intermediate term predictions of earthquakes in italy algorithm m8 large earthquakes in italy are preceded by a specific seismic activation which could be diagnosed by a reproducible intermediate term earthquake prediction method a modification for lower seismic rate areas of the algorithm known as m8 keilis borok and kossobokov 1990 use has been made of the pfg ing catalog of earthquakes compiled on a regular basis to determine areas and times of increased probability for occurrences of m 6 earthquakes in retroactive simulation of forward prediction for the period 1972 1995 both the 1976 friuli m 6 1 and the 1980 irpinia m 6 5 earthquakes are predicted in the experiment where priority magnitude scale is used the times of increased probability for a strong earthquake to occur tips occupy less than a quarter of the total magnitude space time domain and are rather stable with respect to positioning of circles of investiga tion successful stability tests have been made considering a recently compiled catalog cci97 peresan et al 1997 in combination with the cn algorithm results costa et al 1996 the spatio temporal uncertainty of the prediction could be reduced to 5 the use of m8 for the forward prediction requires the computations to be repeated each half year using the updated catalog

volcanism on mercury evidence from the first messenger flyby for extrusive and explosive activity and the volcanic origin of plains the first messenger flyby of mercury obtained images of 21 of the surface not seen by mariner 10 including the center and western half of the caloris basin and regions near the terminator that show details of the nature of smooth and intercrater plains these new data have helped to address and resolve a series of longstanding questions on the existence and nature of volcanism on mercury and the distribution of volcanic materials data from the mercury dual imaging system mdis on the messenger spacecraft have shown the following 1 numerous volcanic vents in the form of irregularly shaped rimless depressions are concentrated around the interior edge of the caloris basin 2 these vents appear to be sources for effusive volcanism that in one case built a shield in excess of 100 km in diameter and in some cases formed bright haloes around the vents that are interpreted to represent pyroclastic eruptions 3 lobate margins of plains units seen previously in mariner 10 data are documented in messenger images with more clarity and are often distinctive in morphology and color properties supporting the interpretation that these features are the edges of lava flow units 4 the interior of the caloris basin is filled with plains units spectrally distinctive from the rim deposits and comparison with the lunar imbrium basin and superposed impact crater stratigraphy provide evidence that these units are volcanic in origin detailed differences in the mineralogy of lava flow units so prominent in imbrium are not seen in the caloris interior 5 some of the smooth plains surrounding the exterior of the caloris basin show distinct differences in color and morphological properties supporting a volcanic origin 6 some smooth and intercrater plains units distant from the caloris basin show evidence of flooding and embayment relations unrelated to caloris ejecta emplacement local and regional geological and color relationships support a volcanic origin for these plains 7 large impact craters show a sequence of embayment of interior floor and exterior ejecta deposits that supports a volcanic origin for the embayment and filling processes 8 crater embayment and flooding relationships in selected areas suggest volcanic plains thicknesses of many hundreds of meters and local thicknesses inside impact craters of up to several kilometers 9 impact crater size frequency distributions for caloris exterior deposits including the facies of the caloris group and relatively high and low albedo smooth plains show that they are younger than plains interior to caloris and thus must be dominantly the product of post caloris volcanism these new data provide evidence that supports and confirms earlier hypotheses from mariner 10 data that volcanism was important in shaping the surface of mercury the emerging picture of the volcanic style of mercury is similar to that of the moon the other small one plate planetary body there are no major shield volcanoes e g comparable to tharsis montes on mars shallow magma reservoirs are rare and there is little evidence for surface deformation or long lived volcanic sources related to sites of upwelling mantle the close association of volcanic plains and surface deformation features suggests that future observations and analyses can help document the relation between the volcanic flux and the evolving state and magnitude of stress in the lithosphere of mercury

the age petrogeneis and tectonic significance of the frontenac formation basalts northern new hampshire and western maine within plate basalts are present across the connecticut valley gaspe trough in new england and canada proposed mechanisms for the extensional magmatism include back arc basin extension slab breakoff and extensional collapse the age and composition of the bimodal frontenac formation of northern new england and southern quebec has bearing on the topic we analyzed zircons from the meta felsic rocks of the formation and determined a silurian age of 432 8 ma we also analyzed the frontenac rocks for major and trace elements and compared their compositions to the other mafic rocks along strike in the connecticut valley gaspe trough these include the comerford intrusive suite and the standing pond volcanic member of the waits river formation of vermont the silurian chaleur group and the early devonian dalhousie group of new brunswick and the gaspe peninsula and to the piscataquis belt rocks of northern maine all these rocks are post taconic within plate tholeiites that span an age range from 432 ma frontenac formation to 419 ma comerford intrusive suite in spite of their similar tectonic setting subtle differences in trace element compositions are evident indicating a multiplicity of sources in the production of the siluro devonian magmas ce yb versus la ta values suggest that the frontenac magmas were derived from spinel peridotite sources in the asthenospheric mantle we suggest that slab rollback and back arc basin extension permitted asthenospheric mantle upwelling to the spinel peridotite stability field causing the frontenac partial melting event at depths as low as 35 km sediments of the frontenac formation were deposited as turbidite successions into a developing trough resulting from extension the coeval influx of sediment and intrusion of basalt produced a sediment sill complex because the upward migration of the basaltic magmas was hindered by the rapidly thickening sediment overburden subsequently slab breakoff may have opened an asthenospheric window generating the younger within plate magmas that occurred from 425 to 418 ma across the connecticut valley gaspe trough

