natural magnetic disturbance fields not precursors preceding the loma prieta earthquake 1 available records of the magnetic indices dst and ap together with standard observatory recordings of 1 min field levels were examined for the period preceding the earthquake of october 1989 centered near loma prieta california the magnetic records showed that the fraser smith et al 1990 report claiming the existence of a 100 s ultralow frequency geomagnetic field precursor signal at corralitos california foretelling a nearby earthquake is not valid my study shows that the stanford ulf signal was not local but rather widespread throughout the western united states and therefore expected to be due to a coincidental geomagnetic solar terrestrial disturbance field

anisotropic inversion of refracted waves in vertical cable data in the presence of dip refracted arrivals are analysed to estimate the near surface anisotropy of marine sediments using a vertical cable vc configuration in the presence of dip the horizontal and vertical ray slownesses are obtained from the observed apparent slownesses in the up and downdip directions using a sum or difference at each azimuth the multiple azimuths generated by a vc geometry permit the ray slowness distribution of the marine sediments to be determined an inversion procedure is developed to provide dip and anisotropy parameters for refractive layers from the measured refraction traveltimes in multilayered azimuthally isotropic and anisotropic media two sets of transversely isotropic models are used to analyse the azimuthal variations of apparent and ray slownesses in the first set we fix the anisotropic parameters of the models but vary the dip 0 5 and 10 to test the effects of the presence of dip in the second set we vary the p wave anisotropy strength 5 2 10 3 15 8 and 22 0 to examine the sensitivity and accuracy of ray slowness approximations which are independent of dip we test this inversion procedure on synthetic p wave vc data calculated for six different models by a finite difference method the results of applications to real vc data acquired from the north sea are also presented

retrospective investigation of geophysical data possibly associated with the ms8 0 wenchuan earthquake in sichuan china abstract the ms8 0 wenchuan earthquake is one of the most catastrophic earthquakes occurred recently although the geophysical network around the epicentral region is not dense enough partially due to the inactivity of the longmenshan fault the retrospective investigation of geophysical data in and around the epicentral region would be helpful for strengthening the understanding of the seismogenic process of the wenchuan earthquake this paper summarized some preliminary results of the retrospective investigation especially focusing on the seismic and electromagnetic data possibly associated with the wenchuan earthquake and its aftershocks the spatio temporal investigation of the seismicity changes indicated that there is an intermediate term seismic quiescence around the epicenter during 2006 2007 the electromagnetic data also showed some anomalous changes including co seismic electromagnetic changes which may be related with the wenchuan earthquake and its aftershocks although further work is definitely required to enhance the reliability of the relationship between the above geophysical changes and the seismogenic process the above preliminary results would provide some useful information for the related study and stimulate further validation study on the precursors of the wenchuan earthquake

seismoelectromagnetic effect associated with the izmit earthquake and its aftershocks in order to investigate the resistivity structure beneath the northern and the southern branches of the western part of the north anatolian fault zone nafz which has been known as a seismic gap area we started wideband magnetotelluric mt measurements on 27 july 1999 along a north south profile crossing the northern branch near izmit and the southern branch near iznik when the izmit kocaeli earthquake m w 7 4 occurred on 17 august 1999 mt fields were being measured at five sites four of which happened to be located near the surface rupture zone associated with the mainshock and large variations in the mt fields were observed in association with seismic waves we propose motional electromagnetic induction in the electrically conducting crust which vibrates under the earth s magnetic field as one of the possible generation mechanisms for such mt field variations for more detailed studies of such a mechanism we installed a wideband mt instrument and a three component seismometer at two of the four sites on 16 september 1999 and made simultaneous measurements during several aftershocks the estimate of the order of the magnitude of motional electromagnetic response derived from the mt fields and ground motion observed during a large aftershock m 4 5 supports our claim that the seismo dynamo effect is a plausible mechanism for variations in the mt fields associated with the seismic waves manuscript received 31 july 2000

are there new findings in the search for ulf magnetic precursors to earthquakes moore 1964 in a letter published in nature reported disturbances in geomagnetic field data prior to the 27 march 1964 alaska earthquake after the publication of this report many papers have shown magnetic changes preceding earthquakes however a causal relationship between preearthquake magnetic changes and impending earthquakes has never been demonstrated as a consequence after 50 years magnetic disturbances in the geomagnetic field are still candidate precursory phenomena some researchers consider the investigation of ultra low frequency ulf 0 001 10 hz magnetic data the correct approach for identifying precursory signatures of earthquakes other researchers instead have recently reviewed many published ulf magnetic changes that preceded earthquakes and have shown that these are not actual precursors the recent studies by currie and waters 2014 and han et al 2014 aim to provide relevant new findings in the search for ulf magnetic precursory signals however in order to contribute to science alleged precursors must be shown to be valid and reproducible by objective testing here we will briefly discuss the state of the art in the search for ulf magnetic precursors paying special attention to the recent findings of currie and waters 2014 and han et al 2014 we do not see in these two reports significant evidence that may support the observation of precursory signatures of earthquakes in ulf magnetic records

