evidence for prehistoric earthquakes on the superstition hills fault from offset geomorphic features offset geomorphic features along the superstition hills fault show evidence for at least one slip event prior to the 1987 surface rupture and possibly as many as four to five earlier prehistoric earthquakes we documented several geomorphic features that appeared offset by multiple events by making detailed topographic maps offset features were abundant along reaches of the fault with high topographic relief and large displacement slip distribution for the penultimate event as recorded by offset rills streams and shrub coppice dunes is very similar to the slip distribution from the 1987 earthquake through april 1988 this similarity may prove to be fortuitous if afterslip from the 1987 event continues to increase the total slip for this earthquake but if afterslip associated with the 1987 event ceases in the near future then the past two earthquakes were nearly identical in slip and the superstition hills fault may be expected to produce characteristic earthquakes of roughly magnitude 6

erosion caused by hyperconcentrated flow on the loess plateau of china abstract hyperconcentrated flows are widely observed in the middle yellow river basin they occur as a result of erosion but once they form on slopes they operate as a strong eroding and sediment carrying force and play an important role in drainage basin erosion and sediment production processes since the energy expenditure is less and sediment carrying capacity is greater hyperconcentrated flows have very high eroding and transporting abilities there exists a strong coupling relation between hyperconcentrated flow transport and gravitational erosion which ensures a rapid removal of mass wasted materials hyperconcentrated flows are an important factor responsible for the high intensity erosion and sediment yield in the middle yellow river basin many previous studies have indicated that the sediment delivery ratio on the loess plateau approaches 1 this can be explained by the action of hyperconcentrated flows as hyperconcentrated flows exhibit some particular behaviors in erosion and sediment production processes the present study suggests that the erosion by hyperconcentrated flows be regarded as a special type of erosion accordingly some countermeasures are proposed to control hyperconcentrated flows and the resulting erosion

surface displacement on the imperial and superstition hills faults triggered by the westmorland california earthquake of 26 april 1981 parts of the imperial and the superstition hills faults moved right laterally at the ground surface at the time of or shortly following the ml 5 6 westmorland earthquake of 26 april 1981 the displacements probably occurred before any significant aftershocks on either fault and thus are classed as triggered slips although the main shock was located in an exceptionally seismogenic part of imperial valley about 20 km distant from either fault no clear evidence of past surface faulting is known in the epicentral area horizontal displacement on the imperial and superstition hills faults southeast and southwest of the epicenter respectively reached maxima of 8 and 14 mm and the discontinuous surface ruptures formed along approximately equal lengths of northern segments of the two structures 16 8 and 15 7 km respectively the maximum vertical component of slip measured on surface cracks on the imperial fault 6 mm was located on the west side of mesquite basin near harris road leveling data at harris road suggest slightly larger vertical movement at the surface there fault dislocation modeling of this leveling data further suggests that the maximum shallow subsurface dip slip component of the triggered movement was as much a factor of 4 larger than that measured at the fault trace the map pattern of the rupture may reveal the principal strand among the several near the north end of the imperial fault no surface displacement was found along traces of the brawley fault zone the san andreas fault or the part of the coyote creek fault that slipped during the 1968 borrego mountain earthquake ground search in the epicentral area of the main shock and in the widely dispersed aftershock region in northern imperial valley failed to locate any definite evidence of new surface faulting

three dimensional records of surface displacement on the superstition hills fault zone associated with the earthquakes of 24 november 1987 seven quadrilaterals constructed at broadly distributed points on surface breaks within the superstition hills fault zone were repeatedly remeasured after the pair of 24 november 1987 earthquakes to monitor the growing surface displacement changes in the dimensions of the quadrilaterals are recalculated to right lateral and extensional components at millimeter resolution and vertical components of change are resolved at 0 2 mm precision the displacement component data for four of the seven quadrilaterals record the complete fault movement with respect to an october 1986 base these data fit with remarkable agreement the power law u t u f b t 1 b t c where u t is a displacement component at time t after the second main shock and uf b and c are constants this power law permits estimation of the final displacement uf from the data obtained within the period of observation data from one quadrilateral located near the epicenter of the second main shock and northeast trending conjugate faults allow that about 5 cm of right lateral slip may have been associated with the first main shock there data from the other quadrilaterals confirm that the surface faulting on most of the superstition hills fault zone did initiate at the time of the second main shock of the 1987 earthquakes the three dimensional motion vectors all describe nearly linear trajectories throughout the observation period and they indicate smooth shearing on their respective fault surfaces the inclination of the shear surfaces is generally nearly vertical except near the south end of the superstition hills fault zone where two strands dip northeastward at about 70 surface displacement on these strands is right reverse another kind of deformation superimposed on the fault displacements has been recorded at all quadrilateral sites it consists of a northwest southeast contraction or component of contraction that ranged from 0 to 0 1 per cent of the quadrilateral lengths between november 1987 and april 1988

