joint inversion of regional and teleseismic earthquake waveforms a least squares joint inversion technique for regional and teleseismic waveforms is presented the mean square error between seismograms and synthetics is minimized using true amplitudes matching true amplitudes in modeling requires meaningful estimates of modeling uncertainties and of seismogram signal to noise ratios this also permits calculating linearized uncertainties on the solution based on accuracy and resolution we use a priori estimates of earthquake parameters to stabilize unresolved parameters and for comparison with a posteriori uncertainties we verify the technique on synthetic data and on the 1983 borah peak idaho m 7 3 earthquake we demonstrate the inversion on the august 1954 rainbow mountain nevada m 6 8 earthquake and find parameters consistent with previous studies

faulting processes of the 1956 san miguel baja california earthquake sequence body waveform modeling is used to determine the source processes of three large earthquakes magnitude 6 8 6 4 6 3 occurring between february 9 and 15 1956 along the san miguel fault in northern baja california mexico results of the modeling suggest that the mainshock on february 9 was responsible for the 20 km of surface faulting observed during the sequence although previous researchers have suggested a complex rupture history for the mainshock uncertainty estimates of source time function shape indicate single or double source models fit the observed waveforms equally well the february 15 aftershock however appears to have consisted of two events locations and focal mechanisms obtained for the three events suggest that the rupture process may have been controlled by cross faults to the main trace of the san miguel fault the good correlation between source parameter information and the surficial geology geometry of the san miguel fault zone demonstrates the usefulness of waveform modeling studies in unravelling the complexities of historic multi event earthquake sequences

short paper palaeocurrent evidence of a northern structural high to the welsh basin during the late llandovery palaeocurrents from the northernmost aberystwyth grits formation are consistently from the north which is at variance with the generally accepted southerly source area for the rest of the formation the anomalous directions appear to indicate a structural high and possible sediment source to the north

inversion of regional pn1 and surface wave data for source parameters of a borah peak aftershock we present results of a comparative source study on one of the largest aftershocks of the borah peak idaho earthquake series the mechanism of this event had been previously studied using first motions and teleseismic p wave data and we report here our results from analysis of regional pn1 and surface waves the pn1 waves gave an estimate of the source duration near 5 sec in agreement with the teleseismic p waves both the source duration and the effect of surface wave dispersion through laterally heterogeneous crustal structures must be accounted for in the moment tensor inversions of intermediate period surface waves all data sources both long period and short gave consistent source mechanisms and the long periods also yield three independent and consistent estimates of the seismic moment the results demonstrate the promise of formal source parameter retrieval techniques applied to regional data for the study of earthquakes with magnitudes below the magnitude threshold of teleseismic source determinations

experimental studies of gas escape and water escape structures mechanisms and morphologies abstract water escape and gas escape structures were generated in the laboratory to assess variations in deformational structures generated during these events particulate fluidization was observed to be the method by which grains were redistributed during water escape resulting structures of particulate fluidization comprised disrupted and downward deflected primary laminations and a massive appearing column of sand above the point source gas experiments with a low flow rate 6 167 10 6 m3 s allowed gas to disperse through fractures and only subtle deformation was achieved aggregative fluidization i e fluid movement through sediment as bubbles was the mechanism for grain displacement during gas escape with increased flow rate 7 67 10 5 m3 s aggregative fluidization occurred and particles were carried upward in the wake of the passing gas bubble aggregative fluidization resulted in broken upwards warping laminations and convoluted bedding experiments illustrate a significant morphological difference between water escape and gas escape water escape structures were bounded by downwards warping laminations consistent with water escape structures encountered in the rock record gas escape structures displayed upwards warping laminations and could represent a formation mechanism for convolute bedding

deflection of oceanic transform motion at a continental margin as deduced from waveform inversion of the 1939 accra ghana earthquake abstract waveform inversion of teleseismic p waves of the 1939 accra ghana earthquake m 6 5 suggests that the earthquake was composed of two events the smaller event m 6 1 occurring 9 5 s before the onset of the larger m 6 4 event the smaller event has a focal mechanism that suggests it occurred immediately north of the intersection of the akwapim and coastal boundary fault inversion results also indicate that the larger event could not have occurred on the reactivated akwapim fault system as suggested by previous researchers instead the larger event appears to have occurred along a strike slip fault that parallels the coastline of ghana these results along with the trend of historic earthquakes indicate that not all the motion along the romanche or chain fracture zones is being transmitted inland along the akwapim fault system but that some is being deflected tangentially along a fault that parallels the ghana coastline

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

the transition from strike slip to oblique subduction in southeastern alaska from seismological studies abstract body waveform modeling of 11 moderate to large earthquakes within southeastern alaska has been incorporated with earthquake relocations and the results of previous seismicity studies to examine the transition from strike slip to oblique subduction in southeastern alaska in the sitka region of extreme southeastern alaska earthquakes indicate seismic slip is parallel to the direction of motion between north america and the pacific plate as the plate margin begins to bend to the west near cross sound and encounters the southeastern edge of the yakutat block partitioning of seismic slip is evident both onshore and offshore although the largest earthquakes magnitude 6 0 in this region have slip parallel to plate motion most moderate sized events have slip vectors rotated clockwise from plate motion offshore the 1973 cross sound sequence indicates that the southern end of the transition zone is seismogenic with the pacific plate being thrust beneath the yakutat block while onshore strike slip faulting has occurred along the fairweather border ranges and denali faults in the st elias region thrust faulting is occurring along and above the plate interface moderate sized events in the st elias show a mix of slip vector orientations in the pamplona zone slip vectors of offshore earthquakes and deformation directions determined onshore from gps studies show a counter clockwise rotation relative to plate motion suggesting that a change in strain field occurs just west of the st elias region

