the 20 and 27 april 1894 locris central greece earthquake sources through coeval records on macroseismic effects newly retrieved coeval records on the effects of the two large earthquakes of 20 and 27 april 1894 in locris central greece have been analyzed to assess macroseismic intensities according to the european macroseismic scale grunthal 1998 an intensity equal or higher than 8 has been estimated at 70 different places the two earthquakes were close in time and both focused on the same area this asked for an interpretation free as much as possible from the prejudice due to the accumulative descriptions implied for instance by the 1894 scientists9 reports to image the earthquake sources and derive the main seismic parameters we processed the macroseismic intensity data by using the boxer method proposed by gasperini et al 1999 on the basis of this approach and our new sets of data we obtain m 6 4 and 6 5 for the 20 and 27 april earthquakes respectively the latter being substantially smaller than the estimates proposed in previous works results obtained from the processing of macroseismic data have been tested and compared to recent geological data our preferred interpretation is that the 20 and 27 april 1894 earthquakes ruptured together the whole atalanti fault the internal structural complexity of the atalanti fault appears to have controlled the rupture propagation the change in strike of the fault trace along with its intersection with the malesina fault near proskinas is interpreted as a geometric barrier that is the boundary between the two individual earthquake sources the 20 april earthquake would have ruptured between proskinas and skroponeri mountain southeast of the village of larimna whereas the 27 april earthquake ruptured between proskinas and the northwest chlomon fault zone north of the town of atalanti

a reappraisal of the 1894 atalanti earthquake surface ruptures central greece this article presents the results of new field and aerial photo surveys of the atalanti fault and of the mesoseismal area of the 20 and 27 april 1894 earth quakes coupled with a reanalysis of contemporary reports and previous investiga tions these are used to gain a better understanding of the faults responsible for these events and their seismic behavior the first shock was smaller and probably located inshore or offshore the malessina peninsula no resolving field evidence has been found to locate the seismogenic structure responsible for this shock on the basis of the limited information available we suggest the malessina escarpment a 12 km long ene trending nw dipping fault as a possible structure responsible for this event on the other hand the second and largest shock is definitely related to the atalanti fault sensu stricto a main wnw trending n dipping active fault extending between the platirema valley a few km nw of the town of atalanti and larymna the total length of the rupture recognized in the field is about 32 km but it can be extended further se up to 40 km no evidence for a longer rupture extending some other 20 km to the nw between the karagiozis river and ag kostantinos is found the complex geometry of the fault with bends and step overs appears to be controlled by preexisting transverse structures minimum coseismic vertical throws measured in the field after more than a century elapsed from the earthquake are 30 80 cm thus consistent with contemporary reports indicating 1 m average slip rates are not well constrained the available estimates fall in the range 0 1 0 5 mm yr confirming the smaller amount of crustal extension taking place in this area with respect to other nearby regions such as the corinth gulf no new data are available to define the average recurrence interval typical of the atalanti fault however a reconsideration of the existing information induced us to rule out the possibility that the famous 426 b c earthquake occurred on the atalanti fault on the basis of the extent and size of the rupture recognized in the field a m 6 8 is estimated for the second and largest shock

role of geological inheritance in australian beach morphodynamics the australian coast contains 10 685 beaches which occupy 49 of the 30 000 km coast and average 1 37 km in length their relatively short length is largely due to the presence of bedrock calcarenite and laterite which form boundaries to many of the beaches as well as occurring as rocks reefs and islands along and off the beaches this geological inheritance plays a major role in australian beach systems determining their length and through wave refraction and attenuation influencing beach location shape type morphodynamics and circulation which in turn influence sediment transport and the backing dune and barrier systems this paper uses a database covering every australian beach to review the role of headlands rocks and reefs on australian beaches major effects are the short average beach length reduction in breaker height resulting in lower energy beach types wave refraction resulting in increased beach curvature the presence of topographic rips on moderate and higher energy beaches and megarips during high wave conditions and the interruption of and or trapping of longshore sand transport leading to beach rotation

global patterns in sandy beach macrofauna species richness abundance biomass and body size abstract global patterns in species richness in sandy beach ecosystems have been poorly understood until comparatively recently because of the difficulty of compiling high resolution databases at continental scales we analyze information from more than 200 sandy beaches around the world which harbor hundreds of macrofauna species and explore latitudinal trends in species richness abundance and biomass species richness increases from temperate to tropical sites abundance follows contrasting trends depending on the slope of the beach in gentle slope beaches it is higher at temperate sites whereas in steep slope beaches it is higher at the tropics biomass follows identical negative trends for both climatic regions at the whole range of beach slopes suggesting decreasing rates in carrying capacity of the environment towards reflective beaches various morphodynamic variables determine global trends in beach macrofauna species richness abundance and biomass are higher at dissipative than at reflective beaches whereas a body size follows the reverse pattern a generalized linear model showed that large tidal range which determines the vertical dimension of the intertidal habitat small size of sand particles and flat beach slope a product of the interaction among wave energy tidal range and grain size are correlated with high species richness suggesting that these parameters represent the most parsimonious variables for modelling patterns in sandy beach macrofauna large scale patterns indicate a scaling of abundance to a body size suggesting that dissipative beaches harbor communities with highest abundance and species with the smallest body sizes additional information for tropical and northern hemisphere sandy beaches underrepresented in our compilation is required to decipher more conclusive trends particularly in abundance biomass and body size further research should integrate meaningful oceanographic variables such as temperature and primary production in deciphering latitudinal trends

palaeomagnetic study of llandovery lower silurian red beds in north west england high unblocking temperature magnetization components carried by haematite have been isolated from 12 sites of llandovery lower silurian red mudstones from nw england the principal deformation phase in this area is acadian mid devonian however some faults with related folds were also active during the later variscan orogeny the site mean magnetization directions pass a regional fold test at the 95 per cent confidence level implying that the magnetization components pre date acadian folding the overall mean direction declination 43 4d inclination 24 1d 95 12 4d gives a pole position at 13 6ds 313 9de and a palaeolatitude of 12ds the low palaeolatitude implies closure of the iapetus ocean between eastern avalonia and laurentia by late llandovery time and is consistent with a recently published palaeolatitude 13ds for the wenlock mid silurian of southern britain comparison of these values with the published palaeolatitude from nw england of 43ds for caradoc late ordovician time implies very rapid at least 15 cm yr 1 northward drift of eastern avalonia during late ordovician early silurian time the new pole position from the llandovery red beds lies close to late silurian and early devonian poles from scotland and wales but is significantly different from a group of mid silurian poles comprising data from scottish intrusions and from swedish sediments this discrepancy may be due to late silurian early devonian pre acadian remagnetization of our sampling sites or local clockwise rotation of the sampling sites during acadian and or variscan deformation however the positive fold test presence of reversals and local deformation history tend to mitigate against these possibilities the more likely interpretation is that although baltica scotland were one continental block from the mid silurian scandian orogeny eastern avalonia did not become part of this block until latest silurian

defining seismogenic sources from historical earthquake felt reports abstract we present a method that uses macroseismic intensity data to assess the location physical dimensions and orientation of the source of large historical earthquakes intensity data contain a great deal of information that can be used to constrain the essential characteristics of the seismic source in particular both the seismological theory and its practice suggest that the orientation of the source of significant earthquakes is reflected in the elongation of the associated damage pattern a plausible and easily manageable way of describing a seismic source is by representing it as an oriented rectangle the length and width of which are obtained from moment magnitude through empirical relationships this rectangle is meant to represent either the actual surface projection of the seismogenic fault or at least the projection of the portion of the earth crust where a given seismic source is likely to be located the systematic application of this method to all the m 5 5 earthquakes that occurred in the central and southern apennines italy in the past four centuries returned encouraging results that compare well with existing instrumental direct geological and geodynamic evidence the method is quite stable for different choices of the algorithm parameters and provides elongation directions that in most cases can be shown to be statistically significant in particular the resulting pattern of source orientations is rather homogeneous showing a consistent appennines parallel trend that agrees well with the ne sw extension style of deformation active in the central and southern portions of the italian peninsula

advances and problems in ordovician palynology of england and wales acritarchs and chitinozoa are used to date ordovician rocks in england and wales but the data base for both groups is poor study of chitinozoa has been neglected in the uk in contrast to north america and southwest europe where biozonations have been established formal definition of acritarcb biozones may soon be possible in the tremadoc arenig but acritarch biostratigraphy in the llanvirn ashgill is insufficiently documented

