Geomorphic evidence for active, co-seismic slip along a low-angle normal fault: Panamint Valley, California

Mapping Intimacies ◽

10.5194/egusphere-egu2020-11523 ◽

2020 ◽

Author(s):

Eric Kirby ◽

Israporn (Grace) Sethanant ◽

John Gosse ◽

Eric McDonald ◽

J Doug Walker

Keyword(s):

Seismic Hazard ◽

Normal Fault ◽

Basin And Range ◽

Detachment Fault ◽

Airborne Lidar ◽

Fault System ◽

Seismic Slip ◽

The Past ◽

Detachment Faults ◽

Fault Scarps

The mechanical feasibility of co-seismic displacement along low-angle normal fault systems remains an outstanding problem in tectonics.&#160; In the southwestern Basin and Range of North America, large magnitude extension during Miocene &#8211; Pliocene time was accommodated along a regionally extensive system of low-angle detachment faults.&#160; Whether these faults remain active today and, if so, whether they rupture during large earthquakes are questions central to understanding the geodynamics of distributed lithospheric deformation and associated seismic hazard.&#160; Here we evaluate the geometric and kinematic relationships of fault scarps developed in Pleistocene &#8211; Holocene alluvial and lacustrine deposits with low-angle detachment faults observed along the western flank of the Panamint Range, in eastern California.&#160; We combine analysis of high-resolution topography generated from airborne LiDAR and photogrammetry with a detailed chronology of alluvial fan surfaces and a calibrated soil chronosequence to characterize the recent activity of the fault system.&#160; The range-front fault system is coincident with a low-angle (15-20&#176;), curviplanar detachment fault that is linked to strike-slip faults at its southern and northern ends. &#160;Fanglomerate deposits in the hanging wall of the detachment are juxtaposed with brecciated bedrock in the footwall across a narrow fault surface marked by clay-rich gouge.&#160; Isochron burial dating of the fanglomerate using the 26Al and 10Be requires displacement in the past ~800 ka.&#160; The degree of soil development in younger alluvial deposits in direct fault contact with the footwall block suggest displacement along the main detachment in the past as ~80-100 ka.&#160; The geometry of recent fault scarps in Holocene alluvium mimic range-scale variations in strike of the curviplanar detachment fault, suggesting that scarps merge with the detachment at depth.&#160; Moreover, fault kinematics inferred from displaced debris-flow levees and from fault striae on the bedrock range front are consistent with slip on a low-angle detachment system beneath the valley.&#160; Finally, paleoseismic results from a trench at the southern end of the fault system suggest 3-4 surface ruptures during past ~4-5 ka, the most recent of which (MRE) occurred ~330-485 cal yr BP.&#160; Scarps related to the MRE can be traced for at least ~50 km northward along the range front and imply surface displacements of 2-4 meters during this event.&#160; Thus, we conclude that ongoing dextral shear along the margin of the Basin and Range is, in part, accommodated by co-seismic slip along low-angle detachment faults in Panamint Valley.&#160; Our results have important implications for the interaction of fault networks and seismic hazard in the region.

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Active fault segmentation and seismic hazard in Hoa-Binh reservoir, Vietnam

Open Geosciences ◽

10.2478/s13533-012-0128-5 ◽

2013 ◽

Vol 5 (2) ◽

Cited By ~ 1

Author(s):

Phan Trinh ◽

Hoang Vinh ◽

Nguyen Huong ◽

Ngo Liem

Keyword(s):

Seismic Hazard ◽

Active Fault ◽

Slip Rate ◽

Normal Fault ◽

Seismic Attenuation ◽

Fault System ◽

Ground Acceleration ◽

Hydropower Dam ◽

Large Dam ◽

Hoa Binh

AbstractBased on remote sensing, geological data, geomorphologic analysis, and field observations, we determine the fault system which is a potential source of earthquakes in Hoa-Binh reservoir. It is the sub-meridian fault system composed of fault segments located in the central part of the eastern and western flanks of the Quaternary Hoa-Binh Graben: the Hoa-Binh 1 fault is east-dipping (75–80°), N-S trending, 4 km long, situated in the west of the Hoa-Binh Graben, and the Hoa-Binh 2 is a west-dipping (75–80°), N-S trending; 8.4 km long fault, situated in the east of the Hoa-Binh Graben. The slip rate of normal fault in Hoa-Binh hydropower dam was estimated at 0.3–1.1 mm/yr. The Maximum Credible Earthquake (MCE) and Peak Ground Acceleration (PGA) in the Hoa-Binh hydropower dam have been assessed. The estimated MCE of HB.1 and HB.2 is 5.6 and 6.1 respectively, and the maximum PGA at Hoa-Binh dam is 0.30 g and 0.40 g, respectively. The assessment of seismic hazard in Hoa-Binh reservoir is a typical example of seismic hazards of a large dam constructed in an area of low seismicity and lack of law of seismic attenuation.

