geomagnetic effects due to an eclipse induced low conductivity ionospheric spot 1 the solar eclipse on 11 august 1999 was quite unique due to its totality belt coverage of the territory of central europe where the facilities for the geophysical monitoring are most dense ionospheric and geomagnetic observations during the eclipse allowed us to study the eclipse induced effects more precisely a mathematical model based on the classical ashour chapman model is considered to show that the decrease up to 40 of the ionospheric total electron content in the region of the totality belt leads finally to geomagnetic disturbances quantitatively dependent on the position of both the quasi circular spot of the ionospheric conductivity decrease and given geomagnetic observatory location the model is generalized for the anisotropic ionosphere the theoretical estimates are compared with observational data from european geomagnetic observatories furstenfeldbruck nagycenk tihany and hurbanovo the last one being nearby the totality belt

controls on overbank deposition in the upper mississippi river abstract floodplains contain valuable stratigraphic records of past floods but these records do not always represent flood magnitudes in a straightforward manner the depositional record generally reflects the magnitude frequency and duration of floods but is also subject to storm scale hysteresis effects flood sequencing effects and decade scale trends in sediment load many of these effects are evident in the recent stratigraphic record of overbank floods along the upper mississippi river umr where the floodplain has been aggrading for several thousand years on low lying floodplain surfaces in iowa and wisconsin 137cs profiles suggest average vertical accretion rates of about 10 mm year since 1954 these rates are slightly less than rates that prevailed earlier in the 20th century when agricultural land disturbance was at a maximum but they are still an order of magnitude greater than long term average rates for the holocene as a result of soil conservation practices accretion rates have decreased in recent decades despite an increase in the frequency of large floods the stratigraphic record of the upper mississippi river floodplain is dominated by spring snowmelt events because they are twice as frequent as rainfall floods last almost twice as long and are sometimes associated with very high sediment concentrations the availability of sediment during floods is also influenced by a strong hysteresis effect peak sediment concentrations generally precede the peak discharges by 1 4 weeks and concentrations are usually low the great flood of 1993 on the mississippi river focused attention on the geomorphic effectiveness and stratigraphic signature of large floods at mcgregor where the peak discharge had a recurrence interval of 14 years the flood was most notable for its long duration 168 days above 1600 m3s 1 high sediment concentrations three episodes 180 mg l and large suspended load 1 71 mt the flood of 2001 despite its greater magnitude recurrence interval 70 years was associated with relatively low sediment concentrations

gps and glonass observations of large scale traveling ionospheric disturbances during the 2015 st patrick s day storm using a comprehensive database of 5300 ground based gnss stations we have investigated large scale traveling ionospheric disturbances lstids during 17 18 march 2015 st patrick s day storm for the first time the high resolution two dimensional maps of the total electron content tec perturbation were made using not only gps but also glonass measurements several lstids originated from the auroral regions in the northern and southern hemispheres were observed simultaneously over europe north america and south america this storm is considered as a two step main phase storm during the first main phase lstids propagated over the whole daytime european region and over high latitudes of north america during the second main phase we report 1 intense lstids propagated equatorward in north america and europe 2 convergence of several lstids originated from the opposite hemispheres in the interference zone over geomagnetic equator in south america 3 super lstids with the wavefront length of more than 10000 km observed simultaneously in north america and europe lstids observed in three sectors had wavelength of 1200 2500 km and wave periods of 50 80 min during the recovery phase on the background of the negative ionospheric storm developed over north america we detect signatures of the stream like structures alongated within the latitudinal range of 29 n 42 n across the usa these structures persisted through the nighttime to the early morning from 04 ut till 13 ut on 18 march 2015 and they were associated with the subauroral polarization streams saps induced nighttime ionospheric flows

geological structure of a long living geothermal system larderello italy we have examined the data of 600 geothermal wells and re interpreted approximately 500 km seismic profiles through the field of larderello italy we conclude that the two main seismic reflectors present below the geothermal area host two different fluids 1 superheated steam in the upper h horizon reached by drillholes and 2 supercritical fluid in the deeper k horizon reached by few unproductive or damaged wells the superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at larderello whereas the supercritical fluid represents a potential unconventional deep seated resource still to be assessed the high temperatures existing in correspondence of the k horizon suggest that the silica rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks unless occasional fluid overpressure and abrupt high strain rates occur

ionospheric effects of the solar eclipse of march 9 1997 as deduced from gps data this paper presents data from first measurements of total electron content tec and its gradient during the solar eclipse of march 9 1997 obtained with the gps radio interferometer at irkutsk the interferometer consists of three receivers one turbo rogue snr 8000 and two ashtech z 12 located at the vertices of a triangle and spaced by about 3 5 km the measured tec variations are indicative of profound changes in the ion production process in the ionosphere attendant on the solar eclipse simultaneously in a large volume of space with a radius of at height 300 km at 300 km altitude the delay of a minimum value of tec with respect to the maximum phase of eclipse at 300 km altitude was about 10 min and the depression depth of tec growth varies from l 3 1016m 2 by analyzing the data on tec gradient variations one is led to conclude that the depression of tec growth during the eclipse is essentially independent of the longitude and of the latitude within the observation ranges 52 6 n and 104 11 e

corrigendum lusi mud eruption triggered by geometric focusing of seismic waves nature geoscience 6 642 646 2013 published online 21 july 2013 corrected after print 28 august 2014 in our 2013 article1 we adopted a published velocity profile2 described as check shot data which we used as an input constraint for our numerical simulations we were subsequently alerted to artefacts in that velocity profile so below we present revised simulation results based on additional data

remotely triggered micro earthquakes in the larderello travale geothermal field italy following the 2012 may 20 mw 5 9 po plain earthquake 1 we report observations of remotely triggered earthquakes at the larderello travale geothermal field italy following the mw 5 9 po plain earthquake on 20 may 2012 four distinct triggered events are recognized within a short 25 s time interval accompanying the sweeping of 10s rayleigh waves triggered sources are clustered at depths in between 4 km and 6 km the magnitude and distance of the mainshock agree well with the triggering threshold previously proposed for the geysers california for three out of four earthquakes the rayleigh wave dynamic stresses are mostly associated with extensional vertical szz and shear sxz components which range up to 5 kpa once considering the structural setting of the area the most likely triggering mechanism involves the rupture of normal faults which are kept close to failure by high pressure crustal fluids

gravity wave signatures in the dip equatorial ionosphere thermosphere system during the annular solar eclipse of 15 january 2010 the present work pertains to the eclipse induced gravity wave modulations in the ionosphere thermosphere region over trivandrum 8 5 n 77 e dip 2 n during the annular solar eclipse of 15 january 2010 electron density and neutral wind rocket payload measured horizontal winds and electron densities at e region altitudes and ionosonde derived fof1 and fof2 parameters are used to analyze the characteristics of the eclipse induced gravity waves the analysis reveals an intensification of gravity waves with periods around 30 100 min during the peak phase of the eclipse the vertical wavelength of the prevalent wave is found to be around 2 km the role of gravity wave induced winds in generating blanketing es over the equator is also examined