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

seismicity of the denali totschunda fault zone in central alaska 1912 1988 and its relation to the 2002 denali fault earthquake sequence i have relocated m 4 5 earthquakes occurring between 1912 and 1988 and smaller magnitude earthquakes occurring between 1971 and 1988 when seismograph stations within central alaska began to increase to examine changes in seismicity preceding the 2002 denali fault earthquake sequence i have also determined focal mechanisms from first motion analysis and waveform modeling for many of the m 5 5 events limited phase and waveform information for the 1912 m s 7 2 earthquake are consistent with rupture at shallow depth on a right lateral strike slip fault although the limited data cannot distinguish between a range of possible mechanisms most other m 4 5 earthquakes occurring within the region prior to 1989 represent thrust reverse faulting or strike slip faulting adjacent to the denali fault system these results highlight the role thrust faulting plays in the deformation of the denali region stress analysis shows continuity in the direction of maximum compressive stress 1 between the western denali fault zone and the castle mountain fault upper cook inlet region suggesting the crust is behaving rigidly to transfer compression to the denali fault zone and faults located to the north

source processes of large m 6 5 earthquakes of the southeastern caribbean 1926 1960 we have conducted body waveform modeling studies of 13 historic earthquakes to provide a better understanding of the long term spatial and temporal pattern of seismicity and deformation within a region extending from barbuda lesser antilles to cumana venezuela our results suggest that shallow earthquakes 50 km deep along the south american caribbean plate margin reflect right lateral and extensional deformation intermediate depth events 100 km show left lateral strike slip motion beneath the paria peninsula of venezuela in the lesser antilles the 1960 barbuda and 1946 martinique earthquakes appear to be interplate thrust events however the greatest moment release in the region has occurred at intermediate depths as a mixture of normal and strike slip faulting generally along trends oblique to the arc the deformation rate estimated from the seismic moment release between 1926 and 1960 is only 1 to 10 of the estimated plate convergence rate for the region

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

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

contributions to the geology and geophysics of northwestern british columbia and southeastern alaska a symposium entitled l i l wansect northwestern in producing succinct yet data rich papers this special issue canadian cordillera was convened by robert anderson and contributions to the geology and geophysics of northwestern g h l at the l i l i i of canada british columbia and southeastern alaska is the result mineralogical association of canada gac mac annual general meeting held in vancouver in may 1990 an impetus for the symposium was the growing geological and geophysical database for the northwest cordillera the mature state of many of the geological and geophysical research projects being carried out by canadian and american university and federal and provincial geological survey groups was another important catalyst the symposium proved an excellent opportunity to bring researchers together and review the state of the art concerning the geology and geophysics of the insular coast and intermontane belts of northwestern british columbia and southeastern alaska as well a collection of papers reviewing the latest advances in the geology and geophysics of the northwest cordillera seemed long overdue not since publication of special volume 8 tectonic history and mineral deposits of the western cordillera by the canadian institute of mining and metallurgy in 1966 has there been a collection of topical papers by an international group of geoscientists encompassing recent geological mapping geophysical and geochemical results that contribute to a revised tectonic framework for the northwestern cordillera from the beginning symposium participants and john clague editor of the canadian journal of earth sciences cjes were enthusiastic about publication of the symposium proceedings in a special issue of cjes papers by h gabrielse and c a evenchick part of the gac mac special session 20 sedimentary and structural evolution of cordilleran interior basins were solicited as well the issue complements rather than supersedes the eagerly awaited cordilleran decade of north american geology dnag volumes e g gabrielse and yorath in press plaflcer and berg in press in providing a synopsis of new data and ideas ensuing from post dnag research to accommodate the anticipated number of contributions yet not monopolize the capacity of a multidisciplinary publication such as cjes authors were asked to limit submissions to 20 manuscript pages or less about two thirds the page limit normally allowed by cjes for articles through the judicious use of well crafted figures tables and data held separately in the depository of unpublished data canadian institute for scien

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

the tatshenshini shear zone new in southwestern yukon canada comparison with the coast shear zone in british columbia and southeastern alaska and implications regarding the shakwak suture the tatshenshini shear zone extends from klukshu lake in southwestern yukon southward to the yukon british columbia border deformation in the shear zone ranges from hundreds of meters to a few kilometers in width and is characterized by protomylonitic and mylonitic turbidites belonging to the dezadeash formation jurassic cretaceous that are overlain by protomylonitic granodiorite of the ruby range batholith late cretaceous tertiary the dezadeash formation ruby range batholith contact bedding and deformation and magmatic fabrics within the tatshenshini shear zone are all coplanar striking northwest southeast and dipping moderately to the northeast kinematic indicators from the dezadeash formation and ruby range batholith record a top to the southwest sense of shear collision of the insular superterrane with the intermontane superterrane by the mid cretaceous resulted in the eastward directed underplating of yukon tanana terrane equivalent rocks by the dezadeash formation and the formation of the tatshenshini shear zone the tatshenshini shear zone preceded and controlled emplacement of the ruby range batholith but magmatism ending 58 56 myr ago outlasted deformation the results of this work support the correlation of the ruby range batholith with the adjacent great tonalite sill in southeastern alaska it also suggests a linkage between the tatshenshini shear zone and the coast shear zone in southeastern alaska and along which the great tonalite sill was emplaced the tatshenshini shear zone and the coast shear zone represent the coda of long lived tectonism along the shakwak suture the accretionary boundary between the insular and intermontane superterranes

a reevaluation of the 1958 fairweather alaska earthquake sequence abstract i have relocated aftershocks performed waveform modeling and modeled induced coulomb failure stress to better determine rupture extent and controls on the rupture process of the 1958 fairweather earthquake sequence in southeastern alaska i estimate a fault rupture length range from 260 km source time function duration to 370 km aftershock zone length i estimate an average slip of 3 5 m from waveform modeling comparable to measured surface 2 3 5 m slip the largest pulses of moment release along the fairweather fault zone may have occurred near lituya bay where a huge landslide and subsequent water wave were produced and near dry bay the location of the mainshock s intensity center the region of high moment release near lituya bay correlates with a gravity high located northeast of the fault zone coulomb failure modeling suggests aftershocks were most likely to have occurred on northwest striking reverse faults these new source parameters indicate the 1958 mainshock was comparable in size to the 2002 m 7 9 denali fault earthquake and shared other similarities with the 2002 event

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

swept away by a turbidity current in mendocino submarine canyon california we present unique observations and measurements of a dilute turbidity current made with a remotely operated vehicle in 400 m water depth near the head of mendocino canyon california the flow had a two layer structure with a thin 0 5 to 30 m relatively dense 0 04 vol and fast up to 1 7 m s wedge shaped lower layer overlain by a thicker up to 89 m more dilute and slower current the fast moving lower layer lagged the slow moving dilute flow front by 14 min which we infer resulted from the interaction of two initial pulses the two layers were strongly coupled and the sharp interface between the layers was characterized by a wave like instability this is the first field scale data from a turbidity current to show i the complex dynamics of the head of a turbidity current and ii the presence of multiple layers within the same event

