scholarly journals The Relationships Between Regional Quaternary Uplift, Deformation Across Active Normal Faults, and Historical Seismicity in the Upper Plate of Subduction Zones: The Capo D'Orlando Fault, NE Sicily

Tectonics ◽  
2018 ◽  
Vol 37 (5) ◽  
pp. 1231-1255 ◽  
Author(s):  
M. Meschis ◽  
G. P. Roberts ◽  
J. Robertson ◽  
R. M. Briant
Keyword(s):  
Subduction Zones ◽  
Historical Seismicity ◽  
Normal Faults ◽  
Ne Sicily ◽  
Uplift Deformation

Inheritance processes of active extensional deformation in ocean-continent subduction zones: the example of the northern Andes compressional margin in Ecuador

2020 ◽  
Author(s):  
Cédric Bulois ◽  
François Michaud ◽  
Marianne Saillard ◽  
Nicolas Espurt ◽  
Marc Regnier ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Normal Faults ◽  
Deformation Pattern ◽  
Accretionary Wedge ◽  
Nazca Plate ◽  
Extensional Deformation ◽  
Northern Andes ◽  
Marine Terraces ◽  
Gulf Of Guayaquil ◽  
Santa Elena

<p>Over the last 23 Myr, the roughly east-directed subduction of the Nazca Plate beneath South America led to the formation of several mountain ranges associated with the overall northern Andes evolution. Along the active southwestern Ecuadorian margin, the compressional setting involves the Cretaceous-Miocene Chongón-Colonche / Santa Elena terranes, overlain by recent sedimentary basins. This geological setting, generally interpreted as an onshore-offshore forearc system, evolves in close relation with the active tectonic escape of the North Andean Sliver and the opening of the Gulf of Guayaquil. This region is characterised by a widespread extensional deformation in the upper plate that overprints moderate subduction and crustal earthquakes.</p><p>To better document such extensional processes, we specifically explore the offshore shelf and the littoral area of the Santa Elena Peninsula using academic and industrial 2D seismic profiles calibrated with local wells and field observations. We document a trench-parallel fault network, composed of >20km-long normal faults that take place on top of the former Chongón-Colonche accretionary wedge. These faults are linearly-steep along the trench, and are listric toward the continent where they clearly control fault-block rotation. They separate flexural basins developing on the platform ahead the Chongón-Colonche Cordillera, and are associated with immerged terraces most likely formed during the Last Glacial Maximum. They also may link to further onshore marine terraces developing since the Pleistocene across the coastline.</p><p>These observations suggest a peculiar dismantlement of the margin, mainly affected by tectonic erosion involving reactivation of former compressional features. Normal faults are specifically interpreted as a regional syn-orogenic collapse of the Chongón-Colonche Cordillera, which may result from transecting subducting ridges, fracture zones and seamounts controlling, at least partially, the geometry and the nature of the deformation along the southwestern Ecuadorian margin. This deformation pattern is likely linked to a weak interseismic coupling along the subduction interface to which the active opening of the Gulf of Guayaquil overlaps. This project is funded by the project ANR MARACAS ANR-18-CE31-0022 (<em>MARine terraces along the northern Andean Coast as a proxy for seismic hazard ASsessment</em>).</p>

Late Miocene thrust tectonics of the Latin Valley: insights from seismic lines (Central Apennines, Italy)

2020 ◽  
Author(s):  
Giuseppe Vico ◽  
Giovanni Luca Cardello
Keyword(s):  
Late Miocene ◽  
Subduction Zones ◽  
Volcanic Field ◽  
Normal Faults ◽  
Past Century ◽  
Central Apennines ◽  
Kinematic Evolution ◽  
Geothermal Fluids ◽  
Thrust Tectonics ◽  
Thrust Sheets

