short paper terrane rotations in the irish caledonides palaeozoic palaeomagnetic data from scotland and ireland have been compared on a terrane model and early caledonide clockwise rotation of a terrane through 65o 30 connemara massif and later anticlockwise rotation of up to 50 in the vicinity of clew bay have been deduced these are the firfirst estimates of terrane rotations in the european part of the caledonian appalachian orogen terrane analysis of orogenic belts is currently a major field of study to a large extent this has been stimulated by studies in the north american cordillera where large rotations and translations have been determined palaeomagnetically see beck et al 1986 and references therein terrane analysis may be applied to older orogenic belts such as the caledonides which have been particularly intensively studied previously published palaeomagnetic data from connemara morris tanner 1977 and nw galway morris et al 1973 had indicated local block rotations but furnished few constraints on either their age and magnitude or on the identities of the blocks this paper relates the currently available palaeomagnetic dataseto a terrane model of w ireland hutton dewey 1986 see fig 1 new data new palaeomagnetic data from the irish caledonides comprise the following connemara gabbro robertson 1988 the dalradian rocks of the connemara massif are unique in the british caledonides in lying to the south of a caledonian ophiolite and also south of a thick sequence of ordovician shales and volcanics of low metamorphic grade in clew bay and the south mayo trough respectively the structural

results for aseismic creep on the hayward fault using polarization persistent scatterer insar abstract we present new results for shallow aseismic creep on the hayward fault in california using a new dinsar technique this method not only provides for the first time the ability to map the displacement field on both sides of the fault it does so over a much shorter time period than earlier results the results provide a good match in the near field to both the regional continuous gps velocities and data from an alinement network that measures long term creep along the fault the average slip rate for the northern segment of the hayward fault is 4 4 mm yr between 2008 and 2011 slightly less than that estimated for longer time periods suggesting that the slip rate may not be constant if the slip rate along the fault is variable on the decadal or longer scale current estimates of its earthquake potential and the associated hazard associated with the slip rate deficit may need to be revised from previous estimates we demonstrate the potential impact of this method to better define the spatial and temporal complexity of aseismic slip and estimate the accumulated elastic strain along one of the most significant sources of seismic hazard in the san francisco bay area

estimating locations and magnitudes of earthquakes in southern california from modified mercalli intensities modified mercalli intensity mmi assignments instrumental moment magnitudes m and epicenter locations of thirteen 5 6 m 7 1 training set events in southern california were used to obtain the attenuation relation mmi 1 64 1 41 m 0 00526 h 2 63 log h where h is the hypocentral distance in kilometers and m is moment magnitude intensity magnitudes m i and locations for five 5 9 m 7 3 independent test events were consistent with the instrumental source parameters fourteen historical earthquakes between 1890 and 1927 were then analyzed of particular interest are the m i 7 2 9 february 1890 and m i 6 6 28 may 1892 earthquakes which were previously assumed to have occurred near the southern san jacinto fault a more likely location is in the eastern california shear zone ecsz these events and the 1992 m 7 3 landers and 1999 m 7 1 hector mine events suggest that the ecsz has been seismically active since at least the end of the nineteenth century the earthquake catalog completeness level in the ecsz is m 6 5 at least until the early twentieth century online material figures and table of empirical mmi site corrections

the fold test in palaeomagnetism summary the fold test suggested by mcelhinny is shown to be inappropriate more correctly one should determine whether the mean direction of a group of sites from one limb of a fold may be distinguished statistically from the mean direction of a group of sites from another limb details of the application of this test are given with examples it is shown that the test indicates significance under far less severe folding than does the test suggested by mcelhinny

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

watching the hayward fault the hayward fault located on the east side of the san francisco bay represents a natural laboratory for seismologists because it does not sleep silently between major earthquakes in his perspective simpson discusses the study by ba rgmann et al who have used powerful new techniques to study the fault the results indicate that major earthquakes cannot originate in the northern part of the fault however surface rupturing earthquakes have occurred in the area suggesting that they originated to the north or south of the segment studied by ba rgmann et al fundamental questions remain regarding the mechanism by which plate tectonic stresses are transferred to the hayward fault

the 2007 m5 4 alum rock california earthquake implications for future earthquakes on the central and southern calaveras fault 1 the similarity of seismograms recorded by two seismic stations demonstrate that the 31 october 2007 moment magnitude m5 4 alum rock earthquake is a repeat of a 1955 ml5 5 earthquake both occurred on oppenheimer et al s 1990 zone v stuck patch on the central calaveras fault providing new support for their model of calaveras fault earthquake activity we suggest that zone v fails only in a family of recurring m 5 4 5 5 earthquakes the 1955 and 2007 earthquakes are the penultimate and ultimate zone v events earthquakes in 1891 and 1864 are possible earlier zone v events the next zone v event is not expected in the next few decades assuming a time dependent recurrence model the mean forecast date is 2064 2035 2104 95 confidence range we further suggest that zones i ii iii and iv fail in recurring m 5 1 5 3 m 5 6 5 8 m 6 1 6 3 and m 4 9 5 0 earthquakes respectively if our earthquake recurrence model is correct the next zone i event is overdue and could occur anytime and m5 6 earthquakes should not occur on zones ii iii and iv before 2014 2012 and 2026 respectively we cannot rule out the possibility that zone vi which lies at the southern end of the mission seismic trend where the southern hayward and central calaveras faults appear to connect at depth fails aseismically or in large events on the southern hayward fault such as last occurred in 1868 or in large events on the adjoining northern calaveras fault segment

the seismicity along the dead sea fault during the last 60 000 years abstract evidence for unchanging slip rate and a gutenberg richter relation for earthquake distribution along the dead sea fault during the past 60 000 yr are presented the evidence comes from three different segments approximately 100 km apart and from three different timescales prehistoric paleoseismic historical and modern instrumental records the paleoseismic data are based on two different methods in the southern arava valley and the northern jordan valley segments the amount of normal displacement along several faults is used while in the dead sea basin the appearance of brecciated beds which are considered as seismites is used we found that for the southern arava valley segment a constant dip slip rate of 0 5 mm yr can explain the cumulative normal slip during the past 45 000 yr this suggests that normal faulting is only 10 of the total left lateral strike slip motion we also found that for all three segments the paleoseismic and historical records of strong earthquakes lie on the linear extrapolation of the frequency magnitude relation of the instrumental record the calculated b values for all three segments are between 0 85 and 1 similar to other major strike slip faults in the world it is concluded that the gutenberg richter distribution is a stable mode in the tectonic setting of the dead sea fault during the past 60 000 yr

intersections of remanence small circles new tools to improve data processing and interpretation in palaeomagnetism summary intersections of remanence small circles are increasingly used in palaeomagnetism to determine the palaeofield direction from synfolding remanences the approach small circle intersection sci method presupposes that remanence small circles from sites tilted to different directions intersect in a common point which is assumed to represent the palaeofield direction the sci method is not restricted to synfolding remanences it can be applied also to derive the palaeofield direction from pre folding remanences in addition to tilt correction and as a cross check for fold tests however the sci method has specific requirements and does not work in all cases the suitability of data sets and reliability of palaeofield estimates have to be assessed carefully and always against the background of local geology this paper examines the occurrence and distribution of sci as a tool of judgement first a data set is most suitable and a palaeofield estimate by sci most reliable when most of the theoretically possible intersections are realized and in addition clearly grouping in a narrow region second the small circles that greatly determine the result of sci are identified by the highest number of intersections they have with the others these criteria allow a systematic investigation of sci estimates upon stability and dependencies moreover scis can be an indicator of irregular unexpected tectonic settings when the intersections disperse strongly although significant bedding strike differences are given relative rotations or other unexpected displacements are likely to have occurred if so the sci estimate will be invalid and probably biased however also fisher mean calculation and most fold tests will be affected in this case the scis can help to separate the data into subsets valid for fisher statistics and sci methods the other possibility is to use tentative reconstructions to infer the true sequence of tilts and rotations and correct the data adequately

magnitudes and locations of the 1811 1812 new madrid missouri and the 1886 charleston south carolina earthquakes we estimate locations and moment magnitudes m and their uncertainties for the three largest events in the 1811 1812 sequence near new madrid missouri and for the 1 september 1886 event near charleston south carolina the intensity magnitude m i our preferred estimate of m is 7 6 for the 16 december 1811 event that occurred in the new madrid seismic zone nmsz on the bootheel lineament or on the blytheville seismic zone m i is 7 5 for the 23 january 1812 event for a location on the new madrid north zone of the nmsz and 7 8 for the 7 february 1812 event that occurred on the reelfoot blind thrust of the nmsz our preferred locations for these events are located on those nmsz segments preferred by johnston and schweig 1996 our estimates of m are 0 1 0 4 m units less than those of johnston 1996b and 0 3 0 5 m units greater than those of hough et al 2000 m i is 6 9 for the 1 september 1886 event for a location at the summerville middleton place cluster of recent small earthquakes located about 30 km northwest of charleston

paleoseismic investigations in the santa cruz mountains california implications for recurrence of large magnitude earthquakes on the san andreas fault trenching microgeomorphic mapping and tree ring analysis provide information on timing of paleoearthquakes and behavior of the san andreas fault in the santa cruz mountains at the grizzly flat site alluvial units dated at 1640 1659 a d 1679 1894 a d 1668 1893 a d and the present ground surface are displaced by a single event this was the 1906 surface rupture combined trench dates and tree ring analysis suggest that the penultimate event occurred in the mid 1600 s possibly in an interval as narrow as 1632 1659 a d there is no direct evidence in the trenches for the 1838 or 1865 earthquakes which have been proposed as occurring on this part of the fault zone in a minimum time of about 340 years only one large surface faulting event 1906 occurred at grizzly flat in contrast to previous recurrence estimates of 95 110 years for the santa cruz mountains segment comparison with dates of the penultimate san andreas earthquake at sites north of san francisco suggests that the san andreas fault between point arena and the santa cruz mountains may have failed either as a sequence of closely timed earthquakes on adjacent segments or as a single long rupture similar in length to the 1906 rupture around the mid 1600 s the 1906 coseismic geodetic slip and the late holocene geologic slip rate on the san francisco peninsula and southward are about 50 70 and 70 of their values north of san francisco respectively the slip gradient along the 1906 rupture section of the san andreas reflects partitioning of plate boundary slip onto the san gregorio sargent and other faults south of the golden gate if a mid 1600 s event ruptured the same section of the fault that failed in 1906 it supports the concept that long strike slip faults can contain master rupture segments that repeat in both length and slip distribution recognition of a persistent slip rate gradient along the northern san andreas fault and the concept of a master segment remove the requirement that lower slip sections of large events such as 1906 must fill in on a periodic basis with smaller and more frequent earthquakes

