observing earthquakes triggered in the near field by dynamic deformations we examine the hypothesis that dynamic deformations associated with seismic waves trigger earthquakes in many tectonic environments our analysis focuses on seismicity at close range within the aftershock zone complementing published studies of long range triggering our results suggest that dynamic triggering is not confined to remote distances or to geothermal and volcanic regions long unilaterally propagating ruptures may focus radiated dynamic deformations in the propagation direction therefore we expect seismicity triggered dynamically by a directive rupture to occur asymmetrically with a majority of triggered earthquakes in the direction of rupture propagation bilaterally propagating ruptures also may be directive and we propose simple criteria for assessing their directivity we compare the inferred rupture direction and observed seismicity rate change following 15 earthquakes m 5 7 to m 8 1 that occurred in california and idaho in the united states the gulf of aqaba syria guatemala china new guinea turkey japan mexico and antarctica nine of these mainshocks had clearly directive unilateral ruptures of these nine seven apparently induced an asymmetric increase in seismicity rate that correlates with the rupture direction the two exceptions include an earthquake preceded by a comparable magnitude event on a conjugate fault and another for which data limitations prohibited conclusive results similar but weaker correlations were found for the bilaterally rupturing earthquakes we studied although the static stress change also may trigger seismicity it and the seismicity it triggers are expected to be similarly asymmetric only if the final slip is skewed toward the rupture terminus for several of the directive earthquakes we suggest that the seismicity rate change correlates better with the dynamic stress field than the static stress change manuscript received 1 march 2002

the 1986 kalamata south peloponnesus earthquake detailed study of a normal fault evidences for east west extension in the hellenic arc tectonic and seismological data collected in the field following the september 13 1986 kalamata earthquake south peloponnesus are presented and analyzed to discuss the earthquake rupture process and the regional tectonics the event occurred on the kalamata normal fault whose trace was mapped with spot images and topographic and field observations this fault is part of an approximately nnw sse en echelon system cutting through the hellenic nappes the fault striking n15 e on the average with a dip of about 50 has a minimum cumulated quaternary throw of the order of 1 km the measured coseismic slip is 6 18 cm over a length of 6 km the main shock focal mechanism obtained from long period waveform modeling strike 201 10 20 dip 45 5 rake 283 10 25 represents almost pure east west extension and is in good agreement with tectonic observations the centroid depth is constrained to 5 3 km and the seismic moment to 7 0 2 5 1017 n m over 700 aftershocks located by a 16 station network installed after the earthquake for a period of 2 weeks define two clusters separated by a gap of aftershock activity from the surface to a depth of about 10 km the main cluster to the south defines a 45 west dipping plane which lies on the downward extension of the fault mapped at the surface focal mechanisms of aftershocks on this fault plane are homogeneous and represent e w extension as the main shock in contrast the majority of focal mechanisms in the uppermost part of the foot wall show more or less e w compression probably corresponding to postseismic stress release the northern cluster of aftershocks is very dense and located away from the surface rupture within a relay zone between the kalamata and the next en echelon faults to the nw the thouria faults there focal mechanisms represent extension from about n115 to n70 and n20 corresponding mostly to fault reactivation in an area where nonrigid deformations prevail the main shock probably initiated in this relay zone 3 4 s before the rupture front reached the main fault plane and released most of the energy there the rupture presumably propagating southward the focal mechanism of the kalamata earthquake and that of the april 27 1965 earthquake located to the northwest of crete as well as the regional active normal fault pattern imply that e w extension oblique to the hellenic arc is presently the dominant tectonic regime e w stretching occurs partly on reactivated nw se faults parallel to the hellenic structures but mostly on newly formed n s normal faults across those structures the latter faults are responsible for the apparent segmentation of the hellenic belt from southern peloponnesus to crete the existence of active e w extension in this region implies a recent change in the tectonic regime and consequently a change in boundary conditions at the subduction zone probably in response to the incoming margin of africa

surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

integrated seismic hazard analysis of the wasatch front utah we examined the combined effects of different sources that influence earthquake hazard of the populated wasatch front utah we first evaluated the fault stress interaction of the two largest historic earthquakes of the intermountain seismic belt isb the 1959 hebgen lake montana m s 7 5 and the 1983 borah peak idaho m s 7 3 earthquakes which experienced multisegment normal faulting ruptures estimates of the static stress change for these events revealed an increase in coulomb failure stress in areas of extended aftershocks these observations suggested that fault stress analysis is applicable in evaluating the spatial distribution of aftershocks after large normal faulting earthquakes in the same extensional stress regime of the eastern basin range including the wasatch front utah which encompasses the 370 km long wasatch fault and surrounding faults on the basis of this result we applied the modeling technique to the historically seismically quiescent wasatch fault and examined the relation between the pattern of stress change and the space time distribution of paleoearthquakes ages and locations of the wasatch fault paleoseismic data imply 17 single segment or 11 multisegment ruptures in the past 5 6 kyr we prefer the multisegment model because almost all of the large historical normal faulting earthquakes in the isb were multisegment fitting the along fault displacements by an analytic half ellipse function provides a first order distribution of the displacement over an entire rupture length and allows new estimates of fault slip rates and seismic moment with these data we also estimated the occurrence rate of m w 6 6 wasatch paleoearthquakes and showed that the rate was about three times higher than that inferred by the historical seismicity this result along with new information from a megatrench on the wasatch fault near salt lake city that revealed no scarp forming earthquakes between ca 9 0 and 15 5 ka suggests that large wasatch fault events in the past 5 6 kyr may be clustered the recurrence rate of large earthquakes estimated by the geodetic measured strain on the other hand is three to four times higher than that estimated by the long term fault slip rate this difference together with the observation of a low regional strain rate from historical seismicity suggests that cumulative aseismic deformation may be significant on the wasatch fault we also examined a major consideration for along strike segmentation namely how stress contagion could affect the probability of failure of adjacent faults including paleoearthquake derived fault slip rates global positioning system derived geodetic moment rates and the effect of stress contagion in the earthquake hazard estimation for a specific location in the salt lake valley revealed an increase in the annual frequency of peak ground acceleration 0 25 g by a factor of 1 4 4 0 and 5 4 respectively compared with that derived from historical seismicity only manuscript received 31 may 2001

earthquake magnitude potential of the intermountain seismic belt usa from surface parameter scaling of late quaternary faults two of the largest historical earthquakes documented for the united states occurred within the past four decades in a zone of anomalous seismicity in the western interior of the country known as the intermountain seismic belt isb paleoseismology has revealed the presence of major active faults throughout this region some of them extending through densely populated area this study presents mean value estimates of the maximum earthquake magnitudes that can be expected from 65 of the most prominent late quaternary fault segments of the isb using surface rupture parameters linear least squares regressions of magnitude on surface rupture length l maximum surface displacement d and dl respectively were computed for an updated worldwide set of historical normal slip earthquakes these were compared with similar regressions from other publications and it was found that a dl based formula restricted to normal faulting mechanisms has a relatively high correlation low standard deviation and tends to yield magnitudes between those given by d and l alone this last property is useful for applications to the isb prehistoric data where the record of historical ground rupturing earthquakes is too sparse to estimate the proportions in which d and l are likely to contribute to seismic energy release of a fault application of regressions to published paleoseismic displacements and estimated earthquake segment lengths for the isb faults shows that d consistently scales a larger magnitude than the corresponding single segment l by an average of 0 2 to 0 3 magnitude unit after accounting for bias from the regressions considerations of uncertainties in paleoseismic displacements suggest that they cannot fully explain the discrepancy since it is known that large earthquakes often encompass multiple segments of a fault these observations indicate that longer rupture lengths should be used to estimate maximum magnitudes for isb faults a dual segment rupture scenario produces better agreement between d and l based magnitudes and is supported by historical and paleoseismic earthquake data from the region magnitudes scaled by the dl based regression for dual segment rupture range from ms 6 8 to 7 5 m 0 20 and the largest are associated with the central segments of the wasatch fault and the swan grand valley teton madison and east bear lake faults

seismicity of the eastern snake river plain region idaho prior to the borah peak idaho earthquake october 1972 october 1983 abstract in december 1971 the idaho national engineering laboratory deployed a network of short period high gain vertical seismographs to monitor earthquake activity within a designated study area 43 0 to 44 5 n 111 5 to 114 0 w centered on the eastern snake river plain in the 11 yr prior to the 28 october 1983 borah peak idaho earthquake there were 102 events located within the study area with a duration magnitude m range of 0 7 m 3 2 three microearthquakes m 1 were detected on the eastern snake river plain seventy five microearthquakes were located northwest of the eastern snake river plain primarily in the birch creek valley beaverhead mountains region during the 11 yr period that the idaho national engineering laboratory seismograph stations have been active there were only two events located inside the study area within 35 km of the epicenter of the borah peak idaho earthquake in the 2 6 yr prior to the borah peak idaho earthquake there were no foreshocks with magnitudes 1 observed within a 20 km radius of the epicenter future large earthquakes in the lost river range lemhi range and segments of the beaverhead mountains may also occur without significant foreshock activity

mining related and tectonic seismicity in the east mountain area wasatch plateau utah u s a as part of a larger multi institutional seismic monitoring experiment during june august 1984 in the eastern wasatch plateau utah data from a subarray of 20 portable seismographs were used to investigate seismicity in the east mountain area an area of active underground coal mining and intense microseismicity eight stations of the subarray were concentrated on top of east mountain about 600 m above mine level at an average spacing of 2 to 3 km the primary objective was the accurate resolution of hypocenters and focal mechanisms for seismic events originating at submine levels data from high resolution seismic reflection profiles and drill hole sonic logs yielded a detailed velocity model this model features a strong velocity gradient in the uppermost 1 km which has a significant effect on takeoff angles for first arriving p waves from shallow seismic events two hundred epicenters located with a precision of 500 m cluster within an area about 5 km in diameter and show an evident spatial association with four sites of longwall mining during the study period a special set of foci rigorously tested for focal depth reliability indicates submine seismicity predominating within 500 m of mine level and extending at least to 1 km and perhaps to 2 km below mine level continuous monitoring for a 61 day period june 15 august 15 bracketed a 16 day mining shutdown july 7 22 during which significant seismicity comparable to that observed before the shutdown was observed ten focal mechanisms for seismic events originating at or down to 2 km below mine level nearly all imply reverse faulting consistent with previous results and the inferred tectonic stress field enigmatic events recorded with all dilatational first motions can be fit with double couple normal faulting solutions if they in fact occur above mine level perhaps reflecting overburden subsidence if these events are constrained to occur at mine level their first motion distributions are incompatible with a double couple source mechanism

