earthquake locations using single station deep borehole recordings implications for microseismicity on the san andreas fault in southern california we have located and estimated source parameters of 109 earthquakes 0 to 5 m using seismograms recorded at 2 5 km depth in the cajon pass borehole southern california the borehole is about 4 km from the san andreas fault at the boundary between the locked almost aseismic mojave and san bernardino segments where the san jacinto fault approaches the san andreas this area is of interest both on account of its tectonic complexity and its high potential seismic hazard the clear relatively unattenuated downhole recordings are rotated to determine the incoming azimuth of the p wave and the delay time between the p and s arrivals is used to estimate the hypocentral distance the difference between the hypocenters located this way and the southern california seismic network scsn locations of the same earthquakes increases with hypocentral distance from the borehole of the earthquakes within 20 km of the borehole 95 are within 1 2 km of the scsn epicenters and all are within 5 km of the scsn depths all but three of the 58 earthquakes located here which the scsn did not record were within 20 km of the borehole and so the location errors are similar to those of scsn a and b quality events most of the small earthquakes occurred within the relatively active san jacinto fault zone but at least eight are located close to or within the san andreas fault zone the stress drops for these events range from 0 1 to 18 mpa these earthquakes appear similar to the other events in this study suggesting that the san andreas fault is similar to other faults at the scale of these small earthquakes the variation in stress drop and slip orientation of these small earthquakes suggests that larger scale heterogeneity continues to these small scales also the location of these small earthquakes in major established fault zones implies that earthquake source dimensions are not geometrically controlled by fault zone width

insar analysis of the 2008 reno mogul earthquake swarm evidence for westward migration of walker lane style dextral faulting and post seismic slip over an area of more than 150 km 2 this earthquake is one of the smallest magnitude events modeled with insar to date in the seismically active western basin and range and it provides new insights into regional neotectonic relations inverse modeling of the insar data suggests that the earthquake swarm was generated by 25 75 cm of dextral displacement on a n44wstriking fault with a 3 km rupture length and a rupture depth of 2 km the insar detected strike slip ground deformation is unique for the reno basin which is in the purely extensional domain of the sierra nevada basin and range transition zone an area dominated by north striking normal faults the insar modeling of the 2008 earthquake swarmsupports the concept of westward migration of walker lane transcurrent faulting and overprinting of extensional basin and range structures in this case the westward migration of dextral shear associated with the northern walker lane into the extension dominated reno basin citation bell j w f amelung and c d henry 2012 insar analysis of the 2008 reno mogul earthquake swarm evidence for westward migration of walker lane style dextral faulting geophys res lett 39 l18306 doi 10 1029 2012gl052795

self similar rupture implied by scaling properties of volcanic earthquakes occurring during the 2004 2008 eruption of mount st helens washington we analyze a group of 6073 low frequency earthquakes recorded during a week long temporary deployment of broadband seismometers at distances of less than 3 km from the crater at mount st helens in september of 2006 we estimate the seismic moment m0 and spectral corner frequency f0 using a spectral ratio approach for events with a high signal to noise snr ratio that have a cross correlation coefficient of 0 8 or greater with at least five other events a cluster analysis of cross correlation values indicates that the group of 421 events meeting the snr and cross correlation criteria forms eight event families that exhibit largely self similar scaling we estimate the m0 and f0 values of the 421 events and calculate their static stress drop and scaled energy er m0 values the estimated values suggest self similar scaling within families as well as between five of eight families i e m0 f0 3 and er m0 constant we speculate that differences in scaled energy values for the two families with variable scaling may result from a lack of resolution in the velocity model the observation of self similar scaling is the first of its kind for such a large group of low frequency volcanic tectonic events occurring during a single active dome extrusion eruption

sedimentary biogeochemistry of an acidic saline groundwater discharge zone in lake tyrrell victoria australia abstract the chemical composition of saline acidic pore waters at a groundwater discharge zone were investigated to delineate the biogeochemical conditions which occur within this zone the discharge area was a surface exposure of a subsurface gradient where regional groundwaters of low ph and salinities similar to seawater were mixing with anoxic sulfidic brines which were refluxing after evaporation within the lake shallow pore water samples collected along transects from the lake edge into the lake revealed large increases in nitrate and iron and small increases in manganese ratios of sulfate to chloride near the shore were similar to those found in seawater while ratios increased further into the lake the mixing of the regional groundwaters with the reflux brines apparently resulted in nitrification sulfur oxidation and iron reduction the sulfide in the brines appeared to have been generated at some remote location probably on the eastern side of the lake where neutral and saline groundwaters discharge and cyanobacterial mats proliferate hence biogeochemical processes occurring in the western discharge zone were fueled primarily by microbial activities in an area situated a few kilometers away

formation of alunite jarosite and hydrous iron oxides in a hypersaline system lake tyrrell victoria australia abstract alunite kal 3 so 4 2 oh 6 and jarosite kfe 3 so 4 2 oh 6 are common weathering products of aluminosilicates and pyrite long range transport of the constituents forming these minerals and the subsequent deposition of alunite and jarosite in an evaporite setting have not been previously documented such conditions for the occurrence of alunite and jarosite were investigated in a hypersaline system where acid groundwater enriched in k al fe iii and so 4 enter a saltplaya lake sediment cores were studied by thin section xrd and sem eds groundwater and pore water chemistries were also analyzed the results show that alunite and jarosite occur together or as individual layers and cements within the top 20 cm of the sediments where the groundwater is most concentrated due to evaporation hydrous fe oxides also occur as cements or vein fillings with the alunite and jarosite but are distributed throughout the 70 cm sediment column studied the results are consistent with a model in which alunite and jarosite precipitate as a result of the evaporation of water thermodynamic modeling indicates that the pore water in the playa sediments maybe in equilibrium with alunite jarosite and hydrous fe oxides

metal partitioning in acid hypersaline sediments lake tyrrell victoria australia abstract oxic metal rich low ph groundwater enters a playa lake system at lake tyrrell partitioning of metals in the playa sediments was studied to determine the fate of the dissolved metals analysis of leachates from sequential extractions of sediment within the top 70 cm of the lake floor indicates that most of the cu pb zn fe and mn are adsorbed onto feoxides cu and to a lesser extent mn are bound to organics or sulfides in discrete thin layers while pb is deposited on exchangeable sites in upper layers possibly as sulfates metal concentrations are not enriched in the sediments which may be due to low ph s and or limited sulfate reduction in the system the lake tyrrell system may represent an ore forming system before extensive precipitation of metal sulfides

rare earth element distribution in lake tyrrell groundwaters victoria australia abstract the rare earth element ree geochemistry of the saline to hypersaline acidic brines of lake tyrrell victoria australia were analyzed in order to determine the relative importance of concentration and modification processes in the lake system several types of brines were identified on the basis of different ree patterns and concentrations regional groundwater flowing into lake tyrrell yields the highest concentrations of ree while a transitional water group is identified on the basis of lower ree concentrations a third water group the reflux brine is characterized by extremely low ree concentrations the ree patterns suggest that ree are introduced to the lake tyrrell system by the regional groundwater which has concentrated ree from the aquifer material in its acidic waters eventually ree are removed from the evolving water mass as higher levels of ph are reached the data of the study strongly suggest that ree are scavenged from solution by fe oxyhydroxide phases which precipitate as the ph of the system rises water rock interactions probably control ph in the lake system and therefore ultimately control the concentration of ree in solution in this system our results are directly correlated with studies of hydrothermal vents and geothermal solutions which have shown the concentration of ree in solution to be dominantly controlled by ph

