early carboniferous carbonate systems an alternative to the cainozoic paradigm abstract an alternative model for carbonate deposition is offered for the early carboniferous the major features of this interval are not explained using late cainozoic analogues early carboniferous low latitude shallow seas were apparently strongly influenced by upwelling and high nutrient levels these conditions favoured highly carbonate productive offshore systems but also resulted in the formation of extensive abiogenic carbonates as muds and ooids if correct the carboniferous serves to illustrate the dangers in extrapolating from present day systems to the geological record

comparison of magnitude estimates for new zealand earthquakes moment magnitude local magnitude and teleseismic body wave magnitude new zealand is one of the more seismically active countries in the world with more than 15 000 earthquakes located each year routine moment tensor analysis of regional seismic data for earthquakes with moment magnitude m w 3 5 4 0 has recently been implemented in new zealand nearly 330 regional moment tensor rmt solutions have been calculated for earthquakes in the new zealand region dating back to late 2003 this complements local magnitude m l the primary magnitude calculated by geonet in new zealand the rmt catalog along with 155 global centroid moment tensor global cmt catalog solutions is used to compare m w with m l for new zealand earthquakes in addition to m w and m l there are more than 330 teleseismic body wave magnitude m b values available from the united states geological survey and international seismological center catalogs for events that also have an m w these are used to examine the relationship between m w m l and m b for new zealand earthquakes there is a clear distinction in the relationship of m l to m w for shallow focus 33 km depth and deep focus 33 km depth earthquakes shallow focus earthquakes show m l to be fairly consistent with m w particularly for events with m w 4 5 and with graphic 1 deep focus earthquakes have m l consistently larger than m w more than a full magnitude unit for some events with graphic 2 m w and m b are in fairly good agreement regardless of the depth whereas m b estimates are consistently smaller than m l for deep events this suggests that m l is overestimated for deep focus events and that the large m ls are not the result of physical properties of the source 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

recent emerged reef terraces of the yenkahe resurgent block tanna vanuatu implications for volcanic landslide and tsunami hazards emerged reef terraces record the extraordinarily rapid holocene uplift rate of the fault bounded yenkahe resurgent block yrb located within a partially submerged quaternary caldera on tanna island vanuatu southwest pacific the presently active volcano yasur is located at the western end of the yrb episodic uplift of the yrb is probably associated with the movement of magma below the yenkahe area a historically recorded uplift at port resolution bay in a d 1878 raised the shoreline 15 m this a d 1878 event was accompanied by a local earthquake and a tsunami that reached 12 m elevation coral samples from terraces at mean altitudes of 155 m and 15 m above present sea level yield 230 th 234 u dates of a d 1002 pm 10 and a d 1868 pm 4 respectively these ages imply a mean uplift of 156 mm yr for the yrb since a d 1002 until a d 1992 this volcanically related uplift occurs within the context of regional uplift of the southern new hebrides arc the late holocene uplift r

stress in western canada from regional moment tensor analysis more than 180 regional moment tensor rmt solutions for moderate sized earthquakes m 4 are used to examine the contemporary stress regime of western canada and provide valuable information relating to earthquake hazard analysis the overall regional stress pattern shows mainly ne sw oriented p axes for most of western canada with local variations in the northern cordillera the maximum compressive stress direction 1 varies from east west to north south to ne sw from south to north the stress direction 1 is consistent with the p axis direction for the largest earthquakes except in the central and northern mackenzie mountains where there is a 16 difference the yakutat collision zone shows a steady change in 1 from east west in the east to north south in the west in the canada united states border region rmt solutions suggest a north south compressional regime may extend through southern british columbia and northern washington to the eastern cordillera in the vancouver island puget sou

the relationship between local and moment magnitude in greece during the period 2008 2016 we perform a systematic comparison between local and moment magnitudes in greece for the period 2008 2016 when both magnitudes have been determined using waveform data recorded by the hellenic unified seismic network husn differences between the two magnitudes scales on average do not exceed 0 2 units as has been found in other regions worldwide a recalculation of local magnitude using magnitude residuals for each husn station shows that station site conditions have very little influence on the difference between local and moment magnitude it is therefore more likely that wave propagation effects and in rare cases anomalous source properties are dominant factors in shaping this difference general orthogonal regression is applied to the whole dataset and also to subsets covering different areas of greece or different time period to calibrate the one magnitude scale against the other using a linear model the resulting relationships differ very little suggesting that there is no significant regional temporal variation between local and moment magnitudes while these relationships predict that local magnitude is very close to moment magnitude if both are determined using husn data the comparison with global cmt moment magnitude with m w in the range 4 5 6 2 shows that it is larger than local magnitude by 0 18 units these results are particularly important for converting local magnitudes to equivalent moment magnitudes and thus homogenize the greek earthquake catalog

moment magnitude local magnitude calibration for earthquakes off canada s west coast local magnitude m l values of earthquakes off canada9s west coast are known to be underestimated by at least 0 5 magnitude units compared with other magnitude scales moment magnitude m w derived from moment tensor analysis provides the most robust estimate of the magnitude of earthquakes moment tensor analysis of regional seismic data in western canada is now possible due to the installation of more than 40 three component broadband stations in western canada the u s pacific northwest and southeast alaska moment tensor solutions are now possible down to m 4 0 more than 230 regional moment tensor solutions have been calculated off canada9s west coast at the geological survey of canada for 1995 2002 these solutions along with 14 previous solutions by oregon state university in 1994 1995 and 13 harvard solutions for 1984 1993 allow a systematic m w m l calibration for earthquakes in this region the study area extends from the queen charlotte islands region in the north to the area off the west coast of southern vancouver island at the northern end of the study area where there is little oceanic crust in the source receiver travel path m w is systematically larger than m l by 0 28 0 08 magnitude units at the southern end of the study area where there is a significant amount of ocean crust in the source receiver travel path m w is systematically larger than m l by 0 62 0 08 magnitude units calibration of m l with m w will allow the western canadian earthquake database to be used more effectively for tectonic studies and seismic hazard analysis