inversion of regional pn1 and surface wave data for source parameters of a borah peak aftershock we present results of a comparative source study on one of the largest aftershocks of the borah peak idaho earthquake series the mechanism of this event had been previously studied using first motions and teleseismic p wave data and we report here our results from analysis of regional pn1 and surface waves the pn1 waves gave an estimate of the source duration near 5 sec in agreement with the teleseismic p waves both the source duration and the effect of surface wave dispersion through laterally heterogeneous crustal structures must be accounted for in the moment tensor inversions of intermediate period surface waves all data sources both long period and short gave consistent source mechanisms and the long periods also yield three independent and consistent estimates of the seismic moment the results demonstrate the promise of formal source parameter retrieval techniques applied to regional data for the study of earthquakes with magnitudes below the magnitude threshold of teleseismic source determinations

structures in segment boundary zones of the lost river and lemhi faults east central idaho geologic mapping and structural analysis of the lost river and lemhi normal faults in east central idaho suggest that many rupture segment boundaries previously inferred from geomorphic data coincide with two classes of structural complexities 1 zones of distributed faults and steps or jogs in the range front faults and 2 intersections with preexisting eocene to oligocene cross faults at 10 15 km depth segment boundaries contain as many as 13 fault splays and are as much as 13 km long and 5 6 km wide in plan view in contrast simple fault traces characterize the range front faults in the interiors of segments thus segment boundaries of normal faults are broad zones of intersecting faults not discrete points the structural data further imply that segment boundaries contain large volumes of fractured and faulted rock and that zones of distributed normal faults have influenced rupture propagation and arrest along these two normal faults intersections of preexisting cross faults and range front faults may also have influenced the locations of rupture boundaries along the lost river and lemhi faults downdip projections of preexisting eocene to oligocene normal faults in the footwall of the lost river and lemhi faults may coincide with four or five segment boundary zones at about 15 km depth the depth at which large earthquakes nucleate in the basin and range province structural analyses also show that some cross faults which coincide with segment boundary zones at the surface are distant from these zones at depth conversely some potentially significant structures present at depth are far removed from the segment boundary zone at the surface thus a close spatial relationship between cross faults and segment boundary zones at the surface cannot prove or disprove a genetic relationship between these features because the near surface geometry of segment boundary zones may differ dramatically from the subsurface geometry of the zones where cross faults define segment boundaries the enhanced fracture toughness of preexisting fault planes and their damage zones may impede or arrest rupture on younger crosscutting faults

the 1983 borah peak idaho earthquake and its aftershocks abstract the 28 october 1983 borah peak idaho earthquake m s 7 3 occurred in an area of low historic seismicity within east central idaho along a segment of the lost river fault active during the holocene a dense network of portable short period seismographs up to 45 stations station spacings of 2 to 10 km was installed beginning several hours after the main shock and operated for 22 days in addition to records from the portable instrumentation data from permanent seismograph stations operating in idaho utah montana oregon washington and wyoming provide a good regional data base no foreshock activity above m c coda magnitude 2 0 was detected for the 2 month period preceding the main shock the epicenter of the main shock is 14 km south southwest of the end of the surface faulting this relationship suggests unilateral rupture propagating to the northwest the distribution of 421 aftershocks of m c 2 defines an epicentral pattern 75 km 10 km trending north northwest parallel to the surface rupture but displaced laterally southwest by 5 to 10 km aftershocks extend to depths of approximately 16 km and in the central and southeastern portion of the aftershock pattern define a zone dipping approximately 45 southwest that intersects the surface near the fault scarp the entire aftershock zone as observed during the first 3 weeks was active shortly after the main shock occurred fault plane solutions for 47 aftershocks show predominantly normal faulting with varying amounts of strike slip motion tension axis orientations indicate a dominant extension direction of nne ssw during the aftershock sequence there is considerable diversity among the aftershock focal mechanisms even along the central and southeast portions of the fault where the hypocenters appear to outline the main fault break we therefore interpret most of the aftershocks to represent complex fracturing on subsidiary structures adjacent to the main fault

analysis of seismological and geological observations formoderate size earthquakes the colfiorito fault system central apennines italy to contribute to the understanding of the relationships between moderate earthquakes and the faults that are recognisable in the geological record we analysed seismological and geological data related to the 1997 98 umbria marche central italy earthquake swarm the seismological recordings collected by local networks allowed accurate location of about 1000 events whereas the geological field observations provided a picture of the structural features and the ground surface deformations we also re examined and utilised some already published data and results mostly about the fault plane solutions and the geology on the basis of earthquake locations fault plane solutions and geological mapping we explored the possible correlation between the earthquake causative fault planes and the normal faults exposed in the area our results show that the two mainshocks that occurred on september 26 1997 mw 5 7 and mw 6 0 originated on the same structure reactivating at depth the colfiorito normal faults both ruptures did not propagate up to the ground surface but triggered gravitational sliding that occurred along pre existing fault scarps the earthquake that occurred on october 14 1997 mw 5 6 originated on another fault branch at a much shallower depth in spite of the lower magnitude this earthquake produced tectonic ruptures where the fault plane projects to the surface in an area where no faults were previously mapped by comparing the paleostress reconstruction based on slickenside lineations analysis and the focal mechanism solutions we also suggest a possible correlation between the long term early middle pleistocene cumulative effects of the colfiorito fault system and the short term behaviour of the fault planes observed during this earthquake swarm favouring the idea of a seismogenic source producing clustered moderate size earthquakes rather than large events scattered in time our results suggest that the integration of geological and seismological observations can constrain the seismotectonic interpretations in regions of low level seismicity and that this integration can pose a reliable basis in the seismic hazard assessment

a m gurnell and m j clark eds 1987 glacio fluvial sediment transfer an alpine perspective chichester etc john wiley and sons ltd

real time measurements of sediment transport and bed morphology during channel altering flow and sediment transport events abstract real time measurements of bed changes over a reach are a missing piece needed to link bed morphology with sediment transport processes during unsteady flows when the bed adjusts quickly to changing transport rates or visual observation of the bed is precluded by fine sediment in the water column a new technique is presented that provides continuous measurement of sediment movement over the length of a flume a bedload monitoring system blms was developed that makes use of pressure pillows under a false flume bottom to measure sediment and water weights over discrete flume channel sections throughout a flow event this paper details the construction of the blms and provides examples of its use in a laboratory setting to reconstruct bed slopes during unsteady flows and to create a real time record of sediment transport rates across the flume channel bed during a sediment transporting flow data gathered from the blms compared well against techniques commonly in use in flume studies when the blms was analyzed in conjunction with bed surface dems and differenced dems a complete transport and bed adjustment picture was constructed the difference dems provided information on the spatial extent of bed morphology changes the blms supplied the data record necessary to reconstruct sediment transport records through the downstream channel including locations and time periods of temporary sediment storage and supply the blms makes it possible to construct a continuous record of the spatial distribution of sediment movement through the flume including areas of temporary aggradation and degradation exciting implications of future research that incorporates a blms include a more informed management of river systems as a result of improved temporal predictions of sediment movement and the associated changes in channel slope and bed morphology

characteristics of the aftershock sequence of the borah peak idaho earthquake determined from digital recordings of the events abstract the u s geological survey menlo park deployed and maintained a network of twelve digital instruments over the 2 weeks following the 28 october 1983 borah peak idaho earthquake the network recorded 45 events with m 3 0 and 6 events with m 4 0 the epicenters are located in a narrow band which parallels the trace of the surface fauiting up to the willow creek summit the depths of the events range from 5 to 16 km in the south the distribution of hypocenters delineate a plane which dips to the southwest at 50 to the north the hypocenters dip steeply to the east composite focal mechanisms for three groups of events show normal faulting mechanisms the mechanism of the aftershocks in the north appear rotated in both strike and dip from the aftershocks in the south the seismic moments of the aftershocks increase with increasing hypocentral depth below 12 km the dynamic stress drops of the events do not show any systematic variation with depth however most of the events with large stress drops are clustered in the northwest limb of the aftershock distribution the average stress drop of the southern events is 31 16 bars while the average stress drop of the events in the northwest limb is 77 52 bars this clustering of events with large stress drops marks an apparent stress concentration possibly associated with the arrest of the main shock rupture propagation by a fracture barrier at depth

inversion for slip distribution using teleseismic p waveforms north palm springs borah peak and michoacan earthquakes we have inverted the teleseismic p waveforms recorded by stations of the global digital seismograph network for the 8 july 1986 north palm springs california the 28 october 1983 borah peak idaho and the 19 september 1985 michoacan mexico earthquakes to recover the distribution of slip on each of the faults using a point by point inversion method with smoothing and positivity constraints in the inversion procedure a fault plane with fixed strike and dip is placed in the region of the earthquake hypocenter and divided into a large number of subfaults rupture is assumed to propagate at a constant velocity away from the hypocenter and synthetic ground motions for pure strike slip and dip slip dislocations are calculated at the teleseismic stations for each subfault the observed seismograms are then inverted to obtain the distribution of strike slip and dip slip displacement for the earthquake results of the inversion indicate that the global digital seismograph network data are useful for deriving fault dislocation models for moderate to large events however a wide range of frequencies which includes periods shorter than those within the passband of the long period global digital seismograph network instruments is necessary to infer the distribution of slip on the earthquake fault although the long period waveforms define the size dimensions and seismic moment of the earthquake data at shorter periods provide additional constraints on the variation of slip on the fault dislocation models obtained for all three earthquakes are consistent with a heterogeneous rupture process where failure is controlled largely by the size and location of high strength asperity regions

