rise and fall of the southern santa cruz mountains california from fission tracks geomorphology and geodesy the santa cruz mountains are closely associated with a left bend along the right lateral san andreas fault the loma prieta area on the northeast side of the san andreas consists of fault bounded blocks that rise along active deeply rooted reverse and oblique slip faults six samples from a transect across this area yield concordant apatite fission track ages averaging 4 6 0 5 ma these ages date the time of cooling below 110 c and suggest that about 3 km of unroofing has occurred over the last 4 6 m y allowing for current elevations of about 1 km this suggests an average uplift rate of the order of 0 8 mm yr over the last 4 6 m y to further define the extent and distribution of this young uplift we used morphometric analyses of the youthful topography of the area steep drainage slopes and high local relief indicate that the area northeast of the san andreas forms a well defined zone of high uplift in contrast the region on the southwest side of the san andreas is characterized by broad upwarping and folding more subdued topography old fission track ages and mean quaternary uplift rates of 0 1 0 4 mm yr geodetic data 1906 san francisco earthquake and subsequent strain transients 20 years of interseismic deformation 1989 loma prieta earthquake and 2 years of post loma prieta earthquake strain show that the southern santa cruz mountains repeatedly rise and subside through a complex sequence of bay area deformation events an additional deformation element that involves reverse slip averaging 2 3 mm yr along the foothills thrust system must occur to explain the longer term uplift pattern in the loma prieta area since the late pliocene the asymmetry in deformation on opposite sides of the san andreas probably reflects the contrasting rock types on opposite sides of the fault the influence of preexisting structures and the interaction with neighboring faults of the san andreas system

fault zone connectivity slip rates on faults in the san francisco bay area california the slip rate of a fault segment is related to the length of the fault zone of which it is part in turn the slip rate of a fault zone is related to its connectivity with adjoining or contiguous fault zones the observed variation in slip rate on fault segments in the san francisco bay area in california is consistent with connectivity between the hayward calaveras and san andreas fault zones slip rates on the southern hayward fault taper northward from a maximum of more than 10 millimeters per year and are sensitive to the active length of the maacama fault

holocene history of the san andreas fault between crystal springs reservoir and san andreas dam san mateo county california abstract the geologic part of a seismic safety investigation of san andreas dam focused on a two mile reach of the fault between the dam and crystal springs reservoir historical documents and detailed mapping revealed that the 1906 faulting caused 7 to 9 ft of right shear in the left eastern abutment and occurred on nearly straight traces that experienced a maximum of 9 ft of slip 90 per cent of which was concentrated within a zone 100 ft wide radiocarbon dates on detrital charcoal from two sites of ponded alluvium established that the 1906 traces have been active for at least the last 3 000 yr deflected stream channels further indicate that the 1906 traces have been the locus of right slip for the last 6500 yr and perhaps for all of holocene time detailed geomorphic and stratigraphic analyses of one site showed that five 1906 magnitude slip events have occurred within the last 1130 160 radiocarbon years from which a minimum strain rate of 1 2 cm yr and an average recurrence frequence of 224 25 yr can be calculated trenches excavated across the 1906 traces of the san andreas fault revealed that the zone of active faulting is marked by a slow upwelling of highly sheared rock materials this apparent vertical movement of fault gouge when coupled with right shear and differential stream erosion has produced most of the distinctive landforms of the rift valley

surface displacements in the 1906 san francisco and 1989 loma prieta earthquakes the horizontal displacements accompanying the 1906 san francisco earthquake and the 1989 loma prieta earthquake are computed from geodetic survey measurements the 1906 earthquake displacement field is entirely consistent with right lateral strike slip on the san andreas fault in contrast the 1989 loma prieta earthquake exhibited subequal components of strike slip and reverse faulting this result together with other seismic and geologic data may indicate that the two earthquakes occurred on two different fault planes

the earthquake deformation cycle recurrence and the time predictable model geodetic and geologic observations from a handful of well studied great plate boundary earthquakes provide a basis for exploring those features of the deformation cycle having the strongest influence on recurrence estimation in ideal circumstances the time predictable model requires knowledge of only the seismic slip and time of the last earthquake and the rate of relative plate motion or fault slip practically indirect measurements must usually suffice local coseismic strain changes rather than seismic slip and local deformation rate rather than slip rate permanent nonrecoverable deformation often roughly half the coseismic strain offset near great thrust earthquakes complicates the inference of interplate seismic slip owing to short and long term postseismic transients commonly 20 40 of the coseismic strain drop deformation rates are variable and not simply related to the plate motion rate at strike slip plate boundaries these complications can sometimes be avoided and seismic slip and slip rate can be obtained more or less directly when these favorable circumstances are absent and when knowledge of the deformation cycle is incomplete recurrence accuracy can be improved by empirically correcting for unknown elements of the cycle systematic features in the spatial distribution of the transients and permanent deformation near subduction zones help identify the regions where these corrections are largest and where the shortcomings of the empirical approach are most severe

