permanent deformation caused by subduction earthquakes in northern chile earth s crust is thought to eventually rebound following an earthquake so that deformation is not permanent field analysis in the atacama desert northern chile however identifies numerous large cracks in the crust implying that the crust here has been permanently deformed by thousands of earthquakes that have occurred over the past million years

long term surface temperature modeling of pluto abstract nasa s new horizons reconnaissance of the pluto system has revealed at high resolution the striking albedo contrasts from polar to equatorial latitudes on pluto as well as the sharpness of boundaries for longitudinal variations these contrasts suggest that pluto must undergo dynamic evolution that drives the redistribution of volatiles using the new horizons results as a template we explore the surface temperature variations driven seasonally on pluto considering multiple timescales these timescales include the current orbit 248 years as well as the timescales for obliquity precession peak to peak amplitude of 23 over 3 million years and regression of the orbital longitude of perihelion 3 7 million years these orbital variations create epochs of extreme seasons where one pole receives a short relatively warm summer and long winter while the other receives a much longer but less intense summer and short winter we use thermal modeling to build upon the long term insolation history model described by earle and binzel 2015 and investigate how these seasons couple with pluto s albedo contrasts to create temperature effects from this study we find that a bright region at the equator once established can become a site for net deposition we see the region informally known as sputnik planitia as an example of this and find it will be able to perpetuate itself as an always available cold trap thus having the potential to survive on million year or substantially longer timescales meanwhile darker low albedo regions near the equator will remain relative warm and generally not attract volatile deposition we argue that the equatorial region is a preservation zone for whatever albedo is seeded there this offers insight as to why the equatorial band of pluto displays the planet s greatest albedo contrasts

surface cracks record long term seismic segmentation of the andean margin understanding the long term patterns of great earthquake rupture along a subduction zone provides a framework for assessing modern seismic hazard however evidence that can be used to infer the size and location of past earthquakes is typically erased by erosion after a few thousand years meter scale cracks that cut the surface of coastal areas in northern chile and southern peru preserve a record of earthquakes spanning several hundred thousand years owing to the hyperarid climate of the region these cracks have been observed to form during and or shortly after strong subduction earthquakes are preserved for long time periods throughout the atacama desert demonstrate evidence for multiple episodes of reactivation and show changes in orientation over spatial scales similar to the size of earthquake segments our observations and models show that crack orientations are consistent with dynamic and static stress fi elds generated by recent earthquakes while localized structural and topographic processes infl uence some cracks the strong preferred orientation over large regions indicates that cracks are primarily formed by plate boundary scale stresses namely repeated earthquakes we invert the crack based strain data for slip along the well known iquique seismic gap segment of the margin and fi nd consistency with gravity anomaly based inferences of long term earthquake slip patterns as well as the magnitude and location of the november 2007 tocopilla earthquake we suggest that the meter scale cracks can be used to map characteristic earthquake rupture segments that persist over many seismic cycles which encourages future study of cracks and other small scale structures to better constrain the persistence of asperities in other arid tectonically active regions

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

crack formation on top of propagating reverse faults of the chuculay fault system northern chile insights from field data and numerical modelling abstract reverse faults in northern chile have formed 20 300 m high scarps that contain open fractures which occur in a zone of 20 1600 m wide two dimensional numerical models were used to explore the geometrical and mechanical parameters needed to produce extension within a bulk contractional regime all of the mechanical models show the same structure as the field a concentration of cracks predominantly at the top rather than on the forelimbs of the scarps in the field case extension begins as soon as a discrete scarp forms with progressive shortening the scarp height increases producing a broadening of the zone in extension the numerical models show that this broadening stabilizes when a maximum in the scarp height is reached to produce concentration of the extension on top of the scarps the reverse fault needs to be weak 10 the models suggest that distribution of this extensional zone depends on the cross sectional geometry of the fault and on the location of the detachment at depth the main mechanism that produces extension on the top of the reverse scarp is stretching of the topographic surface by folding of the hanging wall at the tip of the fault zone