spatial and temporal analysis of a seismic series using a new version of the three point method application to the 1989 antequera spain earthquakes abstract the three point method tpm has been successfully applied to several seismic series and has provided information about the spatial characteristics azimuth and dip of the fault planes activated in the rupture process a new development of the tpm to determine temporal characteristics is presented to obtain the evolution of the fracturing process of an active fault system for the analysis of the 158 microearthquakes and earthquakes that took place in the seismic series of antequera in june 1989 the choice of a threshold magnitude m u 2 5 has permitted the events related to the most relevant fractures to be distinguished secondly only the events between two concentric spheres here named spatial crown with respect to a given earthquake have been used in order to avoid taking into account earthquakes that are too close to each other together with the very distant events that have little relation to the event analysed the spatial crown has permitted some clear results in the antequera series where we have found that the fracturing process began fundamentally with n 80 e planes and evolved to n 65 w planes finally an error analysis enables an estimation of the uncertainty in the results to be obtained from the errors in the data

active tectonics of the north and central aegean sea summary in this paper we examine the connection between the westward motion of turkey relative to europe and the extension in and around the aegean sea the principal new data available since the last attempt to synthesize the tectonics of this region by mckenzie 1978 are much improved focal mechanisms of earthquakes constrained by p and sh body wave modelling as well as by first motions these mechanisms show that the faulting in the western part of the aegean region is mostly extensional in nature on normal faults with a nw to wnw strike and with slip vectors directed nnw to nne there is evidence from palaeomagnetism that this western region rotates clockwise relative to stable europe in the central and eastern aegean and in nw turkey distributed right lateral strike slip is more prevalent on faults trending ne to ene and with slip vectors directed ne palaeomagnetic data in this eastern region is more ambiguous but consistent with very small or no rotations in the northern part and possibly anticlockwise rotations relative to europe in the south the strike slip faulting that enters the central aegean from the east appears to end abruptly in the sw against the nw trending normal faults of greece the kinematics of the deformation is controlled by three factors the westward motion of turkey relative to europe the continental collision between nw greece albania and the apulia adriatic platform in the west and the presence of the hellenic subduction zone to the south as the right lateral slip on the north anatolian fault enters the aegean region it splays out becoming distributed on several parallel faults the continental shortening in nw greece and albania does not allow the rotation of the western margin of the region to be rapid enough to accommodate this distributed e w right lateral shear and thus leads to e w shortening in the northern aegean which is compensated by n s extension as the southern aegean margin can move easily over the hellenic subduction zone the dynamics of the system once initiated is self sustaining being driven by the high topography in eastern turkey and by the roll back of the subducted slab beneath the southern aegean the geometry of the deformation resembles the behaviour of a system of broken slats attached to margins that rotate in spite of its extreme simplicity a simple model of such broken slats is able to reproduce quantitatively most of the features of the instantaneous velocity field in the aegean region including the slip vectors and nature of the faulting in the eastern and western parts the senses and approximate rates of rotation the overall extensional velocity across the aegean and the distribution of strain rates as seen in the seismicity and topography or bathymetry and using geodetic measurements as part of this study we re examined the relation between the surface faulting and the focal parameters determined seismologically for the three large 1981 gulf of corinth earthquakes and reassessed the evidence for associating particular earthquakes in the sequence with observed surface faulting an important result is that in one of the events there is a resolvable discrepancy between the slip vector measured at the surface and that determined from the seismic body waves

surface faulting accompanying the borah peak earthquake central idaho the ms 7 3 borah peak earthquake that struck central idaho on october 28 1983 was one of the strongest historic earthquakes in the intermountain seismic belt much of the 34 km long northwest trending zone of fault scarps and surface ruptures that formed during the earthquake follows holocene and upper pleistocene scarps of the lost river fault throw along the new fault scarps averages 0 8 m exceeds 1 0 m along 43 of their length and attains a maximum of 2 7 m along the broad and complex zone of deformation in the southern section the net slip was normal sinistral averaging 17 cm lateral slip for 100 cm of dip slip the preferred nodal plane from the focal mechanism strikes n22 w dips 59 sw and suggests a much larger component of strike slip than do the geologic data

a general power equation for predicting bed load transport rates in gravel bed rivers 1 a variety of formulae has been developed to predict bed load transport in gravel bed rivers ranging from simple regressions to complex multiparameter formulations the ability to test these formulae across numerous field sites has until recently been hampered by a paucity of bed load transport data for gravel bed rivers we use 2104 bed load transport observations in 24 gravel bed rivers in idaho to assess the performance of eight different formulations of four bed load transport equations results show substantial differences in performance but no consistent relationship between formula performance and degree of calibration or complexity however formulae containing a transport threshold typically exhibit poor performance furthermore we find that the transport data are best described by a simple power function of discharge from this we propose a new bed load transport equation and identify channel and watershed characteristics that control the exponent and coefficient of the proposed power function we find that the exponent is principally a factor of supply related channel armoring transport capacity in excess of sediment supply whereas the coefficient is related to drainage area a surrogate for absolute sediment supply we evaluate the accuracy of the proposed power function at 17 independent test sites

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

shallow seismic study of a fault scarp near borah peak idaho shallow seismic reflection surveys conducted near borah peak idaho define subsurface structure across a segment of the lost river fault that was reactivated in 1983 four different seismic lines using different sets of recording parameters produced reflections from different depth ranges and at different resolutions the combined interpretation shows the lost river fault zone in the upper 50 m to be 180 m wide and to be composed of high angle faults of various ages the northeast edge of the lost river fault is clearly defined at a depth of approximately 43 2 m the dip of the fault plane in the upper 43 2 m is approximately 55 southwest with an uncertainty of 5 the interpretation presented correlates with surface structure as well as with deeper geophysical data

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

the growth of fault bounded tilt blocks a series of uniformly tilted fault bounded blocks is a common feature in actively extending regions such as the basin and range province if the tilted blocks were produced by rigid domino style rotation one would predict large voids at either end of a series of these blocks using tilt data and a simple flexural calculation we suggest that much of the apparent rigid behavior could also be produced by internal block deformation in our model of normal fault growth isostatic elastic uplift of the footwall is coupled with hanging wall downdrop within the region between faults resulting in the appearance of a tilted rigid block we present tilt data sampled at varying distances from several block defining faults within the northeast basin and range province tilt measurements between a series of 30 km spaced block defining faults are found to be uniform while tilts between more widely spaced faults exhibit a pattern of tilt that diminishes to zero in less than 30 km using a simple flexural calculation for internal block deformation we show that for this region the patterns of tilt are consistent with a flexural length scale of 8 12 km and deflections of 2 4 km these estimates are compatible with both the lower limit to seismicity and basin depth determined from earthquake and seismic reflection studies

dynamics of tropical cyclone intensification deep convective cyclonic left movers abstractdeep convective processes play an important role in tropical cyclone tc formation and intensification in this study the authors investigate the interaction between discrete buoyant updrafts and the vertically sheared azimuthal flow of an idealized tc vortex by adapting the updraft shear dynamical framework to the tc the authors argue theoretically that deep updrafts initiating near the tc radius of maximum wind rmw may propagate with a component left of the mean tangential flow or radially inward toward the tc center results suggest that these unique tc updrafts or left movers with respect to the mean azimuthal flow may play an active role in tc intensification the notion that updraft scale convection may propagate with a component transverse to the mean flow is not at all new cyclonic midlatitude supercell thunderstorms often deviate from their mean environmental flow always to the right of the environmental vertical shear vector the deviant motion arises owing to nonlinear intera

stress triggering of conjugate normal faulting late aftershocks of the 1983 ms 7 3 borah peak idaho earthquake the 1984 devil canyon sequence was a late aftershock sequence of the 28 october 1983 ms 7 3 borah peak idaho earthquake the sequence began on 22 august 1984 with the ml 5 8 devil canyon earthquake which nucleated at a depth of 12 8 0 7 km between the surface traces of two normal faults the challis segment of the lost river fault and the lone pine fault two hundred thirty seven aftershocks were recorded by a temporary array during a 3 week period their focal mechanisms and hypocenter distribution define a cross sectional v pattern whose base corresponds to the ml 5 8 event whose tips correspond to the exposed fault traces and whose sides define two planar fault zones oriented n25 w 75 sw challis fault segment and n39 w 58 ne lone pine fault this pattern describes a graben bounded by conjugate normal faults temporal aspects of the devil canyon sequence provide strong evidence that slip on conjugate normal faults occurs sequentially aftershocks occurred primarily along the challis segment until the occurrence of the 8 september 1984 ml 5 0 earthquake along the lone pine fault after which aftershocks primarily occurred along this fault these observations are consistent with worldwide seismologic and geologic observations and with physical andmore numerical models of conjugate normal faulting aftershocks of the devil canyon sequence occurred immediately northwest of the ml 5 8 devils canyon earthquake which itself was immediately northwest of the thousand springs segment of the lost river fault the fault that slipped in association with the ms 7 3 borah peak earthquake coulomb failure stress analysis indicates that stress increases resulting from both the borah peak mainshock and devil canyon ml 5 8 earthquake were sufficient to induce failure on the lone pine fault these space time patterns suggest that conjugate normal faults may transfer stress or accommodate stress changes at the terminations of major normal faults in the basin and range province less

