paleoseismology along the 1980 surface rupture of the irpinia fault implications for earthquake recurrence in the southern apennines italy the irpinia fault was the source of the ms 6 9 1980 irpinia earthquake and produced the first unequivocal historical surface faulting in italy trenching of the 1980 fault scarp at piano di pecore a flat intermontane basin about 5 km south of the 1980 instrumental epicenter provides the first data on earthquake recurrence intervals slip per event and slip rate on a major normal fault in the southern apennines fault zone the trenches exposed evidence of four pre 1980 paleoearthquakes that occurred during the past 8600 years a best estimate average recurrence interval is 2150 years although the time interval between individual events varies by as much as a factor of 2 each paleo earthquake is similar to the 1980 surface rupture in amount of slip and style of deformation which suggests that the 1980 event is characteristic for the irpinia fault slip per event values average 61 cm the net vertical displacement of 2 12 2 36 m since 8600 cal year b p observed in the trenches gives a vertical slip rate of 0 25 0 35 mm yr a dip slip rate of 0 29 0 40 mm yr and an extension rate of 0 14 0 20 mm yr although fault behavior data are only available for the irpinia fault they provide a starting point for evaluating earthquake recurrence and rates of deformation in southern apennines they suggest that 1 fault specific earthquake recurrence intervals based on the historical seismic record overestimates the occurrence of large magnitude m7 earthquakes and 2 the holocene rate of extension across the apennines is 1 mm yr the 1980 earthquake and the paleoseismologic observations show that repeated and localized surface faulting occurs in southern apennines and leaves subtle but distinct geomorphic evidence that can be detected with detailed and careful investigation

holocene turbidites record earthquake supercycles at a slow rate plate boundary ongoing evidence for earthquake clustering calls for records of numerous earthquake cycles to improve seismic hazard assessment especially where recurrence times overstep historical records we show that most turbidites emplaced at the africa eurasia plate boundary off west algeria over the past 8 k y correlate across sites fed by independent sedimentary sources requiring a regional trigger correlation with paleoseismic data inland and ground motion predictions support that m 7 earthquakes have triggered the turbidites the bimodal distribution of paleo events supports the concepts of earthquake supercycles and rupture synchronization between nearby faults 13 paleo earthquakes underpin clusters of 3 6 events with recurrence intervals of 300 600 yr separated by periods of quiescence of 1 6 k y without major events on other faults over the study area this implies broad phases of strain loading alternating with phases of strain release our results suggest that fault slip rates are time dependent and call for revising conventional seismic hazard models

holocene earthquake records from the cascadia subduction zone and northern san andreas fault based on precise dating of offshore turbidites abstract we present preliminary evidence for a 10 000 year earthquake record from two major fault systems based on sediment cores collected along the continental margins of western north america new stratigraphic evidence from cascadia demonstrates that 13 earthquakes ruptured the entire margin from vancouver island to at least the california border since the eruption of the mazama ash 7700 years ago the 13 events above this prominent stratigraphic marker have an average repeat time of 600 years and the youngest event 300 years ago coincides with the coastal record we also extend the record of past earthquakes to the base of the holocene at least 9800 years ago during which 18 events correlate along the same region the sequence of holocene events in cascadia appears to contain a repeating pattern of events a tantalizing first look at what may be the long term behavior of a major fault system the northern california margin cores show a cyclic record of turbidite beds that may represent holoce

a 21 event 4 000 year history of surface ruptures in the anza seismic gap san jacinto fault and implications for long term earthquake production on a major plate boundary fault paleoseismic work completed at hog lake on the san jacinto fault sjf near anza california indicates that at least 21 surface ruptures have occurred in the anza seismic gap over the past 4 000 years the ages of the ruptures are constrained by 111 radiocarbon dates 97 of which fall in stratigraphic order the average recurrence interval for all ruptures for this period is about 185 105 years although some ruptures such as occurred in the april 1918 earthquake caused only minor displacement we rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo ground surface weakly expressed ruptures for example the deformation we interpret to be the result of the historical 1918 earthquake received low scores and are interpreted as smaller earthquakes from this analysis we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake inferred to be the m w 7 3 22 november 1800 earthquake the adjusted recurrence interval for large earthquakes lengthens to approximately 254 years comparison with the rupture history at the mystic lake paleoseismic site on the claremont strand indicates that it is plausible that several of the large ruptures identified at hog lake could have jumped the hemet step over at mystic lake and continued on the claremont strand or vice versa but most of the event ages do not match between the two sites indicating that most ruptures do not jump the step finally comparison with san andreas fault ruptures both to the north and south of its juncture with the sjf suggest that some northern sjf ruptures identified at mystic lake may correlate with events identified at wrightwood but that these northern ruptures have no match at hog lake and can not indicate rupture of the entire sjf onto the saf