mechanical and geological effects of impact cratering on ida asteroids respond to impact stresses differently from either laboratory specimens or large planets gravity is typically so small that seismic disturbances of a few cm s 1can devastate unconsolidated topography yet the presence of regolith and the likelihood that many asteroids are gravitational assemblages tell us that gravity cannot generally be ignored we use numerical models for impact fracture in solids to examine the initial stage of crater formation on asteroid 243 ida up to the cessation of fracture and the establishment of the cratering flow at this stage we can infer final crater diameters but not profiles we find that a modified strength scaling applies for craters up to a few 100 m in diameter forming in rock subject to ida s gravity and that gravity controls all craters larger than 1 km bright annuli around a number of intermediate craters may be the result of low velocity surface disturbances rather than bright proximal ejecta deposits we also consider large impactors to which ida presents a curved finite target surface with irregular gravity these can excavate asymmetrical concavities stresses from large events can refocus and cause fracture far from the crater using the shape of ida as a basis for 3d hydrocode simulations we show that impact genesis of the vienna regio concavity can cause fracture in pola regio where grooves are observed in spacecraft images other simulations indicate that the formation of the 10 km crater azzurra might have reopened these fractures which may account for their fresh appearance this mechanism of groove formation requires an interior which coherently transmits elastic stress while this precludes a classic rubble pile asteroid it does allow well joined fault planes and welded blocks or pores smaller than the stress pulse

ejecta from impact craters an important feature of impacts into solar system bodies is the fate of crater ejecta the near surface material launched during the highly dynamic crater formation process laboratory measurements of impact crater ejecta from 18 studies are summarized the data are examined and used to assess our understanding of how the ejecta velocity and mass distributions depend on the conditions of an impact event the effects of impact speed on the ejecta are reasonably well understood but the dependences on target properties such as strength and porosity are only poorly constrained a point source scaling model for the ejecta mass and velocity distributions is developed and fit to the data for several classes of materials distinguished by porosity

the morphology of craters on mercury results from messenger flybys topographic data measured from the mercury laser altimeter mla and the mercury dual imaging system mdis aboard the messenger spacecraft were used for investigations of the relationship between depth and diameter for impact craters on mercury results using data from the messenger flybys of the innermost planet indicate that most of the craters measured with mla are shallower than those previously measured by using mariner 10 images mdis images of these same mla measured craters show that they have been modified the use of shadow measurement techniques which were found to be accurate relative to the mla results indicate that both small bowl shaped and large complex craters that are fresh possess depth to diameter ratios that are in good agreement with those measured from mariner 10 images the preliminary data also show that the depths of modified craters are shallower relative to fresh ones and might provide quantitative estimates of crater in filling by subsequent volcanic or impact processes the diameter that defines the transition from simple to complex craters on mercury based on messenger data is consistent with that reported from mariner 10 data

mercury cratering record viewed from messenger s first flyby morphologies and size frequency distributions of impact craters on mercury imaged during messenger s first flyby elucidate the planet s geological history plains interior to the caloris basin displaying color and albedo contrasts have comparable crater densities and therefore similar ages smooth plains exterior to caloris exhibit a crater density 40 less than on interior plains and are thus volcanic and not caloris impact ejecta the size distribution of smooth plains craters matches that of lunar craters postdating the late heavy bombardment implying that the plains formed no earlier than 3 8 billion years ago ga at diameters less than or equal to 8 to 10 kilometers secondary impact craters on mercury are more abundant than primaries this transition diameter is much larger than that on the moon or mars a low density of craters on the peak ring basin raditladi implies that it may be younger than 1 ga

on intermediate term earthquake prediction in central italy the time of increased probability tip for the occurrence of a strong earthquake is determined in central italy this is done with an algorithm that has been successfully applied in other regions of the world algorithm cn from the initials of california and nevada where the first diagnoses of tips were made the use of normalized functions allows direct application of the orginal algorithm to the new region being studied without anyad hoc adjustment of the parameters

determining ages of multiple muscovite bearing foliations in phyllonites using the 40ar 39ar step heating method applications to the alleghanian orogeny in central new england

the development of structural geology and the historical context of the journal of structural geology a reflection by bruce hobbs abstract this paper sets the historical context for the journal of structural geology when it was first published in 1979 the major advances in structural geology over the past 40 years are then highlighted finally ten grand challenges for the next decade are nominated

supplemental material zircon and monazite geochronology in the palmer zone of transpression south central new england usa constraints on timing of deformation high grade metamorphism and lithospheric foundering during late paleozoic oblique collision in the northern appalachian orogen analytical methods for zircon u pb and monazite th pb sims geochronology zircon u pb la icp ms geochronology data tables and supporting previous work