production storage and output of coarse upland sediments natural and artificial influences as revealed by research catchment studies rates of sediment production in uk river basins are generally low however upland source areas control both runoff and sediment volumes to he routed through larger basins and there are indications that development pressures on land in upland areas have far reaching implications output rates for bedload from semi natural grassland and commercially afforested catchments are now available for a ten year period at the plynlimon catchments mid wales the influence of forestry drainage practice is to increase bedload yields sixfold suspended load yields are doubled in an attempt to predict yields and to investigate the operation of storage and transport processes on bedload a regression analysis was conducted using the weight of bedload trapped as a dependent variable and selected climatic supply and transport factors as independent variables the climatic supply factors chosen are shown to have little influence on yield relative to transport factors despite evidence of supply limited yields tracer studies indicate that channel storage of material exercises a critical control on yield a factor which is not accommodated by the climate based supply indices implications for field measurement techniques are discussed

long term morphodynamic changes of a desert reach of the yellow river following upstream large reservoirs operation abstract china s yellow river has experienced its dramatically decreasing trend for the flow discharge since the construction and operation of large reservoirs located upstream this low flow regulation has triggered a severe aggradation of the ulan buh desert channel of the yellow river because the declining flow exhibits no capability to scour and carry away large amount input of desert sands from the ulan buh desert twenty monitoring cross sections documented the ulan buh desert channel has experienced its increasing aggradational trend in conjunction with its lateral migration decreasing trend from 1966 to 2005 which is opposite to the normal pattern of aggradation with deepening or symmetrical infilling for a channel located downstream of a reservoir the channel aggradation can also be identified two stages slow aggradation and rapid aggradation slow aggradation is characterized by the channel bed elevation rising 9 5 cm on average between 1968 and 1985 which responded to the operation of the liujiaxia reservoir during this period the flow discharge was similar to pre dam flow conditions but the sediment transport reduced to half of its pre dam value because of about 0 24 108 t of desert sands entering the channel from the ulan buh desert annually this dilute flow indicated not to scour the channel as expected but contrarily to cause the channel aggraded rapid aggradation followed completion of the longyangxia reservoir with the channel bed elevation rising by 73 cm on average between 1986 and 2005 in this period the combined regulation of liujiaxia and longyangxia reservoirs has caused the flow discharge decreasing dramatically which is more beneficial for accumulation of the desert sands 0 19 108 t yr 1 on average in the desert channel and led to the channel aggradation rate accelerated rapidly

the impact of refraction correction on leveling interpretations in southern california recent investigations show that the refraction corrections in leveling are large but can be adequately modeled the corrections are proportional to the temperature differences and the square of the sight lengths changes in sight length with time have resulted in apparent crustal movements when non refraction corrected data were used applying refraction corrections to leveling data in southern california significantly alters the size and configuration of the southern california uplift uplift at palmdale and gorman lebec relative to los angeles bm v32 during the 1953 1978 time period is no greater than 10 cm the bulk of the motion about 6 cm occurs as localized motion along the san gabriel fault during the 1953 1964 time period this motion along the san gabriel fault and uplift of 8 cm directly north of the san fernando fault between 1955 and 1968 may represent precursors to the 1971 san fernando earthquake

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

the superstition hills california earthquakes of 24 november 1987 the 24 november 1987 superstition hills earthquakes occurred on the conjugate northwest striking right lateral superstition hills fault and a previously unknown northeast striking left lateral structure defined by a lineation of hypocenters extending from the superstition hills fault to the brawley seismic zone master event locations of the earthquakes using caltech usgs seismic network data reveal the following the first main shock 33 4 9 n 115 47 7 h 10 6 km m s 6 2 0154 gmt on the northeast striking structure and its foreshocks co locate events on the northeast structure cluster in space and time and some aftershocks occur in the brawley seismic zone the second main shock 33 0 9 n 115 50 9 w h 1 9 km m s 6 6 1315 gmt on the superstition hills fault was 12 hr after the first main shock and initiated at shallow depth where the two trends join aftershocks of the second main shock lie in a northwest trend between the superstition hills and superstition mountain faults and have a sharply defined western edge the extent of the northwest trend aftershocks is not coincident with surface rupture on the superstition hills fault in general the earthquakes in the northeast trend are deep and the earthquakes in the northwest trend are shallow we compare the earthquake distribution to the distribution of crystalline basement rocks defined from a refraction study of fuis et al 1982 the earthquake locations and extent of aftershock activity appear to be controlled by the presence of crystalline basement rocks

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

recent plate motions and crustal deformation reports by u s workers on geodetic measurements of recent plate motions or crustal deformation published in 1987 1990 are reviewed the review begins with global plate motions proceeds through plate boundaries in california alaska and the pacific northwest and finishes with volcanic phenomena monument stability and longevity and gps relative position measurements 184 refs

possibility of biases in the estimation of earthquake recurrence and seismic hazard from geologic data abstract aseismic deformation is an integral part of the earthquake process and may lead to systematic biases in the estimation of earthquake size recurrence and attendant strong ground motions in seismic hazard analyses founded on the geologic description of the locations lengths and slip rates of active faults observations are reviewed and presented to suggest that large earthquakes systematically rupture to increasingly greater depths below the seismogenic layer and that the portion of slip on faults accommodated by aseismic processes may be inversely related to the length of rupture expected to occur on them if so the expected seismic moment per unit area of earthquakes on mapped faults may be systematically overestimated as a function of rupture length when derived from regressions of seismic moment and aftershock area and estimates of seismic moment rate derived from geologic measures of fault offset might be systematically overestimated as an inverse function of the length of rupture expected to recur on a fault