finite fault inversion of dinsar coseismic displacement of the 2009 l aquila earthquake central italy 1 we define the geometric and kinematic characteristics of the fault activated during the mw 6 3 6 april 2009 l aquila earthquake from the modeling of envisat and cosmo skymed the first ever x band interferogram inverted for a coseismic dislocation study dinsar interferograms our best fit solution for the main shock is represented by a normal fault 16 km long and 12 km wide with a small right lateral component dipping 47 sw with a maximum slip of 90 cm although the seismic dislocation probably ended at 1 km depth the updip projection of the fault plane corresponds to the northern segment of the mapped paganica s demetrio fault where alignment of surface breaks was observed in the field the absence of this fault in existing seismic source catalogues suggests that an improved approach involving detailed surface and subsurface geological and geophysical investigations is needed for a better assessment of the seismic hazard at the local scale

on claimed ulf seismogenic fractal signatures in the geomagnetic field 1 during the last ten years fractal analysis of ultra low frequency ulf geomagnetic field components has been proposed as one of the most promising tools to highlight magnetic precursory signals possibly generated by the preparation processes of earthquakes several papers claim seismogenic changes in the fractal features of the geomagnetic field some months before earthquakes occur the target of the present paper is to put forth a qualitative investigation on the fractal characteristics of ulf magnetic signatures that previous authors have claimed to be related without doubt to strong earthquakes this analysis takes into account both the temporal evolution of the geomagnetic field fractal parameters reported in previous researches and the temporal evolution of global geomagnetic activity running averages of the geomagnetic indices kp and ap are plotted into the original figures from the previous publications this simple analysis shows that the fractal features of the ulf geomagnetic field are closely related to the geomagnetic activity both before and after the earthquake occurs the correlation between the geomagnetic field fractal parameters and geomagnetic activity is clearly shown over both long and short time scales in light of this the present paper shows that fractal behaviors of previously claimed seismogenic ulf magnetic signatures depend mainly on geomagnetic activity due to solar terrestrial interaction therefore previously reported association with the preparation process of the earthquake is dubious

on the seismogenic increase of the ratio of the ulf geomagnetic field components abstract following the paper by fraser smith et al 1990 many scientists have focused their research on the ulf geomagnetic field pulsations in the hope of finding possible anomalous signals caused by the seismic activity thereafter many papers have reported ulf geomagnetic field polarization ratio increases which have been claimed to be related to the occurrence of moderate and strong earthquakes even if there is no firm evidence of correlation between the polarization ratio increase and seismic events these publications maintain that these anomalous increases are without doubt precursors of pending earthquakes furthermore several researchers suggest that these seismogenic signals may be considered a promising approach towards the possibility of developing short term earthquake prediction capabilities based on electromagnetic precursory signatures on the contrary a part of the scientific community emphasizes the lack of validation of claimed seismogenic anomalies and doubt their association with the seismic activity since earthquake prediction is a very important topic of social importance the authenticity of earthquake precursors needs to be carefully checked the aim of this paper is to investigate the reliability of the ulf magnetic polarization ratio changes as an earthquakes precursor several polarization ratio increases of the geomagnetic field which previous researchers have claimed to have a seismogenic origin are put into question by a qualitative investigation the analysis takes into account both the temporal evolution of the geomagnetic field polarization ratio reported in previous papers and the global geomagnetic activity behaviour running averages of the geomagnetic index k p are plotted onto the original figures from previous publications moreover further quantitative analyses are also reported here nine cases are investigated which include 17 earthquakes in seven cases it is shown that the suggested association between the geomagnetic field polarization ratio increases and the earthquake preparation process seems to be rather doubtful more precisely the claimed seismogenic polarization ratio increases are actually closely related to decreases in the geomagnetic activity level furthermore the last two investigated cases seem to be doubtful as well although a close correspondence between polarization ratio and geomagnetic activity cannot be unambiguously demonstrated

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

coseismic deformation of the destructive april 6 2009 l aquila earthquake central italy from gps data 1 on april 6 2009 01 32 39 gmt the city of l aquila was struck by a mw 6 3 earthquake that killed 307 people causing severe destruction and ground cracks in a wide area around the epicenter four days before the main shock we augmented the existing permanent gps network with five gps stations of the central apennine geodetic network cageonet bordering the l aquila basin the maximum horizontal and vertical coseismic surface displacements detected at these stations was 10 39 0 45 cm and 15 64 1 55 cm respectively fixing the strike direction according to focal mechanism estimates we estimated the source geometry with a non linear inversion of the geodetic data our best fitting fault model is a 13 15 7 km2 rectangular fault sw dipping at 55 3 1 8 consistent with the position of observed surface ruptures the estimated slip 495 29 mm corresponds to a 6 3 moment magnitude in excellent agreement with seismological data

air hydrate inclusions in fresh ice core one of the characteristic features of polar glacier ice is the abundance of air bubbles1 3 with increasing depth from the surface of the ice sheet the size of the bubbles generally decreases in response to the change of overburden pressure below a certain depth the bubbles start to shrink faster than expected and finally become invisible although not visible to the naked eye unit mass of the bubble free clear ice includes almost the same volume of air as unit mass of bubbly ice4 5 it is hypothesized that the air exists in the ice structure probably in the form of clathrate hydrates as suggested by miller6 7 but until now the location of the air has been unknown direct observations of air hydrate inclusions were carried out for the first time in fresh ice cores from dye 3 greenland when the ice structure surrounding air hydrate was melted an explosive transition occurred releasing a gas bubble into the melt cavity