integration of paleoseismic data from multiple sites to develop an objective earthquake chronology application to the weber segment of the wasatch fault zone utah we present a method to evaluate and integrate paleoseismic data from multiple sites into a single objective measure of earthquake timing and recurrence on discrete segments of active faults we apply this method to the weber segment ws of the wasatch fault zone using data from four fault trench studies completed between 1981 and 2009 after systematically reevaluating the stratigraphic and chro nologic data from each trench site we constructed time stratigraphic oxcal models that yield site probability density functions pdfs of the times of individual earth quakes we next qualitatively correlated the site pdfs into a segment wide earthquake chronology which is supported by overlapping site pdfs large per event displace ments and prominent segment boundaries for each segment wide earthquake we computed the product of the site pdf probabilities in common time bins which emphasizes the overlap in the site earthquake times and gives more weight to the narrowest best defined pdfs the product method yields smaller earthquake timing uncertainties compared to taking the mean of the site pdfs but is best suited to earth quakes constrained by broad overlapping site pdfs we calculated segment wide earthquake recurrence intervals and uncertainties using a monte carlo model five surface faulting earthquakes occurred on the ws at about 5 9 4 5 3 1 1 1 and 0 6 ka with the exception of the 1 1 ka event we used the product method to define the earthquake times the revised ws chronology yields a mean recurrence interval of 1 3 kyr 0 7 1 9 kyr estimated two sigma 2 range based on interevent recurrence these data help clarify the paleoearthquake history of the ws including the important question of the timing and rupture extent of the most recent earthquake and are essential to the improvement of earthquake probability assessments for the wasatch front region

statistical analyses of great earthquake recurrence along the cascadia subduction zone goldfinger et al 2012 interpreted a 10 000 year old sequence of deep sea turbidites at the cascadia subduction zone csz as a record of clusters of plate boundary great earthquakes separated by gaps of many hundreds of years we performed statistical analyses on this inferred earthquake record to test the temporal clustering model and to calculate time dependent recurrence intervals and probabil ities we used a monte carlo simulation to determine if the turbidite recurrence in tervals follow an exponential distribution consistent with a poisson memoryless process the latter was rejected at a statistical significance level of 0 05 we performed a cluster analysis on 20 randomly simulated catalogs of 18 events event t2 excluded using ages with uncertainties from the turbidite dataset results indicate that 13 cata logs exhibit statistically significant clustering behavior yielding a probability of clus tering of 13 20 or 0 65 most 70 of the 20 catalogs contain two or three closed clusters a sequence that contains the same or nearly the same number of events and the current cluster t1 t5 appears consistently in all catalogs analysis of the 13 cat alogs that manifest clustering indicates that the probability that at least one more event will occur in the current cluster is 0 82 given that the current cluster may not be closed yet the probabilities of an m 9 earthquake during the next 50 and 100 years were estimated to be 0 17 and 0 25 respectively we also analyzed the sensitivity of results to including event t2 whose status as a full length rupture event is in doubt the inclusion of t2 did not change the probability of clustering behavior in the csz turbidite data but did significantly reduce the probability that the current cluster would extend to one more event based on the statistical analysis time independent and time dependent recurrence intervals were calculated

