discrete plio pleistocene phases of tilting and counterclockwise rotation in the southeastern aegean arc rhodos greece early pliocene formation of the south aegean left lateral strike slip system the island of rhodos represents an uplifted block in the largely submerged southeastern aegean forearc it has a complex history of subsidence uplift and counterclockwise rotation during the plio pleistocene in response to the interplay between large scale geodynamic processes in this paper we present a new chronostratigraphic framework for the continental pliocene apolakkia basin of southwestern rhodos we combine these time constraints with recently published chronostratigraphic data from the marine plio pleistocene basins of northeastern rhodos to reconstruct rotational and vertical motions our palaeomagnetic results identify two rotation phases for rhodos c 10 9 6 counterclockwise ccw rotation between 3 8 and 3 6 ma and c 17 6 ccw rotation since 0 8 ma between these phases rhodos tilted to the se drowning the southeastern coast to a depth of 500 600 m between 2 5 and 1 8 ma then to the nw which resulted in the re emergence of the drowned relief between 1 5 and 1 1 ma we relate the rotations of rhodos to incipient formation of the south aegean sinistral strike slip system and the foundering of the rhodos basin the previously shown absence of messinian evaporites in the deep marine rhodos basin in combination with the 3 8 ma onset of ccw rotation of rhodos constrains the onset of the formation of the south aegean strike slip system between 5 3 and 3 8 ma the formation of this strike slip system is probably related to the interplay of oblique collision between the southeastern aegean region and the northward moving african plate the westward motion of anatolia gravitational spreading of the overthickened aegean lithosphere and the recently postulated southwestward retreat of the african subducted slab along a subduction transform edge propagator fault

magnetostratigraphy of late miocene continental deposits in samos greece abstract we present a detailed magnetostratigraphic study of the upper part of the mytilini formation marker tuffs and main bone beds of samos island greece seven successive polarity zones have been identified and a correlation with the geomagnetic polarity time scale has established that the sediments of this section were accumulated between 5 7 and 6 8 ma according to these results the upper mammalian fossiliferous levels are found within the reversed polarity zone lying in the time interval 6 1 6 4 ma

influence of changing deep ocean circulation on the phanerozoic oxygen isotopic record isotopic segregation in seawater caused by changing ocean circulation may in part explain the enigmatic oxygen isotopic record of phanerozoic marine carbonates paleoceanographic evidence suggests that circulation of warm saline deep waters has occurred during at least two periods of warm global climate those saline deep waters should have preferentially stored 18o in the deep oceans corresponding depletion of 18o in surface waters would have resulted in lower 18o of marine carbonates deposited on continental shelves modeling of paleoceanographic isotopic data suggests that this storage effect is similar in magnitude but opposite in sign to that of modern enrichment of 18o in the oceans by glacial storage modeling of carbonate compositions through time that takes into account such storage effects as predicted by changing global climate suggests that large changes in the mean oceanic isotopic composition but neither extreme temperatures nor sudden changes in mean ocean compositions are needed to explain the isotopic record

origin and emplacement of an inferred late jurassic subduction accretion complex euboea eastern greece in northern euboea central eastern greece an up to 3 km thick polygenetic melange pagondas complex is structurally interleaved between a triassic jurassic carbonate platform pelagonian zone and an overriding harzburgitic ophiolite the melange mainly comprises late triassic shallow water limestone and calciturbidites radiolarites triassic jurassic tholeiites alkaline basalts and minor andesites the units concerned range from kilometre sized thrust sheets and detached blocks to broken formation and structureless or bedded matrix supported conglomerates diamictite the melange includes remnants of neotethyan oceanic lithosphere overlain by radiolarites hemipelagic carbonates and distal calciturbidites derived from a mesozoic carbonate platform tholeiites were erupted at a triassic jurassic spreading axis whilst within plate type alkali basalts are interpreted mainly as seamounts kilometre scale detached blocks of shallow water coralline limestone are identified as collapsed atolls formed within an ocean and or along the rifted continental margin volcaniclastic sediments are locally interbedded with radiolarite and reflect post volcanic erosion of the ocean floor intra oceanic convergence began apparently in late early jurassic time giving rise to the euboea ophiolite above an inferred westwards dipping subduction zone the pagondas complex then developed as an accretionary prism the subduction trench later collided with the pelagonian passive margin driving the hot euobea ophiolite over the accretionary complex to produce amphibolites and greenschists of the metamorphic sole trench margin collision then drove the entire supra subduction zone complex apparently eastwards downflexing the pelagonian carbonate platform to form a foredeep in which late jurassic kimmeridgian tithonian radiolarian sediments accumulated during emplacement the accretionary complex was disrupted and partly resedimented as debris flows turbiditic volcaniclastic sandstone and shale in a foredeep or foreland basin setting

first palaeomagnetic results from the cycladic massif greece and their implications for miocene extension directions and tectonic models in the aegean abstract the aegean region is characterised by major fault bound blocks with markedly contrasting structural trends recent models account for these variations either through differential block rotation or through a process of radial extension the cycladic massif in the back arc region to the hellenic trench represents a critical area where apparently divergent extension directions are observed this contribution provides the first palaeomagnetic results from this area magnetic remanence and ams data are presented for middle miocene granodiorites on the islands of mykonos and naxos these rocks are exposed in the footwalls of major extensional detachments within the metamorphic core complexes that characterise the cycladic massif a clear correlation between the orientation of an l s fabric developed within the intrusions and the magnetic fabric data is observed demonstrating the presence of a normal magnetic fabric of extensional origin the mean extension directions inferred from the orientations of the maximum axes of the magnetic susceptibility ellipsoids are markedly divergent at 064 mykonos and 351 naxos northeasterly in situ magnetic remanences are observed on mykonos whereas those on naxos are directed to the nnw neither direction corresponds to the appropriate palaeomagnetic reference direction for the miocene standard palaeomagnetic tilt corrections cannot be applied at these sites because of the lack of palaeohorizontal markers deviations of in situ remanences away from the reference direction are potentially due to rotation around any one of an infinite number of net tectonic rotation axes each of these may be arbitrarily decomposed into components of tilting and vertical axis rotation geologically realistic solutions which restore the in situ magnetisations back to the reference direction may be found by consideration of regional structural trends assuming that tilting is controlled by the major block bounding faults these solutions indicate significant components of differential vertical axis rotations across the cyclades mykonos is bound by nw se trending regional faults and is shown to have rotated clockwise by ca 22 in contrast naxos is bound by ene wsw trending structures and has rotated anticlockwise by ca 33 the apparent divergence of extension directions inferred from both the magnetic anisotropy and structural data is resolved by correcting the mean ams data for subsequent rotation using the rotation solutions derived from the magnetic remanence data the data imply that the primary middle miocene extension direction in the cycladic massif was nearly uniform along a nne ssw azimuth we consider that the uniform extension direction and opposing senses of block rotation determined for this portion of the cycladic massif are most consistent with a recent model describing deformation within the aegean in terms of a system of broken fault bounded slats within this scenario mykonos occupies a position on a clockwise rotating slat which continues northwest at least as far as evvia a major ene wsw trending fault between the islands previously identified on shallow seismic sections separates this domain from an anticlockwise rotating slat which includes naxos

