characteristic slip for five great earthquakes along the fuyun fault in china the seismic hazard associated with an individual fault can be assessed from the distributions of slip and recurrence times of earthquakes however seismic cycle models 1 that aim to predict rupture lengths and fault displacements of successive earthquakes on one fault remain poorly validated it is therefore unknown whether individual fault segments rupture independently producing earthquakes with a diverse range of magnitudes and recurrence times or slip by characteristic amounts with characteristic magnitudes here we use highresolution satellite data to document the horizontal offsets of stream channels and terraces created by strike slip motion on the fuyun fault xinjiang china during five historical earthquakes we find that the ms 7 9 11 august 1931 earthquake produced a surface rupture with a length of 160 km dispersed over three different fault segments the 290 measured stream channel and terrace offsets record an average slip of 6 3 m we use the degree of preservation of geomorphological markers to assign relative ages to individual fault offsets and identify at least four distinct older earthquakes we find that these older earthquakes also produced fault offsets with a similar distribution to the 1931 earthquake as the slip distributions during five successive earthquakes were so similar we conclude that ruptures on the fuyun fault obey a characteristic slip model very few large earthquakes are known to have ruptured the same fault segment twice in historical or instrumental time 1 the

three dimensional excavation and recent rupture history along the cholame segment of the san andreas fault a paleoseismic study conducted along the cholame segment of the san andreas fault provides evidence for three earthquakes and the amount of lateral offset for the most recent event 1857 fort tejon earthquake excavations at the las yeguas ly4 site include five fault perpendicular two parallel and several hand dug trenches abruptly truncated sand and silt layers that are not correlative across the fault zone constrain the timing of the penultimate event l2 between cal a d 1030 1300 and 1390 1460 vertical offset shearing and fracturing of silty sand and gravel units that overlie l2 and historical artifacts that bracket the timing of the mre l1 provide evidence that the most recent ground rupturing event l1 occurred between cal a d 1390 1460 and 1865 l1 is likely the 1857 fort tejon earthquake tectonic silt filled fractures that dissect historic gray tan silt and sand suggest a ground shaking or a triggered slip event l0 which occurred after l1 three dimensional excavation of an alluvial fan edge unit 4 indicates that 3 0 0 70 m of near fault brittle slip occurred during the 1857 earthquake at this site

slip in the 1857 and earlier large earthquakes along the carrizo plain san andreas fault the moment magnitude mw 7 9 fort tejon earthquake of 1857 with a 350 kilometer long surface rupture was the most recent major earthquake along the south central san andreas fault california based on previous measurements of its surface slip distribution rupture along the 60 kilometer long carrizo segment was thought to control the recurrence of 1857 like earthquakes new high resolution topographic data show that the average slip along the carrizo segment during the 1857 event was 5 3 1 4 meters eliminating the core assumption for a linkage between carrizo segment rupture and recurrence of major earthquakes along the south central san andreas fault earthquake slip along the carrizo segment may recur in earthquake clusters with cumulative slip of 5 meters

evolution of stress in southern california for the past 200 years from coseismic postseismic and interseismic stress changes summary the seismicity of southern california results from stresses that arise from the relative motion of the pacific and north american plates being accommodated along the san andreas fault saf system and the eastern california shear zone ecsz here we calculate how the stress field in southern california has evolved over the past two centuries due to interseismic loading as inferred from current gps observations of surface velocities from redistributions of static stress induced by large m w 6 5 earthquakes since the 1812 wrightwood quake and postseismic viscoelastic relaxation associated with these events that serves to transfer coseismic stresses from the deep warm lower crust and upper mantle to the overlying seismogenic upper crust we calculate coulomb stress changes on vertical strike slip faults striking parallel to the saf and at the hypocenters on the rupture planes of all m w 6 events over the past two centuries our results suggest that the 1857 m w 8 2 fort tejon earthquake by far the largest event to have occurred in the region over the past two centuries had a profound influence on the state of stress in southern california during the 19th century inducing significant stress increases to the north parkfield region and adjoining creeping saf and south southern saf and san jacinto fault and stress relief across the southern ecsz these stress changes were then greatly magnified by postseismic relaxation through the early part of the 20th century slow interseismic build up of stress further loads all major strike slip faults and works to reload the areas of the ecsz where stress was relieved by the 1857 quake our calculations suggest that only 56 of hypocenters were pushed closer to failure by preceding coseismic stress changes suggesting that the occurrence of large earthquakes is not strongly determined by coseismic coulomb stress changes this percentage rises to 70 when postseismic stress changes are also considered our calculations demonstrate the importance of postseismic viscoelastic relaxation in the redistribution of stress following large earthquakes we find however that postseismic processes associated with events more than about a decade old are near completion and thus do not significantly influence the regional velocity field presently observed in southern california

evidence for large earthquakes on the san andreas fault at the wrightwood california paleoseismic site a d 500 to present we present structural and stratigraphic evidence from a paleoseismic site near wrightwood california for 14 large earthquakes that occurred on the southern san andreas fault during the past 1500 years in a network of 38 trenches and creek bank exposures we have exposed a composite section of interbedded debris flow deposits and thin peat layers more than 24 m thick fluvial deposits occur along the northern margin of the site the site is a 150 m wide zone of deformation bounded on the surface by a main fault zone along the northwest margin and a secondary fault zone to the southwest evidence for most of the 14 earthquakes occurs along structures within both zones we identify paleoearthquake horizons using in filled fissures scarps multiple rupture terminations and widespread folding and tilting of beds ages of stratigraphic units and earthquakes are constrained by historic data and 72 14c ages mostly from samples of peat and some from plant fibers wood pine cones and charcoal comparison of the long well resolved paleoseimic record at wrightwood with records at other sites along the fault indicates that rupture lengths of past earthquakes were at least 100 km long paleoseismic records at sites in the coachella valley suggest that each of the past five large earthquakes recorded there ruptured the fault at least as far northwest as wrightwood comparisons with event chronologies at pallett creek and sites to the northwest suggests that approximately the same part of the fault that ruptured in 1857 may also have failed in the early to mid sixteenth century and several other times during the past 1200 years records at pallett creek and pitman canyon suggest that in addition to the 14 earthquakes we document one and possibly two other large earthquakes ruptured the part of the fault including wrightwood since about a d 500 these observations and elapsed times that are significantly longer than mean recurrence intervals at wrightwood and sites to the southeast suggest that at least the southermost 200 km of the san andreas fault is near failure

propagation and termination of a strike slip fault in an extensional domain the westward growth of the north anatolian fault into the aegean sea abstract geometry and kinematics of the active submarine faults over the north aegean trough a complex and highly deforming boundary zone between the eurasian and the anatolian aegean micro plates were examined to investigate how a strike slip motion propagates through an extensional domain the bathymetric and seismic reflection data analysis show that the investigated area is affected from east to west by three sets of active faults striking ene wsw ne sw and wnw ese the ene wsw and ne sw striking faults are right lateral strike slip faults and are considered strands of the northern branch of the north anatolian fault into the north aegean sea the former set bounds the saros basin and the latter set occupies the eastern and central part of the sporades basin in the eastern and western parts of the north aegean trough respectively the wnw ese striking faults are normal low angle faults and develop at the western parts of the sporades basin it is suggested that the strike slip fault system advances westwards and when it reaches the 23 8 e meridian its right lateral motion is transferred to the wnw ese normal faults system forming a 70 km wide normal faulting zone through which the shear is distributed the interaction between the strike slip and normal faults probably started with the arrival of the northern branch of the north anatolian fault into the western part of the sporades basin since 430 ka bp marine isotopic stage 12 the described fault architecture and their spatial distribution in the north aegean trough are consistent with i the earthquake fault plane solutions and ii the stress and strain pattern prevailing across the area furthermore all these three provide evidence that the northern branch of the north anatolian fault terminates at the western end of the nat and does not continue to central greece

irregular recurrence of large earthquakes along the san andreas fault evidence from trees old trees growing along the san andreas fault near wrightwood california record in their annual ring width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813 paleoseismic data and historical information indicate that this event was the san juan capistrano earthquake of 8 december 1812 with a magnitude of 7 5 the discovery that at least 12 kilometers of the mojave segment of the san andreas fault ruptured in 1812 only 44 years before the great january 1857 rupture demonstrates that intervals between large earthquakes on this part of the fault are highly variable this variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of san andreas fault dynamics

1857 slip on the san andreas fault southeast of cholame california sieh and jahns 1984 forecasted that the next moderate parkfield earthquake might trigger a major earthquake along a fault segment greater than 30 km long southeast of cholame their forecast assumed 1 the slip was 3 4 m in 1857 and characteristic of the segment 2 a slip rate of 3 4 cm yr and 3 full strain release in earthquakes this study represents an independent measurement of channel offsets on 1 2400 scale low sun aerial photographs and by field investigation to estimate the amount of 1857 slip although rainfall is only moderate 30 cm yr few reliable offsets of less than 20 m persist here because cattle grazing and agricultural disking of soft sediments on the steep terrain greatly aggravate erosion reconstruction of offset geometry and size depends heavily on assumptions made about the post 1857 erosion most of the apparent 3 to 4 m offsets of sieh and jahns 1984 can also be measured as 2 to 3 m larger with equal or lower uncertainty the four offsets judged as most reliable range between 5 4 and 6 7 m and the 11 offsets of medium high reliability average 5 8 0 3 m data are too sparse and ambiguous to resolve details of the 1857 slip for this segment but it is distinctly less than the 9 m of the carrizo plain and more than the 3 4 m previously estimated further trenching may refine some measurements but probability calculations for a cholame segment earthquake must allow for large observer dependent uncertainty in the 1857 slip although the probability of an m 7 cholame event seems less than that suggested by a 3 5 m characteristic earthquake model it remains among the highest in the state

case studies of damage to tall steel moment frame buildings in southern california during large san andreas earthquakes on 9 january 1857 a large earthquake of magnitude 7 9 occurred on the san andreas fault with rupture initiating at parkfield in central california and propagating in a southeasterly direction over a distance of more than 360 km such a unilateral rupture produces significant directivity toward the san fernando and los angeles basins indeed newspaper reports of sloshing observed in the los angeles river point to long duration 1 2 min and long period 2 8 sec shaking if such an earthquake were to happen today it could impose significant seismic demand on present day tall buildings using state of the art computational tools in seismology and structural engineering validated using data from the 17 january 1994 magnitude 6 7 northridge earthquake we determine the damage to an existing and a new 18 story steel moment frame building in southern california due to ground motion from two hypothetical magnitude 7 9 earthquakes on the san andreas fault our study indicates that serious damage occurs in these buildings at many locations in the region in one of the two scenarios for a north to south rupture scenario the peak velocity is of the order of 1 m sec 1 in the los angeles basin including downtown los angeles and 2 m sec 1 in the san fernando valley while the peak displacements are of the order of 1 m and 2 m in the los angeles basin and san fernando valley respectively for a south to north rupture scenario the peak velocities and displacements are reduced by a factor of roughly 2

