scholarly journals Tectonics Inversions, Fault Segmentation, and Triggering Mechanisms in the Central Apennines Normal Fault System: Insights From High‐Resolution Velocity Models

Tectonics ◽  
2018 ◽  
Vol 37 (11) ◽  
pp. 4135-4149 ◽  
Author(s):  
M. Buttinelli ◽  
G. Pezzo ◽  
L. Valoroso ◽  
P. De Gori ◽  
C. Chiarabba
Keyword(s):  
High Resolution ◽  
Normal Fault ◽  
Fault System ◽  
Central Apennines ◽  
Fault Segmentation ◽  
Velocity Models ◽  
Triggering Mechanisms

scholarly journals Localized extension in megathrust hanging wall following great earthquakes in western Nepal

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Magali Riesner ◽  
Laurent Bollinger ◽  
Judith Hubbard ◽  
Cyrielle Guérin ◽  
Marthe Lefèvre ◽  
...  
Keyword(s):  
High Resolution ◽  
Hanging Wall ◽  
Ground Surface ◽  
Normal Fault ◽  
Fault Scarp ◽  
Fault System ◽  
Digital Elevation ◽  
Thrust Zone ◽  
Elevation Model ◽  
Short Time

AbstractThe largest (M8+) known earthquakes in the Himalaya have ruptured the upper locked section of the Main Himalayan Thrust zone, offsetting the ground surface along the Main Frontal Thrust at the range front. However, out-of-sequence active structures have received less attention. One of the most impressive examples of such faults is the active fault that generally follows the surface trace of the Main Boundary Thrust (MBT). This fault has generated a clear geomorphological signature of recent deformation in eastern and western Nepal, as well as further west in India. We focus on western Nepal, between the municipalities of Surkhet and Gorahi where this fault is well expressed. Although the fault system as a whole is accommodating contraction, across most of its length, this particular fault appears geomorphologically as a normal fault, indicating crustal extension in the hanging wall of the MHT. We focus this study on the reactivation of the MBT along the Surkhet-Gorahi segment of the surface trace of the newly named Reactivated Boundary Fault, which is ~ 120 km long. We first generate a high-resolution Digital Elevation Model from triplets of high-resolution Pleiades images and use this to map the fault scarp and its geomorphological lateral variation. For most of its length, normal motion slip is observed with a dip varying between 20° and 60° and a maximum cumulative vertical offset of 27 m. We then present evidence for recent normal faulting in a trench located in the village of Sukhetal. Radiocarbon dating of detrital charcoals sampled in the hanging wall of the fault, including the main colluvial wedge and overlying sedimentary layers, suggest that the last event occurred in the early sixteenth century. This period saw the devastating 1505 earthquake, which produced ~ 23 m of slip on the Main Frontal Thrust. Linked or not, the ruptures on the MFT and MBT happened within a short time period compared to the centuries of quiescence of the faults that followed. We suggest that episodic normal-sense activity of the MBT could be related to large earthquakes rupturing the MFT, given its proximity, the sense of motion, and the large distance that separates the MBT from the downdip end of the locked fault zone of the MHT fault system. We discuss these results and their implications for the frontal Himalayan thrust system.

scholarly journals Structural characterization of fault damage zones in carbonates (Central Apennines, Italy)

2021 ◽  
Author(s):  
Miriana Chinello ◽  
Michele Fondriest ◽  
Giulio Di Toro
Keyword(s):  
Fault Zone ◽  
Hanging Wall ◽  
Damage Zone ◽  
Normal Fault ◽  
Vertical Displacement ◽  
Fault System ◽  
Normal Faults ◽  
Central Apennines ◽  
Fault Surface ◽  
Fracture Intensity