the 16 august 1931 valentine texas earthquake evidence for normal faulting in west texas the 1931 valentine texas earthquake occurred in a region near the transition from the southern basin and range rio grande rift physiographic province to the southern great plains province previous studies of this earthquake have presented focal mechanisms from first motion data supporting either pure normal or strike slip faulting with extension oriented in a southwest northeast direction nearly perpendicular to the physiographic boundary between the provinces this study presents the results of an inversion of regional and teleseismic body wave phases to determine earthquake source parameters results of the inversion suggest that the earthquake occurred at a depth of 10 km along a fault dipping 54 to the east with a strike of 10 to 20 and a rake of 155 the strike is similar to that of the southern segment of the nearby mayfield fault a fault that shows evidence for repeated movement during the quaternary seismic and geodetic information suggest unilateral rupture toward the south during the earthquake the t axis for the earthquake shows extension oriented in a northwest southeast direction a direction in agreement with the direction given by geologic stress indicators

seismotectonics and relative plate motions in the scotia sea region source parameter inversion of p and sh waveforms and amplitudes for 20 shallow earthquakes using a singular value decomposition technique provides important constraints on the tectonics and relative plate motions of the scotia sea region the derived focal mechanisms show both thrust and strike slip faulting along the north scotia ridge and normal and strike slip faulting along the south scotia ridge two thrust faulting mechanisms south of tierra del fuego indicate diffuse convergence of the antarctic plate along the western margin of the scotia plate earthquakes are consistent with active subduction and back arc spreading along the south shetland trench and bransfield strait the depths of two earthquakes 35 km and 55 km and one shallow thrust faulting event suggest continued subduction along the south shetland trench but the underthrusting is largely aseismic due to the young plate age and slow subduction rate the magnitude and depth of normal faulting earthquakes along bransfield strait and the south scotia ridge are suggestive of diffuse extension rather than typical organized mid ocean spreading which is generally associated with smaller and shallower earthquakes eight strike slip and thrust faulting events provide well constrained slip vectors showing scotia plate motion relative to the surrounding larger plates using a four plate model scotia sc south sandwich ss antarctica an and south america sa and a fixed sa an euler vector we inverted these data together with published centroid moment tensor slip vectors along the south sandwich trench and published marine magnetic data from the ss back arc spreading center to derive the first quantitative plate motion model for the scotia region the sc sa euler pole is located in the south atlantic and shows large latitudinal uncertainties the sc an pole is better constrained and located in the weddell sea these results predict left lateral strike slip motion with a component of compression along the north scotia ridge left lateral strike slip with a component of extension along the south scotia ridge and east west compression in drake passage although no rate data have been published connecting the scotia plate with the global plate system euler vector magnitudes are obtained through closure the results though poorly constrained suggest relative motion rates of 0 5 cm yr along the north scotia ridge and 1 0 cm yr along the south scotia ridge and in drake passage

ancient continental margin assemblage in the northern coast mountains southeast alaska and northwest canada geologic relations indicate that quartz rich metasedimentary rocks in the northern coast mountains separate strata to the east that belong to the stikine terrane from strata to the west of the alexander wrangellia and taku terranes the quartz rich rocks structurally overlie western terranes along a mid cretaceous thrust fault and are overlain structurally originally stratigraphically by strata of the stikine terrace these rocks are interpreted to be a continental margin assemblage that belongs to the yukon crystalline terrane u pb and nd isotopic data indicate that the metasedimentary rocks were shed from a source terrane consisting at least in part of proterozoic rocks

a re examination of the 1947 manix california earthquake sequence and comparison to other sequences within the mojave block the 10 april 1947 manix california earthquake m l 6 2 is the largest earthquake to have occurred in the mojave block in historic time left lateral movement was observed along the manix fault strike of n70 e following the earthquake however the large aftershocks of the sequence as located by richter and nordquist 1951 align themselves along a trend of n30 w this led richter 1958 to conclude that rupture during the main shock was along the trend of the aftershocks and that the surface faulting was a secondary feature in this study relocation of the larger aftershocks of the sequence verifies the previously observed trend of n30 w suggesting the aftershocks occurred along a fault conjugate to the manix fault body waveform modeling of the main shock indicates that it was composed of two subevents the location of the second subevent with respect to the first subevent suggests unilateral rupture to the southwest along the manix fault although the focal mechanisms of both events are consistent with either faulting along the manix fault or a conjugate fault both subevents occurred at relatively shallow depths 5 to 7 km a study of other recent earthquakes of m l 3 0 within the mojave block indicates that the majority of earthquakes in the region occur at shallow depths 7 km although the heat flow in the area is 10 to 20 mw m2 lower than in surrounding regions where deeper seismicity is present

convolute laminations a theoretical analysis example of a pennsylvanian sandstone abstract data from an outcropping laminated interval were collected and analyzed to test the applicability of a theoretical model describing instability of layered systems rayleigh taylor wave perturbations result at the interface between fluids of contrasting density viscosity and thickness in the special case where reverse density and viscosity interlaminations are developed the deformation response produces a single wave with predictable amplitudes wavelengths and amplification rates physical measurements from both the outcropping section and modern sediments suggest the usefulness of the model for the interpretation of convolute laminations internal characteristics of the stratigraphic interval and the developmental sequence of convoluted beds are used to document the developmental history of these structures

comparison of seismic and geodetic scalar moment rates across the basin and range province scalar moment rates estimated from a 146 year seismicity catalog agree within uncertainties with the deformation rate of the basin and range province determined by using space geodesy seismic moment rates have been estimated from a new catalog of earthquakes complete for m 5 the catalog was compiled from 15 preexisting catalogs supplemented by the review of 44 journal articles throughout the catalog compilation care was taken to obtain the moment magnitude or a reasonable and not inflated equivalent seventy six percent of the moment release occurred during 10 earthquakes of magnitude m w 6 79 the spatial distribution of earthquakes and their moment release matches the geodetic pattern of deformation all three are concentrated in a 200 km wide zone along the western boundary of the great basin with this zone widening to the north several techniques ultimately traceable to kostrov and brune are used to translate the geodetic strain rates into rates of seismic moment release the agreement between geodetic and seismic moment rate suggests that within uncertainties the rate of historic earthquakes within the basin and range province taken as a whole provides a reasonable estimate for the future rate of seismicity these results support the hypothesis that even a few years of detailed geodetic monitoring can provide a good constraint on earthquake occurrence rate estimates for large enough regions