the midlatitude ionosphere during the total solar eclipse of march 9 1997 the total solar eclipse of march 9 1997 was visible from some regions of china mongolia and east siberia during 0045 0130 ut the eclipse coincided with a relatively long geomagnetically quiet period during the total solar eclipse the observations included oblique incidence ionograms recording also measurement the total electron content along specified directions to the visible global positioning system satellites and the doppler sounding on various hf ray paths over the region under consideration were carried out this paper presents results derived from studying the spatial pattern of midlatitude ionospheric response to this eclipse on the basis of a numerical simulations calculations have been executed using a model for ionosphere plasmasphere coupling comparison of model results with data of all measurements showed a good qualitative and quantitative agreement it is shown that by and large the behavior of the ionosphere during the eclipse manifests itself as a short lasting l hour rearrangement to nighttime conditions with the ion flow directed downward from the plasmasphere as a rise of the f2 layer maximum by about 20 km and as a twofold increase in electron density at the height of the maximum during the eclipse s totality phase the electron temperature decreases by 200 400 k while the ion temperature drops only slightly it is found that changes in the spatial distribution of electron density along the hf ray paths during the eclipse give rise to variations of doppler frequency shift with amplitudes of about 1 hz and a duration of about 120 min the findings reported in this paper do not validate the hypothesis that solar eclipses generate atmospheric gravity waves and associated traveling ionospheric disturbances

historical changes in terrestrially derived organic carbon inputs to louisiana continental margin sediments over the past 150 years 1 major rivers and associated deltaic environments provide the dominant pathway for the input of terrestrial derived organic carbon in sediments toct to the ocean natural watershed processes and land use changes are important in dictating the amount and character of carbon being buried on continental margins seven core sites were occupied on the louisiana continental margin aboard the r v pelican in july 2003 along two major sediment transport pathways south and west of the mississippi river mouth lignin profiles in these age dated cores 210pb geochronology indicate artificial reservoir retention as a primary control on organic carbon quantity and quality reaching the margin post 1950 whereas pre 1950 sediments may reflect soil erosion due to land clearing and farming practices lignin 8 concentrations range 0 2 to 1 7 also indicate that toct delivery rates decay processes have probably remained relatively consistent from proximal to distal stations along transects the down core profile at the canyon station seems to be temporally linked and connected to inner shelf deposition suggestive of rapid cross shelf transport sources of terrestrially derived organic carbon were reflective of mixed angiosperms over the last 150 years in cores west and south of the mississippi river delta the lignin phenol vegetation index lpvi range 130 0 to 510 proved to be a sensitive indicator of source changes in these sediments and eliminated some of the variability compared to c v range 0 01 to 0 4 and s v range 0 9 to 2 1 ratios stochastic events such as hurricanes and large river floods have a measurable albeit ephemeral effect on the shelf toct record burial of toct on the river dominated louisiana continental margin is largely driven by anthropogenic land use alterations in the last 150 years land use changes in the mississippi river basin and river damming have likely affected carbon cycling and toct burial on the louisiana continental margin over a large spatial extent as observed by similar trends in cores from across and along the margin

short and long wavelength tids generated by the great american eclipse of 21 august 2017 on the 21 august 2017 the eclipse shadow drastically changed the state of the ionosphere over the united states this effect on the ionosphere is visible in the total electron content measured by global navigation satellite systems gnss the shadow moved with the supersonic speed of 1 000 m s over oregon to 650 m s over south carolina in order to exhaustively explore the ionospheric signature of the eclipse we use data of total electron content from 3 000 gnss stations seeing multiple global positioning system gps and global navigation satellite system glonass satellites to visualize the phenomena this tremendous dataset allows high resolution characterization of the frequency content and wavelengths using an omega k analysis based on 3 d fast fourier transform of the eclipse signature in the ionosphere in order to fully identify traveling ionospheric disturbances tids we confirm the generation of tids associated with the eclipse including tids interpreted as bow waves in previous studies additionally we reveal for the first time short 50 100 km and long 500 600 km wavelength tids with periods between 30 and 65 min the sources of the revealed short wavelength tids are co located with the regions of stronger gradient of the euv related to sunspots our work confirms and describes physical properties of the waves observable in the ionosphere during the great american eclipse

predicting vertical accretion rates at an archaeological site on the mississippi river floodplain effigy mounds national monument iowa abstract the sny magill unit of effigy mounds national monument iowa contains the largest cluster of prehistoric effigy mounds on public land in north america the mounds are situated atop a low terrace of the upper mississippi river where they are slowly being buried by overbank deposition during floods the terrace surface includes forest soils with argillic bt or cambic bw horizons developed in up to 1 m of loamy overbank deposits on top of pleistocene sand and gravel radiocarbon evidence suggests that overbank deposits have accumulated since the end of the mound building period about 700 years bp yielding a vertical accretion rate of about 0 6 mm yr 1 on the basis of 137cs analysis accretion rates over the past 40 50 years average 1 25 2 07 mm yr 1 with some evidence for a decreasing rate since 1964 if these accretion rates are projected forward several of the effigy mounds could be buried by flood deposits within 150 300 years this 137cs derived estimate agrees closely with an estimate of burial times based on flood frequency and observed flood deposit thickness during recent floods however the floodplain and backwater environments of the upper mississippi river are aggrading much more rapidly than the sny magill terrace surface suggesting that burial of the entire terrace could occur within 80 400 years and the entire mound group could be buried within 150 850 years the projected accretion rates and time to burial are subject to large uncertainties because of environmental change in the watershed including recent trends toward increasing flood stages and decreasing suspended sediment loads

evidence for remotely triggered microearthquakes during salt cavern collapse summary microseismicity is a good indicator of spatio temporal evolution of physical properties of rocks prior to catastrophic events like volcanic eruptions or landslides and may be triggered by a number of causes including dynamic characteristics of processes in play or and external forces we show evidence of triggered microseismicity observed in the vicinity of an underground salt cavern prone to collapse by a remote m 7 2 earthquake which occurred 12 000 km away high dynamic range broad band records reveal the strong time correlation between a dramatic change in the rate of local high frequency microseismicity and the passage of low frequency seismic waves including body love and rayleigh surface waves pressure was lowered in the cavern by pumping operations of brine out of the cavern we demonstrate the near critical state of the cavern before the collapse by means of 2 d axisymmetric elastic finite element simulations on this basis we show that the increment of stress necessary for the failure of the dolomite layer which ensures the stability of the whole system is of the same order of magnitude as the maximum dynamic stress magnitude observed during the passage of the earthquakes waves this suggests that the stress oscillations due to the seismic waves correlated with the recorded microearthquakes induced damage of the overburden which eventually led to the collapse of the salt cavern we show that the contribution of rayleigh waves is the most efficient to trigger microseismicity at periods close to the natural fundamental frequency of the cavern system found at about 10 20 s by investigating the impulse response of the cavern overburden brine system

channel morphology changes and their relationship to valley bottom geology and human interventions a case study from the vistula valley in warsaw poland the aim of the study was to determine the role of the geological setting of channel zone in the morphological variability of a river reach situated between engineered and seminatural channel sections investigations were carried out in the vistula river channel in warsaw the study included the drilling of 60 geological boreholes in the river channel and the registering of sedimentary structures of modern river channel sediments the morphology of the channel was defined based on a series of bathymetric measurements of different river levels to identify the reasons for the variation in the channel bed morphology numerical modelling of river flow was performed calculations were made using the fluent cfd computational fluid dynamics model the stabilization of bottom erosion along the engineered reach of the river was found to be associated with a shallow depth to the top of the basement of modern alluvial sediments composed of erosion resistant glacial deposits the suballuvial basement in this part of the river channel also serves as a local base level in relation to the river reach upstream