a numerical simulation of earthquake cycles along the nankai trough in southwest japan lateral variation in frictional property due to the slab geometry controls the nucleation position abstract the occurrence pattern of historical great earthquakes along the nankai trough indicates the existence of rupture segments that seem to correlate with 100 km scale lateral variation in the dip angle of the subducting philippine sea plate for instance the latest earthquakes the 1944 tonankai and the 1946 nankai earthquakes initiated their ruptures off kii peninsula where the dip angle of the slab is steeper than in adjacent areas to investigate how such heterogeneity in slab geometry affects the occurrence of earthquakes we conducted a three dimensional 3d numerical simulation of earthquake cycles for a large source area about 700 km long along the trough and 300 km wide in the dip direction based on a rate and state dependent friction law we used a simple flat dipping plane to model the plate boundary frictional parameters and effective normal stress were assumed to depend on the estimated depth of the real plate boundary based on seismic surveys and seismicity data the depth dependent frictional parameters were mapped on the flat model plane this made lateral variation in frictional property due to the variation in the dip angle of the slab the plate convergence rate in the model decreased eastward along the trough consistent with a recent global positioning system gps analysis in the simulation results preslip occurred and rupture started off kii peninsula both effects of a narrower locked area due to the higher dip angle and a higher plate convergence rate caused the highest stress accumulation rate to be in this area promoting slip nucleation our simple simulation suggests that lateral variation in the dip angle of the slab is one of the factors controlling the nucleation position of great interplate earthquakes

late quaternary coseismic uplift events on the huon peninsula papua new guinea deduced from coral terrace data up to six regressive terraces occur on the holocene raised reef tract and up to 15 occur on late pleistocene raised reef tracts along 40 km of coastline at huon peninsula papua new guinea we suggest that the regressive terraces represent repeated episodic uplift caused by great earthquakes ages of holocene coseismic uplift events are established by radiocarbon dating the late pleistocene events are bracketed by u series ages of the raised reef tracts on which they occur the mean recurrence interval of great earthquakes that caused the uplift events is 970 to 1165 years in the holocene and probably the same in the late pleistocene the interval ranged from about 200 to 1900 years the uplift rate increases parallel to the coast from northwest to southeast and the amplitude of coseismic uplifts generally increases similarly although some events produced uplift with little shore parallel tilting the mean amplitude of coseismic uplifts throughout the study area is 3 m in for both holocene and late pleistocene sequences large late quaternary landslides are numerous and some probably were triggered by the great earthquakes that caused coseismic uplift there appears to be no continuum between historical large earthquakes at huon peninsula of magnitudes 7 that produced no or only minor uplift and the great earthquakes represented by meter scale coseismic uplifts and very large landslides two tectonic subregions are recognized which were uplifted together by some holocene events but not by others there is no surface trace of holocene faulting between the subregions and a buried fault is thought to separate them

evidence for a twelfth large earthquake on the southern hayward fault in the past 1900 years we present age and stratigraphic evidence for an additional paleoearth quake at the tyson lagoon site the acquisition of 19 additional radiocarbon dates and the inclusion of this additional event has resolved a large age discrepancy in our earlier earthquake chronology the age of event e10 was previously poorly con strained thus increasing the uncertainty in the mean recurrence interval ri a critical factor in seismic hazard evaluation reinspection of many trench logs revealed sub stantial evidence suggesting that an additional earthquake occurred between e10 and e9 within unit u45 strata in older u45 are faulted in the main fault zone and overlain by scarp colluviums in two locations we conclude that an additional surface rupturing event e9 5 occurred between e9 and e10 since 91 a d 40 yr 1 11 paleoearthquakes preceded the m 6 8 earthquake in 1868 yielding a mean ri of 161 65 yr 1 standard deviation of recurrence intervals however the standard error of the mean sem is well determined at 10 yr since 1300 a d the mean rate has increased slightly but is indistinguishable from the overall rate within the uncertainties recurrence for the 12 event sequence seems fairly regular the coeffi cient of variation is 0 40 and it yields a 30 yr earthquake probability of 29 the apparent regularity in timing implied by this earthquake chronology lends support for the use of time dependent renewal models rather than assuming a random process to forecast earthquakes at least for the southern hayward fault online material twelve event oxcal model for paleoearthquakes of the hayward fault

major earthquakes occur regularly on an isolated plate boundary fault the scarcity of long geological records of major earthquakes on different types of faults makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult we provide a fault proximal major earthquake record spanning 8000 years on the strike slip alpine fault in new zealand cyclic stratigraphy at hokuri creek suggests that the fault ruptured to the surface 24 times and event ages yield a 0 33 coefficient of variation in recurrence interval we associate this near regular earthquake recurrence with a geometrically simple strike slip fault with high slip rate accommodating a high proportion of plate boundary motion that works in isolation from other faults we propose that it is valid to apply time dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide

late quaternary activity of the pajarito fault rio grande rift of northern new mexico usa the pajarito fault forms the western margin of the rio grande rift in north central new mexico and lies adjacent to los alamos national laboratory a major federal research facility vertical displacement on this normal fault over the past 1 2 ma has created a 50 to 120 m high fault scarp on bandelier tuff 1 2 ma yielding a long term average slip rate of ca 0 1 mm yr in support of a laboratory wide seismic hazards assessment we excavated 14 trenches in the pajarito fault zone to determine the age of the most recent displacement event the recurrence interval between events the displacement per event and the variability in slip rate and recurrence through time the large number of trenches was required by the large height of the fault scarp and the complexity of the fault zone only about half the trenches contained significant thicknesses of holocene deposits but in those trenches there was clear evidence for an early to mid holocene displacement event the previous event was at least 20 40 ka and the average recurrence interval over the past ca 300 ka was about 20 40 kyr we infer that much of the structural relief across this fault developed soon after eruption of the bandelier tuff between 1 0 and 1 2 ma and that slip rate slowed considerably after that time d 2005 published by elsevier b v

timing of large earthquakes since a d 800 on the mission creek strand of the san andreas fault zone at thousand palms oasis near palm springs california paleoseismic investigations across the mission creek strand of the san andreas fault at thousand palms oasis indicate that four and probably five surface rupturing earthquakes occurred during the past 1200 years calendar age estimates for these earthquakes are based on a chronological model that incorporates radiocarbon dates from 18 in situ burn layers and stratigraphic ordering constraints these five earthquakes occurred in about a d 825 770 890 mean 95 range a d 982 840 1150 a d 1231 1170 1290 a d 1502 1450 1555 and after a date in the range of a d 1520 1680 the most recent surface rupturing earthquake at thousand palms is likely the same as the a d 1676 35 event at indio reported by sieh and williams 1990 each of the past five earthquakes recorded on the san andreas fault in the coachella valley strongly overlaps in time with an event at the wrightwood paleoseismic site about 120 km northwest of thousand palms oasis correlation of events between these two sites suggests that at least the southernmost 200 km of the san andreas fault zone may have ruptured in each earthquake the average repeat time for surface rupturing earthquakes on the san andreas fault in the coachella valley is 215 25 years whereas the elapsed time since the most recent event is 326 35 years this suggests the southernmost san andreas fault zone likely is very near failure the thousand palms oasis site is underlain by a series of six channels cut and filled since about a d 800 that cross the fault at high angles a channel margin about 900 years old is offset right laterally 2 0 0 5 m indicating a slip rate of 4 2 mm yr this slip rate is low relative to geodetic and other geologic slip rate estimates 26 2 mm yr and about 23 35 mm yr respectively on the southernmost san andreas fault zone possibly because 1 the site is located in a small step over in the fault trace and so the rate is not be representative of the mission creek fault 2 slip is partitioned northward from the san andreas fault and into the eastern california shear zone and or 3 slip is partitioned onto the banning strand of the san andreas fault zone

statistical aspects of parkfield earthquake sequence and parkfield prediction experiment abstract this note discusses three interconnected statistical problems concerning the parkfield sequence of moderate earthquakes and the parkfield prediction experiment a is it possible that the quasi periodic parkfield sequence of characteristic earthquakes is no uncommon specific phenomenon the research hypothesis but can be explained by a preferential selection from available earthquake catalogs to this end we formulate the null hypothesis earthquakes occur according to the poisson process in time and their size follows the gutenberg richter relation we test whether the null hypothesis can be rejected as an explanation for the parkfield sequence b if the null hypothesis cannot be refuted what is the probability of magnitude m 6 earthquake occurrence in the parkfield region c the direct goal of the parkfield experiment is the registration of precursory phenomena prior to a m6 earthquake however in the absence of the characteristic earthquake can the experiment resolve which of the two competing hypotheses is true in a reasonable time statistical analysis is hindered by an insufficiently rigorous definition of the research model and inadequate or ambiguous data however we show that the null hypothesis cannot be decisively rejected the quasi periodic pattern of intermediate size earthquakes in the parkfield area is a statistical event likely to occur by chance if it has been preferentially selected from available earthquake catalogs the observed magnitude frequency curves for small and intermediate earthquakes in the parkfield area agree with the theoretical distribution computed on the basis of a modified gutenberg richter law gamma distribution using deformation rates for the san andreas fault we show that the size distribution of the parkfield characteristic earthquakes can also be attributed to selection bias according to the null hypothesis the yearly probability of a m 6 earthquake originating in the parkfield area is less than 1 signifying that several more decades of observation may be needed before the expected event occurs by its design the parkfield experiment cannot be expected to yield statistically significant conclusions on the validity of the research hypothesis for many decades

