seismicity and eruptive activity at fuego volcano guatemala february 1975 january 1977 abstract we examine seismic and eruptive activity at fuego volcano 14 29 n 90 53 w a 3800 m high stratovolcano located in the active volcanic arc of guatemala eruptions at fuego are typically short lived vulcanian eruptions producing ash falls and ash flows of high alumina basalt from february 1975 to december 1976 five weak ash eruptions occurred accompanied by small earthquake swarms between 0 and 140 average 10 a type or high frequency seismic events per day with m 0 5 were recorded during this period estimated thermal energies for each eruption are greater by a factor of 10 6 than cumulative seismic energies a larger ratio than that reported for other volcanoes over 4000 a type events were recorded january 3 7 1977 cumulative seismic energy 10 9 joules yet no eruption occurred five 2 hour long pulses of intense seismicity separated by 6 hour intervals of quiescence accounted for the majority of events maximum likelihood estimates of b values range from 0 7 0 2 to 2 1 0 4 with systematically lower values corresponding to the five intense pulses the low values suggest higher stress conditions during the 1977 swarm a tiltmeter located 6 km southeast of fuego recorded a 14 3 microradian tilt event down to sw this value is too large to represent a simple change in the elastic strain field due to the earthquake swarm we speculate that the earthquake swarm and tilt are indicative of subsurface magma movement

constraints on the formation of the martian crustal dichotomy from remnant crustal magnetism the martian crustal dichotomy characterizing the topographic difference between the northern and southern hemispheres is one of the most important features on mars however the formation mechanism for the dichotomy remains controversial with two competing proposals exogenic e g a giant impact and endogenic e g degree 1 mantle convection mechanisms another important observation is the martian crustal remnant magnetism which shows a much stronger field in the southern hemisphere than in the northern hemisphere and also magnetic lineations in this study we examine how exogenic and endogenic mechanisms for the crustal dichotomy are constrained by the crustal remnant magnetism assuming that the dichotomy is caused by a giant impact in the northern hemisphere we estimate that the average thickness of ejecta in the southern hemisphere is 20 25 km while such a giant impact may cause crustal demagnetization in the northern hemisphere we suggest that the impact could also demagnetize the southern hemisphere via ejecta thermal blanketing impact demagnetization and heat transfer from the hot layer of ejecta thus posing a challenge for the giant impact model we explore how the pattern of magnetic lineations relates to endogenic theories of dichotomy formation specifically crustal production via degree 1 mantle convection we observe that the pattern of lineations roughly corresponds to concentric circles about a single pole and determine the pole for the concentric circles at 76 5 e and 84 5 s which nearly overlaps with the centroid of the thickened crust in the southern hemisphere we suggest that the crustal magnetization pattern magnetic lineations and crustal dichotomy i e thickened crust in the highlands can be explained by a simple endogenic process one plume convection causes melting and crustal production above the plume in the southern hemisphere and strong crustal magnetization and magnetic lineations are formed in the southern hemisphere as crustal production fronts spread radially out from the plume center and as the newly created crust cools in the presence of a dynamo with polarity reversals

geochemistry of central tethyan upper permian and lower triassic strata abadeh region iran nearly 2 km of upper permian to lower triassic limestones are exposed in the hambast mountain abadeh region iran lime mud matrix and most bioclasts of permian age are recrystallized into large calcite crystals and contain 600 4000 ppm sr suggesting a probable aragonite precursor low bulk rock 18 o values 7 to 10 pdb and recrystallized textures are also indicative of diagenetic alteration within the murghabian and abadehian two gradual upward increases in carbonate and organic matter 13 c compositions each roughly 3 pdb in magnitude are documented both are attributed to increased organic productivity and sequestration of organic matter in sediments within the julfian and across the permian triassic p t boundary two sharp upward decreases in carbonate and organic matter 13 c values each 4 pdb in magnitude are observed both are best explained by mixing of a deep water mass having low 13 c values and a shallow water mass having high 13 c compositions early triassic 13 c values initially low 1 pdb increase to 3 pdb within 100 m above the p t boundary variations in 13 c compositions of carbonate and organic matter and changes in 13 c 13 ccar 13 corg indicate that early triassic 13 c values were controlled by productivity cycles

stable isotopes of carbon and sulphur as indicators of environmental change past and present stable isotopes of carbon 12 c and 13 c and sulphur 32 s and 34 s are fractionated during some of the transformations between reservoirs in the global carbon and sulphur cycles the main processes controlling the isotopic composition of earth surface reservoirs are for carbon photosynthesis respiration and equilibration between oceanic dissolved inorganic carbon and atmospheric co 2 and for sulphur bacterial sulphate reduction and sulphide reoxidation thus the different reservoirs of carbon and sulphur in the global cycles attain characteristic isotopic compositions that can be used as a fingerprint for different carbon and sulphur sources and to track changes in the balance of carbon and sulphur stored in different reservoirs these isotopic signals can be used both to examine contemporary anthropogenic impacts on the cycling of carbon and sulphur and where isotopic compositions are faithfully preserved in ancient sediments to examine historical changes in global geochemical cycles through geological time a number of case studies are discussed to illustrate how isotopic techniques represent one of the most powerful and important tools available in the study of both the causes and affects of ancient and modern global environmental change

infrasonic waves and volcanic tremor at stromboli the origin of the volcanic tremor is still under debate many theories have been proposed in the last years but none has yet been completely accepted in 1993 highly sensitive pressure sensors 2 175 pa volt used to monitor the explosive activity at stromboli have revealed unexpected correlation between small spike shaped pressure signals 1 2 pa and volcanic tremor these pressure pulses repeat regularly in time with a recurrent period of ca 1 s video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents the striking correlation 0 971 between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain infrasonic and seismic signal share the same spectral content 3 hz for every station within a range of 700 m around the craters correlations in time and frequency domain remained unaltered during the 1994 field experiments moreover during 1994 the increased degassing activity has been followed by an increase in pressure release 7 8 pa and by a shift towards higher frequencies 8 hz both in the infrasonic and seismic records infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents appearing therefore to be produced by the same dynamical process on this basis we claim that volcanic tremor at stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

geophysical consequences of planetary scale impacts into a mars like planet all planetary bodies with old surfaces exhibit planetary scale impact craters vast scars caused by the large impacts at the end of solar system accretion or the late heavy bombardment here we investigate the geophysical consequences of planetary scale impacts into a mars like planet by simulating the events using a smoothed particle hydrodynamics sph model our simulations probe impact energies over two orders of magnitude 2 10 27 6 10 29 j impact velocities from the planet s escape velocity to twice mars orbital velocity 6 50 km s and impact angles from head on to highly oblique 0 75 the simulation results confirm that for planetary scale impacts surface curvature radial gravity the large relative size of the impactor to the planet and the greater penetration of the impactor contribute to significant differences in the geophysical expression compared to small craters which can effectively be treated as acting in a half space the results show that the excavated crustal cavity size and the total melt production scale similarly for both small and planetary scale impacts as a function of impact energy however in planetary scale impacts a significant fraction of the melt is sequestered at depth and thus does not contribute to resetting the planetary surface complete surface resetting is likely only in the most energetic 6 10 29 j slow and head on impacts simulated a crater rim is not present for planetary scale impacts with energies 10 29 j and angles 45 but rather the ejecta is more uniformly distributed over the planetary surface antipodal crustal removal and melting is present for energetic 10 29 j fast 6 km s and low angle 45 impacts the most massive impactors with both high impact energy and low velocity contribute sufficient angular momentum to increase the rotation period of the mars sized target to about a day impact velocities of 20 km s result in net mass erosion from the target for all simulated energies and angles the hypothesized impact origin of planetary structures may be tested by the presence and distribution of the geochemically distinct impactor material

