electrokinetic experimental study on saturated rock samples zeta potential and surface conductance summary it is important to know the electrokinetic properties of crustal rocks for interpreting the conductivity mechanisms and seismoelectric phenomena during earthquakes and seismoelectric well logging in this study electrokinetic experiments are conducted using a special coreholder by employing an ac lock in technique a series of experiments are conducted on 10 sandstone samples to measure the streaming potentials and streaming currents and the experiments on each sample are done at six different salinities the streaming potential coefficient and streaming current coefficient are calculated from the measured streaming potentials and streaming currents the experimental results show that streaming potential coefficient and streaming current coefficient decrease as the salinity increases the dependence of these two coefficients on permeability and pore radius are analysed and compared with previous works at low salinities the streaming potential coefficient and streaming current coefficient increase with the increasing permeability and pore radius at high salinities the streaming potential coefficient streaming current coefficient almost share a same value for 10 different samples this conclusion indicates that the differences of rock parameters can only be well recognized at lower salinities and the electrokinetic signals are invalid at high salinities which offers a restrictive condition for using the amplitude of electrokinetic signals to estimate rock parameters the zeta potential have also been estimated through combined measurements of streaming potential and streaming current the surface conductivity and its contribution to electrokinetic effects are determined from a comparison of zeta potentials by two different methods and then the validation of the helmholz smoluchowski equation for a capillary tube is tested in rocks we also compare our date with theoretical and experimental works and set up an expression about the relationship between zeta potential and salinity which fits the experimental data well

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

mineralized and unmineralized calderas in spain part i evolution of the los frailes caldera the cabo de gata volcanic field of southeastern spain contains several recently recognized calderas some of the calderas are mineralized with epithermal gold alunite and base metal deposits and others are barren and yet they formed under generally similar conditions comparison of the magmatic geochemical and physical evolution of the los frailes rodalquilar and lomilla calderas provides insight into the processes of caldera evolution that led to precious metal mineralization the los frailes caldera formed at 14 4 ma and is the oldest caldera it formed in response to multiple eruptions of hornblende dacite magma following each eruption the area collapsed and the caldera was invaded by the sea dacite domes fill the lower part of the caldera pyroxene andesites were erupted through the solidified core of the caldera and were probably initially responsible for magma generation the los frailes caldera did not evolve to rhyolites nor was it subjected to the amount of structural development that the younger mineralized rodalquilar and lomilla calderas were

stress strain state monitoring of the geological medium based on the multi instrumental measurements in boreholes experience of research at the petropavlovsk kamchatskii geodynamic testing site kamchatka russia we present the results of the long term study which make it possible to assess the possibilities of two methods used at the petropavlovsk kamchatskii geodynamic site russia for continuous monitoring of the stress strain state of geoenvironment the methods are based on the borehole geoacoustic measurements and electromagnetic measurements with underground electric antennas combined with hydrogeochemical and hydrogeodynamic borehole measurements these methods allow monitoring the changes in the parameters of geological environment and identifying the stages in the changes of its stress strain state as the examples we present the results of the measurements in the time vicinities of the strongest seismic events that occurred during the period of joint borehole geoacoustic and electromagnetic measurements at the petropavlovsk kamchatskii geodynamic site we also analyze the data obtained in the time vicinities of the tohoku mega earthquake march 11 2011 japan mw 9 1 and a close strong zhupanovskoe earthquake january 30 2016 mw 7 2 that occurred at the epicentral distances r 107 km from petropavlovsk kamchatskii it is shown that the discussed methods are promising for medium and short term forecasting of the earthquakes

dynamic modeling of the 2004 mw 6 0 parkfield california earthquake 1 we present two spontaneous rupture models of the 2004 mw 6 0 parkfield earthquake constrained by near source ground motions we start with a stress drop distribution calculated from a kinematic slip distribution using a linear slip weakening friction law we utilize trial and error to obtain both the stress conditions and frictional parameters on the fault that produce synthetics consistent with records the material contrast across the san andreas fault is incorporated using different one dimensional velocity structures on each side of the fault an approximately constant s parameter of 0 3 and a uniform slip weakening distance of 0 15 m are used in the dynamic models in our preferred dynamic model consistent with the ground motion and gps the slip is bounded by seismicity streaks at 5 and 10 km depths confirming a locked zone at depth the stress drop is approximately 10 mpa in the hypocentral region and about 2 mpa elsewhere the material contrast across the fault causes significant normal stress variations 1 mpa leading to a larger strength drop to the southeast than to the northwest the main rupture front propagates at nearly a constant subshear rupture velocity 3 km s in both directions the total radiated energy determined from the preferred dynamic model is 1 1 1013 j seismic moment is 1 0 1018 nm and fracture energy is 3 0 1013 j the limited number of aftershocks in the slipped area suggests the important role of stress on the distribution of seismicity in the locked zone

