Basement sliding and the formation of fault systems on Mt Etna volcano

The influence of faulting on the eruptive mechanisms of Mt Etna has been intensively studied, especially regarding the importance of regional tectonics, magma pressure, gravitational spreading and east flank instability. Here we examine the influence of an additional process: the wholesale sliding of the Etna massif along its sloping basement. Using laboratory analogue experiments, we create a series of model volcanoes on sloping basements, with obstructions to represent the mountains and hills surrounding Etna, and an unconstrained downslope edge to represent the unbuttressed seaward slopes. We find that analogues of all the Etna fault systems can be produced in the same model. Furthermore, we find that the relative velocities of transcurrent faulting and extension of each model flank fault system match those of Mt Etna in every case. We also find convincing evidence that gravitational spreading of the summit cone, combined with downslope sliding, controls the position of future eruptive vents around the summit, by creating faults and fractures that form paths of least resistance for magma intrusions. The intruding magma in turn augments fracture opening by an order of magnitude, in a feedback process that dominates within the summit graben. We conclude that gravitational spreading and sliding are the dominant processes in creating faults at Etna, and that these two processes, augmented by magma pressure, are responsible for the rapid seaward movement of the eastern slopes, tectonically cut off from the stable western flanks. The influence of regional tectonism is up to two orders of magnitude lower. The conceptual model derived here could make an important contribution to the investigation and monitoring of eruptive, seismic and landslide hazards, by providing a unified mechanical system that can be used to understand deformation.

Quaternary Geometry, Kinematics and Paleoearthquake History at the Intersection of the Strike-Slip North Island Fault System and Taupo Rift, New Zealand

<p>The North Island of New Zealand sits astride the Hikurangi margin along which the oceanic Pacific Plate is being obliquely subducted beneath the continental Australian Plate. The North Island Fault System1 (NIFS), in the North Island of New Zealand, is the principal active strike-slip fault system in the overriding Australian Plate accommodating up to 30% of the margin parallel plate motion. This study focuses on the northern termination of the NIFS, near its intersection with the active Taupo Rift, and comprises three complementary components of research: 1) the investigation of the late Quaternary (c. 30 kyr) geometries and kinematics of the northern NIFS as derived from displaced geomorphic landforms and outcrop geology, 2) examination of the spatial and temporal distribution of paleoearthquakes in the NIFS over the last 18 kyr, as derived by fault-trenching and displaced landforms, and consideration of how these distributions may have produced the documented late Quaternary (c. 30 kyr) kinematics of the northern NIFS, and 3) Investigation of the temporal stability of the late Quaternary (c. 30 kyr) geometries and kinematics throughout the Quaternary (1-2 Ma), derived from gravity, seismic-reflection, drillhole, topographic and outcrop data. The late Quaternary (c. 30 kyr) kinematics of the northern NIFS transition northward along strike, from strike-slip to oblique-normal faulting, adjacent to the rift. With increasing proximity to the Taupo Rift the slip vector pitch on each of the faults in the NIFS steepens gradually by up to 60 degrees, while the mean fault-dip decreases from 90 degrees to 60 degrees W. Adjustments in the kinematics of the NIFS reflect the gradual accommodation of the NW-SE extension that is distributed outside the main physiographic boundary of the Taupo Rift. Sub-parallelism of slip vectors in the NIFS with the line of intersection between the two synchronous fault systems reduces potential space problems and facilitates the development of a kinematically coherent fault intersection, which allows the strike-slip component of slip to be transferred into the rift. Transfer of displacement from the NIFS into the rift accounts for a significant amount of the northeastward increase of extension along the rift. Steepening of the pitch of slip vectors towards the northern termination of the NIFS allows the kinematics and geometry of faulting to change efficiently, from strike-lip to normal faulting, providing an alternative mechanism to vertical axis rotations for terminating large strike-lip faults. Analyses of kinematic constraints from worldwide examples of synchronous strike-lip and normal faults that intersect to form two or three plate configurations, within either oceanic or continental crust, suggest that displacement is often transferred between the two fault systems in a similar manner to that documented at the NIFS - Taupo Rift fault intersection. The late Quaternary (c. 30 kyr) change in the kinematics of the NIFS along strike, from dominantly strike-slip to oblique-normal faulting, arises due to a combination of rupture arrest during individual earthquakes and variations in the orientation of the coseismic slip vectors. At least 80 % of all surface rupturing earthquakes appear to have terminated within the kinematic transition zone from strike-slip to oblique-normal slip. Fault segmentation reduces the magnitudes of large surface rupturing earthquakes in the northern NIFS from 7.4-7.6 to c. 7.0. Interdependence of throw rates between the NIFS and Taupo Rift suggests that the intersection of the two fault systems has functioned coherently for much of the last 0.6-1.5 Myr. Oblique-normal slip faults in the NIFS and the Edgecumbe Fault in the rift accommodated higher throw rates since 300 kyr than during the last 0.6-1.5 Myr. Acceleration of these throw rates may have occurred in response to eastward migration of rifting, increasing both the rates of faulting and the pitch of slip vectors. The late Quaternary (e.g. 30 kyr) kinematics, and perhaps also the stability, of the intersection zone has been geologically short lived and applied for the last c. 300 kyr.</p>

