the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

quaternary blind thrusting in the southwestern sacramento valley california patterns of microearthquakes and quaternary surface deformation suggest that the tectonic setting of the sw sacramento valley is similar to areas of the western san joaquin valley known to be underlain by seismogenic blind thrust faults on the basis of previous work and analysis of geologic and seismic reflection data the following late cenozoic tectonic features and processes are identified 1 uplift of the northern coast ranges beginning approximately 3 4 ma and eastward propagation of uplift into the southwestern sacramento valley by 1 0 ma 2 uplift and homoclinal flexure of plio pleistocene strata at the eastern coast ranges mountain front 3 uplift and folding above blind thrusts approximately 15 km east of the mountain front in the southwestern sacramento valley similar associations of structures and processes have been observed in thrust belts in pakistan the peruvian andes and the canadian cordillera and are commonly attributed to thrusting within an intercutaneous wedge or triangle zone by using other thrust belts as analogs the propagation of an eastward tapering triangle zone is interpreted to be the principal mechanism for uplift and homoclinal flexure at the eastern coast ranges mountain front seismic reflection profiles reveal that 1 the triangle zone consists primarily of east vergent blind thrusts and 2 west vergent backthrusts exposed in the the eastern coast ranges and southwestern sacramento valley are rooted in the east vergent thrusts transfer of slip from the east vergent blind thrusts to the west vergent backthrusts occurs locally beneath the southwestern sacramento valley fault bend folding in the hanging walls of the backthrusts has created a north northwest striking chain of low hills approximately 15 km east of the mountain front the folds deform 3 4 1 0 ma fluvial sediments and thus are middle pleistocene in age or younger local variations in strike suggest that the fold chain is segmented like the new idria coalinga kettleman hills segmented fold chain in the southwestern san joaquin valley stein and ekstrom 1989 these data have implications for seismic hazard assessment anecdotal accounts indicate that two m 6 0 events of the 1892 winters vacaville earthquake sequence probably occurred beneath the eastern coast ranges dale 1977 toppozada et al 1981 ground cracking was observed following the main shocks along the mountain front in the southwestern sacramento valley we propose that the earthquakes were generated by slip on a blind thrust beneath the coast ranges and that the ground cracking in the valley represents propagation of the eastward tapering triangle zone the 1892 earthquake sequence suggests that blind thrusts beneath the southwestern sacramento valley are active and capable of generating moderate to large magnitude earthquakes

the 2007 m5 4 alum rock california earthquake implications for future earthquakes on the central and southern calaveras fault 1 the similarity of seismograms recorded by two seismic stations demonstrate that the 31 october 2007 moment magnitude m5 4 alum rock earthquake is a repeat of a 1955 ml5 5 earthquake both occurred on oppenheimer et al s 1990 zone v stuck patch on the central calaveras fault providing new support for their model of calaveras fault earthquake activity we suggest that zone v fails only in a family of recurring m 5 4 5 5 earthquakes the 1955 and 2007 earthquakes are the penultimate and ultimate zone v events earthquakes in 1891 and 1864 are possible earlier zone v events the next zone v event is not expected in the next few decades assuming a time dependent recurrence model the mean forecast date is 2064 2035 2104 95 confidence range we further suggest that zones i ii iii and iv fail in recurring m 5 1 5 3 m 5 6 5 8 m 6 1 6 3 and m 4 9 5 0 earthquakes respectively if our earthquake recurrence model is correct the next zone i event is overdue and could occur anytime and m5 6 earthquakes should not occur on zones ii iii and iv before 2014 2012 and 2026 respectively we cannot rule out the possibility that zone vi which lies at the southern end of the mission seismic trend where the southern hayward and central calaveras faults appear to connect at depth fails aseismically or in large events on the southern hayward fault such as last occurred in 1868 or in large events on the adjoining northern calaveras fault segment

seismotectonics of the coast ranges in the vicinity of lake berryessa northern california tectonic deformation as manifested by seismicity and active faulting in the coast ranges in the vicinity of lake berryessa appears to be concentrated along the green valley cedar roughs fault trend and to a lesser degree the coast ranges sierran block crsb boundary zone the green valley cedar roughs fault trend appears to be a complex discontinuous or segmented shear zone consisting of multiple faults geomorphic evidence of quaternary displacement exists along many portions of the fault trend with holocene features and evidence for fault creep occurring along the green valley fault in contrast no historic earthquakes greater than ml 5 are known to have occurred along the fault trend earthquakes relocated in this study from 1970 to 1988 occur in the vicinity of mapped faults however the seismicity is discontinuous with a strong tendency to occur in clusters also superimposed on the general north northwest fault trend are north south epicentral trends not associated with any mapped faults focal mechanisms suggest predominantly right lateral strike slip faulting on both north and north northwest trending planes the existence of reverse and normal focal mechanisms also attests to the complex faulting occurring along the green valley cedar roughs trend in general the geologic and seismogenic characteristics are consistent with the hypothesis that the green valley cedar roughs fault trend represents young faulting possibly related to a newly developing plate boundary east of the san andreas fault earthquakes are confined to the top 12 km of the upper crust seismicity within the crsb boundary zone since 1970 has been generally confined to a sequence in 1978 near madison with a mainshock of ml 4 2 thrust reverse faulting appears to be the source of this activity consistent with the seismogenic processes observed along other segments of the boundary zone only one earthquake has occurred since 1970 in the epicentral area of the 1892 ml 6 vacaville winters earthquake the state of stress in the lake berryessa region as exhibited by focal mechanisms appears to be characterized by ne directed tectonic compression as observed elsewhere away from the san andreas fault system in northern and central california

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

effective discharge recurrence intervals of illinois streams abstract effective discharge values are routinely used to characterize the geomorphic impact work that different flows have on streams and watersheds effective discharge values are also routinely employed in stream restoration design reliable flow frequency and sediment rating curves are needed to compute effective discharge values but are not available for many streams in lieu of regional effective discharge data researchers engineers often assume that a stream s effective discharge is the same as the 1 5 year flow event for that stream however research shows that this is not always true hence demand exists for developing regional effective discharge values that can be applied at ungaged stream locations a regional study of effective discharge values within illinois is performed eighty eight monitoring sites were identified as locations where effective discharge values could potentially be computed twenty of these sites were determined to have sufficient data to compute effective discharge values for these stations effective discharge values were computed using two different sediment discharge relationships a power curve and an alternative mean approach the mean approach estimates effective discharge values that are on average 1 9 times larger than those estimated using the power curve the sediment load carried by flows less than or equal to the effective discharge value are on average 2 7 times larger when the mean approach is used both the power curve and mean approaches typically yield effective discharge values greater than the stream s mean flow and less than its 1 1 year annual maximum series flow event some of the computed effective discharge values are less than the stream s mean flow computing effective discharge values remains a subjective process with large uncertainties involved class interval size sediment rating curve fitting techniques and available sediment data influence effective discharge results a paucity of monitoring data for illinois streams draining 2 where many geomorphic analyses and stream restoration projects take place hinders the regional applicability of effective discharge results the uncertainties associated with effective discharge values and the inability to validate effective discharge values as a stream s dominant discharge makes channel design using effective and dominant discharge theory problematic suggestions for improving regional effective discharge studies and effective discharge estimates are provided

river terrace systems in north west europe an archive of environmental change uplift and early human occupation abstract staircases of large scale aggradational river terraces are a notable feature of many valleys in the temperate lattitudes particularly in areas beyond the reach of the erosive activities of pleistocene ice sheets it is now recognized that the cyclic fluctuations of climate during the quaternary have driven the generation of terraces through the direct and indirect influence of both temperature and precipitation on fluviatile activity where fossiliferous deposits are preserved within terrace sequences it is often possible to date these and to correlate them with the oceanic record thus providing an important framework for the evidence of environmental change on land middle and late pleistocene terraces in different areas can commonly be seen to have formed in synchrony with glacial interglacial cycles or with longer periodicity megacycles climatic forcing alone is insufficient to cause terraces to form however uplift is also necessary so that terrace sequences can provide a useful record of crustal movement in northwest europe where some of the best known studies of river terrace sequences have been carried out the fluviatile deposits are also an important repository for palaeolithic artefacts from which a record of early human occupation can be reconstructed

valley and interfluve sediments in the southern ganga plains india exploring facies and magnetic signatures the western ganga plains of india show narrow incised valleys that contain the major himalayan sourced rivers separated by broad interfluves traversed by small plains fed rivers from analysis of four cores and outcrop sections to 50 m sub surface this geomorphic setting appears to be of late quaternary antiquity a major river paleo ganga has been located near its present position since at least 26 ka bp with indications of southward migration between 11 and 6 ka valley fill cores show repeated cycles of valley aggradation in response to late quaternary climatic oscillations in accord with simulation models of drainage basin response to climate change and reflect interplay of discharge and sediment supply floodplain sediments within the valley fill show a generally weakly magnetic signature and only modest pedogenic activity the valley margin records a major discontinuity that marks reduction of discharge in the ganga river during the last glacial maximum when monsoonal precipitation was greatly reduced and lakes and eolian dunes occupied areas distant from the main channel the lacustrine facies show marked magnetic enhancement probably reflecting bacterial action and the availability of organic matter the interfluve record yields no indication of major river activity during the past 100 ka instead the near continuous activity of small plains fed rivers generated cycles of alluviation and pedogenesis the latter yielding strong magnetic signatures enhanced magnetic signatures are apparent in both valley and interfluve holocene records possibly linked to increased monsoonal strength warmer conditions and enhanced rates of pedogenesis

geomorphic effectiveness a linear concept in a non linear world geomorphic effectiveness has been an influential concept in geomorphology since its introduction by reds wolman and john miller in 1960 it provided a much needed framework to assess the significance of an event by comparing event magnitude to the resultant geomorphic effects initially this concept was applied primarily in river channels under the linear assumption that geomorphic responses to similarly sized flood events will be consistent numerous authors have since attempted to quantify a direct proportional relationship between event magnitude and different forms of geomorphic response in a variety of geomorphic settings in doing so these investigations applied an array of metrics that were difficult to compare across different spatiotemporal scales and physiographic and geomorphic environments critically the emergence of other geomorphic concepts such as sensitivity connectivity thresholds and recovery has shown that relationships between causes events and geomorphic effects responses are often complex and non linear this paper disentangles the complex historical development of the geomorphic effectiveness concept and reviews the utility of various metrics for quantifying effectiveness we propose that total energy joules is the most appropriate metric to use for quantifying the magnitude of disturbance events cause and volumetric sediment flux associated with landform modification is the most appropriate metric for quantifying geomorphic effects while both metrics are difficult to quantify they are the only ones which facilitate comparison across a range of spatiotemporal scales comparability in a variety of geomorphic environments flexibility the geomorphic effectiveness concept can continue to be useful provided that geomorphologists use flexible and comparable metrics today geomorphologists are better prepared to consider the influence of non linear processes on determinations of geomorphic effectiveness allowing investigators to not only determine if a disturbance event was effective but also to explain why or why not copyright

evolution of the stress field in the northern aegean sea greece summary the evolution of the stress field in the area of the northern aegean sea during the 20th century has been studied the area is dominated by dextral strike slip faulting and is characterized by frequent strong earthquakes coulomb stress changes dcff were calculated assuming that earthquakes can be modelled as static dislocations in an elastic half space and taking into account both the coseismic slip in large mi7 0 earthquakes and the slow tectonic stress build up along the major fault segments the stress change calculations were performed for strike slip faults of strike dip and rake appropriate to the large events we evaluate whether these stress changes brought a given large earthquake closer to or farther from failure it was found that each of the large events occurred in regions of increased calculated coulomb stress moreover the majority of smaller events for which reliable fault plane solutions are available were also located in areas of positive dcff by extending the calculations to 2020 and assuming that no additional large mi7 0 earthquake occurs between 1999 and 2020 possible sites of future large earthquakes are identified

holocene paleoclimates of india we present a comprehensive summary of the available palaeoclimate records from india and compare the results from different proxies the results indicate i fluctuating lake levels during the early holocene the period of relatively higher lake levels from increased precipitation efficiency was reached only 7 2 6 0 cal kyr bp possibly due to increased contribution from winter rainfall ii the onset of aridity in nw india could have begun as early as 5 3 cal kyr bp subsequently there were multiple wet events but of shorter duration and smaller magnitude than during the mid holocene iii there is evidence of several short term climate events in the proxy record however in the absence of a rigorous chronological framework a detailed regional correlation is not possible at this stage finally a comparison between marine and terrestrial records indicates that episodes of strongest and weakest monsoon winds were not always associated with wettest and driest episodes respectively in the nw indian lakes

seismic activity on neighbouring faults as a long term precursor to large earthquakes in the san francisco bay area activity in moderate size earthquakes accelerated in the several decades before the large california earthquakes of 1989 1906 and 1868 this type of precursor seems to require the presence of several major faults in close enough proximity to one another that moderate size shocks are selectively triggered on surrounding faults during the latter stages of the cycle of strain buildup to large earthquakes it may be possible to use quantitative aspects of similar seismic precursors to make predictions of large earthquakes on timescales of a few years to one decade

channel change bankfull and effective discharges on a vertically accreting meandering gravel bed river along the lower reaches of the waipaoa river new zealand cross section survey data indicate there was a 23 per cent decrease in bankfull width and a 22 per cent reduction in channel cross section area between 1948 and 2000 as the channel responded to increased inputs of fine suspended sediment following deforestation of the headwaters in late c19 and early c20 we determined the bankfull discharge within a 39 km long reach by routing known discharges through the one dimensional mike 11 flow model the model runs suggest that the bankfull discharge varies between 800 and 2300 m3 s 1 and that the average recurrence interval is 4 2 years on the annual maximum series by contrast the effective flow 360 m3 s 1 is equaled or exceeded three times a year the variability in bankfull discharge arises because the banks tend to be lower in places where flood flows are constricted than in reaches where overbank flow is dispersed over a wide area and because scour has counteracted aggradation in some locations there is no downstream variation in shields stress or in relative shear stress within the study reach bankfull shear stress is on average five times greater than the shear stress required to initiate motion at the effective discharge it is more than twice the threshold value the effective discharge probably has more relevance than the bankfull discharge to the overall picture of sediment movement in the lower reaches of the waipaoa river but because width is constrained by the stability and resistance of the bank material to erosion during high flows that also scour the bed the overall channel geometry is likely determined by discharges at or near bankfull copyright 2006 john wiley sons ltd

morphologic changes in the parana river channel argentina in the light of the climate variability during the 20th century recent studies regarding the climate variability in south america during the 20th century revealed the existence of climate cycles that influenced the hydrologic conditions in the parana river basin one of the largest in the continent how that variability affected the channel morphology of this river in its middle reach is quantitatively analyzed in this paper the link between climate hydrology and channel morphology is obtained through the computation of effective discharge this discharge implicitly synthesizes the point hydrologic and bed sediment transport changes in an alluvial stream during a relatively long period the results were obtained studying with increasing detail two channel reaches 373 km and 25 km long respectively the analysis involved the processing of more than 180 bathymetric charts satellite images and hydraulic and sedimentologic data recorded in the parana river since the very beginning of the 20th century a rather detailed description of the treatment made with this information is given in the paper it is shown that three periods of different effective discharges fairly well correlated with reported climatic fluctuations occurred during the last 100 years i e two periods of high discharges at the century beginning and from 1970 till present and another of relatively low discharges between 1930 and 1970 morphologic parameters of the main channel such as mean width thalweg sinuosity braided index and aspect ratio increased or decreased in correspondence with those variations in transitional channels between meandering and braided like the parana river careful study of the thalweg behavior is a key issue if a proper approach to the dynamic of morphologic processes operating on the whole channel is intended finally on the basis of theoretical extreme hypotheses approach and empirical results it is suggested that the parana river main channel would not be adjusted to the present high values of effective discharge thus larger erosion of banks channel widening and increases in the other cited morphologic characteristics will occur if those values persist

linking hydrology and sediment dynamics of large alluvial rivers to landscape diversity in the ganga dispersal system india discharge and sediment load data for several stations along the ganga river and its major tributaries in the western ganga plains wgp for a period of 30 years have been analysed to understand the hydrological characteristics and sediment dynamics in terms of hydrology the rivers are less flood prone than believed exceeding bankfull discharges less frequently than the expected 1 5 year return interval this has been attributed to the rivers of this region occupying incised valleys formed in the late quaternary period rivers draining the wgp are supply limited systems compared to those draining the eastern ganga plains egp which have been characterised as transport limited systems we suggest that such geomorphic diversity as a function of spatial variability in precipitation regime and hinterland geology has existed for at least late quaternary period and they in turn influence the modern day hydrology of the river systems in a significant way this article is protected by copyright all rights reserved

changes in static stress on southern california faults after the 1992 landers earthquake the magnitude 7 5 landers earthquake of 28 june 1992 was the largest earthquake to strike california in 40 years the slip that occurs in such an earthquake would be expected to induce large changes in the static stress on neighbouring faults these changes in stress should in turn affect the likelihood of future earthquakes stress changes that load faults towards failure have been cited as the cause of small1 5 moderate6 and large7 earthquakes conversely those that relax neighbouring faults have been related to a decrease in seismicity5 here we use an elastic half space model8 to estimate the stress changes produced by the landers earthquake on selected southern california faults including the san andreas we find that the estimated stress changes are consistent with the triggering of four out of the five aftershocks with magnitude greater than 4 5 and that the largest changes 1 10 bar occurring on part of the san bernardino segment of the san andreas fault may have decreased the time to the next magnitude 8 earthquake by about 14 years

seismicity in the twenty years preceding the loma prieta california earthquake persistent seismicity occurred at a low rate during at least the twenty years before the loma prieta earthquake along the 60 km long rupture zone the depth distribution of this seismicity forms a broad u shape that delineates the previously locked rupture zone relocations of seismicity during the ten years before the earthquake relative to the loma prieta aftershocks show that this u shaped distribution can be partitioned lengthwise into activity on two adjacent subparallel structures a vertical fault beneath the san andreas fault trace and an eastward dipping blind fault beneath the sargent fault trace the 11 18 km deep southwest dipping part of the loma prieta rupture was not active during at least the preceding ten years the slip geometry of intersecting fault structures in this zone could contribute to both the preparation process and the complexity of the rupture

surface displacements in the 1906 san francisco and 1989 loma prieta earthquakes the horizontal displacements accompanying the 1906 san francisco earthquake and the 1989 loma prieta earthquake are computed from geodetic survey measurements the 1906 earthquake displacement field is entirely consistent with right lateral strike slip on the san andreas fault in contrast the 1989 loma prieta earthquake exhibited subequal components of strike slip and reverse faulting this result together with other seismic and geologic data may indicate that the two earthquakes occurred on two different fault planes

fault plane solutions for the 1984 morgan hill california earthquake sequence evidence for the state of stress on the calaveras fault fault plane solutions for 946 aftershocks of the april 24 1984 morgan hill california m6 2 earthquake reveal a pattern of complex faulting within a 10 km wide zone surrounding the calaveras fault the fault plane solutions fall into three groups strike slip mechanisms located along the calaveras fault with north northwest striking dextral slip planes nearly parallel to the fault strike slip mechanisms located northeast of the calaveras fault with north striking dextral slip planes and reverse mechanisms located southwest of the calaveras fault with northeast or southwest dipping slip planes the average azimuth of p axes for aftershocks located on the calaveras fault is n10 1 e in contrast the average azimuths of p axes for aftershocks northeast and southwest of the calaveras fault are n49 7 e and n37 3 e respectively by assuming that the earthquakes occur on preexisting cracks in response to a uniformly oriented regional stress field we are able to infer from the observed average slip directions an orientation for 1 the axis of maximum horizontal compression 63 80 from the local strike of the calaveras fault such a high angle orientation of 1 is incompatible with the classical andersonian model of strike slip faulting but is consistent with an alternate model in which a weak calaveras fault is driven by plate motion slightly convergent with respect to the san andreas fault system in central california if this inferred high angle uniform stress field is combined with the changes in the static stress field calculated with elastic dislocation theory for the 1984 morgan hill main shock the resulting stress field predicts most of the observed spatial pattern of the aftershocks and their fault plane solutions the orientations of the inferred aftershock slip planes are generally consstent with the fracture orientations predicted by the coulomb failure criterion areas with predicted increases in the coulomb failure function of only a few tenths of a megapascal correspond to areas of intense aftershock activity the invariance of focal mechanisms in the vicinity of the south end of the main shock rupture before and after the main shock suggests that the magnitude of compressive stress in this area is at least 10 mpa in addition to explaining a preponderance of the seismic observations of the aftershock sequence the presence of a predominantly fault normal compressive regional stress field accounts for the contemporary development of folds reverse faults and topographic relief observed throughout the central california coast ranges

understanding confluence dynamics in the alluvial ganga ramganga valley india an integrated approach using geomorphology and hydrology abstract confluence dynamics in the ganga ramganga valley in the western ganga plains of india has been studied through systematic mapping of channel configuration using multi date remote sensing images and topographic sheets for a period spanning nearly 100 years 1911 2000 the study has been supplemented with a detailed analysis of the channel morphology hydrology and sediment transport characteristics of the different rivers our study indicates that new confluences have been created during this period and that the confluence points have moved both upstream and downstream on a historical time scale apart from major avulsions other processes that have controlled the confluence movements include river capture cut offs and aggradation in the confluence area river capture occurs through lateral bank erosion and migration encroachment by the master stream and beheading of smaller rivers resulting in upstream movement of the confluence point another process which influences the upstream migration of the confluence is an increase in sinuosity of one of the channels near the confluence and then a cut off aggradation in the confluence area and local avulsions of the primary channel in a multi channel system seem to be the major process controlling the downstream movement of the confluence point analysis of channel morphology hydrology and sediment budget for the study period supports our interpretations

the magnitude and frequency characteristics of fluvial transport in a devon drainage basin and some geomorphological implications summary magnitude and frequency analysis of fluvial transport based on long and detailed record has been lacking for british rivers continuous monitoring of suspended sediment and solute concentrations for the river creedy devon since october 1972 has provided an opportunity to establish the medium term magnitude and frequency characteristics of river transport in a sizeable 262 km 2 drainge basin results reveal the importance of solute removal substantial variations in the relative magnitude of annual dissolved and suspended sediment yields clear differences in the temporal distribution of sediment and solute removal and contrasts in the magnitude and recurrence of extreme values of dissolved and suspended solids transport consideration of discharge levels most effective for transporting river loads in relation to a natural channel cross section has stressed the importance of events of moderate magnitude and frequency in this drainage system

soil aggregation response to long and short term differences in rainfall amount under arid and mediterranean climate conditions soil structure variables aggregate stability as mean weight diameter mwd microparticles percentage mip and macroparticles percentage map organic matter content om electrical conductivity ec and sodium and potassium adsorption ratio spar were monitored for 3 years at seven research sites the sites are located along a climatic transect extending from the judean mountains mean annual rainfall 700 mm annual mean temperature 17 c to the dead sea mean annual rainfall 100 mm annual mean temperature 23 c and represent four climatic regions multiple regression relating soil structure variables to om spar and ec highlighted the importance of organic matter in determining soil structure a high correlation was found between mean annual rainfall representing its long term effect and annual rainfall variability representing its short term effect and some aggregation variables as increased while mip decreased with decreasing rainfall the rate of change along the climatic transect was non linear a step like threshold exists in the semi arid zone meaning that this area is threatened by land degradation even with a small decrease in mean annual rainfall mip was found to be very sensitive to rainfall amount even at the patch scale no patches of low mip values were found in the arid zone even in a very wet year and no patches of high mip values were found in the mediterranean zone even in a very wet year the main conclusion is that mip is the best indicator for assessing the impact of the expected climate change on soil structure and erosion

geomorphic impacts of flash flooding in a forested headwater basin abstract geomorphic impacts of a july 2001 flood in the hungry mother basin near marion virginia were examined to shed light on the relationships between channel characteristics and the frequency of channel modifying discharges creeks in the study area have been observed for many years with no significant channel changes since at least 1985 the 2001 flood had a recurrence interval of 200 years and caused the only channel change bank erosion and transport of coarse channel material observed in recent decades the paucity of fines in channels before or after the flood and the absence of sub sand sized material in the flood deposits indicates that normal frequent well below bankfull flows are sufficient to transport the apparently limited supply of fines the large particles transported during the 2001 flood after years of inactivity indicate that relatively rare floods are necessary to mobilize this material this suggests the notion of a bimodal dominant discharge on the one hand frequent flows considerably below bankfull levels are sufficient to maintain the channel and prevent significant accumulation of fine sediments and organic matter on the other hand rare floods are necessary to transport the coarser bed material and erode channel banks in the hungry mother area bed material has no relationship to normal flows or to flows with recurrence intervals on the order of 1 3 years bankfull discharge is apparently not related to either the maintenance or channel changing dominant discharges these results suggest that the use of channel dimensions and or bed material as surrogate indicators of hydrologic regimes can be quite complicated and that in some streams bankfull flow has no particular significance in terms of sediment transport and channel modifications

dislocation model for aseismic crustal deformation at hollister california geodetic observations at many active plate margins reveal relatively steady aseismic motion during the time between major earthquakes we model the aseismic motion by the relative motion between several blocks that suffer frictional resistance in the upper crust frictional drag is represented by uniform dislocation on a fault surface we assume that friction occurs only on the upper brittle zone of each block boundary and that frictionless sliding occurs below this zone using a bayesian inversion procedure we invert geodetic data to determine the parameters of the block and dislocation model parameters to be estimated include the two horizontal components of velocity for each block and the dislocation rate dip angle slip angle and width of each rectangular fault patch for hollister we assume five blocks and nine rectangular fault patches rates of length change on 92 lines observed by trilateration make up the data triangulation leveling very long baseline interferometry satellite ranging and global positioning system data can also be easily included in our model our inversion procedure uses prior estimates of all block and fault parameters based on geological and seismological data the block parameters are estimated from geological observations of fault displacement rates while the widths of the fault patches are estimated from earthquake hypocentral depths we choose prior estimates of the dislocation rate to match observed creep rates the estimated block motion is well resolved by the geodetic data and agrees well with the geological estimates this suggests that the block motion is steady on time scales from 10 years to 1 m y the net motion across the san andreas calaveras fault system is 38 3 mm yr oriented s38 e thus some additional displacement possibly offshore is needed to match the rate of 56 mm yr predicted by plate tectonic models the depth of the transition from frictional to free sliding varies considerably from 0 4 km on the southern calaveras to 11 km on the central san andreas fault two segments of the san andreas north of 36 50 and south of 36 40 have the greatest potential for moderate to large earthquakes

horizontal deformation associated with the loma prieta earthquake abstract co seismic horizontal displacements for the 1989 loma prieta earthquake were derived from preseismic triangulation trilateration observations and post seismic gps observations as part of this process the empirical model entitled tdp h91 was applied to correct the preseismic measurements for the crustal motion that occurred during the seven decades spanned by these data these newly derived displacements were combined with previously documented geodetic results to generate a dislocation model for the earthquake our preferred model consists of a vertically segmented rupture surface represented by two rectangles that share a common edge at a depth of 9 km the upper rectangle dips 90 and the lower rectangle dips 70 sw via a trial and error technique the following estimates were found for the remaining parameters strike 134 4 0 7 fault length 32 4 0 7 km upper depth 4 8 0 1 km lower depth 15 1 0 3 km right lateral strike slip 1 86 0 06 m for the upper rectangle and 1 96 0 13 m for the lower rectangle and thrusting dip slip 1 06 0 06 m for the upper rectangle and 2 30 0 18 m for the lower rectangle

mechanisms of seismic quiescences in the past decade there have been major advances in understanding the seismic cycle in terms of the recognition of characteristic patterns of seismicity over the entire tectonic loading cycle the most distinctive types of patterns are seismic quiescences of which three types can be recognized post seismic quiescence which occurs in the region of the rupture zone of an earthquake and persists for a substantial fraction of the recurrence time following the earthquake intermediate term quiescences which appear over a similar region and persist for several years prior to large plate rupturing earthquakes andshort term quiescences which are pronounced lulls in premonitory swarms that occur in the hypocentral region hours or days before an earthquake although the frequency with which intermediate term and short term quiescences precede earthquakes is not known and the statistical significance of some of the former has been challenged there is a need if this phenomena is to be considered a possibly real precursor to consider physical mechanisms that may be responsible for them the characteristic features of these quiescences are reviewed and possible mechanisms for their cause are discussed post seismic quiescence can be readily explained by any simple model of the tectonic loading cycle as due to the regional effect of the stress drop of the previous principal earthquake the other types of quiescence require significant modification to any such simple model of the possibilities considered only two seem viable in predicting the observed phenomena dilatancy hardening and slip weakening intermediate term quiescences typically occur over a region equal to or several times the size of the rupture zone of the later earthquake and exhibit a relationship between the quiescence duration and size of the earthquake they thus involve regional hardening or stress relaxation and agree with the predictions of the dilatancy diffusion theory short term quiescences on the other hand are more likely explained by fault zone dilatancy hardening and or slip weakening within a small nucleation zone because seismicity is a locally relaxing process seismicity should follow a behaviour known in rock mechanics as the kaiser effect in which only a very slight increase in strength due to dilatancy hardening or decrease in stress due to slip weakening is required to cause quiescence this is in contrast to other precursory phenomena predicted by dilatancy which require large dilatant strains and complete dilatancy hardening

use of high water marks and effective discharge calculation to optimize the height of bank revetments in an incised river channel abstract in deeply incised rivers bankfull discharge i e the flow filling the channel to the top of the banks does not represent channel forming flow and increasingly large flows are associated with increasingly large boundary shear stress in such rivers solid bank revetments rip rap gabions retaining wall are usually constructed to the top of the banks similarly as in vertically stable rivers despite the fact that the upper parts of the banks may never be flooded to optimize the height of solid bank revetments in deeply incised channels it is thus important to determine whether a flood magnitude can be identified for which the combination of flow duration and bedload transport rate results in the highest river efficiency to transport bedload and perform geomorphic work this question was explored in the moravka river czech carpathians which deeply incised into non resistant flysch bedrock over the past few decades observations of high water marks e g trash lines wash lines after a flood in 2014 enabled reconstruction of the peak flood stage in the deeply incised reach and the adjacent vertically stable reach these observations together with post flood measurements of cross sectional channel geometry distances between consecutive cross sections and estimates of channel roughness were used in one dimensional hydraulic modelling aimed to determine a peak discharge of the flood in a number of cross sections in both reaches despite the close proximity of both reaches markedly higher discharge values were obtained for the incised reach and the discrepancy was used to calibrate roughness coefficients for the incised reach a flow duration curve determined on the basis of a 25 year series of daily discharges in the upstream gauging station together with data about channel geometry and roughness in the incised cross sections were used to simulate bedload transport at successive discharges with the bags sediment transport model the calculations indicated the effective discharge for bedload transport in the incised reach to have the recurrence interval of 7 12 years the upper limit of the reach average effective discharge is associated with the stage slightly higher than a half of the bankfull depth this highlights the disparity between effective and bankfull discharges and indicates that in incised channels channel forming flow should be linked with the former the vertical extent of the reach average effective discharge is proposed as an indicator of the optimal cost effective height of solid bank protection structures in the deeply incised channel and the suitability of this approach is discussed

small earthquakes tectonic forces earthquake scaling and frequency of occurrence relations require that small earthquakes be just as important as larger ones in redistributing the forces that drive relative displacements across active faults of any dimension including plate boundaries

lateglacial and holocene environmental changes in ganga plain northern india abstract stable isotope elemental geochemistry and pollen analysis of a sediment profile from sanai lake central ganga plain were used to document climatic oscillations during the last 15 000 yr in indian subcontinent micaceous sandy sediments at the base of the profile indicate an active channel and humid conditions before 15 000 14c yr bp the channel was abandoned during comparatively arid conditions 15 000 13 000 14c yr bp and converted into a swamp enhanced humidity around 13 000 14c yr bp led to submergence of marshes and establishment of a large lake a dry phase is also identified around an estimated age of 11 500 10 500 14c yr bp which might correspond to the younger dryas event witnessed globally the early to mid holocene climatic optimum 10 000 5800 14c yr bp is characterised by a lake environment occurence of warmth loving aquatic plants lower 18o values of gastropod aragonite heavier 13corg values indicate a sensitive response of the lake ecology to the climatic warming and increased rainfall this is followed by an arid event during 5000 2000 14c yr bp and from 1700 14c yr bp there is evidence of climatic amelioration the sequence and magnitude of the millenium scale climatic oscillations documented along the lake profile correlate well with records from other parts of the indian subcontinent indicating that the recorded changes are an expression of broad scale probably global and climatic change

man made changes of seismicity rates seismicity catalogs contain important information about processes which occur in seismically active regions of the earth many authors have examined these catalogs for patterns and variations in patterns which might reflect changes in these processes we have found that these catalogs include a complex mixture of real and man made changes one must identify and account for the man made changes before the real ones can be identified and understood many man made changes in seismicity catalogs are manifested as changes in seismicity rates and can therefore be identified through careful examination of these rates obvious effects include increases or decreases in the detection and reporting of smaller events which accompany the installation or closure of seismic stations these types of changes can be recognized by examining the distribution of seismicity rate changes in the magnitude domain they are characterized by increases or decreases in the number of small events in the catalog at times when the number of larger events remains constant systematic changes in the magnitudes assigned to events can also be identified by examining seismicity rates because they cause apparent changes in rates of data sets with magnitude cutoffs the sign of the apparent rate change depends on the sign of the magnitude change and the type of cutoff used the effects of detection changes can be easily remedied by using a magnitude cutoff which eliminates the smaller events from consideration the techniques we have developed allow one to determine the optimum cutoff magnitude corrections are necessary for remedying the effects of systematic changes in magnitude estimates these corrections can be determined through modeling of observed rate changes caused by these shifts man made changes are present in all seismicity catalogs whether local regional or teleseismic they must be accounted for if these catalogs are to provide meaningful information on real process changes in the earth

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

river systems and their sediment flux indo gangetic plains northern bihar india river systems of part of the himalayan foreland northern bihar plains india are described in terms of their channel morphology hydrology and suspended sediment characteristics a simple classification of the river systems based mainly on the source area characteristics is proposed i mountain fed ii foothills fed iii plains fed and iv mixed fed rivers distinct differences are noted between these classes of river systems most rivers show evidence of channel movement mainly by avulsion but cut offs also occur locally the mountain fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains fed rivers have relatively low discharge and high suspended sediment concentration the foothill fed rivers have moderate values of discharge and suspended sediment concentration the mountain fed rivers have built megafans of large extent whereas the foothills fed and plains fed rivers have formed muddy interfan areas semi quantitative estimates of water and sediment flux suggest that about 99 9 of the mass transfer into the plains is water with the remaining 0 1 being sediment and that 10 s of the latter 0 01 of the total is retained in the basin the remainder being transferred to the bengal fan

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

monsoon control of effective discharge yunnan and tibet analysis of suspended sediment transport data for rivers in yunnan and tibet shows that monsoon fl ows control effective discharge we calculate effective discharge defi ned as the discharge that transports the most sediment for 44 stations for which there is at least one complete year of daily suspended sediment concentration and mean daily discharge data and fi nd that the effective discharge is approximately the mean monsoon discharge for all stations the correspondence of the effective discharges with the mean annual fl ow and monsoon discharge for all stations demonstrates that monsoon fl ow dominates suspended sediment transport in the region rather than storm fl ow during discrete short duration storm events in this region the monsoon lasts for 4 months june september and during that time transports 86 of the suspended sediment load in contrast to the general observation from temperate environments that infrequent stochastic storm events dominate sediment transport with 90 of the suspended sediment transport occurring in 10 of the time our fi ndings show that the mean monsoon discharge dominates sediment transport in the rivers draining the southeastern tibetan plateau

geodetic estimate of coseismic slip during the 1989 loma prieta california earthquake offsets in the relative positions of geodetic stations resulting from the loma prieta earthquake can be explained with a dislocation model that includes buried oblique slip on a rupture surface extending 37 km along the strike of the san andreas fault dipping 70 degree to the sw and extending from a depth of about 5 to 17 5 km assuming uniform slip on a rectangular surface the mean values for a range of reasonable fault geometries are 1 6 plus minus 0 3 m right lateral strike slip and 1 2 plus minus 0 3 m reverse slip slip on an adjacent extension of the rupture to the southeast recorded in the aftershock sequence is not well constrained by the geodetic data the geodetic data clearly preclude rupture extending near the surface

stress near geometrically complex strike slip faults application to the san andreas fault at cajon pass southern california slip on an undulatory strike slip fault induces predictable residual stresses in the adjacent crust elastic analytic and finite element models are developed to quantify these stresses for arbitrary fault geometries across fault parallel planes domains of reverse normal right lateral and left lateral residual stresses are induced near the bends in the fault these residual stresses increase in magnitude from one slip event to the next typically reaching failure level after several events a two dimensional analytic elastic plate model for slip on a sinusoidal fault provides general results on the scales and patterns of slip induced stresses and fourier synthesis allows for the solution with arbitrary but small fault distortions maximum fault normal residual stress is proportional to the square of the wavenumber of the sinusoidal trace and decays exponentially away from the fault reduced to 2 e times the maximum value at a distance equal to 1 wavenumber this fault parallel residual shear stress oscillates between dextral and sinistral along the fault with maximum magnitude adjacent to the maximum excursions in the fault trace fault parallel residual shear stress is maximum at a distance from the fault of 1 wavenumber where its magnitude is 1 e times the maximum normal stress on the fault two and three dimensional finite element analyses extend the analytic model they account for depth decaying fault perturbation amplitude and slip deficit and are valid for large fault undulations application of the model to the san andreas fault in the cajon pass region produces the complex distribution of fault parallel normal reverse right lateral and left lateral structures recognized near the main trace left lateral stresses on planes subparallel to the san andreas fault at the cajon pass well are predicted by this model

re evaluation of 1906 surface faulting geomorphic expression and seismic hazard along the san andreas fault in the southern santa cruz mountains the lack of through going right lateral surface rupture accompanying the loma prieta earthquake has raised questions about the behavior of the san andreas fault in the southern santa cruz mountains we re evaluated previously published reports of ground deformation due to the 1906 earthquake in this region to determine if san andreas fault surface rupture accompanied this event and whether any of the reported values of offset are reliable in addition our search for historical data has brought to light new information about the 1906 earthquake in the southern santa cruz mountains none of the reports provides indisputable evidence for 1906 san andreas fault surface rupture however taken together with a study of the geomorphology of the fault zone and relationships exposed in excavations across the fault they do provide a basis for believing that surface rupture extended through the region in 1906 none of the reported values for 1906 offset is a reliable measurement however calling into question current and pre 1989 seismic hazard assessments for the loma prieta area the geologic and geomorphic relationships indicate that shallow right lateral crustal strain is typically expressed as surface rupture across a narrow san andreas fault zone in contrast to the 1989 loma prieta earthquake

changes in crustal seismic deformation rates associated with the 1964 great alaska earthquake we calculated seismic moment rates from crustal earthquake information for the upper cook inlet region including anchorage alaska for the 30 yr prior to and 36 yr following the 1964 great alaska earthquake our results suggest over a factor of 1000 decrease in seismic moment rate in units of dyne centimeters per year following the 1964 mainshock we used geologic information on structures within the cook inlet basin to estimate a regional geologic moment rate assuming the structures extend to 30 km depth and have near vertical dips the geologic moment rates could underestimate the true rates by up to 70 since it is difficult determine the amount of horizontal offset that has occurred along many structures within the basin nevertheless the geologic moment rate is only 3 7 times lower than the pre 1964 seismic moment rate suggesting the 1964 mainshock has significantly slowed regional crustal deformation if we compare the geologic moment rate to the post 1964 seismic moment rate the moment rate deficit over the past 36 yr is equivalent to a moment magnitude 6 6 7 0 earthquake these observed differences in moment rates highlight the difficulty in using seismicity in the decades following a large megathrust earthquake to adequately characterize long term crustal deformation

rock magnetic and geochemical record in a sediment core from the eastern arabian sea diagenetic and environmental implications during the late quaternary abstract rock magnetic concentration grain size and mineralogy parameters together with organic carbon calcium carbonate redox sensitive elements 18 o of globigerinoides ruber and radiocarbon dating were carried out on a 445 cm long sediment core collected at 1380 m depth off mangalore southwestern margin of india the top 290 cm sediments of the core correspond to the last 18 kabp the 18 o and magnetic records exhibit major events at 16 kabp 14 5 kabp 11 5 kabp and 9 8 8 6 kabp related to start and intensity of the summer monsoon and climate change and are synchronous with that of the western arabian sea and north atlantic the sediments with high magnetic susceptibility correlate with high sedimentation rates the sediments are dominated by fine grained magnetite but intervals of 1 2 3 8 kabp and 10 13 5 kabp were subjected to diagenetic changes resulting in the dissolution of fine grained magnetites and enrichment of redox sensitive trace elements cu ni zn v mo and u the sediments between 290 cm and 445 cm correspond to 18 27 kabp and are characterized by distinct decrease in magnetic concentration grain size and mineralogy parameters high organic carbon low concentrations of redox sensitive trace elements and abundant pyritized tubules the reductive diagenetic conditions indicated by rock magnetic properties are in contrast with the weak sub oxic conditions revealed by low concentrations of trace elements in the sediments the seasonal organic matter flux produced during the winter monsoon and moderate sedimentation rates favoured reductive diagenesis in the sediments at and below the last glacial maximum lgm intermittent bioturbation however allowed oxidants to penetrate into the sediments remobilized redox sensitive trace elements into the water column and modified the primary geochemical signal of the sedimentary environment

geomorphology and endangered fish habitats of the upper colorado river 2 linking sediment transport to habitat maintenance alluvial reaches of the colorado river near grand junction colorado provide important habitat for the endangered colorado squawfish this paper examines recent changes in the geomorphology of the colorado river and addresses the question of what can be done to improve existing fish habitats observations of channel change during periods of above average runoff from 1993 through 1995 indicate minor scour and fill of the main channel but more significant scour and enlargement of side channel and backwater habitats and flushing of fine sediment from the bed modeled relations between discharge and dimensionless shear stress indicate that the threshold of bed load transport 0 03 occurs at about half the bank full discharge these flows are exceeded about 26 days per year on average the bank full discharge produces an average of 0 047 and is exceeded about 8 days per year the width and depth of the channel thus appear to be set by a discharge that produces an average boundary shear stress of 1 5 times greater than the critical shear stress the effective discharge is slightly less than the bank full discharge and approximately 80 of the total sediment load is carried by the highest 10 of all discharges

contemporary seismicity and tectonics of the northern and central coast ranges sierran block boundary zone california abstract beneath the physiographic boundary between the coast ranges and the great valley a fundamental tectonic boundary exists between the coast ranges province and the sierran block recent geophysical studies have revealed the coast ranges sierran block crsb boundary zone to be a complex region of compressional tectonics wherein wedges of comparatively ductile franciscan complex of the coast ranges have overridden the competent sierran block basement and peeled up the overlying sediments of the great valley sequence the boundary zone was the probable source of the two 1892 winters earthquakes ml 6 7 and the 1983 coalinga earthquake ml 6 7 we evaluated the seismicity within the northern and central portions of the zone from red bluff south to san luis reservoir for the period 1969 1985 seismicity was spatially diffuse most of the earthquakes occurred in somewhat isolated concentrations within the upper crust a low activity level temporal clustering and episodic behavior also characterized this seismicity the largest earthquake in the boundary zone was a ml 4 2 event near madison 20 events exceeded ml 3 0 in a few cases the seismogenic sources appear to be eastward dipping high angle reverse faults although some right slip north trending faults also appear to be seismogenic in comparison the coalinga and 1985 kettleman hills main shocks in the southern portion of the zone appeared to involve gently westward dipping thrust faults although aftershocks also occurred on moderately to steeply dipping reverse faults fault plane solutions along the zone exhibited a tectonic stress field of ne to e trending compression normal to the boundary such compression may be a consequence of one or a combination of several influences 1 the westward movement of the sierran block against the coast ranges due to late cenozoic crustal extension in the great basin 2 slightly convergent motion between the pacific and north american plates and 3 fault normal crustal compression due to the low shear strength of the san andreas fault the tectonic deformation manifested by the coalinga and recent moderate sized earthquakes in the southern zone appears to be occurring along the full extent of the boundary albeit at varying rates for different segments thus the potential for large earthquakes may exist along segments of the crsb boundary and the 1892 main shock may represent a characteristic earthquake for that portion of the zone

integrating channel form and processes in the gangetic plains rivers implications for geomorphic diversity abstract geomorphic diversity at a variety of spatial and temporal scales has been studied in the western ganga plains wgp india to isolate the dominating factors at each scale that have the potential to cause major geomorphic change the ganga river and its major tributaries draining the wgp have been investigated in terms of longitudinal cross sectional and planform morphology to assess the influence of potential controls such as climate geology topography land use hydrology and sediment transport these data were then compared with those from the rivers draining the eastern ganga plains egp to understand the geomorphic diversity across the ganga plains and the causal factors our investigations suggest that in channel geomorphic diversity over decadal scale in rivers with low width to depth w d ratio is caused by periodic incision aggradation but it is driven by channel avulsion in rivers characterized by high w d ratio similarly planform reach scale parameters such as sinuosity and braid channel ratio are influenced by intrinsic factors such as changes in hydrological conditions and morphodynamics cutoffs small scale avulsion that are in turn impacted by natural and human induced factors finally we have isolated the climatic and hydrologic effects on the longitudinal profile concavity of alluvial trunk channels in tectonically stable and unstable landscapes we demonstrate that the rivers flowing through a tectonically stable landscape are graded in nature where higher discharge tends to create more concave longitudinal profiles compared to those in tectonically unstable landscape at 103 year scale

effective sediment transporting discharge from magnitude frequency analysis the long term effectiveness of a geomorphic event of a particular magnitude is the product of the effect of a single event of that magnitude times the frequency with which it recurs magnitude frequency analysis if discharge frequency of a stream is assumed to be log normally distributed and if sediment transport rate is assumed to be a power function of discharge then transport effectiveness attains a maximum value at some discharge termed here the effective discharge that moves the most sediment over the long term the effective discharge and its recurrence interval may be predicted if both assumptions are correct analysis of 55 u s streams demonstrates that the observed and the predicted recurrence intervals of the effective discharge are in poor agreement this lack of agreement results from the failure of the power function of discharge to predict adequately the sediment transport rate above some high discharge threshold or thresholds the observed recurrence interval of the effective discha

a framework for the hydrological assessment of at site bankfull discharge width for semi incised ganga river in middle ganga plains abstract floods and corresponding plains are very important to the river to fulfill its complex bio geomorphological functions these functions vary in importance from one river to another river hence in this work an attempt has been made to evaluate bankfull discharge and its width the analysis is carried out at seven central water commission cwc hydro meteorological sites on main stem of ganga river the bankfull discharge is assessed using an approach of partial duration series rationally in flood frequency analysis for each cwc site the region covering at least a part of its flood plain i e bankfull width is derived using rating curve of respective cwc site and validated using pre post monsoon cross sections and google earth imageries at all cwc sites the present methodology overcomes the problem of incised and semi incised rivers the results are indicative of the likely minimal river space both essential and desirable for the seven locations but unexplained anomalies exist in terms of discharges along the length of the river

probabilities of occurrence of large plate rupturing earthquakes for the san andreas san jacinto and imperial faults california 1983 2003 the san andreas san jacinto and imperial faults in california are divided into 19 segments conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake i e an event that breaks the entire down dip extent of the seismogenic zone during the next 20 years the sizes of such events which account for most of the slip that occurs seismically appear to vary greatly for different segments of these faults repeat time of large shocks coseismic displacement moment release rupture length and seismic magnitude appear to correlate with one another and to be a function of the tectonic style of different parts of those fault zones tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks it is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size since repeat time varies however for a given segment of a fault a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment using as input the time of the last large shock the average recurrence time and the standard deviation of time intervals between events dates of the last large shocks are available for most of the segments investigated repeat times are estimated from times of historic and prehistoric events tectonic similarity and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup the standard deviation of time intervals divided by the average repeat time is close to 1 3 for three fault segments in california for which data are available on historic and prehistoric earthquakes that normalized value is adopted for all calculations of conditional probability magnitudes and seismic moments of future plate rupturing events are estimated for each fault segment several of the segments have well constrained probabilities for rupture during the next 20 years whereas others have large uncertainties eight of the segments constituting about 40 of the total lengths of the three faults have moderate to high probability and thus should be instrumented and studied extensively so as to provide shorter time warnings in some cases two adjacent segments may be nearly in phase in their loading history and may break in a single event the segment of the san andreas fault from opposite san jose to san juan bautista which ruptured less than 1 5 m in 1906 and which probably also broke in 1838 is calculated to have a moderate to high probability of an earthquake of magnitude 6 to during the next 20 years a 325 km section of the southern san andreas between tejon pass and the salton sea has about a 25 chance of rupturing in a shock of magnitude near 8 during the next 20 years all the other segments have only a small chance i e less than 5 to 10 of rupturing in an event of magnitude near 8 during that interval

changes in state of stress on the southern san andreas fault resulting from the california earthquake sequence of april to june 1992 the april to june 1992 landers earthquake sequence in southern california modified the state of stress along nearby segments of the san andreas fault causing a 50 kilometer segment of the fault to move significantly closer to failure where it passes through a compressional bend near san gorgonio pass the decrease in compressive normal stress may also have reduced fluid pressures along that fault segment as pressures are reequilibrated by diffusion that fault segment should move closer to failure with time that fault segment and another to the southeast probably have not ruptured in a great earthquake in about 300 years

suspended sediment transport effectiveness of three large impounded rivers u s gulf coastal plain suspended sediment transport effectiveness was examined near the mouths of three large impounded rivers rio grande brazos and pearl rivers in differing precipitation regimes in the u s gulf coastal plain magnitude and frequency analysis of suspended sediment transport was performed by examining the effectiveness of both discharge and time in transporting suspended sediment bivariate plots of discharge with infrequent values of silt clay and sand provide an insight into the relative proportion of coarse versus fine grained sediment transport for the three rivers despite the aridity of the rio grande and brazos drainage basins which is often associated with infrequent or episodic transport of sediment the duration of the effective discharge is similar to humid basins described in the literature the majority of sediment transport occurs during the moderate discharge events having a duration of 2 4 1 5 and 4 4 for the rio grande brazos and pearl rivers respectively this may be due to the influence of scale or the influence of upstream dams and reservoirs on discharge and sediment transport findings from this research suggest that magnitude and frequency analysis of discharge and suspended sediment near the mouths of large rivers may provide a useful framework for understanding the timing and delivery of riverine sediments to the nearshore coastal environment from rivers draining a range of geologic and climatic settings

a 350 000 year summer monsoon multi proxy stack from the owen ridge northern arabian sea five summer monsoon proxies from the northern arabian sea are combined using stacking and principal components analysis pca to create two very similar multi proxy records of summer monsoon variability the five individual proxies all respond to monsoon variability but are largely independent in terms of the processes that complicate their interpretation as summer monsoon indicators e g preservation dissolution diagenesis sediment reworking as such stacking and pca average out non monsoon variance yielding a more pure monsoon signal these stacked and pca records hereafter summer monsoon stack and summer monsoon factor allow evaluation of relative monsoon strength through time as well as the relative concentration of variance within orbital bands these two parameters are less reliable when estimated from individual proxy records in fact the summer monsoon factor smf accounts for only 33 of the total variance in the five records suggesting that relative amplitude variations in each individual proxy time series are influenced by non monsoon processes the summer monsoon stack sms and smf are spectrally very similar dominated by variance in the 41 k y obliquity and 23 k y precession bands there is very little variance at the 100 k y eccentricity band associated with large scale changes in global ice volume indeed equally strong monsoons occur in both glacial and interglacial intervals within the 23 k y precession cycle monsoon maxima fall at 121 relative to precession minima june 21 perihelion maximum northern hemisphere nh summer insolation this phase falls midway between 18o minima 78 and december 21 perihelion 180 indicating that two mechanisms exert equal influence in determining the timing of strong summer monsoons within the precession band 1 sensible heating of the asian plateau which is maximized at times of ice volume minima 78 and 2 latent heat export from the southern subtropical indian ocean which is maximized at times of december 21 perihelion 180 the seasonal cycle at december 21 perihelion is characterized by warm southern hemisphere sh summers followed by cold sh winters a combination that preconditions the ocean to export latent heat during the boreal summer monsoon season summer monsoon winds transport this latent heat into asia where it is released during precipitation enhancing the asian monsoon low within the 41 k y obliquity cycle monsoon maxima are in phase with obliquity maxima this indicates that two mechanisms quite similar to those in the precession band influence the timing of strong summer monsoons in the obliquity band 1 sensible heating of the asian plateau but with no ice volume delay and 2 latent heat export from the southern subtropical indian ocean which is maximized at times of obliquity maxima again the seasonal cycle at obliquity maximum is characterized by warm sh summers followed by cold sh winters ideal for maximizing latent heat export during the boreal summer monsoon

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

aggradation incision and interfluve flooding in the ganga valley over the past 100 000 years testing the influence of monsoonal precipitation abstract in order to investigate fluvial responses to climate forcing stratigraphic data from seven cores in the ganga valley of india and a valley margin cliff section 1 3 km long are compared with proxy records for the intensity of the southwest indian monsoon luminescence dates indicate that the strata cover the past 100 ka five aggradational periods separated by incisional episodes are apparent in the valley fill some of which have correlative strata along the valley margin during marine isotope stages mis 4 and 5 the valley experienced fluvial activity with thin floodplain successions and probable discontinuities along the interfluve margin modest fluvial activity characterised the mid part of mis 3 at about 37 ka aggradation of channel sands preceded by incision is documented for late mis 3 23 to 30 ka as well as for late mis 2 to early mis 1 11 16 ka with fluvial dates focused around the younger dryas period of monsoon reduction the most recent aggradational period took place in the latest holocene

suspended sediment transport rates at the 1 5 year recurrence interval for ecoregions of the united states transport conditions at the bankfull and effective discharge historical flow and suspended sediment transport data from more than 2900 sites across the united states have been analyzed in the context of estimating flow and suspended sediment transport conditions at the 1 5 year recurrence interval flow q1 5 this is particularly relevant with the renewed focus on stream restoration activities and the urgency in developing water quality criteria for sediment data were sorted into the 84 level iii ecoregions to identify spatial trends in suspended sediment concentrations and yields to meaningfully describe suspended sediment transport rates across the united states arguments are developed that in lieu of form based estimates of say the bankfull level a flow of a given recurrence interval q1 5 is more appropriate to integrate suspended sediment transport ratings for the purpose of defining long term transport conditions at a site the effective discharge the use of the q1 5 as a measure of the effective discharge for suspended sediment transport is justified on the basis of literature reports and analytic results from hundreds of sites in 17 ecoregions that span a diverse range of hydrologic and topographic conditions i e coast range arizona new mexico plateau mississippi valley loess plains middle atlantic coastal plain there is sufficient data to also develop regional curves for the q1 5 in all but eight of the ecoregions at the q1 5 the highest median suspended sediment concentrations occur in semiarid environments southwest tablelands arizona new mexico plateau and the mojave basin and range the highest yields occur in humid regions with erodible soils and steep slopes or channel gradients mississippi valley loess plains mvlp and the coast range suspended sediment yields for stable streams are used to determine background or reference sediment transport conditions in eight ecoregions where there is sufficient field data the median value for stable sites within a given ecoregion are generally an order of magnitude lower than for nonstable sites

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

source study of the 1906 san francisco earthquake all quality teleseismic recordings of the great 1906 san francisco earthquake archived in the 1908 carnegie report by the state earthquake investigation commission were scanned and digitized first order results were obtained by comparing complexity and amplitudes of teleseismic waveforms from the 1906 earthquake with well calibrated similarly located more recent earthquakes 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes at nearly co located modern stations peak amplitude ratios for calibration events indicated that a localized moment release of about 1 to 1 5 10 27 dyne cm was responsible for producing the peak the teleseismic body wave arrivals at longer periods 50 to 80 sec we found spectral amplitude ratios of the surface waves require a total moment release between 4 and 6 10 27 dyne cm for the 1906 earthquake comparable to previous geodetic and surface wave estimates thatcher 1975 we then made a more detailed source analysis using morgan hill s body waves as empirical green s functions in a finite fault subevent summation the morgan hill earthquake was deemed most appropriate for this purpose as its mechanism is that of the 1906 earthquake in the central portion of the rupture from forward and inverse empirical summations of morgan hill green s functions we obtained a good fit to the best quality teleseismic waveforms with a relatively simple source model having two regions of localized strong radiation separated spatially by about 110 km assuming the 1906 epicenter determined by bolt 1968 this corresponds with a large asperity on the order of the loma prieta earthquake in the golden gate san francisco region and one about three times larger located northwest along strike between point reyes and fort ross this model implies that much of the 1906 rupture zone may have occurred with relatively little 10 to 20 sec radiation consideration of the amplitude and frequency content of the 1906 teleseismic data allowed us to estimate the scale length of the largest asperity to be less than about 40 km with rough constraints on the largest asperity size and magnitude we produced a suite of estimated synthetic ground velocities assuming a slip distribution similar to that of the loma prieta earthquake but with three times as much slip for purposes of comparison with the recent abundant loma prieta strong motion data set we moved the largest 1906 asperity into loma prieta region peak ground velocity amplitudes are substantially greater than those recorded during the loma prieta earthquake and are comparable to those predicted by the attenuation relationship of joyner and boore 1988 for a magnitude m w 7 7 earthquake

historic creep rate and potential for seismic slip along the hayward fault california the hayward fault is considered the most likely source of one or more major earthquakes in the san francisco bay area in the next few decades historically at least one and probably two major earthquakes about m 6 8 occurred along the hayward fault one in 1836 and another in 1868 little is known about the 1836 event but the 1868 earthquake was accompanied by a surface rupture that extended as much as 41 km along the southern part of the fault although the amount of surface slip in 1868 is uncertain right slip including afterslip reached at least several centimeters and possibly several decimeters in places this paper documents the spatial variation of creep rate along the hayward fault since the 1868 earthquake creep aseismic fault slip occurs over at least 66 km and may extend over the fault s entire 82 km length of which about 13 km lies underwater creep rate seems nearly constant over decades but short term variations occur we derive creep rate mainly from our own systematic surveying of offset cultural features curbs fences and buildings on each feature we solve directly for accumulated creep by using multiple linear regression creep rate mostly falls in the range of 3 5 6 5 mm yr but systematic variation occurs along strike fault segments with distinctly higher and lower rates generally correspond to parts of the fault most salient from the overall average alinement of the fault most distinctive is a 4 km long section near the south end of the fault that creeps at about 9 mm yr such a high rate has occurred there at least since the 1920s and probably since the 1868 earthquake as indicated by an offset railroad track built in 1869 we suggest that this 9 mm yr slip rate may approach the long term or deep slip rate that controls average recurrence interval between major earthquakes if so assuming an elastic rebound model the potential for slip in large earthquakes below the surficial creeping zone is now 1 1 m in the southern 1868 segment of the fault and 1 4 m in the northern 1836 segment subtracting surface creep rates from a long term slip rate of 9 mm yr gives present potential for surface slip in large earthquakes of up to 0 8 m with an average of 0 6 m in the northern segment and 0 4 m in the southern segment we present a simple hypothesis for rupture potential that is compatible with historic creep rate microseismicity distribution and geodetic data if seismic rupture occurs on segments 41 km long by 10 km deep 7 km fully locked 3 km creeping today s potential for seismic moment release is 1 4 1019 and 1 1 1019 n m for both 1836 and 1868 segments respectively and 2 5 1019 n m for both segments jointly converting moment to magnitude gives ml 6 8 in the northern segment ml 6 7 in the southern segment and ml 7 0 for simultaneous rupture of both

sediment transporting flows in headwater streams the equilibrium alluvial stream channel has a geometry that allows it to pass the water and sediment supplied from the watershed at the same time the equilibrium alluvial channel is built and maintained by the flows and sediment delivered to it a prerequisite for understanding the creation of the equilibrium channel is an understanding of the sediment conveyance and competence of the flows the channel receives this study describes the bed load transport regime as it is linked to hydrology and geomorphology in 23 headwater gravel bed streams in snowmelt dominated parts of central and northern idaho at sites drainage areas range from 1 29 to 381 km 2 stream gradients range from 0 0042 to 0 0747 and median bed surface particle sizes range from 4 to 207 mm stream architecture includes riffle pool planar and step pool beds the bed load is much finer than the surface and subsurface material suggesting selective transport of the finer sizes nonetheless the majority of the load is sand at all flow discharges progressively coarser sediment was collected as flow discharge increased and painted rock experiments documented the transport of coarser particles at higher discharges the supply of sediment to the streams appears limited as indicated by observed clockwise hysteresis in bed load transport rates during each spring snowmelt and by the coarse surface armor observed at sites flows above bankfull discharge move 37 of the bed load whereas flows between mean annual discharge and bankfull move 57 of the bed load the bed load effective discharge has a recurrence interval that averages 1 4 yr and the magnitude of effective discharge averages 80 of bankfull discharge the recurrence interval of bankfull discharge averages 2 0 yr the ratio of effective discharge to bankfull discharge is independent of basin size grain size and gradient although the ratio increases with the relative magnitude of large infrequent events

slip partitioning of the calaveras fault california and prospects for future earthquakes examination of main shock and microearthquake data from the calaveras fault during the last 20 years reveals that main shock hypocenters occur at depths of 8 9 km near the base of the zone of microearthquakes the spatial pattern of pre main shock microseismicity surrounding the coyote lake and morgan hill hypocenters is similar to the pattern of the post main shock microseismicity microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones estimates of the fault regions which slipped during the coyote lake and morgan hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic we propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes from the pattern of microearthquake locations we recognize six aseismic zones where we expect future main shocks will rupture the calaveras fault from an analysis of historic seismic data we establish the main shock rupture history for each aseismic zone and identify two zones that are the most likely sites for the next m 5 earthquakes the first zone is located near gilroy and was last ruptured by a m5 2 earthquake in 1949 the second zone is located south of calaveras reservoir and north of the 1988 m5 1 alum rock earthquake it has not slipped seismically since at least 1903 and the size of the aseismic region is sufficiently large to sustain a m5 5 earthquake

strain localization along the san andreas fault consequences for loading mechanisms the orientation of the near fault strain accumulation associated with the relative motion between the pacific and north american plates is better predicted by the orientation of the local faulting than by the orientation of the regional plate motion this observation follows from consideration of shear strain results from geodetic studies ranging from the imperial valley to shelter cove along the san andreas fault system this set of results includes calculations from regions where the faulting and plate motion are considerably oblique to each other both the localization of the strain associated with pacific north american motion and the orientation of the associated strain can be simply caused by failure of the lithosphere as opposed to localization of plate driving forces two types of models for the rheology and geometry of lithospheric failure have been prevalent in the geodetic literature 1 viscoelastic models which are dominated by horizontal layering of the crust and 2 elastic half space models with geometry which is dominantly vertical horizontal models can accommodate the observed strain results only if postseismic relaxation times are long compared to the repeat times of large earthquakes vertical models produce strains which are parallel to the local structure at all times if the horizontal detachments of the viscoelastic models exist they must be at depths 2 3 times the seismogenic thickness geologic studies also indicate that major transcurrent features extend as ductile shear zones to depths much larger than would be expected in horizontal models these considerations lead us to favor models with vertical geometries the vertical structure of these models can be reconciled with laboratory measurements of rock strength through the strain softening processes associated with flow of composite materials such as quartzo feldspathic rocks independent of the horizontal rheological layering in the starting low strain material progressive deformation will lead to preferential weakening in the plane of shear and to the development of a shear zone which will always be weaker than the surrounding material thus shear zones such as the san andreas system develop vertical tabular geometries which extend far below the brittle plastic transition and which are mechanically persistent

stratigraphy and correlation of the glacial deposits on the montana plains till units representing at least three pre illinoian continental glaciations at least one illinoian glaciation and a late wisconsin glaciation have been identified on the montana plains early wisconsin or middle wisconsin till units have not been identified the southernmost limit of late wisconsin glaciation is in montana more than 170 km south of the lethbridge moraine in alberta canada figs 1 and 2 an interpretation that the lethbridge moraine is the limit of late wisconsin glaciation stalker 1977 1980 1983b stalker and harrison 1977 rutter 1980 1981 jackson 1983 is incompatible with stratigraphic and morphologic evidence from montana

discontinuity bounded alluvial sequences of the southern gangetic plains india aggradation and degradation in response to monsoonal strength abstract discontinuity bounded late quaternary sequences in the southern gangetic plains himalayan foreland basin reflect floodplain aggradation and degradation in response to forcing by the powerful southwest indian monsoon the major himalayan and cratonic rivers in this area occupy narrow incised valleys and do not inundate the adjoining broad interfluves which display soil development small plains fed rivers lakes eolian deposits and badland ravines however these areas formerly experienced active alluviation because thick floodplain muds underlie the interfluve an age model suggests that interfluve areas near the major rivers aggraded periodically between about 27 ka and 90 ka marine oxygen isotope stages 3 5 they subsequently degraded or accumulated sediment only locally probably reflecting decreased monsoonal precipitation around the last glacial maximum marine isotope stage 2 when major river valleys moved to an underfit condition increased precipitation during the 15 to 5 ka period of monsoon recovery probably increased discharge and promoted incision and widespread badland formation discontinuities at deeper levels reflect earlier degradation phases and are marked by reworked gravel lenses thin channel bodies and carbonate cemented surfaces carbonate veins infilled joints that cut strata below but not above one discontinuity suggest some local tectonic influence there is no evidence that sea level fluctuations influenced stratal patterns in this elevated inland region discontinuity bounded sequences linked to climate change may characterize alluvial successions in many continental settings especially along the cratonic margins of foreland basins where subsidence rates are modest