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

seismic and aseismic deformation associated with the 1952 kern county california earthquake and relationship to the quaternary history of the white wolf fault synthesis of geodetic geologic and seismic data from the white wolf fault california indicates that the fault separates an area of late quaternary and continuing rapid uplift in the tehachapi mountains and transverse ranges from even more rapid subsidence in the southern san joaquin valley on july 21 1952 rupture of the white wolf fault produced the ml 7 2 kern county earthquake we used the aftershock zone to delimit the size of the faulted slip surface and applied constraints imposed by the known 1952 1953 horizontal shear strains to model the measured coseismic vertical displacements with an elastic dislocation model a curved fault trace with decreasing fault depth 27 to 10 km from the surface vertically to the base slip 3 to 1 m and dip 75 to 20 from the 1952 epicenter at the southwest end of the fault toward the northeast provides the fit most consistent with the geodetic record the measured seismic moment the fault plane solution and the pattern of surface rupture two short releveled lines near the 1952 epicenter tilted 4 and 17 rad down to the north from 5 10 years before the earthquake the preseismic tilts differ significantly from ten other surveys of these lines left lateral fault crossing shear strain from 0 2 20 years before the quake was two times greater than both preseismic off fault strains and the post seismic fault crossing strains during the first seven years after the earthquake aseismic deformation was negligible from 1959 to 1972 uplift reached 160 mm over an area larger than the aftershock zone rising first in the epicentral region and then at the northeast end of the fault this was unaccompanied by any surface fault slip reconstruction of the vertical separation on the white wolf fault from late quaternary and late miocene stratigraphic marker beds shows that the rate of reverse fault slip increased forty fold from 0 1 0 2 mm yr to 3 9 mm yr between the past 10 15 m y and the most recent 0 6 1 2 m y we estimate a 170 to 450 yr average recurrence interval for earthquakes on the white wolf fault with slip equivalent to that in 1952 the 1952 earthquake appears to be characteristic of the quaternary record of fault displacement in the increase in white wolf slip toward the san andreas fault the ratio of reverse to lateral slip 1 3 1 and the ratio of vertical fault slip to emergence of the hanging wall block 3 1 the 8500 m deep sedimentary basin on the down thrown block cannot be explained by repeated slip of the white wolf fault in an elastic medium

paleoseismological trenching across the atalanti fault central greece evidence for the ancestors of the 1894 earthquake during the middle ages and roman times the atalanti fault bounds to the southwest the evoikos gulf one of the major extensional basins of central greece this fault ruptured during the 1894 earth quakes producing at the surface a complex ca 30 km long rupture paleoseismo logical trenching performed at three sites along this fault provided the first insights on its seismogenic behavior unfavorable trench stratigraphy and scarcity of datable material made the identification and characterization of individual paleoearthquakes quite difficult however by integrating paleoseismological geological historical and archaeoseismological data we defined three surface faulting earthquakes the most recent event is the 1894 earthquake the penultimate occurred during the middle ages between a d 770 and 1160 whereas the third event back occurred in roman times between 50 b c and a d 230 and is interpreted to be the opus earthquake of a d 105 these results suggest that 1894 type earthquakes repeat each 660 1120 yr the average minimum slip per event and vertical slip rates are of the order of 45 cm and 0 4 1 6 mm yr respectively these values are in agreement with other geological estimates and with geodetic measurements because of the short time elapsed since the 1894 earthquake the atalanti fault does not appear to contain an important seis mogenic potential on the other hand these results may shed light on the potential of other seismogenic sources threatening the area

evolution of the northern belt southern uplands implications for the southern uplands controversy conodont and graptolite dating provide a high resolution biostratigraphical framework for correlation across the southern upland fault the establishment of an early caradoc age for the red chert and volcanic sequences within the northern belt of the southern uplands confounds the accretionary prism model and our data support the view that following the obduction of the ballantrae ophiolite fan complexes prograded southeastwards across a narrow fault bounded shelf into the deep basin of the northern belt the fan complexes were initiated by uplift in the hinterland caused by the intrusion of plutons into the midland valley terrane sedimentation was controlled by regional extension subsidence and eustasy through the llanvirn and caradoc basic lavas with attenuated within plate geochemical signatures were erupted during the early caradoc peak of extension and may have just post dated the initiation of southwards subduction beneath the lake district

the timing of ordovician magmatism in the english lake district and cross fell inliers volcanic and hypabyssal intrusive rocks of the lower palaeozoic english lake district and cross fell inliers are elements of the ordovician destructive plate margin system of microcontinental avalonia two igneous sheets within the marine sedimentary skiddaw group of these inliers previously described as lavas are reinterpreted as sills sedimentary rocks enclosing these sills are of late tremadoc early arenig c 493 ma and early llanvirn 476 ma age and breccias along the upper contacts of both were produced by steam explosivity and fluidization ahead of theadvancing tips of the intrusions previous interpretation of the breccias on the older sheet as sediment deposited on the eroded top of a lava flow implied an early ordovician onset of arc magmatism such early magmatism would have been virtually coincident with the latest tremadoc initiation of arc magmatism in wales but evidence for such a near synchronous response tothe putative onset of subduction is lacking respective onsets of magmatismwere probably separated by at least 17 m y and possibly by as much as 29 m y the apparent contemporaneity of mid and late ordovician volcanic episodes in england and wales and similarities in extensional tectonic style suggest that the two areas then were part of the same subduction system responding similarly to plate scale magma generating and tectonic processes the early ordovician situation is uncertain but the absence of arc volcanic rocks of this age in the english lake district suggests that this area and wales are not tectonically juxtaposed elements of a former simple linear arc

source complexity of the october 1 1987 whittier narrows earthquake long and short period body waveform data recorded at regional and teleseismic distances are modeled to obtain the source parameters of the whittier narrows earthquake of october 1 1987 although the long period data can be satisfied by a simple thrust earthquake on a plane striking 280 at a depth of 14 km we require a double source solution to satisfy both the long and short period teleseismic data the first subevent has a focal mechanism of strike 250 dip 30 n and a slip vector 90 the second is 280 40 n and 98 the second event occurred 1 0 s after the first was 5 times larger 1 2 1025 dyn cm for the second 0 23 1025 for the first in terms of seismic moment and was also shallower 12 km whereas the first subevent was at 15 km the two subevents probably occurred on a north dipping listric fault but may have occurred on two subparallel faults these features were determined by studying a variety of phases including teleseismic p and sh and regional pnl the whittier narrows earthquake was a high stress drop event but a single value for stress drop cannot be obtained because of the complex nature of the source if we define the fault area as the aftershock area we obtain a stress drop of about 750 bars

the environmental seismic intensity scale esi 2007 in greece addition of new events and its relationship with magnitude in greece and the mediterranean preliminary attenuation relationships abstract the environmental seismic intensity esi scale has been officially released in 2007 and is based on the quantification of earthquake environmental effects due to its quantitative nature the scale improves the process of assessing macroseismic intensities particularly in the epicentral area of those cases in which sole traditional intensity scales prove to be ineffective following a large number of publications that applied this relatively newly established scale there is some need for parametrization this is because this intensity scale can offer new insights to seismic hazard assessment and has the potential to reduce the uncertainties that stem from traditional macroseismic scales this study has three main goals firstly to enrich and compile an esi 2007 database from earthquakes in greece by adding 4 new events secondly to extract a relationship between magnitude and the esi 2007 for greece and the mediterranean thirdly to offer a preliminary estimate of how the intensity attenuates with distance after developing a code in python language to assist this process the esi 2007 scale was applied in the 1995 ms 6 6 kozani grevena earthquake the 1978 mw 6 5 thessaloniki earthquake the historic 1894 atalanti earthquake sequence m 6 4 and m 6 8 and the 365ad event in crete m 8 4 these events were selected because they have well documented and extensive co seismic effects including primary and secondary surface ruptures rockfalls landslides and liquefaction phenomena for the kozani earthquake extracted results were correlated with sar interferograms in order to provide a complete and high spatial resolution of the ground deformation both the kozani grevena and the thessaloniki events produced a maximum intensity ix on the esi 2007 scale the atalanti earthquake produced a maximum intensity x and the 365ad crete earthquake a maximum intensity xii overall the esi 2007 scale compares fairly well with the traditional macroseismic scales except for some villages in the kozani grevena epicentral area where due to the poor quality of buildings existing scales overestimated the intensity by one degree compared to the esi 2007 it is interesting to note that both for greece and the mediterranean area a strong correlation exists between mw and the esi 2007 scale in particular the following relationships between the mw and the esi scale have been extracted i for greece io esi 2007 3 1427 exp 0 1643mw and ii for the mediterranean io esi 2007 3 3543exp 0 1557mw however more events and more data regarding the intensity distributions are required to establish the intensity attenuation with distance

surface deformation associated with the november 23 1977 caucete argentina earthquake sequence leveling data are combined with seismic observations from the november 23 1977 ms 7 4 caucete earthquake in western argentina in order to constrain models of crustal deformation in the sierras pampeanas tectonic province the spatial pattern and amount of uplift 1 m that accompanied this earthquake suggest 4 m of slip on a north south trending west dipping fault with a dip of 35 a downdip width of 24 km and a length of 80 km the top of the fault is 17 km below the surface these fault parameters are generally consistent with the seismic focal mechanism and moment of the main shock which occurred near the top of the fault the fault length is derived from the distribution of local and relocated teleseismic aftershocks and from analysis of the main shock a double event in which the two shocks occurred 21s apart and were separated by 65 km along the proposed fault plane strike the fault width is determined from the locations of the larger hypocenters along the preferred fault plane this fault is buried beneath the north south striking sierra pie de palo a laramide style crystalline basement uplift in the western part of the sierras pampeanas province the buried fault model is consistent with the lack of observed coseismic surface faulting and the broad east west symmetric character of the overlying sierra pie de palo by combining the 1977 earthquake observations with topographic relief and with estimates of the age of deformation for the sierras pampeanas basement uplifts we calculate a shortening rate of the order of 10 mm yr for the past 5 m y for this andean back arc province and estimate an average recurrence time of the order of 1000 years for earthquakes of this magnitude beneath the sierra pie de palo