double thresholds in scour fill processes and some implications in channel adjustment abstract through an analysis of data collected from the yellow river and its tributaries on the loess plateau of china the phenomenon of double thresholds in scour fill processes of wide range water sediment two phase flows has been shown thresholds located in non hyperconcentrated flows may be called the lower threshold and that in hyperconcentrated flows the upper threshold this double threshold phenomenon leads to complicated sediment transport behavior of heavily sediment laden rivers with an increase in suspended sediment concentration the channel sediment delivery ratio increases initially and becomes higher than 1 followed by a decrease and finally becomes lower than 1 again controlled by the double thresholds in the scour fill processes channel adjustment of the lower yellow river is non linear and complex when the suspended concentrations were lower than the lower threshold or higher than the upper threshold scour or bed downcutting was the dominant channel forming process channel shape tends to be narrower and deeper and the channel thalweg became more sinuous when the suspended concentrations lay between the lower and upper thresholds deposition of sediment was the dominant channel forming process channel shape tended to be shallower and wider and channel thalweg became less sinuous

fault slip in southern california measurements of slip on major faults in southern california have been performed over the past 18 yr using principally theodolite alignment arrays and tautwire extensometers they provide geodetic control within a few hundred meters of the fault traces which complements measurements made by other techniques at larger distances approximately constant slip rates of from 0 5 to 5 mm yr over periods of several years have been found for the southwestern portion of the garlock fault the banning and san andreas faults in the coachella valley the coyote creek fault the superstition hills fault and an unnamed fault 20 km west of el centro these slip rates are typically an order of magnitude below displacement rates that have been geodetically measured between points at greater distances from the fault traces exponentially decaying postseismic slip in the horizontal and vertical directions due to the 1979 imperial valley earthquake has been measured it is similar in magnitude to the coseismic displacements analysis of seismic activity adjacent to slipping faults has shown that accumulated seismic moment is insufficient to explain either the constant or the decaying postseismic slip thus the mechanism of motion may differ from that of slipping faults in central california which move at rates close to the plate motion and are accompanied by sufficient seismic moment seismic activity removed from the slipping faults in southern california may be driving their relatively aseismic motion

the elmore ranch and superstition hills earthquakes of 24 november 1987 introduction to the special issue on 24 november 1987 two significant earthquakes occurred along the southern san jacinto fault zone and related structural elements in southern california not far from the international border these two events the elmore ranch earthquake m 6 2 at 0154 gmt and the superstition hills earthquake m 6 6 at 1315 gmt both moment magnitudes from sipkin 1989 and their aftershocks have yielded a rich harvest of geological seismological and engineering data pertinent to the cause and effect of earthquakes in this region where the southern san jacinto fault zone enters the salton depression from the peninsula ranges bordering it on the southwest fig 1 this special issue of the bulletin presents 18 geologic and seismologic investigations of these earthquakes a collection of papers born in el centro california on 8 and 9 february 1988 at a meeting attended by approximately 60 scientists interested in these earthquakes for one reason or another

bulk friction modeling of afterslip and the modified omori law abstract afterslip data from the superstition hills fault in southern california a creep event on the same fault the modified omori law and cumulative moments from aftershocks of the 1957 aleutian islands earthquake all indicate that the original formulation by dieterich 1981 constitutive properties of faults with simulated gouge agu geophys monogr 24 103 120 for friction evolution is more appropriate for systems far from instability than the commonly used approximation developed by ruina 1983 slip instability and state variable friction laws j geophys res 88 10359 10370 to study instability the mathematical framework we use to test the friction models is a one dimensional massless spring slider under the simplifying assumption proposed by scholz 1990 the mechanics of earthquakes and faulting cambridge university press and used by marone et al 1991 on the mechanics of earthquake afterslip j geophys res 96 8441 8452 that the state variable takes on its velocity dependent steady state value throughout motion in response to a step in stress this assumption removes explicit state variable dependence from the model obviating the need to consider state variable evolution equations anti derivatives of the modified omori law fit our data very well and are very good approximate solutions to our model equations a plausible friction model with omori law solutions used by wesson 1988 dynamics of fault creep j geophys res 93 8929 8951 to model fault creep and generalized by rice 1983 constitutive relations for fault slip and earthquake instabilities pure appl geophys 121 443 475 to a rate and state variable friction model yields exactly omori s law with exponents greater than 1 but yields unstable solutions for omori exponents less than 1 we estimate from the dieterich formulation the dimensionless parameter a which is equal to the product of the nominal coefficient of friction and the more commonly reported friction parameter a we find that a is typically positive qualitatively consistent with laboratory observations although our observations are considerably larger than laboratory values however we also find good model fits for a when data correspond to omori exponents less than 1 a modification of the stability analysis by rice and ruina 1983 stability of steady frictional slipping j appl mech 50 343 349 indicates that a is not a consequence of our assumption regarding state variable evolution a consistent interpretation of a in terms of laboratory models appears to be that the data are from later portions of processes better characterized by two state variable friction models a is explained by assuming that our data cannot resolve the co seismic evolution of a short length scale state variable to a velocity weakening state our parameterization leads to an apparent negative instantaneous viscosity we estimate the largest critical slip distance associated with afterslip to be 1 10 cm consistent with other estimates for near surface materials we assume that our observed large values for a reflect the fact that our model ignores the geometrical complexities of three dimensional stresses in fractured crustal materials around a fault zone with frictional stresses that vary on a fault surface our one dimensional model parameters reflect spatially averaged bulk stress and frictional properties of a fault zone where we clearly cannot specify the details of the averaging process our analysis of omori s law suggests that bulk frictional properties of a fault zone are well described by our simple laboratory based models but they would need to change during the seismic cycle for a mainshock instability to recur unless a mainshock aftershock sequence were characterized by a process similar to the arrested instabilities possible in two state variable systems

