late holocene strike slip offset of a subsurface channel interpreted from three dimensional seismic data eastern offshore trinidad a right lateral strike slip fault offset of a shallowly buried fluvial paleochannel is interpreted from three dimensional 3 d seismic data in the eastern offshore area of trinidad the fault represents the eastern offshore continuation of the main south america caribbean plate boundary zone in trinidad the central range fault zone previous global positioning system based geodetic studies and trenching have shown that the 50 km long on land segment of the central range fault zone accommodates a significant part of the present day interplate motion the 3 d seismic data shown here reveal that the 60 km long offshore continuation of the central range fault zone forms a prominent seafloor lineament and dextrally offsets a shallowly buried 83 m below sea level late quaternary fluvial channel by 322 506 m based on the eustatic sea level curve we infer that the channel began to be incised during the beginning of the last glacial maximum ca 30 ka and was subsequently offset by the central range fault zone using the offset amounts and our inferred age for the filled channel we can estimate a long term slip along the fault of 17 19 mm yr for the central range fault zone because no documented earthquake has occurred on the central range since a d 1800 as much as 3 7 m of elastic strain may have accumulated on the central range fault zone that could be released by a future magnitude m7 5 earthquake

cenozoic collision of the lesser antilles arc and continental south america and the origin of the el pilar fault it is proposed that the cenozoic tectonic record of the southern lesser antilles arc and northeastern continental south america can be explained by ongoing right oblique collision between the arc and continent the collision has proceeded by the transport of the leading edge of the arc across the slope and outer shelf of a former north facing passive margin of the south american continent the overriding began in the study region near the gulf of cariaco in eastern venezuela in late eocene or oligocene time and has migrated with a generally se vector suturing has occurred between the arc and continent after the attainment of a critical distance of overlap today s point of suturing lies in the paria peninsula east of there overriding continues major tectonic elements engaged in or created by the collision are the southern lesser antilles magmatic arc forearc basin the araya tobago terrane a south american foreland thrust and fold belt and a foreland basin the araya tobago terrane is thought to consist of sediments of south american provenance that were accreted to the lesser antilles forearc during its transit of an ocean basin and the continental slope and outer shelf the emplacement of the magmatic arc and the araya tobago terrane caused tectonic imbrication of shelf strata to propagate ahead of the arc front as a foreland thrust and fold belt tectonic loading of the shelf also caused subsidence of a major foreland basin on the continentward side of the thrust belt it is proposed the el pilar fault exists between the gulf of cariaco and the paria peninsula as an active right slip fault but not east of paria it is not a throughgoing transform fault between the south american and caribbean plates the el pilar fault exists where the overlapping arc and the continent are sutured and takes up a suture parallel component of convergence between arc and continent the eastern tip of the fault propagates east with the point of suturing reconstructions of the cenozoic collision of the lesser antilles arc and the south american continent suggest that the arc lay somewhat north and west of its present position in the eocene this conclusion differs from that of plate reconstructions that assume that the arc was the leading edge of a caribbean plate that has moved east from pacific longitudes since the eocene

evolution of southern caribbean plate boundary vicinity of trinidad and tobago two processes oblique collision of an island arc and strike slip motion parallel to the south american coast have been suggested as dominant in the tectonic evolution of the southeastern corner of the caribbean field work in the el pilar fault zone of trinidad and interpretation of offshore seismic data lead us to conclude that the dominant process was strike slip motion on five or more major fault systems within a 250 km wide east west trending plate boundary zone extending north to south from grenada to the mouth of the orinoco river during the last 30 m y movements in this fault zone 1 diverted the orinoco river eastward 2 juxtaposed blocks with diverse stratigraphic characteristics and 3 generated secondary extensional compressional and strike slip str ctures including anticlines of northeast to north northeast trend of which the tobago arch the central range of trinidad and the deformed mud diapirs off the southeastern coast of trinidad are the most prominent

late quaternary transpressional earthquakes on a long lived intraplate fault a case study of the southern yangsan fault se korea abstract the nne ssw striking yangsan fault in southeastern korea has been regarded as one of the most prominent seismogenic structures in the korean peninsula on the basis of instrumental and historical seismicity and paleoseismic records along the fault zone its seismic behavior is however still uncertain due to long recurrence intervals of strong earthquakes and insufficient historical and geologic records we conducted a detailed paleoseismic investigation including an 8 m deep excavation in order to understand recent earthquake faulting events along the southern yangsan fault our observations indicate that at least two and possibly four dominantly strike slip surface faulting events have occurred along a subsidiary fault in the eastern boundary of the fault valley since the late pleistocene stratigraphic features and osl ages of the stratigraphy exposed in the trenches indicate that the most recent rupture s occurred after 29 2 1 4 ka and the timing of earlier ruptures are constrained to between 70 0 3 7 ka and 29 2 1 4 ka using a contact of the oldest dated unit that has at least 7 5 m of vertical separation we calculate a minimum vertical slip rate during the late quaternary of 0 11 mm yr the minimum horizontal slip rate is presumed to be two times that of the vertical slip rate based on striations observed on clasts next to the fault core we also propose that the late quaternary earthquake faulting kinematics along the yangsan fault expressed as contractional dextral slip with east side up geometry is strongly dependent on a pre existing fault zone architecture with a strike of n10 20 e that dips to the east and the direction of neotectonic maximum horizontal stress ene wsw to e w

gps estimate of relative motion between the caribbean and south american plates and geologic implications for trinidad and venezuela global positioning system gps data from eight sites on the caribbean plate and five sites on the south american plate were inverted to derive an angular velocity vector describing present day relative plate motion both the caribbean and south american velocity data fit rigid plate models to within 1 2 mm yr the gps velocity uncertainty the caribbean plate moves approximately due east relative to south america at a rate of 20 mm yr along most of the plate boundary significantly faster than the nuvel 1a model prediction but with similar azimuth pure wrenching is concentrated along the approximately east striking seismic el pilar fault in venezuela in contrast transpression occurs along the 068 trending central range warm springs fault in trinidad which is aseismic possibly locked and oblique to local plate motion

aftershock sequence and statistics of the 2017 mw 5 5 pohang south korea earthquake implications of fault heterogeneity and postseismic relaxation

statistical tests of additional plate boundaries from plate motion inversions we have investigated the application of the f ratio test a standard statistical technique to the results of relative plate motion inversions the method tests whether the improvement in fit of the model to the data resulting from the addition of another plate to the model is greater than that expected purely by chance this approach appears to be useful in determining whether additional plate boundaries are justified we confirm previous results favoring separate north american and south american plates with a boundary located between 30 n and the equator using chase s global relative motion data we show that in addition to separate west african and somalian plates separate west indian and australian plates with a best fitting boundary between 70 e and 90 e can be resolved these results are generally consistent with the observation that the indian plate s internal deformation extends somewhat westward of the ninetyeast ridge the relative motion pole is similar to minster and jordan s and predicts the nw se compression observed in earthquake mechanisms near the ninetyeast ridge

long term monitoring of creep rate along the hayward fault and evidence for a lasting creep response to 1989 loma prieta earthquake we present results from over 30 yr of precise surveys of creep along the hayward fault along most of the fault spatial variability in long term creep rates is well determined by these data and can help constrain 3d models of the depth of the creeping zone however creep at the south end of the fault stopped completely for more than 6 years after the m7 1989 loma prieta earthquake lpeq perhaps delayed by stress drop imposed by this event with a decade of detailed data before lpeq and a decade after it we report that creep response to that event does indeed indicate the expected deficit in creep

current block motions and strain accumulation on active faults in the caribbean the caribbean plate and its boundaries with north and south america marked by subduction and large intra arc strike slip faults are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes here we use most of the available campaign and continuous gps measurements in the caribbean to derive a regional velocity field expressed in a consistent reference frame we use this velocity field as input to a kinematic model where surface velocities results from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain while allowing for partial locking along the lesser antilles puerto rico and hispaniola subduction we test various block geometries guided by previous regional kinematic models and geological information on active faults our findings refine a number of previously established results in particular slip rates on the strike slip faults systems bounding the caribbean plate to the north and south and the kinematics of the gonave microplate our much improved gps velocity field in the lesser antilles compared to previous studies does not require the existence of a distinct northern lesser antilles block and excludes more than 3 mm yr of strain accumulation on the lesser antilles puerto rico subduction plate interface which appears essentially uncoupled the transition from a coupled to an uncoupled subduction coincides with a transition in the long term geological behavior of the caribbean plate margin from compressional hispaniola to extensional puerto rico and lesser antilles a characteristics shared with several other subduction systems