quantitative relations of seismic source parameters and a classification of earthquakes abstract relations between earthquake parameters moment m0 fault area s fault length l and width w stress drop time characteristics and magnitudes and faulting type dip slip ds and strike slip ss are quantitatively analyzed using a dataset of 240 events m 5 the analysis is carried further toward an earthquake systematization by introducing earthquake classes the results are 1 1 l w 2 1 for ds l w 2 30 for ss and l w 3 7 for giant m0 1029 dyne cm earthquakes respectively 2 2 log m0 1 5 log s 22 2 s in km2 and tentatively log m0 2 45 log s 17 49 for ds and ss and giant earthquakes respectively 3 3 the large scatter of data in m0 s dependences is the result of the combined effect of the variation in and l w 4 4 the concept of constant is replaced by variable to explain the large variations in relations between m0 s l and w for both ds and ss earthquakes and partly between body and surface wave magnitudes low intermediate and high stress drop gd 30 30 60 and 60 bar respectively earthquakes are defined 5 5 a relation of reciprocity exists between seismic slip fault length and width and stress drop 6 6 a saturation of s for some very large earthquakes is suggested from the interpretation of actual data on m0 s l w etc 7 7 the total source duration tsd increases with m0 in relation with earthquake type and tentatively log m0 2 16 log tsd 24 50 holds for ds earthquakes 8 8 log m0 1 5 mm 16 1 holds for mm brune engen mantle wave magnitude 8 5 8 75 9 9 more magnitudes of shorter or longer period on both body and surface wave basis are useful in constraining significant earthquake features 10 10 low and high frequency earthquakes can be distinguished using the gutenberg richter relation ms mb as a reference relation or a relation between ms and mmaxb 11 11 aki s similarity conditions are extended by adding two more conditions as to express more specifically four basic features geometry deformation frequency and time of the earthquake source 12 12 a reference earthquake is defined by criteria consistent with the similarity conditions 13 13 on this basis and in view of nonsimilarity of earthquakes in their totality a scheme for earthquake classification is proposed

geological control of beach morphodynamic state the concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid 1980s and expansion in the 1990s much of the pioneering work was undertaken in australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3 dimensional morphology and the dean s parameter h b wst was established subsequently the relative tidal range parameter h b tr was extended to beaches of all tidal ranges in this paper observations are presented from 25 beaches around the north coast of ireland these beaches exist on an environmental gradient that encompasses marked tidal and wave energy variability micro to macrotidal and low to high wave energy each beach was visually categorised into one of several established beach states described in the literature on the basis of field observations for each beach the rtr and dean s parameter were calculated for the immediately antecedent period and used to predict the beach state using published relationships observed and predicted beach states were then compared comparison of observed and predicted beach states showed that while beaches with observed dissipative morphology typically matched the expected criteria most other beach states did not lack of agreement between predicted and observed beach states has been reported elsewhere and attributed to failings in the rtr and dean s parameter in addition this study identifies geological factors as important constraints on actual beach state in the majority of beaches studied inherited geological factors appear to be more important determinants of beach morphology than contemporary dynamics c 2005 elsevier b v all rights reserved

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

an acadian mountain front in the english lake district the westmorland monocline the structure of the southern and central english lake district is that of a southeast facing monocline named here the westmorland monocline this 10 km wide zone of highly cleaved southeast dipping rocks separates gently dipping poorly cleaved borrowdale volcanic group to the north from extensively folded but regionally subhorizontal windermere group foreland basin rocks to the south the monocline formed early in the local acadian deformation sequence and accommodates at least 8 km of uplift it coincides with the steep concealed margin of the lake district batholith a major northwest dipping shear zone is revealed in the deepest levels now exposed within the monocline in the skiddaw group rocks of the black combe inlier the monocline has the characteristics of a mountain front providing significant tectonic elevation across a foreland dipping panel of rocks with no hinterland dipping thrust visible at the surface we interpret the uplift as the consequence of a southeast vergent thrust with a gently northwest dipping ramp beneath the central lake district continuing southeastwards as a flat detachment beneath the windermere group a displacement up the ramp of about 20 km is accommodated by backthrusting within the monocline and by shortening within the windermere group of the hangingwall southeast of the monocline the tip lies beyond the limit of the lower palaeozoic inlier beneath carboniferous cover

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

source complexity of the 1988 armenian earthquake evidence for a slow after slip event we analyzed teleseismic p and s waves using a multiple event deconvolution method to investigate the source process of the spitak armenia earthquake of december 7 1988 teleseismic long period body waves exhibit complex waveforms significantly more complex than those normally seen for an event of this size we identified two groups of subevents one is a group of strike slip events during the first 20 s the other is a dip slip event initiating at about 30 s after the initial rupture the tensor sum of all the subevents is essentially strike slip strike 302 dip 59 rake 143 with a scalar moment of 1 47 10 19 n m the seismic moment of the dip slip event strike 89 dip 60 rake 88 is 5 6 10 18 n m nearly 40 of the total and the moment release rate is slower than the other subevents with a strike slip mechanism we call this event a slow after slip event the mechanism of the after sup event is consistent with the present day deformation pattern in the caucasus where north south compression is predominant due to the continental collision between the arabian plate and the russian platform this result suggests that in a region where both strike slip motion and crustal shortening are taking place like southern california a large strike slip event may accompany large thrust events and vice versa in order to determine the total coseismic deformation pattern it is essential to resolve these multiple events in time space and mechanism

slump folds and gravity slide structures in a lower palaeozoic marginal basin sequence the skiddaw group nw england major folds with associated thrust faults and a major olistostrome are described from the skiddaw group a lower ordovician turbidite sequence in the lake district of nw england the style and geometry of the structures are shown to be compatible with their generation as submarine slumps or slide masses although they are much larger than any slump structures hitherto described from britain the predominant strain is shown to be simple shear spatial and temporal variations in strain permit a developmental model to be erected the opposing vergence of the structures across the mapped area indicates a relatively narrow probably fault controlled depositional basin

broadband study of the 1989 loma prieta earthquake we determined the source characteristics of the oct 18 1989 loma prieta california earthquake using teleseismic data the solution from body waves gives a mechanism with dip 70 rake 138 and strike 128 and a seismic moment of 3 10 26 dyne cm m w 6 9 this solution is similar to those obtained from long period rayleigh and love waves p nl waves and first motion data the body wave form suggests a depth of about 15 km the effective duration of the source is 6 sec which suggests a fault length of 30 km and 15 km for bilateral and unilateral faulting respectively considering the extent of the aftershock area we used 35 km as an estimate of the total rupture length the strike slip and the thrust components of the coseismic slip are 177 and 159 cm respectively the large thrust component raises an important question regarding the recurrence pattern if the loma prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 years the 159 cm displacement implies a long term uplift rate of about 1 cm year which appears too large for this region three hypotheses for reconciling this apparent conflict are 1 the geometry of plate motion along the santa cruz mountain segment changes over a time scale of several thousand years so that the coseismic displacement has not accumulated enough to produce high topographic relief 2 the coseismic shp direction varies from event to event 3 the slip plane of the 1989 loma prieta earthquake is different from the major boundary between the pacific and the north american plates if this is the case the loma prieta earthquake is a rather rare non characteristic event the surface slip of about l m for the 1906 san francisco earthquake is one of the key data in long term forecasting no surface slip was observed for the 1989 loma prieta earthquake even if the horizontal slip at depth is as large as 1 8 m this points to a risk of relying too heavily on surface observations for long term seismic risk analysis

ganderia laurentia collision in the caledonides of great britain and ireland during terrane convergence an influx of clastic sediment from an upper plate onto a lower plate is an early indication of terrane juxtaposition in the caledonides of great britain and ireland units accreted to laurentia during the early palaeozoic era include peri gondwanan terrane assemblages that earlier separated from west gondwana however the southern uplands terrane contains detrital zircon populations apparently derived entirely from laurentia characterized by a large asymmetric mesoproterozoic peak and a scarcity of zircon at 600 ma and 2 1 ga in contrast cambrian and ordovician rocks from the lake district and the leinster massif of ireland show abundant grains with these ages together with a range of mesoproterozoic zircon these characteristics are shared with the monian terrane of anglesey and with ganderia in the appalachians indicating probable derivation from amazonia in west gondwana silurian sandstones from the lake district show an influx of laurentia derived zircon and lack the peri gondwanan signal this indicates that in the caledonides ganderia was not accreted to the laurentian margin until c 430 ma in contrast to the ordovician accretion of ganderian fragments recorded in the appalachians suggesting that the configuration of the closing iapetus ocean varied significantly along the strike of the orogen supplementary material details of sample coordinates analytical procedure and u pb detrital zircon analytical data are available at www geolsoc org uk sup18739

