b value of statistics based on rupture area ba is about 1 but are strongly enhanced with respect to self similarity for events larger than a critical size this is interpreted as a direct manifestation of our 3 d elastic stress transfer calculations beyond certain rupture area and potency seismic moment divided by rigidity release values the event is usually unstoppable and it continues to grow to a size limited by a characteristic model dimension this effect is not accounted for by cellular automata and block spring models in which the adopted simplified stress transfer laws fail to scale properly with increasing rupture size the simulations suggest that local maxima in observed frequency magnitude statistics correspond to dimensions of coherent brittle zones such as the width of the seismogenic layer or the length of a fault segment bounded by barriers the analysis indicates that a single cell size representing approximately a single scale of geometric disorder cannot induce self similarity in a 3 d elastic model over a broad range of magnitudes a representation of geometric disorder covering a range of scales may thus be required to generate a wide domain of self similar gutenberg richter statistics our simulations show a great diversity in the mode of failure of the parkfield asperity the earthquakes themselves define an irregular sequence of events the modeling like many other discrete fault models suggests that expectations for periodic parkfield earthquakes and or simple precursory patterns repeating from one event to the other are unrealistic

regional deformation near palmdale california 1973 1983 the tehachapi trilateration network spans the intersection of the san andreas and garlock faults in southern california in the big bend region of the san andreas fault analysis of data from 1973 1983 shows strain differences between the northwest and southeast regions of the network and slip at depth on both faults the palmdale network spanning the san andreas fault entirely within the tehachapi network showed increases of about 1 strain in both east west and north south extension in late 1979 the tehachapi strains also jumped at this time but the magnitude of the increase was only about one third that of palmdale the principal strain rates for tehachapi over the time interval 1973 1983 are e 1 0 08 0 01 strain yr and e 2 0 12 0 01 strain yr with the 1 axis directed n76 e strains were also computed for two subregions the principal strain rates for the southeast tehachapi region are e 1 0 14 0 02 strain yr and e 2 0 16 0 02 strain yr with the 1 axis directed n73 e this result differs significantly from the principal strain rates at palmdale e 1 0 21 0 02 strain yr e 2 0 17 0 01 strain yr with the 1 axis directed n71 e for the northwest tehachapi region e 1 0 11 0 02 strain yr and e 2 0 06 0 02 strain yr with the 1 axis directed n93 e

earthquake deformation cycle on the san andreas fault near parkfield california six moderate earthquakes are thought to have ruptured the parkfield segment of the san andreas fault since 1857 the similar characteristics of the three seismically recorded events together with the quasi regular 22 year recurrence interval have led to the forecast of a similar event in 1988 5 years in this study the potential for the hypothesized earthquake is assessed by estimating the time required for interseismic straining to recover the strain energy released by the most recent june 1966 parkfield earthquake for a simple model of the earthquake cycle this interval is proportional to the ratio of the 1966 seismic moment to the interseismic moment deficit rate baseline lengths measured before and after the 1966 earthquake are inverted to estimate the magnitude and distribution of the combined coseismic and transient postseismic slip although the geodetic data determine only broad spatial averages of the fault slip they do require that slip at depth exceeded the surface offsets measured in 1966 inversions with extreme prior models are calculated to assess the range of seismic moment and moment deficit rates consistent with the available geodetic data inversions assuming only that the slip distributions are to some degree smooth yield strain energy recovery intervals of 14 25 years extreme values range from as little as 6 years to as much as 29 years in comparison historic recurrence intervals of parkfield earthquakes range from 12 to 32 years these results are consistent with the expectation of a magnitude 5 6 earthquake near parkfield by 1993

earthquake aftereffects and triggered seismic phenomena the physical basis for delayed aftereffects of large crustal earthquakes is analyzed these effects apparently range in scale from typical aftershocks near the source region of a prior earthquake to the triggering of groundwater and deformation related anomalies possibly including other large earthquakes at locations as much as a few hundred kilometers from the source of a great earthquake observational reports of such aftereffects are reviewed and possible mechanisms for their occurrence are discussed

fault coupling and potential for earthquakes on the creeping section of the central san andreas fault the 150 km long central section of the san andreas fault csaf in central california creeps at the surface and has not produced a large earthquake historically however sections of the san andreas fault to the north and south are known to have ruptured repeatedly in m 7 8 earthquakes it is currently unclear whether the creeping csaf could rupture in large earthquakes either individually or along with earthquakes on the locked sections to the north and south we invert global positioning system and interferometric synthetic aperture radar data with elastic block models to estimate the degree of locking on the csaf and place bounds on the moment accumulation rate on the fault we find that the inferred moment accumulation rate is highly dependent on the long term fault slip rate which is poorly constrained along the csaf the inferred moment accumulation rate normalized by shear modulus ranges from 3 28 104 to 5 85 107 m3 yr which is equivalent to a mw 5 5 7 2 earthquake every 150 years for a long term slip rate of 26 mm yr and mw 7 3 7 65 for a long term slip rate of 34 mm yr the comparisons of slip distributions with microseismicity and repeating earthquakes indicate a possible locked patch between 10 and 20 km depth on the csaf that could potentially rupture with mw 6 5

earliest art in the americas incised image of a proboscidean on a mineralized extinct animal bone from vero beach florida abstract a fragmented fossil bone incised with the figure of a proboscidean was recently found at vero beach florida near the location where late pleistocene fauna and human bones were recovered from 1913 to 1916 this engraving may represent the oldest and only existing example of terminal pleistocene art depicting a proboscidean in the americas because of the uniqueness rarity and potential antiquity of this specimen caution demanded that a variety of tests be used in an attempt to verify its authenticity the mineralized bone was identified as mammoth mastodon or giant sloth rare earth element analysis was consistent with the fossil bone being ancient and originating at or near the old vero site 8 ir 9 forensic analysis suggests the markings on the bone are not recent optical microscopy results show no discontinuity in coloration between the carved grooves and the surrounding material indicating that both surfaces aged simultaneously scanning electron microscopy sem revealed that the edges of the inscription are worn and show no signs of being incised recently or that the grooves were made with metal tools in addition the backscattered sem images suggest there is no discontinuity in the distribution of light and heavy elements between the scribed region and the surrounding bone indicating that both surfaces aged in the same environment this is very different from an intentional mark made on the bone for comparison energy dispersive x ray spectroscopy edxs shows that the surface contains significant amounts of calcium phosphorus oxygen and carbon typical of a mineralized bone surface examination of a cast and mold of the incised bone by reflectance transformation imaging rti also provided no evidence that the engraving was made recently all of these results are consistent with the mammoth engraving being authentic

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr