self driven mode switching of earthquake activity on a fault system theoretical results based on two different modeling approaches indicate that the seismic response of a fault system to steady tectonic loading can exhibit persisting fluctuations in the form of self driven switching of the response back and forth between two distinct modes of activity the first mode is associated with clusters of intense seismic activity including the largest possible earthquakes in the system and frequency size event statistics compatible with the characteristic earthquake distribution the second mode is characterized by relatively low moment release consisting only of small and intermediate size earthquakes and frequency size event statistics following a truncated power law the average duration of each activity mode scales with the time interval of a large earthquake cycle in the system the results are compatible with various long geologic paleoseismic and historical records the mode switching phenomenon may also exist in responses of other systems with many degrees of freedom and nonlinear dynamics 1999 elsevier science b v all rights reserved

folsom drought and episodic drying on the southern high plains from 10 900 10 200 14c yr b p the paleoenvironments of late pleistocene and early holocene time on the southern high plains have been studied for decades but regionally extensive or long term easily recoverable proxy climate indicators are difficult to find the stratigraphy of valley fill and upland eolian deposits and stable carbon isotope data in addition to geographically limited paleontological data now provide clues to the environment during this time which includes the earliest or paleoindian period 11 200 8000 14c yr b p of human occupation during the clovis occupation 11 200 10 900 14c yr b p valleys contained perennial streams this was followed in folsom time 10 900 10 200 14c yr b p by an abrupt change to lakes and ponds with water levels fluctuating between several meters depth and no surface water and marshes and accumulation of sheet sands on uplands starting the earliest phase of construction of the regional dune fields these changing conditions indicate a shift from relatively wetter to relatively drier conditions with episodic drought stable c isotopes further indicate that warming characterized the clovis folsom transition during the rest of the paleoindian period the environment was relatively cool but fluctuated between wetter and drier conditions with an overall trend toward drying that resulted in further enlargement of the dune fields and culminated in the warm dry altithermal beginning 8000 14c yr b p clovis time probably was the wettest of any paleoindian period in terms of runoff and spring discharge the folsom period was drier and was the earliest episode of regional wind erosion and eolian deposition and may have been the warmest of paleoindian times evidence of a previously hypothesized clovis drought in this region is sparse

southern san andreas fault seismicity is consistent with the gutenberg richter magnitude frequency distribution the magnitudes of any collection of earthquakes nucleating in a region are generally observed to follow the gutenberg richter gr distribution on some major faults however paleoseismic rates are higher than a gr extrapolation from the modern rate of small earthquakes would predict this along with other observations led to the formulation of the characteristic earthquake hypothesis which holds that the rate of small to moderate earthquakes is permanently low on large faults relative to the large earthquake rate wesnousky et al 1983 schwartz and coppersmith 1984 we examine the rate difference between recent small to moderate earthquakes on the southern san andreas fault ssaf and the paleoseismic record hypothesizing that the discrepancy can be explained as a rate change in time rather than a deviation from gr statistics we find that with reasonable assumptions the rate changes necessary to bring the small and large earthquake rates into alignment agree with the size of rate changes seen in epidemic type aftershock sequence modeling where aftershock triggering of large earthquakes drives strong fluctuations in the seismicity rates for earthquakes of all magnitudes the necessary rate changes are also comparable to rate changes observed for other faults worldwide these results are consistent with paleoseismic observations of temporally clustered bursts of large earthquakes on the ssaf and the absence of m 7 earthquakes on the ssaf since 1857

prospects for larger or more frequent earthquakes in the los angeles metropolitan region far too few moderate earthquakes have occurred within the los angeles california metropolitan region during the 200 year long historic period to account for observed strain accumulation indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries long interseismic period between much larger moment magnitude m w 7 2 to 7 6 events geologic slip rates and relations between moment magnitude average coseismic slip and rupture area show that either of these hypotheses is possible but that the latter is the more plausible of the two the average time between m w 7 2 to 7 6 earthquakes from a combination of six fault systems within the metropolitan area was estimated to be about 140 years

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

amount effect recorded in oxygen isotopes of late glacial horse equus and bison bison teeth from the sonoran and chihuahuan deserts southwestern united states stable oxygen isotopes from fossils both vertebrate and invertebrate or inorganic sedimentary minerals frequently have been used to make interpretations about ancient global climates oxygen isotope values measured from terrestrial vertebrates or sedimentary carbonates provide information about paleotemperature and amounts of precipitation at a particular site in general these inferences are made on the centennial to millennial scale serial i e ontogenetic sampling of equus and bison tooth enamel provides climatic data on the scale of months to a few years we present models showing how annual environmental patterns of d 18 o would be replicated in the tooth enamel of equus and bison changes in d 18 o due to shifts in temperature in terrestrial environments d 18 o increases with increased temperature and amount and timing of precipitation increased precipitation may result in a decrease in d 18 o a phenomenon called the amount effect are archived in both equus and bison teeth the input signal is better resolved in bison due to its more rapid enamel growth modeled patterns are compared with actual data from modern sites in the sonoran and chihuahuan deserts of the southwestern united states the isotopic patterns from modern teeth agree with that predicted from known variations in meteoric water known floral and faunal assemblages as well as computer models suggest summer rain for the chihuahuan desert of late glacial time 15 000 10 000 years ago but little summer rain for the sonoran desert at that same time serial data from fossil teeth show a clear pattern interpreted to represent the amount effect that includes increased summer rains in the chihuahuan desert and only minor summer rains in the sonoran desert d 2004 elsevier b v all rights reserved

tracking mammoths and mastodons reconstruction of migratory behavior using strontium isotope ratios variations in the strontium isotope ratio 87 sr 86 sr of tooth enamel are used to examine the migration patterns of late pleistocene mammoths and mastodons from florida an animal s 87 sr 86 sr ratio tracks the ratios of its environment which vary with differences in bedrock and soil consequently the environmentally controlled differences in 87 sr 86 sr ratio recorded in mineralized tissue such as tooth enamel may be used to reconstruct the movement patterns of an individual we map variations in local 87 sr 86 sr ratios across modern florida and georgia through analysis of rodent teeth plants and surface water then use this map to interpret the movement patterns of extinct mammals mastodons from northern and central florida have higher 87 sr 86 sr ratios than both modern environmental samples from florida and fossils from nonmigratory species suggesting that mastodons migrated north into georgia mammoths display ratios similar to those of environmental samples and resident species suggesting that they did not migrate outside florida

magnitude frequency distribution in the european mediterranean earthquake regions abstract the european mediterranean earthquake catalogue from 1901 to 1985 which comprises uniformly determined magnitudes ms and mb h 60 km of 13300 events was used in the study of cumulative magnitude frequency relationships nc m compiled for 75 earthquake regions and 25 larger provinces in the whole magnitude range observed the gutenberg richter formula log nc m a bm very rarely fits the cumulative lognc m distributions the b values of log linear segments of nc m vary regionally from b 0 7 to b 1 3 averaging of all values leads to b 0 92 shallow events ms and b 0 56 h 60 km m b most distributions pertain to the mediterranean area b 0 86 from the graph for shallow events and many of them indicate the existence of characteristic earthquakes in accordance with the theoretical single fault model other observed shapes of nc m can be explained by the superposition of populations of different mmax values or by the presence of swarm type activity the observed nc m distributions depend very much on the delineation of earthquake regions i e on the number and dimension of seismoactive faults in the investigated region a premonitory enhancement of medium earthquake activity m 4 5 5 5 can be observed only very rarely