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

evolution of moderate seismicity in the san francisco bay region 1850 to 1993 seismicity changes related to the occurrence of large and great earthquakes the rate of seismic activity of moderate size m 5 5 earthquakes in the san francisco bay sfb region has varied considerably during the past 150 years as measured by the rate of seismic moment release seismic activity in the sfb region is observed to accelerate prior to m 7 0 earthquakes in 1868 1906 and 1989 and then to decelerate following them we examine these seismicity changes in the context of the evolution of the stress field in the sfb region as a result of strain accumulation and release using a model of dislocations in an elastic halfspace we use a coulomb failure function cff to take into account changes in both shear and normal stresses on potential failure planes of varying strike and dip in the sfb region we find that the occurrence of a large or great earthquake creates a stress shadow a region where the stress driving earthquake deformation is decreased interseismic strain accumulation acts to reverse this process gradually bringing faults in the sfb region out of the stress shadow of a previous large or great earthquake and back into a state where earthquake failure is possible as the stress shadow generated by a large or great earthquake disappears it migrates inward toward the fault associated with that large or great event the observed changes in the rate of occurrence of moderate earthquakes in the sfb region are broadly consistent with this model in detail the decrease in seismicity throughout most of the sfb region and a localized increase in the monterey bay region following the great 1906 earthquake is consistent with our predicted stress changes the timing and location of moderate size earthquakes when the rate of seismicity increases again in the 1950s is consistent with areas in which the 1906 stress shadow had been eliminated by strain accumulation in the sfb region those earthquakes that are most inconsistent with our stress evolution model including the 1911 earthquake southeast of san jose are found to occur in regions where dip slip faulting is common in addition to strike slip the 1906 earthquake brought that zone of dip slip faulting closer to failure suggesting that the 1911 event may have been a reverse faulting earthquake rather than a strike slip one similar to the 1984 morgan hill earthquake the occurrence of activity on faults very close to the san andreas such as the lake elsman earthquakes of 1988 and 1989 appear to be associated with the last disappearence of the stress shadow on the loma prieta segment of the san andreas fault thus events of that type may represent an intermediate term precursor to a large earthquake such as the 1989 loma prieta event much of the moderate size earthquake activity in the sfb region appears to be modulated in time by the buildup and release of stress in large and great earthquakes a tensorial approach to earthquake prediction i e taking into account changes in the components of the stress tensor has several advantages over examining scalar changes such as those in seismic activity and moment release rates this tensorial approach allows for both activation and quiescence but in different subregions prior to as well as after large earthquakes

two hourly surface change on supra tidal rock marengo victoria australia a traversing micro erosion meter was used to measure rock surface micro topography over 40 cm2 on a supra tidal cliff face from early morning to late evening in late spring from 06 00 hours to 22 00 hours the relative heights of 188 coordinates were obtained using the meter at 2 hour intervals resulting in a data set of 1607 readings monitoring shows that rock surfaces are dynamic entities with significant rise and fall relative to the first measurement at shorter timescales than previously reported the maximum positive rise between readings was 0 261 mm and lowering was 0 126 mm the pattern of change did not relate as expected to environmental variables such as temperature or insolation rather the surface showed greater surface change in the early morning and late afternoon it is hypothesized that this pattern relates to the expansion and contraction of lichen thalli as moisture is absorbed during higher humidity in the morning and late afternoon the implications of these results for weathering studies are considered copyright 2006 john wiley sons ltd

effective discharge for suspended sediment transport of the ganga river and its geomorphic implication abstract effective discharge q e for suspended sediment transport in the alluvial reaches of the ganga river in the western ganga plains wgp has been computed using analytical and an alternative magnitude frequency approach thirty years of mean monthly discharge data from various sites of the ganga river have been assessed and the abundance of discharge occurrence has been determined our analysis shows that less than 40 of the flow causes effective sediment transport in the ganga and this can be considered as the effective discharge for suspended sediment transport alternatively 50 of the sediment load for all studied sites is moved by a discharge varying between 14 and 40 of the total discharge effective discharges calculated over the period of record are well below the bankfull discharges q b a few events are close to the bankfull level but with a high return period ri 40 years and therefore not effective to transport most of the available sediments our computation shows that the mean annual discharge ri 2 33 yrs can transport only 0 to 10 of the total available sediments the computation of effective discharge also provided important insights to understand the linkage between hydrology and channel morphology sediment storage and removal processes which are reflected in sediment budget cause changes in cross sectional area channel bathymetry at various sites but the channel margins are not affected a high ratio of bankfull to effective discharge q b q e forces the flow lines to be concentrated to the thalweg position and channels are incised our study also implies that incision and aggradation of the river valley during a relatively long period are caused by changes in effective discharge we argue that the valley incision and filling episodes in the western ganga plains at late quaternary timescales in response to monsoonal fluctuations were primarily affected by changes in the effective discharges of the rivers

re evaluation of several large historic earthquakes in the vicinity of the loma prieta and peninsular segments of the san andreas fault california abstract the size and location of several of the largest 19th century earthquakes in the san francisco bay area including the june 1838 8 october 1865 21 october 1868 and 24 april 1890 events are re evaluated by comparing these historic events to several modern events in particular the 1989 loma prieta earthquake similar high intensities in the monterey bay area during both the 1989 and 1838 events indicate that the 1838 shock probably ruptured the loma prieta segment in addition to the peninsular segment of the san andreas fault if so the resulting earthquake would have been of moment magnitude m w 7 2 thus like segments of many other plate boundaries the loma prieta segment exhibits heterogeneous rupture in that sometimes it ruptures with the peninsular segment as in 1906 and probably in 1838 and at other times it ruptures alone as in 1989 in contrast the area of high intensities generated by the 1865 earthquake was centered in the santa clara valley and the eastern foothills of the santa cruz mountains indicating that the 1865 shock probably was located northeast of the loma prieta rupture and not on the san andreas fault in addition the felt areas taken to be one of the best measures of relative source size of modified mercalli intensities mmi v and vi for the 1865 shock are considerably smaller than that of the 1989 event relationships between felt areas of intensities v and vi and moment magnitude are developed for the san francisco bay area based on these relationships the average computed moment magnitudes for the 1865 1868 and 1890 earthquakes are 6 51 0 18 6 84 0 20 and 6 32 0 16 respectively if these results are correct then the loma prieta segment taken to include all faults within the san andreas fault zone i e within a zone up to a few kilometers wide appears to rupture with or without the peninsular segment every 76 11 years these data on repeat times may be the most accurate information now available for ascertaining the date of future rupture of that segment and for testing recurrence models the smaller size of the 1865 earthquake would be consistent with it being part of the long term seismic build up to the 1868 event rather than being paired with it as events of similar size if the 1865 earthquake did occur northeast of the loma prieta segment then a future source of that type located closer to san jose and the santa clara valley could pose a considerable hazard to the southern san francisco bay area on going searches of letters and diaries of missionaries and early settlers could yield new information that should help to further constrain the locations and magnitudes of these and other historic earthquakes

quaternary fluvial and eolian deposits on the belan river india paleoclimatic setting of paleolithic to neolithic archeological sites over the past 85 000 years abstract archeological sites in the bedrock belan valley at the southern margin of the ganga plains of india have unearthed paleolithic to neolithic artifacts and the first known evidence for rice cultivation we present a sedimentological and paleoclimatic analysis for belan sections incorporating new luminescence and radiocarbon dates and a compilation of previous research some 20 m of strata are exposed in fluvial terraces commencing with pedogenic and channel calcretes linked to groundwater ponding on the underlying bedrock overlying alluvium deposited from mixed load meandering rivers yields dates between 85 11 and 72 8 kyr before present bp implying sustained fluvial activity during marine isotope stage 5 and later these strata contain middle paleolithic artifacts thin reworked gravels with upper paleolithic artifacts are dated at 21 31 kyr bp and may represent declining alluviation and floodplain gully erosion during reduced monsoonal activity around the last glacial maximum lgm younger channel fills contain shell rich eolian sand and mounds of shelly sand lie inland from the river five osl dates from the sands span 14 to 7 kyr bp corresponding to a period of climatic instability that includes the younger dryas as the monsoon intensified following the lgm although suggesting more arid phases the source bordering eolian material has a small volume and the grains are partially bleached indicating local wind action overlying floodplain muds reflect renewed alluviation after which the river incised during peak monsoon flow the mesolithic settlement of chopani mando spans a period of reduced monsoon activity and climatic instability following the lgm subsequent neolithic settlements were probably established under stronger monsoon conditions suitable for the development of agriculture mesolithic habitation may have ended when a nearby bedrock channel was abandoned as the reinvigorated belan cut a new course along which neolithic settlements were later established

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

earthquake travel time tomography of the southern santa cruz mountains control of fault rupture by lithological heterogeneity of the san andreas fault zone the 1989 loma prieta earthquake occurred along the stretch of the san andreas fault zone within the southern santa cruz mountains that last failed as a major earthquake in 1906 the southeastern end of the 1989 rupture marks the transition from stable aseismic slip on the central creeping section of the san andreas fault to unstable failure on the locked 1906 segment we investigate this transition and the rupture characteristics of the 1989 earthquake using a three dimensional p wave velocity model of the southern santa cruz mountains section of the fault zone the velocity model was determined by joint progressive inversion of 5422 p wave arrival times from 173 earthquakes which included aftershocks of the 1989 earthquake and premainshock background events recorded by the u s geological survey central california network this velocity model was used to relocate 424 background earthquakes the loma prieta mainshock and 292 aftershocks the velocity model is calibrated in terms of lithology using laboratory data for california coast ranges rock types and available seismic refraction profiles and is shown to be in good agreement with the surface geology the model images a large anomalous high velocity body at midcrustal depths within the rupture zone of the 1989 earthquake that the available evidence suggests might have gabbroic or other mafic composition on the basis of the relationship of the lithological features interpreted from the velocity model to the seismicity and surface creep we propose a model in which the high velocity body is primarily responsible for the transition from stable to unstable fault slip at pajaro gap the active plane of the san andreas fault cuts throughout the body the fault system attempts to circumvent this barrier by transferring slip to secondary faults including splay faults that have propagated along the frictionally favorable contact between the high velocity rock mass and franciscan country rocks however the near arrest of stable sliding causes stress to concentrate within the body and the high strength unstable contact within it evolves from a barrier to the asperity that failed in the 1989 earthquake the general features of the 1989 rupture predicted by this asperity model agree with several rupture histories computed for the earthquake the model implies that as proposed by other workers the loma prieta earthquake did not involve a repeat of the 1906 slip which has an important bearing on earthquake recurrence estimates for the santa cruz mountains segment of the fault