isotopic evidence for the source of ca and s in soil gypsum anhydrite and calcite in the atacama desert chile abstract the origin of pedogenic salts in the atacama desert has long been debated possible salt sources include in situ weathering at the soil site local sources such as aerosols from the adjacent pacific ocean or salt encrusted playas salars and extra local atmospheric dust to identify the origin of ca and s in atacama soil salts we determined 34 s and 87 sr 86 sr values of soil gypsum anhydrite and 87 sr 86 sr values of soil calcite along three east west trending transects our results demonstrate the strong influence of marine aerosols on soil gypsum anhydrite development in areas where marine fog penetrates inland results from an east west transect located along a breach in the coastal cordillera show that most soils within 90 km of the coast and below 1300 m in elevation are influenced by marine aerosols and that soils within 50 km and below 800 m in elevation receive 50 of ca and s from marine aerosols 34 s values 14 and 87 sr 86 sr values 0 7083 in areas where the coastal cordillera is 1200 m in elevation however coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced most pedogenic salts from inland soils have 34 s values between 5 0 to 8 0 and 87 sr 86 sr ratios between 0 7070 and 0 7076 these values are similar to average 34 s and 87 sr 86 sr values of salts from local streams lakes and salars 5 4 2 34 s and 0 70749 0 00045 87 sr 86 sr in the andes and atacama suggesting extensive eolian reworking of salar salts onto the surrounding landscape ultimately salar salts are precipitated from evaporated ground water which has acquired its dissolved solutes from water rock interactions both high and low temperature along flowpaths from recharge areas in the andes therefore the main source for ca and s in gypsum anhydrite in non coastal soils is indirect and involves bedrock alteration not surficially on the hyperarid landscape but in the subsurface by ground water followed by eolian redistribution of ground water derived salar salts to soils the spatial distribution of high grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local marine and salar salt supporting arguments for tropospheric nitrogen as the main source for soil nitrate

nature and tectonic significance of co seismic structures associated with the mw 8 8 maule earthquake central southern chile forearc abstract the mw 8 8 maule earthquake on february 27 2010 affected the central southern chilean forearc of the central andes here we show the results of field investigations of surface deformation associated with this major earthquake observations were carried out within three weeks after the seismic event mostly in the central and northern part of the forearc overlying the rupture zone we provide a detailed field record of co seismic surface deformation and examine its implications on active andean tectonics surface rupture consisted primarily of extensional cracks push up structures fissures with minor lateral displacements and a few but impressive extensional geometries similar to those observed in analogical modeling of rift systems a major group of nw wnw striking fractures representing co seismic extensional deformation is found at all localities these appear to be spatially correlated to long lived basement fault zones the nw striking normal focal mechanism of the mw 6 9 aftershock occurred on march 11 demonstrates that the basement faults were reactivated by the mw 8 8 maule earthquake the co seismic surface ruptures show patterns of distributed deformation similar to those observed in mapped basement involved structures we propose that co seismic reactivation of basement structures play a fundamental role in stress release in the upper plate during large subduction earthquakes the fundamental mechanism that promotes stress relaxation is largely driven by elastic rebound of the upper plate located right above the main rupture zone

coseismic extension from surface cracks reopened by the 2014 pisagua northern chile earthquake sequence the a d 2014 pisagua earthquake sequence reactivated ancient surface cracks along the entire rupture length in the northern chilean forearc these subtle brittle strain features that are 50 km above the subduction zone interface in the hyperarid atacama desert record deformation from the single earthquake sequence in this study we document how ancient cracks formed during thousands of plate boundary earthquake cycles were reopened during the 2014 earthquake sequence we show that crack orientations along the rupture length reflect deformation from the m w 8 1 mainshock and from an m w 7 7 aftershock 100 km to the south as documented by displacements calculated from continuous geodetic observations we suggest that cracks form during the passage of surface waves and repeated opening and closing enhance crack aperture the orientation and opening of the oldest cracks in the forearc are indicative of the modal or most common rupture area of major megathrust earthquakes in the region while the long term preservation of cracks may be limited to northern chile similar features likely form during strong earthquakes at other subduction zones and represent permanent forearc deformation