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Permian rifting and detachment faults and their role in Alpine collisional tectonics

10.5194/egusphere-egu21-16307 ◽

2021 ◽

Author(s):

Nikolaus Froitzheim ◽

Linus Klug

Keyword(s):

Normal Fault ◽

Southern Alps ◽

Detachment Fault ◽

Metamorphic Core Complex ◽

Rift System ◽

Early Permian ◽

Core Complex ◽

Detachment Faults ◽

The North ◽

Metamorphic Core

The Permian was a time of strong crustal extension in the area of the later-formed Alpine orogen. This involved extensional detachment faulting and the formation of metamorphic core complexes. We describe (1) an area in the Southern Alps (Valsassina, Orobic chain) where a metamorphic core complex and detachment fault have been preserved and only moderately overprinted by Alpine collisional shortening, and (2) an area in the Austroalpine (Schneeberg) where Alpine deformation and metamorphism are intense but a Permian low-angle normal fault is reconstructed from the present-day tectonometamorphic setting. In the Southern Alps case, the Grassi Detachment Fault represents a low-angle detachment capping a metamorphic core complex in the footwall which was affected by upward&#8208;increasing, top&#8208;to&#8208;the&#8208;southeast mylonitization. Two granitoid intrusions occur in the core complex, c. 289 Ma and c. 287 Ma, the older of which was syn-tectonic with respect to the extensional mylonites (Pohl, Froitzheim, et al., 2018, Tectonics). Consequently, detachment&#8208;related mylonitic shearing took place during the Early Permian and ended at ~288 Ma, but kinematically coherent brittle faulting continued. Considering 30&#176; anticlockwise rotation of the Southern Alps since Early Permian, the extension direction of the Grassi Detachment Fault was originally ~N&#8208;S and the sense of transport top-South. In this area, there is no evidence of Permian strike-slip faulting but only of extension. In the Schneeberg area of the Austroalpine, a unit of Early Paleozoic metasediments with only Eoalpine (Cretaceous) garnet, the Schneeberg Complex, overlies units with two-phased (Variscan plus Eoalpine) garnet both to the North (&#214;tztal Complex) and to the South (Texel Complex). The basal contact of the Schneeberg Complex was active as a north-directed thrust during the Eoalpine orogeny. It reactivated a pre-existing, post-Variscan but pre-Mesozoic, i.e. Permian low-angle normal fault. This normal fault had emplaced the Schneeberg Complex with only low Variscan metamorphism (no Variscan garnet) on an amphibolite-facies metamorphic Variscan basement. The original normal fault dipped south or southeast, like the Grassi detachment in the Southern Alps. As the most deeply subducted units of the Eoalpine orogen (e.g. Koralpe, Saualpe, Pohorje) are also the ones showing the strongest Permian rift-related magmatism, we hypothesize that the Eoalpine subduction was localized in a deep Permian rift system within continental crust.

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Recent Activity and Kinematics of the Bounding Faults of the Catanzaro Trough (Central Calabria, Italy): New Morphotectonic, Geodetic and Seismological Data

Geosciences ◽

10.3390/geosciences11100405 ◽

2021 ◽

Vol 11 (10) ◽

pp. 405

Author(s):

Claudia Pirrotta ◽

Graziella Barberi ◽

Giovanni Barreca ◽

Fabio Brighenti ◽

Francesco Carnemolla ◽

...

Keyword(s):