earthquake frequency distribution and the mechanics of faulting the level of intraplate seismicity in japan generally shows a positive correlation with the density of quaternary faulting in southwest japan where intraplate seismicity is concentrated on land rates of seismic moment release m 0 are similar when calculated from either the 400 year historical record of seismicity or geologically determined slip rates of quaternary faults a data set of 18 earthquakes with seismic moments m0 ranging from 0 01 to 3 1027 dyn cm shows a relationship between rupture lengthl and m0 log m0 23 5 1 94 log l when seismic moment on each quaternary fault is assumed to occur in discrete events every t m0 m 0g years where m0 is estimated for a rupture extended over the entire fault length and m 0g is proportional to the slip rate of each quaternary fault the moment frequency distribution of earthquakes log n a b log m0 predicted from the geologic record is virtually identical to that seen with the 400 year record of seismicity in contrast if it is assumed that earthquakes on each fault occur according to the gutenberg richter relation we obtain poor agreement with the observed seismicity thus while regional seismicity satisfies the relation log n a b log m0 or equivalently log n a b log m where m is magnitude it appears that seismicity on individual faults does not this further implies that the primary factor that leads to the magnitude frequency distribution in regional seismicity studies is the relative distribution of the slip rates and lengths of preexisting faults

applicability of the gutenberg richter relation for major active faults in new zealandapplicability of the gutenberg richter relation for major active faults in new zealand

the effects of late quaternary climate and pco2 change on c4 plant abundance in the south central united states the late quaternary was a time of substantial environmental change with the past 70 000 years exhibiting global changes in climate atmospheric composition and terrestrial floral and faunal assemblages we use isotopic data and couple climate and vegetation models to assess the balance between c3 and c4 vegetation in texas during this period the carbon isotope composition of fossil bison mammoth and horse tooth enamel is used as a proxy for c3 versus c4 plant consumption and indicates that c4 plant biomass remained above 55 through most of texas from prior to the last glacial maximum lgm into the holocene these data also reveal that horses did not feed exclusively on herbaceous plants consequently isotopic data from horses are not reliable indicators of the c3 c4 balance in grassland biomes estimates of c4 percentages from coupled climate vegetation models illuminate the relative roles of climate and atmospheric carbon dioxide co2 concentrations in shaping the regional c4 signal c4 percentages estimated using observed modern climate vegetation relationships and late quaternary climate variables simulated by a global climate model are much lower than those indicated by carbon isotope values from fossils when the effect of atmospheric co2 concentration on the competitive balance between c3 and c4 plants is included in the numerical experiment however estimated c4 percentages show better agreement with isotopic estimates from late quaternary mammals and soils this result suggests that low atmospheric co2 levels played a role in the observed persistence of c4 plants throughout the late quaternary

a model of characteristic earthquakes and its implications for regional seismicity regional seismicity i e that averaged over large enough areas over long enough periods of time has a size frequency relationship the gutenberg richter law which differs from that found for some seismic faults the characteristic earthquake relationship but all seismicity comes in the end from active faults so the question arises of how one seismicity pattern could emerge from the other the recently introduced minimalist model of vazquez prada et al of characteristic earthquakes provides a simple representation of the seismicity originating from a single fault here we show that a characteristic earthquake relationship together with a fractal distribution of fault lengths can accurately describe the total seismicity produced in a region the resulting earthquake catalogue accounts for the addition of both all the characteristic and all the non characteristic events triggered in the faults the global accumulated size frequency relationship strongly depends on the fault length fractal exponent and for fractal exponents close to 2 correctly describes a gutenberg richter distribution with a b exponent compatible with real seismicity

low angle extensional faulting reactivated mylonites and seismic reflection geometry of the newark basin margin in eastern pennsylvania low angle 25 to 35 dips have been determined for the border fault of the newark basin near riegelsville pennsylvania on the basis of a vibroseis profile and two continuously cored drill holes across faults at the basin margin a group of moderately strong planar reflections in a zone 0 5 km thick in gneiss and carbonate rocks of the footwall block coincides with the updip projection of imbricate fault slices and mylonites associated with the musconetcong thrust system of drake et al 1967 contrasts in acoustic impedance among mylonitic dolostone and mylonitic gneiss and their protoliths determined from measurements on samples from a third cored hole are sufficiently large to account for reflections seen in the footwall block analysis of drill core and surface outcrops supports the conclusion that low angle extensional faulting in the early mesozoic was localized by reactivation of paleozoic imbricate thrust faults in the basement rocks extension in the northwest southeast quadrant was approximately perpendicular to the strike of the ancient thrust faults in eastern pennsylvania the data presented here are the most explicit three dimensional information obtained thus far in the eastern united states in support of the concept of fault reactivation in controlling formation of early mesozoic extensional basins

late pleistocene c4plant dominance and summer rainfall in the southwestern united states from isotopic study of herbivore teeth abstract patterns of climate and c4plant abundance in the southwestern united states during the last glaciation were evaluated from isotopic study of herbivore tooth enamel enamel 13c values revealed a substantial eastward increase in c4plant consumption formammuthusspp bisonspp equusspp andcamelopsspp the 13c values were greatest inbisonspp 6 9 to 1 7 andmammuthusspp 9 0 to 0 3 and in some locales indicated c4 dominated grazing the 13c values of antilocaprids were lowest among taxa 12 5 to 7 9 and indicated c3feeding at all sites on the basis of modern correlations between climate and c4grass abundance the enamel data imply significant summer rain in parts of southern arizona and new mexico throughout the last glaciation enamel 18o values range from 19 0 to 31 0 and generally increase to the east this pattern could point to a tropical or subtropical source of summer rainfall at a synoptic scale the isotope data indicate that interactions of seasonal moisture temperature and lowered atmospheric pco2determined glacial age c4abundance patterns

are earthquakes predictable summary the answer to the above question depends on the definition of earthquake prediction we discuss several definitions and possible classifications of earthquake prediction methods we also consider various measures of prediction efficiency review several recent examples of earthquake prediction and describe the methods that can be used to verify prediction schemes we conclude that an empirical search for earthquake precursors that forecast the size of an impending earthquake has been fruitless despite considerable effort in several countries no statistically rigorous validation of proposed precursory phenomena is available therefore reported cases of precursors can be explained by random noise or by chance coincidence we present evidence that earthquakes are non linear chaotic scale invariant phenomena the most probable consequence of earthquake self similarity is a lack of earthquake predictability as popularly defined that is a forecast of a specific individual earthquake many small earthquakes occur throughout any seismic zone demonstrating that the critical conditions for earthquake nucleation are satisfied almost everywhere apparently any small shock can grow into a large event thus it is likely that an earthquake has no preparatory stage this sceptical view of current earthquake prediction efforts should not be interpreted as a statement that any further attempts to mitigate the destructive effects of earthquakes are futile the seismic moment conservation principle when combined with geodetic deformation data offers a new way to evaluate the seismic hazard not only for tectonic plate boundaries but also for areas of low seismicity that is the interiors of continents earthquake clustering with a power law temporal decay omori s law can be used to estimate the rate of future earthquake ocurrence realtime seismology can facilitate relief efforts after large earthquakes and eventually provide an immediate warning of severe shaking a few seconds or tens of seconds before the shaking starts

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

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

multi scale seismicity model for seismic risk for a general use of the frequency magnitude fm relation in seismic risk assessment we formulate a multi scale approach that relies on the hypothesis that only the ensemble of events that are geometrically small compared with the elements of the seismotectonic regionalization can be described by a log linear fm relation it follows that the seismic zonation must be performed at several scales depending upon the self similarity conditions of the seismic events and the linearity of the log fm relation in the magnitude range of interest the analysis of worldwide seismicity using the harvard catalog where the seismic moment is recorded as the earthquake size corroborates the idea that a single fm relation is not universally applicable the multi scale model of the fm relation is tested in the italian region

oxygen isotope analyses of co existing carbonate and phosphate in biogenic apatite a way to monitor diagenetic alteration of bone phosphate abstract the oxygen isotopic composition of phosphate 18 op and structural carbonate 18 oc of hydroxylapatite was determined in 31 bone and tooth samples of modern mammals from different countries these two variables are highly correlate r 2 0 98 and the calculated best fit of linear regression is very similar to the equation calculated from the phosphate and carbonate palaeotemperature equations 1 2 according to previous measurements 3 6 on fossils of different ages from different areas it seems quite improbable to find isotopically altered skeletal remains showing a good correlation between 18 op and 18 oc as is the case with modern samples it therefore seems possible at least in some cases to use these measurements for monitoring fossil bone and tooth diagenetic alteration when a set of points lie on the equilibrium line or close to it the 18 o values could be considered close to the original values in contrast when the points lie to the left or to the right of this line this probably means that the values are diagenetically modified due to interaction with meteoric water or 18 o enriched water respectively

earthquake slip distribution a statistical model 1 the purpose of this paper is to interpret slip statistics in a framework of extended earthquake sources we first discuss deformation pattern of the earth s surface from earthquakes and suggest that continuum versus block motion controversy can be reconciled by a model of the fractal distribution of seismic sources we consider earthquake slip statistical distributions as they can be inferred from seismic moment frequency relations and geometrical scaling for earthquakes using various assumptions on temporal earthquake occurrence these distributions are synthesized to evaluate the accuracy of geologic fault slip determinations and to estimate uncertainties in long term earthquake patterns based on paleoseismic data because the seismic moment distribution is a power law pareto a major part of the total seismic moment is released by major earthquakes m 10 19 5 n m moment magnitude m 7 for these large earthquakes the rupture is confined to the upper brittle crust layer we review the various moment frequency and earthquake scaling relationships and apply them to infer the slip distribution at area and site specific regions simulating the seismic moment and strain accumulation process demonstrates that some synthetics can be interpreted as examples of a quasiperiodic sequence we demonstrate the application of the derived slip statistical relations by analyzing the slip distribution and history of the san andreas fault at wrightwood california

what can physical source models tell us about the recurrence time of earthquakes abstract earthquake prediction no matter what the timescale has been and continues to be a contentious subject and it is indubitably a prominent challenge for modern seismology and earthquake physics indeed few natural events can have the catastrophic consequences of earthquakes earthquakes today account for about 60 of natural fatalities a physical description of an earthquake represents an amenable approach to the prediction but it suffers of some limitations basically due to the notorious ignorance about the initial state of a given fault and about the physical law controlling its traction evolution independent on those intrinsic epistemic limitations the concept of the earthquake recurrence based upon the idea of the cyclic or characteristic earthquake has been often invoked to describe and thus to predict subsequent instability events on a seismogenic structure in this paper by using the simplest analog fault model the one degree of freedom mass spring system we quantitatively show that the concepts of the recurrence time and the earthquake cycle have limitations even making them meaningless we will discuss in a compendious synopsis all the possible physical mechanisms which can dramatically affect the recurrence time our conclusions emphasize again that the competing mechanisms potentially occurring during faulting even in the simplest and idealized condition of an isolated fault can significantly complicate the regular cyclicity of earthquakes predicted by the analog fault system these conclusions can contribute to the debate about the role of the physical modeling of earthquakes in the contest of seismic hazard assessment

earthquake prediction a critical review summary earthquake prediction research has been conducted for over 100 years with no obvious successes claims of breakthroughs have failed to withstand scrutiny extensive searches have failed to find reliable precursors theoretical work suggests that faulting is a non linear process which is highly sensitive to unmeasurably fine details of the state of the earth in a large volume not just in the immediate vicinity of the hypocentre any small earthquake thus has some probability of cascading into a large event reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible key word earthquake prediction

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

local magnitudes and apparent variations in seismicity rates in southern california redetermination of local magnitudes for moderate earthquakes recorded by the southern california seismographic network scsn from 1932 to 1990 has shown that the magnitudes have not been consistently determined over that time period the amplitudes of ground velocities recorded on wood anderson instruments were systematically overestimated prior to 1944 compared to present reading procedures leading to a significant overestimation of local magnitudes in addition the change from human to computerized estimation of event magnitude from a suite of amplitudes in 1975 led to slightly lower event magnitudes for the time after 1975 compared to the time before these changes contribute to an apparently higher rate of seismicity in the 1930s and 1940s than later in the catalog which had been interpreted as a decrease in seismicity rate after the 1952 kern county m w 7 5 earthquake wood anderson amplitudes have been reread and consistent magnitudes recalculated using uniform procedures for all earthquakes with a catalog magnitude of 4 5 and greater within the scsn from 1932 to 1943 and those with a catalog magnitude of 4 8 and greater from 1944 to 1990 so as to create a complete list of all earthquakes with a modern local magnitude of 5 0 or greater using these new magnitudes we find that the rate of m l 5 0 and greater earthquakes in southern california over this 59 year period to be poissonian with no changes in rate significant above the 90 level from this rate in any 30 year period the poissonian probability of a m 6 earthquake is 99 7 the probability of an m 7 earthquake is 65 and the probability of an m 8 event is 18