slip distribution of the 2014 mw 8 1 pisagua northern chile earthquake sequence estimated from coseismic fore arc surface cracks the 2014 mw 8 1 iquique pisagua chile earthquake sequence ruptured a segment of the nazca south america subduction zone that last hosted a great earthquake in 1877 the sequence opened 3 700 surface cracks in the fore arc of decameter scale length and millimeter to centimeter scale aperture we use the strikes of measured cracks inferred to be perpendicular to coseismically applied tension to estimate the slip distribution of the mainshock and largest aftershock the slip estimates are compatible with those based on seismic geodetic and tsunami data indicating that geologic observations can also place quantitative constraints on rupture properties the earthquake sequence ruptured between two asperities inferred from a regional scale distribution of surface cracks interpreted to represent a modal or most common rupture scenario for the northern chile subduction zone we suggest that past events including the 1877 earthquake broke the 2014 pisagua source area together with adjacent sections in a through going rupture

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

contribution to the glaciology of northern greenland from satellite radar interferometry interferometric synthetic aperture radar insar data from the ers 1 and ers 2 satellites are used to measure the surface velocity topography and grounding line position of the major outlet glaciers in the northern sector of the greenland ice sheet the mass output of the glaciers at and above the grounding line is determined and compared with the mass input we find that the grounding line output is approximately in balance with the input except for the three largest glaciers for which the mass loss is 4 3 km3 ice year 1 or 11 8 of the mass input along the coast we detect a systematic retreat of the grounding lines between 1992 and 1996 with insar which implies that the outlet glaciers are thinning the inferred coastal thinning is too large to be explained by a few warm summers glacier thinning must be of dynamic origin that is caused by spatial and temporal changes in ice velocity iceberg production from the glaciers is uncharacteristically low it accounts for only 8 of the ice discharge to the ocean about 55 of the ice is lost through basal melting 5 8 m ice year 1 on average from the underside of the floating glacier tongues that are in contact with warm ocean waters mass losses are highest in the first 10 km of floating ice where ice reaches the greatest depths and basal melting is 3 times larger than on average only a small increase in basal melting would suffice to disintegrate the floating glacier tongues copyright 2001 by the american geophysical union

focused synthetic aperture radar processing of ice sounder data collected over the greenland ice sheet the authors developed a synthetic aperture radar sar processing algorithm for airborne spaceborne ice sounding radar systems and applied it to data collected in greenland by using focused sar phase corrected coherent averaging they improved along track resolution by a factor of four and provided a 6 db processing gain over unfocused sar coherent averaging without phase correction based on a point target analysis for a greenland ice sounding data set also they demonstrated that the focused sar processing reduced clutter and enabled them to identify bedrock interface returns buried in clutter using focused sar technique they processed data collected over a key 360 km long portion of the 2000 m contour line of southwest greenland to the best of their knowledge these are the first high quality radar ice thickness measurements over this key location moreover these ice thickness measurements have been used for improving mass balance estimates of the greenland ice sheet

the geodetic signature of the earthquake cycle at subduction zones model constraints on the deep processes recent megathrust events in tohoku japan maule chile and sumatra indonesia were well recorded much has been learned about the dominant physical processes in megathrust zones partial locking of the plate interface detailed coseismic slip relocking afterslip viscoelastic mantle relaxation and interseismic loading these and older observations show complex spatial and temporal patterns in crustal deformation and displacement and significant differences among different margins a key question is whether these differences reflect variations in the underlying processes like differences in locking or the margin geometry or whether they are a consequence of the stage in the earthquake cycle of the margin quantitative models can connect these plate boundary processes to surficial and far field observations we use relatively simple cyclic geodynamic models to isolate the first order geodetic signature of the megathrust cycle coseismic and subsequent slip on the subduction interface is dynamically and consistently driven a review of global preseismic coseismic and postseismic geodetic observations and of their fit to the model predictions indicates that similar physical processes are active at different margins most of the observed variability between the individual margins appears to be controlled by their different stages in the earthquake cycle the modeling results also provide a possible explanation for observations of tensile faulting aftershocks and tensile cracking of the overriding plate which are puzzling in the context of convergence compression from the inversion of our synthetic gnss velocities we find that geodetic observations may incorrectly suggest weak locking of some margins for example the west aleutian margin