tectonic history and setting of a seismogenic intraplate fault system that lacks microseismicity the saline river fault system southern united states abstract although the northwest striking saline river fault system of southeastern arkansas is not defined by microseismicity it is associated with sand blows and shows evidence of pleistocene and holocene surface ruptures suggesting a significant seismogenic potential this fault system is within the northern gulf of mexico interior coastal plain a region only recently recognized as containing seismogenic faults to better characterize this active fault system we reconstructed its post paleozoic history using petroleum and coal industry wire line well log and seismic reflection subsurface data the saline river fault system initiated as a series of northwest striking grabens during triassic jurassic uplift and incipient gulf of mexico rifting along the basement alabama oklahoma transform margin of the north american proterozoic craton during post rift subsidence these grabens were buried by gulf sediments until mid cretaceous uplift and igneous activity resulted in minor extensional reactivation of graben faults faulting style changed from extension to transpression during the late cretaceous due to compression of eastern north america as the north atlantic rapidly widened and due to thermal weakening of the alabama oklahoma transform lithospheric discontinuity as it obliquely crossed a mantle hot spot in the late cretaceous graben faults experienced contractional reactivation and steep deeply rooted transpressional faults developed within and parallel to the graben system these transpressional faults locally displace eocene pleistocene and holocene sediments fault activity continues on the saline river fault system due to thin crust along the alabama oklahoma transform and to high heat flow which act together to weaken the crust and promote seismogenic tectonism the fault system may lack appreciable microseismicity because the aftershock sequence of the last large earthquake has had time to dissipate

channel adjustment of an unstable coarse grained stream opposing trends of boundary and critical shear stress and the applicability of extremal hypotheses channel adjustments in the north fork toutle river and the toutle river main stem were initiated by deposition of a 2 5 km3 debris avalanche and associated lahars that accompanied the catastrophic eruption of mount st helens washington on 18 may 1980 channel widening was the dominant process in combination adjustments caused average boundary shear stress to decrease non linearly with time and critical shear stress to increase non linearly with time at the discharge that is equalled or exceeded 1 per cent of the time these trends converged by 1991 1992 so that excess shear stress approached minimum values extremal hypotheses such as minimization of unit stream power and minimization of the rate of energy dissipation minimum stream power are shown to be applicable to dynamic adjustments of the toutle river system maximization of the darcy weisbach friction factor did not occur but increases in relative bed roughness caused by the concomitant reduction in hydraulic depths and bed material coarsening were documented predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991 1992 geometries and bed material characteristics measured in the field it is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision retreat of stream side hummocks and establishment of riparian vegetation to limit the destabilizing effects of large floods further prediction of energy slope and consequently stream power by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained sand and gravel bank materials relative to the coarsened channel bed from bank retreat and from upstream terrace erosion

the impact of the january 15 2010 annular solar eclipse on the equatorial and low latitude ionospheric densities 1 the january 15 2010 solar annular eclipse crossed the magnetic equator in the middle of the day over india in a region instrumented with several magnetometers total electron content stations using gps data and an ionosonde located very near the center of the eclipse with the help of a one dimensional model appropriate for the region of interest we show that the ionosonde data was consistent with a lower f region plasma that was moving upwards with only modest velocities in the morning hours and moving resolutely downwards in the afternoon hours this motion agreed well with the local magnetometer data which revealed a weakened electrojet taking place in the morning hours while a full blown counter electrojet was present in the afternoon hours we show that the unusual solar eclipse induced electrodynamics resulted in a reduction in the total electron content depletion not just at the magnetic equator but also more markedly in the equatorial ionization anomaly eia zone a further 10 degrees to the north this latter point clearly shows that the eclipse led to a cut off in the supply of plasma provided through the equatorial fountain by altering a fundamental aspect of the equatorial electrodynamics

the 2010 mw 8 8 chile earthquake triggering on multiple segments and frequency dependent rupture behavior 1 multi frequency back projection results of the february 27 2010 mw 8 8 chile earthquake reveal that this earthquake consists of distinct subevents with different slip characteristics the subevent south of the epicenter releases its energy at low frequencies 0 05 0 1 hz implying slow slip and has a rupture speed around 0 8 km s two subevents north of the epicenter are characterized by high frequency energy 1 5 hz release the first of these subevents appears to trigger slip on the second segment to the north which has higher amplitude energy release and a fast propagation speed of about 2 9 km s in addition to these rupture details high frequency energy release is observed at the rupture front followed by lower frequency energy release this observation suggests that the rupture of large earthquakes involves dynamic weakening of faults and hence their rupture properties may not be related easily to those of small earthquakes these distinct slip behaviors point out the need to consider data from a wide range of frequencies to fully assess the rupture process and associated hazards of giant earthquakes

thermal modelling of the larderello geothermal field tuscany italy we present a 3 d thermal model of the larderello geothermal field tuscany to evaluate 1 the extent and contribution of the heat transfer mechanisms conduction vs convection at the intermediate upper crust levels 2 the variability of the heat and mass fluxes entering from below and 3 the crucial role of the formation permeability the model composed by three main layers considers the upper 10 km of the crust to better constrain the simulations with experimental data from borehole fluid inclusion studies and hypocentral distributions several sets of simulations were carried out with different bottom boundary temperatures and different formation permeabilities for the two deeper layers the results indicate that the present temperature t and pressure distributions in the larderello field require deep reservoir rocks with higher permeability than the overlying capping units and underlying intermediate crust permeability values of 1 mdarcy for the reservoir rocks are enough to allow fluid convection if the temperature at 10 km depth is as high as 500 50 c the presence of localized zones with formation permeability 50 100 times higher than the surrounding rocks strongly favours the migration of over pressurized fluids which episodically break through the overburden feeding the presently exploited geothermal fields

formation and maintenance of single thread tie channels entering floodplain lakes observations from three diverse river systems 1 tie channels connect rivers to floodplain lakes on many lowland rivers and thereby play a central role in floodplain sedimentology and ecology yet they are generally unrecognized and little studied here we report the results of field studies focused on tie channel origin and morphodynamics in the following three contrasting systems the middle fly river papua new guinea the lower mississippi river and birch creek in alaska across these river systems tie channels vary by an order of magnitude in size but exhibit the same characteristic morphology and appear to develop and evolve by a similar set of processes in all three systems the channels are characterized by a narrow leveed single thread morphology with maximum width approximately one tenth the width of the mainstem river the channels typically have a v shaped cross section unlike most fluvial channels these channels develop as lakes become isolated from the river by sedimentation narrowing of the connection between river and lake causes a sediment laden jet to develop levees develop along the margins of the jet leading to channel emergence and eventual levee aggradation to the height of the mainstem levees bidirectional flow in these channels is common outflows from the lake scour sediment and prevent channel blockage we propose that channel geometry and size are then controlled by a dynamic balance between channel narrowing by suspended sediment deposition and incision and widening by mass failure of banks during outflows tie channels are laterally stable and may convey flow for hundreds to a few thousand of years

