spatial variation in the crustal anisotropy and its temporal variation associated with a moderate sized earthquake in the tokai region central japan summary spatial and temporal variations in seismic anisotropy in the crust are investigated using earthquakes in the crust and the subducting philippine sea plate beneath the tokai region central japan we use a total of 351 high quality waveform data recorded from 1986 december until 1999 august by the microearthquake observation network of the research center for seismology and volcanology nagoya university the leading shear waves are polarized in an approximately e w direction independent of the focal depth showing consistency with the direction of regional horizontal maximum compressive stress in the tokai region the time delay increases for greater focal depth down to 30 km these results indicate that the regional compressive stress controls anisotropy not only in the upper crust but also in the lower crust assuming a uniform distribution of anisotropy the degree of anisotropy is estimated to be 0 6 per cent in the lower crust an increase in time delay is found after the aichi ken tobu earthquake m 5 7 in 1997 at station stn this variation is statistically significant and is not an apparent change due to the variation in hypocentre distribution or any kind of artificial effect on the other hand no temporal variation in time delay is found at station inu the spatial pattern of the temporal variation in time delay is consistent with the change in the coulomb failure function cff caused by both coseismic and post seismic fault slips we therefore conclude that the observed temporal change in time delays might be caused by increasing crack density as well as pore fluid pressure due to the static stress change accompanied with the aichi ken tobu earthquake

a synthetic seismicity model for southern california cycles probabilities and hazard the absence of a long historical catalog of observed seismicity with which to constrain earthquake recurrence behaviors is a fundamental stumbling block to earthquake prediction in california conceding that this limitation is not likely to relax in the foreseeable future alternative approaches must be sought to extend the catalog artificially in this article i evaluate the long term behaviors of earthquakes on a map like set of southern california faults through computer simulations that incorporate the physics of earthquake stress transfer and are constrained by excellent but restricted bodies of geological and seismological data i find that model seismicity fluctuates on both short decades and long centuries timescales but that it possesses a well defined mean and standard deviation seismicity fluctuations correlate across different magnitudes and the long term cycles of smaller events seem to lead cycles of larger events short period seismicity fluctuations do not exhibit this tendency and short term changes in low magnitude m5 seismicity are not likely to be an effective predictor of future large events at least for the region as a whole as do real faults the model faults produce characteristic and power law quakes in variable ratios with diverse periodic and nonperiodic behaviors generally larger events tend to occur quasi periodically and smaller ones tend to cluster however only for a few earthquake classes and certain locations is recurrence notably non poissonian an important use of synthetic seismicity is in the construction of earthquake hazard maps because it firmly grounds previously ad hoc assumptions regarding frequency magnitude distributions multiple segment failure statistics and rupture extents while satisfying a spectrum of geological constraints such as fault slip rate segment recurrence interval and slip per event with its depth of temporal and spatial coverage synthetic seismicity also provides a means to investigate the time dependence of seismic hazard because hazard likelihood is a concatenation of the recurrence statistics from many seismic sources in only about 40 50 of the regions near the major faults do sequences of 0 1 g or 0 2 g exceedances differ from poissonian

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

assimilation of paleoseismic data for earthquake simulation simulation of the complete earthquake generation process requires assimilation of observational data on long term behavior of faults over multiple rupture cycles paleoseismology the study of pre instrumental earthquakes from geological field investigations provides the only observations of long term fault behavior paleoseismic data present challenges for assimilation into models because data sets are small sparse analog and contain qualitative uncertainties observations can be categorized as primary measurements from field data or non primary extrapolations or interpretations of primary data assimilation of non primary data could yield biased simulation results we present a primary data set for the san andreas and imperial faults for comparison with non primary data in existing databases and propose standard formats and structure for paleoseismic data assimilation into numerical simulation models

visibility of fault strands in exploratory trenches and timing of rupture events many estimates of seismic risk depend crucially on how well the date of faulting events can be determined from the stratigraphic position of fault strands exposed in exploratory trenches however fault strands cut by trenches may seem to die out where they are in fact only poorly expressed or they may actually die out such ambiguity can lead to misinterpretation of the time of the most recent displacement and also of the recurrence interval between faulting events to investigate the frequency of occurrence and other characteristics of strands that falsely appear to die out or that actually do die out more than 1200 fault strands were analyzed for strands associated with individual faulting events 45 could not be visibly traced in the trench walls to the ground surface that existed at the time of faulting for reverse and strike slip faults the number exceeds 70 thus any apparent upward termination of a fault strand that is thought to indicate the date of a faulting event requires critical examination and corroboration from other evidence nonvisibility i e dieout upward obscure segments and dieout downward is more common on strike slip and reverse faults than on normal faults and is more common in soil horizonsmore than in clay and gravel nonvisibility occurs on strands that have had large 1m as well as small displacements less