the martian hemispheric dichotomy may be due to a giant impact mars is divided into two fundamentally different geological provinces of approximately hemispherical extent1 3 the more southerly province is heavily cratered contains relatively old geological units and superficially resembles the lunar and mercurian highlands the northern province is relatively lightly cratered and contains younger geological units including extensive plains volcanic edifices and volcanic calderas except for the tharsis and elysium regions and other large volcanoes most of the younger northern province consists of lowlands which lie an average of 3 km below the highlands lowlands occupy about one third of mars they are separated from the highlands by a distinct scarp or by a sloping transitional zone as much as 700km wide in which highland materials have been disrupted and partly replaced by lowland deposits fig 1 the transition is characterized by a variety of landforms unknown on other planets the highlands and lowlands are in isostatic equilibrium across the transitional zone4 no generally accepted explanation for the cause of the highland lowland dichotomy has been proposed although thinning of the lithosph re in the northern hemisphere by internal processes has been suggested5 large impacts which were a feature of early solar system history have also been suggested as an important cause of such early planetary surface heterogeneities3 6 7 subcircular lowlands such as argyre chryse hellas and isidis planitia and the plains south of tharsis occupy previously recognized impact basins8 10 we propose here that the largest expanse of lowlands also results from formation of a large impact basin early in mars history that has profoundly shaped the planet s surface

seismicity associated with eruptive activity at langila volcano papua new guinea abstract during periods of eruptive activity at langila volcano various combinations of low frequency earthquakes and high frequency air waves have been recorded ranging from earthquakes alone to air waves alone it is shown that these different types of events are part of a continuous range of events which are all interpreted to be explosions at or near the summit continuous tremor is also often recorded for durations of several minutes to hours and is classified into two types harmonic and non harmonic spectral analysis shows that the non harmonic tremor resembles a string of low frequency events in contrast the spectra of harmonic tremor show simple modal characteristics which indicate some type of resonating source this source is thought to include a gas filled cavity above the magma body within the volcano

multidisciplinary observations of the 2011 explosive eruption of telica volcano nicaragua implications for the dynamics of low explosivity ash eruptions we present multidisciplinary observations of the march june 2011 vei 2 eruptive episode of the basalticandesite telica volcano nicaragua which allow for a comprehensive study of the eruption mechanics of low explosivity eruptions at persistently active volcanoes the observations are from a dense network of seismic and gps instrumentation augmented by visual observations of the eruptive episode geochemical and petrologic analysis of eruptive products plume so2 measurements and temperature measurements of fumaroles inside and outside the active vent the 2011 eruptive episode was telica s most explosive since 1999 and consisted of numerous vulcanian explosions with maximum column heights of 1 5 2 km above the crater rim depositing a low volume of dominantly hydrothermally altered ash based on observed variations in seismicity temperature and so2 flux the lack of deformation of the edifice the non juvenile origin of and predominance of accretionary lapilli in the ash we propose that temporary sealing of the hydrothermal system between similar to 0 5 and 2 km depth allowed pressure to build up prior to vulcanian explosions making this a phreatic eruptive episode

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

impact megadomes and the origin of the martian crustal dichotomy abstract we show that a sufficiently energetic impact can generate a melt volume which after isostatic adjustment and differentiation forms a spherical cap of crust with underlying depleted mantle depending on impact energy and initial crustal thickness a basin may be retained or impact induced crust may be topographically elevated retention of a martian lowland scale impact basin at impact energies 3 1028 3 1029 j requires an initial crustal thickness greater than 10 km formation of impact induced crust with size comparable to the martian highlands requires a larger impact energy 1 3 1030 j and initial crustal thickness

depth of faulting on mercury implications for heat flux and crustal and effective elastic thickness 1 topographic profiles across a lobate fault scarp on mercury have been used to constrain the depth of faulting to 30 40 km here we use this depth to place constraints on the crustal thickness and heat flow into the base of the crust with no crustal heat production the mantle heat flux on mercury at the time of scarp formation was 30 50 mwm 2 however higher crustal heat production rates allow significantly lower mantle heat fluxes in all cases the mantle heat flux exceeds the likely radiogenic heat flux 4 gyr ago it is likely that secular cooling accounted for the remainder irrespective of crustal heat generation a crustal thickness of 140 km is required to satisfy both the faulting observations and the requirement that the base of the crust does not melt the effective elastic thickness of the lithosphere at the time of faulting is predicted to be 25 30 km

hemispheres apart the crustal dichotomy on mars the hemispheric dichotomy is a fundamental feature of mars expressed by a physiographic and geologic divide between the heavily cratered southern highlands and the relatively smooth plains of the northern lowlands the origin of the dichotomy which may have set the course for most of the subsequent geologic evolution of mars remains unclear internally driven models for the dichotomy form the lowlands by mantle convection plate tectonics or early mantle overturn externally driven models invoke one giant impact or multiple impacts areal densities of buried basins expressed by quasicircular depressions and subsurface echoes in radar sounding data suggest that the dichotomy formed early in the geologic evolution of mars tectonic features along the dichotomy boundary suggest late stage modification by flexure or relaxation of the highlands after volcanic resurfacing of the northern lowlands subsequent deposition and erosion by fluvial aeolian and glacial processes shaped the present day dichotomy boundary

an origin for the linear magnetic anomalies on mars through accretion of terranes implications for dynamo timing the proposed existence of magnetic lineations in the terra cimmeria and terra sirenum regions of mars was initially explained by earth like sea floor spreading here we argue instead that these lineations could have been formed at a convergent plate margin through collision and accretion of terranes a similar process produced banded magnetic anomalies similar in geometry and even in size to those in earth s north american cordillera because only sparse and generally weak anomalies have been detected in the martian northern lowlands which could constitute an analog to the terrestrial oceanic crust it is possible that the magnetic field stopped its activity while crustal recycling was still active in mars

amazonian modification of moreux crater record of recent and episodic glaciation in the protonilus mensae region of mars abstract morphologic characteristics of ice rich landforms in the martian mid latitudes record evidence for significant modification of the landscape in response to spin axis orbital parameter driven shifts in the late amazonian climate these landforms are spatially distributed across the mid latitudes and their co existing presence has so far not been observed from a single crater to infer how exactly a terrain has been modified while mars was undergoing major moderate minor shifts in its late amazonian climate we have therefore carried out an in depth investigation of moreux crater 135 km centered at 41 66 n 44 44 e in the protonilus mensae region for identification of features associated with recent and episodic glacial events and for emphasizing the role played by these glacial events in the modification of the crater evidence for extensive modification of the surfaces over crater rim wall and around central peak by emplacement of multiple scales of ice rich landforms that represents large history of glacial activities was found from our results we document phases of major moderate minor glacial activities within the crater as 1 piedmont lobes lobate debris aprons linear valley fills 1 ga 100 ma 2 viscous flow features 30 0 1 ma and 3 gullies thermal contraction crack polygons 2 1 0 4 ma the form and distribution of the random valleys observed within moreux suggests their formation by pressure induced melting and flow occurring beneath an extensive layer of ice we also suggest that central peak of moreux probably acted as the locus for accumulation of ice snow and the diversity of glacial periglacial features within the crater was possibly controlled by differences in the amount of accumulated ice snow and the rate at which the terrain responded to the shifts in climate during subsequent periods of obliquity changes taken together these ice rich deposits within moreux suggest that sequential modification of the crater surfaces over the rim wall and around central peak has occurred over the last tens of millions of years of martian history this new evidence thus adds another well documented case to rapidly accumulating evidences for widespread glacial activity in the middle latitudes of mars in recent martian history

paleomagnetic poles of mars revisited 1 the huge amount of data acquired by mars global surveyor during its mapping period provides a unique opportunity to reassess the paleomagnetic pole positions of mars previously determined on the basis of the limited low altitude magnetic data we identify nine small and isolated magnetic anomalies on the basis of the global magnetic maps and model each anomaly using a vertical prism of elliptical cross section both high altitude 360 430 km and low altitude 100 200 km magnetic data are used simultaneously we calculate a paleomagnetic pole position assuming that the body is magnetized by a dipole core field although the new pole positions do not cluster as closely as the old ones the new cluster overlaps the older cluster the clustering suggests that mars rotation axis has likely wandered by 50 60 in the last 4 gyr the number of north and south poles in the cluster suggests at least one reversal of the core field during the time the source bodies acquired magnetization

