bitumen veins and eocene transpression neuquen basin argentina abstract in the northwestern part of the petroleum rich neuquen basin veins of solid hydrocarbon bitumen have been reported from over 150 localities the bitumen veins are mostly steeply dipping and show intrusive relationships with their wall rocks the largest are some 8 m wide 8 km long and probably several kilometres deep the bitumen probably formed in the earliest stages of thermal maturation of organically rich source rocks the most likely source rocks for the bitumen as well as for most of the oil and gas in the neuquen basin are black marine shales of the vaca muerta and agrio formations these were deposited in a rift setting during the late jurassic and early cretaceous according to subsidence models the source rocks should have reached thermal maturity in the latest cretaceous or paleocene and should have remained in the oil window ever since although the bitumen has not been dated directly the veins probably formed soon after maturation of the source rocks in other words in the paleocene or eocene the wall rocks of the veins are mostly the source rocks themselves other veins have been emplaced into overlying strata of early cretaceous to paleocene ages or into underlying sediments of jurassic age the bitumen veins have preferred orientations the dominant trend is 060 and subsidiary trends are either 000 to 020 or 100 as in other basins worldwide the majority of bitumen veins in the neuquen basin probably formed by tensile failure in orientations perpendicular to the least compressive stress under the combined effects of regional tectonics and fluid overpressures the orientations of the veins are compatible with the direction of oblique convergence between continental south america and the oceanic nazca plate in the eocene many major structures in the neuquen basin are also of eocene age and may have formed under right lateral transpression

the 1904 ms 7 3 earthquake in central alaska abstract on 27 august 1904 seismic stations from around the globe recorded an m 7 earthquake originating from central alaska very little was known about this earthquake one felt report from rampart alaska had been attributed to the notes of harry fielding reid yet its original source was unknown here we present five felt reports for the 1904 earthquake that show evidence of felt shaking across most of central alaska using the 1904 arrival time data we estimate an epicentral location near lake minchumina at the northeastern extent of the iditarod nixon fault our preferred fault for the 1904 earthquake is the right lateral iditarod nixon fault which though relatively seismically quiet generated an m 6 2 earthquake in 1935 paleoseismic investigations are needed to search for evidence of fault activity including the 1904 earthquake rupture in the tectonically complex region of the 1904 earthquake electronic supplement tables of arrival time figures of station registers visualization of nonlinloc nll solution for the 1904 alaska earthquake distribution of depths of the posterior probability for the 1904 and 1935 events epicenter and samples of the posterior probability distribution for the 1904 and 1935 earthquakes map of southward shift of epicenters and estimated epicenters for the 3 february 2000 kaltag earthquake

hypocentre determination offshore of eastern taiwan using the maximum intersection method summary the maximum intersection maxi method which derives from the master station method msm determines within a 3 d velocity model the absolute hypocentral location based on observed arrival times first the spatial node that better satisfies the arrival time differences computed at all station pairs plus or minus an error tolerance value in seconds is defined as the preliminary hypocentral solution pred second because pred depends neither on the estimate of origin time nor on the residual root mean square rms residual outliers are objectively detected and cleaned out from the original data set without any iterative process or weighting third a statistical minimization residual rms is conducted in a small domain around the pred node which results in a unique final solution the maxi method is applied to the determination of earthquake hypocentres with the proper station correction terms in the southernmost extremity of the ryukyu subduction zone where several dense seismic clusters occur near the seismogenic plate interface the location of earthquakes recorded at both the taiwanese and japanese networks is obtained for about a thousand events between 1992 and 1997 the process uses a detailed 3 d velocity model based on multiple geophysical data sources obtained in the junction area between subduction and collision east of taiwan the earthquake clustering and the significant drop in residual statistics 1 20 0 80 and 0 35 s for taiwanese catalogue msm and maxim solutions respectively indicate the accuracy of the method which can be used to routinely determine absolute hypocentre location based on observed arrival times

anisotropy of magnetic susceptibility and p wave velocity in core samples from the taiwan chelungpu fault drilling project tcdp the anisotropy of magnetic susceptibility ams and anisotropy of p wave velocity apv were characterized in core samples retrieved from the tcdp hole a at depths ranging from 600m to 1400m thus cutting across the thrust fault that ruptured during the 1999 chi chi earthquake our data show that the ams was similar for all the samples regardless of the lithologic contrasts with a magnetic fabric characteristic of weakly deformed sedimentary rocks that had undergone layer parallel shortening this robust observation applies to both the siltstones and sandstones at all depths investigated in contrast the apv data reflect fundamental differences between the elastic fabrics in the two facies while apv of the siltstone samples is controlled by a preferred orientation of the matrix minerals the apv of the sandstones is greatly influenced by microcrack porosity with a preferred orientation parallel to the maximum principal direction of paleostress and tectonic deformation these ams and apv data obtained in tcdp hole a at locations not directly impacted by the coseismic rupture provide a first order petrofabric framework for the characterization of hydromechanical anisotropy in the chelungpu fault system

forces controlling the present day state of stress in the andes the present day state of stress in the andes is expected to be controlled primarily by two different types of forces 1 the resistive force exerted on the western overriding margin of the south american plate and 2 forces that arise from the thickened crust of the andes i e the effect of topography and its compensating crustal root we have studied these forces on the basis of a model for the dynamics of the entire south american plate in which the andes are embedded in this model a given set of forces is constrained by the criterion that the net torque on the plate should vanish a thin elastic shell representation is used to calculate the intra plate stress field associated with the various force distributions we define a reference model for the present study that incorporates a uniform magnitude for the resistance associated with convergence along the western plate margin fpcr plate contact resistance and does not include the effects of topography subsequently we investigate the effect of lateral variation in the magnitude of fpcr and add the topography related forces the main results are 1 a uniform magnitude of fpcr leads to a better match with the observations than a magnitude that is a function of the dip of the lithosphere subducting below the western plate margin 2 the amount of horizontal compression across the andes found in the case that ridge push is considered to be the only force driving the south american plate is small compared to the value required to sustain the andes

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

kinematic models of basement cover interaction insights from the malargue fold and thrust belt mendoza argentina abstract we investigate through natural examples from the malargue fold and thrust belt the manner in which the basement structures interact with the cover in a thick skinned fold and thrust belt our work suggests that there is a broad spectrum of basement cover interaction mechanisms with two end members coupled and uncoupled interactions the kind of bonding between basement and cover is related to the propagation to slip ratio p s because high values of this ratio indicate rapid forward propagation of shortening into the cover while low values favour welding between basement and cover structures we analyse the factors controlling the kinematics of basement cover deformation and find that not only the strength of the cover its thickness and its mechanical anisotropy control the p s and basement cover bonding but also the strain rate the thickness of synorogenic strata and the presence of pre existing faults

strain fabric analysis applied to hydrothermal ore deposits emplaced during changing geodynamical conditions infiernillo and las picazas san rafael massif argentina abstract infiernillo and las picazas are two small hydrothermal ore deposits in the northern san rafael massif argentina they are genetically linked to the permian choiyoi volcanic province which reflects the transition from a convergent plate margin to an extensional regime calc alkaline early permian lower choiyoi magmatism was syntectonic with transpressional deformation of the san rafael orogeny whereas transitional late permian upper choiyoi sequences were emplaced under a transtensional regime during the post san rafael extension infiernillo is a cu mo porphyry type deposit hosted by pyroclastic rocks of the lower choiyoi it consists of a central quartz plug surrounded by a potassic and a phyllic halo and a set of peripheral polymetallic cu pb zn veins cropping out close to the alteration zone the las picazas deposit consists of a group of low sulfidation epithermal galena bearing veins hosted by early palaeozoic meta sediments strain fabric and available 2 d and 3 d kinematic analyses were performed in order to define the relationships between both deposits and the geodynamic scenario these data reveal that a porphyry emplacement at infiernillo occurred during the declination of the san rafael orogeny shortly before the change in stress regime and b las picazas low sulfidation epithermal veins were emplaced during the subsequent transtensional post san rafael regime these results prove that each ore deposit is linked to a different stress regime reflecting the change in geodynamical conditions that prevailed during the emplacement of the choiyoi volcanism thus strain fabric analysis at both ore deposits allows us to confirm that the tectonic regime is a major factor in controlling the mineralization style of hydrothermal ore deposits