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

combined oxygen isotope compositional studies of some granitoids from the grenville province of ontario canada implications for source regions oxygen isotopic compositions of whole rocks and coexisting quartz feldspar pairs have been determined for nine pre and syn to late kinematic granitoid plutons in the grenville province of ontario these new data demonstrate that granitoid rocks algonquin mulock in migmatite terrain of the ontario gneiss segment possess normal 18o values 9 0 in accord with previous results in the algonquin sodic suite a gross covariance of 18o with compositional indices is present from 6 4 sio2 50 5 wt gabbro to 8 7 sio2 72 wt trondhjemite resulting from combined assimilation fractional crystallization mafic members of the sodic suite are 18o enriched overall 5 8 7 9 relative to fresh tholeiites 5 7 0 3 implicating some 18o contamination of the protolith the dispersion of 18o values in the

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

stress state and its influence on drilling performance in the brighton marine field trinidad abstract characterisation of stress state is fundamental to geomechanical descriptions for engineering purposes in high stress plate boundary environments leak off test results may be rare and the structural setting may involve a mixture of structural styles and implied faulting regimes in shale dominated successions pore pressure may be high and the pressure determinations sparsely distributed at the onset of field rehabilitation these restrictions may be compounded by a complete lack of log data acquired using modern techniques all these conditions and constraints encountered in the rehabilitation of the brighton marine field offshore southwest trinidad were significantly offset by records of the drilling of 275 wells some 35 45 yr ago it is inferred that drilling performance was governed by a relatively uncommon process which may be typical of such highly overpressured strike slip environments the stress state is quantitatively characterised based on the inferences obtained from diverse data sources the characterisation is compatible with both engineering and geological observations and allows for the variation of principal stress magnitude with variation of pore pressure in the shale succession

miocene to recent structure and basinal architecture along the central range strike slip fault zone eastern offshore trinidad abstract previous gps based geodetic studies and onland paleoseismologic studies in trinidad have shown that the 50 km long linear onland segment of the central range fault zone crfz accommodates at least 60 of the total rate of right lateral displacement 20 mm yr between the caribbean and south american plates 2d and 3d seismic reflection data from a 60 km long and 30 km wide swath of the eastern shelf of trinidad block 2ab were used to map the eastern offshore extension of this potentially seismogenic and hazardous fault system and to document its deeper structure and tectonic controls on middle miocene to recent clastic stratigraphy two unconformity surfaces and seafloor were mapped using 3d seismic data to generate isochron maps and to illustrate the close control of the crfz and associated secondary faults on small clastic basins formed along its anastomosing strands and the east west striking north darien ridge fault zone ndrfz that exhibits a down to the north normal throw mapped surfaces include 1 the middle miocene angular unconformity a prominent regional unconformity surface separating underlying thrust deformed rocks from a much less deformed overlying section this regional unconformity is well studied from onland outcrops in trinidad and in other offshore areas around trinidad 2 a late neogene angular unconformity developed locally within block 2ab that is not recognized in trinidad and 3 the seafloor of the eastern trinidad shelf which exhibits linear scarps for both the crfz and the east west striking north darien ridge fault zone clastic sedimentary fill patterns identified on these isochron maps indicate a combined effect of strike slip and reverse faulting i e tectonic transpression produced by active right lateral shear on the crfz which is consistent with the obliquity of the strike of the fault to the interplate slip vector known from gps studies in onland trinidad the ndrfz and a sub parallel and linear family of east west striking faults with normal and possibly transtensional motions also contributed to the creation of accommodation space within localized post middle miocene clastic depocenters south of the crfz

thermochronology constraints on miocene exhumation in the central range mountains trinidad the central range fault zone is a continental transform that accommodates most of the present day slip between the caribbean and south american plates in trinidad global positioning system data and paleoseismic work suggest that this zone is active today and has been active for at least the past several thousand years the modern fault zone overprints a middle miocene fold and thrust belt therefore the strain recorded in the central range fault zone is the sum of both middle miocene and more recent events thermochronology data from eocene and oligocene sandstones in the central range were collected to evaluate the timing of exhumation driven by crustal shortening and thickening u th he zircon analysis of subhedral zircons collected from eight samples indicated that the burial temperatures of these sedimentary rocks did not exceed 180 c suggesting that these grains record detrital u th he dates apatite fission track aft analysis of 10 samples yielded mixed results with cooling ages ranging from 30 to 15 ma however most sites failed the 2 test suggesting that multiple age cohorts are present pooled aft ages suggest that rocks presently at the surface were exhumed through their aft closure temperature ca 11 18 ma cooling and exhumation thus most likely resulted from middle miocene shortening across the fold and thrust belt in response to early oblique convergence between the caribbean and south america plates post miocene deformation associated with more recent transform tectonics has therefore resulted in more limited 4 km if any exhumation

velocity field across the southern caribbean plate boundary and estimates of caribbean south american plate motion using gps geodesy 1994 2000 global positioning system gps observations between 1994 and 2000 at twenty two sites in the lesser antilles and northern south america indicate that the caribbean plate along its southern boundary slips at a rate of 20 5 2 mm a with an azimuth of n 84 2 e at 65 w relative to the south american plate east of 68 w 80 of the dextral slip is contained within a 80 km wide shear zone centered on the el pilar san sebastian fault system west of 68 w the plate boundary broadens to more than 300 km with dextral shear shared between the northeast trending bocono fault 9 11 mm a in western venezuelan and an offshore system near the northern coast