high resolution carbon isotope changes in the permian triassic boundary interval chongqing south china implications for control and growth of earliest triassic microbialites abstract high resolution 13 c carb analysis of the permian triassic boundary ptb interval at the laolongdong section beibei near the city of chongqing south china encompasses the latest permian and earliest triassic major facies changes in the south china block scb microbialites form a distinctive unit in the lowermost 190 cm above the top of the changhsing formation latest permian at laolongdong comparable to a range of earliest triassic sites in low latitudes in the tethyan area the data show that declining values of 13 c carb well known globally began at the base of the microbialite high positive values 3 to 4 ppt of 13 c carb in the late permian are interpreted to indicate storage of 12 c in the deep waters of a stratified ocean that was released during ocean overturn in the earliest triassic contributing to the distinctive fall in isotope values this interpretation has been stated by other authors and is followed here the 13 c carb curve shows fluctuations within the microbialite unit which are not reflected in the microbialite structure comparisons between microbialite branches and adjacent micritic sediment show little difference in 13 c carb demonstrating that the microbialite grew in equilibrium with surrounding seawater the early triassic microbialites are interpreted to be a response to upwelling of bicarbonate rich poorly oxygenated water in low latitudes of tethys ocean consistent with current ocean models for the ptb interval however the decline of 13 c carb may be due to a combination of processes including productivity collapse resulting from mass extinction return of deep water to ocean surface oxidation of methane released from methane hydrate destabilisation and atmospheric deterioration nevertheless build up of bicarbonate rich anoxic deep waters may be expected as a result of the partial isolation of tethys due to continental geography release of bicarbonate rich deep water by ocean upwelling in the earliest triassic may have been an inevitable consequence of this combination of circumstances

magnetic lineations in the ancient crust of mars the mars global surveyor spacecraft in a highly elliptical polar orbit obtained vector magnetic field measurements above the surface of mars altitudes 100 kilometers crustal magnetization mainly confined to the most ancient heavily cratered martian highlands is frequently organized in east west trending linear features the longest extending over 2000 kilometers crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude groups of quasi parallel linear features of alternating magnetic polarity were found they are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on earth but with a much larger spatial scale they may be a relic of an era of plate tectonics on mars

dike intrusion as a possible cause of linear martian magnetic anomalies a model in which the ancient 100 200 km wide magnetic lineations in the southern hemisphere of mars are formed by repeated dike intrusion is proposed on the basis of magnetizations observed at terrestrial mid ocean ridges a likely upper bound on the martian crustal magnetization is about 15 a m 1 this upper bound gives a minimum magnetized layer thickness of 35 60 km because the magnetic material is likely to be magnetite the long term stability of the anomalies probably requires ilmenite lamellae to have exsolved from the magnetite this exsolution process provides an upper bound on the cooling time available of 102 105 yr these bounds can be satisfied if the magnetic anomalies are created by successive intrusion of dikes from 20 to 2000 m wide production of a martian crust 35 60 km thick by rifting requires either mantle potential temperatures in excess of 1430 c or stretching factors greater than 5

methane driven oceanic eruptions and mass extinctions focusing on the permian triassic boundary ca 251 ma i explore the possibility that mass extinction can be caused by an extremely fast explosive release of dissolved methane and other dissolved gases such as carbon dioxide and hydrogen sulfide that accumulated in the oceanic water masses prone to stagnation and anoxia e g in silled basins the mechanism of the explosive release is the same as in the lake nyos disaster of 1986 i e a water column eruption caused by the interplay of buoyancy forces and exsolution of dissolved gas the eruption brings to the surface deep anoxic waters that cause extinctions in the marine realm terrestrial extinctions are caused by explosions and conflagrations that follow the massive release of methane the air methane mixture is explosive at methane concentrations between 5 and 15 and by the eruption triggered floods this scenario accounts well for the available data and may be relevant to other phenomena

tectonic implications of mars crustal magnetism mars currently has no global magnetic field of internal origin but must have had one in the past when the crust acquired intense magnetization presumably by cooling in the presence of an earth like magnetic field thermoremanent magnetization a new map of the magnetic field of mars compiled by using measurements acquired at an 400 km mapping altitude by the mars global surveyor spacecraft is presented here the increased spatial resolution and sensitivity of this map provide new insight into the origin and evolution of the mars crust variations in the crustal magnetic field appear in association with major faults some previously identified in imagery and topography cerberus rupes and valles marineris two parallel great faults are identified in terra meridiani by offset magnetic field contours they appear similar to transform faults that occur in oceanic crust on earth and support the notion that the mars crust formed during an early era of plate tectonics

high resolution local magnetic field models for the martian south pole from mars global surveyor data we present two high resolution local models for the crustal magnetic field of the martian south polar region models sp130 and sp130m were derived from three component measurements made by mars global surveyor at nighttime and at low altitude 200 km the availability area for these data covers the annulus between latitudes 76 and 87 and contains a strongly magnetized region southern parts of terra sirenum adjacent to weakly magnetized terrains such as prometheus planum our localized field inversions take into account the region of data availability a finite spectral bandlimit spherical harmonic degree l 130 and the varying satellite altitude at each observation point we downward continue the local field solutions to a sphere of martian polar radius 3376 km while weakly magnetized areas in model sp130 contain inversion artifacts caused by strongly magnetized crust nearby these artifacts are largely avoided in model sp130m a mosaic of inversion results obtained by independently solving for the fields over individual subregions robust features of both models are magnetic stripes of alternating polarity in southern terra sirenum that end abruptly at the rim of prometheus planum an impact crater with a weak or undetectable magnetic field from a prominent and isolated dipole like magnetic feature close to australe montes we estimate a paleopole with a best fit location at longitude 207 and latitude 48 from the abruptly ending magnetic field stripes we estimate average magnetization values of up to 15 a m

degree 1 mantle convection and the crustal dichotomy on mars the surface of mars consists of an old heavily cratered and elevated southern hemisphere and younger resurfaced and depressed northern hemisphere a feature often termed the crustal dichotomy the global crustal structure zuber et al 2000 revealed by topography and gravity data from the mars global surveyor spacecraft and the possible late formation of the boundary zone between the hemispheres mcgill and dimitriou 1990 have been proposed to indicate an endogenic origin for the dichotomy however degree 1 mantle convection that is required for any endogenic process to be viable cannot be produced with conventional mantle convection models schubert et al 1990 we have studied the role of radially stratified viscosity on mantle deformation by using rayleigh taylor instability analyses in a spherical shell geometry our analyses reveal that when mantle viscosity is stratified with a weak asthenosphere deformation at long wavelengths is more efficient than that at short wavelengths the weaker the asthenosphere the longer the wavelength at which the deformation is the most efficient a thicker asthenosphere also favors the deformation at long wavelengths both the rayleigh taylor instability analyses and numerical modeling of mantle convection show that degree 1 convection can be produced within the martian mantle provided that the mantle had a weak asthenosphere v500 km thick and v10 2 times weaker than the underlying mantle early in planetary history the degree 1 convection causes preferential heating of one hemisphere that may explain the primary features associated with the dichotomy in crustal structure fl 2001 elsevier science b v all rights reserved