<p>In west-directed subduction zones, as the compression moves towards the foreland, the accretionary prism progressively expands to follow the hinge migration towards the east. Although late Miocene foreland propagation implies the shift of the thrust front, in the central Apennines, the effects of the Messinian compression can be observed on a much broader area, implying out-of-sequence thrusting in the rear.</p><p>In order to understand the Messinian involvement of the previously formed Tortonian belt-foredeep system, a regional reinterpretation is here provided. The analysis of publicly available 2D seismic reflection lines across the upper and middle Latin Valley and 10 wells enables the identification of two main seismostratigraphic units: i) the Meso-Cenozoic neritic carbonates and ii) the upper Tortonian siliciclastic pelitic and arenaceous turbiditic associations of the Frosinone Formation.</p><p>The most evident reflectors are the upper Cretaceous and upper Serravallian top paraconformities, which, due to tectonic repetition can be followed at different depths. We find that minor reflectors can be attributed to the several thrusts affecting folded Meso-Cenozoic neritic carbonates. This observation allows us, together with field and well evidences, to trace several thrust sheets characterized by a general top-to-the NE sense of shear. In a few sections from the Latin Valley (e.g. Line FR-309-80), we recognized the Meso-Cenozoic neritic carbonates being thrusted together with the Tortonian Frosinone Formation, on top of a laterally variably thick siliciclastic succession. This further syn-orogenic unit could be related to the early Messinian sandstones of the Torrice Formation, implying that out-of-sequence thrusting took place in the Latin Valley during the wedge-top sedimentation. The thin-skinned fold-and-thrust fabric is defined by en-échelon distributed thrusts, NNE- and ENE striking tear faults and minor pop-up structures often determining ideal traps for hydrocarbon and geothermal fluids. Finally, conjugated NW-striking high-angle normal faults crosscut the orogenic heritage and sets a horst and graben structure associated with continental deposition and the Volsci Volcanic Field.</p><p>The limited oil exploitation over the past century has targeted only the shallower siliciclastic traps and some evidences in the shallower neritic carbornate thrust sheets. At the light of our new interpretation, the deeper carbonate units could be a new focus for hydrocarbon accumulation and may furnish targets for geothermal and/or hydrocarbon research in the area. Future work aims at quantify the Tortonian and Messinian amount of shortening by taking into consideration the adjoining Volsci Range. Finally, our findings bear implications on geodynamic reconstructions and may represent an example of the geometry and kinematic evolution of platform derived thrust sheets and similar belts worldwide associated with W-directed subduction zones.</p>

scholarly journals Timor Collision Front Segmentation Reveals Potential for Great Earthquakes in the Western Outer Banda Arc, Eastern Indonesia

2021 ◽  
Vol 9 ◽  
Author(s):  
Aurélie Coudurier-Curveur ◽  
Satish C. Singh ◽  
Ian Deighton
Keyword(s):  
Active Faults ◽  
Accretionary Prism ◽  
Historical Seismicity ◽  
Normal Faults ◽  
Seismic Reflection Data ◽  
Spatially Correlated ◽  
Eastern Indonesia ◽  
The North ◽  
Reflection Data ◽  
Banda Arc

In Eastern Indonesia, the western Outer Banda arc accommodates a part of the oblique Australian margin collision with Eurasia along the Timor Trough. Yet, unlike the Wetar and Alor thrusts of the Inner Banda arc in the north and the adjacent Java subduction zone in the west, both recent and historical seismicity along the Timor Trough are extremely low. This long-term seismic quiescence questions whether the Banda Arc collision front along the Timor Trough is actually fully locked or simply aseismic and raises major concerns on the possible occurrence of large magnitude and tsunamigenic earthquakes in this vulnerable and densely populated region. Here, we jointly analyze multibeam bathymetry and 2D seismic reflection data acquired along the Timor Trough to characterize the location, nature, and geometry of active faults. Discontinuous narrow folds forming a young accretionary prism at the base of the Timor wedge and spatially correlated outcropping normal faults on the bending northwest Australian shelf reveal two concurrent contrasting styles of deformation: underthrusting and frontal accretion. We find that those tectonic regimes and their associated seismic behaviors depend on 1) the thickness of the incoming and underthrusting Cenozoic sedimentary sequence, 2) the vergence of inherited normal faults developed within the continental shelf, and 3) the depth of the décollement beneath the Timor wedge. Based on the along-strike, interchanging distinct deformation style, we identify the mechanical and seismic segmentation along the Banda arc collision front and discuss the implications for earthquake and tsunami hazards along the western Outer Banda arc region.