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

structure and deformation history of the northern range of trinidad and adjacent areas conflicting models have been proposed for both the evolution of northern south america and the neotectonics of the south caribbean plate boundary zone the trinidadian portion of the margin is particularly controversial but surprisingly it has been little studied we present a structural analysis of trinidad s northern range pertinent updates of the island s stratigraphy and sedimentology and new zircon fission track age determinations and use them to constrain trinidad s geologic history and to better understand the controlling tectonic processes in our interpretation trinidad s three e ene striking ranges which are separated by late neogene recent depocenters expose 1 the northern range group generally greenschist metamorphosed upper jurassic to cretaceous north facing continental slope sediments of the northern range deposited on the northern south american passive margin 200 400 km to the wnw and 2 the trinidad group cretaceous paleogene shelf slope sediments of the central and southern trinidad deposited less than 100 km wnw of their present location a small allochthon composing the sans souci group cretaceous tholeiitic volcaniclastic basaltic and gabbroic rocks sans souci formation and sediments toco formation now in the northeastern northern range has been transported hundreds of kilometers from the west with the caribbean plate despite earlier references to cretaceous orogenesis all deformation in trinidad is of cenozoic age the first deformation in the northern range d1 formed north vergent nappes and induced greenschist metamorphism probably in the late eocene or oligocene the nappes developed either by the underthrusting of the proto caribbean crust beneath south america due to convergence between north and south america or as gravity slides caused by oversteepening induced by this convergence and or the passage of the caribbean plate s peripheral bulge and arrival of its foredeep northern range d2 deformation is south vergent and represents the incorporation of northern range metasediments into the caribbean accretionary prism the transition to d3 brittle transpressive right lateral strike slip faulting is interpreted to be due to the uplift and east southeastward transpressive emplacement of northern range caribbean prism rocks onto the south american stepped shelf this emplacement formed the miocene transpressive thrust belts and foreland basin in central and southern trinidad in the final phase of northern range deformation d4 e w normal faults and shear zones and conjugate nnw sse and ne sw normal faults developed and displacement on preexisting e w right lateral strike slip faults continued the 11 ma northern range zircon fission track ages suggest rapid uplift from the late miocene to recent late miocene subsidence of the tobago platform immediately to the north of the northern range and greater than 3 km of normal down to the north displacement indicated for the north coast fault zone separating the northern range and tobago platform leads us to postulate that the rapid uplift of the northern range was in response to the northward detachment of the tobago platform from above the northern range along the north dipping transtensional north coast fault zone this late miocene change in deformation style can be explained by a change from caribbean south american right lateral transpression to right lateral strike slip generally striking 080 this has generally induced a component of extension on pre existing faults striking at greater than 080 and a component of compression on faults striking at less than 080

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

recent eruptions at bezymianny volcano a seismological comparison abstract for the past few decades bezymianny volcano has erupted once to twice per year here i examine eight eruptive events between 2006 and 2010 this is the first time period for which proximal or broadband seismic data have been recorded at bezymianny several recurring patterns are demonstrated in advance of eruptions eruptions are generally preceded by 12 36 h of tremor energy elevated by 2 to 3 orders of magnitude locatable earthquake activity is quite erratic in the days before eruptions for eruptions of juvenile magma however the cumulative moment magnitude increases with the repose time since the previous eruption though tenuous this relationship is statistically significant and could improve forecasts of bezymianny eruptions the most energetic eruptions demonstrate increasing multiplet activity in the run up followed by a rapid cessation at the time of eruption when present this behavior marks increasing pressure in the conduit system as degassing eclipses the capacity for venting very long period seismicity 20 s periods accompanies some eruptions these tend to be the same short lived high energy eruptions that exhibit multiplet precursors four eruptions are examined in detail to illustrate the variety in eruption mechanisms lava dome collapses sustained eruptions singular paroxysmal explosions and post explosion lava flows occur in different combinations demonstrating that more than one eruption trigger is regulating bezymianny compared to bezymianny s fifty year modern history recent eruptions have been shorter lived and separated by longer repose times some evidence suggests that these eruptions may be increasingly explosive a speculation that carries significant hazard implications if true however this threat is tempered by solid evidence that the most explosive eruptions are preceded by the clearest precursors suggesting an ability to improve the already excellent eruption forecasts available for bezymianny

tectonic inversion in the caribbean south american plate boundary gps geodesy seismology and tectonics of the mw 6 7 22 april 1997 tobago earthquake on 22 april 1997 the largest earthquake recorded in the trinidad tobago segment of the caribbean south american plate boundary zone mw 6 7 ruptured a shallow 9 km ene striking 250 azimuth shallowly dipping 28 dextral normal fault 10 km south of tobago in this study we describe this earthquake and related foreshock and aftershock seismicity derive coseismic offsets using gps data and model the fault plane and magnitude of slip for this earthquake coseismic slip estimated at our episodic gps sites indicates movement of tobago 135 6 to 68 6 mm nne and subsidence of 7 9 to 0 mm this earthquake was anomalous and is of interest because 1 its large component of normal slip and ene strike are unexpected given the active e w dextral shearing across the caribbean south american plate boundary zone 2 it ruptured a normal fault plane with a low 28 dip angle and 3 it reactivated and inverted the preexisting tobago terrrane south america ocean continent thrust boundary that formed during early tertiary oblique plate convergence

estimation of possible maximum earthquake magnitudes of quaternary faults in the southern korean peninsula the korean peninsula is located in the intraplate regime of the eurasian plate and numerous historical and instrumental earthquakes have been recorded among these the largest earthquakes were recorded in and around the gyeongju and ulsan areas in the southeastern part of the korean peninsula we recently reexamined faults in jinhyun and jintee part of the ulsan fault swarm to clarify the average slip rate and the maximum potential magnitude of future earthquakes the jinhyun fault extends to the tabgol fault j t fault and the jintee fault extends to the singye s j fault the faults cut through alluvial fans and are covered by unconsolidated granite washes on tertiary granite all of these faults show reverse sense of motion such that the tertiary granite has been moved upward with a high angle relative to the quaternary sediments most sediment samples from the jinhyun and jintee faults showed quartz osl ages of ca 40 60 ka the calculated vertical slip rate for the jinhyun and jintee faults is in the range of 0 18 0 28 mm y based on maximum earthquake magnitudes calculated from geological survey results as well as historical and instrumental earthquake information the maximum potential magnitudes of future earthquakes in the gyeongju area are estimated to range from 4 6 to 5 6 this suggests that the potential maximum magnitude in the southern korean peninsula is presumably not more than 6

new kinematic models for pacific north america motion from 3 ma to present i evidence for steady motion and biases in the nuvel 1a model we use velocities derived from 2 4 5 years of continuous gps observations at 21 sites on the pacific and north american plates along with a subset of the nuvel 1a data to examine the steadiness of pacific north america motion since 3 16 ma the transfer of baja california to the pacific plate and the magnitude of biases in the nuvel 1a estimate of pacific north america motion we find that pacific north america motion has remained steady since 3 16 ma but at rates significantly faster than predicted by nuvel 1a in the vicinity of baja california our gps derived model and recent seafloor spreading rates in the southern gulf of california both indicate that the nuvel 1a model underestimates pacific north america rates by 4 2 mm yr 1 steady pacific north america motion since 3 16 myr and increasing seafloor spreading rates since 3 58 myr in the gulf of california imply that pacific north america motion was partitioned between seafloor spreading in the gulf of california and decelerating slip along faults in or offshore from the baja peninsula

the offshore yangsan fault activity in the quaternary se korea analysis of high resolution seismic profiles abstract the nne trending dextral yangsan fault is a 190 km long structure in the korean peninsula traced to the southeastern coast the scarcity of quaternary deposits onland precludes any detailed investigation of the quaternary activity and structure of the yangsan fault using seismic reflection profiling we acquired offshore high resolution seismic profiles to investigate the extension of the yangsan fault and constrain its quaternary activity using stratigraphic markers the seismic profiles reveal a nne trending fault system consisting of a main fault and an array of subsidiary faults that displaced quaternary sequences stratigraphic analysis of seismic profiles indicates that the offshore faults were activated repeatedly in the quaternary the up to the east sense of throw on the main fault and plan view pattern of the fault system are explained by dextral strike slip faulting the main fault when projected toward the korean peninsula along its strike aligns well with the yangsan fault we suggest that the offshore fault system is a continuation of the yangsan fault and has spatial correlation with weak but ongoing seismicity