variability of displacement at a point implications for earthquake size distribution and rupture hazard on faults abstract to investigate the nature of earthquake magnitude distributions on faults we compare the interevent variability of surface displacement at a point on a fault from a composite global data set of paleoseismic observations with the variability expected from two prevailing magnitude frequency distributions the truncated exponential model and the characteristic earthquake model we use forward modeling to predict the coefficient of variation cv for the alternative earthquake distributions incorporating factors that would effect observations of displacement at a site the characteristic earthquake model with a characteristic magnitude range of 0 25 produces cv values consistent with the data cv 0 5 only if the variability for a given earthquake magnitude is small this condition implies that rupture patterns on a fault are stable in keeping with the concept behind the model this constraint also bears upon fault rupture hazard analysis which for lack of point specific information has used global scaling relations to infer variability in average displacement for a given size earthquake exponential distributions of earthquakes from m 5 to the maximum magnitude give rise to cv values that are significantly larger than the empirical constraint a version of the model truncated at m 7 however yields values consistent with a larger cv 0 6 determined for small displacement sites although this result allows for a difference in the magnitude distribution of smaller surface rupturing earthquakes it may reflect in part less stability in the displacement profile of smaller ruptures and or the tails of larger ruptures online material global surface displacement data and identified sources of uncertainty

order and diversity in the modes of circum pacific earthquake recurrence recurrence characteristics of great circum pacific earthquakes and determinations of spatial distribution of seismic moment release are surveyed in order to delineate their general features and relate earthquake slip distribution to models of recurrent rupture as noted by others the pattern of moment release is typically very irregular with strong concentrations in a few isolated regions of a much larger aftershock zone despite this complexity rupture nucleation is notably systematic with mainshock epicenter showing a strong tendency to locate in or immediately adjacent to identified regions of high moment release this generalization suggests that earthquake recurrence is more likely to be controlled by maximum rather than average fault slip well documented case histories from twelve plate boundary regions demonstrate that seismic strain release tends to be temporally well ordered while source dimensions slip and cumulative moment release vary considerably from cycle to cycle on none of the segments studied do earthquakes consistently recur in nearly identical events instead individual great earthquakes differ significantly from cycle to cycle or rerupture takes place in a sequence of two or more smaller events despite these differences the duration of the seismic cycle is approximately uniform furthermore when strain release occurs in a sequence of large earthquakes these events take place towards the end of the cycle and occur with increasing rupture length and magnitude these ordered and irregular features of earthquake recurrence argue for the existence of corresponding elements on plate boundary faults the ordered characteristics are identified with zones of concentrated moment release that slip comparable amounts in each cycle and have high shear strength the irregular features are associated with intervening weaker regions that move in response to the stress concentration of dynamic rupture and slip by differing amounts in each event although these mechanistic associations are indirect and tentative the features of recurrent behavior documented here have implications for long term earthquake hazard assessment that are not dependent on the models proposed to explain them chief among these are the cycle to cycle differences among gap filling events and the absence of shocks that fill major slip deficient regions early in the seismic cycle

late pleistocene paleohydrology near the boundary of the sonoran and chihuahuan deserts southeastern arizona usa abstract ground water discharge gwd deposits form in arid environments as water tables rise and approach or breach the ground surface during periods of enhanced effective precipitation where preserved these deposits contain information on the timing and elevation of past ground water fluctuations here we report on the investigation of a series of gwd deposits that are exposed in discontinuous outcrops along a 150 km stretch of the san pedro valley in southeastern arizona near the boundary of the sonoran and chihuahuan deserts chronologic isotopic geochemical faunal assemblage ostracodes and gastropods and sedimentological evidence collectively suggest that the elevation of the regional water table in the valley rose in response to a change in climate 50 ka ago and remained relatively high for the next 35 ka before falling during the bolling allerod warm period rebounding briefly during the younger dryas cold event and falling again at the onset of the holocene the timing of these hydrologic changes coincides closely with variations in 18o values of calcite from a nearby speleothem to the west and changes in lake levels at pluvial lake cochise to the east thus in southeastern arizona the assumption that changes in climate are reflected in all aspects of the hydrologic cycle of a region simultaneously is validated the timing of these changes also broadly coincides with variations in the gisp2 18o record which supports the hypothesis that atmospheric teleconnections existed between the north atlantic and the deserts of the american southwest during the late pleistocene

probabilistic models for earthquakes with large return periods in himalaya region determination of the frequency of large earthquakes is of paramount importance for seismic risk assessment as large events contribute to significant fraction of the total deformation and these long return period events with low probability of occurrence are not easily captured by classical distributions generally with a small catalogue these larger events follow different distribution function from the smaller and intermediate events it is thus of special importance to use statistical methods that analyse as closely as possible the range of its extreme values or the tail of the distributions in addition to the main distributions the generalised pareto distribution family is widely used for modelling the events which are crossing a specified threshold value the pareto truncated pareto and tapered pareto are the special cases of the generalised pareto family in this work the probability of earthquake occurrence has been estimated using the pareto truncated pareto and tapered pareto distributions as a case study the himalayas whose orogeny lies in generation of large earthquakes and which is one of the most active zones of the world has been considered the whole himalayan region has been divided into five seismic source zones according to seismotectonic and clustering of events estimated probabilities of occurrence of earthquakes have also been compared with the modified gutenberg richter distribution and the characteristics recurrence distribution the statistical analysis reveals that the tapered pareto distribution better describes seismicity for the seismic source zones in comparison to other distributions considered in the present study

a reappraisal of large earthquake scaling abstract twelve years ago i pointed out that observations indicate that the slip in large earthquakes scales with their length rather than their width as expected from the canonical model romanowicz 1992 has recently argued that more recent data show that the opposite is true which has obliged me to re examine the question i point out here a defining flaw in her analysis in that she allowed mo the moment at the cross over from small to large earthquakes to be a free variable in her curve fitting whereas this parameter can be defined independently when this parameter is independently fixed i find that the up dated data set confirms my earlier conclusion that for large crustal earthquakes m0 scales with l 2 a little over a decade ago i pointed out that obser vations indicate that the slip in large earthquakes scales with their rupture length scholz 1982 several sub sequent papers provided additional data supportive of this view chen and molnar 1983 shimazaki 1986 scholz et al 1986 large earthquakes are defined in this con text as those that rupture the entire seismogenic thick ness w0 and are thus constrained to propagate farther in a horizontal direction only for crustal earthquakes w0 is nearly constant 15 km so this scaling conflicts with conventional models of earthquakes such as dislocation models because they predict that slip scales with width which is invariant for these earthquakes i offered two alternative ways to interpret these observations one is that such conventional w models are correct but that stress drop could no longer be regarded as scale invariant but must scale with fault length as an alternative i sug gested the possibility of what i termed an l model in which slip intrinsically scales with fault length this created a minor crisis in seismology which has yet to be resolved it is no exaggeration to say that my l model suggestion has not attracted a noticeable coterie of admirers nor has my other suggestion and there has been no other model proposed in the interim that ex plains the observed l scaling although heaton 1990 has suggested a way in which length may scale with stress drop a variation of my w model scaling alternative in the face of this an alternative is to question the obser vations which is what romanowicz 1992 has recently chosen to do in her interpretation of an updated data set she concluded that seismic moment m0 scales lin early with rupture length l for large earthquakes which is consistent with w models and implies that slip u is scale invariant for large crustal earthquakes this great discrepancy with the earlier result she implies is due to the presence of superior modern measurements in the updated data set this issue has major implications both practical and theoretical and merits some debate here i present my own reappraisal of the data in which the conclusions are very different reappraisal of the data romanowicz s conclusions were based on a log log plot of m0 versus l for a data set of strike slip earth quakes she showed that the data in this figure could be better fit by two straight lines one with slope 3 in the lower scale range and one with slope 1 in the upper scale range than with a single line of slope 2 for small earth quakes which grow in both dimensions with l w m0 should scale with l 3 for large earthquakes where w has saturated at w0 and growth only occurs in the l di rection m0 should scale with l according to conven tional models hence the problem produced by my ob servation that m0 scales with l 2 for those events superficially then it appears that she has resolved the issue the problem however is that she has allowed the cross over length l which separates small from large earthquakes to be a free variable in her curve fitting ex ercise she thus obtains a cross over moment of 0 6 to 0 8 x 1020 n m which is appropriate for a rupture length of 60 to 70 km by adding an additional free parameter to the curve fitting one would expect a much better fit to be achieved the question is whether such a step is justified if small earthquakes grow with l w then the transition to large earthquakes defined as an event that ruptures the entire seismogenic thickness would be l w0 10 to 20 km for the data being studied this may be checked observationally because large earth quakes almost invariably nucleate near the base of the seismogenic layer das and scholz 1983 it follows that the transition to large earthquakes is at the length at which one begins to consistently see surface ruptures inspec tion of the earthquakes in romanowicz s 1992 figure 215