stress evolution during the megathrust earthquake cycle and its role in triggering extensional deformation in subduction zones abstract great moment magnitude mw 8 0 and larger subduction megathrust earthquakes are commonly followed by increased rates of normal faulting seismicity extensional activity within the subducting slab is amplified when megathrust slip propagates close to the trench and forearc extension is triggered by the largest magnitude mw 8 5 and larger events to better understand these observations we develop an earthquake cycle model with a realistic slab geometry and stresses that are in balance with plate interface slip and bulk viscous relaxation the modeled stresses represent perturbations to the long term background tectonic stress field the steady state inter seismic earthquake cycle stresses are compressive and their magnitudes depend on the interface locking configuration from 25 mpa for a fully locked seismogenic zone to 5 mpa for discrete asperities on an otherwise unlocked plate interface the co seismic slip and corresponding co seismic stress changes are similar in these models independent of the locking configuration the co seismic stress change magnitudes are up to 5 mpa this implies that the earthquake cycle stresses after the mainshock would still be compressive in the case of a continuous seismogenic zone but would be widely reset to zero in the case of discrete asperities models with co seismic slip confined to shallow depths produce tensional stress changes in the slab and the forearc near the trench whereas events rupturing the base of the seismogenic zone produce tensional stress changes limited to region immediately surrounding the rupture the locations of normal faulting aftershocks generally correlate well with the tensional co seismic stress changes greater than 1 mpa following the mainshock rapid afterslip occurring down dip of the megathrust rupture expands the region of relative extension but reduces its magnitude and does not promote additional normal faulting events bulk viscous relaxation does little to the state of stress in the elastic parts of the model continued plate convergence across a re locked interface returns the system to the pre earthquake state of compression

pluto s insolation history latitudinal variations and effects on atmospheric pressure abstract since previous long term insolation modeling in the early 1990s new atmospheric pressure data increased computational power and the upcoming flyby of the pluto system by nasa s new horizons spacecraft have generated new motivation and increased capabilities for the study of pluto s complex long term million years insolation history the two primary topics of interest in studying pluto s insolation history are the variations in insolation patterns when integrated over different intervals and the evolution of diurnal insolation patterns over the last several decades we find latitudinal dichotomies when comparing average insolation over timescales of days decades centuries and millennia where all timescales we consider are short relative to the predicted timescales for pluto s chaotic orbit depending on the timescales of volatile migration some consequences of these insolation patterns may be manifested in the surface features revealed by new horizons we find the maximum diurnal insolation mdi at any latitude is driven most strongly when pluto s obliquity creates a long arctic summer or midnight sun beginning just after perihelion pluto s atmospheric pressure as measured through stellar occultation observations during the past three decades shows a circumstantial correlation with this midnight sun scenario as quantified by the mdi parameter

gradual unlocking of plate boundary controlled initiation of the 2014 iquique earthquake a long foreshock series unlocked the south american plate boundary until eventually initiating the m 8 1 iquique chile earthquake two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure on 1 april 2014 northern chile was struck by a magnitude 8 1 earthquake following a protracted series of foreshocks the integrated plate boundary observatory chile monitored the entire sequence of events providing unprecedented resolution of the build up to the main event and its rupture evolution here we show that the iquique earthquake broke a central fraction of the so called northern chile seismic gap the last major segment of the south american plate boundary that had not ruptured in the past century1 2 since july 2013 three seismic clusters each lasting a few weeks hit this part of the plate boundary with earthquakes of increasing peak magnitudes starting with the second cluster geodetic observations show surface displacements that can be associated with slip on the plate interface these seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion leading up to this earthquake the b value of the foreshocks gradually decreased during the years before the earthquake reversing its trend a few days before the iquique earthquake the mainshock finally nucleated at the northern end of the foreshock area which skirted a locked patch and ruptured mainly downdip towards higher locking peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch we conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure distinguishing the iquique earthquake from most great earthquakes finally only one third of the gap was broken and the remaining locked segments now pose a significant increased seismic hazard with the potential to host an earthquake with a magnitude of 8 5