seismic activity on neighbouring faults as a long term precursor to large earthquakes in the san francisco bay area activity in moderate size earthquakes accelerated in the several decades before the large california earthquakes of 1989 1906 and 1868 this type of precursor seems to require the presence of several major faults in close enough proximity to one another that moderate size shocks are selectively triggered on surrounding faults during the latter stages of the cycle of strain buildup to large earthquakes it may be possible to use quantitative aspects of similar seismic precursors to make predictions of large earthquakes on timescales of a few years to one decade

the ordovician evolution of the south mayo trough western ireland the south mayo trough a broad synclinorium containing a 10 km sequence of early ordovician turbidites passing up into shallow water sandstones is interpreted as a forearc basin with an ophiolitic basement that formed a backstop to an accretionary prism on the northern edge of a north facing arc the arc collided with the laurentian margin in early llanvirn times to deform the dalradian supergroup rifted margin clastic sequence prior to the late llandovery sinistral transcurrent faulting transposed the connemara dalradian terrane to its present position on the outboard ocean ward side of the south mayo trough the south mayo trough was fed principally by arc and ophiolite derived elastics during the arenig with an increasing metamorphic component during the llanvirn the late ordovician transpressional docking of connemara provided the southerly source for high grade metamorphic clasts in the deny veeny formation

seismic activity of the san francisco bay region moment magnitude m with objective confidence level uncertainties are estimated for felt san francisco bay region earthquakes using bakun and went worth s 1997 analysis strategy for seismic intensity observations the frequency magnitude distribution is well described for m 5 5 events since 1850 by a gutenberg richter relation with a b value of 0 90 the seismic moment rate m yr since 1836 is 2 68 1018 n m yr 95 confidence range 1 29 1018 n m yr to 4 07 1018 n m yr the seismic moment rate since 1850 is nearly the same m yr in the 56 years before 1906 is about 10 times that in the 70 years after 1906 in contrast m yr since 1977 is about equal that in the 56 years before 1906 80 1 14 of the plate motion moment accumulation rate is available for release in earthquakes the historical m yr and the portion of the plate motion moment accumulation rate available for release in earthquakes are used in a seismic cycle model to estimate the rate of seismic activity in the twenty first century high and low rates of future seismic activity are both permissible given the range of possible seismic cycle recurrence times t and the uncertainties in the historical m and in the percentage of plate motion available for release in earthquakes if the historical seismic moment rate is not greater than the estimated 2 68 1018 n m yr and the percentage of the plate motion moment accumulation available for release in earthquakes is not less than the estimated 80 then for all t the rate of seismic moment release from now until the next 1906 sized shock will be comparable to the rate from 1836 to 1905 when m 6 1 2 shocks occurred every 15 to 20 years

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

a geological and tectonic cross section of the caledonides of western ireland geological and geophysical criteria allow division of the caledonides of western ireland into four principal zones zone 1 in the north contains grenvillian basement with late proterozoic supra crustals zone 2 contains the westport complex the deer park complex and the south mayo trough connemara and the delany dome formation occupy zone 3 zone 4 contains the south connemara group and mid to late ordovician and silurian sediments and volcanic rocks the various tectonic models proposed for these zones are discussed and a minimum tectonic model is presented which involves early ordovician collision of the northern part of zone 2 with the laurentian margin zone 1 followed by subduction flip northern part of zone 4 the site of early collision between zones 1 and 2 subsequently underwent orogenic collapse and strike slip dismemberment leading to the sinistral transpressive emplacement of zone 3 assemblages in zone 4 were accreted to the now south facing arc northwards stress transfer consequent on suturing deformed the thinned crust and overlying silurian sequences in zones 2 and 3

response of the san andreas fault to the 1983 coalinga nunez earthquakes an application of interaction based probabilities for parkfield 1 the parkfield cholame section of the san andreas fault site of an unfulfilled earthquake forecast in 1985 is the best monitored section of the world s most closely watched fault in 1983 the m 6 5 coalinga and m 6 0 nunez events struck 25 km northeast of parkfield seismicity rates climbed for 18 months along the creeping section of the san andreas north of parkfield and dropped for 6 years along the locked section to the south right lateral creep also slowed or reversed from parkfield south here we calculate that the coalinga sequence increased the shear and coulomb stress on the creeping section causing the rate of small shocks to rise until the added stress was shed by additional slip however the 1983 events decreased the shear and coulomb stress on the parkfield segment causing surface creep and seismicity rates to drop we use these observations to cast the likelihood of a parkfield earthquake into an interaction based probability which includes both the renewal of stress following the 1966 parkfield earthquake and the stress transfer from the 1983 coalinga events we calculate that the 1983 shocks dropped the 10 year probability of a m 6 parkfield earthquake by 22 from 54 22 to 42 23 and that the probability did not recover until about 1991 when seismicity and creep resumed our analysis may thus explain why the parkfield earthquake did not strike in the 1980s but not why it was absent in the 1990s we calculate a 58 17 probability of a m 6 parkfield earthquake during 2001 2011 index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 7260 seismology theory and modeling keywords coalinga earthquake parkfield stress change earthquake probability seismicity rate

the cape mendocino california earthquakes of april 1992 subduction at the triple junction the 25 april 1992 magnitude 7 1 cape mendocino thrust earthquake demonstrated that the north america gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the cascadia region the shock occurred just north of the mendocino triple junction and caused strong ground motion and moderate damage in the immediate area rupture initiated onshore at a depth of 10 5 kilometers and propagated up dip and seaward slip on steep faults in the gorda plate generated two magnitude 6 6 aftershocks on 26 april the main shock did not produce surface rupture on land but caused coastal uplift and a tsunami the emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity

probabilistic seismic hazard in the san francisco bay area based on a simplified viscoelastic cycle model of fault interactions 1 we construct a viscoelastic cycle model of plate boundary deformation that includes the effect of time dependent interseismic strain accumulation coseismic strain release and viscoelastic relaxation of the substrate beneath the seismogenic crust for a given fault system time averaged stress changes at any point not on a fault are constrained to zero that is kinematic consistency is enforced for the fault system the dates of last rupture mean recurrence times and the slip distributions of the assumed repeating ruptures are key inputs into the viscoelastic cycle model this simple formulation allows construction of stress evolution at all points in the plate boundary zone for purposes of probabilistic seismic hazard analysis psha stress evolution is combined with a coulomb failure stress threshold at representative points on the fault segments to estimate the times of their respective future ruptures in our psha we consider uncertainties in a four dimensional parameter space the rupture peridocities slip distributions time of last earthquake for prehistoric ruptures and coulomb failure stress thresholds we apply this methodology to the san francisco bay region using a recently determined fault chronology of area faults assuming single segment rupture scenarios we find that future rupture probabilities of area faults in the coming decades are the highest for the southern hayward rodgers creek and northern calaveras faults this conclusion is qualitatively similar to that of working group on california earthquake probabilities but the probabilities derived here are significantly higher given that fault rupture probabilities are highly model dependent no single model should be used to assess to time dependent rupture probabilities we suggest that several models including the present one be used in a comprehensive psha methodology as was done by working group on california earthquake probabilities

the 16 may 1909 northern great plains earthquake abstract the largest historical earthquake in the northern great plains occurred on 16 may 1909 our analysis of intensity assignments places the earthquake location 48 81 n 105 38 w close to the montana saskatchewan border with an intensity magnitude m i of 5 3 5 4 observations from two seismic observatories in europe give an average m s value of 5 3 the 1909 earthquake is near an alignment of epicenters of small earthquakes in montana and saskatchewan and on strike with the mapped hinsdale fault in montana thus the 1909 earthquake may have occurred on a 300 km long seismically active fault which could have seismic hazard implications for the region particularly for the hydraulically emplaced earth filled fort peck dam constructed in the 1930s on the missouri river in northeast montana

carbonate production by rudist bivalves the record of late barremian requieniid communities from provence se france abstract rudist bearing sediments from platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france were investigated on a 46 km wide transect after seven stratigraphic sections to quantify the role of rudists in the corresponding stratigraphic system by using various proxies the regional stratigraphic contribution of total thickness of rudist beds is relatively high 43 1 each rudist community type possesses a specific skeletal contribution of skeletal content in the range of 19 2 to 31 5 at a stratigraphic scale including rudist rich and rudist free beds the skeletal contribution drops to 13 8 this value is derived from the standard skeletal contribution obtained for each community type combined with the stratigraphic contribution of rudist beds in vertical successions and horizontal stratigraphic units a closely related value 12 8 is obtained from calculations using specific lateral dimensions of rudist bodies and their spacing i e modules depending on community types each community has a particular potential quantitative contribution to the overall regional stratigraphic system rudist production is deduced from the cyclostratigraphic approach of accumulation rates for each community type estimates of caco 3 net production are in the range of 19 to 50 kg m 2 ka 1 these values are very low when compared with those obtained at a biological scale for modern bivalves late cretaceous rudists and recent coral reefs the geological scale used for our estimates may partly account for this difference whereas low accommodation rates linked to cretaceous greenhouse conditions appear a potential important factor in this respect the low net production of requieniid dominated communities sediment dwellers not framework builders also reflects their limited sedimentogenetic power

subsurface fault damage zone of the 2014 mw 6 0 south napa california earthquake viewed from fault zone trapped waves the aftershocks of the 24 august 2014 m w 6 0 south napa earthquake generated prominent fault zone trapped waves fztws that were recorded on two 1 9 km long seismic arrays deployed across the northern projection array 1 a1 and the southern part a2 of the surface rupture of the west napa fault zone wnfz we also observed fztws on an array a3 deployed across the intersection of the franklin and southampton faults which appear to be the southward continuations of the wnfz a1 a2 and a3 consisted of 20 20 and 10 l28 4 5 hz three component seismographs we analyzed waveforms of fztws from 55 aftershocks in both time and frequency to characterize the fault damage zone associated with this m w 6 0 earthquake post s coda durations of fztws increase with epicentral distances and focal depths from the recording arrays suggesting a low velocity waveguide along the wnfz to depths in excess of 5 7 km locations of the aftershocks showing fztws combined with 3d finite difference simulations suggest the subsurface rupture zone having an s wave speed reduction of 40 50 between a1 and a2 coincident with the 14 km long mapped surface rupture zone and at least an 500 m wide deformation zone the low velocity waveguide along the wnfz extends further southward to at least a3 but with a more moderate velocity reduction of 30 35 at ray depth this last fztw observation suggests continuity between the wnfz and franklin fault the waveguide effect may have localized and amplified ground shaking along the wnfz and the faults farther to the south see a companion paper by catchings et al 2016