on the relationship between the postmidnight thermospheric equatorial mass anomaly and equatorial ionization anomaly under geomagnetic quiet conditions the equatorial mass anomaly ema in the thermosphere and equatorial ionization anomaly eia in the ionosphere are two interesting phenomena in low equatorial latitude regions previous studies have shown that the ema appears between 1000 and 2000 local time lt and its location of trough is aligned with dip equator indicating the plausible role of the eia structure in the development of ema in this report we conducted a statistical study of the occurrence of postmidnight ema and eia on the basis of the champ in situ measurements during 2002 2008 our results revealed that clear ema and eia structures are sometimes visible in the postmidnight sector 0100 0600 lt during geomagnetic quiet periods kp 3 the postmidnight ema is not necessarily accompanied by the eia signature in both case study and statistics sense being distinct from the daytime situation in addition the occurrence rates of postmidnight ema and eia display contrasting behavior with respect to their local time longitudinal and solar activity dependences the highest occurrence rate for ema is 8 at around 0300 lt while the occurrence rate of the eia decreases gradually from about 30 at around 2300 lt to similar to 5 at 0600 lt longitudinal occurrence of postmidnight eia presents a wave like pattern however no salient feature appears for the longitudinal occurrence of ema postmidnight ema is more likely to occur at lower solar activity whereas an opposite trend presents in the eia on the basis of above results our findings imply that a simple eia ema cause effect relationship does not hold in the postmidnight sector

influence of hydrogeology microbiology and landscape history on the geochemistry of acid hypersaline waters n w victoria abstract there is now evidence that naturally occurring acid water is more abundant than previously thought and that it has been important in the geologic past understanding the processes leading to the formation of such systems is required to appreciate the role of acid systems in geologic processes and to develop indicators for recognizing the geologic environmental importance of these systems in the past this paper characterizes the hydrogeology hydrogeochemistry microbial biogeochemistry and landscape attributes of acid groundwater surface water systems in australia with an emphasis on a well studied playa lake system lake tyrrell murray valley a model for the origin of these acid brines is presented and the importance of acid brine producing systems is speculated upon data include porewater and groundwater geochemical measurements collected during a 10 day field campaign and results from geochemical modeling and graphics e g piper diagrams and x y plots of seawater evaporation trajectories key characteristics of the system are 1 aquifer materials have low acid buffering capacities 2 saline groundwater flowing onto playa surfaces is an oxic h2so4 solution 3 authigenic minerals include combinations of jarosite kfe3 so4 2 oh 6 alunite kal3 so4 2 oh 6 and fe oxides that can form as evaporite minerals 4 a source for solutes can be marine aerosols and 5 the formation of ironstones groundwater acidification by various processes including sulfide oxidation and ferrolysis and at many different times are the unique aspects for evolution of these acid brines and they can be considered another end member of the eugster jones hardie model for the evolution of brines in closed basins acid hypersaline groundwater and playa systems such as lake tyrrell may be an example of expected changes in the hydrogeochemistry of terrestrial water during late stage continental denudation under arid conditions historically these systems may have been integral to the formation of opal bauxite some low temperature ore deposits of authigenic k feldspars and continental redbeds natural acid saline systems such as those in australia may also be representative of acid saline systems on mars

effects of long term fluid injection on induced seismicity parameters and maximum magnitude in northwestern part of the geysers geothermal field the long term temporal and spatial changes in statistical source and stress characteristics of one cluster of induced seismicity recorded at the geysers geothermal field u s are analyzed in relation to the field operations fluid migration and constraints on the maximum likely magnitude two injection wells prati 9 and prati 29 located in the northwestern part of the field and their associated seismicity composed of 1776 events recorded throughout a 7 year period were analyzed the seismicity catalog was relocated and the source characteristics including focal mechanisms and static source parameters were refined using first motion polarity spectral fitting and mesh spectral ratio analysis techniques the source characteristics together with statistical parameters b value and cluster dynamics were used to investigate and understand the details of fluid migration scheme in the vicinity of injection wells the observed temporal spatial and source characteristics were clearly attributed to fluid injection and fluid migration toward greater depths involving increasing pore pressure in the reservoir the seasonal changes of injection rates were found to directly impact the shape and spatial extent of the seismic cloud a tendency of larger seismic events to occur closer to injection wells and a correlation between the spatial extent of the seismic cloud and source sizes of the largest events was observed suggesting geometrical constraints on the maximum likely magnitude and its correlation to the average injection rate and volume of fluids present in the reservoir

first detection of the supersonic upward plasma flow structures in the early morning sector we present the first observations of the supersonic updrafting plasma drifts in the predawn sector two dmsp satellites quasi simultaneously detected two fast speed events one of 385 km spatial extension and with the maximum upward velocity of 1683 m s appeared at 3 lt and the other of 1500 km large with maximum speed of 1770 m s occurred at 5 lt both supersonic structures were observed above the eastern pacific region separated by 35 of longitude in space and by 45 min in time the events occurred at the recovery phase of the geomagnetic storm of 19 february 2014 during rapid oscillations of the interplanetary magnetic field b z and the interplanetary electric field e y components which increased the eastward electric field in the equatorial nighttime ionosphere and triggered the generation of plasma irregularities the storm time penetration electric fields seem to be the principal driver of the observed supersonic events

coseismic and postseismic deformation due to the 2007 m5 5 ghazaband fault earthquake balochistan pakistan time series analysis of interferometric synthetic aperture radar data reveals coseismic and postseismic surface displacements associated with the 2007 m5 5 earthquake along the southern ghazaband fault a major but little studied fault in pakistan modeling indicates that the coseismic surface deformation was caused by 9 cm of strike slip displacement along a shallow subvertical fault the earthquake was followed by at least 1 year of afterslip releasing 70 of the moment of the main event equivalent to a m5 4 earthquake this high aseismic relative to the seismic moment release is consistent with previous observations for moderate earthquakes m 6 and suggests that smaller earthquakes are associated with a higher aseismic relative to seismic moment release than larger earthquakes

broadband modeling of local earthquakes three component broadband waveforms of two small earthquakes near upland california recorded on the pasadena broadband high dynamic range instrument were modeled to obtain useful green s functions for this path and to examine the sensitivity of the synthetic seismograms to perturbations of the crustal model we assumed that the source of each event was both simple and known as determined from the caltech usgs array first motions a trapezoidal time function was chosen to fit the width of the direct s wave generalized rays reflectivity and finite difference techniques were used to compute the synthetic seismograms we found that a simple layer over a half space model is an adequate approximation of the upper crust along this profile in particular the waveforms are controlled by a relatively slow 4 km thick surficial layer 4 5km s 1 2 6 km s 1 over a faster layer 5 9 km s 1 3 5 km s 1 the relative amplitudes of direct and multiple s indicate that the main shock occurred at a depth of 6 km while the aftershock occurred at a depth of 8 to 9 km sensitivity analyses indicate that for distances less than 50 km and for periods longer than 1 sec the synthetic seismograms are not very sensitive to perturbations of the deep crustal structure analysis of upper crustal model perturbations revealed that the surficial layer is between 3 to 5 km thick in addition the contact between this layer and the underlying material can be smoothed with a 2 km wide velocity gradient without adversely affecting the fit to the data two dimensional finite difference calculations show that a ridge structure beneath the recorder acts as a lowpass filter the lower frequency phases are largely unaffected other two dimensional models with ridges between the source and receiver clearly did not fit the data synthetic seismograms computed for the best fitting model were used to estimate a long period moment of 6 2 1022 dyne cm ml 4 6 and 1 1022 dyne cm ml 3 7 with identical triangular source time durations of 0 3 sec assuming the same fault dimension of 0 4 km from standard scaling laws stress drop estimates of 410 and 70 bars are obtained for the two events respectively generally we found that it is possible to reproduce local waveforms at frequencies up to 1 hz without a complete knowledge of fine structural detail resulting green s functions can be useful in studying historic events and in simulations of large events from a given source region