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

hyperconcentrated flow and sediment transport at steep slopes in order to simulate a fine material slurry of a debris flow a clay suspension of various concentrations was recirculated in a steep flume the effect of an increasing fluid density and viscosity on the flow behavior and the bed load transport capacity of the flow was examined viscous effects were found to become important below a limiting particle reynolds number of about 10 above this limiting value density effects cause an increase in the bed load transport rates as compared to similar conditions with clear water as transporting fluid the experimental data in this range can be described with conventional newtonian formulas and is analyzed together with other bed load transport data two different calculation schemes are proposed for the steep slope range is n n 10 where the bed load concentration is significant with respect to the total flow depth below the critical particle reynolds number of 10 the bed load transport rates decreased strongly

observations of bedload transport in a gravel bed river during high flow using fiber optic dts methods the question how does a streambed change over a minor flood does not have a clear answer due to lack of measurement methods during high flows we investigate bedload transport and disentrainment during a 1 5 year flood by linking field measurements using fiber optic distributed temperature sensing dts cable with sediment transport theory and an existing explicit analytical solution to predict depth of sediment deposition from amplitude and phase changes of the diurnal near bed pore water temperature the method facilitates the study of gravel transport by using near bed temperature time series to estimate rates of sediment deposition continuously over the duration of a high flow event coinciding with bar formation the observations indicate that all gravel and cobble particles present were transported along the riffle at a relatively low shields number for the median particle size and were re deposited on the lee side of the bar at rates that varied over time during a constant flow approximately 1 6 of the bed was predicted to be mobile during the 1 5 year flood indicating that large inactive regions of the bed particularly between riffles persist between years despite field observations of narrow zones of local transport and bar growth on the order of 3 5 times the median particle size in contrast during a 7 year flood approximately 8 55 of the bed was predicted to become mobile indicating that the continuous along stream mobility required to mobilize coarse gravel through long pools and downstream the next riffle is infrequent

localized rotation during paleogene extension in east central idaho paleomagnetic and geologic evidence we collected paleomagnetic data from 137 sites in middle eocene volcanic rocks of the northeastern basin and range province in order to characterize the three dimensional kinematics of continental extension in the lost river and lemhi ranges idaho and to test previous block rotation models statistically significant flattening of directions at three of 10 localities reflects either insufficient averaging of paleosecular variation or erroneous tilt corrections five of the seven remaining locality means are statistically indistinguishable from the middle eocene reference direction this indicates that vertical axis rotation did not accompany post 50 ma normal faulting discordant declinations from two localities in the northern lost river range indicate 30 40 of counterclockwise rotation of a large domain of nnw striking volcanic rocks inclination flattening at one of the two rotated localities is moderate but statistically significant f f 9 9 6 5 in total the paleomagnetic data conflict with earlier predictions of uniform clockwise rotation in response to right lateral transtension adjacent to the eastern snake river plain there is a close correspondence between counterclockwise rotated localities and domains of nnw striking volcanic rocks and between unrotated localities and domains of north striking volcanic rocks new mapping shows that counterclockwise rotated localities are all in the hanging wall of a major west dipping low angle normal fault the donkey fault named for the first time this fault loses displacement southwards was active in eocene oligocene time and is probably a tilted high angle fault the spatial distribution of rotated and unrotated localities is best explained by counterclockwise rotation of the hanging wall of the donkey fault during opening of a southward tapering half graben according to this hanging wall rotation model the footwall of the donkey fault remained fixed relative to its rotating hanging wall our proposed kinematic model is generally applicable to extending continental lithosphere and provides a mechanism for coeval crustal thinning and vertical axis rotation thus vertical axis rotation may occur in the absence of strike slip faults in extensional orogens

surface rupture of the 1857 southern italian earthquake in october 1862 robert mallet published an extensive study of a large earthquake that occurred on 16 december 1857 150 km south east of naples this event is one of the most destructive ever recorded in italy although continental earthquakes of similar size are almost invariably associated with surface faulting mallet did not identify any surface rupture and subsequent workers have also failed to find surface traces using satellite images and aerial photographs as a guide we examined two prominent quaternary normal fault systems in the field flanking the val d agri and the val di diano both trend nw se and dip to the sw the distribution of damage suggests that one or both moved in 1857 on one fault segment in val d agri we found a 2 5 m high scarp whose youthfulness and height suggest it is due to the 1857 earthquake comparison of the observed slip with rates derived from geomorphic evidence suggests a recurrence time for 1857 type events of about 3000 years while the new data we provide are consistent with the event having a magnitude of ms 7 0 there are also grounds for supposing it might have been bigger

field testing of three bedload samplers efficiency in a gravel bed river spitsbergen abstract a comparative study of the three bedload traps was accomplished to determine the effectiveness differences between the devices the research was carried out in two transverse sections of the proglacial gravel bedded scott river sw svalbard using three devices to perform direct measurements of bedload transport in the river channels several samplers are used for field measurements but none of them has gained widespread acceptance as a standard so far the paper compares transport rates collected in three bedload samplers that differ in structure and functionality i a portable helley smith pressure difference bedload sampler h s ii an anchored river bedload trap rbt and iii the portable sampler used by the polish hydrological services pihm type c all three samplers are constructed using the same components a frame made of thin stainless steel sheet and a nylon bag with the same 2 mm mesh size except pihm measurements were conducted within three consecutive days in two cross sections in the same vertical profiles and at the same time at intervals of 30 and 60 min measurements of bedload transport and water velocity were performed simultaneously in order to determine the effectiveness and representativeness of short term measurements using particular devices the masses of the samples were converted into a specific rate of bedload transport and compared to the results of long term continuous measurement 24 h measurement cycle the results confirm that both specific transport indicators and the mass of the samples collected by the tested devices show a significant variation generally the highest mass and specific transport indicators were obtained using the h s sampler the rbt produced moderate transport rates while the pihm sampler gave the lowest rates the bedload transport rate in a profile estimated on the short term measurements was compared to results of the continuous measurements conducted in the same cross sections in the 7 cases we obtained underestimation to max 10 times and in the next 7 cases overestimation to max 114 times only in four cases were the results of short term measurements similar to the continuous ones the results obtained from the rbt sampler show the smallest variability among all tested devices

aftershocks of the campania lucania italy earthquake of 23 november 1980 abstract the result of a study of 1130 aftershocks of the 1980 campania lucania earthquake are presented the data were collected primarily with a dense array of portable smoked drum seismographs deployed in the epicentral region a few days after the main shock tests performed on subsets of the data to establish the location accuracy are described in detail and epicentral maps and cross sections are presented and discussed one hundred and sixty well constrained fault plane solutions using upward traveling rays are presented the distribution of aftershocks forms an elongate cloud which does not define a plane this is not because the events are poorly located a subset of events located with epicentral errors of less than 1 km and depth errors less than 2 km forms a similar cloud to the complete aftershock set the aftershock mechanisms are very varied some are similar to the main event but many differ profoundly these include events on shallow or vertical planes and thrust events the latter include some events which require contraction in the direction in which the main event indicates extension the aftershocks of all mechanisms are intermixed in space in such a way that no simple system of faults can explain them a model to explain the aftershocks and the lack of surface ruptures in the main event is offered it is proposed that the main shock cuts between two aseismic detachment surfaces and that the aftershocks are a consequence of the complicated deformation that such a geometry demands whatever interpretation is adopted the results are a challenge to the commonly accepted view that aftershocks even approximately define simple fault planes or that aftershock mechanisms replicate the mechanism of the main shock defects in interpretations of the main shock and aftershocks process arise largely from a lack of information about the geometry of structures at depth in the epicentral region suitable deep reflection profiles could help to resolve this problem

strain rates and contemporary deformation in the snake river plain and surrounding basin and range from gps and seismicity we used new horizontal global positioning system gps velocities along with earthquakes faults and volcanic features to assess how strain is accommodated in the northern basin and range province we estimated horizontal velocities for 132 stations within the snake river plain and the surrounding basin and range from gps phase data collected from 1994 to 2007 these velocities show regional scale clockwise rotation suggestive of driving forces beyond those associated with the yellowstone hotspot within the western centennial tectonic belt the gps measurements indicate that the basin and range is extending at a rate an order of magnitude greater than the snake river plain which explains its low seismicity between these two regions we discern the centennial shear zone a ne trending zone of right lateral shear with estimated slip rates that increase northeastward from 0 9 0 3 mm yr in the sw to 1 7 0 2 mm yr in ne we interpret the new gps velocities to indicate 1 right lateral shear may be accommodated by strike slip earthquakes on ne trending faults in the centennial shear zone 2 three basin and range faults lost river lemhi and beaverhead terminate at the snake river plain margin and 3 extension in the snake river plain occurs at a much lower rate than the rate of normal faulting in the western centennial tectonic belt

crustal structure of the eastern snake river plain determined from ray trace modeling of seismic refraction data ray trace travel time modeling of the seismic refraction record sections for a profile from near soda springs idaho to near mckay idaho was used to derive a crustal model across the eastern snake river plain esrp the derived crustal model is consistent with the velocity structure interpreted from a profile along the axis of the esrp the interpretation also indicates that significant lateral inhomogeneities exist in the upper crust beneath the esrp when compared with the upper crust beneath the adjoining northern rocky mountain and basin and range provinces the most prominent features of the crustal structure inferred by the ray trace modeling are as follows 1 the northwest margin of the esrp was modeled as a fault structure downthrown on the srp side se with an offset of greater than 4 km the southeast margin conversely appears to be downwarped with possible minor faulting paleozoic sedimentary rocks are present beneath the cenozoic volcanics of the esrp possibly to and beyond 40 km from the southeastern margin of the esrp near blackfoot idaho 2 the modeling indicates no abrupt variation in the depth to the top of the lower crustal layer near the margins of the esrp 3 an intermediate 6 5 km s layer occurring beneath the esrp interpreted from a refraction profile located along the axis of the esrp was found to be localized within the esrp margins this layer is interpreted as a pervasive intrusion of higher velocity material from the upper mantle into the highly fractured upper crustal layer in this region 4 a density model of the crust across the esrp was prepared with the densities selected using the interpreted seismic velocities as a constraint the gravity field calculated from this model resulted in a good match to observed gravity data over the eastern snake river plain

