Shallow Dip Research Articles

Analysis of ground deformation based on GPS in Sanshandao gold mine, China

Sanshandao Gold Mine is the first and largest mine operating below sea level in China. Mining has been practiced in this region for at least 25 years. In recent years, buildings above the mining area have been extensively damaged. GPS (with 315 monitoring points) was used to monitor the ground deformation since 2009. Ground deformation induced by mining is much more complex in metal mine than that in coal mines due to the well-developed joints, high tectonic stress and several intersecting faults. All of the factors are analyzed in this study. The results show that discontinuous deformation has occurred on the surface because of the sliding to F3 (name of fault), and there are two motion patterns of F3 during the mining process. Additionally, joints in rock masses with steep dip angles contribute to the vertical displacement and joints with shallow dip angles contribute to the horizontal displacement. Meanwhile, high tectonic stress dramatically enlarges the scale of ground deformation, especially with respect to the horizontal displacement. This deformation results in a striped formation of compressed and stretched regions. Additionally, high-risk and potential risk areas are identified in this study. Finally, the successive data measured since 2009 can contribute to a deeper understanding of ground deformation in metal mine.

Characterizing Fracture Geometry from Borehole Images

The use of borehole image logs in natural-fracture evaluation has traditionally focused on mapping the strikes and dips of the individual fractures that intersect the borehole, estimating their apertures, and from these computing fracture attributes such as fracture density. These fracture attributes are commonly used to build three-dimensional fracture-network models. However, these attributes do not directly constrain an important aspect of these models—fracture geometry—specifically, the size, shape, and rotation of three-dimensional fractures within the model. The published formulas of Ozkaya estimate the radius of circular fractures from the statistics of fracture intersections observed in a borehole image. These formulas are shown to be approximate, only applying to circular fractures with shallow relative dip, and are replaced with exact formulas for elliptical fractures that are valid over the entire range of relative dip. A new statistic is defined, the measured distribution of relative azimuths for fracture-trace midpoints, that is sufficient for estimating both the elongation ratio and the rotation angle of elliptically shaped fractures. As estimation accuracy for this fracture geometry is dependent on the number of observed fracture traces, practical methodologies are provided for computing the uncertainty of these estimates. Finally, since natural fracture size is typically not constant, but follows a distribution such as a power law, solutions are provided for using these same borehole image statistics to estimate the fracture-size distribution. Numerical examples with exponential and Pareto distributions demonstrate that a single parameter of a parametric size distribution can be estimated along with its uncertainty.

Slab interactions in 3-D subduction settings: The Philippine Sea Plate region

The importance of slab–slab interactions is manifested in the kinematics and geometry of the Philippine Sea Plate and western Pacific subduction zones, and such interactions offer a dynamic basis for the first-order observations in this complex subduction setting. The westward subduction of the Pacific Sea Plate changes, along-strike, from single slab subduction beneath Japan, to a double-subduction setting where Pacific subduction beneath the Philippine Sea Plate occurs in tandem with westward subduction of the Philippine Sea Plate beneath Eurasia. Our 3-D numerical models show that there are fundamental differences between single slab systems and double slab systems where both subduction systems have the same vergence. We find that the observed kinematics and slab geometry of the Pacific–Philippine subduction can be understood by considering an along-strike transition from single to double subduction, and is largely independent from the detailed geometry of the Philippine Sea Plate. Important first order features include the relatively shallow slab dip, retreating/stationary trenches, and rapid subduction for single slab systems (Pacific Plate subducting under Japan), and front slabs within a double slab system (Philippine Sea Plate subducting at Ryukyu). In contrast, steep to overturned slab dips, advancing trench motion, and slower subduction occurs for rear slabs in a double slab setting (Pacific subducting at the Izu–Bonin–Mariana). This happens because of a relative build-up of pressure in the asthenosphere beneath the Philippine Sea Plate, where the asthenosphere is constrained between the converging Ryukyu and Izu–Bonin–Mariana slabs. When weak back-arc regions are included, slab–slab convergence rates slow and the middle (Philippine) plate extends, which leads to reduced pressure build up and reduced slab–slab coupling. Models without back-arcs, or with back-arc viscosities that are reduced by a factor of five, produce kinematics compatible with present-day observations.