trench parallel shortening in the northern chilean forearc tectonic and climatic implications in the central andes the frictional coupling between south america and the subducting nazca plate occurs beneath the coastal cordillera of northern chile one of the most distinctive characteristics of the coastal cordillera is a suite of ew topographic scarps located between 19 and 21 6 s latitude these scarps are associated with predominantly south dipping reverse faults that have almost pure dip slip and produce shortening parallel to the plate boundary limited geochronology as well as more regional studies indicate that the scarps formed during the late miocene and early pliocene though some show activity extending into the quaternary in several areas the scarps dammed local drainages producing internally drained basins that accumulated evaporites this relationship indicates that the coastal cordillera was probably moister during the late miocene and pliocene than it is today and also indicates that the coastal cordillera has been significantly uplifted or that the coastal escarpment of northern chile has advanced significantly eastward since the pliocene the limited latitudinal extent of the ew scarps and their location symmetrically about the axis of topographic and wadati benioff zone symmetry suggest that they owe their origin to the concave seaward shape of the continental margin due to prior formation of the bolivian orocline

present and past glaciation on pluto abstract modern n2 ice glaciers flow from highlands to the east of the 750 1400 km2 lowland of sputnik planum sp and merge with the ices of similar composition on sp we explore the possibility that glaciation may be fed by n2 sublimation from sp followed by redeposition on the highlands the uplands to the northeast north and west of sp have been erosionally sculpted into a variety of dissected terrains that feature linear depressions valleys locally in dendritic networks we interpret these dissected terrains to have been carved by n2 glaciers formerly covering the uplands depositional glacial landforms moraines eskers outwash have not been identified however n2 glaciation would have a different erosional manifestation because the substrate porous water ice and ch4 rich mantles probably has lower density than n2 and also because of the lack of freeze thaw weathering if sufficiently thick 1 4 km n2 glaciers might have experienced basal melting past flow of n2 glaciers from the highlands into sp may have detached and transported the prominent mountainous water ice mountains along the western border of sp

active faulting in northern chile ramp stacking and lateral decoupling along a subduction plate boundary two large features parallel to the coastline of northern chile have long been suspected to be the sites of young or active deformation 1 the 700 km long coastal scarp with average height above sea level of about 1000 m 2 the atacama fault zone that stretches linearly for about 1100 km at an average distance of 30 50 km from the coastline new field observations combined with extensive analysis of aerial photographs demonstrate that both the coastal scarp and the atacama fault are zones of quaternary and current fault activity little degraded surface breaks observed in the field indicate that these fault zones have recently generated large earthquakes m 7 8 normal fault offsets observed in marine terraces in the coastal scarp at mejillones peninsula require tectonic extension roughly orthogonal to the compressional plate boundary strike slip offsets of drainage observed along the salar del carmen and cerro moreno faults atacama fault system imply left lateral displacements nearly parallel to the plate boundary the left lateral movement observed along the atacama fault zone may be a local consequence of e w extension along the coastal scarp but if also found everywhere along strike left lateral decoupling along the atacama fault zone would be in contradiction with the right lateral component of nazca south america motion predicted by models of present plate kinematics clockwise rotation with left lateral slicing of the andean orogen south of the arica bend is one way to resolve this contradiction the coastal scarp and the atacama fault zone are the most prominent features with clear traces of activity within the leading edge of continental south america the great length and parallelism of these features with the subduction zone suggest that they may interact with the subduction interface at depth we interpret the coastal scarp to be a west dipping normal fault or flexure and propose that it is located over an east dipping ramp stack at the subduction interface the similar flexure at the western edge of the altiplano may have the same origin ramp stacking along the subduction zone a mechanism disregarded so far may be an important thickening process in the andes and perhaps the basic cause of the uplift of the altiplano

pervasive cracking of the northern chilean coastal cordillera new evidence for forearc extension despite convergence across the strongly coupled seismogenic interface between the south american and nazca plates the dominant neotectonic signature in the forearc of northern chile is arc normal extension we have used 1 m resolution ikonos satellite imagery to map nearly 37 000 cracks over an area of 500 km2 near the salar grande 21 s these features which are best preserved in a ubiquitous gypcrete surface layer have both nontectonic and tectonic origins however their strong preferred orientation perpendicular to the plate convergence vector suggests that the majority owe their formation to approximate east west extension associated with plate boundary processes such as interseismic loading coseismic and postseismic strain and long term instability resulting from subduction erosion similar structures were formed during or shortly after the 1995 mw 8 0 earthquake near the city of antofagasta south of salar grande and in conjunction with the 2001 mw 8 2 8 4 arequipa peru event cracks such as these may form in other forearcs but remain largely unexposed because of vegetative cover or marked fluvial erosion factors that are absent in northern chile as a result of its hyperarid climate