recent morphological evolution of the lower mississippi river abstract this study documents slope and stream power changes in the lower mississippi river during the pre cutoff 1880s 1930s and post cutoff 1943 1992 periods the study reach extends from new madrid mo to natchez ms a distance of about 900 km analyses for six major reaches and 13 sub reaches for the pre and post cutoff periods indicate that the river presently has a much larger slope and stream power than prior to the cutoffs the largest increases have occurred between fulton tn and lake providence la where slope and stream power increases range from about 27 to 36 and 20 to 38 respectively increases in slope and stream power in reaches upstream and downstream have also occurred but to a lesser degree previous investigations have shown that no coarsening of the bed material has occurred since 1932 and that the bed material may actually be somewhat finer overall as the lower mississippi river is not a sediment starved system an increase in stream power with no change in d50 would be expected to be offset by an increase in the bed material load as the river adjusts towards equilibrium previous investigators have inferred a reduction in the sediment loads on the mississippi river this century based on analyses of total measured suspended loads however these results should be viewed as primarily representing the changes in wash load and should not be taken to imply that bed material loads have also decreased therefore the bed material loads in the study reach should be greater than in the pre cutoff period excess stream power in the sub reaches directly affected by cutoffs resulted in scour that increased downstream bed material load these elevated sediment loads play a key role in driving morphological adjustments towards equilibrium in the post cutoff channel the stability status of the channel in the study reach currently ranges from dynamic equilibrium in the farthest upstream reaches through severe degradation to dynamic equilibrium in the middle reaches and aggradation in the lowest reaches these evolutionary trends cannot be explained by consideration of changes in slope and stream power alone changes in the incoming bed material load to each reach generated by upstream channel evolution must also be considered

meander cutoffs nonlocally accelerate upstream and downstream migration and channel widening nonlocal influence of cutoffs the hydrologic and sediment dynamics within and near cutoffs have long been studied establishing them as effective agents of rapid local geomorphic change however the morphodynamic impact of individual cutoffs at the reachwide scale remains unknown mainly due to insufficient observations of channel adjustments over large areal extents and at high temporal frequency here we show via annually resolved landsat derived channel masks of the dynamic meandering ucayali river in peru that cutoffs act as perturbations that nonlocally accelerate river migration and drive channel widening both up and downstream of the cutoff locations by tracking planform changes of individual meander bends near cutoffs we find that the downstream distance of cutoff influence scales linearly with the length of the removed reach the discovery of nonlocal cutoff influence supports the hypothesis of avalanche type behavior in meander cutoff dynamics and presents new challenges in modeling and prediction of rivers self adjusting responses to perturbations

remotely triggered microearthquakes and tremor in central california following the 2010 mw 8 8 chile earthquake 1 we examine remotely triggered microearthquakes and tectonic tremor in central california following the 2010 mw 8 8 chile earthquake several microearthquakes near the coso geothermal field were apparently triggered with the largest earthquake ml 3 5 occurring during the large amplitude love surface waves the chile mainshock also triggered numerous tremor bursts near the parkfield cholame section of the san andreas fault saf the locally triggered tremor bursts are partially masked at lower frequencies by the regionally triggered earthquake signals from coso but can be identified by applying high pass or matched filters both triggered tremor along the saf and the ml 3 5 earthquake in coso are consistent with frictional failure at different depths on critically stressed faults under the coulomb failure criteria the triggered tremor however appears to be more phase correlated with the surface waves than the triggered earthquakes likely reflecting differences in constitutive properties between the brittle seismogenic crust and the underlying lower crust

recent morphological channel changes in a deltaic environment the case of the rhone river france abstract channel morphological changes were measured at two sites within the rhone delta along the main channel of the rhone river over one century results show an average erosion rate of 2 8 mm year 1 during the 20th century and decreasing to

observations of traveling ionospheric disturbances with a satellite beacon radio interferometer seasonal and local time behavior we have operated a very long baseline interferometer array at a northern midlatitude site illuminated by vhf radio beacons from two geosynchronous satellites quasi continuously for over a year the array can detect and measure the trace velocity of traveling ionospheric disturbances tids via their signatures in the line of sight total electron content tec the system noise level is of the order of 1013 m 2 in the tec so that even very weak perturbations can be studied we have used the year long tid detection velocimetry data set to describe local time and seasonal dependences of the wave parameters the most striking finding is that the preferred azimuths of tids in the data set tend to belong to either of two modes the first mode strongest at midday and in the early afternoon particularly around winter equinox propagates southward the second mode strongest in the evening especially during summer solstice through autumn equinox propagates west northwestward the two modes are disposed in local time such as to suggest the agency of clockwise rotation of the tid preferred azimuths versus time as expected by wind filtering in the thermospheric diurnal tide however there is a gap between the two modes azimuth bands moreover the two modes exist in all trace speed quartiles of the data set tids a finding which is at variance with the hypothesis of wind filtering being the primary explanation of these modes

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

two pool to pool spacing periods on large sand bed rivers mega pools on the madeira and mississippi abstract the madeira river thalweg includes two pool to pool spacing periods first standard pool crossing sequences form 6 to 8 m deep pools these pool crossing sequences recur approximately every six channel widths 9 7 km or 6 8 w on average however the madeira study reach between manicore and porto velho in northern brazil is relatively straight making these pools more frequent than meanders second much deeper pools 13 to 30 m deep also form at relatively regular but much longer spacing 50 60 km about 40 channel widths apart the deeper mega pools occur where the river reaches the edge of the holocene alluvium encountering resistant units e g granite mud clasts and conglomerates in the confining pleistocene units these two pool scales also occur on the lower mississippi river downstream of tarbert landing this study identified pool formation processes responsible for these two pool depth and spacing scales on two large sand bed rivers the analyses computed pool statistics and correlated the deepest pools with planform controls two distinct pool formation hypotheses explain the two pool types the standard pools are rhythmic features developed by macro turbulent feedbacks while the mega pools are forced features imposed by the regional geology the former are fundamentally periodic the latter are not however periodogram analysis indicates that mega pools on the madeira form a second relatively regular pool period the regional geology including the confining pleistocene bluffs and potentially orthogonal neotectonic lineaments imposed periodic regularity to these mega pools on the madeira river that is not observed on the mississippi river a comparably sized sand bed river with mega pools

modeling the geomagnetic effects caused by the solar eclipse of 11 august 1999 1 the solar eclipse of 11 august 1999 was total along a belt crossing central europe where there is a high density of magnetic observatories we studied the transient geomagnetic effects produced by the temporary cutoff of the ionizing solar radiations during the eclipse it is the first case in which the phenomenon has been analysed in a multisite context for observatories along the umbra path a model based on the equivalent electric current schema is proposed

gps detection of ionospheric perturbations following the january 17 1994 northridge earthquake sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements are known to produce pressure waves that propagate at infrasonic speeds in the atmosphere at ionospheric altitudes low frequency acoustic waves are coupled to ionospheric gravity waves and induce variations in the ionospheric electron density using global positioning system gps data recorded by the permanent gps network operating in southern california we computed ionospheric electron content time series for several days preceding and following the january 17 1994 mw 6 7 northridge earthquake we observe an anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter the signal frequency and phase velocity are consistent with results from numerical models of atmospheric ionospheric acoustic gravity waves excited by seismic sources as well as previous electromagnetic sounding results we believe that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the northridge earthquake

surface wave potential for triggering tectonic nonvolcanic tremor corrected abstract source processes commonly posed to explain instances of remote dynamic triggering of tectonic nonvolcanic tremor by surface waves include frictional failure and various modes of fluid activation the relative potential for love and rayleigh wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike slip faults under the coulomb griffith failure criteria as a function of incidence angle are anticorrelated over the 15 to 30 km depth range that hosts tectonic tremor love wave potential is high for strike parallel incidence on low angle reverse faults and null for strike normal incidence the opposite holds for rayleigh waves love wave potential is high for both strike parallel and strike normal incidence on vertical strike slip faults and minimal for 45 incidence angles the opposite holds for rayleigh waves this pattern is consistent with documented instances of tremor triggered by love waves incident on the cascadia megathrust and the san andreas fault saf in central california resulting from shear failure on weak faults apparent friction is 0 2 documented instances of tremor triggered by surface waves with strike parallel incidence along the nankai megathrust beneath shikoku japan however are associated primarily with rayleigh waves this is consistent with the tremor bursts resulting from mixed mode failure crack opening and shear failure facilitated by near lithostatic ambient pore pressure low differential stress with a moderate friction coefficient 0 6 on the nankai subduction interface rayleigh wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process except perhaps for an indirect role on the saf in sustaining tremor into the rayleigh wave coda that was initially triggered by love waves