pacific north america plate boundary reorganization in response to a change in relative plate motion offshore canada 1 the transition from subduction in cascadia to the transform queen charlotte fault along western canada is often drawn as a subduction zone yet recent studies of gps and earthquake data from northern vancouver island are not consistent with that model in this paper we synthesize seismic reflection and gravity interpretations with microseismicity data in order to test models of 1 microplate subduction and 2 reorganization of the preexisting strike slip plate boundary we focus on the critical region of outer queen charlotte sound and the adjacent offshore on much of the continental shelf several million years of subsidence above thin crust are a counterindicator for subduction an undated episode of compression uplifted the southernmost shelf but subsidence patterns offshore show that recent subduction is unlikely to be responsible previously unremarked near vertical faults and a mix of extensional and compressional faults offshore indicate that strike slip faulting has been a significant mode of deformation seismicity in the last 18 years is dominantly strike slip and shows large amounts of moment release on the revere dellwood fault and its overlap with the queen charlotte fault the relative plate motion between the pacific and north american plates rotated clockwise 6 ma and appears to have triggered formation of an evolving array of structures we suggest that the paleo queen charlotte fault which had defined this continental margin retreated northward as offshore distributed shear and the newly formed revere dellwood fault propagated to the northwest

estimation of source parameters of local earthquakes originated in shillong mikir plateau and its adjoining region of northeastern india abstract we estimate the source parameters seismic moment source radius stress drop and source displacement and scaling laws for local earthquakes that occurred in the shillong mikir plateau assam valley and arunachal himalaya in northeast india during 2001 2008 the source parameters were determined using the spectral analysis of p waves from the vertical component seismograms after correction for attenuation seismic moments are observed within the range from 9 51 10 12 to stress drop ranges from 4 10 5 to 9 10 7 pa for the brune model and 7 10 5 to 1 10 8 pa for the madariaga model seismic events in this study are prominent with an average stress drop of 0 1 10 mpa the effect of site geology may be a contributing factor for such a variation in stress drop source dimensions are however found to be smaller within the major part of the plateau it is suggested that local earthquakes in the region are associated with a brittle shear failure mechanism on fault segments and or the presence of weakened zones and earthquakes are triggered by low deviatoric stress empirical relations between m w m l and m 0 m l are developed leading to the future prediction of calibration coefficients for the local earthquakes in the shillong mikir plateau and its adjoining region online material tables of source parameters

the control of overburden thickness on resurgent domes insights from analogue models abstract resurgent doming consists of the uplift usually accompanied by volcanic activity of part of a collapse caldera analogue models were used to investigate the architecture of resurgent domes dry sand simulates the brittle crust uprising silicone located at the base of the sand pack simulates magma the deformation pattern depends mainly upon 1 the ratio aspect ratio between the thickness of the sand overburden and the width of the silicone intrusion 2 the duration of experiment for aspect ratios 1 two concentric domes develop the first formed outer dome is bordered by inward dipping reverse ring faults while the inner dome by outward dipping normal ring faults the layers inside the dome are uniformly dipping for aspect ratios 0 4 the dome shows a crestal depression surrounded by radial fractures followed by an apical extrusion of silicone the internal structure of the dome is made up of domed layers independently from the aspect ratio the duration of the experiment enhances silicone extrusion a consistent structure is observed in most resurgent domes in nature the comparison between experiments and nature suggests that two distinct resurgence modes occur mainly depending on the aspect ratio thickness width of the crust overlying the magma chamber aspect ratios 1 develop a resurgent block with uniformly dipping layers and peripheral volcanic activity ischia and pantelleria type aspect ratios 0 4 develop a resurgent dome with a crestal depression domed layers within and peripheral and internal volcanic activity valles and long valley type

seismicity in the vicinity of the snorcle corridors of the northern canadian cordillera the slave northern cordillera lithospheric evolution snorcle corridors of the northern cordillera sample some of the most and least seismically active regions of canada the earthquake history of this region is short precise determination of earthquake locations and depths is not possible even today nonetheless significant gains in our knowledge of the seismicity of this region have been made in recent years from studies of historic earth quakes microseismicity studies and advances in waveform modelling techniques combined with broadband data that allow for determination of focal mechanisms and depths for moderate earthquakes this article summarizes our current knowledge of the seismicity and seismic hazards across the region these detailed analyses have shown that i the largest historical earthquakes have occurred in regions of ongoing microseismicity ii the largest earthquakes have occurred in pairs or in swarms suggesting that stress triggering is important in this region iii the active faults are concentrated in the offshore region iv there is a concentration of seismicity in the fold and thrust belt several hun dred kilometres from the active plate margin and v there is no seismicity associated with the quaternary volcanic zone in northern british columbia potentially damaging magnitude m 5 earthquakes can be expected every few years in the vicinity of the northern cordillera the mw 7 9 denali alaska earthquake where mw is the moment magnitude was a good reminder that the effects of a large earthquake can be substantial even hundreds of kilometres from the epicentre detailed studies of seismicity earth structure and tectonics with the latter made possible in large part by the snorcle transect will allow for informed decision making for resource development and the design of safe structures and infrastructure in the northern canadian cordillera resume les corridors du projet snorcle de la cordillere septentrionale permettent d echantillonner quelques unes des regions sismiques les plus et les moins actives du canada l histoire des seismes de cette region est breve meme