Slab dip, surface tectonics: How and when do they change following an acceleration/slow down of the overriding plate?

We present analogue models simulating the subduction of an oceanic lithosphere beneath an overriding plate advancing at variable rates. The convergence velocity is imposed by lateral boundary conditions in this experimental set. We analyze the geometry of the slab and the deformation of the overriding plate. Experiments confirm the strong correlation between the absolute velocity of the overriding plate on the one hand, the geometry of the subducting plate and the deformation of the overriding plate on the other hand. Following an instantaneous change in kinematic boundary conditions, the subduction system progressively shifts to a new steady-state regime. Models suggest that the adjustment time necessary to shift from the previous to the new equilibrium is independent of the imposed upper plate velocity. Transient stage lasts ∼ 12.5 ± 6 m.y. for the shallow slab dip (100–150-km depth), ∼ 29.2 ± 10 m.y. for the deeper slab dip (300–350-km depth), and ∼ 2.2 ± 2 m.y. for the upper plate deformation. The analysis of present-day subduction zones and their evolution through the last 20 m.y suggests an adjustment time of ∼15 m.y. for shallow slab dip and ∼20 m.y. for deep slab dip in Nature. Since only few subduction zones have shown a constant upper plate velocity over the last 15 m.y., it suggests that most of them are in a transient stage at present-day.

How fast can low-angle normal faults slip? Insights from cosmogenic exposure dating of the active Mai’iu fault, Papua New Guinea

Abstract Is there an upper limit to normal fault slip rates? The Mai’iu fault, located within the rapidly extending Woodlark Rift, Papua New Guinea, is one of few active continental low-angle normal faults (LANFs) globally. There is ongoing debate regarding how commonly normal faults slip at shallow (<30°) dips, and at what rates. We present a global compilation of reported slip rates on active and inactive extensional detachments that suggests that such faults may slip at >10–20 mm/yr—faster than any reported high-angle normal fault. Cosmogenic nuclide exposure dating (10Be in quartz) of the lowermost Mai’iu fault scarp supports this finding, indicating slip at 11.7 ± 3.5 mm/yr over the past ∼5.5 k.y. Our results highlight the long-term viability of LANFs, and show that the Mai’iu fault represents one of Earth’s fastest active continental normal faults. Rapid and large-displacement slip is likely enabled by extremely low fault frictional strength.

Igneous sills record far-field and near-field stress interactions during volcano construction: Isle of Mull, Scotland

Sill emplacement is typically associated with horizontally mechanically layered host rocks in a near-hydrostatic far-field stress state, where contrasting mechanical properties across the layers promote transitions from dykes, or inclined sheets, to sills. We used detailed field observations from the Loch Scridain Sill Complex (Isle of Mull, UK), and mechanical models to show that layering is not always the dominant control on sill emplacement. The studied sills have consistently shallow dips (1°–25°) and cut vertically bedded and foliated metamorphic basement rocks, and horizontally bedded cover sedimentary rocks and lavas. Horizontal and shallowly-dipping fractures in the host rock were intruded with vertical opening in all cases, whilst steeply-dipping discontinuities within the sequence (i.e. vertical fractures and foliation in the basement, and vertical polygonal joints in the lavas) were not intruded during sill emplacement. Mechanical models of slip tendency, dilation tendency, and fracture susceptibility for local and overall sill geometry data, support a radial horizontal compression during sill emplacement. Our models show that dykes and sills across Mull were emplaced during NW–SE horizontal shortening, related to a far-field tectonic stress state. The dykes generally accommodated phases of NE–SW horizontal tectonic extension, whereas the sills record the superposition of the far-field stress with a near-field stress state, imposed by emplacement of the Mull Central Volcano. We show that through detailed geometric characterisation coupled with mechanical modelling, sills may be used as an indication of fluctuations in the paleostress state.