the deep structure of the larderello travale geothermal field from 3d microearthquake traveltime tomography 1 with the aim of exploring the deep structure of the larderello travale lt geothermal field a high resolution 3 d tomographic inversion of microearthquake traveltimes has been performed results show that the deep part of the larderello travale field is characterized by the presence of a structure having a velocity range of 6 0 6 5 km s and a convex shape deepening towards the northeastern and the southeastern sides of the field earthquakes are mostly concentrated on the top of the high velocity structure and below the k horizon implying a transition of rheological properties at depth the reported dependence on time of ts tp observed at one station located above an earthquake cluster suggests that the variation in pore fluid pressure might be responsible for the transition of rheological properties along the contact in such an area changes in pore fluid pressure might be related to time dependent hydraulic mechanisms that are very effective in crustal rocks at elevated temperatures index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8045 structural geology role of fluids 8180 tectonophysics tomography 8424 volcanology hydrothermal systems citation vanorio t r de matteis a zollo f batini a fiordelisi and b ciulli 2004 the deep structure of the larderello travale geothermal field from 3d microearthquake traveltime tomography geophys res lett 31 l07613

geomorphic adjustment to hydrologic modifications along a meandering river implications for surface flooding on a floodplain abstract responses of large regulated rivers to contemporary changes in base level are not well understood we used field measurements and historical analysis of air photos and topographic maps to identify geomorphic trends of the lower white river arkansas usa in the 70 years following base level lowering at its confluence with the mississippi river and concurrent with flood control by dams incision was identified below a knickpoint area upstream of st charles ar and increases over the lowermost 90 km of the study site to 2 m near the confluence with the mississippi river mean bankfull width increased by 30 m 21 from 1930 to 2010 bank widening appears to be the result of flow regulation above the incision knickpoint and concomitant with incision below the knickpoint hydraulic modeling indicated that geomorphic adjustments likely reduced flooding by 58 during frequent floods in the incised lowermost floodplain affected by backwater flooding from the mississippi river and by 22 above the knickpoint area dominance of backwater flooding in the incised reach indicates that incision is more important than flood control on the lower white river in altering flooding and also suggests that the mississippi river may be the dominant control in shaping the lower floodplain overall results highlight the complex geomorphic adjustment in large river floodplain systems in response to anthropogenic modifications and their implications including reduced river floodplain connectivity

alterations of channel parameters in response to river regulation works since 1840 on the lower tisza river hungary abstract in the last few years an increase in the frequency and magnitude of floods was detected on the tisza river endangering large areas of hungary the causes of these record floods were complex including both natural and human induced factors this paper focuses on river management works and their effect on planimetric and cross sectional parameters with special attention to the flood conductivity changes to the river channel during 19th century river regulation works half of the total length of the tisza river was altered by cut offs while in the 20th century mostly revetments and groynes were constructed subsequently horizontal and vertical channel parameters have changed considerably due to semi natural bed processes in order to reveal changes hydrological map series 1842 1890 1929 1957 1976 and 1999 and cross sectional surveys from the same dates were analysed prior to the intensive human interventions before 1890s the river s course was highly sinuous with some very sharp bends due to cut offs both the length and sinuosity of the tisza river decreased by 35 while the lengths of straight sections and the river s slope doubled as a consequence the river incised by up to 3 8 m until the 1929 survey resulting better flood conductivity which improved flood safety in the 1920s river management favoured bank stabilisation in order to stop the lateral migration of the channel despite these measures meander development has continued however in a distorted manner this is reflected by the opposing processes of lengthening centre line on the one hand and gradually decreasing radius of curvature on the other these processes can be explained by the continuous development of natural point bars on the convex bank and the lack of lateral retreat on the concave stabilised bank the width of the river decreased by 17 45 while its mean and maximum depth increased by 5 48 the area of cross sections influenced by revetments decreased by 6 19 resulting in a 6 15 decline in flood conductivity the non stabilised sections were influenced by upstream revetments therefore their parameters show similar changes but with a smaller rate at present the flood conductivity of the channel is worse than it was in its natural state in all it was found that the ongoing process of cross sectional distortion is a significant factor in increasing flood stage and hazard and high floods can be expected more frequently in the future partly due to this factor

on the co seismic ionospheric disturbances cids in the rapid run ionosonde observations over allahabad following mw 7 8 nepal earthquake on april 25 2015

gps tec response to the 22 july 2009 total solar eclipse in east asia 1 the longest total solar eclipse of this century occurred in east and south asia on 22 july 2009 the eclipse was accompanied with a medium magnetic storm whose main phase onset occurred 27 min after the passage of the moon s umbral shadow using tec data from 60 gps stations we construct differential tec maps to investigate the ionosphere response to the solar eclipse in central china in the range of 26 n 36 n 108 e 118 e i e the magnetic latitude 15 n 25 n during the eclipse s totality a shadow in the ionosphere shown as tec depletion area was formed 100 km south of the moon s umbral path with a maximum decrease of 5 tecu the tec depletion area moved eastward following the movement of the totality area with a time lag of 10 min enhancements of tec due to the storm are observed after the main phase onset the relative drop of tec due to the solar eclipse is evidently larger at lower latitudes than that at higher ones and around noontime than that in the morning by modeling work we find that the latitudinal dependence of the tec response may result from latitudinal variation of magnetic inclination which influences the diffusion of ionization among different layers besides the local time dependence of tec response is closely related to the local time variation of background atmosphere density which affects the electron loss efficiency in the ionosphere

enhancement and hf doppler observations of sporadic e during the solar eclipse of 22 july 2009 1 the sporadic e es frequently emerging in midlatitude during summer is a very special layer in the ionosphere and its formation mechanism is different to from that of other layers the total solar eclipse of 22 july 2009 provided a very unique opportunity to study the relationship of es and solar radiation during the solar eclipse day and the days before and after the vertical incidence ionosonde was located in wuhan to record the ionograms for this event two oblique incidence high frequency radio systems were used to record the waves from wuhan to suzhou and from wuhan to huaian the enhancement of es during the eclipse period was observed in the vertical and oblique incidence ionograms the quasi periodic fluctuations in the critical frequency and doppler frequency shift curves indicated the possible existence of the gravity waves which may be responsible for the es enhancement however we find that the enhancement occurred earlier than the appearance of gravity waves and consider that there may be other mechanisms which contribute to the observed enhancement in the ionosphere a hypothesis is put forward that the cooling effect of the lunar shadow induced powerful airflow from the northern and southern limits of the shadow toward its center which accelerated the irregularities in es to produce the large scale doppler shift in the reflected waves and form the meridional windshear both the windshear and the gravity waves may affect the es layer and increase the electron concentration many observed phenomena are in accordance with this