on and off fault deformation associated with the september 2013 mw 7 7 balochistan earthquake implications for geologic slip rate measurements abstract the 24 september 2013 mw7 7 balochistan pakistan earthquake ruptured a 200 km long stretch of the hoshab fault in southern pakistan and produced the second largest lateral surface displacement observed for a continental strike slip earthquake we remotely measured surface deformation associated with this event using high resolution 0 5 m pre and post event satellite optical imagery we document left lateral near field on fault offsets 10 m from fault using 309 laterally offset piercing points such as streams terrace risers and roads peak near field displacement is 13 6 2 5 3 4 m we characterize off fault deformation by measuring medium 350 m from fault displacement using manual 259 measurements and automated image cross correlation methods respectively off fault peak lateral displacement values are 15 m and exceed on fault displacement magnitudes for 85 of the rupture length our observations suggest that for this rupture coseismic surface displacement typically increases with distance away from the surface trace of the fault however nearly 100 of total surface displacement occurs within a few hundred meters of the primary fault trace furthermore off fault displacement accounts for on average 28 of the total displacement but exhibits a highly heterogeneous along strike pattern the best agreement between near field and far field displacements generally corresponds to the narrowest fault zone widths our analysis demonstrates significant and heterogeneous mismatches between on and off fault coseismic deformation and we conclude that this phenomenon should be considered in hazard models based on geologically determined on fault slip rates

geodetic measurement of horizontal deformation in the northern san francisco bay region california analysis of geodolite observations in the coast ranges of northern california indicates that relative plate motion is spread over a wide zone little or no deformation occurs to the southwest of the san andreas fault itself to the northeast of the san andreas fault a region transected by the parallel rodgers creek and maacama faults 25 6 mm yr of right lateral slip is distributed over about 60 km there is a peak shear strain of 0 6 0 1 rad yr near the san andreas fault elsewhere in the deforming zone shear strain rates are 0 3 0 04 rad yr at the northeastern boundary of the study area the strain rate is less than 0 2 rad yr except for the high strain rate near the san andreas fault there is no evidence of any localization of deformation to the surface traces of the faults nor is there any evidence of creep or aseismic slip on any of the faults in the area the data indicate that the relative motion between the pacific and north american plate occurs primarily to the northeast of the san andreas fault the observations are inconsistent with models that include slip at depth on only the san andreas fault the data can be fit equally well by models with slip at depth on all three of the major faults or with motion distributed across the entire zone from the san andreas fault to the napa valley fault preliminary analysis of observations to the farallon islands about 40 km southwest of the san andreas fault suggests that little or no additional relative motion is accommodated on that side of the san andreas fault in particular it is unlikely that the 20 mm yr difference between the plate motion rate about 55 mm yr and the san andreas fault system rate about 35 mm yr can be explained by deformation between the san andreas fault and the farallon islands

higher plant vegetation changes during pliocene sapropel formation the 13 c values of higher plant wax c 27 33 n alkanes were determined in three time equivalent pliocene 2 943 ma sapropels and homogeneous calcareous ooze from three different sites forming an east west transect in the eastern mediterranean basin in order to study the composition of the vegetation on the continents surrounding the mediterranean sea a two end member mixing model transformed the measured 13 c values into the contribution of c 4 plants to the terrestrial vegetation these calculations indicated a high c 4 plant contribution i e 40 50 in the periods just before and just after sapropel formation during sapropel deposition the c 4 plant contribution increased by up to 20 at all sites this is interpreted to record the increased overall plant coverage of the mediterranean borderlands resulting from the change in formerly barren desert areas into c 4 grass dominated savannahs as a response to the wetter climate during sapropel deposition enhanced accumulation rates ars of long chain n alkanes c 27 33 and n alkan 1 ols c 26 30 towards the middle of the sapropel in concert with a decrease in the ti al ratio confirm an increased delivery of terrigenous organic matter at all sites these biomarkers were probably predominantly fluvially transported to the mediterranean sea not only by the nile but by fossil wadi river systems on the northern african continent

