A new global high-resolution stereogrammetric and photogrammetric topographic map and updated 3-color global mosaic of Enceladus reveal that the shape of this active icy ocean world is distorted from a simple triaxial ellipsoid. Although the topographic range (high-to-low) of Enceladus, when referenced to its global triaxial figure, is the narrowest among icy bodies mapped globally thus far, the global DEM indicates a pronounced zonal latitudinal zoning of topography, with the north polar region and mid-southern latitudes being ∼300–400 m higher and south polar and mid-northern latitudes being ∼400 m lower on average than the triaxial figure. Dynamically, both north and south poles are low, but the south remarkably so, by >1 km. Spherical harmonic analysis also indicates the tidal axis of the body is located ∼4°W of the current IAU-defined prime meridian. Superposed on this global pattern are topographic features associated with geologic units within each terrain, as well as several prominent regional 100-km-scale basins, 1-to-1.8 km deep, previously reported. The shapes of these large basins depend on the terrains they formed in; those in older cratered terrains are relatively simple (i.e., ovate) in shape, but those in resurfaced terrains are more complex in shape, often correlating with geologic features and units within those terrains. Thus, while these basins exhibit no explicit local-scale geologic deformation or disruption of the icy shell in association with their elevations/formation, they are partially controlled by the physical characteristics of the terrains they formed in, suggesting that the icy shell can be heterogenous in character. Most of these basins occur on the trailing hemisphere and although a few of these are aligned, we find that they do not form a global great circle pattern, weakening previous arguments for true polar wander. Our preferred hypothesis is that these basins are due to isostatic adjustment of the ice shell in response to thermal anomalies from below and suggest that they may be surface manifestations of diffused hydrothermal plumes originating at the surface of Enceladus' rocky core. If so, similar patterns in core activity might be revealed once global topographic mapping is complete on Europa. 

New global topography of Enceladus: Hypsometry, basins, spherical harmonics, shell thickness, and true polar wander revisited

Variations in fault maturity have intermittently been invoked to explain variations in some seismological observations for large earthquakes. However, the lack of a unified geological definition of fault maturity makes quantitative assessment of its importance difficult. We evaluate the degree of empirical correlation between field measurements indicative of fault zone maturity and remotely measured seismological source parameters of 34 large shallow strike-slip events. Metrics based on fault segmentation, such as number of primary rupture segments and surface rupture azimuth, correlate best with seismic source attributes and the correlations with cumulative fault slip are somewhat weaker. Average rupture velocity shows the strongest correlation with metrics of maturity, followed by relative aftershock productivity. Mature faults have relatively lower aftershock productivity and higher rupture velocity. A more complex relation is found with moment-scaled radiated energy. There appears to be distinct behavior of very immature events with no prior mapped fault and < 1 km cumulative slip, which radiate modest seismic energy, while moderately mature faults have events with higher moment-scaled radiated energy and very mature faults with increasing cumulative slip tend to have events with reducing moment-scaled radiated energy. We also explore qualitative and composite assessments of maturity and arrive at similar trends. This empirical approach establishes that there are relationships between remote seismological observations and fault system maturity that can help to understand variations in seismic hazard among different fault environments and to assess the relative maturity of blind fault systems for which direct observations of maturity are very limited.

Seismological Indicators of Geologically Inferred Fault Maturity


 The 15 May 2020 Mw 6.5 Monte Cristo Range earthquake (MCRE) in Nevada, United States, is the largest instrumental event in the Mina deflection—a zone of east-trending left-lateral faults accommodating a right step between northwest-trending right-lateral faults of the Walker Lane. The MCRE ruptured a highly distributed faulting area with muted geomorphic expressions, motivating us to characterize the behavior of an earthquake on a structurally immature fault system. Inverse modeling of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) displacements reveals left-lateral slip on an east-striking, eastern fault and left-lateral–normal slip on an east-northeast-striking, western fault. Unusually, the two faults cross one another and ruptured together in the mainshock. The maximum slip of 1 m occurs at 8–10 km depth, but less than 0.1 m of slip reaches the surficial model fault patches, yielding a pronounced shallow slip deficit (SSD) of 91%. Relocated hypocenters indicate that the mainshock initiated at 9 km depth and that aftershocks span depths of 1–11 km, constraining the local seismogenic thickness. Our new field observations of fracturing and pebble-clearing in the western MCRE characterize a third, shorter, northern fault that is at the resolution limit of the InSAR–GNSS modeling. The segmented and intersecting fault geometry, off-fault aftershocks with variable mechanisms, distributed surface fractures, limited long-term geomorphic offsets, and a 600–700 m (cumulative) bedrock offset are all characteristic of a structurally immature fault system. However, the large SSD is not unusual for an earthquake of this magnitude, and a larger compilation of InSAR models (28 Mw≥6.4 strike-slip events) shows that SSDs correlate with magnitude rather than structural maturity. This study demonstrates the importance of integrating geodesy, seismology, and field observations to capture the full complexity of large earthquakes, and further suggests that seismic hazard assessments in shattered crustal regions consider the potential for multi- and cross-fault rupture.