coral evidence for earthquake recurrence and an a d 1390 1455 cluster at the south end of the 2004 aceh andaman rupture coral records of relative sea level change provide a history of vertical interseismic and coseismic deformation along the coast of northern simeulue island sumatra and reveal details about earthquakes in the 10th and 14th 15th centuries a d along the southern end of the december 2004 m w 9 2 sunda megathrust rupture over a 56 year period between a d 1390 and 1455 northern simeulue experienced a cluster of megathrust ruptures associated with total uplift that was considerably more than in 2004 uplifted corals at two sites constrain the first event of the cluster to a d 1393 3 and 1394 2 2 a smaller but well substantiated uplift occurred in northern simeulue in 1430 3 an inferred third uplift in a d 1450 3 killed all corals on the reef flats of northern simeulue the amount of uplift during this third event though confirmed only to have exceeded 28 and 41 cm at two sites probably surpassed the 100 and 44 cm that occurred respectively at those sites in 2004 and it was likely more than in 2004 over all of northern simeulue the evidence for past earthquake clustering combined with the inference of considerably greater uplift in a d 1390 1455 than in 2004 suggests that strain may still be stored along the southernmost part of the 2004 rupture interseismic subsidence rates recorded by northern simeulue coral microatolls have varied by up to a factor of 4 at some sites from one earthquake cycle to another

earthquake recurrence on the south hayward fault is most consistent with a time dependent renewal process 1 elastic rebound and stress renewal are important components of earthquake forecasting because if large earthquakes can be shown to be periodic then rupture probability is time dependent while renewal models are used in formal forecasts it has not been possible to exclude the alternate view that repeated large earthquakes can happen in rapid succession without requiring time for stress regeneration here a consistency test between time dependent and time independent recurrence distributions is made using a monte carlo method to replicate the paleoseismic series on the south hayward fault time dependent distributions with recurrence interval of 210 years and coefficient of variation of 0 6 reproduce the event series on the south hayward 5 times more often than any exponential distribution a highly significant difference as determined using a two tailed z test for relative proportions therefore large hayward fault earthquakes are quasi periodic and are most consistent with a stress renewal process

long term earthquake clustering a 50 000 year paleoseismic record in the dead sea graben the temporal distribution of earthquakes in the dead sea graben is studied through a 50 000 year paleoseismic record recovered in laminated sediments of the late pleistocene lake lisan paleo dead sea the lisan represents more than 10 times the 4000 years of historical earthquake records it is the longest and most complete paleoseismic record along the dead sea transform and possibly the longest continuous record on earth it includes unique exposures of seismite beds earthquake induced structures associated with slip events on syndepositional faults the seismites are layers consisting of mixtures of fragmented and pulverized laminae the places where the seismites abut syndepositional faults are interpreted as evidence for their formation at the sediment water interface during slip events on these faults thicker sediment accumulation above the seismites in the downthrown blocks indicates that a seismite formed at the water sediment interface on both sides of the fault scarps modern analogs and the association with surface ruptures suggest that each seismite formed during a m l 5 5 earthquake the 230 th 234 u ages of a columnar section obtained by thermal ionization mass spectrometry give a mean recurrence time of 1600 years of m l 5 5 earthquakes in the dead sea graben the earthquakes cluster in 10 000 year periods separated by quiet periods of similar length this distribution implies that a long term behavior of the dead sea transform should be represented by a mean recurrence of at least 20 000 year record this observation has ramifications for seismic hazard assessment based on shorter records