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

geodetic measurement of crustal deformation on the san andreas hayward and calaveras faults near san francisco california analysis of a geodetic network of 115 lines crossing the san andreas hayward and calaveras faults in the vicinity of san francisco bay and measured repeatedly between 1970 and 1980 has revealed details about the accommodation of relative plate motion in this area the most striking result is that the deformation is not uniformly distributed across the area in the east bay along the hayward and calaveras faults all motion appears to take place as slip directly on the fault with no accumulation of strain in the adjacent crust on both the calaveras and the hayward faults the rate obtained for the 1970 to 1980 period agrees with geologic rates spanning a few million years and with creep rates spanning a few decades the hayward fault slip rate is 7 1 mm yr the calaveras fault slip rate is 7 1 mm yr with perhaps half of this slip distributed across a zone a few kilometers wide probably as inelastic deformation of weak near surface material the absence of strain accumulation in the east bay is surprising since the hayward and calaveras faults have been the site of large earthquakes in the past a block located east of the calaveras fault and south of the las positas fault has been rotating clockwise at a rate of 0 3 0 1 rad yr with very little internal deformation along the san francisco peninsula no detectable slip occurs less than 1 5 mm yr at the surface but appreciable strain is accumulating near fault shear strain rates are 0 6 0 1 strain yr engineering with direction n47 w 9 the slip rate near the san andreas fault is 12 2 3 9 mm yr distributed across a broad zone the relative motion across the whole region during the period 1970 1980 is 32 1 7 4 mm yr supplement available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington d c 20009 document j81 011 1 00 payment must accompany order

long term fault creep observations in central california the u s geological survey usgs has been monitoring aseismic fault slip in central california for more than 10 years as part of an earthquake prediction experiment since 1968 the usgs creep network has grown from one creep meter at the cienega winery south of hollister to a 44 station network that stretches from hayward east of san francisco bay to palmdale in southern california in general the long term slip pattern is most variable on sections of the faults where several magnitude 4 and larger earthquakes occurred during the recording period e g calaveras fault near hollister and san andreas fault between san juan bautista and bear valley these fault sections are the most difficult to characterize with a single long term slip rate in contrast sections of the faults that are seismically relatively quiet e g san andreas fault between bear valley and parkfield produce the steadiest creep records and are easiest to fit with a single long term slip rate appendix is available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington d c 20009 document j82 004 1 00 payment must accompany order

forecasts of the 1989 loma prieta california earthquake abstract the magnitude m w 6 9 loma prieta earthquake struck the san francisco bay area of central california at 5 04 p m local time on 17 october 1989 killing 62 people and generating billions of dollars in property damage scientists were not surprised by the occurrence of a destructive earthquake in this region and had in fact been attempting to forecast the location of the next large earthquake in the san francisco bay area for decades this article summarizes more than 20 scientifically based predictions made before the 1989 loma prieta earthquake for a large earthquake that might occur in the loma prieta region the predictions geographically closest to the actual earthquake primarily specified slip on the san andreas fault northwest of san juan bautista a number of the predictions did encompass the magnitude of the actual earthquake and at least one approximately encompassed the along strike rupture length post loma prieta studies of the 1906 san francisco california earthquake in the loma prieta region of the san andreas fault zone show the loma prieta and 1906 events with different senses of slip and fault plane dip therefore some have argued that the 1989 earthquake was not foreseen even though 1 this earthquake appears to have released much of the horizontal strain accumulated since 1906 and 2 not all of the forecasts were based on 1906 behavior

review of the upper cretaceous lower tertiary sequence on seymour island antarctica the thick sequence of fossiliferous marine and non marine sandstones and siltstones on seymour i represents the most complete well exposed section of upper cretaceous to lower tertiary rocks known in the southern hemisphere the succession has been divided into the upper campanian to possibly lowermost tertiary marambio group comprised of the lopez de bertodano and sobral formations and the lower tertiary cross valley and la meseta formations of the seymour island group the lopez de bertodano formation consists of c 1067 m of medium grained to silty concretionary sandstones of middle campanian to possibly maestrichtian age and the sobral formation of c 210 m of medium to coarse grained glauconitic concretionary sandstones the precise age of the sobral formation is uncertain but may be maestrichtian to possibly danian the lower 110 m of the seymour island group consists of non marine gravelly to pebbly sandstones and tuffaceous plant bearing siltstones of the cross valley formation overlying which are 450 m of fine grained marine sandstones and siltstones with interbedded fossiliferous pebbly conglomerates recent studies of the diverse and abundant faunas and floras of the seymour island group have shown that they are older than previously thought the cross valley formation being palaeocene and the la meseta formation late eocene to possibly earliest oligocene