<p>The Italian Central Apennines are one of the most seismically active areas in the Mediterranean (e.g., L’Aquila 2009, Mw 6.3 earthquake). The mainshocks and the aftershocks of these earthquake sequences propagate and often nucleate in fault zones cutting km-thick limestones and dolostones formations. An impressive feature of these faults is the presence, at their footwall, of few meters to hundreds of meters thick damage zones. However, the mechanism of formation of these damage zones and their role during (1) individual seismic ruptures (e.g., rupture arrest), (2) seismic sequences (e.g., aftershock evolution) and (3) seismic cycle (e.g., long term fault zone healing) are unknown. This limitation is also due to the lack of knowledge regarding the distribution, along strike and with depth, of damage with wall rock lithology, geometrical characteristics (fault length, inherited structures, etc.) and kinematic properties (cumulative displacement, strain rate, etc.) of the associated main faults.</p><p>Previous high-resolution field structural surveys were performed on the Vado di Corno Fault Zone, a segment of the ca. 20 km long Campo Imperatore normal fault system, which accommodated ~ 1500 m of vertical displacement (Fondriest et al., 2020). The damage zone was up to 400 m thick and dominated by intensely fractured (1-2 cm spaced joints) dolomitized limestones with the thickest volumes at fault oversteps and where the fault cuts through an older thrust zone. Here we describe two minor faults located in the same area (Central Apennines), but with shorter length along strike. They both strike NNW-SSE and accommodated a vertical displacement of ~300 m.</p><p>The Subequana Valley Fault is about 9 km long and consists of multiple segments disposed in an en-echelon array. The fault juxtaposes pelagic limestones at the footwall and quaternary deposits at the hanging wall. The damage zone is < 25 m  thick  and comprises fractured (1-2 cm spaced joints) limestones beds with decreasing fracture intensity moving away from the master fault. However, the damage zone thickness increases up to ∼100 m in proximity of subsidiary faults striking NNE-SSW. The latter could be reactivated inherited structures.</p><p>The Monte Capo di Serre Fault is about 8 km long and characterized by a sharp ultra-polished master fault surface which cuts locally dolomitized Jurassic platform limestones. The damage zone is up to 120 m thick and cut by 10-20 cm spaced joints, but it reaches an higher fracture intensity where is cut by subsidiary, possibly inherited, faults striking NNE-SSW.</p><p>Based on these preliminary observations, faults with similar displacement show comparable damage zone thicknesses. The most relevant damage zone thickness variations are related to geometrical complexities rather than changes in lithology (platform vs pelagic carbonates).  In particular, the largest values of damage zone thickness and fracture intensity occur at fault overstep or are associated to inherited structures. The latter, by acting as strong or weak barriers (sensu Das and Aki, 1977) during the propagation of seismic ruptures, have a key role in the formation of damage zones and the growth of normal faults.</p>

A deep resistivity Full Waver survey unravels the 3D structure of the Castelluccio basin in relation to the source of the 2016 Mw 6.5 Norcia earthquake (central Italy)

2020 ◽  
Author(s):  
Vincenzo Sapia ◽  
Fabio Villani ◽  
Federico Fischanger ◽  
Matteo Lupi ◽  
Paola Baccheschi ◽  
...  
Keyword(s):  
High Resolution ◽  
Spatial Scales ◽  
Sedimentary Cover ◽  
Central Italy ◽  
3D Structure ◽  
Normal Fault ◽  
Fault System ◽  
High Resistivity ◽  
Low Resistivity ◽  
Regularized Inversion

<p>The Castelluccio basin in the central Apennines (Italy) is a ~20-km<sup>2</sup>-wide intramontane Quaternary depression located in the hangingwall of the NW-trending and SW-dipping Vettore-Bove normal fault system (VBFS). This system is responsible for the 2016-2017 seismic sequence, culminated with the 30 October 2016 Mw 6.5 Norcia earthquake that caused widespread surface faulting affecting also the northern part of the Castelluccio basin. Available borehole and geophysical data are not enough to constrain the basin structure, infill architecture and their relations with the long-term activity of the VBFS. Therefore, we carried out an extensive 3D survey using the innovative Fullwaver (FW) technology, conceived to perform deep electrical resistivity tomography (DERT). We aimed at: a) mapping the geometry of the pre-Quaternary limestone basement and the basin infill thickness down to a depth of ~1 km; b) mapping the subsurface structure of known faults and their extent underneath the alluvial cover; c) mapping possible blind faults splays.</p><p>The 3D survey covered a 23 km<sup>2 </sup>area and it was designed with the aim to map the region as regularly as possible, taking into account the rugged topography and logistic issues. We used a series of independent 2-channels receivers connected each to three grounded steel electrodes, 200 m spaced, to record the electrical field generated by a five kilowatt current regulated Time Domain Induced Polarization transmitter. Data were modelled with ViewLab software via a regularized inversion with smoothness constraints to cope with the expected subsurface strong resistivity changes, and to obtain a robust 3D resistivity model.</p><p>The FW technology allowed us to constrain the geometry of the basin. The infill material is imaged as a wide, N-trending moderately resistive (< 300 Ωm) to conductive  (< 100 Ωm) region, likely made of silty sands and gravels, deepening down to 500 m b.g.l. in the southern sector, suggesting the occurrence of two main depocenters. All over the basin, we identify paired high-resistivity (> 500-1000 Ωm) and low-resistivity (< 400 Ωm) belts related to the limestone basement and to the basin infill, respectively. They display NNE and NNW dominant trends. We interpret the sharp boundaries of NNE-trending belts as related to early extensional faults promoting the basin inception. The NNW-trending belts suggest the occurrence of faults that locally cross-cut the previous ones, and that we interpret as splays of the VBFS buried under the basin sedimentary cover. The recognition of different systems of extensional faults is coherent with results of high-resolution seismic profiling carried out recently in the basin. A high-resolution 2D transect with 15 m-spaced electrodes across the 2016 surface ruptures shows details of the active VBFS splay down to 300 m depth. Moreover, in the eastern sector of the survey area, low-resistivity round-shaped anomalies in the Mesozoic substratum hints for deep Miocene compressional structures. Therefore, our DERT imaging suggests a complex tectonics in the subsurface of the Norcia earthquake fault. In particular, the currently active NNW-trending faults seem to overprint a pre-existing structural framework, promoting fault segmentation at different spatial scales</p>

scholarly journals High-resolution surface faulting from the 1983 Idaho Lost River Fault Mw 6.9 earthquake and previous events