a silent mw 4 7 slip event of october 2006 on the superstition hills fault southern california 1 during october 2006 the 20 km long superstition hills fault shf in the salton trough southern california slipped aseismically producing a maximum offset of 27 mm as recorded by a creepmeter we investigate this creep event as well as the spatial and temporal variations in slip history since 1992 using ers 1 2 and envisat satellite data during a 15 year period steady creep is punctuated by at least three events the first two events were dynamically triggered by the 1992 landers and 1999 hector mine earthquakes in contrast there is no obvious triggering mechanism for the october 2006 event field measurements of fault offset after the 1999 and 2006 events are in good agreement with the interferometric synthetic aperture radar data indicating that creep occurred along the 20 km long fault above 4 km depth with most of the slip occurring at the surface the moment released during this event is equivalent to a mw 4 7 earthquake this event produced no detectable aftershocks and was not recorded by the continuous gps stations that were 9 km away modeling of the long term creep from 1992 to 2007 creep using stacked ers 1 2 interferograms also shows a maximum creep depth of 2 4 km with slip tapering with depth considering that the sediment thickness varies between 3 km and 5 km along the shf our results are consistent with previous studies suggesting that shallow creep is controlled by sediment depth perhaps due to high pore pressures in the unconsolidated sediments

probabilistic estimates of surface coseismic slip and afterslip for hayward fault earthquakes we examine the partition of long term geologic slip on the hayward fault into interseismic creep coseismic slip and afterslip using monte carlo simulations we compute expected coseismic slip and afterslip at three alinement array sites for hayward fault earthquakes with nominal moment magnitudes ranging from about 6 5 to 7 1 we consider how interseismic creep might affect the coseismic slip distribution as well as the variability in locations of large and small slip patches and the magnitude of an earthquake for a given rupture area we calibrate the estimates to be consistent with the ratio of interseismic creep rate at the alinement array sites to the geologic slip rate for the hayward fault we find that the coseismic slip at the surface is expected to comprise only a small fraction of the long term geologic slip the median values of coseismic slip are less than 0 2 m in nearly all cases as a result of the influence of interseismic creep and afterslip however afterslip makes a substantial contribution to the long term geologic slip and may be responsible for up to 0 5 1 5 m median plus one standard deviation s d of additional slip following an earthquake rupture thus utility and transportation infrastructure could be severely impacted by afterslip in the hours and days following a large earthquake on the hayward fault that generated little coseismic slip inherent spatial variability in earthquake slip combined with the uncertainty in how interseismic creep affects coseismic slip results in large uncertainties in these slip estimates

experimental analysis of slip distribution along a fault segment under stick slip and stable sliding conditions abstract this paper presents the results of an experimental study of slip distribution along fault models with different sliding surface morphologies submitted to various orientations of fault and loading direction uniaxial compression tests were done on pmma plates to measure the relative displacement of markers perpendicular to the sliding surfaces slip distribution profiles were then constructed for different stages of shortening of the samples it was shown that fault morphology determines both the sliding regime and the slip distribution along the sliding surfaces along fault models with grounded surfaces fmgs stable sliding giving a symmetrical smooth distribution was observed for fault models with natural fracture surfaces fmns stick slip was observed in this case the slip distribution exhibited significant irregularities in a generally symmetrical profile analysis of this profile enabled four types of local slip behaviour to be identified which may provide a physical basis for the interpretation of coseismic slip distributions the local slip behaviours were interpreted in terms of interaction of irregular asperities and helped understand the discrepancy observed between theoretical slip distributions and the displacement measured along the active faults analysis of the slip distribution profiles along the fmgs and the fmns also showed that they evolved systematically after the appearance of branching for a large amount of shortening mode i branching was observed at the tips of the sliding surfaces after its development the global amount of slip along the faults increased and the slip gradient between the centre and the tips of the faults decreased this effect is consistent with numerical modelling studies finally the observed profiles were compared with the linear the tapered and the elliptic theoretical models using two different procedures we conclude that in the case of the fmns where the sliding surface topography is complex no model could correctly describe the slip distribution and that in both cases of fmns and fmgs branching caused a change in the shape of the slip distribution profiles