probabilities of occurrence of large plate rupturing earthquakes for the san andreas san jacinto and imperial faults california 1983 2003 the san andreas san jacinto and imperial faults in california are divided into 19 segments conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake i e an event that breaks the entire down dip extent of the seismogenic zone during the next 20 years the sizes of such events which account for most of the slip that occurs seismically appear to vary greatly for different segments of these faults repeat time of large shocks coseismic displacement moment release rupture length and seismic magnitude appear to correlate with one another and to be a function of the tectonic style of different parts of those fault zones tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks it is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size since repeat time varies however for a given segment of a fault a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment using as input the time of the last large shock the average recurrence time and the standard deviation of time intervals between events dates of the last large shocks are available for most of the segments investigated repeat times are estimated from times of historic and prehistoric events tectonic similarity and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup the standard deviation of time intervals divided by the average repeat time is close to 1 3 for three fault segments in california for which data are available on historic and prehistoric earthquakes that normalized value is adopted for all calculations of conditional probability magnitudes and seismic moments of future plate rupturing events are estimated for each fault segment several of the segments have well constrained probabilities for rupture during the next 20 years whereas others have large uncertainties eight of the segments constituting about 40 of the total lengths of the three faults have moderate to high probability and thus should be instrumented and studied extensively so as to provide shorter time warnings in some cases two adjacent segments may be nearly in phase in their loading history and may break in a single event the segment of the san andreas fault from opposite san jose to san juan bautista which ruptured less than 1 5 m in 1906 and which probably also broke in 1838 is calculated to have a moderate to high probability of an earthquake of magnitude 6 to during the next 20 years a 325 km section of the southern san andreas between tejon pass and the salton sea has about a 25 chance of rupturing in a shock of magnitude near 8 during the next 20 years all the other segments have only a small chance i e less than 5 to 10 of rupturing in an event of magnitude near 8 during that interval

source study of the 1906 san francisco earthquake all quality teleseismic recordings of the great 1906 san francisco earthquake archived in the 1908 carnegie report by the state earthquake investigation commission were scanned and digitized first order results were obtained by comparing complexity and amplitudes of teleseismic waveforms from the 1906 earthquake with well calibrated similarly located more recent earthquakes 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes at nearly co located modern stations peak amplitude ratios for calibration events indicated that a localized moment release of about 1 to 1 5 10 27 dyne cm was responsible for producing the peak the teleseismic body wave arrivals at longer periods 50 to 80 sec we found spectral amplitude ratios of the surface waves require a total moment release between 4 and 6 10 27 dyne cm for the 1906 earthquake comparable to previous geodetic and surface wave estimates thatcher 1975 we then made a more detailed source analysis using morgan hill s body waves as empirical green s functions in a finite fault subevent summation the morgan hill earthquake was deemed most appropriate for this purpose as its mechanism is that of the 1906 earthquake in the central portion of the rupture from forward and inverse empirical summations of morgan hill green s functions we obtained a good fit to the best quality teleseismic waveforms with a relatively simple source model having two regions of localized strong radiation separated spatially by about 110 km assuming the 1906 epicenter determined by bolt 1968 this corresponds with a large asperity on the order of the loma prieta earthquake in the golden gate san francisco region and one about three times larger located northwest along strike between point reyes and fort ross this model implies that much of the 1906 rupture zone may have occurred with relatively little 10 to 20 sec radiation consideration of the amplitude and frequency content of the 1906 teleseismic data allowed us to estimate the scale length of the largest asperity to be less than about 40 km with rough constraints on the largest asperity size and magnitude we produced a suite of estimated synthetic ground velocities assuming a slip distribution similar to that of the loma prieta earthquake but with three times as much slip for purposes of comparison with the recent abundant loma prieta strong motion data set we moved the largest 1906 asperity into loma prieta region peak ground velocity amplitudes are substantially greater than those recorded during the loma prieta earthquake and are comparable to those predicted by the attenuation relationship of joyner and boore 1988 for a magnitude m w 7 7 earthquake