influence of deformation and fluids on ar retention in white mica dating the dover fault newfoundland appalachians abstract white mica 40ar 39ar analyses may provide useful constraints on the timing of tectonic processes but complex geological and thermal histories can perturb ar systematics in a variety of ways ductile shear zones represent excellent case studies for exploring the link s between dynamic re neo crystallization of white mica and coeval enhanced fluid flow and their effect on 40ar 39ar dates white mica 40ar 39ar dates were collected from compositionally similar granites that record different episodes of deformation with proximity to the dover fault a terrane bounding strike slip shear zone in the appalachian orogen newfoundland canada 40ar 39ar data were collected in situ by laser ablation and by step heating single crystals results were compared to each other and against complementary u pb zircon and monazite and k ar fault gouge analysis although step heat 40ar 39ar is a widely applied method in orogenic settings this dataset shows that relatively flat step heat 40ar 39ar spectra are in contradiction with wide spreads in in situ 40ar 39ar dates from the same samples and that plateau dates in some cases yielded mixed dates of equivocal geological significance this result indicates that the step wise release of ar from white mica likely homogenizes and obscures spatially controlled ar isotope reservoirs in white mica from sheared rocks in contrast in situ laser ablation 40ar 39ar analysis preserves the spatial resolution of 40ar reservoirs that have been variably reset by deformation and fluid interaction this study therefore suggests that laser ablation is the best method for dating the timing of deformation recorded by white mica final interpretation of results should be guided by microstructural analysis estimation of deformation temperature chemical characterization of white mica and complementary chronometers overall the dataset shows that granitic protoliths were emplaced between 430 and 422 ma u pb zircon high strain deformation along the wing pond shear zone occurred between ca 422 405 ma u pb monazite and 40ar 39ar subsequent patchy ar loss in white mica occurred locally during low t shear

thickness constraints on the icy shells of the galilean satellites from a comparison of crater shapes a thin outer ice shell on jupiter s large moon europa would imply easy exchange between the surface and any organic or biotic material in its putative subsurface ocean1 2 3 4 the thickness of the outer ice shell is poorly constrained however with model dependent estimates ranging from a few kilometres5 6 to ten or more kilometres7 here i present measurements of depths of impact craters on europa ganymede and callisto that reveal two anomalous transitions in crater shape with diameter the first transition is probably related to temperature dependent ductility of the crust at shallow depths 7 8 km on europa the second transition is attributed to the influence of subsurface oceans on all three satellites3 8 9 which constrains europa s icy shell to be at least 19 km thick the icy lithospheres of ganymede and callisto are equally ice rich but europa s icy shell has a thermal structure about 0 25 0 5 times the thicknesses of ganymede s or callisto s shells depending on epoch the appearances of the craters on europa are inconsistent with thin ice shell models1 and indicate that exchange of oceanic and surface material could be difficult

craters hosting radar bright deposits in mercury s north polar region areas of persistent shadow determined from messenger images 1 radar bright features near mercury s poles were discovered in earth based radar images and proposed to be water ice present in permanently shadowed areas images from messenger s one year primary orbital mission provide the first nearly complete view of mercury s north polar region as well as multiple images of the surface under a range of illumination conditions we find that radar bright features near mercury s north pole are associated with locations persistently shadowed in messenger images within 10 of the pole almost all craters larger than 10 km in diameter host radar bright deposits there are several craters located near mercury s north pole with sufficiently large diameters to enable long lived water ice to be thermally stable at the surface within regions of permanent shadow craters located farther south also host radar bright deposits and show a preference for cold pole longitudes thermal models suggest that a thin insulating layer is required to cover these deposits if the radar bright material consists predominantly of long lived water ice many small 10 km diameter and low latitude extending southward to 66 n craters host radar bright material and water ice may not be thermally stable in these craters for 1 gy even beneath an insulating layer the correlation of radar bright features with persistently shadowed areas is consistent with the deposits being composed of water ice and future thermal modeling of small and low latitude craters has the potential to further constrain the nature source and timing of emplacement of the radar bright material

volcanism on mercury evidence from the first messenger flyby the origin of plains on mercury whether by volcanic flooding or impact ejecta ponding has been controversial since the mariner 10 flybys 1974 75 high resolution images down to 150 meters per pixel obtained during the first messenger flyby show evidence for volcanic vents around the caloris basin inner margin and demonstrate that plains were emplaced sequentially inside and adjacent to numerous large impact craters to thicknesses in excess of several kilometers radial graben and a floor fractured crater may indicate intrusive activity these observations coupled with additional evidence from color images and impact crater size frequency distributions support a volcanic origin for several regions of plains and substantiate the important role of volcanism in the geological history of mercury

laser altimeter observations from messenger s first mercury flyby a 3200 kilometers long profile of mercury by the mercury laser altimeter on the messenger spacecraft spans approximately 20 of the near equatorial region of the planet topography along the profile is characterized by a 5 2 kilometer dynamic range and 930 meter root mean square roughness at long wavelengths topography slopes eastward by 0 02 degrees implying a variation of equatorial shape that is at least partially compensated sampled craters on mercury are shallower than their counterparts on the moon at least in part the result of mercury s higher gravity crater floors vary in roughness and slope implying complex modification over a range of length scales

morphometry of impact craters on mercury from messenger altimetry and imaging abstract data acquired by the mercury laser altimeter and the mercury dual imaging system on the messenger spacecraft in orbit about mercury provide a means to measure the geometry of many of the impact craters in mercury s northern hemisphere in detail for the first time the combination of topographic and imaging data permit a systematic evaluation of impact crater morphometry on mercury a new calculation of the diameter d t at which craters transition with increasing diameter from simple to complex forms and an exploration of the role of target properties and impact velocity on final crater size and shape measurements of impact crater depth on mercury confirm results from previous studies with the exception that the depths of large complex craters are typically shallower at a given diameter than reported from mariner 10 data secondary craters on mercury are generally shallower than primary craters of the same diameter no significant differences are observed between the depths of craters within heavily cratered terrain and those of craters within smooth plains the morphological attributes of craters that reflect the transition from simple to complex craters do not appear at the same diameter instead flat floors first appear with increasing diameter in craters at the smallest diameters followed with increasing diameter by reduced crater depth and rim height and then collapse and terracing of crater walls differences reported by others in d t between mercury and mars despite the similar surface gravitational acceleration on the two bodies are confirmed in this study the variations in d t between mercury and mars cannot be adequately attributed to differences in either surface properties or mean projectile velocity