Quaternary Geometry, Kinematics and Paleoearthquake History at the Intersection of the Strike-Slip North Island Fault System and Taupo Rift, New Zealand

<p>The North Island of New Zealand sits astride the Hikurangi margin along which the oceanic Pacific Plate is being obliquely subducted beneath the continental Australian Plate. The North Island Fault System1 (NIFS), in the North Island of New Zealand, is the principal active strike-slip fault system in the overriding Australian Plate accommodating up to 30% of the margin parallel plate motion. This study focuses on the northern termination of the NIFS, near its intersection with the active Taupo Rift, and comprises three complementary components of research: 1) the investigation of the late Quaternary (c. 30 kyr) geometries and kinematics of the northern NIFS as derived from displaced geomorphic landforms and outcrop geology, 2) examination of the spatial and temporal distribution of paleoearthquakes in the NIFS over the last 18 kyr, as derived by fault-trenching and displaced landforms, and consideration of how these distributions may have produced the documented late Quaternary (c. 30 kyr) kinematics of the northern NIFS, and 3) Investigation of the temporal stability of the late Quaternary (c. 30 kyr) geometries and kinematics throughout the Quaternary (1-2 Ma), derived from gravity, seismic-reflection, drillhole, topographic and outcrop data. The late Quaternary (c. 30 kyr) kinematics of the northern NIFS transition northward along strike, from strike-slip to oblique-normal faulting, adjacent to the rift. With increasing proximity to the Taupo Rift the slip vector pitch on each of the faults in the NIFS steepens gradually by up to 60 degrees, while the mean fault-dip decreases from 90 degrees to 60 degrees W. Adjustments in the kinematics of the NIFS reflect the gradual accommodation of the NW-SE extension that is distributed outside the main physiographic boundary of the Taupo Rift. Sub-parallelism of slip vectors in the NIFS with the line of intersection between the two synchronous fault systems reduces potential space problems and facilitates the development of a kinematically coherent fault intersection, which allows the strike-slip component of slip to be transferred into the rift. Transfer of displacement from the NIFS into the rift accounts for a significant amount of the northeastward increase of extension along the rift. Steepening of the pitch of slip vectors towards the northern termination of the NIFS allows the kinematics and geometry of faulting to change efficiently, from strike-lip to normal faulting, providing an alternative mechanism to vertical axis rotations for terminating large strike-lip faults. Analyses of kinematic constraints from worldwide examples of synchronous strike-lip and normal faults that intersect to form two or three plate configurations, within either oceanic or continental crust, suggest that displacement is often transferred between the two fault systems in a similar manner to that documented at the NIFS - Taupo Rift fault intersection. The late Quaternary (c. 30 kyr) change in the kinematics of the NIFS along strike, from dominantly strike-slip to oblique-normal faulting, arises due to a combination of rupture arrest during individual earthquakes and variations in the orientation of the coseismic slip vectors. At least 80 % of all surface rupturing earthquakes appear to have terminated within the kinematic transition zone from strike-slip to oblique-normal slip. Fault segmentation reduces the magnitudes of large surface rupturing earthquakes in the northern NIFS from 7.4-7.6 to c. 7.0. Interdependence of throw rates between the NIFS and Taupo Rift suggests that the intersection of the two fault systems has functioned coherently for much of the last 0.6-1.5 Myr. Oblique-normal slip faults in the NIFS and the Edgecumbe Fault in the rift accommodated higher throw rates since 300 kyr than during the last 0.6-1.5 Myr. Acceleration of these throw rates may have occurred in response to eastward migration of rifting, increasing both the rates of faulting and the pitch of slip vectors. The late Quaternary (e.g. 30 kyr) kinematics, and perhaps also the stability, of the intersection zone has been geologically short lived and applied for the last c. 300 kyr.</p>

Revealing Geometry and Fault Interaction on a Complex Structural System Based on 3D P-Cable Data: The San Mateo and San Onofre Trends, Offshore Southern California

Deformation observed along the San Mateo (SMT) and San Onofre trends (SOT) in southern California has been explained by two opposing structural models, which have very different hazard implications for the coastal region. One model predicts that the deformation is transpressional in a predominantly right lateral fault system with left lateral step-overs. Conversely in the alternative model, the deformation is predicted to be compressional associated with a regional blind thrust that reactivated detachment faults along the continental margin. State-of-the-art 3D P-Cable seismic data were acquired to characterize the geometry and linkage of faults in the SMT and SOT. The new observations provide evidence that deformation along the slope is more consistent with step-over geometry than a regional blind thrust model. For example, regions in the SOT exhibit small scale compressional structures that deflect canyons along jogs in the fault segments across the slope. The deformation observed in the SMT along northwesterly trending faults has a mounded, bulbous character in the swath bathymetry data with steep slopes ( ∼ 25°) separating the toe of the slope and the basin floor. The faulting and folding in the SMT are very localized and occur where the faults trend more northwesterly (average trend ∼ 285°) with the deformation dying away both towards the north and east. In comparison, the SOT faults trend more northerly (average trend ∼ 345°). The boundary between these fault systems is abrupt and characterized by shorter faults that appear to be recording right lateral displacement and possibly accommodating the deformation between the two larger fault systems. Onlapping undeformed turbidite layers reveal that the deformation associated with both major fault systems may be inactive and radiocarbon dating suggests deformation ceased in the middle to late Pleistocene (between 184 and 368 kyr). In summary, our preferred conceptual model for tectonic deformation along the SMT and SOT is best explained by left lateral step-overs along the predominantly right lateral strike-slip fault systems.