a comparison of miocene and archean rhyolite hyaloclastites evidence for a hot and fluid rhyolite lava abstract in this paper we compare the geology and petrography of miocene and archean submarine rhyolite hyaloclastites the hyaloclastites are sparsely 10 or less plagioclase quartz and pyroxene phyric the hyaloclastites consist of a feeder dyke from which branch lava lobes and irregularly shaped lava pods the lava bodies consist of a holocrystalline core with microlitic texture grading outward into a flow layered rim zone and finally into obsidian the proportion of plagioclase and pyroxene microlites decreases outward some layers of the rim zone may be pumiceous vesicularity up to 50 vesicle size 1 mm or less but most of the lava has less than 5 vesicles one or a few cm long the obsidian shows perlitic fracture patterns the lava bodies grade through an in situ breccia into a hyaloclastite composed of angular obsidian granules and in many cases of fragments of lava lobes evidence for alteration at high temperature is as follows in the archean rhyolite hyaloclastites plagioclase microlites are overgrown by quartz albite spherulites furthermore parts of the miocene and archean hyaloclastite have been cemented and granules have been marginally replaced by quartz and albite hyaloclastite cemented at high temperature locally shows columnar joints at low temperatures obsidian has been hydrated and or has been replaced by clay minerals zeolites chlorite or prehnite chess board albite and fibroradial prehnite in archean hyaloclastite is possibly a pseudomorph after zeolites the sparsely porphyritic nature of the lava and the absence of microlites from the quenched glass suggests that the thyolite hyaloclastites extruded at high near liquidus temperature furthermore pumice is present only locally in the flow layered rim zone and in fragments derived from that zone these features suggest that vesiculation was inhibited by the weight of the water column high temperature and possibly the volatile h 2 o content explain the relatively low viscosity and shear strength of the lava and resulted in the flow morphology particular to this type of hyaloclastic rhyolite flows

a model for submarine rhyolite dome growth ponza island central italy abstract the late pliocene rhyolitic submarine volcanic rocks of ponza island italy can be interpreted as the subaqueous equivalent of subaerial dome complexes in terms of geometry and structure three coalescing domes of about 1 km radius and aligned along a ne trending regional fracture have been identified the main difference between subaqueous and subaerial lava domes is that in a subaqueous environment lava is likely to undergo pervasive hyaloclastic brecciation so that domes are mainly composed of variously brecciated in situ to clast rotated hyaloclastite rather than coherent lava we suggest that the shape and rheologic behaviour through time of submarine domes are closely controlled by the development and thickness of the particulate hyaloclastic carapace which assumes the role of the solid crust of domes in subaerial environment the thickness of the hyaloclastic carapace at ponza is greater than 150 m and emplaced during several different pulses or eruptions in the earliest pulses lava is directly extruded on the seafloor and produces hyaloclastite the degree of brecciation of which decreases inward to the coherent flow banded rhyolite lava of the feeder dike once the hyaloclastic carapace is formed further pulses of magma combined with increase in height of the dome result in a local stress pattern characterised by a vertical 1 2 3 producing concentric and radial fractures and normal faults the newly rising magma shielded by the hyaloclastic carapace can intrude along these fault and fracture systems and invade previously emplaced but still water saturated hyaloclastite this produces the characteristic pattern of dikes observed at ponza as a series of concentric dikes that are progressively less inclined outward with respect to the dome centre these late stage dikes in turn produce hyaloclastite at their margins but generally less fragmented than the embedding hyaloclastite probably because the ascending magma is better shielded from direct contact with sea water periodic gravity collapses of the dome maintain the equilibrium between height and radius of the dome as suggested at ponza by the presence of mass flow deposits and the development of small topographic basins on top of the domes probably related to debris removal some of these topographic depressions host subaqueous pyroclastic deposits suggesting that if due to vertical growth of the dome water depth above the dome becomes shallower hydromagmatic explosions may occur

submarine pyroclastic deposits formed at the soufriere hills volcano montserrat 1995 2003 what happens when pyroclastic flows enter the ocean the soufriere hills volcano montserrat west indies has undergone a series of dome growth and collapse events since the eruption began in 1995 over 90 of the pyroclastic material produced has been deposited into the ocean sampling of these submarine deposits reveals that the pyroclastic flows mix rapidly and violently with the water as they enter the sea the coarse components pebbles to boulders are deposited proximally from dense basal slurries to form steep sided near linear ridges that intercalate to form a submarine fan the finer ash grade components are mixed into the overlying water column to form turbidity currents that flow over distances 30 km from the source the total volume of pyroclastic material off the east coast of montserrat exceeds 280 106 m3 with 65 deposited in proximal lobes and 35 deposited as distal turbidites