magnetic field observations in the near field the 28 june 1992 mw 7 3 landers california earthquake recent reports suggest that large magnetic field changes occur prior to and during large earthquakes two continuously operating proton magne tometers lsbm and ochm at distances of 17 3 and 24 2 km respectively from the epicenter of the 28 june 1992 mw 7 3 landers earthquake recorded data through the earthquake and its aftershocks these two stations are part of a differentially connected array of proton magnetometers that has been operated along the san andreas fault since 1976 the instruments have a sensitivity of 0 25 nt or better and transmit data every 10 min through the goes satellite to the usgs headquarters in menlo park california seismomagnetic offsets of 1 2 0 6 and 0 7 0 7 nt were observed at these sites in comparison offsets of 0 3 0 2 and 1 3 0 2 nt were observed during the 8 july 1986 mt 5 9 north palm springs earthquake which occurred directly beneath the ochm magnetometer site the observations are generally consistent with seismomagnetic models of the earthquake in which fault geometry and slip have the same form as that determined by either inversion of the seismic data or inversion of geodetically determined ground displacements produced by the earthquake in these models right lateral rupture occurs on connected fault seg ments in a homogeneous medium with average magnetization of 2 a m the fault slip distribution has roughly the same form as the observed surface rupture and the total moment release is 1 1 1020 nm there is no indication of dif fusion like character to the magnetic field offsets that might indicate these ef fects result from fluid flow phenomena it thus seems unlikely that these earth quake generated offsets and those produced by the north palm springs earthquake were generated by electrokinetic effects also there are no indications of en hanced low frequency magnetic noise before the earthquake at frequencies be low 0 001 hz

fractal analysis of ulf geomagnetic data associated with the guam earthquake on august 8 1993 this paper presents a fractal analysis of the ulf electromagnetic data obtained at guam observatory during a strong ms 8 0 earthquake occurred on august 8 1993 near the guam island we have already reported the presence of seismogenic ulf emissions for this quake hayakawa et al grl 1996 the chosen period covered four months before and two months after the earthquake it was found that the spectrum of emissions at noon exhibited a power law behavior f which is typical for self organized critical dynamics the slope of the spectrum in the noon sector fluctuates in a range from 2 5 to 0 7 with a tendency to gradually decrease during the process of the earthquake preparation we consider this to be a candidate for a precursory signature the similar effect was found for the night sector we suggest that the focal zone was at the critical stage of self organized criticality process before the quake related to active microfracturing processes followed by the generation of ulf emissions as we detected

orbital tuning chronology for the vostok climate record supported by trapped gas composition abstract we present data on the o2 n2 ratios of trapped gas samples for the entire length of the vostok climate record as in other cores o2 n2 ratios in these samples are less than the atmospheric ratio by a small and variable amount because o2 is selectively excluded during the gas trapping process and because o2 is also preferentially lost in poorly preserved core samples samples younger than 150 ka have large and variable o2 depletions samples older than 200 ka have o2 n2 ratios that replicate well and vary smoothly with depth we plot o2 n2 ratios of well replicated samples older than 160 ka using a chronology derived by matching the 18o of paleoatmospheric o2 18oatm to northern hemisphere june insolation on this timescale o2 n2 varies coherently with local 78 s summertime insolation based on time series analysis of the o2 n2 record and the dynamics of snow metamorphism at the surface we conclude that summertime insolation influences physical properties of ice grains that control the degree of o2 exclusion during bubble closeoff o2 n2 in vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core we show that the 18oatm chronology supported by the coincidence of o2 n2 ratios with insolation is also compatible with recent radiometric dating of corals from high sea stands we further successfully test the 18oatm tuning chronology by showing that it predicts a chronology for the gisp2 core which is essentially indistinguishable from the standard gisp2 chronology and therefore in excellent agreement with the radiometric chronology of hulu cave china an accurate chronology for the vostok ice core is now in place

air clathrate crystals from the grip deep ice core greenland a number size and shape distribution study we performed microscopic observations and a statistical study of the number size and shape distribution of clathrates in the grip greenland ice core project deep ice core using 185 samples from a depth range of 1016 3014m spanning a period of 6 to 110 ka sp and encompassing the holocene wisconsin and eemian periods the number concentration of the clathrates varied considerably with climatic changes it was possible to detect the rapid climatic oscillations in the last glacial between 13 and 110 ka bp the dansgaard oeschger cycles in the number concentration profile of clathrates the mean volume of clathrates is less clearly influenced by climatic factors with a tendency towards greater volumes in warmer periods but also a growth of clathrates with depth could be detected this growth rate was calculated to be 3 1 x 10 12 cm 3 a 1 the amount of gases captured in the clathrates is estimated to be significantly smaller than the total amount of air determined by gas concentration measurements this points to diffusion processes of atmospheric gases within the ice matrix