neotectonic deformation in the western sector of tectonic escape in anatolia palaeomagnetic study of the afyon region central turkey abstract following final closure of the neotethyan ocean during the late miocene deformation in central turkey has led to crustal thickening and uplift to produce the anatolian plateau followed by westward extrusion of terranes by strike slip widespread volcanism has accompanied this latter neotectonic phase and palaeomagnetic study of the volcanism shows a coherent record of differential block rotations indicating that the anatolian region is not a plate or platelet sensu stricto but is undergoing distributed internal deformation to evaluate the scale of neotectonic rotations in the transition zone near the western limit of tectonic escape and the border of the extensional domain in central west turkey we have studied the palaeomagnetism at 82 sites in volcanic suites distributed along a 140 km lineament with north south trend and ranging in age from 18 to 8 ma comparable deflection of magnetic remanence from the present field direction is identified along the full length of the lineament a mean clockwise rotation of 12 3 4 2 is determined for this western sector of the anatolian strike slip province since similar rotations are observed in the youngest and oldest units this cumulative rotation occurred after the late miocene when interpreted together with results elsewhere in anatolia it is inferred that the rotation is later than crustal thickening and uplift of the anatolian plateau and entirely a facet of the tectonic escape inclinations are mostly 10 shallower than the predicted miocene field and are considered to reflect the presence of a persistent inclination anomaly in the mediterranean region larger rotations departing from the regional trend are also observed within the study region but are confined to the vicinity of major faults notably those bounding the afyon aksehir graben the pattern of neotectonic declinations across anatolia identifies strong anticlockwise rotation in the east near the arabian pincer with progressive reduction in the amount of rotation towards the west it becomes zero or slightly clockwise at the western extremity of the accreted terrane collage rotations also appear to become generally younger towards the south crustal deformation has therefore been distributed and the net effect of terrane extrusion to the west and south has been to expand the curvature of the tauride arc the westward radial expansion of the extruded terranes is inferred to combine with backroll on the hellenic arc to produce the contemporary extensional province in western turkey

first paleomagnetic results from mio pliocene series of the hellenic sedimentary arc abstract paleomagnetic measurements have been conducted on the mio pliocene series along the external sedimentary hellenic arc in order to detect the presence or absence of rotational deformations in different sections of the arc in the central eastern part of the arc crete and rhodes paleomagnetic directions are very closely aligned along the north south direction showing that this portion of the arc has not undergone significant rotation since at least 7 m y for crete and 4 m y for rhodes in the western and northwestern parts results from south peloponnesos zakinthos kephallinia and corfu indicate that this section of the arc has undergone a clockwise rotation detailed analysis of the data from the three ionian islands shows that their rotation began about 5 m y b p and has proceeded since then at roughly 5 m y giving a total amplitude of about 26 it is suggested that the beginning of this rotation is related to the lower pliocene compressive phase which most probably initiated the tectonic activity of the present day ionian margin

structure and tectonic development of the ghab basin and the dead sea fault system syria we examine the structure and evolution of the ghab basin that formed on the active yet poorly understood northern segment of the dead sea transform fault system the basin formed in plio quaternary time at a complex step over zone on the fault subsidence occurred along cross basin and transform parallel faults in two asymmetric depocentres the larger depocentre in the south of the basin is asymmetric towards the east the margin along which most active transform displacement apparently occurs the syrian coastal ranges located directly west of the ghab basin are a consequence of late cretaceous and cenozoic regional compression heavily modified by the dead sea fault system and ghab basin formation we prefer a model whereby the dead sea fault system in northwest syria developed in plio quaternary time consistent with previously proposed models of two phase dead sea fault system movement and red sea spreading