why earthquake hazard maps often fail and what to do about it abstract the 2011 tohoku earthquake is another striking example after the 2008 wenchuan and 2010 haiti earthquakes of highly destructive earthquakes that occurred in areas predicted by earthquake hazard maps to be relatively safe here we examine what went wrong for tohoku and how this failure illustrates limitations of earthquake hazard mapping we use examples from several seismic regions to show that earthquake occurrence is typically more complicated than the models on which hazard maps are based and that the available history of seismicity is almost always too short to reliably establish the spatiotemporal pattern of large earthquake occurrence as a result key aspects of hazard maps often depend on poorly constrained parameters whose values are chosen based on the mapmakers preconceptions when these are incorrect maps do poorly this situation will improve at best slowly owing to our limited understanding of earthquake processes however because hazard mapping has become widely accepted and used to make major decisions we suggest two changes to improve current practices first the uncertainties in hazard map predictions should be assessed and clearly communicated to potential users recognizing the uncertainties would enable users to decide how much credence to place in the maps and make them more useful in formulating cost effective hazard mitigation policies second hazard maps should undergo rigorous and objective testing to compare their predictions to those of null hypotheses including ones based on uniform regional seismicity or hazard such testing which is common and useful in similar fields will show how well maps actually work and hopefully help produce measurable improvements there are likely however limits on how well hazard maps can ever be made because of the intrinsic variability of earthquake processes

earthquake rate analysis abstract earthquake rate analysis explores the quantitative relationship between earthquake occurrence rates and geological deformation rates one application is the estimation of tectonic deformation rates from seismicity for comparison with tectonic models another application is the use of geological models to help quantify seismic hazards seismicity is described by a catalog of the largest earthquakes in the region the contribution of small earthquakes towards causing geological deformation is insignificant although the occurrence rate of small events may be predictable from the occurrence rate of large events by a b value relationship the critical information about each earthquake is its seismic moment or better still its seismic moment tensor when moment is not available directly it can be estimated from the earthquake magnitude although this increases uncertainties considerably the average annual moment from all the earthquakes in the catalog is the seismic moment rate uncertainties in seismic estimates of moment rate arise from the short time period of observations from the magnitude moment relationship from the shape of the distribution function giving number of earthquakes as a function of magnitude and from uncertainties in the physical properties of the earth near the source geological models for deformation rates are described by slip rates on individual faults or by regional strain rates a regional strain rate can be derived as a limiting case where there are numerous individual faults such a strain rate is a particularly useful concept where information about each of the faults is limited in the case of either faulting or regional strain the average seismic moment rate is proportional to the deformation rate geological uncertainties arise from difficulties in estimating slip rates or strain rates from fault creep and other aseismic deformation from uncertainty in the part of the fault that fails during earthquakes and boundaries of the deforming region and from uncertainty about the earth s physical properties the seismic moment rate is the critical factor for relating the earthquake occurrence rate and the geological deformation rate using this intermediate parameter one can infer earthquake occurrence rates from deformation rates or infer deformation rates from earthquake occurrence rates generally it is found that deformation rates and earthquake occurrence rates are consistent within uncertainties where both are well constrained they are generally consistent within a factor of two or three

probabilistic prediction of rupture length slip and seismic ground motions for an ongoing rupture implications for early warning for large earthquakes earthquake earlywarning eew predicts future ground shaking based on presently available data long ruptures present the best opportunities for eew since many heavily shaken areas are distant from the earthquake epicentre and may receive long warning times predicting the shaking from large earthquakes however requires some estimate of the likelihood of the future evolution of an ongoing rupture an eew system that anticipates future rupture using the present magnitude or rupture length together with the gutenberg richter frequencysize statistics will likely never predict a large earthquake because of the rare occurrence of extreme events however it seems reasonable to assume that large slip amplitudes increase the probability for evolving into a large earthquake to investigate the relationship between the slip and the eventual size of an ongoing rupture we simulate suites of 1 d rupture series from stochastic models of spatially heterogeneous slip we find that while large slip amplitudes increase the probability for the continuation of a rupture and the possible evolution into a big one the recognition that rupture is occurring on a spatially smooth fault has an even stronger effect we conclude that aneewsystem for large earthquakes needs some mechanism for the rapid recognition of the causative fault e g from real time gps measurements and consideration of its smoothness an eew system for large earthquakes on smooth faults such as the san andreas fault could be implemented in two ways the system could issue a warning whenever slip on the fault exceeds a few metres because the probability for a large earthquake is high and strong shaking is expected to occur in large areas around the fault a more sophisticated eew system could use the present slip on the fault to estimate the future slip evolution and final rupture dimensions and using this information could provide probabilistic predictions of seismic ground motions along the evolving rupture the decision on whether an eew system should be realized in the first or in the second way or in a combination of both is user specific

shear zones formed along long straight traces of fault zones during the 28 june 1992 landers california earthquake surface rupturing during the 28 june 1992 landers california earthquake east of los angeles accommodated right lateral offsets up to about 6 m along segments of distinct en echelon fault zones with a total length of 80 km the offsets were accommodated generally not by faults distinct slip sur faces but rather by shear zones tabular bands of localized shearing along simple stretches of fault zones at landers the rupture is characterized by telescoping of shear zones and intensification of shearing broad shear zones of mild sheafing containing narrow shear zones of more intense sheafing containing even nar rower shear zones of very intense sheafing which may contain a fault thus the ground ruptured across broad belts of shearing with clearly defined subparallel walls oriented nw each broad belt consists of a broad zone of mild sheafing extending across its entire width 50 to 200 m and much nan ower a few meters wide shear zones that accommodate most of the offset of the belt and are por trayed by en echelon tension cracks in response to right lateral shearing the slices of ground bounded by the tension cracks rotated in a clockwise sense producing left lateral sheafing and the slices were forced against the walls of the shear zone producing thrusting even narrower shear zones formed within the narrow shear zones although these probably are guides to right lateral fault segments below the surface rupturing during the earthquake is characterized not by faulting but by the formation of shear zones at various scales

geoarchaeological and paleohydrological evidence for a clovis age drought in north america and its bearing on extinction abstract at the murray springs clovis site in southeastern arizona stratigraphic and geomorphic evidence indicates that an abnormally low water table 10 900 yr b p was followed soon thereafter by a water table rise accompanied by the deposition of an algal mat the black mat that buried mammoth tracks clovis artifacts and a well this water table fluctuation correlates with pluvial lake fluctuations in the great basin during and immediately following clovis occupation of that region many elements of pleistocene megafauna in north america became extinct during the dry period oxygen isotope records show a marked decrease in 18o correlated with the younger dryas cold dry event of northern europe which ended 10 750 yr b p essentially the same time as the water table began to rise in southeastern arizona clovis hunters may have found large game animals easier prey when concentrated at water holes and under stress if so both climate and human predation contributed to pleistocene extinction in america

isotopic paleoecology of clovis mammoths from arizona the causes of megafaunal extinctions in north america have been widely debated but remain poorly understood mammoths mammuthus spp in the american southwest were hunted by clovis people during a period of rapid climate change just before the regional onset of younger dryas cooling and mammoth extirpation thus these mammoths may provide key insights into late pleistocene extinction processes here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the san pedro valley of arizona using the carbon 13c 12c and oxygen 18o 16o isotope compositions of tooth enamel these records suggest that clovis mammoths experienced a warm dry climate with sufficient summer rainfall to support seasonal c4 plant growth monsoon intensity may have been reduced relative to the preceding time period but there is no isotopic evidence for severe drought however it is possible that the clovis drought inferred from stratigraphic evidence occurred suddenly at the end of the animals lives and thus was not recorded in the enamel isotopic compositions unlike mammoths that lived before the last glacial maximum clovis mammoths regularly increased c4 grass consumption during summer probably seeking seasonally green grasslands farther from the river valley this predictable seasonal behavior may have made mammoths easier to locate by clovis hunters furthermore clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction

earthquakes in the los angeles metropolitan region a possible fractal distribution of rupture size although there is debate on the maximum size of earthquake that is possible on any of several known fault systems in the greater los angeles metropolitan region it is reasonable to assume that the distribution of earthquakes will follow a fractal distribution of rupture areas for this assumption and an overall slip rate for the region of approximately 1 centimeter per year roughly one magnitude 7 4 to 7 5 event is expected to occur every 245 to 325 years a model in which the earthquake distribution is fractal predicts that additionally there should be approximately six events in the range of magnitude 6 6 in this same span of time a higher rate than has occurred in the historic record

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

new seismic gap hypothesis five years after we use earthquake data from 1989 1994 to test a forecast by nishenko based on the seismic gap theory we refer to this forecast as the new seismic gap hypothesis because it is the first global forecast based on the seismic gap hypothesis that considers the recurrence time and characteristic earthquake magnitude specific to each plate boundary segment nishenko s forecasts gave probabilities that each of about 100 zones would be filled by characteristic earthquakes during periods of 5 10 and 20 years beginning on the first day of 1989 only the first of these can be tested now we used three tests based on 1 the total number of zones filled by characteristic earthquakes 2 the likelihood that the observed list of filled zones would result from a process with the probabilities specified in nishenko s hypothesis and 3 the likelihood ratio to that of a poissonian null hypothesis the null hypothesis uses a smoothed version of seismicity since 1977 and assumes a gutenberg richter magnitude distribution we used both the harvard centroid moment tensor and the national oceanic and atmospheric administration preliminary determination of epicenters catalogs in our test we also used several different magnitude cutoffs in our tests because nishenko s forecast did not specify a clear relationship between the characteristic earthquake magnitude and the threshold magnitude for a successful prediction using a strict interpretation that only earthquakes equal to or larger than the characteristic magnitude should be counted both catalogs show only two qualifying earthquakes in the entire area covered by the forecast the predicted number is 9 2 and the discrepancy is too large to result from chance at the 99 confidence level the new seismic gap hypothesis predicts too many characteristic earthquakes for three reasons first forecasts were made for some zones specifically because they had two or more earthquakes in the previous centuries biasing the estimated earthquake rate second open intervals before the first event and after the last event are excluded in calculation of recurrence rate third the forecast assumes that all slip in each zone is released in characteristic earthquakes of the same size while in fact considerable slip is released by both smaller and larger earthquakes the observed size distribution of earthquakes is inconsistent with the characteristic hypothesis instead of a deficit of earthquakes above the characteristic limit earthquake numbers are distributed according to the standard gutenberg richter relation by lowering the magnitude threshold for qualifying earthquakes it is possible to reduce the discrepancy between the observed and predicted number of earthquakes to an acceptable level however for every magnitude threshold we tried the new seismic gap model failed the test on the number of filled zones or the likelihood ratio test or both at least at the 95 confidence level

earthquake scaling relations for mid ocean ridge transform faults 1 a mid ocean ridge transform fault rtf of length l slip rate v and moment release rate can be characterized by a seismic coupling coefficient ae at where ae v is an effective seismic area and at l3 2v 1 2 is the area above an isotherm tref a global set of 65 rtfs with a combined length of 16 410 km is well described by a linear scaling relation 1 ae at which yields 0 15 0 05 for tref 600 c therefore about 85 of the slip above the 600 c isotherm must be accommodated by subseismic mechanisms and this slip partitioning does not depend systematically on either v or l rtf seismicity can be fit by a truncated gutenberg richter distribution with a slope 2 3 in which the cumulative number of events n0 and the upper cutoff moment mc dcac depend on at data for the largest events are consistent with a self similar slip scaling dc ac1 2 and a square root areal scaling 2 ac at1 2 if relations 1 and 2 apply then moment balance requires that the dimensionless seismic productivity 0 0 atv should scale as 0 at 1 4 which we confirm using small events hence the frequencies of both small and large earthquakes adjust with at to maintain constant coupling rtf scaling relations appear to violate the single mode hypothesis which states that a fault patch is either fully seismic or fully aseismic and thus implies ac ae the heterogeneities in the stress distribution and fault structure responsible for relation 2 may arise from a thermally regulated dynamic balance between the growth and coalescence of fault segments within a rapidly evolving fault zone

stable carbon and oxygen isotopes of pedogenic carbonates ajo mountains southern arizona implications for paleoenvironmental change abstract in this study we compare the stable isotope composition of late holocene pedogenic carbonate from a late holocene soil developed on the pediment below the ajo mountains in southern arizona usa with measurements of the 18 o of the soil water throughout the seasonal cycle and with 18 o and 13 c measurements on older dated soils the comparison with the soil water composition shows that the pedogenic carbonate is forming in equilibrium with highly evaporated soil water at the highest summer temperatures the 13 c of the carbonate apparently reflects equilibrium with co 2 of an isotopic composition consistent with the present mixture of c3 desert shrubs and cam cactus comparison with glacial period soil carbonates shows that there has been little change in the 18 o but that the 13 c was about 4 5 heavier independent evidence indicates that glacial period summer temperatures were probably much cooler and that the 18 o of precipitation was also lighter the increase in the carbonate water fractionation factor with decreasing temperature probably counteracted the decrease in the 18 o of precipitation producing little net change in the 18 o of the soil carbonate we attribute the decrease in the 13 c to replacement of a glacial period c4 grassland by holocene c3 cam desert shrubs and succulents this replacement was probably in response to an increase in temperature and reduction in summer precipitation at the end of the last glacial period the 13 c of older soil carbonates indicates that landscape was dominated by grassland for most of the past 700 ka and that the present vegetation likely represents a relatively brief anomaly

probabilistic tsunami hazard assessment at seaside oregon for near and far field seismic sources 1 the first probabilistic tsunami flooding maps have been developed the methodology called probabilistic tsunami hazard assessment ptha integrates tsunami inundation modeling with methods of probabilistic seismic hazard assessment psha application of the methodology to seaside oregon has yielded estimates of the spatial distribution of 100 and 500 year maximum tsunami amplitudes i e amplitudes with 1 and 0 2 annual probability of exceedance the 100 year tsunami is generated most frequently by far field sources in the alaska aleutian subduction zone and is characterized by maximum amplitudes that do not exceed 4 m with an inland extent of less than 500 m in contrast the 500 year tsunami is dominated by local sources in the cascadia subduction zone and is characterized by maximum amplitudes in excess of 10 m and an inland extent of more than 1 km the primary sources of uncertainty in these results include those associated with interevent time estimates modeling of background sea level and accounting for temporal changes in bathymetry and topography nonetheless ptha represents an important contribution to tsunami hazard assessment techniques viewed in the broader context of risk analysis ptha provides a method for quantifying estimates of the likelihood and severity of the tsunami hazard which can then be combined with vulnerability and exposure to yield estimates of tsunami risk

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time

non poissonian earthquake occurrence in coupled stress release models and its effect on seismic hazard summary most seismic hazard estimations are based on the assumption of a poisson process for earthquake occurrence even though both observations and models indicate a departure of real seismic sequences from this simplistic assumption instrumental earthquake catalogues show earthquake clustering on regional scales while the elastic rebound theory predicts a periodic recurrence of characteristic earthquakes on longer timescales for individual events recent implementations of time dependent hazard calculations in california and japan are based on quasi periodic recurrences of fault ruptures according to renewal models such as the brownian passage time model however these renewal models neglect earthquake interactions and the dependence on the stressing history which might destroy any regularity of earthquake recurrences in reality to explore this we investigate the coupled stress release model a stochastic version of the elastic rebound hypothesis in particular we are interested in the time variability of the occurrence of large earthquakes and its sensitivity to the occurrence of gutenberg richter type earthquake activity and fault interactions our results show that in general large earthquakes occur quasi periodically in the model the occurrence probability of large earthquakes is strongly decreased shortly after a strong event and becomes constant on longer timescales although possible stress interaction between adjacent fault zones does not affect the recurrence time distributions in each zone significantly it leads to a temporal clustering of events on larger regional scales the non random characteristics especially the quasi periodic behaviour of large earthquakes are even more pronounced if stress changes due to small earthquakes are less important the recurrence time distribution for the largest events is characterized by a coefficient of variation from 0 6 to 0 84 depending on the relative importance of small earthquakes

younger dryas black mats and the rancholabrean termination in north america of the 97 geoarchaeological sites of this study that bridge the pleistocene holocene transition last deglaciation approximately two thirds have a black organic rich layer or black mat in the form of mollic paleosols aquolls diatomites or algal mats with radiocarbon ages suggesting they are stratigraphic manifestations of the younger dryas cooling episode 10 900 b p to 9 800 b p radiocarbon years this layer or mat covers the clovis age landscape or surface on which the last remnants of the terminal pleistocene megafauna are recorded stratigraphically and chronologically the extinction appears to have been catastrophic seemingly too sudden and extensive for either human predation or climate change to have been the primary cause this sudden rancholabrean termination at 10 900 50 b p appears to have coincided with the sudden climatic switch from allerod warming to younger dryas cooling recent evidence for extraterrestrial impact although not yet compelling needs further testing because a remarkable major perturbation occurred at 10 900 b p that needs to be explained

moisture variability in the southwestern united states linked to abrupt glacial climate change the atmospheric response to millennial scale circulation changes in the north atlantic ocean during the last glacial period has been difficult to constrain cave deposits from southwestern north america reveal that atmospheric moisture in this region increased in response to slowdowns of the atlantic meridional overturning circulation

characteristic earthquake model and seismicity around late quaternary active faults in japan a total of 172 late quaternary active fault zones in japan are examined to determine whether the gutenberg richter relationship or the characteristic earthquake model more adequately describes the magnitude frequency distribution during one seismic cycle by combining seismicity data for more than 100 active fault zones at various stages in their seismic cycles we reduced the short instrumental observation period compared to the average recurrence interval in only 5 of the active fault zones were the number of observed events equal to or larger than the number of events expected by the gutenberg richter relationship the average and median frequency ratios of the number of observed events to the number of expected events from the gutenberg richter relationship are only 0 33 and 0 06 respectively suggesting that the characteristic earthquake model more appropriately describes the magnitude frequency distribution along the late quaternary active faults during one seismic cycle moreover the larger an average slip rate is or the shorter an average recurrence interval the larger the gap in magnitude tends to be between the characteristic earthquake and the largest among other events a fault zone with a shorter average recurrence interval and or a larger average slip rate has generally produced more earthquakes in the past or is likely to be at a more mature or developed stage thus these tendencies may reflect a change in the magnitude frequency distribution related to the maturity or development of fault zones