rupture of a seismic gap in southeastern alaska the 1972 sitka earthquake ms 7 6 abstract the sitka alaska earthquake of july 30 1972 m s 7 6 is one of the largest strike slip events since 1963 this earthquake is thought to have ruptured the pacific north america plate boundary segment between the large strike slip events in 1949 and 1958 and the sitka earthquake was heralded as one of the first successful forecasts of an earthquake based on the seismic gap hypothesis another motivation to study this event is the availability of a strong ground motion recording 50 km from the epicenter which is near the middle of the 180 km long plate boundary segment the teleseismically located aftershocks occur only in the southern half of this segment we have analyzed rayleigh waves and p waves recorded by wwssn long period vertical instruments a total of 25 very long period rayleigh phases r2 r5 define a symmetric four lobed radiation pattern from which we can infer a nearly pure right lateral strike slip fault striking 340 n20 w and a bilateral rupture comparison of synthetic and observed rayleigh waves yields a seismic moment of 3 10 27 dyn cm m w 7 6 the p waves are characterized by a dominant complex pulse in the first 40 s and a succession of smaller pulses after that the source time functions are deconvolved from 32 p waves with good azimuthal distribution to obtain the moment depth extent and rupture history the mean moment of the source time functions is 5 0 2 4 10 27 dyn cm and the depth extent is 0 10 km tomographic inversion of the source time functions produces an image of the earthquake rupture process this procedure maps the moment release of the complex pulse into two high displacement regions i e asperities 1 the epicentral area to 40 km north and 2 between 60 and 90 km south of the epicenter the main asperity just north of the epicenter coincides with a quiescent zone of microaftershocks while the overall average seismic displacement is 6 m the displacement at the main asperity is 7 m the same value as the tectonic displacement accumulated since the previous earthquake in 1848 the fault averaged stress drop is 100 bars while the asperity stress drop is 130 bars tomographic imaging of the source time functions thus resolves several features of the rupture process notably the bilateral propagation and rupture initiation at the largest asperity this is in contrast to the large 1976 guatemala strike slip earthquake where the largest displacements occurred away from rupture initiation

the foreshock sequence of the february 4 1975 haicheng earthquake m 7 3 we have examined the locations and radiation patterns of the foreshocks of the february 4 1975 haicheng earthquake m 7 3 using arrival times from six local seismic stations the foreshocks and mainshock were located relative to a master event the foreshocks occurred in a tight cluster that elongated with time before the largest foreshock the activity was located within a small approximately equidimensional volume with a diameter of about 2 km after the largest foreshock the activity spread northwest and southeast forming a 6 km long northwest trending zone first motions and ratios of p to s amplitudes indicate that two different faulting mechanisms occurred during the foreshock sequence the two radiation patterns can tentatively be correlated with different parts of the zone the hypocenter of the mainshock was not located on the same fault as that defined by the foreshocks hypocenters but rather was located 6 km south of and several kilometers shallower than the foreshock cluster we think this large separation between foreshocks and mainshock in a direction perpendicular both to the plane of rupture of the mainshock and to the trend of the foreshocks might be the result of an en echelon step in the fault that slipped during the mainshock an analysis of the change in stress due to slip during the foreshocks shows that the increase in shear stress on the mainshock fault caused by the foreshocks is very small and that direct triggering of the mainshock by the foreshocks is unlikely

caradocian land plant microfossils from libya the oldest paleontologically well dated spore tetrads and cuti clelike sheets of cells have been recovered from beds of caradoc mid ordovician age from boreholes in the murzuk murzuq and rhadames ghad mis basins of western libya these microfossils together with late llandovery early wenlock vascular plant megafossils lycophytes and psilophyton known from libya lead us to conclude that land plants including vascular plants probably had a long pre silurian record extending at least into the basal caradocian additonal evidence suggests that this record does not extend as far back as the earlier late cambrian dresbachian

source mechanisms of three moderate california earthquakes of july 1986 abstract we studied the source processes of three moderate size earthquakes in california the m s 6 0 event of july 8 1986 near palm springs the m s 5 8 shock of july 13 1986 offshore of oceanside and the m s 6 2 event of july 21 1986 in the chalfant valley on the east side of the sierra nevada the centroidal source parameters are estimated by inversion of long period p and sh waves recorded at teleseismic distances by seismographs of worldwide networks a more detailed description of the source is then obtained by analyzing broadband seismograms the north palm springs earthquake had a simple rupture process most of the seismic moment was released in the first 3 sec in a single step the strike of the source fault plane follows the average trend of the banning fault and its dip agrees with the dip of the fault plane delineated by the aftershocks the faulting mechanism of the main shock is right lateral strike slip with a sizable reverse component that is consistent with uplift north of the banning fault the earthquake offshore of oceanside had a slightly more complex rupture process the far field source time function consists of two pulses that represent the release of most of the moment in the first 3 sec the source mechanism indicates reverse faulting with the compressional axis trending northeast almost perpendicular to the trend of mapped faults offshore the event does not appear to be associated with major mapped faults in the area but the strike of one of the nodal planes agrees with the trend of the major mapped faults offshore and its mechanism is consistent with the missing component of plate convergence not taken up by the onshore strike slip fault systems and the idea of a weak san andreas fault system the rupture process of the chalfant valley earthquake was yet more complicated the source time function indicates that in a 4 sec time window three asperities were broken the source mechanism indicates right lateral strike slip faulting with a small normal faulting component on a fault that dips approximately 50 southwest earthquake activity suggests that presently the deformation in the northern part of the owens valley which includes the chalfant valley is dominated by conjugate strike slip faults which strike obliquely to the main range bounding normal faults the waveforms indicate the presence of a low velocity zone at a depth of about 20 km in the crust in the chalfant valley a synthesis of information from waveform modeling first motion fault plane solutions and aftershock distributions indicates that the nucleation and or termination of rupture for the north palm springs and the chalfant valley events were controlled by preexisting fault geometry

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

source parameters of earthquakes in the nevada seismic zone 1915 1943 the nevada seismic zone has historically been one of the most active seismic regions of the intermountain west although all large m 7 0 earthquakes located within this zone occurred prior to the establishment of a worldwide seismograph network most have been well recorded instrumentally this study uses available instrumental data to determine the source parameters for some of the earliest earthquakes occurring within the region namely the 1915 m 7 6 pleasant valley and 1932 m 7 2 cedar mountain earthquakes and several smaller events of 5 5 m 6 5 occurring within the cedar mountain region between 1934 and 1943 results of body waveform inversions suggest that the pleasant valley earthquake at the northern end of the nevada seismic zone is a complex event best fit by a multiple source time function waveform and first motion information for the cedar mountain earthquake located within the walker lane suggest the earthquake was composed of two events each having significant components of right lateral strike slip motion rakes of 176 to 179 waveforms of the m 6 5 excelsior mountain earthquake located only 40 km southwest of cedar mountain suggest the earthquake was a simple rupture along a normal fault rake of 90 20 although surface faulting indicates that the event had a component of left lateral strike slip motion

centroid moment tensor solutions for 35 earthquakes in western north america 1977 1983 abstract seismic records from the gdsn sro asro dwwssn rstn and ida networks were used to obtain long period t 45 sec focal mechanisms for 35 earthquakes in western north america longitude 140 to 110 latitude 30 to 60 employing the centroid moment tensor method of dziewonski et al 1981 and dziewonski and woodhouse 1983 the same algorithm was applied to all events the smallest m 0 6 4 10 23 dyne cm being an aftershock to the 1979 imperial valley california earthquake and the largest m 0 8 5 10 26 dyne cm the 1980 eureka california earthquake all events were analyzed with and without the constraint m r m r 0 on the moment tensor an ad hoc criterion on the relative variance reduction was employed to determine a favored solution our solutions show general agreement with other published results as well as with tectonic structures agreement with results obtained using the abundant local and regional data confirms the adequacy of the method in determining long period source parameters and verifies its applicability in regions where local and regional data are scarce or nonexistent in some cases disagreement between our solution and results from first motion studies appears to be related to source complexities our moment tensor represents the total stress release of the composite event a consistent westward movement of the centroid locations reflects lateral heterogeneities in the crust and mantle

source parameters of earthquakes along the coastal margin of west africa and comparisons with earthquakes in other coastal margin settings abstract the coastal margins of western africa and most of the eastern americas are considered to be stable continental interiors where large earthquakes occur infrequently since these regions have similar geologic and tectonic histories it might seem reasonable to expect similarities between their large earthquakes on the other hand current plate forces acting on these regions differ and may lead to regional differences in earthquakes to examine the similarities of coastal margin earthquakes we first determined the source parameters for six earthquakes of m 5 5 occurring along the coastal margin of west africa a region that has not previously been studied in detail results of this analysis indicate that the earthquakes are shallow 8 15 km strike slip events along high angle faults dips generally 80 with nodal planes having orientations similar to those of faults mapped in the exposed precambrian basement five out of seven events show complexities in their source time functions east of the cameroon line most p axes trend northeast southwest to east west earthquakes west of the cameroon line show less coherency of stress field with p axes for onshore events trending northwest southeast and for offshore events north south to northeast southwest in contrast m 5 5 earthquakes of the eastern coastal margin of north and south america have reverse mechanisms with more moderate dips on nodal planes 45 70 and over 50 have east west oriented p axes which reflect stresses caused by the motion of north and south america relative to europe and africa in north america earthquakes appear to occur on faults that cannot be associated with surficial geology occur shallower or deeper than west african events and have shorter rupture lengths for the equivalent moment these differences suggest that west african events may not serve as useful analogs for events expected along the american coastal margin