the livermore valley california sequence of january 1980 abstract at 19 h 00 m 09 46 s utc on 24 january 1980 a strong earthquake m l 5 5 that caused a surprising amount of damage occurred north of livermore valley about 12 km to the southeast of mt diablo and was associated with surface rupture along the greenville fault there was a foreshock m l 2 7 a minute and a half earlier and a sequence of 59 events m l 2 5 in the ensuing 6 days on 27 january at 02 h 33 m 35 96 s a larger magnitude earthquake occurred in the sequence m l 5 6 this second principal shock was located 14 km to the south of the first principal earthquake toward the southern end of the greenville fault preliminary estimates of the seismic moments of the two principal shocks are 5 3 10 24 and 1 3 10 24 dyne cm respectively in addition to the lower seismic moment the m l 5 6 shock on 27 january exhibits a clearly focused radiation pattern with large amplitudes toward the northeast field investigations after the first principal shock indicated surfaced rupture along the greenville fault zone for at least 6 km with both right lateral strike slip and some dip slip motion with the northeast side up variable offsets on surface cracks suggested displacements of a few centimeters with evidence of increases in some places after the second 27 january earthquake there were eight earthquakes with m l 4 0 in the sequence up to 5 february 1980 no foreshocks near the greenville fault m l 1 5 were observed by the university of california seismographic stations in the prior 3 months rapid deployment of field seismographs by a number of seismological organizations permitted precise locations and fault plane solutions some results on seismicity are as follows 1 the rupture propagated over 15 km to the southeast along the marsh creek greenville faults on 24 january and stopped in the vicinity of highway 580 this southern progression may have had some causal connection with the relatively high intensities reported near the southwest end of the greenville fault 2 the two principal shocks of the sequence have slight but significant differences in the fault plane solutions both are predominantly right lateral strike slip but the strike of the northern one is n13 w whereas the strike of the southern one is n39 w this change in strike is not evident in the mapped strikes of the marsh creek and the greenville faults 3 in contrast to the second principal earthquake the first principal shock was followed by two others m l 4 0 in rapid succession one 53 sec and the other 97 sec after this repetition gave a relatively long duration to the shaking on 24 january and was commented on in felt reports it may explain the greater intensity reported in many localities on 24 january compared to 27 january 4 the b value 0 64 0 13 for the sequence is somewhat lower than the b 0 70 0 17 for the recent coyote lake earthquake sequence on the calaveras fault on 5 august 1979 there are fewer earthquakes than normal in the range 3 0 m l

the distribution of modified mercalli intensity in the 18 april 1906 san francisco earthquake we analyze boatwright and bundock s 2005 modified mercalli intensity mmi map for the 18 april 1906 san francisco earthquake reviewing their interpretation of the mmi scale and testing their correlation of 1906 cemetery damage with mmi intensity we consider in detail four areas of the intensity map where boatwright and bundock 2005 added significantly to the intensity descriptions compiled by lawson 1908 we show that the distribution of off fault damage in sonoma county suggests that the rupture velocity approached the p wave velocity along tomales bay in contrast the falloff of intensity with distance from the fault appears approximately constant throughout mendocino county the intensity in humboldt county appears somewhat higher than the intensity in mendocino county suggesting that the rupture process at the northern end of the rupture was relatively energetic and that there was directivity consistent with a subsonic rupture velocity on the section of the fault south of shelter cove finally we show that the intensity sites added in santa cruz county change the intensity distribution so that it decreases gradually along the southeastern section of rupture from corralitos to san juan bautista and implies that the stress release on this section of rupture was relatively low

mmi attenuation and historical earthquakes in the basin and range province of western north america earthquakes in central nevada 1932 1959 were used to develop a modified mercalli intensity mmi attenuation model for estimating moment mag nitude m for earthquakes in the basin and range province of interior western north america m is 7 4 7 5 for the 26 march 1872 owens valley california earthquake in agreement with beanland and clark s 1994 m 7 6 that was estimated from geologic field observations m is 7 5 for the 3 may 1887 sonora mexico earthquake in agreement with natali and sbar s 1982 m 7 4 and suter s 2006 m 7 5 both estimated from geologic field observations mmi at sites in california for earthquakes in the nevada basin and range appar ently are not much affected by the sierra nevada except at sites near the sierra nevada where mmi is reduced this reduction in mmi is consistent with a shadow zone produced by the root of the sierra nevada in contrast mmi assignments for earthquakes located in the eastern sierra nevada near the west margin of the basin and range are greater than predicted at sites in california these higher mmi values may result from critical reflections due to layering near the base of the sierra nevada

oroclinal bending in the caledonides of western ireland new palaeomagnetic data from the caledonides of western ireland indicate that the silurian rocks of south mayo underwent oroclinal bending following folding in siluro devonian time bending was accommodated on faults cutting the silurian sequence and was driven by strike slip motion across the antrim galway line a recently recognized major curvilinear lineament we propose that the silurian rocks in the east of the region suffered up to 30 clockwise rotation increasing towards the west to approximately 70 this newly inferred differential rotation of the silurian rocks about a sub vertical axis implies that the underlying dalradian rocks of the connemara massif to the south must also have undergone clockwise rotation in late silurian early devonian time this is consistent with published palaeomagnetic data from the connemara gabbro and accounts for the swing in strike of the caledonian orogen in this part of western ireland from this we deduce that the swing in strike of the caledonian rocks elsewhere on the west coast of ireland might have a similar explanation

a revision of ordovician series and stages from the historical type area this paper is a revision of the standard chronostratigraphy of the ordovician of the historical type area in england and wales the revision is a response to the need for more precise definitions of series and stages especially for practical international correlation in some cases this has entailed moving horizons for series bases away from those in the classical sections the scheme will be used as the standard for a forthcoming revision of the correlation chart of the british ordovician system the ordovician is divided into five series tremadoc arenig llanvirn caradoc and ashgill the llanvirn is extended to include part of the classical llandeilo series which is included within it as a stage where stage subdivisions of standard series have not yet been defined as in the tremadoc they are proposed in this paper however bancroft s fine stadial divisions of the caradoc which have been criticized for their brevity and local utility are combined into four new stages which will have wider application the former caradoc subdivisions are retained as substages for the purposes of regional correlation

the caledonian strike swing and associated lineaments in nw ireland and adjacent areas sedimentation deformation and igneous intrusion patterns part of the major swing in strike associated with the greenland labrador promontory of the north atlantic caledonides is exposed in considerable detail in the metasedimentary and meta igneous rocks of the neo proterozoic dalradian supergroup in northwest ireland we show that the strike swing controlled dalradian stratigraphy and sedimentation patterns and is therefore at least c 600 ma in age our interpretation of the stratigraphy allows a reconstruction of this promontory in the laurentian continental margin and shows that it separated a ne trending gently inclined and broad continental shelf in the north from an e trending more steeply inclined and narrower shelf to the south once established in the geometry of the dalradian sequence the strike swing and basement promontory had a major influence on caledonian deformation patterns it controlled the nucleation of major folds the geometry of the regionally developed primary cleavages the facing direction of the early folds and it also acted as a major buttress in perturbing and deflecting on a regional scale the orogenic transport vector accurate restoration of the sinistral displacement on a late caledonian fault system shows that the apices of the strike swing at different stratigraphic levels and their associated sedimentary facies changes define a line trending approximately n12oe this line is coincident with again after fault restoration six out of the eight devonian donegal granites the vast majority of the mantle related ultrabasic appinite suite with most of these bodies concentrated at the intersection of this line and the ne trending main donegal granite shear zone and the highest density of the neo proterozoic basic tholeiite suite thes e and other data are used to suggest that the donegal lineament is the expression of a major steeply inclined fault in the basement beneath the dalradian which is intimately related to the morphology of the promontory the fault which might be as old as 1800 ma probably reached down into the lithospheric mantle controlling igneous activity including the ascent emplacement site and perhaps sources of the magmas another complementary strike swing and parallel lineament is described from the dalradian rocks of the adjacent part of scotland it is suggested that these and other major lineaments i e old pre caledonian faults which have either nne ne or ese trends reflect not so much the location of the northern british isles at a 120o triple junction during iapetus rifting but rather the exploitation of these pre existing trends in the pre caledonian atlantic borderlands during iapetus opening

quantitative stratigraphy of rudist limestones and its bearing on spatial organisation of rudist communities the late barremian urgonian sequences of provence s e france abstract rudist beds in platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france possess a substantial lateral continuity 40 km whereas associated rudist bodies tend to be less continuous transition probabilities markov chain analysis are used at a regional scale to test the lateral continuity of rudist bodies and their four associated rudist assemblages each rudist assemblage has a specific probability to be adjacent to itself or to any one at a local scale analysing the variations of transition probabilities as a function of distance using various proxies shows a periodic spatial trend the style of which depends on the type of rudist assemblage i e community type the foregoing documents two groups with different properties group 1 includes two communities characterised by small forms restricted to very shallow and muddy settings organised spatially into small patches c 1000 1500 m with moderate spacing c 1500 2000 m group 2 includes two communities characterised by mixed size or large forms typical of deeper water and more sandy settings organised spatially into large patches c 3000 m with a larger spacing c 3000 4000 m the internal architecture and the dimensions of these rudist bodies argue against a reefal nature quantitative estimates of lateral continuity and spatial variations of rudist bodies have a significant potential for reservoir modelling of hydrocarbon bearing rudist rich platform carbonates

linearized inversion for fault rupture behavior application to the 1984 morgan hill california earthquake we present a technique to infer the rupture history of an earthquake from near source records of ground motion unlike most previous studies each point on the fault is assumed to slip only once when the rupture front passes with a spatially variable slip intensity in this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture time we perform a linearized inversion for slip intensity and rupture time by iteratively perturbing an assumed starting model the inverse problem for the model perturbation is solved using a tomographic back projection technique smoothing and inequality constraints are applied to ensure that the resulting solution is stable and feasible asymptotic ray theory is used to calculate theoretical seismograms and partial derivatives with respect to model parameters in test cases with noisy synthetic data sets we found that it is possible to distinguish between rupture models having variable slip amplitude and models having variable rupture velocity provided the station coverage is adequate we apply the technique to recordings of the april 24 1984 morgan hill earthquake the results indicate that slip amplitude on the fault plane was extremely variable and that the rupture front did not propagate uniformly away from the hypocenter in particular rupture was delayed on a 12 km2 section of the fault approximately 14 km to the southeast of the hypocenter the rupture front surrounded the region which subsequently failed with a component of rupture propagation back toward the hypocenter similar behavior has been observed in dynamic rupture models with stress or strength inhomogeneities this segment of the fault ruptured with a large slip amplitude releasing 12 of the total seismic moment from 4 of the total area of the aftershock zone the surface trace of this section of the fault is characterized by a complex left step that could act to increase the normal stress acting across the fault however the distribution of aftershocks suggests that the fault at depth is simpler and that it may bend to the right in either case our rupture model suggests that this segment of the fault represents an asperity which initially resisted rupture but eventually ruptured massively we estimate the shear fracture energy for this earthquake to be 2 106 j m2