1 1 ga k rich alkaline plutonism in the sw grenville province u pb zircon and baddeleyite dating of six syenitic stocks establishes that the ultrapotassic potassic alkaline and shoshonitic magmatism with island arc affinities in the central metasedimentary belt cmb of the southwestern grenville province canada took place between 1089 and 1076 ma along a 400 km long northeast trending plutonic belt these ages indicate that ultrapotassic rocks with arc affinities are not unique to the phanerozoic west to east emplacement ages along a northern and southern cross section of this belt range from 1083 2 ma kensington through 1081 2 ma lac rouge to 1076 1 3 ma loranger in the north and from 1089 3 4 ma loon lake and 1088 2 ma calabogie to 1076 2 ma westport in the south although closely spaced in time in detail these ages suggest a slight younging of this magmatic activity to the southeast integration of the geochronological data with the spatial extent and potassic character of the plutons shows that the k rich alkaline suite is distinct from the nepheline syenite belt of the bancroft terrane and from the syenite monzonite suite of the frontenac terrane of the cmb and it is considered to be a magmatic episode unique to the elzevir terrane and its gatineau segment the timing and the postmetamorphic emplacement of these plutons indicate that the regional greenschist to granulite facies metamorphism of the country rock precise age unknown is older than 1089 ma throughout the entire elzevir terrane the potassic magmatism is interpreted as the initiation of the 1090 1050 ma ottawan orogeny in the elzevir terrane thus the regional metamorphism in this terrane previously assigned to the ottawan orogeny is an earlier event the contemporaneous emplacement of this postmetamorphic plutonic belt with keweenawan volcanism is at variance with current tectonic models which consider the keweenawan rift to be formed at the same time as regional metamorphism in the cmb

southern california hypocenter relocation with waveform cross correlation part 1 results using the double difference method we present the results of relocating 327 000 southern california earthquakes that occurred between 1984 and 2002 we apply time domain waveform cross correlation for p and s waves between each event and 100 neighboring events identified from the catalog based on a 3d velocity model to simplify the computation we first divide southern california into five polygons such that there are 100 000 events or less in each region the polygon boundaries are chosen to lie in regions of sparse seismicity we calculate and save differential times from the peaks in the cross correlation functions and use a spline interpolation method to achieve a nominal timing precision of 0 001 sec these differential times together with existing p and s phase picks are input to the double difference program of waldhauser and ellsworth 2000 2002 to calculate refined hypocenters we divide the southern california region into grid cells and successively relocate hypocenters within each grid cell the overall resulting pattern of seismicity is more focused than the previously determined pattern from 1d or 3d models the new improved locations are more clustered in many cases by a factor of two or three and often show clear linear alignments in particular the depth distribution is improved and less affected by layer boundaries in velocity models or other similar artifacts

regional structure and tectonic history of the obliquely colliding columbus foreland basin offshore trinidad and venezuela abstract cenozoic eastward migration of the caribbean plate relative to the south american plate is recorded by an 1100 km long venezuela trinidad foreland basin which is oldest in western venezuela 65 55 ma of intermediate age in eastern venezuela 34 20 ma and youngest beneath the shelf and slope area of eastern offshore trinidad submarine columbus basin 15 0 ma recent in this study of the regional structure fault families and chronology of faulting and tectonic events affecting the hydrocarbon rich columbus foreland basin of eastern offshore trinidad we have integrated approximately 775 km of deep penetration 2d seismic lines acquired by the 2004 broadband ocean land investigations of venezuela and the antilles arc region bolivar survey 325 km of vintage gulfrex seismic data collected by gulf oil company in 1974 and published industry well data that can be tied to some of the seismic reflection lines top cretaceous depth structure maps in the columbus basin made from integration of all available seismic and well data define for the first time the elongate subsurface geometry of the 11 15 km thick and highly asymmetrical middle miocene recent depocenter of the columbus basin the main depocenter located 150 200 km east of trinidad and now the object of deepwater hydrocarbon exploration is completely filled by shelf and deepwater sediments derived mainly from the orinoco delta the submarine darien ridge exhibits moderate 20 140 m seafloor relief forms the steep 12 24 northern structural boundary of the columbus basin and is known from industry wells to be composed of 0 5 4 5 km thick folded and thrust imbricated hydrocarbon bearing section of cretaceous and early tertiary limestones and clastic rocks the eastern and southern boundaries of the basin are formed by the gently 1 7 4 5 northward dipping cretaceous paleogene passive margin of south america that is in turn underlain by precambrian rocks of the guyana shield interpretation of seismic sections tied to wells reveals the following fault chronology 1 middle miocene thrusting along the darien ridge related to highly oblique convergence between the caribbean plate and the passive margin of northern south america continuing thrusting and transpression in an oblique foreland basin setting through the early pleistocene 2 early pliocene recent low angle normal faults along the top of the cretaceous passive margin these faults were triggered by oversteepening related to formation of the downdip structurally and bathymetrically deeper and more seaward columbus basin large transfer faults with dominantly strike slip displacements connect gravity driven normal faults that cluster near the modern shelf slope break and trend in the downslope direction to the south no normal faults are present because the top cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin 3 early pliocene recent strike slip faults parallel the trend of the darien ridge and accommodate present day plate motions

esr dating of the subsidiary faults in the yangsan fault system korea abstract the yangsan fault system is located near heavy industrial complexes and nuclear power plants in the korean peninsula we carried out esr dating of fault rocks from the wonwonsa and ihwa faults two subsidiary faults of the yangsan fault system esr ages are divided into three groups in order of decreasing confidence multiple plateau esr ages single plateau esr ages and maximum esr ages the wonwonsa fault was reactivated at least 4 times and the ihwa fault at least 2 times within the quaternary period long term cyclic fault activity of some subsidiary faults of the yangsan fault system occurred in the pleistocene and suggests the possibility of continued activity on this fault system

a gps estimate of relative motion between north and south america gps velocity data are used to estimate the euler vector describing rigid body motion of north america relative to south america assuming the boundary between the north and south american plates is located near the fifteen twenty fracture zone in the equatorial atlantic the euler vector predicts extension across the royal trough up to 1 mm yr and convergence across the barracuda ridge at about 2 mm yr in agreement with geological estimates averaged over tens of millions of years further west convergence between north and south america at rates up to 8 mm yr may contribute to deformation of the caribbean plate along its southwest boundary with south america

dynamic deformation of the accretionary prism excites very low frequency earthquakes 1 we have detected anomalous very low frequency earthquakes within the accretionary prism along the nankai trough southwestern japan centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at 10 km depth above the upper surface of the subducting philippine sea plate and within 50 70 km landward of the trough axis the focal mechanisms indicate reverse faulting their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea floor topography these observations suggest that the occurrence of very low frequency earthquakes is related to numerous reverse fault systems within the accretionary prism and that the earthquakes reflect the dynamics of deformation within this accretionary prism

transient quaternary erosion and tectonic inversion of the northern range trinidad abstract cosmogenic 10be measured in sediments from northern range catchments on the island of trinidad reveals low millennial scale rates of erosion average 40 mm ka that increase roughly eightfold from 11 to 92 mm ka eastward across the mountain range these results in conjunction with an analysis of mountain morphometrics are consistent with quaternary east side up tilting of the northern range which has occurred recently 100 ka the highest millennial scale erosion rates coincide spatially with quaternary east side surface uplift albeit not in magnitude high modern rainfall rates low topographic relief and convex longitudinal stream profiles indicating transient quaternary erosion we interpret that hillslope adjustment and erosion of the northern range is buffered from climatic and tectonic forcings by dense tropical vegetation cover thick saprolite and porous regolith compared with longer term thermochronology exhumation rates we document that an order of magnitude deceleration of and reversal in the locus of erosion and exhumation has occurred during the pliocene to the holocene we suggest that these combined data sets highlight distinct syn and post collisional phases of northern range development that are related to a major change in relative caribbean south american plate motion from oblique convergence to transform motion oblique collision during the mid miocene likely caused relatively higher rates of and asymmetric exhumation of the northern range post collisional mountain scale tilting is likely caused by a combination of crustal extension in the gulf of paria and by deep subsurface lithospheric detachment processes that drives dynamic topography