studies of the continental crust by near vertical reflection methods a review abstract the development of near vertical reflection methods for investigating the continental crust is strongly related to progress that has been made in seismic prospecting and in wide angle observation in crustal refraction studies owing to the good structural resolution of near vertical reflection methods many details concerning first order interfaces in the upper and lower crust have been established while reflectors in the upper crust often appear to resemble thrust faults or diffractions from dome like structures increased reflectivity of the lower crust often provides indications of strong interactions with the underlying mantle differences in reflection density in u s and w german surveys may be attributed mainly to the different tectonic styles rather than to the use of different techniques the occurrence of some reflectors with negative polarity within the band of reflections in the lower crust supports the concept of a laminated crust mantle transition a negative reflection polarity has also been detected at a low velocity gouge containing thrust fault in the upper crust the velocity resolution of near vertical techniques can be improved over that of wide angle methods by using spread lengths greater than 15 km regarding the accretion of the crust both autochthonous creation from the underlying mantle and horizontal allochthonous accretion along thrust faults play a major role the detection of sediments below such thrust planes and of magma bodies along other fault zones provides an interesting new view for prospecting surveys

static stress impact of the 1992 landers earthquake sequence on nucleation and slip at the site of the 1999 m 7 1 hector mine earthquake southern california the proximity in time 7 years and space 20 km between the 1992 m 7 3 landers earthquake and the 1999 m 7 1 hector mine event suggests a possible link between the quakes we thus calculated the static stress changes following the 1992 joshua tree landers big bear earthquake sequence on the 1999 m 7 1 hector mine rupture plane in southern california resolving the stress tensor into rake parallel and fault normal components and comparing with changes in the post landers seismicity rate allows us to estimate a coefficient of friction on the hector mine plane seismicity following the 1992 sequence increased at hector mine where the fault was unclamped this increase occurred despite a calculated reduction in right lateral shear stress the dependence of seismicity change primarily on normal stress change implies a high coefficient of static friction 0 8 we calculated the coulomb stress change using 0 8 and found that the hector mine hypocenter was mildly encouraged 0 5 bars by the 1992 earthquake sequence in addition the region of peak slip during the hector mine quake occurred where coulomb stress is calculated to have increased by 0 5 1 5 bars in general slip was more limited where coulomb stress was reduced though there was some slip where the strongest stress decrease was calculated interestingly many smaller earthquakes nucleated at or near the 1999 hector mine hypocenter after 1992 but only in 1999 did an event spread to become a m 7 1 earthquake

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

slip history of the 1944 bolu gerede earthquake rupture along the north anatolian fault system implications for recurrence behavior of multisegment earthquakes 1 recent research shows that active fault systems produce multisegment earthquakes however we have yet to understand the faulting behavior of various spatial patterns of segments we conducted a three dimensional trenching survey to reconstruct the detailed slip history of a fault segment that ruptured as one of the multisegment ruptures along the north anatolian fault system the trench site on the gerede segment recorded a maximum right lateral slip of up to 6 m that was associated with the 1944 bolu gerede earthquake m 7 4 fault exposures show evidence of four paleoearthquakes radiocarbon dates a refined probability density distribution and correlation with historical earthquakes place the mean repeat time at 330 years four discrete paleoslips yield a slip per event of 5 0 0 8 m with a coefficient of variation of 0 2 our research suggests that multisegment earthquakes exhibit various spatial patterns regardless of recurrence with quasiperiodicity and characteristic slip coincidentally the fault geometry exhibits extremely linear traces suggesting simple stress accumulation and release through earthquake cycles furthermore the 1944 event did not occur in a single segment and the gerede segment probably ruptured within a slip pulse like rupture during a multisegment earthquake a comparable geological slip rate of 17 mm a 1 based on a gps based strain rate supports the persistence of macroscopic asperity through recent geological time therefore we conclude that a segment with simple fault geometry along a strike slip fault system plays an important role in forecasting the timing of future multisegment earthquakes but the spatial extent of such earthquakes needs to be explored further