co seismic slip from the 1995 july 30 mw 8 1 antofagasta chile earthquake as constrained by insar and gps observations summary we analyse radar interferometric and gps observations of the displacement field from the 1995 july 30 mw 8 1 antofagasta chile earthquake and invert for the distribution of slip along the co seismic fault plane using a fixed fault geometry we compare the use of singular value decomposition and constrained linear inversion to invert for the slip distribution and find that the latter approach is better resolved and more physically reasonable separate inversions using only gps data only insar data from descending orbits and insar data from both ascending and descending orbits without the gps data illustrate the complimentary nature of gps and the presently available insar data the gps data resolve slip near gps benchmarks well while the insar provides greater spatial sampling the combination of ascending and descending insar data contributes greatly to the ability of insar to resolve the slip model thereby emphasizing the need to acquire this data for future earthquakes the rake distribution of slip and seismic moment of our preferred model are generally consistent with previous seismic and geodetic inversions although significant differences do exist gps data projected in the radar line of sight los and corresponding insar pixels have a root mean square rms difference of about 3 cm comparison of our predictions of vertical displacement and observed uplift from corraline algae have an rms of 10 cm our inversion and previous results reveal that the location of slip might be influenced by the 1987 mw 7 5 event our analysis further reveals that the 1995 slip distribution was affected by a 1988 mw 7 2 event and might have influenced a 1998 mw 7 0 earthquake that occurred downdip of the 1995 rupture our slip inversion reveals a potential change in mechanism in the southern portion of the rupture consistent with seismic results predictions of the satellite los displacement from a seismic inversion and a joint seismic gps inversion do not compare favourably with the insar observations

the geology of pluto and charon through the eyes of new horizons nasa s new horizons spacecraft has revealed the complex geology of pluto and charon pluto s encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection with a crater retention age no greater than 10 million years surrounding terrains show active glacial flow apparent transport and rotation of large buoyant water ice crustal blocks and pitting the latter likely caused by sublimation erosion and or collapse more enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures pluto also has ancient cratered terrains up to 4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes charon does not appear to be currently active but experienced major extensional tectonism and resurfacing probably cryovolcanic nearly 4 billion years ago impact crater populations on pluto and charon are not consistent with the steepest impactor size frequency distributions proposed for the kuiper belt

the formation of charon s red poles from seasonally cold trapped volatiles a unique feature of pluto s large satellite charon is its dark red northern polar cap similar colours on pluto s surface have been attributed to tholin like organic macromolecules produced by energetic radiation processing of hydrocarbons the polar location on charon implicates the temperature extremes that result from charon s high obliquity and long seasons in the production of this material the escape of pluto s atmosphere provides a potential feedstock for a complex chemistry gas from pluto that is transiently cold trapped and processed at charon s winter pole was proposed as an explanation for the dark coloration on the basis of an image of charon s northern hemisphere but not modelled quantitatively here we report images of the southern hemisphere illuminated by pluto shine and also images taken during the approach phase that show the northern polar cap over a range of longitudes we model the surface thermal environment on charon and the supply and temporary cold trapping of material escaping from pluto as well as the photolytic processing of this material into more complex and less volatile molecules while cold trapped the model results are consistent with the proposed mechanism for producing the observed colour pattern on charon

from decades to epochs spanning the gap between geodesy and structural geology of active mountain belts geodetic data from the global navigation satellite system gnss and from satellite interferometric radar insar are revolutionizing how we look at instantaneous tectonic deformation but the significance for long term finite strain in orogenic belts is less clear we review two different ways of analyzing geodetic data velocity gradient fields from which one can extract strain dilatation and rotation rate and elastic block modeling which assumes that deformation is not continuous but occurs primarily on networks of interconnected faults separating quasi rigid blocks these methods are complementary velocity gradients are purely kinematic and yield information about regional deformation the calculation does not take into account either faults or rigid blocks but where gnss data are dense enough active fault zones and stable blocks emerge naturally in the solution block modeling integrates known structural geometry with idealized earthquake cycle models to predict slip rates on active faults future technological advances should overcome many of today s uncertainties and provide rich new data to mine by providing denser more uniform and temporally continuous observations