an improved shadow measurement technique for constraining the morphometry of simple impact craters the lengths of the shadows cast within simple bowl shaped impact craters have been used to constrain their depths on a variety of planetary bodies this technique however only yields the true crater depth if the shadow transects the crater center where the floor is deepest in the past attempts have been made to circumvent this limitation by choosing only craters where the shadow tip lies very near the crater center but this approach may introduce serious artifacts that adversely affect the slope of the regressed depth vs diameter data and its variance here we introduce an improved method for deriving depth information from shadow measurements that considers three basic shape variations of simple craters paraboloidal conical and flat floored we show that the shape of the cast shadow can be used to constrain crater shape and we derive improved equations for finding the depths of these simple craters

the morphology of mercury s caloris basin as seen in messenger stereo topographic models a digital terrain model 1000 m effective spatial resolution of the caloris basin the largest well characterized impact basin on mercury was produced from 208 stereo images obtained by the messenger narrow angle camera the basin rim is far from uniform and is characterized by rugged terrain or knobby plains often disrupted by craters and radial troughs in some sectors the rim is represented by a single marked elevation step where height levels drop from the surroundings toward the basin interior by approximately 2 km two concentric rings with radii of 690 km and 850 km can be discerned in the topography several pre caloris basins and craters can be identified from the terrain model suggesting that rugged pre impact topography may have contributed to the varying characteristics of the caloris rim the basin interior is relatively smooth and shallow comparable to typical lunar mascon mare basins supporting the idea that caloris was partially filled with lava after formation the model displays long wavelength undulations in topography across the basin interior but these undulations cannot readily be related to pre impact topography volcanic construction or post volcanic uplift because errors in the long wavelength topography of the model cannot be excluded confirmation of these undulations must await data from messenger s orbital mission phase

the evolution of mercury s crust a global perspective from messenger mapping the distribution and extent of major terrain types on a planet s surface helps to constrain the origin and evolution of its crust together messenger and mariner 10 observations of mercury now provide a near global look at the planet revealing lateral and vertical heterogeneities in the color and thus composition of mercury s crust smooth plains cover approximately 40 of the surface and evidence for the volcanic origin of large expanses of plains suggests that a substantial portion of the crust originated volcanically a low reflectance relatively blue component affects at least 15 of the surface and is concentrated in crater and basin ejecta its spectral characteristics and likely origin at depth are consistent with its apparent excavation from a lower crust or upper mantle enriched in iron and titanium bearing oxides

seismotectonic models and cn algorithm the case of italy the cn algorithm is utilized here both for the intermediate term earthquake prediction and to validate the seismotectonic model of the italian territory using the results of the analysis made through the cn algorithm and taking into account the seismotectonic model three main areas one for northern italy one for central italy and one for southern italy are defined two transition areas between the three main areas are delineated the earthquakes which occurred in these two areas contribute to the precursor phenomena identified by the cn algorithm in each main area

geology of the caloris basin mercury a view from messenger the caloris basin the youngest known large impact basin on mercury is revealed in messenger images to be modified by volcanism and deformation in a manner distinct from that of lunar impact basins the morphology and spatial distribution of basin materials themselves closely match lunar counterparts evidence for a volcanic origin of the basin s interior plains includes embayed craters on the basin floor and diffuse deposits surrounding rimless depressions interpreted to be of pyroclastic origin unlike lunar maria the volcanic plains in caloris are higher in albedo than surrounding basin materials and lack spectral evidence for ferrous iron bearing silicates tectonic landforms contractional wrinkle ridges and extensional troughs have distributions and age relations different from their counterparts in and around lunar basins indicating a different stress history

multi methods combined analysis of future earthquake potential prior to an earthquake natural seismicity is correlated across multiple spatial and temporal scales many studies have indicated that an earthquake is hard to accurately predict by a single time dependent precursory method in this study we attempt to combine four earthquake prediction methods i e the pattern informatics pi load unload response ratio lurr state vector sv and accelerating moment release amr to estimate future earthquake potential the pi technique is founded on the premise that the change in the seismicity rate is a proxy for the change in the underlying stress we first use the pi method to quantify localized changes surrounding the epicenters of large earthquakes to objectively quantify the anomalous areas hot spots of the upcoming events next we delineate the seismic hazard regions by integrating with regional active fault zones and small earthquake activities then we further evaluate the earthquake potential in the seismic hazard regions using the lurr sv and amr methods retrospective tests of this new approach on the large earthquakes m 6 5 which have occurred in western china over the last 3 years show that the lurr and sv time series usually climb to an anomalously high peak months to years prior to occurrence of a large earthquake and the asymptote time t c predicted by the amr method correspond to the time of the actual events the results may suggest that the multi methods combined approach can be a useful tool to provide stronger constraints on forecasts of the time and location of future large events