high resolution spatial rupture pattern of a multiphase flower structure rex hills nevada new insights on scarp evolution in complex topography based on 3 d laser scanning fault scarps represent the most obvious expression of tectonic activity at the earth9s surface studies on scarp morphology place constraints on fault kinematics and scarp degradation processes and were often based on geomorphic dating techniques fault scarps exposed in areas of simple topography facilitate data acquisition and interpretation whereas little work had been done where fault scarps are superimposed on complex dissected topography fault scarps developed in complex topography are commonly observed along flower structures and at tips of strike slip faults such structures are important elements for evaluating the evolution and linking of strike slip fault systems and appear to be scale independent from several meters to hundreds of kilometers we examined the detailed meter to hundred meter scale structure and surface expression of a flank of one fault scarp bounded pressure ridge rex hills flower structure by combining field mapping with high resolution digital elevation model dem analysis based on terrestrial laser scanning we generated a detailed dem and extracted high resolution topographic cross sections which enabled us to identify fault scarps and to determine their relative ages and geometry our study site is located on the transpressional left bend between the pahrump and amargosa segments of the dextral stateline fault system the topography is characterized by alternating valleys and ridges each 100 m long relief of 4 m we observed the following the southern rex hills slope exhibits three fault scarps related to three reverse fault branches the basal scarp scarp 1 is most continuous and exhibits five segments the upper two scarps scarps 2 and 3 are less continuous furthermore fault scarps exposed on ridge crests are more numerous up to four to five scarps and smaller 5 m high valleys often exhibit single large 10 m high smoothed scarps to easily detect differences between the scarps we evaluated the height and slope angle of the scarps using topographic cross sections our analysis indicates that scarp shape is influenced by fault dip lithology and degradation processes resulting in large scatter and broad overlap in scarp height slope angle space the analysis further indicates that scarp degradation is stronger in the valleys and that the preservation potential of small individual fault scarps is therefore greater on the ridge crests we compared our fault scarp data with published calibrated data yielding an age of 2 ka for the rex hills scarps consistent with an earlier finding this suggests that the scarp shape mainly reflects progressive degradation since the most recent surface rupture our approach of analyzing high resolution topographic data of closely spaced fault scarps is promising especially when combined with subsurface data as well as geochronological and paleoseismic data and it provides a basic scheme for analyzing scarp populations in a complex topographic region despite the absence of subsurface data our approach allowed the study of complex high resolution fault scarp morphologies across a flower structure for the first time

paleoseismic evidence of clustered earthquakes on the san andreas fault in the carrizo plain california exposures we have excavated across the san andreas fault contradict the hypothesis that part of the fault in the carrizo plain is unusually strong and experiences relatively infrequent rupture the exposures record evidence of at least seven surface rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in situ plants five large earthquakes have occurred since 1218 a d the most recent earthquake event a was the 1857 fort tejon earthquake which we have associated with 6 6 10 m of dextral slip along the main fault trace the penultimate earthquake event b most likely occurred within the period a d 1405 1510 slip from either events b and c combined or from event b alone totals 7 11 m three earthquakes events c d and e occurred in a temporal cluster prior to event b and after approximately a d 1218 the average recurrence interval within this cluster is 73 116 years depending on assumptions events f and g occurred after 200 years b c a depositional hiatus between events e and f may hide evidence of additional earthquakes events b and d within the carrizo cluster of a d 1218 1510 may correlate with events t a d 1329 1363 and v a d 1465 1495 at pallett creek on the mojave segment of the fault this suggests two fault ruptures similar in length to that of 1857 events c and e apparently did not rupture the mojave section which suggests that the carrizo segment has ruptured independently or in combination with segments to the north irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic supercycles

simulating gravity changes in topologically realistic driven earthquake fault systems first results currently gps and insar measurements are used to monitor deformation produced by slip on earthquake faults it has been suggested that another method to accomplish many of the same objectives would be through satellite based gravity measurements the gravity recovery and climate experiment grace mission has shown that it is possible to make detailed gravity measurements from space for climate dynamics and other purposes to build the groundwork for a more advanced satellite based gravity survey we must estimate the level of accuracy needed for precise estimation of fault slip in earthquakes we turn to numerical simulations of earthquake fault systems and use these to estimate gravity changes the current generation of virtual california vc simulates faults of any orientation dip and rake in this work we discuss these computations and the implications they have for accuracies needed for a dedicated gravity monitoring mission preliminary results are in agreement with previous results calculated from an older and simpler version of vc computed gravity changes are in the range of tens of gal over distances up to a few hundred kilometers near the detection threshold for grace

san andreas fault rupture scenarios from multiple paleoseismic records stringing pearls we present a new method to objectively combine paleoseismic event data from multiple sites into rupture scenarios and apply it to the southern san andreas fault ssaf of california first a pool is constructed of all ruptures between sites allowed by fault geometry and available event age probability distribution functions pdfs scenarios constructed by drawing from this pool are evaluated by the average quality of agreement event dating evidence by the degree of misfit of cumulative displacement over all ruptures compared to a prediction from the fault slip rate and elapsed time and by the number of events in the scenario three slip rate models from the 2008 working group on california earthquake probabilities wgcep were considered scenarios with full fault length ruptures tend to be inconsistent with low slip rates through the san bernardino and san gorgonio sections of the ssaf favorable scenarios tend to include 1857 like ruptures for three of the most recent five prehistoric ruptures in the northern half of the ssaf from carrizo to approximately wrightwood they also include one to two ruptures that involve the southern half of the ssaf but most earthquakes there appear shorter and exhibit less consistency from event to event by combining paleoseismic data into ensembles of scenarios and selecting viable scenarios using external constraints our method provides rupture histories useful for seismic hazard assessment without having to first settle which event at a site correlates with those at adjoining sites this opens a way for paleoseismic data to be used with greater power to understand the seismic hazard posed by faults like the southern san andreas

temporal slip rate stability and variations on the hope fault new zealand during the late quaternary abstract the hope fault transfers slip from hikurangi subduction to the alpine fault in the northern south island of new zealand it accommodates mainly dextral strike slip and currently carries the highest slip rate in the marlborough fault system displacements displacement rates and earthquake recurrence intervals have been determined using a combination of high resolution lidar for 59 dextral displacements 2 5 200 m together with calibrated radiocarbon ages 130 yr to 13 000 yr for abandoned stream channels terrace risers and alluvial fans mean single event displacement sed of 3 0 6 m 2 2 to 4 6 m for 21 measurements and mean recurrence interval of 266 100 yr range 128 to 560 yr have been determined for the five most recent surface rupturing earthquakes on time scales 2300 yr the dextral slip rate is uniform at 12 2 2 4 mm yr however when averaged over time intervals of 230 to 1700 yr slip rates range from 4 to 46 4 mm yr this order of magnitude variability in slip rate over shorter timescales cannot be fully attributed to errors in displacement and age data and is at least partly due to variations in earthquake recurrence interval and inferred sed short term non characteristic earthquake behaviour may be due to changes in fault loading arising from stress interactions between different segments of the hope fault and nearby faults

morphologic dating of fault scarps using airborne laser swath mapping alsm data 1 models of fault scarp morphology have been previously used to infer the relative age of different fault scarps in a fault zone using labor intensive ground surveying we present a method for automatically extracting scarp morphologic ages within high resolution digital topography scarp degradation is modeled as a diffusive mass transport process in the across scarp direction the second derivative of the modeled degraded fault scarp was normalized to yield the best fitting in a least squared sense scarp height at each point and the signal to noise ratio identified those areas containing scarp like topography we applied this method to three areas along the san andreas fault and found correspondence between the mapped geometry of the fault and that extracted by our analysis this suggests that the spatial distribution of scarp ages may be revealed by such an analysis allowing the recent temporal development of a fault zone to be imaged along its length

1855 and 1991 surveys of the san andreas fault implications for fault mechanics two monuments from an 1855 cadastral survey that span the san andreas fault in the carrizo plain have been right laterally displaced 11 0 2 5 m by the 1857 fort tejon earthquake and associated seismicity and afterslip this measurement confirms that at least 9 5 0 5 m of slip occurred along the main fault trace as suggested by measurements of offset channels near wallace creek the slip varied by 2 to 3 m along a 2 6 km section of the main fault trace using radiocarbon dates of the penultimate large earthquake and measurements of slip from the 1857 earthquake we calculate an apparent slip rate for the last complete earthquake cycle that is at least 25 lower than the late holocene slip rate on the main fault trace comparison of short term broad aperture strain accumulation rates with the narrow aperture late holocene slip rate indicates that the fault behaves nearly elastically over a time scale of several earthquake cycles therefore slip in future earthquakes should compensate the slip rate deficit from the 1857 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

estimating surface rupture length and magnitude of paleoearthquakes from point measurements of rupture displacement we present a method to estimate paleomagnitude and rupture extent from measurements of displacement at a single point on a fault the variability of historic ruptures is summarized in a histogram of normalized slip then scaled to give the probability of finding a given displacement within a rupture for any magnitude considered the histogram can be inverted assuming any magnitude earthquake is as likely as another yielding probability density functions of magnitude and rupture length for any given displacement measurement to improve these distributions we include a term to account for the probability that the earthquake would cause ground rupture and two alternative distributions of earthquake magnitude the gutenberg richter magnitude distribution predicts shorter rupture lengths and smaller magnitudes than does a uniform distribution where any magnitude earthquake is considered equally likely longer ruptures and larger magnitudes than the uniform model are predicted by an alternative magnitude distribution designed to return site average displacement this model is a generalization of the characteristic earthquake model and reasonably describes paleoseismic findings on the southern san andreas fault where slip is accommodated by average displacements of a few meters and earthquake recurrence times of 100 250 years our results should increase the value of paleoseismic displacement measurements for hazard assessment in particular they quantify probability estimates of earthquake magnitude and rupture length where point observations of rupture displacement are available and so can contribute to probabilistic seismic hazard analyses online material rupture profiles used to sample rupture variability

surficial offsets on the central and eastern garlock fault associated with prehistoric earthquakes geomorphic features offset along the central and eastern garlock fault record the amount of surface slip associated with prehistoric earthquakes along the easternmost 90 km of the fault the smallest offsets cluster around 2 3 m of left lateral slip apparently associated with the most recent earthquake on this portion of the fault larger offsets along this part of the fault especially in pilot knob valley cluster around values consistent with 2 4 m of slip in each of the past several events farther west south of el paso mountains offset geomorphic features suggest that each of the past two earthquakes on this stretch of the garlock fault was produced by about 7 m of slip whereas the third event back was produced by about 4 m of slip vertical displacements of geomorphic features range from 0 to 30 of the left lateral offsets within pilot knob valley along the southern side of the slate range vertical displacements are consistently up on the northern side whereas within the avawatz mountains both north and south side up vertical displacements are present on the basis of the geomorphic offsets the geometry of the garlock fault and the precedents set by historical strike slip earthquakes elsewhere a number of different rupture patterns are plausible these range from rupture of the entire garlock fault in a single event with a maximum magnitude of about mw 7 8 to separate rupture of the western segment and of the central and eastern segments combined with approximate magnitudes mw 1 1 and mw 7 5 respectively to separate rupture of even shorter segments producing earthquakes of magnitudes mw 6 6 to mw 7 5 in conjunction with available slip rates for the garlock fault the geomorphic offsets suggest that average recurrence intervals are probably within the range of 600 1200 years south of el paso mountains about 200 750 years in searles valley about 200 1300 years in pilot knob valley and about 200 3000 years near leach lake and in the avawatz mountains

revised dates of large earthquakes along the carrizo section of the san andreas fault california since a d 1310 30 1 precise knowledge of the age and magnitude of past earthquakes is essential for characterizing models of earthquake recurrence and key to forecasting future earthquakes we present 28 new radiocarbon analyses that refine the chronology of the last five earthquakes at the bidart fan site along the carrizo section of the south central san andreas fault which last ruptured during the fort tejon earthquake in a d 1857 the new data show that the penultimate earthquake in the carrizo plain occurred not earlier than a d 1640 and the modeled 95th percentile ranges of the three earlier earthquakes and their mean are a d 1540 1630 1585 a d 1360 1425 1393 and a d 1280 1340 1310 indicating an average time interval of 137 44 years between large earthquakes since a d 1310 30 a robust earthquake recurrence model of the carrizo section will require even more well dated earthquakes for thorough characterization however these new data imply that since a d 1310 30 the carrizo section has failed more regularly and more often than previously thought