coulomb stress accumulation along the san andreas fault system 1 stress accumulation rates along the primary segments of the san andreas fault system are computed using a three dimensional 3 d elastic half space model with realistic fault geometry the model is developed in the fourier domain by solving for the response of an elastic half space due to a point vector body force and analytically integrating the force from a locking depth to infinite depth this approach is then applied to the san andreas fault system using published slip rates along 18 major fault strands of the fault zone gps derived horizontal velocity measurements spanning the entire 1700 200 km region are then used to solve for apparent locking depth along each primary fault segment this simple model fits remarkably well 2 43 mm yr rms misfit although some discrepancies occur in the eastern california shear zone the model also predicts vertical uplift and subsidence rates that are in agreement with independent geologic and geodetic estimates in addition shear and normal stresses along the major fault strands are used to compute coulomb stress accumulation rate as a result we find earthquake recurrence intervals along the san andreas fault system to be inversely proportional to coulomb stress accumulation rate in agreement with typical coseismic stress drops of 1 10 mpa this 3 d deformation model can ultimately be extended to include both time dependent forcing and viscoelastic response

quantitative study of a hippuritid rudist lithosome in a santonian carbonate platform in the southern central pyrenees abstract the santonian carbonate platform deposits of the sant corneli anticline in the southern central pyrenees contain distinctive lenticular to tabular lithosomes formed by congregations of slender hippuritid rudists here we make a quantitative study of one of the lithosomes in the sant pere de vilanoveta member in the northern side of sant corneli it is exposed over some 4 km along a wnw ese section and shows a remarkably persistent thickness up to a maximum of 5 15 m though for the most part it is less than 3 m thick in the lithosome hippuritid shells are mostly preserved inclined about 30 60 from the perpendicular with respect to bedding the majority of inclined shells lean towards the southwestern to southeastern quadrants the inferred principal downstream direction hippuritids are loosely clustered and supported in a fine bioclastic matrix percentage cover of hippuritids ranges from 19 8 at the base to 31 9 in the middle and top of the lithosome the preliminary data on numerical densities number of individuals per unit area of hippuritids show some clustering around values of about 290 750 individuals per m2 the inclined orientation of hippuritid shells seems original and the result of active growth by the animals the high numerical density of hippuritids at the base of the lithosome may indicate that the hippuritid congregation grew rapidly the congregation appears to have reached an optimal level of density by the middle of the lithosome and to have maintained it through time during the development of the rudist congregation the lithosome lacks relief and has no evidence of any rigid framework

the antrim galway line a resolution of the highland border fault enigma of the caledonides of britain and ireland the westward continuation of the highland border fault of scotland hbfz into ireland is problematic it is widely thought to follow a pronounced magnetic and gravity lineament the fair head clew bay line fcl the advantage of this interpretation is that it places all the ordovician ophiolitic complexes and associated sedimentary basins to the south of the fcl which would represent the contact between laurentia and the outboard terranes its main shortcomings are that both the deep structure and timing of strike slip are different on the hbfz and fcl in ireland the fcl is a north dipping feature that can be traced to the moho on birps profiles while the hbfz has no such signature terrane amalgamation in western ireland was completed by the late ordovician while in scotland the midland valley terrane did not finally dock until the early devonian these considerations suggest that in western ireland a branch of the hbfz exists which was active in post ordovician time and must lie south of connemara an examination of irish geological geophysical and image processed magnetic data shows that a profound lineament can be traced from antrim to galway bay the antrim galway line stitching plutons date movement on it as pre 405 ma we propose that the antrim galway line represents the continuation of the scottish hbfz while the fcl is a preserved ordovician splay of the hbfz system whose northdipping geometry is a product of ordovician collapse of the orogen in western ireland

end silurian modifications of ordovician terranes in western ireland the ordovician elements in the caledonides of western ireland may be divided into the clew bay south mayo north connemara and south connemara sub zones evidence suggests the presence of a number of proximal suspect terranes and the remnants of one or possibly two arc complexes palaeontological and sedimentary evidence suggests an allochthonous relationship between the silurian rocks of croagh patrick and north galway these successions may therefore not represent a single sedimentary overlap to the ordovician suspect terranes end silurian deformation was the result of transpression which was responsible in part for the present configuration of the area s geology deep seated shear zones with fuchsite and gold mineralization were foci for lateral translation concomitant with southward directed thrusting northward directed back thrusts and variable degrees of metamorphism being of higher grade in the north the end silurian event is intermediate between the high grade metamorphism in parts of the appalachians and the non metamorphic silurian sequences of scotland

facies architecture and high resolution sequence stratigraphy of an upper cretaceous platform margin succession southern central pyrenees spain abstract excellent exposures of upper cretaceous santonian carbonate platforms on the northern flank of sant corneli anticline southern central pyrenees provide detailed information of facies architecture in both depositional strike and dip directions basic accretional units are differentiated by facies contrast across mappable surfaces these surfaces do not show clear evidence of subaerial erosion and are correlated basinward with bedding planes across which there are subtle changes in skeletal composition two types of basic accretional units have been identified based on bedding patterns internal facies architecture and skeletal composition 1 rudist buildups consist of a rudist and coral belt at the platform margin passing landward into a slender hippuritid lithosome locally overlain by a bioclastic blanket that passes basinward into bioclastic apron like clinobeds and into fine grained packstone wackestone 2 calcarenite wedges consist of yellow brown benthic foraminifer rich grainstones to grain dominated packstones with scattered rudist shells and small coral colonies passing basinward into mud dominated packstones to wackestones with variable siliciclastic content quartz sand to silt and clay rudist buildups and calcarenite wedges alternate although not rhythmically these changes in platform skeletal composition reflect changes in the dominant type of carbonate producing biota independently of the changes in accommodation both types of basic accretional units rudist buildups and calcarenite wedges form simple sequences and parasequences according to internal lithofacies arrangement and inferred sea level cyclicity cycles or paracycles high frequency sea level cyclicity fits in the milankovitch frequency band long term changes in accommodation governing aggradation progradation and backstepping of basic sequences and parasequences reflect tectonic influence rather than long term changes in eustatic sea level

some comparisons of the structure and evolution of the southern appalachian ouachita orogen and portions of the trans european suture zone region abstract many aspects of the tectonic history of the appalachian ouachita orogen and the trans european suture region are similar in a tectonic sense they are geographically linked because at the end of the paleozoic one could travel from texas to poland following a continuous orogenic belt much of each of these orogenic belts is however buried by younger strata and thus geophysical studies are a key element of efforts to better understand them many more geophysical data are needed to provide a comprehensive picture of the deep structure but in several areas new models of the lithospheric structure are emerging in this paper we review some of these models and introduce two new ones for the southern appalachians in addition we explore the implications of these models for the evolution of these orogenic belts drawing attention to similarities and differences in their structure and evolution the appalachian and caledonian orogens represent temporally parallel development along irregular late proterozoic continental margins but the crustal structure is different because of different accretionary elements and complications in the geometry of the original margins lateral transport via thrusting can confuse efforts to tie geologic structures identified on the surface with deep structures for example in the appalachian ouachita orogen the thrust related transport distance for major features such as the blue ridge piedmont sheet and the benton uplift is at least 200 km on a crustal scale deformation in the appalachian ouachita orogen varies greatly in style and intensity in the ouachita orogen the late proterozoic continental margin seems to be preserved while in the northern appalachians crustal scale deformation is intense along the us appalachians the major crustal structure variation is the thin dense crust of avalonia abutting the relatively thick crust of laurentia along the ouachita orogen several large crustal blocks can be identified that are unlike anything seen along the appalachians

estimating locations and magnitudes of earthquakes in eastern north america from modified mercalli intensities we use 28 calibration events 3 7 m 7 3 from texas to the grand banks newfoundland to develop a modified mercalli intensity mmi model and associated site corrections for estimating source parameters of historical earthquakes in eastern north america the model batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mathrm mmi 1 41 1 68 times mathbf m 0 00345 times delta 2 08 mathrm log delta end document where is the distance in kilometers from the epicenter and m is moment magnitude provides unbiased estimates of m and its uncertainty and if site corrections are used of source location the model can be used for the analysis of historical earthquakes with only a few mmi assignments we use this model mmi site corrections and bakun and wentworth s 1997 technique to estimate m and the epicenter for three important historical earthquakes the intensity magnitude m i is 6 1 for the 18 november 1755 earthquake near cape ann massachusetts 6 0 for the 5 january 1843 earthquake near marked tree arkansas and 6 0 for the 31 october 1895 earthquake the 1895 event probably occurred in southern illinois about 100 km north of the site of significant ground failure effects near charleston missouri manuscript received 14 march 2002

association of earthquakes and faults in the san francisco bay area using bayesian inference bayesian inference provides a method to use seismic intensity data or instrumental locations together with geologic and seismologic data to make quan titative estimates of the probabilities that specific past earthquakes are associated with specific faults probability density functions are constructed for the location of each earthquake and these are combined with prior probabilities through bayes theorem to estimate the probability that an earthquake is associated with a specific fault results using this method are presented here for large preinstrumental his torical earthquakes and for recent earthquakes with instrumental locations in the san francisco bay region the probabilities for individual earthquakes can be summed to construct a probabilistic frequency magnitude relationship for a fault segment other applications of the technique include the estimation of the probability of back ground earthquakes that is earthquakes not associated with known or considered faults and the estimation of the fraction of the total seismic moment associated with earthquakes less than the characteristic magnitude results for the san francisco bay region suggest that potentially damaging earthquakes with magnitudes less than the characteristic magnitudes should be expected comparisons of earthquake locations and the surface traces of active faults as determined from geologic data show sig nificant disparities indicating that a complete understanding of the relationship be tween earthquakes and faults remains elusive

resolution of fault slip along the 470 km long rupture of the great 1906 san francisco earthquake and its implications data from all available triangulation networks affected by the 1906 earthquake have been combined to assess the trade off between slip resolution and its uncertainty and to construct a conservative image of coseismic slip along the rupture because of varying network aperture and station density slip resolution is very uneven although slip is determined within uncertainties of 1 0 m along 60 of the fault constraints are poor on the remaining mostly offshore portions of the rupture slip decreases from maxima of 8 6 and 7 5 m at shelter cove and tomales bay to 4 5 m near mount tamalpais and 2 7 m at loma prieta the geodetically derived slip distribution is in poor agreement with estimates based on analysis of s wave seismograms probably because these waves register only 20 30 of the total seismic moment obtained from longer period surface waves consideration of a range of fault geometries for 1906 slip near loma prieta indicates right lateral motions lie between 2 3 and 3 1 m these values are considerably greater than the 1 5 m of measured surface slip on which several assessments of high earthquake hazard for this fault segment were based this factor along with the absence of 1989 slippage where 1906 surface slip was used to make the forecasts casts doubt on some claims of success in predicting the 1989 m 6 9 loma prieta earthquake