an optimization of using the m8 algorithm for prediction of major m7 0 earthquakes in the iranian plateau the casualties and financial losses caused by large earthquakes have led to an awareness of prediction importance of such earthquakes the earthquake prediction is divided into four categories long term intermediate term short term and immediate the m8 algorithm is one of the intermediate term middle range prediction algorithms primarily used to predict earthquake of magnitude 8 or more and is applied later for smaller magnitudes the iranian plateau is less exposed to earthquake with magnitude 8 or more and it is observed that the seismicity rate in this region is generally low thus the original m8 is not suitable for applying in this region the objective of this study is to modify the m8 algorithm for prediction of major m7 0 earthquakes in the iranian plateau the major earthquake of magnitude 7 or more in the iranian plateau from 1975 to 2018 is considered as the target earthquakes the hit rate times 1 minus alarm rate is defined as objective function and the particles swarm optimization meta heuristic algorithm is used to maximize it the optimum m8 could predict 14 out of 17 large earthquakes in the iranian plateau while occupying 31 7 of the spatio temporal space as the alarm the results show that by employing an optimization algorithm we can modify the m8 algorithm for efficient prediction of the target magnitudes less than 8 in the regions with low seismicity rate

dating slate belts using 40 ar 39 ar geochronology and zircon ages from crosscutting plutons a case study from east central maine usa abstract we report the ages of cleavage development in a normally intractable lower greenschist facies slate belt the central maine aroostook matapedia belt in east central maine we have attacked this problem by identifying the minimum ages of muscovite in a regional acadian cleavage s 1 and in a local ductile fault zone cleavage s 2 using 40 ar 39 ar geochronology and the ages of crosscutting plutons our success stems from the regional low grade metamorphism of the rocks in which each crystallization event preserves a 40 ar 39 ar crystallization age and not a cooling age evidence for recrystallization via a pressure solution mechanism comes from truncations of detrital authigenic and in some rocks s 1 muscovite and chlorite grains by new cleavage forming muscovite and chlorite grains low blank furnace age spectra from meta arkosic and slaty rocks climb from moderate temperature devonian age steps dominated by cleavage forming muscovite to ordovician age steps dominated by a detrital muscovite component s 1 and s 2 cleaved rocks were hornfelsed by granitoids of 407 and 377 ma respectively the combination of these minimum ages with the maximum metamorphic crystallization ages establishes narrow constraints on the timing of these two cleavage forming events 410 ma s 1 and 380 ma s 2 these two events coincide in time with a change in the plate convergence kinematics from the arrival of the avalon terrane acadian orogeny to a right lateral transpression arrival of the meguma terrane in the neoacadian orogeny

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

explosive volcanism on mercury analysis of vent and deposit morphology and modes of eruption abstract the messenger mission revealed for the first time conclusive evidence of explosive volcanism on mercury several previous works have cataloged the appearance and location of explosive volcanism on the planet using a variety of identifying characteristics including vent presence and deposit color as seen in multispectral image mosaics we present here a comprehensive catalog of vents of likely volcanic origin our classification scheme emphasizes vent morphology we have analyzed the morphologies of all vents in our catalog and recognize three main morphologies simple vent pit vent and vent with mound the majority of vents we identify are located within impact craters the spatial distribution of vents does not correlate with the locations of volcanic smooth plains deposits in contrast to the moon nor do vents correlate with the locations of large impact basins except for the caloris and tolstoj basins using the degradation state of the vent host crater as a proxy for maximum age we suggest that vent formation has been active through the mansurian and into the kuiperian periods although the majority of vents were likely formed much earlier in mercurian history the morphologies and locations of vents are used to investigate a set of plausible formation geometries we find that the most likely and most prevalent formation geometry is that of a dike stalled at depth which then explosively vents to the surface we compare the vent and deposit size of mercurian pyroclastic deposits with localized and regional lunar pyroclastic deposits and find a range of possible eruption energies and corresponding variations in eruption style localized lunar pyroclastic deposits and the majority of mercurian pyroclastic deposits show evidence for eruption that is consistent with the magmatic foam at the top of a dike reaching a critical gas volume fraction a subset of mercurian vents including the prominent copland rachmaninoff vent to the northeast of the rachmaninoff basin indicates eruption at enhanced gas volume fractions this subset of vents shows a similar eruptive behavior to the lunar orientale dark mantle ring deposit suggesting that the dikes that formed these vents and deposits on mercury underwent some form of additional volatile build up either through crustal volatile incorporation or magma convection within the dike there also exists a population of mercurian vents that no longer retain a visible associated pyroclastic deposit we hypothesize that the visible signature of the pyroclastic deposit has been lost through space weathering and regolith mixing processes together these results provide a comprehensive analysis of explosive volcanism on mercury and inform continued research on the thermal history of mercury and magma composition and evolution

geometric properties of martian impact craters preliminary results from the mars orbiter laser altimeter the mars orbiter laser altimeter mola acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of mars during the fall of 1997 it sampled 98 minimally degraded impact craters between the latitudes of 80 n and 12 s the best fitting depth d versus diameter d power law relationship for these craters is d 0 14 d0 90 for simple varieties and d 0 25 d0 49 for complex structures the simple to complex transition diameter is 8 km 0 5 km the cross sectional shape of the crater cavities was determined by fitting a power function to each profile variation in the exponent n suggest the craters flatten with increasing diameter and impact energy the ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for mars in most cases