Horizontal mantle flow controls subduction dynamics

It is generally accepted that subduction is driven by downgoing-plate negative buoyancy. Yet plate age –the main control on buoyancy– exhibits little correlation with most of the present-day subduction velocities and slab dips. “West”-directed subduction zones are on average steeper (~65°) than “East”-directed (~27°). Also, a “westerly”-directed net rotation of the lithosphere relative to the mantle has been detected in the hotspot reference frame. Thus, the existence of an “easterly”-directed horizontal mantle wind could explain this subduction asymmetry, favouring steepening or lifting of slab dip angles. Here we test this hypothesis using high-resolution two-dimensional numerical thermomechanical models of oceanic plate subduction interacting with a mantle flow. Results show that when subduction polarity is opposite to that of the mantle flow, the descending slab dips subvertically and the hinge retreats, thus leading to the development of a back-arc basin. In contrast, concordance between mantle flow and subduction polarity results in shallow dipping subduction, hinge advance and pronounced topography of the overriding plate, regardless of their age-dependent negative buoyancy. Our results are consistent with seismicity data and tomographic images of subduction zones. Thus, our models may explain why subduction asymmetry is a common feature of convergent margins on Earth.

Velocity models and hypocenter relocations for the Charlevoix Seismic Zone

AbstractThree‐dimensional P and S wave velocity (Vp and Vs) models and hypocenter relocations are determined for the Charlevoix Seismic Zone (CSZ) using local arrival time tomography. The CSZ is located along the St. Lawrence River about 100 km downstream from Quebec City, Canada, and is one of the most active seismic zones in eastern North America. Earthquakes occur in Grenvillian basement rocks affected by Iapetan Ocean rifting and a large Devonian meteor impact. Low Vp and Vs are associated with the impact structure to a depth of 12 km. Relocated hypocenters form a semicircle delineating the eastern margin of the impact structure. Northeast of the impact, hypocenters cluster into two groups separated by a region of high Vp and Vs velocity. Hypocenters within each group align along planar surfaces, suggesting the presence of distinct seismogenic faults. The planes trend NE, in the same direction as the Iapetan rift faults, and dip to the SE. One plane is located beneath the north shore of the St. Lawrence River and extends to a depth of at least 30 km. Two other planes with shallower dips are located beneath the river and extend to depths of 12 and 15 km. All three planes are disrupted within the impact zone but can be followed, suggesting partial preservation of rift‐parallel fault fabric.

Trench motion‐controlled slab morphology and stress variations: Implications for the isolated 2015 Bonin Islands deep earthquake

AbstractThe subducted old and cold Pacific Plate beneath the young Philippine Sea Plate at the Izu‐Bonin trench over the Cenozoic hosts regional deep earthquakes. We investigate slab morphology and stress regimes under different trench motion histories with mantle convection models. Viscosity, temperature, and deviatoric stress are inherently heterogeneous within the slab, which we link to the occurrence of isolated earthquakes. Models expand on previous suggestions that observed slab morphology variations along the Izu‐Bonin subduction zone, exhibited as shallow slab dip angles in the north and steeper dip angles in the south, are mainly due to variations in the rate of trench retreat from the north (where it is fast) to the south (where it is slow). Geodynamic models consistent with the regional plate tectonics, including oceanic plate age, plate convergence rate, and trench motion history, reproduce the seismologically observed principal stress direction and slab morphology. We suggest that the isolated ~680 km deep, 30 May 2015 Mw 7.9 Bonin Islands earthquake, which lies east of the well‐defined Benioff zone and has its principal compressional stress direction oriented toward the tip of the previously defined Benioff zone, can be explained by Pacific slab buckling in response to the slow trench retreat.