the ml scale in southern california measurements 9 941 of peak amplitudes on wood anderson instruments or simulated wood anderson instruments in the southern california seismographic network for 972 earthquakes primarily located in southern california were studied with the aim of determining a new distance correction curve for use in determining the local magnitude m l events in the mammoth lakes area were found to give an unusual attenuation pattern and were excluded from the analysis as were readings from any one earthquake at distances beyond the first occurrence of amplitudes less than 0 3 mm the remaining 7 355 amplitudes from 814 earthquakes yielded the following equation for m l distance correction log a 0 log a 0 1 110log r 100 0 00189 r 100 3 0 where r is hypocentral distance in kilometers a new set of station corrections was also determined from the analysis the standard deviation of the m l residuals obtained by using this curve and the station corrections was 0 21 the data used to derive the equation came from earthquakes with hypocentral distances ranging from about 10 to 700 km and focal depths down to 20 km with most depths less than 10 km the log a 0 values from this equation are similar to the standard values listed in richter 1958 for 50 200 km the effect at close distances is consistent with that found in several other studies and is simply due to a difference in the observed 1 r geometrical spreading for body waves and the 1 r 2 spreading assumed by gutenberg and richter in the construction of the log a 0 table m l s computed from our curve and those reported in the caltech catalog show a systematic dependence on magnitude small earthquakes have larger magnitudes than in the catalog and large earthquakes have smaller magnitudes by as much as 0 6 units to a large extent these systematic differences are due to the nonuniform distribution of data in magnitude distance space small earthquakes are preferentially recorded at close distances relative to large earthquakes for large earthquakes however the difference in the two magnitudes is not solely due to the new correction for attenuation magnitudes computed using richter s log a 0 curve are also low relative to the catalog values the differences in that case may be due to subjective judgment on the part of those determining the catalog magnitudes the use of data other than the caltech wood anderson seismographs the use of different station corrections or the use of teleseismic magnitude determinations whatever their cause the departures at large magnitude may explain a 1 0 0 7 proportionality found by luco 1982 between m l s determined from real wood anderson records and those from records synthesized from strong motion instruments if it were not for the biases in reported magnitudes luco s finding would imply a magnitude dependent shape in the attenuation curves we studied residuals in three magnitude classes 2 0 m l 3 5 3 5 m l 5 5 and 5 5 m l 7 0 and found no support for such a magnitude dependence based on our results we propose that local magnitude scales be defined such that m l 3 correspond to 10 mm of motion on a wood anderson instrument at 17 km hypocentral distance rather than 1 mm of motion at 100 km this is consistent with the original definition of magnitude in southern california and will allow more meaningful comparison of earthquakes in regions having very different attenuation of waves within the first 100 km

palaeogeography of the western pelagonian continental margin in beotia greece during the cretaceous biostratigraphy and isotopic compositions δ13c δ18o of calcareous deposits the palaeogeography of beotia greece during the cretaceous is outlined on the basis of biostratigraphic evidence derived predominantly from the distribution of rudist bivalves and planktonic foraminifera observed facies trends are evaluated together with carbon and oxygen isotopic compositions of limestones and rudist shells the interaction between global sea level fluctuations and gradual subsidence of the pelagonian continental margin controlled facies distribution during most of the cretaceous the sedimentary record begins with berriasian flysch type deposits that accumulated during incipient eohellenian orogenic movements barremian deposits with similar sedimentological characteristics probably belong to the same tectonostratigraphic unit during aptian cenomanian times terrigenous clastics with a few intercalated marine limestones accumulated in south beotia the fossil content of patch reefs presents important biostratigraphic marks in this terrigenous sequence carbon and oxygen isotopic compositions recorded unstable marine environments and subsequent decrease of continental influx continuous subsidence and rising sea levels are evident in the late turonian onlap of rudist limestones on the eohellenian basement of the ptoon mountains as well as in the interfingering of calcareous slope deposits and basinal globotruncana mudstones of south beotia during late coniacian early santonian a marked regression finally led to a regional emersion and the development of a karst relief this regression is predated by heavy oxygen isotopic compositions in the coniacian limestones which probably resulted from isolation of a larger marine embayment from oceanic circulation the subsequent late santonian campanian transgression flooded all of beotia its sediments lie over allochthonous laterites extended rudist biostromes developed as soon as continental influx ceased as indicated both by the stable isotope compositions of rudish shells and embedding limestones during the late campanian the rather uniform platform type depositional environments differentiated and pelagic sedimentation recurred in south beotia whereas depositional environments to the north remained shallow incipient tectonics movements were responsible for a late maastrichtian emersion of north beotia while basinal conditions persisted in the south the onset of flysch type sedimentation occurred simultaneously during the late paleocene in north beotia as well as in the adjacent parnassus and pindos zones however this important facies transition has not yet been precisely dated in south beotia

the cretaceous sedimentary history of the pindos basin greece the cretaceous sedimentary rocks of the pindos zone in western greece document the evolution of a tethyan deep water basin new sedimentological and micropalaeontological studies reveal a complex basin history siliceous sediments with abundant radiolaria and organic rich facies prevailed up to the early late cretaceous within the sediment starved pre middle cenomanian marked black shale levels appear that are probably linked to oceanic anoxic events at the change from the late early to the early middle cenomanian the sedimentary regime altered abruptly the early late cretaceous is characterized by major calcareous redepositional events orbitoline horizons and often associated siliciclastic turbidite deposition submarine fan environments in the late late cretaceous carbonate supply increased rapidly resulting in the evolution of a carbonate slope and basin plain setting pelagic and allodapic limestones recorded basinwide blooms in planktonic foraminifera elevata event and a polyphase redepositional history that is interpreted to reflect the sensitivity of the basin to the tectonic evolution of apulia

deformational behaviour of continental lithosphere deduced from block rotations across the north anatolian fault zone in turkey abstract theoretical considerations of lithosphere deformation across transform plate boundaries predict an expression in terms of 3istributed deformation the magnitude of rotation is expected to diminish away from the fault zone in a way which depends on the length of the fault the amount of displacement and the ductility of the lithosphere palaeomagnetic studies across the north anatolian transform fault zone which separates the eurasian plate and anatolian block in northern turkey show that clockwise rotations predicted from the sense of dextral motion are indeed present and have attained finite rotations of up to 270 during the 5 ma history of neotectonic deformation such rotations are however confined to narrow 10 km wide zones between system bounding faults and appear to have resulted from rotation in ball bearing fashion of equidimensional blocks a few kilometres in size outside of this zone only anticlockwise rotations are observed these are unrelated to deformation across the fault zone and record regional anticlockwise rotation of turkey which is complementing clockwise rotation of greece and accompanying neogene opening of the aegean sea the observed behaviour of continental lithosphere satisfies no plausible value of power law behaviour we therefore conclude that relative motion across this transform boundary occurs as a discrete zone of intense deformation within a brittle layer comprising the seismogenic upper crust this is presumed to be detached from a continuum deformation response to shearing in the lower crust and mantle beneath