on postmidnight low latitude ionospheric irregularities during solar minimum 2 c nofs observations and comparisons with the equatorial atmosphere radar 1 a detailed comparison between the observations of the communication navigation outage forecasting system c nofs satellite and the 47 mhz equatorial atmosphere radar ear in west sumatra indonesia 10 36 s dip latitude on the postmidnight irregularities is presented the zonal and meridional e b drift velocities measured by the vector electric field instrument on the c nofs are consistent with the westward propagation of backscatter echoes and the line of sight doppler velocities observed with the ear respectively the plasma density depletions are observed in the postmidnight sector for several consecutive orbits which suggests the depletions grow slowly during the premidnight period and reach the spacecraft altitude around local midnight the convergence of the equatorward wind which could be responsible for the midnight temperature maximum may produce a preferable condition for the growth of the rayleigh taylor instability around midnight electric field fluctuations of medium scale traveling ionospheric disturbances may play an important role in seeding the instability both equatorial and midlatitude type plasma instabilities could be operational at the ear latitude sector which together would foster a high occurrence of postmidnight irregularities during solar minimum

geochemistry of the rare earth elements in hypersaline and dilute acidic natural terrestrial waters complexation behavior and middle rare earth element enrichments rare earth element ree speciation was modelled in acid 2 9 ph 3 5 hypersaline groundwaters from australia and from the palo duro basin in texas usa using a combined specific ion interaction pitzer model and ion pairing model the free metal ion species i e ln3 is the dominant form of dissolved rees in these systems accounting for 40 70 of the dissolved metal in groundwater from lake tyrrell victoria australia 50 90 of the rees in groundwater from lake gilmore western australia and always 90 of each ree in the texas groundwaters lakes tyrrell and gilmore are actually dry lakes that act as groundwater discharge zones the abundance of the free metal ion species increases in these waters with increasing ionic strength and with decreasing ph the free metal ion species is followed in abundance by ree sulfate and ree chloride complexes that account for 20 50 and 10 15 respectively of the dissolved rees in the groundwaters from lake tyrrell 15 30 and 5 20 respectively in the groundwaters from lake gilmore and 3 and 7 respectively in the palo duro basin groundwaters the groundwaters of the lake tyrrell system and the palo duro basin are enriched in the middle rees mrees compared to both the light rees lrees and the heavy rees hrees only nd sm and dy were determined in the lake gilmore groundwaters and consequently it is unclear whether these acid groundwaters are also enriched in the mrees previous investigators suggested that fe rich organic flocs ree phosphate complexation and solid liquid exchange reactions between terrestrial waters and mree enriched surface fe mn coatings suspended particulates or secondary mineral phases within aquifer materials may promote the development of mree enrichments in natural waters we propose that organic colloids and ree phosphate complexes are insignificant in acidic natural waters in regards to mree enrichments instead solid liquid exchange reactions or dissolution of surface coatings suspended particulates and or secondary phases as well as sulfate complexation more likely controls the development of mree enrichments in acidic natural terrestrial waters

variability of fault slip behavior along the san andreas fault in the san juan bautista region an improved understanding of the time history of fault slip at depth is an essential step toward understanding the underlying mechanics of the faulting process using a waveform cross correlation approach we document spatially and temporally varying fault slip along the northernmost creeping section of the san andreas fault near san juan bautista sjb california by systematically examining spatiotemporal behaviors of characteristically repeating earthquakes cres the spatial distribution of pre 1998 sjb earthquake 1984 1998 fault slip rate inferred from the cres reveals a 15 km long low creep or partially locked section located near the 1998 mw 5 1 sjb earthquake rupture a finite fault slip inversion reveals that the rupture of the 1998 sjb earthquake is characterized by the failure of a compact 4 km2 asperity with a maximum slip of about 90 cm and corresponding peak stress drop of up to 50 mpa whereas the mean stress drop is about 15 mpa following the 1998 earthquake the cre activity was significantly increased in a 5 10 km deep zone extending 2 7 km northwest of the main shock which indicates triggering of substantial aseismic slip the postseismic slip inferred from the cre activity primarily propagated to the northwest and released a maximum slip of 9 cm in this 5 10 km depth range the estimated postseismic moment release is 8 6 1016 n m which is equivalent to mw 5 22 the aseismic slip distribution following the 1998 earthquake is not consistent with coseismic stress driven afterslip but represents a triggered long lasting slow earthquake

fractal dimension and b value on creeping and locked patches of the san andreas fault near parkfield california we tested the hypotheses 1 that the fractal dimension d of hypocenters are different in a locked and a creeping segment of the san andreas fault and 2 that the relationship d 2b holds approximately where b is the slope of the frequency magnitude relationship the test area was the 30 to 50 km fault segment north of park eld for which two earthquake catalogs exist the borehole high resolution seismic network data and the u s geological survey data which have a minimum magnitude of completeness of mc 0 4 and mc 1 0 1 2 respectively the relative location errors in the two catalogs are estimated as 0 25 km and less than 1 km respectively the periods of high quality data available extend from 1987 to 1998 5 and 1981 to 2000 2 respectively furnishing 2609 and 3775 events for analysis in the two catalogs in the locked part 0 5 b 0 7 and 0 96 d 1 14 whereas in the creeping segment 1 1 b 1 6 and 1 45 d 1 72 however the spatial distribution of the hypocenters in the creeping segment is not well approximated by a fractal distribution we conclude 1 that the frequency magnitude distribution as described by b as well as the fractal dimension d are different in the locked and creeping segments near park eld 2 that the spatial distribution in the creeping segment is not well approximated by a fractal distribution and 3 that the relationship d 2b holds in the locked segment where both parameters can be measured accurately thus we propose that the heterogeneity of seismogenic volumes lead to differences in d and b and that these differences where established by high quality data may furnish clues concerning properties of fault zones

a dayside plasma depletion observed at midlatitudes during quiet geomagnetic conditions in this study we investigate a dayside midlatitude plasma depletion dmlpd encountered on 22 may 2014 by the swarm and grace satellites as well as ground based instruments the dmlpd was observed near puerto rico by swarm near 10 lt under quiet geomagnetic conditions at altitudes of 475 520 km and magnetic latitudes of 25 30 the dmlpd was also revealed in total electron content observations by the saint croix station and by the grace satellites 430 km near 16 lt and near the same geographic location the unique swarm constellation enables the horizontal tilt of the dmlpd to be measured 35 clockwise from the geomagnetic east west direction ground based airglow images at arecibo showed no evidence for plasma density depletions during the night prior to this dayside event the c nofs equatorial satellite showed evidence for very modest plasma density depletions that had rotated into the morningside from nightside however the equatorial depletions do not appear related to the dmlpd for which the magnetic apex height is about 2500 km the origins of the dmlpd are unknown but may be related to gravity waves

c nofs observations of deep plasma depletions at dawn 1 the communication navigation outage forecasting system c nofs satellite was launched in 2008 during solar minimum conditions an unexpected feature in the c nofs plasma density data is the presence of deep plasma depletions observed at sunrise at all satellite altitudes ionospheric irregularities are often embedded within these dawn depletions their frequencies strongly depend on longitude and season dawn depletions are also observed in coincident satellite passes such as dmsp and champ in one example the depletion extended 50 14 in the n s and e w directions respectively these depletions are caused by upward plasma drifts observed in c nofs and ground based measurements the reason for these upward drifts is still unresolved we discuss the roles of dynamo electric fields over shielding and tidal effects as sources for the reported depletions