a microbialite carbonate crust at the permian triassic boundary in south china and its palaeoenvironmental significance a 1 m thick carbonate crust layered and commonly domal caps crinoidal limestones on reef complexes of the top permian changxing formation in the huaying mountains eastern sichuan china the crust s stratigraphic level lies at a sharp change in facies and is overlain by poorly fossiliferous laminated micrites and shales of the lower triassic feixianguan formation the crust therefore appears to coincide with the end permian extinction event although the dating of the strata is currently imprecise the crust is composed mostly of digitate carbonate locally thrombolitic with remnant lobate fabric and resembles microbialites but is mostly recrystallised and a microbial origin is unconfirmed it is enclosed in micrite with pyrite crystals ostracode and other shell debris the crust is absent from interreef areas previous interpretations of karstification and calcrete formation are not upheld and the facies were deposited under water overlying sediments are low energy with abundant ferroan calcite and pyrite reflecting anoxia associated with rising sea level various interpretations of the crust are possible 1 it was organic and microbia grew preferentially on topographic highs of reef tops 2 microbia were a disaster biota in the absence of grazers 3 microbia took advantage of favourable conditions for calcification associated with a rapidly rising environmental co2 content during the late permian 4 the crust was an inorganic precipitate associated with co2 rich water microbial crusts are rare after the cambrian but whether this crust is organic or not its presence in these strata reinforces the view that oceanic atmospheric conditions in the permian triassic boundary interval were unusual

impact constraints on the age and origin of the lowlands of mars 1 visible and buried impact basins seen as quasi circular depressions qcds in mola data provide important new constraints on the age of the martian lowlands the buried lowlands are no younger than early noachian at least as old as the oldest exposed visible surface units in the highlands a model absolute age for these buried lowlands is 4 04 4 11 gy or earlier but similar model ages for the largest lowland basins are older yet 4 08 4 18 gy the lowland crust both formed and became low no later than 500 million years after mars formed and likely even earlier this constrains models for the origin of the fundamental crustal topographic dichotomy on mars mechanisms which operated both early and quickly during the earliest history of mars e g large impacts may be more likely than those requiring extended periods of time i e endogenic models

small inflation sources producing seismic and infrasonic pulses during the 2000 eruptions of miyake jima japan abstract during the 2000 activity of miyake jima volcano japan we detected long period seismic signals with initial pulse widths of 1 2 s accompanied by infrasonic pulses with almost the same pulse widths the seismic signals were observed from 13 july 2000 a day before the second summit eruption the occurrences of the seismic signals were intermittent with a gradual increase in their magnitudes and numbers building toward a significant explosive eruption on 18 august after the eruption the seismic and infrasonic events ceased the results of a waveform inversion show that the initial motions were excited by an isotropic inflation source beneath the south edge of the caldera at a depth of 1 4 km on the other hand the sources of the infrasonic pulses were located in the summit caldera area the times at which the infrasonic pulses were emitted at the surface were delayed by about 3 s from the origin times of the seismic events it is suggested that small isotropic inflations excited seismic waves in the crust and simultaneously caused acoustic waves that traveled in the conduit and produced infrasonic pulses at the crater bottom considering the observed time differences and gas temperatures emitted from the vent the conduit should have been filled with vapor mixed with so 2 gas and volcanic ash the change of the time differences between the seismic and infrasonic signals suggests that the seismic source became shallower within half a day before the august 18 explosive eruption we interpret the source process as a fragmentation process of magma in which gas bubbles burst and quickly released part of the pressure that had been sustained by the tensional strength of magma

very long period seismic signals observed before the caldera formation with the 2000 miyake jima volcanic activity japan 1 very long period seismic signals whose waveform consists of an initial impulsive signal and a later oscillatory wave with 0 2 or 0 4 hz in dominant frequency were observed before the caldera formation in the 2000 activity of miyake jima volcano japan the results of waveform inversion show that the initial and later parts can be explained by a northward single force of 1 5 108 n working at a depth of 2 km beneath the summit and a moment tensor solution at a depth of 5 km below and 2 km southwest of the summit with 1012 nm respectively a clear positive correlation of the amplitudes between the two sources strongly suggests that the shallow single force triggers the deeper moment source in spite of the several km distance between the two sources to analyze the source time functions of the moment tensor that do not always oscillate in phase we introduce a new method of moment tensor diagonalization which is performed in the frequency domain according to the analysis the two principal components have similar amplitudes and are greater than the third principal component suggesting an axially symmetric oscillation one of the possible systems is a combination of two cracks intersecting perpendicularly our interpretation is that the single force was generated when magma containing rock blocks suddenly began to move in a choked subsurface magma path and the resultant pressure waves propagated and excited a resonance oscillation of the two cracks

seismic and acoustic observations at mount erebus volcano ross island antarctica 1994 1998 volcanic activity at mount erebus is dominated by eruptive activity within a phonolitic summit lava lake common eruption styles range from passive degassing to strombolian explosions which typically occur several times daily and occasionally in swarms of up to 900 per day shallow explosions although generally the result of steady exsolution of volatiles from depth can be triggered by surficial input of h 2o through mass wasting of rock snow and ice from the crater walls broadband observations of strombolian explosions document very long period vlp signals with strong spectral peaks near 20 12 and 7 s which are polarized in the vertical radial plane these signals precede lava lake surface explosions by 1 5 s are highly repeatable and persist for up to 200 s first motions indicate a deflationary source with any precursory inflation being below the 30 s passband of our instruments particle motions suggest a vlp source residing up to 800 m below the lava lake surface however this depth could be exaggerated by near field radial tilt seismic and acoustic signals associated with lava lake explosions commonly show evidence for multiple bubble bursts in corresponding complexity features resulting from varying time delays and relative sizes of superimposed bursts a systematic decrease in seismic acoustic ratio for smaller surface explosions suggests that either the seismic energy from the smallest shallowest bubble bursts experiences much greater seismic attenuation than energy arising from larger events which may involve a deeper less attenuative portion of the magma column and or that the shallowest layer is seismically isolated from deeper parts of a stratified magma column which are not excited by the smallest explosions due to sharp impedance contrasts across distinct layers tremor at erebus is uncommon with only a few isolated instances identified in five years of monitoring some tremor events are nearly monochromatic and some exhibit numerous gliding harmonic spectral lines q 2000 elsevier science b v all rights reserved

viscoelastic evolution of lunar multiring basins 1 we investigate the evolution of multiring basins on the moon the orbital geophysical and geochemical data collected by lunar prospector allow three distinct groups of basins to be identified group 1 basins show well preserved topography a bull s eye gravity signature and little mare basalt fill group 2 basins contain large amounts of mare basalt and show mare dominated gravity and topography signatures group 3 basins are characterized by low amplitude topographic relief and weak gravity anomalies while the crustal structures of group 1 and 2 basins appear to date from the collapse of the transient cavity group 3 basins are highly degraded and show very little crustal thinning using a viscoelastic model we explore the evolution of the lunar multiring basins with the goal of explaining the degraded condition of group 3 basins our results show that while viscous relaxation is a plausible explanation for the state of group 3 farside basins requiring heat flux 25 40 mw m 2 the thin nearside crust renders subsolidus ductile flow in the crust unlikely the existence of many degraded basins on the nearside points to a weakened and possibly partially molten lower crust that south pole aitken appears not to have relaxed suggests that similar conditions did not exist there and that the nearside was hotter than the farside early on this is likely a consequence of the nearside farside crustal thickness dichotomy which would have caused the farside to reach full crystallization first leaving the nearside with the remaining liquid and an excess of heat producing elements

towards self consistent modeling of the martian dichotomy the influence of one ridge convection on crustal thickness distribution in order to find an explanation for the origin of the martian crustal dichotomy a number of recent papers have examined the effect of layered viscosity on the evolution of a degree 1 mantle convection e g roberts and zhong roberts j h zhong s 2006 j geophys res 111 e06013 and yoshida and kageyama yoshida m kageyama a 2006 j geophys res 111 doi 10 1029 2005jb003905 b03412 it was found that a mid mantle viscosity jump combined with highly temperature and depth dependent rheology are effective in developing a degree 1 convection within a short timescale such a layered viscosity profile could be justified by martian mineralogy however the effect of a degree 1 convective planform on the crustal thickness distribution has not yet been demonstrated it is not obvious whether a thinner crust due to sublithospheric erosion and crustal thinning or a thicker crust due to enhanced crustal production would form above the hemisphere of mantle upwelling also the general shape of the dichotomy which is not strictly hemispherical has not yet been fully investigated here we propose a model of the crustal patterns produced by numerical simulations of martian mantle convection using the finite volume multigrid code stagyy tackley p j 2008 phys earth planet int 107 7 18 doi 10 1016 j pepi 2008 08 005 a self consistent treatment of melting crustal formation and chemical differentiation has been added to models of three dimensional thermal convection this allows us to obtain global maps of the crustal thickness distribution as it evolves with time the obtained results demonstrate that it is indeed possible to form a crustal dichotomy as a consequence of near degree 1 mantle convection early in mars history we find that some of the observed patterns show intriguing first order similarities to the elliptical shape of the martian dichotomy in all models the region of thick crust is located over the region of mantle upwelling which itself is a ridge like structure spread over roughly one half of the planet a planform we describe as one ridge convection