cyclic eruptions and sector collapses at monowai submarine volcano kermadec arc 1998 2007 1 repeated multibeam bathymetric surveys at monowai cone a shallow submarine basaltic volcano and part of the monowai volcanic center in the northern kermadec arc were conducted in 1998 2004 and 2007 these surveys document dramatic depth changes at the volcano including negative changes up to 176 m from two sector collapses and positive changes up to 138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars one sector collapse occurred on the se slope between 1998 and 2004 with a volume of 0 09 km3 and another occurred on the sw slope between 2004 and 2007 with a volume of 0 04 km3 the volume of positive depth change due to addition of volcanic material by eruption is of the same order 0 05 km3 between 1998 and 2004 and 0 06 km3 between 2004 and 2007 during these time intervals monitoring by the polynesian seismic network detected frequent t wave swarms at monowai indicative of explosive eruptive activity every few months an unusual t wave swarm on 24 may 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys but no similarly anomalous t waves were detected between 2004 and 2007 probably because the polynesian seismic network stations were acoustically shadowed from the second slide event we interpret that the sector collapses on monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano 20 moreover there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano volumetric rate calculations suggest that these two processes may be more or less in equilibrium the repeated collapses at monowai are relatively modest in volume involving only 0 1 0 5 of the edifice volume have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes and may be characteristic of how persistently active shallow submarine arc volcanoes grow

eruption fed particle plumes and volcaniclastic deposits at a submarine volcano nw rota 1 mariana arc 1 nw rota 1 is an active submarine volcano in the mariana arc with a summit depth of 517 m and an explosively erupting volcanic vent southwest of the summit at a depth of 530 560 m during a period of ongoing explosive eruptions particle plumes surrounded the volcano and at least 3 3 107 m3 of volcaniclastic material was deposited on the southern flank particle plumes over the summit were magmatic hydrothermal in origin characterized by 3he enrichment hydrothermal precipitates and low ph values plumes at multiple depths below the summit surrounded the volcano and were composed overwhelmingly of fresh glassy shards of basalt rare anhydrite particles were present but there was a complete absence of other hydrothermal components in the deep plume samples these short lived anhydrite particles indicate the source of the deep plumes is from within or very near the eruptive vent and the mechanism for transport down the flanks of the volcano must be far faster than settling of individual particles the deep plumes most likely originated from sediment gravity flows generated by explosive eruptions or slope failure and landslides of unstable materials that had accumulated near the eruptive vent suspended sediments detach from the volcano slopes at multiple depths and are transported laterally up to tens of kilometers where they contribute to fall out deposits in distal sediments these observations link mechanisms for the transport of volcanic ash in the submarine environment to the types of deposits common in volcaniclastic aprons and fine ash layers in distal sediments

catastrophic debris avalanche from ancestral mount shasta volcano california a debris avalanche deposit extends 43 km northwestward from the base of mount shasta across the floor of shasta valley california where it covers an area of at least 450 km 2 the surface of the deposit is dotted with hundreds of mounds hills and ridges all formed of blocks of pyroxene andesite and unconsolidated volcaniclastic deposits derived from an ancestral mount shasta individual hills are separated by flat topped laharlike deposits that also form the matrix of the debris avalanche and slope northwestward about 5 m km radiometric ages of rocks in the deposit and of a postavalanche basalt flow indicate that the avalanche occurred between about 300 000 and 360 000 yr ago an inferred average thickness of the deposit plus a computed volume of about 4 km 3 for the hills and ridges indicate an estimated volume of about 26 km 3 making it the largest known quaternary landslide on earth

early electromagnetic waves from earthquake rupturing i theoretical formulations yongxin gao 1 2 xiaofei chen 1 2 hengshan hu3 and jie zhang1 2 1school of earth and space sciences university of science and technology of china hefei 230026 china e mail gaoyongxin1982 yahoo com cn 2laboratory of seismology and physics of earth s interior university of science and technology of china hefei 230026 china 3department of astronautics and mechanics harbin institute of technology harbin 150001 china

internal structural variations in a debris avalanche deposit from ancestral mount shasta california usa various parameters of the internal structure of a debris avalanche deposit from ancestral mount shasta size and percentage of block facies in each exposure number and width of jigsaw cracks and number of rounded clasts in matrix facies were measured in order to study flow and emplacement mechanisms three types of coherent blocks were identified blocks of massive or brecciated lava flows or domes blocks of layered volcaniclastic deposits and blocks of accidental material typically from sedimentary units underlying shasta valley the mean maximum dimension of the three largest blocks of layered volcaniclastic material is 220 m and that of the lava blocks 110 m this difference may reflect plastic deformation of blocks of layered volcaniclastic material blocks of massive or brecciated volcanic rock deformated brittly and may have split into several smaller blocks the blocks in the deposit are one order of magnitude larger and the height of collapse 1100 m higher than the pungarehu debris avalanche deposit at mount egmont new zealand although the degree of fracturing is about the same this suggests either that the shasta source material was less broken or that the intensity of any accompanying explosion was smaller at ancestral mount shasta the shasta debris avalanche deposit covered the floor of a closed basin the flanks of the basin may have retarded the opening of jigsaw cracks and the formation of stretched and deformed blocks such as those of the pungarehu debris avalanche deposit