surface slip subsequent to the 24 november 1987 superstition hills california earthquake monitored by digital creepmeters three creepmeters of new design were operated on the superstition hills fault following the 24 november 1987 earthquake each creepmeter consists of a digital displacement sensor interrogated periodically by a computer at the end of each hour the computer determines a recording rate appropriate to the velocity of the slip on the fault in that hour no data are recorded if the fault is inactive data are recorded at a maximum rate of one sample per minute if slip on the fault is detected the resolution and range of the creepmeters are 10 m and 15 cm respectively fault activity is observed to be confined to periods of episodic slip creep events with mean amplitudes 3 to 6 mm and durations less than 4 hr a total of 80 creep events were recorded during the first week following the earthquake creep events occurred several times each day after 6 months events occurred every 3 weeks this increase in the mean time interval between creep events results in the observed decay in afterslip rate between creep events the fault is inactive although more than 200 microstrain of fault zone deformation may accumulate before each event although creep events were observed to propagate unilaterally in both directions along the fault the most impulsive events appeared to propagate bilaterally from a dilatant offset separating the northern and southern halves of the 24 km long fault zone maximum propagation velocities of 30 m sec were observed aftershocks 2 m 4 7 were observed to occur near the creepmeters following 6 to 9 cm of surface slip on the fault a future aftershock in this region is anticipated in mid 1989 based on afterslip rates in the year following the main shock

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

the greenville fault preliminary estimates of its long term creep rate and seismic potential abstract once assumed to be locked we show that the northern third of the greenville fault gf creeps at 2 mm yr based on 47 yr of trilateration net data this northern gf creep rate equals its 11 ka slip rate suggesting a low strain accumulation rate in 1980 the gf easternmost strand of the san andreas fault system east of san francisco bay produced an m w 5 8 earthquake with a 6 km surface rupture and dextral slip growing to 2 cm on cracks over a few weeks trilateration shows a 10 cm post 1980 transient slip ending in 1984 analysis of 2000 2012 crustal velocities on continuous global positioning system stations allows creep rates of 2 mm yr on the northern gf 0 1 mm yr on the central gf and 0 mm yr on its southern third modeled depth ranges of creep along the gf allow 5 25 aseismic release greater locking in the southern two thirds of the gf is consistent with paleoseismic evidence there for large late holocene ruptures because the gf lacks large 1 km discontinuities likely to arrest higher 1 m slip ruptures we expect full length 54 km ruptures to occur that include the northern creeping zone we estimate sufficient strain accumulation on the entire gf to produce m w 6 9 earthquakes with a mean recurrence of 575 yr while the creeping 16 km northern part has the potential to produce an m w 6 2 event in 240 yr it may rupture in both moderate 1980 and large events these two dimensional model estimates of creep rate along the southern gf need verification with small aperture surveys online material green net data file

rheology heterogeneities on fault surfaces inferred from the time history of afterslip events a model of shallow afterslip on transcurrent vertical faults is presented the creeping region is represented with a 2 d quasi static crack open to the earth surface the fault gouge is treated as a viscoplastic layer with vertically heterogeneous bingham rheology and a deep earthquake is assumed to generate a two level stress distribution on the fault plane in the deeper level the stress drops to values less than the plastic threshold of the fault gouge while in the shallower level the earthquake concentrates stress to values greater than the plastic threshold in this region aseismic slip takes place initially the creeping region is assumed to extend from the earth surface to the depth of transition between stress levels but subsequently it penetrates deeper thanks to the stress concentration created by the crack beyond its tip slip at the earth surface is computed for some stress drop distributions and viscosity profiles and the results are compared with afterslip observations on three california faults the whole evolution is sensibly affected by the initial stress profile variations mainly because the crack gradually extends to increasing depths the initial part of the evolution is also affected by the viscosity profile assumed on the fault plane in particular the advanced phase of the evolution is not affected by a shallow region with low viscosity on the fault plane the fast relaxation of this region in fact provides a quick displacement superimposed from the beginning on a slip evolution very similar to that with a uniform viscosity after removal from the data of this initial displacement treated as a free parameter since it is not well constrained from data themselves a suitable choice of the stress parameter values gives a good reproduction of the data in all the cases analysed even if a uniform viscosity on the fault plane is assumed in all the analysed cases these parameter values are consistent with a temporal deepening of the creeping region even if the computed displacement at the earth surface along a direction orthogonal to the fault strike is scarcely sensitive to maximum depth of creep