forward waveform modelling procedure for 1 d crustal velocity structure and its application to the southern korean peninsula summary we propose a full grid search procedure for broad band waveform modelling to determine a 1 d crustal velocity model the velocity model can be more constrained because of the use of broad band waveforms instead of traveltimes for the crustal phases although only a small number of event station pairs were employed despite the time consuming nature of the full grid search method to search the whole model parameter space the use of an empirical relationship between the p and s wave velocities can significantly reduce computation time the proposed method was applied to a case in the southern korean peninsula broad band waveforms obtained from two inland earthquakes that occurred on 2007 january 20 mw 4 6 and 2004 april 26 mw 3 6 were used to test the method the three layers over half space crustal velocity model of the p and s wave velocities was estimated comparisons of waveform fitness between the final model and previously published models demonstrate advancements in the average value of waveform fitness for the inland earthquakes in addition 1 d velocity models were determined for three distinct tectonic regions namely the gyonggi massif the okcheon belt and the gyeongsang basin which are all located inside the study area a comparison between the three models demonstrates that the crustal thickness of the southern korean peninsula increases from nw to se and that the lower crustal composition of the okcheon belt differs from that of the other tectonic regions

is there a northern lesser antilles forearc block 1 a systematic discrepancy exists between slip vectors of thrust fault earthquakes at the lesser antilles trench lat and the predicted direction of north american caribbean convergence a possibility has been that the discrepancy resulted because neither was well constrained estimating caribbean motion has been challenging owing to the limited data along the plate s complex boundaries similarly earlier studies had few slip vectors because interplate thrust events are infrequent to address these difficulties we estimate a new caribbean north america euler vector using recently available gps data from sites in the presumably stable interior of the caribbean and compare the predicted velocities to a larger set of slip vectors the discrepancy persists suggesting the northern lesser antilles forearc nlaf moves as a distinct entity from both the caribbean and north america for simplicity we treat its motion as a coherent block but because gps sites are not within the nlaf distributed deformation is also possible although there is no geologic evidence for the boundaries of the presumed nlaf block gps data show that the motions of martinique barbados and trinidad are similar to that of the caribbean suggesting that none are on the nlaf block and the southern lat is weakly coupled

the itrf96 realization and its associated velocity field this text intends to present and to analyse the quality of the new 1996 edition of the international terrestrial reference system called the itrf96 the itrf96 represents a key step forward in the activity of the iers terrestrial system determinations a new physical combination model has been developed as well as a new stochastic model for the first time the level of accuracy has reached 1 cm or better in position for about 50 of itrf96 stations and 30 of the stations have their velocities determined free of any aditional tectonic plate model assumption with an uncertainty better than 3 mm yr the itrf96 also provides a more complete solution a new software has been developed which makes available the itrf96 full variance covariance matrix whereas this information was restricted to station positions in the previous itrf94 edition moreover the network coverage is clearly the largest set of globally distributed terrestrial space geodesy stations that have ever been computed 521 stations located among 290 sites in addition station velocities are also determined at a very accurate level allowing possible determination of kinematic plate motion models free of any geological assumption

lead isotope analyses of leached feldspars constraints on the early crustal history of the grenville orogen abstract lead isotopic data on leached k feldspars plagioclases and muscovite provide constraints on the premetamorphic evolution of the grenville orogen in ontario and new york a boundary between reworked archean crust to the northwest and new mantle derived crust generated during mid proterozoic times to the southeast is identified within the northern portion of the gneiss belt of ontario the identification of juvenile mid proterozoic crust at the southeastern margin of the orogen is consistent with previous investigations based on neodymium model ages however near the grenville front lead isotopes indicate the presence of reworked archean crust rather than primary early proterozoic crust postulated on the basis of neodymium model ages this discrepancy between the lead and neodymium isotopic terranes underscores the necessity of using a multidisciplinary approach to identify possible terrane boundaries only through a combination of the lead with neodymium isotopes is it possible to distinguish between crust that formed during a single major orogenic cycle and crust that represents a mixture of old with new mantle derived material the combined neodymium and lead data imply that the grenville orogen in ontario consists essentially of reworked archean crust and juvenile mantle derived material generated around 1 5 ga the grenville orogen involved archean crust that was depleted in thorium and uranium several hundred ma before high grade metamorphism at ca 1 1 ga such a depletion may have a significant impact on the geotherm achieved during orogeny and may explain the lower metamorphic thermal gradients observed for the gneiss belt

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

constraining neotectonic orogenesis using an isostatically compensated model of transpression abstract current models of transpression allow upward flow of material to compensate for shortening in the horizontal plane we present an isostatically compensated model of transpression where material is allowed to flow both upwards to create topographic relief and downwards to form a crustal root our model also incorporates the effects of erosion to more accurately examine the developing topography in orogenic systems the modeling results suggest that topographic relief and crustal root thickness developed in transpressional orogens are most dependent on the magnitude of shortening the initial thickness of the crust and the density contrast between the crust and mantle in contrast the rate of convergence and final width of the deformed zone are relatively unimportant parameters in this model application to the alpine fault system in new zealand a well constrained active transpressional plate boundary shows good agreement between topography based model estimates of shortening and those derived from plate reconstructions application of our model to the central range fault zone in trinidad suggests 2 1 km of neotectonic shortening the strain analysis approach presented here may be useful for isolating the effects of modern deformation in a region that has reactivated an ancient contractional belt

prehistoric earthquakes on the caribbean south american plate boundary central range fault trinidad recent geodetic studies suggest that the central range fault is the principal plate boundary structure accommodating strike slip motion between the caribbean and south american plates our study shows that the fault forms a topographically prominent lineament in central trinidad results from a paleoseismic investigation at a site where holocene sediments have been deposited across the central range fault indicate that it ruptured the ground surface most recently between 2710 and 550 yr b p if the geodetic slip rate of 9 15 mm yr is representative of holocene slip rates our paleoseismic data suggest that at least 4 9 m of potential slip may have accumulated on the fault and could be released during a future large earthquake m 7

remote triggering of tremor along the san andreas fault in central california received 30 august 2008 accepted 16 april 2009 published 18 july 2009 1 we perform a systematic survey of triggered tremor along the san andreas fault in central california for the 31 teleseismic earthquakes with mw 7 5 since 2001 we identify 10 teleseismic events associated with clear triggered tremor about 52 of the tremor is concentrated south of parkfield near cholame where ambient tremor has been identified previously and the rest is widely distributed in the creeping section of the san andreas fault north of parkfield tremor is generally initiated and is in phase with the love wave particle velocity however the pattern becomes complicated with the arrival of the rayleigh waves and sometimes tremor continues after the passage of the surface waves we identify two cases in which tremor is triggered during the teleseismic pkp phase these results suggest that while shear stress from the passage of the love waves plays the most important role in triggering tremor in central california other factors such as dilatational stresses from the rayleigh and p waves also contribute we also examine the ambient tremor occurrence rate before and after the teleseismic events and find a transient increase of stacked tremor rate during the passage of the teleseismic surface waves this observation implies that the occurrence time of tremor is temporally advanced by the dynamic stresses of the teleseismic waves the amplitude of the teleseismic waves correlates with the occurrence of triggered tremor and the inferred tremor triggering threshold is 2 3 kpa the relatively low triggering threshold indicates that the effective stress at the tremor source region is very low most likely due to near lithostatic fluid pressure