Inductive electromagnetic data interpretation using a 3D distribution of 3D magnetic or electric dipoles

In inductive electromagnetics, the magnetic field measured in the air at any instant can be considered to be a potential field. As such, we can invert measured magnetic fields (at a fixed time or frequency) for the causative subsurface current system. These currents can be approximated with a 3D subsurface grid of 3D magnetic (closed-loop current) or electric (line current) dipoles whose location and orientation can be solved for using a potential-field-style smooth-model inversion. Because the problem is linear, both inversions can be solved quickly even for large subsurface volumes; and both can be run on a single data set for complementary information. Synthetic studies suggest that for discrete induction dominated targets, the magnetic and electric dipole inversions can be used to determine the center and top edge of the target, respectively. Furthermore, the orientation of plate targets can be estimated from visual examination of the orientations of the 3D vector dipoles and/or using the interpreted location of the center and top edge of the target. In the first field example, ground data from a deep massive sulfide body (mineral exploration target) was inverted and the results were consistent with the conclusions drawn from the synthetic examples and with the existing interpretation of the body (shallow dipping conductor at a depth of approximately 400 m). A second example over a near-surface mine tailing (a near-surface environmental/engineering study) highlighted the strength of being able to invert data using either magnetic or electric dipoles. Although both models were able to fit the data, the electric dipole model was considerably simpler and revealed a southwest−northeast-trending conductive zone. This fast approximate 3D inversion can be used as a starting point for more rigorous interpretation and/or, in some cases, as a stand-alone interpretation tool.

Simplifying drill-hole domains for 3D geochemical modelling: An example from the Kevitsa Ni-Cu-(PGE) deposit

A 3D geology model is a simplified version of the true geology, designed to give a visual summary of the geometry and distribution of major geological elements in a specified region. Drill holes provide detailed data of the subsurface that can be classified into geological units that are the fundamental elements of the 3D model. Due to software limitations, upscaling (‘lumping’) is usually required to reduce the number of geological units in the drill holes prior to model building. Upscaling is a subjective process, which means that different geologists will group in different ways and will typically not record the rationale behind their decision; this means the “experiment” is not reproducible. In our study we use a method of upscaling geological units, in this case based on assay data, using the continuous wavelet transform (CWT) and tessellation methods. This method reduces subjectivity and can easily be repeated (e.g. on an updated or new drill hole) by using the same parameters, ensuring that the upscaling process is consistent over all drill hole data. We apply this technique to a large assay database (>90,000 samples) from the Kevitsa Nickel-Copper-Platinum group element (PGE) deposit in Finland.The Kevitsa Ni-Cu-(PGE) disseminated sulfide orebody is hosted in a Proterozoic layered intrusion in northern Finland. Internal geological subdivision and correlation within the intrusion is very difficult to do consistently using lithological observations, owing to general homogeneity of rock types and an overprint of alteration, but distinct variability is evident in Ni and PGE sulfide tenors. In its raw form, the tenor variation dataset appears noisy and unsystematic. We have applied the tessellation method to classifying ore types based on tenor variations, consistently and objectively reducing the number of units in each drill hole to create a simplified 3D model of the orebody. Our results reveal shallow inward dipping cryptic layering defined by sulfide composition, which are interpreted as reflecting an increase in Ni and PGE tenor with time during emplacement of the sulfide-bearing cumulates. We interpret this as a progressive increase in silicate-sulfide mixing efficiency (R factor) as the intrusion developed from an interconnected sill sediment-complex choked with country rock inclusions into a freely convecting magma chamber. Based on this case study, we show that the tessellation method can add considerable value by distinguishing the wood from the trees in large 3D geochemical databases. The method may be widely applicable in other Ni-Cu-PGE deposits where tenor variations appear, at first sight, to be chaotic and uninterpretable.

Finite‐fault slip model of the 2016 Mw 7.5 Chiloé earthquake, southern Chile, estimated from Sentinel‐1 data

AbstractSubduction earthquakes have been widely studied in the Chilean subduction zone, but earthquakes occurring in its southern part have attracted less research interest primarily due to its lower rate of seismic activity. Here I use Sentinel‐1 interferometric synthetic aperture radar (InSAR) data and range offset measurements to generate coseismic crustal deformation maps of the 2016 Mw 7.5 Chiloé earthquake in southern Chile. I find a concentrated crustal deformation with ground displacement of approximately 50 cm in the southern part of the Chiloé island. The best fitting fault model shows a pure thrust‐fault motion on a shallow dipping plane orienting 4° NNE. The InSAR‐determined moment is 2.4 × 1020 Nm with a shear modulus of 30 GPa, equivalent to Mw 7.56, which is slightly lower than the seismic moment. The model shows that the slip did not reach the trench, and it reruptured part of the fault that ruptured in the 1960 Mw 9.5 earthquake. The 2016 event has only released a small portion of the accumulated strain energy on the 1960 rupture zone, suggesting that the seismic hazard of future great earthquakes in southern Chile is high.