relationship between metamorphism and structure in the skiddaw group english lake district regional variation of white mica illite crystallinity in the skiddaw group is set against the structural interpretation of hughes cooper stone 1993 this issue in which early or pre ludlow deformation and slaty cleavage development s1 were succeeded by southward thrusting and an associated development of s1 and s1 crenulation cleavages possibly during early devonian times kubier index ki values are plotted in relation to geological structure for a major part of the skiddaw group and cross sections constructed the pattern is interpreted in terms of three processes 1 diagenetic to low anchizonal burial metamorphism under a relatively high geothermal gradient during the late arc stage early to mid silurian which preceded the orogenic phase and formation of s1 2 upper anchizonal to epizonal metamorphism due to tectonic thickening and slaty cleavage development during the early to pre ludlow orogenic phase following closure of iapetus 3 late tectonic uplift of already metamorphosed rocks by southward directed movement on the loweswater gasgale gill and causey pike thrusts possibly during early devonian time an analogous interpretation is made for the skiddaw area though with the addition of major post s1 contact metamorphism

source characteristics of the loma prieta california earthquake of october 18 1989 from global digital seismic data displacement velocity and acceleration records of p and sh body waves recorded at teleseismic distances are analyzed to determine the static and dynamic source parameters of the loma prieta california earthquake of october 18 1989 m sub b 6 6 m sub s 7 1 three distinct bursts of energy corresponding to three subevents can be recognized in most records the displacement waveforms indicate that the first subevent contributes negligible moment while the largest releases of moment and energy are controlled by the second and third subevents the second and third subevents are located north and south of the initial nucleation a fourth small subevent needed to model later features of the p waveforms suggests that slow slip continued after the major releases of energy occurred the waveforms are fit with a fault plane solution having strike 130 degree dip 65 degree and slip 140 degree for all the subevents the focal depths of the two major subevents are 16 and 12 km and their asperity radii are 4 0 and 6 0 km respectively the seismic moment m sub o is 2 2 times 10 sup 26 dyne cm from spectral analysis of teleseismic velocity the radiated energy e sub s is estimated to be 1 1 times 10 sup 22 dyne cm implying an apparent stress of 15 bars more from the high frequency level of the teleseismic acceleration spectrum and a rupture area of 440 km sup 2 the authors derive a dynamic stress drop of 51 bars less

short paper the subaerial setting of the ordovician borrowdale volcanic group english lake district most ordovician volcanic rocks of southern britain were produced in volcanic island settings and the borrowdale volcanic group bvg of the lake district has traditionally been interpreted in this way however a review of lithofacies associations in the bvg indicates a subaerial environment pyroclastic surge deposits thin welded tuff beds lava flow morphologies abundant erosional unconformities and fluviatile and laharic facies indicate widespread subaerial emplacement volcano tectonic subsidence aided preservation of subaerial facies although a preservation bias favoured lacustrine deposits erosional unconformities above subaerial aggradational volcanic sequences are to be expected so the sub windermere group unconformity does not necessarily imply tectonic uplift

the spitak armenia earthquake of 7 december 1988 field observations seismology and tectonics the epicentre of the destructive earthquake that devastated northern armenia the strongest in the region since historical times is located within the lesser caucasus a mountain country subjected to north south compression by the push of the arabian plate a french soviet field expedition studied surface breaks and aftershock activity the fault scarp could be followed for 13 kilometres and showed a reverse dislocation of 1 6 metres aftershocks are shallower than 13 kilometres and delimit a ruptured surface of about 300km2

morphodynamic characteristics and classification of beaches in england and wales abstract the use of beach classification models has become widespread in literature in recent years beach classification models that recognise distinct modal beach states in response to environmental conditions are most widely used these models were developed largely in high energy micro to meso tidal sandy environments and subsequent attention has focussed on extending their use into other beach environments here the applicability of these traditional beach classification models to the highly diverse coastline of england and wales was assessed through collection of detailed morphodynamic characteristics of 92 beaches yielding a comprehensive multi variate data set containing morphological sedimentological and hydrodynamic information the complex and diverse study region incorporates beach morphology covering the full spectrum from reflective to dissipative and non barred to multi barred cluster analysis supplemented by mds ordination resulted in the identification of 9 distinct beach types traditional morphodynamic indices and rtr were found to be effective in discriminating between beach groups providing some support for the beach state models derived using information from australian beaches it was found that absolute wave energy wave power is important as well in controlling beach type for intermediate beaches a wave energy flux p h 2 t value of 3 kw m 1 was found to differentiate between beaches with p 3 kw m 1 and without p 1 three dimensional bar rip morphology a key component controlling recreational beach hazard levels observations presented here inform a beach classification model to be used as the basis for a national beach risk assessment programme beach classification models based on environmental parameters are by necessity simplifications and should be used as tools for understanding morphodynamic systems rather than beach type prediction

holocene palaeoenvironmental changes in agia paraskevi prehistoric settlement lamia central greece abstract holocene palaeoenvironmental changes in the area of the prehistoric settlement of megali vrysi close to the village of agia paraskevi in central greece 5 km east of lamia city were investigated the area is situated in the low flat alluvial plain on the outskirts of sperchios valley that is bordered nnw to ene by a rocky hilly ridge of the othrys mountain foothills 5 5 km away from the present coastline the megali vrysi site is considered to be an important mediterranean prehistoric commercial centre reconstruction of the palaeoenvironmental changes of the broader area adds new information concerning the general palaeogeographical setting of the settlement multidisciplinary research involved a detailed geomorphological survey combined with stratigraphical palaeontological and geophysical studies the penetrated strata differentiated into 4 units from top to bottom the first represents the archaeological strata the second consists of the freshwater marshy sediments while the third is the transition layer between the second and the deeper fourth group of marine lagoonal sediments the holocene stratigraphy data was combined with the 14 c ams dating results and showed a marine palaeoenvironment 5500 bc gradually having shifted to a coastal lagoonal one 3500 bc and finally changed to a freshwater marshy environment 2500 bc the comparison between ages and depths of the relative sea level points allowed the estimation of the sea level rise rate for the agia paraskevi area which is considerably lower than the one proposed for the aegean sea in the same time period this considerable offset is attributed to the intensive tectonic uplift of the study area due to the tectonic deformation of the sperchios valley and this is probably why the prehistoric coastal settlement remained on the surface and unaffected from the sea transgression for more than 7000 yrs during holocene

the stratigraphy correlation provenance and palaeogeography of the skiddaw group ordovician in the english lake district a new lithostratigraphy is presented for the skiddaw group lower ordovician of the english lake district two stratigraphical belts are described five formations are defined in the northern fells belt ranging in age from tremadoc to early llanvirn they are all mudstone or sandstone dominated of turbidite origin in ascending order they are named the bitter beck watch hill hope beck loweswater and kirk stile formations two formations are defined in the central fells belt ranging in age from late arenig to llanvirn these are the buttermere formation a major olistostrome deposit overlain by the tarn moor formation consisting of turbidite mudstones with volcaniclastic turbidite sandstone beds a revised graptolite and new acritarch biostratigraphy for the skiddaw group is presented with eight graptolite biozones and thirteen acritarch assemblages and sub assemblages the provenance of the group is assessed from detailed petrographical and geochemical work this suggests derivation in the early ordovician largely from an old inactive continental arc terrane lying to the south east with the appearance of juvenile volcanic material in the llanvirn comparisons and correlations of the skiddaw group are made with the isle of man and eastern ireland

foreland basin development and tectonics on the northwest margin of eastern avalonia the early palaeozoic convergence of avalonia and laurentia created a foreland basin at the suture zone of the former lapetus ocean sedimentological and stratigraphic evidence of shallowing and contemporaneous shortening suggests that the southern part of the basin the windermere group became detached from its basement in the late ludlow and began to invert the detachment beneath the basin rooted into a northwest dipping mid crustal thrust system contemporaneous uplift to the north of the late silurian basin involved shortening of the avalonian foreland basement by thrusting basin inversion occurred ahead of a southeastward advancing mountain front we postulate a foreland southeast prograding sequence of thrusting through the ludlow in the lake district the basin continued to migrate onto the avalonian foreland through the early devonian ahead of an advancing orogenic wedge finally coming to a stop in the emsian

the 1971 san fernando earthquake a double event evidence is presented which suggest that the 1971 san fernando earthquake may have been a double event that occurred on two separate subparallel thrust faults it is postulated that the initial event took place at depth on the sierra madre fault zone which runs along the base of the san gabriel mountains rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km a second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the sierra madre fault zone the surface trace of this fault coincides with the san fernando fault zone which was the principal fault associated with surface rupture it is postulated that rupture propagated from a depth of 8 km to the free surface the moments of the first and second events are approximately 0 7 10 26 dyne cm and 1 0 10 26 dyne cm respectively this model is found to explain the combined data sets of strong ground motions teleseismic p and s waveforms and static offsets better than previous models which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth nevertheless many features of the observed motions remain unexplained and considerable uncertainty still exists regarding the faulting history of the san fernando earthquake