seismicity based earthquake forecasting techniques ten years of progress abstract earthquake fault systems interact over a broad spectrum of spatial and temporal scales and in recent years studies of the regional seismicity in a variety of regions have produced a number of new techniques for seismicity based earthquake forecasting while a wide variety of physical assumptions and statistical approaches are incorporated into the various methodologies they all endeavor to accurately replicate the statistics and properties of both the historic and instrumental seismic records as a result the last ten years have seen significant progress in the field of intermediate and short term seismicity based earthquake forecasting these include general agreement on the need for prospective testing and successful attempts to standardize both evaluation methods and the appropriate null hypotheses here we differentiate the predominant approaches into models based upon techniques for identifying particular physical processes and those that filter or smooth the seismicity comparison of the methods suggests that while smoothed seismicity models provide improved forecast capability over longer time periods higher probability gain over shorter time periods is achieved with methods that integrate statistical techniques with our knowledge of the physical process such as the epidemic type aftershock sequence etas model or those related to changes in the b value for example in general while both classes of seismicity based forecasts are limited by the relatively short time period available for the instrumental catalog significant advances have been made in our understanding of both the limitations and potential of seismicity based earthquake forecasting there is general agreement that both short term forecasting on the order of days to weeks and longer term forecasting over five to ten year periods is within reach this recent progress serves to illuminate both the critical nature of the different temporal scales intrinsic to the earthquake process and the importance of high quality seismic data for the accurate quantification of time dependent earthquake hazard

testing an earthquake prediction algorithm the 2016 new zealand and chile earthquakes the 13 november 2016 m7 8 54 km nne of amberley new zealand and the 25 december 2016 m7 6 42 km sw of puerto quellon chile earthquakes happened outside the area of the on going real time global testing of the intermediate term middle range earthquake prediction algorithm m8 accepted in 1992 for the m7 5 range naturally over the past two decades the level of registration of earthquakes worldwide has grown significantly and by now is sufficient for diagnosis of times of increased probability tips by the m8 algorithm on the entire territory of new zealand and southern chile as far as below 40 s the mid 2016 update of the m8 predictions determines tips in the additional circles of investigation cis where the two earthquakes have happened thus after 50 semiannual updates in the real time prediction mode we 1 confirm statistically approved high confidence of the m8 msc predictions and 2 conclude a possibility of expanding the territory of the global test of the algorithms m8 and msc in an apparently necessary revision of the 1992 settings

modification of caloris ejecta blocks by long lived mass wasting a volatile driven process abstract the caloris basin is the largest well preserved impact basin on mercury as such caloris ejecta afford us an opportunity to study material from mercury s deep interior with remote sensing we have made observations of the geomorphology colour distribution and flank slopes of the circum caloris knobs our observations suggest that these circum caloris knobs are modified ejecta blocks from the caloris impact high resolution messenger images show that knobs are conical and relatively uncratered compared with the surrounding plains which implies the knobs have undergone resurfacing we have observed material that has sloughed off knobs superposing impact craters that demonstrably postdate the caloris impact which requires some knob modification to have been more recent we have observed hollows depressions in mercury s surface generally believed to have been caused by volatile loss on and closely associated with several knobs which indicates that many knobs contain volatile material and that knob modification could extend into mercury s recent past our measurements show that knob flanks typically have slopes of 21 which is steep for a mound of unconsolidated material that was originally emplaced 3 8 ga the conical shape of knobs their steep slopes the dearth of superposed craters on knobs and knob superposition relationships with other landforms suggest that caloris ejecta blocks of arbitrary original shape were modified into their present shapes by long lived mass wasting mass wasting must have dominated over impact gardening which would have produced domal morphologies only we suggest that mass wasting was probably driven by volatile loss in a manner analogous to terrestrial landforms called molards if the circum caloris knobs are analogous to molards then they represent a landform and a process hitherto undocumented on mercury with implications for the volatile content of the planet s interior these knobs therefore are prime targets for bepicolombo which could search for fresh failures and volatile exposures in the knobs

a revised control network for mercury an improved control net for mercury has been completed by utilizing images acquired during the three mariner 10 flybys in 1974 1975 relative positional errors within the net are 1 km on average and absolute locations are estimated to be better than 25 km the analytical triangulation resulted in new values for focal lengths camera a 1493 6 mm camera b 1500 1 mm w0 329 548 and camera orientation angles for 811 images acquired during all three flybys of mercury

topography of the northern hemisphere of mercury from messenger laser altimetry laser altimetry by the messenger spacecraft has yielded a topographic model of the northern hemisphere of mercury the dynamic range of elevations is considerably smaller than those of mars or the moon the most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains within this lowland is a broad topographic rise that experienced uplift after plains emplacement the interior of the 1500 km diameter caloris impact basin has been modified so that part of the basin floor now stands higher than the rim the elevated portion of the floor of caloris appears to be part of a quasi linear rise that extends for approximately half the planetary circumference at mid latitudes collectively these features imply that long wavelength changes to mercury s topography occurred after the earliest phases of the planet s geological history