waveform analysis of two preshock main shock aftershock sequences in utah we use waveform cross correlation to study clustering of small earthquakes that occurred from 1981 to 1983 within 20 km of 1 an ml 4 3 main shock near salt lake city utah on 8 october 1983 and 2 an ml 4 0 main shock near richfield utah on 24 may 1982 no clusters of earthquakes were observed prior to the salt lake city event during the time period studied however a cluster of four nearly identical preshocks within 80 m of each other possibly representing the failure of a critical asperity occurred 5 km northwest of the richfield event during a 4 hour period 10 months before the main shock we found no similar clusters among the other preshocks within the richfield study area all of which were located more than 10 km from the main shock the aftershocks in both study regions during the first 17 days after the respective main shocks occupied areas smaller than the rupture areas estimated for the main shocks from initial pulse width measurements both aftershock sequences showed a spatial migration of the initial events that could only be discerned from the waveform data one possible explanation for this migration could be propagating stress changes caused by the occurrence of the aftershocks themselves or by postseismic creep

magmatism and extension the thermal and mechanical effects of the yellowstone hotspot currently there is a parabolic shaped pattern of seismicity and latest quaternary faulting which centers on the axis of the eastern snake river plain srp and has its apex at the yellowstone plateau the pattern of activity surrounds a region of aseismicity that includes the eastern srp geologic evidence suggests that this pattern has migrated in tandem with rhyolitic volcanism induced by the yellowstone hotspot during its 16 m y trek across western north america similarly there is a migration in the onset of basaltic lava flows and the emplacement of up to 12 km of midcrustal mafic intrusions that follows the track of rhyolitic volcanism these observations suggest that the intrusion of magmas has a significant influence on the pattern of seismicity and faulting we present a one dimensional finite difference thermomechanical model that accounts for the observed pattern of increased faulting followed by fault quiescence within the circum eastern srp in this model mafic magmas are intruded into a lithosphere that is already extending the intrusions heat the surrounding rocks resulting in locally increased strain rates as the intruded magmas solidify the length of time required to return strain rates to their pre intrusion level is then determined the model assumes constant horizontal tectonic forces and maps strain rate as a function of yield strength and time since intrusion we vary model parameters such as crustal thickness initial geothermal gradient and amount of magma intruded in order to assess how they affect turnaround time for strain rates the amount and timing of intruded material allowed by the model are constrained by seismic refraction data as well as by regional geochronologic and petrologic studies we assume intruded rock rheology to be a maryland diabase mantle rheology we base on dry olivine we represent the crust by both dry granite and dry anorthosite rheologies our results suggest that 2 to 3 m y appears to be a reasonable length of time for strain rates to return to levels present before a midcrustal mafic intrusion equivalent in magnitude to the yellowstone intrusion this corresponds closely to the length of time between the onset of along axis accelerated faulting and subsequent fault quiescence assuming a hotspot velocity of 3 5 to 4 0 cm yr relative to the north american plate

field measurements of the energy delivered to the channel bed by moving bed load and links to bedrock erosion 1 impact driven fluvial erosion is directly related to the energy delivered to the channel bed by moving bed load using a novel protocol we have measured this energy in four mountain streams in austria and switzerland similar to bed load transport rates the energy delivered to the bed displays large scatter over several orders of magnitude even for a constant discharge we found that only a small fraction 1 of the total energy available to the stream is delivered to the bed and can be used for erosive work empirical predictive equations can be defined for specific sites but there is large site to site variability prediction of energy delivered to the bed using the saltation abrasion model of bedrock erosion only provides the observed trends when measured bed load transport rates are used as input using an empirical transport law calibrated to the conditions at one of the study streams leads to overprediction of delivered energies by more than 2 orders of magnitude this overprediction decreases with increasing discharge and thus at high discharges better predictive results are obtained we find a correlation between the channels bed slope or characteristic grain sizes of the channel bed and the fraction of energy delivered to the bed of the total energy available to the stream this observation provides a tentative link between fundamental fluvial incision processes to the stream power model family that has widely been used to model fluvial bedrock incision in landscape evolution simulations

seismotectonics of the portland oregon region abstract portland oregon lies in the southern half of an approximately rectangular basin measuring 30 by 50 km since 1969 there have been no earthquakes with m 4 0 in or on the margins of the portland basin but this level of seismicity may not be characteristic of the region using microseismicity data collected by the university of washington regional short period seismograph network for the period mid 1982 through 1989 we have determined p wave focal mechanisms for four individual earthquakes and three groups of earthquakes we have also relocated the 6 november 1962 m w 5 2 portland earthquake and analyzed regional surface wave recordings of this event using the seismic moment tensor inversion technique the results of these seismic analyses along with geologic and other geophysical data are integrated into a seismotectonic model of the portland basin the p wave mechanisms are compatible with dextral strike slip motion along approximately nw striking fault zones bounding the eastern and western margins of the basin we speculate that there is a dextral strike slip fault zone which we call the frontal fault zone along the eastern margin of the portland basin the western margin has been previously recognized as a zone of dextral strike slip faulting known as the portland hills fault zone the epicenter of the 1962 earthquake is located between the two fault zones and lies approximately 15 km ne of downtown portland our preferred mechanism is normal faulting on ne or nne trending fault planes these results support the hypothesis posed by previous investigators that the portland basin is a pull apart basin and are evidence for contemporary crustal extension between the frontal and portland hills fault zones

continuous measurement of sediment transport in the erlenbach stream using piezoelectric bedload impact sensors we report on bedload transport observations using piezoelectric bedload impact sensors pbis an indirect method of estimating the volume of bedload transport of coarse sediment the pbis device registers vibrations produced by bedload particle diameter 20 mm and records the signal as a sum of the number of impulses per time sediment transport at the erlenbach stream has been continuously monitored with a pbis array starting in 1986 the sensor array spans the width of an entire cross section and is mounted flush with the surface of a check dam immediately upstream of a sediment retention basin we compare pbis data with long term sedimentation records obtained from repeated surveys of material stored in the sediment retention basin with artificial sediment input under controlled conditions in the field and also with laboratory experiments the rate of bedload transport is proportional to the number of impacts on the sensor per unit time the reliability of the calibration relationship increases with the length of the observation period e g for higher numbers of impacts and larger bedload volumes sediment volumes for individual flood events estimated with the pbis method are in agreement with volumes estimated using an independent empirical method based on the effective runoff volume of water the peak water discharge and the critical discharge for the onset of sediment transport copyright 2007 john wiley sons ltd

analysis of tilting near normal faults using calculus of variations implications for upper crustal stress and rheology abstract an initially horizontal surface in the surroundings to a normal fault will after extension tilt towards the fault if in the hanging wall or away from it if in the footwall coseismic deformation of these surroundings can be validly modelled as flexure cumulative deformation on geological time scales has been regarded as flexure also but this has led to the apparent paradox that many observed structures require the effective elastic thickness of the brittle upper crust to be much smaller than its seismogenic thickness this article presents a possible alternative that cumulative deformation of the upper crust near some active normal faults may be regarded instead as partitioned into separation of the blocks that comprise their surroundings through the horizontal component of dip slip on the fault and distributed vertical simple shear in their surroundings which causes them to tilt and takes up the vertical slip on the fault a generalized profile of tilting near a normal fault which approximates a parabola can be derived following two assumptions first the brittle layer retains an elastic term in its rheology on geological time scales such that it resists arbitrary length changes second the brittle layer minimizes its overall vertical deflection thus minimizing the buoyancy force acting on it maximum stress and total strain energy associated with observed profiles of tilting are typically smaller for distributed vertical simple shear favouring this mechanism over flexure

reverse drag revisited why footwall deformation may be the key to inferring listric fault geometry abstract although reverse drag the down warping of hanging wall strata toward a normal fault is widely accepted as an indicator of listric fault geometry previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry in this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near surface deformation by directly comparing patterns of displacement stress and strain around planar and listric faults as predicted by elastic boundary element models in agreement with previous work we find that models with finite planar planar detached and listric detached faults all develop hanging wall reverse drag folds all of these model geometries also predict a region of tension and elevated maximum coulomb stress in the hanging wall suggesting that the distribution and orientation of near surface joints and secondary faults may also be of limited utility in predicting subsurface fault geometry the most notable difference between the three models however is the magnitude of footwall uplift footwall uplift decreases slightly with introduction of a detachment and more significantly with the addition of a listric fault shape a parametric investigation of faults with constant slip ranging from nearly planar to strongly listric over depths from 1 to 15 km reveals that footwall fold width is sensitive to fault geometry while hanging wall fold width largely reflects fault depth application of a graphical approach based on these results as well as more complete inverse modeling illustrates how patterns of combined hanging wall and footwall deformation may be used to constrain subsurface fault geometry

strong ground motion in the 1983 borah peak idaho earthquake and its aftershocks abstract thirteen strong motion accelerographs sited in a permanent array at the idaho national engineering laboratory inel were the closest instruments to the m s 7 3 1983 borah peak idaho earthquake they recorded the event at epicentral distances of 90 to 110 km the peak horizontal accelerations or peak ground accelerations pgas at the basement and free field sites of the array ranged from 0 022 to 0 078 g for 2 weeks after the main shock the u s geological survey maintained an array of digital seismographs in the epicentral area these instruments recorded six large aftershocks at epicentral distances of 4 to 45 km the largest of these aftershocks also triggered four accelerographs in the inel array pgas for the main shock are estimated by two separate analyses first the attenuation of the pgas from the largest aftershock is used to extrapolate the far field pga into the near field obtaining estimates of 0 54 0 58 0 21 and 0 24 g at epicentral distances of 11 12 16 and 18 km respectively second paired recordings for a set of small aftershocks obtained from a near field station u s geological survey portable instrument and a far field station inel telemetered station were used together with an inel main shock acceleration time history to generate four synthetic accelerograms for a hypothetical recording site 18 km southeast of the main shock the pgas measured from these synthetic accelerograms are 0 08 0 14 0 15 and 0 23 g