the use of strontium isotopes in determining groundwater mixing and brine fingering in a playa spring zone lake tyrrell australia j hydrol 167 225 239 playas in arid and semi arid regions can be important regional groundwater discharge zones located in the northwestern portion of victoria australia lake tyrrell is a large playa that serves as a major discharge zone of regional groundwater the chemistry of the regional groundwater is unique having salinities of approximately 30 g 1 1 and ph values as low as 2 8 as the regional groundwater is discharged along the western edge of the playa in the spring zone it is evapo concentrated into a dense brine which sinks through the playa sediments macumber s pioneering work on the geohydrology of this region established that this denser reflux brine below the playa surface has evolved from the evaporation of regional groundwaters we have measured the 87sr 86sr ratio of a number of groundwater samples taken at shallow depths along the spring zone at the playa edge and compared them with the regional groundwaters and the reflux brine our data reveal a rather complex pattern of mixing of the various water masses associated with the playa system most probably the result of density driven convective plumes two types of regional groundwater can be identified based on their 87sr 86sr values with groundwater from the south being less radiogenic than that flowing from the north i e 0 7108 vs 0 7142 vertical variations in 87sr 86sr in the regional groundwaters observed in wells adjacent to the spring zone can also be identified along a vertical gradient in the spring zone besides the hydrogeological information provided by these measurements the strontium isotope variations allow us to evaluate the source of strontium to these waters the regional groundwaters south of the lake are very similar in 87sr 86sr ratio to the reflux brines whereas the northern regional groundwaters are comparatively enriched in 87sr this enhanced 87sr signature indicates the addition of sr along the flow path via the weathering of the aquifer material the miocene parilla sand the southern waters have 87sr 86sr values closer to that of present day seawater and or miocene seawater indicating that the major source of sr to the system is from one or both of these sources our results demonstrate that strontium isotopes can be extremely useful in studying the dynamics as well as the geochemistry of surface water groundwater interactions

europa s crust and ocean origin composition and the prospects for life abstract we have considered a wide array of scenarios for europa s chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below we postulate that following formation of the jovian system the europan evolutionary sequence has as its major links a initial carbonaceous chondrite rock b global primordial aqueous differentiation and formation of an impure primordial hydrous crust c brine evolution and intracrustal differentiation d degassing of europa s mantle and gas venting e hydrothermal processes and f chemical surface alteration our models were developed in the context of constraints provided by galileo imaging near infrared reflectance spectroscopy and gravity and magnetometer data low temperature aqueous differentiation from a carbonaceous ci or cm chondrite precursor without further chemical processing would result in a crust ocean enriched in magnesium sulfate and sodium sulfate consistent with galileo spectroscopy within the bounds of this simple model a wide range of possible layered structures may result the final state depends on the details of intracrustal differentiation devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean crust compositions e g an ocean crust of sodium carbonate or sulfuric acid or a crust containing abundant clathrate hydrates realistic chemical physical evolution scenarios differ greatly in detailed predictions but they generally call for a highly impure and chemically layered crust some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and or cryovolcanism we describe some plausible geological consequences of the physical chemical structures predicted from these scenarios these predicted consequences and observed aspects of europa s geology may serve as a basis for further analys is and discrimination among several alternative scenarios most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms

local and duration magnitudes in northwestern italy and seismic moment versus magnitude relationships in the present work we develop some local magnitude scales for northwestern italy based on vertical short period records this study is motivated by the possibility of applying the computed scales to an instrumental catalog of more than 25 000 local earthquakes as this region has been continuously monitored by 12 short period vertical component 1c stations since the mid 1980s furthermore a digital network of three component 3c broadband or 5 second sensors has monitored northwestern italy since 1996 today a significant number of earthquakes have been simultaneously recorded by both networks allowing the calibration of the 1c local scale by using magnitudes computed according to a scale derived for the 3c digital network moreover because station sant anna di valdieri houses both a 3c code stv2 and 1c code stv sensors the magnitude scales for the two networks can be developed using the same reference station the magnitude scale m l log a log r 100 0 0054 r 100 3 s is derived for the 3c digital network with the requirement that the correction s of station stv2 is zero this scale is based on 10 057 maximum amplitudes 2822 earthquakes computed from horizontal synthesized wood anderson seismograms in the hypocentral distance 10 to 310 km and in the range 0 m l 5 with respect to an carlier magnitude scale derived for the 3c network constraining the sum of all the station corrections to zero the magnitudes predicted by the previous equations show an average bias of 0 2 0 1 which can be ascribed to the different constraint applied to the station corrections the magnitudes predicted by the scale for the 3c network are used to calibrate magnitude scales based on either total duration or maximum amplitude from synthesized wood anderson seismograms computed for each short period vertical recording the magnitude scale obtained considering maximum amplitudes from vertical short period recordings is m l log a log r 100 0 0041 r 100 3 s the reliability of the obtained magnitude scales is assessed using 827 earthquakes different from those we considered in the regression analysis finally the following seismic moment versus local magnitude relations are valid in the western alps in the range 0 where m l3c is the local magnitude computed starting from the horizontal component of broadband flat frequency response from 0 033 to 50 hz or semibroadband flat frequency response from 0 2 to 40 hz sensors and m l1c is the magnitude computed starting from the vertical short period recordings 1 embed graphic 1 gif

comparison of penetration electric fields created by the solar wind with jicamarca data using swage 1 swage solar wind acting on the geophysical environment calculates the global ionospheric electric field generated by high latitude electrodynamics drivers determined from the time shifted solar wind data measured at l1 by joining the hill siscoe polar cap potential model with the n c ionospheric potential solver of particular interest are the conditions under which the eastward equatorial penetration electric field near twilight contributes to the pre reversal enhancement pre in the present model it is found that a steeper terminator conductance gradient leads to a more pronounced pre the model is statistically consistent with the jicamarca vertical drift data at twilight during quiet times for eighty two days in the years 1998 2005 the model is also consistent with the jicamarca vertical drift data during the november 2004 magnetic superstorms dst 250 nt and highlights the importance of including the lt dependence of the ionospheric response in this comparison disturbance dynamo dd effects are also included comparison is much better using the conductance model with a shallower terminator gradient and indicates that the conductance lt profile was relatively unchanged throughout the storms

coherent and incoherent scatter radar study of the climatology and day to day variability of mean f region vertical drifts and equatorial spread f

organic degradation sulphate reduction and ammonia production in the sediments of loch eil scotland abstract the rates of degradation and mineralization of organic matter in sediments from two stations in loch eil were studied a particular feature of this site is a major input of cellulose fibre from a pulp and paper mill which affected both sediments and benthic fauna the input may be regarded as an additional terrigenous input having a high c n ratio the effect of this input on organic degradation sulphate reduction and ammonia production was determined in both field samples and using sediment incubation experiments the result of the cellulose input is a spatial condensation of the normal biogeochemical zones in the sediment bringing the sulphate reducing zone to the sediment surface at e70 the station receiving the highest input rates of sulphate reduction are comparable to those measured at other sea loch sites and differences between the rates of sulphate reduction measured by 35so42 technique and jar incubation are demonstrated alkalinity and ammonium production may be related to sulphate reduction by previously accepted stoichiometry and model calculations suggest that the organic matter being mineralized in the sulphate reducing zone has a c n ratio similar to that in marine planktonic material e70 7 e24 8 at e70 there is apparently production of ammonia in excess of that produced by sulphate reduction the potential for nitrate reduction to ammonia was demonstrated in the surface sediments degradation of cellulose which was active only in the near surface sediments was not related directly to sulphate reduction and it is suggested that this is due to production of organic intermediates and cell carbon only a percentage of the carbon being mineralized comparison of estimated inputs of organic carbon to the sediments with the turnover of sulphate suggests that sulphate reduction can account for degradation of an amount of carbon equivalent to the total estimated primary production in loch eil about half the total carbon input mineralization of carbon by aerobic and anaerobic processes appears to balance the estimated input of carbon but this does not account for the carbon content of the sediments up to 8 and it is suggested that net mineralization has been overestimated

