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

one hundred million years of geomagnetic polarity history since 1968 absolute ages have been assigned to the late cretaceous cenozoic geomagnetic reversal time scale by fixing the ages of two or more calibration points in a composite marine magnetic anomaly profile and interpolating between or extrapolating beyond these points assuming constant spreading rates in each interval previously no more than 4 calibration points were used but it is now possible to specify 11 calibration points in addition to the 0 m y datum this improvement is based on magnetostratigraphic studies in italian pelagic limestones these studies closely tie the geomagnetic reversal sequence to the foraminiferal and coccolith zonations absolute ages of calibration points are provided by the best available dates on stage boundaries which are located from the biostratigraphic zonation the greatest changes from previous scales come in the late paleocene early eocene where the new ages are as much as 3 m y younger than in the 1977 scale of labrecque and others and as much as 1 8 m y younger than in the 1980 scale of ness and others

statistical analysis of the induced basel 2006 earthquake sequence introducing a probability based monitoring approach for enhanced geothermal systems summary geothermal energy is becoming an important clean energy source however the stimulation of a reservoir for an enhanced geothermal system egs is associated with seismic risk due to induced seismicity seismicity occurring due to the water injection at depth have to be well recorded and monitored to mitigate the seismic risk of a damaging event an appropriate alarm system needs to be in place for each individual experiment in recent experiments the so called traffic light alarm system based on public response local magnitude and peak ground velocity was used we aim to improve the pre defined alarm system by introducing a probability based approach we retrospectively model the ongoing seismicity in real time with multiple statistical forecast models and then translate the forecast to seismic hazard in terms of probabilities of exceeding a ground motion intensity level one class of models accounts for the water injection rate the main parameter that can be controlled by the operators during an experiment by translating the models into time varying probabilities of exceeding various intensity levels we provide tools which are well understood by the decision makers and can be used to determine thresholds non exceedance during a reservoir stimulation this however remains an entrepreneurial or political decision of the responsible project coordinators we introduce forecast models based on the data set of an egs experiment in the city of basel between 2006 december 2 and 8 approximately 11500 m 3 of water was injected into a 5km deep well at high pressures a six sensor borehole array was installed by the company geothermal explorers limited gel at depths between 300 and 2700 m around the well to monitor the induced seismicity the network recorded approximately 11200 events during the injection phase more than 3500 of which were located with the traffic light system actions where implemented after an ml 2 7 event the water injection was reduced and then stopped after another ml 2 5 event a few hours later an earthquake with ml 3 4 felt within the city occurred which led to bleed off of the well a risk study was later issued with the outcome that the experiment could not be resumed we analyse the statistical features of the sequence and show that the sequence is well modelled with the omori utsu law following the termination of water injection based on this model the sequence will last 31 29 14 years to reach the background level we introduce statistical models based on reasenberg and jones and epidemic type aftershock sequence etas models commonly used to model aftershock sequences we compare and test different model setups to simulate the sequences varying the number of fixed and free parameters for one class of the etas models we account for the flow rate at the injection borehole we test the models against the observed data with standard likelihood tests and find the etas model accounting for the on flow rate to perform best such a model may in future serve as a valuable tool for designing probabilistic alarm systems for egs experiments

connection between igneous activity and extension in the central mojave metamorphic core complex california the development of metamorphic core complexes and associated low angle detachment faults commonly is intimately associated with synextensional igneous activity in most areas studied to date the relation of magmatism to extension is obscured by imprecise dating and by the overprint of later tectonic events we present data from the early miocene central mojave metamorphic core complex cmmcc which indicate that extension was accompanied by igneous activity as reflected by prekinematic synkinematic and postkinematic plutons and coeval volcanic rocks deposited in the associated extensional basins the principal intrusion is an early miocene granite pluton exposed in outcrops across an area greater than 400 km2 dikes adjacent to the pluton are common in the mitchel range at the buttes and at fremont peak the overall orientation of the pluton and associated dikes is west northwest roughly perpendicular to the extension direction results of u pb analyses on zircon from two pluton and two dike samples yield ages of 20 to 23 ma two other dike samples yield inconclusive results synextensional basins formed by detachment faulting during the core complex development rocks in these basins compose the jackhammer and pickhandle formations and filled an elongate nw trending trough more than 50 km long the 4oar 39ar ages for tuff beds are as old as 23 8 0 3 ma near the base of the lower pickhandle formation and as young as 21 3 0 5 ma in the uppermost lower pickhandle hence volcanism and plutonism are coeval the diversity of intrusive relations relative to the timing and development of the mylonitic fabric in the cmmcc precludes any simple cause and effect relationship between magmatism and extensional deformation rather magmatism and extension may have been localized at a releasing bend in a transfer fault system which links extension in the cmmcc with extension in the colorado river area to the east

subsurface imaging of the garlock fault cantil valley california imaging of the garlock fault from seismic reflection data tests tectonic models for the mojave desert region of southern california models developed from geologic and geodetic evidence of fault movement rates disagree on whether the garlock fault should dip north or south such models are further at odds with focal mechanism and dislocation analyses consistent with a vertical strike slip fault our analysis demonstrates a nonvertical southward dip for the garlock fault consortium for continental reflection profiling mojave line 5 collected seismic reflection data across the garlock in cantil valley where the 3 km deep cantil pull apart basin has developed between the southwest and east branches of the fault we analyze the reflection data for evidence of the fault s structure to 5 km depths garlock fault plane reflections on unprocessed shot gathers merge with the first arrival as the source progresses to the surface trace of the east branch explicitly tracing the garlock fault as a seismic reflector from depth to the mapped contemporary fault trace the apparent velocity of these reflections gives a 37 10 south dip for the east branch of the fault a prestack kirchhoff sum migration images the east branch reflector with a 45 south dip our migration process fully accounts for the bending of seismic rays through the strong lateral velocity variations in cantil basin the south dip of the garlock s east branch together with basement steps that decrease to the south suggest that cantil basin developed from a 0 4 1 mm yr component of extension normal to the fault development of the basin by detachment provides a mechanism to widen it as left lateral motion lengthens it allowing the pull apart to maintain the globally constant length to width ratio of 3 detachment by the garlock at cantil valley similarly requires 0 4 1 mm yr of dextral strike slip on a northwest striking fault such as the helendale that cuts the mojave between the garlock and pinto mountain faults such motion is consistent with regional tectonic models

clathrites archives of near seafloor pore fluid evolution δ44 40ca δ13c δ18o in gas hydrate environments aragonitic clathrites are methane derived precipitates that are found at sites of massive near seafloor gas hydrate clathrate accumulations at the summit of southern hydrate ridge cascadia margin these platy carbonate precipitates form inside or in proximity to gas hydrate which in our study site currently coexists with a fluid that is highly enriched in dissolved ions as salts are excluded during gas hydrate formation the clathrites record the preferential incorporation of 18o into the hydrate structure and hence the enrichment of 16o in the surrounding brine we measured 18o values as high as 2 27 relative to peedee belemnite that correspond to a fluid composition of 1 18 relative to standard mean ocean water the same trend can be observed in ca isotopes ongoing clathrite precipitation causes enrichment of the 44ca in the fluid and hence in the carbonates carbon isotopes confirm a methane source for the carbonates our triple stable isotope approach that uses the three main components of carbonates ca c o provides insight into multiple parameters influencing the isotopic composition of the pore water and hence the isotopic composition of the clathrites this approach provides a tool to monitor the geochemical processes during clathrate and clathrite formation thus recording the evolution of the geochemical environment of gas hydrate systems

model for late mesozoic early tertiary tectonics of coastal california and western mexico and speculations on the origin of the san andreas fault cretaceous and early tertiary arc and forearc rocks found along the coast in southern california and baja california have been shown by paleomagnetic measurements to have originated many hundreds or even several thousands of kilometers south of their current locations northward transport also is found in cretaceous batholithic rocks near the edge of the continent in washington and british columbia the consistency of this pattern suggests that slices of arc and forearc rock originating on the western edge of north america have been translated along the coast by strike slip faulting strike slip faults are shown to be an expected response to north oblique subduction of the farallon and or kula plates faulting and subduction probably were concurrent activities i e the arc and forearc grew and were displaced simultaneously because displacement was dominantly parallel to subduction related lithic belts arc and forearc rocks may have traveled large distances without producing either significant hiatuses in the rock record or conspicuous disruptions in the distribution of lithic belts subduction related strike slip faulting is shown to be favored by high angles of oblique convergence shallow dip of the subducting slab relatively easy slip on potential faults within the arc or forearc and the existence of a place for the moving sliver to go it is suggested that these conditions are not difficult to satisfy and that subduction related strike slip faulting may thus be a common feature of convergent orogens the location of the san andreas fault inboard from the continental margin may be attributable to localization of the pacific north american transform by a system of precollision subduction related faults

injection induced seismicity and fault slip potential in the fort worth basin texasinjection induced seismicity and fault slip potential in the fort worth basin texas

paleomagnetic constraints on rotation within mount abbot quadrangle central sierra nevada california the regional photolineament pattern in mount abbot quadrangle in the central sierra nevada is sigmoidal in plan view the fractures in the southwest section of the quadrangle near florence lake strike n10 20 e while those in the central section along bear creek strike n50 70 e and those in the northeast strike n25 40 e a paleomagnetic investigation was undertaken to determine if this sigmoidal pattern was formed by kinking of originally straight photolineaments after the rock mass cooled below the blocking temperature if the inner limb of the kink rotated 40 60 clockwise with respect to the outer limbs then there should be a similar difference in the paleomagnetic declinations between the florence lake and bear creek areas the paleomagnetic results indicate a clockwise difference in declination of 13 4 7 of the bear creek area with respect to florence lake thus the sigmoidal pattern could not have formed entirely by rotation after cooling below the blocking temperature it is also possible that the observed declination discrepancy is due to tilting apparent polar wander or paleomagnetic dispersion instead of rotation sigmoidal patterns formed by kink folding occur on the outcrop scale with inner limb rotations of 15 30 three of these kinks were sampled to test the paleomagnetic method in an area of demonstrable rotation the data from these sites indicate that although no difference in declination is evident a reheating event may have occurred which could have removed any rotation from the paleomagnetic record reheating possibly due to the circulation of hydrothermal fluids may have been causally related to the outcrop scale kinking since reheating is not observed away from the outcrop scale kinks the data further indicate that there may have been continuous deformation of the rock mass during the formation of the kinks

pyritization induced by anaerobic oxidation of methane aom an example from the upper devonian shale succession western new york usa abstract the diagenetic history of the upper devonian rhinestreet shale of the western new york region of the appalachian basin appears to reflect the upward diffusion of methane through these deposits shortly after their accumulation the most obvious diagenetic signature of this process is numerous horizons of authigenic calcium carbonate concretions interpreted to reflect mineralization induced by the anaerobic oxidation of methane aom focused along the sulfate methane transition smt zone additionally a 2 m thick section of the lower rhinestreet preserves a diagenetic record consistent with aom in the form of two pyritiferous stratigraphic horizons the stratigraphically lowest horizon is a 2 cm thick layer containing abundant 34 s enriched 11 8 and 18 4 v cdt coarsely crystalline pyrite the thinness of this interval suggests that aom related diagenesis remained fixed at this stratigraphic position for a brief period of time before these deposits were buried below the smt or the smt shifted position within the sediment column a second paleo smt appears to have stabilized 60 to 80 cm above the 2 cm thick pyritiferous horizon meter scale carbonate concretions being the most obvious evidence of this episode of aom more than this though the apparently fe limited nature of the host black shale induced the downward diffusion of 34 s enriched hydrogen sulfide produced by aom resulting in the precipitation of 34 s enriched 23 1 to 27 3 v cdt pyrite below the smt the maximum depth of diffusion of the sulfidization front was limited by the amount of hydrogen sulfide produced within and near the smt as well as by the availability of reactive iron in underlying deposits the focusing of aom related diagenesis at the two stratigraphic positions was likely caused by non steady state sedimentation however it is impossible to decipher relative timing of formation of the two paleo smts

the spatial footprint of injection wells in a global compilation of induced earthquake sequences fluid injection can cause extensive earthquake activity sometimes at unexpectedly large distances appropriately mitigating associated seismic hazards requires a better understanding of the zone of influence of injection we analyze spatial seismicity decay in a global dataset of 18 induced cases with clear association between isolated wells and earthquakes we distinguish two populations the first is characterized by near well seismicity density plateaus and abrupt decay dominated by square root space time migration and pressure diffusion injection at these sites occurs within the crystalline basement the second population exhibits larger spatial footprints and magnitudes as well as a power law like steady spatial decay over more than 10 kilometers potentially caused by poroelastic effects far reaching spatial effects during injection may increase event magnitudes and seismic hazard beyond expectations based on purely pressure driven seismicity

high rate injection is associated with the increase in u s mid continent seismicity an unprecedented increase in earthquakes in the u s mid continent began in 2009 many of these earthquakes have been documented as induced by wastewater injection we examine the relationship between wastewater injection and u s mid continent seismicity using a newly assembled injection well database for the central and eastern united states we find that the entire increase in earthquake rate is associated with fluid injection wells high rate injection wells 300 000 barrels per month are much more likely to be associated with earthquakes than lower rate wells at the scale of our study a well s cumulative injected volume monthly wellhead pressure depth and proximity to crystalline basement do not strongly correlate with earthquake association managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes

paleolatitude of the butano sandstone california and its implications for the kinematic histories of the salinian terrane and the san andreas fault the lower to middle eocene butano sandstone of the santa cruz mountains california is part of the central portion of the salinian terrane a slivered granitic fragment west of the san andreas fault the butano sandstone has been correlated with the point of rocks sandstone across the san andreas fault approximately 315 km to the southeast the magnitude of this offset is the same as the amount of neogene san andreas fault offset documented in other studies thus the correlation of these two eocene units implies that no pre san andreas system motion of the butano sandstone has occurred paleomagnetic studies indicating large northward translations of cretaceous and paleocene rocks of coastal california however raise the possibility of continued northward motion of the salinian terrane during or after deposition of the butano sandstone to better our understanding of the eocene position of the salinian terrane the paleolatitude of the butano sandstone was determined by paleomagnetic analysis of azimuthally unoriented cores from exploratory oil wells specimens from 30 core intervals from the top to the middle or lower parts of the formation were subjected to alternating field and thermal demagnetization the resulting paleolatitudes group better when bedding is horizontal than in their drill hole attitudes providing a positive fold test several magnetic polarity zones are present the mean paleolatitude 34 6 2 5 is significantly lower than that expected if the rocks were deposited in their present day location on an underformed north american craton when neogene slip on the san andreas and on smaller inboard faults is restored however the measured paleolatitude does not differ significantly from that expected this result supports the correlation of the butano and point of rocks sandstones and implies that the salinian terrane experienced no significant motion between deposition of the butano sandstone and establishment of the neogene san andreas dextral fault system

tracking induced seismicity in the fort worth basin a summary of the 2008 2018 north texas earthquake study catalogtracking induced seismicity in the fwb a summary of the 2008 2018 north texas earthquake study catalog

pore water evolution during sediment burial from isotopic and mineral chemistry of calcite dolomite and siderite concretions abstract coal measures often contain concretions segregations of diagenetic minerals originally formed within unconsolidated sediments three different types calcite pyrite dolomite pyrite and siderite occurring spatially quite close together in the central pennine region of england vary widely in carbon isotope composition 10 35 13c 21 49 and in major cation chemistry ca mg fe mn within some siderite concretions very high mn fe ratios were found in central subsamples these were also most enriched in 13c the fe mg ratio decreases systematically from centre to edge early shallow to deeper later precipitation the calcite pyrite and dolomite pyrite concretions developed completely prior to significant burial both have high mn fe ratios but negative 13c values calcite 21 49 dolomite 8 67 to 10 48 all of these patterns can be equated precisely with theories of pore water evolution developed on the basis of geochemical investigations of modem sediments microbial processes sulphate reduction methanogenesis contributed significantly as did thermal decarboxylation to siderite precipitated at considerable burial depth mn iv and fe iii acted differentially as oxidants producing co2 and increasing alkalinity the interplay of fresh and marine depositional waters is seen most obviously in the presence or absence of sulphate reduction this controlled mineral type iron sulphide or carbonate as well as isotopic and mineral chemistry

continental tectonics selected topics cause and effect relations between plate boundary processes and orogeny were investigated using new and refined plate models for the mesozoic and cenozoic terrane accretion and large components of horizontal shear were shown to be fundamental aspects of orogen evolution deep crustal thrust systems with large lateral transport and vertical stacking of slices of crystalline basement were documented in the cordillera and appalachians new geomechanical models of crystalline thrust sheets and foreland thrust belts emphasized the dominance of tectonic rather than gravitational stresses lithospheric thickening was shown to cause buoyancy forces that control the lateral spread of deformation outward from the interior of an orogen and may modify regional stresses in the vicinity of topographic fronts resulting in extension within the upper part of the lithosphere coeval with shortening at depth

cenozoic crustal rotations in the mojave desert from paleomagnetic studies around barstow california paleomagnetic data from the mojave desert around barstow california suggest 55 to 75 of clockwise rotation of this area in earliest miocene time followed by 23 of counterclockwise rotation in the early miocene and no rotation after 18 ma earliest miocene clockwise rotation of the barstow area is suggested by data from nine sites in the oligocene miocene lane mountain quartz latite and jackhammer formation and may be related to oroclinal bending of the southern sierra nevada batholith data from 13 sites in the early miocene pickhandle formation indicate counterclockwise rotation which coincides with early miocene e ne w sw extension and detachment faulting in the mojave desert other parts of the mojave desert experienced variable senses and amounts of rotation at this time which may be related to drag along transfer zones within the upper plate while the lower plate was not rotated these results suggest that miocene extension in the mojave desert is related to similarly oriented extension in the colorado river extensional corridor early miocene to pliocene rocks of the andesite and dacite of the calico mountains barstow formation andesite of murphy s well and black mountain basalt show no evidence for significant rotation of the barstow area after 18 ma most other paleomagnetic data from elsewhere in the mojave are consistent with a lack of significant post 18 ma rotations suggesting that post 10 ma right lateral faulting there has produced relatively little crustal rotation the exception to this generalization is the northeast corner of the mojave desert which underwent substantial post 18 ma clockwise rotation paleomagnetic flattening data also indicate that post oligocene n s translation of crustal blocks in the mojave desert has been insignificant

source characteristics of seismicity associated with underground wastewater disposal a case study from the 2008 dallas fort worth earthquake sequence oil and natural gas production from shale formations using hydraulic fracturing or hydrofracking techniques has grown rapidly since 2008 and represents a vital and growing domestic energy resource the waste fluids from increased production called brine are typically injected into deep underground disposal wells to avoid discharge into streams and other sensitive drinking water supplies the environmental protection agency estimates that approximately 400 million gallons of brine are currently disposed of on a daily basis in more than 28 000 wells in the united states and the volume of injection continues to grow dramatically this process has recently been implicated as the source of some potentially induced seismicity in gas producing states such as oklahoma texas arkansas and ohio

active faulting and block rotations in the western transverse ranges california the geometry of faulting slip vectors of major earthquakes and results of very long baseline interferometry vbli are consistent with active clockwise rotation of crustal blocks in the western transverse ranges about vertical axes oblique left lateral thrust faults trending roughly east west across the western transverse ranges apparently separate long east west blocks of upper crust and the large components of lea lateral shear on east striking planes suggest that the blocks rotate with respect to the san andreas fault in the mojave region between the western transverse ranges and the mojave desert paleomagnetic declinations indicate some 35 and possibly 60 of clockwise rotation since about 10 ma and more importantly the relative velocity between the only two frequently measured vbli sites in the western transverse ranges is consistent with a rotation rate of 6 ma 3 ma during a 5 year period in the 1980s azimuths of slip vectors of major earthquakes are essentially orthogonal to the segment of the san andreas fault across the western mojave desert indicating that crustal shortening across the region is absorbed by crustal thickening and not by lateral translation extension of material parallel to that segment of the fault plate motions late quaternary offsets on the san andreas and san jacinto faults and geodetic measurements in the mojave region yield a calculated direction of relative motion between the san gabriel mountains and the pacific plate across the western transverse ranges that also is perpendicular to the san andreas fault in the mojave region rotation rates associated with simple mechanisms for applying essentially normal tractions to the lateral margins of blocks are not consistent with the observed geometry of faulting and with average rotation rates the rotation rate of 2 8 5 3 ma calculated assuming that the long east west blocks rotate in response to a uniform compression of a viscous substratum to the western transverse ranges however overlaps the range of observed average rotation rates thus the hypothesis that blocks of continental crust move as if carried passively by a substratum undergoing continuous deformation passes one test that can be made of it

block rotation and deformation by strike slip faults 2 the properties of a type of macroscopic discontinuous deformation study of the general features of deformation by systems of subparallel strike slip faults shows that the governing constraints are kinematic the fault blocks must remain in contact with each other and the deformed area must fit with its surroundings as a result fault blocks that move laterally without significant internal deformation also rotate about vertical axes relative to boundaries of the fault domain by an amount that is quantitatively related to fault slip spacing and orientation areas where left and right lateral faults move simultaneously are usually divided into domains that contain faults of one kind only deformation of such multidomain areas is nonhomogeneous but the differences between domains can compensate for each other so that the regional deformation is quite simple strike slip faulting combined with block rotation is an efficient mechanism of deformation because modest offsets and rotations change the linear dimensions of faulted areas by several tens of percents which may often greatly exceed the results of other types of coeval deformation paleomagnetic data can provide an independent measure of block rotations and should be used to supplement structural data block rotation changes the initial angles between right and left lateral faults and also their orientation relative to the stress field the faults probably tend to rotate away from the axis of maximum compression rotated faults continue to move because they are weak surfaces since the deformation depends on geometric factors such as fault orientation and domain geometry it is not simply related to the stress field these properties including rotation of material units characterize discontinuous deformation in general

paleomagnetic evidence that the central block of salinia california is not a far traveled terrane new paleomagnetic results from late cretaceous 75 85 m y red beds on the central block of salinia indicate that salinia was located within 6 in latitude of its current cratonal north american position during the late cretaceous after correction for neogene san andreas fault transport the red beds formed as alluvial fan overbank deposits with hematite cement deposited directly on salinian granites in the la panza range paleomagnetic analysis shows two components of magnetization in the red beds a low blocking temperature present day overprint residing in goethite and a high blocking temperature 600 component residing in hematite the hematite magnetization is a chemical remanent magnetization which formed soon after deposition during pedogenesis the bedding corrected hematite remanence contains a magnetic polarity stratigraphy with antipodal normal and reversed directions twenty three class i sites 95 20 have an average hematite direction with inclination 54 4 and declination 18 2 95 6 1 after structural correction these paleomagnetic data suggest that salinia resided at about 35 n latitude during the late cretaceous within 6 of its current location adjacent to cratonal north america by contrast a summary of paleomagnetic data from the peninsular ranges terrane and the sur obispo terrane which are currently outboard of salinia shows northward transport of these terranes of 12 to 22 relative to their current locations in north america since the cretaceous the offsets increase systematically away from the craton with the most outboard sur obispo terrane which is composed of accretionary prism and distal forearc material showing the largest degree of northward translation

modeling sulfate reduction in methane hydrate bearing continental margin sediments does a sulfate methane transition require anaerobic oxidation of methane the sulfate methane transition smt a biogeochemical zone where sulfate and methane are metabolized is commonly observed at shallow depths 1 30 mbsf in methane bearing marine sediments two processes consume sulfate at and above the smt anaerobic oxidation of methane aom and organoclastic sulfate reduction osr differentiating the relative contribution of each process is critical to estimate methane flux into the smt which in turn is necessary to predict deeper occurrences of gas hydrates in continental margin sediments to evaluate the relative importance of these two sulfate reduction pathways we developed a diagenetic model to compute the pore water concentrations of sulfate methane and dissolved inorganic carbon dic by separately tracking dic containing 12c and 13c the model also computes 13c dic values the model reproduces common observations from methane rich sediments a well defined smt with no methane above and no sulfate below and a 13c dic minimum at the smt the model also highlights the role of upward diffusing 13c enriched dic in contributing to the carbon isotope mass balance of dic a combination of osr and aom each consuming similar amounts of sulfate matches observations from site u1325 integrated ocean drilling program expedition 311 northern cascadia margin without aom methane diffuses above the smt which contradicts existing field data the modeling results are generalized with a dimensional analysis to the range of smt depths and sedimentation rates typical of continental margins the modeling shows that aom must be active to establish an smt wherein methane is quantitatively consumed and the 13c dic minimum occurs the presence of an smt generally requires active aom

dallas fort worth earthquakes coincident with activity associated with natural gas production on 31 october 2008 and the following day numerous dallas fort worth dfw residents called 911 to report experiencing several small earthquakes accompanied by loud booming noises and the shaking of walls and furniture using data recorded by regional seismic stations the usgs national earthquake information center neic located nine earthquakes with magnitudes between 2 5 and 3 0 on 16 may 2009 this scenario repeated itself as local residents felt three earthquakes and the neic located four largest magnitude 3 3 a third sequence of felt events began on 2 june 2009 approximately 65 km southwest near the city of cleburne texas but has not yet been studied in detail figure 1

growth mechanisms and geochemistry of carbonate concretions from the cambrian wheeler formation utah usa carbonate concretions provide unique records of ancient biogeochemical processes in marine sediments typically they form in organic rich mudstones where a significant fraction of the bicarbonate required for carbonate precipitation is supplied from the decomposition of organic matter in the sediments as a result carbonates that comprise concretions are usually characterized by broad ranges in 13c and include values that are significantly depleted relative to seawater this article reports results from a physical petrographic and geochemical analysis of 238 concretions from the wheeler formation cambrian series 3 utah usa which are unusual in several respects most prominently they formed in organic poor mudstones total organic carbon 0 1 to 0 5 and are characterized by a narrow range of 13c that onlaps the range of contemporaneous seawater values subtle centre to edge trends in 13c demonstrate that concretion precipitation was initiated by local chemical gradients set up by microbial activity in the sediments but was sustained during growth by a large pool of inorganic bicarbonate probably derived from alkaline bottom waters the large inorganic pool appears to have been important in facilitating rapid precipitation of the concretion matrix which occurred via both displacive and replacive carbonate precipitation during early diagenesis stable isotope data from cogenetic pyrite 34s and silica 18o phases provide insight into the evolution of biogeochemical processes during concretion growth and suggest that concretions were formed almost entirely during sulphate reduction with only minor modification thereafter concretions of the wheeler formation appear to represent an end member system of concretion formation in which rapid growth was promoted by ions supplied from sea water as such they offer insight into the spectrum of processes that may influence the growth of carbonate concretions in marine sediments

correlation between the geologic record and computed plate motions for central california we have attempted to correlate geologic events in part of central california with computed motions of oceanic plates relative to cratonic north america three composite terranes are considered 1 the sierra nevada 2 the coast ranges northeast of the san andreas fault and 3 the salinian block in the sierra nevada jurassic plutonism ending about 147 m y b p and cretaceous plutonism 120 80 m y b p correlate with deduced farallon north america fa na convergence as does the nevadan orogeny 158 153 m y b p however the gap in plutonism 146 121 m y b p outlasted by far an apparent minimum in convergence 145 135 m y b p magmatism ceased in the sierra and uplift slowed during the laramide orogeny 75 45 m y b p when tectonic activity had moved east to the site of the rockies presumably because of a low angle of subduction but volcanisin resumed in the sierra about 33 m y b p indicating that a steeper angle was reestablished apparently east west compression slackened when the pacific north america pa na transform regime developed basalt was erupted in the southern sierra 12 3 m y b p and during this same time the range started its most rapid rise as a normal fault bounded block the coast ranges north east of the san andreas fault are underlain by the franciscan complex the older parts of the complex were probably assembled in a subduction zone far south of their present location but we believe that the same fa na convergence that was cited for sierran plutonism was responsible despite the disparity in latitude as the farallon plate was probably in contact with most of the western margin of north and south america a perceived strong pulse in convergence 100 85 m y b p evidently produced the coast range thrust which on geologic grounds alone most likely originated between 96 and 88 m y b p some of the northwesterly transport of franciscan rocks relative to north america is ascribed to oblique kula north america ku na convergence 85 43 m y b p during which period the coast range thrust was revived about 60 m y b p the farallon plate again influenced the california margin after the kuia plate had moved northward and fa na convergence caused the accretion of the coastal belt and king range terranes of the neo franciscan the advent of pacific north america pa na interaction was marked by local volcanism which advanced from the southeast toward the northwest in consonance with the passage of the mendocino triple junction dickinson and snyder 1978 in the salinian block plutons 107 82 m y old can be ascribed to the same fa na convergence as the contemporary cretaceous plutons of the sierra nevada although the salinian intrusives originated much farther south paleomagnetic results champion et al 1980 from the salinian related pigeon point formation 75 71 m y in age suggest about 2500 km of poleward essentially coastwise movement this postulated large movement during part or all of the last 75 m y poses the greatest dilemma in our study the kuia is the only known plate whose computed obliquely convergent motion is appropriate for the late cretaceous paleogene part of the migration and even this motion is inadequate for the estimated transport within the most likely time window furthermore the farallon plate seems ideally suited for the laramide orogeny 70 45 m y b p both plates could not have been in contact with the same part of the margin at the same time oblique convergence of the kula plate could possibly have caused large coastwise transport and also the laramide orogeny the coast ranges northeast of the san andreas fault and the salinian block both experienced strike slip faulting and en echelon folding correlative with pa na interaction indicating that they were close together by neogene time faulting and folding have been particularly marked since the inception of spreading in the gulf of california and attachment of westernmost california to the pacific plate about 4 m y b p the rise of individual coastal ranges commencing 3 1 m y b p may possibly have been caused by slight convergence which appears in computed pa na relative motions from 5 m y b p to the present

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

paleomagnetic results from the central sierra nevada constraints on reconstructions of the western united states paleomagnetic results from three plutons of the central sierra nevada limit the motion of the sierra nevada relative to the north american craton to 5 8 of poleward motion and 7 11 of clockwise rotation since about 90 ma the indicated rotation and translation are not significant at the 95 confidence level a new tectonic model is presented that is consistent with all available paleomagnetic data from the sierra nevada great valley klamaths oregon coast range cascades and western nevada the paleogeographic reconstructions of this model associate the displacement of major crustal blocks with basin and range extension starting at about 30 ma this model accounts for about 15 of clockwise rotation of the klamaths and southern cascades about 2 of clockwise rotation of the sierra nevada and great valley and 26 of clockwise rotation of the oregon coast range since 30 ma the model is consistent with 40 of clockwise rotation of the oregon coast range before 30 ma as proposed by magill and cox 1980 the amount of basin and range extension in this model at latitude 41 n is 225 km directed e w and at latitude 35 n is 245 km directed wsw ene

paleomagnetic evidence for motions of parts of the canadian cordillera abstract paleomagnetic evidence from major terranes of the western cordillera in canada referred to collectively as baja british columbia indicates that they have moved as a whole about 2300 km from the south and rotated 60 clockwise relative to north america in the late cretaceous and earliest tertiary 85 50 ma sometime between the early jurassic and the mid cretaceous 190 100 ma these same terranes moved south over 1000 km and underwent irregular but where well constrained counter clockwise rotations the terranes amongst themselves seem to have shared much the same paleolatitude during and since the late triassic although they may have undergone relative rotations in the later jurassic and early cretaceous these motions are now known to be broadly consistent with the motions of oceanic plates to the west as calculated by independent procedures and indicate that the terranes of the western cordillera were for part of their existence coupled to oceanic plates first to the farallon plate during the late jurassic and early cretaceous and then to the kula plate during the late cretaceous and early tertiary it was this change of allegiance from farallon to kula that caused first the southerly and then the northerly motion the paleomagnetic evidence despite claims to the contrary is consistent with geologically inferred displacements along major faults in the canadian cordillera when due account is taken of the age constraints on those motions

improving the location of induced earthquakes associated with an underground gas storage in the gulf of valencia spain abstract on september 2013 increased seismic activity was recorded near the castor offshore underground gas storage ugs in the gulf of valencia spain according to the reports by the spanish instituto geografico nacional ign more than 550 events occurred during two months the strongest having a magnitude of m w 4 2 which took place two weeks after the gas injection stopped the low magnitude of the events with only 17 earthquakes having m blg greater than 3 the lack of nearby stations and the inhomogeneous station distribution made the location problem a great challenge here we present improved locations for a subset of 161 well recorded events from the earthquake sequence using a probabilistic nonlinear earthquake location method a new 3 d shear wave velocity model is also estimated in this work from surface wave ambient noise tomography to further improve the locations waveform cross correlations are computed at each station for every event pair and new locations are obtained from an inverted set of adjusted travel time picks the resulting hypocentral solutions show a tighter clustering with respect to the initial locations and they are distributed in a nw se direction most of the earthquakes are located near the injection well at depths of about 6 km our results indicate that the observed seismicity is closely associated with the injection activities at the castor underground gas storage and may have resulted from the reactivation of pre existing unmapped faults located a few kilometers below the reservoir

spatio temporal evolution of frequency magnitude distribution and seismogenic index during initiation of induced seismicity at guy greenbrier arkansas abstract in this study we carry out detailed analyses of the spatio temporal variations of seismic b value during the onset of the potentially induced earthquake sequence between guy and greenbrier arkansas to investigate correlations with pore pressure change the range of b values suggests that the seismicity in the guy greenbrier area is mostly a result of the activation of pre existing faults the spatial distribution of b value correlates with modeled pore pressure changes in the northern segment of the fault b value increases with depth due to large pore pressure changes and opening of new fractures in the deeper part and stress relaxation in the shallower parts whereas in the southern segment the shallower part shows higher b values due to higher pore pressure fluctuations but the deeper part in the crystalline basement has low b value due to higher confining stress the correlation between the temporal variation of b value and hypocentral depth explains a previously observed temporal drop of b value this suggests that temporal variations should be interpreted along with the spatial variations estimation of the seismogenic indices for the guy greenbrier fault is provided our analysis suggests that monitoring changes in b value and seismogenic indices during an injection period might be used to avoid the occurrence of significant events if injection volume is reduced at critical times

evolution of the southern san joaquin basin and mid tertiary transitional tectonics central california a cenozoic tectonic and sedimentary history is proposed for the southern san joaquin basin ssjb and tehachapi mountains that evolved adjacent to the plate margin off central california seismic reflection borehole field biostratigraphic and paleomagnetic data are integrated into geologic and fault structure maps cross sections and geohistory plots and are analyzed with previous work in the region to develop a model relating the sequence timing and distribution of complex tectonically linked events the largely buried structures and strata in the ssjb preserve an unusually complete record of the mid tertiary transition from convergent to transform plate boundary as well as the regional transition to contraction during the pliocene significant structural relief existing across both extensional and contractile features is preserved in the subsurface and an active fold thrust belt propagates basinward along the margin of the u shaped tejon embayment the cenozoic evolution of the ssjb reflects the regional deformation of central california as different tectonic events followed each other along the adjacent north american plate margin five oligocene miocene basin phases are identified in the ssjb 1 late oligocene early miocene extensional subsidence with high and low angle normal faulting accompanied by volcanism and deposition of coarse syntectonic conglomerates 2 middle miocene uplift 3 later mid miocene transtensional subsidence to lower bathyal depths 4 alternating subsidence and uplift until the late miocene and 5 flexural subsidence due to pliocene to recent contraction reconstructions of mid tertiary california place the southern san joaquin tehachapi extensional terrane as a paleotectonic block located between the western mojave terrane then to the east and the western california terrane then to the south and west regional extension occurred during a long transition period between convergent and transform boundaries along the north american plate margin significant slip along the san andreas transform postdates this extensional event its origin apparently coincided with a regional middle miocene uplift event indicating that the san andreas fault is younger than previously supposed the tertiary ssjb has subsided due to extension transtension crustal tilting and thrust related loading the maricopa subbasin floor is likely composed of ensimatic and mafic rocks like those along the west side of the sierra nevada and locally has subsided beyond 12 km in contrast the relatively stable tejon embayment underlain by sierran crystalline crust achieved its maximum subsidence in the miocene since pliocene time the ssjb has filled and continued to deepen after the basin was tectonically shut off from the pacific ocean

provenance and stratigraphy of the eocene tejon formation western tehachapi mountains san emigdio mountains and southern san joaquin basin california abstract the eocene tejon formation of the western tehachapi and san emigdio mountains of california provides a unique east west trending outcrop belt of otherwise deeply buried strata that underlie the san joaquin basin to the north its stratigraphy and framework mineralogy have been used to define offsets along the san andreas fault a major neogene plate boundary transform fault that has translated coastal california northward more than 300 km by right slip the tejon formation was deposited directly on crystalline basement rocks as a result of an eastward transgression of at least 45 km from the early to the late middle eocene followed by a major regression in the late middle eocene the basal uvas conglomerate member consists entirely of coarse grained transgressive system tract tst deposits characterized by abundant current formed sedimentary structures it is overlain by offshore marine shales of the liveoak shale member which consist of lower tst deposits overlain by highstand system tract hst deposits the overlying regressive metralla sandstone member consists mostly of highly bioturbated fine grained shallow marine hst sandstones with local thin bedded turbidites present in some western exposures the quartzofeldspathic sandstones grand mean qm51 12f42 12lt7 4 of the tejon formation suggest a provenance consisting of plutonic metamorphic and volcanic rocks such as those present in the basement of the san emigdio and techachapi mountains northwestern mojave desert and southern sierra nevada petrologic parameters however suggest variable contributions from these source areas through time three distinctive petrofacies coincide with the three principal lithostratigraphic subdivisions the shallow marine tst sandstones from the uvas conglomerate member are more quartzose than those of the hst metralla sandstone member possibly because higher energy deposition preferentially preserved quartz thin bedded turbidites in the western exposures of the metralla sandstone in contrast have more abundant feldspar and volcanic lithic fragments than the uvas and liveoak members the composition of the tejon formation suggests derivation from a basement uplift provenance with progressive upsection changes from qm60 f33 lt8 uvas to qm46 f44 lt10 liveoak and qm 43 f52 lt5 metralla the composition and provenance of the tejon formation is different from that of the coeval butano sandstone and point of rocks sandstone submarine fan deposits to the north and west

deep injection and closely monitored induced seismicity at paradox valley colorado the u s bureau of reclamation s paradox valley unit pvu extracts aquifer brine from nine shallow wells along the dolores river paradox valley in southwestern colorado and after treating high pressure injects the brine 4 3 4 8 km below the surface pvu injects at rates between 800 and 1300 l min since 1991 pvu has emplaced over 4 106 m3 of fluid and induced more than 4000 surface recorded seismic events the events are recorded on the local 15 station paradox valley seismic network the induced seismicity at paradox separates into two distinct source zones a principle zone 95 of the events asymmetrically surrounding the injection well to a maximum radial distance of 3 km and a secondary ellipsoidal zone 2 5 km long and centered 8 km northwest of the injection well the expansion of these zones has stabilized since mid 1999 about three years after the onset of continuous injection within the principal zone hypocenters align in distinct linear patterns showing at depth stratigraphy and the local wray mesa fracture and fault system the primary faults of the wray mesa system are aseismic striking subparallel to the inferred maximum principal stress direction with one or more faults probably acting as fluid conduits to the secondary seismic zone individual seismic events in both zones do not discernibly correlate with short term injection parameters however a 0 5 km2 region immediately northwest of the injection well responds to long term large scale changes in injection rate and the surpassing of a threshold injection pressure focal mechanisms of the induced events are consistent with simple double couple strike slip moments and subhorizontal extension to the northeast in addition the fault planes are consistent with principal stress directions determined from borehole breakouts more than 99 9 of the pvu seismicity is below human detection m 2 5 however approximately 15 events have been felt locally with the largest being a magnitude m 4 3 because of the m 4 3 and two earlier felt m 3 5 events and injection economics pvu changed injection strategies three times since 1996 these changes reduced seismicity from 1100 events year to as low as 60 events year

ongoing seismicity in the dallas fort worth area we report on and discuss the continuous seismic activity in the dallas fort worth dfw area there was no reported seismic activity by usgs neis until 31 october 2008 approximately seven weeks after the start of salt water disposal at a nearby injection well in the southern part of the dfw airport the salt water disposal injection ceased in august 2009 the event detection based on crosscorrelation between several template events from dfw area and continuous seismic record shows that the seismic activity has been continuous for more than three years continuous monitoring at a local station allows us to complete the catalog down to a magnitude of zero providing more detailed information on seismicity in the dfw area this seismic activity migrated in space from a cluster southwest of the injection well to a cluster 2 km northeast of the injection well after may 2010 we show that the crosscorrelation detection at the wmok regional station is not able to detect both south and northeast clusters of even

deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off namibia abstract porewater concentrations of sulfate methane and other relevant constituents were determined on four sediment cores from the high productivity upwelling area off namibia which were recovered from the continental slope at water depths of 1300 and 2000 m at all four stations a distinct sulfate methane transition zone was observed several meters below the seafloor in which both sulfate and methane are consumed nutrient porewater concentration profiles do not show gradient slope changes at the depths of the transition zones flux calculations carried out on the basis of the determined porewater profiles revealed that anaerobic methane oxidation accounts for 100 of deep sulfate reduction within the sulfate methane transition zone and consumes the total net diffusive sulfate flux a significant contribution of organic carbon oxidation to the reduction of sulfate at these depths could therefore be excluded we state that porewater profiles of sulfate with constant gradients above the transition zones are indicative for anaerobic methane oxidation controlling sulfate reduction

tectonics of pliocene removal of lithosphere of the sierra nevada california pliocene ca 3 5 ma removal of dense eclogitic material under the sierra nevada has been proposed from variations in the petrology and geochemistry of neogene volcanic rocks and their entrained xenoliths from the southern sierra the replacement of eclogite by buoyant warm asthenosphere is consistent with present day seismologic and magnetotelluric observations made in the southern sierra a necessary consequence of replacing eclogite with peridotite is that mean surface elevations and gravitational potential energy both increase an increase in potential energy should increase extensional strain rates in the area if these forces are insuffi cient to signifi cantly alter pacifi c north american plate motion then increased extensional strain rates in the vicinity of the sierra must be accompanied by changes in the rate and style of deformation elsewhere changes in deformation in california and westernmost nevada agree well with these predictions existing geologic evidence indicates that a period of rapid uplift along the sierran crest of more than 1 km occurred between 8 and 3 ma most likely as a consequence of removal of lower lithosphere about this same time extensional deformation was initiated within 50 km of the eastern side of the sierra 5 3 ma and regional shortening began to produce the california coast ranges 5 3 ma we suggest that these events were induced by the 1 2 10 12 n m increase of gravitational potential energy generated by the sierran uplift evidence for pliocene uplift adjoining crustal extension and shortening in directly opposing parts of the coast ranges is found along nearly the entire length of the sierra nevada and implies that lithosphere was removed beneath all of the presentday mountain range the uplifted area lies between two large upper mantle high pwave velocity bodies under the south end of the san joaquin valley and the north end of the sacramento valley these high velocity bodies plausibly represent the present position of material removed from the base of the crust lithospheric removal may also be responsible for shifting of the distribution of transform slip from the san andreas fault system to the eastern california shear zone a prediction that awaits better defi ned slip histories on both faults overall the late cenozoic deformational history of the sierra nevada and vicinity illustrates that locally derived forces can infl uence deformation kinematics within plate boundary zones

towards quantifying the reaction network around the sulfate methane transition zone in the ulleung basin east sea with a kinetic modeling approach abstract we present a kinetic model based upon pore water data collected from eight sites drilled during the second ulleung basin gas hydrate drilling expedition ubgh2 in 2010 three sites were drilled at locations where acoustic chimneys were identified in seismic data and the rest were drilled on non chimney i e background environments our model coupled a comprehensive compositional and isotopic data set is used to illustrate the different biogeochemical processes at play in those two environments in terms of reactions around the sulfate methane transition zone smtz organic matter decomposition is an important process for production of methane dissolved inorganic carbon dic and consumption of sulfate in the non chimney sites whereas anaerobic oxidation of methane aom dominates both carbon and sulfur cycles in the chimney environment different sources of methane mediate aom in the two settings internally produced methane through co 2 reduction cr and methanogenesis fuels aom in the non chimney sites whereas aom is sustained by methane from external sources in the chimney sites we also simulate the system evolution from non chimney to chimney conditions by increasing the bottom methane supply to a non chimney setting we show that the higher ch 4 flux leads to a higher microbial activity of aom and more organic matter decomposition through methanogenesis a higher methanogenesis rate and a smaller cr contribution relative to aom in the chimney sites is responsible for the isotopically light dic and heavy methane in this environment relative to the non chimney sites

rotation of the southernmost sierra nevada california structural paleogeographic and magmatic trends of the sierra nevada batholith swing from a characteristic nnw trend in the northern and central parts of the batholith to a nearly e w trend in the tehachapi and san emigdio mountains paleomagnetic results from eight sites in the upper cretaceous 80 86 m y bear valley springs pluton in the tehachapi mountains yield a mean direction d 022 i 56 k 97 95 5 6 this mean direction is significantly different from the expected late cretaceous field direction for this locality and suggests that the pluton has undergone a clockwise rotation of 45 14 in accord with the change in structural trend in that area lower to middle miocene volcanic and sedimentary rocks of the kinnick formation overlie the plutonic rocks and yield a mean direction d 354 i 64 a paleomagnetic pole derived from this mean direction is not significantly different from the expected miocene pole for north america this constrains the time of rotation of the pluton to be between about 80 and 20 m y probably predating establishment of the present san andreas transform in this area we suggest that the observed rotation is part of a large oroclinal bend affecting to different degrees the entire southern sierra nevada the driving mechanism for such a bending may be right lateral shear along a proto san andreas transform for which there is now a significant body of evidence

analysis of the cleburne texas earthquake sequence from june 2009 to june 2010 on 9 june 2009 an graphic 1 2 8 earthquake shook cleburne texas a community not known to have previously experienced earthquakes over 50 small earthquakes followed by the end of december 2009 a temporary network of four and then five iris passcal broadband systems was deployed from june 2009 to june 2010 recording data that were used to locate 38 events with the most confident p and s arrival picks event locations were distributed along a 2 km long north northeast trend the location centroid was at 32 298 n 97 372 w and at 3 6 km depth this location is approximately 1 3 km from a saltwater disposal well that began injection in october 2007 and 3 2 km away from a second injection well that was active from september 2005 to late july 2009 focal mechanisms estimated for the best recorded events suggest a north northeast south southwest trending normal fault with a dip of 50 and a component of oblique motion rake of 80 this average solution is generally consistent with the north northeast trending extensional faults that are prevalent across parts of texas oklahoma louisiana and arkansas stress drops calculated from p and s spectra for seven different events ranged from 3 9 to 90 bars with most estimates between 40 and 50 bars typical values for intraplate earthquakes because there were no known previous earthquakes and the located events were close to the two injection wells and near the injection depth the possibility exists that earthquakes may be related to fluid injection online material tables of absolute and relative earthquake locations and a figure summarizing focal mechanism solutions 1 embed inline graphic 1 gif

modeling of neogene crustal block rotation case study of southeastern california numerical modeling using a two dimensional distinct element method dem was performed to give an additional understanding of the mechanism of crustal block rotation in a highly active portion of the pacific north america transform plate boundary paleomagnetic and structural investigations have shown that large 30 50 horizontal rotations of crustal blocks occurred in the eastern transverse zone and the northeast mojave block southeastern california since the end of early miocene the main aspect of the modeling was to investigate whether an anisotropic horizontal stress state can be responsible for the rotation of crustal blocks with a length of 100 km or not the simulations were performed using different stress boundary conditions and different parameters of the fault strength applying an assumed ratio of 2 for the horizontal stress components as boundary condition block rotations in the order of 40 only occur if 1 the major horizontal stress sh is oriented n20 e with a maximal deviation of 15 to the east or west and 2 the fault strength described by the friction coefficient is smaller than 0 12 or 14 only of the value 0 85 for intact rocks byerlee s law for a weakening model of the fault strength an initial friction coefficient of 0 85 allows also rotations of about 40 if the friction coefficient decreases rapidly due to an increasing shear displacement to a basic friction coefficient of 0 12 or smaller for the same amount of rotation 40 a decreasing stress ratio requires a lowering of the friction coefficient used whereas an increase of the ratio allows a higher friction coefficient the simulation also show that the modeling with elastic blocks can adequately describe the observed main features of the crustal deformation especially the cumulative slip values discrepancies in the observations and modeling results for the western parts of the mojave desert are the result of a neglect of the three dimensional deformation in our two dimensional modeling

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

role of extrusion of the rand and sierra de salinas schists in late cretaceous extension and rotation of the southern sierra nevada and vicinity the rand and sierra de salinas schists of southern california were underplated beneath the southern sierra nevada batholith and adjacent mojave salinia region along a shallow segment of the subducting farallon plate in late cretaceous time various mechanisms including return flow isostatically driven uplift upper plate normal faulting erosion or some combination thereof have been proposed for the exhumation of the schist we supplement existing kinematic data with new vorticity and strain analysis to characterize deformation in the rand and sierra de salinas schists these data indicate that the schist was transported to the ssw from deep to shallow crustal levels along a mylonitic contact the rand fault and salinas shear zone with upper plate assemblages crystallographic preferred orientation patterns in deformed quartzites reveal a decreasing simple shear component with increasing structural depth suggesting a pure shear dominated westward flow within the subduction channel and localized simple shear along the upper channel boundary the resulting flow type within the channel is that of general shear extrusion integration of these observations with published geochronologic thermochronometric thermobarometric and paleomagnetic studies reveals a temporal relationship between schist unroofing and upper crustal extension and rotation we present a model whereby trench directed channelized extrusion of the underplated schist triggered gravitational collapse and clockwise rotation of the upper plate

paleomagnetism and the motion of large and small plates the focus of paleomagnetic research during past decades has varied greatly the first generation in paleomagnetism might be defined as beginning with the pioneering studies aimed at discovering whether the geomagnetic field has been a reliable reference frame for measuring and timing continental displacements an enormous effort followed in the form of individual paleomagnetic studies of cratonic rocks culminating with the construction of apw apparent polar wander paths for the continents which could be used to test paleogeographic reconstructions coupled with parallel research in marine geophysics and geology the refined apwp which result from this effort have helped to develop a reasonable first order history of cenozoic mesozoic paleogeography for the major plates

thermobarometric constraints on the depth of exposure and conditions of plutonism and metamorphism at deep levels of the sierra nevada batholith tehachapi mountains california we present thermodynamic estimates of pressures temperatures and volatile activities in variably deformed gabbroic to granitic cretaceous 115 100 ma batholithic and framework rocks of the tehachapi mountains southernmost sierra nevada california al contents of hornblende in granitoids imply igneous emplacement at 8 kbar in the southernmost tehachapi mountains with lower pressures 3 7 kbar to the north metamorphic pressures and temperatures for garnet bearing paragneisses and metaigneous rocks were estimated on the basis of garnet hornblende plagioclase quartz and garnet biotite plagioclase quartz thermobarometers disparate results for the metaigneous rocks from the latter system point to the difficulty of applying pelite based thermobarometers to rocks of contrasting composition and mineralogy preferred pressures cluster at 7 1 9 4 and 3 6 4 3 kbar incomplete knowledge of reaction histories however limits our interpretation of the lower pressures because they are minimum estimates the 4 kbar samples are all from a small area and if our interpretation is correct they imply a local more shallow event superimposed on crust once residing at deeper structural levels garnet hornblende and garnet biotite temperatures are less coherent likely owing to retrograde fe mg exchange and range from 570 to 790 c the majority of the rocks are igneous and affected by recrystallization and metamorphism during subsolidus cooling they are not granulites country rock paragneisses are typically migmatized at peak metamorphic conditions near that of the wet granite solidus 690 c veinlike paragenesis of garnet in the metaigneous rocks suggests formation related to the presence of a fluid phase thermodynamic estimates of volatile activities in these garnet bearing assemblages suggest variable mostly co 2 rich fluid compositions in the absence of any pervasive fluid flux the igneous rocks of the tehachapi mountains were thus intruded at depths of 30 km making them the deepest known exposed components of the cretaceous sierra nevada batholith metamorphism occurred at these great depths and perhaps locally after 15 km of uplift before 87 ma implying an uplift rate of 1 2 mm yr a minimum uplift rate is 0 6 mm yr this original uplift and possible subsequent uplift events may have been related to underthrusting of a block of rand schist from what is now the southeast with concomitant widespread ductile deformation the deduced pressure temperature and uplift history is similar to those of high pressure high temperature cretaceous batholithic rocks in salinia and the san gabriel mountains but direct correlation is not wan anted when compared with higher level intrusive rocks from analogous portions of the sierra nevada batholith to the north the tehachapi rocks reveal a deep batholith that is more heterogeneous and somewhat more mafic on average but displaying a similar level of isotopic hybridization involving mantle and crustal sources the batholith is quartz rich at these levels suggestive of a weak ductile middle crust susceptible to prolonged deformation and possible delamination

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

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

style and age of late oligocene early miocene deformation in the southern stillwater range west central nevada paleomagnetism geochronology and field relations paleomagnetic and geochronologic data combined with geologic mapping tightly restrict the timing and character of a late oligocene to early miocene episode of large magnitude extension in the southern stillwater range and adjacent regions of west central nevada the southern stillwater range was the site of an oligocene to early miocene volcanic center comprising 1 28 3 to 24 3 ma intracaldera ash flow luffs lava flows and subjacent plutons associated with three calderas 2 24 8 to 20 7 ma postcaldera silicic dikes and domes and 3 unconformably overlying 15 3 to 13 ma dacite to basalt lava flows plugs and dikes the caldera related luffs lava flows and plutons were tilted 60 70 either west or east during the initial period of cenozoic deformation that accommodated over 100 extension directions of remanent magnetization obtained from these extrusive and intrusive caldera related rocks are strongly deflected from an expected miocene direction in senses appropriate for their tilt a mean direction for these rocks after tilt correction however suggests that they were also affected by a moderate 33 4 11 8 component of counterclockwise vertical axis rotation paleomagnetic data indicate that the episode of large tilting occurred during emplacement of 24 8 to 20 7 ma postcaldera dikes and domes in detail an apparent decrease in rotation with decreasing age of individual isotopically dated bodies of the postcaldera group indicates that most tilting occurred between 24 4 and 24 2 ma the onset of tilting immediately following after the final caldera eruptions suggests that the magmatism and deformation were linked deformation was not driven by magma buoyancy however because tilting equally affected the caldera systems of different ages including their plutonic roots it is more likely that regional extension was focused in the southern stillwater range due to magmatic warming and reduction of tensile strength of the brittle crust faults that accommodated deformation in the southern stillwater range initially dipped steeply and cut deeply to expose more than 9 km of crustal section the exposed crustal sections are probably rotated blocks above an unexposed basal detachment that lay near the early miocene brittle ductile transition

statistics of fracture strength and fluid induced microseismicity 1 in this paper we develop an approach for estimating the strength of rocks by analyzing fluid induced microseismicity the strength corresponds to the value of critical pressure in the pore space that must be exceeded in order to activate preexisting fractures i e to trigger earthquakes we assume that during hydraulic injection experiments in boreholes microseismicity is mainly triggered by a diffusive process of pore pressure perturbation an analytical solution can be applied to find time dependent pore pressure perturbations in rocks caused by fluid injections characteristics of the spatiotemporal evolution of microseismic clouds can be then used to estimate minimum and maximum pressures necessary to trigger earthquakes moreover we present a method for reconstruction of the full spectrum of rock strength that is we show how to estimate the probability density function of the critical pressure we verify the approach using numerical data and apply it to real data of injection induced microseismicity from two hot dry rock tests in crystalline rocks and one hydraulic fracturing experiment in a sedimentary rock the results show that such an analysis of microseismicity is able to provide us with a completely new feature of natural fractured rocks in situ namely the statistics of their strength we find that very low critical pressures in the range 0 001 1 mpa characterize the strength of preexisting cracks for all data sets analyzed the range of critical pressures is broadly distributed within 3 to 4 orders of magnitude however the probability density functions of critical pressure change very quickly from the zero level to significant values and from significant values to the zero level at the lower and upper limits of their nonvanishing value ranges respectively the lower bound of critical pressure is possibly defined by the magnitude of tidal induced stresses permanently occurring and relaxing in the earth

a decade of induced slip on the causative fault of the 2015 mw 4 0 venus earthquake northeast johnson county texas on 7 may 2015 a mw 4 0 earthquake occurred near venus northeast johnson county texas in an area of the bend arch fort worth basin that reports long term high volume wastewater disposal and that has hosted felt earthquakes since 2009 in the weeks following the mw 4 0 earthquake we deployed a local seismic network and purchased nearby active source seismic reflection data to capture additional events characterize the causative fault and explore potential links between ongoing industry activity and seismicity hypocenter relocations of the resulting local earthquake catalog span 4 6 km depth and indicate a fault striking 230 dipping to the west consistent with a nodal plane of the mw 4 0 regional moment tensor fault plane solutions indicate normal faulting with b axes striking parallel to maximum horizontal compressive stress seismic reflection data image the reactivated basement fault penetrating the ordovician disposal layer and mississippian production layer but not displacing post lower pennsylvanian units template matching at regional seismic stations indicates that low magnitude earthquakes with similar waveforms began in april 2008 with increasing magnitude over time pressure data from five saltwater disposal wells within 5 km of the active fault indicate a disposal formation that is 0 9 4 8 mpa above hydrostatic we suggest that the injection of 28 000 000 m3 of wastewater between 2006 and 2015 at these wells led to an increase in subsurface pore fluid pressure that contributed to inducing this long lived earthquake sequence the 2015 mw 4 0 event represents the largest event in the continuing evolution of slip on the causative fault

collapse of southwestern north america and the evolution of early miocene detachment faults metamorphic core complexes the sierra nevada orocline and the san andreas fault system plate reconstructions indicate that early miocene pacific north american relative motion was not parallel to the transform but was instead oblique and transtensional we propose that the western edge of the north american plate east of the transform gravitationally collapsed to the southwest in response to this divergence the northern and eastern edges of the collapsed region underwent extension between 24 and 20 ma whereas extension in southeastern california and southern arizona during this interval was coaxial with the overall s50 60 w collapse direction the extension direction along the northern oundary mojave extensional belt was north south and the result of the combined effects of the southwestward collapse and the independent northwestward translation of the region to the north collapse continued between 20 and 16 ma and extension persisted in southeastern california and southern arizona extension along the northern boundary waned owing to the apparent cessation of motion of the region to the north thus the kinematics of the northern boundary changed to dextral shear and extension along what is here named the trans mojave sierran shear zone this east west zone of mainly right shear oroclinally folded the southern tail of the sierra nevada and the central mojave desert rocks within this 83 110 km wide zone were rotated approx 40 60 clockwise about vertical axes finally as collapse moved the north american plate progressively west across the locus of transform shear its western edge became increasingly subject to the motion of the pacific plate over time the edge of north america was truncated by faults of the san andreas system and transferred to the pacific plate

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

paleomagnetic assessment of oroflexural deformation in west central nevada and significance for emplacement of allochthonous assemblages abrupt westerly deflections of north south trending facies boundaries the isopleth of 87sr 86sr 0 076 and arcuate structural trends of paleozoic mesozoic and cenozoic age in the west central basin and range province have been explained by 1 post early jurassic oroflexural folding and shear 2 the existence of a pre late jurassic resistant block along the western continental margin possibly representing late precambrian breakup and 3 regional flexure mina deflection prior to intrusion of late cretaceous plutons which crosscut flexure related structural trends paleomagnetic data gathered from late cretaceous plutons and remagnetized metasedimentary rocks along and north of the northern margin of the zone of east west structural trends are not in support of significant oroflexural folding and attending major clockwise rotation since late cretaceous time the data water canyon pluton d 1 i 57 95 4 k 9 n 132 gunmetal pluton d 354 i 60 95 6 k 21 n 29 east garfield hills pluton d 349 i 74 95 11 k 14 n 12 la panta pluton d 22 i 66 95 10 k 16 n 13 gillis canyon pluton d 354 i 50 95 4 k 20 n 50 and folded units of the excelsior mountains d 309 i 79 95 7 k 12 n 37 are dispersed from expected cretaceous directions for the mina deflection region but they do not conform to a model of major systematic regional clockwise rotation the generally small deflections of unit means from expected directions could be explained by irregular components of late cenozoic tilting and or rotation the paleomagnetic data do not deny the possibility of pre late cretaceous oroclinal bending nevertheless regional structural analysis complimented by the paleomagnetic results indicate that the mina deflection is in all likelihood a primary feature whose geometry reflects the late precambrian fragmentation of western north america structures related to the accretion of allochthonous assemblages between middle devonian and cretaceous time in this part of the cordillera also reflect the primary nature of this feature

simple shear of southern california during neogene time suggested by paleomagnetic declinations we have studied the paleomagnetism of various neogene age rocks in southern california as a means of determining the amounts of oligocene and younger tectonic rotation and translation which has occurred in this region our results suggest that fully 25 of this area in particular the transverse ranges has undergone extreme clockwise rotation work in southeastern california implies that 40 of clockwise rotation has occurred here although paleomagnetic declinations adjacent to a major right lateral fault are apparently rotated over 200 the crustal block bounded by the san gabriel and san andreas fault has undergone a net clockwise rotation of 35 although the data here can be interpreted to show that an original early miocene rotation of about 50 was followed by a late miocene or pliocene counterclockwise rotation of 15 paleomagnetic results from the offshore islands suggests that san clemente santa barbara and san nicolas islands have not rotated but santa catalina has undergone about 90 of clockwise rotation all of the northern channel islands including anacapa santa cruz santa rosa and san miguel are implied to have rotated 70 or 80 clockwise this result is also found for the santa monica mountains east of anacapa island in the santa ynez range north of the channel islands paleomagnetic study of the monterey formation also indicates large clockwise rotations of near 90 these data also suggest that the santa maria basin is not rotated and that the north boundary of the rotated region is the santa ynez river fault stratigraphic control on the paleomagnetic data from the monterey formation implies that the rotation began about 16 m y ago and may be continuing today in the western region paleomagnetic inclination data from our study show that the northern channel islands in particular may have translated 15 northward since middle miocene time however equally valid interpretations of these same data are that the low inclinations are due to the combined effects of erroneous structural corrections non dipole magnetic field behavior and right offset on the san andreas fault system palinspastic reconstruction of southern california regions for the early miocene implies that parts of the transverse ranges structures were once aligned with north trending extensional structures in the southwestern united states we propose that pacific american plate interactions both rifted the continental crust to create this pattern and rotated the western most structures within a dextral simple shear zone which had a half width of about 400 km

a full vector paleomagnetic secular variation record psv from pyramid lake nevada from 47 17 ka evidence for the successive mono lake and laschamp excursions abstract we have carried out a paleomagnetic study of late pleistocene pyramid lake core plc08 1 1680 cm our goals were to develop a full vector paleomagnetic secular variation psv record for the core establish a paleomagnetic chronostratigraphy for the lake based on correlation of the psv record to other dated psv records in the region compare that chronostratigraphy with previously developed radiocarbon and ash chronologies and search for evidence of the mono lake excursion and laschamp excursion we have recovered a full vector psv record inclination declination relative paleointensity for the interval 47 ka to 17 ka twenty radiocarbon dates and four dated ashes provided a chronostratigraphic framework for this record we have also used the link between our psv and other dated psv records to develop an independent psv chronostratigraphy for the core the psv chronostratigraphy is not significantly different from that estimated by the radiocarbon and ash chronologies we note the existence of two intervals of anomalous paleomagnetic directions the younger interval centered at 34 1 0 4 ka has the characteristic vector component features of the mono lake excursion the older interval centered at 40 9 0 5 ka has the characteristic paleomagnetic signature of the laschamp excursion this is the first time both intervals of excursional behavior have been found in the same sediment record from the western usa our new psv record also corroborates previous estimates of the mono lake excursion directional field behavior liddicoat and coe 1979 and age benson et al 2003

clockwise rotation and implications for northward drift of the western transverse ranges from paleomagnetism of the piuma member sespe formation near malibu california 1 new paleomagnetic results from mid tertiary sedimentary beds in the santa monica mountains reinforce the evidence for large scale rotation of the western transverse ranges and anisotropy measurements indicate that compaction induced inclination flattening may resolve a long standing controversy regarding the original paleolatitude of the rotated block previously published paleomagnetic data indicate that post oligocene rotation amounts to 70 110 clockwise affecting the channel islands santa monica mountains and santa ynez mountains the sespe formation near malibu consists of a lower member dominated by nonmarine sandstone and conglomerate and an upper section the piuma member which consists of gray red sandstone and mudstone interbedded with minor tuff and limestone beds the piuma member has a paleomagnetic pole at 36 6 n 326 7 e a95min 5 0 a95max 9 6 obtained by thermal demagnetization of 34 oriented cores from oligocene and early miocene beds after correcting for plunge of the geologic structure the data are consistent with significant clockwise rotation 77 7 of the region relative to stable north america rotation of the western transverse ranges is generally viewed as a consequence of pacific north american plate interactions after 28 ma when east west subduction gave way to northwest transform motion in southern california inclinations from the piuma study indicate a paleolatitude anomaly of 11 7 and are consistent with a mean northward drift that exceeds generally accepted san andreas fault displacement by a factor of 3 however sedimentary inclination error may accentuate the anomaly anisotropy of isothermal remanent magnetization indicates inclination flattening of approximately 8 and correction for the effect reduces the paleolatitude anomaly to 5 3 5 8 compaction may explain the inclination flattening in these sedimentary rocks but the process does not adequately explain lower than expected inclinations found in previous studies of miocene volcanic rocks of the western transverse ranges

significance of stable carbon isotope trends in carbonate concretions formed in association with anaerobic oxidation of methane aom middle and upper devonian shale succession western new york state usa abstract carbonate concretions are concentrated along discrete stratigraphic horizons within middle and upper devonian carbonaceous black and organic deficient gray shale of western new york state textural characteristics preserved throughout studied concretions including a clay grain microfabric typical of flocculated clay and spherical algal cysts are consistent with a model entailing the formation of low density compaction resistant calcium carbonate masses at shallow burial depth within the zone of bacterial sulfate reduction burial of nascent concretions to the sulfate methane transition zone smtz was accompanied by the nearly complete infilling of porosity the diagenetic consequence of the anaerobic oxidation of methane aom each concretionary horizon then defines the position of the smtz stabilized during an episode of reduced sedimentation rate most analyzed concretions 75 of the middle devonian marcellus formation into the upper devonian gowanda formation display center to edge profiles of increasing bulk 13c far fewer concretions are characterized by radial profiles of decreasing 13c the common radial profiles of increasing 13c can be attributed to aom related kinetic carbon isotope fractionation under diagenetic conditions of limited methane which favors the production of dissolved inorganic carbon of increasing 13c less common concretions displaying center to edge profiles of diminishing 13c may record the anaerobic oxidation of more strongly 13c depleted methane produced by carbon dioxide reduction methanogenesis related to the degradation of organic matter within and near the smtz or aom back flux an enzyme mediated equilibrium isotope effect these processes are favored by sulfate limited diagenetic conditions more typical of the lower smtz and immediately underlying upper methanogenic zone mez contradictory isotope profiles of texturally similar concretions can be accounted for by diagenesis associated with an extended smtz esmtz comprising the methane limited smtz and the underlying sulfate deficient upper mez vertical shifts of the diagenetic horizons of the esmtz induced by variable methane flux would have juxtaposed concretions displaying seemingly incompatible isotopic histories