near surface geophysical techniques for geohazards investigations some canadian examples over the last 40 years there has been an expansion of activity in applications of near surface geophysical techniques for various types of geohazards investigations in canada numerous national and international research groups have been working with the near surface geophysics section of the geological survey of canada to develop techniques for specific canadian engineering and environmental geohazards problems a few of the more interesting examples from widespread parts of the country are discussed in this paper

seismic survey for detecting scour depths downstream of the srisailam dam andhra pradesh india abstract during the construction of the srisailam dam deep scour was observed near the dam toe various protection measures were taken between 1977 and 1987 but in 1987 soundings revealed a scour hole at a distance of 206 m downstream of the reference line in 1995 this scour hole was about 61 m upstream it was thus feared that scouring may affect the stability of the downstream protection works to define this problem more clearly a seismic reflection survey was conducted along 24 traverses covering an area of 67 000 m2 and a seismic refraction survey was carried out along eight profiles with shots at either end the refraction profiling using an array of vertical hydrophones was carried out in the deepest part of the downstream pool of water this survey revealed an overburden with a velocity varying from 2000 to 2600 m s that was underlain by quartzite with a velocity of 4000 to 5500 m s the depth to rock varied between 2 0 and 14 0 m from the river bed seismic reflection results determined the areal configuration of the river bed and the sediment thickness the river bed level varied from 137 2 to 155 4 m and slopes steeply from both the banks the rock level is 152 4 m at a distance of 50 m from the reference line of the dam towards the power house and is 134 1 m at a distance of 130 m the rock levels towards the left bank are deeper than the 1968 1969 borehole rock levels indicating that scouring has taken place and the depth of scouring was found to vary from 2 to 4 m

variation in n2 o2 ratio of occluded air in dome fuji antarctic ice ancient atmospheric gases are trapped in polar ice sheets the gas molecules are stored in air bubbles at shallow depth and are incorporated into clathrate hydrates below a depth at which the hydrostatic pressure becomes greater than the formation pressure of the air clathrate hydrate significant gas fractionation has been found from measurements of the depth profile of the n2 o2 composition ratios in clathrate hydrates and air bubbles of vostok antarctic ice to investigate the effect of the ice condition on the fractionation process we measured the n2 o2 ratios in clathrate hydrates and air bubbles from dome fuji antarctic ice using raman spectroscopy the results showed that the n2 o2 ratios in the clathrate hydrates of the dome fuji ice are slightly lower than those of the vostok ice although the tendency of the variation of the n2 o2 ratio with depth is similar the difference in the n2 o2 ratio between the dome fuji ice and the vostok ice for the transition zone is attributed to the difference of the ice temperature and the snow accumulation rate on the other hand it is concluded that the difference in the bubble free ice zone was caused by gas loss from the ice core after coring the n2 o2 ratio of clathrate hydrate increases after coring because of higher diffusion rate and lower dissociation pressure of o2 than of n2 our data suggest that the effect of gas loss in the dome fuji ice is relatively small and so the gas composition in the dome fuji ice can be a precise paleoenvironmental indicator

a vertical array method for shallow seismic refraction surveying of the sea floor in recent years specific requirements of offshore geotechnical site investigations as well as detailed defense research studies have stimulated research interest in methods for measuring seismic velocities of sea floor sediments on the continental shelves investigations have used wide angie subbottom reflection measurements mckay and mckay 1982 bottom laid refraction cables hunter et al 1979 and towed refraction arrays both on the surface hunter and hobson 1974 and at depth fortin et al 1987 fagot 1983

co seismic geoelectric potential changes observed in japan co seismic signals of geoelectric potential have been observed for several earthquakes eqs in japan it has been argued that if there are precursory changes stronger signals should be at the time of eq our results prove that co seismic signals do exist but they start with the arrival of seismic waves and not at the origin time of eqs their amplitude does not scale with the dipole length both facts indicate that the changes are local effects of passing seismic waves and not due to electric signals emitted from the seismic source observed changes contain two components oscillatory and offset decay ones the former is synchronized with seismic waves whereas the latter with a rise time of a few seconds and a decay time of 0 1 1 hour is suspected to be related to eq induced subsurface hydrological change in both cases the origin of electric potential variations may be electrokinetic

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

head wave data inversion for geoacoustic parameters of the ocean bottom off vancouver island head wave signals from small explosive charges have been analyzed to determine a geoacoustic profile for a shallow water site off the west coast of vancouver island the experimental design contained a vertical aperture provided by a vertical line array and a synthetic horizontal aperture from shots at different ranges from the vertical line array the simultaneous use of travel time and amplitude data for both apertures provided improved accuracy and vertical resolution of the estimated geoacoustic profile travel time vs range data from head waves from three distinct sub bottom interfaces were used to measure compressional speeds in the layers below the interfaces and estimate the layers thicknesses spatial filtering of the vertical line array data was necessary to resolve the head wave arrival from the shallowest layers analysis of the interference structure of the head wave power spectra at the vertical line array provided the means to measure the travel time of the head wave from the deepest layer in addition the head wave power spectra were used to estimate the compressional wave attenuation using a method based on the variation with range of the logarithmic derivative with respect to frequency of the head wave spectrum