variability in earthquake stress drop and apparent stress 1 we apply empirical green s function coda based analysis to four earthquake sequences in japan that span a magnitude range of 1 8 to 6 9 to measure radiated energy corner frequency and stress drop we find no systematic dependence of apparent stress or stress drop on seismic moment for these sequences and find they both are log normally distributed however we identify several anomalous events both energetic and enervated that show sharply different spectral signatures from the rest of the population these events indicate that much of the variation in apparent stress and stress drop is statistically significant which may have important implications for seismic hazard analysis

early morning irregularities detected with spaceborne gps measurements in the topside ionosphere a multisatellite case study we present observations of the equatorial plasma bubbles epb in the topside ionosphere at early morning hours 05 08 lt in the recovery phase of the 18 19 february 2014 geomagnetic storm this rare type of irregularities was detected in the pacific sector using gps measurements on board several low earth orbit leo satellites we use a multisatellite constellation consisted of the three swarm and one terrasar x satellites that on 19 february flew in the same region and at similar altitudes 500 km the epb occurrence in the leo gps data was observed for several consecutive orbits from 11 ut to 16 17 ut on 19 february 2014 which suggests the following 1 rather long duration hours of favorable conditions for epb generation 2 formation and evolution of epb over wide longitude range of the pacific ocean and 3 possible movement of the epb region in the westward direction with dawn registration of the early morning epb in leo gps data was supported by concurrent in situ swarm and dmsp defense meteorological satellite program and ground based ionosonde and gps measurements leo based gps technique is found to be essential and promising data source to study the topside epb over regions with lack of the ground based facilities in addition we use the prompt penetration model and the thermosphere ionosphere electrodynamics global circulation model tie gcm to identify the possible mechanisms responsible for the observed phenomenon the model simulation results indicate the occurrence of the zone with the enhanced vertical plasma drift 40 45 m s owing to the disturbance dynamo action in the predawn dawn sector during 09 17 ut

source pulse enhancement by deconvolution of an empirical green s function observations of the earthquake source time function are enhanced if path recording site and instrument complexities can be removed from seismograms assuming that a small earthquake has a simple source its seismogram can be treated as an empirical green s function and deconvolved from the seismogram of a larger and or more complex earthquake by spectral division when the deconvolution is well posed the quotient spectrum represents the apparent source time function of the larger event this study shows that with high quality locally recorded earthquake data it is feasible to fourier transform the quotient and obtain a useful result in the time domain in practice the deconvolution can be stabilized by one of several simple techniques in this paper the method is implemented and tested on high quality digital recordings of aftershocks of the jan 9 1982 miramichi new brunswick earthquake in particular seismograms from a jan 17 aftershock 017 13 33 gmt local mag 3 5 exhibit path or site effects which complicate the determination of source parameters after deconvolution the apparent far field source of this event is a simple pulse in displacement with duration 0 07 second for both p and s

self consistent modeling of equatorial dawn density depletions with sami3 1 large scale dawn density depletions in the equatorial ionosphere have been observed by instruments on the stpsat1 and champ satellites the naval research laboratory nrl ionosphere model sami3 sami3 is also a model of the ionosphere is used to study this new phenomenon using a self consistent electric field two empirical horizontal wind models hwm are used in the simulation study hwm93 and hwm07 dawn density depletions are found using hwm07 but not with hwm93 the cause of the depletions is a post midnight enhancement of the eastward electric field that generates an upward plasma drift this drift lifts low density plasma to high altitudes i e 600 km we compare our model results to remote sensing data and to in situ satellite data

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

the magnitude frequency distribution of earthquakes recorded with deep seismometers at cajon pass southern california abstract the cumulative b value the slope of the gutenberg richter relationship between earthquake occurrence rate and magnitude is commonly found to be constant 1 network catalogues however reveal a decrease at small magnitudes b value is not just an artifact of catalogue incompleteness but that small earthquakes are really not as numerous as a constant b value extrapolated from larger events would predict in the cajon pass area southern california the b value of seismicity recorded by the local network scsn appears to decrease below about m l 1 6 in order to investigate whether this decrease is real or simply represents the network detection threshold we use seismicity recorded by the deep 1 5 and 2 5 km seismometers deployed in the cajon pass scientific drillhole between april 1992 and october 1994 the maximum amplitudes recorded downhole are compared to scsn magnitudes for events recorded by the network to determine the relationship between amplitude and m l as a function of hypocentral distance from the borehole magnitudes are then calculated for 1300 earthquakes which occurred within 40 km of the borehole magnitude frequency curves are calculated for those events within 18 km of the borehole and a constant b value is observed to m l 0 5

stress drops and radiated seismic energies of microearthquakes in a south african gold mine 1 we estimate stress drops and radiated seismic energies of 20 microearthquakes 0 0 mw 1 3 in a south african gold mine to investigate their rupture characteristics and scaling relationships to large earthquakes we analyze seismograms of borehole accelerometers recorded with high sampling rate 15 khz within 200 m of the hypocenters at the depth of 2650 m the waveform data have very high signal to noise ratio and no significant later phases are observed at all stations corner frequencies and quality factors of the anelastic attenuation q are estimated from spectra of velocity seismograms by assuming the omega squared model of boatwright 1978 we also investigate moment tensors for double couple solutions and volumetric components from the waveform inversion static stress drops of the 20 earthquakes calculated from the model of madariaga 1976 are from 3 2 to 88 mpa and scaled energies er mo the ratio of the radiated energy er to the seismic moment mo are from 4 2 10 6 to 1 1 10 4 we find that both the static stress drops and the scaled energies of the analyzed earthquakes are comparable to those values of larger earthquakes our results indicate that the dynamic rupture processes of these microearthquakes are similar to those of larger earthquakes

interface locking along the subduction megathrust from b value mapping near nicoya peninsula costa rica 1 to understand controlling factors for seismogenesis and strain accumulation in subduction megathrusts we examine seismicity patterns across nicoya costa rica to determine the overall and spatial variability in the earthquake frequency magnitude distribution along the interface the mean reduction in earthquake activity with magnitude b value is higher 1 06 than global subduction zone averages 0 6 0 8 suggesting the interface here is weakly coupled strong spatial variations in b are anticorrelated 0 53 with geodetic estimates of interface locking of e norabuena et al 2004 high b prevails in two regions including the subducted fisher seamount chain a broad zone of reduced b is observed at and offshore the central nicoya coast extending towards an imaged locked patch these results suggest b value studies may be useful in identifying regions of increased interface locking in subduction zones which may indicate regions capable of large slip in future large earthquakes

characteristics of the large scale traveling atmospheric disturbances during geomagnetically quiet and disturbed periods simulated by a whole atmosphere general circulation model 1 we have investigated characteristics of the large scale traveling atmospheric disturbances ls tads generated during geomagnetically quiet and disturbed periods using a whole atmosphere general circulation model gcm the gcm simulations show that various tads appear in association with passages of regions with large temperature gradients near the solar terminator midnight temperature anomaly and auroral oval which move with the earth s rotation these tads which are superimposed on each other appear even when a geomagnetically quiet period the tads generated during a geomagnetically quiet period show structures extending in the longitudinal direction at high latitude and in the latitudinal direction at mid and low latitude these structures disappear after their short range propagations the tads generated during a geomagnetically disturbed period show structures extending widely in the longitudinal direction and propagate from high to low latitude these simulation results suggest the different generation mechanisms and features between the tads generated during geomagnetically quiet and disturbed periods