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

characterising sandy beaches into major types and states implications for ecologists and managers abstract sandy beaches are dynamic systems that host a diverse range of fauna whose habitat is controlled by the interactions among sand waves and tides in recent decades much of the study of sand beach ecology has focused on community type and structure across the range of beach types as well as regional variations in order to compare different studies accurate information is required on the nature of the environment studied sand particle size tide range and wave conditions unfortunately this has not always been provided by beach ecologists our understanding of sandy beach processes has advanced to the stage where ecologists can no longer omit assessing the role of wave climate even if this cannot be done precisely as can be done for sand and tides in this paper we provide a method to quantify wave conditions and in combination with sand particle size and tide range determine the beach type and state for waves we first highlight the concepts sea and swell as distinct from the terms sheltered and exposed we then provide a method to estimate breaker height we then develop a model with two steps first breaker height is combined with tide range to identify whether waves or tides are the primary driver of beach morphology and thereby the define the beach type wave dominated tide modified or tide dominated then using breaker height period and sand particle size the beach state is determined seven main beach morphodynamic types states are defined at the narrow and steep extreme are wave dominated reflective beaches and at the wide and low gradient extreme are tide dominated flats the physical and ecological features typical of the seven types states are presented as well as some management implications

application of an iterative least squares waveform inversion of strong motion and teleseismic records to the 1978 tabas iran earthquake an iterative least squares technique is used to simultaneously invert the strong motion records and teleseismic p waveforms for the 1978 tabas iran earthquake to deduce the rupture history the method solves for both slip amplitudes and rupture times on a finite fault several inversions of the data are done to determine the best fitting hypocenter average rupture velocity and source time function within the range of our parameter search the effects of using different data sets and different parametrizations of the problem linear versus nonlinear are also considered teleseismic body waves are shown to be essential to obtain a reliable solution due to the sparse coverage of the fault plane by strong motion stations a simple triangular source time function is compared with a modified kostrov source time function for a circular rupture and a constant propagating stress drop although the waveforms used in the inversions can not resolve between these two time functions the kostrov source time function gives a moment estimate and maximum fault displacement more consistent with long period surface waves and field observations the results of the iterative inversion for slip amplitudes and rupture times are compared with the results of a linear inversion for slip amplitudes in which the rupture velocity is fixed flexibility in the sequence of faulting for the linear inversion is obtained by allowing multiple rupture intervals a consensus of all the inversion runs indicates a complex multiple source for the tabas earthquake with four main source regions over a fault length of 90 km and an average rupture velocity of 2 5 km sec

the july 1986 oceanside ml 5 3 earthquake sequence in the continental borderland southern california an earthquake of m l 5 3 occurred at 32 58 7 n 117 51 5 w southwest of oceanside in san diego county at 13 47 13 july 1986 ut this main shock was followed by an extensive aftershock sequence with 55 events of m l 3 0 during july 1986 the epicenters of the main shock and aftershocks are located at the northern end of the san diego trough bahia soledad fault zone sdt bs where it changes strike from northwest to a more westerly direction through a left offset or a bend in the fault the northwest striking sdt bs is one of three strike slip fault systems that constitute the offshore agua blanca fault system the spatial distribution of the aftershocks indicates a unilateral 7 to 9 km long rupture to the east southeast away from the epicenter of the main shock the focal mechanism of the main shock also has an east southeast striking and south dipping plane with mostly reverse movement on it focal mechanisms of the m l 3 0 aftershocks show both reverse and strike slip movement the reverse focal mechanisms indicate that this sequence may have occurred on a thrust fault that provides for a left stepping offset or a bend in the san diego trough fault as movement is transferred to the west along the santa cruz catalina island escarpment some of the aftershocks that are located to the southeast of the main shock and have strike slip focal mechanisms suggest activation of the northwest trending san diego trough fault a stress inversion of the focal mechanism data shows that the maximum principal stress determined from the focal mechanisms of the main shock and 22 aftershocks that occurred within 36 hours of the main shock has an azimuth of s30 w plunging 18 the maximum principal stress determined from 30 aftershocks that occurred from 15 july to 2 october 1986 has an azimuth of s20 w plunging 18 the values the measure of the relative sizes of the principal stresses are approximately 0 07 and 0 1 respectively indicating that the intermediate and minimum principal stress are of similar magnitude the results of the stress inversion and the focal mechanisms that showed reverse faulting suggest that the inner continental borderland offshore from oceanside is not currently a pure strike slip tectonic regime but rather a strike slip mixed with reverse faulting regime when the 52 aftershock focal mechanisms are divided into four groups and the stress inversion is repeated the change in stress can be described as a progressive counter clockwise rotation of 14 of the orientation of the maximum principal stress to a more southerly direction with the greatest change in stress orientation observed shortly after the main shock the abundance of aftershocks may be related to the large temporal variation in stress orientation that in turn may have resulted from the small stress drop of the main shock

the irpinia italy 1980 earthquake detailed analysis of a complex normal faulting a detailed analysis of near source strong motion and leveling data together with the results of teleseismic waveform modeling by westaway and jackson 1987 and aftershock studies by deschamps and king 1984 allows a satisfactory kinematic description of the complex normal faulting associated with the magnitude ms 6 9 november 23 1980 irpinia earthquake southern italy the three main rupture episodes starting at about 0 20 and 40 s are here associated with better constrained source parameters than in previous studies we first evaluated the triggering time for the 11 closest accelerometers by using the well recorded 40 s strong motion phases this gave the absolute time and location of the dominant episodes of faulting the first rupture propagated mainly toward the northwest on a ne dipping normal fault at a mean velocity close to 3 km s for about 20 km and continued 15 km further on smaller subfaults it was associated with surface breakage in the southeastern part the second rupture started from the southeastern end of the first rupture about 18 s after it and propagated about 20 km toward the southeast on a low angle normal fault dipping 20 ne it was associated with secondary faulting on steeper planes reaching the surface the third and last episode at 39 s nucleated near the first hypocenter at shallower depth and the rupture possibly propagated on a 10 to 15 km long normal fault striking se antithetic to the first activated fault a clear correlation appears between the strength of the geological formations and the existence of surface breakage and shallow aftershock activity

aftershocks of the western argentina caucete earthquake of 23 november 1977 some tectonic implications an aftershock survey using a network of eight portable and two permanent seismographs was conducted for the western argentina caucete earthquake ms 7 3 of november 23 1977 monitoring began december 6 almost 2 weeks after the main shock and continued for 11 days the data set includes 185 aftershock hypocenters that range in the depth from near surface to more than 30 km the spatial distribution of those events occupied a volume of about 100 km long 50 km wide 30 km thick the volumnar nature of the aftershock distribution is interpreted to be a result of a bimodal distribution of foci that define east and west dipping planar zones efforts to select which of those zones was associated with the causal faulting include special attention to the determination of the mainshock focal depth and dislocation theory modeling of the coseismic surface deformation in the epicentral region our focal depth 25 35 km and modeling studies lead us to prefer an east dipping plane as causal a previous interpretation by other investigators used a shallower focal depth 17 km and similar modeling calculations in choosing a west dipping plane our selection of the east dipping plane is physically more appealing because it places fault initiation at the base of the crustal seismogenic layer rather than in the middle of that layer which requires fault propagation to be updip rather than downdip

changes in the tectonic regime above a subduction zone of andean type the andes of peru and bolivia during the pliocene pleistocene this paper adresses the changes in the tectonic regime in the peruvian and bolivian andes that have occurred since the upper miocene when the present day elevation of the cordillera above sea level has been almost reached the stress patterns are deduced essentially from a field study of fault kinematics and a numerical inversion of the slip vector data measured on the fault planes the cuzco fault system in southern peru is chosen as an example to illustrate the methodology used in this region striations on both active and holocene faults are in agreement with a n s extension but faults affecting early pleistocene deposits exhibit two families of striations the younger results from the previous n s extension the older involving reverse motions results from either an e w or a n s compression faults affecting pliocene formations often show an oldest family of striations resulting from a ne sw or an e w trending extension thus three tectonic regimes are demonstrated which are also supported by regional unconformities and sedimentological data 1 a pliocene extensional regime 2 a lower pleistocene compressional regime and 3 a mid pleistocene present day extensional regime similar analyses conducted in the pacific and sub andean lowlands allow sketching of the successive pliocene pleistocene stress patterns in the central andes the quaternary and present day stress pattern is characterized by a n s extension in the high andes and in the pacific lowlands and by an e w compression in the sub andean lowlands and at the contact between the nazca and south american plates this stress pattern is interpreted at a large wavelength 100 km as an effect of compensated topography this model supposes that the vertical lithospheric stress zz increases with the topography the crustal thickness and the low density mantle beneath and that the lithospheric maximum compressional horizontal stress hmax trending e w roughly parallel to the convergence is fairly constant on both edges of the andes the tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then the e w trending hmax is 2 and hmin trending n s is 3 allowing extension to occur in this direction the pliocene stress pattern was characterized by a ne sw or an e w trending extension in the high andes in the pacific lowlands and possibly in the sub andean lowlands this stress pattern was clearly different from the present day one because the e w trending stress was hmin this required a weak push or eventually tractional boundary forces acting on the south american lithosphere it is suggested that this might result from a strong slab pull due to a long steeply dipping slab which decreased the value of the xx stress transmitted to the overriding plate the early pleistocene state of stress was compressional since the elevation of the andes had not markedly decreased during this period this required an increase of the e w trending stress value this resulted from a strong coupling between the two lithospheric plates possibly due to a rupture of a long slab under its own weight other spatial changes in the stress pattern are related to the particular situation of the forearc to the subduction of the buoyant nazca ridge and to the different dips of the slab extension in the high andes is of small magnitude of the order of 1 during the last 1 2 m y in a few basins it may have attained 40 during the pliocene 5 3 m y