early transient superplumes and the origin of the martian crustal dichotomy 1 the large temperature difference between the core and mantle of mars at the end of planetary accretion creates a hot internally convecting thermal boundary layer at the base of the mantle whose viscosity is several orders of magnitude lower than the viscosity of the mantle above it theoretical analysis and numerical simulations of the instability of this thermal boundary layer show that it is likely that only one large plume forms this superplume may play a role in the formation of crustal dichotomy and generation of the magnetic field in the early history of mars

modeling of major martian magnetic anomalies further evidence for polar reorientations during the noachian abstract maps of the vector components of the mars crustal magnetic field are constructed at the mapping altitude 360 to 410 km using a selected set of data obtained with the mars global surveyor magnetometer during 2780 orbits of the planet in 1999 forward modeling calculations are then applied to six relatively strong and isolated dominantly dipolar magnetic anomalies for the primary purpose of estimating bulk directions of magnetization assuming that the magnetizing field was a dipolar core dynamo field centered in the planet paleomagnetic pole positions are calculated for the six primary source bodies together with that for a seventh anomaly analyzed earlier in agreement with several previous studies it is found that six of the seven pole positions are clustered in what is now the northern lowlands in a region centered northwest of olympus mons mean pole position 34 10 n 202 58 e assuming that the dynamo dipole moment vector was approximately parallel to the rotation axis the modeling results therefore suggest a major reorientation of mars relative to its rotation axis after magnetization was acquired such a reorientation may have been stimulated by internal mass redistributions associated with the formation of the northern lowlands and tharsis for example a comparison of the mean paleo magnetic equator to the global distribution of crustal fields shows that magnetic anomalies tend to occur at low paleolatitudes the same appears to be true for the noachian aged valley networks which exhibit a broad spatial correlation with the magnetic anomalies a possible interpretation is that the formation of magnetic anomalies and the valley networks was favored in the tropics where melting of water ice and snow was a stronger source of both surface valley erosion and groundwater recharge during the earliest history of the planet this would be consistent with models in which hydrothermal alteration of crustal rocks played a role in producing the unusually strong martian magnetic anomalies

migration of tharsis volcanism on mars caused by differential rotation of the lithosphere as a single plate planet mars cannot support large scale motion of the lithosphere according to the standard theory of stagnant lid convection but such motion is required to explain the position of the tharsis rise modelling work suggests that differential rotation of the lithosphere can resolve this problem

an altitude normalized magnetic map of mars and its interpretation techniques developed for the reduction and analysisofterrestrialsatellitemagneticelddataareusedto better understand the magnetic eld observations made by mars global surveyor a global distribution of radial br magnetic eld observations and associated uncertainties is invertedfor an equivalentsource magnetization distribution and then used to generate an altitude normalized map of br at 200 km the observations are well represented by a potential function of crustal origin consistent with a rema nent origin for the martian magnetic features the correla tion between the 40546 br observations andbr calculated from the magnetization solution at observation locations is 0 978 for a magnetization distribution connedto a 50 km layer calculatedmagnetizationsrangefrom 22to 17a m we see correlations with tectonics that were only hinted at in earlier maps magnetic features appear to be truncated against valles marineris and ganges chasma suggestive of a major change in crustal properties associated with fault ing

estimates of martian crustal thickness from viscous relaxation of topography isostatically compensated crustal thickness variations and associated topographic contrasts at the surface of a planet result in lateral pressure gradients which may cause the lower crust to flow and reduce the relief areas of thicker crust are generally associated with more rapid relaxation of topography on mars topographic features such as impact basins and the hemispheric dichotomy have survived for 4 gyr we use a finite difference representation of depth dependent non newtonian lower crustal flow to investigate how topography decays with time for a dry diabase rheology total radiogenic concentrations 80 of terrestrial values and crustal radiogenic concentrations similar to terrestrial basalts we find that an upper bound on the mean planetary crustal thickness is 100 km in the probably unrealistic case where all the radiogenic elements are in the crust this maximum crustal thickness can be increased to 115 km the main uncertainty in these results is the total radiogenic abundances on mars comparing our results with the observed shape of the crustal dichotomy provides no evidence that this slope is primarily the result of lower crustal flow both hellas and the dichotomy are isostatically compensated if the mechanism is airy isostasy then the lower bound on mean crustal thickness is 30 km crustal thicknesses of 30 100 km on mars can be produced by mid ocean ridge spreading at potential temperatures of 1350 1600 c however for such crustal thicknesses the lithosphere is likely to be positively buoyant making subduction difficult

fluctuations in epeiric sea carbonate production during silurian positive carbon isotope excursions a review of proposed paleoceanographic models positive excursions in the carbon isotopic ratio of marine carbonates 13ccarb are commonly attributed to an increase in the burial ratio of organic versus carbonate carbon in the global oceans regardless of whether this increased deposition of organic carbon was oceanographically or biologically induced the fact that high carbon isotope values are most often attributed to the sequestration and burial of organic carbon remains the notion that high 13ccarb values should be the result of organic rich deposition in epeiric sea settings is not surprising considering that the overwhelming majority of organic carbon burial in the modern oceans occurs in continental shelf and margin settings what is surprising is that major positive carbon isotope excursions during the silurian are recorded in clean carbonate successions with little to no appreciable black shale deposition in epeiric seas in fact silurian 13ccarb excursions occurred during intervals of prolific reef development and an overall expansion of carbonate platform environments globally this discrepancy has sparked considerable debate among silurian carbon isotope specialists but has offered a valuable opportunity to re examine the intricate connections among nutrients primary productivity carbonate sedimentology and the global carbon cycle in the lower paleozoic here we consider several sedimentological and geochemical features of one of these silurian positive carbon isotope 13ccarb excursions and discuss the broader implications of current silurian 13ccarb models to the interpretation of lower paleozoic carbonate sequences

martian plate tectonics the northern lowlands of mars may have been produced by plate tectonics preexisting old thick highland crust was subducted while seafloor spreading produced thin lowland crust during late noachian and early hesperian time in the preferred reconstruction a breakup margin extended north of cimmeria terra between daedalia planum and isidis planitia where the highland lowland transition is relatively simple south dipping subduction occurred beneath arabia terra and east dipping subduction beneath thatsis montes and tempe terra lineations associated with gordii dotsum are attributed to ridge parallel structures while phelegra montes and scandia colles are interpreted as transform parallel structures or ridge fault fault triple junction tracks other than for these few features there is little topographic roughness in the lowlands seafloor spreading if it occurred must have been relatively rapid quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower c 0 4 g gravity of mars the absence of vertical scarps from age differences across fracture zones and the smooth axial topography to the first order the height of vertical scarps across fracture zones does not involve gravity crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity thus the velocity of the rough smooth transition for axial topography also scales inversely with gravity plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age possible plate reorganizations for example the end of spreading through alba patera occur when the ridge axis is far from the trench that is rapid plate motions are inferred to have placed young oceanic crust far from the ridge axis the preferred full spreading rate 900 from the plate pole is 80 mm yr 1 plate tectonics if it occurred dominated the thermal and stress history of the planet a geochemical implication is that the lower gravity of mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the earth age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses about mars plate tectonics