provenance and pathways of late quaternary turbidites in the deep water agadir basin northwest african margin a series of individual turbidites correlated over distances 100 km are present in the recent fill of the agadir basin offshore northwest africa the aim here is to unravel multiple turbidite source areas and flow pathways and show how turbidite provenance studies contribute to interpretation of flow processes agadir basin turbidites are sourced from four main areas with the majority originating from the siliciclastic morocco shelf their sand mud distribution is strongly controlled by flow sediment volume with relatively low volume flows dying out within the agadir basin and large volume flows bypassing significant sediment volumes to basins further downslope two large volume volcaniclastic turbidites are attributed to a canary islands landslide source while several small mud dominated turbidites are interpreted to be locally sourced from hemipelagic draped seamounts e g turbidite ab10 finally turbidite ab1 1 ka is only present in the western agadir basin and is linked to recent re activation of the sahara slide headwall the muddy suspension clouds of three large volume flows all linked to large scale landslides have covered huge areas of seafloor and flowed along or even slightly upslope for long distances it is proposed that northeastwards flowing bottom currents have aided transport of these dilute flow fractions into and across the agadir basin

structural and geochronologic relations along the western flank of the coast mountains batholith stikine river to cape fanshaw central southeastern alaska abstract geologic and u pb geochronologic studies in central southeastern alaska provide constraints on the mid cretaceous to mid tertiary deformation west of the coast mountains batholith the ne dipping sumdum and fanshaw faults record the w directed emplacement of the ruth assemblage yukon tanana terrane and taku terrane over the subjacent gravina belt and alexander terrane ductile fabrics of the sumdum fanshaw fault system truncate early formed foliation and thrust faults in albian and older gravina belt strata u pb age data from syn and post tectonic plutons suggest that deformation was ongoing at 92 9 3 0 ma but had mostly ceased by 90 ma the sumdum fanshaw fault system marks the tectonic boundary between the alexander wrangellia terrane and inboard yukon tanana and stikine terranes and lies within a thrust belt that extends from southern alaska to northern washington mid cretaceous structures are truncated to the east by ne dipping ductile fabrics of the coast shear zone sheet like paleocene tonalites were emplaced into and deformed within the shear zone undeformed mid eocene dikes cross cut the tonalites kinematic relations in the coast shear zone suggest a complex displacement history that includes both east side up reverse and west side up normal shear the shear zone probably accommodated the collapse of overthickened crust developed during mid cretaceous shortening

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

sedimentological and geochemical evidence for multistage failure of volcanic island landslides a case study from icod landslide on north tenerife canary islands 1 volcanic island landslides can pose a significant geohazard through landslide generated tsunamis however a lack of direct observations means that factors influencing tsunamigenic potential of landslides remain poorly constrained the study of distal turbidites generated from past landslides can provide useful insights into key aspects of the landslide dynamics and emplacement process such as total event volume and whether landslides occurred as single or multiple events the northern flank of tenerife has undergone multiple landslide events the most recent being the icod landslide dated at 165 ka the icod landslide generated a turbidite with a deposit volume of 210 km3 covering 355 000 km2of seafloor off northwest africa the icod turbidite architecture displays a stacked sequence of seven normally graded sand and mud intervals named subunits sbu1 7 evidence from subunit bulk geochemistry volume basal grain size volcanic glass composition and sand mineralogy combined with petrophysical and geophysical data suggests that the subunit facies represents multistage retrogressive failure of the icod landslide the basal subunits sbu1 3 indicate that the first three stages of the landslide had a submarine component whereas the upper subunits sbu4 7 originated above sea level the presence of thin non bioturbated mud intervals between subunit sands suggests a likely time interval of at least several days between each stage of failure these results have important implications for tsunamigenesis from such landslides as multistage retrogressive failures separated by several days and with both a submarine and subaerial component will have markedly lower tsunamigenic potential than a single block failure

seismicity of the kodiak island region 1964 2001 and its relation to the 1964 great alaska earthquake earthquake relocation first motion and waveform modeling studies of m 5 5 earthquakes are used to examine the seismicity associated with the kodiak island region since the 1964 great alaska earthquake our results indicate that the most intense seismicity and moment release in this region occurred within the pacific plate and along the plate interface of the southwestern edge of the kodiak segment where slip during the 1964 mainshock was less than 5 m few earthquakes have occurred within the north american plate the intense seismicity correlates well with the northern edge of a zone of high plate interface coupling detected by global positioning system geodesy studies our studies suggest that during 1964 1974 faulting within the pacific plate was characterized by normal and normal oblique faulting however since 1974 reverse oblique faulting has become more common in the pacific plate seismic moment release has been over 6 times greater in the kodiak region than in the prince william sound cook inlet region during the past 37 years unlike the prince william sound region there is also a lack of down dip migration of seismicity since 1964 manuscript received 23 october 2001

earthquakes in the pamplona zone yakutat block south central alaska the pamplona zone is a region of complex deformation and moderate seismicity located within the yakutat block a region that has been relatively aseismic since a series of large m 7 8 earthquakes in 1899 in 1970 a sequence of moderate to large sized earthquakes occurred within the pamplona zone largest event of mw 6 7 together with a mw 6 1 event in 1958 these events are the only m 5 5 events known to have occurred in the pamplona region since 1900 thus these events give important information on internal deformational processes within the yakutat block waveform modeling of three earthquakes in april 1970 showed rupture complexity along low angle thrust faults focal depths indicate that two of the events occurred above the wrangell aleutian megathrust while the largest event may have occurred on the megathrust events in 1958 and february 1970 indicate that deformation within the western pamplona zone is occurring along high angle 60 faults with reverse oblique motion we believe the pamplona spur the easternmost part of the pamplona zone may have behaved as an asperity during the 1899 sequence the location of the spur may be influenced by a north south trending fault zone in the subducting pacific plate that appears to be responsible for the 1987 1992 gulf of alaska sequence occurring 50 to 200 km south of the pamplona zone

extensional tectonics in northern utah southern idaho u s a and the 1934 hansel valley sequence abstract the hansel valley pocatello valley region of northern utah and southern idaho is one of the most seismically active areas of the eastern basin and range study of the seismicity of this region provides insight into the crustal processes taking place near the physiographic boundary between the basin and range and the middle rocky mountains this study presents source parameters determined for the march 12 1934 hansel valley utah mainshock and largest aftershock these results are then integrated with studies of regional and local seismicity to determine better the tectonic processes currently active in the region

a fault controlled depositional model for the aberystwyth grits turbidite system the aberystwyth grits group was the first in a series of southerly supplied sandstone rich turbidite systems that invaded the welsh basin during the telychian stage late llandovery silurian structural and stratigraphical evidence indicates that deposition of the sand dominated parts of the system was largely restricted to the east by a zone of syndepositional faulting now marked by a major vergence divide downfaulting and reverse drag along the fault hangingwall created a bathymetric low which focused deposition of high density sand carrying turbidite flows and flow components allowing substantial thicknesses of sediment to accumulate in contrast low density mud rich turbidites were deposited over a wider area enhancing the topographic relief generated by uplift above the fault footwall to form a feature which restricted the spread of the coeval easterly supplied turbidites of the devil s bridge formation