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

ground motions for earthquakes in southwestern british columbia and northwestern washington crustal in slab and offshore events regional ground motion generation and propagation must be charac terized to adequately assess seismic hazard in the cascadia region of southwestern british columbia and northwestern washington the ground motion issues are par ticularly complex because of the contributions to hazard from five distinct types of events all of which behave differently in terms of their ground motion propagation characteristics 1 shallow earthquakes occurring in the continental crust 2 shallow earthquakes occurring offshore in oceanic crust 3 earthquakes occurring within the subducting juan de fuca slab beneath the continent e g puget sound 4 earth quakes occurring within the subducting juan de fuca slab at the edge of the continent e g transitional events along the west coast of vancouver island and 5 great subduction earthquakes on the interface between the subducting juan de fuca plate and the overriding north american plate in this study empirical data recorded within the cascadia region are used to evaluate the source and attenuation characteristics of ground motion amplitudes from the first four of these event types crustal off shore in slab and transitional and examine their implications for regional ground motion relations for crustal earthquakes in cascadia a simple application of the hybrid empirical approach is used to suggest appropriate regional ground motion relations the ground motions are obtained by multiplying california ground motion relations by a frequency dependent factor to account for regional differences in crustal amplifica tion the developed ground motion relations for cascadia earthquakes are in rea sonable agreement with recorded ground motions in the region the proposed rela tions are the first region specific ground motion relations to be developed for the cascadia region and they provide a useful alternative to california relations for use in seismic hazard analysis

earthquake magnitude relationships for the saint peter and saint paul archipelago equatorial atlantic we have investigated several relationships between ml m neic and mw for the earthquakes locally recorded in the saint peter and saint paul archipelago spspa equatorial atlantic because we only have one station in the area we could not derive attenuation relations for events recorded at different distances at different stations our approach was then to compare our ml estimates with magnitudes reported by neic this approach produced acceptable results particularly for epicentral distance smaller than 100 km for distances greater that 100 km there is a systematic increase in the residuals probable due to the lack of station correction and our inability to accurately estimate q we also investigate the mw m neic relationship we find that mw estimates using s wave produce smaller residuals when compared with both m neic finally we also investigate the ml mw relationship and observe that given the data set we have the 1 1 holds we believe that the use of the present methodologies provide consistent magnitude estimates between all the magnitudes investigated that could be used to better assess seismic hazard in the region

empirical distance attenuation and the local magnitude scale for the central united states seismic waveform data from the cooperative new madrid seismic network cnmsn the u s national seismograph network usnsn and stations operated by the u s geological survey and the incorporated research institutions for seismology iu are corrected to the theoretical wood anderson response and the peak amplitudes are used to determine a local magnitude scale for the central united states the distance correction function can be expressed as graphic 1 with amplitude a in millimeters and hypocentral distance r in kilometers showing a weak attenuation with distance synthetic seismograms are calculated based on a detailed crustal model obtained from local well log acoustic data in the mississippi embayment to examine the effect of structure on station factors the results show that the mississippi embayment sediment as a whole may amplify seismic waves at some specific frequencies such as 0 5 and 5 0 6 0 hz with a factor less than 4 0 and may not amplify seismic waves in the frequency band from 0 5 to 9 9 hz on average even though the amplification factors do increase with the source magnitude estimations for b values and magnitudes of earthquakes with a return period of 500 yr in the central united states are performed based on the original new madrid catalog m d or m blg and the newly created m l catalog results show that the b value is smaller for the m l catalog 0 790 yielding one m 7 5 event every 500 yr a result that converges with the paleoearthquake estimate for the region on average the relation between m l and m d or m blg for 1 5 m d 5 0 can be expressed as m l 1 008 m d 0 0714 1 embed inline graphic 1 gif

california integrated seismic network cisn local magnitude determination in california and vicinity determining local magnitude m l in a manner that is uniform and internally consistent for earthquakes throughout california and the vicinity is an important component of the california integrated seismic network cisn we present a new local magnitude attenuation function and corresponding station adjustments that are valid throughout california the new attenuation function is an analytic function of the radial hypocentral distance between 1 and 500 km associated station adjustments are also available for 1185 horizontal seismometer and accelerometer channels from five seismic networks operating in california the new attenuation function and adjustments provide several advantages to cisn they allow a more robust m l computation the m ls are more consistent between northern and southern california than they have been in the past and because adjustments are now available for more station network channel location codes sncls m ls can be computed for small earthquakes in more locations than was previously possible in addition to describing our method for calibrating the new cisn m l we also present a tool for adding adjustments for new or upgraded stations

temporal and spatial variations of local magnitudes in alaska and aleutians and comparison with body wave and moment magnitudes abstract we evaluated temporal and spatial variability of local magnitudes m l in the earthquake catalog of alaska earthquake information center regionally recorded hypocenters in mainland alaska are available in the catalog beginning in the early 1970s no comprehensive aleutian wide m l statistics exist prior to the mid 1990s we identify four time intervals with similar magnitude residual trends between m l versus body wave magnitude m b 1971 1976 1977 1989 1990 1999 5 and 1999 5 2008 the three latter intervals are also identified in m l versus moment magnitude m w residual trends these time intervals correspond to the periods with different data processing procedures we find that the latest time interval has the best correspondence between m l and m w values in mainland alaska especially for shallow depth m l versus m b and m l versus m w are present in the catalog for the pre 1990 data the largest discrepancies are observed for the gulf of alaska earthquakes for the latest time period 1999 5 2008 the largest residuals between m l and m b or m w are observed for the earthquakes located within the oceanic segment of the aleutian arc and within 100 km of the trench we calculated a set of magnitude corrections for mainland alaska and the aleutians that need to be applied to homogenize magnitude values in the catalog in time and space

revised ml determination for crustal earthquakes in taiwan the local magnitude scale m l is an empirically derived scale anchored to a zero magnitude reference event richter defined the amplitude of ground shaking at an epicentral distance of 100 km for a zero magnitude earthquake in southern california the crustal attenuation characteristics of taiwan result in a relatively high ml when compared to moment magnitude mw we therefore define a revised ml scale for crustal earthquakes in the taiwan region that is more consistent with mw using observed peak ground shaking and mw we determine a new log a0 curve of ground shaking versus hypocentral distance r for a zero magnitude earthquake and station correction factors the log a0 curve determined in this study is log a r 0 332 1 568 log r 0 280 0 using this new log a0 curve and station corrections the new ml is more consistent with mw with a 0 2 magnitude unit uncertainty the new log a0 curve has a value of 2 80 at the distance of 100 km compared to the anchor point of log a0 3 at the same distance as defined by richter for southern california this means that the current ml estimates in taiwan which use richter s definition average 0 2 magnitude units larger than their mw the station correction factors also determined are large from 0 40 to 0 52 magnitude units the use of station corrections in routine seismic network operation in taiwan will improve magnitude estimates this is particularly important for smaller events when recording stations may be pre dominantly on either hard rock or soft soil sites which could lead to under or overestimates of the magnitude by up to half a magnitude unit