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

growth and mass wasting of volcanic centers in the northern south sandwich arc south atlantic revealed by new multibeam mapping new multibeam swath bathymetric sonar data acquired using an em120 system on the rrs james clark ross supplemented by sub bottom profiling reveals the underwater morphology of a not vert similar 12 000 km2 area in the northern part of the mainly submarine south sandwich volcanic arc the new data extend between 55 45 s and 57 20 s and include protector shoal and the areas around zavodovski visokoi and the candlemas islands groups each of these areas is a discrete volcanic center the entirely submarine protector shoal area close to the northern limit of the arc forms a 55 km long east west trending seamount chain that is at least partly of silicic composition the seamounts are comparable to small subaerial stratovolcanoes in size with volumes up to 83 km3 indicating that they are the product of multiple eruptions over extended periods zavodovski visokoi and the candlemas island group are the summits of three 3 3 5 km high volcanic edifices the bathymetric data show evidence for relationships between constructional volcanic features including migrating volcanic centers structurally controlled constructional ridges satellite lava flows and domes and mass wasting of the edifices mass wasting takes place mainly by strong erosion at sea level and dispersal of this material along chutes probably as turbidity currents and other mass flows that deposit in extensive sediment wave fields large scale mass wasting structures include movement of unconsolidated debris in slides slumps and debris avalanches volcanism is migrating westward relative to the underlying plate and major volcanoes are asymmetrical being steep with abundant recent volcanism on their western flanks and gently sloping with extinct eroded volcanic sequences to their east this is consistent with the calculated rate of subduction erosion of the fore arc

robust features of the source process for the 2004 parkfield california earthquake from strong motion seismograms summary we explore a recently developed procedure for kinematic inversion based on an elliptical subfault approximation in this method the slip is modelled by a small set of elliptical patches each ellipse having a gaussian distribution of slip we invert near field strong ground motion forthe2004september28mw 6 0parkfield california earthquake thedatasetconsistsof10 digital three component 18 s long displacement seismograms the best model gives a moment of 1 21 10 18 n m with slip on two distinct ellipses one with a high slip amplitude of 0 91 m located 20 km northwest of the hypocentre the average rupture speed of the rupture process is 2 7 kms 1 we find no slip in the top 5 km at this depth a lineation of small aftershocks marks the transition from creeping above to locked below in the interseismic period the highslip patch coincides spatially with the hypocentre of the 1966 mw6 0 parkfield california earthquake the larger earthquakes prior to the 2004 parkfield earthquake and the aftershocks of the 2004 earthquake mw 3 also lie around this high slip patch where our model images a sharp slip gradient this observation suggests the presence of a permanent asperity that breaks during large earthquakes and has important implications for the slip deficit observed on the parkfield segment which is necessary for reliable seismic hazard assessment

kinematic inversion of the 2004 m 6 0 parkfield earthquake including an approximation to site effects the 2004 m 6 0 parkfield earthquake yielded one of the largest amounts of near source strong ground motion seismic data ever we invert strong motion seismograms to obtain a model for the space time distribution of coseismic slip on the fault to reduce noise in the inversion we take into account local amplifications that affect each station by using records of the 1983 m 6 5 coalinga earthquake site amplification correlates well with large peak ground velocities registered during the 2004 parkfield mainshock the inversion for a kinematic rupture model yields a nonunique solution we therefore analyze various rupture models that explain the data equally well our preferred rupture model identifies a primary zone of high slip surrounding the hypocenter where the maximum slip is 57 cm a secondary slip area over which contours are not well resolved is located northwest of the hypo center the rupture speed is highly heterogeneous we infer an average rupture ve locity of 2 8 km sec close to the hypocenter and of 3 3 km sec in the secondary region of large slip to the northwest of the hypocenter by correlation of our rupture model with both microseismicity and velocity structure we identify six patches on the fault plane that behave in seismically distinct ways online material kinematic rupture model parameters