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

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

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

nursing weaning and tooth development in woolly mammoths from old crow yukon canada implications for pleistocene extinctions abstract this study investigates differences in the 13ccol 15n 13csc 18osc sr ca and ba ca values of juvenile and adult woolly mammoths mammuthus primigenius from old crow yukon canada the data indicate that nursing in woolly mammoths lasted at least three years and was associated with minimal decreases in 13ccol 0 2 large decreases in 13csc 1 5 and large increases in 15n 2 and 18osc 2 values sr ca and ba ca ratios suggest that woolly mammoth juveniles began consuming plant foods between 2 and 3 african elephant years of age much later than the initiation of weaning in modern elephants we hypothesize that delayed weaning was an adaptation to increased predation risk and decreased food quality quantity during the extended hours of darkness that occur in winter at high latitudes prolonged nursing and delayed weaning may have made mammoths particularly vulnerable to climatic stressors or human hunting

reconstructing the migration patterns of late pleistocene mammals from northern florida usa abstract we used analyses of the strontium isotope 87sr 86sr ratios of tooth enamel to reconstruct the migration patterns of fossil mammals collected along the aucilla river in northern florida specimens date to the late glacial period and before the last glacial maximum pre lgm deer and tapir displayed low 87sr 86sr ratios that were similar to the ratios of florida environments which suggest that these taxa did not migrate long distance outside of the florida region mastodons mammoths and equids all displayed a wide range of 87sr 86sr ratios some individuals in each taxon displayed low 87sr 86sr ratios that suggest they ranged locally while other animals had high 87sr 86sr ratios that suggest they migrated long distances 150 km outside of the florida region mastodons were the only taxa from this region that provided enough well dated specimens to compare changes in migration patterns over time pre lgm mastodons displayed significantly lower 87sr 86sr ratios than late glacial mastodons which suggests that late glacial mastodons from florida migrated longer distances than their earlier counterparts this change in movement patterns reflects temporal changes in regional vegetation patterns

statistics of characteristic earthquakes statistical methods are used to test the characteristic earthquake hypothesis several distributions of earthquake size seismic moment frequency relations are described based on the results of other researchers as well as my own tests evidence of the characteristic earthquake hypothesis can be explained either by statistical bias or statistical artifact since other distributions of earthquake size provide a simpler explanation for available information the hypothesis cannot be regarded as proven

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

the reconstruction of mammal individual history refining high resolution isotope record in bovine tooth dentine abstract longitudinal and transverse carbon isotope profiles were performed on tooth dentine from five steers bos taurus initially fed c3 and subsequently c4 dominant food comparison of different protocols for bioapatite extraction revealed that the use of naocl considerably reduced the amplitude of variation of 13c within a tooth increasing contribution of c4 food to the carbon isotope composition of bioapatite was found from the tip of the tooth crown to the neck and from the enamel dentine junction toward the pulp cavity these findings confirm that the model of dentine growth as a succession of stacked cones applies to bovines temporal resolution is estimated to be 4 months in transverse profiles significantly better than in longitudinal dentine profiles 8 9 months or even in profiles derived from enamel of the same individual 6 7 months temporal resolution could be improved by a factor of two by selecting a different sampling zone or refining our sampling protocol this sampling strategy could also be applied to dentine collagen and has important ecological and archaeological implications including determination of the season of weaning or the reconstruction of mobility strategies

the preservation of glacial interglacial climatic signatures in the oxygen isotopes of elephant skeletal phosphate abstract phosphate 18o values 18op of modern elephant bone and teeth are found to vary linearly according to the 18o of local meteoric water 18omw a parameter with close ties to regional and local climatic conditions enamel dentine cementum and bone separates from individual fossil elephant specimens of late pleistocene age have op values which vary by up to elephant specimens the larger spread in the 18op values of the various skeletal phases for the fossil samples is interpreted as evidence for post depositional alterantion of primary 18op signatures of some if not all of these fossil skeletal components in the fossil samples investigated enamel and dentine phases have systematically lower 18o values than associated bone and cementum phases differential re equilibration with soil waters either by the wholesale replacement of primary apatite or by processes of isotopic exchange is suggested as a mechanism to account for the observed spread in the fossil phosphate 18o data

a 36 000 yr vegetation history from the peloncillo mountains southeastern arizona usa a 36 200 cal yr b p vegetation history was developed from macrofossils and pollen from 55 packrat middens from 1287 to 1442 m elevation in the peloncillo mountains of southeasternmost arizona usa today these elevations are dominated by semidesert grassland with a mixture of chihuahuan and sonoran desert shrubs including an eastern disjunct population of jojoba simmondsia chinensis from 36 200 to 15 410 cal yr b p rocky areas just above large pluvial lakes that occupied what are now dry playas supported pinus edulis juniperus osteosperma juniperus cf coahuilensis quercus cf turbinella and a rich understory of summer flowering c4 annuals and grasses indicating abundant summer rains and mild winters after 15 410 cal yr b p p edulis declined in abundance and disappeared briefly at 13 925 cal yr b p coincident with expansion of more xeric species and paleohydrological evidence for regional aridity during the bolling allerod warm interval p edulis rebounded briefly during the younger dryas at 12 405 cal yr b p before disappearing along with other mesic woodland species sometime after 12 100 cal yr b p the few middens dating from the early to middle holocene 10 000 4000 yr b p indicate wetter conditions than today at 7790 cal yr b p followed by a general drying trend the 35 middens from the late holocene detail the sequential arrival of desertscrub species as vegetation became more modern in character

earthquake prediction a political problem earthquake prediction is an area of research of great scientific and public fascination the reason for this is not only that earthquakes can cause extremely large numbers of fatalities in a short time but also because earthquakes can have a large social and economic impact on society earthquake prediction in the sense of making deterministic predictions about the place time and magnitude of earthquakes may very well be fundamentally impossible however based on a variety of data earth scientists can make statements about the probability that earthquakes with a certain size will occur in a certain region over a specified time period in this context one speaks of earthquake forecasting a number of methods to achieve this are presented however it is not obvious how society should respond to these forecasts it is shown that there is a fundamental dilemma for decision makers that statements of scientists concerning earthquake occurrence either contain very specific information but are very uncertain or contain very general information but are very certain earthquake hazard can to a large extent be reduced by formulating and enforcing appropriate building codes however given the fact that the majority of the population that is threatened by earthquakes is living in the third world it is clear that this cannot easily be realized for these reasons earthquake prediction is not only a scientific problem it also has a complex political dimension

seismic moment frequency relation for shallow earthquakes regional comparison we determine the parameter values for the seismic moment frequency relation using flinn engdahl s regionalization of global seismicity and the harvard centroid moment tensor data the earthquake size distribution is approximated by the gamma law a version of the gutenberg richter distribution with an exponential taper at the maximum moment there is no statistically significant variation of the fj value the analog of the b value for all seismic regions except for the midocean ridge systems for the latter regions fj 0 93 whereas for all other zones fj 0 63 the maximum moment mxg can be statistically evaluated only for subduction zones treated as a whole mxg 10 21 2 x 10 22 newton m which corresponds to the worldwide mxg value for other regions as well as for single subduction zones mxg is determined by comparing the number of events in each zone with the seismic moment rate calculated on the basis of the nuvel 1 model of plate motion for subduction zones we obtain the estimate of mxg which agrees with the statistical value giving evidence that most tectonic deformation is released by earthquakes we test the hypothesis that no statistically significant variation in mxg occurs in subduction and continent collision zones the hypothesis cannot be rejected with available data for the midocean ridges the mxg estimate cannot be unambiguously determined it is quite possible that the estimate is significantly biased because only a small part of tectonic deformation at the ridges is released by earthquakes these results have importance in evaluating seismic risk and may also lead to developing a physical theory for earthquake generation