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

tidal triggering of earthquakes in the northeast pacific ocean summary there have been many searches for evidence of tidal triggering in earthquake catalogues with the exception of volcanically active regions the more rigorous studies in continental settings tend to find no correlation or only a very weak correlation in the oceans the effect of loading by the ocean tides can increase tidal stresses by about an order of magnitude over continental settings in recent years several studies have reported evidence of tidal triggering in oceanic regions and such observations can represent a useful constraint on models of earthquake rupture in this paper i systematically search for a link between ocean tide height and the incidence of earthquakes in the northeast pacific ocean a region of high amplitude open ocean tides the focal mechanisms of most of the earthquakes in these catalogues are unknown but it can be shown that tidal stresses will in most instances promote failure at low tides i investigate three declustered data sets comprising 1 earthquakes from 1980 to 2007 on the juan de fuca plate and in the queen charlotte fault region from land based catalogues 2 earthquakes from 1992 to 2001 on the juan de fuca plate located with the us navy s sound surveillance system sosus hydrophone array and 3 earthquakes from 1980 to 2001 south of alaska and the aleutians located with land based networks i look at the distributions of earthquakes with ocean tide phase height and tidal range and apply schuster and binomial tests and monte carlo simulations to determine if they deviate significantly from random the results show no evidence of triggering during intervals of increased tidal range but all three data sets show a significant increase in earthquake incidence at low tides the signal is particularly strong in the land based catalogue for the juan de fuca plate and queen charlotte fault regions where there is a 15 per cent increase in the rate of seismicity within 15 of the lowest tides the signal is weakest in the sosus data set which may reflect the lower average tidal range at epicentres in this data set or an analysis that is influenced by gaps in the catalogue the triggering signal in the alaska aleutian may be partially obscured by earthquakes in the aleutians where the total tidal stresses can be significantly out of phase with the ocean tide height the increase in the rates of seismicity i observe at low tides is less than observed by local networks on mid ocean ridges similar to the prediction from an analysis of global thrust earthquakes and greater than inferred by extrapolating laboratory simulations of fault failure under tidal loading

coastal evolution at a rapidly uplifting volcanic island iwo jima western pacific ocean abstract iwo jima is the emergent part of a large submarine volcano on the izu ogasawara island arc approximately 25 marine terraces form the major geomorphic components of the island these have been formed in response to rapid domal uplift and marine abrasion both of which may have been irregular in time and in space the oldest marine terrace at about 110 m above sea level has an age of 500 800 14 c bp indicating an average uplift rate of 150 200 mm year surrounding the island is a ca 1 km wide wave cut and wave built platform less than 15 m deep marine planation has maintained the platform at nearly the same level despite rapid uplift

a revised magnitude recurrence relation for shallow crustal earthquakes in southwestern british columbia considering the relationships between moment magnitude and regional magnitudes an important component of seismic hazard analysis is the magnitude recurrence relation which provides the cumulative rate of occurrence of earthquakes within a seismic source zone as a function of magnitude in the national seismic hazard maps developed for the 2005 national building code of canada the magnitude recurrence relation for the cascade mountains zone of southwestern british columbia casr the seismic zone in which vancouver and victoria are located is based mainly on earthquakes measured on the local scale m l richter scale but other scales including body wave magnitude m b coda duration magnitude m c and moment magnitude m have been used for some of the events the mixture of magnitude types is a potential source of bias in the relations by using data from recently calculated regional moment tensor solutions a local magnitude moment magnitude relationship is developed for magnitudes of 2 9 m l 6 0 in the casr zone this relation along with relations from other sources for m b and m c and specific moment magnitude values where available are used to develop a homogeneous moment magnitude catalog for use in the formulation of a new casr zone magnitude recurrence relation the use of a homogeneous moment magnitude scale produces a significant change in the shape of the magnitude recurrence curve in the casr zone perhaps more importantly the use of a homogeneous catalog reduces the uncertainty in the recurrence rates of moderate to large earthquakes in casr by nearly an order of magnitude we conclude that the use of a homogeneous magnitude scale is critical to producing unbiased magnitude recurrence relations

a seismic swarm and regional hydrothermal and hydrologic perturbations the northern endeavour segment february 2005 the february 2005 swarm at the overlapping spreading center osc on the northern end of the endeavour segment is the first swarm on the juan de fuca ridge recorded on a local seafloor seismic network the swarm included several larger earthquakes and caused triggered seismicity and a hydrothermal response in the endeavour vent fields as well as regional scale hydrologic pressure perturbations the spatial and temporal pattern of over 6000 earthquakes recorded during this seismic sequence is complex small magnitude events dominate and seismicity rates wax and wane indicating a magmatic process the main swarm initiates at the northern end of the endeavour ridge however most of the moment release including six strike slip events occurs in the southwest endeavour valley where the swarm epicenters generally migrate south the main swarm is contemporaneous with a hydrologic pressure response at four sealed seafloor boreholes 25 105 km away we infer that the seismic sequence is driven by a largely aseismic magma intrusion at the northern endeavour axis resulting stress changes trigger slip on tectonic faults and possibly dike propagation at the opposing limb of the endeavour osc in the southwest endeavour valley consistent with the eventual decapitation of the endeavour by the west valley segment furthermore 2 5 days after the start of the main swarm seismicity is triggered beneath the endeavour vent fields and temperature increases at a diffuse vent in the mothra field we infer that this delayed response is due to a hydrologic pressure pulse that diffuses away from the main magma intrusion