sources of low latitude ionospheric e b drifts and their variability 1 the complete mechanism of how upward propagating tropospheric tides connect to the upper atmosphere is not yet fully understood one proposed mechanism is via ionospheric wind dynamo however other sources can potentially alter the vertical e b drift gravity and plasma pressure gradient driven current the geomagnetic main field and longitudinal variation in the conductivities in this study we examine the contribution to the vertical drift from these sources and compare them we use march equinox results from the thermosphere ionosphere mesosphere electrodynamics general circulation model we found that the gravity and plasma pressure gradient driven current and the longitudinal variation of the conductivities excluding the variation due to the geomagnetic main field do not change the longitudinal variation of the vertical drift significantly modifying the geomagnetic main field will change the vertical drift at 5 6 lt 18 19 lt and 23 24 lt at almost all longitudes in general the influence of the geomagnetic main field on the vertical drift is larger with respect to the maximum difference at 18 19 lt and 23 24 lt equal at 5 6 lt and smaller at 14 15 lt than the influence due to nonmigrating tidal components in the neutral winds examination of the contribution from e and f region neutral winds to the vertical drift shows that their importance depends on the local time and the solar activity this implies that the vertical drift has to be analyzed at specific local times to examine the relation between the wave number in the vertical drift and in the neutral winds

scaling of small repeating earthquakes explained by interaction of seismic and aseismic slip in a rate and state fault model because of short recurrence times and known locations small repeating earthquakes present a rare predictable opportunity for detailed field observations they are used to study fault creeping velocities earthquake nucleation stress drops and other aspects of tectonophysics earthquake mechanics and seismology an intriguing observation about repeating earthquakes is their scaling of recurrence time with seismic moment which is significantly different from the scaling based on a simple conceptual model of circular ruptures with stress drop independent of seismic moment and no aseismic slip here we show that a model of repeating earthquakes based on laboratory derived rate and state friction laws reproduces the observed scaling in the model a small fault patch governed by steady state velocity weakening friction is surrounded by a much larger velocity strengthening region long term slip behavior of the fault is simulated using a methodology that fully accounts for both aseismic slip and inertial effects of occasional seismic events the model results in repeating earthquakes with typical stress drops and sizes comparable with observations for a fixed set of friction parameters the observed scaling is reproduced by varying the size of the velocity weakening patch in simulations a significant part of slip on the velocity weakening patches is accumulated aseismically even though the patches also produce seismic events the proposed model supplies a laboratory based framework for interpreting the wealth of observations about repeating earthquakes provides indirect evidence that rate and state friction acts on natural faults and has important implications for possible scenarios of slip partition into seismic and aseismic parts

a method for calibration of the local magnitude scale based on relative spectral amplitudes and application to the san juan bautista california area we develop and use a spectral empirical green s function approach to estimate the relative source amplitudes of earthquakes near san juan bautista california we isolate the source amplitudes from path effects by comparing the recorded spectra of pairs of events with similar location and focal mechanism without computing the path effect with this method we estimate the relative moments of 1600 m 1 5 4 local earthquakes and we use these moments to recalibrate the duration magnitude scale in this region the estimated moments of these small earthquakes increase with catalog magnitude m d roughly proportionally to 101 1 m d slightly more slowly than a moment magnitude scaling of 101 5 m w this more accurate magnitude scaling can be used in analyses of the local earthquakes such as comparisons between the seismic moments and geodetic observations electronic supplement 1 additional description and figures showing estimated source amplitudes obtained with different parameters and observed amplitudes of some earthquakes with large misfits 1 http www bssaonline org lookup suppl doi 10 1785 0120160141 dc1

extremely acid permian lakes and ground waters in north america evaporites hosted by red beds red shales and sandstones some 275 265 million years old extend over a large area of the north american mid continent1 they were deposited in non marine saline lakes pans and mud flats2 settings that are typically assumed to have been alkaline here we use laser raman microprobe analyses of fluid inclusions trapped in halites from these permian deposits to argue for the existence of highly acidic ph 1 lakes and ground waters these extremely acidic systems may have extended over an area of 200 000 km2 modern analogues of such systems may be natural acid lake and groundwater systems ph 2 4 in southern australia3 4 5 6 7 8 9 both the ancient and modern acid systems are characterized by closed drainage arid climate low acid neutralizing capacity and the oxidation of minerals such as pyrite to generate acidity the discovery of widespread ancient acid lake and groundwater systems demands a re evaluation of reconstructions of surface conditions of the past and further investigations of the geochemistry and ecology of acid systems in general

study of the equatorial and low latitude electrodynamic and ionospheric disturbances during the 22 23 june 2015 geomagnetic storm using ground based and spaceborne techniques we use a set of ground based instruments global positioning system receivers ionosondes magnetometers along with data of multiple satellite missions swarm c nofs dmsp guvi to analyze the equatorial and low latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22 23 june 2015 which is the second largest storm in the current solar cycle our results show that at the beginning of the storm the equatorial electrojet eej and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields ppef the ppef were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside and downward drift on the nightside furthermore about 45 min after the storm commencement the interplanetary magnetic field imf bz component turned northward leading to the eej changing sign to westward and to overall decrease of the vertical total electron content vtec and electron density on the dayside at the end of the main phase of the storm and with the second long term imf bz southward turn we observed several oscillations of the eej which led us to conclude that at this stage of the storm the disturbance dynamo effect was already in effect competing with the ppef and reducing it our analysis showed no significant upward or downward plasma motion during this period of time however the electron density and the vtec drastically increased on the dayside over the asian region we show that this second positive storm was largely influenced by the disturbed thermospheric conditions

responses in the polar and equatorial ionosphere to the march 2015 st patrick day storm the st patrick day storm of 2015 17 march 2015 occurred at a unique time when there were multiple spacecraft observing the earth s ionosphere between 350 and 885 km observations of the plasma flows and densities from the five operational polar orbiting dmsp spacecraft combined with those from the equatorial orbiting c nofs spacecraft provided a comprehensive global record of the both the polar and equatorial ionosphere regions responses to the storm this paper presents an overview of the data from this suite of spacecraft focusing on the following aspects 1 the polar cap ionosphere s reaction to the storm 2 the change in the penetration electric field in the midlatitude region as a function of time and the solar local time during the storm 3 the equatorial ionosphere s response of the meridional vertical flows to the penetration electric field and the disturbance dynamo during the storm and 4 the creation of a predawn ionospheric bubble system near the equator during the storm s main phase that was observed at low altitudes by c nofs and later at high altitudes by several dmsp examining these phenomenon enable us to trace the dynamic flow of energy from the solar wind input in the polar ionosphere all the way to the equatorial ionosphere

microbial biogeochemistry and bioturbation in the sediments of great bay new hampshire the influence of bioturbation on certain aspects of the biogeochemistry of sulfur and iron was examined in shallow water sediments of great bay estuary new hampshire a bioturbated jel and non bioturbated squam site were compared annual sulfate reduction measured with 35s was 4 5 times more rapid at jel a significant portion of this difference was attributed to rapid rates which occurred throughout the upper 12 cm of sediment at jel due to infaunal reworking activities sulfate reduction decreased rapidly with depth at squam fes in the upper 2 cm at jel increased in concentration from 3 to 45 mol ml 1 from early may to late july while only increasing from 3 to 8 mol ml 1 at squam infaunal irrigation and reworking activities caused rapid and continous subsurface cycling of iron and sulfur at jel this maintained dissolved iron concentrations at 160 170 m throughout the summer despite rapid sulfide production therefore dissolved sulfide never accumulated in jel pore waters although dissolved organic carbon doc was generated during sulfate reduction bioturbation during summer caused a net removal of doc from jel pore waters sulfate reduction rates decomposition stoichiometry and nutrient concentrations were used to calculate turnover times of nutrients in pore waters nutrient turnover varied temporally and increased three to five fold during bioturbation a secondary maximum in the abundance of recoverable sulfate reducing bacteria occurred at 10 cm in jel sediments only during periods of active bioturbation demonstrating the influence of macrofaunal activities on bacterial distributions