the formation of convolute lamination in mud rich turbidites convolute lamination is a common fold structure within turbidite beds attributed to the deformation of sediment during or soon after deposition of the host bed despite the prevalence of this feature the formational processes are still not well understood possible mechanisms are investigated here through redescription and analysis of convolute lamination from the aberystwyth grits group silurian west wales uk in which convolute bedding was first defined internal bed structures have been studied in clean coastal exposures and on high resolution optical scans of cut surfaces convolute lamination occurs in intervals 2 10 cm thick spanning the top of the very fine sand bouma c division through the d division of interlaminated silt and clay observed growth geometries confirm that the structure formed during sedimentation of the host graded bed folds show a down flow asymmetry and doubly vergent diapiric geometries mushroom shaped structures grain size measurements from a modern turbidite icod bed 165 ka mor occan turbidite system suggest there is an optimal window of average grain size and mud content parameter space within which convolute lamination develops it is proposed that this window coincides with a bed density inversion created during deposition of a graded bed as clean sand with pore spaces infilled by water fines upwards into mud rich sand with pores infilled by an increasing proportion of mud porosity decreases and bulk bed density correspondingly increases the resulting unstable density gradient may lead to vertical buoyancy driven overturn manifest as growing folds subsequent amplification of the folds due to density differences and modification due to horizontal shear imposed by the depositing turbidity current may then occur the bed density gradient stabilises with deposition of low permeability mud suppressing further fold development quantitatively both rayleigh taylor instability and kelvin helmholtz instability are theoretically possible in forming folds in this context

source parameters of montana earthquakes 1925 1964 and tectonic deformation in the northern intermountain seismic belt waveform modeling and first motion analysis are used to determine the source parameters of six 5 8 m 6 8 earthquakes that occurred between 1925 and 1964 within the northern intermountain seismic belt of montana results of this study suggest that the 1925 clarkston earthquake occurred along an oblique normal fault with a trend similar to the southern end of the clarkston valley fault the two largest earthquakes of the 1935 helena sequence occurred along right lateral strike slip faults with trends similar to the bald butte and helena valley faults the 1947 virginia city earthquake occurred along a northwest southeast trending segment of the madison fault movement at depth was along a fault with strike similar to that of the 1959 hebgen lake main shock a reanalysis of a m 6 0 aftershock of the 1959 hebgen lake sequence suggests the earthquake occurred at a depth of 8 km along a fault that is not seen at the surface an m 5 8 earthquake in 1964 located about 10 km from the 1959 aftershock may have occurred along steeply dipping fault planes 48 to 80 at depths of 8 to 14 km most events could be modeled as simple ruptures

geometry evolution and tectonic framework of the skeena fold belt north central british columbia the intermontane belt of the canadian cordillera has long been viewed as a passive relatively rigid block between two metamorphic plutonic belts the coast plutonic complex and the omineca belt however the skeena fold belt which spans most of the width of the northern intermontane belt exhibits shortening comparable with that in the rocky mountain fold and thrust belt the skeena fold belt has many features of thin skinned fold and thrust belts such as thrust faults which sole into a detachment a wide variety of structural styles which depend on rock type a foreland basin which was cannibalized by continued deformation a frontal triangle zone and a hinterland of metamorphic and plutonic rocks coast plutonic complex the skeena fold belt thus is comparable with the rocky mountain fold and thrust belt but rather than deforming a continental terrace wedge it developed in a terrane stikinia which had accreted to north america in the early mesozoic and in jurassic and cretaceous clastic successions bowser lake and sustut groups which overlie stikinia structural and stratigraphic relationships show that the earliest deformation occurred between oxfordian and albian time and that the last folds developed in latest cretaceous or early tertiary time as much as 160 km of northeastward shortening in the skeena fold belt was broadly contemporaneous with crustal thickening in the coast plutonic complex and omineca belt with dextral strike slip faulting east of the skeena fold belt and with shortening in the rocky mountain fold and thrust belt therefore between latest jurassic and early tertiary times horizontal shortening occured across most of the width of the northern canadian cordillera concurrent shortening across the cordillera suggests that a common detachment or detachments fed all of these zones as far east as the rocky mountain fold and thrust belt

source parameters of large historical 1918 1962 earthquakes south island new zealand we have studied 18 earthquakes of m w 5 5 within the north island new zealand region to determine fault parameters for earthquake hazards and regional tectonic studies since most large m w 6 5 earthquakes in the north island occurred prior to 1961 these events provide important information to supplement studies of more recent seismicity our results indicate that no large plate interface earthquakes have occurred in the central and southern north island for the past 80 years although six strike slip earthquakes of m w 6 8 occurred within the australian upper plate during an extremely active 25 year period that began in 1917 only the m w 7 2 strike slip events were associated with surface faulting indicating the difficulties that may arise in attempting to identify active faults within this region two earthquakes m w 6 9 7 1 off the northeastern north island in 1947 appear to have occurred along the plate interface and were associated with local tsunamis having runup heights of up to 10 m two m w 6 8 events also occurred within the pacific lower plate highlighting the hazards related to intraslab events slip vectors for the earthquakes studied suggest that the majority of transcurrent motion along the plate margin is accommodated within the australian plate similar to the results obtained from studies of more recent smaller earthquakes pure thrusting occurs along the plate interface and t axes of intraslab events indicate downdip tension in the pacific plate

a study of historic earthquakes of the prince william sound alaska region we have investigated the character of seismicity that occurred in the prince william sound cook inlet region during 40 years prior to the 1964 great alaskan earthquake we have relocated all events of magnitude 5 5 focal mechanisms have been determined from body waveform modeling and first motion analysis for the larger generally magnitude 6 3 events the results suggest a number of similarities and differences between pre and post 1964 mainshock seismicity similarities include the persistence of normal faulting at depths of 40 to 60 km within the subducted slab in both the tazlina glacier and columbia bay regions north of prince william sound and among deeper events within northern cook inlet differences include a higher level of shallow seismicity 40 km depth in the upper cook inlet region and north of cook inlet prior to 1964 higher levels of seismicity within the subducting plate in the south central and eastern kenai peninsula prior to 1964 and a lower level of seismicity in the offshore prince william sound region prior to 1964 much of the lower plate seismicity for the past 70 years appears to cluster immediately downdip of the 1964 asperity two of the events in this study caused notable damage modified mercalli intensity vii to viii in the anchorage area the first in 1933 m w 6 9 appears to have occurred at 9 km depth along a strike slip fault within northern cook inlet the second in 1954 m w 6 7 occurred within the subducting plate at 60 km depth beneath the northern kenai peninsula analysis of these events as well as smaller events we have studied will greatly improve models of seismic hazard for the anchorage region manuscript received 18 september 2000