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

calcite and quartz microstructural geothermometry of low grade metasedimentary rocks northern range trinidad abstract the northern range of trinidad is a mountainous exposure of deformed metasedimentary rocks with mesozoic depositional ages and tertiary metamorphic ages located in the caribbean south american plate boundary zone these rocks lack precise mineralogical indicators of metamorphic grade using temperature sensitive quartz and calcite microstructures and fission track data we identify describe quantify and map a nearly continuous spectrum of relatively low l50 c to relatively high 250 400 c deformation temperatures from east to west across the range average estimated rock exhumation rates also increase systematically along this trend the analysis illuminates a sharp east west trending major thermal discontinuity i e a fault along the southern boundary of the range kinematic analysis of faults and shear bands adjacent to this boundary and modeling indicate that the fault probably dips southward at 80 85 and accommodated normal dip slip at rates that decreased from west to east earlier experimental studies at high strain rates illustrated a strong strain rate dependency for quartz microstructural transitions our work indicates a possible strong temperature control for quartz microstructural transitions at natural strain rates

on the interaction of the north andes plate with the caribbean and south american plates in northwestern south america from gps geodesy and seismic data

continuous monitoring of surface deformation at long valley caldera california with gps continuous global positioning system gps measurements at long valley caldera an active volcanic region in east central california have been made on the south side of the resurgent dome since early 1993 a site on the north side of the dome was added in late 1994 special adaptations for autonomous operation in remote regions and enhanced vertical precision were made the data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber measurement precisions 1 standard error for absolute position coordinates i e relative to a global reference frame are 3 4 mm north 5 6 mm east and 10 12 mm vertical using 24 hour solutions corresponding velocity uncertainties for a 12 month period are about 2 mm yr in the horizontal components and 3 4 mm yr in the vertical component high precision can also be achieved for relative position coordinates on short 10 km baselines using broadcast ephemerides and observing times as short as 3 hours even when data are processed rapidly on site comparison of baseline length changes across the resurgent dome between the two gps sites and corresponding two color electronic distance measurements indicates similar extension rates within error 2 mm yr once we account for a random walk noise component in both systems that may reflect spurious monument motion both data sets suggest a pause in deformation for a 3 5 month period in mid 1995 when the extension rate across the dome decreased essentially to zero three dimensional positioning data from the two gps stations suggest a depth 5 8 1 6 km and location west side of the resurgent dome of a major inflation center in agreement with other geodetic techniques near the top of a magma chamber inferred from seismic data gps systems similar to those installed at long valley can provide a practical method for near real time monitoring and hazard assessment on many active volcanoes

oblique collision and tectonic wedging of the south american continent and caribbean terranes our studies of the surface structures seismicity and gravity anomalies of the caribbean south american plate boundary zone of northeast venezuela and trinidad show that the crustal and upper lithospheric structure and kinematics of this zone are complex and differ markedly along strike we propose a model of the zone9s lateral transition from near trinidad west to caracas emphasizing three concepts 1 the steepening detachment and then sinking away of atlantic oceanic lithosphere that is was attached to the northern edge of continental south america 2 the wedging seaward and imbricate thickening of the northern margin of the continent in the region of the detaching atlantic slab the continental wedge overrides the slab and is overridden by terranes attached to the caribbean plate and 3 that the structural and kinematic transitions are a consequence of the progressive oblique collision between continental south america and the overriding caribbean terranes

fault slip analysis of quaternary faults in southeastern korea abstract the quaternary stress field has been reconstructed for southeast korea using sets of fault data the subhorizontal direction of the maximum principal stress 1 trended ene and the direction of the minimum principal stress 3 was nearly vertical the stress ratio 2 3 1 3 value was 0 65 two possible interpretations for the stress field can be made in the framework of eastern asian tectonics 1 the hmax trajectory for southeast korea fits well with the fan shaped radial pattern of maximum principal stress induced by the india eurasia collision thus we suggest that the main source for this recent stress field in southeast korea is related to the remote india eurasia continental collision 2 the stress field in korea shows a pattern similar to that in southwestern japan the origin for the e w trending hmax in japan is known to be related to the mantle upwelling in the east china sea thus it is possible that quaternary stress field in korea has evolved synchronously with that in japan we suggest further studies gps and in situ stress measurement to test these hypotheses

seismotectonics and fault structure of the california central coast abstract i present and interpret new earthquake relocations and focal mechanisms for the california central coast the relocations improve upon catalog locations by using 3d seismic velocity models to account for lateral variations in structure and by using relative arrival times from waveform cross correlation and double difference methods to image seismicity features more sharply focal mechanisms are computed using ray tracing in the 3d velocity models seismicity alignments on the hosgri fault confirm that it is vertical down to at least 12 km depth and the focal mechanisms are consistent with right lateral strike slip motion on a vertical fault a prominent newly observed feature is an 25 km long linear trend of seismicity running just offshore and parallel to the coastline in the region of point buchon informally named the shoreline fault this seismicity trend is accompanied by a linear magnetic anomaly and both the seismicity and the magnetic anomaly end where they obliquely meet the hosgri fault focal mechanisms indicate that the shoreline fault is a vertical strike slip fault several seismicity lineations with vertical strike slip mechanisms are observed in estero bay events greater than about 10 km depth in estero bay however exhibit reverse faulting mechanisms perhaps reflecting slip at the top of the remnant subducted slab strike slip mechanisms are observed offshore along the hosgri san simeon fault system and onshore along the west huasna and rinconada faults while reverse mechanisms are generally confined to the region between these two systems this suggests a model in which the reverse faulting is primarily due to restraining left transfer of right lateral slip

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

lateral variation in the source parameters of earthquakes in the korean peninsula to elucidate the seismic characteristics of earthquakes in the korean peninsula we investigated seismic source parameters of 651 earthquakes that occurred between 2001 and 2014 with magnitudes greater than 1 9 we estimated the seismic moment corner frequency and stress drop of an event from s wave source spectra comparison of our estimates with the results of previous studies confirmed the reliability of our findings breakdown in the self similarity of an earthquake source may occur at around a seismic moment of 1021 dyn cm as suggested by previous studies although nonnegligible variation still appears in the corner frequency of low magnitude events we also found that earthquakes in two regions near pyongyang and on the western margin of the east sea sea of japan occurred with low stress drops these regions have distinctively higher seismicity than other regions the largest earthquake m w 6 2 in the korean peninsula in the past century occurred in the low stress drop region near pyongyang the western margin of the east sea reportedly has earthquake focal mechanisms that differ from those of earthquakes in other regions in the peninsula therefore we suggest that lateral variation in stress drops in the korean peninsula could be related to the distinctive seismic characteristics in these regions

the dynamic behavior of shallow marine reservoirs insights from the pliocene of offshore north trinidad the pliocene reservoirs of the north coast marine area block ncma 1 comprise shallow marine shoreface to shelf sandstones up to 30 m 98 ft thick and interbedded shelfal mudstones organized into stacked upward coarsening parasequences ca 25 70 m thick production behavior is strongly conditioned by the interplay of subregional sand distribution and aquifer connectivity and intrafield reservoir architecture complexity commonly in the form of clinoforms the m2 parasequence is a well connected reservoir unit and forms part of a late highstand systems tract with a strongly progradational architecture large scale reservoir connectivity can be demonstrated by pressure communication in producing fields up to 10 km 6 mi apart the widespread nature of the sand also links the reservoir to a significant aquifer that provides pressure support during field depletion in contrast clinoforms that dominate the m2 reservoir architecture at a variety of scales reduce lateral connectivity wells situated in individual sand bodies show significant pressure interference during production whereas wells that straddle bounding clinoforms possible parasequence boundaries although in pressure communication show more subtle pressure interference in the chaconia field clinoforms that bound lobate sand bodies in the m2 reservoir have also apparently slowed the onset of water cut within the field by several years and therefore increased reserves recovery similarly in the m6 reservoir of the ixora field a significant bounding clinoform has partitioned the field through much of its production life but production data are now suggesting breakdown and late stage pressure support across the same clinoform the m6 parasequences form part of a lower quality early highstand systems tract and are more discontinuous than their m2 counterpart due to well developed bounding clinoforms as such they are not characterized by large active aquifers and do not benefit from such prominent long term pressure support the m4 reservoir is an isolated sand body complex that forms part of a high frequency lowstand complex it shows similar stratigraphic heterogeneity to that displayed in the m2 with variations in pressure decline exhibited within individual wells of the same reservoir unit its isolated geometry means it is not connected to a regional aquifer and is therefore undergoing volumetric decline with no water breakthrough