magnetic fabrics and strain in pencil structures of the knobs formation valley and ridge province us appalachians pencil structures which are found in weakly deformed mudrocks reflect the bedding cleavage intersection in weak to moderatelycleaved rocks their presence indicates conditions where bedding and cleavage fabrics are approximately equal in intensity we have determined the anisotropy of magnetic susceptibility ams in pencil structures from a sequence of mudstones of the ordovician knobs formation in the valley and ridge province of the us appalachians magnetic mineralogy was determined by x ray analysis and lowtemperature susceptibility measurements distribution of the magnetic ellipsoid axes is consistent with the incipient tectonic fabric of the pencil mudstones the maximum susceptibility axes parallel the pencils long axes while the minimum axes of susceptibility are normal to the primary sedimentary fabric independent strain quantification permits a correlation between magnetic fabric and tectonic strain an exponential relationship between the ams shape parameter t and tectonic shortening has been found for the interval of 10 25 shortening shortening 17 p exp t this relationship appears to be supported by tectonic strains up to 40 the t parameter t lnf 2 lnl lnl lnf where l lineation is kmax kint and f foliation is kint kmin describes the shape of the magnetic susceptibility ellipsoid which appears more sensitive to strain than past correlation attempts with the magnetic intensity parameter p or p 0 whereas this correlation between strain and ams is only valid within a restricted window of strain 10 40 shortening it establishes the magnitude and directions of tectonic strain in weakly deformed clay rich rocks where strain indicators are otherwise lacking or are poorly developed q 2003 published by elsevier science ltd

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

short and long term effects of gps measured crustal deformation rates along the south central andes in this study we present the contemporary crustal deformation field along the central and southern andes 17 42 s estimated from four global positioning sys tem gps campaigns conducted in 1994 97 we find that the majority of the observed crustal deformation field is relatively homogenous roughly parallel to the plate conver gence direction with decreasing velocities away from the trench we attribute this type of deformation pattern to the inter seismic phase of an earthquake deformation cycle caused by 100 locking of the thrust interface between the subducting nazca and the overrid ing south american plates we have also detected a strong post seismic deformation sig nal in the vicinity of the 1995 mw8 0 antofagasta 22 26 s and 1960 mw9 5 chile 38 43 s earthquakes this type of deformation can be described as short term in nature compared to geological timescales the above conclusions are based on the results of the 3 d andean elastic dislocation model aedm by subtracting the aedm predicted deformation rates from the observations we obtained a residual velocity field that high lights the post seismic as well as more long term deformation eects for example we find a strong evidence for the continuing crustal shortening across the back arc reach ing its maximum 4 mm yr in the very north of our study area in addition between latitudes 29 34 s there is an indication of e w oriented extension within the fore arc in accordance with the recent geologic findings for the n s oriented normal faulting

stress trajectories across the northeast alaska range a single earthquake on the southeast portion of the denali fault in 1981 and two earthquake swarms occurring in 1981 and 1984 on the northern flanks of the alaska range south of fairbanks indicate that the axis of maximum horizontal compressive stress is oriented in a nw se direction in the region this is in accord with earlier findings by nakamura et al 1980 that tectonic trends signal a similar orientation of maximum horizontal compressive stress trajectories here

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

stress modeling in the andes constraints on the south american intraplate stress magnitudes regions of high topography which exhibit both compressional and extensional deformation provide a natural laboratory to place constraints on horizontal intraplate stress magnitudes an elastic finite element analysis of the lithospheric stress field in the cordillera bianca region of peru has been used to evaluate the lithospheric stress state and constrain the south american intraplate stress magnitudes the orthogonal orientation of the andean high topography to the east west regional stress field in conjunction with the well documented change in deformation style from compression to extension across the cordillera provides a unique setting for the stress modeling a two dimensional finite element grid consisting of an assembly of isotropic elastic quadrilateral elements in a state of plane strain was used to represent the lithosphere an isostatically balanced crustal density model was used to calculate the stresses associated with the lateral density variations between the andean topography and the brazilian shield in some models horizontal stress was concentrated at midcrustal depths by including vertical variation in young s modulus the modeling results indicate bounds of 10 and 75 mpa for the magnitude of the average horizontal stress averaged over a 100 km thick lithosphere a preferred value of 25 mpa is obtained on the basis of fitting all of the data for the rheological models considered and predicting a transition from extension to compression near the 3000 m elevation contour such a far field average stress is consistent with a ridge push origin because the modeling performed in this study assumes that the topographic load is entirely compensated by the buoyancy of the deflected moho these estimates represent upper bounds the effect of incorporating thermal support for the topographic load of the cordillera bianca would be to further reduce our estimate of the intraplate stress magnitudes analysis of the distribution of calculated stress with depth indicates that previous assumptions about the vertical plane shear stress within the lithosphere being negligible are acceptable for the geometry of the andes

temporal and spatial relationships of thick and thin skinned deformation a case study from the malargue fold and thrust belt southern central andes abstract in this paper we analyse two end member models of temporal and spatial interactions between thick and thin skinned structures in a thrust front with pre existing rift structures in the most commonly accepted model a hinterland to foreland sequence of inversion of pre existing normal faults is proposed as a result the emplacement of shallow thrust sheets in the sedimentary cover occurs before the basement inversion in the foreland in the other model basin inversion occurs early in the deformation history of the external part of a fold and thrust belt as the result of a foreland to hinterland sequence of inversion the malargue fold and thrust belt 34 36 s formed in response to compression of the mesozoic neuquen basin during neogene to pleistocene times integrating detailed structural data from the northern part of this belt with new ar ar dating we propose a revised kinematic model of thick and thin skinned interaction and define the temporal spatial evolution of the belt comparison of the timing of deformation in the thick and thin skinned areas strongly supports the hypothesis that the reactivation of normal faults was coeval with the insertion of shallow detachments and low angle thrusting along the migrating front of the thrust belt and occurred from the foreland to the hinterland detachments occur at several stratigraphic horizons including a deep basement decollement related to the basement involved thrusting and shallow detachments located within the jurassic and cretaceous beds these shallow and deep detachments were coeval producing simultaneous development of thrusts during the complex deformation of the thrust front between 15 and 8 ma

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

magnetic fabric of clay sediments from the external northern apennines italy abstract we report on the anisotropy of magnetic susceptibility ams analyses of fine grained sediments deposited during the messinian in foredeep basins at the front of the northern apenninic chain the data refer to 32 sampling sites mostly distributed in the fine grained intervals of the laga and colombacci formations extending along the belt for a total length of about 300 km rock magnetism analyses indicate that the magnetic susceptibility and its anisotropy are in most cases dominated by the paramagnetic minerals of the clay matrix in order to delineate the contribution of the ferrimagnetic fraction to the overall susceptibility fabric the anisotropy of the anhysteretic remanent magnetisation was investigated at some representative sites the magnetic fabric of the studied sediments mostly reflects the effects of compaction showing a predominant magnetic foliation parallel to the bedding plane at all the sites a well distinct magnetic lineation was also found which is parallel to the fold axes and thrust fronts both at local and regional scales this feature is maintained in sequences that differ for sedimentological character and age implying that the magnetic lineation was produced by a mild tectonic overprint of the primary sedimentary compactional fabric the relationship between the magnetic lineation trends and the vertical axis rotations detected by speranza et al speranza f sagnotti l mattei m 1997 j geophys res 102 3153 3166 indicates that the magnetic lineation formed during the compressive phases of the messinian early pliocene when the apenninic front was almost rectilinear and oriented n320

cenozoic deformation and tectonic style of the andes between 33 and 34 south latitude 1 the andes of argentina and chile between latitudes 33 and 34 s are composed from west to east of an oligocene to miocene volcanic arcs and the neogene east vergent aconcagua fold and thrust belt of the cordillera principal and the basement block faulted cordillera frontal a regional cross section suggests that shortening across the andes was achieved by thrusting along detachments at several levels in the crust while thin skinned deformation along newly formed thrusts occurred in mesozoic sequences of the eastern cordillera principal reactivation of preexisting jurassic and oligocene normal faults has resulted in additional hybrid thick and thin skinned structures in the western cordillera principal five major thrusting events are recognized in this part of the andes 1 early to middle miocene tectonic inversion of the extensional faults in the western cordillera principal 2 middle to late miocene development of the aconcagua fold and thrust belt 3 late miocene uplift of cordillera frontal 4 late miocene early pliocene out of sequence thrusting in the cordillera principal and 5 pliocene to present deformation of the foreland