high resolution topography derived offsets along the 1857 fort tejon earthquake rupture trace san andreas fault the great fort tejon earthquake of 1857 with an 350 km long surface rupture was the most recent major earthquake along the south central san andreas fault saf prior reconstruction of its surface slip distribution and reconstruction of preceding earthquakes along the 1857 rupture trace have contributed to formulation of the characteristic earthquake cem and uniform slip models usm for earthquake recurrence that find wide application in seismic hazard assessment and earthquake forecasting we used the high resolution b4 light detection and ranging lidar topographic data set sufficient for depiction of meter scale tectonic landforms to reevaluate the distribution of surface displacement along the 1857 rupture trace we present 450 offset measurements with displacements below 60 m increasing observation density relative to previous studies by a factor of 2 our results show that the 1857 earthquake had overall an average displacement below 3 5 m with 4 6 m released along the northwestern half of the rupture its along fault slip distribution is smooth at 10 km length scales at 28 less than prior estimates assuming a 10 km rupture depth and a 30 gpa shear modulus reconstruction of pre 1857 earthquakes is impeded by an exponential decrease in observation density with increasing displacement amount offset observation density soon reaches a level where only tentative and nonunique reconstructions are permitted the results of this study question prior surface slipreconstructions of pre 1857 rupture s that were based on a distinctly lower number of offset observations challenging the applicability of the aforementioned earthquake recurrence models to explain saf rupture behavior online material catalog of offset measurements along the 1857 surface rupture trace as well as an annotated map 1 embed inline graphic 1 gif

high resolution topography along surface rupture of the 16 october 1999 hector mine california earthquake mw 7 1 from airborne laser swath mapping in order to document surface rupture associated with the hector mine earthquake in particular the area of maximum slip and the deformed surface of lavic lake playa we acquired high resolution data using relatively new topographic mapping methods we performed a raster laser scan of the main surface breaks along the entire rupture zone as well as along an unruptured portion of the bullion fault the image of the ground surface produced by this method is highly detailed comparable to that obtained when geologists make particularly detailed site maps for geomorphic or paleoseismic studies in this case however for the first time after a surface rupturing earthquake the detailed mapping is along the entire fault zone rather than being confined to selected sites these data are geodetically referenced using the global positioning system thus enabling more accurate mapping of the rupture traces in addition digital photographs taken along the same flight lines can be overlaid onto the precise topographic data improving terrain visualization we demonstrate the potential of these techniques for measuring fault slip vectors

recovering paleoearthquake slip record in a highly dynamic alluvial and tectonic region hope fault new zealand from airborne lidar knowing the slip amplitudes that large earthquakes produced in prehistorical times is one key to anticipate the magnitude of large forthcoming events it is long known that the morphology is preserving remnants of paleoearthquake slips in the form of fault offset landforms however the measured offsets that can be attributed to the most recent paleoearthquakes are generally few along a fault so that they rarely allow recovering the slip distributions and largest slips of these earthquakes we acquired 1 m resolution airborne lidar data on a 30 km stretch of a fast slipping strike slip fault eastern hope fault new zealand located in a region of high alluvial dynamics where landforms are rapidly evolving data analysis reveals 200 offset landforms only 30 allow a good to moderate quality offset measurement from these good to moderate quality measures we recover the slip length distributions and largest slips of the four most recent large paleoearthquakes and find evidence of 4 6 prior events the record suggests that large earthquake slip recurred in multiples of about 4 m along the 30 km stretch although they have larger uncertainties the more numerous lower quality offsets that we also measured reveal a similar earthquake slip record this shows that although offset landforms are partly degraded in dynamically active landscapes they store valuable information on paleoearthquake slips this information might be recovered provided that the morphology is analyzed at high resolution and continuously over a significant fault length remote lidar data are powerful to perform such analyses

paleoearthquakes on the southern san andreas fault wrightwood california 3000 to 1500 b c a new method for evaluating paleoseismic evidence and earthquake horizons we present evidence of 11 14 earthquakes that occurred between 3000 and 1500 b c on the san andreas fault at the wrightwood paleoseismic site earthquake evidence is presented in a novel form in which we rank high moderate poor or low the quality of all evidence of ground deformation which are called event indicators event indicator quality reflects our confidence that the morphologic and sedimentologic evidence can be attributable to a ground deforming earthquake and that the earthquake horizon is accurately identified by the morphology of the feature in four vertical meters of section exposed in ten trenches we document 316 event indicators attributable to 32 separate stratigraphic horizons each stratigraphic horizon is evaluated based on the sum of rank rs maximum rank rm average rank ra number of observations obs and sum of higher quality event indicators rs 1 of the 32 stratigraphic horizons 14 contain 83 of the event indicators and are qualified based on the number and quality of event indicators the remaining 18 do not have satisfactory evidence for further consideration eleven of the 14 stratigraphic horizons have sufficient number and quality of event indicators to be qualified as probable to very likely earthquakes the remaining three stratigraphic horizons are associated with somewhat ambiguous features and are qualified as possible earthquakes although no single measurement defines an obvious threshold for designation as an earthquake horizon rs rm and rs 1 correlate best with the interpreted earthquake quality earthquake age distributions are determined from radiocarbon ages of peat samples using a bayesian approach to layer dating the average recurrence interval for the 10 consecutive and highest quality earthquakes is 111 93 131 years and individual intervals are 50 of the average with comparison with the previously published 14 15 earthquake record between a d 500 and present we find no evidence to suggest significant variations in the average recurrence rate at wrightwood during the past 5000 years

the magnitude distribution of declustered earthquakes in southern california abstract the binned distribution densities of magnitudes in both the complete and the declustered catalogs of earthquakes in the southern california region have two significantly different branches with crossover magnitude near m 4 8 in the case of declustered earthquakes the b values on the two branches differ significantly from each other by a factor of about two the absence of self similarity across a broad range of magnitudes in the distribution of declustered earthquakes is an argument against the application of an assumption of scale independence to models of main shock earthquake occurrence and in turn to the use of such models to justify the assertion that earthquakes are unpredictable the presumption of scale independence for complete local earthquake catalogs is attributable not to a universal process of self organization leading to future large earthquakes but to the universality of the process that produces aftershocks which dominate complete catalogs

lidar and field observations of slip distribution for the most recent surface ruptures along the central san jacinto fault we measured offsets on tectonically displaced geomorphic features along 80 km of the clark strand of the san jacinto fault sjf to estimate slip per event for the past several surface ruptures we identify 168 offset features from which we make over 490 measurements using b4 light detection and ranging lidar imagery and field observations our results suggest that lidar technology is an exemplary supplement to traditional field methods in slip per event studies displacement estimates indicate that the most recent surface rupturing event mre produced an average of 2 5 2 9 m of right lateral slip with maximum slip of nearly 4 m at anza a m w 7 2 7 5 earthquake average multiple event offsets for the same 80 kms are 5 5 m with maximum values of 3 m at anza for the penultimate event cumulative displacements of 9 10 m through anza suggest the third event was also similar in size paleoseismic work at hog lake dates the most recent surface rupture event at ca 1790 a poorly located large earthquake occurred in southern california on 22 november 1800 we relocate this event to the clark fault based on the mre at hog lake we also recognize the occurrence of a younger rupture along 15 20 km of the fault in blackburn canyon with 1 25 m of average displacement we attribute these offsets to the 21 april 1918 m w 6 9 event these data argue that much or all of the clark fault and possibly also the casa loma fault fail together in large earthquakes but that shorter sections may fail in smaller events online material topographic contour maps and hillshades generated from b4 lidar data corresponding field photographs and data tables comparing lidar based and field based slip measurements for individual geomorphic features along the clark fault

superposed lateral ramps in the pell city thrust sheet appalachian thrust belt alabama abstract in the appalachian thrust belt in alabama thrust sheets of paleozoic strata generally strike northeastward and are imbricated northwestward four transverse zones cross the regional strike of the thrust belt the large scale pell city thrust sheet ends southwestward at an oblique lateral ramp within the harpersville transverse zone where the leading edge of the thrust sheet the pell city fault curves abruptly 55 counterclockwise the northwest striking segment of the pell city fault conforms to the geometry of an oblique lateral ramp in the footwall furthermore the pell city fault cuts up section in the hanging wall southwestward toward the transverse zone indicating a hanging wall lateral ramp emplaced over the footwall oblique lateral ramp in the hanging wall adjacent to the northwest trending segment of the pell city fault a pervasive train of upright isoclinal folds with 50 apparent shortening trends n15 w oblique to the regional translation direction the fold train is limited to the southwestern part of the pell city thrust sheet farther northeast the regional northeasterly strike prevails the isoclinal folds in the hanging wall indicate contractional crowding perpendicular to the footwall oblique lateral ramp

reassessment of a slip budget along the parkfield segment of the san andreas fault historically the parkfield segment has represented a transition in fault behavior along the san andreas fault saf despite a 33 mm yr long term slip rate along the saf slip has not been observed on the cholame segment since the great 1857 fort tejon earthquake during that time the parkfield segment has experienced slip from at least six m 6 0 earthquakes aseismic fault creep and from minor earthquakes data from aseismic slip rate studies and historical earthquake studies allow us to estimate the total slip released along this portion of the saf since 1857 assuming the saf should slip at the long term slip rate a slip deficit of 5 m exists along the cholame segment since 1857 the slip deficit is approximately equivalent to 1857 offsets measured on the cholame and the southeast portion of the parkfield segment thus the slip deficit in southeast parkfield and cholame may be as great as the slip accommodated along these segments in 1857 the slip deficit abruptly decreases to the northwest across the parkfield segment it is 2 m near the town of parkfield and 0 m northwest of middle mountain an m 7 event rupturing all or part of the cholame segment and the southeastern parkfield segment slip decreasing to the northwest would release the accumulated slip and is plausible importantly this study also shows that the change in the pattern of strain release occurs in the middle of the parkfield segment rather than at its ends online material tables showing aseismic and coseismic slip estimations and calculations

structure and earthquake offsets on the san andreas fault at the wrightwood california paleoseismic site thirty eight trenches and natural exposures across the san andreas fault zone four km northwest of wrightwood california reveal the structure and stratigraphy of this paleoseismic site a 25 m thick stratigraphic section of late holocene peat debris flows and fluvial sediments have accumulated syntectonically and are deformed in a complicated flower or flake structure within the fault zone whereas slip is everywhere parallel to the trend of the san andreas fault layering within the fan shaped section guides the surface faulting and transtensive portions of the structure are connected to transpressive portions by bedding parallel detachment faults the structure has grown through time widely distributing the evidence for individual earthquakes the broad zone of deformation and rapid sedimentation permit the characterization of an unusually large number of prehistoric earthquakes the presence of at least four geomorphically similar sites within 10 km along the fault zone suggests that this kind of site is common and other sites should be exploited to date the upper 12 m of section deposited during the past 1600 yr has been completely characterized and dated to show evidence of 14 prehistoric earthquakes the a d 1857 earthquake produced only 1 2 m of slip here commensurate with the site9s proximity to the southern end of the rupture six to 10 m of slip accumulated during the past three earthquakes and 30 60 m of cumulative slip occurred during the past 14 events suggesting a mean displacement of 2 4 m per event at the site coupled with the mean recurrence interval of slightly more than 100 yr this implies a slip rate of 2 4 cm yr for the san andreas fault north of its junction with the san jacinto fault