geochemistry of acid brines lake tyrrell victoria australia abstract pore water groundwater and sediments were collected from lake tyrrell to study the evolution of brines in an acidic environment lake tyrrell is a 150 km2 inland salt playa acid saline groundwater enters the playa through springs along the lake margin and is evapo concentrated past halite precipitation the brines were found to contain sea salts but some solutes do not follow the seawater evaporation curve processes that occur in neutral alkaline systems e g gypsum formation occur here but precipitation of alunite kal3 so4 2 oh 6 jarosite kfe3 so4 2 oh 6 and fe oxides also affect solute behavior processes that occur in the recharge area and along the groundwater flow path k uptake calcrete and gypcrete formation affect the brine s chemical signature regardless of the chemical variability found among the samples solutes have evolved from a common source sea salt acidification which appears to occur early in the evolution of the groundwater is related to pyrite oxidation and may be enhanced by precipitation of fe oxides alunite and jarosite and evaporation acidity is maintained in the system because of the lack of buffering capacity of aquifer minerals we suggest that this acid brine from australia is another end member in the eugster jones hardie model for the evolution of water by evaporation in closed basins

radiated seismic energy from coda measurements and no scaling in apparent stress with seismic moment 1 the seismic coda consists of scattered waves that leave the earthquake source in a variety of directions the averaging of source radiation that results leads to stable ground motion spectra that we use as the basis for a robust measurement of radiated wave energy we apply an empirical green s function egf method to the seismic coda in order to investigate scaling of the radiated seismic energy we correct for path effects in the spectra of earthquakes by using a stack of closely located small earthquakes as an egf we apply this approach to four earthquake sequences in western north america that span a magnitude range from mw 3 0 mw 7 1 our estimates of scaled energy are consistent with independent measurements where available we find no dependence in individual seismic energy estimates on source station distance which validates the egf approximation we find that a constant scaled energy of 3 5 10 5 provides a reasonable fit to the data with no dependence of the scaled energy on seismic moment

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

observations of dc electric fields in the low latitude ionosphere and their variations with local time longitude and plasma density during extreme solar minimum 1 dc electric fields and associated e b plasma drifts detected with the double probe experiment on the c nofs satellite during extreme solar minimum conditions near the june 2008 solstice are shown to be highly variable with weak to moderate ambient amplitudes of 1 2 mv m 25 50 m s average field or drift patterns show similarities to those reported for more active solar conditions i e eastward and outward during day and westward and inward at night however these patterns vary significantly with longitude and are not always present daytime vertical drifts near the magnetic equator are largest in the prenoon sector observations of weak to nonexistent prereversal enhancements in the vertical drifts near sunset are attributable to reduced dynamo activity during solar minimum as well as seasonal effects enhanced meridional drifts are observed near sunrise in certain longitude regions precisely where the enhanced eastward flow that persisted from earlier local times terminates the nightside ionosphere is characterized by larger amplitude structured electric fields dominated by horizontal scales of 500 1500 km even where local plasma densities appear relatively undisturbed data acquired during successive orbits indicate that plasma drifts and densities are persistently organized by longitude the high duty cycle of the c nofs observations and its unique orbit promise to expose new physics of the low latitude ionosphere

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

stress drops of repeating earthquakes on the san andreas fault at parkfield i calculate well resolved corner frequencies and stress drops for 25 earthquakes 1989 2006 in the three repeating sequences targeted by the san andreas fault observatory at depth using borehole data and multiple highly correlated empirical green s functions egfs the earthquakes in the largest magnitude m 2 1 cluster exhibit source spectra well fit by a circular source model the corner frequencies correlate with those from the regional study by allmann and shearer 2007 suggesting that the interevent variability is resolvable the earthquakes have stress drops between 25 and 65 mpa with a gradual increase before the 2004 m6 earthquake followed by an immediate decrease then a rapid return to previous levels the spectra of the cluster of m 1 9 earthquakes include high frequency energy not fit by simple source models and so stress drops are unreliable and probably underestimated 1 20 mpa there is no correlation with previous studies and interevent variation is not resolvable the earthquakes in the smallest magnitude cluster m 1 8 have the highest corner frequencies but similar stress drops 4 120 mpa the stress drops exhibit the same temporal variation as the first cluster but there is poor correlation with allmann and shearer 2007 probably because their frequency bandwidth is too limited

source parameters of picoseismicity recorded at mponeng deep gold mine south africa implications for scaling relations abstract we investigate the source parameters of picoseismic and nanoseismic events m w 4 1 recorded with a high sensitivity seismic network at the mponeng gold mine in south africa to gain new insights into the scaling of small seismic events the japanese german underground acoustic emission research in south africa jaguars network composed of one three component 3c accelerometer sensitivity 50 hz to 25 khz and 8 acoustic emission ae sensors sensitivity 1 khz to 180 khz is located at a depth of 3268 m and covers the limited volume of approximately 300 300 300 m the ae sensors are calibrated with respect to the 3c accelerometer in the frequency band 400 hz 17 khz the waveform data of two datasets are analyzed 1 the aftershock sequence of an m w 1 9 event that occurred approximately 30 m from our network and 2 the postblasting activity recorded during working days located at a distance 90 m from the network at the exploitation level for the analysis we applied spectral fitting and spectral ratio methods the calculated values of m w range from 0 8 down to 4 1 with corner frequencies 0 8 khz 13 6 khz source sizes from 8 cm to 1 3 m we observe static stress drops ranging from 1 mpa to 10 0 mpa with apparent stresses of 0 01 mpa 1 00 mpa stress drops are independent of the moment suggesting self similar behavior in the analyzed magnitude range 4 1 m w

spatial and temporal stress drop variations in small earthquakes near parkfield california 1 we estimate source parameters from spectra of 42367 earthquakes between 1984 and 2005 that occurred in the parkfield segment of the san andreas fault in central california we use a method that isolates the source term of the displacement spectra based on a convolutional model and correct the observed p wave source spectra with a spatially varying empirical green s function egf our brune type stress drop estimates vary from 0 1 to over 100 mpa with a median value of 6 75 mpa which is nearly constant with moment implying self similarity over the ml 0 5 to 3 0 range of our data the corner frequency decreases for earthquakes at shallower depths consistent with slower rupture velocities and reduced shear wave velocities in local velocity models the estimated median stress drops show significant lateral variations we find lower stress drops in the middle mountain asperity and along the creeping fault section and higher stress drops in the hypocentral region of the 2004 m6 0 parkfield earthquake the main shock did not alter the overall pattern of high and low stress drop regions however a statistical test reveals areas with significant changes in computed stress drops after the main shock which we compare to estimated absolute shear stress changes from a main shock slip model by calculating t from the spectral egf ratio we also identify areas with increased attenuation after the main shock and we are able to distinguish source effects and near source attenuation effects in the spectral analysis these results are confirmed independently from spectral ratios of repeating microearthquake clusters

topside ionospheric irregularities as seen from multisatellite observations we use in situ data from champ and dmsp satellites along with data of gps receiver onboard champ satellite and ground based gps receivers to study the occurrence and global distribution of ionospheric irregularities during the main phase of the geomagnetic storm of 29 31 august 2004 minimum dst excursion of a128 nt using the champ gps measurements we created maps of gps phase fluctuation activity and found two specific zones of the most intense irregularities 1 the region of the auroral oval at high latitudes of both hemispheres and 2 the low latitudes equatorial region between africa and south america at high latitudes the topside ionospheric irregularities appeared to be more intensive in the southern hemisphere which is most likely due to seasonal variations in the interhemispheric field aligned currents system an analysis of multi instrumental observations reveals reinforcement of the equatorial ionization anomaly after sunset in atlantic sector on 30 august and formation of the significant plasma depletions and irregularities over a large longitudinal range equatorial irregularities were also found in the morning sector at the recovery phase of the storm in addition to low earth orbit leo gps measurements we analyze the leo in situ measurements and we show that these two techniques cannot be interchangeable in all cases because of the altitudinal extent of plasma irregularities overall we demonstrate that the leo gps technique can serve a useful tool for detection of the topside ionospheric irregularities during space weather events and may essentially contribute to other methods based on various instruments