re evaluation of 1906 surface faulting geomorphic expression and seismic hazard along the san andreas fault in the southern santa cruz mountains the lack of through going right lateral surface rupture accompanying the loma prieta earthquake has raised questions about the behavior of the san andreas fault in the southern santa cruz mountains we re evaluated previously published reports of ground deformation due to the 1906 earthquake in this region to determine if san andreas fault surface rupture accompanied this event and whether any of the reported values of offset are reliable in addition our search for historical data has brought to light new information about the 1906 earthquake in the southern santa cruz mountains none of the reports provides indisputable evidence for 1906 san andreas fault surface rupture however taken together with a study of the geomorphology of the fault zone and relationships exposed in excavations across the fault they do provide a basis for believing that surface rupture extended through the region in 1906 none of the reported values for 1906 offset is a reliable measurement however calling into question current and pre 1989 seismic hazard assessments for the loma prieta area the geologic and geomorphic relationships indicate that shallow right lateral crustal strain is typically expressed as surface rupture across a narrow san andreas fault zone in contrast to the 1989 loma prieta earthquake

ground motion modeling of hayward fault scenario earthquakes part ii simulation of long period and broadband ground motions abstract we simulate long period t 1 0 2 0 s and broadband t 0 1 s ground motions for 39 scenario earthquakes m w 6 7 7 2 involving the hayward calaveras and rodgers creek faults for rupture on the hayward fault we consider the effects of creep on coseismic slip using two different approaches both of which reduce the ground motions compared with neglecting the influence of creep nevertheless the scenario earthquakes generate strong shaking throughout the san francisco bay area with about 50 of the urban area experiencing modified mercalli intensity vii or greater for the magnitude 7 0 scenario events long period simulations of the 2007 m w 4 18 oakland earthquake and the 2007 m w 5 45 alum rock earthquake show that the u s geological survey s bay area velocity model version 08 3 0 permits simulation of the amplitude and duration of shaking throughout the san francisco bay area for hayward fault earthquakes with the greatest accuracy in the santa clara valley san jose area the ground motions for the suite of scenarios exhibit a strong sensitivity to the rupture length or magnitude hypocenter or rupture directivity and slip distribution the ground motions display a much weaker sensitivity to the rise time and rupture speed peak velocities peak accelerations and spectral accelerations from the synthetic broadband ground motions are on average slightly higher than the next generation attenuation nga ground motion prediction equations we attribute much of this difference to the seismic velocity structure in the san francisco bay area and how the nga models account for basin amplification the nga relations may underpredict amplification in shallow sedimentary basins the simulations also suggest that the spudich and chiou 2008 directivity corrections to the nga relations could be improved by increasing the areal extent of rupture directivity with period

re evaluation of the 1836 hayward fault and the 1838 san andreas fault earthquakes abstract current seismic hazard models include two major earthquakes m 7 in the san francisco bay area that are close in space and time an 1836 event on the northern hayward fault and an 1838 event on the peninsula section of the san andreas fault analysis and interpretation of the available historical accounts indicate that the 1836 event occurred east of monterey bay far from the hayward fault and was of m 6 also the 1838 event was not confined to the 60 km peninsula san andreas as current models indicate instead faulting probably extended from san francisco to san juan bautista 140 km indicating a significantly larger earthquake m 7 than previously thought damaging effects of the 1836 earthquake were reported only from santa clara to carmel and no contemporary effects were reported to the north of santa clara or near the hayward fault the illusion of an 1836 hayward earthquake evolved from a newspaper reminiscence published following the 1868 hayward earthquake stating that the 1868 effects in the east bay were similar to those of an 1836 event the article describes various strong effects in the east bay that differ completely from the effects recorded for the 1836 earthquake but are very similar to those documented for the major 1838 san andreas earthquake that caused extensive damage on both sides of san francisco bay based on this and other evidence we conclude that the reminiscence describes the destructive june 1838 effects but it erroneously indicates the date as june 1836 there is no evidence for any major historical earthquakes in the san francisco bay area before the 1838 earthquake back to the founding of mission san francisco dolores in 1776 during the 1838 san andreas fault earthquake the shaking intensity in monterey was as strong as or stronger than during the great 1906 san andreas fault earthquake this suggests that the 1838 san andreas fault rupture may have extended to san juan bautista as it did in 1906 numerous probable aftershocks were felt in the area south of san juan bautista these damaged carmel and santa cruz in 1840 and alisal 16 km west of the san andreas fault in 1841 the northern end of the 1838 faulting was previously assumed to be 25 km south of san francisco however mission san francisco dolores was damaged in 1838 but not in 1906 suggesting that the 1838 faulting extended to san francisco also the 1838 aftershocks were felt in oakland as frequently and violently as those following the major 1868 hayward earthquake suggesting that the 1838 faulting on the san andreas extended to the latitude of oakland the 1838 fault segment ruptured again 68 years later as part of the overlapping 1906 san andreas fault rupture this and similar evidence from southern california indicates that m 7 san andreas fault earthquakes can recur at intervals of 68 years or less when they are followed by m 8 earthquakes on overlapping segments of the fault

geochemical evolution of an ordovician island arc south mayo ireland early ordovician volcanic rocks exposed in the south mayo region of western ireland document the history of a volcanic arc complex produced following the initiation of south dipping subduction within the iapetus ocean in the late cambrian or early ordovician lavas of the lough nafooey group tremadoc arenig show an eruption history marked by an initial period of tholeiitic basaltic volcanism followed by a shift to increasing silica compositions of calc alkaline affinity subsequent volcanism of the tourmakeady group arenig shows a mixture of rhyolitic and andesitic compositions which are in turn succeeded by tuffs of the rosroe and mweelrea formations of the murrisk group llanvirn these are also rhyolitic and andesitic but are generally more siliceous the overall increase in silica contents may reflect increasing fractional crystallization due to crustal thickening trace element studies of the basaltic members of the lough nafooey group show a strong subduction zone influence while absolute levels of immobile trace and rare earth elements decrease upsection relative depletion of the most incompatible elements decreases over the same time period these trends suggest decreasing degrees of partial melting of a progressively more depleted source mantle upsection the basaltic bohaun volcanic formation tremadoc arenig shows greater depletion in its incompatible trace elements than the lough nafooey group so indicating a more depleted mantle source comparison with modern arc systems suggests that the bohaun volcanic formation was probably generated shortly after the initiation of subduction and was erupted in a more trenchward position than the lough nafooey group i e in the forearc this confirms a south dipping polarity to the subduction zone and suggests an age of initiation during the late cambrian or earliest ordovician

distinguishing core and flank facies based on shell fabrics in lower jurassic lithiotid shell beds abstract lower jurassic larger bivalves mostly represented by the monospecific lithiotid genera lithiotis cochlearites and lithioperna formed large shell accumulations in the shallow water carbonate tethyan and panthalassa margins a quantitative analysis of lithiotid accumulations from the trento platform northern italy was carried out in order to distinguish the distribution of autochthonous parautochthonous and allochthonous lithiotids in the accumulation core and flanks various representative accumulations are characterized with respect to systematic content shell cover shell density disarticulation shell fragmentation and orientation of individual shells lithioperna shows a high shell cover within the accumulation core while that of cochlearites is variable and lithiotis is rare all three lithiotids occur in high densities in the accumulation flanks as expected autochthonous individuals of all three genera are frequent in the accumulation cores where they are preserved in life position in the flanks most bivalves are parautochthonous except for lithioperna which can grow in life position all bivalves in allochthonous shell beds are highly fragmented and disarticulated the studied traits are potentially useful as proxies for distinguishing core or flank facies when the accumulation does not crop out as a whole

palaeozoic terrane accretion in the western irish caledonides the southern boundary of the early caledonides in the british isles the dalradian supergroup is represented by the major highland boundary fair head clew bay line in the west of ireland accretion along this laurasian margin occurred by sinistral strike slip during two phases the earliest was responsible for the docking of the connemara terrane a displaced part of the dalradian outboard of the south mayo trough in the llanvirnian llandeilian this event is recorded independently by radiometrically dated sinistral strike slip deformation in the ox mountains of western ireland following deposition of a silurian overlap sequence sinistral movements were renewed between the upper llandoverian and the siegennian this event is part of a major phase of sinistral strike slip throughout the british isles involving accretion of the cadomian terrane and the devonian accretion of the avalon terrane in the northern appalachians

probabilistic estimates of surface coseismic slip and afterslip for hayward fault earthquakes we examine the partition of long term geologic slip on the hayward fault into interseismic creep coseismic slip and afterslip using monte carlo simulations we compute expected coseismic slip and afterslip at three alinement array sites for hayward fault earthquakes with nominal moment magnitudes ranging from about 6 5 to 7 1 we consider how interseismic creep might affect the coseismic slip distribution as well as the variability in locations of large and small slip patches and the magnitude of an earthquake for a given rupture area we calibrate the estimates to be consistent with the ratio of interseismic creep rate at the alinement array sites to the geologic slip rate for the hayward fault we find that the coseismic slip at the surface is expected to comprise only a small fraction of the long term geologic slip the median values of coseismic slip are less than 0 2 m in nearly all cases as a result of the influence of interseismic creep and afterslip however afterslip makes a substantial contribution to the long term geologic slip and may be responsible for up to 0 5 1 5 m median plus one standard deviation s d of additional slip following an earthquake rupture thus utility and transportation infrastructure could be severely impacted by afterslip in the hours and days following a large earthquake on the hayward fault that generated little coseismic slip inherent spatial variability in earthquake slip combined with the uncertainty in how interseismic creep affects coseismic slip results in large uncertainties in these slip estimates