dynamics of fault creep observations along the surface traces of active faults in california and elsewhere indicate that tectonic displacement can occur as seismic slip or as aseismic fault creep fault creep occurs as secular displacement and as displacement episodes called creep events which last a few hours to days and include from a millimeter or less to a few tens of millimeters of displacement instrumental measurements of displacement versus time during creep events show that many events have a characteristic simple form including a steep beginning followed by a gradual decay in the rate of displacement some creep events display small amounts of precursory slip and many seem to be composed of several discrete simple events propagation of creep events along the san andreas calaveras and imperial faults in california has been inferred from the nearly simultaneous observation of creep events at nearby creepmeters and from kinematic modeling of continuous measurements of strain during creep events fault creep can be viewed as arising from the interplay of three factors stress applied to the fault from external sources stress caused by the geometry and distribution of displacement on the fault arising from the elastic response of the surrounding medium to the displacements within the anelastic fault zone itself and the constitutive relations characterizing the resistance to slip on the fault analytic solutions are presented for a simple rectangular dislocation quasi static model of nonpropagating fault creep assuming viscous and quasi plastic power law creep fault zone rheology and for a multi element composed of several rectangular or striplike dislocation surfaces quasi static model assuming a viscous rheology viscous rheology implies solutions composed of exponentials that decay with time the simple one element quasi plastic model is in agreement with the form of creep events observed at melendy ranch california a matrix formulation is presented to calculate dislocation stresses on a fault zone in a half space or plate the formulation involves the division of the dislocation surface into strips or rectangles and the use of published solutions to calculate the stress resulting from displacement on each individual element results from the matrix method agree with analytic results for equilibrium displacements on stress free cracks the matrix formulation is then used as the basis for a numerical method to simulate one and two dimensional propagating creep assuming a quasi plastic rheology on the fault zone results from this method agree reasonably well with observations of afterslip from the 1966 parkfield 1975 oroville and 1979 imperial valley california earthquakes and of a propagating creep event observed along the southern calaveras fault central california during july 1977 this method of analysis and the assumption that creep at each point on the fault zone follows a power law rheology after the applied stress reaches a spatially varying yield stress can explain the secular and episodic nature of fault creep afterslip the simple shape of some individual events and the multiple composite shape of others and the propagation of creep events on the southern calaveras fault observations of propagating creep indicate a yield stress near zero at the surface and throughout much of the fault zone however they also indicate the presence of a zone at a depth of about 0 5 km and about 5 km long with a yield stress of about 15 bars 1 5 mpa the methods of solution presented here should be applicable to many problems in the dynamics of faulting

long term creep rates on the hayward fault evidence for controls on the size and frequency of large earthquakes the hayward fault hf in california exhibits large m w 6 5 7 1 earthquakes with short recurrence times 161 65 yr probably kept short by a 26 78 aseismic release rate including postseismic its interseismic release rate varies locally over time as we infer from many decades of surface creep data earliest estimates of creep rate primarily from infrequent surveys of offset cultural features revealed distinct spatial variation in rates along the fault but no detectable temporal variation since the 1989 m w 6 9 loma prieta earthquake lpe monitoring on 32 alinement arrays and 5 creepmeters has greatly improved the spatial and temporal resolution of creep rate we now identify significant temporal variations mostly associated with local and regional earthquakes the largest rate change was a 6 yr cessation of creep along a 5 km length near the south end of the hf attributed to a regional stress drop from the lpe ending in 1996 with a 2 cm creep event north of there near union city starting in 1991 rates apparently increased by 25 above pre lpe levels on a 16 km long reach of the fault near oakland in 2007 an m w 4 2 earthquake initiated a 1 2 cm creep event extending 10 15 km along the fault using new better constrained long term creep rates we updated earlier estimates of depth to locking along the hf the locking depths outline a single 50 km long locked or retarded patch with the potential for an m w 6 8 event equaling the 1868 hf earthquake we propose that this inferred patch regulates the size and frequency of large earthquakes on hf online material 2007 event creep models plots of creepmeter data maps and cross sections of relocated microearthquakes and active fault traces and iterative solutions for depth of creep

an approximation of the sediment budget of the lower mississippi river prior to major human modification a sediment budget is constructed for the lower mississippi river prior to the introduction of most human modifications components of the budget are derived from historical data including mississippi river commission hydrographic survey maps for the period from 1877 to 1924 a quantitative estimate of major sediment sources sinks and storage locations in the lower mississippi valley suggest that the most important sediment source was from bank caving and that at least 50 per cent more sediment was deposited in short term channel storage than in longer term overbank storage the budget indicates that the proportion of sediment transported as bedload was significantly greater than previously estimated the magnitude and variability of these sediment budget components are discussed the results of the study suggest that prior to modifications the river was aggrading over much of its length

fluvial sediment budget of a mediterranean river the lower tordera catalan coastal ranges ne spain abstract the lower tordera river is a representative case of water and sediment dynamics and uses in a large river in the western mediterranean region along the study reach the fluvial regime of the river changes shifting from a perennial water and sediment circulation in the upper parts to an ephemeral flow pattern in the lower sections the fluvial sediment budget of the lower tordera was estimated based on field measurements of suspended and bedload and a survey of cross sections field data were obtained between january 1997 and june 1999 a period that was dryer than the average most sediment is transported as bedload more than 3 4 of the total load both at the entrance section of the river reach and at the outlet section close to the mediterranean sea a total of 156 700 tonnes of sediment 62 680 tonnes year entered the system mostly during discharges below bankfull while 107 000 tonnes 42 800 tonnes year were exported to the sea almost exclusively during floods the net accumulation of sediment was 14 600 tonnes per year as bedload especially during the dry years of 1998 and 1999 when small floods circulated through the upper sections but did not reach the lowermost part of the river as a consequence a mean aggradation of the riverbed of around 6 8 mm year has occurred a figure that has been corroborated after the analysis of a series of cross sections residence time of sediment in the perennial reach calculated at a long term ranges from 6 years for sediments in the active base flow channel to 164 years for sediment placed above bankfull level which is only entrained during high flows residence time of sediment in the ephemeral reach calculated for the period 1997 1999 is only slightly higher than that of the perennial part of the river this fact can be related to the current adjustment of the river system to historical mining the riverbed is slowly adjusting to the new conditions and important sedimentation is taking place in many upstream sections while erosion still occurs in the lowermost reaches thus causing the relatively low residence time of sediment