volcano infrasound a review abstract exploding volcanoes which produce intense infrasound are reminiscent of the veritable explosion of volcano infrasound papers published during the last decade volcano infrasound is effective for tracking and quantifying eruptive phenomena because it corresponds to activity occurring near and around the volcanic vent as opposed to seismic signals which are generated by both surface and internal volcanic processes as with seismology infrasound can be recorded remotely during inclement weather or in the dark to provide a continuous record of a volcano s unrest moreover it can also be exploited at regional or global distances where seismic monitoring has limited efficacy this paper provides a literature overview of the current state of the field and summarizes applications of infrasound as a tool for better understanding volcanic activity many infrasound studies have focused on integration with other geophysical data including seismic thermal electromagnetic radiation and gas spectroscopy and they have generally improved our understanding of eruption dynamics other work has incorporated infrasound into volcano surveillance to enhance capabilities for monitoring hazardous volcanoes and reducing risk this paper aims to provide an overview of volcano airwave studies from analog microbarometer to modern pressure transducer and summarizes how infrasound is currently used to infer eruption dynamics it also outlines the relative merits of local and regional infrasound surveillance highlights differences between array and network sensor topologies and concludes with mention of sensor technologies appropriate for volcano infrasound study

seismic and infrasonic evidences for an impulsive source of the shallow volcanic tremor at mt etna italy during a seismo acoustic experiment we recorded volcanic tremor around the summit craters of mt etna volcano tremor shows amplitude modulation which disappear 900 m from the crater area the infrasonic wavefield is coherent even at distances of 750 m time delay between infrasonic transient is stable around 1 3 s and is consistent with the position of the source in the voragine crater amplitude modulation of tremor is well correlated 0 72 with infrasound amplitude with a time lag of 0 37 s coherent with a shallow position of the source amplitude of volcanic tremor decays over increasing distances according to geometrical spreading of body waves tremor wavefield shows a linear polarization following the same time occourrence as the infrasonic pulses polarization azimuth indicates that wavefield rectilinearity is mostly due to p waves we infer that most of the volcanic tremor we recorded at mt etna is generated by superimposition of small impulsive sources acting at 1 2 s rate caused by pressure instability during magma degassing

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

seismic and infrasound signals at mt etna modeling the north east crater conduit and its relation with the 2008 2009 eruption feeding system abstract on 13 may 2008 an eruption began at mt etna from an eruptive fissure that opened on the upper eastern flank of the volcano during 12 13 may 157 infrasonic events together with the related seismic transients were collected we carried out several analyses to obtain dominant frequencies pseudospectrograms peak to peak amplitudes source locations and time lags between infrasonic and seismic events spectra of the infrasonic events show two main spectral peaks in the frequency bands 0 4 0 7 hz and 1 5 2 0 hz respectively both infrasonic and seismic events were separately located below the north east crater where no eruptive activity was observed moreover significant changes in infrasound spectral content as well as in the infrasonic seismic lags were found a few hours before the beginning of the eruption on the basis of the collected information the infrasound source mechanism was modeled as a superposition of pipe and helmholtz resonance also leading to outline the geometry of the shallower portion of the north east crater plumbing system the occurrence of these seismo infrasonic events together with other geological and geophysical evidences led us to inferring a direct link between north east crater activity and the eruptive fissure further based on variations over time of both spectral features and seismic infrasonic time lag shallowing phenomena of the free magma column inside north east crater conduit were hypothesized such an uprise of magma was likely caused by a pressure increase inside the plumbing system occurring before the beginning of the 2008 2009 eruption

magnetization paleomagnetic poles and polar wander on mars abstract using the geometry of an areocentric dipole field we have remodeled the anomalies observed in the terra sirenum and terra cimmeria regions by the mars global surveyor mgs for the origin of the anomalies we used both magnetic stripe and magnetic shell hypotheses for magnetic stripe models we assume that sea floor spreading formed the anomalies in the presence of a reversing axial dipole field we found that a simple magnetic stripe model with constant magnetization and crustal thickness results in poor agreement with the observed anomalies however by allowing the intensity of magnetization to vary freely between and along the stripes a reasonable fit to the observed data can be found while maintaining the observed polarity along the stripes applying the simple magnetic stripe model to the terra sirenum and terra cimmeria anomalies results in best fit spreading centers located well to the north of the surviving magnetic stripes this could possibly explain the apparent lack of symmetry that has been noted in the anomalies for the magnetic shell hypothesis we assume that a monopolarity dipole field magnetized the early crust of mars the anomalies that persist today would then be the result of partial demagnetization of the original magnetic shell by more recent processes the magnetic anomalies in terra sirenum and terra cimmeria are consistent with this model especially if the magnetization of the original magnetic shell was laterally inhomogeneous if the monopolarity magnetic shell hypothesis is correct best fit magnetic paleopole locations for the original magnetization lie in a sub equatorial belt centered near the prime meridian if the ancient magnetic pole of mars coincided with the spin pole this result implies that either apparent or true polar wander has occurred on mars apparent polar wander would be consistent with plate tectonics having occurred after the formation of the magnetic anomalies true polar wander has previously been proposed to explain certain morphologic features found on mars

degree 1 convection in the martian mantle and the origin of the hemispheric dichotomy 1 the surface of mars appears dramatically different between the northern and southern hemispheres any endogenic origin for this hemispheric dichotomy must involve a pattern of mantle convection that reflects the shape of the dichotomy primarily spherical harmonic degree 1 we investigated two mechanisms by which degree 1 convection may be initiated in the martian mantle 1 an endothermic phase change near the cmb and 2 viscosity layering in the mid mantle using two dimensional 2 d and 3 d spherical finite element convection models we explored the conditions under which each mechanism can produce degree 1 structures the phase transition is only effective at generating degree 1 structures when the mantle viscosity is constant or weakly temperature dependent activation energy 100 kj mol but the degree 1 pattern requires several billion years to develop increasing convective vigor in phase change models leads to reduced wavelengths for convective structures degree 1 convection can also develop in a layered viscosity mantle with temperature and depth dependent viscosity an overall sublithospheric radial viscosity variation of a factor of 100 including a factor of 8 25 jump in the midmantle can lead to formation of degree 1 structure in a timescale ranging from 100 my to several hundred my consistent with the timescale for the formation of the dichotomy neither convective vigor nor the internal heating rate greatly affects the formation of degree 1 structures we propose that degree 1 mantle convection induced by a layered viscosity structure may be responsible for the formation of the crustal dichotomy

high frame rate thermal imagery of strombolian explosions implications for explosive and infrasonic source dynamics 1 explosive activity at stromboli volcano is analyzed using a high frame rate 50 hz thermal camera and differential pressure transducers we develop a thermal image based decomposition method to derive vertical and horizontal exit velocities of the explosive cloud peak vertical velocity ranges between 23 and 203 m s slightly higher than previous estimates and rapidly decreasing to a constant value of 30 50 m s within the first 0 1 s plume velocities are consistent with an elongated cloud expanding much faster vertically than horizontally and indicating the interaction with the conduit wall considering a vent radius of 2 m we estimate a volumetric flux of 200 600 m3 s which converts to total volumes of gas particles of 103 104 m3 for a single eruption these volumes are proportional to the thermal energy recorded by the camera providing a means to convert thermal radiance to volumes comparing the thermal onset of the explosions with the arrival time of the acoustic pressure we demonstrate that infrasound is propagating 0 14 1 7 s ahead of the explosive front the time difference between thermal and acoustic onsets constrains the infrasonic source within the conduit at 15 35 m below the crater rim peak amplitudes of acoustic pressure show a power law relationship p u2 with the exit vertical velocities consistent with the energy balance of a two phase flow rapidly accelerated in the conduit by gas decompression our results support monopole isotropic acoustic radiation of a source embedded within the conduit walls and indicate that explosive dynamics undergo strong accelerations of 103 104 m s2

catastrophic soil erosion during the end permian biotic crisis organic geochemical analyses of sedimentary organic matter from a marine permian triassic transition sequence in northeastern italy reveal a significant influx of land derived diagenetic products of polysaccharides this unique event reflects massive soil erosion resulting from destruction of land vegetation due to volcanogenic disturbance of atmospheric chemistry the excessive supply of soil materials to the oceans provides a direct link between terrestrial and marine ecological crises suggesting that ecosystem collapse on land could have contributed to the end permian marine extinctions