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2

palaeoclimatic and archaeological evidence for a 200 yr recurrence of floods and droughts linking california mesoamerica and south america over the past 2000 years conspicuous grey clay rich flood deposits in the predominantly olive varved sediment in the central santa barbara basin california were dated via varve counting to c ad 212 440 603 1029 1418 and 1605 the 200 yr quasi periodicity and the timing of individual floods match time periods of known supraregional climatic changes and the documented 200 yr periodicity in palaeoclimate records elsewhere the floods of c ad 440 and ad 1418 occurred during global reorganizations of atmospheric circulation cold spells seem to have accompanied the floods of c ad 1029 and ad 1605 california floods and other palaeoclimate records suggest that expressions of regional climates are modulated by solar variability with a 200 yr periodicity our compilation of palaeoclimatic and mesoamerican and south american archaeological records provides evidence that palaeoenvironmental and cultural changes were often coincident within their respective dating uncertainties and occurred in 200 yr steps the matching patte

serial ruptures of the san andreas fault carrizo plain california revealed by three dimensional excavations 1 it is poorly known if fault slip repeats regularly through many earthquake cycles well documented measurements of successive slips rarely span more than three earthquake cycles in this paper we present evidence of six sequential offsets across the san andreas fault at a site in the carrizo plain using stream channels as piercing lines we opened a latticework of trenches across the offset channels on both sides of the fault to expose their subsurface stratigraphy we can correlate the channels across the fault on the basis of their elevations shapes stratigraphy and ages the three dimensional excavations allow us to locate accurately the offset channel pairs and to determine the amounts of motion for each pair we find that the dextral slips associated with the six events in the last millennium are from oldest to youngest 5 4 0 6 8 0 0 5 1 4 0 5 5 2 0 6 7 6 0 4 and 7 9 0 1 m in this series three and possibly four of the six offset values are between 7 and 8 m the common occurrence of 7 8 m offsets suggests remarkably regular but not strictly uniform slip behavior age constraints for these events at our site combined with previous paleoseismic investigations within a few kilometers allow a construction of offset history and a preliminary evaluation of slip and time predictable models the average slip rate over the span of the past five events between a d 1210 and a d 1857 has been 34 mm yr not resolvably different from the previously determined late holocene slip rate and the modern geodetic strain accumulation rate we find that the slip predictable model is a better fit than the time predictable model in general earthquake slip is positively correlated with the time interval preceding the event smaller offsets coincide with shorter prior intervals and larger offset with longer prior intervals

the gutenberg richter or characteristic earthquake distribution which is it abstract paleoearthquake and fault slip rate data are combined with the cit usgs catalog for the period 1944 to 1992 to examine the shape of the magnitude frequency distribution along the major strike slip faults of southern california the resulting distributions for the newport inglewood elsinore garlock and san andreas faults are in accord with the characteristic earthquake model of fault behavior the distribution observed along the san jacinto fault satisfies the gutenberg richter relationship if attention is limited to segments of the san jacinto that are marked by the rupture zones of large historical earthquakes or distinct steps in fault trace the observed distribution along each segment is consistent with the characteristic earthquake model the gutenberg richter distribution observed for the entirety of the san jacinto may reflect the sum of seismicity along a number of distinct fault segments each of which displays a characteristic earthquake distribution the limited period of instrumental recording is insufficient to disprove the hypothesis that all faults will display a gutenberg richter distribution when averaged over the course of a complete earthquake cycle but given that 1 the last 5 decades of seismicity are the best indicators of the expected level of small to moderate size earthquakes in the next 50 years and 2 it is generally about this period of time that is of interest in seismic hazard and engineering analysis the answer to the question posed in the title of the article at least when concerned with practical implementation of seismic hazard analysis at sites along these major faults appears to be the characteristic earthquake distribution

surface slip during large owens valley earthquakes data sets and expanded results contributing to this study are available in the supporting information the earthscope southern and eastern california lidar project available online at http opentopo sdsc edu involved data acquisition and processing for the plate boundary observatory pbo by ncalm http www ncalm org unavco operates the pbo for earthscope http www earthscope org supported by the national science foundation ear 0350028 and ear 0732947 funding for this study was provided by the southern california earthquake center scec project 12140 the geological society of america graduate student research fund the community foundation of san bernardino county and the western washington university geology department we thank g seitz m price and k morgan for assistance in the field and s bacon j arrowsmith r weldon k scharer j unruh c madden madugo and d haddad for helpful discussions constructive reviews by d schwartz r briggs e schermer d clark and one anonymous reviewer substantially improved the paper we also thank the staff at the uc white mountain research center for facilitating this work any use of trade firm or product names is for descriptive purposes only and does not imply endorsement by the u s government

interseismic deformation along the san andreas fault in southern california eight trilateration networks located along the san andreas fault in southern california have been surveyed 8 to 19 times within a 14 to 17 year interval between 1971 and 1992 the data measurements of distances between the same 10 to 32 pairs of geodetic monuments within a network in each of the surveys have been corrected for coseismic offsets from nearby earthquakes calculated from dislocation models the corrected data a total of 2027 measurements are displayed in the form of plots of measured distance versus time for each of the 167 lines measured the hypothesis that the interseismic deformation is steady is tested by examining whether deviations from linear fits to the data in the plots are within the range expected for observational error a significant deviation from steady deformation is found only for the network located neax palmdale california in that network many of the measurements made in the survey of early 1982 deviate from the trend defined by the measurements in other surveys the deviations are not of the form fixed proportional error one would generally expect from systematic survey error if the survey of early 1982 is excluded the remaining data at palmdale are consistent with steady deformation thus the apparent strain event observed near palmdale in 1982 was transient

coseismic slip variation assessed from terrestrial lidar scans of the el mayor cucapah surface rupture abstract we analyze high resolution 103 points m2 terrestrial lidar surveys of the 4 april 2010 el mayor cucapah earthquake rupture baja california mexico collected at three sites 12 18 days after the event using point cloud based tools in an immersive visualization environment we quantify coseismic fault slip for hundreds of meters along strike and construct densely constrained along strike slip distributions from measurements of offset landforms uncertainty bounds for each offset determined empirically by repeatedly measuring offsets at each site sequentially illuminate measurement uncertainties that are difficult to quantify in the field these uncertainties are used to define length scales over which variability in slip distributions may be assumed to reflect either recognizable earthquake mechanisms or measurement noise at two sites characterized by 2 3 m of concentrated right oblique slip repeat measurements yield 2 uncertainties of 11 12 each site encompasses 200 m along strike and a smoothed linear slip gradient satisfies all measurement distributions implying along fault strains of 10 3 conversely the common practice of defining the slip curve by the local slip maxima distorts the curve overestimates along fault strain and may overestimate actual fault slip by favoring measurements with large positive uncertainties at a third site characterized by 1 2 5 m of diffuse normal slip repeat measurements of fault throw summed along fault perpendicular profiles yield 2 uncertainties of 17 here a low order polynomial fit through the measurement averages best approximates surface slip however independent measurements of off fault strain accommodated by hanging wall flexure suggest that over the 200 m length of this site a linear interpolation through the average values for the slip maxima at either end of this site most accurately represents subsurface displacement in aggregate these datasets show that given uncertainties of greater than 11 2 slip distributions over shorter scales are likely to be less uneven than those derived from a single set of field or lidar based measurements this suggests that the relatively smooth slip curves we obtain over 102 m distances reflect real physical phenomena whereas short wavelength variability over 100 101 m distances can be attributed to measurement uncertainty

fault slip and earthquake recurrence along strike slip faults contributions of high resolution geomorphic data article i nfo understanding earthquake eq recurrence relies on information about the timing and size of past eq ruptures along a given fault knowledge of a fault s rupture history provides valuable information on its potential future behavior enabling seismic hazard estimates and loss mitigation stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing eqs analysis of the latter data sets culminated during the mid 1980s in the formulation of now classical eq recurrence models now routinely used to assess seismic hazard within the last decade light detection and ranging lidar surveying technology and other high resolution data sets became increasingly available to tectono geomorphic studies promising to contribute to better informed models of eq recurrence and slip accumulation patterns after reviewing motivation and background we outline requirements to successfully reconstruct a fault s offset accumulation pattern from geomorphic evidence we address sources of uncertainty affecting offset measure ment and advocate approaches to minimize them a number of recent studies focus on single eq slip distribu tions and along fault slip accumulation patterns we put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation cv for eq inter event time and slip per event and find that a single event offsets vary over a wide range of length scales and the sources for offset variability differ with length scale b at fault segment length scales single event offsets are essentially constant c along fault offset accumulation as resolved in the geomorphic record is dominated by essentially same size large offset in crements and d there is generally no one to one correlation between the offset accumulation pattern constrained in the geomorphic record and eq occurrence as identified in the stratigraphic record revealing the higher resolution and preservation potential of the latter while slip accumulation along a fault segment may be dominated by repetition of large nearly constant offset increments timing of surface rupture is less regular

active fold deformation and crustal shortening rates of the qilian shan foreland thrust belt ne tibet since the late pleistocene abstract quantification of crustal shortening rates across foreland fold and thrust belts is essential for evaluating how convergence is accommodated throughout the orogenic belt and analyzing seismic hazard in neighboring cities in this study we focused on active fold along the western portion of the qilian shan foreland thrust belt in ne tibet the shortening rate across the hujiatai anticline ha along the eastern segment of the fodongmiao hongyazi fault fhf is 0 8 0 2 mm a based on terrestrial cosmogenic nuclide tcn dating of deformed late pleistocene fluvial terrace when this rate is combined with the shortening rates of 1 1 1 4 mm a and 0 7 1 2 mm a along the western and central segments obtained by previous studies it is apparent that crustal shortening rates along the fhf gradually decrease to the east this eastward decrease in fault activity may be a result of the northward propagation of the fhf or partitioning of strain off to nearby faults or folds furthermore tectonic geomorphology and trenching suggest that several thrust faults around the ha ruptured during the historical 1609 earthquake combining the shortening rate of 0 6 0 8 mm a across the north side of the jiudong basin with our rate we suggest that the total crustal shortening rate across the basin is about 1 3 2 2 mm a assuming little internal deformation which accounts for roughly 20 40 of the amount of crustal shortening deformation across the qilian block these results demonstrate that the qilian shan foreland basin plays an important role in accommodating the crustal deformation of northeastern tibet

flume experiments on the horizontal stream offset by strike slip faults flume experiments in which the middle section of an erosion channel is displaced horizontally have been conducted to assess the response of streams to horizontal displacement by a strike slip fault the experimental erosion channel was developed in a mixture of sand and clay which provided relatively stable banks with its cohesiveness horizontal displacement of a strike slip fault perpendicular to the channel is expected to add a flat section to its longitudinal profile along the fault line the experimental stream eliminated this flat section with downstream degradation upstream aggradation and lateral channel shift as a result a roughly continuous longitudinal profile was maintained this maintenance of a continuous longitudinal profile along channel is considered to be the principle of stream response to horizontal displacement by a strikeslip fault downstream degradation was the dominant process of this stream response in the overall tendency of erosion without sand supply when the rate of fault displacement was low long recurrence interval the experimental stream eroded the fault surface jutting laterally into the channel like a scarp and deflected the channel within the recurrence interval this lateral channel shift gave some gradient to the reach created by fault displacement offset reach and the downstream degradation occurred as much as completing the remaining longitudinal profile adjustment when the rate of fault displacement was high short recurrence interval the lateral erosion on the first fault surface was interrupted by the next fault displacement the displacement was then added incrementally to the existing channel offset making channel shift by lateral erosion increasingly difficult the channel offset with sharp bends persisted without much modification and downstream degradation and upstream aggradation became evident with the effect of the offset channel course which worked like a dam in this case a slight local convexity which was incidentally formed by downstream degradation and upstream aggradation tended to remain in the roughly continuous longitudinal profile as long as the horizontal channel offset persisted in either case once the experimental stream obtained a roughly continuous gradient further channel adjustment seemed to halt horizontal channel offset remained to a greater or lesser extent at the end of each run long after the last fault displacement copyright 2004 john wiley sons ltd