Reconstructing the Gorte and Spiaz de Navesele Landslides, NE of Lake Garda, Trentino Dolomites (Italy)

We applied a multi-method approach to reconstruct the Gorte rock avalanche (85–95 Mm3) located at the northeastern end of Lake Garda. The combination of field mapping, characterization of bedrock discontinuities, Dan3D-Flex runout modeling and dating of boulders with cosmogenic 36Cl supports the conclusion that the deposits stem from a single rock avalanche at 6.1 ± 0.8 ka. The Gorte event may have triggered the Spiaz de Navesele–Salto della Capra landslide (3.2 Mm3), whose deposits cover the southern end of the Gorte deposits. First-order controls on detachment were the NNE–SSW- and WNW–ESE-oriented fractures in the limestone bedrock, related to the Giudicarie and Schio-Vicenza fault systems, respectively. Dan3D-Flex runout modeling sufficiently reproduced the Gorte rock avalanche, which involved detachment and sliding of a quasi-intact block, likely along marly interbeds, followed by rapid disintegration. The frictional rheology in the source area and the turbulent frictional rheology (Voellmy) in the remaining part best replicate the observed deposit extent and thickness. Heavy precipitation that occurred at that time may have contributed to failure at Gorte. Nonetheless, its timing overlaps with the nearby (<15 km) Dosso Gardene (6630–6290 cal BP) and Marocca Principale (5.3 ± 0.9 ka) landslides, making a seismic trigger plausible.

Geological structure of central Vietnam by interpretation processing of gravitational survey data using the “COSCAD 3D” computer technology

Background. The central regions of Vietnam are of strategic importance for the Republic, being, in fact, the gateway to the ASEAN countries. Investing in the exploration and evaluation of mineral resources, in particular ore minerals hidden at great depths, is a specific and necessary task for the country.Aim. To clarify the structural-tectonic scheme of the analysed area and to identify the main fault systems and zoning of the Central Vietnam area by the gravitational field based on classification algorithms.Materials and methods. The objectives were achieved by assessing the total gradient of the gravitational field, analysing the distribution of the field variance and the results of tracing the axes of the gravitational field anomaly. Interpretation processing of gravity data was carried out using the “COSCAD 3D” computer technology of statistical and spectral correlation data analysis.Results. The defined fault systems, which play an important role in the processes of mineral formation, have a northwestern, northeastern and latitudinal strike. The zoning of the study area according to the gravitational field, its characteristics and available geological information made it possible to identify 13 homogeneous areas. Each area is characterised by a certain level of gravitational field, the values of dispersion and total field gradient, as well as correlations between attributes. The classification results confirms the complexity of the geological structure of the area under study and the presence of three main strikes of the systems of tectonic dislocations – northwestern, northeastern and latitudinal.Conclusions. A large number of tectonic dislocations of various strikes and intensities, revealed using the methods of the probabilistic-statistical approach, implemented in the “COSCAD 3D” computer technology, indicates that the area under study is promising in terms of ore deposits.

Disposition of magmatic eruptions and fault distribution in northwestern Saudi Arabia using pseudo-depth slice magnetic anomaly

This study presents the disposition of magmatic eruptions with a fault distribution in northwestern Saudi Arabia, where intensive magma invades the lithosphere. Structural and magmatic features are traced at successive depths through high-resolution magnetic anomaly pseudo-depth slices. The total horizontal gradient technique is applied to pseudo-depth slice magnetic anomalies to enhance the linear trends of faults and related magmatic activity. A comprehensive cross-section constructed from the projection of gradient horizontal maxima relative to pseudo-slices allows the visualization of the vertical behavior of faults and magma sources. Three major fault systems were identified, primarily aligned in the N–S, NE–SW and NW–SE directions. They are characterized by increasing length and width with depth. The N-S fault system is a major non-planar deep system throughout the area, affected by the NW–SE and NE–SW deep discontinuities. The evolution of these discontinuities with depth successfully shows magma uprising zones represented by a circular horizontal gradient, which starts to appear at a depth of 4500 m with a vertical continuity to the surface. They are interpreted as possible locations of ascending magma chambers or vents. The disposition of these magma sources with fault distribution can show a close relationship between the fault systems and the magma eruptions. The interpreted magma vents appear where the NE-trending transform faults intersect the NW or N–S fault zone. These intersections may represent weak zones that act as vertical conduits through which magma discontinuously erupts into the overlying crust, forming major volcanic fields in the eastern Red Sea.