revision of magnitudes of large shallow earthquakes 1897 1912 abstract in previous research trace amplitudes of surface wave maxima recorded by undamped milne seismographs were used to determine the surface wave magnitudes ms of large shallow earthquakes which occurred prior to 1912 for this purpose the effective gain of these instruments was calibrated by using the surface wave magnitudes ms gr which were calculated from the unpublished worksheets for seismicity of the earth of gutenberg and richter in this paper the real quality of ms gr is critically re evaluated by using independent sets of data it is found that ms gr for the period 1904 1909 is considerably overestimated the average excess from the real ms is 0 5 units for 1904 1906 0 4 for 1907 0 3 for 1908 1909 and 0 0 for 1910 1912 this overestimation is so systematic and large that the previous results are all redetermined the average effective gain of milne instruments is revised to be 21 9 previously the gain depended on ms this revision results in systematic reduction in the previously assigned magnitudes the revised values of ms for 264 shallow earthquakes with ms 6 8 and over in the period 1897 1912 inclusive are listed the present revision is large enough to preclude the possibility of the high activity of large shallow earthquakes around the turn of the century the present results have a direct effect on all the magnitude catalogues of shallow earthquakes which occurred prior to 1909

location of the focus and tectonics of the focal region of the california earthquake of 18 april 1906 modern relocation constrains the hypocenter of the 18 april 1906 california earthquake within an 8 24 km southwest northeast trending zone to the north of san francisco that intersects the offshore san andreas fault system west of san francisco here we further constrain the location of the 1906 focus and examine the tectonics of the focal region using recent microseismicity relocated in a 3d model along with other seismological geological and marine evidence in agreement with previous work we associate the 1906 focus with an extensional right stepover in the san andreas fault system a zone of sea floor subsidence and complex normal and strike slip faulting we define a likely focal volume between lake merced and offshore of the golden gate centered near 37 77 n 122 55 w and 10 km depth we hypothesize possible 1906 rupture in this region by normal deformation around a 10 km long steeply west dipping structure trending about 20 clockwise to the san andreas fault zone and bilateral strike slip fault rupture along the san andreas fault system away from this structure rupture to the northwest on a vertical currently aseismic faulting structure under the golden gate fault and rupture to the southeast under the san francisco peninsula either along a steeply southwest dipping structure showing present day extensional tectonism or along a near vertical currently aseismic fault zone all three of these structures extend from the near surface to about 10 km depth we also identify a deeper 15 20 km long linear trend of clustered seismicity at 10 13 km depth rotated about 6 clockwise relative to the strike of the san andreas fault which connects the north end of the focal volume with the south end of the seismicity defining the southwest dipping structure under the san francisco peninsula we propose that this trend shows faulting at the base of a brittle upper crust in response to underlying shear in a ductile lower crust these interpretations on the focal region of the 1906 earthquake have implications for seismotectonic understanding earthquake monitoring and seismic hazard assessment in the san francisco bay area

predicting orogenic wedge styles as a function of analogue erosion law and material softening 1 the evolution of a compressive frictional wedge on a weak frictional and planar decollement subjected to frontal accretion is predicted with a two step method called sequential limit analysis the first step consists in finding with the kinematic approach of limit analysis the length of the active decollement and the dips of the emerging ramp and of the conjugate shear plane composing the emerging thrust fold the second step leads to a modification of the geometry first because of the thrust fold development due to compression and second because of erosion erosion consists in removing periodically any material above a fictitious line at a selected slope as done in analogue experiments this application of sequential limit analysis generalizes the critical coulomb wedge theory since it follows the internal deformation development with constant frictional properties the deformation is mostly diffuse a succession of thrust folds being activated so that the topographic slope reaches exactly the theoretical critical value frictional weakening on the ramps results in a deformation style composed of thrust sheets and horses applying an erosion slope at the critical topographic value leads to exhumation in the frontal central or rear region of the wedge depending on the erosion period and the weakening erosion at slopes slightly above or below the critical value results in exhumation toward the foreland or the hinterland respectively regardless of the erosion period exhumation is associated with duplexes imbricate fans antiformal stacks and major backthrusting comparisons with sandbox experiments confirm that the thickness dips vergence and exhumation of thrust sheets can be reproduced with friction and erosion parameters within realistic ranges of values

migration of cenozoic deformation in the eastern cordillera of colombia interpreted from fission track results and structural relationships implications for petroleum systems previously unreleased fission track results and regional structural relationships are used to interpret the migration of deformation during cenozoic orogenesis in the eastern cordillera cordillera oriental of the colombian andes low temperature thermochronological results are based on apatite and zircon fission track analyses of 41 samples collected along vertical and horizontal transects across the eastern cordillera at 4 7n latitude inverse modeling of fission track results helps delimit the most probable cooling histories caused by exhumation linked to upper crustal deformation these inverse models are constrained by known structural geometries chronostratigraphy biostratigraphy and vitrinite reflectance data fission track data and modeling results indicate a close correspondence in the timing and style of deformation along the western and eastern flanks of the eastern cordillera east directed fold thrust deformation along the eastern boundary with the llanos foreland basin was underway by the late oligocene and early miocene similarly west directed fold thrust structures along the western boundary with the intermontane middle magdalena valley basin became active at approximately the same time less well known is the time of initial shortening within the axial segment of the eastern cordillera although fission track results suggest active exhumation by the early miocene shortening may have commenced much earlier during the late eocene timing relationships for the eastern cordillera have important implications for the generation migration and accumulation of petroleum in the middle magdalena valley intermontane basin and the llanos foreland basin our study provides a regional context to assess the timing of structural trap development and improve exploration and development of new and existing reservoirs in colombia and analogous fold thrust systems elsewhere

near field deformation from the el mayor cucapah earthquake revealed by differential lidar large moment magnitude m w 7 continental earthquakes often generate complex multifault ruptures linked by enigmatic zones of distributed deformation here we report the collection and results of a high resolution nine returns per square meter airborne light detection and ranging lidar topographic survey of the 2010 m w 7 2 el mayor cucapah earthquake that produced a 120 kilometer long multifault rupture through northernmost baja california mexico this differential lidar survey completely captures an earthquake surface rupture in a sparsely vegetated region with pre earthquake lower resolution 5 meter pixel lidar data the postevent survey reveals numerous surface ruptures including previously undocumented blind faults within thick sediments of the colorado river delta differential elevation changes show distributed kilometer scale bending strains as large as 10 3 microstrains in response to slip along discontinuous faults cutting crystalline bedrock of the sierra cucapah

evidence for and implications of a bering plate based on geodetic measurements from the aleutians and western alaska 1 global positioning system gps measurements are used to examine the hypothesis of a clockwise rotating bering plate originally proposed on the basis of seismicity the bering plate encompasses the bering sea western alaska and the aleutian islands gps measurements from the bering plate s interior show south to southwest motions of 3 5 mm a where a is years we construct elastic dislocation models to determine the spatial distribution and intensity of locked patches on the aleutian subduction interface we use these to remove interseismic strain from the gps observation and determine an arc translation velocity for each region of the aleutians revealing south and southwest motions of 4 8 mm a we combine the arc translation rates with measurements from the bering plate s interior sites and estimate the euler pole for the bering plate relative to north america to be located at 42 5 n 121 3 e with an angular speed of 6 0 ma the clockwise rotation of the bering plate may cause left lateral faulting in interior alaska the bering plate s interaction with south central alaska may be responsible for the decreased slip rate on the western denali fault and for contraction across the central alaska range we analyze slip partitioning along the aleutian arc on the basis of both gps measurements and slip azimuths of thrust earthquakes and find a systematic discrepancy between plate convergence direction and slip azimuths we conclude that slip partitioning in the back arc only develops west of amchitka pass whereas slip partitioning in the fore arc is present throughout the arc