the coalescence and organization of lahars at semeru volcano indonesia we present multi parameter geophysical measurements of rainfall induced lahars at semeru volcano east java using two observation sites 510 m apart 11 5 km from the summit our study site in the curah lengkong channel is composed of a 30 m wide box valley with a base of gravel and lava bedrock representing an ideal geometry for high density measurements of active lahars instrumentation included pore pressure sensors stage a broad band seismograph arrival times vibrational energy and turbulence video footage and direct bucket sampling a total of 8 rainfall induced lahars were recorded with durations of 1 3 h heights 0 5 2 m and peak velocities 3 6 m s flow types ranged from dilute to dense hyperconcentrated flows these recorded flows were commonly composed of partly coalesced discrete and unsteady gravity current packets represented by multiple peaks within each lahar these packets most likely originate from multiple lahar sources and can be traced between instrument sites those with the highest concentrations and greatest wetted areas were often located mid lahar at our measured reach accelerating towards the flow front as these lahars travel downstream the individual packets thus coalesce and the flow develops a more organised structure observations of different degrees of coalescence between these discrete flow packets illustrate that a single mature debris flow may have formed from multiple dynamically independent lahars each with different origins

structural and fluid chemical properties of seismogenic normal faults abstract structures in extensional fault zones can be classified using the configuration of fault branch lines and tip lines important classes include the segment bend segment termination segment branch cross fault intersection and segment offset the effect of these structures on rupture history is not necessarily consistent neither between individual earthquakes nor between different fault zones rupture behavior is dependent on several other factors including loading conditions regional and localized rupture tip stress fields fluid mechanical processes and chemical processes fracture toughness is partly controlled by the angular discordance between slip directions on adjacent fault segments greater discordance between slip directions and intersection lines of fault segments results in greater strain incompatibility an internal fracture network generally evolves within a segment boundary to maintain compatibility and transfer slip between the segments the dimensions and structure of this fracture network may also partly control rupture propagation presumably activation of a fault network with large angular discordances between slip directions and intersection lines will generate numerous asperities as the subsidiary faults mutually interact and offset each other the geometry of a segment boundary may change with depth and the three dimensional nature of the structure may be important in controlling rupture history fluids influence rupturing via fluid pressure effects and time dependent chemical processes fracture propagation by stress corrosion may favor instability and chemical alteration may produce minerals of lower strengths allowing time dependent creep sealing and healing of fractures however may remove damage and increase strength elementary computations indicate that representative times for sealing and chemical alteration are between 1 and 1000 years for reasonable physical conditions well within the recurrence intervals of most large earthquakes time to failure for stress corrosion cracking is more highly variable and strongly sensitive to applied stress and fluid pressure

application of an automatic method for determining normal fault geometries abstract an automatic method is used to determine the geometries of normal faults on depth converted seismic reflection profiles from the gulf of mexico and from the north sea the general method has previously been tested on synthetic and sand box data and assumes that the hanging wall deforms within the plane of section by a combination of arbitrarily inclined bulk simple shear and differential compaction the range of possible solutions is systematically investigated using inverse modelling we assume that the fault surface does not significantly change shape during deformation however inversion of flexural forward models shows that when the fault surface does change shape the misfit function at an automatically determined solution is unacceptably large and featureless consequently spurious solutions obtained when the principal assumptions break down can be identified the approximations used in modelling the effects of differential compaction are justified by a range of appropriate synthetic models we reiterate that the inversion procedure is dependent upon careful identification of a two or more deformed horizons within the hanging wall and b the regional levels of deformed horizons before deformation the numerical stability of the scheme is demonstrated by inverting synthetic data to which random and systematic noise have been added the solutions we have obtained are good and indicate that the method works regardless of the scale and shape of the faults throughout we emphasize the importance of combining inverse theory with a simple kinematic model in order to investigate the solution space and the resolution of the model parameters obtained

structure of a fault segment boundary in the lost river fault zone idaho and possible effect on the 1983 borah peak earthquake rupture abstract the 1983 borah peak earthquake m s 7 3 initiated within the southern part of the thousand springs segment in the lost river fault zone east central idaho the earthquake rupture propagated unilaterally to the northwest over a distance of 36 km and was accompanied by sinistral normal slip within the fault zone at the surface the southern most part of the rupture zone is marked by a bend in the lost river fault zone at the intersection between the thousand springs segment to the north and the mackay segment of the fault zone to the southeast the intersection between the two fault segments is a lens shaped area that contains numerous nw and ne striking faults that cut the paleozoic bedrock several of the faults within the intersection zone ruptured at the surface during the 1983 earthquake a three dimensional geometrical model of the intersection zone between the thousand springs and mackay fault segments was constructed from geological mapping in conjunction with previously published interpretations of geodetic and seismological data the longitudinal axis of the intersection zone plunges to the southwest where its projected position in the subsurface roughly coincides with the location of the 1983 earthquake9s hypocenter at a depth of 15 to 16 km the intersection zone between the two fault segments may have played a dual role during the borah peak earthquake both marking the site of rupture nucleation but also acting to arrest spread of the rupture to the southeast onto the adjacent mackay segment

the december 1872 washington state earthquake the largest historical earthquake in eastern washington occurred on 15 december 1872 we used modified mercalli intensity mmi assignments for 12 twentieth century earthquakes to determine attenuation relations for different regions in the pacific northwest mmi attenuation for propagation paths east and west of the cascade mountains differs significantly only for epicentral distances greater than about 225 km we used these attenuation relations and the mmi assignments for the 15 december 1872 earthquake to conclude that its epicentral region was east of the cascade mountains near lake chelan washington and most probably near the south end of lake chelan the intensity magnitude m i is 6 8 and moment magnitude m is 6 5 7 0 at the 95 confidence level manuscript received 23 october 2001

determination of bedload transport using naturally magnetic tracers first experiences at squaw creek gallatin county montana pebbles and cobbles constitute an important part of the sediment discharge of many streams data on the movement of this coarse bedload is important to a variety of studies including analysis of total sediment yield resevoir filling rates bridge erosion and trout spawning habitat despite the importance of knowledge regarding coarse bedload transport measurement remains difficult and unreliable a new detector has been constructed which records the movement of naturally magnetic pebbles and cobbles the detector was installed at a log sill in the bed of squaw creek gallatin county montana to evaluate the detector under natural conditions during a flood in may 1981 the detector recorded the passage of magnetic particles larger than 32 mm extrapolation of the data allows estimation of total bedload transport based on the composition of an unvegetated gravel bar upstream of the detector and on measurements of turbidity during the flood bedload accounted for approximately 66 of the solid material leaving the drainage basin since many coarse bed streams probably contain material as magnetic as the andesitic rocks in squaw creek the procedure should be widely applicable

measuring bed load transport rates by grain size fraction using the swiss plate geophone signal at the erlenbach abstractthe swiss plate geophone system is a bed load surrogate monitoring technique that is used to quantify bed load transport in steep streams the amplitude of the signal recorded by the swiss plate geophone contains information about the grain size distribution of the transported bed load to extract this information the authors computed the number of impulses and packets representing a single particle impact registered for different amplitude ranges the so called amplitude histograms for 46 samples when bed load was measured independently with automatic basket samplers at the erlenbach amplitude histograms can be interpreted as a statistical distribution of the signal s amplitude over a given time interval using the number of bed load particles per unit mass absolute bed load masses for each grain size class can be calculated the results show that the grain size distribution of the transported bed load for particles larger than 9 5 mm can be continuously monitored at the erlenbach with the

contemporary seismicity in the eastern snake river plain idaho based on microearthquake monitoring microearthquake monitoring by a permanent network operated since 1971 and two recent temporary surveys performed by the idaho national engineering laboratory suggest that infrequent small magnitude earthquakes are characteristic of eastern snake river plain esrp seismicity although a total of only 19 earthquakes have been observed to date and not all have well constrained focal depths their relatively shallow occurrence at depths of 8 km is consistent with the hypothesis that elevated crustal temperatures in the esrp confine the brittle portion of the crust and hence seismogenesis to the upper 6 to 10 km a composite focal mechanism of two microearthquakes located near the axis of the esrp indicates normal faulting with a minor component of strike slip motion the northeast southwest trending t axis indicated by this composite mechanism is consistent with the direction of extension indicated by holocene volcanic rift zones within the esrp and normal faults in the adjacent basin and range province to the northwest based on this low level of small magnitude seismicity deviatoric stresses appear to be small in the esrp

the influence of landsliding on sediment supply and channel change in a steep mountain catchment abstract rates of sediment supply by landsliding to an alluvial channel in a small catchment in central switzerland were estimated over an 11 month study period fluvial sediment transport in the channel is independently monitored at the upstream and downstream ends of the study reach yielding a unique opportunity to quantitatively compare the volume of sediment supplied to the channel with the volume in fluvial transport landslide derived sediment discharge to the channel was greatest during the winter and spring months while most of the fluvial sediment transport occurred during short intense summer storms approximately 98 m 3 of sediment was delivered directly to the study reach by landsliding 80 m 3 was transported into the reach from upstream and 70 m 3 was transported out of the reach thus there was a net accumulation of 100 m 3 of sediment during the 11 month study decadal scale channel aggradation was independently assessed by comparing channel longitudinal profiles in 1993 and 2004 during this 11 year period a total of 1500 m 3 of sediment has accumulated in the study reach aggradation has occurred largely in two broad zones that correspond with both the locations of major landslide complexes and reaches of high channel slope indicating that hillslope sediment input left an imprint on the morphology of the channel bed that appears to be stable over at least decadal time scales

centroid depths of mid ocean ridge earthquakes dependence on spreading rate from inversions of teleseismic p and sh waveforms we have determined the source parameters of 50 large earthquakes that occurred during 1962 1983 on slowly spreading mid ocean ridges all events are characterized by predominantly normal faulting on planes that dip at approximately 45 and strike parallel to the local trend of the ridge axis centroid depths range from 1 to 6 km beneath the seafloor the p waves from these earthquakes show strong water column reverberations suggesting that fault rupture extended to the seafloor under the assumption that the centroid depth marks the mean depth of fault slip earthquake faulting extended to a depth of 2 10 km for these earthquakes the water depths inferred from the predominant periods of the water column reverberations constrain the epicenters of these earthquakes to lie within the relatively deep inner floor of the median valley the maximum centroid depths of ridge crest earthquakes decrease with increasing spreading rate and the maximum seismic moment may also decrease with increasing spreading rate these results indicate a general decrease with spreading rate in maximum thickness of the mechanically strong layer beneath the ridge axis region the concentration of large earthquakes within the deepest parts of the median valley and the depth extent of seismic faulting support lithospheric necking models for the origin of the median valley

the pocatello valley idaho utah border earthquake sequence of march to april 1975 abstract an earthquake sequence during march and april 1975 which included a main shock of magnitude m l 6 0 on 28 march was centered in pocatello valley on the idaho utah border a foreshock of magnitude m l 4 2 preceded the main shock by 22 hr and was followed by at least 156 microearthquakes that behaved as aftershocks of the first event accurate locations of 587 aftershocks that occurred during the first 20 days after the main shock define irregular zones of concentrated activity beneath the south central western and northern parts of pocatello valley the main shock is interpreted to have involved nonuniform dipslip rupture without surface faulting on a previously unrecognized normal fault that dips nw obliquely transecting the north trending pocatello valley graben the speace time pattern of aftershocks and composite focal mechanisms indicate subsidiary faulting and the interaction of diverse fracture trends resulting in a mixture of normal strike slip and oblique faulting details of the earthquake sequence imply a complex episode of basin and range graben subsidence that may typify similar source regions elsewhere in utah9s wasatch front area