global river slope a new geospatial dataset and global scale analysis abstract a rivers longitudinal gradient i e slope is a key parameter in fluvial hydrology hydraulics and geomorphology it affects a multitude of fluvial variables such as flow velocity and sediment transport limitations in river slope data both its availability and accuracy constrain the fidelity of fluvial modeling particularly at larger or global scales traditional slope calculation algorithms cannot accurately predict river slopes as these are based on cell by cell calculation which is only suitable for hillslopes and small mountainous streams this paper presents a methodology for calculating global river slope and a procedure to upscale it for relatively coarse resolution suitable for global scale modeling the methodology is based on a simple principle of calculating slope from elevation depression over the length of a river segment which is automated to allow global scale calculations version 1 0 of the global river slope glors geospatial dataset is introduced and shown to be a step improvement over a previous product nhdplus for the contiguous united states and compares favorably to observed slope data collected from the literature statistical analysis of earth s continents and large basins highlights interesting spatial trends a semi empirical regression analysis between basin average river slope and other basin scale parameters show that terrain slope accounts for 67 of the variability in basin average river slope with average discharge sediment load and basin temperature contributing additional improvements to global predictions of 3 4 and 3 respectively

remote triggered seismicity caused by the 2011 m9 0 tohoku oki japan earthquake 1 seismic waves from large earthquakes have been shown to trigger seismicity large distances from a mainshock and this is termed remotely or dynamically triggered seismicity we performed a global search for seismicity potentially triggered by the seismic waves from the 2011 m9 0 tohoku oki japan earthquake using seismograms from global seismic networks and an event catalog we search for earthquakes and tremors instantaneously triggered during the passing of the seismic waves as well as for statistically significant changes in local and global seismic rates after the passing of the waves for earthquakes we find potential cases of instantaneous triggering in the united states russia china ecuador and mexico while for tremors we find evidence for triggering in taiwan armenia cuba and the united states in addition we observed a potential case of delayed triggering of larger magnitude earthquakes including a m5 2 in baja california mexico

geomorphic response of lillooet river british columbia to meander cutoffs and base level lowering abstract a detailed record of channel profiles slopes and stream discharge on lillooet river provides an opportunity to study the effects of natural and artificial channel changes that have occurred over the past century we analyze the long term effects of channel alterations that may affect flood hazard in the mid 1940s several meanders were artificially severed side channels blocked off and the level of downstream lillooet lake was lowered these measures were thought to increase hydrologic efficiency and decrease flood risk in the largely agricultural valley between 1947 and 1994 average channel width in the upper reaches decreased by 50 most of which occurred by the late 1950s between 1945 and 1969 lillooet river degraded its bed elevation by 3 4 m 12 5 to 16 7 cm a 1 in the upper reaches and up to 2 m 8 3 cm a 1 in the lower reaches this sudden and profound degradation compares to average bed elevation increases of 2 4 cm a 1 prior to the engineering works between 1969 and 1985 the cross section area increased by 22 in the upper reaches and 13 in the lower reaches and decreased to 12 and 8 respectively for the time period 1985 to 2000 the increased sediment supply that was caused by channel straightening accelerated delta advance in lillooet lake from 7 m a 1 1858 to 1948 to 30 m a 1 for the five year period following the 1948 channel works these rates have decreased over time but with a current advance rate of 10 5 m a 1 1986 2009 are still above the long term average prior to the channel changes this study demonstrates the time scale direction and magnitude of channel changes following significant artificial river alterations while the initial goal of decreasing flood risk had been achieved in the short term the lower river apparently is slowly returning to an overall aggradational phase ongoing delta advance will ultimately increase channel elevations in the lower reaches and lead to significant flood hazards for populated areas

contrasted sediment processes and morphological adjustments in three successive cutoff meanders of the danube delta abstract since the 1980s intensive anthropogenic disturbances have affected the channel of the st george branch the southern distributary of the danube river the meander cutoff programme since 1984 1988 induced different hydrosedimentary impacts on the local distribution of river flow velocities discharge and sediment fluxes between the former meanders and the man made canals ichim and radoane 1986 popa 1997 panin 2003 this paper selects three large cutoff meander reaches of the st george branch the mahmudia dunav de sus and dunav de jos meanders noted here as m1 m2 and m3 respectively as an example to analyse the human impact in the danube river delta the diversion of the flow induces strong modifications by acceleration of the fluxes through the artificial canals combined with dramatically enhanced deposition in the former meander where it was observed in two cases m1 and m3 with slight modifications in m2 an exceptional flood that occurred in april 2006 offered a good opportunity for scanning different cross sections of the meander systems bathymetry flow velocity suspended load concentration and liquid and solid discharge data were acquired throughout several cross sections of both natural channels and artificial canals of the three cutoffs using acoustic doppler current profiler adcp technology in order to investigate the distribution of the flow and sediment and its impact on the hydrosedimentary processes in each channelized reach and adjacent former meander therefore the results obtained during the 2006 flood were referred to a long term evolution 1970 2006 analysed by gis techniques

flow and sediment processes in a cutoff meander of the danube delta during episodic flooding abstract this article analyzes the water and suspended solid fluxes through a straightened meander of the southern branch of the danube delta the st george branch during episodic flooding the mahmudia study site corresponds to a vast natural meander which was cut off in 1984 1988 by an artificial canal opened to shipping the meander correction accelerated fluxes through the artificial canal and dramatically enhanced deposition in the former meander after his formation the cutoff meander acted as sediment storage locations essentially removing channel and point bar sediments from the active sediment budget of the main channel increases in slope and stream power in reaches upstream and downstream have also occurred but to a lesser degree during the one hundred year recurrent flood in april 2006 bathymetry flow velocity and discharge data were acquired across several sections of both natural and artificial channels with an acoustic doppler current profiler adcp workhorse sentinel 600 khz teledyne rdi in order to investigate the distribution of the flow and sediment and his impact on sedimentation in a channelized reach and its adjacent cutoff the contrasting hydro sedimentary processes at work in both channels and bifurcation confluence nodal points are analyzed from the measured flux distribution morphological profiles and velocity and concentration patterns in the cutoff a diminishing of the intensity of the flow velocity c 50 and of the ssc was observed correlated with the aggradation of the river bed in the bifurcation confluence nodal points and in the artificial canal were observed the most intensive hydrodynamic activity high flow velocity ssc concentration degradation of the river bad both the event scale and long term morphological trends of the alluvial system are discussed analyzing the boundary shear stress and ssc variability excess boundary shear stress in the sub reaches directly affected by cutoffs resulted in scour that increased downstream bed material load these high sediment loads play a key role in driving morphological adjustments towards equilibrium in the cutoff channel the approach followed in this paper combines detailed episodic in situ adcp measurements and robust numerical 1d modeling in order to provide a practical comprehension of the relevant morphodynamical processes the 1d model reproduces robustly the continuity of hydrodynamical variables along the streamwise axes of the two channel network the simulated are used in the paper for highlighting reach scale morphological processes at both event and long term scales

nighttime ionospheric enhancements induced by the occurrence of an evening solar eclipse 1 the solar eclipse on 15 january 2010 traversed asia and completed its travel on the shandong peninsula in china at sunset two vertical incidence ionosondes at wuhan and beijing and the oblique incidence ionosonde network in north china were implemented to record the ionospheric response to the solar eclipse following the initial electron density decrease caused by the eclipse the ionosphere was characterized by a strong premidnight enhancement and a subsequent ionospheric decay and a 10 h later postmidnight enhancement neither geomagnetic disturbance occurred during the eclipse day nor did obvious nighttime peak appear for the 10 day mean of the f2 layer critical frequency fof2 the electron density profilogram of the beijing ionosonde indicates that the two enhancements were the result of the plasma flux downward from the top ionosphere possibly due to the steep decrease of the ionospheric electron density and plasma temperature during the solar eclipse the two dimensional differential fof2 maps present the regional variations of the nighttime electron density peaks and decay both the pre and postmidnight enhancements initially appeared in a belt almost in parallel with the eclipse track and then drifted southward the different magnitudes of greatest eclipse in the umbra and outside tend to account for the different occurrence times of the plasma flux the ionospheric decay following the premidnight enhancement is also considered as a consequence of the eclipse shade