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

slip budget and potential for a m7 earthquake in central california the slip rate budget of the san andreas fault saf in central california which is approximately 33 mm yr is accounted for by a change in the slip release mechanism along the fault in the nw section of the fault between bear valley and monarch peak creep apparently accounts for the slip budget with the seismicity contributing negligibly the section at parkfield marks the transition from a creeping to a locked fault trace since the m8 1857 earthquake five m6 earthquakes have occurred but have not completely accounted for the slip budget southeast of parkfield the saf has been locked since 1857 from cholame to bitterwater valley this section now lags the deep slip by the amount of slip released in 1857 consequently faulting in this section could occur at the time of the next parkfield earthquake if this earthquake releases the slip deficit accumulated in the transition zone and in the locked zone the earthquake will have a moment magnitude m7 2

the most recent large earthquake on the rodgers creek fault san francisco bay area the rodgers creek fault rcf is a principal component of the san andreas fault system north of san francisco no evidence appears in the historical record of a large earthquake on the rcf implying that the most recent earthquake mre occurred before 1824 when a franciscan mission was built near the fault at sonoma and probably before 1776 when a mission and presidio were built in san francisco the first appearance of nonnative pollen in the stratigraphic record at the triangle g ranch study site on the south central reach of the rcf confirms that the mre occurred before local settlement and the beginning of livestock grazing chronological modeling of earthquake age using radiocarbon dated charcoal from near the top of a faulted alluvial sequence at the site indicates that the mre occurred no earlier than a d 1690 and most likely occurred after a d 1715 with these age constraints we know that the elapsed time since the mre on the rcf is more than 181 years and less than 315 years and is probably between 229 and 290 years this elapsed time is similar to published recurrence interval estimates of 131 to 370 years preferred value of 230 years and 136 to 345 years mean of 205 years calculated from geologic data and a regional earthquake model respectively importantly then the elapsed time may have reached or exceeded the average recurrence time for the fault the age of the mre on the rcf is similar to the age of prehistoric surface rupture on the northern and southern sections of the hayward fault to the south this suggests possible rupture scenarios that involve simultaneous rupture of the rodgers creek and hayward faults a buried channel is offset 2 2 1 2 0 8 m along one side of a pressure ridge at the triangle g ranch site this provides a minimum estimate of right lateral slip during the mre at this location total slip at the site may be similar to but is probably greater than the 2 0 3 0 2 m measured previously at the nearby beebe ranch site

paleoseismic features as indicators of earthquake hazards in north coastal san diego county california usa abstract new road cut and mass grading excavations in the north coastal area of san diego county california expose heretofore generally unrecognized probable late holocene tsunami deposits and paleoseismically deformed sediments remnant tsunami deposits occur up to 100 m in elevation around the margins of modern coastal lagoons and estuaries and combined with local mima mounds of possible sand blow origin provide indirect but compelling evidence for the late quaternary activity of onshore and offshore faults in the immediate study area probable paleoliquefaction features are regionally widespread and range from fissures filled with sediments derived from overlying marine terrace sand and soil to the more traditional sand filled injection dikes and sills lateral spreads and filled craterlets the source of most liquefied sediment is underlying tertiary bedrock sand and local quaternary marine terrace deposits a paleoseismic liquefaction origin rather than soft sediment loading is deduced for these features based on morphology internal stratigraphy field setting and near proximity to known seismogenic sources some paleoseismic events impacted late holocene indian middens and burial sites the last seismic event probably occurred within the past 1 to 3 ka and possibly even records the historic earthquakes of either november 22 1800 or may 27 1862 the liquefaction features also affect marine terrace sediments tens of meters above modern regional water levels inferentially recording paleoseismic events in this mediterranean type climatic region during winter rains when high level perched water saturates the several meter thick source sediments based on their regional extent the paleoseismic features were likely caused by m 7 tectonic events inferentially generated by the nearby offshore newport inglewood rose canyon fault system or possibly by smaller recently exposed related and localized faults accordingly the seismic hazard of the north coastal area of san diego county may be substantially higher than previously assumed and hence of concern owing to the rapid ongoing and projected population increase

the parkfield california earthquake prediction experiment five moderate magnitude 6 earthquakes with similar features have occurred on the parkfield section of the san andreas fault in central california since 1857 the next moderate parkfield earthquake is expected to occur before 1993 the parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process observations and reports of seismicity and aseismic slip associated with the last moderate parkfield earthquake in 1966 constitute much of the basis of the design of the experiment