earthquakes series preceding very long period seismic signals observed during the 2000 miyakejima volcanic activity 1 unusual earthquakes series were observed one to two hours before a very long period vlp seismic pulse that happened once or twice a day during the 2000 activity of miyakejima volcano japan the series on july 11 and 12 have particularly a clear feature the time intervals of the earthquakes in the series decrease at a constant rate in the manner of geometric progression the maximum amplitude of each earthquake is initially almost constant but linearly decreases with time from few minutes before the occurrence of a vlp pulse hypocenters of these earthquakes are below the south western region of the crater and near the sea level in depth we interpret these earthquakes series as repetition of a gradual stress accumulation and release under the variable critical stress level the critical stress level is first constant but linearly decreases later

the cause for the north south orientation of the crustal dichotomy and the equatorial location of tharsis on mars the crustal dichotomy and the tharsis rise are the most prominent topographic features on mars the dichotomy is largely an expression of different crustal thicknesses in the northern and southern hemispheres while tharsis is centered near the equator at the dichotomy boundary however the cause for the orientation of the dichotomy and the equatorial location of tharsis remains poorly understood here we show that the crustal thickness variations associated with the dichotomy may have driven true polar wander establishing the north south orientation of the dichotomy very early in martian history such a reorientation that placed the dichotomy boundary near the equator would also have constrained the tharsis region on the dichotomy boundary to have originated near the equator we present a scenario for the early generation and subsequent reorientation of the hemispheric dichotomy although the reorientation is independent of the formation mechanism our results also have implications for the sharply different remanent magnetizations between the two hemispheres

geological evidence for a migrating tharsis plume on early mars abstract the tharsis bulge is the largest magmatic volcanic center on mars and in the solar system having a volume of 3 10 8 km 3 with the majority of its mass emplaced more than 3 7 billion years ago the igneous history of tharsis has been implicated in the generation of an atmosphere and hydrosphere capable of clement conditions on early mars it has been proposed that an early plume migration from the southern highlands of mars relative to a one plate lithosphere led to the development of the tharsis bulge in its current location along the martian crustal dichotomy we used geologic mapping crustal magnetic data crater age dating and crater morphometry to detail a previously unidentified path of putative plume migration our results indicate that extensive volcanic resurfacing occurred from a location near the present south pole to the equator around 3 8 billion years ago obliterating older cratered terrains the resurfacing path is manifest as smooth volcanic plains embaying ancient massifs and infilling large impact craters as well as a lack of a magnetic signature in this portion of the crust our results have significant ramifications for mantle dynamics and the early geologic history of mars

crustal heat production and the thermal evolution of mars the chemical composition of soils and rocks from the pathfinder site and phobos 2 orbital gamma ray spectroscopy indicate that the martian crust has a bulk composition equivalent to large ion lithophile lil and heat producing element k th u enriched basalt with a potassium content of about 0 5 a variety of radiogenic isotope data also suggest that separation of lil enriched crust and depleted mantle reservoirs took place very early in martian history 4 0 ga accordingly if the enriched martian crust is 30 km thick it is likely that a large fraction up to at least 50 of the heat producing elements in mars was transferred into the crust very early in the planet s history this would greatly diminish the possibility of early widespread melting of the martian mantle

long wavelength stagnant lid convection with hemispheric variation in lithospheric thickness link between martian crustal dichotomy and tharsis 1 a dynamic link between the early evolution of tharsis and the crustal dichotomy on mars was recently proposed by zhong 2009 we address in detail the fundamental aspects of the proposed model using 3 d spherical shell modeling of convection we investigate the conditions under which a spherical harmonic degree 1 flow is produced in the mantle of mars in layered viscosity models with different depths of viscosity layering and different viscosity ratios between the bottom and top layers we find that a thinner weak layer requires a larger viscosity decrease in order to produce degree 1 planform in qualitative accordance with existing analytical studies a lithospheric keel of hemispheric extent which may represent melt residue after dichotomy formation process is then introduced in the models as a consequence thermal upwellings are first formed and oriented below the center of the melt residue cap for keels of maximum thickness 100 km a rotation of the entire single plate lithosphere relative to the underlying mantle follows until the plume is stabilized near the edge of the keel which can be identified as the dichotomy boundary this model may explain the early migration of the tharsis volcanic center from southern latitudes to the vicinity of the dichotomy boundary for keels 200 km thick the modeled time scales agree with observationally inferred migration rate if the tharsis migration is caused by the rotation of the lithosphere the requirement on the amount and location of upper mantle melting would argue for an endogenic origin of the dichotomy

stable carbon isotope stratigraphy across the permian triassic boundary in shallow marine carbonate platforms nanpanjiang basin south china a distinct negative 13c excursion is documented in two permian triassic sections heping and taiping in shallow marine carbonate platform deposits in the nanpanjiang basin south china these sections span from the changhsingian to the dienerian and are characterized by a distinct marine boundary facies change from massive skeletal lime packstone in the changhsingian to distinctive calcimicrobial framestone in the griesbachian hindeodus parvus zone the 13corg and 13ccarb excursions occur directly after the onset of the calcimicrobial framestone herein termed the permian triassic boundary event and before the first occurrence of h parvus the isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon toc content the shift towards depleted values in 13corg and 13ccarb at the permian triassic boundary event together with low toc contents persists throughout the griesbachian h parvus zone these data document a corresponding negative shift of 13corg and 13ccarb values and low toc contents with the onset of growth of calcified microbial framestones a postextinction disaster facies immediately below the base of the griesbachian h parvus zone based on paleontological evidence the first occurrence of the disaster facies follows the extinction event which implies that the 13c depleted values above this facies postdate the event this suggests that two separate events had to account for the initiation of the extinction and the 13c excursion however the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of early triassic ecosystems based on data from ptb sections worldwide of a greater 13c offset in high compared with low latitudes we propose that methane eruptions from thermal destabilization of high latitude clathrate deposits may have led to the negative 13c shift and may have caused long term adverse ecological conditions

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

a spatially continuous magnetization model for mars 1 using a three component magnetic field data set at over 100 000 satellite points previously compiled for spherical harmonic analysis we have produced a continuously varying magnetization model for mars the magnetized layer was assumed to be 40 km thick an average value based on previous studies of the topography and gravity field the severe nonuniqueness in magnetization modeling is addressed by seeking the model with minimum root mean square rms magnetization for a given fit to the data with the trade off between rms magnetization and fit controlled by a damping parameter our preferred model has magnetization amplitudes up to 20 a m it is expressed as a linear combination of the green s functions relating each observation to magnetization at the point of interest within the crust leading to a linear system of equations of dimension the number of data points although this is impractically large for direct solution most of the matrix elements relating data to model parameters are negligibly small we therefore apply methods applicable to sparse systems allowing us to preserve the resolution of the original data set thus we produce more detailed models than any previously published although they share many similarities we find that tectonism in the valles marineris region has a magnetic signature and we show that volcanism south of the dichotomy boundary has both a magnetic and gravity signature the method can also be used to downward continue magnetic data and a comparison with other leveling techniques at mars surface is favorable

mars paleomagnetic field as the result of a single hemisphere dynamo mars crustal magnetic field was most likely generated by dynamo action in the planet s early history unexplained characteristics of the field include its strength concentration in the southern hemisphere and lack of correlation with any surface features except for the hemispheric crustal dichotomy we used numerical dynamo modeling to demonstrate that the mechanisms proposed to explain crustal dichotomy formation can result in a single hemisphere dynamo this dynamo produces strong magnetic fields in only the southern hemisphere this magnetic field morphology can explain why mars crustal magnetic field intensities are substantially stronger in the southern hemisphere without relying on any postdynamo mechanisms