numerical simulation of coseismic electromagnetic fields associated with seismic waves due to finite faulting in porous media summary the electrokinetic effect is one mechanism that causes the coupling between seismic and electromagnetic energies this study deals with the numerical simulation of the electrokinetically induced coseismic electromagnetic fields associated with seismic waves created by a finite faulting in porous media the key point of our numerical technique is to combine the point source stacking method with the luco apsel chen generalized reflection and transmission method after some validation test of our simulation method we show several numerical simulation examples through a near field model we show that the point source approximation is not accurate in this configuration as well as that the position of the rupture starting point and rupture speed obviously affect the coseismic em fields then we numerically investigate the influence of different media properties on seismic waves and coseismic em fields we also carry out simulations of multilayer half space models and show the characteristics of the coseismic em fields the preliminary results indicate that our numerical technique provides an effective approach of studying coseismic electromagnetic fields associated with seismic waves due to a finite faulting in porous media

revision of the epica dome c co2 record from 800 to 600 kyr before present the european project for ice coring in antarctica dome ice core from dome c edc has allowed for the reconstruction of atmospheric co2 concentrations for the last 800 000 years here we revisit the oldest part of the edc co2 record using different air extraction methods and sections of the core for our established cracker system we found an analytical artifact which increases over the deepest 200 m and reaches 10 1 2 4 ppm in the oldest deepest part the governing mechanism is not yet fully understood but it is related to insufficient gas extraction in combination with ice relaxation during storage and ice structure the corrected record presented here resolves partly but not completely the issue with a different correlation between co2 and antarctic temperatures found in this oldest part of the records in addition we provide here an update of 800 000 years atmospheric co2 history including recent studies covering the last glacial cycle

retrospective investigation of geomagnetic field time series during the 2009 l aquila seismic sequence abstract this paper reports the analyses of ulf ultra low frequency geomagnetic field observations coming from the geomagnetic observatory of l aquila during the period 2008 2009 this period includes the l aquila 2009 seismic sequence where the main shock of 6 april heavily damaged the medieval centre of the town and its surrounding area causing 308 deaths more than 1000 injuries and about 60 000 displaced people recently several publications have documented the observation of precursory signals which occurred before the 6 april earthquake e g eftaxias et al 2009 2010 while others do not find any pre earthquake anomaly e g villante et al 2010 di lorenzo et al 2011 in light of this the goal of this study is to carry out further retrospective investigations ulf magnetic field data are investigated by means of conventional analyses of magnetic polarization ratio improved magnetic polarization ratio and fractal analysis in addition total geomagnetic field data coming from the ingv central italy tectonomagnetic network have also been investigated using the simple inter station differentiation method within the limits of these methods no magnetic anomalous signal which may be reasonably characterized as a precursor of the l aquila earthquakes has been found

on the reported magnetic precursor of the 1989 loma prieta earthquake among the most frequently cited reports in the science of earthquake prediction is that by fraser smith et al 1990 and bernardi et al 1991 they found anomalous enhancement of magnetic field noise levels prior to the 18 october 1989 loma prieta earthquake in the ultra low frequency range 0 0110 10 001 hz from a ground based sensor at corralitos ca just 7 km from the earthquake epicenter in this analysis we re examine all of the available corralitos data 21 months from january 1989 to october 1990 and the logbook kept during this extended operational period we also examine 1 0 hz 1 s data collected from japan 0 0167 hz 1 min data collected from the fresno ca magnetic observatory and the global kp magnetic activity index the japanese data are of particular importance since their acquisition rate is sufficient to allow direct comparison with the lower frequency bands of the corralitos data we identify numerous problems in the corralitos data evident from both straightforward examination of the corralitos data on their own and by comparison with the japanese and fresno data sets the most notable problems are changes in the baseline noise levels occurring during both the reported precursory period and at other times long before and after the earthquake we conclude that the reported anomalous magnetic noise identified by fraser smith et al and bernardi et al is not related to the loma prieta earthquake but is an artifact of sensor system malfunction 2008 elsevier b v all rights reserved

compressional wave velocity measurement in seabed materials by use of equipment deployed near but above the bottom for the measurement at midaudio frequencies of the acoustic compressional wave velocity methods are described which make use of either the refraction or the wide angle reflection techniques in ways which do not require station keeping by the survey vessel as when equipment is deployed on the bottom but still minimize the adverse effect of a long water column between the sensing equipment and the seabed some results from areas on the nova scotia shelf are presented ranging from about 3 0 km s in a nearshore sedimentary rock sequence through 1 6 km s on a shelf edge sandbank to 1 25 km s in a deep intrashelf basin

erosion rates during rapid deglaciation in icy bay alaska 1 contemporary glacial erosion rates based on sediment yields in southeast alaska merit considerable attention because they are unsurpassed worldwide and they significantly exceed long term exhumation rates in the region two issues are likely to contribute to these high rates contemporary sediment yields in fjords 1 have generally been overestimated by failing to account for the considerable input of subaerially derived material and 2 are exceptionally high because tidewater glaciers in southeast alaska have been anomalously dynamic and erosive during the past century of rapid retreat to investigate these influences and to quantify the rate at which tyndall glacier erodes its basin we present seismic data defining the volume of sediments in taan fjord icy bay we subtract the contribution of subaerially derived sediments from the fjord sediment package to determine the sediment yield directly from tyndall glacier during the most recent period of retreat 1962 1999 using a numerical model of proglacial glacimarine sedimentation we then calculate the annual sediment yield from and the corresponding erosion rate of tyndall glacier during this period which averages 28 5 mma 1 a strong correlation emerges between glacial retreat rates and glacial sediment yields implying that most contemporary sediment yield data from retreating tidewater glaciers may correspond to contemporary erosion rates that are a factor of 3 5 1 5 higher than in the long term hence we estimate the long term erosion rate for tyndall glacier to be 9 2 mma 1