Slow-slip, earthquake-swarms and fault-interactions at the western-end of the Hellenic Subduction System precede the Mw 6.9 Zakynthos Earthquake, Greece 

2021 ◽  
Author(s):  
Vasiliki Mouslopoulou ◽  
Gian Maria Bocchini ◽  
Simone Cesca ◽  
Vasso Saltogianni ◽  
Jonathan Bedford ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Normal Faults ◽  
Earthquake Swarms ◽  
Slow Slip ◽  
Epicentral Area ◽  
Slow Slip Event ◽  
Slip Event ◽  
Fault Interactions ◽  
Aseismic Deformation ◽  
Subduction System

<p>The month-to-year-long deformation of the Earth’s crust where active subduction zones terminate is poorly explored. Here we report on a multidisciplinary dataset that captures the synergy of slow-slip events, earthquake swarms and fault-interactions during the ~5 years leading up to the 2018 M<sub>w</sub> 6.9 Zakynthos Earthquake at the western termination of the Hellenic Subduction System (HSS). It appears that this long-lasting preparatory phase initiated due to a slow-slip event that lasted ~4 months and released strain equivalent to a ~M<sub>w</sub> 6.3 earthquake. We propose that the slow-slip event, which is the first to be reported in the HSS, tectonically destabilised the upper 20-40 km of the crust, producing alternating phases of seismic and aseismic deformation, including intense microseismicity (M<4) on neighbouring faults, earthquake swarms in the epicentral area of the M<sub>w</sub> 6.9 earthquake ~1.5 years before the main event, another episode of slow-slip immediately preceding the mainshock and, eventually, the large (M<sub>w </sub>6.9) Zakynthos Earthquake. Tectonic instability in the area is evidenced by a prolonged (~4 years) period of overall suppressed b-values (<1) and strong earthquake interactions on discrete strike-slip, thrust and normal faults. We propose that composite faulting patterns accompanied by alternating (seismic/aseismic) deformation styles may characterise multi-fault subduction-termination zones and may operate over a range of timescales (from individual earthquakes to millions of years).</p>

scholarly journals Seismic hazard of the Western Makran subduction zone: Effect of heat flow on frictional properties combining mechanical and thermo-mechanical modelling approaches

2021 ◽  
Author(s):  
sepideh pajang ◽  
Nadaya Cubas ◽  
Laetitia Le-pourhiet ◽  
Eloise Bessiere ◽  
Jean Letouzey ◽  
...  
Keyword(s):  
Heat Flow ◽  
Subduction Zones ◽  
Normal Fault ◽  
Large Earthquake ◽  
Normal Faults ◽  
Accretionary Wedge ◽  
Makran Subduction Zone ◽  
Frictional Properties ◽  
High Convergence Rate ◽  
Mechanical Modelling