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

crustal structure of southwestern montana and east central idaho results of a reversed seismic refraction line on october 20 1982 we collected seismic refraction data on a 250 km line segment between butte montana and challis idaho these data are from two open pit mine blasts one at anaconda minerals companys southeast berkely pit and the other at cyprus mines corporations thompson creek mine eight of our ten recorders wrote clear records of both blasts with measured travel times accurate to 0 2 seconds we supplemented these data with data from permanent stations in the butte area the pg crustal velocity is 5 8 km s to the southwest and 6 0 km s to the northeast the pn mantle velocity is 7 9 km s to the northeast and 8 1 km s to the southwest total travel times are equal the s wave velocity in the crust is about 3 5 km s the symmetry of the travel time results with their intersection within one kilometer of the midpoint between the pit blasts strongly suggests the refraction line overlies a horizontal moho or parallels the strike line of a dipping moho surface these data indicate the crust in southwestern montana and east central idaho is approximately 33 km thick contrasting tectonic processes compression and thickening during the laramide orogeny with extension and thinning since the paleocene resulted in a crust with slightly less than normal thickness

structure of the warm spring and northern thousand springs fault segments lost river fault zone idaho possible effects on rupturing during the 1983 borah peak earthquake abstract scarps on the warm spring and northern part of the thousand springs segments of the lost river fault zone idaho were surveyed and analyzed to determine fault orientation and near surface fault roughness scarps formed along these two segments during the 1983 borah peak earthquake and the evolution of the rupture appears to have been related to the large scale geometry of the fault segments and to fault roughness the warm spring and thousand springs segments are divided into approximately planar sections that in detail show roughness at varying scales individual fault sections within these main segments have lengths of 2 to 5 km and average dips of about 30 to 50 to the wsw to ssw the boundary between the warm spring and thousand springs segments is marked by the willow creek hills a large ridge of bedrock that extends across the hanging wall basin no surface faulting occurred along the two main segments within this boundary during the 1983 borah peak earthquake although the presence of discontinuous holocene scarps indicates that the boundary has ruptured during previous earthquakes the willow creek hills lie above a large sw plunging ridge in the southern part of the warm spring segment a smaller ridge is located within the northern end of the thousand springs segment within a region of rupture branching between this segment and the arentson gulch fault the scarps and aftershock distributions indicate secondary faulting within the segment boundary as the result of the borah peak earthquake scarps along both flanks of the willow creek hills formed as the hanging walls of the thousand springs and warm spring segments moved downward relative to the boundary which is structurally perched upon the underlying ridge within the lost river fault zone local surface faulting in the willow creek hills and aftershock activity beneath them reflect continuing deformation as the result of the heterogeneous strain field in the segment boundary fault roughness measured as the mean deviation of fault surfaces from a best fit plane continuously increases with distance along a profile at scales from 50 to 500 m mean deviation in amplitude is related to incremental distance along the surface using a power law function with an exponent between 0 6 and 0 8 detailed surveying and three dimensional analysis of fault scarps along the strike of the fault zone augments common paleoseismological methods of scarp profiling trenching and morphological analysis of mountain fronts the procedures developed in this study may be easily applied to fault zones in many parts of world where scarps cut across suitable topography the results have important implications for better defining the structure of fault zones and the influence this structure may have on fault displacement seismiciry and strong ground motion

the pyrenean earthquake of february 29 1980 an example of complex faulting abstract an m b 5 1 earthquake occurred on february 29 1980 in the western pyrenees near arudy france the telemetred network of the i p g p operating in this area since 1978 allowed a good localization of this earthquake 43 4 21 n 0 24 59 w depth 4km during the two years preceding this earthquake the seismic activity exhibited a gradual decrease a foreshock of magnitude 1 6 was recorded three hours before the main shock a temporary network set up in the epicentral area a few days after the main shock permitted a precise study of the aftershock sequence fifty fault plane solutions for earthquakes ranging from magnitude 1 5 4 were obtained a complex pattern of faulting was revealed with both strike slip and normal faulting however a regional tectonic stress tensor can be proposed from a detailed investigation of the aftershock sequence this stress tensor is in agreement with previous results in this area

revised velocity structure of western montana using a one dimensional 1d layered earth approach we determined a new crust and upper mantle velocity model for western montana to improve earthquake hypocenter locations p wave arrival times recorded on 280 stations from 1432 well recorded earthquakes provided input for a sparse damped least squares sensitivity matrix we solved for 1d velocity structure refractor depths station corrections and hypocentral positions by minimizing travel time residuals the new model has three layers with p wave velocities of 5 70 6 12 and 6 53 km sec with corresponding interface depths of 7 0 19 8 and 39 7 km below the surface the upper mantle velocity is 8 00 km sec we determined station corrections and show that the yellowstone caldera is the only regional geologic feature not adequately modeled by our new 1d velocity model use of the new model and station corrections reduced hypocenter location uncertainties and travel time residuals implying improved hypocenter locations for western montana earthquakes online material table of seismographic stations

prediction of sediment transport in step pool channels 1 in mountainous drainage networks sediment mobilized on hillslopes must first pass through steep streams before reaching lower gradient channels the bed of steep channels is typically composed of large relatively immobile boulders and finer more mobile gravel most sediment transport equations overpredict sediment flux in steep streams by several orders of magnitude because they do not account for the stress borne by immobile grains and the limited availability of the more mobile sediment we previously developed and tested in flume experiments a sediment transport equation that accounts for these two effects here we modify the parker 1990 bed load equation to include the resistance borne by steps and selective transport of the relatively mobile sediment using a range of hiding functions we test a number of resistance equations and hiding functions combined with our modified and the original parker equations against measured flow and sediment transport in three steep channels our modified sediment transport equation generally predicts the transported sediment volumes to within an order of magnitude of the measured values whereas the unmodified equations do not the most accurate sediment flux predictions were obtained from using our modified equation combined with a hiding function that calculates highly selective transport of the relatively mobile sediment furthermore this hiding function has a critical shields stress that is similar to those reported for lower gradient channels the effects of the immobile steps on flow and sediment transport are not adequately captured by simply increasing the critical shields stress to values reported in steep streams

instrumental seismicity of central idaho hypocenters of regionally recorded earthquakes that occurred in central idaho from 1944 through october 1985 have been recomputed with travel times calibrated by locally recorded aftershocks of the borah peak idaho earthquake of 1983 the effect of the relocation is to define more sharply the sizes and relative positions of seismic source zones in central idaho and to move epicenters systematically south often by more than 10 km from their previously cataloged positions the distribution of epicenters of the borah peak main shock and early aftershocks suggests that the fault segment that ruptured in the main shock was approximately a parallelogram with one pair of sides parallel to the zone of surface fault scarps associated with the earthquake and with the other pair of sides parallel to the slip vector of the earthquake such a rupture shape would be expected on geometrical grounds if the 1983 rupture zone were terminated on the north and south by intersection with adjacent segments of the lost river fault that have the same slip vector as the 1983 rupture epicenters of earthquakes occurring before 1983 define a seismic zone the white cloud peaks zone that is approximately parallel to the borah peak aftershock zone but situated from 30 to 40 km to the west the relocated epicenters may also be interpreted as defining a north northeast trending seismic zone near seafoam and a north northeast trending seismic zone that is situated north and west of challis here called the twin peaks myers cove zone the seafoam zone includes the epicenter of the largest instrumentally recorded central idaho earthquake prior to the borah peak earthquake the magnitude 6 1 shock of 12 july 1944 the region within 25 km of the epicenter of the borah peak main shock was quiescent for at least two decades before the main shock for magnitudes mb lg of 3 5 and greater

quaternary tectonic setting of the 1983 borah peak earthquake central idaho the 1983 borah peak earthquake was accompanied by extensive surface faulting along a part of the lost river fault that has abundant evidence of latest quaternary last 15 000 yr offset this fault and two similar range front normal faults along the lemhi range and beaverhead mountains lie in an area of basinand range structure in central idaho that is part of a roughly v shaped belt of latest quaternary surface faulting that extends from the wasatch fault through the yellowstone area to the lost river fault the position of this belt may be related to the outward migration of a thermal front associated with the northeastward progression of late cenozoic silicic volcanism along the yellowstonesnake river plain axis the central segments of the lost river lemhi and beaverhead faults have been active more recently and probably more active throughout quaternary time than the southern and northern segments the main 1983 surface faulting occurred in an area of high structural relief along a central segment of the lost river fault that has ruptured in latest quaternary time which suggests that comparable areas along other range fronts in the area should be regarded as likely sites of future surface faulting other perspective of fault behavior suggest additional possible sites and all segments of the range front faults are regarded as capable of surface faulting