the 1911 m 6 6 calaveras earthquake source parameters and the role of static viscoelastic and dynamic coulomb stress changes imparted by the 1906 san francisco earthquake the occurrence of a right lateral strike slip earthquake in 1911 is inconsistent with the calculated graphic 1 static stress decrease imparted by the 1906 rupture at that location on the calaveras fault and 5 yr of calculated post 1906 viscoelastic rebound does little to reload the fault we have used all available first motion body wave and surface wave data to explore possible focal mechanisms for the 1911 earthquake we find that the event was most likely a right lateral strike slip event on the calaveras fault larger than but otherwise resembling the 1984 m w 6 1 morgan hill earthquake in roughly the same location unfortunately we could recover no unambiguous surface fault offset or geodetic strain data to corroborate the seismic analysis despite an exhaustive archival search we calculated the static and dynamic coulomb stress changes for three 1906 source models to understand stress transfer to the 1911 site in contrast to the static stress shadow the peak dynamic coulomb stress imparted by the 1906 rupture promoted failure at the site of the 1911 earthquake by 1 4 5 8 bar perhaps because the sample is small and the aftershocks are poorly located we find no correlation of 1906 aftershock frequency or magnitude with the peak dynamic stress although all aftershocks sustained a calculated dynamic stress of 3 bar just 20 km to the south of the 1911 epicenter we find that surface creep of the calaveras fault at hollister paused for 17 yr after 1906 about the expected delay for the calculated static stress drop imparted by the 1906 earthquake when san andreas fault postseismic creep and viscoelastic relaxation are included thus the 1911 earthquake may have been promoted by the transient dynamic stresses while calaveras fault creep 20 km to the south appears to have been inhibited by the static stress changes 1 embed inline graphic 1 gif

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

the spatial and temporal distribution of grain size breaks in turbidites grain size breaks are surfaces where abrupt changes in grain size occur vertically within deposits grain size breaks are common features in turbidites around the world including ancient and modern systems despite their widespread occurrence grain size breaks have been regarded as exceptional and not included within idealized models of turbidity current deposition this study uses ca 100 shallow sediment cores from the moroccan turbidite system to map out five turbidite beds for distances in excess of 2000 km the vertical and spatial distributions of grain size breaks within these beds are examined five different types of grain size break are found type i in proximal areas between coarse sand and finer grained structureless sand type ii in proximal areas between inversely graded sand overlain by finer sand type iii in proximal areas between sand overlain by ripple cross laminated finer sand type iv throughout the system between clean sand and mud and type v in distal areas between mud rich debrite sand and mud this article interprets types i and v as being generated by sharp vertical concentration boundaries controlled by sediment and clay concentrations within the flows whilst types ii and iii are interpreted as products of spatial temporal fluctuations in flow capacity type iv are interpreted as the product of fluid mud layers which hinder the settling of non cohesive grains and bypasses them down slope decelerating suspensions with sufficient clay will always form cohesive layers near to bed promoting the generation of type iv grain size breaks this may explain why type iv grain size breaks are widespread in all five turbidites examined and are commonplace within turbidite sequences studied elsewhere therefore type iv grain size breaks should be understood as the norm not the exception and regarded as a typical feature within turbidite beds

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

turbidite depositional architecture across three interconnected deep water basins on the north west african margin the moroccan turbidite system mts on the north west african margin extends 1500 km from the head of the agadir canyon to the madeira abyssal plain making it one of the longest turbidite systems in the world the mts consists of three interconnected deep water basins the seine abyssal plain sap the agadir basin and the madeira abyssal plain map connected by a network of distributary channels excellent core control has enabled individual turbidites to be correlated between all three basins giving a detailed insight into the turbidite depositional architecture of a system with multiple source areas and complex morphology large volume 100 km3 turbidites sourced from the morocco shelf show a relatively simple architecture in the madeira and seine abyssal plains sandy bases form distinct lobes or wedges that thin rapidly away from the basin margin and are overlain by ponded basin wide muds however in the agadir basin the turbidite fill is more complex owing to a combination of multiple source areas and large variations in turbidite volume a single very large turbidity current 200 300 km3 of sediment deposited most of its sandy load within the agadir basin but still had sufficient energy to carry most of the mud fraction 500 km further downslope to the map large turbidity currents 100 150 km3 of sediment deposit most of their sand and mud fraction within the agadir basin but also transport some of their load westwards to the map small turbidity currents 35 km3 of sediment are wholly confined within the agadir basin and their deposits pinch out on the basin floor turbidity currents flowing beyond the agadir basin pass through a large distributary channel system individual turbidites correlated across this channel system show major variations in the mineralogy of the sand fraction whereas the geochemistry and micropalaeontology of the mud fraction remain very similar this is interpreted as evidence for separation of the flow with a sand rich erosive basal layer confined within the channel system overlain by an unconfined layer of suspended mud large volume turbidites within the mts were deposited at oxygen isotope stage boundaries during periods of rapid sea level change and do not appear to be specifically connected to sea level lowstands or highstands this contrasts with the classic fan model which suggests that most turbidites are deposited during lowstands of sea level in addition the three largest turbidites on the map were deposited during the largest fluctuations in sea level suggesting a link between the volume of sediment input and the magnitude of sea level change

the seismicity seismotectonics and earthquake hazards of libya with detailed analysis of the 1935 april 19 m 7 1 earthquake sequence summary we have investigated the seismicity of libya in order to understand better the earthquake hazards the tectonics of the region and the present day evolution of the sirt basin we first relocated all events occurring between 1931 and 1988 using a bootstrap location technique we then determined focal mechanisms from firstmotion data finally we used waveform modelling techniques to determine source parameters for the 1935 main shock and its two largest aftershocks relocation of the 1930s events are in some cases significantly different from those given by the international seismological summary iss the first motion results suggest a combination of strike slip and normal faulting for the 1935 and 1939 sequences the waveform modelling results of the 1935 mainshock suggest a strike slip mechanism with one fault plane similar to the strike of the eastern edge of the hun graben about 5 hr after the mainshock an aftershock mb 6 0 occurred about 40 km to the south which was followed about 9 hr later by another aftershock mb 6 4 in the same area waveform modelling results for this earthquake sequence suggest focal depths ranged from 15 21km with rupture lengths of 14 16 km an average displacement of 1 8 m is estimated for the mainshock but no surface rupture has been noted for the event in the vicinity of the hun graben area the number of large earthquakes that have been reported through history is an indication that the area is seismically active most of the activity appears to be concentrated along the eastern margin of the nw se trending hun graben the focal mechanisms suggest that the maximum compressive stress in northwestern libya is oriented wnw in the north eastern part of the country the stress direction changes to a more ne sw orientation as evidenced by the 1963 february 21 al marj and the 1967 al jabal al akhdar mainshocks