slopes of western galapagos volcanoes from airborne interferometric radar the distribution of slopes on the six basaltic shield volcanoes in the western galapagos islands is investigated using a digital elevation model derived from airborne interferometric radar topsar data these measurements have a spatial sampling of 10 m pixel a vertical accuracy of 3 to 5 m and constitute the highest resolution most complete topographic data set available for the islands volcano heights are determined to range from 1 124 m sierra negra to 1 710 m wolf over extensive areas of each volcano slopes exceed 25 with the highest slopes being 37 on wolf and 36 on fernandina we confirm that two morphologic subgroups exist cerro azul fernandina and wolf with deep calderas depth between 40 60 of the subaerial height of the volcano and steep 20 maximum slopes at elevations between 60 and 80 of the volcano height and alcedo darwin and sierra negra with shallow calderas depth 25 of subaerial height and slopes that remain 15 until 90 of the total height is reached our data show that steep slopes are not uniquely correlated with the occurrence of arcuate fissures at the summit leaving the origin of the steep slopes unresolved

morphological and sedimentological characteristics of the neogene submarine coherent lavas and hyaloclastites in southwest hokkaido japan abstract the neogene formations in southwest hokkaido japan are mostly composed of submarine volcanic products such as submarine coherent lavas and hyaloclastites associated with feeder dikes this paper presents criteria for recognition of submarine effusion products through description of the morphological and sedimentological characteristics of coherent lavas such as pillow lobes sheet flow lava lobes and pseudo pillow lavas and hyaloclastites and feeder dikes and a small amount of associate pyroclastic rocks

seismoelectric and electroseismic responses to a point source in a marine stratified model abstract we investigate the seismoelectric electroseismic wavefields excited by a point source in an air seawater three layered porous medium configuration containing a hydrocarbon layer the results show that if an explosive source for excitation is used receivers at seafloor can record the coseismic electromagnetic fields accompanying the p s fluid acoustic waves and the interface responses converted from the acoustic waves at seafloor interface and from the seismic waves at the interfaces beneath the seafloor employing a vertical electric dipole source shows that with the exception of the interface responses converted from electromagnetic waves at seafloor the interface responses converted from transmitted electromagnetic waves at the interfaces beneath the seafloor can also be identified given that the strength of the explosive source is within excitation capability of industry air guns the generated interface responses from the hydrocarbon layer can be detected by current electromagnetic sensors considering the low ambient noise at the seafloor our results demonstrate the feasibility of the seismoelectric method applied to marine hydrocarbon exploration electroseismic modelling results suggest that it is not practical to employ this method to prospect marine hydrocarbon layer due to the weak interface response signal unless a much larger current is injected into seafloor

cyclic growth and mass wasting of submarine los frailes lava flow and dome complex in cabo de gata se spain abstract the los frailes formation lava flow and dome complex is a miocene succession that is part of the cabo de gata volcanic zone of se spain the complex comprises dominantly dacitic subaqueous dome rocks and interstratified sedimentary horizons emplaced over a few tens of thousands of years facies of the los frailes formation include coherent lava in situ hyaloclastite locally with microfossil bearing siltstone matrix pumiceous and block rich tuff and massive monomict breccia and megabreccia in which clasts are locally several metres in diameter the monomict megabreccias display both block facies and matrix facies architecture and show internal deformation at the block matrix contacts they are inferred to have derived from debris avalanches facies are divided into four volcanic units separated by fossiliferous marine sedimentary units emplaced during hiatuses in volcanism the los frailes formation lava flow and dome complex were emplaced in a shallow setting that may have included emergent areas lava flows and the margins of dome edifices interacted with sea water to form hyaloclastite and pyroclastic currents deposited pumiceous materials sector collapse of marine domes fed small volume debris avalanches with generally the same facies and distribution of facies as the larger scale equivalents on which traditional models are built

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

measurement of streaming potential coupling coefficient in sandstones saturated with high salinity nacl brine 1 we present measurements of the streaming potential coupling coefficient in intact sandstone samples saturated with nacl brines at concentrations up to 5 5 moll 1 the values we record at low salinity are consistent with those reported previously as brine salinity increases the coupling coefficient decreases in magnitude but is still measureable up to the saturated concentration limit the magnitude of the zeta potential also decreases with increasing salinity but approaches a constant value at high salinity this behaviour is not captured by current models of the electrical double layer our results suggest that streaming potential measurements may be used to monitor flow in saline subsurface environments such as deep saline aquifers and hydrocarbon reservoirs however they were obtained at laboratory temperature future work will focus on the effect of elevated temperatures at high salinity