The 2020 Mw 6.5 Monte Cristo Range, Nevada, Earthquake: Anatomy of a Crossing-Fault Rupture through a Region of Highly Distributed Deformation

The Mw 6.4 right‐lateral Petrinja earthquake (2020, Croatia) is one of the largest continental earthquakes of central Europe for decades. The slip pattern of such events is usually difficult to retrieve with terrestrial geodesy due to limited monitoring means. This study takes advantage of a unique data set of dense measurements of coseismic displacement in the epicentral area, obtained by repeated measurements of benchmark networks designed for civilian purposes, and supplemented by far‐field continuous GNSS measurements. Elastic modeling of these data shows two coseismic slip patches that extend over a 15 × 10 km rupture plane, locally reaching the surface, and that a right‐lateral sub‐parallel secondary fault in the central part of the rupture likely accommodated part of the coseismic deformation. This study demonstrates that rapid re‐measurement of pre‐existing civilian networks offers unique coseismic constrains in the near‐field where InSAR or optical image correlation may decorrelate.

https://hal.archives-ouvertes.fr/hal-03902533/file/Geophysical%20Research%20Letters%20-%202022%20-%20Henriquet%20-%20Rapid%20Remeasure%20of%20Dense%20Civilian%20Networks%20as%20a%20Game%E2%80%90Changer%20Tool%20for.pdf

Rapid Remeasure of Dense Civilian Networks as a Game‐Changer Tool for Surface Deformation Monitoring: The Case Study of the Mw 6.4 2020 Petrinja Earthquake, Croatia


 Widespread distributed fracturing during earthquakes threatens infrastructure and lifelines. We combine high-resolution rupture maps from the five major surface-rupturing strike-slip earthquakes in southern California and northern Mexico since 1992 to incorporate the displacements produced by distributed ruptures into a probabilistic displacement hazard analysis framework. Through analysis of the spatial distribution of mapped ruptures and displacements for each of these events, we develop a magnitude-dependent expression for the probability per unit area of finding a distributed rupture that accommodates a displacement that exceeds a displacement threshold at a given distance from the principal fault. Our model is best applied to estimating expected distributed displacements for strike-slip earthquakes, similar to those analyzed, with widespread ruptures across immature fault zones.

Displacement Hazard from Distributed Ruptures in Strike-Slip Earthquakes

On 29 December 2020, a shallow earthquake of magnitude Mw 6.4 struck northern Croatia, near the town of Petrinja, more than 24 hours after a strong foreshock (Ml 5). We formed a reconnaissance team of European geologists and engineers, from Croatia, Slovenia, France, Italy and Greece, rapidly deployed in the field to map the evidence of coseismic environmental effects. In the epicentral area, we recognized surface deformation, such as tectonic breaks along the earthquake source at the surface, liquefaction features (scattered in the fluvial plains of Kupa, Glina and Sava rivers), and slope failures, both caused by strong motion. Thanks to this concerted, collective and meticulous work, we were able to document and map a clear and unambiguous coseismic surface rupture associated with the main shock. The surface rupture appears discontinuous, consisting of multi-kilometer en échelon right stepping sections, along a NW-SE striking fault that we call the Petrinja-Pokupsko Fault (PPKF). The observed deformation features, in terms of kinematics and trace alignments, are consistent with slip on a right lateral fault, in agreement with the focal solution of the main shock. We found mole tracks, displacement on faults affecting natural features (e. g. drainage channels), scarplets, and more frequently breaks of anthropogenic markers (roads, fences). The surface rupture is observed over a length of ~13 km from end-to-end, with a maximum displacement of 38 cm, and an average displacement of ~10 cm. Moreover, the liquefaction extends over an area of nearly 600 km2 around the epicenter. Typology of liquefaction features include sand blows, lateral spreading phenomenon along the road and river embankments, as well as sand ejecta of different grain size and matrix. Development of large and long fissures along the fluvial landforms, current or ancient, with massive D ow naded rom http/academ ic.p.com /gji/advance-artic.1093/gji/ggac123/6554549 by IN IT-C N R S IN SU user on 30 M arch 2022

Environmental effects and seismogenic source characterization of the December 2020 earthquake sequence near Petrinja, Croatia