use geopedological methods for the evaluation of sedimentation rates on river floodplains southern quebec canada abstract this article pertains to the fluvial dynamics of rivers in southern quebec in particular to the aggradation and pedogenetic processes observed in floodplains affected by periodic floods the frequency of flood events notably along the saint francois river and its main tributaries leads to fine materials being frequently deposited on floodplains and affected development of alluvial soils particle size and physical and chemical analyses have led to a better understanding of the dynamics involved in the formation of floodplains and the development of soils related to this fluvial environment also sedimentological analyses layer texture and thickness microstructure combined with radiocarbon dating 14c and isotopic methods 210pb 226rd enabled the determination of sedimentation rates along the floodplains the radiocarbon dating results obtained from the organic layers buried in alluvial soils show relatively variable ages i e between 2210 60 and 30 70 years bp the data gathered reveal an active overbank deposition which shows evidence of the high flood recurrence in many rivers of the basin it is estimated that the annual floodplain aggradation ranges from 1 0 to 7 6 mm yr 1 on average which causes increases in floodplain elevations vertical accretion the sedimentation rates obtained using the constant rate supply dating model 210pb show average values that range from 2 1 to 10 7 mm yr 1 also the presence of contaminated layers at the lower level 100 cm of the floodplains suggested an active sedimentation rates along the rivers affected by floods

suspension of bed material over sand bars in the lower mississippi river and its implications for mississippi delta environmental restoration 1 understanding specific pathways for sand transport in the lower reaches of large rivers including the mississippi is a key for addressing multiple significant geologic problems such as delta building and discharge to the oceans and for environmental restoration efforts in deltaic environments threatened by rising sea levels field studies were performed in the mississippi river 75 100 km upstream of the gulf of mexico outlet in 2010 2011 to examine sand transport phenomena in the tidally affected river channel over a range of discharges methods included mapping bottom morphology multibeam sonar cross sectional and longitudinal measurements of water column velocity and acoustic backscatter suspended sediment sampling and channel bed sampling substantial interaction was observed between the flow conditions in the river boundary shear stress channel bed morphology size and extent of sandy bedforms and bed material sand transport quantity transport mode and spatial distribution a lateral shift was observed in the region of maximum bed material transport from deep to shallow areas of subaqueous sand bars with increasing water discharge bed material was transported both in traction and in suspension at these water discharges and we posit that the downriver flux of sand grains is composed of both locally and drainage basin sourced material with distinct transport pathways and relations to flow conditions we provide suggestions for the optimal design and operation of planned river diversion projects

lusi mud eruption triggered by geometric focusing of seismic waves the lusi mud eruption in indonesia has been ongoing since 2006 numerical simulations show that a parabolic shaped layer in the rock surrounding the site of the lusi eruption could have amplified and focussed incoming seismic energy from an earthquake which then triggered the mud eruption

large extensional aftershocks in the continental forearc triggered by the 2010 maule earthquake chile summary the mw 8 8 maule earthquake occurred off the coast of central chile on 2010 february 27 and was the sixth largest earthquake to be recorded instrumentally this subduction zone event was followed by thousands of aftershocks both near the plate interface and in the overriding continental crust here we report on a pair of large shallow crustal earthquakes that occurred on 2010 march 11 within 15 min of each other near the town of pichilemu on the coast of the o higgins region of chile field and aerial reconnaissance following the events revealed no distinct surface rupture we infer from geodetic data spanning both events that the ruptures occurred on synthetic sw dipping normal faults the first larger rupture was followed by buried slip on a steeper fault in the hangingwall the fault locations and geometry of the two events are additionally constrained by locations of aftershock seismicity based on the international maule aftershock data set the maximum slip on the main fault is about 3 m and consistent with field results the onshore slip is close to zero near the surface satellite radar data also reveal that significant aseismic afterslip occurred following the two earthquakes coulomb stress modelling indicates that the faults were positively stressed by up to 40 bars as a result of slip on the subduction interface in the preceding megathrust event in other words the pichilemu earthquakes should be considered aftershocks of the maule earthquake the occurrence of these extensional events suggests that regional interseismic compressive stresses are small several recent large shallow crustal earthquakes in the overriding plate following the 2011 mw 9 0 tohoku oki earthquake in japan may be an analogue for the triggering process at pichilemu

transient tectonic regimes imposed by megathrust earthquakes and the growth of nw trending volcanic systems in the southern andes abstract geophysical data show that megathrust earthquakes can promote transient tectonic regimes lasting up to several decades however such variations are not trivial to be recognises in the geological records of volcanic arcs to better understand the occurrence of transient tectonic regimes we study the inter and post seismic deformation in the upper crust of the andean volcanic arc affected by the m8 8 2010 maule earthquake we focus on the region around the nevados de chillan volcanic complex southern central chile where we compare geological and earthquakes data this nw oriented andean transverse volcanic complex faces one of the regions that slipped the most during the 2010 m8 8 maule earthquake field fault slip data from lithostratigraphic units forming the basement of nevados de chillan volcanic complex point out three tectonic regimes the principal is driven by a sub horizontal and ne oriented 1 transpressional kinematics this regime is compatible with today s gps data recorded during inter seismic periods the second and third tectonic regimes are less abundant and indicate transpression 1 sub horizontal and nw oriented and normal 1 sub vertical and e w oriented faulting respectively the geological record was also compared with seismic data acquired from 2010 to 2015 in the investigated region the moderate magnitude seismic activity occurred beneath the volcanic arc after the maule earthquake points out an enhanced crustal deformation if compared to inter seismic periods the inversion of focal mechanisms suggests that intra arc regions may experience a short lived post seismic transtensional regime with an e w oriented 1 with a dip of about 45 our work suggests that megathrust earthquakes impose transient stress variations in the volcanic arc possibly reactivating oligo miocene nw striking inherited crustal structures upon which volcanic edifices develop this may help explaining the occurrence of andean transverse volcanic complexes oriented sub perpendicular to the ne oriented 1 driving convergence in the southern andes

the midlatitude f2 layer during solar eclipses observations and modeling national natural science foundation of china 40725014 40674090 40636032 national important basic research project 2006cb806306

deep tremor in new zealand triggered by the 2010 mw8 8 chile earthquake 1 deep non volcanic tremor nvt is usually associated with episodic slow slip events new zealand is one notable exception where numerous slow slip events have been identified yet nvt has remained undetected here we present the first known case of triggered nvt at new zealand s hikurangi subduction margin following the mw8 8 chilean earthquake of february 27 2010 we identify coherent high frequency tremor signals that are in phase with and modulated by the passing rayleigh waves this is consistent with the surface wave triggering potential for strike normal incidence on a low angle thrust fault after constraining the tremor depth on the plate interface we locate the tremor source within 20 km of the source area of episodic slow slip the tremor location is also near the edge of a region with high seismic attenuation that marks the boundary between dehydrated subducted slab and inferred hydrated underplated sediment we speculate that reduced interface friction and high fluid pressures provided by fluid rich underplated sediment facilitates the tremor generation