40ar 39ar age of the cabo de gata volcanic series and displacements on the carboneras fault zone se spain the sw ne trending carboneras fault zone of se spain separates a terrain comprising uplifted massifs of the metamorphic basement of the betic cordilleras and intervening neogene sedimentary basins from the cabo de gata volcanic series along the southeastern boundary of the carboneras fault burdigalian marls and tuffs mark the beginning of the volcanic episode rest unconformably on the basement and were tilted to the vertical during the earliest stages of movement on the fault zone 40 ar 39 ar dating of hornblende grains and igneous clasts from the tuffs constrain the onset of the volcanic episode at 21 ma some 4 ma earlier than previously reported volcanic rocks higher in the sequence that overstep unconformably onto the southern edge of the fault zone yielded an age of 11 ma thus constraining the earliest episode of motion on the fault zone between these age limits the main phase of left lateral strike slip movement on the carboneras fault may be later than this time movements on more northerly strands of the fault zone including the uplift of the sierra cabrera basement block to the nw continued at least through pliocene times the onset of volcanism is broadly coeval with the unroofing of the orogen by extensional collapse and supports earlier inferences of very rapid rates of uplift and cooling of the basement rocks

tomographic images of p wave velocity variation at parkfield california tomographie inversion is applied io delay times from local earthquakes to image three dimensional velocity variations near parkfield california the 25 20 square km region is represented by nearly cubic blocks of 0 5 km per side arrival times of p waves from 551 local earthquakes with depths of 0 to 15 km were used as sources producing 3135 rays covering the target region the data were recorded on low noise downhole seismographs a conjugate gradient method is used to invert the resulting sparse system of simultaneous equations to diminish the effects of noisy data the laplacian of the model parameters is constrained to be small within horizontal layers providing smoothing of the model the resolution of the model is estimated by calculating point spread functions at blocks of interest estimates of standard errors of the model parameters are calculated by the jackknife statistical procedure the results of the inversion show correlation with some of the local geological and geophysical features station corrections removed the long wavelength anomaly associated with the contrast of the salinian block southwest of the san andreas fault versus the franciscan to the northeast a velocity low located a few kilometers northwest of parkfield depth 2 5 3 5 km appears to lie along the gradient of the large bouguer gravity anomaly associated with the parkfield syncline the south southeastward extension of the low velocities may relate to reflections observed on the parkfield consortium for continental reflection profiling cocorp lines we speculate on the geological meaning of these features and interpret them either as part of the local strike slip tectonics or a shallow crustal detachment the correlation of higher velocity features and seismic activity may indicate that earthquakes are occurring in more competent zones while aseismic slip takes place in zones of lower velocity less competent rocks

direct magnetic signals from earthquake rupturing iwate miyagi earthquake of m 7 2 japan abstract the key point of this paper is that for the first time we successfully observed co rupturing earth s magnetic field changes due to the piezomagnetic effect caused by earthquake rupturing electromagnetic changes associated with earthquakes have been investigated previously most of them are coseismic step like offsets in the geomagnetic field which are regarded as the piezomagnetic effect caused by the total static stress changes resulting from an earthquake proton precession magnetometers have so far been mainly used to detect seismomagnetic effects for which the measurement interval was usually 1 or 10 min and the measurement accuracy was 0 1 nt for seismomagnetic observations we employed flux gate magnetometers whose specifications are the measurement with accuracy of 0 01 nt and with the sampling interval of 0 5 or 1 s by virtue of such highly sensitive magnetometers we show observations of magnetic signals accompanying fault movement our observation site happened to be situated at an epicentral distance of 26 km from the 2008 iwate miyagi nairiku earthquake of m 7 2 in ne japan magnetic field components began to change almost simultaneously with the onset of the earthquake rupture and grew non linearly until the first p wave arrival such magnetic signals are most probably generated by the changing stress field due to rupturing i e the piezomagnetic effect rather than the seismic dynamo effect or electromagnetic induction within the conducting crust because they lack oscillatory features like seismic waves we attempt to interpret the observations with the aid of quasi static piezomagnetic model calculation which strongly supported our observation results