inverting measurements of surface slip on the superstition hills fault we derive and test a set of inversions of surface slip measurements based on the empirical relation u t uf 1 t t c proposed by sharp and saxton 1989 to estimate the final slip uf the power law exponent c and the power law duration t at short times sharp s relation behaves like the simple power law u t u 1 tc where u 1 is the initial slip that is the slip at 1 day after the earthquake at long times the slip approaches the final slip asymptotically the inversions are designed in part to exploit the accuracy of measurements of differential slip that is measurements of surface slip which are made relative to a set of nails or stakes emplaced after the earthquake we apply the inversions to slip measurements made at 53 sites along the superstition hills fault for the 11 months following the m 6 2 and 6 6 earthquakes of 24 november 1987 in general estimates of the initial slip and the power law exponent are well resolved while estimates of the power law durations and the final slip are less well resolved because the durations of the surface slip measurements are often less than the derived power law durations the slip on the three fault strands is a relatively smooth function of position the initial slip and final slip are well correlated the time dependence of surface slip at the 53 sites is roughly similar along the entire fault where the power law exponents are distributed as c 0 14 0 04 and the power law durations range from 100 t 1000 days

sediment storage in the reach of the middle yellow river located in the fenwei graben china fenwei graben is a famous sediment sink the longmen sanmexia sediment sink of middle yellow river is located in the middle part using the sediment budget based on annual data from the period 1920 2006 and flood event data from 154 flood events from the period 1950 1985 the variations in sediment storage release and transport have been analysed data from different methods and sources indicate that during an 1800 year period the variation of sedimentation rate in this sink has undergone a cycle from increase to decline the cause for this can be found in the changes in the manner and intensity of human activities over 87 years sediment storage in this sink can be separated into four stages which showed different trends depending on changing human activities such as reservoir construction soil and water conservation and water diversion stepwise multiple regression shows that the runoff and sediment yield from three major source areas have differing influences on sediment storage in the sink copyright c 2012 john wiley sons ltd

slip along the superstition hills fault associated with the 24 november 1987 superstition hills california earthquake surficial slip along the entire mapped length of the superstition hills fault in southern california occurred in association with the superstition hills earthquake m s 6 6 of 24 november 1987 we made repeated measurements of surface slip at 36 sites along the fault and occupied 64 sites at least once at our sites dextral slip was as high as 48 5 cm 1 day after the earthquake and 71 cm 2 months after the measurements show that slip during the period from hr to several hundred hr following the event is described by a simple power law of time extrapolation to t 1 min indicates that co seismic slippage ranged from 5 to 23 cm at 10 of our best recorded sites suggesting that finite co seismic slippage occurred along the length of the fault these extrapolations are supported by a measurement made at imler road 30 min after the shock measurements are complete through october 1988 at many sites the form of slip rate was decay changed from power law to a function of log time during the interval between 300 and 500 hr after the earthquake logarithmic slip rate decay in time was observed for a period of several yr after the parkfield borrego mountain and imperial valley earthquakes those measurements may have begun too late to resolve power law behavior at early times if current logarithmic behavior of the superstition hills fault persists right lateral slippage will approach 90 cm 10 yr after the rupture changes in the along fault displacement profile correlate well with geometric features including a fault bend and a major fault step moreover slip behavior appears to be correlated to the thickness of sedimentary cover along the fault also the northern half of the fault is bounded by a large block of continental crystalline basement the presence of this block may have contributed to the relatively uniform early slip behavior observed there

eureka peak fault afterslip following the 28 june 1992 landers earthquake abstract although surface ruptures of the principal landers faults apparently slipped co seismically surface slip on the 10 km long eureka peak fault has continued at a decreasing rate during the year following the mainshock three creepmeters installed on the fault as early as 4 days after the mainshock have recorded afterslip amplitudes of more than 8 cm on the northern half of the mapped fault the maximum observed slip 1 yr after the earthquake is 23 2 cm and an additional 1 to 3 cm of afterslip may occur on the fault in the next decade if the current rate of slip decrease remains steady should this occur it will bring surface slip amplitudes close to the 25 cm of slip inferred from geodetic data to have occurred at depth on the northern 4 km of the fault creepmeters on the fault record both episodic creep events and slow background slip but although changes in creep rate occur they do not correlate well with seismic moment release in volumes near the fault zone as is the case with many afterslip processes and other creeping faults in california the eureka peak fault cuts through sediments it is possible that such sedimentary layers and corresponding depths to which afterslip is occurring are relatively shallow or that the fault lacks a well developed gouge zone near sites where episodic creep is absent