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

co2 and o2 n2 variations in and just below the bubble clathrate transformation zone of antarctic ice cores co2 measurements on the epica european project for ice coring in antarctica dml ice core in depth levels just below the bubble ice clathrate ice transformation zone 1230 2240 m depth were performed in the youngest part 1230 1600 m they reveal variations of up to 25 ppmv around the mean atmospheric concentration within centimetres corresponding to a snow deposition interval of a few years similar results are found at corresponding depth regions of the dome c and the talos dome ice cores since we can exclude all hitherto known processes altering the concentration of co2 in ice cores we present a hypothesis about spatial fractionation of air components related to episodically increasing clathrate formation followed by diffusion processes from bubbles to clathrates this hypothesis is supported by optical line scan observations and by o2 n2 measurements at the same depth where strong co2 variations are detected below the clathrate formation zone this small scale fractionation process is slowly smoothed out most likely by diffusion regaining the initial mean atmospheric concentration although this process compromises the representativeness of a single co2 measurement on small ice samples in the clathrate formation zone of an ice core it does not affect the mean atmospheric co2 concentration if co2 values are averaged over a sufficiently long depth scale 10 cm in case of the epica dml ice core

northern hemisphere forcing of climatic cycles in antarctica over the past 360 000 years the milankovitch theory of climate change proposes that glacial interglacial cycles are driven by changes in summer insolation at high northern latitudes the timing of climate change in the southern hemisphere at glacial interglacial transitions which are known as terminations relative to variations in summer insolation in the northern hemisphere is an important test of this hypothesis so far it has only been possible to apply this test to the most recent termination because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined here we present a new chronology of antarctic climate change over the past 360 000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the dome fuji and vostok ice cores this ratio is a proxy for local summer insolation5 and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter the accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation our results indicate that orbital scale antarctic climate change lags northern hemisphere insolation by a few millennia and that the increases in antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of northern hemisphere summer insolation these results support the milankovitch theory that northern hemisphere summer insolation triggered the last four deglaciations

high resolution variations in size number and arrangement of air bubbles in the epica dml antarctica ice core abstract we investigated the large scale 10 1000m and small scale mm cm variations in size number and arrangement of air bubbles in the epica dronning maud land edml antarctica ice core down to the end of the bubble hydrate transition bht zone on the large scale the bubble number density shows a general correlation with the palaeo temperature proxy d18o and the dust concentration which means that in holocene ice there are fewer bubbles than in glacial ice small scale variations in bubble number and size were identified and compared above the bht zone there exists a strong anticorrelation between bubble number density and mean bubble size in glacial ice layers of high number density and small bubble size are linked with layers with high impurity content identified as cloudy bands therefore we regard impurities as a controlling factor for the formation and distribution of bubbles in glacial ice the anticorrelation inverts in the middle of the bht zone in the lower part of the bht zone bubble free layers exist that are also associated with cloudy bands the high contrast in bubble number density in glacial ice induced by the impurities indicates a much more pronounced layering in glacial firn than in modern firn

physicochemical properties of bottom ice from dome fuji inland east antarctica the deepest ice in inland antarctica is expected to preserve the oldest ice records and to potentially contain microorganisms however little is known about the physicochemical conditions in the deepest part of ice sheets this study investigates the physicochemical properties of the bottom section 3000 3035 m of the dome fuji inland ice core which is located immediately above unfrozen bedrock the ubiquitous presence of air hydrates and the water isotope composition of ice comparable to the upper main ice core show that the bottom ice is meteoric however ion concentrations exhibit abnormal drops at the greatest depths approximately below 3033 m in the same depth range microscopic investigations reveal that considerable relocation of air hydrates and micro inclusions water soluble impurities occurs suggesting that the observed reduction in ion concentration results from the segregation of inclusions to ice grain boundaries and the subsequent discharge of chemicals through liquid water veins principal component analysis of ion data supports the meteoric ice hypothesis suggesting that the bottom ice had similar original chemistry through all depths statistical analyses of chemical data suggest that the water soluble impurities attached to hydrates or dust water insoluble the ice soluble chemical species such as chlorine and solid particles are less affected by this chemical displacement phenomenon it is also noteworthy that in the bottom ice impurity chemicals which are limiting nutrients for ice dwelling microorganisms are concentrated largely to ice hydrate interfaces where oxygen another vital matter for aerobic microorganisms is also enriched