past epochs of significantly higher pressure atmospheres on pluto abstract pluto is known to have undergone thousands of cycles of obliquity change and polar precession these variations have a large and corresponding impact on the total average solar insolation reaching various places on pluto s surface as a function of time such changes could produce dramatic increases in surface pressure and may explain certain features observed by new horizons on pluto s surface including some that indicate the possibility of surface paleo liquids this paper is the first to discuss multiple lines of geomorphological evidence consistent with higher pressure epochs in pluto s geologic past and it also the first to provide a mechanism for potentially producing the requisite high pressure conditions needed for an environment that could support liquids on pluto the presence of such liquids and such conditions if borne out by future work would fundamentally affect our view of pluto s past climate volatile transport and geological evolution this paper motivates future more detailed climate modeling and geologic interpretation efforts in this area

invited review paper neogene to quaternary tectonics of the coastal cordillera northern chile abstract the extreme aridity of the northern chilean coastal cordillera enables the complete preservation of permanent deformation related to the coupling between nazca and south america the region between antofagasta and arica is characterized by four types of late cenozoic structures ew striking reverse faults ns striking normal faults sparse wnw and nnw striking right lateral strike slip faults and unimodal and bimodal populations of surface cracks the ew reverse faults occur only between 19 and 21 40 s latitude and have been active since at least 6 ma to present a march 2007 earthquake demonstrates that this deformation can occur during the interseismic phase of the plate boundary seismic cycle the ns normal faults are most abundant near antofagasta and mejillones and diminish in significance northward several of these faults in both the antofagasta and the salar grande area have been reactivated as reverse faults causing minor topographic inversion we suggest that normal faults move during both interseismic and coseismic deformation and are fundamentally very weak surface cracks are ubiquitous throughout the region and form by both non tectonic and tectonic mechanisms a significant proportion forms during coseismic deformation and thus may be used to identify long lived rupture segments on the plate boundary overall forearc deformation is very slow with permanent strain rates of 1 5 nstrain year and fault slip rates less than 0 5 mm year

the iquique earthquake sequence of april 2014 bayesian modeling accounting for prediction uncertainty the subduction zone in northern chile is a well identified seismic gap that last ruptured in 1877 on 1 april 2014 this region was struck by a large earthquake following a two week long series of foreshocks this study combines a wide range of observations including geodetic tsunami and seismic data to produce a reliable kinematic slip model of the mw 8 1 main shock and a static slip model of the mw 7 7 aftershock we use a novel bayesian modeling approach that accounts for uncertainty in the green s functions both static and dynamic while avoiding nonphysical regularization the results reveal a sharp slip zone more compact than previously thought located downdip of the foreshock sequence and updip of high frequency sources inferred by back projection analysis both the main shock and the mw 7 7 aftershock did not rupture to the trench and left most of the seismic gap unbroken leaving the possibility of a future large earthquake in the region

improvement of radar ice thickness measurements of greenland outlet glaciers using sar processing extensive aircraft based radar ice thickness measurements over the interior and outlet glacier regions of the greenland ice sheet have been obtained by the university of kansas since1993 with the latest airborne surveys conducted in may 2001 the radar has evolved during this period to a highly versatile system capable of charac terizing ice thickness over a wide variety of ice sheet conditions before 1997 the digital system was limited only capable of storing incoherent data or coherent data with a very large number of presumed signals at a low pulse repetition frequency in1998 the radar was upgraded with modern components allowing coherent datato be stored with a small number of presumed returns for1024 range cellsat a highpulse repetition frequency the new data on icethickness of greenlandoutlet glaciers arearchivedand made availableto the scientific community in the form of radar echograms and derived ice thickness at http tornado rsl ukans edu greenlanddata htm the u s national snow and ice data center nsidc also provides a link to these data and nsidc will eventually serve as the permanent archive of these data improvements in radar sensitivity in outlet glacier regions have been achieved by collecting coherent radar data and applying various signal processing techniques deep outlet glacier channels that were previously unre solvedwith incoherentdata can nowbemappedusingacoherent signal signalcondition ing and synthetic aperture radar sar processing