epicentre accuracy based on seismic network criteria summary we establish reliable and conservative estimates for epicentre location accuracy using data that are readily available in published seismic bulletins a large variety of seismic studies rely on catalogues of event locations making proper assessment of location uncertainty critical event location and uncertainty parameters in most global regional and national earthquake catalogues are obtained from traditional linearized inversion methods using a 1 d earth model to predict traveltimes reported catalogue uncertainties are based on the assumption that error processes are gaussian zero mean and uncorrelated unfortunately these assumptions are commonly violated leading to the underestimation of true location uncertainty especially at high confidence levels we find that catalogue location accuracy is most reliably estimated by station geometry we make use of two explosions with exactly known epicentres to develop local network location 0 2 5 accuracy criteria using monte carlo simulations of network geometry we find that local network locations are accurate to within 5 km with a 95 per cent confidence level when the network meets the following criteria 1 there are 10 or more stations all within 250 km 2 an azimuthal gap of less than 110 3 a secondary azimuthal gap of less than 160 and 4 at least one station within 30 km to derive location accuracy criteria for near regional 2 5 10 regional 2 5 20 and teleseismic 28 91 networks we use a large data set of exceptionally well located earthquakes and nuclear explosions beyond local distances we find that the secondary azimuthal gap is sufficient to constrain epicentre accuracy and location error increases when the secondary azimuthal gap exceeds 120 when station coverage meets the criterion of a secondary azimuth gap of less than 120 near regional networks provide 20 km accuracy at the 90 per cent confidence level while regional and teleseismic networks provide 25 km accuracy at the 90 per cent confidence level

quality assessment of seismic recording the tehran seismic telemetry network the tehran seismic telemetry network commenced operation in 1996 but it has never published any bulletins and there has been no systematic evaluation of the precision and reliability of its seismic recording in this paper a standard approach is presented to evaluate the quality of operation of the network our findings show no serious gaps in data coverage and the threshold of completeness is about magnitude 2 within the network we show that incorrect phase reading is the major reason for errors in identifying the phases and the large scatter in arrival times we propose a number of suggestions for the improvement of network operation q 2004 elsevier ltd all rights reserved

calibration of an ml scale in the alborz region northern iran we have calculated empirical attenuation curves for the local magnitude scale ml in the alborz region of northern iran the maximum trace amplitudes de rived from synthetic wood anderson seismograms of 1290 records of 59 events in the distance range of 8 5 550 km recorded by the short period iranian seismic telemetry network istn were inverted for the attenuation curve magnitudes and station cor rections the earthquakes ranged from ml3 25 to 5 65 and were recorded at 26 sta tions in the region we used both nonparametric and parametric least squares methods for inversion the resulting parametric equation is loga0 1 1725logr 0 0021r 0 4450 the two methods yielded very similar results and are very close to richter s original attenuation curve for southern california the station corrections vary between 0 42 and 0 47 suggesting that local site effects may have a strong influence on the amplitudes

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

diagenetic stabilization of aragonite and low mg calcite ii stable isotopes in rudists abstract cretaceous rudists having thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of phreatic vadose meteoric diagenesis on their microstructural and isotopic attributes rudist skeletal components with preserved original mineralogy of aragonite and low mg calcite and with preserved microstructures have isotopic signatures analogous to holocene marine bivalves this similarity argues for a comparable isotopic composition of the cretaceous and holocene seawater as well as for a similar mode of incorporation of stable isotopes into their shells diagenetic stabilization of rudist shells appears to have been a two stage process with low mg calcite diagenetic calcite lmc dlmc and particularly aragonite diagenetic calcite a dlmc transformation as the first step and cementation as a later development the direct a dlmc mineralogical transformation calcitization results in initial depletion in 18o of 2 and the subsequent diagenetic precipitation of ferroan calcite spar causes depletion in 13c as well as an additional decrease in 18o the former due to introduction of organically derived co2 into the diagenetic aquifer in contrast 13o and 13c isotopic depletions in the originally lmc skeletal components are both related to the precipitation of the late diagenetic ferroan sparry calcite cement the earlier calcitization stage being of subordinate importance only

paleomagnetic reconstruction of the cenozoic evolution of the eastern mediterranean abstract a total of 113 paleomagnetic sites were sampled along an anatolian s n transect from the arabian platform the hatay region the eastern taurides the kirsehir block the sivas basin and the eastern pontides reliable characteristic remanent paleomagnetic directions were retrieved from 37 of these sites spanning in time from paleocene to miocene in a general way declinations are westerly deviated and inclinations are shallower than the geocentered dipole value at the present latitudes when combined with previously published results these data indicate that a large scale counterclockwise rotation of anatolia of some 25 has occurred since the miocene assuming that the pole of rotation of anatolia with respect to europe has remained constant in time at the location given by macclusky et al j geophys res 105 2000 5695 on the basis of the geodetic data this rotation implies that a large westward displacement 500 km at the average latitude of 40 has taken place assuming that the rotation was initiated by the arabia europe collision about 12 ma ago this corresponds to an average displacement of about 40 mm year together with previous results from the western part of the aegean arc these results indicate that the main trends of the cenozoic evolution of the eastern mediterranean appear to consist of two post early miocene rotations of opposite senses a clockwise rotation of the western part of the aegean tectonophysics 146 1988 183 around a pole situated in northern albania and a counterclockwise rotation around the pole given by mcclusky et al j geophys res 105 2000 5695 comparison with gps data suggest that both rotations are still active today