experimental evidence of electrification processes during the 2009 l aquila earthquake main shock two types of coseismic magnetic field events are simultaneously observed transient offset events and magnetic field signal that occurred at the destructive mw6 1 l aquila earthquake main shock the offset event conventionally interpreted as a signature of piezomagnetic effects however could not be explained as such in the second type of coseismic event the transient magnetic signal starts simultaneously with the offset event and reaches amplitude of 0 8 nt in the total magnetic field the signal is a local one its amplitude shape resembles diffusion like form with time scale characteristics that are indicative for a source deep in the crust the polarity of the transient signal is in the horizontal plane and nearly parallel to the l aquila fault strike

formation of air clathrate hydrates in polar ice sheets heterogeneous nucleation induced by micro inclusions to investigate factors influencing nucleation of air clathrate hydrates in polar ice sheets we have performed high resolution mapping of the distributions of soluble impurities air bubbles and air hydrate crystals versus depth in the dome fuji antarctic ice significant correlation observed between the concentrations of air inclusions and impurities in ice along with frequent occurrence of impurities inside hydrate crystals suggest that micro inclusions promote hydrate nucleation in the ice matrix our observations also show that the diffusive macroscopic scale redistribution of air constituents in ice in the bubble hydrate transition zone is controlled by the original sedimentary layering of soluble impurities acting as nucleation helpers the results of this study are important for the correct interpretation of high resolution gas analyses of ice cores and for better understanding the global bubble to hydrate transformation process in polar ice sheets

air bubbles and clathrate hydrates in the transition zone of the ngrip deep ice core abstract field studies of air bubble and clathrate inclusions in the ngrip ice core reveal two stages of clathrate formation in the transition zone translucent primary clathrates with rough surfaces and irregular shapes formed from individual bubbles split up and form smaller specimens deeper down in the transition zone 1100 m clathrate metamorphosis sets in giving rise to the formation of transparent secondary clathrates with smooth and regular often poly hedral or faceted shapes rod like crystals of great length 2 mm often show signs of separation into smaller units that fragment into smaller specimens these findings imply that the simplified picture of one bubble forming one clathrate has to be modified

crystal growth of air hydrates over 720 ka in dome fuji antarctica ice cores microscopic observations of morphological changes below 2000 m depth air hydrate crystals store most of the ancient air contained in deep ice sheets we carried out microscopic observations of air hydrate crystals below 2000 m depth within the ice core from dome fuji antarctica to obtain their number and size distributions we found that the number density continuously decreased with depth whereas the average size increased in contrast to findings from shallower depths in addition the characteristic perturbations in both number density and average size distribution with climatic changes almost disappeared although they are clearly observed in shallow cores these results indicate that the air hydrate crystals grow considerably in deeper parts of the ice sheet and this growth is accompanied by the diffusion of air molecules in the ice the permeation coefficient of the air molecules in the ice sheet was estimated from the geometric parameters of the air hydrate distributions this is the first practical evidence comparable to the previous model estimations it allows us to evaluate the impacts of the air molecule migration in the ice sheet on the paleoclimatic information recorded in the deep ice cores

seismomagnetic effects from the long awaited 28 september 2004 m 6 0 parkfield earthquake precise measurements of local magnetic fields have been obtained with a differentially connected array of seven synchronized proton magnetometers located along 60 km of the locked to creeping transition region of the san andreas fault at parkfield california since 1976 the m 6 0 parkfield earthquake on 28 september 2004 occurred within this array and generated coseismic magnetic field changes of between 0 2 and 0 5 nt at five sites in the network no preseismic magnetic field changes exceeding background noise levels are apparent in the magnetic data during the month week and days before the earthquake or expected in light of the absence of measurable precursive deformation seismicity or pore pressure changes obser vations of electric and magnetic fields from 0 01 to 20 hz are also made at one site near the end of the earthquake rupture and corrected for common mode signals from the ionosphere magnetosphere using a second site some 115 km to the northwest along the fault these magnetic data show no indications of unusual noise before the earthquake in the ulf band 0 01 20 hz as suggested may have preceded the 1989 ml 7 1 loma prieta earthquake nor do we see electric field changes similar to those suggested to occur before earthquakes of this magnitude from data in greece uni form and variable slip piezomagnetic models of the earthquake derived from strain displacement and seismic data generate magnetic field perturbations that are con sistent with those observed by the magnetometer array a higher rate of longer term magnetic field change consistent with increased loading in the region is apparent since 1993 this accompanied an increased rate of secular shear strain observed on a two color edm network and a small network of borehole tensor strainmeters and increased seismicity dominated by three m 4 5 5 earthquakes roughly a year apart in 1992 1993 and 1994 models incorporating all of these data indicate increased slip at depth in the region and this may have played a role in the final occurrence of the 28 september 2004 m 6 0 parkfield earthquake the absence of electric and magnetic field precursors for this and other earthquakes with m 5 7 3 elsewhere in the san andreas fault system indicates useful prediction of damaging earthquakes seems unlikely using these electromagnetic data