<p>Western Makran is one of the few subduction zones left with a largely unconstrained seismogenic potential. According to the sparse GPS stations, the subduction is accumulating some strain to be released during future earthquakes. Mechanical modelling is first used to retrieve the spatial variations of the frictional properties of the megathrust, and discuss its seismogenic potential. To do so, we first build a structural map along the Iranian part of the Oman Sea and investigate three N-S seismic profiles. The profiles are characterized by a long imbricated thrust zone that takes place at the front of the wedge. A diapiric zone of shallow origin lies in between the imbricated zone and the shore. Along the eastern and western shores, active listric normal faults root down to the megathrust. Eastern and western domains have developed similar deformation, with three zones of active faulting: the normal faults on shore, thrusts ahead of the mud diapirs, and the frontal thrusts. On the contrary, no normal faults are identified along the central domain, where a seamount is entering into subduction. From mechanical modelling, we show that along the eastern and western profiles, a transition from very low to extremely low friction is required to activate the large coastal normal fault. To propagate the deformation to the front, an increase of friction along the imbricated zone is necessary. These along-dip transitions could either be related to a transition from an aseismic to seismic behavior or the brittle-viscous transition.</p><p>To decipher, we run 2-D thermo-mechanical modelling incorporating temperature evolution, with a heat flow boundary condition. Our simulations are first calibrated to reproduce the heat flow estimates based on the BSR depth. Then the effects of the illite-smectite and brittle-viscous transitions on the deformation are investigated. The decrease in heat flow landward is due to the landward deepening of the oceanic plate and thickening of sediments of the accretionary wedge. Deformation starts at the rear of the model and migrates forming in-sequence, forward verging thrust sheets. The two brittle-viscous and illite-smectite transitions affect the topographic slope and friction. A reduction of friction due to the illite-smectite transition reduces the slope by normal faulting that does not appear in the brittle-viscous transition simulations. Therefore, the presence of normal faults could permit to distinguish viscously creeping segments from segments that deform seismically. As a consequence, the normal fault is most probably related to the presence of a seismic asperity, and the difference in deformation along strike would thus reveal the existence of two different patches, one along the eastern domain and a second along the western domain. Since no large earthquake has been historically reported and given the high convergence rate, a major earthquake will strike the Makran region. We suggest that the magnitude of this event will depend on the behavior of the Central region, and the ability of the earthquake to propagate from the eastern to the western asperity or the Pakistani Makran.</p>

Faults distribution and seismogenic potential in the Calabrian back-arc domain, SE Tyrrhenian Sea

2020 ◽  
Author(s):  
Camilla Palmiotto ◽  
Maria Filomena Loreto ◽  
Francesco Muto ◽  
Valentina Ferrante ◽  
Franco Pettenati ◽  
...  
Keyword(s):  
Active Faults ◽  
Normal Fault ◽  
Historical Seismicity ◽  
Normal Faults ◽  
Transitional Region ◽  
Tyrrhenian Sea ◽  
Seismic Profiles ◽  
Offshore Area ◽  
Fault Systems ◽  
Back Arc

<p>The Western Calabrian margin (Italy) is the most active segment of the Apennine back-arc system, formed in response to the slow Africa – Eurasia convergence. The offshore area represents the transitional region between the arc and the back-arc: it is affected by several fault systems, most of them able to trigger highly destructive earthquakes. Indeed, the Calabria and its western offshore are characterized by the highest seismic moment release of the entire Apennines, also evidenced by historical seismicity catalogue, the most accurate over the world. During last decades, scientific community invested huge resources in assessment of seismic and tsunami hazards. Furthermore, during last years several local-scale works allowed of improving knowledge of the faults geometry, magmatism, seismogenic and tsunamigenic potential along the western offshore region (Loreto et al., 2017; Brutto et al., 2016; De Ritis et al., 2019). Some active faults, belonging to NE-SW-trending normal fault systems accommodating the inner-arc collapse related to slab-decupling, are also responsible of the most destructive historical sequences, still to be adequately characterized. Using vintage SPARKER 30 Kj acquired in the seventies and recent multichannel seismic profiles together with middle resolution morpho-bathymetric data we produced a new tectonic map of the Calabria back-arc system. Further, we characterized some before-unknown faults and linked them with shallow structures, as ridges and slumps / slides. This area seemingly less populated of faults compared to the peri-Tyrrhenian margin, where several faults belong to different systems, i.e. (i) the rifting system active that allowed the opening of the Tyrrhenian Basin and (ii) the slab-decupling related normal faults system currently active. The comparison with historical and instrumental seismicity allowed us to highlight possible seismic gaps that, if considered, could strongly improve the map of seismogenic potential of the Tyrrhenian back-arc system.</p><p> </p><p>Bibliography</p><p>Brutto, F. et al. (2016). The Neogene-Quaternary geodynamic evolution of the central Calabrian Arc: A case study from the western Catanzaro Trough basin. Journal of Geodynamics, 102, 95-114.</p><p>Loreto, M. F. (2017). Reconstructed seismic and tsunami scenarios of the 1905 Calabria earthquake (SE Tyrrhenian sea) as a tool for geohazard assessment. Engineering geology, 224, 1-14.</p><p>Tripodi, V. et al. (2018). Neogene-Quaternary evolution of the forearc and backarc regions between the Serre and Aspromonte Massifs, Calabria (southern Italy). Marine and Petroleum Geology, 95, 328-343.</p>