3d_fault_offsets a matlab code to automatically measure lateral and vertical fault offsets in topographic data application to san andreas owens valley and hope faults measuring fault offsets preserved at the ground surface is of primary importance to recover earthquake and long term slip distributions and understand fault mechanics the recent explosion of high resolution topographic data such as lidar and photogrammetric digital elevation models offers an unprecedented opportunity to measure dense collections of fault offsets we have developed a new matlab code 3d fault offsets to automate these measurements in topographic data 3d fault offsets mathematically identifies and represents nine of the most prominent geometric characteristics of common sublinear markers along faults especially strike slip in 3 d such as the streambed minimum elevation top free face and base of channel banks or scarps minimum laplacian maximum gradient and maximum laplacian and ridges maximum elevation by calculating best fit lines through the nine point clouds on either side of the fault the code computes the lateral and vertical offsets between the piercing points of these lines onto the fault plane providing nine lateral and nine vertical offset measures per marker through a monte carlo approach the code calculates the total uncertainty on each offset it then provides tools to statistically analyze the dense collection of measures and to reconstruct the prefaulted marker geometry in the horizontal and vertical planes we applied 3d fault offsets to remeasure previously published offsets across 88 markers on the san andreas owens valley and hope faults we obtained 5 454 lateral and vertical offset measures these automatic measures compare well to prior ones field and remote while their rich record provides new insights on the preservation of fault displacements in the morphology

reconstruction of a channel offset in 1857 by the san andreas fault near cholame california abstract the u s geological survey has formally forecast the next moderate m 6 parkfield earthquake for 1988 5 yr sieh and jahns 1984 forecast that a m 7 earthquake is likely to accompany the next parkfield earthquake the latter forecast rests on interpretation of 3 to 4 m of 1857 slip on eight gullies near cholame and slip loading rate of 3 5 cm yr since 1857 but lienkaemper 1987 interprets 1857 slip here as 4 to 8 m these eight gullies yield larger slip when one includes slip on secondary faults at three gullies and one picks gully centerlines judging the post 1857 alteration differently at five sites our goal in this paper is to show our interpretation of slip on one gully deemed the least ambiguous of these eight as they appear in large scale 1966 aerial photographs we interpret slip as 2 m larger at this key site suggesting a much lower likelihood of the next parkfield earthquake triggering a larger cholame earthquake our detailed studies of many sites showing 1857 slip are continuing and will be published later using 1966 aerial photos we infer the shape of this key gully before fault offset by eliminating effects of later natural and artificial processes of alteration on 1986 photos right lateral offset seems 3 5 0 5 m but on 1966 photos we measure 5 7 0 7 m differencing precise 1966 and 1986 topographic maps shows that little incision occurred but soil deposited up to a 1 m thickness on the left bank probably drifted downslope from agricultural disking in the adjacent field this soil deposit forced the channel bottom 2 m away from the left bank upstream from fault only causing offset in 1986 to appear 2 m smaller than in 1966 this 2 m alteration presumably occurred before sieh 1978 interpreted 3 3 m slip here

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

lateral offsets on surveyed cultural features resulting from the 1999 izmit and duzce earthquakes turkey surveys of offset linear cultural features that cross the surface ruptures of the 17 august and 12 november 1999 earthquakes on the north anatolian fault in turkey yield slip values as large as or larger than those recorded by near field measurements in the same areas immediately after the earthquake using long linear alignments of trees fence lines walls and canals we demonstrate as much as a 2 m increase in observed slip over the initial field measurements on an average we observed about 15 of the total lateral slip as off fault deformation with values ranging from 0 to 40 of the total slip part of this lateral deformation is accom modated by bending or drag in a zone as much as 30 m in width although usually the zone varies between 5 and 20 m in width this supports the idea that substantial nonbrittle off fault deformation is associated with ruptures in areas of alluvial fill alternatively there may have been substantial afterslip although none has been recognized on postearthquake repaired structures our observations suggest that post earthquake measurements of fault slip using tape measures on offset geomorphic features may underestimate the actual amount of slip in that event where the non linearity of the offset feature does not allow recognition of the warping surveys of multiple tree lines within groves of poplar trees planted in straight lines across the fault prior to the earthquake show surprisingly large lateral varia tions in one grove slip increases by nearly 1 8 m or 35 of the maximum measured value over a lateral distance of nearly 100 m this and other observations along the 1999 ruptures suggest that the lateral variability of slip observed from displaced geomorphic features in many earthquakes of the past may represent a combination of 1 actual differences in slip at the surface and 2 the difficulty in recognizing distributed nonbrittle deformation

stream channel offset and late holocene slip rate of the san andreas fault at the van matre ranch site carrizo plain california sets of well preserved channels offset across the san andreas fault saf at the van matre ranch vmr site in the northwestern elkhorn hills area of the carrizo plain offer the opportunity to measure slip rate and examine geomorphic development of the channels the fault zone and offset channels were exposed by excavation in one fault perpendicular and five fault parallel trenches the geomor phology and stratigraphy in the channels reveal a record of filling by fluvial sedi mentation lateral colluviation and pedogenesis the buried thalweg of the currently active channel is offset 24 8 1 m while the geomorphic channel is offset approx imately 27 6 1 m seventeen samples were collected from channel margin deposits for 14 c dating an oxcal model of the radiocarbon dates with stratigraphic control suggests that the oldest date for channel incision was a d 1160 minimum and maximum slip rates ranging from 29 3 to 35 6 mm yr are derived from different assumptions about the timing of channel incision and offset the resulting slip rates at vmr agree well with the late holocene slip rate of 33 9 2 9 mm yr at wallace creek approximately 18 km to the northwest and imply that within measurement uncertainty the 30 37 mm yr velocity gradient across the saf from decadal time scale geodetic measurements is accommodated across the several meter wide saf zone at vmr over the last millennium

strain accumulation across the carrizo segment of the san andreas fault california impact of laterally varying crustal properties 1 major strike slip faults juxtapose geologically dissimilar terrain which may vary in mechanical properties leading to an asymmetric pattern of strain accumulation we present new gps data on the carrizo segment of the san andreas fault separating the salinian block southwest of the fault from franciscan terrane northeast of the fault to better quantify asymmetric strain accumulation we also present a series of finite element models to investigate the possible role of variable elastic layer thickness and material properties of the upper crust the geodetic data are well fit with a simple model comprising a weak upper crustal zone 10 25 km wide northeast of the fault this model is also consistent with geologic data on the distribution of major rock types and corresponding laboratory data on their material properties as well as paleoseismic seismic and magnetotelluric data using this model we estimate a long term average over several seismic cycles slip rate for the san andreas fault of 36 1 5 2 mm yr in agreement with the known holocene rate within uncertainties and a viscosity for the combined lower crust upper mantle of 2 5 1019 pa s

identification of paleoearthquakes based on geomorphological evidence and their tectonic implications for the southern part of the active anqiu juxian fault eastern china abstract this study utilized an unmanned aerial vehicle uav photogrammetry system to acquire orthoimages and generate a digital elevation model dem covering the southern part of the anqiu juxian fault for geomorphological analysis and paleoearthquake identification six offset gullies were identified and analyzed on the orthoimages our results indicate that at least three large and several moderate earthquakes have occurred along the fault zone knickpoints recognized from the dem reveal several paleoearthquakes an average holocene horizontal slip rate of 2 86 0 35 mm yr 1 was estimated from the offset gullies which is consistent with previous results from field surveys the tectonic evolution of this fault zone is most likely related to subduction of the pacific plate under the eurasian plate which gave rise to the right lateral strike slip and thrust movement of the tan lu fault zone this study provided valuable information regarding fault activity and paleoearthquake occurrence along the anqiu juxian fault zone during the holocene and demonstrated the potential of using uavs for studies involving tectonic geomorphology

century long average time intervals between earthquake ruptures of the san andreas fault in the carrizo plain california paleoseismological data constrain the age location and associated magnitude of past surface rupturing earthquakes these are critical parameters for developing and testing fault behavior models and characterizing seismic hazard we present new earthquake evidence and radiocarbon analyses that refi ne the chronology of the six most recent earthquakes that ruptured the south central san andreas fault in the carrizo plain california united states at the bidart fan site modeled 95 percentile ranges of the earthquakes prior to the a d 1857 earthquake are a d 1631 1823 1580 1640 1510 1612 1450 1475 and 1360 1452 the average time interval between the last six earthquakes that ruptured the san andreas fault in the carrizo plain is 88 41 yr this is less than the time since the most recent a d 1857 earthquake less than all reported average intervals of prehistoric earthquakes along the entire san andreas fault and signifi cantly shorter than the 235 yr average used in recent seismic hazard evaluations the new chronological data combined with recent slip studies imply that the magnitudes of the earthquakes that ruptured the southern san andreas fault in the carrizo plain since ca a d 1360 were variable and suggest that the widely held view of rare but great surface rupturing earthquakes along this portion of the southern san andreas fault should be reevaluated 118

a 100 year average recurrence interval for the san andreas fault at wrightwood california evidence for five large earthquakes during the past five centuries along the san andreas fault zone 70 kilometers northeast of los angeles california indicates that the average recurrence interval and the temporal variability are significantly smaller than previously thought rapid sedimentation during the past 5000 years in a 150 meter wide structural depression has produced a greater than 21 meter thick sequence of debris flow and stream deposits interbedded with more than 50 datable peat layers fault scarps colluvial wedges fissure infills upward termination of ruptures and tilted and folded deposits above listric faults provide evidence for large earthquakes that occurred in a d 1857 1812 and about 1700 1610 and 1470

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

paleoseismic event dating and the conditional probability of large earthquakes on the southern san andreas fault california we introduce a quantitative approach to paleoearthquake dating and apply it to paleoseismic data from the wrightwood and pallett creek sites on the southern san andreas fault we illustrate how stratigraphic ordering sedimentolog ical and historical data can be used quantitatively in the process of estimating earth quake ages calibrated radiocarbon age distributions are used directly from layer dating through recurrence intervals and recurrence probability estimation the method does not eliminate subjective judgements in event dating but it does provide a means of systematically and objectively approaching the dating process date dis tributions for the most recent 14 events at wrightwood are based on sample and contextual evidence in fumal et al 2002 and site context and slip history in weldon et al 2002 pallett creek event and dating descriptions are from published sources for the five most recent events at wrightwood our results are consistent with pre viously published estimates with generally comparable or narrower uncertainties for pallett creek our earthquake date estimates generally overlap with previous results but typically have broader uncertainties some event date estimates are very sensitive to details of data interpretation the historical earthquake in 1857 ruptured the ground at both sites but is not constrained by radiocarbon data radiocarbon ages peat accumulation rates and historical constraints at pallett creek for event x yield a date estimate in the earliest 1800s and preclude a date in the late 1600s this event is almost certainly the historical 1812 earthquake as previously concluded by sieh et al 1989 this earthquake also produced ground deformation at wrightwood all events at pallett creek except for event t about a d 1360 and possibly event i about a d 960 have corresponding events at wrightwood with some overlap in age ranges event t falls during a period of low sedimentation at wrightwood when conditions were not favorable for recording earthquake evidence previously pro posed correlations of pallett creek x with wrightwood w3 in the 1690s and pallett creek event v with w5 around 1480 fumal et al 1993 appear unlikely after our dating reevaluation apparent internal inconsistencies among event layer and dating relationships around events r and v identify them as candidates for further inves tigation at the site conditional probabilities of earthquake recurrence were estimated using poisson lognormal and empirical models the presence of 12 or 13 events at wrightwood during the same interval that 10 events are reported at pallett creek is reflected in mean recurrence intervals of 105 and 135 years respectively average poisson model 30 year conditional probabilities are about 20 at pallett creek and 25 at wrightwood the lognormal model conditional probabilities are somewhat higher about 25 for pallett creek and 34 for wrightwood lognormal variance rln estimates of 0 76 and 0 70 respectively imply only weak time predictability conditional probabilities of 29 and 46 respectively were estimated for an em pirical distribution derived from the data alone conditional probability uncertainties are dominated by the brevity of the event series dating uncertainty contributes only secondarily wrightwood and pallett creek event chronologies both suggest varia tions in recurrence interval with time hinting that some form of recurrence rate modulation may be at work but formal testing shows that neither series is more ordered than might be produced by a poisson process