patterns of historical earthquake rupture in the iranian plateau the iranian plateau accommodates the 35 mrn yr convergence rate be tween the eurasian and arabian plates by strike slip and reverse faults with relatively low slip rates in a zone 1000 km across although these faults have only locally been the subject of paleoseismological studies a rich historical and archeological record spans several thousand years long enough to establish recurrence intervals of 1000 to 5000 yr on individual fault segments several clusters of earthquakes provide evidence of interaction among reverse and strike slip faults probably due to adjacent faults being loaded by individual earthquakes the dasht e bayaz sequence of 1936 to 1997 includes earthquakes on left lateral right lateral and reverse faults the neyshabur sequence of four earthquakes between 1209 and 1405 respected the seg ment boundary between the neyshabur and binalud reverse fault systems the two pairs of earthquakes may have ruptured different faults in each segment similar to the 1971 and 1994 san fernando california earthquakes the 1978 tabas reverse fault earthquake was preceded by the 1968 ferdows earthquake part of the dasht e bayaz sequence the north tabriz fault system ruptured from southeast to north west in three earthquakes from 1721 to 1786 a previous cluster may have struck this region in 855 to 958 the mosha fault north of tehran ruptured in three earthquakes in 958 1665 and 1830 five large earthquakes struck the tehran region from 743 to 1177 but only two that large have struck the area since 1177 other earthquakes occurred in pairs in the talesh mountains near the caspian sea 1863 1896 the iran turkey border 1840 1843 and the nayband gowk fault system both 1981 other historical events did not occur as parts of sequences the historic seismic moment release in iran accounts for only a small part of the plate convergence rate which may be due to aseismic slip or to the iranian historical record long as it is being too short to sample long term deformation across the plateau no historic earthquakes of m 8 have struck iran however several long straight strike slip faults doruneh west neh east neh and nayband have not sustained large historical earthquakes raising the possibility that these long faults could produce earthquakes of m 8 thereby removing at least part of the apparent slip deficit an increased understanding of iran s seismic hazard could be obtained by an extensive paleoseismology program and space geodetic arrays supplementing the abundant historical and archaeological record

from obduction to continental collision new data from central greece the aim of this paper is to contribute to deciphering the evolutionary history of the hellenides by the study of a large sector of the chain located between the front of the ophiolitic units and the external zones classically attributed to the continental margin of adria in particular the tectonic units located in boeotia a key area located in central greece at the boundary between the internal and external hellenides were studied from structural stratigraphic and biostratigraphic points of view addressing the main debated aspects concerning the origin of the ophiolite nappe s the tectonic evolution of the hellenic orogen was revised with a particular emphasis on the period between obduction and continental collision new findings were compared with consolidated data concerning the main metamorphic events recorded in the more internal hellenides geochemistry and age of the ophiolites and main stratigraphic constraints obtained in other sectors of the belt finally a new reconstruction of the tectonic evolution of this area was introduced and in the context of the dispute concerning the origin of the ophiolitic belts as a possible record of multiple oceanic basins we put forward for consideration a single ocean tectonic model spanning from triassic up to tertiary times and valid for the whole hellenic albanian sector

empirical distance attenuation and the local magnitude scale for northwest iran abstract we have derived an empirical attenuation curve for a local magnitude scale in northwest iran using a large data set of local earthquakes that occurred from 1996 to 2009 investigation shows that using one half the peak to peak value tends to underestimate the magnitude of an event by as much as 0 07 magnitude units in comparison with using the zero to peak value additionally using a vector sum of horizontal measurements overestimates the m l values by 0 16 magnitude units in comparison with magnitude values that are determined using arithmetic means of horizontal measurements we simulated the corresponding wood anderson seismograms for over 133 000 available waveforms after preliminary analysis the data set was subdivided in order to derive a local magnitude scale for northwestern iran the distance attenuation curve station correction terms and the magnitude of events were simultaneously estimated using parametric and nonparametric approaches in both approaches estimations and separate attenuation curves were determined by using vertical and horizontal measurements these two approaches yielded very similar results the distance attenuation curves that resulted in a nonparametric approach are given by log a 0 0 9252log 0 0030 0 8496 and log a 0 0 9993log 0 0029 0 7114 for the vertical and horizontal components respectively where is the epicentral distance in kilometers the distances considered ranged from 1 to 500 km applying these distance correction terms to the data set show that there are no obvious trends in magnitude residual with distance also using the station corrections reduces the magnitude residuals by as much as 0 07 magnitude units

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

tertiary and quaternary volcanism of the erzurumkars area eastern turkey geochronological data and geodynamic evolution abstract this paper presents new geochemical and geochronological data on the neogene and quaternary volcanic products from the area of erzurum and kars eastern turkey the affinity of most of the volcanic rocks concerned is calc alkaline with the exception of minor quaternary alkaline rocks that outcrop in the kars sector ages range from 8 m y to 1 3 m y the time space distribution of the calc alkaline volcanism in eastern turkey nw iran is characterized by a sudden northward jump that occurred around 6 m y ago from the van erzurum southern belt to the kars northern belt available data indicate that this northward migration of volcanism was due to changes in the subduction geometry of the arabian plate under eurasia

local and regional p wave spectral attenuation model for iran a robust frequency dependent local and regional p wave attenuation model is estimated for continental paths in the iranian plateau in order to calculate the average attenuation parameters 46 337 vertical component waveforms related to 9267 earthquakes which are recorded at the iranian seismological center irsc stations have been selected in the distance range 10 1000 km the majority of the event s magnitudes are less than 4 5 this collection of records provides high spatial ray path coverage results indicate that the shape of attenuation p wave curve versus distance is not uniform and has three distinct sections with hinges at 90 and 175 km a trilinear model for attenuation of p wave amplitude in the frequency range 1 10 hz is proposed in this study fourier spectral amplitudes are found to decay as r 1 2 where r is hypocentral distance corresponding to geometric spreading within 90 km from the source there is a section from 90 to 175 km where the attenuation is described as r 0 8 and the attenuation is described well beyond 175 km by r 1 3 moreover the average quality factor for pg and pn waves qpg and qpn related to anelastic attenuation is obtained as qpg 54 2 2 6 f 1 0096 0 07 and qpn 306 8 7 4 f 0 51 0 05 there is a good agreement between the results of the model and observations also the attenuation model shows compatibility with the recent regional studies from the results it turns out that the amplitude of p waves attenuates more rapidly in comparison with the global models in local distances