global equatorial plasma bubble occurrence during the 2015 st patrick s day storm an analysis of the occurrence of equatorial plasma bubbles epbs around the world during the 2015 st patrick s day geomagnetic storm is presented a network of 12 global positioning system receivers spanning from south america to southeast asia was used in addition to colocated vhf receivers at three stations and four nearby ionosondes the suppression of postsunset epbs was observed across most longitudes over 2 days the epb observations were compared to calculations of the linear rayleigh taylor growth rate using coupled thermosphere ionosphere modeling which successfully modeled the transition of favorable epb growth from postsunset to postmidnight hours during the storm the mechanisms behind the growth of postmidnight epbs during this storm were investigated while the latter stages of postmidnight epb growth were found to be dominated by disturbance dynamo effects the initial stages of postmidnight epb growth close to local midnight were found to be controlled by the higher altitudes of the plasma i e the gravity term modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low latitude region which made the plasma more susceptible to rayleigh taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight epbs

effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread f we use radar observations from the jicamarca observatory from 1968 to 1992 to study the effects of the f region vertical plasma drift velocity on the generation and evolution of equatorial spread f the dependence of these irregularities on season solar cycle and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts in the early night sector the bottomside of the f layer is almost always unstable the evolution of the unstable layer is controlled by the history of the vertical drift velocity when the drift velocities are large enough the necessary seeding mechanisms for the generation of strong spread f always appear to be present the threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux the geomagnetic control on the generation of spread f is season solar cycle and longitude dependent these effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields the occurrence of early night spread f decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset the generation of late night spread f requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour these irregularities occur most often at 0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes the occurrence of late night spread f is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

comparative analysis of spread f signature and gps scintillation occurrences at tucuman argentina 1 we analyze data recorded from october 2010 to september 2011 during the ascending phase of the 24th solar cycle from an advanced ionospheric sounder istituto nazionale di geofisica e vulcanologia ionosonde and a gps ionospheric scintillation and total electron content tec monitor scintillation receiver colocated at low latitude in the southern american longitudinal sector tucuman 26 9 s 294 6 e magnetic latitude 15 5 s argentina the site offers the opportunity to perform spread f and gps scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly spread f signatures classified into four types strong range spread f ssf range spread f frequency spread f fsf and mixed spread f the phase and amplitude scintillation index and s4 respectively the tec and the rate of tec parameter marker of the tec gradients that can cause scintillations are considered the seasonal behavior results as follows the occurrence of all four types of spread f is higher in summer and lower in winter while the occurrence of scintillations peaks at equinoxes in the postsunset sector and shows a minimum in winter the correspondence between ssf and scintillations seems to be systematic and a possible correlation between s4 and fsf peaks is envisaged at the terminator the investigation focused also on two particular periods from 12 to 16 march 2011 and from 23 to 29 september 2011 both characterized by the simultaneous presence of ssf signatures and scintillation phenomena allowing to discuss the role of traveling ionospheric disturbances as a strong candidate causing ionospheric irregularities

denitrification in a major limestone aquifer abstract the chalk aquifer of eastern central england is seriously affected by nitrates leached from agricultural land and like many similar aquifers its future as a potable resource must depend considerably on the nature and rates of denitrification the regional distribution of nitrate supports a viewpoint based on thermodynamic criteria that denitrification is actively occurring and that the problem will be short lived more detailed considerations based on major ion and environmental isotope data however indicate that denitrification is not significant and that the apparent lowering of nitrate concentration from 10 to 1 no 3 n in the apparent direction of flow is due primarily to mixing between waters of different origins presence of reduced nitrogen species is possible evidence of denitrification in some older waters 4000 yr b p it is concluded that denitrification can not be relied upon to reduce elevated concentrations of nitrate in modern recharge waters

radar and satellite global equatorial f region vertical drift model we present the first global empirical model for the quiet time f region equatorial vertical drifts based on combined incoherent scatter radar observations at jicamarca and ion drift meter observations on board the atmospheric explorer e satellite this analytical model based on products of cubic b splines and with nearly conservative electric fields describes the diurnal and seasonal variations of the equatorial vertical drifts for a continuous range of all longitudes and solar flux values our results indicate that during solar minimum the evening prereversal velocity enhancement exhibits only small longitudinal variations during equinox with amplitudes of about 15 20 m s is observed only in the american sector during december solstice with amplitudes of about 5 10 m s and is absent at all longitudes during june solstice the solar minimum evening reversal times are fairly independent of longitude except during december solstice during solar maximum the evening upward vertical drifts and reversal times exhibit large longitudinal variations particularly during the solstices in this case for a solar flux index of 180 the june solstice evening peak drifts maximize in the pacific region with drift amplitudes of up to 35 m s whereas the december solstice velocities maximize in the american sector with comparable magnitudes the equinoctial peak velocities vary between about 35 and 45 m s the morning reversal times and the daytime drifts exhibit only small variations with the phase of the solar cycle the daytime drifts have largest amplitudes between about 0900 and 1100 lt with typical values of 25 30 m s we also show that our model results are in good agreement with other equatorial ground based observations over india brazil and kwajalein

the trace metal geochemistry of the lake tyrrell system brines victoria australia abstract we have analyzed the waters of the lake tyrrell system for the trace metals fe mn pb cu and zn in a number of samples both dissolved fe t and fe 2 were also determined great care was exercized to minimize any contamination of the samples not surprisingly the highest metal concentrations occur in the low ph high eh regional groundwaters with much lower values observed in the reflux brines and the neutral wahpool timboram waters it is thought that the source of these metals to the groundwaters is the dissolution of a suite of heavy minerals within the aquifer the pliocene parilla sand as the acid groundwaters flow toward the lake some metals are removed near lake edge at depth the metal concentrations in the spring zone region indicate an extremely dynamic system where at different times of the year due to changes in the hydrologic regime metals can be either removed or solubilized

empirical green s function analysis taking the next step an extension of the empirical green s function egf method is presented that involves determination of source parameters using standard egf deconvolution followed by inversion for a common attenuation parameter for a set of colocated events recordings of three or more colocated events can thus be used to constrain a single path attenuation estimate i apply this method to recordings from the 1995 1996 ridgecrest california earthquake sequence i analyze four clusters consisting of 13 total events with magnitudes between 2 6 and 4 9 i first obtain corner frequencies which are used to infer brune stress drop estimates i obtain stress drop values of 0 3 53 mpa with all but one between 0 3 and 11 mpa with no resolved increase of stress drop with moment with the corner frequencies constrained the inferred attenuation parameters are very consistent they imply an average shear wave quality factor of approximately 20 25 for alluvial sediments within the indian wells valley although the resultant spectral fitting using corner frequency and is good the residuals are consistent among the clusters analyzed their spectral shape is similar to the the theoretical one dimensional response of a layered low velocity structure in the valley an absolute site response cannot be determined by this method because of an ambiguity between absolute response and source spectral amplitudes i show that even this subtle site response can significantly bias estimates of corner frequency and if it is ignored in an inversion for only source and path effects the multiple egf method presented in this paper is analogous to a joint inversion for source path and site effects the use of colocated sets of earthquakes appears to offer significant advantages in improving resolution of all three estimates especially if data are from a single site or sites with similar site response