the effects of sea level and palaeotopography on lithofacies distribution and geometries in heterozoan carbonates south eastern spain this study utilized three dimensional exposures to evaluate how sea level position and palaeotopography control the facies and geometries of heterozoan carbonates heterozoan carbonates were deposited on top of a neogene volcanic substrate characterized by palaeotopographic highs palaeovalleys and straits that were formed by subaerial erosion possibly original volcanic topography and faults prior to carbonate deposition the depositional sequence that is the focus of this study ds1b consists of 7 10 fining upward cycles that developed in response to relative sea level fluctuations a complete cycle has a basal erosion surface overlain by deposits of debrisflows and high density turbidity currents which formed during relative sea level fall overlying tractive deposits most likely formed during the lowest relative position of sea level overlying these are debrites grading upward to high density turbidites and low density turbidites that formed during relative sea level rise the tops of the cycles consist of hemipelagic deposits that formed during the highest relative position of sea level the cycles fine upward because upslope carbonate production decreased as relative sea level rose due to less surface area available for shallow water carbonate production and partial drowning of substrates the cycles are dominated by two end member types of facies associations and stratal geometries that formed in response to fluctuating sea level position over variable substrate palaeotopography one end member is termed flank flow cycle because this type of cycle indicates dominant sediment transport down the flanks of palaeovalleys those cycles drape the substrate have more debrites high density turbidites and erosion on palaeovalley flanks and in general the lithofacies fine down the palaeovalley flanks into the palaeovalley axes the second end member is termed axial flow cycle because it indicates a dominance of sediment transport down the axes of palaeovalleys those cycles are characterized by debrites and high density turbidites in palaeovalley axes and lap out of strata against the flanks of palaeovalleys where and when an axial flow cycle or flank flow cycle developed appears to be related to the intersection of sea level with areas of gentle or steep substrate slopes during an overall relative rise in sea level results from this study provide a model for similar systems that must combine carbonate principles for sediment production palaeotopographic controls and physical principles of sediment remobilization into deep water

rupture process of the 2004 parkfield earthquake from near fault seismic waveform and geodetic records 1 the 28 september 2004 parkfield earthquake arguably the best recorded earthquake ever allows for detailed investigation of finite source models and their resolution we have developed finite source models using gps and interferometric synthetic aperture radar geodetic data and seismic strong motion waveform data f 0 5 hz both independently and combined the preferred model shows that the rupture is predominantly unilateral to the nw with a small component to the se slip is concentrated into two primary patches one near the hypocenter and the other between 10 and 23 km to the nw within a narrow depth range 5 13 km the scalar seismic moment is 1 3 1018 n m mw 6 0 the overall rupture length is 23 km the peak slip is 0 45 m and the rupture velocity is 2 6 km s the average static stress drop obtained from the spatially distributed slip model is 2 3 mpa and peak values are 10 mpa a detailed sensitivity and resolution analysis shows that the recovered slip the average rupture velocity risetime and slip velocity are well resolved

ultra low frequency electromagnetic measurements associated with the 1998 mw 5 1 san juan bautista california earthquake and implications for mechanisms of electromagnetic earthquake precursors abstract ultra low frequency ulf 0 01 10 hz magnetic field anomalies prior to m 6 0 earthquakes have been reported in various regions of the world here we test whether smaller magnitude earthquakes have associated ulf anomalies by using continuous measurements made 9 km above and 2 km ne of the epicenter of the m w 5 1 8 12 98 san juan bautista ca earthquake half hour spectral averages of the magnetic field data in nine different ulf frequency bands show no long term days to weeks magnetic field anomaly prior to the earthquake in addition magnetic and electric field polarization shows no anomalous behavior clearly associated with seismic activity an 0 02 nt increase in activity for 2 h prior to the earthquake is close to the background noise levels precluding identification of a precursor we present scaling calculations to show if precursory ulf anomalies are related to the size of the earthquake the observed 0 02 nt increase is the approximately expected magnetic anomaly prior to the san juan bautista sbj earthquake based on the anomaly observed prior to the 1989 loma prieta lp earthquake our reexamination of previously proposed dilatant conductive and piezomagnetic mechanisms for ulf precursors shows that these effects are consistent with the observations prior to the sjb earthquake based on the observations i e lack of a strong precursor in contrast previously proposed electrokinetic and magnetohydrodynamic mhd mechanisms do not appear to be appropriate for this particular earthquake this analysis further supports the hypothesis that precursory ulf signals are related to the size of the earthquake

inversion for the physical parameters that control the source dynamics of the 2004 parkfield earthquake a fully dynamic inversion for the earthquake source process in which the geometry of the rupture area the stress conditions and frictional properties on the fault are obtained is carried out by inverting displacement records for the 2004 mw 6 0 parkfield california earthquake the rupture area of the earthquake is modeled using elliptical patches and seismograms from 10 near field digital stations are used synthetic tests to investigate the performance of the inversion in retrieving the rupture process demonstrate that we can reliably recover the large scale features of the spatiotemporal distribution of slip to investigate the stress conditions and frictional properties of the fault under which we produce a rupture model that fits the observed data we explore the parameter space using a monte carlo method and find an optimal region where the source models fit the data well the best fitting rupture process is shown to occur mainly within one horizontal elliptical region 22 km long along strike and 4 km wide along depth the seismic moment is 1 2 1018 n m and the stress drop over the ellipse is 4 mpa the rupture speed nearly constant during the entire rupture process is 2 9 km s the dimensionless quantity roughly the strain energy change per unit fault surface divided by the energy release rate which includes information on the stress and frictional properties on the fault is found to be 1 4 for the ellipse and strongly controls the rupture process along with the size of the initial circular patch that initiates the earthquake