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

long term seismic potential of the san andreas fault southeast of san francisco california the long term decade or longer seismic potential of the peninsular san andreas fault the 125 km long segment southeast of san francisco has been assessed by comparing the slip accompanying the 1906 mw 7 7 earthquake with the amount of this slip deficit made up since 1906 of particular importance is the longstanding factor of 2 inconsistency between 1906 surface offsets 1 5 m and geodetically determined coseismic slip 2 7 m on the southern 90 km of the peninsular san andreas in reexamining this issue we find that the discrepancy cannot be attributed to either large observational uncertainties in the geodetic data or shortcomings in fault modeling rather the problem lies in the complexity of this 90 km long fault reach where the san andreas trend changes by 6 the zone of recent deformation is 0 5 2 km wide and much of the fault is heavily vegetated and inaccessible farther northwest on the 1906 rupture where the fault geometry is much simpler evidence from deformed fences shows that right lateral coseismic slip was commonly distributed across a zone 20 600 m wide with only about 70 of the total slip occurring at the main fault trace the general importance of distributed coseismic deformation and the evidence for fault zone complexity indicate that the best estimate of 1906 slip on this 90 km fault segment is the geodetically constrained value of 2 6 0 2 m farther northwest on the peninsular san andreas the coseismic slip ranges from 3 4 to 4 4 m and geodetic slip and surface offsets show considerably better agreement following previous work we have assessed the risk posed to the southern peninsular san andreas by two broad classes of earthquakes these appraisals use the geodetic slip distribution apply a long term slip rate of 15 mm yr suggested by geologic and geodetic studies and assume the approximate correctness of the time predictable recurrence model the possibility of an m 6 1 2 earthquake on the 30 km long segment northwest of san juan bautista cannot be completely precluded but the evidence bearing on its likelihood is contradictory in contrast with several previous assessments we find that the risk of an earthquake of m 7 rupturing the southern 90 km of the peninsular san andreas during the next several decades is quite low

seismic potential for large and great interplate earthquakes along the chilean and southern peruvian margins of south america a quantitative reappraisal the seismic potential of the chilean and southern peruvian margins of south america is reevaluated to delineate those areas or segments of the margin that may be expected to experience large or great interplate earthquakes within the next 20 years 1984 2004 long term estimates of seismic potential or the conditional probability of recurrence within a specified period of time are based on 1 statistical analysis of historic repeat time data using weibull distributions and 2 deterministic estimates of recurrence times based on the time predictable model of earthquake recurrence both methods emphasize the periodic nature of large and great earthquake recurrence and are compared with estimates of probability based on the assumption of poisson type behavior the estimates of seismic potential presented in this study are long term forecasts only as the temporal resolution or standard deviation of both methods is taken to range from 15 to 25 of the average or estimated repeat time at present the valparaiso region of central chile 32 35 s has a high potential or probability of recurrence in the next 20 years coseismic uplift data associated with previous shocks in 1822 and 1906 suggest that this area may have already started to rerupture in 1971 1973 average repeat times also suggest this area is due for a great shock within the next 20 years flanking segments of the chilean margin coquimbo illapel 30 32 s and talca concepcion 35 38 s presently have poorly constrained but possibly quite high potentials for a series of large or great shocks within the next 20 years in contrast the rupture zone of the great 1960 earthquake 37 46 s has the lowest potential along the margin and is not expected to rerupture in a great earthquake within the next 100 years in the north the seismic potentials of the mollendo arica 17 18 s and arica antofagasta 18 24 s segments which last ruptured during great earthquakes in 1868 and 1877 are also high but poorly constrained

the black mountain asperity seismic hazard of the southern san francisco peninsula california black mountain a 860 m high wedge of franciscan formation mostly comprising basic ultrabasic rock sw of palo alto and just ne of the san andreas fault marks an abrupt bend in the fault at the northern end of a 100 km long segment of the fault that strikes 9 more e w than the fault to the north or south it also bounds a marked change in the physiographic setting of the fault which to the north follows a well developed linear fault valley and to the south follows a poorly defined topographic trace that traverses the rugged santa cruz mountains the bend at black mountain had a profound effect on the 1906 rupture the 75 km section to the se of this point slipped only 1 1 4 m as compared to the 2 5 4 m typical of the rupture on the san francisco peninsula to the nw this 75 km long slip deficit region from black mountain to san juan bautista if ruptured in its entirety would produce a ms 6 9 earthquake the conditional probability of this rupturing in the near future is the highest of any section of the san andreas fault except parkfield this earthquake would rupture 30 km farther northwest and be about 3 times larger than that previously proposed by others and this constitutes a greater risk to the southern san francisco peninsula than previously expected