Geometry and spatial variations of seismic reflection intensity of the upper surface of the Philippine Sea plate off the Boso Peninsula, Japan

In the region off the Boso Peninsula, Japan, the Pacific plate is subducting westward beneath both the Honshu island arc and Philippine Sea plate, while the Philippine Sea plate is subducting northwestward beneath the Honshu island arc. These complex tectonic interactions have caused numerous seismic events occurred in the past. To better understand these seismic events, it is important to determine the geometry of the plate boundary, in particular the upper surface of the Philippine Sea plate. We conducted an active-source seismic refraction survey in July and August 2009 from which we obtained a 2-D P-wave velocity structure model along a 216-km profile. We used the velocity model and previously published data that indicate a P-wave velocity of 5.0km/s for the upper surface of the subducting Philippine Sea plate to delineate its boundary with the overriding Honshu island arc. Our isodepth contours of the upper surface of the Philippine Sea plate show that its dip is shallow at depths of 10 to 15km, far off the Boso Peninsula. This shallow dip may be a result of interference from the Pacific plate slab, which is subducting westward under the Philippine Sea plate. Within our survey data, we recognized numerous seismic reflections of variable intensity, some of which came from the upper surface of the Philippine Sea plate. An area of high seismic reflection intensity corresponds with the main slip area of the Boso slow slip events. Our modeling indicates that those reflections can be explained by an inhomogeneous layer close to the upper surface of the Philippine Sea plate.

Shallow dipping structure associated to the Cimandiri Fault: evidence from single station teleseismic receiver function analysis

The Cimandiri fault zone is located in the eastern part of the boundary between the oblique subduction of the Indo-Australian plate along Sumatera and the frontal subduction along Java. Even though some geological and geophysical investigations have been conducted and focused on this area, the geometry of the fault zone remains poorly resolved. To provide better constraints on the geometry of the Cimandiri fault zone, we analyze teleseismic receiver functions from single permanent seismic station located in the fault zone. We observe that the computed receiver functions show back azimuthal variation in the amplitude converted waves at the first 2 second of receiver functions providing clear evidence for the presence of complicated shallow structure. We implement forward modelling technique using synthetic seismograms with the same parameters as the observed receiver functions. The modelling reveals at least 2 km thick low velocity zone dipping N-E at 30°, which might be correlated to the Cimandiri fault.

Geology, fluid inclusion and stable isotope study of the Yueyang Ag-Au-Cu deposit, Zijinshan orefield, Fujian Province, China

The large Yueyang Ag-Au-Cu deposit is commonly regarded as a low-sulfidation epithermal deposit in the Zijinshan orefield, Fujian Province, southeastern China. The Ag-Ag-Cu orebodies hosted in the Zijinshan granitic batholith are mainly stratoid and lens in shape, and controlled by a series of NW-trending listric faults with shallow dip angles. Four mineralization stages are recognized on the basis of mineral assemblage, ore fabrics, and crosscutting relationships of the ore veins, namely: pre-ore (pyrite+sericite+quartz±chlorite), main Cu (chalcopyrite+pyrite+sericite+quartz±bornite), main Ag-Au (Ag and Au minerals+pyrite+quartz+adularia±calcite±apatite±chalcopyrite±galena±sphalerite) and post-ore (quartz±chalcedony±calcite) stages. Fluid inclusions (FIs) in the deposit include aqueous liquid-rich (WL-), aqueous vapor-rich (WV-), and minor carbonic (C-) and daughter mineral-bearing (S-) type ones. WL-subtype is the main inclusion type in the Yueyang deposit, accounting for more than 90% in proportion in each stage. Minor WV-subtype inclusions occur in both the main Cu and Ag stages, while the C-type and S-type ones are only observed in the main Cu stage. Fluid inclusion and H-O isotope study indicated that the ore-forming fluid of the main Cu stage is primarily magmatic vapor, which further underwent fluid boiling and mixing with meteoric water, while the ore-forming fluid of the main Ag stage is meteoric water-dominated, and the precipitation of silver and gold was mainly resulted from fluid boiling and the precipitation of other sulfides. On the basis of the aforementioned geological, fluid inclusion and stable isotope studies, we proposed a two-stage model for the Yueyang deposit, including a magmatic vapor-related porphyry type Cu mineralization and meteoric water-related low-sulfidation epithermal Ag-Au-Cu mineralization, although the porphyry Cu mineralization is very limited in scale. The mineralization and exhumation depths of the Yueyang deposit are estimated to be 448‒527m and 18‒97m, respectively. By comparison with the exhumation depths of other deposits in the Zijinshan orefield, it is suggested that more epithermal deposits could be found in the southwest of the orefield due to less uplift and exhumation therein.