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

seismotectonics of the explorer region 1 the explorer region offshore western canada is a tectonically complex area surrounded by the pacific north america and juan de fuca plates existing tectonic models for the region differ fundamentally proposed plate configurations range from multiple independent plate fragments to an explorer plate now fused to north america along the continental margin and cut by pacific north america transform faults in the west we present new seismological data constraining the region s current tectonics we use three component regional waveforms to determine the source parameters of 84 earthquakes with magnitude greater than 4 combined with 34 harvard centroid moment tensor solutions they represent the region s largest earthquake source parameter data set obtained by robust waveform modeling techniques in addition we perform joint epicenter determination to relocate larger earthquakes recorded since 1918 the source parameters and improved locations provide a consistent tectonic picture earthquake slip vector azimuths along the pacific plate boundary change smoothly and are significantly less northerly oriented than the pacific north america plate motion direction requiring an independent explorer plate the present day pacific explorer boundary is formed by transform faults subparallel to the revere dellwood wilson fault plate motion vectors indicate that the winona block is part of the explorer plate current explorer motion is more northerly than indicated by magnetic anomalies prior to 2 ma implying a recent change possibly coinciding with a northwestward ridge jump near explorer plate s northern end transferring the winona block from the pacific to the explorer plate in response to these plate motion changes the region north of the western sovanco fracture zone was assimilated into the pacific plate the region around the eastern sovanco fracture zone characterized by broadly distributed seismicity is composed of well defined sets of conjugate faults bounding rotating crustal blocks earthquake fault strikes agree with the dominant northwest southeast fault sets however the conjugate sets must be also active to fully accommodate present day explorer plate motion the sw portion of the strike slip nootka fault zone the explorer juan de fuca plate boundary is well defined by focused seismicity however its full extent under nootka island remains unresolved the explorer north america boundary shows sporadic low magnitude seismicity our explorer north america rotation pole predicts convergence varying from negligible at the boundary s northwest end to 2 cm yr at the se end this convergence can be accommodated either by subduction or by crustal thickening extending to the north american continent we favor subduction based on low deformation rates observed by onshore gps sites the present explorer plate system configuration is a result of stepwise reorientation of the explorer ridge system each step successively reducing the subduction rate relative to north america

rapid identification of earthquake rupture plane using source scanning algorithm summary accurate identification of an earthquake s rupture plane is critical in many aspects ranging from scientific such as seismology and plate tectonics to societal such as emergency rescue planning we modify the recently developed source scanning algorithm ssa to rapidly image the rupture pattern of an earthquake using waveform data recorded at local and regional distances the method calculates the brightness function of a grid point by summing the observed amplitudes of the p wave envelopes at the corresponding predicted arrival times at all stations the composite image consisting of brightness functions of all grid points within a prescribed source volume and time interval illuminates the locations on the rupture plane where significant seismic energy is emitted synthetic tests indicate that the proposed method is robust even under the presence of hypocentral mislocation and origin time errors application of this method to the 2003 san simeon and 2004 parkfield earthquakes both occurred in central california clearly identifies the nw se striking planes as the actual rupture planes a conclusion consistent with all available evidences limited azimuthal distribution of seismic stations will not severely affect the identification result making this method ideal for offshore earthquake studies because the proposed method is able to identify the rupture plane using seismic waveform data only it is perfectly suited for near real time operation and may enable routine report of earthquake rupture planes by local seismic networks in the future

moment magnitude local magnitude calibration for earthquakes in western canada local magnitude m l is the primary magnitude scale calculated for western canada by the geological survey of canada gsc moment magnitude m w derived from moment tensor analysis provides a more robust estimate of the magnitude of earthquakes but is more demanding to calculate moment tensor analysis of regional seismic data for earthquakes with magnitudes larger than 3 5 in western canada is now possible owing to the installation of more than 40 three component broadband stations in western canada the pacific northwest of the united states and southeast alaska more than 100 regional moment tensor solutions have been calculated in the canadian cordillera and vancouver island puget sound region for 1996 2004 at the gsc these solutions along with 45 prior solutions allow the calibration of m w m l throughout much of western canada continental crust events in the canadian cordillera and vancouver island puget sound region are found to have m w m l for earthquakes with m l 3 6 in contrast earthquakes located within the subducting slab in the vancouver island puget sound region where there are complex source receiver travel paths have m w systematically larger than m l by nearly 0 6 magnitude units the calibrations of m w with m l are an important result that will allow the western canadian earthquake database to be used more effectively for tectonic studies and seismic hazard analysis

fault parameters of the nisqually earthquake determined from moment tensor solutions and the surface deformation from gps and insar the magnitude 6 8 nisqually earthquake occurred on 28 february 2001 at a depth of 50 60 km within the subducting juan de fuca plate the fault parameters are estimated from moment tensor solutions and by comparing the surface displacements from global positioning system gps data and from satellite interferometry with predictions from elastic deformation models the simple deformation model calculates the coseismic surface displacements caused by an earthquake on an extensional rectangular fault in a uniform half space continuous gps stations within 200 km of the epicenter resolved horizontal displacements as great as 9 mm 210 and vertical displacements as great as 13 mm of subsidence near the epicenter the near vertical displacements were also determined from a differential interferogram created from synthetic aperture radar insar data from radarsat the only satellite data available for the event a maximum vertical subsidence of approximately 20 mm is observed 30 km east of the epicenter the gps insar and moment tensor solutions provide a consistent solution for the rupture parameters of the nisqually earthquake the fault has a strike of 180 and a dip of 20 and is centered at 47 10 n and 122 67 w 4 km east and 6 km south of the epicenter or has a strike of 360 and a dip of 70 and is centered at 47 10 n and 122 69 w 2 km east and 6 km south the trade off between fault area and rupture displacement is not resolved by our data but a good fit is found with the main rupture having an area of 230 km2 and an along strike length of 23 km and downdip width of 10 km the rupture area is centered at a depth of 51 km with a scalar moment of 2 0 1019 n m and with the given area an average rupture displacement of 1 4 m to refine the interpretation of the gps and insar data a 3d heterogeneous numerical model was generated having realistic shear moduli structure a 3d model of the subducting slab and a spherical earth the results are similar to those from the half space model but there is significant refinement with a deeper rupture center at 60 km manuscript received 9 april 2003