Introduction: Saturn’s icy moon Dione has been extensively resurfaced and is second only to Enceladus in terms of geologic complexity [1]. Dione may thus represent a fossil version of that active moon. It is also currently in a 2:1 mean-motion orbital resonance with Enceladus and is experiencing modestly enhanced heating (possibly greater in the past). Like Enceladus, Cassini acquired global stereo imaging of Dione. Here we report on construction of an updated global DEM, with emphasis on global properties, influence of large impacts on that shape, and comparisons with Enceladus. Topographic Mapping of Dione: To produce a global topographic map of Dione (Fig. 1) referenced to the limb-derived triaxial shape of the body [2] we use the same approach used for our high resolution global topographic map of Enceladus [3, 4]. Using ISIS tools, we first register the complete Dione image library using match points and solve for the camera pointing vectors of those images using bundle adjustment, simultaneous solving for match point radii relative to the center of the body. Stereogrammetric digital elevation models (DEMs) are then produced, with each DEM mapped to the global match point radius map. The result is a highresolution global map of elevations on Dione relative to the triaxial figure (Fig. 1); produced at a base resolution of 400 m. Weakest stereo coverage is south of 60°S, where imaging resolutions were > 750 m/pixel.

Global topography of dione: effects of large impacts on global shape.

Introduction: The subset of presolar grains extracted from meteorites, and made up of s-process isotopes, likely formed around thermally pulsing asymptotic giant branch (AGB) stars “after third dredge-up” of newly made carbon atoms [1]. In particular the core\rim subset of micron-size carbon spheres in presolar collections e.g. from the meteorite Murchison contain unlayered graphene sheets in their core [2,3], whose size and abundance likely provide information on the thermal history during formation. Laboratory evidence for supercooled droplet formation during carbon vapor condensation [4,5], the spherical nature of the cores with their atomically-abrupt transition from core to rim, and TEM evidence for unlayered graphene structures (some in the form of faceted pentacones), have in particular prompted us to construct models for nucleation and growth of these sheets from a supercooled carbon melt for various cooling rates [6]. In particular we show how a Debye scattering analysis of electron powder diffraction profiles from both laboratory grown and presolar onion cores [7] can be used to estimate mass weighted average sheet size and number density, and how a first-order analytical nucleation and growth model can be used therewith to estimate the stellar atmosphere cooling rate during solidification from a given microtome-sliced core\rim particle. In particular the literature on containerless solidification of metallic liquids suggests that carbon liquid may supercool further than for common metals, e.g. to 50% of the effective melting temperature. TEM characterization: The Debye scattering equation [8] allows one to calculate the interference effect of small randomly-oriented crystalline clusters on otherwise diffuse atomic scattering from a specimen. It is ideal for working with oddly-shaped clusters (like unlayered graphene sheets, and faceted carbon pentacones) because molecule shape effects (like the high-frequency tails on powder diffraction peaks from atom-thick sheets [9]) are automatically taken into account in its predictions. Electron powder diffraction (and HRTEM) observations of presolar onion cores suggest an average graphene sheet size of about 40A coherence width, or N ≈ 612 atoms per cluster. Diffraction from the labgrown cores instead suggest sheets with only 12A coherence width, or N ≈ 60 atoms per cluster. This is not surprising since the small size of our oven interior suggests that condensed particles impact an oven wall within about 10 milliseconds, while containerless cooling of carbon condensate in a red giant photosphere might take place over much longer times (limited only e.g. by radiation pressure ejection). One way to estimate the fraction crystalline at each peak is to measure three heights at the peak frequency on a model "100%-crystalline" Debye system with comparable peak width, namely the total peak height s2, the estimated background height s1 beneath the peak, and the "diffuse-scattering baseline" height sx. Then on an "experimental profile" (see Fig. below) measure the observed total peak height h2 and the corresponding peak background h1 beneath the peak.