caldera collapse during the 2000 eruption of miyakejima volcano japan a collapsed caldera 1 6 km in diameter and 450 m in depth was formed at the summit of miyakejima volcano during the 2000 eruption the collapsed caldera appeared on 8 july with a minor phreatic eruption 12 days after seismic activity and magma intrusion occurred northwest of the volcano growth of the caldera took from 8 july to the middle of august with seismic swarms associated with the continuous intrusion of magma northwest of the volcano the growth rate of the caldera was about 1 4 107 m3 day and the final volume of the collapsed caldera was about 6 108 m3 major phreatomagmatic eruptions produced a total of about 1 6 1010 kg 1 1 107 m3 of volcanic ash after caldera growth the caldera structure and the nature of the eruptive materials of the first collapse on 8 july suggest that the surface subsidence was caused by the upward migration of a steam filled cavity with stoping of the roof rock above the magma reservoir the diameter of the stoping column was estimated to be 600 700 m from circumferential faults that developed in the caldera floor and the collapse of the caldera wall enlarged the diameter of the caldera to 1 6 km the total volume of the caldera and the horizontal diameter of the stoping column gave a subsidence of the caldera floor of 1 6 2 1 km

large impact basins and the mega impact origin for the crustal dichotomy on mars the origin of the fundamental crustal dichotomy on mars remains the outstanding unsolved problem in martian geologic evolution the hypothesis that this dichotomy is due to a single giant mega impact early in martian history is tested by comparing the observed number of large impact basins on mars with the number expected from a d 2 distribution this test is based on the assumption that the mega impact borealis basin is the largest member of such a distribution the difference between observed and expected basins is the number of missing basins that might have been obscured by subsequent geologic events if the borealis basin were the largest member of a d 2 impact population there would be a very large number of missing basins on mars 1 larger than 5000 km 10 larger than 2000 km and 40 50 larger than about 1000 km diameter the area occupied by these missing basins allowing for overlap is too large to be hidden by the younger surface units a large population of presently unrecognized large impact basins would have to be located in the well preserved cratered highlands by contrast if chryse is the largest member of a d 2 impact population the more modest number of missing basins could in principle be confined to areas of mars that have been resurfaced or reworked by subsequent geologic processes a possible alternative to the mega impact hypothesis is that the crustal dichotomy is due to the cumulative effects of multiple overlapping large but not giant impacts

permo triassic boundary superanoxia and stratified superocean records from lost deep sea pelagic cherts of japan and british columbia canada recorded a long term and worldwide deep sea anoxic oxygen depleted event across the permo triassic or paleozoic and mesozoic boundary 251 2 million years ago the symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean panthalassa became totally stratified for nearly 20 million years across the boundary the timing of onset climax and termination of the oceanic stratification correspond to global biotic events including the end guadalupian decline the end permian extinction and mid triassic recovery

a global marine sedimentary response to the end permian mass extinction examples from southern turkey and the western united states the end permian mass extinction greatly diminished marine diversity and brought about a whole scale restructuring of marine ecosystems these ecosystem changes also profoundly affected the sedimentary record data presented here attained through facies analyses of strata deposited during the immediate aftermath of the end permian mass extinction southern turkey and at the close of the early triassic southwestern united states in combination with a literature review show that sedimentary systems were profoundly affected by 1 a reduction in biotic diversity and abundance and 2 long term environmental fluctuations that resulted from the end permian crisis lower triassic strata display widespread microbialite and carbonate seafloor fan development and contain indicators of suppressed infaunal bioturbation such as flat pebble conglomerates and wrinkle structures facies considered unusual in post cambrian subtidal deposits our observations suggest that depositional systems too respond to biotic crises and that certain facies may act as barometers of ecologic and environmental change independent of fossil assemblage analyses close investigation of facies changes during other critical times in earth history may serve as an important tool in interpreting the ecology of metazoans and their environment

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

new perspectives on ancient mars mars was most active during its first billion years the core mantle and crust formed within 50 million years of solar system formation a magnetic dynamo in a convecting fluid core magnetized the crust and the global field shielded a more massive early atmosphere against solar wind stripping the tharsis province became a focus for volcanism deformation and outgassing of water and carbon dioxide in quantities possibly sufficient to induce episodes of climate warming surficial and near surface water contributed to regionally extensive erosion sediment transport and chemical alteration deep hydrothermal circulation accelerated crustal cooling preserved variations in crustal thickness and modified patterns of crustal magnetization

magnetization of the martian crust 1 this paper presents the lateral variations of the vertically averaged magnetization model of the martian crust determined from the degree 50 spherical harmonic model of the magnetic potential the model potential is derived using the mars global surveyor low altitude magnetic data acquired within elevations of 85 200 km the potential model is first verified by comparing the three orthogonal components of the corresponding vector field with the observed high altitude 380 km data using the paleopole positions calculated through modeling 10 isolated small magnetic anomalies the model potential is inverted to determine the vertically averaged magnetization of a nominal 50 km thick crust the crust is highly magnetic with a magnetization contrast peak to trough as high as 35 a m the lack of distinct magnetic signatures for the giant impact basins hellas argyre and isidis and the absence of a magnetic anomaly associated with the north south topographic dichotomy indicate that the upper parts of the crust are low magnetic and that the strong magnetic source bodies are in the lower parts

effects of volcano topography on seismic broad band waveforms volcano seismology often deals with rather shallow seismic sources and seismic stations deployed in their near field the complex stratigraphy on volcanoes and near field source effects have a strong impact on the seismic wavefield complicating the interpretation techniques that are usually employed in earthquake seismology in addition as most volcanoes have a pronounced topography the interference of the seismic wavefield with the stress free surface results in severe waveform perturbations that affect seismic interpretation methods in this study we deal predominantly with the surface effects but take into account the impact of a typical volcano stratigraphy as well as near field source effects we derive a correction term for plane seismic waves and a plane free surface such that for smooth topographies the effect of the free surface can be totally removed seismo volcanic sources radiate energy in a broad frequency range with a correspondingly wide range of different fresnel zones a 2 d boundary element method is employed to study how the size of the fresnel zone is dependent on source depth dominant wavelength and topography in order to estimate the limits of the plane wave approximation this approximation remains valid if the dominant wavelength does not exceed twice the source depth further aspects of this study concern particle motion analysis to locate point sources and the influence of the stratigraphy on particle motions furthermore the deployment strategy of seismic instruments on volcanoes as well as the direct interpretation of the broad band waveforms in terms of pressure fluctuations in the volcanic plumbing system are discussed

carbon isotope excursions and microfacies changes in marine permian triassic boundary sections in hungary abstract several permian triassic boundary sections occur in various structural units within hungary these sections represent different facies zones of the western palaeotethys margin the gardony core in the ne part of the transdanubian range typically represents the inner ramp while the balvany section in the bukk mountains of northern hungary represents an outer ramp setting the two sections have different patterns for their 13 c values the balvany section shows a continuous change towards more negative 13 c values starting at the first biotic decline followed by a sharp quasi symmetric negative peak at the second decline the appearance of the 13 c peak has no relationship to the lithology and occurs within a shale with low overall carbonate content indicating that the peak is not related to diagenesis or other secondary influences instead the shift and the peak reflect primary processes related to changes in environmental conditions the continuous shift in 13 c values is most probably related to a decrease in bioproductivity whereas the sharp peak can be attributed to an addition of c strongly depleted in 13 c to the ocean atmosphere system the most plausible model is a massive release of methane hydrate the quasi symmetric pattern suggests a rapid warming cooling cycle or physical unroofing of sediments through slope failure and releasing methane hydrate the gardony 1 core shows a continuous negative 13 c shift starting below the p t boundary however the detailed analyses revealed a sharp 13 c peak in the boundary interval just below the major biotic decline although its magnitude doesn t reach that observed in the balvany section based on careful textural examination and high resolution stable isotope microanalyses we suggest that the suppression of the 13 c peak that is common in the oolitic boundary sections is due to combined effects of condensed sedimentation sediment reworking and erosion as well as perhaps diagenesis