geometric relationships of pristine martian complex impact craters and their implications to mars geologic history 1 based on the depths of pristine complex craters on mars we have estimated the final post modification phase depth dr to diameter d function of martian complex craters we suggest that the dr d function determined here holds globally for complex craters 12 km diameter the global nature of this function may be due to the stability of slopes in the highly fractured rock that makes up the steep interior walls of post modification phase craters the stability of such slopes should be controlled mainly by such factors as the nature of the fractures and not target strength this function is an essential benchmark for studies that utilize crater geometry as their basis for example the function can be used in gradation history of mars to predict the magnitude of degradation for instance an example 20 km diameter middle early noachian age crater that initially formed in the mid latitudes of mars with a depth of 1800 m instead of 1404 m as predicted by the fresh craters function has lost 1450 m of its depth over its history 350 m in the noachian 400 m during an intense episode of degradation at the end of the noachian and 700 m thereafter no evidence of the period of intense degradation is found in the high latitudes although those regions appear to have been affected by a process that reduced crater depth soon after they form

intermediate term earthquake prediction in the area of greece application of the algorithm m8 the 3 strongest earthquakes m 7 0 which have occurred since 1973 in the area of greece were preceded by a specific increase of the earthquake activity in the lower magnitude range this activation is depicted by algorithm m8 this algorithm of intermediate term earthquake prediction was originally designed for diagnosis by times of increased probability tips of the strongest earthquake m 8 0 worldwide keilis borok andkossobokov 1984 at present the algorithm is retrospectively tested for smaller magnitudes in different seismic regions keilis borok andkossobokov 1986 1988 a tip refers to a time period of 5 years and an area whose linear size is proportional and several times larger than that of the incipient earthquake source altogether the tips diagnosed by the algorithm m8 in the area of greece occupy less than 20 and the times of expectation tes about 10 of the total space time domain considered also there is a current tip for the southeastern aegean sea and 1988 1992 it may specify the long term prediction given inwyss andbaer 1981a b

characterizing and navigating small bodies with imaging data recent advances in the characterization of small body surfaces with stereophotoclinometry are discussed the principal data output is an ensemble of landmark maps l maps high resolution topography albedo maps of varying resolution that tile the surface of the body because they can have a resolution comparable to the best images and can be located on a global reference frame to high accuracy l maps provide a significant improvement in discriminatory power for studies of small bodies ranging from regolith processes to interior structure these techniques are now being used to map larger bodies such as the moon and mercury l maps are combined to produce a standard global topography model gtm with about 1 57 million vectors and having a wide variety of applications they can also be combined to produce high resolution topography maps that describe local areas with much greater detail than the gtm when combined with nominal predictions from other data sources and available data from other instruments such as lidar or radar solutions for the spacecraft position and camera pointing are the most accurate available examples are drawn from studies of phobos eros and itokawa including surface characterization gravity analysis spacecraft navigation and incorporation of lidar or radar data this work has important implications for potential future missions such as deep interior and the level of navigation and science that can be achieved

reaction softening by dissolution precipitation creep in a retrograde greenschist facies ductile shear zone new hampshire usa we describe strain localization by a mixed process of reaction and microstructural softening in a lower greenschist facies ductile fault zone that transposes and replaces middle to upper amphibolite facies fabrics and mineral assemblages in the host littleton schist near claremont new hampshire here na poor muscovite and chlorite progressively replace first staurolite then garnet and finally biotite porphyroblasts as the core of the fault zone in approached across the transect higher grade fabric forming na rich muscovite is also progressively replaced by fabric forming na poor muscovite the mineralogy of the new phyllonitic fault rock produced is dominated by na poor muscovite and chlorite together with late albite porphyroblasts the replacement of the amphibolite facies porphyroblasts by muscovite and chlorite is pseudomorphic in some samples and shows that the chemical metastability of the porphyroblasts is sufficient to drive replacement in contrast element mapping shows that fabric forming na rich muscovite is selectively replaced at high strain microstructural sites indicating that strain energy played an important role in activating the dissolution of the compositionally metastable muscovite the replacement of strong high grade porphyroblasts by weaker na poor muscovite and chlorite constitutes reaction softening the crystallization of parallel and contiguous mica in the retrograde foliation at the expense of the earlier and locally crenulated na rich muscovite defined foliation destroys not only the metastable high grade mineralogy but also its stronger geometry this process constitutes both reaction and microstructural softening the deformation mechanism here was thus one of dissolution precipitation creep activated at considerably lower stresses than might be predicted in quartzo feldspathic rocks at the same lower greenschist facies conditions this article is protected by copyright all rights reserved

40ar 39ar muscovite dating of thrust activity a case study from the axial zone of the pyrenees abstract the pyrenees belt features well exposed deformation structures that make it ideally suited to study thrust faults in this paper we present the first 40ar 39ar age of the pic de port vieux thrust ppvt located in the south western part of the pyrenean axial zone the ppvt is a secondary thrust related to the major gavarnie thrust gt with a footwall comprising upper cretaceous limestones and a hanging wall made of lower triassic pelites and sandstones a vertical transect in the fault hanging wall was investigated to characterize the deformation mechanism and to date the thrust activity by using 40ar 39ar step heating technique on muscovite petrographic observations confirm that pressure solution and recrystallization dissolution processes in presence of fluids are the main mechanisms that controlled the chemical textural changes in the fault core zone three groups of muscovite are identified in the fault zone i e detrital diagenetic and newly formed muscovites the detrital and diagenetic muscovites are mainly present in the damage zone while the newly formed muscovite is abundant in the core zone and is synkinematic to the fault activity the fractions 50 16 m 16 2 m 2 0 5 m