Tem data & thermal history models for presolar core\rim carbon spheres

Introduction: Pluto’s Sputnik basin, a ~1650 km by 870 km wide, elliptical impact basin in Pluto’s equatorial region [1], is a unique structure for the outer Solar System. Previous studies have compared the dimensions of Sputnik to large impact basins in the inner Solar System [2-4]. However, such basins are typically multiring structures, with two or more concentric asymmetric ring scarps surrounding a central depression. No such multiring structure has been previously documented for Sputnik Basin. Here, we show that the topography and morphology of Sputnik basin are consistent with a peak-ring or multiring structure similar to basins on the Moon, Mars and Mercury. Sputnik basin is partially filled with an N2 rich volatile deposit with a north-south trending chain of water-ice mountain blocks rising ~1.5 km above the fill, ~120 km from the western rim [1,2,5]. Previous studies have proposed that the chain of mountain blocks was emplaced in the N2 ice deposit by either floating and then becoming grounded [1,2] or basal siding after fragmentation of the water ice crust during the basinforming impact [6]. We instead interpret this chain of water-ice mountain blocks to be the exposed remnant of the inner ring of Sputnik basin. We compare the morphology and topography of Sputnik basin to 19 peak/multi-ring basins in the inner solar system. Where the basin floor is covered by N2 ice, we use the convection cell patterns to constrain the topography of the basin floor. The interpretation of Sputnik as a peakring or multiring structure would have implications for basin compensation [7-9] and basin formation processes on icy outer Solar System bodies. Methods: For topographic and morphologic comparison, we utilized a stereo Digital Elevation Model (DEM) [2,5] for Pluto, the LOLA DEM [10] for the lunar basins and the MOLA DEM [11] for martian basins (Fig. 1). Average radial profiles from the center of the each basin were scaled and compared to average radial profiles of Sputnik Basin. Sputnik basin was distorted to circularize the main basin rim prior to averaging. For each basin, including Sputnik, we measured the diameters of the rings and the crustal thinning within the inner rings of the basins with respect to the background values [7,9, -12]. For Sputnik, we estimate the pre-fill basin depth based on the observed depth and estimated fill thickness, taking into account the degree of compensation expected for the load, and calculate the shell thinning for isostatic compensation of a water ice shell above a liquid water ocean, consistent with a model of the basin’s formation [8]. These parameters were compared to the inner ring diameter of each basin. We then found the residuals for each basin relative to the linear fit for the tested parameters and tested whether Sputnik could be considered an outlier based on its residual, as well as using a Grubbs outlier test.

Pluto’s sputnik basin as a peak-ring basin: a comparative study

Introduction: Mars today is cold and dry, although liquid water might occur episodically as dense brines or melt. Studying the nature and distribution of hydrated/altered minerals within the north and south PLD would reveal the history of water activity during Amazonian Mars, where fluids are saline, acidic, and rare [1]. Different alteration minerals are formed in unique redox and geochemical environment, so, their detection at the PLD directly influences our understanding of the habitability conditions in this period. Previously, sulfates have been detected in the north polar sand sea, suggesting the recent presence of liquid water in north polar terrains [2-4]. The glass in the sand sea also appears to have been subjected to aqueous alteration, most likely acid leaching to form silica rinds [5]. Hydrated sulfates are widespread in the sediments on the NPLD, which could either indicate aqueous alteration of NPLD lithics [4] or that the salts are atmospheric precipitates that accumulated in sublimation lags [6,7]. Observations from the Phoenix lander support the presence of active perchlorate brines in polar soils, including transient liquid droplets, dielectric permittivity consistent with brines, and clumping of perchloratebearing soils [8-10]. A possible perchlorate absorption band has been detected based on ~2.15 μm in NPLD sediments [6]. However, recent studies have shown that this could also be an artifact in CRISM I/F data [11]. At southern high latitudes, detection of hydrated sulfates suggests aqueous activity also occurred in the south polar region of Mars [12-13]. However, sulfates and perchlorates have not been detected on or around the SPLD. Instead, weak hydration from smectites has been detected in SPLD sediments [14], but it is unknown whether they formed in situ or are sourced from nearby Noachian/Hesperian bedrock. These observations suggest that the poles may have experienced different aqueous alteration histories, but additional work is needed to understand the occurrence and distribution of alteration minerals within both north and south PLD. In this study, we attempt to look for diversity in secondary minerals at the PLD. We hypothesize that the alteration histories of NPLD and SPLD may be different due to many factors. The SPLD lies over the southern highlands and has much higher elevation than its northern counterpart which results is a different atmospheric condition in both regions. Axial tilt influencing temperature and duration of winter drives accumulation and ablation differently at the two PLD. Moreover, SPLD being older provides a geologic window to look deeper into climatic history of Amazonian Mars [15,16]. Methods: CRISM MTRDR and TRR3 hyperspectral image cubes from both north and south PLD (Figure 1) were analyzed using the CRISM Analysis Toolkit (CAT). The 18-40 m/pixel data is examined at visible and nearinfrared wavelengths (VNIR, 0.7-2.6 μm) for presence of altered minerals like oxides, salts, smectites, zeolite, and leached glass (Figure 2): ferric oxide (hematite) cause an strong absorption at 0.86 μm; sulfate salts show hydration bands at 1.44 and 1.92 μm along with a spectral shoulder at 2.4 μm; smectites also display hydration bands in addition to have a hydroxylation band between 2.1 and 2.4 μm whose center shifts depending on the element bonded with an hydroxyl ion; zeolite have an absorption band centered around 2.5 μm along with hydration bands at 1.44 and 1.92 μm; and leached glass which shows strong blue spectral slope with negligible to weak ferrous iron absorption at 1 and 2 μm.

Polar opposites: distinct alteration minerals within the north and south po- lar layered deposits (pld) and implications for amazonian aqueous history

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