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

bounds on the holocene slip rate of the haiyuan fault north central china abstract we measured the offsets of six stream valleys of 30 to 90 m along the northwest southeast trending left lateral haiyuan strike slip fault in north central china minimum ages of these offsets were determined to estimate lower bounds for the holocene slip rate the most reliable bounds are 7 6 1 0 and 6 7 1 0 mm yr with three others that are smaller 3 4 0 7 3 5 0 9 and 4 1 0 4 mm yr and one large value 16 4 5 9 mm yr that we doubt thus the average holocene slip rate of the haiyuan fault is larger than 6 mm yr and probably exceeds 7 mm yr if the average slip rate of 5 to 10 mm yr for the quaternary period is applicable to the holocene epoch the average rate is 8 2 mm yr

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

the pyrenean earthquake of february 29 1980 an example of complex faulting abstract an m b 5 1 earthquake occurred on february 29 1980 in the western pyrenees near arudy france the telemetred network of the i p g p operating in this area since 1978 allowed a good localization of this earthquake 43 4 21 n 0 24 59 w depth 4km during the two years preceding this earthquake the seismic activity exhibited a gradual decrease a foreshock of magnitude 1 6 was recorded three hours before the main shock a temporary network set up in the epicentral area a few days after the main shock permitted a precise study of the aftershock sequence fifty fault plane solutions for earthquakes ranging from magnitude 1 5 4 were obtained a complex pattern of faulting was revealed with both strike slip and normal faulting however a regional tectonic stress tensor can be proposed from a detailed investigation of the aftershock sequence this stress tensor is in agreement with previous results in this area

rupture complexity of a moderate sized mb 6 0 earthquake broadband body wave analysis of the north yemen earthquake of 13 december 1982 abstract the occurrence of the north yemen earthquake of 13 december 1982 provides an important opportunity to study source properties of earthquakes in the southern arabian peninsula although moderate in size m b 6 0 this earthquake is the largest to have occurred in the region since the deployment of the global digital seismograph network p waves recorded at teleseismic distances can be obtained from stations of this network and of the graefenberg array that are flat to displacement and velocity in the frequency range from 0 01 to 5 0 hz the broad bandwidth of the data is necessary for deriving a dynamic description of the earthquake as well as the static properties of the source in contrast inversions using only long period data provide much less insight into the complexity of rupture by fitting the displacement pulse shapes with synthetics we find that the yemen earthquake was a complex rupture consisting of two events that occurred about 3 0 sec apart the depth of both hypocenters is estimated to be 7 km the focal mechanisms of the events each have a nodal plane that strikes 340 and dips 60 to the east however the slip directions of the focal mechanisms are in slightly different directions 230 and 300 respectively the total moment of the earthquake is 3 0 10 25 dyne cm with the second event having three times the moment of the initial event by inverting p wave arrival time differences at each station we find the second hypocenter is located 7 5 km from the initial hypocenter in a direction that is nearly colinear with the nnw striking nodal plane of the focal mechanisms of each event the trend of extensional ground cracks in the epicentral region and the predominant strike of composite focal mechanisms of locally recorded aftershocks are also in a nnw direction from the consistency of these observations we infer that the east dipping nnw striking nodal planes are the fault planes the static stress drop of the first and second events are 44 and 31 bars respectively inverting the energy flux in the velocity waveforms we find the energy radiated by the earthquake is 4 8 10 20 dyne cm this implies an average apparent stress of 4 bars at different times during the aftershock sequence seismicity tended to cluster about one or another of two different planes which although having roughly the same strike had conjugate dips one of these planes delineated late in the aftershock sequence coincides with the inferred fault plane for the main shock the complexity of the main shock and of the aftershock sequence suggests that strain accumulated on a system of strongly interdependent faults as the region became critically loaded the effect of a major rupture was to critically stress faults adjacent to the initial nucleation the second event of the main shock represents the rapid release of stress from the fault system while the ensuing aftershock sequence represents the gradual release of stress

coulomb stress triggering of earthquakes along the atalanti fault central greece two april 1894 m6 events and stress change patterns abstract two m6 events occurred 15 20 km apart in central greece on april 20 and april 27 1894 we identify the april 27 1894 rupture 2nd in the sequence with the atalanti segment of the atalanti fault zone because of unequivocal surface rupturing evidence reported by skouphos skouphos t 1894 die swei grossen erdbeben in lokris am 8 20 und 15 27 april 1894 zeitschrift ges erdkunde zu berlin vol 24 pp 409 474 coulomb stress transfer analysis and macroseismic evidence suggest that the april 20 1894 event 1st in the sequence may be associated with the martinon segment of the same fault zone our stress modelling suggests that this segment may have ruptured in an m 6 4 event producing a 15 km long rupture which transferred 1 14 bar in the epicentral area of the april 27th 1894 event thus triggering the second m 6 6 earthquake along the atalanti segment and producing a 19 km long rupture we also examined three alternative fault sources for the first event however all these produce smaller stress stresses for triggering the second event the proposed slip model for the second earthquake is capable of producing coastal subsidence of the order of centimetres to decimetres which fits the geological data the 1894 earthquake sequence was followed by a difference in the timing of subsequent m 5 events in each of the relaxed areas stress shadows a negative change in coulomb failure stress 0 6 bar which terminated between 22 37 years north and 80 years south

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

aftershocks of the 1988 january 22 tennant creek australia intraplate earthquakes evidence for a complex thrust fault geometry summary on 1988 january 22 three earthquakes of ms 6 3 6 7 occurred in a 12 hr period near tennant creek northern territory in the proterozoic north australian craton and produced 32 km of surface rupture on two main scarps the lake surprise scarp is shaped like a boomerang with the east arm trending ese and the west arm wsw the kunayungku scarp lies 7 km to the northwest and trends ese locations of 211 aftershocks determined using data from portable seismograph arrays define a 10 km by 40 km aftershock zone elongated parallel to the trend of the surface ruptures in the western and eastern part of the fault zone aftershocks occur only south of the kunayungku and eastern lake surprise scarps respectively in the central section in contrast aftershocks lie primarily to the north of the western arm of the lake surprise scarp focal depths range from the surface to 8km in all sections the shallowest earthquakes lie closest to the scarps whereas deeper events lie further away in cross section the aftershocks lie in three distinct inclined zones which delineate fault surfaces ruptured by the main shocks aftershocks are concentrated near the edges of the inferred fault surfaces suggesting that stress was relieved in the centre of the faults by rupture during the main shocks the inferred fault plane dips are 45 to the ssw for the kunayungku fault 55 to the nnw for the western lake surprise fault and 35 to the ssw for the eastern lake surprise fault these dip directions are consistent with the sense of thrust movement inferred from surface deformation the reversal of fault dip and sense of movement between the central and end segments requires a complicated fault geometry the aftershock data would allow a second south dipping plane in the central section that does not intersect the surface this blind fault may be responsible for much of the moment release interpreted from the modelling of broad band teleseismic waveforms choy bowman 1989 rupture of the north dipping plane may have been controlled by a pre existing fault marked at the surface by a quartz ridge 5 km long and may be of secondary importance although the quartz ridge suggests previous faulting the absence of significant topographic relief together with estimates of erosion rates suggest an average repeat time in excess of 104yr preliminary interpretation of water withdrawal histories and water level data from a borefield adjacent to the eastern lake surprise scarp does not support a causal relationship between the borefield and the occurrence of the earthquakes the nearby warramunga wra seismic array provides a record of local earthquake activity from 1965 to the present the fault area was essentially aseismic until two small earthquakes in 1986 february and a series of six magnitude 4 5 earthquakes in 1987 january which were followed by more than 1000 aftershocks the frequency of occurrence of aftershocks declined very slowly in 1987 with p 0 2 in the modified omori formula whereas for the 1988 aftershock sequence p 1 the low p during 1987 may have been diagnostic of high stress in the source and water authority provided partial financial support for j r b and g g