comparison of various inversion techniques as applied to the determination of a geophysical deformation model for the 1983 borah peak earthquake abstract a number of techniques are employed to overcome nonuniqueness and instability inherent in linear inverse problems to test the factors that enter into the selection of an inversion technique for fault slip distribution we used a penalty function with smoothness pf s a damped least squares method dls damped least squares method with a positivity constraint dls p and a penalty function with smoothness and a positivity constraint pf s p for inverting the elevation changes for slip associated with the 1983 borah peak earthquake unlike solving an ill posed inverse problem using a gradient technique ward and barrientos 1986 we have restored the well posed character between the elevation changes and normal slip distribution studies showed that the constraints based on sound understanding of the physical nature of the problem are crucial in the derivation of a meaningful solution and dictates primarily the selection of a particular inversion technique all available geological and geophysical information were used to determine a geophysical deformation model for the earthquake it is suggested that the pf s p solution for a fault length of 75 km is the preferred model the long wavelength features in the estimated slip distribution are similar to those obtained by ward and barrientos 1986 whereas the shorter wavelength features differ between two solutions the fault dips 49 to the southwest the slipped zones deepen from the surface at the northwest to about 20 km downdip depth at the southeast the fault extends to the southeast beyond the epicenter of the mainshock it is also shown that only the long wavelength features of the slip distribution are well resolved the resolution is better at shallower levels than at deeper levels the resolution deteriorates when the deformation sources are away from the leveling lines smoothness constraints provide better resolution than damping does at depth the addition of a positivity constraint significantly improves the model resolution

on the origin of diverse aftershock mechanisms following the 1989 loma prieta earthquake summary we test the hypothesis that the origin at the diverse suite of aftershock mechanisms following the 1989 m 7 1 loma prieta california earthquake is related to the post main shock static stress field we use a 3 d boundary element algorithm to calculate static stresses combined with a coulomb failure criterion to calculate conjugate failure planes at aftershock locations the post main shock static stress field is taken as the of a sum of a pre existing stress field and changes in stress due to the heterogeneous slip across the loma prieta rupture plane the background stress field is assumed to be either a simple shear parallel to the regional trend of the san andreas fault or approximately fault normal compression a suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared allowing for uncertainties in both mechanism parameters and earthquake locations to well constrained mechanisms reported in the us geological survey northern california seismic network catalogue we also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes assuming either plane to be a likely rupture plane various permutations of the assumed background stress field fractional coefficients of aftershock fault planer methods of comparisons etc explain between 52 and 92 per cent of the aftershock mechanisms we can explain a similar proportion of mechanisms however by comparing a randomly reordered catalogue with the various suites of synthetic aftershocks the inability to duplicate aftershock mechanisms reliably on a one to one basis is probably a function of the combined uncertainties in models of main shock slip distribution the background stress field and aftershock locations in particular we show theoretically that any specific main shock slip distribution and a reasonable background stress field are able lo generate a highly variable suite of failure planes such that quite different aftershock mechanisms may be expected to occur within a kilometre of less of each other this scale of variability is less than the probable location error of aftershock earthquakes in the loma prieta region we successfully duplicate a measure of the variability in the mechanisms of the entire suite of aftershocks if static stress changes are responsible for the generation of aftershock mechanisms we are able to place quantitative constraints on the level of stress that must have existed in the upper crust prior to the loma prieta rupture this stress level appears to be too low to generate the average dip across the main shock rupture plane possible reasons for this result range from incorrect initial assumptions of homogeneity in the background stress field friction and fault geometry to driving stresses that arise from deeper in the crust or upper mantle alternatively aftershock focal mechanisms may be determined by processes other than or in addition to static stress changes such as pore pressure changes or dynamic stresses

a new interpretation of deformation rates in the snake river plain and adjacent basin and range regions based on gps measurements we evaluate horizontal global positioning system gps velocities together with geologic volcanic and seismic data to interpret extension shear and contraction within the snake river plain and the northern basin and range province u s a we estimate horizontal surface velocities using gps data collected at 385 sites from 1994 to 2009 and present an updated velocity field within the stable north american reference frame snarf our results show an ene oriented extensional strain rate of 5 9 0 7 x 10 sup 9 yr sup 1 in the centennial tectonic belt and an e oriented extensional strain rate of 6 2 0 3 x 10 sup 9 yr sup 1 in the intermountain seismic belt combined with the northern great basin these extensional strain rates contrast with the regional north south contraction of 2 6 1 1 x 10 sup 9 yr sup 1 calculated in the snake river plain and owyhee oregon plateau over a 125 x 650 km region tests that include dike opening reveal that rapid extension by dike intrusion in volcanic rift zones does not occur in the snake river plain at present this slow internal deformation in the snake river plain is in contrast to the rapidly extending adjacent basin and range provinces and implies shear along boundaries of the snakemore river plain we estimate right lateral shear with slip rates of 0 5 1 5 mm yr along the northwestern boundary adjacent to the centennial tectonic belt and left lateral oblique extension with slip rates of 10 sup 6 yrs the low strain field in the snake river plain and owyhee oregon plateau would extend through the quaternary less

kinematic evidence for the effect of changing plate boundary conditions on the tectonics of the northern u s rockies we derive surface velocities from gps sites in the interior northwest u s relative to a fixed north american reference frame to investigate surface tectonic kinematics from the snake river plain srp to the canadian border the centennial tectonic belt ctb on the northern margin of the srp exhibits west directed extensional velocity gradients and strain distributions similar to the main basin and range province brp suggesting that the ctb is part of the brp north of the ctb however the vergence of velocities relative to north america switches from westward to eastward along with a concomitant rotation of the principal stress axes based on available seismic focal mechanisms revealing paired extension in the northern rockies and shortening across the rocky mountain front this change in orientation of surface velocities suggests that the change in the boundary conditions on the western margin of north america influences the direction of gravitational collapse of laramide thickened crust throughout the study region fault slip rate estimates calculated from the new geodetic velocity field are consistently larger than previously reported fault slip rates determined from limited geomorphic and paleoseismic studies

foreshocks and aftershocks of large m 5 5 earthquakes within the western cordillera of the united states source parameters of foreshocks and aftershocks of 27 large m 5 5 earthquake sequences occurring within the western cordillera of the united states between 1915 and 1988 have been used to examine the properties of foreshocks and aftershocks and to determine how foreshocks and aftershocks relate to faulting properties of their main shocks to physiographic province and to heat flow this study examines only the largest foreshocks and aftershocks occurring within 2 months and 40 km of the main shocks results of this study show that nearly 60 per cent of western cordilleran earthquakes have foreshocks and that 58 per cent of the foreshocks occurred within 24 hours of their main shocks most aftershocks appear to be occurring on a fault plane with the same or similar orientation to the fault that ruptured in the main shock at or slightly above the main shock depth the average magnitude difference between main shocks and their largest aftershocks is 1 03 0 47 the difference between main shock and aftershock magnitude appears to decrease with increasing heat flow sixty percent of the aftershocks occurred within 24 hours of their main shocks but nearly one third occurred more than 1 week after their main shocks

the evolution of the gulf of corinth greece an aftershock study of the 1981 earthquakes summary a preliminary study of the aftershocks of three earthquakes that occurred near to corinth greece in 1981 is combined with observations of the morphology and faulting to understand the evolution of the eastern gulf of corinth the well located aftershocks form a zone 60km long and 20km wide they do not lie on the main fault planes and are mostly located between the north dipping faulting on which the first two earthquakes occurred and the south dipping faulting associated with the third event a cluster of aftershocks also lies in the footwall of the eastern end of the south dipping fault of the third event morphologically it is observed that in the evolution of the eastern gulf of corinth antithetic faulting apparently predates the appearance of the main faulting at the surface this evolution can be explained by motion on a deep seated shallow angle aseismic normal fault a model based on such a fault also accounts for the aftershock distribution of the 1981 earthquakes

the incidence and nature of bedload transport during flood flows in coarse grained alluvial channels a continuous record reveals that the incidence of bedload in a coarse grained river channel changes from flood to flood long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood wave but when floods follow each other closely the bed material is comparatively loose and offers less resistance to entrainment in this case substantial amounts of bedload are generated on the rising limb this is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season this produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse grained channels besides this the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion this adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory bedload is shown to be characterized by a series of pulses with a mean periodicity of 1 7 hours in the absence of migrating bedforms it is speculated that this well documented pattern reflects the passage of kinematic waves of particles in a slow moving traction carpet the general pattern of bedload including pulsations is shown to occur more or less synchronously at different points across the stream channel

coarse sediment transport in mountain streams in colorado and wyoming usa since the early 1990s us forest service researchers have made thousands of bedload measurements in steep coarse grained channels in colorado and wyoming usa in this paper we use data from 19 of those sites to characterize patterns and rates of coarse sediment transport for a range of channel types and sizes including step pool plane bed pool riffle and near braided channels this effort builds upon previous work where we applied a piecewise regression model to 1 relate flow to rates of bedload transport and 2 define phases of transport in coarse grained channels earlier the model was tested using bedload data from eight sites on the fraser experimental forest near fraser colorado the analysis showed good application to those data and to data from four supplementary channels to which the procedure was applied the earlier results were however derived from data collected at sites that for the most part have quite similar geology and runoff regimes in this paper we evaluate further the application of piecewise regression to data from channels with a wider range of geomorphic conditions the results corroborate with those from the earlier work in that there is a relatively narrow range of discharges at which a substantial change in the nature of bedload transport occurs the transition from primarily low rates of sand transport phase i to higher rates of sand and coarse gravel transport phase ii occurs on average at about 80 per cent of the bankfull 1 5 year return interval discharge a comparison of grain sizes moved during the two phases showed that coarse gravel is rarely trapped in the samplers during phase i transport moreover the movement and capture of the d16 to d25 grain size of the bed surface seems to correspond with the onset of phase ii transport particularly in systems with largely static channel surfaces however while there were many similarities in observed patterns of bedload transport at the 19 studied sites each had its own bedload signal in that the rate and size of materials transported largely reflected the nature of flow and sediment particular to that system published in 2005 by john wiley sons ltd