low frequency tremors intraslab and interplate earthquakes in southwest japan from a viewpoint of slab dehydration 1 low frequency tremors lft recently found in the southwest japan fore arc likely occur due to hydro fracturing from fluids leaving the dehydrating philippine sea slab however there are some places without such lft they are n izu kanto e shikoku and s kyushu these are the places where island arc type crust is subducting we propose that dehydration of the subducted crust does not occur beneath these regions because it is composed mainly of tonalite lacking the quantity of hydrous minerals seen in normal subducting oceanic crust we show that almost no earthquake occurs within the subducted crust in such regions consistent with dehydration embrittlement hypothesis for intraslab seismicity the lack of dehydration from the crust would also affect the mode of occurrence of interplate earthquakes because pore fluid pressure is more difficult to rise at the thrust zone this might be reflected in the irregular occurrence of great earthquakes in these regions

rupture history of the 1997 cariaco venezuela earthquake from teleseismic p waves a two step finite fault waveform inversion scheme is applied to the broadband teleseismic p waves recorded for the strike slip cariaco venezuela earthquake of 9 july 1997 to recover the distribution of mainshock slip the earthquake is first analyzed using a long narrow fault with a maximum rise time of 20 sec this line source analysis indicates that slip propagated to the west with a constant rupture velocity and a relatively short rise time the results are then used to constrain a second inversion of the p waveforms using a 60 km by 20 km two dimensional fault the rupture shows a zone of large slip 1 3 m peak near the hypocenter and a second broader source extending updip and to the west at depths shallower than 5 km the second source has a peak slip of 2 1 meters and accounts for most of the moment of 1 1 1026 dyne cm 6 6 mww estimated from the p waves the inferred rupture pattern is consistent with macroseismic effects observed in the epicentral area

using orthographic projection with geographic information system gis data to constrain the kinematics the central range fault zone trinidad abstract fold geometry versus axis orientation can be used to constrain the kinematics of transpressional plate boundaries this approach is typically based on bedding orientation data collected in the field however in some regions outcrop quality is insufficient to provide enough measurements we extract orientation data from a georeferenced geologic map and a digital elevation model and to constrain the kinematics of a poorly exposed active transpressional boundary the central range fault zone in trinidad strike and dip orientations are calculated based on contact positions extracted from the digital geologic and topographic datasets the uncertainties in the both horizontal position and elevation of the contact are propagated into the final kinematic analysis analysis of folds adjacent to the central range fault suggests the angle of oblique convergence in transpression varies from 20 to 85 the majority of folds however are consistent with a large component of contraction i e 50 the analysis also suggests folding in the central range records a minimum of 3 9 km of contraction 3 km of strike slip motion and 4 9 km of total plate motion the range of values reflects uncertainties in the position of the folded contacts we interpret the overall kinematics of deformation amount of shortening and homogeneity of the finite strain field to indicate that active deformation on the central range fault zone has not yet accumulated enough strain to overprint the effects of earlier pre strike slip pre middle miocene fold and thrust style tectonics

seismicity and tectonics of the southeastern caribbean we present 33 new focal mechanisms for se caribbean earthquakes 1963 1988 we use these mechanisms in conjunction with 28 previously available mechanisms to distinguish between two models of plate boundary zone interaction in the se caribbean the trench trench transform and hinge faulting model and the right oblique collision model shallow 0 70 km and intermediate 70 200 km depth earthquakes occur in the study region we focus on the tectonic causes of these events and the motions they delineate the shallow earthquakes are in a broad linear zone which trends ne from the paria peninsula of venezuela towards barbados intermediate depth earthquakes cluster beneath and nw of the peninsula and deepen to the nw perpendicular to the ne trending shallow events the vertical distribution of the earthquakes suggests a slab with steep nw dip shallow dextral strike slip on e striking faults is restricted to a 60 km wide linear zone between the gulf of cariaco and the western margin of the gulf of paria dextral strike slip is active only as far east as the gulf of paria and not within or east of trinidad shallow thrust events with ene striking planes distributed between the araya peninsula and the gulf of paria indicate collision at crustal levels between south america and caribbean and that folding and thrusting are still active over a 60 km interval south of the araya paria isthmus active thrusting in venezuela corroborates predictions of transpression between caribbean and south america and discounts transtensional motions between the two plates in the se caribbean the conjunction of shallow thrust strike slip and normal earthquakes in the gulf of paria at around 62 3 may be the expression of unpartitioned oblique compressive deformation in the plate boundary zone intermediate 165 km h 70 km depth thrust and dip slip events within the nw dipping slab indicate that oceanic lithosphere probably originally attached to south america subducts to the nw beneath the caribbean plate shallow normal faulting events e and ne of trinidad are expressions of plate bending about near horizontal axes parallel to the lesser antilles subduction zone we conclude that the earthquake mechanisms provide strong support for the right oblique collision model of caribbean south american plate interaction

high precision earthquake location and three dimensional p wave velocity determination at redoubt volcano alaska 1 redoubt volcano alaska poses significant volcanic hazard to the cook inlet region and overlying flight paths during and following the most recent eruption in 1989 1990 the alaska volcano observatory deployed up to 10 seismometers to improve real time monitoring capabilities at redoubt and continues to produce an annual earthquake catalog with associated arrival times for this volcano we compute a three dimensional p wave velocity model using double difference tomography combined with waveform cross correlation techniques to identify families of similar earthquakes and increase earthquake location precision at redoubt absolute and differential times for well constrained events are used to simultaneously invert for hypocenter location and p wave velocity structure shot and earthquake arrival times recorded by temporary stations deployed on redoubt in july 1991 supplement the catalog picks double difference tomography reduces uncertainties associated with absolute and relative earthquake locations and provides a clearer picture of three dimensional velocity heterogeneity all redoubt data available through november 2005 are relocated through the three dimensional model and we investigate seismicity associated with the 1989 1990 eruption and compare cross correlation coefficients to identify similar earthquakes within the catalog waveform similarity is high at redoubt especially during the eruptive phases and event families include long period shallow summit hybrid and both shallow summit and midcrust level volcano tectonic earthquakes we do not resolve a low velocity feature in the three dimensional p wave model that can be interpreted as a source magma chamber and prefer the idea of an interconnected body of dikes and sills as the source of magma erupted in 1989 1990

large scale relocation of two decades of northern california seismicity using cross correlation and double difference methods 1 we simultaneously reanalyzed two decades 1984 2003 of the digital seismic archive of northern california using waveform cross correlation cc and double difference dd methods to improve the resolution in hypocenter locations in the existing earthquake catalog generated at the northern california seismic network ncsn by up to three orders of magnitude we used a combination of 3 billion cc differential times measured from all correlated pairs of events that are separated by less than 5 km and 7 million p wave arrival time picks listed in the ncsn bulletin data were inverted for precise relative locations of 311 273 events using the dd method the relocated catalog is able to image the fine scale structure of seismicity associated with active faults and revealed characteristic spatiotemporal structures such as streaks and repeating earthquakes we found that 90 of the earthquakes have correlated p wave and s wave trains at common stations and that 12 are colocated repeating events an analysis of the repeating events indicates that uncertainties at the 95 confidence level in the existing network locations are on average 0 7 km laterally and 2 km vertically correlation characteristics and relative location improvement are remarkably similar across most of northern california implying the general applicability of these techniques to image high resolution seismicity caused by a variety of plate tectonic and anthropogenic processes we show that consistent long term seismic monitoring and data archiving practices are key to increase resolution in existing hypocenter catalogs and to estimate the precise location of future events on a routine basis