medium term forecast of the 1988 north east india earthquake abstract northeast india is seismically one of the most active intra continental regions in the world it has been a site of 10 earthquakes of magnitude m 7 5 during the last 100 years gupta and singh j geol soc india 28 1986 367 406 systematically analysed the time series of earthquakes associated with several main shocks in an area bound by 20 n and 32 n latitude and 87 e and 100 e longitude and concluded 1 moderate magnitude to great earthquakes in the north east india region are found to be preceded generally by well defined earthquake swarms and quiescence periods 2 on the basis of an earthquake swarm and quiescence period an area bound by 21 n and 25 5 n latitude and 93 e and 96 e longitude is identified to be the site of a possible future earthquake of m 8 0 5 with a focal depth of 100 40 km this earthquake should occur any time from now onwards should it not occur till the end of 1990 this forecast could be considered as a false alarm this medium term earthquake forecast came true with the occurrence of the m 7 3 earthquake on august 6 1988 within the specified spatial and temporal parameters the forecast of this earthquake was based on the concept of precursory swarms and quiescence preceding main shocks it is worthwhile noting that in the entire region under study the august 6 1988 earthquake was the largest since the august 17 1952 earthquake of m 7 5 this lends support to the worldwide effort to study and identify spatial and temporal variation of seismicity and recognise patterns that precede major earthquakes

the morphology of small fresh craters on mars and the moon the depth diameter ratio for new meter to decameter scale martian craters formed in the last 20 years averages 0 23 only slightly deeper than that expected for simple primary craters on rocky surfaces large variations in depth diameter d d between impact sites indicate that differences between the sites such as target material properties impact velocity angle and physical state of the bolide s are important in determining the depth of small craters in the strength regime on the moon the d d of random fresh small craters with similar diameters averages only 0 10 indicating that either the majority of them are unrecognized secondaries or some proportion are degraded primaries older craters such as these may be shallower due to erosional infilling which is probably not linear over time but more effective over recently disturbed and steeper surfaces processes that are not yet acting on the new martian craters brand new meter to decameter scale craters such as the martian ones studied here are statistically easily distinguishable as primaries but the origins of older craters of the same size such as the lunar ones in this study are ambiguous

nonuniform cratering of the terrestrial planets article history we estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets bottke w f morbidelli a jedicke r petit j m levison h f michel p metcalfe t s 2002 icarus 156 399 433 after determining the planetary impact probabilities as a function of the relative encounter velocity and encounter inclination the impact positions are calculated analytically assuming the projectiles follow hyperbolic paths during the encounter phase as the source of projectiles is not isotropic latitudinal variations of the impact flux are predicted the calculated ratio between the pole and equator is 1 05 for mercury 1 00 for venus 0 96 for the earth 0 90 for the moon and 1 14 for mars over its long term obliquity variation history by taking into account the latitudinal dependence of the impact velocity and impact angle and by using a crater scaling law that depends on the vertical component of the impact velocity the latitudinal variations of the cratering rate the number of craters with a given size formed per unit time and unit area is in general enhanced with respect to the equator the polar cratering rate is about 30 larger on mars and 10 on mercury whereas it is 10 less on the earth and 20 less on the moon the cratering rate is found to be uniform on venus the relative global impact fluxes on mercury venus the earth and mars are calculated with respect to the moon and we find values of 1 9 1 8 1 6 and 2 8 respectively our results show that the relative shape of the crater size frequency distribution does not noticeably depend upon latitude for any of the terrestrial bodies in this study nevertheless by neglecting the expected latitudinal variations of the cratering rate systematic errors of 20 30 in the age of planetary surfaces could exist between equatorial and polar regions when using the crater chronology method

non intrusive measurements of crater growth abstract an experimental technique to measure crater growth is presented whereby a high speed video captures profiles of a crater forming after impact obtained using a vertical laser sheet centered on the impact point unlike previous so called quarter space experiments where projectiles were launched along a transparent plexiglas sheet so that growth of half a crater could be viewed the use of the laser sheet permits viewing changes in crater shape without any physical interference to the cratering process this technique indicates that for low velocity impacts 300 m s into 220 m glass beads that are without cohesion and where the projectile is not disrupted craters initially grow somewhat proportionally but that later their depths remain essentially constant while their diameters continue to expand in addition these experiments indicate that as the impact velocity increases the rate of growth and the transient depth to diameter ratio at the end of ejecta excavation decreases these last two observations are probably due to the large time of penetration of the projectile which becomes a significant fraction of the time of crater formation this is contrary to the expectations for the scaling rules which assumes a point source very high curtain angles 45 are also seen and could be due to the low friction angle of the target significant crater modification which is rarely seen in quarter space experiments is also observed and appears to be controlled by the dynamic angle of repose of the target these latter observations indicate that differences in target friction angles may need to be considered when determining near rim ejecta mass distributions and large scale crater modification processes on the planets

stratigraphy of the caloris basin mercury abstract the 1300 km diameter caloris impact basin is surrounded by well defined ejecta units that can be recognized from more than 1000 km radially outward from the basin edge a formal rock stratigraphic nomenclature is proposed for the caloris ejecta units which are collectively called the caloris group each of the individual formations within the group are described and compared to similar rock units associated with the lunar imbrium and orientale basins a crater degradation chronology linked the the caloris event is also proposed to assist in stratigraphic correlation on a mercury wide basis