spatial variations in slip rate along the death valley fish lake valley fault system determined from lidar topographic data and cosmogenic 10be geochronology 1 the death valley fish lake valley fault zone dv flvfz is a prominent dextral fault system in the eastern california shear zone ecsz combining offset measurements determined with lidar topographic data for two alluvial fans with terrestrial cosmogenic nuclide 10be ages from the fan surfaces yields a late pleistocene slip rate of 2 5 to 3 mm yr for the northern part of the dv flvfz in fish lake valley these rates are slower than the late pleistocene rate determined for the system in northern death valley indicating that slip rates decrease northward along this major fault zone when summed with the slip rate from the white mountains fault the other major fault in this part of the ecsz our results suggest that either significant deformation is accommodated on structures east of fish lake valley or that rates of seismic strain accumulation and release have not remained constant over late pleistocene to holocene time

evidence for two surface ruptures in the past 500 years on the san andreas fault at frazier mountain california we conducted paleoseismic studies in a closed depression along the san andreas fault on the north flank of frazier mountain near frazier park california we recognized two earthquake ruptures in our trench exposure and interpreted the most recent rupture event 1 to represent the historical 1857 earthquake we also exposed evidence of an earlier surface rupture event 2 along an older group of faults that did not rerupture during event 1 radiocarbon dating of the stratigraphy above and below the earlier event constrains its probable age to between a d 1460 and 1600 because we documented continuous unfaulted stratigraphy between the earlier event horizon and the youngest event horizon in the portion of the fault zone exposed we infer event 2 to be the penultimate event we observed no direct evidence of an 1812 earthquake in our exposures however we cannot preclude the presence of this event at our site due to limited age control in the upper part of the section and the possibility of other fault strands beyond the limits of our exposures based on over lapping age ranges event 2 at frazier mountain may correlate with event b at the bidart fan site in the carrizo plain to the northwest and events v and w4 at pallett creek and wrightwood respectively to the southeast if the events recognized at these multiple sites resulted from the same surface rupture then it appears that the san andreas fault has repeatedly failed in large ruptures similar in extent to 1857

estimating prehistoric earthquake magnitude from point measurements of surface rupture abstract we have developed a method for estimating the magnitude of prehistoric earthquakes using displacement data that usually can be collected from paleoseismic investigations this method is necessary because essentially all current magnitude estimates for prehistoric events rely on determining the total length of coseismic surface rupture which is rarely measurable or rely on segmentation scenarios for which uncertainties cannot be quantified although surface rupture length is a better predictor of magnitude than displacement for historic earthquakes paleoseismic investigations are better at providing measurements of the amount of displacement at a site along a fault the key to our method is to incorporate the variability in displacement observed in 14 modern events which allows a formal uncertainty in magnitude to be assigned to prehistoric ruptures we show how multiple measurements along a preserved fraction of a rupture can be combined to reduce the uncertainty in the estimate of magnitude our analysis shows that uncertainty asymptotically approaches the natural variability of ruptures so 5 to 10 displacement measurements are sufficient to characterize paleomagnitude we conclude that sampling of scarps with lengths of even 10 of the original rupture can provide magnitude values that reasonably estimate the earthquake tests of the method using randomly sampled data from the 1992 m w 7 3 landers and 1954 m s 6 8 dixie valley earthquakes provide close approximations of the actual magnitudes

high resolution satellite imagery mapping of the surface rupture and slip distribution of the mw 7 8 14 november 2001 kokoxili earthquake kunlun fault northern tibet china the mw 7 8 kokoxili earthquake of 14 november 2001 which ruptured a 450 km long stretch of the sinistral kunlun strike slip fault at the northeastern edge of the tibet plateau china ranks as the largest strike slip event ever recorded instrumentally in asia newly available high resolution satellite hrs images pixel size 1 m acquired in the months following the earthquake proved a powerful tool to complement field investigations and to produce the most accurate map to date of the coseismic displacements along the central kusai hu segment of the rupture the coseismic rupture geometry south and west of buka daban feng near the earthquake epicenter was also investigated in detail along the kusai hu segment slip parti tioning is for the first time observed to occur simultaneously during a single event with two parallel strands 2 km apart localizing almost pure strike slip and normal faulting in all 83 new hrs coseismic offset measurements some of which calibrated by field work show large well constrained variations 100 of the slip function over distances of only25 km tension cracks opening ahead of the shear dislocation and later offset by the upward propagating strike slip rupture were observed dem onstrating that the rupture front propagated faster at depth than near the surface the triple junction between the central kusai hu segment the kunlun pass fault where the rupture ended and the xidatan dongdatan segment which could be the next segment to fail along the main kunlun fault acted as a strong barrier implying that direct triggering of earthquake rupture on the xidatan dongdatan segment by kokoxili type earthquakes may not be the rule

lateral offsets and revised dates of large prehistoric earthquakes at pallett creek southern california recent excavation and new radiocarbon dates of sediments at pallett creek are the basis for new conclusions regarding the late holocene history of the san andreas fault systematic dissection of a 50 m long 15 m wide 5 m deep volume of earth centered on the fault enables documentation in three dimensions of fault patterns lateral offsets and vertical deformation associated with large earthquakes of the past the excavations expose evidence for 12 earthquakes that occurred between about 260 and 1857 a d with an average recurrence interval of about 145 years prehistoric slip events that occurred in 1720 50 1550 70 1350 50 1080 65 and 845 75 a d have lateral offsets that are comparable to those of the most recent great earthquake of 1857 thus all of these events represent earthquakes of large magnitude the lateral offsets of two other events in 935 85 and 1015 100 a d are an order of magnitude smaller and may be interpreted in several ways with regard to the size of these events the new data constrain the average recurrence interval for large earthquakes at this site to between 145 and 200 years but suggest a monotonic decrease in individual intervals to below this range during the past 900 years on the basis of these data the probability of a large earthquake with surficial fault rupture at this site is between 0 2 and 5 during 1984 and 7 and 60 by the year 2000

dogtails versus rainbows synthetic earthquake rupture models as an aid in interpreting geological data geologists have been collecting for decades information from historical and paleoearthquakes that could contribute to the formulation of a big picture of the earthquake engine observations of large earthquake ruptures unfortunately are always going to be spotty in space and time so the extent to which geological information succeeds in contributing to a grander view of earthquakes is going to be borne not only by the quantity and quality of data collected but also by the means by which it is interpreted this article tries to understand geological data more fully through carefully tailored computer simulations of fault ruptures dogtails and rainbows are two types of fault rupture terminations that can be recognized in the field and can be interpreted through these models rainbows are concave down ruptures that indicate complete stress drop and characteristic slip rainbow terminations usually coincide with fault ends or strong segment boundaries dogtails are concave up ruptures that indicate incomplete stress drop and noncharacteristic slip dogtail terminations can happen anywhere along a fault or fault segment the surface slip pattern of the magnitude 6 6 1979 imperial valley california earthquake shows both dogtail and rainbow terminations the rainbow confirms the presence of a strong fault segment boundary 6 km north of the international border that had been suggested by sieh 1996 the dogtail implies that the displacement observed in 1979 is not characteristic by combining paleoseismic information with the surface slip patterns from this event and the magnitude 7 1 1940 imperial valley earthquake i develop a quantitative imperial fault model with northern central and southern segments possessing 50 110 and 50 bar strength respectively both the 1940 and 1979 events caused 1 m amplitude dogtailed ruptures of the northern segment however characteristic slip of the segment is more likely to be about 3 m to illustrate the full spectrum of potential rupture modes models were run forward in time to generate a 2000 year rupture encyclopedia even with well constrained segmentation and strengths modest changes in two friction law parameters produce several plausible histories further discrimination awaits analysis of the extensive paleoseismic record that geologists believe exists in the shore deposits of the intermittent lakes of the salton trough

investigating paleoseismicity using fault scarp morphology of the dushanzi reverse fault in the northern tian shan china abstract this study uses the morphology of fault scarps to study the paleoseismic history of the dushanzi reverse fault drf in the northern tian shan region china using high resolution lidar dems to create a large number of scarp profiles we detected slope breaks in the fault scarp morphology to quantify the number of paleoearthquakes that occurred on the scarps and obtained the along strike scarp height distribution to determine the cumulative and single event vertical displacements our results revealed four surface rupturing events with similar co seismic vertical displacements of 1 4 m via the statistical analysis of displacement datasets and slope breaks which were in agreement with the findings from paleoseismic trenching we then assessed the paleomagnitudes using the empirical scaling relationships between moment magnitude and rupture parameters and the recurrence interval for surface rupturing events using the formation ages of the displaced terrace surfaces the results indicate that the possible magnitudes range from mw 6 5 to 6 7 even reaching mw 7 2 in the case of a multi fault rupture of the entire anticline fault belt with an average recurrence interval of 2 4 3 0 ka this study also demonstrates the importance of using high resolution topographic data in paleoseismic investigations which enables the determination of fine scale tectono geomorphic interpretations and detailed offset measurements over large regions along the fault

holocene rate of slip and tentative recurrence interval for large earthquakes on the san andreas fault cajon pass southern california abstract detailed mapping of the san andreas fault zone where it crosses cajon creek southern california has revealed a number of late quaternary deposits and geomorphological features offset by the fault radiocarbon dates from alluvial and swamp deposits provide a detailed chronology with which to characterize the activity of the san andreas fault four independent determinations of the slip rate on the san andreas fault yield an average rate of 24 5 3 5 mm yr for the past 14 400 years the similarity of the four values which span different intervals of time from 5900 to 14 400 years ago suggest that the slip rate has been constant during this period the slip rate confirms that the san andreas fault is accumulating slip faster than any other fault in the plate boundary throughout california also the sum of the slip rates on the san andreas 24 5 mm yr and the san jacinto 10 mm yr faults south of their junction is the same as the san andreas north of their junction 35 mm yr an excavation provided evidence for at least two and up to four earthquakes that caused rupture on the fault between 1290 and 1805 a d and tentative evidence for six earthquakes in about the last 1000 years both lines of evidence imply an average recurrence interval for large earthquakes of about 1 to 2 centuries combined with the historic record this investigation indicates that the last major earthquake at cajon creek was probably at the beginning or middle of the 18th century while the record at cajon creek may suggest that the next major earthquake on the san andreas fault is overdue the data can be interpreted to indicate that the recurrence interval for earthquakes on the san andreas south of the 1857 rupture is 3 to 4 centuries and that the anticipated event should not be expected until the next century