eye and sheath folds in turbidite convolute lamination aberystwyth grits group wales eye and sheath folds are described from the turbidites of the aberystwyth group in the silurian of west wales they have been studied at outcrop and on high resolution optical scans of cut surfaces the folds are not tectonic in origin they occur as part of the convolute laminated interval of each sand mud turbidite bed the thickness of this interval is most commonly between 20 and 100 mm lamination patterns confirm previous interpretations that convolute lamination nucleated on ripples and grew during continued sedimentation of the bed the folds amplified vertically and were sheared horizontally by continuing turbidity flow but only to average values of about 1 the strongly curvilinear fold hinges are due not to high shear strains but to nucleation on sinuous or linguoid ripples the aberystwyth group structures provide a warning that not all eye folds in sedimentary or metasedimentary rocks should be interpreted as sections through high shear strain sheath folds highlights eye folds occur in turbidite convolute lamination viewed down the palaeoflow direction the convolutions formed during bed deposition and are overturned down flow by current shear the eye folds are sections through non cylindrical sheath folds due to this shear average shear strains are less than 1 0 lower than generally necessary to generate sheath folds instead sheath folds nucleate on already sinuous current ripples lower in the turbidite bed

seismicity of the prince william sound region for over thirty years following the 1964 great alaskan earthquake in this paper we present results of body wave form modeling of 19 earthquakes generally m b 5 7 occurring from 1964 to 1983 in the vicinity and down dip of the large asperity within the prince william sound region that ruptured in 1964 these data are supplemented with source parameters from studies of more recent post 1980 events our results suggest that moderate earthquakes which occurred in the region between 1964 and 1984 were predominantly located in the vicinity of the prince william sound asperity and could be assigned to two groups the first group consists of events occurring above the plate interface within prince william sound along reverse faults or low angle thrusts the second group occurs at 35 to 60 km depth in the region north of prince william sound and represents normal to normal oblique faulting within the subducted pacific crust or upper mantle these earthquakes occur below the northern edge of the 1964 asperity in a region where the subducting plate undergoes a rapid change in strike and dip a third group of events occurs in cook inlet well down dip of the 1964 asperity and below the plate interface these events exhibit a variety of mechanisms and many at depths of 50 to 70 km may be associated with complexities in the shape of the downgoing slab most of the cook inlet events occurred after 1984 whereas a few events of similar magnitude have occurred in the vicinity of the prince william sound asperity since 1984

relocation and waveform modeling of the 1924 orotina costa rica earthquake ms 7 0 abstract we have determined the location and focal mechanism for the 1924 orotina earthquake using two different relocation algorithms developed for the analysis of historic earthquakes and forward waveform modeling of teleseismic body waves our relocation results suggest that the 1924 earthquake occurred 50 km southeast of orotina near the pacific coast the heavy damage reported in the orotina region coupled with a low population density to the southeast had led previous researchers to believe that the earthquake occurred near orotina possibly on the tarcoles or bijagual faults our waveform modeling results indicate rupture on a thrust fault at a depth 25 5 km near the plate interface with mw 6 4 6 7 these are inconsistent with slip on any mapped surface faults located near orotina and with the mechanism of the nearby 2004 mw 6 4 damas earthquake that indicates transtensional deformation in the upper crust this suggests that the 1924 event may be one of a sequence of events 1924 1990 1999 generated by subduction of the central costa rica seamount belt

an experimental investigation of sand mud suspension settling behaviour implications for bimodal mud contents of submarine flow deposits the settling behaviour of particulate suspensions and their deposits has been documented using a series of settling tube experiments suspensions comprised saline solution and noncohesive glass ballotini sand of particle size 35 5 m

faulting within the eastern baikal rift as characterized by earthquake studies earthquake relocations focal mechanism determinations waveform modeling and stress analyses using focal mechanism information are used to examine the faulting processes within the western baikal rift 95 to 108 5 results of the study show that high angle dip 70 faulting is most likely to occur in the more youthful parts of the rift and is most likely to be associated with m 4 5 events like the eastern rift nearly all earthquakes occurred on faults dipping 30 suggesting that in no part of the rift is significant deformation occurring on low angle structures focal mechanism information does not indicate there is a sharp boundary to the western rift as observed in the eastern rift less normal faulting rakes 60 to 120 occurs in the western rift than the eastern rift waveform modeling of the two largest earthquakes 1950 mondy and 1959 srednebaikal in the western rift gives focal depths of 10 to 15 km the 1959 event appears to have occurred along the eastern boundary fault on lake baikal just to the north of proval bay a feature created a m 7 1 earthquake in 1862 the 1950 event may have occurred along the southern boundary fault of the tunka depression stress orientation information indicates a near horizontal nw se to wnw ese striking 3 in the eastern part of the western rift

source characteristics of earthquakes along the southern san jacinto and imperial fault zones 1937 to 1954 abstract body waveform inversion techniques are used to study the source parameters of four earthquakes occurring between 1937 and 1954 along the southern san jacinto and imperial faults 1937 buck ridge 1940 imperial valley 1942 borrego mountain and 1954 salada wash events all earthquakes had simple rupture histories with the exception of the 1940 imperial valley main shock which consisted of at least four subevents whose relative locations indicate unilateral rupture toward the southeast earthquakes in regions of high heat flow 80 mw m 2 had focal depths near the base of the seismogenic zone 8 to 10 km the 1937 buck ridge earthquake located in a region of lower heat flow however appears to have occurred at a shallow 3 2 km depth the location mechanism and aftershock distribution for the 1942 borrego mountain earthquake suggest it could have occurred along the split mountain fault a recently identified northeast trending cross fault located between the elsinore and coyote creek faults or along an unnamed fault that parallels the trend of the coyote creek fault moment and rupture length estimates obtained from this study agree well with estimates obtained in previous studies that used different data sets