piezomagnetic fields arising from the propagation of teleseismic waves in magnetized crust with finite conductivity summary to determine whether the piezomagnetic effect is a plausible mechanism in explaining variations in the magnetic field that occur synchronously with the propagation of teleseismic waves a set of solutions are derived for the electromagnetic field the situation is considered in which the earth s conductivity has a stratified structure and seismic waves are expressed as a plane wave the piezomagnetic field in this situation is expressed by an analytically closed form using the obtained solution quantitative aspects of the piezomagnetic field that accompanies seismic rayleigh waves are discussed it is shown that the finite conductivity of the earth s crust sometimes acts as an enhancer of the magnitude of the piezomagnetic field however the expected piezomagnetic field is substantially small even in the case that the initial magnetization around the observation site is as large as 5 a m 1 the expected amplitudes in the piezomagnetic field are at most 0 1 nt this result means that the piezomagnetic effect is not a reasonable mechanism to sufficiently explain variations in magnetic fields that occur synchronously with ground motions if the initial magnetization is horizontally uniform

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod 1 arrival time data from 453 local earthquakes and 6 explosions at parkfield ca are inverted for earthquake locations and three dimensional vp and vp vs structure the structure is dominated by the velocity contrast across the saf with the southwest side about 20 25 faster consistent with previous studies nearly all the earthquakes occur almost directly beneath the fault trace we find high vp vs anomalies that correlate with low resistivity features in a magnetotelluric model that are interpreted to represent fluids we locate a magnitude 2 earthquake that is a potential target event for the final stage of safod drilling yielding a depth of 3 1 km below surface and an epicenter 100 m southwest of the fault trace nonlinear analyses indicate 95 confidence relative and absolute uncertainties on the order of 500 700 m vertically and 200 300 m horizontally for this target earthquake

an archaean submarine volcanic debris avalanche deposit yilgarn craton western australia with komatiite basalt and dacite megablocks the product of dome collapse abstract the boorara domain of the kalgoorlie terrane eastern goldfields superterrane western australia contains excellent exposure of archaean felsic and ultramafic breccias characterised by facies associations interpreted to reflect a volcanic debris avalanche mode of deposition such archaean volcanic deposits are typically difficult to identify due to poor preservation and exposure however primary volcanological and sedimentological features are preserved within the relatively low strain and low metamorphic grade up to lower greenschist facies boorara domain that allow accurate facies reconstruction the breccia deposit is characterised by two clast populations a block facies comprised of metre to decimetre scale megablocks of dacite basalt and komatiite is preserved within a mixed matrix breccia facies of angular coarse sand to boulder sized clasts the megablocks preserve original stratigraphy and show fracturing and jigsaw fit textures within the poorly sorted unstratified genetically related matrix overlying the volcanic debris avalanche deposit are a series of stratified horizons these deposits show evidence of hydraulic sorting within bedforms exhibiting normal grain size grading and tractional scour and fill structures along their basal contacts the stratified facies is interpreted to have been deposited by high concentration high competency turbidity currents triggered by slope stabilization slides in the source region primary contacts and volcanic textures preserved in decimetre scale volcanic blocks allow reconstruction of the pre collapse palaeovolcanological history of the source region the volcanic debris avalanche deposit together with the associated stratified sedimentary horizons were produced by sector collapse of a submarine dacitic volcanic dome contemporaneous komatiite intrusion into the dacite dome may have caused dome flank instability however the volcanic debris avalanche trigger is interpreted to be a post lithification tectonic influence

seismological studies at parkfield i simultaneous inversion for velocity structure and hypocenters using cubic b splines parameterization a model for the 3d p and s wave velocity structure at parkfield has been developed by the systematic inversion of arrival times for microearthquakes and surface vibroseis sources recorded by nearby calnet stations and by the local borehole installed 10 station high resolution seismic network there a modification of the linear b splines model parameterization method of thurber 1983 to a cubic b splines formulation through tests inverting synthetic data sets for the parkfield configuration is found to produce smooth velocity distributions that still retain some small scale features application of the method to 953 p wave and 288 s wave arrivals from 111 microearthquakes and 8 vibroseis locations throughout the study area yields a velocity structure having variable resolution a low velocity zone appears to coincide with the creeping segment of the san andreas fault zone northwest of the 1966 parkfield earthquake epicenter an increase of about 15 per cent in seismic velocities is seen from the northeast to southwest across this segment of the fault zone the higher velocities to the southwest apparently correspond to the granitic basement the contrast across the fault is subdued to the southeast along the 1966 rupture zone a high vp vs ratio of 1 9 is seen in a 2 km wide volume near the location of the 1966 main shock hypocenter presumably the nucleation zone for the expected m 6 parkfield earthquake