Architecture of the intracontinental Jaibaras Rift, Brazil, based on geophysical data

Qualitative and quantitative integration and interpretation of magnetic, gravity and magnetotelluric data help to determine the internal architecture of the Jaibaras rift, and allow assessing the evolution of the Jaibaras Rift within the Precambrian crystalline basement of Borborema Province, NE Brazil. This was achieved by 2D joint modeling of magnetic and gravity data in five sections across the main axis of the Jaibaras Rift. Surface data, rock density measurements, depth constraints from 2D Euler deconvolution and geophysical information from previous work in the area were integrated to constrain the modeling. The magnetic and gravity profiles of the Jaibaras Rift indicate estimated source bodies at depths up to 2.5 km, showing complex configuration for the structural framework, with a set of asymmetric grabens and horsts. The 2D magnetotelluric inversion shows that the Jaibaras Rift is marked by low resistivity values, and maximum thickness of the sedimentary package up to approximately 3 km. Shallow dipping conductive material may represent either a suture zone between the Ceará Central and Médio Coreaú domains or a set of fractures due to horizontal σ1 stress in the Ceará Central Domain. The Jaibaras Rift displays a very complex internal structure, with discontinuous sequences of grabens and horsts, and a significant volume of surface and subsurface volcanic rocks. The sedimentary packages with volcanic rift sequences have variable thicknesses, from 1 to 3 km. These rock units are controlled by normal faults that developed from older discontinuities, such as the Transbrasiliano lineament.

A new tectonic model for Abu-Dabbab seismogenic zone (Eastern Desert, Egypt): evidence from field-structural, EMR and seismic data

Abu-Dabbab area is the most active seismic zone in the central Eastern Desert of Egypt, where seismic activities are daily recorded. The reported earthquakes are microearthquakes of local magnitudes (ML < 2.0). A spatial distribution of these microearthquakes shows that the earthquakes of the area follow an ENE–WSW trending pattern, which is nearly perpendicular to the Red Sea Rift. Focal mechanisms of different fault styles were recognized with dominant normal faulting (with a strike-slip component) events characterized by focal depths greater than 7 km and reverse ones of shallower focal depths. Several lines of evidence indicating that the brittle-ductile transition zone underlies the Abu-Dabbab area occurs at a relatively shallow depth (10–12 km) and it is acting as a low-angle normal shear zone (LANF). Field-structural, EMR and seismic data (this study) reveal that the maximum compressive stress (σ1) in the area is perturbed from the regional NW–SE direction to ENE–WSW orientation. This stress rotation is evidently akin to the reactivation of the crustal scale Najd Fault System (NFS), where such reactivation is attributed to the ongoing activity/opening of the Red Sea. Our tectonic model proposes that the continuous activity on the brittle-ductile transition zone including the LANF led to stress localization, which triggering a brittle deformation in the upper crustal-levels and associated shallow dipping thrusts. Such bimodal tectonic model suggests that the deep earthquakes are owing to the tectonic movement on the LANF (transtension), whereas the shallow earthquakes are related to a brittle deformation inside the fault blocks of the upper crust (transpression). Deformation creep along this zone didn’t permit continuous accumulation of strain and hence reduce the possible occurrence of large earthquakes.