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Simone Bello ◽  
Chelsea P. Scott ◽  
Federica Ferrarini ◽  
Francesco Brozzetti ◽  
Tyler Scott ◽  
...  
Keyword(s):  
High Resolution ◽  
Scaling Laws ◽  
Normal Fault ◽  
Fault System ◽  
Pixel Resolution ◽  
High Resolution Mapping ◽  
Digital Elevation ◽  
Aerial Vehicle ◽  
Resolution Mapping ◽  
Fault Length

AbstractWe present high-resolution mapping and surface faulting measurements along the Lost River fault (Idaho-USA), a normal fault activated in the 1983 (Mw 6.9) earthquake. The earthquake ruptured ~35 km of the fault with a maximum throw of ~3 m. From new 5 to 30 cm-pixel resolution topography collected by an Unmanned Aerial Vehicle, we produce the most comprehensive dataset of systematically measured vertical separations from ~37 km of fault length activated by the 1983 and prehistoric earthquakes. We provide Digital Elevation Models, orthophotographs, and three tables of: (i) 757 surface rupture traces, (ii) 1295 serial topographic profiles spaced 25 m apart that indicate rupture zone width and (iii) 2053 vertical separation measurements, each with additional textual and numerical fields. Our novel dataset supports advancing scientific knowledge about this fault system, refining scaling laws of intra-continental faults, comparing to other earthquakes to better understand faulting processes, and contributing to global probabilistic hazard approaches. Our methodology can be applied to other fault zones with high-resolution topographic data.

Cross-cutting relationships between the Sibillini Mts. Thrust and Mt. Vettore normal fault system (Central Apennines, Italy)

2021 ◽  
Author(s):  
Fabbi Simone ◽  
Stendardi Francesca ◽  
Capotorti Franco ◽  
Bigi Sabina ◽  
Ricci Valeria ◽  
...  
Keyword(s):  
Hanging Wall ◽  
Normal Fault ◽  
Geological Mapping ◽  
Fault System ◽  
Normal Faults ◽  
Accretionary Wedge ◽  
Fold Axis ◽  
Central Apennines ◽  
Debris Cover ◽  
The Cross

<p>We present the results of a detailed geological mapping project performed in the southernmost part of the Sibillini Mts., where the Sibillini Thrust (ST), one of the longest compressional structures of the Central Apennines, crops out. In the studied area the Meso-Cenozoic Umbria-Marche carbonate succession overthrusts the Messinian siliciclastic deposits of the adjacent Laga foredeep Basin. After the Messinian/Pliocene compressional tectonic phase, linked with the development of essentially W-dipping thrust systems, the E-verging Apennines accretionary wedge was affected by a Quaternary extensional tectonic phase during which SW-dipping normal fault systems developed. Among these normal faults, the Mt. Vettore extensional system (which includes the Castelluccio Plain fault (CPF) and the Mt. Vettoretto fault (MVF)) is one of the most important, being capable to produce destructive earthquakes (Mw 6.5 October 20, 2016). A long-lasting debate exists in literature concerning the cross-cutting relationships between the ST and the Mt. Vettore normal fault system: i.e., the thrust was alternatively considered as being nondisplaced by the normal faults or variously displaced with throws ranging between ~200 m and >2 km. Unfortunately, where normal faults should cut the thrust, a thick debris cover hides the tectonic structures and only speculative hypotheses can, thus, be done about this issue. In addition, important evidence of pre-thrusting extension is known in the area, that make difficult to discriminate the effective Quaternary activity of faults if the intersection with the compressional structures is not exposed. The aim of this study is to constrain the position of the ST under the debris cover and its relationship with the CPF and MVF, based on the following field data: i) thrust plane attitude; ii) position of the Laga Fm. outcrops, representing the footwall of the ST; iii) hanging wall anticline geometry; iv) geometry of normal faults and their recent activity; v) thickness of the Castelluccio Plain Quaternary infill at the hanging wall of the ST. The thrust position under the debris cover has been determined considering the variation of the hanging wall anticline geometry. In fact, where the Jurassic-Paleogene basinal formations crop out, the hanging wall anticline is well developed with vertical to overturned forelimb and fold axis essentially parallel to the thrust trend. This is crucial, because the occurrence in the field of an incomplete anticline (i.e., lacking the vertical to overturned forelimb) juxtaposed to the Laga Fm. (originally the footwall of the thrust) suggests the displacement of the anticline by a normal fault, allows us to infer the cross-cutting relationship between the tectonic lineaments and to estimate Quaternary normal fault throws. We conclude that the ST was displaced by the CPF with max throw ~250 m, which is consistent with the thickness of the Quaternary infill of the Castelluccio Plain. Both the CPF and the ST are in turn cut by the MVF (the youngest fault of the area, active in the 2016 earthquake) with a ~50 m throw, and is also inferred to partly reuse with negative inversion the ST plane where the plane geometry was favorable to extension.</p>

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