attenuation of ground motion spectral amplitudes and its variations across the central alborz mountains we selected 136 earthquakes recorded at stations of the institute of geo physics of the university of tehran igut during 1996 2007 in order to estimate the average attenuation parameters and variations of station corrections across the central alborz mountains the northern extension of the alpine himalayan orogeny in wes tern asia the selected events provide 1260 high signal to noise ratio snr records with relatively good spatial coverage we graphically find the distances at which the nature of geometrical spreading attenuation r b changes significantly using a locally weighted scatterplot smoothing lowess local regression smoothing method called robust lowess a trilinear function with hinges at distances of about 80 and 160 km describes the geometric spreading attenuation with distance by regressing to the hinged trilinear function we found that b1 1 15 0 21 b2 0 09 0 31 and a fixed b3 0 5 minimize the average absolute value of the fourier spectrum amplitude residuals using an anelastic attenuation coefficient at different frequencies the direct quality factor q in the central alborz region is obtained as q 109 2f 0 64 0 04 the geographical distribution of station corrections at 1 hz can be clearly separated along a dividing line connecting the north tehran mosha and attari faults into two regions the northern low attenuating and the southern high attenuating regions the stations with strong positive station corrections clearly align along the dividing line this suggests the existence of a higher attenuation zone south of the dividing line the presence of thick tertiary quaternary sedimentary rocks with thick layers of salt in the southern region may explain the observed greater attenuation of seismic waves

palaeomagnetic study of tertiary volcanic domains in southern turkey and neogene anticlockwise rotation of the arabian plate abstract following collision with eurasia the arabian shield indenter has continued to deform into the weak anatolian collisional collage that resulted from subduction of the neotethyan ocean differential movements have involved rotation and continuing northwards translation and have been accommodated mainly by slip along major transforms including the northward extension of the dead sea fault zone dsfz and the east anatolian fault zone eafz to aid in evaluating post collisional motions the palaeomagnetism of extensive volcanic domains at the northern margin of the stable shield in southern turkey is reported here together with the timing of emplacement as constrained by k ar study the age dating results indicate that volcanic activity occurred mainly during mid late miocene times corresponding to the final stages of suturing volcanic fields in the east of the investigated region are younger and correspond to neotectonic volcanism in brunhes and matuyama chrons thermal and alternating field demagnetization of 399 cores from 83 sites in basaltic lavas identifies 29 units of normal and 43 of reversed polarity with 11 sites having transitional or random directions volcanic fields west of the euphrates kilis gaziantep region with ages in the range 7 0 20 3 ma average 14 9 ma sd 4 3 ma have mean remanence d i 353 52 38 sites 5 3 lava fields east of the euphrates urfa region are dated 10 4 12 1 ma and yield a comparable mean remanence d i 350 50 17 sites 6 0 these collections are shown to have properly recorded palaeosecular variation with only minimal inclination shallowing and inferred anticlockwise rotations with respect to eurasia since mid miocene times are 10 9 4 3 and 14 0 5 0 respectively these contrast with clockwise rotation of 6 3 4 3 derived from late matuyama brunhes epoch volcanic rocks immediately to the north west of the arabian margin where rotational impingement of the shield indenter into fault blocks within the karasu rift at the northern extension of the dsfz interacts with left lateral motion at a rate of 0 5 cm year along this zone to produce small scale vertical axis rotations results from the volcanic suites sited on the stable shield are compared with other results from the arabian plate to conclude that it did not rotate significantly following closure of the bitlis suture until late miocene early pliocene times since when it has rotated anticlockwise at a rate of 1 0 myr this is comparable to the present day rate of rotation deduced from gps and correlates with crustal separation and sea floor spreading in the red sea it also temporally links the rotation of the arabian plate to the initiation of the intracontinental transforms north and east anatolian fault zones within anatolia and to the subsequent extrusion of blocks within this accretionary domain by tectonic escape to the west

palaeomagnetic study of the karacadag volcanic complex se turkey monitoring neogene anticlockwise rotation of the arabian plate abstract the karacadag volcanic centre in south east turkey is a major basaltic complex sited at the northern margin of the arabian plate and emplaced in several pulses between 11 ma and late quaternary times we have sampled 71 sites in lavas of this complex to constrain the palaeomagnetic record and hence the chronology of magmatic activity and regional rotation palaeomagnetic study at sixty two sites yields significant component definition with mixed normal and reversed polarities from age dating and morphologic criteria we identify three major episodes of lava emplacement and site mean directions of magnetisation for these divisions resolve migration of the palaeofield direction for the northern sector of the arabian plate since mid miocene times successive reversed polarity group mean directions are d i 175 50 5 n 37 r 33 13 95 4 1 for the oldest siverek division mean age estimate 11 1 6 7 ma d i 173 4 46 0 n 16 r 15 67 95 5 5 for the middle karacadag division mean age 3 3 ma and d i 167 7 47 6 n 6 r 5 93 95 7 9 for the youngest ovabag division 1 9 ma present the first two results merit a tectonic interpretation and consistent anticlockwise rotation of 9 is recognised in the karacadag volcanic centre between 11 and 3 3 ma the mean directions conform to palaeomagnetic results from other undeformed neogene igneous complexes of comparable age range further to the west along the northern perimeter of the arabian plate the amount of tectonic rotation observed in late pliocene and older volcanic units from this plate is found to be statistically constant tectonism responsible for rotation therefore appears to have been temporally confined to the last 2 myr which is long after collision with the anatolides and closure of the bitlis suture this conclusion conforms to the young distributed block rotations recognised in the anatolides and aegean and correlates with the regime of tectonic escape of terranes to the west

the pelagonian zone in greece a polyphase deformed fragment of the cimmerian continent and its role in the geotectonic evolution of the eastern mediterranean data from macedonia greece correlated with those reported from the pontides turkey indicate that the pelagonian zone of the hellenides represents a fragment of the cimmerian continent which separated the paleo tethys and neo tethys oceans a permo triassic age is suggested for separation of the paleozoic continent and initial rifting in the two oceanic basins as the pelagonian zone represented the northwestern european end of the cimmerian continent the paleo tethys and the northern branch of neo tethys would have been very close to each other on either side of this zone thus both oceans at their european end closed within a short time of each other in the late jurassic early cretaceous the sequential development of the two oceans outlines a model for the geotectonic evolution of the internal hellenides in which a correlation of thrusting and folding phases is also given