seismic signals and noise recorded on a seafloor vertical hydrophone array and a colocated obs during the lfase experiment abstract during the lfase experiment conducted in the summer of 1989 a vertical hydrophone array vha was deployed at the site of dsdp hole 534b in the blake bahama basin the vha consisted of 16 hydrophones spaced 30 m apart rising vertically above the seafloor with the bottom of the array anchored to a digital recording package located on the seafloor the main purpose of the experiment was to record seismic signals and noise above on and beneath the seafloor at the same site the vha recorded data from above the seafloor an ocean bottom seismograph obs was on the seafloor and a borehole geophone array bha was in a borehole beneath the seafloor signal to noise measurements of p waves made for airgun shots recorded simultaneously by the vha and the obs show that the obs has a signal to noise ratio snr 5 to 10 db greater than that of a single hydrophone but p wave stacks of the vha data have snrs for body waves 10 to 15 db greater than the obs this implies that a vertical array is capable of recording distinct body waves out to significantly greater ranges than is a single receiver and so might be a useful tool in seismic refraction experiments other stacks of the vha data revealed s waves not visible on the data from a single hydrophone or geophone the vha was also used to construct images of the wavefronts arriving from a distant source and to determine the vertical direction of the source this array processing capability shows the potential of vhas for use in 3d seismic reflection surveys particularly in cases where it is not convenient to use a multi channel streamer

geomagnetic field changes in response to the 2011 off the pacific coast of tohoku earthquake and tsunami abstract does the geomagnetic field change in association with earthquakes this question was first raised more than 100 years ago and since that time theoretical and observational researches have been conducted in order to obtain an answer to this question large earthquakes provide an opportunity to examine this problem because large signals are generally expected in association with large earthquakes we herein present a brief report on simultaneous measurements of the geomagnetic field in association with the 2011 tohoku earthquake m9 0 and tsunami by magnetometers at 14 stations operating in japan since the earthquake occurred during a geomagnetic storm we used time series after correcting the effect of external disturbances and induced fields a coseismic change of the geomagnetic field was observed at several stations located relatively close to the epicenter the magnitude of this coseismic change was only about 0 8 nt at one station and much smaller at other stations which prevented us from quantitatively comparing these observations with predictions based on piezomagnetic theory more distinct and rapid changes were observed during the hours following the main shock these changes are supposed to be caused either by motional induction of the tsunami or by ionospheric disturbance contrary to the significant observations of these coseismic and postseismic geomagnetic changes in response to the tohoku earthquake and tsunami we did not observe any clear precursors

spatial and temporal variations in growth rates along active normal fault systems an example from the lazio abruzzo apennines central italy abstract the geometry kinematics and rates of active extension in lazio abruzzo italian apennines have been measured in order to gain a better understanding of the spatial and temporal variations in fault growth rates and seismic hazards associated with active normal fault systems we present fault map traces throws throw rates and slip directions for 17 parallel en echelon or end on active normal faults whose 20 40 km lengths combine to form a soft linked fault array ca 155 km in length and ca 55 km across strike throw rates derived from observations of faulted late glacial features and holocene soils show that both maximum throw rates and throw rate gradients are greater on centrally located faults along the strike of the array total throws and throw gradients show similar spatial variations but with weaker relationships with distance along strike when summed across strike throw rates are increasingly high towards the centre of the array relative to summed throws we interpret the above to suggest that throw rates have changed in the recent past ca 0 7 ma from spatially random fault growth rates initiating at 2 5 3 3 ma to growth rates that are greater on centrally located faults we interpret this as evidence for fault interaction producing throw rate variations that drive throw profile readjustment on these crustal scale soft linked faults the results are used to discuss seismic hazards in the region which are quantified in a second paper in this issue

air bubble to clathrate hydrate transformation in polar ice sheets a reconsideration based on the new data from dome fuji ice core 1 mapping the spatial distribution of air bubbles and clathrate hydrates in thick sections of antarctic ice from dome fuji station reveals a considerable redistribution of the inclusions in terms of number and volume in the bubble to hydrate transition zone analysis of the data indicated that more than 10 of the hydrates nucleated outside the preceding bubbles and more than 30 of the bubbles completely expired due to the gas outflow toward the coexisting hydrates these features of the gas hydrate ice nonequilibrium system are of major importance for modeling the global bubble to hydrate transformation in polar ice sheets and thus the results may help improve our ability to extract paleoclimatic information from air inclusions in ice cores

crystalline texture of the 2083 m ice core at vostok station antarctica crystalline texture and c axis orien tation of the 2083 m ice core at vostok station covering more than 150 kyear reveal the existence of strong anisotropies changes in crystal size with depth are compatible with the growth of grains driven by the free energy of grain boundaries a smaller growth rate appears to be associated with cold periods a gradual increase in the horizontal elongation of grains was observed between 350 and 680 m but the mean value of the coefficient of the linear dimensional orientation of grains does not cha nge below 700 m the e axis orientation of ice grains tends to orientate perpendicular to the direction of the elongation of grains forming a vertical girdle patt ern this charac teristic fabric has been interpreted as resulting from the gradual rotation of grains by basal glide under uniaxial longit udi nal tension the rotation of grains was calcu lated with respect to the total strain simulating the form ation of the girdle fabric pattern the fabric enhance ment factor was calculated at various depths it appears that vostok ice hardens gradua lly