Application of the airborne electromagnetic method for Banded Iron-Formation mapping in the Hamersley Province, Western Australia

Stratigraphy of the Hamersley Province in Western Australia, featuring alternating units of banded iron-formations and shales with contrasting electrical properties in a mostly gently undulating shallow dipping layered geometry, is particularly favourable to airborne time-domain electromagnetic mapping techniques. Manipulated vertical cross-sections of modelled conductivity obtained from laterally constrained 1D inversion of SkyTEM304 data enable the exploration geologist to interpret weathering profiles, shallow dipping stratigraphy and steep structures, all of which are crucial aspects of bedded iron ore deposits genesis models. Five potential interpretation pitfalls have nevertheless been encountered. Occasional obvious artefacts can be present in inverted models but their causative sources should be easily identifiable in the measured channel data. The inverted models coherence is generally compromised when acquisition system terrain clearance cannot be maintained below approximately 80 m. The in-loop setup and processing routines have inherent limitations over steep stratigraphy. Complex stratigraphy geometries can result in off line responses to be artificially incorporated in the 1D inverted conductivity cross-sections. Lastly, lateral interfaces between fresh and altered rocks could easily be misinterpreted as fault contacts.

Fossil landscapes and youthful seismogenic sources in the central Apennines: excerpts from the 24 August 2016, Amatrice earthquake and seismic hazard implications

&lt;p&gt;&lt;em&gt;We show and discuss the similarities among the 2016 Amatrice (Mw 6.0), 1997 Colfiorito-Sellano (Mw 6.0-5.6) and 2009 L’Aquila (Mw 6.3) earthquakes. They all occurred along the crest of the central Apennines and were caused by shallow dipping faults between 3 and 10 km depth, as shown by their characteristic InSAR signature. We contend that these earthquakes delineate a seismogenic style that is characteristic of this portion of the central Apennines, where the upward propagation of seismogenic faults is hindered by the presence of pre-existing regional thrusts. This leads to an effective decoupling between the deeper seismogenic portion of the upper crust and its uppermost 3 km.The decoupling implies that active faults mapped at the surface do not connect with the seismogenic sources, and that their evolution may be controlled by passive readjustments to coseismic strains or even by purely gravitational motions. Seismic hazard analyses and estimates based on such faults should hence be considered with great caution as they may be all but representative of the true seismogenic potential.&lt;/em&gt;&lt;/p&gt;&lt;em&gt;&lt;/em&gt;

Sedimentological evidence for a deltaic origin of the western fan deposit in Jezero crater, Mars and implications for future exploration

We examine the stratigraphic architecture and mineralogy of the western fan deposit in the Jezero crater paleolake on Mars to reassess whether this fan formed as a delta in a standing body of water, as opposed to by alluvial or debris flow processes. Analysis of topography and images reveals that the stratigraphically lowest layers within the fan have shallow dips (<2°), consistent with deltaic bottomsets, whereas overlying strata exhibit steeper dips (∼2–9°) and downlap, consistent with delta foresets. Strong clay mineral signatures (Fe/Mg-smectite) are identified in the inferred bottomsets, as would be expected in the distal fine-grained facies of a delta. We conclude that the Jezero crater western fan deposit is deltaic in origin based on the exposed stratal geometries and mineralogy, and we emphasize the importance of examining the stratigraphic architecture of sedimentary fan deposits on Mars to confidently distinguish between alluvial fans and deltas. Our results indicate that Jezero crater contains exceptionally well-preserved fluvio-deltaic stratigraphy, including strata interpreted as fine-grained deltaic bottomsets that would have had a high potential to concentrate and preserve organic matter. Future exploration of this site is both geologically and astrobiologically compelling, and in situ analyses would be complementary to the ongoing in situ characterization of fluvio-lacustrine sediment in the Gale crater paleolake basin by the Curiosity rover.