kinematics and ophiolite obduction in the gerania and helicon mountains central greece abstract new structural petrofabric and palaeostress data from the beotia area central greece were used to investigate the tectonic evolution of the suture zone between the external parnassus microplate and internal hellenides pelagonian microplate petrofabric studies of ultramafic rocks were done using conventional u stage analysis and the electron backscatter diffraction ebsd technique detailed structural analysis enabled us to distinguish three main deformation phases that took place from the triassic to the eocene triassic jurassic deformation is related to continental rifting and the progressive formation of an ocean basin ophiolites formed above a westward dipping supra subduction zone ssz in the early late jurassic trench margin collision resulted in the southeastward emplacement of the ophiolite nappe over the pelagonian margin there is also evidence for a north westward thrusting of ophiolitic rocks over the gerania and helicon units during berriasian time this latter tectonic process is closely related to the deposition of beotian flysch into a foreland basin an extensional phase of deformation accompanied by shallow water carbonate sedimentation is documented in the upper cretaceous later during paleocene the area was subjected to a compressional deformation phase characterised by sw directed thrusting and folding as well as ne verging backthrusts and backfolds our proposed geotectonic model suggests the consumption of the ocean between the parnassus and pelagonian microplates this model includes late jurassic eastward ophiolite obduction followed by early cretaceous west directed ophiolite thrusting

synthesis of wood anderson seismograms from broadband digital records abstract wood anderson torsion seismograms are synthesized by convolution with cosited broadband digital seismograph recordings and compared with the photographically recorded wood anderson seismograms at berkeley and mt hamilton the objective is to use routinely the synthesized seismograms to determine local magnitude comparison of local magnitude values calculated from both synthesized and photographic seismograms shows that the variation in local magnitude between the two types of seismograms is less than the variation among the photographic seismograms consequently broadband digital recordings can provide reliable local magnitude estimates without introducing significant bias it is shown that the static magnification of standard t s 0 8 sec wood anderson torsion seismographs determined from measurement of the free period and tilt sensitivity is 2080 60 and not 2800 as often reported this discrepancy is due to the erroneous assumption that the taught wire suspension in a wood anderson seismograph does not distort significantly thus leading to an incorrect estimate of the radius of gyration and consequently to a theoretical geometrical magnification of 2800

palaeotemperatures indicated by upper jurassic kimmeridgian tithonian fossils from mallorca determined by oxygen isotope composition abstract the oxygen and carbon composition of calcite has been determined for belemnites ammonite aptychi and the matrix surrounding these fossils from the kimmeridgian tithonian of mallorca petrography cathodoluminescence and trace element analyses indicate that both ammonite aptychi and matrix has been diagenetically altered whereas the belemnites have been undergone minimal or no modification the belemnites give the heaviest oxygen isotope values of 0 04 to 0 99 pdb and lighter values of 0 71 to 3 98 pdb come from the ammonite aptychi and matrix the carbon isotopic compositions obtained from all the fossils are positive and are similar to those derived from modern marine shallow water skeletons palaeotemperatures calculated on the basis of the oxygen isotopic composition of the belemnites give a range of values from 13 6 to 16 c these results agree with late jurassic palaeotemperatures from similar palaeolatitudes

a local magnitude scale ml for the kachchh rift basin an active intraplate region gujarat indiaa local magnitude scale ml for the kachchh rift basin

the northern red sea and the dead sea rift abstract the results of geophysical measurements at sea when combined with mesostructural measurements on land demonstrate systematic extensional features in the region of the northern red sea and the dead sea rift rifts and diapirs were encountered in the northern red sea showing an arcuate trend whereas the faulted continental margins at that region are oriented nw se the rifts and the diapirs changed their trend northwards from nnw sse to n s systems of rifts and diapirs are considered to be extensional features therefore the tectonic extensional axis probably changed its orientation accordingly a series of rifts and diapirs was found also in the gulf of elat trending approximately parallel to the coastlines and is interpreted to be the northern extension of the red sea rift and diapir system mesostructural measurements that were carried out in the western flank of the dead sea rift indicated further evidence for structural extension trending e w to ene wsw in addition to measurements of left lateral offset of approximately 10 km all these data when combined with the geophysical measurements of the characteristics of the earth crust underneath the dead sea rift suggest a tectonic regime of oblique extension in the region of the red sea and the dead sea rift this tectonic regime indicates that the red sea spreading center extends northwards along the dead sea rift and the clockwise change of the axial trend imposed a sinistral offset to the tectonic extension thus it is suggested that the dead sea rift is an incipient oblique spreading center

structure of the intraplate eastern palmyride fold belt syria the palmyride fold belt is an aulacogen within the arabian plate linked to the levantine continental margin which contains 10 km of phanerozoic sediments inversion of this mesozoic basin began during late cretaceous time although most deformation was clearly post oligocene recent field mapping shows that almost all the structures have resulted from a phase of northwest southeast compression followed by major dextral transpression early northwest southeast compression resulted in northeast southwest aligned fold axes in the central and southeast palmyrides many of which were subsequently rotated by progressive dextral simple shear during neogene to recent time the north south aligned sinistral dead sea fault is the major wrench fault aligned at 45 to the maximum compressive stress the conjugate east west striking dextral jhar fault and the northwest southeast aligned bishri fault have accommodated limited dextral shear and clockwise rotation of northeast southwest aligned folds jebels mrah ash shaer in the northern palmyrides dextral strike slip faults aligned along reidel fractures r1 cut the flanks of earlier domal structures jebel abu rajmein subordinate antithetic r2 reidel shears aligned north northeast south southwest are trans tensional sinistral strike slip faults showing minor extension that cut through the earlier domal structures for example ras al hawa depression in jebel abu rajmein northwest southeast aligned faults for example jebel bilas cross trend faults show northeast southwest extension at right angles to the palmyride shortening direction this extension parallels the major euphrates graben trend in eastern syria and northwestern iraq and also parallels some aligned pliocene pleistocene volcanic rifts south of damascus and in the jebel druze jebel arab region of southern syria and northern jordan a regional palmyride strain ellipse is presented to explain the geometry of all these structures the ad daww depression is a northeast southwest aligned transpressional basin containing around 2 km thickness of tertiary sediments the basin is bounded to the west by a sinistral shear couple along the cherrife structural trend in the central palmyrides along the north by the dextral jhar fault and along the southeast by the compressional southeast palmyrides in the southeast palmyrides structural style is one of a series of northeast southwest aligned narrow anticlines in the mesozoic platform sediments with upright to north west dipping southeast facing axial planes shortening amounts are very small in the eastern palmyrides 1 km and taken up almost entirely by folding but these increase slightly toward the west to probably 20 km in the cherrife region tight box folds and slightly asymmetric folds in the southeast palmyrides have a localized basal detachment along the triassic gypsum horizon which in some examples flows into the fold core jebel hayyan there is no evidence for a major basal detachment underlying the palmyrides all folding and faulting can be related to disharmonic folding of the mesozoic sediments above a triassic evaporite sequence and subsequent dextral transpression the lack of overthrusting explains the absence of any foreland basin caused by lithospheric flexuring on the rutbah platform the major palmyride deformation in miocene pliocene times was concomitant with the opening of the red sea with the closing of the bitlis zagros suture zone in eastern turkey and central iran and with the main sinistral strike slip motion along the dead sea fault