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

suppression of large earthquakes by stress shadows a comparison of coulomb and rate and state failure stress shadows generated by california s two most recent great earthquakes 1857 fort tejon and 1906 san francisco substantially modified 19th and 20th century earthquake history in the los angeles basin and in the san francisco bay area simple coulomb failure calculations which assume that earthquakes can be modeled as static dislocations in an elastic half space have done quite well at approximating how long the stress shadows or relaxing effects should last and at predicting where subsequent large earthquakes will not occur there has however been at least one apparent exception to the predictions of such simple models the 1911 m 6 0 earthquake near morgan hill california occurred at a relaxed site on the calaveras fault we examine how the more complex rate and state friction formalism based on laboratory experiments might have allowed the 1911 earthquake rate and state time to failure calculations are consistent with the occurrence of the 1911 event just 5 years after 1906 if the calaveras fault was already close to failure before the effects of 1906 we also examine the likelihood that the entire 78 years of relative quiet only four m 6 earthquakes in the bay area after 1906 is consistent with rate and state assumptions given that the previous 7 decades produced 18 m 6 earthquakes combinations of rate and state variables can be found that are consistent with this pattern of large bay area earthquakes assuming that the rate of earthquakes in the 7 decades before 1906 would have continued had 1906 not occurred these results demonstrate that rate and state offers a consistent explanation for the 78 year quiescence and the 1911 anomaly although they do not rule out several alternate explanations

strain accumulation rates in the san francisco bay area 1972 1989 maps of the strain accumulation rate in the san francisco bay area have been constructed from trilateration observations extending from about 1972 until the loma prieta earthquake in late 1989 the observations were corrected to remove offsets imposed by shallow fault creep and by four m 6 earthquakes that occurred in the bay area during that time interval the bay area was divided into 32 contiguous polygons and the uniform in both space and time strain rates that best explain the changes in the corrected earthquake and shallow fault creep offsets removed distances within each polygon were calculated in a coordinate system with the 1 axis directed n58 e and the 2 axis n32 w perpendicular and parallel to the local tangent to the small circle drawn about the pacific sierra nevada pole of rotation the averages of these 32 strain rates each weighted by the area of the polygon are e11 9 2 7 4 e12 160 7 4 6 and e22 8 2 6 2 nanostrain yr where extension is reckoned positive and quoted uncertainties are standard deviations as expected from the pacific sierra nevada relative plate motion the overall strain rate is predominantly right lateral shear across a vertical plane striking n32 w the net increase in the 12 225 km2 area of the trilateration network is only 212 110 m2 yr which arises from almost equal extensions in the n32 w and n58 e directions within the network the strain rates vary from polygon to polygon significant areal dilatation rates are observed in almost of the individual polygons and the n32 w extension rates tend to be negative to the west of the hayward rodgers creek fault trend and positive east of it the n58e extension rate is positive in 22 out of 32 polygons a proportion that is significantly larger than would be expected by chance if the n58 e extension rate were zero or negative the pre 1989 strain accumulation across the eventual site of the loma prieta rupture involves fault normal contraction as well as right lateral shear consistent with the rupture mechanism

a record of large earthquakes during the past two millennia on the southern green valley fault california we document evidence for surface rupturing earthquakes events at two trench sites on the southern green valley fault california sgvf the 75 80 km long dextral sgvf creeps 1 4 mm yr we identify stratigraphic horizons disrupted by upward flowering shears and infilled fissures unlikely to have formed from creep alone the mason rd site exhibits four events from 1013 ce to the present the lopes ranch site lr 12 km to the south exhibits three events from 18 bce to present including the most recent event mre 1610 52 yr ce 1 and a two event interval 18 bce 238 ce isolated by a millennium of low deposition using oxcal to model the timing of the four event earthquake sequence from radiocarbon data and the lr mre yields a mean recurrence interval ri or of 199 82 yr 1 and 35 yr standard error of the mean the first based on geologic data the time since the most recent earthquake open window since mre is 402 yr 52 yr well past 200 yr the shape of the probability density function pdf of the average ri from oxcal resembles a brownian passage time bpt pdf i e rather than normal that permits rarer longer ruptures potentially involving the berryessa and hunting creek sections of the northernmost gvf the model coefficient of variation cv is 0 41 but a larger value cv 0 6 fits better when using bpt a bpt pdf with of 250 and cv of 0 6 yields 30 yr rupture probabilities of 20 25 versus a poisson probability of 11 17 online material oxcal model for ages of paleoearthquakes lopes site 1998 logs and description of a model for estimation of rupture frequency

palaeozoic palaeogeography of laurentia and its margins a reassessment of palaeomagnetic data summary the recognition of wide spread remagnetization events during the palaeozoic has greatly added to the problems of reconstructing the palaeozoic drift history of laurentia and in recent years increasing emphasis has been placed on evaluating the relative reliability of palaeomagnetic data in an attempt to overcome some of these difficulties in the light of these developments a revised apparent polar wander apw path has been constructed following a rigorous evaluation of all published palaeozoic palaeomagnetic data from laurentia and its palaeozoic margins i e north america northern britain northern ireland and greenland the use of data from the laurentian margins when corrected for the opening of the north atlantic has resulted in a revision of previously published palaeozoic palaeogeographic reconstructions and these new palaeogeographic reconstructions for laurentia are in good agreement with faunal and lithological data a comparison of this new apw path with other apw paths from avalonia and baltica reveals a very close agreement between all three paths from mid silurian times onwards indicating that the closure of the iapetus ocean and the tornquist sea was essentially complete by this time laurentia occupied equatorial latitudes from cambrian to early silurian times and its drift history was dominated by anti clockwise rotation up to 0 7 ma 1 and low latitudinal drift rates up to 3 cm yr 1 late silurian and early devonian times were characterized by increased rates of anti clockwise rotation up to 1 3 ma 1 and southerly directed latitudinal drift rates up to 13 cm yr 1 of the continent which place laurentia in moderate southerly latitudes 30 40 s by the early devonian these palaeolatitudes are comparable with those from avalonia and baltica for this time indicating that the amalgamation of eurmerica had already taken place by late devonian time laurentia had begun to drift north rates up to 5 cm yr 1 towards equatorial latitudes by mid carboniferous time

the 1984 morgan hill california earthquake the morgan hill california earthquake magnitude 6 1 of 24 april 1984 ruptured a 30 kilometer long segment of the calaveras fault zone to the east of san jose although it was recognized in 1980 that an earthquake of magnitude 6 occurred on this segment in 1911 and that a repeat of this event might reasonably be expected no short term precursors were noted and so the time of the 1984 earthquake was not predicted unilateral rupture propagation toward the south southeast and an energetic late source of seismic radiation located near the southeast end of the rupture zone contributed to the highly focused pattern of strong motion including an exceptionally large horizontal acceleration of 1 29g at a site on a dam abutment near the southeast end of the rupture zone

relation between stratigraphic architecture and multi scale heterogeneities in carbonate platforms the barremian lower aptian of the monts de vaucluse se france abstract understanding the relationship between multi scale sedimentary heterogeneities and the stratigraphic architectures of carbonate platforms improves the interpretation of paleoenvironmental evolution in time and space such an approach improves the prediction of the spatial distribution of reservoir properties within carbonate stratigraphic units the reservoir scale stratigraphic anatomy and the growth history of a barremian aptian carbonate platform monts de vaucluse se france was based on 1 high resolution measured sections on outcrops 2 detailed microfacies analyses 3 paleoenvironmental interpretations 4 biostratigraphy using rudist bivalves foraminifera calcareous algae and locally echinoderm and ammonites and 5 sequence stratigraphic interpretations with a special focus on the identification of discontinuity surfaces with a significant stratigraphic correlation potential and critical environmental meaning the platform succession consists of subtidal mainly infralittoral with rare inter to supratidal deposits thirty types of elementary facies grouped in 12 facies associations have been defined the vertical and lateral changes in paleoenvironments together with the development of remarkable stratigraphic surfaces such as subaerial exposures marine erosional surfaces and drowning surfaces allow the definition of five stratigraphic sequences ranging from the late barremian to the earliest aptian these depositional sequences can be grouped into two distinct carbonate sedimentary systems characterized by specific sedimentary profiles and skeletal and non skeletal components 1 a carbonate platform with stronger hydrodynamic gradients rimmed by a narrow belt of high energy deposits with corals and rudistid rudstone facies and 2 a carbonate ramp dominated by orbitolinids fine grained facies including an elongated high energy oolitic shoal the two dimension architecture of the depositional sequences dimensioned geometries thickness and facies variations and the morphology of the shelf reflect a strong interaction between tectonic differential subsidence sediment production and global environmental conditions at the km scale the gorges de la nesque stratigraphic motif could represent a nested stratigraphic structure within the large scale model which could be implemented for up scaling petrophysical properties from the well to a full field model the association of coral facies to the rudist dominated system in the provence platform is a very clear proxy of the polarity of the carbonate platform and is critical for subsurface facies property modeling based on well data finally at the global scale the stratigraphic architecture and the step wise drowning events of the provence platform confirm and document the precursor events associated with environmental perturbations that affected the carbonate factory prior the oceanic anoxic event 1a oae1a

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

off fault ground ruptures in the santa cruz mountains california ridge top spreading versus tectonic extension during the 1989 loma prieta earthquake the ms 7 1 loma prieta earthquake of 18 october 1989 produced abundant ground ruptures in an 8 by 4 km area along summit road and skyland ridge in the santa cruz mountains predominantly extensional fissures formed a left stepping crudely en echelon pattern along ridges of the hanging wall block southwest of the san andreas fault about 12 km northwest of the epicenter the fissures are subparallel to the san andreas fault and appear to be controlled by bedding planes faults joints and other weak zones in the underlying tertiary sedimentary strata of the hanging wall block the pattern of extensional fissures is generally consistent with tectonic extension across the crest of the uplifted hanging wall block also many displacements in laurel creek canyon and along the san andreas and sargent faults are consistent with right lateral reverse faulting inferred for the mainshock additional small tensile failures along the axis of the laurel anticline may reflect growth of the fold during deep seated compression however the larger ridge top fissures commonly have displacements that are parallel to the north northeast regional slope directions and appear inconsistent with east northeast extension expected from this earthquake measured cumulative displacements across the ridge crests are at least 35 times larger than that predicted by the geodetically determined surface deformation these fissures also occur in association with ubiquitous landslide complexes that were reactivated by the earthquake to produce the largest concentration of co seismic slope failures in the epicentral region the anomalously large displacements and the apparent slope control of the geometry and displacement of many co seismic surface ruptures lead us to conclude that gravity is an important driving force in the formation of the ridge top fissures shaking induced gravitational spreading of ridges and downslope movement may account for 90 or more of the observed displacements on the linear fissures similar fissures occurred in the same area and elsewhere near the san andreas fault during the predominantly right lateral 1906 san francisco earthquake and suggest that the loma prieta ground ruptures may in large part be independent of fault kinematics