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

the quantitative characteristics of earthquake sources as determined in the seismological practice of the u s s r abstract the source parameter determinations in the u s s r from seismological observations using standard instruments including a station with digital registration stsr and frequency selective equipment tchiss are discussed to determine magnitude from p waves with short period instruments a calibrating function of the homogeneous magnitude system hms is recommended for seismological practice in the u s s r for assessment of source parameters seismic moment displacement and stress drop a special multi factor procedure for focal spectra analysis is developed magnitudes and focal dynamic parameters of 30 strong earthquakes are presented and compared with analogue parameters of the neis and harvard solutions it is proved that magnitudes determined by surface wave m lh essn edinaya systema seismicheskih nabludenii the unified system of seismic observations and m s neis practically coincide magnitude m b neis has been systematically underestimated as compared with m pv essn seismic moments by essn m p o and neis m o cmt are linearly dependent a comparison of fault plane solutions shows almost full agreement in about half the number of the earthquakes considered the orientation of nodal planes and axes of principal stresses coincide despite their belonging to different stages of faulting the time frequency fields by tchiss data for earthquakes with equal magnitudes and seismic moments show a different character of energy release

the age and correlation of skiddaw group early ordovician sediments in the cross fell inlier northern england the skiddaw group in the cross fell inlier comprises the catterpallot formation of latest tremadoc or earliest arenig age the murton formation of arenig age and the kirkland formation of early llanvirn age each of these formations can be correlated with formations in the skiddaw group of the lake district the faulted contact of the catterpallot and kirkland formations is the probable extension of the causey pike fault cpf which separates two distinct sequences in the skiddaw inlier of the northern lake district contrasts across the cpf in the cross fell inlier reflect those seen in the skiddaw inlier the cpf is a major basement structure separating markedly different successions in the ordovician strata of northern england

determination of magnitudes of ancient earthquakes from dimensions of observed seismodislocations abstract equations to estimate the magnitude of ancient earthquakes where seismotectonic crustal deformations normal faults strike slip faults etc have been preserved in the epicentral region are presented the equations are based on the results of over one hundred earthquakes including 96 recent continental earthquakes in the magnitude range 5 2 8 7

structural analysis of recent and active faults and regional state of stress in the epicentral area of the 1978 thessaloniki earthquakes northern greece during spring and summer 1978 macedonia greece suffered damaging seismic activity during the two main shocks which occurred on may 23 mb 5 7 and june 20 mb 6 1 seismic open cracks and faults were formed in the epicentral area 25 km nne from thessaloniki they have been mapped and their kinematics analyzed these studies have shown that they result from the reactivation of existing faults of pleistocene recent and historical age and that the crust is stretching along a n s to nne ssw direction in that part of the north aegean principal stress directions have been computed from the slip vectors measured on recent neotectonic faults and seismic cracks and faults this computation utilizing a simple mechanical model homogeneous deformation through the addition of small and independent displacements of rigid blocks in a highly fractured body a striking feature of this analysis is that the tensional directions 3 deduced from seismic faulting and from recent neotectonic faulting are nearly the same they are compatible with the regional tension axis deduced from focal mechanisms of north aegean and with the focal mechanisms of the 1978 thessaloniki main shocks they are also compatible with in situ stress measurements in this region studies of superficial seismic faulting strongly support previous assumptions proposed from aftershock distribution the 1978 thessaloniki earthquakes resulted from reactivation of several different faults situated within the same ne dipping fault zone of upper eocene lower oligocene age and older separating the serbo macedonian massif from the peonias east vardar zone

rupture patterns and preshocks of large earthquakes in the southern san jacinto fault zone we relocated the large 1937 1942 and 1954 earthquakes in the san jacinto fault zone the epicenters of the main shocks aftershocks and some preshocks were determined using empirical station corrections from recent small events in the study areas the 1937 ml 5 9 earthquake has an epicenter between the surface traces of the san jacinto and buck ridge faults and aftershocks suggest about 7 km of rupture predominantly to the northwest a significant increase in small earthquake activity occurred about formula yr before this event the 1954 m l 6 2 earthquake is located at the southeast end of the mapped trace of the san jacinto fault and aftershocks suggest about 15 km of rupture further southeast into an area of folded young sediments with no surface fault trace this event was preceded by a cluster of small earthquakes which occurred within an 8 hr period 10 weeks before the main event and in the eventual rupture zone the 1942 m l 6 3 earthquake is located southwest of the southeast end of the coyote creek fault large aftershocks of this event are spread over a 15 by 18 km area southwest of the coyote creek fault and are not associated with any one fault the relation of the 1942 event to the san jacinto fault zone is not simple

the 1988 and 1990 upland earthquakes left lateral faulting adjacent to the central transverse ranges two earthquakes m l 4 6 and m l 5 2 occurred at almost the same location in upland southern california in june 1988 and february 1990 and had similar strike slip focal mechanisms with left lateral motion on a northeast striking plane the focal mechanisms and aftershock locations showed that the causative fault was the san jose fault an 18 km long concealed fault that splays west southwest from the frontal fault of the central transverse ranges left lateral strike slip faults adjacent to the frontal faults may play an important role in the deformation of the transverse ranges and the los angeles basin as suggested by these upland earthquakes the left lateral strike slip 1988 m l 4 9 pasadena earthquake on the raymond fault 30 km to the west of upland and scattered background seismicity along other active left lateral faults these faults may transfer slip away from part of the frontal fault toward the south alternatively these faults could represent secondary faulting related to the termination of the northwest striking right lateral strike slip faults to the south of the range front the 1988 and 1990 upland earthquakes ruptured abutting or possibly overlapping segments of the san jose fault the edges of the overlapping aftershock zones which are sharply defined together with background seismicity outline a 14 km long aseismic segment of the san jose fault the 1988 mainshock originated at 9 5 km depth and caused aftershocks between 5 and 12 km in contrast the 1990 mainshock focus occurred at the top of its aftershock zone at 5 km and caused aftershocks down to 13 km depth these deep aftershocks tapered off within 2 weeks the rate of occurrence of aftershocks in magnitude time space was the same for both sequences the state of stress reflected in the focal mechanisms of the aftershocks is identical to that determined from background activity and did not change with time during the aftershock sequence the constant stress state suggests that the 1988 and 1990 events did not completely release all the stored slip on that segment of the fault the presence of 14 km of unbroken fault the abrupt temporal termination of deep aftershocks and the constant stress state all suggest that a future moderate sized earthquake m l 6 0 6 5 on the san jose fault is possible with a rupture length of at least 14 km and possibly 18 km

modelling aftershock migration and afterslip of the san juan bautista california earthquake of october 3 1972 abstract the san juan bautista earthquake of october 3 1972 m l 4 8 located along the san andreas fault in central california initiated an aftershock sequence characterized by a subtle but perceptible tendency for aftershocks to spread to the northwest and southeast along the fault zone the apparent dimension of the aftershock zone along strike increased from about 7 10 km within a few days of the earthquake to about 20 km eight months later in addition the mainshock initiated a period of accelerated fault creep which was observed at 2 creep meters situated astride the trace of the san andreas fault within about 15 km of the epicenter of the mainshock the creep rate gradually returned to the preearthquake rate after about 3 yrs both the spreading of the aftershocks and the rapid surface creep are interpreted as reflecting a period of rapid creep in the fault zone representing the readjustment of stress and displacement following the failure of a stuck patch or asperity during the san juan bautista earthquake numerical calculations suggest that the behavior of the fault zone is consistent with that of a material characterized by a viscosity of about 3 6 10 14 p although the real rheology is likely to be more complicated in this model the mainshock represents the failure of an asperity that slips only during earthquakes aftershocks represent the failure of second order asperities which are dragged along by the creeping fault zone

the evolution of the gulf of corinth greece an aftershock study of the 1981 earthquakes summary a preliminary study of the aftershocks of three earthquakes that occurred near to corinth greece in 1981 is combined with observations of the morphology and faulting to understand the evolution of the eastern gulf of corinth the well located aftershocks form a zone 60km long and 20km wide they do not lie on the main fault planes and are mostly located between the north dipping faulting on which the first two earthquakes occurred and the south dipping faulting associated with the third event a cluster of aftershocks also lies in the footwall of the eastern end of the south dipping fault of the third event morphologically it is observed that in the evolution of the eastern gulf of corinth antithetic faulting apparently predates the appearance of the main faulting at the surface this evolution can be explained by motion on a deep seated shallow angle aseismic normal fault a model based on such a fault also accounts for the aftershock distribution of the 1981 earthquakes

discussion on evidence for an unconformity at the base of the eycott volcanic group millward molyneux 1992 have presented convincing evidence for the existence of a major unconformity between the eycott volcanic group and the underlying skiddaw group we agree with their conclusion that the new interpretation re opens the debate about a pre volcanic phase of deformation in the ordovician of the english lake district the continuing british geological survey mapping programme has provided further evidence that there was such a phase its nature and products are crucial to the understanding of the deformation history of the lake district lower palaeozoic inlier particularly with respect to the structural complexity of the skiddaw group