contrasts between source parameters of m 5 5 earthquakes in northern baja california and southern california summary earthquake source processes are determined for four historic events that occurred in baja california between 1915 and 1954 these results are combined with previous studies of recent and historic seismicity to compare earthquake processes along the san jacinto imperial cerro prieto and northern baja fault systems of southern california and northern mexico observed regional differences in rupture complexity fault rupture lengths and aftershock foreshock activity appear to be related to variations in heat flow and total fault offset there appear to be no systematic variations in stress drop as measured from far field observations between earthquakes along the imperial cerro prieto fault zone and those within the peninsular ranges of northern baja california slip rates estimated from historical seismicity between 1915 and 1992 fall 1 5 cm yr 1 short of the estimated relative plate motion between the pacific plate and north america for this region

modeling the pnl waveforms of the fairview peak dixie valley nevada u s a earthquake sequence 1954 1959 abstract the 1954 1959 fairview peak dixie valley earthquakes produced one of the most complex and extensive sequences of faulting in the intermountain u s during historic time study of this sequence provides insight into the processes of crustal extension that are currently taking place in the basin and range province we have modeled the pnl waveforms of earthquakes of this sequence to 1 determine the source parameters for smaller m m 6 3 with the results of teleseismic studies 3 determine whether strainmeter records of pn1 waveforms can also be used to estimate source parameters source parameters obtained for the larger events from pn1 modeling are in agreement with previous studies source parameters estimated from strainmeter records also agree well with results of teleseismic analysis suggesting the pn1 strainmeter records may provide a useful addition to other studies of large earthquakes in the western u s focal mechanisms obtained from modeling the smaller earthquakes varied 10 20 in strike and rake from fault plane solutions determined from first motion studies the pn1 data support the results of previous studies that suggest the earthquakes of this sequence occurred along high angle faults dip of 40 70 with significant components of right lateral strike slip motion rakes of 135 to 145

historical seismicity 1918 1964 of the kodiak island region i have relocated 35 earthquakes and conducted waveform modeling studies of 12 events located primarily within the kodiak portion of the 1964 great alaska earthquake rupture zone and the northeasternmost portion of the 1938 semidi earthquake rupture zone these results show that there is considerable similarity between earthquakes occurring before the 1964 mainshock pre 1964 mainshock seismicity and after the 1964 mainshock post 1964 mainshock seismicity persistent seismicity has occurred for the past 85 years at the southwestern end of the 1964 rupture zone a region where global positioning system gps geodesy studies indicate the plate interface is currently locked earthquakes also occurred frequently within the kennedy entrance region where the transition between the kodiak and kenai block of the subducting pacific plate occurs the seismic moment rate for post 1964 mainshock seismicity is about two times larger than for premainshock seismicity this is in contrast to the prince william sound portion of the 1964 rupture zone where post 1964 mainshock moment rates are orders of magnitude lower than pre 1964 mainshock rates and the pattern of seismicity has changed considerably with time these observations reinforce previous studies that indicate the behavior of plate subduction beneath the kodiak island region is much different from that beneath the prince william sound region

historic earthquakes 1918 to 1923 and an assessment of source parameters along the san jacinto fault system body waveform modeling is used to determine the source parameters of two earthquakes that occurred along the northern san jacinto fault system in 1918 and 1923 the 1918 earthquake parameters are consistent with a 20 to 25 km rupture along the claremont fault at a depth of 7 5 km limited data for the 1923 event are more consistent with rupture on the san jacinto fault than rupture along the san andreas fault or a buried cross fault although the greatest damage associated with the earthquake occurred closer to the san andreas fault using the results of this study and previous studies of historic earthquakes along the southern san jacinto fault the relationships between rupture length and magnitude focal depth and heat flow and other parameters are examined in an effort to estimate the source properties of future events that are expected along currently quiescent portions of the fault zone one important observation is that rupture lengths along the san jacinto fault are shorter for an equivalent moment magnitude than those along the imperial valley mexicali fault system the higher heat flow of the imperial valley region may be responsible for this difference

multi objective analysis of body and surface waves from the market rasen uk earthquake summary the 2008 february 27 market rasen uk earthquake mb 4 5 is used to show how earthquake source parameters can be estimated using a multi objective optimization approach to the joint inversion of teleseismic body wave and regional surface wave observations to estimate the source depth short period teleseismic seismograms are interpreted in terms of p and the depth phases pp and sp using the f statistic and its associated probability theory results of this analysis are inconclusive as two possible source depths are identified to identify our preferred depth a method of estimating source depth and mechanism by modelling surface wave amplitude spectra is applied to data recorded at regional distances a source depth of 22 km is found to be consistent with the observed body and surface waves upper and lower amplitude bounds and polarities are then placed on the phases interpreted as p pp and sp for a source depth of 22 km the gaussian relative amplitude method is used to calculate a likelihood for all possible orientations of the double couple source a multi objective optimization approach can then used to compare these likelihoods with calculated misfits between observed and synthetic surface wave amplitude spectra for all orientations of the double couple source our preferred focal mechanism s 205 50 and 15 is found by normalizing and summing both misfits to find the focal mechanism with the lowest combined misfit synthetic body wave seismograms surface wave amplitude spectra and seismograms are in good agreement with the observed data for our preferred focal mechanism and depth

the seismicity of chihuahua mexico and the 1928 parral earthquake abstract studies of the seismicity of chihuahua mexico and determination of source parameters for the 1928 parral earthquake suggest that the eastern portion of chihuahua is currently undergoing extension the parral earthquake has similar source parameters to other southern basin and range rio grande rift events the focal mechanism for the parral event however indicates northeast southwest oriented extension a direction that is parallel to neither the east west oriented extension seen near the us mexican bordern nor to the physiographic province boundary between the sierra madre occidental and the southern basin and range where the earthquake occurred intensity information for the parral event and the 1931 valentine texas earthquake suggests that attenuation within the region lies somewhere between relationships developed for the eastern and cordilleran portions of the usa

an enigmatic earthquake in the continental mantle lithosphere of stable north america abstract the existence of earthquakes within continental lithospheric mantle remains a highly controversial topic here we present a detailed set of seismological analyses confirming the occurrence of a mantle earthquake beneath the wind river range of central wyoming combining regional waveform inversion with the analysis of the delay and relative amplitudes of teleseismically observed depth phases we demonstrate that the 2013 wind river earthquake a m w 4 7 highly oblique thrust faulting event occurred at 75 8 km well beneath the base of the crust the magnitude mechanism and location of this earthquake suggest that it represents simple brittle failure at relatively high temperatures within the mantle lithosphere as a result of tectonic rather than magmatic processes

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in