quasi periodic recurrence of large earthquakes on the southern san andreas fault it has been 153 yr since the last large earthquake on the southern san andreas fault california united states but the average interseismic interval is only 100 yr if the recurrence of large earthquakes is periodic rather than random or clustered the length of this period is notable and would generally increase the risk estimated in probabilistic seismic hazard analyses unfortunately robust characterization of a distribution describing earthquake recurrence on a single fault is limited by the brevity of most earthquake records here we use statistical tests on a 3000 yr combined record of 29 ground rupturing earthquakes from wrightwood california we show that earthquake recurrence there is more regular than expected from a poisson distribution and is not clustered leading us to conclude that recurrence is quasi periodic the observation of unimodal time dependence is persistent across an observationally based sensitivity analysis that critically examines alternative interpretations of the geologic record the results support formal forecast efforts that use renewal models to estimate probabilities of future earthquakes on the southern san andreas fault only four intervals 15 from the record are longer than the present open interval highlighting the current hazard posed by this fault

a reevaluation of the pallett creek earthquake chronology based on new ams radiocarbon dates san andreas fault california 1 the pallett creek paleoseismic record occupies a keystone position in most attempts to develop rupture histories for the southern san andreas fault previous estimates of earthquake ages at pallett creek were determined by decay counting radiocarbon methods that method requires large samples which can lead to unaccounted sources of uncertainty in radiocarbon ages because of the heterogeneous composition of organic layers in contrast accelerator mass spectrometry ams radiocarbon dates may be obtained from small samples that have known carbon sources and also allow for a more complete sampling of the section we present 65 new ams radiocarbon dates that span nine ground rupturing earthquakes at pallett creek overall the ams dates are similar to and reveal no dramatic bias in the conventional dates for many layers however individual charcoal samples were younger than the conventional dates leading to earthquake ages that are overall slightly younger than previously reported new earthquake ages are determined by bayesian refinement of the layer ages based on stratigraphic ordering and sedimentological constraints the new chronology is more regular than previously published records in large part due to new samples constraining the age of event r the closed interval from event c to 1857 has a mean recurrence of 135 years 83 2 years and a quasiperiodic coefficient of variation cov of 0 61 we show that the new dates and resultant earthquake chronology have a stronger effect on cov than the specific membership of this long series and dating precision improvements from sedimentation rates

a probabilistic analysis of episodic preferential flow into superheated fractured rock the amount of water seeping into waste emplacement tunnels is important for the long term performance of the proposed geologic nuclear waste repository at yucca mountain nevada the repository site is located in thick partially saturated fractured tuff that will be heated to above boiling temperatures as a result of heat generation from the decay of nuclear waste since water infiltrating down towards the repository will be subject to vigorous boiling for a significant time period the superheated zone i e rock temperature above the boiling point of water may form an effective vaporization barrier that reduces the possibility of water arrival at emplacement drifts in this paper we analyze the behavior of episodic preferential flow events that penetrate down into the hot fractured rock zone and evaluate the impact of such flow behavior on the effectiveness of the vaporization barrier the characteristic features of episodic preferential flow are estimated from laboratory experiments and described by appropriate probability distributions a semi analytical solution is utilized to determine the complex flow processes in the hot rock environment the solution is applied at several discrete times after emplacement in order to cover the time period of strongly elevated temperatures at yucca mountain

the 1999 izmit turkey earthquake a 3d dynamic stress transfer model of intraearthquake triggering before the august 1999 izmit kocaeli turkey earthquake theoretical studies of earthquake ruptures and geological observations had provided estimates of how far an earthquake might jump to get to a neighboring fault both numerical simulations and geological observations suggested that 5 km might be the upper limit if there were no transfer faults the izmit earthquake appears to have followed these expectations it did not jump across any step over wider than 5 km and was instead stopped by a narrower step over at its eastern end and possibly by a stress shadow caused by a historic large earthquake at its western end our 3d spontaneous rupture simulations of the 1999 izmit earthquake provide two new insights 1 the west to east striking fault segments of this part of the north anatolian fault are oriented so as to be low stress faults and 2 the easternmost segment involved in the august 1999 rupture may be dipping an interesting feature of the izmit earthquake is that a 5 km long gap in surface rupture and an adjacent 25 restraining bend in the fault zone did not stop the earthquake the latter observation is a warning that significant fault bends in strike slip faults may not arrest future earthquakes manuscript received 30 august 2000