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

miocene deformation in the orogenic front of the malargue fold and thrust belt 35 30 36 s controls on the migration of magmatic and hydrocarbon fluids abstract the integration of surface observations and sub surface data wellbore and seismic from the orogenic front of the malargue fold and thrust belt allows us to study its kinematics and to interpret the local stress field and its control over fluid magmatic and hydrocarbon migration reverse faults correspond to inverted nnw striking mesozoic normal faults and n s striking cenozoic low angle thrusts parallel to the orogen oblique structures with strike slip movement are also present the magmatic activity in the study area was strongly controlled by this structural framework and the in situ stress field miocene dykes and sills were emplaced in relation to strike slip and reverse faults respectively we propose an evolution of the study region from a foredeep sector in the early middle miocene to a peak in deformation in the late miocene and finally a waning of deformation from the pliocene to the present our structural model suggests that during the evolution of the thrust front the in situ stress field changed from a compressional to strike slip compressional stress field favouring the synchronous emplacement of sills and dykes this alternation of stress regimes favours hydrocarbon migration through both thrusts and subvertical strike slip faults this exchange between both stress regimes is likely related to the similar values of the minimum 3 and intermediate 2 principal stress with an e w oriented maximum principal stress 1 according to the plate convergence vector

neogene to quaternary broken foreland formation and sedimentation dynamics in the andes of nw argentina 25 s 1 the northwest argentine andes constitute a premier natural laboratory to assess the complex interactions between isolated uplifts orographic precipitation gradients and related erosion and sedimentation patterns here we present new stratigraphic observations and age information from intermontane basin sediments to elucidate the neogene to quaternary shortening history and associated sediment dynamics of the broken salta foreland this part of the andean orogen which comprises an array of basement cored range uplifts is located at 25 s and lies to the east of the arid intraorogenic altiplano puna plateau in the salta foreland spatially and temporally disparate range uplift along steeply dipping inherited faults has resulted in foreland compartmentalization with steep basin to basin precipitation gradients sediment architecture and facies associations record a three phase 10 5 and 2 ma east directed yet unsystematic evolution of shortening foreland fragmentation and ensuing changes in precipitation and sediment transport the provenance signatures of these deposits reflect the trapping of sediments in the intermontane basins of the andean hinterland as well as the evolution of a severed fluvial network present day moisture supply to the hinterland is determined by range relief and basin elevation the conspiring effects of range uplift and low rainfall help the entrapment and long term storage of sediments ultimately raising basin elevation in the hinterland which may amplify aridification in the orogen interior

matrix deformation in a basement involved fold and thrust belt a case study in the central andes malargue argentina abstract an analysis of the anisotropy of magnetic susceptibility ams is used to investigate the matrix strain record of weakly deformed clastic rocks including sandstones and shales along a cross section of the malargue fold and thrust belt mftb argentina we collected 339 oriented cores from the tres esquinas sandstones the red beds of the tordillo and neuquen formations as well as from shales silts of the mendoza group overall 90 of the magnetic fabrics are well defined and are related to the strain imprint of the layer parallel shortening among the tectonic related fabrics 40 show the development of a magnetic lineation at right angle of the shortening type ii 38 display an apparent loss of magnetic foliation type iii and 21 develops a magnetic foliation at right angle of the shortening type iv there is no lithological control on magnetic fabric typology despite contrasting ferromagnetic mineralogy between the red sandstones and dark shales thin section observations highlight the good match between the orientation of both the susceptibility ellipsoid and microstructure orientation which enables us to infer the preferred orientations of the petrofabric i e finite strain directions in this way two trends can be recognized in the study area shortening directions trending n110 in the north and trending n80 in the south in addition the spatial distribution of magnetic fabric typology and burial data suggests an atypical pattern of deformation from the foreland to hinterland such a pattern contrasts with previous studies in fold thrust belt settings suggesting that at the matrix scale the deformation even in a pre folding setting is compartmentalized and controlled by the occurrence of deep seated thrusts localized along inherited structures from the analysis of cross sections we can distinguish several domains each of them reflecting distinct states of matrix deformation

the fracture network a proxy for mesoscale deformation constraints on layer parallel shortening history from the malargue fold and thrust belt argentina an analysis was performed of the fracture networks in the n s trending thick skinned malargue fold and thrust belt mftb a total of 2000 planar structures including joints and veins were measured in different structural domains ranging from surficial thin skinned systems detached in the cover to large scale structures such as basement cored folds the investigated stratigraphic section ranges from the middle jurassic cuyo group to the paleocene malargue group including sandstones siltstones shales and limestones four main fracture sets are identified trending e w nw se ne sw and n s the abutting relationships provide a reliable chronology between the four fracture sets which are ubiquitously found in the mftb throughout the various structural domains due to this observation we assume the fracture signal to be regional and developed in response to both large scale processes and folding in particular based on a fold test and the characteristics of data dispersion the fracture sets i ii and iii exhibit a prefolding origin while set iv shows a synfolding origin a regional interpretation of the various fractures is proposed involving several stages of fracture formation from compaction to folding including prefolding layer parallel shortening the fracture signal yields useful insights about the structural history of the mftb and the spatiotemporal evolution of the foreland tectonic regime since late cretaceous times we then place the various identified fracture sets into the known pattern of geodynamic evolution since the late cretaceous

aptian to recent compressional deformation foothills of the neuquen basin argentina abstract the neuquen basin lies in north western patagonia on the eastern foreland of the andes it formed as a rift basin in the early mesozoic and contains some 5000 m of triassic to aptian sediment mainly marine as a result of andean orogeny the western edge of the basin now forms part of the foothills we describe some of the main compressional structures drawing on surface and sub surface data we argue that regional eastward dips are due to west verging thrust displacements on the andacollo loncopue fault system during a late cretaceous peruvian phase aptian to campanian continental sediment accumulated in a retro arc foreland basin which was mainly of flexural origin nevertheless more than 1500 m of late cretaceous sediment accumulated in the footwall of the east verging agua amarga thrust the peruvian phase was responsible also for transpressional reactivation of a rift transfer zone the huincul arch the incaic phase eocene was responsible for north westerly trending folds and thrusts reactivation of cretaceous thrusts abundant andesitic lavas and high level intrusions and a swarm of north easterly trending bitumen dykes the quechua phase miocene to recent produced northerly trending folds and thrusts and a miocene foreland basin containing some 1000 m of basalt lava flows structures that formed during the incaic and quechua phases are broadly compatible with the history of convergence at the pacific margin of south america as deduced from plate reconstructions

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

the magnetic fabric of weakly deformed late jurassic shales from the southern subalpines chains french alps evidence for sw directed tectonic transport direction abstract extensive magnetic fabric investigations have been conducted on the late jurassic sedimentary black shales 37 sites 362 samples the so called terres noires formation from the southern subalpine chains western alps this study completes a previous study done in the northern subalpine chains which demonstrated that the terres noires formation preserves a subtle magnetic lineation related to tectonic transport direction in the southern subalpine chains diois devoluy embrunais digne nappe similar magnetic fabrics have been found the shape of the magnetic fabric is oblate and locally mirrors the gradient of deformation in the embrunais footwall the magnetic foliation is parallel to the bedding or to the slaty cleavage about 50 of the magnetic lineations have down dip magnetic directions while the other magnetic lineations are sub horizontal or parallel to the intersection bedding cleavage the tectonic magnetic fabrics recorded in the embrunais confirm the ability of the terres noires to record tectonic transport direction the magnetic fabric geometry suggests sw directed tectonic transport in the southern subalpine chains the diois appears as a tip zone where transport directions are abruptly clockwise rotated from nw directed in the northern subsalpine chains to sw directed the magnetic fabric from the digne nappe exhibits a fan pattern of transport directions in close agreement with the arcuate shape of the thrust

cenozoic foreland basin system in the central andes of northwestern argentina implications for andean geodynamics and modes of deformation 1 cenozoic strata in the central andes of northwestern argentina record the development and migration of a regional foreland basin system analogous to the modern chaco parana alluvial plain paleocene lower eocene fluvial and lacustrine deposits are overlain by middle upper eocene hypermature paleosols or an erosional disconformity representing 10 15 myr this supersol disconformity zone is traceable over a 200 000 km2 area in the andean thrust belt and is overlain by 2 6 km of upward coarsening eastward thinning upper eocene through lower miocene fluvial and eolian deposits middle miocene pliocene fluvial lacustrine and alluvial fan deposits occupy local depocenters with contractional growth structures paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments detrital zircon ages from cenozoic sandstones cluster at 470 491 522 544 555 994 and 1024 1096 ma proterozoic mesozoic clastic and igneous rocks in the puna and cordillera oriental yield similar age clusters and served as sources of the zircons in the cenozoic deposits arc derived zircons become prominent in oligo miocene deposits and provide new chronostratigraphic constraints sediment accumulation rate increased from 20 m myr during paleocene eocene time to 200 600 m myr during the middle to late miocene the new data suggest that a flexural foreland basin formed during paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front despite differences in deformation style between bolivia and northwestern argentina lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late paleocene time

evidence of active shortening along the eastern border of the san rafael basement block characterization of the seismic source of the villa atuel earthquake 1929 mendoza province argentina on the 30 may 1929 a massive earthquake occurred in the san rafael area southern mendoza province leading to the destruction of the villa atuel and las malvinas towns the region affected by the ground shaking covers a large part of southern south america although no surface breaks have been detected on the surface several authors have pointed out active faults that could be related to the event of 1929 using satellite imagery and field observations we investigated two active faults situated on the eastern border of the san rafael block srb close to or within the epicentral area the most prominent faults are the c 40 km long las malvinas and c 30 km long cerro negro reverse faults which are located near the epicentral area geological and morphological observations allow us to describe late pleistocene activity and estimate the long term slip rates of these faults possible ruptures that match our observations and which are compatible with the cartographic length of these faults would account for a seismic moment magnitude of m 0 2 8 10 19 n m and a moment magnitude of m w 6 9 the morphological signatures of these fault segments and the occurrence of the san rafael earthquake suggests that the southern mendoza province is still currently submitted to shortening

cenozoic contractional reactivation of mesozoic extensional structures in the eastern cordillera of colombia 1 the eastern cordillera of colombia is key to understanding the role of inherited basement anisotropies in the evolution of active noncollisional mountain belts in particular the rio blanco guatiquia region of the eastern cordillera is exemplary in displaying a variety of phenomena that document the importance of the orientation geometry and segmentation of preorogenic anisotropies we document the first unambiguous evidence that extensional basement structures played an important role in determining the locus of deformation during contractional reactivation in the eastern cordillera detailed structural field mapping and analysis of industry seismic reflection profiles have helped to identify the inherited san juanito naranjal and servita normal faults and associated transfer faults as important structures that were inverted during the cenozoic andean orogeny apparently the more internal faults in the former rift basin were not properly oriented for an efficient reactivation in contraction however these faults have a fundamental role as strain risers as folding is concentrated west of them in contrast reactivated normal faults such as the more external servita fault are responsible for uplifting the eastern flank of the eastern cordillera in addition these structures are adjacent and intimately linked to the development of thin skinned faults farther east in part the superimposed compression in this prestrained extensional region is compensated by lateral escape the dominant presence of basement involved buckling and thrusting and the restricted development of thin skinned thrusting in this inversion orogen makes the eastern cordillera a close analog to the intraplate atlas mountains of morocco and other inverted sectors of the andean orogen farther south

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

anisotropy of magnetic susceptibility in the scaglia rossa pelagic limestone abstract during folding of the scaglia rossa limestone in umbria italy deformation was mainly accommodated by pressure solution cleavage fossils between the cleavage planes appear visibly undeformed yet the limestone possesses a weak magnetic fabric the maximum and intermediate principal axes of the magnetic anisotropy ellipsoid define a distinct magnetic foliation plane within which a weak concentration of the maximum axes forms a magnetic lineation neither of these features is of sedimentary origin results from a slumped outcrop where bedding and a cleavage induced by overburden compaction have different attitudes show that the magnetic foliation is caused by the compaction comparisons with field derived structural data suggest that the magnetic lineation was produced tectonically during deformation of the apennine fold belt

contemporary stress orientations in the andean retroarc between 34 s and 39 s from borehole breakout analysis 1 in this paper we present the results of the analysis of borehole breakouts from 115 wells drilled within neuquen basin in the andean retroarc between 34 and 39 s argentina the first order present day stress orientation in the andean retroarc is expected to be mainly controlled by the plate boundary forces azimuth 80 and the topographic forces e w the obtained maximum horizontal stress shmax has a preferred trend with a resultant direction of azimuth 88 7 and a 95 confidence interval of 13 3 consistent with the expected trend the horizontal stress trajectory map achieved for this region shows that the shmax along the study area is not completely uniform to the north of colorado river the shmax shows an ese tendency interpreted as significant influenced by the topographic forces to the south of colorado river shmax has an ene trend similar to the expected based on plate boundary forces to the southeast of the region a ne direction was found probably showing a basement structural control in the stress field geometry the stress orientations obtained for the whole region show that plate boundary forces drag basal and topographic forces are strongly controlling the stress direction distribution

kinematic constraints on intra arc shear and strain partitioning in the southern andes between 38 s and 42 s latitude 1 on the basis of structural field work fault kinematic analysis and the analysis of digital imagery we describe the northern part of the southern andean intra arc liquine ofqui fault zone lofz as an sc like fault zone system accommodating part of the nazca south american plate convergence obliquity kinematic modeling suggests that the lofz accommodated 124 24 21 km of dextral displacement between 40 s and 42 s and 67 13 11 km between 38 s and 40 s since the pliocene associated vertical axis rotations are 31 4 clockwise and 9 1 counterclockwise along synthetic and antithetic faults respectively mean pliocene to recent shear rates along the lofz decrease northward from 32 6 mm yr to 13 3 mm yr compatible with partitioning of half of the convergence obliquity into the intra arc zone north of 40 s and complete partitioning to the south the displacement gradient along the intra arc zone results in margin parallel shortening of the fore arc

surface rupture on the denali fault interpreted from tree damage during the 1912 delta river mw 7 2 7 4 earthquake implications for the 2002 denali fault earthquake slip distribution during the 3 november 2002 denali fault earthquake surface rupture propagated through a small old growth forest in the delta river valley and damaged many trees growing on the fault damage was principally the result of fault offset of tree roots and tilting of trees some trees were split by surface faults that intersected the base of their trunks or large taproots a few trees appear to have been damaged by strong shaking many of the older trees damaged in 2002 were deformed and scarred some of these scarred trees exhibit past damage indicative of surface faulting and have abrupt changes in their annual ring patterns that coincide with the past damage annual ring counts from several of these older scarred trees indicate the damage was caused by surface rupture on the denali fault in 1912 the only earthquake of sufficient magnitude that fits the requirements for timing and general location as recorded by the damaged trees is a widely felt m s 7 2 7 4 earthquake on 6 july 1912 informally referred to as the 1912 delta river earthquake seismologic data and intensity distribution for the 1912 delta river earthquake indicate that its epicenter was within 60 90 km of the delta river and that rupture probably propagated toward the west inferred fault length displacement and rupture direction suggest the 1912 rupture was probably largely coincident with the western lower slip section of the 2002 rupture

processes of oscillatory basin filling and excavation in a tectonically active orogen quebrada del toro basin nw argentina intramontane basins may act as important sediment storage areas serve as recorders of the history of deformation record syntectonic deposition and document the evolution of climatic conditions during deposition we document the timing cyclicity and processes that led to the filling and reexcavation of the intramontane quebrada del toro basin in nw argentina geomorphic and geologic observations indicate that the basin was filled with sediment that has been subsequently excavated at least two times in the last 8 m y the last filling and excavation cycle occurred within the last 0 98 m y and has led to the deposition and removal of 61 4 km 3 of material from the basin leading to a basin wide averaged minimum denudation rate of 0 16 mm yr aggradation within the basin took place due to channel steepening of the downstream fluvial system that connects the intramontane basin to the foreland this portion of the fluvial system is actively incising through an uplifting bedrock zone we use observations within the toro to test a quasi physically based model of channel aggradation behind a rising base level that rises due to downstream channel steepening our work shows that the bedrock incision rate constant required to reproduce conditions observed within the toro basin is consistent with values measured independently in similar rock types therefore in intramontane basins that experience similar processes of filling and evacuation this model may be used to assess the relative importance of tectonic rock uplift bedrock resistance to fluvial incision and climate in determining the geomorphic and sedimentologic history of these basins

exhumation history of the andean broken foreland revisited the andean broken foreland in west central argentina located 400 800 km from the peru chile trench is associated with flat subduction linked to collision of the oceanic juan fernandez ridge while the conditions associated with flat subduction would be expected to produce increases in rock uplift and exhumation where thrusting and dynamic forces work together a prevalence of pre cenozoic apatite fission track aft cooling ages suggests that there is no such link the lack of cenozoic cooling ages is at odds with structural reconstructions and basin studies along the foreland that show several kilometers of exhumation this paradox can be reconciled by taking into account the thermal effects of flat subduction that removed the mantle wedge and a significant source of heat flow into the crust reinterpretation of published aft exhumation data 320 ages using more realistic lower geothermal gradient values allows for substantial exhumation and explains the lack of cenozoic exhumation ages across the foreland region

new constraints on tectonics of interior alaska earthquake locations source mechanisms and stress regime we used the joint hypocenter determination jhd method to relocate 3611 crustal earthquakes that occurred from 1988 to 1999 in central alaska the new earthquake locations provide more details on the structure of the kantishna cluster and better locations for the aftershock sequence of the 29 november 2000 m l 5 6 earthquake in the minto flats seismic zone the jhd locations for the aftershocks of the 1995 m w 6 0 minto flats earthquake and 22 october 1996 m w 5 8 earthquake near the denali fault are also available a catalog of 196 fault plane solutions consisting of the moment tensor solutions for the earthquakes with magnitude 4 0 or above and p wave first motion solutions for the earthquakes with magnitude 3 4 and above that occurred from 1988 to 2000 was composed moment tensor solutions were calculated using regional broadband data this catalog was used to calculate principal stress orientations in the crust the stress orientations change across central alaska in particular the maximum principal stress orientation rotates clockwise from se nw to ssw nne direction as one moves from west to east these stress orientations are consistent with the stress field transferred from the plate convergence in southern alaska in addition we tested different velocity structures in the moment tensor inversion procedure to identify velocity models for calculating the green s functions the moment tensor inversion study shows that it is possible to obtain a reliable moment tensor solution for moderate sized earthquakes m l 4 using three component records from a single broadband station when the epicentral distances are between 50 and 300 km manuscript received 8 june 2001

rapid three dimensional hypocentral determination using a master station method a master station ms method is presented in this paper to rapidly determine hypocenters in three dimensional 3 d heterogeneous velocities an equal differential time edt surface is defined as the collection of all spatial points that satisfy the time difference between two arrivals which can be two picks at two stations or two different phase picks at one station the edt surface is independent of the origin time and will contain the hypocenter for an event with j arrivals there are j 1 independent edt surfaces the ms method determines the hypocenter that satisfies two types of constraints to be traversed by most edt surfaces and to yield minimum travel time residual statistics the statistics include both the residual variance and the amplitude of the origin time error the combined use of the edt surfaces and residual statistics allows for a unique determination of the hypocenter and origin time using different types of phase arrivals in principle only three arrivals are minimally required to constrain a unique solution if three different stations are used for a 3 d velocity model the edt surfaces and the residual statistics can be computed efficiently using a reference file created by moser s 1991 ray tracing method an illustration of the ms method is given for 27 small events that occurred in southern california using a p wave velocity model modified from that of magistrale et al 1992 the average misfit between the bulletin hypocenters and the new solutions is 3 8 km if a 3 d velocity model is accurate the ms method can be a viable means of hypocenter determination

determination of magnitude for large shallow earthquakes 1898 1917 abstract in order to arrive at a uniform basis for a study of the global seismicity the surface wave magnitude ms of shallow earthquakes for 1898 1917 is newly determined by using maximum amplitudes of surface waves recorded by undamped milne and omori seismographs the effective gain of these instruments needs to be calibrated with great care because of the lack of a damping device the calibration of milne instruments is based on a comparison of amplitudes measured by milne instruments with those by more modern damped instruments the effective gain varies from 7 to 20 in the range of ms from 6 to 8 5 the reported amplitudes for the years 1910 1912 are twice as large as the standard and need to be corrected by applying these results to a wealth of the milne data ms is determined for a large number of earthquakes between 1898 and 1912 to supplement the data for 1913 1917 records of undamped omori seismographs are used for the entire period from 1898 to 1917 308 shallow earthquakes with m s 7 0 are listed here both this list and the previous catalogue of abe 1981 for 1918 1980 provide a catalogue of large shallow earthquakes much more uniform than any previously established between 1899 and 1910 the annual frequency of shocks with m s 7 0 is 20 which is twice as large as the annual average of 10 during 1911 and 1980

decelerating nazca south america and nazca pacific plate motions space geodetic estimates of the rate of nazca south america convergence and nazca pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average nuvel 1a model the implied rates of deceleration are consistent with longer term trends extending back to at least 20 ma about the time of initiation of andes growth and may reflect consequences of ongoing subduction and construction of the andes e g increased friction and viscous drag on the subducted slab as the leading edge of south america thickens

environmental implications of oncoids and associated sediments from the remoredo formation lower jurassic mendoza argentina abstract lower jurassic deposits of the middle member 19 m of the remoredo formation at arroyo montanesito southwestern mendoza province neuquen basin argentina and its oncoids are described four lithofacies constitute the lacustrine deposits of the remoredo formation 1 laminated green to gray calcareous shales 2 laminated to massive dark gray mudstones 3 massive to upward coarsening dark gray oncolite wackestones and 4 massive dark gray packstones with abundant macro oncolites according to layer configuration two types of oncoids were recognized a those having distinctly banded well defined concentric and continuous lamination type i and b those having a vertical arrangement of irregular and discontinuous laminae type i 3 i the continuous micritic laminations suggest growth during agitated conditions and the discontinuous laminations reflect short periods of non agitation or tranquility in the water mass the oncolites are associated with a well preserved faunal assemblage of ostracods darwinula sp and possible members of the subfamily iliocypridinae and some fragments of bivalves that are indicative of shallow water conditions the facies association is a coarsening upward sequence interpreted as the product of deposition in a shallow nearshore lacustrine environment and a progressive infilling by pyroclastic subaereal flows

retroarc volcanism in the northern san rafael block 34 35 30 s southern central andes occurrence age and tectonic setting article i nfo one of the major retroarc volcanic provinces in the southern central andes 34 and 37 s is developed in the andean foothills of the san rafael region between the orogenic front and foreland basement uplifts of late miocene age here we present the first comprehensive geochronological study of the quaternary volcanism previously dated mainly on the basis of stratigraphy the new unspiked k ar radiometric and two radiocarbon determinations encompass many volcanic centers most of them monogenetic and of basaltic composition exposed between 34 and 35 30 s the data constrains the basaltic volcanism to between 1 8 ma and the holocene the spatiotemporal distribution of the ages indicates that eruption in the retroarc was episodic with some distinct patterns the orogenic front of the san rafael block is associated with 1 8 0 7 ma volcanic eruptions while the malargue fold and thrust belt front in the andean foothills is related to younger eruptions produced at 0 1 0 01 ma both areas are associated with late cenozoic normal faults that dismembered an uplifted a late miocene peneplain as indicated by younger over older fault relationships between paleozoic rocks and tertiary strata this linkage indicates a major relationship between pleistocene holocene retroarc eruptions of the basaltic centers and extensional collapse of the foreland region that shows a migration of the last volcanic activity towards the trench

new magnetic fabric data and their comparison with palaeostress markers in the western fars arc zagros iran tectonic implications the zagros simply folded belt zsfb is an active fold and thrust belt resulting from the still continuing continental collision between the arabian plate and the iranian plate which probably started in the oligocene the present day shortening n25 is well documented by focal mechanisms of earthquakes and global positioning system gps surveys we propose in this study a comparison of published palaeostress markers including magnetic fabric brittle deformation and calcite twinning data in addition we describe the magnetic fabric from palaeocene carbonates 10 sites and mio pliocene clastic deposits 15 sites the magnetic fabrics are intermediate with magnetic foliation parallel to the bedding and a magnetic lineation mostly at right angles to the shortening direction this suggests that the magnetic fabric retains the record of an early layer parallel shortening lps that occurred prior to folding the record of lps allows the identification of originally oblique folds such as the mand fold which have developed in front of the kazerun fault the shape parameter of the magnetic fabric indicates a weak strain compatible with the development of detachment folds in the zsfb the palaeostress datasets covering the palaeocene to pleistocene time interval support several folding episodes accompanied by a counter clockwise rotation of the stress field direction the palaeocene carbonates in the zsfb record a n47 lps during early to middle miocene detachment folding in the high zagros belt hzb the mio pliocene clastic deposits recorded a n38 lps prior to and during detachment folding within the zsfb at the end of the miocene pliocene similarly fault slip and calcite twin data from the zsfb also support a counter clockwise rotation from ne to n20 between the pre folding stage and the late rejuvenation of folds this counter clockwise trend of palaeostress data agrees with fault slip data from the hzb during the late stage of folding in the zsfb the plio quaternary palaeostress trends are consistently parallel to the present day shortening direction

episodic orogenic front migration in the northern andes constraints from low temperature thermochronology in the eastern cordillera colombia 1 new thermochronometric data from the eastern cordillera of the colombian andes reveal diachronous exhumation associated with cenozoic contractional deformation in this sector of the northern andes we present a comprehensive account of exhumation patterns along a 150 km long across strike transect between 4 and 6 n by integrating 29 new apatite fission track aft ages and 17 new zircon fission track zft ages with sparse published thermochronological data from this area our data reveal episodic eastward migration of the orogenic front at an average rate of 2 5 2 7 mm a during the late cretaceous cenozoic we identify three major stages of orogen propagation 1 slow propagation 0 5 3 1 mm a until early eocene 2 rapid orogenic advance 4 0 18 0 mm a during middle late eocene which accounts for 86 of the orogen s present width and 3 slow orogen propagation 1 2 2 1 mm a from oligocene to holocene times our data demonstrate that in the course of changes in plate kinematics the presence of inherited crustal anisotropies such as the former rift bounding faults of the eastern cordillera favor a nonsystematic progression of foreland basin deformation through time by preferentially concentrating accommodation of slip and thrust loading along these zones of weakness

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

spatial distribution of turn of the century seismicity along the alaska aleutian arc abstract epicenters determined for instrumentally observed earthquakes occurring around the turn of the century have figured prominently in estimates of seismic hazard along the alaska aleutian arc unfortunately because of poor timing control and a sparse station distribution the locations quoted in the older catalogs can be very unreliable more reliable epicenter estimates and quantitative assessments of the errors associated with these estimates are needed to address issues related to seismic hazard seventeen earthquakes with surface wave magnitudes above 6 8 that were recorded between 1898 and 1917 are relocated using a modified least squares criterion epicentral estimates are determined using p s and s p arrival times with the a priori constraint that the final location must be near the geographically defined arc although epicenters determined using a standard least squares criterion can be located up to 800 km from the arc the arc proximity constraint provides tectonically more meaningful locations which to a high degree of confidence fit the travel time observations as well as the unconstrained locations epicentral shifts of up to 1 200 km are observed between the relocations and those reported in the earlier catalogs seventy five per cent confidence bounds on the along arc location of each event vary from 30 to 400 km several large events m s 6 9 occurred within or near the rupture zone of the 1965 rat islands earthquake and may indicate that this zone failed in a sequence of events around the turn of the century of the four events previously suggested as being possible candidates for rupturing either the shumagin or unalaska seismic gaps none relocate near these arc segments the relocation of a large m s 7 9 earthquake which occurred in 1917 within the shumagin islands region however provides the first strong evidence of largescale seismic moment release within this intensely studied seismic gap

evaluating magnetic lineations ams in deformed rocks magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility kmax of the anisotropy of magnetic susceptibility ams tensor in deformed rocks magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones our ams determinations based on a variety of samples that were taken from mudstones slates and schists from the pyrenees and appalachians show that strain is not the only factor controlling the development of magnetic lineation we find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original ams tensor which in turn depends on the lithology and the deformation intensity rocks having a weak pre deformational fabric will develop magnetic lineations that more readily will track the tectonic extension

anisotropy of magnetic susceptibility of magnetically oriented rock powders to estimate the maximum magnetic anisotropy of the ensemble of magnetic carriers present in a rock we measured the anisotropy of magnetic low field susceptibility ams of magnetically oriented rock powder we studied basaltic rock chaine des puys massif central france and metasediments coffs harbour australia in the basaltic powder psd titanomagnetites show maximum anisotropy of l 1 16 in the metasediments the foliation anisotropy is constant f 1 3 controlled by iron bearing phyllosilicates the linear anisotropy goes up to l 2 in pyrrhotite bearing rocks in contrast magnetite bearing samples show low linear anisotropy l 1 1

estimating earthquake location and magnitude from seismic intensity data analysis of modified mercalli intensity mmi observations for a training set of 22 california earthquakes suggests a strategy for bounding the epicentral region and moment magnitude m from mmi observations only we define an intensity magnitude m i that is calibrated to be equal in the mean to m m i mean m i where m i mmi i 3 29 0 0206 i 1 68 and i is the epicentral distance km of observation mmi i the epicentral region is bounded by contours of rms m i rms m i m i rms m i m i where rms is the root mean square rms m i m i is the minimum rms over a grid of assumed epicenters and empirical site corrections and a distance weighting function are used empirical contour values for bounding the epicenter location and empirical bounds for m estimated from m i appropriate for different levels of confidence and different quantities of intensity observations are tabulated the epicentral region bounds and m i obtained for an independent test set of western california earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes the analysis strategy is particularly appropriate for the evaluation of pre 1900 earthquakes for which the only available data are a sparse set of intensity observations

a quantitative inference model for conductivity using non marine ostracode assemblages on san salvador island bahamas paleosalinity records from two lakes abstract quantitative records of past environments are needed to understand natural variability in ecosystems and their responses to climate change changes in ostracode assemblages through time can provide such records as ostracode species are sensitive to changes in their local environments before they can be used to indicate past environments however is it necessary to understand how distributions of assemblages change across environmental gradients to that end thirty two lakes on san salvador island bahamas were sampled for both ostracodes and nineteen limnological variables multivariate fuzzy set ordination indicates that change in ostracode assemblages is significantly and independently correlated with three environmental variables electrical conductivity salinity dissolved oxygen and alkalinity a transfer function was created to reconstruct past conductivity since changing conductivity of lakes on san salvador is influenced by changes in climate and sea level a 2 component weighted averaging partial least squares model performed best as a transfer function for conductivity with an apparent r 2 of 0 76 and an r 2 of 0 69 between observed and predicted conductivity as assessed by leave one out cross validation the resulting transfer function was then applied to two mid to late holocene sediment cores from which ostracode assemblages were sampled the late holocene conductivity records show that changes in conductivity of lakes on san salvador are broadly synchronous with times of enhanced enso activity corresponding to elevated conductivity in response to lower atlantic hurricane occurrence these results demonstrate that changing ostracode assemblages through time provide a reliable means to reconstruct past salinity and demonstrates the strong effect of enso on bahamian aridity

rampart seismic zone of central alaska abstract this paper describes the characteristics of the rampart seismic zone by means of the aftershock sequence of the rampart earthquake m l 6 8 which occurred in central alaska on 29 october 1968 the magnitudes of the aftershocks ranged from about 1 6 to 4 4 which yielded a b value of 0 96 0 09 the locations of the aftershocks outline a nne ssw trending aftershock zone about 50 km long which coincides with the offset of the kaltag fault from the victoria creek fault the rupture zone dips steeply 80 to the west and extends from the surface to a depth of about 10 km fault plane solutions for a group of selected aftershocks which occurred over a period of 22 days after the main shock show simultaneous occurrences of strike slip and normal faults a comparison of the trends in seismicity between the neighboring areas shows that the rampart seismic zone lies outside the area of underthrusting of the lithospheric plate in southcentral and central alaska the seismic zone outlined by the aftershock sequence appears to represent the formation of an intraplate fracture caused by regional northwest compression

transtensional tectonics of the minto flats fault zone and nenana basin central alaska abstract central alaska is a broad zone of crustal deformation that is produced by collision and flat slab subduction within central alaska there are large scale right lateral strike slip faults such as the denali fault 2002 m w 7 9 as well as smaller scale fold and thrust belts and a set of left lateral strike slip fault zones one of which is the minto flats fault zone mffz we use seismological evidence to document a pair of overlapping left lateral faults that define the mffz microseismicity delineates this 180 km long fault zone using body waves and surface waves we perform moment tensor inversions for the 11 best recorded earthquakes in the fault zone moment tensors reveal consistent left lateral faulting throughout the fault zone a finite source model for the 1995 m w 6 0 earthquake is consistent with left lateral faulting and provides rupture details for the largest known event in the fault zone the two main faults are separated by 10 km and overlap by 67 km forming a releasing stepover geometry within a local transtensional setting between the faults is a 90 km long 12 km wide and 8 km deep sedimentary basin the nenana basin we interpret the transtensional faulting to be responsible for the development of the basin over the past 6 ma the distances of fault overlap and fault separation are key parameters for determining 1 the 3d morphology of the sedimentary basin and 2 the likelihood of earthquake ruptures jumping from one fault to the next the structure of the nenana basin is consistent with shear motion accommodated by the identified faults the 10 km fault separation suggests that ruptures are not likely to span the entire fault zone earthquakes as large as m w 7 0 7 5 could occur on the faults the transtensional fault zone provides an important constraint for understanding the larger scale intraplate tectonic setting of central alaska online material figures of waveform fits depth estimation for moment tensors variation in seismicity and fault plane identification

cenozoic tectonics of the high andes of west central argentina 30 36 s latitude abstract the structure of the central andes shows three distinctive segments characterized by different geometries these geometries are superimposed on the present large scale plate tectonic setting characterized by distinct subduction segments the northern la ramada segment is a thick skinned fold and thrust belt formed by tectonic inversion of a late triassic rift the central aconcagua segment consists of a thin skinned fold and thrust belt while the southern malargue segment like the first one is a thick skinned fold and thrust belt developed by tectonic inversion of a late triassic early jurassic rift system during late cenozoic times the amount of shortening gradually decreases from north to south as indicated by the crustal roots of the central andes the different geometries along the principal cordillera controlled the abrupt changes in the shortening among segments the structure of precordillera and sierras pampeanas has also been considered in order to account for the total shortening in the la ramada segment the main shortening occurred in the precordillera in the aconcagua segment in the principal cordillera while in the malargue segment the shortening is widely distributed in a broader principal cordillera because south of the flat slab subduction segment the precordillera and sierras pampeanas are missing

mechanisms of basin contraction and reactivation in the basement involved malargue fold and thrust belt central andes 34 36 s we have conducted a structural study of both the basement involved malargue fold and thrust belt mftb and the active san rafael block srb which are located in the central andes at latitude 34 36 s based on several field examples located both in the inner and frontal part of belt and from the distal foreland zone we focus on the relationships between basement and cover deformation with respect to the known palaeogeography and structural inheritance in several zones we point out similarities in the structural and sedimentary responses to andean shortening the recent morphologic response has also been investigated through the analysis of active deformation along the eastern border of the srb we show that these structural and sedimentary processes are continuous in time and space since they can be applied in the various parts of the fold belt and also at different stages of fold and thrust belt building as well finally we propose the illustration of those mechanisms by complete cross section along the rio grande valley and a possible kinematic scenario of deformation propagation

layer parallel shortening across the sevier fold thrust belt and laramide foreland of wyoming spatial and temporal evolution of a complex geodynamic system abstract varying patterns of layer parallel shortening lps and vertical axis rotations from the thin skin sevier fold thrust belt to the thick skin laramide foreland of wyoming are quantified from integrated structural anisotropy of magnetic susceptibility ams and paleomagnetic analyses within the sevier belt widespread early lps was accommodated by spaced cleavage fracture sets minor folds and minor faults lps directions are subperpendicular to structural trends of systematically curved thrust sheets of the wyoming salient reflecting a combination of primary dispersion and secondary rotation during thrusting within the laramide foreland limited lps was accommodated mostly by minor faults with conjugate wedge and strike slip geometries lps directions in gentler fold limbs vary from perpendicular to acute with structural trends of variably oriented anastomosing basement cored arches steep forelimbs display more complex relations including younger fault sets that developed during evolving stress states and localized vertical axis rotations although internal strain is limited weak ams lineations defined by kinked and rotated phyllosilicates are widely developed and consistently oriented perpendicular to measured lps directions palinspastically restored lps directions corrected for paleomagnetically determined vertical axis rotations vary on average from w e in the sevier belt to wsw ene in the laramide foreland in detail lps directions display deflections related to primary sedimentary wedge geometry and basement fabrics lps in the sevier belt is interpreted to partly reflect stress transmitted from the hinterland through the growing orogenic wedge and topographic stress along the front of the wedge lps in the laramide foreland is interpreted to partly reflect basal traction during flat slab subduction beneath thick cratonic lithosphere with spatial temporal variations in stress trajectories related to basement heterogeneities and evolving fault systems evidence for significant late n s laramide shortening as proposed by multi stage shortening models is not observed

a reanalysis of the hypocentral location and related observations for the great 1906 california earthquake we determine probabilistic hypocentral locations for the foreshock and mainshock of the great 1906 california earthquake through reanalysis of arrival time observations in conjunction with modern velocity models and advanced event location techniques we obtain two additional observations for the mainshock and one for the foreshock that were not used in previous location studies using a robust likelihood function for event location we generate a usable subset of the predominantly unreliable teleseismic readings and determine new wave type identifications for some of the local and teleseismic readings our locations are much better constrained than those of earlier studies even though we do not assume that the epicenter lies on the san andreas fault as did previous authors we confirm the conclusions of earlier studies that the local and teleseismic arrival time observations can be explained by a single foreshock focus and a single mainshock focus on the san andreas fault and that there is no single unique hypocenter that satisfies all available local observations the maximum likelihood point latitude 37 78 n longitude 122 51 w for our preferred mainshock location indicates a hypocenter to the west of san francisco close to the san andreas fault zone this hypocenter has a 68 confidence error of about 8 km parallel to the san andreas fault and about 24 km perpendicular to the fault and a depth in the midcrust of about 12 7 km the closest point on the san andreas fault to this hypocenter lies about 10 km to the northwest of the widely accepted mainshock epicenter of bolt 1968 our mainshock location is consistent with the association of initial rupture of the 1906 mainshock with a dilatational right bend or step over in the submerged san andreas fault system offshore of the golden gate our foreshock location is less well constrained than our mainshock location but is consistent with the foreshock hypocenter being at the same location as the mainshock hypocenter online material visualization of 3d probabilistic hypocentral locations associated with the 1906 earthquake

preface to the issue dedicated to the 2002 denali fault earthquake sequence on 3 november 2002 a m w 7 9 earthquake the largest continental strike slip earthquake in north america since the 1857 fort tejon california event occurred in central alaska the earthquake began with reverse faulting on a 40 km extent of the previously unknown susitna glacier fault but rupture transferred eastward to the right lateral denali fault and continued for over 200 km finally transferring to rupture 70 km of the totschunda fault this large complex event we term the denali fault earthquake dfe after the major crustal fault that carried most of the displacement the initiation of the rupture the susitna glacier fault is in a remote region of central alaska that under normal circumstances is sparsely instrumented on 23 october of that year however a large earthquake of m w 6 7 referred to as the nenana mountain earthquake nme occurred only 22 km to the west of the dfe epicenter the nme in hindsight recognized as a foreshock to the dfe prompted deployment of a temporary network by the alaska earthquake information center aeic hence the area was under significantly enhanced seismic surveillance at the time of the dfe 10 days later which was further augmented by the addition of 19 more stations following the dfe mainshock as a result high quality data were available in the near field providing enhanced coverage for aftershock activity from the susitna glacier fault initiation point along the denali fault as far as the western portion of the totschunda fault to augment regional and teleseismic data for this sequence as the rupture proceeded eastward the richardson highway one of the two north south roads connecting the central and southern parts of the state was disrupted where it crosses the denali fault trace also significantly displaced was the trans alaska pipeline operated by the alyeska pipeline