slip on the san andreas fault at parkfield california over two earthquake cycles and the implications for seismic hazard parkfield california which experienced m 6 0 earthquakes in 1934 1966 and 2004 is one of the few locales for which geodetic observations span multiple earthquake cycles we undertake a comprehensive study of deformation over the most recent earthquake cycle and explore the results in the context of geodetic data collected prior to the 1966 event through joint inversion of the variety of parkfield geodetic measurements trilateration two color laser and global positioning system including previously unpublished two color data we estimate the spatial distribution of slip and slip rate along the san andreas using a fault geometry based on precisely relocated seismicity although the three most recent parkfield earthquakes appear complementary in their along strike distributions of slip they do not produce uniform strain release along strike over multiple seismic cycles since the 1934 earthquake more than 1 m of slip deficit has accumulated on portions of the fault that slipped in the 1966 and 2004 earthquakes and an average of 2 m of slip deficit exists on the 33 km of the fault southeast of gold hill to be released in a future perhaps larger earthquake it appears that the fault is capable of partially releasing stored strain in moderate earthquakes maintaining a disequilibrium through multiple earthquake cycles this complicates the application of simple earthquake recurrence models that assume only the strain accumulated since the most recent event is relevant to the size or timing of an upcoming earthquake our findings further emphasize that accumulated slip deficit is not sufficient for earthquake nucleation online material model fault geometry fit to the data for the inversions and model resolution

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

partitioned fault movement and aftershock triggering evidence for fault interactions during the 2017 mw 5 4 pohang earthquake south korea

triangulation to gps and gps to gps geodesy in trinidad west indies neotectonics seismic risk and geologic implications we estimated horizontal velocities at 25 sites first surveyed in a 1901 1903 british ordnance survey triangulation and then resurveyed with gps in 1994 1995 to identify trinidad s principal active on land faults quantify fault slip rates and test for elastic locking our best fit single fault elastic dislocation model put 12 3 mm yr of dextral strike slip on the central range fault 1 2 km locking depth an apparently aseismic active fault the estimated motions also showed statistically insignificant horizontal motion 2 2 1 8 mm yr of right slip 2 7 2 0 mm yr of n s shortening on the eastward on strike extension of the el pilar fault known to be the active transform fault in venezuela repeat gps measurements made between 1994 and 2005 at two sites spanning the island north to south showed a1 4 3 mm yr eastward plate motion parallel dextral velocity differential consistent with our best fit historic 1901 1995 fault slip rate paleoseismology trenching demonstrates that the central range fault cuts 5000 year old sediment and is capped by w550 year old sediment suggesting that it may be locked and may have ruptured at least once during this time interval about w5 mm yr of slip could be taken up on the los bajos fault and additional faults in the offshore south of trinidad the existing 1901 1995 and 1994 2005 geodetic data alone cannot resolve whether the central range fault is

fertile granites of precambrian rare element pegmatite fields is geochemistry controlled by tectonic setting or source lithologies abstract a total of twenty fertile granites and their rare element pegmatite aureoles was examined to correlate their tectonic position relative to the preceding orogenic event with their geochemical signature namely li rb cs be ga sn nb ta y ree sc ti zr be th u f nyf the range of t time difference between metamorphism and or deformation and granite intrusion is 20 to 465 ma for the examined cases there is some tendency toward syn to late orogenic origin of lct s as opposed to post to anorogenic timing of nyf s but the correlation is poor compared to the previously accepted stereotype similarly both metaluminous and peraluminous fertile granites are about equally spread among syn late and anorogenic environments lct systems are largely associated with peraluminous granites whereas all metaluminous to peralkaline plutons bear the nyf signature tectonic control on geochemistry of granite pegmatite suites is poor and secondary to the fundamental influence of the source lithologies yielding granitic melts the lct type suites are derived from undepleted upper crustal lithologies suffering their first anatectic event which mobilizes the most volatile components into low temperature low percentage melts supracrustal sequences as well as ortho and para lithologies of their basement serve as protoliths with variable degrees of involvement the nyf type suites whose plutons have the geochemical signature of a granites may be derived by melting of depleted lower crustal sources residual after preceding anatectic events or possibly by melting of juvenile lithologies with short crustal residence differentiation from mantle derived magmas is highly improbable volatile extraction of nyf elements from the mantle and their pre enrichment in protoliths or melts seems to be required the few mixed systems with variable expressions of a nyf lct signature are derived basically as nyf suites but contaminated by the lct elements from undepleted upper crust via several possible mechanisms

geodetic exploration of strain along the el pilar fault in northeastern venezuela we use global navigation satellite systems observations in northeastern venezuela to constrain the el pilar fault epf kinematics and to explore the effects of the variable elastic properties of the surrounding medium and of the fault geometry on inferred slip rates and locking depth the velocity field exhibits an asymmetric velocity gradient on either side of the epf we use five different approaches to explore possible models to explain this asymmetry first we infer a 1 6 km locking depth using a classic elastic half space dislocation model second we infer a 1 5 km locking depth and a 0 33 asymmetry coefficient using a heterogeneous asymmetric model including contrasting material properties on either side of a vertical fault suggesting that the igneous metamorphic terranes on the northern side are 2 times more rigid than the sedimentary southern side third we use a three dimensional elastostatic model to evaluate the presence of a compliant zone suggesting a 30 reduction of rigidity in the upper 3 km at the depth of a 1 to 5 km wide fault zone fourth we evaluate the distribution of fault slip revealing a widespread partial creep pattern in the eastern upper segment while the upper western segment exhibits a partially locked area which coincides with the rupture surface of the 1797 and 1929 earthquakes to supplement these models we upgrade the previously published displacement simulation method using nonvertical dislocations with data acquired between 2003 and 2013 the localized aseismic displacement pattern associated with creeping or partially creeping fault segments could explain the low level of historic seismicity

rb sr geochronology of granitoid rocks from the pampean ranges argentina a reconnaissance rb sr geochronological investigation of granitoid rocks from the pampean range provides a framework whereby four culminations of igneous activity are delineated granitoids emplaced prior to 500 ma pre and synkinematic bodies ca 475 ma late kinematic bodies and ca 440 and 340 ma post kinematic bodies a number of the post kinematic granitoids have disturbed sr isotope systematics which is related to the formation of microcline megacrysts the carboniferous granitoids are distinguished by their high initial sr ratios i e 0 710 a feature compatible with an origin involving reworking of upper crust or crustal contamination there appears to be no systematic e w migration of granitoid emplacement during the ca 300 ma evolution of the basement rocks in the pampean ranges

how rigid is the stable interior of the north american plate we analyze data from eight permanent gps stations broadly distributed through the interior of the north american plate and use the resulting velocities to estimate an euler vector describing motion of stable north america as a single rigid plate the site velocities fit the single plate model with a mean residual of 1 3 mm yr the residuals do not appear to reflect post glacial rebound and tests for differential motion between eastern and western north america at the new madrid seismic zone show no resolvable motion within uncertainties the residuals likely reflect observational error and thus our estimate of the stability of the plate interior is likely an upper bound

isotopic and trace element study of the loon lake pluton grenville province ontario the loon lake pluton is a small reversely zoned pluton with subordinate isolated bodies of diorite and granodiorite gneiss this pluton is located within the hastings basin of the grenville provin