palaeomagnetism of silurian sediments in w ireland evidence for block rotation in the caledonides summary a palaeomagnetic study of mid silurian wenlock sediments of the salrock formation in nw galway yields a reliable silurian palaeomagnetic pole position for w ireland at latitude 1 6 s longitude 287 7 e dp 2 5 dm 4 6 n 27 sites a further 12 sampling sites were located in silurian redbeds on clare island s mayo where a palaeomagnetic remanence of silurian age was also identified both remanences pre date local late caledonian folding however the clare island result has an anomalous azimuth when compared with the salrock result and with published silurian results for britain the two irish results can be reconciled by anticlockwise block rotation of the clare island region through 40 50 the rotation brings both palaeomagnetic and structural trends within the two sampling regions into alignment strike slip displacement across the clew bay fault zone producing a sinistral shear couple might have enabled such a rotation the timing and geographic extent of the proposed block rotation is as yet poorly defined however a younger age limit for rotation is provided by a late devonian or carboniferous partial magnetic overprint observed throughout both study areas and from geological evidence it seems likely that rotation is confined to the clew bay fault zone the dalradian rocks of the connemara massif located to the south of the salrock district have an e w structural grain some workers have proposed clockwise rotation of the connemara massif of ca 30 at between 500 and 390 ma which would bring the structural trends in w ireland into parallelism with caledonian trends in scotland because the silurian salrock succession which rests unconformably on the dalradian basement of connemara shows no such anomaly it provides a younger age limit for the possible rotation of connemara

a new silurian palaeolatitude for eastern avalonia and evidence for crustal rotations in the avalonian margin of southwestern ireland summary palaeomagnetic data are presented from mid silurian homerian upper wenlock 425 ma sediments from the dingle peninsula sw ireland which forms part of thenorthern margin of the palaeozoic microcontinent of avalonia three remanencecomponents were recognized after removal of a low temperature component l oriented parallel to the present earth eld at the sampling area two higher stabilitycomponents were isolated an intermediate unblocking temperature component i with mean in situ d 196 9 i 11 0 a95 10 8 with a corresponding palaeopole at330 0 e 30 6 s dp 5 6 dm 11 0 and a high unblocking temperature component h with mean tilt corrected d 218 6 i 22 1 a95 7 9 with a correspondingpalaeopole at 309 5 e 18 3 s dp 4 4 dm 8 4 a primary wenlock age is indicatedfor the h component by a positive intraformational conglomerate test whereas the i component is thought to be a secondary mid carboniferous partial remagnetization these data con rm that the sector of the iapetus ocean between avalonia andlaurentia was essentially closed within the limits of palaeomagnetic resolution by thewenlock there is still however a discrepancy between the declinations recorded bysimilar aged sequences to the north and south of the iapetus suture these point toeither an approximately 30 clockwise rotation of the entire avalonian microcontinentrelative to laurentia during closure or local vertical axis rotations of the samplingsites in southern britain

slip in the 1868 hayward earthquake from the analysis of historical triangulation data despite the importance of the hayward fault for earthquake hazards in the san francisco bay area neither the rupture length nor the average coseismic slip in the most recent major earthquake which occurred in 1868 is well known we estimate slip in the 1868 earthquake by analyzing triangulation data collected between 1853 1860 and 1876 1891 we apply a denuisancing procedure that projects out the dependence of that data on station coordinates allowing their displacements to be estimated directly the best fit to the data is obtained with a 52 km long by 10 km deep rupture that extends from warm springs to near berkeley considerably longer than the 30 km of reported surface breakage the estimated slip for an earthquake of this length is 1 9 0 4 m and the seismic moment is m0 3 0 0 7 1019 n m corresponding to mw 7 0 the data are inconsistent with regionally high strain rate prior to the 1906 earthquake as had been previously suggested the triangulation data record northeastward displacement of station loma prieta presumably as a result of the 1865 earthquake the fault normal displacement is not easily explained by slip on either the san andreas fault or the 1989 loma prieta rupture surface this observation is however consistent with an mw 6 3 4 thrust event northeast of the san andreas fault in the southern santa cruz mountains thrust belt

macroseismic interpretation of the 1812 earthquakes in venezuela using intensity uncertainties and a priori fault strike information we applied the bakun and wentworth 1997 method to the 26 march 1812 venezuelan earthquake previous studies have shown that it had at least two large subevents one associated with the bocono fault and an intensity center between barquisimeto and san felipe the other associated with the san sebastian fault near caracas we used the method with two modifications first we introduced intensity intervals to account for the uncertainties associated with historical information second we incorporated a correction that considers the fault s strike but not its actual position these modifications were tested with three earthquakes the 1989 loma prieta a 1980 m w 5 2 event in tachira venezuela and the 1967 earthquake in caracas m w 6 6 the third one was important for the interpretation of the 1812 caracas subevent for the barquisimeto san felipe subevent we obtained m wi 7 4 0 35 and an intensity center 10 20 n 69 95 w that lies between barquisimeto and san felipe our preferred rupture length was between 90 and 100 km the caracas subevent had m wi 7 1 0 33 with an intensity center 10 60 n 67 10 w close to the venezuelan north coast the expected rupture length was on the order of 70 km

chlorozoan versus foramol lithofacies in upper cretaceous rudist limestones abstract the study of upper cretaceous limestones of the nurra region northwestern sardinia italy that crop out with open shelf rudist rich deposits has shown that during the early senonian coniacian santonian interval sediments characterized by assemblages dominated by molluscs with variable amounts of red algae bryozoa and echinoids replaced sediments including hermatypic corals green algae and variable amounts of non skeletal grains these latter components were largely dominant in the previous carbonate shelf contexts of the nurra during jurassic early cretaceous times becoming less numerous until they disappeared in the transgressive deposits that followed the tectonically induced middle cretaceous emersion phase a rhodalgal association typical of anomalous tropical areas or transitional ones has been recognized in the replacing limestones that may be more generically considered foramol type deposits this seems to document conditions of stress in the waters impinging on the nurra carbonate platform during the coniacian santonian transition the observation that in the late cretaceous a similar evolutionary trend seems to have characterized many shallow neritic successions from many different areas leads us to hypothesize more general causes of stress e g induced upwellings on the marginal sectors of the shelves increased oceanic overturns and hyperproductivity due to terrestrial runoff on post emersive transgressed substrata peculiar oceanic conditions were able to create depositional contexts that were considerably changed with respect to the previous ones such that the more opportunistic forms of the foramol assemblages flourished the change in dominant assemblages resulted in a different organization of the sediment as a response to the different producing communities the resulting temperate type carbonate shelves were characterized by a low growth potentiality essentially due to a higher dispersion rate and this could have facilitated their drowning

slip partitioning of the calaveras fault california and prospects for future earthquakes examination of main shock and microearthquake data from the calaveras fault during the last 20 years reveals that main shock hypocenters occur at depths of 8 9 km near the base of the zone of microearthquakes the spatial pattern of pre main shock microseismicity surrounding the coyote lake and morgan hill hypocenters is similar to the pattern of the post main shock microseismicity microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones estimates of the fault regions which slipped during the coyote lake and morgan hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic we propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes from the pattern of microearthquake locations we recognize six aseismic zones where we expect future main shocks will rupture the calaveras fault from an analysis of historic seismic data we establish the main shock rupture history for each aseismic zone and identify two zones that are the most likely sites for the next m 5 earthquakes the first zone is located near gilroy and was last ruptured by a m5 2 earthquake in 1949 the second zone is located south of calaveras reservoir and north of the 1988 m5 1 alum rock earthquake it has not slipped seismically since at least 1903 and the size of the aseismic region is sufficiently large to sustain a m5 5 earthquake

calabrian arc oroclinal bending the role of subduction 1 paleomagnetic data collected in the last 30 years indicate that a simple orocline model is not sufficient to describe the complex evolution of the calabrian arc present day curvature of the calabrian arc is the result of a different tectonic history between the edges of the arc namely the southern apennines and sicily and its core the calabria peloritani domain these differences mirror the structural architecture and deep lithospheric configuration of the calabrian arc which are related to the geometry and evolution of the ionian subduction system in particular the presence of lateral heterogeneities in the subducting lithosphere and the subsequent progressive decrease in width of the trench during subduction are likely the main causes of calabrian arc formation and of its present day narrow tight shape

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

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

evolution of moderate seismicity in the san francisco bay region 1850 to 1993 seismicity changes related to the occurrence of large and great earthquakes the rate of seismic activity of moderate size m 5 5 earthquakes in the san francisco bay sfb region has varied considerably during the past 150 years as measured by the rate of seismic moment release seismic activity in the sfb region is observed to accelerate prior to m 7 0 earthquakes in 1868 1906 and 1989 and then to decelerate following them we examine these seismicity changes in the context of the evolution of the stress field in the sfb region as a result of strain accumulation and release using a model of dislocations in an elastic halfspace we use a coulomb failure function cff to take into account changes in both shear and normal stresses on potential failure planes of varying strike and dip in the sfb region we find that the occurrence of a large or great earthquake creates a stress shadow a region where the stress driving earthquake deformation is decreased interseismic strain accumulation acts to reverse this process gradually bringing faults in the sfb region out of the stress shadow of a previous large or great earthquake and back into a state where earthquake failure is possible as the stress shadow generated by a large or great earthquake disappears it migrates inward toward the fault associated with that large or great event the observed changes in the rate of occurrence of moderate earthquakes in the sfb region are broadly consistent with this model in detail the decrease in seismicity throughout most of the sfb region and a localized increase in the monterey bay region following the great 1906 earthquake is consistent with our predicted stress changes the timing and location of moderate size earthquakes when the rate of seismicity increases again in the 1950s is consistent with areas in which the 1906 stress shadow had been eliminated by strain accumulation in the sfb region those earthquakes that are most inconsistent with our stress evolution model including the 1911 earthquake southeast of san jose are found to occur in regions where dip slip faulting is common in addition to strike slip the 1906 earthquake brought that zone of dip slip faulting closer to failure suggesting that the 1911 event may have been a reverse faulting earthquake rather than a strike slip one similar to the 1984 morgan hill earthquake the occurrence of activity on faults very close to the san andreas such as the lake elsman earthquakes of 1988 and 1989 appear to be associated with the last disappearence of the stress shadow on the loma prieta segment of the san andreas fault thus events of that type may represent an intermediate term precursor to a large earthquake such as the 1989 loma prieta event much of the moderate size earthquake activity in the sfb region appears to be modulated in time by the buildup and release of stress in large and great earthquakes a tensorial approach to earthquake prediction i e taking into account changes in the components of the stress tensor has several advantages over examining scalar changes such as those in seismic activity and moment release rates this tensorial approach allows for both activation and quiescence but in different subregions prior to as well as after large earthquakes