deducing paleoearthquake timing and recurrence from paleoseismic data part ii analysis of paleoseismic excavation data and earthquake behavior along the central and southern san andreas fault we present an analysis of paleoseismic data along the central and southern san andreas fault that seeks to establish the timing recurrence and along fault correlation of paleoearthquakes we use bayesian methods to compute a series of probability density functions pdfs that cast paleoearthquake timing in the context of yearly probabilities to quantify the uncertainties present in the paleoseismic dataset based on stratigraphic interpretations we use a scenario based approach in which different viable stratigraphic interpretations are used to infer paleoearthquake timing using these pdfs we attempt to correlate earthquakes along the fault through time to image a time series of past fault ruptures we find that site to site correlation is often difficult due to significant uncertainties nonetheless some ruptures could be correlated from site to site assuming the paleoseismic record is complete these inferences may indicate that ruptures begin and terminate more or less randomly in space the results of our analysis may prove beneficial to future probabalistic seismic hazard assessments of this area and may serve as inputs to studies that seek to quantitatively test rupture models against data in the paleoseismic record

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

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

rapid climatic change in coastal southern california inferred from pollen analysis of san joaquin marsh pollen analysis and five radiocarbon dates of a 687 cm core provide a detailed chronology of environmental change in a marsh at the head of newport bay orange county california sediment deposition kept pace with sea level rise during the early history of the marsh from ca 7000 to 4500 yr b p the site was a freshwater marsh trees were more abundant than today and grassland was the regional vegetation as sea level rose salt marsh gradually invaded the site brief periods of freshwater marsh 3800 2800 2300 and after 560 yr b p correlate with episodes of global cooling during the neoglacial the historic period is marked by the appearance of exotic species particularly erodium cf cicutarium and eucalyptus and the spores of fungi sporormiella and thecaphora peak influx of pollen spores and charcoal probably reflect greater frequency of flooding and erosion ca 5000 yr b p and during the last 1000 yr

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

s wave splitting in the aftershock region of the 1995 hyogo ken nanbu earthquake the 1995 hyogo ken nanbu earthquake kobe earthquake m7 2 occurred on january 17 1995 a temporary aftershock observation was carried out by the geophysical research group organized by universities for prediction seismology in 1995 from october 1995 to january 1996 a dense seismic network was deployed in and around the aftershock region and some seismic stations were set directly on the active fault traces we analyze the s wave splitting in and around the aftershock region of the hyogo ken nanbu earthquake we detect a spatial variation of s wave splitting which can be related to crack orientations in an area where a large earthquake has occurred at stations more than 1 km away from the hyogo ken nanbu earthquake fault zone the leading shear wave polarization directions lspd are found to be parallel to the axis of the regional maximum horizontal compressional stress e w suggesting that cracks caused by regional tectonic stress exist in the area however at stations within 500 m of the earthquake fault zones the lspds are parallel to the fault strikes n45 50 e this suggests that new fractures were produced parallel to the faults by shear faulting of the hyogo ken nanbu earthquake and resulted in s wave splitting along the earthquake fault zone nevertheless shear fault origin anisotropy was not evident at stations on the active faults which ruptured in 1596 this implies that healing processes have already closed the fractures produced by shear faulting in 1596 therefore we can expect that s wave splitting can be a useful tool for monitoring healing processes of active faults

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

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

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

uncharacteristic earthquakes on the san andreas fault one model of earthquake recurrence holds that large quakes exhibit regular or characteristic rupture patterns combined with a simple picture of how elastic strain accumulates in the faults this implies that characteristic earthquakes occur at regular intervals in her perspective grant proposes that recent data from study sites along the san andreas fault are difficult to understand with this model the earthquake activity is more irregular and more clustered than the model would suggest

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

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

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

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

estimating earthquake location and magnitude from seismic intensity data analysis of modified mercalli intensity mmi observations for a training set of 22 california earthquakes suggests a strategy for bounding the epicentral region and moment magnitude m from mmi observations only we define an intensity magnitude m i that is calibrated to be equal in the mean to m m i mean m i where m i mmi i 3 29 0 0206 i 1 68 and i is the epicentral distance km of observation mmi i the epicentral region is bounded by contours of rms m i rms m i m i rms m i m i where rms is the root mean square rms m i m i is the minimum rms over a grid of assumed epicenters and empirical site corrections and a distance weighting function are used empirical contour values for bounding the epicenter location and empirical bounds for m estimated from m i appropriate for different levels of confidence and different quantities of intensity observations are tabulated the epicentral region bounds and m i obtained for an independent test set of western california earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes the analysis strategy is particularly appropriate for the evaluation of pre 1900 earthquakes for which the only available data are a sparse set of intensity observations