surface faulting along the superstition hills fault zone and nearby faults associated with the earthquakes of 24 november 1987 the m 6 2 elmore desert ranch earthquake of 24 november 1987 was associated spatially and probably temporally with left lateral surface rupture on many northeast trending faults in and near the superstition hills in western imperial valley three curving discontinuous principal zones of rupture among these breaks extended northeastward from near the superstition hills fault zone as far as 9 km the maximum observed surface slip 12 5 cm was on the northern of the three the elmore ranch fault at a point near the epicenter twelve hours after the elmore ranch earthquake the m 6 6 superstition hills earthquake occurred near the northwest end of the right lateral superstition hills fault zone surface rupture associated with the second event occurred along three strands of the zone here named north and south strands of the superstition hills fault and the wienert fault for 27 km southeastward from the epicenter in contrast to the left lateral faulting which remained unchanged throughout the period of investigation the right lateral movement on the superstition hills fault zone continued to increase with time a behavior that was similar to other recent historical surface ruptures on northwest trending faults in the imperial valley region we measured displacements over 339 days at as many as 296 sites along the superstition hills fault zone and repeated measurements at 49 sites provided sufficient data to fit with a simple power law data for each of the 49 sites were used to compute longitudinal displacement profiles for 1 day and to estimate the final displacement that measured slips will approach asymptotically several years after the earthquakes the maximum right lateral slip at 1 day was about 50 cm near the south central part of the north strand of superstition hills fault and the predicted maximum final displacement is probably about 112 cm at imler road near the center of the south strand of the superstition hills fault the overall distributions of right lateral displacement at 1 day and the estimated final slip are nearly symmetrical about the midpoint of the surface rupture the average estimated final right lateral slip for the superstition hills fault zone is about 54 cm the average left lateral slip for the conjugate faults trending northeastward is about 23 cm the southernmost ruptured member of the superstition hills fault zone newly named the wienert fault extends the known length of the zone by about 4 km the southern half of this fault south of new river expressed only vertical displacement on a sinuous trace the maximum vertical slip by the end of the observation period there was about 25 cm but its growth had not ceased photolineaments southeast of the end of new surface rupture suggest continuation of the superstition hills fault zone in farmland toward mexico

high resolution mapping of near field deformation with airborne earth observation data a comparison study we present an investigation into different approaches for high resolution mapping of near field surface displacement for strike slip earthquakes airborne laser scanning als and optical imagery are two common sources of earth observation data available to geoscientists for earthquake documentation and studies optical image correlation and point cloud differencing techniques are among the most widely used methods for retrieving displacement signals in the near field we compare the performances of these techniques for estimating near field deformation using pre and postevent high resolution als and airborne imagery of the august 24 2014 mw 6 0 napa california earthquake estimates of deformation agree with field observations within a decimeter at the expected accuracy level of the data we show that the correlation of intensity images from als data can unveil the near field deformation successfully and outperforms optical image correlation in vegetated areas as well as in the absence of geodetic markers man made structures furthermore we illustrate that the point clouds generated with structure from motion perform comparably to als point clouds for retrieving the displacement signal in unvegetated areas overall we conclude that als data are generally better than imagery for estimating near field deformation regardless of the estimation methodology and that the iterative closest point algorithm was more effective at recovering the displacement signal

surface slip associated with the 2004 parkfield california earthquake measured on alinement arrays although still continuing surface slip from the 2004 parkfield earth quake as measured on alinement arrays appears to be approaching about 30 35 cm between parkfield and gold hill this includes slip along the main trace and the southwest fracture zone swfz slip here was higher in 1966 at about 40 cm the distribution of 2004 slip appears to have a shape similar to that of the 1966 event but final slip is expected to be lower in 2004 by about 3 15 cm even when continuing slip is accounted for proportionately this difference is most notable at the south end at highway 46 where the 1966 event slip was 13 cm compared to the 2004 slip of 4 cm continuous global positioning system and creepmeters suggest that significant surface coseismic slip apparently occurred mainly on the swfz and perhaps on middle mountain the latter possibly caused by shaking langbein et al 2005 creepmeters indicate only minor 0 2 cm surface coseismic slip occurred on the main trace between parkfield and gold hill we infer that 3 6 cm slip accumulated across our arrays in the first 24 hr at highway 46 slip appears complete whereas the remaining sites are expected to take 2 6 years to reach their background creep rates following the 1966 event afterslip at one site persisted as much as 5 10 years the much longer recurrence intervals between the past two parkfield earthquakes and the decreasing slip per event may suggest that larger slip deficits are now growing along the parkfield segment

contemporary plate motion and crustal deformation the measurement of relative plate velocities during the past few years is a signal accomplishment in earth science leading to refinement of the precepts of steady motion of plate interiors and cyclic deformation along plate margins regrettably deformation premonitory to an earthquake has yet to be detected with confidence delineation of the spatial and temporal buildup of strain between earthquakes however has put limits on models of the earthquake cycle a diverse set of fault structures and crustal rheologic conditions can explain the pattern of surface strain accumulation and release along strike slip faults in contrast the geometry of thrusts and normal faults revealed by earthquake deformation has been found to differ markedly from expectations geodetic observations have proved vital to monitor the ascent of magma through the earth s crust and to predict volcanic eruptions at the earth s surface episodic vertical and horizontal deformation in southern california remains a subject of dispute if anything it is less certain than it once seemed