carbonate ramp depositional systems from a late jurassic epeiric platform iberian basin spain a combined computer modelling and outcrop analysis

lg wave attenuation in britain summary the lg wave quality factor qlg in britain has been modelled using data from the uk seismic network operated by the british geological survey the data set consists of 631 vertical mostly short period recordings of lg waves from 64 earthquakes 2 7 4 7 ml and 93 stations we have inverted for both regional average qlg and tomographic images of qlg and simultaneously a source term for each event and a site term for each station for 22 frequencies in the band 0 9 10 0 hz the regional average model is 266 f 0 53 between 1 0 and 10 0 hz and indicates that attenuation in britain is slightly higher than in france and significantly higher than in eastern north america and scandinavia tomographic inversions at each frequency indicate that qlg varies spatially broadly speaking southeastern england the lake district and parts of the east irish sea basin and a small region between the highland boundary fault and the southern uplands fault are characterized by higher than average attenuation southwestern england eastern central england and northwestern scotland are regions of relatively low attenuation to some extent these regions correlate with what is known about the tectonics and structure of the crust in the uk

remote dynamic triggering of earthquakes in three unconventional canadian hydrocarbon regions based on a multiple station matched filter approachremote dynamic triggering of earthquakes in three unconventional canadian hydrocarbon regions

the ischia debris avalanche first clear submarine evidence in the mediterranean of a volcanic island prehistorical collapse sector or flank collapse with related debris avalanches is increasingly recognized as a relatively common volcanic behaviour in particular for large hot spot related oceanic islands here we report the case of a catastrophic collapse that occurred at ischia volcanic island in prehistorical times and was driven by the volcano tectonic uplift of mt epomeo the major relief of the island the collapse left a subaerial to submarine horseshoe scar on the southern flank of the island and generated a debris avalanche incorporating thousands of giant blocks dispersed as far as 50 km from the island during the emplacement part of the debris avalanche evolved into a debris flow covering an area of 250 300 km2 this constitutes the first clear evidence of a submarine debris avalanche in the mediterranean sea the major collapse was followed and probably also preceded by recurrent less catastrophic terrestrial and underwater failures two other undersea hummocky deposits are found north and west of the island and might tentatively be correlated to the major southern collapse such volcanic behaviour previously unknown for ischia volcano has likely triggered tsunami waves over the entire bay of naples raising the question of their impact on prehistorical historical communities

structural seismic and hydrothermal features at the border of an active intermittent resurgent block ischia island italy resurgent blocks are uplifted parts of volcanoes where most of the deformation uplift is accommodated along peripheral faults the island of ischia italy has an active resurgent block uplifted 1000 m in the last 30 ka which allows us to investigate the deformation associated with a strong uplift in volcanic areas air photo interpretation was matched with field work 1 5000 scale mapping and structural analysis throughout the resurgent block these results have been matched with a review of the seismic and hydrothermal activity at ischia the results show that the block has a polygonal shape in map view and is characterized by a trapdoor uplift which results in a 15 tilt towards the se the northern most uplifted part is bordered by e w and ne sw trending faults arranged in parallel segments over an area 1 5 km wide i0 5 mcs degree shallow 1 1 6 km depth earthquakes focused in correspondence with the outermost set of faults on the northernmost part of the block here variations in the hydrothermal activity have been observed during seismic events previously performed analogue models show that resurgent blocks are bordered by inward dipping high angle reverse faults outermost fault system and outward dipping normal faults innermost fault system we propose a model of trapdoor uplift of a block which induces reverse faulting responsible for seismicity and hydrothermal variations along the most uplifted part outward dipping normal faults in the innermost part form as a consequence of the gravitational sliding of the volumes bordered by the reverse faults the further reactivation of the outermost reverse faults triggers a new cycle of intermittent trapdoor uplift of the block

a local magnitude relation for earthquakes in the western canada sedimentary basin a local magnitude m l relation for the western canada sedimentary basin wcsb is developed using a rich ground motion dataset compiled from local and regional networks in the area the assessment of amplitude decay with distance suggests that joining direct waves with postcritical reflections from moho discontinuity modifies the attenuation pattern in the 100 200 km distance range the m l distance correction is parameterized using a trilinear function that accounts for the observed attenuation attributes regression of ground motion amplitudes results in the following distance correction model log a for earthquakes in wcsb graphic 1 in which r is the hypocentral distance km the standard m l relations fail to capture the rates and shape of amplitude attenuation in the region resulting in overestimated magnitudes by 0 3 0 6 units the overestimation is larger for local networks due to the increased discrepancy between standard m l relations and actual attenuation properties at close distances the derived relationship results in unbiased m l magnitude estimates in wcsb over a wide distance range 2 600 km which ensures consistent magnitude estimates from local and regional networks 1 embed inline graphic 1 gif

effects of seismicity models and new ground motion prediction equations on seismic hazard assessment for four canadian cities seismicityratesandground motionpredictionequations gmpes arethe key uncertainties in probabilistic seismic hazard analysis psha we explore the impact of new findings and knowledge from seismological and ground motion studies on seismic hazard assessment for eastern and western canada updated information includes the reevaluation of seismicity rates and their interpretation in terms of seismic source zones and the use of new gmpes we refer to our model as an interim updated seismic hazard model as it does not treat all uncertainties comprehensively rather we address the impact of key uncertainties based on our updated interim seismic hazard model uniform hazard spectra uhs at four major cities across canada are obtained and compared with uhs in the current seismic hazard maps of canada 2005 2010 whicharebasedona1995seismichazardmodeldevelopedbythegeologicalsurveyof canada sensitivity analysis highlights the significant impact of seismicity smoothing in low to moderate seismic regions eastern canada while gmpes are important for all regions moreover our interim updated seismic hazard model can readily produce seismic hazard curves as well as seismic hazard deaggregation results for various site conditionsandformultipleprobabilitylevels thiscapabilityisessentialforcarryingout advanced earthquake engineering analyses

a late ordovician high energy temperate water carbonate ramp southern quebec canada implications for late ordovician oceanography the trenton group late ordovician the youngest carbonate unit in the taconic foreland basin of southern quebec is a tripartite unit with a distinctive coarse grained middle part the deschambault formation lithofacies of the deschambault formation are dominated by coarse grained bioclastic intraclastic limestones finer grained lithofacies are ubiquitous but subordinate the complete spectrum of lithofacies indicates sedimentation ranging from above fairweather to below storm wave base skeletal components are indicative of the modern temperate water bryomol association non skeletal elements are represented by peloids and intraclasts accretion rates from areas of continuous sedimentation were low 14 cm 103 years from sedimentological and faunal evidence it is proposed that the late ordovician deschambault ramp was bathed by temperate waters the model compares favourably with modern cool water shelves rimming the southern edge of the australian continent palaeomagnetic data locate southern quebec in a low latitudinal setting during the late ordovician upper ordovician facies distribution in eastern canada and progressive disappearance of some faunal provinces through late ordovician time are used to conclude that the initiation of the late ordovician glaciation that covered most of gondwana was instrumental in easing northward movement of cold oceanic currents this resulted in the rapid contraction of the southern hemisphere warm water tropical belt from a 30 latitudinal wide zone in the early caradoc to a 15 zone in the late caradoc

deposition of upper jurassic fine grained limestones in the western subalpine basin france abstract the fine grained carbonate sequence on the western margin of the french subalpine basin provides information about the depositional conditions of the late jurassic nodular lithofacies which closely resemble the age equivalent ammonitico rosso of the mediterranean and central atlantic domains a variety of rock textures can be distinguished including lumpy nodular restricted sense and conglomeratic the formation of these textures is referred to different sedimentological processes cyclic marl limestone deposition bioturbation winnowing early lithification gravity displacement etc in addition the development of deep water cryptalgal carbonate constructions which include stromatolites and small mud mounds is noted outer shelf deep marine palaeoenvironments 100 s m are inferred from the sedimentary structures biotic associations and facies distributions the callovian oxfordian discontinuity is believed to have resulted from a sediment starved environment part of the overlying fine grained carbonate material was then presumably derived from an adjacent platform oscillations in nature and quantity of carbonate and clay input onto the margin probably reflect cyclic climatic and sea level changes

empirical mw ml mb and ms conversions in western china local magnitude m l body wave magnitude m b and surface wave magnitude m s which are saturated at certain values and may lead to an incorrect energy estimation of a large earthquake are largely used in quantifying the size of an earthquake in western china based on the catalog from the china earthquake data center cedc and moment magnitude m w provided by the global centroid moment tensor global cmt project we test the general orthogonal regression gor and the ordinary least squares ols methods in m w m l m s and m b conversions for earthquakes in three different tectonic structures of western china for m l and m b linear trends vary according to tectonic structures which implies different body wave attenuations in the three structures for m s the results are similar whether using the gor or the ols method but slopes of regression lines are not close to 1 which indicates routine misestimates of m s in western china the gor slopes are uniformly larger than the ols slopes in all magnitude conversions standard deviations are between 0 06 and 0 13 for the gor method but are between 0 12 and 0 25 for the ols thus the gor is found to be superior to the ols method and its use is recommended conversions of different magnitudes to m w not only imply different patterns of seismic wave attenuations but will also benefit immediate assessment of seismic damage after occurrence of a destructive earthquake in the future online material earthquake catalog and tables showing differences between magnitude estimates for m w m l m b and m s

mafic injection as a trigger for felsic magmatism a numerical study 1 the origin of crustal scale silicic magmatism remains a matter of debate and notable uncertainty exists concerning the physical mechanisms that drive ascent and emplacement of felsic magmas in upper crustal regions a 2 d numerical model demonstrates that injection of mantle derived mafic magma into a partially molten hot zone in the lower crust can drive felsic magma ascent and intrusion into upper crustal levels the injection of mafic magma induces overpressure in the reservoir which increases crustal stresses and triggers development of brittle plastic shear zones and can drive significant surface uplift the emerging topography causes a nonuniform overpressure distribution in the reservoir and can trigger felsic magma ascent along crustal shear zones based on systematic numerical experiments we investigate the influence of crustal strength and injection rate the initial upper crustal strength controls the degree of crustal faulting and surface uplift and therefore whether felsic magma ascent can be initiated or not the final upper crustal strength influences the depth and final style of felsic intrusion the injection rate of mafic magma determines the time scale of overpressure growth and surface uplift stage in contrast the duration of the subsequent felsic ascent and intrusion emplacement stages remains nearly constant our results imply that mafic underplating and intrusion into the lower crust may not only be a prime control for the generation of felsic magmas in the lower crust but may also be an important physical driving mechanism for felsic magma ascent and intrusion into upper crustal levels

assessment of ground motion models for use in the british columbia north coast region canada abstract the 28 october 2012 m w 7 8 haida gwaii earthquake was the second largest earthquake instrumentally recorded in canada s territory and was strongly felt across the british columbia north coast bcnc region data from the haida gwaii sequence and other events in the region are compiled for 56 earthquakes between moment magnitude m w 4 6 and 7 8 that occurred between 1996 and 2014 pseudospectral accelerations psa at 5 damping are calculated and compared against several modern ground motion models gmms using different binning criteria e g distance magnitude mechanism source to site azimuth and event chronology overall no single model is found to be appropriate for the bcnc region with gmms generally overestimating recorded near source i e earthquake motions recorded prior to and including the 2012 m w 7 8 earthquake were generally more comparable with some gmms at longer spectral periods but still possessed significant biases based on residual analyses additionally earthquakes with normal mechanisms gave less short to mid period shaking relative to strike and reverse slip events online materials summary of the candidate ground motion prediction equations indicating their distance metrics and conditions of use

interaction between local tectonics and glacial unloading on the pacific margin of canada abstract variations in late quaternary coastal deformation along the pacific margin of canada reflect not only differences in glacial history but also local non glacial tectonics a forebulge developed to the north in the queen charlotte basin qcb from 13 2 until after 9 7 ka bp resulting in exposure of the currently submerged shelf whereas similar exposure was not evident to the south in the georgia basin a semi quantitative effective elastic lithosphere thickness of between 10 and 20 km is estimated for the qcb we propose that this warm relatively thin lithosphere combined with tectonic movement influenced crustal displacement particularly the decoupling of the north american plate along the queen charlotte qc fault which may have allowed the qcb to behave like a hinge in response to glacial unloading this would explain large magnitude crustal tilting 2 1 m km 1 observed adjacent to the qc fault the 50 m of depression observed in the early and mid holocene may imply that the western edge of the north america plate flexed down below present elevation producing a second wave of response to ice loading and unloading

seismicity and rates of relative motion on the plate boundaries of western north america summary the consistency of earthquake data and plate tectonic models and other estimates of fault slip may be tested by estimating rates of motion from the earthquakes using the concept of seismic moment the contribution of individual events may simply be summed but a generally better estimate of long term average slip rate is obtained by integration over magnitudefrequency of occurrence relations estimates of fault motion rates associated with earthquakes are possible within about a factor of 2 using this approach if the major sources of uncertainty are given careful consideration e g incompleteness and inaccuracies in the earthquake data empirical moment magnitude relations and the effect of their stochasticity fault widths or depth extents the recurrence relations maximum magnitudes and the form of truncation at the maximum magnitude a formulation for the recommended magnitude density truncation is developed application of the latter method to the earthquake data of the offshore transform faults of the juan de fuca ridge system the queen charlotte fault zone and the northern vancouver island area in each case gives good agreement with rates from plate tectonic models for the southern san andreas fault and gulf of california area there is also good agreement with previous estimates obtained by summing the contributions of individual events however the displacement rate in the margin convergence zone of southern british columbia washington and oregon computed from the seismicity is at least a factor of 10 lower than from plate models and from other convergence estimates and primarily aseismic slip is suggested the fault motions as a function of time computed from the seismicity records have also been plotted and compared to the longterm average rates the plots permit estimates of the minimum present accumulated elastic strain and show if there are any temporal relations among earthquake displacements on different fault zones

carbonate ramp depositional systems from a late jurassic epeiric platform iberian basin spain a combined computer modelling and outcrop analysis no counterparts to epeiric sea carbonate ramps are known in present day environments this hinders the interpretation of the factors controlling the growth and evolution of these depositional settings in this study we analyse the facies and geometries of two jurassic examples both from outcrop study and through computer modelling this analysis is constrained by two important features of these oxfordian and kimmeridgian ramps firstly they are very well exposed allowing accurate reconstruction of a 200 km section from proximal to distal ramp environments and secondly a time framework for correlation section reconstruction and modelling is provided by a well defined ammonite biostratigraphy the modelling results in a synthetic stratigraphy which closely matches the reconstructed cross sections and when integrated with the field study constrains and provides additional quantitative data on the following aspects of carbonate ramp systems resedimentation by storms is an important process in maintaining the ramp profile through time down ramp transport distances of between 25 and 40 km are indicated from the distribution of storm beds and shallow water allochems and from model matching known stratigraphic thicknesses and geometries modelling sediment production within the time constraints from the ammonite biozones indicates that shallow water carbonate production was 1 2 orders of magnitude less than that predicted for present day open marine carbonate platforms deeper water production rates were reduced by lesser amounts these proportionally higher outer ramp production rates also help to maintain ramp geometries through time the enigmatic slope crest of ramps is shown to result from a combination of higher shallow water production and erosion rates together with loss of accommodation during highstands and high stillstands in the modelled sea level curves the most parsimonious modelling of the two ramp sequences comes from a relative sea level curve composed of a linear subsidence component superposed by 20 and 100 kyr cycles on a third order cycle the third order cycles and their timing do not correspond to those of the exxon curve

moment magnitude m w and local magnitude m l relationship for earthquakes in northeast india an attempt has been made to examine an empirical relationship between moment magnitude mw and local magnitude ml for the earthquakes in the northeast indian region some 364 earthquakes that were recorded during 1950 2009 are used in this study focal mechanism solutions of these earthquakes include 189 harvard cmt solutions mw 4 0 for the period 1976 2009 61 published solutions and 114 solutions obtained for the local earthquakes 2 0 ml 5 0 recorded by a 27 station permanent broadband network during 2001 2009 in the region the mw ml relationships in seven selected zones of the region are determined by linear regression analysis a significant variation in the mw ml relationship and its zone specific dependence are reported here it is found that mw is equivalent to ml with an average uncertainty of about 0 13 magnitude units a single relationship is however not adequate to scale the entire northeast indian region because of heterogeneous geologic and geotectonic environments where earthquakes occur due to collisions subduction and complex intra plate tectonics