scholarly journals Outer trench slope flexure and faulting at Pacific basin subduction zones

2019 ◽  
Vol 218 (1) ◽  
pp. 708-728 ◽  
Author(s):  
Emmanuel Soliman M Garcia ◽  
David T Sandwell ◽  
Dan Bassett
Keyword(s):  
Subduction Zones ◽  
Gravity Data ◽  
Bending Moment ◽  
Normal Faults ◽  
Nonlinear Inversion ◽  
Outer Rise ◽  
Trench Axis ◽  
Effective Elastic Thickness ◽  
Age Model ◽  
Trench Slope

SUMMARY Flexure and fracturing of the seafloor on the outer trench wall of subduction zones reflect bending of the lithosphere beyond its elastic limit. To investigate these inelastic processes, we have developed a full nonlinear inversion approach for estimating the bending moment, curvature and outer trench wall fracturing using shipboard bathymetry and satellite altimetry-derived gravity data as constraints. Bending moments and downward forces are imposed along curved trench axes and an iterative method is used to calculate the nonlinear response for 26 sites in the circum-Pacific region having seafloor age ranging from 15 to 148 Ma. We use standard thermal and yield strength envelope models to develop the nonlinear moment versus curvature relationship. Two coefficients of friction of 0.6 and 0.3 are considered and we find that the lower value provides a better overall fit to the data. The main result is that the lithosphere is nearly moment saturated at the trench axis. The effective elastic thickness of the plate on the outer trench slope is at least three times smaller than the elastic thickness of the plate before bending at the outer rise in agreement with previous studies. The average seafloor depth of the unbent plate in these 26 sites matches the Parsons & Sclater depth versus age model beyond 120 Ma. We also use the model to predict the offsets of normal faults on the outer trench walls and compare this with the horst and graben structures observed by multibeam surveys. The model with the lower coefficient of friction fits the fault offset data close to the trench axis. However, the model predicts significant fracturing of the lithosphere between 75 and 150 km away from the trench axis where no fracturing is observed. To reconcile these observations, we impose a thermoelastic pre-stress in the lithosphere prior to subduction. This pre-stress delays the onset of fracturing in better agreement with the data.

scholarly journals Recognizing fracture pattern signatures contributed by seismic loadings

2020 ◽  
Vol 8 (4) ◽  
pp. SP95-SP108
Author(s):  
Shiqing Xu
Keyword(s):  
Fault Zone ◽  
Subduction Zones ◽  
Experimental Studies ◽  
Fracture Pattern ◽  
Normal Faults ◽  
Depth Range ◽  
Seismic Loadings ◽  
Main Fault ◽  
Entire Depth ◽  
Splay Faults

The impacts of seismic loadings to fault zone rocks still are not well understood. Although field and experimental studies have suggested several markers, such as pseudotachylytes and pulverized rocks, for indicating seismic loadings, the corresponding markers of other types or at larger scales still are lacking. Drawing from the results of dynamic ruptures with off-fault damage, we have recognized several additional fracture features that may be used to reflect the involvement of seismic loadings. For strike-slip faults stressed at moderate to high angles, synthetic R shear is more favored during rupture propagation, but pronounced antithetic R′ shear can be generated around the termination end of the rupture. In addition, suitably oriented weak structures off the main fault can further facilitate the activation of R′ shear. For low-angle thrust faults such as subduction zones, splay faults in the form of forethrusts and backthrusts still can be generated above the coseismic rupture zone. These faults show an increased spatial extent toward the updip direction, effectively defining an outer wedge susceptible to pervasive compressional failure over its entire depth range. Moreover, a deeply nucleated megathrust rupture that eventually reaches the trench can sequentially load the frontal wedge in compression and then in extension, with the potential to leave a mixture of triggered reverse and normal faults at the final stage. Because the above results also are supported by many observations, they raise a caution that existing fault models ignoring dynamic effects should be used with care and that seismic loadings must be considered more seriously by future fault zone studies.