depth variation of coseismic stress drop explains bimodal earthquake magnitude frequency distribution 1 an essential part of seismic hazard analysis is the earthquake size frequency relationship used to estimate earthquake recurrence time and thus probability a key feature of those distributions is their bimodal character small to moderate magnitude earthquakes follow the gutenberg richter gr inverse power law relation while large magnitude characteristic earthquakes are more frequent than anticipated from gr following approximately a gaussian distribution around the maximum magnitude limited by fault geometry using a numerical earthquake simulator we show that the temperature dependence of friction behavior and therefore the depth variation of coseismic stress drop derived from laboratory friction experiments presents a simple and comprehensive explanation for the observed bimodal seismicity distribution characteristic earthquakes are the result of an abrupt increase in rupture width at the transition from small to large earthquakes

quantifying fault zone activity in arid environments with high resolution topography 1 high resolution airborne laser swath mapping alsm topography illuminates active faulting with unprecedented clarity we contrast alsm topography of two dextral faults in arid regions of california with slip rates that differ by an order of magnitude the lenwood fault with rate of 1 mm yr and the clark fault a strand of the san jacinto fault with net slip rate 10 mm yr visualization of alsm data reveals abundant fault scarps and deflected channels that when reconstructed can yield powerful slip constraints though many of these features may also be detected in existing aerial photography these data are limited by stereo depth resolution and fixed illumination angle

surface rupture and slip distribution along the lenglongling fault in the ne tibetan plateau implications for faulting behavior abstract the lenglongling fault lllf is located in the western section of the tianzhu seismic gap along the qilian haiyuan fault zone in the ne tibetan plateau between the 1920 m8 5 haiyuan and the 1927 m8 0 gulang earthquakes there is little information about the paleoseismic history of the lllf and understanding the faulting history of the lllf is important for determining the seismic hazards of both the fault and the seismic gap using uav based photogrammetry high resolution satellite imagery and field investigations we mapped the surface trace of the fault in detail and measured 192 left lateral offsets of geomorphic markers along the fault trace a binned cumulative offset probability density copd distribution was calculated to analyze single event and multi event cumulative offsets as a result we find that the lllf has fresh scarps along the entire 120 km length indicating that the most recent event might have ruptured the full segment of the fault the coseismic offset of the most recent event changes along the fault trace and has an asymmetrical bell shaped distribution the maximum offset was 7 m located in the middle eastern section of the fault and the offset decreases progressively towards both ends the minimum offset located at the western end was 3 0 m and the average coseismic offset was 4 8 m the cumulative offsets of the four most recent paleoearthquakes are multiples of the coseismic offset of the most recent event and show similar slip distributions indicating that the fault ruptures with a characteristic slip the fault slip distribution estimated recurrence interval and estimated moment magnitude imply that the lllf releases accumulated strain energy mainly by repeatedly producing mw 7 5 7 8 earthquakes every 1000 200 years we also show that the binned copd technique performs well to separate single event and multi event cumulative offsets

displacement across the cholame segment of the san andreas fault between 1855 and 1893 from cadastral surveys changes since 1855 in reported section line lengths and positions of survey monuments that span the san andreas fault saf were used to measure displacement interpreted to be from the 1857 fort tejon earthquake in south central california in 1855 1856 james e freeman established township and range lines across the saf between rancho cholame and the northern carrizo plain at least 26 1 mile sections lines spanned the saf in the area between present day california highways 46 and 58 each section line was marked by monuments at the midpoint and endpoints section lines across portions of the saf were resurveyed in 1893 by j m gore we projected changes in line length onto the fault zone to measure displacement the measurements indicate right lateral displacement of 16 2 6 0 m across the fault zone the resulting tectonic displacement exceeds the maximum reported geomorphic offsets 6 7 m attributed to the 1857 earthquake along the cholame segment although we recognize great uncertainties in the accuracy of our small historical data set we tentatively conclude that total displacement in the 1857 earthquake along the saf over this 2 km wide aperture was significantly greater than the 3 to 6 m slip previously reported for the cholame segment from narrower aperture geomorphic and trenching studies these differences may be compatible if slip along the fault increases down dip rapidly from 3 6 m at the surface to 20 m within several hundred meters of the surface our inference of high slip along this portion of the cholame segment in 1857 is at odds with most rupture models of the central saf and suggests that geomorphic offsets may not represent total displacement across the fault zone

three dimensional investigation of a 5 m deflected swale along the san andreas fault in the carrizo plain topographic maps produced from light detection and ranging lidar data are useful for paleoseismic and neotectonic research because they pro vide submeter representation of faulting related surface features offset measurements of geomorphic features made in the field or on a remotely sensed imagery commonly assume a straight or smooth i e undeflected pre earthquake geometry here we present results from investigation of an 20 cm deep and 5 m wide swale with a sharp bend along the san andreas fault saf at the bidart fan site in the carrizo plain california from analysis of lidar topography images and field measure ments the swale was initially interpreted as a channel tectonically offset 4 7 m our observations from exposures in four backhoe excavations and 25 hand dug trenchettes show that even though a sharp bend in the swale coincides with the trace of the a d 1857 fault rupture the swale formed after the 1857 earthquake and was not tectonically offset subtle fractures observed within a surficial gravel unit overlying the 1857 rupture trace are similar to fractures previously documented at the phelan fan and ly4 paleoseismic sites 3 and 35 km northwest of bidart fan respectively collectively the fractures suggest that a post 1857 moderate magnitude earthquake caused ground cracking in the carrizo and cholame stretches of the saf our obser vations emphasize the importance of excavation at key locations to validate remote and ground based measurements and we advocate more geomorphic characterization for each site if excavation is not possible online material figures of trench logs

late holocene slip rate of the san andreas fault and its accommodation by creep and moderate magnitude earthquakes at parkfield california investigation of a right laterally offset channel at the miller9s field paleoseismic site yields a late holocene slip rate of 26 2 6 4 4 3 mm yr 1 for the main trace of the san andreas fault at parkfield california this is the first well documented geologic slip rate between the carrizo and creeping sections of the san andreas fault this rate is lower than holocene measurements along the carrizo plain and rates implied by far field geodetic measurements 35 mm yr however the rate is consistent with historical slip rates measured to the northwest along the creeping section of the san andreas fault

san andreas fault zone california m 5 5 earthquake history the san andreas fault zone has been a very significant source of major california earthquakes from 1812 to 1906 it generated four major earthquakes of m 7 or larger in two pairs on two major portions of the fault a pair of major earthquakes occurred on the central to southern region where the 1857 faulting overlapped the 1812 earthquake faulting a pair of major earthquakes occurred on the northern region where the 1906 faulting overlapped the 1838 earthquake faulting also earthquakes of m 7 occurred in the san francisco bay area on the hayward fault in 1868 and the santa cruz mountains near loma prieta in 1989 and on the imperial fault near the border with mexico in 1940 the 1838 earthquake s damage effects throughout the bay area from san francisco to santa clara valley and monterey were unequalled by any historical earthquake other than the 1906 event this and numerous strong possible aftershocks during the following 3 years in the san juan bautista vicinity suggest 1838 faulting from san francisco to san juan bautista cycles of seismicity and quiescence were associated with the bay area earthquakes of 1868 1906 and 1989 the 1868 earthquake on the hayward fault was preceded by 12 earthquakes of m 5 5 from 1855 to 1866 within 60 km of the hayward fault and was followed by 13 quiet years the 1906 san andreas fault event was preceded from 1881 to 1903 by 18 earthquakes of m 5 5 and was followed by quiescence with only three earthquakes of m 5 5 until 1954 the bay area has been seismically quiet at the m 5 5 level since the 1989 loma prieta earthquake and its 1990 aftershocks which contrasts with the 10 years before 1989 when five m 5 5 6 2 events occurred the loma prieta earthquake is of similar magnitude to the 1868 hayward event and could be followed by a similarly short quiet period the 1857 earthquake had immediate foreshocks in the lonoak bitterwater region 50 km northwest of parkfield in the northern end zone of the 1857 rupture extending southeast from bitterwater 70 km to parkfield the rate of seismic moment release has decreased with time since 1857 this may reflect the decay with time of the stress loading due to the 9 m 1857 fault displacements 80 km southeast of parkfield and explain why the predicted earthquake which was based on the assumption of regular recurrence of parkfield earthquakes has not yet occurred the extent of the 1812 earthquake fault rupture is not well defined jacoby et al 1988 estimated that it extended 170 km from cajon pass to tejon pass based on this estimate we present the hypothesis that the rupture occurred in two segments in december 1812 the eastern segment generated the 8 december earthquake that damaged san juan capistrano san gabriel san fernando and san buenaventura thirteen days later the western segment ruptured generating the earthquake that damaged san fernando and san buenaventura again as well as santa barbara santa ynez and purisima concepcion

stratigraphic evidence for seven meters of dextral slip on the san andreas fault during the 1857 earthquake in the carrizo plain the smallest geomorphic offsets along a 35 km section of the san andreas fault in the carrizo plain vary from 7 to 10 m our three dimensional excavation of alluvial deposits a few km southeast of wallace creek confirms that at least 6 6 to 6 9 m of dextral slip occurred there during the latest large earthquake in 1857 dates on detrital charcoal suggest that the last event prior to the 1857 earthquake occurred before a date within the range a d 1305 to 1623 the 3 m range in smallest offsets along this portion of the fault may reflect either a 3 m variation in slip along the san andreas in 1857 or 2 to 3 m of slip during an event prior to 1857 observations made after the recent landers earthquake are compatible with the hypothesis of large local variations in slip during a single earthquake but do not explain the cause of such variations off fault dextral rotations would be one plausible explanation however paleoseismic data in the carrizo plain are too sparse to allow rejection of the alternative hypothesis that slip in the event prior to 1857 was only 2 to 3 m an amount of slip which would be several times too small to fit a time predictable model

tectonic geomorphology of the san andreas fault zone from high resolution topography an example from the cholame segment abstract high resolution topographic data along fault zones are important aids in the delineation of recently active breaks a 15 km long portion of the south central san andreas fault saf along the southern cholame segment contains well preserved tectonic landforms such as benches troughs scarps and aligned ridges that indicate recurring earthquake slip recently acquired lidar topographic data along the entire southern saf b4 project have shot densities of 3 4 m 2 computed from the lidar returns digital elevation models dems of 0 25 to 0 5 m resolution using local binning with inverse distance weighting and 0 8 m or larger search radii depict the tectonic landforms at paleoseismic sites well enough to assess them confidently mapping of recently active breaks using a lidar only based approach compares well with aerial photographic and field based methods the fault zone varies in width from meters to nearly 1 km and is comprised of numerous en echelon meter to kilometer length overlapping sub parallel fault surfaces bounding differentially moving blocks that elongate parallel to the saf the semantic variations of what constitutes active and the importance of secondary traces influence the breadth and complexity of the resulting fault trace maps

recent rupture history of the san andreas fault southeast of cholame in the northern carrizo plain california we conducted a paleoseismic study on the san andreas fault saf southeast of cholame california to investigate the record of earthquakes along an 80 km paleoseismic data gap between parkfield and the carrizo plain at the ly4 site located 37 5 km southeast of highway 46 along the saf we excavated a fault perpendicular trench on the distal end of an alluvial fan that emanates from the temblor mountains to the northeast we found evidence of three and possibly four ruptures recorded within the stratigraphy the only age constraints are radiocarbon dates on a paleosol three units 50 cm below the oldest event horizon and the presence of recently introduced exotic pollen species in an upper unit the radiocarbon dates indicate there have been at least three surface rupturing events at the ly4 site since cal a d 1058 1291 exotic historic pollen in the top of a unit possibly cut by the youngest event suggests that an earthquake affected at the ly4 site close to a d 1873 1874 manuscript received 11 january 2000