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

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

eddy induced heat transport in a coupled ocean atmospheric anomaly model the midlatitude meridional heat transport in the ocean can be partitioned into a transport by the mean flow and an eddy transport this heat transport has been studied in several ocean only models surprisingly it was found that eddy resolving and coarse resolution models have similar total heat transport this is caused by a compensation mechanism in which poleward eddy transport is counterbalanced by an eddy induced meridional circulation recently it was shown that this compensation depends on details of the atmospheric forcing and in fact only occurs for weak thermal coupling where thermal coupling is defined as the rate of change of the surface heat flux with respect to the sea surface temperature sst the thermal coupling varies with the spatial scale of the sst anomaly to study the actual strength of this coupling on the eddy length scale the authors have coupled an isopycnic ocean model with embedded mixed layer to an atmospheric anomaly model by comparing coarse resolution and eddy resolving simulations it is found that 1 the thermal coupling is strong on the eddy length scale and 2 the aforementioned compensation does not occur consequences for the temperature boundary condition in ocean only models the gent and mcwilliams eddy parameterization and climate modeling are discussed

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

focal zone of a future tokai earthquake inferred from the seismicity pattern around the plate interface abstract a future large tokai earthquake has been considered to be the most urgent problem of impending disasters in the central part of the japanese islands since the first warning was announced in 1976 recent progress in observations has provided a great amount of data thus making a detailed investigation possible in this study based on the seismicity and the focal mechanism patterns of microearthquake data the mechanical situation that governs plate interactions around the tokai district was investigated it was found that the seismicity in the subducting philippine sea slab is composed of three characteristic groups of activities intense activity beneath lake hamana a linear cluster extending from lake hamana toward the northwest and a broad cluster expanding over the inland area in the west of suruga bay we propose that these activities occur inside the subducting oceanic crust and reflect the present stress state acting there the mechanism inducing these activities is assumed to come from two stress sources the lateral stretching of the slab and the partial locking between both plates this interpretation leads to the hypothesis that the broad cluster in the west of suruga bay represents a stress concentration due to locking the activity beneath lake hamana is proposed to represent shearing motion induced there and is interpreted to form the boundary between the rupture zones of the 1944 tonankai earthquake and a future large tokai earthquake these analyses resulted in identifying the wide inland area extending from the west coast of suruga bay to lake hamana to be a focal zone of a future tokai earthquake the zone proposed in this study indicates a significant deviation in its strike from the original model proposed by ishibashi in that the former parallels the nankai trough while the latter parallels the suruga trough

spatiotemporal evolution of surface creep in the parkfield region of the san andreas fault 1993 2004 from synthetic aperture radar the parkfield section of the san andreas fault saf is defined as a transitional portion of the fault between slip release behavior types in the creeping section of the saf to the northwest and the apparently locked section to the southeast the parkfield section is characterized by complex frictional fault behavior because it represents a transition zone from aseismic creep to stick slip regime at least six historic earthquakes of mw 6 have occurred in this area in 1881 1901 1922 1934 1966 and 2004 it was observed in the 2004 mw 6 0 parkfield earthquake that 70 of the total coseismic and postseismic moment release occurred aseismically to understand the saf behavior in this area it is of particular interest to measure and analyze not only the spatial evolution of the surface displacement in this area but also its evolution over time using radar data acquired by the european space agency s european remote sensing ers1 2 satellites we constructed descending interferograms and retrieved time series of surface displacements along the central saf for the decade preceding the 2004 parkfield earthquake we focus on characterizing the space and time evolution of surface creep in the parkfield and cholame sections the spatial pattern of the interseismic displacement rate indicates that tectonic strain was not uniformly distributed along the strike of the fault between 1993 and 2004 our data indicate not only a decrease in the creep rate from the parkfield section to south of highway 46 from 1 4 0 3 cm y to 0 6 0 3 cm y but also a small but significant creep rate increase in the cholame section to 0 2 0 1 cm y the evidence for episodic creep in the cholame section of the saf south east of parkfield is in contrast with previously published interpretations of gps and trilateration data the cholame section of the saf merits close monitoring because it was likely the nucleation site of the 1857 fort tejon earthquake and because it has shown recent evidence of deep slow slip as revealed by deep tremors