ionospheric total electron content response to solar eclipses on october 24 1995 and march 9 1997 two solar eclipse events occur it is therefore of interest to investigate how the ionosphere responded to the eclipses five global positioning system gps ground based receivers are specifically designed to observe large scale ionospheric variations over the geomagnetic equatorial equatorial anomaly crest and midlatitude regions two dimensional images of ionospheric total electron content tec during the two eclipse periods are constructed the deviations in the tec images on eclipse days from those on reference days show that during the eclipse days the ionosphere experienced some large scale changes four features of the tec deviations pre ascension pa major depression md sunset ascension sa and secondary depression sd have been observed a detailed study shows that in geomagnetic low latitudes pas are possibly related to the locations of the equatorial anomaly crest the latitudinal location amplitude and occurrence time of mds suggest that the fountain effect is essential sas and sds occurring in geomagnetic equatorial and low latitudes and appearing respectively before around and after local sunset indicate that the prereversal enhancement plays an important role

three dimensional tomography and rock properties of the larderello travale geothermal area italy in a geothermal area a detailed knowledge of the three dimensional velocity structures aids the management of the field and the further development of the geothermal source here we present a high resolution study of the three dimensional s wave velocity structures from microearthquake travel times for the larderello travale geothermal field italy we have also deduced the vp vs and vp vs parameters for this area to emphasize the deep variations in the physical rock properties due to fluid content and porosity furthermore effective porous medium modelling has been performed for site relevant lithologies to improve our interpretation of the results in terms of rock physics signatures this has allowed us to estimate the variation range of the seismological parameters investigated as well as their sensitivity for suitable rock under specific physical conditions low vp vs anomalies arising from a lower vp compared to vs dominate the geothermal field of larderello travale these have been interpreted as due to steam bearing formations on the contrary analysis of vp vs images provides information on the relative changes in rock porosity at depth comparison of tomographic section images with previously interpreted seismic lines suggests that the reflective k horizon delineates a transition between zones that have different porosities or crack gatherings the k horizon also lies on low vp vs anomalies which suggests a steam saturation zone despite the reduced porosity at this depth

three dimensional and trans hemispheric changes in ionospheric electron density caused by the great solar eclipse in north america on 21 august 2017

ionospheric and geomagnetic response to the total solar eclipse on 1 august 2008 over northern hemisphere 1 the ionospheric and geomagnetic response to the total eclipse of the sun on 1 august 2008 over northern hemisphere has been examined using 14 gps three isr radar and three magnetometer ground based stations three different approaches were employed to examine the tec depletion occurrence at the gps stations determination of the tec depletion parameters during the solar eclipse with respect the quiet day tec variations comparison of the total tec tec during the solar eclipse period with respect to quiet day tec measurements for the same period of time and determination of the average daily tec obtained from eight gps stations and compares the values with the average quiet day tec at these stations the gps observations indicate obvious tec depression occurrence at all stations with the values was varying between 11 and 40 the observations show that tec depression at most gps stations started on the neck of the first contact of the eclipse followed by deeper negative deviation while the area of optical disk obscured getting larger periods of tec depletion were also observed before the first contact time of solar eclipse and after the fourth contact of solar eclipse due to earlier and later obscuration of the solar corona before and after the eclipse observation time the incoherent scatter radar observations at svalbard tromso and sondrestrom also show clear depletion occurrence in electron density electron temperature ion velocity and plasma cutoff frequency during the solar eclipse passage at these stations radar measurements show obvious difference in the ionospheric response between the e and f layers of ionosphere and between ion and electron temperature in the f layer the geomagnetic field response to the solar eclipse at cbb reso and nur stations was examined by using two different techniques first by comparing the daily variations of geomagnetic field during the eclipse period with the variations on the day before and day after the eclipse and second by determination the magnetic field with respect to the average quiet geomagnetic field the results show obvious decrease in the total field x and z components of geomagnetic field and obvious increase in the y component at both cbb and reso stations the depletion in x z and total field was in the range between 15 and 28 nt while the increase in the y component was 18 22 nt

evidence suggesting fluid flow beneath japan due to periodic seismic triggering from the 2004 sumatra andaman earthquake 1 we show that very large surface waves from the 2004 sumatra andaman earthquake m9 2 triggered deep low frequency dlf seismic tremors beneath japan over a 500 km wide region the triggered seismicity was periodically excited synchronized with the amplitudes and phases of the oscillatory surface waves incident on the region periodic excitation implies that the specific phase of the surface waves plays an important role for the triggering estimation of stress changes in the source regions showed that the volumetric dilatation larger than 10 8 was the predominant factor for triggering thereby strongly supporting the hypothesis that dlf events are caused by processes related to fluid flow

seismicity rate changes along the central california coast due to stress changes from the 2003 m 6 5 san simeon and 2004 m 6 0 parkfield earthquakes abstract we investigated the relationship between seismicity rate changes and modeled coulomb static stress changes from the 2003 m 6 5 san simeon and the 2004 m 6 0 parkfield earthquakes in central california coulomb stress modeling indicates that the san simeon mainshock loaded parts of the rinconada hosgri and san andreas strike slip faults along with the reverse faults of the southern los osos domain all of these loaded faults except for the san andreas experienced a seismicity rate increase at the time of the san simeon mainshock the parkfield earthquake occurred 9 months later on the loaded portion of the san andreas fault the parkfield earthquake unloaded the hosgri fault and the reverse faults of the southern los osos domain which both experienced seismicity rate decreases at the time of the parkfield event although the decreases may be related to the decay of san simeon triggered seismicity coulomb stress unloading from the parkfield earthquake appears to have altered the aftershock decay rate of the southern cluster of san simeon aftershocks which is deficient compared to the expected number of aftershocks from the omori decay parameters based on the pre parkfield aftershocks dynamic stress changes cannot explain the deficiency of aftershocks providing evidence that static stress changes affect earthquake occurrence however a burst of seismicity following the parkfield earthquake at ragged point where the static stress was decreased provides evidence for dynamic stress triggering it therefore appears that both coulomb static stress changes and dynamic stress changes affect the seismicity rate

morphological adjustments in a meandering reach of the middle yangtze river caused by severe human activities abstract in the past 50 years the shishou reach in the middle yangtze river underwent significant channel evolution owing to the implementation of an artificial cutoff the construction of bank revetment works and the operation of the three gorges project tgp based on the measured hydrological data and topographic data the processes of channel evolution in this reach were investigated mainly from the adjustments in planform and cross sectional geometries the variation in planform geometry obtained in this study indicates that i the artificial cutoff at zhongzhouzi caused the river regime to adjust drastically with the mean rate of thalweg migration at reach scale of 42 0 m a over the period 1966 1975 ii then the effect of this artificial cutoff reduced gradually with the mean migration rate decreasing to 40 m a owing to the occurrence of high water levels in 1993 1998 and iii the average annual rate of thalweg migration decreased to 29 3 m a because of the impacts of various bank protection engineering and the tgp operation during the period 2002 2015 however remarkable thalweg migration processes still occurred in local regions after the tgp operation which resulted in significant bankline migration in local reaches of beimenkou shijiatai and tiaoxiankou in addition the adjustments of bankfull channel geometry were investigated at section and reach scales after the tgp operation calculated results show that lateral channel migration in this reach was restricted by various river regulation works and that channel evolution was mainly characterized by an increase in bankfull depth and cross sectional area empirical relationships were developed between the reach scale bankfull dimensions depth and area the bankfull widths at specified sections and the previous 5 year average fluvial erosion intensity during flood seasons with high correlation degrees between them being obtained