Platinum-group element geochemistry to track magmatic evolution of the Yerington porphyry copper district (Nevada, USA)

2020 ◽  
Author(s):  
Monika Misztela ◽  
Ian Campbell
Keyword(s):  
Subduction Zones ◽  
Porphyry Copper ◽  
Volcanic Rocks ◽  
Isotope Dilution Method ◽  
Normal Faults ◽  
Clear Correlation ◽  
Dilution Method ◽  
Sulfide Saturation ◽  
Bottom Line ◽  
Platinum Group

<p>The Yerington batholith is located in western Nevada (USA) within a volcanic-arc area. This pluton is approximately 15 km in diameter, extends to 7-8 km in vertical dimension and consists of 3 granitic units: the McLeod Hill quartz monzodiorite (1,000km<sup>3</sup>), the Bear quartz monzonite (256 km<sup>3</sup>) and the Luhr Hill granite (70 km<sup>3</sup>), together with three mineralized porphyry centres: Yerington, Bear, MacArthur and Ann-Mason porphyry copper deposits. It is overlain by coeval the Artesia Lake and Fulstone Spring volcanic rocks. The batholith was emplaced into Triassic and Jurassic volcanic and sedimentary rocks at ca. 168 Ma. This event was related to the subduction of the Pacific plate, west of California. It was a part of a belt of Andean-type arc magmatism that developed on the continental margin in both North and South Americas. The complex was then cut by three sets of normal faults, which caused the batholith to drop ca. 2.5 km deep along the faults that tilted the area, so that it is now exposed in cross-section.  This event now allows sampling of volcanic and plutonic rocks from each unit, which were originally emplaced at depths of 1 to 8 km.</p><p>It is widely accepted that porphyry deposits are genetically related to subduction zones but what is not understood is why some porphyry systems are ore-bearing while others, apparently similar systems, are barren. The key question remains unanswered: what controls magma fertility? Understanding the processes involved in the creation of metal deposits is a crucial aspect for the exploration industry. A bottom line in determining the fertility of a porphyry suite is likely to be the relative timing of sulfide and volatile saturation. If sulfide saturation occurs early, the chalcophile elements may be locked in an underlying magma chamber at depth and unavailable to enter the hydrothermal fluid when magma eventually becomes volatile saturate.</p><p>Plots of whole-rock concentrations of SiO<sub>2</sub>, total FeO, CaO and V against MgO show that all samples, from all three units, cumulate and volcanic rocks, follow the same trend line, and are therefore likely to be related by fractional crystallization. Attempts to determine the timing of sulfide saturation using Cu were unsuccessful. A plot of whole-rock Cu against MgO showed that the Cu concentrations are scattered, with no clear correlation, which is attributed to overprinting by hydrothermal mineralization. For this reason, the behaviours of Cu during magma processes cannot be deducted. As a consequence, we have turned to the platinum group elements (PGE) to determine the timing of sulfide saturation. The PGE have the advantage of having much higher partition coefficient into immiscible sulfide melts than Cu, and lower solubilities into hydrothermal fluids, so that they are less affected by secondary processes. We will address the problem of identifying sulfide saturation by reporting the concentration of PGE, Re and Au, measured by fire-assay isotope dilution method, for 20 samples from the Yerington batholith. Detection limits are ca. 15 ppt of Pd and less than 1 ppt for the other PGE.</p>

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