karst landforms revealed at various scales using lidar and uav in semi arid brazil consideration on karstification processes and methodological constraints abstract this paper analyzes different types of karst landforms and their relationships with fracture systems sedimentary bedding and fluvial processes we mapped karst features in the cretaceous carbonates of the jandaira formation in the potiguar basin brazil we used high resolution digital elevation models acquired using lidar and aerial orthophotographs acquired using an unmanned aerial vehicle uav we grouped and described karst evolution according to scale and degree of karstification these degrees of karst evolution are coeval fractures are opened by dissolution forming vertical fluid conduits whereas coeval dissolution occurs along horizontal layers this conduit system acts as pathways for water flow the enlargement of conduits contributes to the collapse of blocks in sinkholes and expansion of caves during an intermediate degree of karstification propagation of dissolution can cause the coalescence of sinkholes and the capture of small streams fluvial processes dominate karst dissolution at an advanced degree of karstification comparisons with previously published ground penetrating radar gpr borehole and seismic surveys in sedimentary basins indicate that these structures can be partially preserved during burial

quantifying near field and off fault deformation patterns of the 1992 mw 7 3 landers earthquake coseismic surface deformation in large earthquakes is typically measured using field mapping and with a range of geodetic methods e g insar lidar differencing and gps current methods however either fail to capture patterns of near field coseismic surface deformation or lack preevent data consequently the characteristics of off fault deformation and the parameters that control it remain poorly understood we develop a standardized method to fully measure the surface near field coseismic deformation patterns at high resolution using the cosi corr program by correlating pairs of aerial photographs taken before and after the 1992 m w 7 3 landers earthquake cosi corr offers the advantage of measuring displacement across the entire zone of surface deformation and over a wider aperture than that available to field geologists for the landers earthquake our measured displacements are systematically larger than the field measurements indicating the presence of off fault deformation we show that 46 of the total surface displacement occurred as off fault deformation over a mean deformation width of 154 m the magnitude and width of off fault deformation along the rupture is primarily controlled by the macroscopic structural complexity of the fault system with a weak correlation with the type of near surface materials through which the rupture propagated both the magnitude and width of distributed deformation are largest in stepovers bends and at the southern termination of the surface rupture we find that slip along the surface rupture exhibits a consistent degree of variability at all observable length scales and that the slip distribution is self affine fractal with dimension of 1 56

riser diachroneity lateral erosion and uncertainty in rates of strike slip faulting a case study from tuzidun along the altyn tagh fault nw china 1 at late quaternary timescales offset fluvial terrace risers are among the most common landforms used to determine rates of strike slip faulting although diachroneity in the age of riser segments on opposite sides of the fault has been noted previously an unexplored source of uncertainty associated with deriving slip rates from these markers centers on quantifying the size of the displacement uncertainty such diachroneity introduces to evaluate the impact of riser diachroneity we investigated the tuzidun site 37 73 n 86 72 e along the cherchen he reach of the active central altyn tagh fault the east bank of the channel is flanked by a left laterally offset terrace riser while the measured offset is 54 3 m geochronologic measurements and analysis of riser topography indicate that the downstream riser segment formed between 6 0 0 8 ka and 5 7 0 4 ka while the upstream riser segment may have been laterally refreshed as recently as 0 5 0 2 ka a valley wall on the west bank of the channel places a maximum limit of 38 6 m on the amount of possible lateral erosion of the upstream riser this bound in turn limits the total offset since formation of the downstream riser to range from 54 3 to 89 7 m together these observations bracket the millennial altyn tagh fault slip rate to range from 9 0 1 3 to 15 5 1 7 mm a 1 more generally this investigation shows that the observed riser displacement does not necessarily correlate with the age of either riser segment downstream or upstream of the fault in cases where one segment is displaced while the other is subjected to lateral erosion if this diachroneity goes undetected erroneous slip rate measurements are likely to result

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

surficial slip distribution on the central emerson fault during the june 28 1992 landers earthquake california we present the results of our mapping of a 5 6 km length of the central emerson fault that ruptured during the 1992 landers earthquake in the southwestern mojave desert california the right lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone in some locations a total of up to 110 cm of additional right lateral slip occurred on secondary faults up to 1 7 km away from the main rupture zone other secondary faults carried up to several tens of centimeters of left lateral or thrust displacement the maximum net vertical displacement was 175 cm east side up the sense of vertical slip across the main fault zone varied along strike but in most cases it was consistent with the sense of vertical slip in previous earthquakes as indicated by the locations of areas of older uplifted and abandoned alluvial fan surfaces although variations in surficial slip have been reported along previous strike slip ruptures our closely spaced slip measurements allow a much more detailed study of slip variability than was possible previously we document variations in slip as large as 1 m or more over distances ranging from 1 2 km to a few tens of meters suggesting that strains of the order of 10 1 may have occurred locally within the surficial sediments the long wavelength kilometer scale variations in surficial slip may be influenced by fault geometry and perhaps by the thickness of unconsolidated sediments the slip variations over shorter length scales tens of meters may be caused by variations in the proportion of the total shear that occurs on visible brittle fractures versus that which occurs as distributed shear warping or rotation the variability of slip along the ruptures associated with the landers earthquake calls for caution in interpreting geomorphic offsets along prehistoric fault ruptures

paleoseismic and postseismic observations of surface slip along the parkfield segment of the san andreas fault parkfield is considered a transitional segment along the san andreas fault saf between continuous fault creep to the northwest and segments to the southeast that last slipped in the great 1857 fort tejon earthquake historically creep and recurring m 6 0 earthquakes have been observed at parkfield california but the segment s relevance in great saf earthquakes has remained uncertain this paleoseismic study of the central parkfield segment provides a 2000 year record of tectonically deformed fluvial and sag stratigraphy two fault perpendicular excavations across a pressure ridge and a sag pond 200 m north of carr hill exposed five primary fault zones displaying apparent vertical offsets upward splaying clay shear bands and warped stratigraphy four of five fault zones extended into the uppermost stratigraphy suggesting recent surface offset and fault creep several antithetic fault splays and one primary fault zone displayed upward terminations but strong indicators of large magnitude earthquakes with meter scale surface offset and rupture such as filled fissures and colluvial scarp deposits were not observed the absence of evidence for large magnitude earthquakes does not preclude the possibility of 1857 style earthquakes extending into the parkfield segment however all deformation exposed within these trenches is consistent with repeated small ground rupture and fault creep the 2004 m 6 0 parkfield earthquake ruptured through the site and activated at least three of the five fault zones exposed in our excavations comparison between 2004 vertical offset and vertical offsets within the exposed stratigraphy suggests a recurrence interval between 8 and 188 years for m 6 0 earthquakes at parkfield online material supplemental unit descriptions unanalyzed radiocarbon samples and trench logs and photos

late pleistocene slip rate of the central haiyuan fault constrained from optically stimulated luminescence 14c and cosmogenic isotope dating and high resolution topography the haiyuan fault is a major left lateral active fault of the india asia collision zone while the 1000 km long fault between hala lake in the west to liupan shan in the east accommodates eastward displacement of northeast tibet relative to the gobi alashan to the north the amount of slip accumulated and its slip rate remain debated we revisit the site of daqing or sangedun at 102 7 e in gaudemer et al 1995 to better constrain the long term slip rate of the haiyuan fault in its central part we used terrestrial lidar to build a high resolution dem and unmanned aerial vehicle to build an aerial photomosaic with 0 1 m resolution to survey the offset terraces their geomorphology and the fault trace we refine the geomorphological interpretation of the site measure riser offsets and determine their relation to terrace formation the well constrained age of the highest terrace t3 at 13 7 1 5 ka determined from the combination of surface and sub surface osl 14 c and terrestrial in situ 10 be cosmogenic nuclide dating associated with the maximum lower terrace riser offset of 88 m yield a minimum slip rate of 6 4 1 2 mm yr over the late pleistocene the age of the intermediate terrace t2 is bracketed between 8 0 ka 14 c and 12 ka 10 be the ages and vertical offsets of the 2 highest terraces is used to infer the age of t2 offset vertically 5 7 m at 5 4 1 ka its 29 2 m offset is consistent with a rate of 6 5 mm yr given the vertical offset youngest terrace t1 of 1 3 0 2 m its age is estimated at 1 2 0 2 ka in agreement with the youngest surface exposure age overall a slip rate of 5 8 mm yr fits all offset and age data at the daqing site the smallest offset of a gully incised into t1 of 6 0 0 5 m is potentially associated with the most recent slip event that occurred in the last millennia

palaeoseismology in steep terrain the big bend of the san andreas fault transverse ranges california transpressional tectonics are typically associated with restraining bends on major active strike slip faults resulting in uplift and steep terrain this produces dynamic erosional and depositional conditions and difficulties for established lines of palaeoseismological investigation consequently in these areas data are lacking to determine tectonic behaviour and future hazard potential along these important fault segments the big bend of the san andreas fault in the transverse ranges of southern california exemplifies these problems however landslides probably seismically triggered are widespread in the rugged terrain of the big bend fluvial reworking of these deposits rapidly produces geomorphic planes and lines that are markers for subsequent fault slip the most useful are offset and abandoned stream channels for these are relatively high precision markers for identifying individual faulting events palaeoseismological studies from the central big bend involving 14c ages of charcoal fragments from trench exposures illustrate these points and indicate that the past three faulting events including the great 1857 earthquake were relatively similar in scale each producing offsets of about 7 7 5 m the mean recurrence interval is 140 220 years the pre 1857 event here may be the 1812 event documented south of the big bend or an event which took place probably between 1630 and 1690 ground breakage in both events extended south of the big bend unlike the 1857 event where rupture was skewed to the north the preceding faulting event ruptured both to the north and south of the big bend and probably occurred between 1465 and 1495 all these events centred on the big bend and may be typical for this fault segment suggesting that models of uniform long term slip rates may not be applicable to the south central san andreas a slip rate estimate of 34 51 mm a 1 for the central big bend although uncertain may also imply higher slip in the big bend and highlights difficulties in correlating slip rates between sites with different tectonic settings slip rates on the san andreas may increase within the broad compressional tectonics zone of the big bend compared to the north and south where the plate boundary is a relatively linear and sub parallel series of dominantly strike slip faults partitioning slip within the big bend is inherently uncertain and insufficient suitably comparable data are available to sustain a uniform slip model although such models are a common working assumption

six similar sequential ruptures of the san andreas fault carrizo plain california we document the precise sizes but not the dates of the six latest offsets across the san andreas fault at wallace creek california three and perhaps four of these including the latest in 1857 show dextral offset of 7 5 8 m the third and fourth offsets however are just 1 4 and 5 2 m the predominance of similar offsets for the latest six events suggests that the fundamental properties of the fault system that control slip size do not vary greatly from event to event the large offsets imply that ruptures involving this site are typically more than 200 km long

inferring segment strength contrasts and boundaries along low friction faults using surface offset data with an example from the cholame carrizo segment boundary along the san andreas fault southern california rupture segmentation arises from changes in fault geometry and strength we use boundary element models of frictionless strike slip fault segments to quantify how fault geometry and strength change earthquake surface offset distributions using these relationships between fault geometry strength and surface offsets we can infer fault strength from the surface offsets in cases where the fault geometry can be independently constrained this article includes normalized plots of the surface offset distribution expected from rupture along low friction fault segments with strength contrasts of 1 4 1 3 1 2 1 2 3 and 4 for a range of fault segment geometries these plots may be used with offset data to constrain the strength of two coplanar adjacent fault segments this analysis is applied to the cholame and carrizo segments of the san andreas fault the available surface offset data suggest that the offset increases where the fault deepens in addition the observed offset gradient at the segment boundary requires a 2 3 1 4 strength ratio of the cholame to the carrizo segment