strike slip terranes and a model for the evolution of the british and irish caledonides evidence is presented that many of the major strike faults in the british and irish caledonides were active as sinistral strike slip zones in the end silurian to pre mid devonian period some such as the highland boundary fault moved in this way at an earlier stage in the ordovician these data allow the caledonian rocks lying between the laurentian miogeocline whose basement is represented by the lewisian moine and possibly the dalradian and the gondwanaland miogeocline midland platform and welsh basin to be re analysed as a group of disorganized terranes which originated to the southwest in north america and southwest europe africa prior to the silurian the highland border terrane and northern belt terrane are interpreted as duplicated pieces of a mid ordovician sequence which was a back are to northwest subduction the midland valley terrane is interpreted as a slice of laurentian foreland onto which ophiolites were obducted in the lower ordovician but which became the basement of a continental margin arc to northwest subduction in the mid ordovician the cockburnland terrane is inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip the connemara terrane is regarded as an allochthonous piece of the dalradian miogeocline and the south mayo terrane as a remnant of an early ordovician arc and fore arc which in mid ordovician times became a back arc marginal basin to northwest subduction the lake district wexford terrane is part of an arc to southeast subduction under gondwanaland whose activity climaxed in the mid ordovician the central terrane is interpreted as a silurian overstep assemblage which blankets the junction between laurentian and gondwanaland derived oceanic terranes and therefore iapetus is regarded as an ordovician ocean which closed prior to the silurian the model suggests that at the end of the silurian a clockwise rotating gondwanaland having carried laurentia into collision with baltica broke free and created a major sinistral strike slip zone which disrupted the ordovician palaeogeography in the british isles north american sector of iapetus

strong ground motions generated by earthquakes on creeping faults a tenet of earthquake science is that faults are locked in position until they abruptly slip during the sudden strain relieving events that are earthquakes whereas it is expected that locked faults when they finally do slip will produce noticeable ground shaking what is uncertain is how the ground shakes during earthquakes on creeping faults creeping faults are rare throughout much of the earth s continental crust but there is a group of them in the san andreas fault system here we evaluate the strongest ground motions from the largest well recorded earthquakes on creeping faults we find that the peak ground motions generated by the creeping fault earthquakes are similar to the peak ground motions generated by earthquakes on locked faults our findings imply that buildings near creeping faults need to be designed to withstand the same level of shaking as those constructed near locked faults

the growth fabric of gregarious rudist elevators hippuritids in a santonian carbonate platform in the southern central pyrenees abstract the growth fabrics of living congregations of erect sessile epifauna range between two extremes with superstratal growth the growing skeletons project well metres above the ambient sedimentary surface creating an upstanding framework which may be secondarily filled by sediment as in modern tropical coral reefs with constratal growth by contrast the growing tips of the skeletons project little centimetres from the seafloor such that the bulk of the skeletal fabric is embedded in and supported by the accumulating interstitial sediment as in pinna and oyster beds here we investigate the original growth fabrics and palaeorelief of hippuritid congregations in the santonian rudist formations around the sant corneli anticline near tremp in the southern central pyrenees the study particularly concentrates on a hippuritid lithosome exposed over some 0 25 km2 on the northern flank of the anticline four aspects are analysed 1 the lithosome is shown to have a tabular biostromal geometry and like others in the area is covered by a laterally accreted bioclastic blanket 2 specimens in upright life position show that the pioneers of the paucispecific congregations grew in bouquets but later recruits settled on the flanks of established and fallen shells adults were only loosely clustered and supported by the accumulating interstitial sediment 3 most shells however are now horizontal with respect to the bedding and densely stacked dense horizontal fabric or d h f this fabric is shown to be a result of current induced removal of sediment and toppling of shells 4 in contrast to the open marine aspect of the overlying bioclastic sediments the fine matrix sediment of the hippuritid lithosomes is faunally restricted and appears largely derived from the in situ biodegradation of shells we conclude that the hippuritid congregations grew constratally i e without any supporting biogenic framework and that they formed biostromal accumulations lacking relief so there is no justification for calling them reefs as some authors have done rather these rudists grew as gregarious sediment dwellers in the restricted waters of the platform top where they were sporadically disturbed by storms and eventually blanketed by bioclastic material swept in from the platform margin

gravity magnetic and high precision relocated seismicity profiles suggest a connection between the hayward and calaveras faults northern california 1 gravity magnetic and seismicity data profiled across the hayward fault zone were generated as part of ongoing studies to help determine the geologic and tectonic setting of the san francisco bay region these data combined with previous geophysical studies that indicate that the hayward fault zone dips 75 ne near san leandro and follows a preexisting structure reveal a possible direct connection between the seismogenic portion of the hayward and calaveras faults at depth although the relocated seismicity data are regional in nature they suggest that the dip of the hayward fault zone may vary from near vertical in the northwestern part of the fault to about 75 ne at san leandro in the central part of the fault to about 50 ne in the southeastern part of the fault gravity and magnetic data profiled across the hayward fault zone were processed using standard geophysical techniques cross sections of high precision relocated hypocenters were constructed along each profile from the northwestern to the southeastern end of the hayward fault zone profiles and cross sections are referenced to pinole point where the hayward fault enters san pablo bay and are spaced 2 5 km apart topographic profiles shown on the seismicity cross sections were generated using u s geological survey usgs 7 5 min 30 m digital elevation models relocation of seismicity data was accomplished using a regional double difference method the double difference method incorporates ordinary travel time measurements and cross correlation of p and s wave differential travel time measurements relative locations between earthquakes have hypocentral errors of about 100 m horizontally and 250 m vertically absolute location uncertainties were not determined but are probably dramatically improved compared to the usgs s northern california seismic network catalog data

crustal structure of the trans european suture zone region along polonaise 97 seismic profile p4 1 the large scale polonaise 97 seismic experiment investigated the velocity structure of the crust and upper mantle in the trans european suture zone tesz region between the precambrian east european craton eec and paleozoic platform that comprises terranes added during the caledonian and variscan orogenies 530 370 and 370 225 ma respectively this experiment included 64 shots recorded by 613 seismic stations during two deployments very good quality data were recorded along five profiles and the longest and most important one p4 is the focus of this paper clear first arrivals and later phases of waves reflected refracted in the crust and moho were interpreted using two dimensional 2 d tomographic inversion and ray tracing techniques the crustal thickness along the profile varies from 30 35 km in the paleozoic platform area to 40 km below and due northeast of the tesz to 43 km in the polish part of the eec and to 50 km in lithuania the paleozoic platform and eec are divided by the polish basin so the upper crustal structure varies considerably in the area of the polish basin the p wave velocity is very low vp 6 1 km s down to depths of 15 20 km indicating that a very thick sedimentary sequence is present we suggest two possible tectonic interpretations of the velocity models 1 baltica indented avalonia obducting its upper crust and underthrusting its lower crust in a tectonic flake structure and 2 a rifted margin of baltica underlies the polish basin this model is similar to other interpretations of seismic profiles recorded in the baltic sea the second model implies that the paleozoic platform solely consists of avalonian lithosphere and the eec of baltica lithosphere it offers a simple explanation of the difference in crustal thickness of the two platforms it also implies that the caledonian and variscan orogenies in this area were relatively soft collisions that left this continental margin largely intact

re evaluation of several large historic earthquakes in the vicinity of the loma prieta and peninsular segments of the san andreas fault california abstract the size and location of several of the largest 19th century earthquakes in the san francisco bay area including the june 1838 8 october 1865 21 october 1868 and 24 april 1890 events are re evaluated by comparing these historic events to several modern events in particular the 1989 loma prieta earthquake similar high intensities in the monterey bay area during both the 1989 and 1838 events indicate that the 1838 shock probably ruptured the loma prieta segment in addition to the peninsular segment of the san andreas fault if so the resulting earthquake would have been of moment magnitude m w 7 2 thus like segments of many other plate boundaries the loma prieta segment exhibits heterogeneous rupture in that sometimes it ruptures with the peninsular segment as in 1906 and probably in 1838 and at other times it ruptures alone as in 1989 in contrast the area of high intensities generated by the 1865 earthquake was centered in the santa clara valley and the eastern foothills of the santa cruz mountains indicating that the 1865 shock probably was located northeast of the loma prieta rupture and not on the san andreas fault in addition the felt areas taken to be one of the best measures of relative source size of modified mercalli intensities mmi v and vi for the 1865 shock are considerably smaller than that of the 1989 event relationships between felt areas of intensities v and vi and moment magnitude are developed for the san francisco bay area based on these relationships the average computed moment magnitudes for the 1865 1868 and 1890 earthquakes are 6 51 0 18 6 84 0 20 and 6 32 0 16 respectively if these results are correct then the loma prieta segment taken to include all faults within the san andreas fault zone i e within a zone up to a few kilometers wide appears to rupture with or without the peninsular segment every 76 11 years these data on repeat times may be the most accurate information now available for ascertaining the date of future rupture of that segment and for testing recurrence models the smaller size of the 1865 earthquake would be consistent with it being part of the long term seismic build up to the 1868 event rather than being paired with it as events of similar size if the 1865 earthquake did occur northeast of the loma prieta segment then a future source of that type located closer to san jose and the santa clara valley could pose a considerable hazard to the southern san francisco bay area on going searches of letters and diaries of missionaries and early settlers could yield new information that should help to further constrain the locations and magnitudes of these and other historic earthquakes

oroclinal bending in the caledonides of western ireland a mid palaeozoic feature controlled by a pre existing structural grain abstract the caledonides of the west of ireland mark a segment of the caledonian appalachian orogen where the structural grain swings from the ne sw trend that typifies the caledonides of northern britain to an e w orientation the origin of this arcuate structure has previously been proposed to be either primary reflecting the original geometry of promontories and embayments in the laurentian margin in this sector of the orogen or secondary as evidenced by palaeomagnetically determined clockwise rotations in silurian rocks in the region we report the results of a palaeomagnetic investigation of the early to middle ordovician mweelrea ignimbrites llanvirn from an accreted taconic arc the south mayo trough in that part of the western irish caledonides that has an e w trend after removal of a low temperature component of magnetisation l interpreted to represent a viscous component of the earth s present field a high temperature component of magnetisation h was isolated at fifteen sites in four ignimbrite flows h passes a palaeomagnetic fold test yielding a tilt corrected mean remanence direction d 132 6 i 29 1 95 17 9 which corresponds to a palaeopole at 36 4 e 9 9 s the pole is in reasonable agreement with established early to middle ordovician reference poles for laurentia and indicates that no significant rotation occurred between the e w south mayo trough and the laurentian margin after accretion and therefore that the curvature of this segment of the orogen is likely to be primary this contrasts with other results from silurian sequences to the south which record significant post silurian clockwise rotations examination of all reliable palaeomagnetic data from the region indicates that the clockwise rotations are restricted to the rocks south of the south mayo trough we propose that the rotations in the south are linked with the superposition of the pre existing structural grain on the younger rock units during late silurian and early devonian sinistral transpression

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr