dynamical excitation of the tropical pacific ocean and enso variability by little ice age cooling tropical pacific ocean dynamics during the medieval climate anomaly mca and the little ice age lia are poorly characterized due to a lack of evidence from the eastern equatorial pacific we reconstructed sea surface temperature el nino southern oscillation enso activity and the tropical pacific zonal gradient for the past millennium from galapagos ocean sediments we document a mid millennium shift mms in ocean atmosphere circulation around 1500 1650 ce from a state with dampened enso and strong zonal gradient to one with amplified enso and weak gradient the mms coincided with the deepest lia cooling and was probably caused by a southward shift of the intertropical convergence zone the peak of the mca 900 1150 ce was a warm period in the eastern pacific contradicting the paradigm of a persistent la nina pattern

the evolution of el nino past and future abstract we review forecasts of the future of el nino and the southern oscillation enso a coupled instability of the ocean atmosphere system in the tropical pacific with global impacts enso in the modern world is briefly described and the physics of the enso cycle is discussed particular attention is given to the bjerknes feedback the instability mechanism which figures prominently in enso past and future our knowledge of enso in the paleoclimate record has expanded rapidly within the last 5 yr the enso cycle is present in all relevant records going back 130 kyr it was systematically weaker during the early and middle holocene and model studies indicate that this results from reduced amplification in the late summer and early fall a consequence of the altered mean climate in response to boreal summer perihelion data from corals shows substantial decadal and longer variations in the strength of the enso cycle within the past 1000 yr it is suggested that this may be due to solar and volcanic variations in solar insolation amplified by the bjerknes feedback there is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future but it is very far from conclusive the comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of enso s future some predict more enso activity some less with the highly uncertain consensus forecast indicating little change

simulation and inversion of borehole temperature profiles in surrogate climates spatial distribution and surface coupling a heat conduction forward model driven by ground surface temperature from three 1000 year climate simulations with the state of the art echo g model has been used to simulate underground temperature perturbation profiles an inversion approach has been applied to reconstruct ground surface temperature histories from the simulated profiles and to compare them with the climate model temperatures results support the skill of borehole inversion methods to retrieve long term temperature trends and the robustness of using the present day borehole network for reconstructing sat variations

constraining earthquake source inversions with gps data 2 a two step approach to combine seismic and geodetic data sets 1 we present a new method to combine static and wavefield data to image earthquake ruptures our combined inversion is a two step procedure following the work of hernandez et al 1999 and takes into account the differences between the resolutions of the two data sets the first step consists of an inversion of the static field which yields a map of slip amplitude this inversion exploits a special irregular grid that takes into account the resolution of the static data the second step is an inversion of the radiated wavefield it results in the determination of the time evolution of slip on the fault in the second step the slip amplitude is constrained to resemble the static slip amplitude map inferred from the gps inversion using this combined inversion we study the source process of the 2004 m6 parkfield california earthquake we conclude that slip occurred in two main regions of the fault each of which displayed distinct rupture behaviors slip initiated at the hypocenter with a very strong bilateral burst of energy here slip was localized in a narrow area approximately 10 km long the rupture velocity was very fast 3 5 km s and slip only lasted a short period of time 1 s then the rupture proceeded to a wider region 12 20 km northwest of the hypocenter here the earthquake developed in a more moderated way the rupture velocity slowed to 3 0 km s and slip lasted longer 1 2 s the maximum slip amplitude was 0 45 m

waveform modeling of historical seismograms of the 1930 irpinia earthquake provides insight on blind faulting in southern apennines italy 1 the southern apennines chain is related to the west dipping subduction of the apulian lithosphere the strongest seismic events mostly occurred in correspondence of the chain axis along normal nw se striking faults parallel to the chain axis these structures are related to mantle wedge upwelling beneath the chain in the foreland faulting develops along e w strike slip to oblique slip faults related to the roll back of the foreland similarly to other historical events in southern apennines the i0 xi mcs intensity scale 23 july 1930 earthquake occurred between the chain axis and the thrust front without surface faulting this event produced more than 1400 casualties and extensive damage elongated approximately e w the analysis of the historical waveforms provides the chance to study the fault geometry of this anomalous event and allow us to clarify its geodynamic significance our results indicate that the ms 6 6 1930 event nucleated at 14 6 3 06 km depth and ruptured a north dipping n100 e striking plane with an oblique motion the fault propagated along the fault strike 32 km to the east at about 2 km s the eastern fault tip is located in proximity of the vulture volcano the 1930 hypocenter similarly to the 1990 mw 5 8 southern apennines event is within the mesozoic carbonates of the apulian foredeep and the rupture developed along a blind fault the 1930 fault kinematics significantly differs from that typical of large southern apennines earthquakes which occur in a distinct seismotectonic domain on late pleistocene to holocene outcropping faults these results stress the role played by pre existing blind faults in the apennines subduction setting

a 3d approach to study the interaction between hydraulic and natural fracture a real 3d model is developed to study the interaction between hydraulic fracture and natural fracture the hydraulic fracture propagation behavior and fracture geometry under impact of natural fracture are studied through a series of numerical results different horizontal stress anisotropies intersection angles friction coefficients as well as hydraulic parameters the final results demonstrate the key role of horizontal stress anisotropy on the interaction between hydraulic fracture and natural fracture under a higher intersection angle it is difficult for hydraulic fracture to cross the natural fracture with low horizontal stress anisotropy in addition the natural fracture at a lower intersection angle has a higher probability to capture the hydraulic fracture normally the natural fracture is more likely to be activated in the top branch at a low intersection angle as the lower branch is located in the induced stress shadow of hydraulic fracture by contrast two different branches especially two symmetrical braches at the intersection of 90 are activated on the other hand a higher friction coefficient slows down the propagation in natural fracture even prevents the activation of natural fracture besides increased injection rate as well as fluid viscosity will promote the fracture propagation under the same conditions to lead to a longer and wider fracture

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

implications of the pore pressure and in situ stress for the coalbed methane exploration in the southern junggar basin china abstract the southern junggar basin hosts abundant coalbed methane cbm resources and is expected to be an important cbm production base in china the pore pressure and in situ stress are key factors that influence the exploration and development of cbm however these factors are poorly understood in this area based on extended leak off test data mathematical models were established for pore pressure and in situ stress prediction using regression analysis subsequently the correlations between the pore pressure in situ stress and permeability were analyzed and the stress ratios were investigated finally the forming mechanism of stress zonation in the study area was discussed the results show that cbm reservoirs are generally underpressured and partly overpressured at depths greater than 800 m in the study area the study area is characterized by notable stress zoning the stress regime varies from reverse to strike slip to normal faulting with increasing depth significantly positive correlations exist between the pore pressure maximum principal stress minimum principal stress vertical stress and principal stress difference the minimum horizontal stress is approximately 70 of the vertical stress in the study area a mud weight window varying from the pore pressure to the most likely breakdown pressure is suggested at depths greater than 600 m a relatively high principal stress difference is observed which indicates that deep coals have a relatively high mechanical strength and their permeability can be enhanced by hydraulic fracturing the depth dependent stress zonation is mainly due to the influence of thrusting on the in situ stress which diminishes with increasing depth the compressional stress regime in the shallow area benefits the sealing of faults and the preservation of cbm resources in the study area the deep cbm resources have a development potential the outcomes of this study contribute to the cbm exploration and development in the study area

iterative deconvolution of regional waveforms and a double event interpretation of the 2003 lefkada earthquake greece the moment tensor inversion for multiple point sources based on kikuchi and kanamori 1991 was extended to full waveform data at regional or local distances the new code proved to be efficient for retrieving major source contributions of the 2003 lefkada greece earthquake the source model was derived from five three component regional stations epicentral distances 140 km at periods 10 20 s two main events dominated the rupture process one at the lefkada island comprising three subevents of total moment 0 9 1018 n m and the other at the cephalonia island comprising one subevent of 0 5 1018 n m their spatial and temporal separation is 40 km and 14 s respectively they can be understood as two earthquakes the uncertainty estimate based on reduced data sets repeatedly excluding a station shows that the cephalonia subevent and the major lefkada subevent are very well resolved regarding their position time and focal mechanism the source model explains well the aftershock distribution characterized by two clusters at the lefkada and cephalonia islands respectively the focal mechanisms of the two main subevents are predominantly right lateral strike slip of south southwest north northeast orientation the cephalonia subevent occurred on a less steeply dipping fault with a small thrust component large deviations from pure double couple were found but interpreted as artifacts the new software developed in this article fortran code and matlab graphic user interface is freely available online material color graphics and 3d visualization of the 2003 lefkada earthquake sequence

kinematic source parameters for the 1989 loma prieta earthquake from the nonlinear inversion of accelerograms we describe a technique to infer the kinematic parameters of the earth quake rupture process by the nonlinear inversion of near source high frequency seis mic records the model assumes that each point on the fault plane slips when the rupture front passes with a variable slip amplitude for a given rupture model syn thetic seismograms are computed by using the ray theory and a plane layered velocity structure the rupture velocity and the final slip are specified at a set of control points on the fault plane and the values at any point on the fault are then obtained by a bicubic interpolation the final slip and rupture velocity at the fault grid nodes are determined by searching for the minimum of a misfit function by using the genetic algorithm the number of control points is progressively increased to move from a high to low wavelength description of final slip and rupture velocity on the fault plane the optimal model parameter set is chosen according to the minimum of the corrected akaike information criterion parameter the uncertainty on the source parameters has been estimated through the analysis of cross correlation of the misfit function in the neighborhood of the final best fit rupture model the method is applied to near source strong motion records of the 1989 loma prieta earthquake we find that the most earthquake slip occurred in two regions located northwest and southeast of the hypocenter consistent with previous models obtained using other data and techniques moreover we find that the rupture propagated faster toward the southeast than in the northwest direction the total duration of the rupture is found to be approximately 9 sec

twentieth century tropical sea surface temperature trends revisited 1 this study compares the global distribution of 20th century sst and marine air temperature trends from a wide variety of data sets including un interpolated archives as well as globally complete reconstructions apart from the eastern equatorial pacific all datasets show consistency in their statistically significant trends with warming everywhere except the far northwestern atlantic the largest warming trends are found in the middle latitudes of both hemispheres two of the sst reconstructions exhibit statistically significant cooling trends over the eastern equatorial pacific in disagreement with the un interpolated sst and marine air temperature datasets which show statistically significant warming in this region twentieth century trends in tropical marine cloudiness precipitation and slp from independent data sets provide physically consistent evidence for a reduction in the strength of the atmospheric walker circulation accompanied by an eastward shift of deep convection from the western to the central equatorial pacific

tropical river flow and rainfall reconstructions from coral luminescence great barrier reef australia 1 rainfall and river flow in northeast queensland australia are highly seasonal and show high interannual and decadal variability that is modulated by el nino southern oscillation enso events and the pacific decadal oscillation pdo reconstructions of october september freshwater input to the great barrier reef lagoon and october september queensland rainfall are developed from visual assessment of the occurrence and intensity of luminescent lines in massive porites from up to 25 coral cores from 15 nearshore reefs regularly influenced by river flood plumes separate reconstructions are developed for four rivers herbert burdekin pioneer and fitzroy and these are used to reconstruct total annual freshwater flow into the great barrier reef 69 74 variance calibrated and an index of queensland rainfall 53 57 variance calibrated the reconstructions extend back to 1631 but are most reliable from 1661 and capture significant decadal variability the reconstructions provide insights into long term tropical rainfall and river flow variability and the behavior of enso and the pdo over several centuries significant though weak relationships are found between these reconstructions and an independent reconstruction of enso the reconstructions highlight that observations from the instrumental records of high interannual and decadal rainfall and river flow variability in northeast australia also characterize the past few centuries although there appears to be no overall trend toward wetter or drier conditions the reconstructions suggest that the variability of rainfall and river flow has increased during the twentieth century with more very wet and very dry extremes than in earlier centuries as projected for the region as a consequence of global warming

earthquake early warning system in southern italy methodologies and performance evaluation we investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity pgv from moderate to large earthquakes occurring in the southern apennines italy simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the pgv following an evolutionary probabilistic approach the system performance is measured through the effective lead time elt i e the time interval between the arrival of the first s wave and the time at which the probability to observe the true pgv value within one standard deviation becomes stationary and the probability of prediction error ppe which provides a measure of pgv prediction error the regional maps of elt and ppe show a significant variability around the fault up to large distances thus indicating that the system s capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault

asymmetry in the duration of el nino and la nina abstract el nino and la nina are not a simple mirror image but exhibit significant differences in their spatial structure and seasonal evolution in particular sea surface temperature sst anomalies over the equatorial pacific cold tongue are larger in magnitude during el nino compared to la nina resulting in positive skewness of interannual sst variations the associated atmospheric deep convection anomalies are displaced eastward during el nino compared to la nina because of the nonlinear atmospheric response to sst in addition to these well known features an analysis of observational data for the past century shows that there is a robust asymmetry in the duration of el nino and la nina most el ninos and la ninas develop in late boreal spring summer when the climatological cold tongue is intensifying and they peak near the end of the calendar year after the mature phase el ninos tend to decay rapidly by next summer but many la ninas persist through the following year and often reintensify in

the impact of convection on enso from a delayed oscillator to a series of events abstract the ncar community climate system model version 3 ccsm3 exhibits persistent errors in its simulation of the el nino southern oscillation enso mode of coupled variability the amplitude of the oscillation is too strong the dominant 2 yr period too regular and the width of the sea surface temperature response in the pacific too narrow with positive anomalies extending too far into the western pacific two changes in the parameterization of deep convection result in a significant improvement to many aspects of the enso simulation the inclusion of convective momentum transport cmt and a dilution approximation for the calculation of convective available potential energy cape are used in development integrations and a striking improvement in enso characteristics is seen an increase in the periodicity of enso is achieved by a reduction in the strength of the existing short circuited delayed oscillator mode the off equatorial response is weaker and less tropically confined largely as a

deep soil temperature as proxy for surface air temperature in a coupled model simulation of the last thousand years 1 the relationship between terrestrial deep soil temperature tdst and surface temperature sat at interannual and centennial timescales has been investigated in a simulation of the last millennium with a three dimensional climate model driven by estimations of historical external forcing tdst is loosely related to borehole temperature profiles which have been recently used to reconstruct long term temperature trends in the last centuries recently questions about the validity of boreholes based reconstructions have been raised in the simulation at interannual time scales the connection between tdst and sat is stable being stronger in the summer half year than in the winter half year at long timescales annual tdsl is a good proxy for annual sat and their variations are almost indistinguishable from each other both tdsl and terrestrial sat overestimate the variations of global mean sat this may be a source for the disagreement between statistical reconstructions of global sat and terrestrial borehole measurements

el nino southern oscillation enso and decadal scale climate variability at 10 n in the eastern pacific from 1893 to 1994 a coral based reconstruction from clipperton atoll we have developed a 101 year 1893 1994 subseasonal oxygen 18o and carbon 13c isotopic time series from clipperton atoll in the eastern pacific using the coral porites lobata in agreement with linsley et al 1999 we find that seasonal and interannual coral 18o variability at clipperton results from variability in both water temperature and salinity three new coral time series demonstrate the reproducibility of a secular coral 18o trend of 0 35 since 1910 but show varying 13c trends strong decadal scale variability in the 18o record appears related to the pacific decadal oscillation pdo through postulated changes in the strengths of the equatorial counter current and north equatorial current interannual variability in this coral 18o record is directly related to the el nino southern oscillation enso and isolation of this frequency band indicates reduced enso variability in the eastern equatorial pacific in the period 1925 to 1940 in agreement with instrumental and other pacific coral records

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

the effectiveness of a distant accelerometer array to compute seismic source parameters the april 2009 l aquila earthquake case history the 6 april 2009 mw 6 3 l aquila earthquake central italy has been recorded by the irpinia seismic network isnet about 250 km southeast of the epicenter up to 19 three component accelerometer stations could be used to infer the main source parameters with different seismological methods we obtained an approximate location of the event from arrival times and array based back azimuth measurements and estimated the local magnitude 6 1 from an at tenuation relation for southern italy assuming an omega square spectral model we inverted s wave displacement spectra for moment magnitude 6 3 corner frequency 0 33 hz stress drop 2 5 mpa and apparent stress 1 6 mpa waveform modeling using a point source and an extended source model provided consistent moment tensors with a centroid depth around 6 km and a prevalently normal fault plane solution with a dominant directivity toward the southeast the relatively high corner frequency and an overestimated moment magnitude of 6 4 from moment tensor inversions are attributed to the rupture directivity effect to image the rupture geometry we implemented a beamforming technique that back projects the recorded direct p wave amplitudes into the earthquake source region a northwest southeast striking rupture of 17 km length is imaged propagat ing with an average velocity up to 3 km s this value is significantly higher than our estimate of 2 2 km s from s wave spectra our case study demonstrates that the use of array techniques and a dense accelerometer network can provide quick and robust estimates of source parameters of moderate sized earthquakes located outside the network

unprecedented recent warming of surface temperatures in the eastern tropical pacific ocean climate variability in the tropical pacific ocean influences climate across much of the planet a diatom based record of sea surface temperatures from el junco lake galapagos reveals that the most recent half century is the warmest 50 year period in the past 1 200 years through its intimate connection with the el nino southern oscillation system climate variability in the tropical pacific ocean influences climate across much of the planet but the history of temperature change in the tropical pacific ocean during recent millennia is poorly known the available annually resolved records1 2 are discontinuous and rarely span more than a few centuries longer records at coarser temporal resolution suggest that significant oceanographic changes observed at multi year to multi century resolution have had important effects on global climate3 4 5 here we use a diatom record from el junco lake galapagos to produce a calibrated continuous record of sea surface temperature in the eastern tropical pacific ocean at subdecadal resolution spanning the past 1 200 years our reconstruction reveals that the most recent 50 years are the warmest 50 year period within the record because our diatom based sea surface temperature index resembles northern hemisphere temperature reconstructions we suggest that with continued anthropogenic warming the eastern tropical pacific ocean may continue to warm

hydrologic changes in colorado during the mid holocene and younger dryas abstract the stratigraphy of upper big creek lake ubc an overflowing lake in northern colorado indicates that the lake responded to a series of hydroclimatic changes over the past 13 000 years modern sediments in eight comparator lakes from across wyoming and colorado facilitate the stratigraphic interpretation by showing that littoral sediments have exponentially higher sand content lower loss on ignition loi and lower net accumulation rates than off shore sediments sand layers in two near shore cores from ubc share the characteristics of the modern littoral sediments 80 sand 1 9 m below its outlet from 12 500 to 11 300 and from 7500 to 2100 cal yr bp ground penetrating radar gpr profiles consistent with the low water episodes show correlative sand layers and submerged wave cut scarps around the lake margin the stratigraphic features correlate with those formed in the comparator lakes during extensive droughts at 11 300 6900 6000 and 4800 3400 cal yr bp as well as a series of north south anti phased droughts between 5800 and 1200 cal yr bp lake closure at ubc amplified the local changes and demonstrates that climate changes can increase the extent of intermittent streamflow in the rocky mountains relative to today

assessing millennial scale variability during the holocene a perspective from the western tropical pacific we investigate the relationship between tropical pacific and southern ocean variability during the holocene using the stable oxygen isotope and magnesium calcium records of cooccurring planktonic and benthic foraminifera from a marine sediment core collected in the western equatorial pacific the planktonic record exhibits millennial scale sea surface temperature sst oscillations over the holocene of 0 5 c while the benthic 18oc document 0 10 millennial scale changes of upper circumpolar deep water ucdw a water mass which outcrops in the southern ocean solar forcing as an explanation for millennial scale sst variability requires 1 a large climate sensitivity and 2 a long 400 year delayed response suggesting that if solar forcing is the cause of the variability it would need to be considerably amplified by processes within the climate system at least at the core location we also explore the possibility that sst variability arose from volcanic forcing using a simple red noise model our best estimates of volcanic forcing falls short of reproducing the amplitude of observed sst variations although it produces power at low frequency similar to that observed in the md81 record although we cannot totally discount the volcanic and solar forcing hypotheses we are left to consider that the most plausible source for holocene millennial scale variability lies within the climate system itself in particular ucdw variability coincided with deep north atlantic changes indicating a role for the deep ocean in holocene millennial scale variability

mechanisms of enso forcing of hemispherically symmetric precipitation variability summary the patterns of precipitation anomalies forced by the el nino southern oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and in the mid latitudes have a prominent zonally symmetric component observations of global precipitation variability and the moisture budget within atmospheric reanalyses are examined to argue that the zonally symmetric component is caused by interactions between transient eddies and tropically forced changes in the subtropical jets during el nino events the jets strengthen in each hemisphere and shift equatorward changes in the subtropical jet influence the transient eddy momentum fluxes and the eddy driven mean meridional circulation during el nino events eddy driven ascent in the mid latitudes of each hemisphere is accompanied by low level convergence and brings increased precipitation this changes in the transient eddy and stationary eddy moisture fluxes almost exactly cancel each other and in sum do not contribute to the zonal mean precipitation anomalies propagation of anomalous stationary waves disrupts the zonal symmetry flow around the deeper aleutian low and the eastward extension of the pacific jet stream supply the moisture for increased precipitation over the eastern north pacific and the western seaboard of the united states while transient eddy moisture convergence supplies the moisture for increased precipitation over the southern united states in each case increased precipitation is fundamentally caused by anomalous ascent forced by anomalous heat and vorticity fluxes

role of tropical pacific ssts in global medieval hydroclimate a modeling study 1 the role of tropical pacific ssts in driving global medieval hydroclimate is assessed using fossil coral records from palmyra atoll tropical pacific sea surface temperature sst boundary conditions are derived for the period 1320 1462 a d these boundary conditions consist of la nina like mean state conditions in the tropical pacific with inter annual and decadal variability about that altered state the reconstructed ssts in the tropical pacific are used to force a 16 member ensemble of atmospheric general circulation model agcm simulations coupled to a one layer ocean model outside of the tropical pacific the agcm simulations of medieval climate are compared with modern climate simulations for the period 1856 2005 a d and are shown to reproduce many aspects of medieval hydroclimate found in paleo proxy records for much of the western hemisphere northern eurasia and the northern tropics these results suggest that many features of global medieval hydroclimate changes can be explained by changes in tropical pacific ssts though the potential role for other oceans is also discussed

a pacific centennial oscillation predicted by coupled gcms internal climate variability at the centennial time scale is investigated using long control integrations from three state of the art global coupled general circulation models in the absence of external forcing all three models produce centennial variability in the mean zonal sea surface temperature sst and sea level pressure slp gradients in the equatorial pacific with counterparts in the extratropics the centennial pattern in the tropical pacific is dissimilar to that of the interannual el nino southern oscillation enso in that the most prominent expression in temperature is found beneath the surface of the western pacific warm pool some global repercussions nevertheless are analogous such as a hemispherically symmetric atmospheric wave pattern of alternating highs and lows centennial variability in western equatorial pacific sst is a result of the strong asymmetry of interannual ocean heat content anomalies while the eastern equatorial pacific exhibits a lagged bjerknes like response to temperature and convection in the west the extratropical counterpart is shown to be a flux driven response to the hemispherically symmetric circulation anomalies emanating from the tropical pacific significant centennial length trends in the zonal sst and slp gradients rivaling those estimated from observations and model simulations forced with increasing co 2 appear to be inherent features of the internal climate dynamics simulated by all three models unforced variability and trends on the centennial time scale therefore need to be addressed in estimated uncertainties beyond more traditional signal to noise estimates that do not account for natural variability on the centennial time scale

el nino southern oscillation extrema in the holocene and last glacial maximum 1 the el nino southern oscillation enso is the largest engine of interannual climate variability on the planet yet its past behavior and potential for future change are poorly understood and vigorously contested reconstructions of past enso are indispensable for testing climate models tasked with predicting future enso activity in a warming world but suitable geologic archives are scarce especially for the last glacial period here we reconstruct mean climate and enso variability in the holocene and last glacial maximum lgm from oxygen isotopic ratios 18o of individual foraminifera retrieved from deep sea sediments our results document coordinated adjustments of the tropical pacific enso system between two diametrically opposite states an amplified enso state in the lgm associated with a reduced zonal temperature gradient and a damped enso state in the mid holocene with enhanced gradient orbital precession provided the switch between these states and acted as the dominant external driver of the tropical pacific enso system in the past 25 000 years the linked response of the mean state and variability to orbital forcing provides an integrated framework for testing enso theory and models

constraining earthquake source inversions with gps data 1 resolution based removal of artifacts 1 we present a resolution analysis of an inversion of gps data from the 2004 mw 6 0 parkfield earthquake this earthquake was recorded at thirteen 1 hz gps receivers which provides for a truly coseismic data set that can be used to infer the static slip field we find that the resolution of our inverted slip model is poor at depth and near the edges of the modeled fault plane that are far from gps receivers the spatial heterogeneity of the model resolution in the static field inversion leads to artifacts in poorly resolved areas of the fault plane these artifacts look qualitatively similar to asperities commonly seen in the final slip models of earthquake source inversions but in this inversion they are caused by a surplus of free parameters the location of the artifacts depends on the station geometry and the assumed velocity structure we demonstrate that a nonuniform gridding of model parameters on the fault can remove these artifacts from the inversion we generate a nonuniform grid with a grid spacing that matches the local resolution length on the fault and show that it outperforms uniform grids which either generate spurious structure in poorly resolved regions or lose recoverable information in well resolved areas of the fault in a synthetic test the nonuniform grid correctly averages slip in poorly resolved areas of the fault while recovering small scale structure near the surface finally we present an inversion of the parkfield gps data set on the nonuniform grid and analyze the errors in the final model

moment tensor resolution case study of the irpinia seismic network southern italy abstract we present an analysis of the reliability of focal mechanisms obtained through moment tensor inversion at the irpinia seismic network southern italy our analysis is based on the methods proposed by zahradnik and custodio 2012 and sokos and zahradnik 2013 we present two different studies 1 we compute maps of theoretical focal mechanism resolution for the irpinia region and 2 we study the reliability of the solutions obtained from waveform inversion of five regional earthquakes theoretically we find that when data error is the dominant source of error focal mechanism resolution is better close to the spots of higher station density rather than at the center of the network using real data we were able to successfully study four of the five regional events in spite of the large source station distances up to 280 km and significant azimuthal gaps 319 we used variance reduction double couple percentage signal to noise ratio condition number and focal mechanism variability index to assess the quality of the solutions our quality assessment is validated by comparison with independent focal mechanism solutions

3d geomechanical modeling and numerical simulation of in situ stress fields in shale reservoirs a case study of the lower cambrian niutitang formation in the cen gong block south china abstract an analysis of the in situ state of stress in a shale reservoir was performed based on comprehensive information about the subsurface properties from wellbores established during the development of an oil and gas field industrial level shale gas production has occurred in the niutitang formation of the lower cambrian cen gong block south china in this study data obtained from hydraulic fracturing drilling induced fractures borehole breakout global positioning system gps and well deviation statistics have been used to determine the orientation of the maximum horizontal principal stress additionally hydraulic fracturing and multi pole array acoustic logging xmac were used to determine the vertical variations in the in situ stress magnitude based on logging interpretation and mechanical experiments the spatial distributions of mechanical parameters were obtained by seismic inversion and a 3d heterogeneous geomechanical model was established using a finite element stress analysis approach to simulate the in situ stress fields the effects of depth faults rock mechanics and layer variations on the principal stresses horizontal stress difference horizontal stress difference coefficient k h and stress type coefficient s p were determined the results show that the direction of the maximum principal stress is ese 120 additionally the development zones of natural fractures appear to correlate with regions with high principal stress differences at depths shallower than 375 m the stress type is mainly a thrust faulting stress regime at depths ranging from 375 to 950 m the stress type is mainly a strike slip faulting stress regime when the depth is 950 m the stress type is mainly a normal faulting stress regime depth fault orientation and rock mechanics all affect the type of stress the knowledge regarding the cen gong block is reliable and can improve borehole stability casing set point determination well deployment optimization and fracturing area selection

tracking the extent of the south pacific convergence zone since the early 1600s 1 the south pacific convergence zone spcz is the largest and most persistent spur of the intertropical convergence zone at the southeastern edge of the spcz near 170 w and 15 20 s a surface ocean salinity frontal zone exists that separates fresher western pacific warm pool water from saltier and cooler waters in the east this salinity front is known to shift east and west with the phase of the el nino southern oscillation we have generated subannually resolved and replicated coral oxygen isotopic time series from fiji 17 s 179 e and rarotonga 21 5 s 160 w that have recorded interannual displacements of the salinity front over the last 380 years and also indicate that at lower frequencies the decadal mean position of the salinity front and eastern extent of the spcz has shifted east west through 10 to 20 of longitude three times during this interval the most recent and largest shift began in the mid 1800s as the salinity front progressively moved eastward and salinity decreased at both sites our results suggest that sea surface salinity at these sites is now at the lowest levels recorded and is evidence for an unprecedented expansion of the spcz since the mid 1800s the expansion of the spcz implies a gradual change in the south pacific to more la nina like long term mean conditions this observation is consistent with the ocean thermostat mechanism for the pacific coupled ocean atmosphere system whereby exogenous heating of the atmosphere would result in greater warming in the western pacific and a greater east west surface temperature gradient components 8034 words 7 figures 2 tables

are large differential stresses required for straight fracture propagation paths abstract fracture growth geometries in linear elastic materials are sensitive to the ratio between the remote differential stress or t stress and the fracture driving stress two mechanically interacting fractures follow straighter paths for greater values of this ratio we demonstrate that the degree of curvature that develops between two mechanically interacting fractures is also controlled by such factors as sub critical fracture growth and fracture surface roughness sub critical fracture growth limits the development of fracture curvature by decreasing the fracture driving stress needed for propagation fracture surface roughness can affect the development of fracture curvature by limiting the magnitude of the shear displacement discontinuity that can be accommodated along the fracture thus propagation paths for two mechanically interacting fractures can be quite straight even in the presence of small to moderate differential stresses consequently the absence of fracture curvature does not necessarily imply a high differential stress state

megadroughts in southwestern north america in echo g millennial simulations and their comparison to proxy drought reconstructions abstractsimulated hydroclimate variability in millennium length forced transient and control simulations from the echam and the global hamburg ocean primitive equation echo g coupled atmosphere ocean general circulation model aogcm is analyzed and compared to 1000 years of reconstructed palmer drought severity index pdsi variability from the north american drought atlas nada the ability of the model to simulate megadroughts in the north american southwest is evaluated nasw 25 42 5 n 125 105 w megadroughts in the echo g aogcm are found to be similar in duration and magnitude to those estimated from the nada the droughts in the forced simulation are not however temporally synchronous with those in the paleoclimate record nor are there significant differences between the drought features simulated in the forced and control runs these results indicate that model simulated megadroughts can result from internal variability of the modeled climate system rather than as a response to changes

elastic wave evaluation of downhole hydraulic fracturing modeling and field applications abstractwe numerically simulate elastic wave propagation along a fluid filled borehole with a hydraulically fractured formation the numerical model is based on the results of hydraulic fracturing on laboratory specimens two typical models are simulated a main fracture crossing the borehole and a fracture network extending from the borehole in addition both models contain small secondary fractures surrounding the borehole our result indicates that wave propagation in the main fracture model is characterized by significant s wave anisotropy for polarization along and normal to the fracture orientation with the magnitude of anisotropy depending on the fracture aperture and filling material in contrast no significant anisotropy is observed for the fracture network model in both models wave propagation is significantly affected by small fracture induced near borehole velocity variation our modeling results provide a theoretical foundation for evaluating hydraulic fracturing using the borehole acou

coral oxygen isotope records of interdecadal climate variations in the south pacific convergence zone region 1 the south pacific convergence zone spcz a region of high rainfall is a major feature of subtropical southern hemisphere climate and contributes to and interacts with circulation features across the pacific yet its past temporal variability and forcing remain only partially understood here we compare coral oxygen isotopic 18o series spanning a d 1997 1780 and a d 2001 1776 from two genera of hermatypic corals in fiji located within the spcz to examine the fidelity of these corals in recording climate change and spcz interdecadal dynamics one of these coral records is a new 225 year subannually resolved 18o series from the massive coral diploastreaheliopora diploastrea s use in climate reconstructions is still relatively new but this coral has shown encouragingly similar interannual variability to porites the coral genus most commonly used in pacific paleoclimate studies in fiji we observe that interdecadal 18o variance is also similar in these two coral genera and diploastrea contains a larger amplitude interdecadal signal that more closely tracks instrumental based indices of pacific interdecadal climate change and the spcz than porites both coral 18o series record greater interdecadal variability from 1880 to 1950 which is consistent with the observations of folland et al 2002 who reported higher variability in spcz position before 1945 these observations indicate that diploastrea will likely provide a significant new source of long term climate information from the spcz region

a critical revision of the seismicity of northern apulia adriatic microplate southern italy and implicationsfor the identification of seismogenic structures abstract northern apulia is an emerged portion of the adriatic microplate representing the foreland foredeep area of a stretch of the apennine chain in southern italy the interaction between the relatively rigid microplate and the contiguous more deformable domains is responsible for the intense seismicity affecting the chain area however strong sometimes even disastrous earthquakes have also hit northern apulia on several occasions the identification of the causative faults of such events is still unclear and different hypotheses have been reported in literature in order to provide guidelines and constraints in the search for these structures a comprehensive re examination and reprocessing of all the available seismic data has been carried out taking into consideration 1 the characteristics of historical events 2 the accurate relocation of events instrumentally recorded in the last 20 years 3 the determination of focal mechanisms and of the regional stress tensor the results obtained bring to light a distinction between the foreland and foredeep areas in the first region there is evidence of a regional stress combining nw compression and ne extension thus structures responsible for major earthquakes should be searched for among strike slip faults possibly with a slight transpressive character these structures could be either approximately n s oriented sinistral or e w dextral faults in the foredeep region there is a transition toward transtensive mechanisms with strikes similar to those of the previous zone or maybe also towards nw oriented normal faults more similar to those prevailing in the southern apennine chain in relation to a dominant ne extension this appears to be the effect of a reduction of the nw compression probably due to a decrease in efficiency of stress transmission along the more tectonised border of the adriatic microplate

reduced enso variability at the lgm revealed by an isotope enabled earth system model studying the el nino southern oscillation enso in the past can help us better understand its dynamics and improve its future projections however both paleoclimate reconstructions and model simulations of enso strength at the last glacial maximum lgm 21 ka bp have led to contradicting results here we perform model simulations using the recently developed water isotope enabled community earth system model icesm for the first time model simulated oxygen isotopes are directly compared with those from enso reconstructions using the individual foraminifera analysis ifa we find that the lgm enso is most likely weaker comparing with the preindustrial the icesm suggests that total variance of the ifa records may only reflect changes in the annual cycle instead of enso variability as previously assumed furthermore the interpretation of subsurface ifa records can be substantially complicated by the habitat depth of thermocline dwelling foraminifera and their vertical migration with a temporally varying thermocline

rupture history of the 2009 l aquila italy earthquake from non linear joint inversion of strong motion and gps data 1 we image the rupture history of the 2009 l aquila central italy earthquake using a nonlinear joint inversion of strong motion and gps data this earthquake ruptured a normal fault striking along the apennines axis and dipping to the sw the inferred slip distribution is heterogeneous and characterized by a small shallow slip patch located up dip from the hypocenter 9 5 km depth and a large deeper patch located southeastward the rupture velocity is larger in the up dip than in the along strike direction this difference can be partially accounted by the crustal structure which is characterized by a high velocity layer above the hypocenter and a lower velocity below the latter velocity seems to have affected the along strike propagation since the largest slip patch is located at depths between 9 and 14 km the imaged slip distribution correlates well with the on fault aftershock pattern as well as with mapped surface breakages

a global search inversion for earthquake kinematic rupture history application to the 2000 western tottori japan earthquake 1 we present a two stage nonlinear technique to invert strong motions records and geodetic data to retrieve the rupture history of an earthquake on a finite fault to account for the actual rupture complexity the fault parameters are spatially variable peak slip velocity slip direction rupture time and risetime the unknown parameters are given at the nodes of the subfaults whereas the parameters within a subfault are allowed to vary through a bilinear interpolation of the nodal values the forward modeling is performed with a discrete wave number technique whose green s functions include the complete response of the vertically varying earth structure during the first stage an algorithm based on the heat bath simulated annealing generates an ensemble of models that efficiently sample the good data fitting regions of parameter space in the second stage appraisal the algorithm performs a statistical analysis of the model ensemble and computes a weighted mean model and its standard deviation this technique rather than simply looking at the best model extracts the most stable features of the earthquake rupture that are consistent with the data and gives an estimate of the variability of each model parameter we present some synthetic tests to show the effectiveness of the method and its robustness to uncertainty of the adopted crustal model finally we apply this inverse technique to the well recorded 2000 western tottori japan earthquake mw 6 6 we confirm that the rupture process is characterized by large slip 3 4 m at very shallow depths but differently from previous studies we imaged a new slip patch 2 2 5 m located deeper between 14 and 18 km depth

combining strong motion insar and gps data to refine the fault geometry and source kinematics of the 2011 mw 6 2 christchurch earthquake new zealand the space time distribution of coseismic slip of the 2011 february 21 mw 6 2 christchurch earthquake new zealand is explored differently from all previous studies through a joint inversion of geodetic and strong motion data the geodetic data consist of both global position system gps from campaign and continuous stations and synthetic aperture radar sar interferograms from two ascending satellite tracks the strong motion data consist of 10 stations located in the canterbury plains these stations offering a good azimuthal coverage of the event the kinematic rupture model for the analysed event was obtained using the parametrization and non linear inversion scheme proposed by delouis et al in particular for any subfault we explore for the local source time function local slip history slip direction and rupture onset time the geometry of the fault plane used for the kinematic inversion is inferred from the analysis of the geodetic data to validate our results we perform a resolution study for both the single and complete data sets and an errors analysis of our final kinematic rupture model considering the complexity highlighted by superficial deformation data we adopted a fault model consisting of two partially overlapping segments with dimensions 15 11 and 7 7 km2 corresponding to different faulting types this two fault model instead of single fault model is needed to reconstruct the complex shape of the superficial deformation data the total seismic moment resulting from the joint inversion is 3 0 1025 dyne cm mw 6 2 with an average rupture velocity of 2 0 km s 1

toward understanding slip inversion uncertainty and artifacts 1 the main concept of seismic source tomography the projection lines along which the observed signals are back projected to the fault is extended to complete wavefields the so called dynamic projection strips dpss are defined and a method to construct the strips from individual waveforms is described in this way each individual station role in the inversion can be better understood synthetic models with two asperities two unilateral and one bilateral rupture scenarios are used as examples they are analyzed using two independent slip inversion methods with similar results bias of the rupture speed for all scenarios and a strong false asperity in the middle of the bilateral fault both artifacts can be explained by the dps analysis as inherent nonuniqueness of the inverse problem due to the joint effect of the two true asperities removal of some slip artifacts by imposing various constraints is discussed but most of the constraints are hardly applicable in practice as such it is recommended to look at least for possible indications of the most significant inversion artifacts this seems to be feasible through combining dpss derived from real data and synthetic models of various rupture scenarios for a given fault and stations the ideas are applied to the movri mountain earthquake in greece mw6 3 8 june 2008 it appears that the earthquake was predominantly unilateral however with a nonunique space time slip pattern few equivalent nonsmooth models all fitting the data equally well are illustrated

normal faults and thrusts reactivated by deep fluids the 6 april 2009 mw 6 3 l aquila earthquake central italy 1 on 6 april 2009 a mw 6 3 earthquake occurred in the central apennines italy damaging the city of l aquila and the surrounding country we relocate the october 2008 to 6 april 2009 foreshocks and about 2000 aftershocks occurred between 6 and 30 april 2009 by applying a double difference technique and determine the stress field from focal mechanisms the events concentrate in the upper 15 km of the crust three main nw se to nnw sse striking 30 45 and 80 90 dipping faults were activated during the seismic sequence among these a normal fault and a thrust were reactivated with dip slip movements in response to ne sw extension the structural maturity of the seismogenic fault system is lower than that displayed by other systems in southern apennines because of the lower strain rate of the central sector of the chain with respect to the southern one vp vs increases progressively from october 2008 to the 6 april 2009 main shock occurrence along a nw se strike because of an increment in pore fluid pressure along the fault planes pore pressure diffusion controls the space time evolution of aftershocks a hydraulic diffusivity of 80 m2 s 1 and a seismogenic permeability of about 10 12 m2 suggest the involvement of gas rich co2 fluids within a highly fractured medium suprahydrostatic high fluid pressure about 200 mpa at 10 km of depth within overpressurized traps bounded by preexisting structural and or lithological discontinuities at the lower upper crust boundary are required to activate the april 2009 sequence traps are the storage zone of co2 rich fluids uprising from the underlying about 20 km deep metasomatized mantle wedge these traps easily occur in extensional regimes like in the axial sector of apennines but are difficult to form in strike slip regimes where subvertical faults may cross the entire crust in the apennines fluids may activate faults responsible for earthquakes up to mw 5 6 deep fluids more than tectonic stress may control the seismotectogenesis of accretionary wedges

mechanisms of hemispherically symmetric climate variability inspired by paleoclimate evidence that much past climate change has been symmetric about the equator the causes of hemispherically symmetric variability in the recent observational record are examined using the national centers for environmental prediction national center for atmospheric research reanalysis dataset and numerical models it was found that the dominant cause of hemispherically symmetric variability is the el nino southern oscillation during an el nino event the tropics warm at all longitudes and the subtropical jets in both hemi spheres strengthen on their equatorward flanks poleward of the tropical warming there are latitude belts of marked cooling extending from the surface to the tropopause in both hemispheres at all longitudes and in all seasons the midlatitude cooling is caused by changes in the eddy driven mean meridional circulation changes in the transient eddy momentum fluxes during an el nino event force upper tropospheric ascent in midlatitudes through a balance between the eddy fluxes and the coriolis torque the eddy driven ascent causes anomalous adiabatic cooling which is primarily balanced by anomalous diabatic heating using a quasigeostrophic spherical model forced by an imposed surface eddy disturbance of chosen wave number and frequency it is shown that the anomalous eddy momentum fluxes are caused by the impact that the changes in the tropically forced subtropical jets have on the propagation in the latitude height plane of transient eddies changes in zonal winds and associated changes in the meridional gradient of potential vorticity create an anomalous region of low meridional wavenumber in the midlatitudes that refracts waves away both poleward and equatorward tropical forcing of variability in the eddy driven mean meridional circulation is another way in addition to rossby wave teleconnections whereby the tropics can influence extratropical climate unlike teleconnections this mechanism causes climate variability that has strong zonally and hemispherically symmetric components and operates throughout the seasonal cycle

el nino events and their relation to the southern oscillation 1925 1986 relationships among sea surface temperatures ssts at the coast of peru and offshore river discharge in northern peru and sea level pressure at darwin australia during the period 1925 1986 are investigated using time series plots frequency distributions and a simple statistical analysis it is shown that ssts undergo a larger seasonal cycle offshore than at the coast exhibit more interannual variability during the warm than the cool season are positively skewed during much of the year and exhibit greatest month to month persistence during the cool season many but not all episodes of above normal coastal ssts are accompanied by enhanced river discharge in northern peru comparison of the darwin pressure and coastal sst records during the past 60 years shows that el nino events episodes of above normal ssts along the coast of peru have occurred both in advance of and subsequent to major negative swings of the southern oscillation and associated climatic changes in the central equatorial pacific in addition el nino events and negative swings of the southern oscillation have occurred separately hence el nino and the southern oscillation are more loosely coupled than other studies would imply