on the roles of escape erosion and the viscous relaxation of craters on pluto abstract pluto and its satellites will be the most distant objects ever reconnoitered when nasa s new horizons spacecraft conducts its intensive flyby of this system in 2015 the size frequency distribution sfd of craters on the surfaces in the pluto system have long been expected to provide a useful measure of the size distribution of kuiper belt objects kbos down to much smaller size scales than presently observed however currently predicted escape rates of pluto s atmosphere suggest that of order one half to several kilometers of nitrogen ice has been removed from pluto s surface over geologic time because this range of depths is comparable to or greater than most expected crater depths on pluto one might expect that many craters on pluto s surface may have been removed or degraded by this process biasing the observed crater sfd relative to the production function crater sfd further if pluto s surface volatile layer is comparable to or deeper than crater depths and if the viscosity of this layer surface ice is low like the viscosity of pure n 2 ice at pluto s measured 35 k surface temperature or as low as the viscosity of ch 4 ice at warmer but plausible temperatures on isolated pure ch 4 surfaces on pluto then craters on pluto may also have significantly viscously relaxed also potentially biasing the observed crater sfd and surface crater retention age here we make a first exploration of how these processes can affect the displayed cratering record on pluto we find that pluto s surface may appear to be younger owing to these effects than it actually is we also find that by comparing pluto s cratering record to charon s it may be possible to estimate the total loss depth of material from pluto s surface over geologic time and therefore to estimate pluto s time averaged escape rate

megathrust and accretionary wedge properties and behaviour in the makran subduction zone this work forms part of the nerc and esrc funded project earthquakes without frontiers and was partially supported by the nerc large grant looking inside the continents from space cp is funded by an nerc studentship the facilities of iris data services and specifically the iris data management center were used for access to waveforms related metadata and or derived products used in this study iris data services are funded through the seismological facilities for the advancement of geoscience and earthscope sage proposal of the national science foundation under cooperative agreement ear 1261681

estimation of ice sheet motion using satellite radar interferometry method and error analysis with application to humboldt glacier greenland satellite radar interferometry provides glaciologists with an important new tool for determining the motion and topography of large ice sheets we examine the sources of error in interferometrically derived ice motion measurements including those errors due to inaccurate estimates of the interferometric baseline several simulations are used to assess baseline accuracy in terms of tie point error and the number and distribution of tie points these results give insight into how best to select tie points and also demonstrate the level of accuracy that can be achieved examination of two representative cases likely to occur in mapping ice sheet motion leads to the conclusion that with adequate tie point information ice velocity can be measured accurately to within a few meters per year a method to correct horizontal velocity estimates for the effect of vertical displacement using surface slopes is also developed finally we estimate the single component velocity field for an area on humboldt glacier northern greenland using interferograms formed from ers i sar images we estimate that these velocity measurements are accurate to within 2 3 m year 1

upper plate reverse fault reactivation and the unclamping of the megathrust during the 2014 northern chile earthquake sequence after 137 years without a great earthquake the mw 8 1 pisagua event of 1 april 2014 occurred in the central portion of the southern peru northern chile subduction zone this megathrust earthquake was preceded by more than 2 weeks of foreshock activity migrating 3 5 km day toward the mainshock hypocenter this foreshock sequence was triggered by an mw 6 7 earthquake on a reverse fault in the upper plate that strikes at a high angle to the trench similar to well documented reverse faults onshore these margin oblique reverse faults accommodate north south shortening resulting from subduction across a plate boundary that is curved in map view reverse slip on the crustal fault unclamped the subduction interface precipitating the subsequent megathrust foreshock activity that culminated in the great pisagua earthquake the combination of crustal reverse faults and a curved subduction margin also occurs in cascadia and northeastern japan indicating that there are two additional localities where great megathrust earthquakes may be triggered by upper plate fault activity