accommodation of late cenozoic oblique shortening in the alborz range northern iran abstract the alborz range northern iran deforms by strain partitioning of oblique shortening onto range parallel left lateral strike slip and thrust faults deformation is due to the north south arabia eurasia convergence and westward motion of the adjacent south caspian relative to iran roughly north south shortening occurs on thrusts that dip inwards from the range margins precambrian basement is not exposed because of detachment along upper proterozoic evaporites and the thickness of overlying strata 10 km other detachments occur within phanerozoic sediments active left lateral strike slip faults trend ene in the east of the range wnw in the west the eastern mosha fault has a left lateral offset of 30 35 km shortening across the range is 30 km 25 30 at the longitude of tehran this is hard to reconcile with the crustal thickness of 35 km which is similar to adjacent basins percentage shortening across the alborz is similar to the adjacent kopet dagh but because the latter is twice as wide finite shortening is roughly half the difference may be accommodated by subduction of the adjacent south caspian basin northwards under the middle caspian south caspian sediments began folding in the pliocene the present kinematics of the alborz may have begun at this time including a reversal from range parallel right lateral to left lateral strike slip faulting but the regional stratigraphy indicates uplift as early as the mid tertiary

why are there no clockwise rotations along the north anatolian fault zone mechanical analysis of lithospheric deformation associated with an intracontinental transform fault suggests that it should be associated with a pattern of vertical axis rotations governed by the length of the fault its displacement and the mechanical properties of the lithosphere paleomagnetic results from two transects across the north anatolian fault zone indicate that there have been no measurable clockwise rotations on a regional scale associated with neogene dextral strike slip motion along the fault the data come from two groups of volcanic rocks that have been dated by k ar whole rock geochronology and have yielded ages ranging from 45 3 3 1 m y to 41 8 1 3 m y eocene and 21 7 1 5 m y to 7 5 0 2 m y miocene the absence of clockwise rotations suggests one of the following explanations 1 in contrast to the assumptions underlying current mechanical analyses deformation in the upper crust may not directly reflect the flow in the lithosphere and is localized along a single fault trace 2 deformation is distributed but rotations have been prevented by the presence of elongate fault blocks subparallel to the trace of the main fault 3 displacement along the north anatolian fault may be too small or the rheologic properties of the lithosphere such that rotations about vertical axes cannot be resolved instead of the predicted clockwise rotations measured declinations show that there has been approximately 30 of anticlockwise rotation of both the eocene and miocene volcanic rocks this suggests that no significant rotation occurred between eocene and miocene times and that the anticlockwise rotation occurred either immediately before or concurrent with the plio pleistocene slip on the north anatolian fault

calibration of an ml scale in northwestern turkey from 1999 izmit aftershocks a local magnitude scale is derived for northwestern turkey using data collected by a temporary network installed by the german task force for earthquakes after the 1999 izmit earthquake m w 7 4 and the permanent sapanca bolu network we computed wood anderson seismograms for over 5353 arrivals at 27 three component stations from 530 earthquakes the hypocentral distances considered range from 5 to 140 km with the best represented range being from 5 to 70 km we inverted the measured amplitudes following both the nonparametric richter s 1958 and parametric bakun and joyner 1984 approaches these methods yield consistent magnitude values and station corrections however the calculated nonparametric distance correction log a implies that ground motion attenuation is higher than what is accounted for by the equation calibrated in central california in the range 5 62 km the best fit is provided by log a log r 17 0 00960 r 17 2 this equation is obtained constraining the geometrical spreading parameter n to 1 the calculated value of k 0 00960 confirms that in this range of distance seismic waves could propagate through a low q volume station corrections which allow for a significant reduction of m l residuals range between 0 5 magnitude units suggesting a strong influence of local site effects on the amplitude of ground motion in accord with the obtained attenuation and station corrections the magnitudes of the considered events range from 0 4 to 4 8

a local magnitude scale for the western great basin eastern sierra nevada from synthetic wood anderson seismograms abstract we have computed synthetic wood anderson seismograms for over 1100 arrivals at 10 three component broadband digital stations in the unr western great basin eastern sierra nevada network these represent all the available records from local earthquakes over magnitude 3 5 between 1990 and june of 1993 plus selected events of smaller magnitude there were 77 events ranging in magnitude from 2 2 to 5 9 including four events over magnitude 5 the distances considered ranged from 15 to 600 km with the best represented range being from 30 to 450 km we invert these measurements to determine distance and station corrections appropriate for a local magnitude scale constrained by richter9s original definition that an earthquake of m l 3 will cause a 1 mm zero to peak deflection of the wood anderson seismogram at 100 km from the epicenter the results between 30 and 450 km were essentially independent of choice of curve fitting parameters in the 30 to 500 km distance region the smooth distance correction curves were very similar to that determined by richter 1958 which is still used for southern california earthquakes we propose to use richter9s distance correction curve in reporting amplitude magnitudes from our digital network