Scaling Laws ◽

Normal Fault ◽

Historical Earthquakes ◽

Fault System ◽

Normal Faults ◽

The North ◽

Seismological Data ◽

Geomorphic Features ◽

Half Graben ◽

Fault Scarps

A multidisciplinary work integrating structural, geodetic and seismological data was performed in the Catanzaro Trough (central Calabria, Italy) to define the seismotectonic setting of this area. The Catanzaro Trough is a structural depression transversal to the Calabrian Arc, lying in-between two longitudinal grabens: the Crati Basin to the north and the Mesima Basin to the south. The investigated area experienced some of the strongest historical earthquakes of Italy, whose seismogenic sources are still not well defined. We investigated and mapped the major WSW–ENE to WNW–ESE trending normal-oblique Lamezia-Catanzaro Fault System, bounding to the north the Catanzaro Trough. Morphotectonic data reveal that some fault segments have recently been reactivated since they have displaced upper Pleistocene deposits showing typical geomorphic features associated with active normal fault scarps such as triangular and trapezoidal facets, and displaced alluvial fans. The analysis of instrumental seismicity indicates that some clusters of earthquakes have nucleated on the Lamezia-Catanzaro Fault System. In addition, focal mechanisms indicate the prevalence of left-lateral kinematics on E–W roughly oriented fault plains. GPS data confirm that slow left-lateral motion occurs along this fault system. Minor north-dipping normal faults were also mapped in the southern side of the Catanzaro Trough. They show eroded fault scarps along which weak seismic activity and negligible geodetic motion occur. Our study highlights that the Catanzaro Trough is a poliphased Plio-Quaternary extensional basin developed early as a half-graben in the frame of the tear-faulting occurring at the northern edge of the subducting Ionian slab. In this context, the strike-slip motion contributes to the longitudinal segmentation of the Calabrian Arc. In addition, the high number of seismic events evidenced by the instrumental seismicity, the macroseismic intensity distribution of the historical earthquakes and the scaling laws relating to earthquakes and seismogenic faults support the hypothesis that the Lamezia-Catanzaro Fault System may have been responsible for the historical earthquakes since it is capable of triggering earthquakes with magnitude up to 6.9.

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Mixed-Mode Seismic Slip and Aseismic Creep on a Highly Active Low-Angle Normal Fault System in Papua New Guinea

10.5194/egusphere-egu2020-230 ◽

2020 ◽

Author(s):

James Biemiller ◽

Laura Wallace ◽

Luc Lavier

Keyword(s):

Papua New Guinea ◽

Normal Fault ◽

New Guinea ◽

Fault System ◽

Normal Faults ◽

Fault Mechanics ◽

Fault Rocks ◽

Near Surface ◽

Geological Evidence ◽

Seismic Slip

Whether low-angle normal faults (LANFs; dip < 30&#176;) slip in large earthquakes or creep aseismically is a longstanding problem in fault mechanics. Although abundant in the geologic record, active examples of these enigmatic &#8216;misoriented&#8217; structures are rare and extension rates across them are typically less than a few mm/yr. As such, geodetic and seismological observations of LANFs are sparse and can be difficult to interpret in terms of earthquake cycles. With a long-term slip rate of ~1 cm/yr, the Mai&#8217;iu fault in Papua New Guinea may be the world&#8217;s most active LANF and thus offers an outstanding natural laboratory to evaluate seismic vs. aseismic behavior of LANFs. Here, we use new results from a campaign GPS network to determine the degree of locking vs. aseismic creep on the Mai&#8217;iu fault and evaluate these results in the context of geological evidence for mixed seismic and aseismic slip in exhumed Mai&#8217;iu fault rocks.We derive velocities from GPS measurements with 3-4 km station spacing above the shallowest portions of the fault, which dips 21-25&#176; at the surface. Dislocation modeling of these velocities is consistent with 6-8 mm/yr of horizontal extension, corresponding to ~1 cm/yr dip-slip rates on a 27-35&#176;-dipping fault. Strain rates and vertical derivatives of horizontal stress rates derived from these velocities confirm localized extension across the fault. We compare and evaluate two interseismic locking models that fit the data best: one in which the fault deforms by shallow near-surface creep updip of a deeper zone of increased interseismic coupling which soles into a steadily creeping shear zone at depth, and one in which the fault creeps steadily downdip of a shallowly locked patch. These results combined with field and microstructural evidence from the exhumed fault rocks suggest that the fault slips by a mixture of brittle frictional (seismic slip, fracturing, and cataclastic creep) and viscous (stress-driven dissolution-precipitation creep, or pressure solution) processes. Using depth-constrained mechanical properties and stress conditions inferred from exhumed fault rocks, we model the time-dependent competition between frictional slip and viscous creep to assess where and how elastic strain accumulates along the Mai&#8217;iu fault, and whether the fault is capable of hosting or nucleating earthquakes.

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Discussion on the Cenozoic tectonic evolution and dynamics of southern Tibet

Earth sciences and subsoil use ◽

10.21285/2686-9993-2020-43-3-307-324 ◽

2020 ◽

Vol 43 (3) ◽

pp. 307-324

Author(s):

Demin Liu ◽

Weiran Yang ◽

Tieying Guo ◽

Jiangtao Ru ◽

Aimin Xiong

Keyword(s):

Normal Fault ◽

Thrust Fault ◽

Fault Zones ◽

Detachment Fault ◽

Fault System ◽

Gravitational Potential Energy ◽

The South ◽

Main Central Thrust ◽

Southern Tibet ◽

South Tibet

Opening-closing tectonics is a new idea for exploring the global tectonics, which holds that every tectonic movement of all materials and geological bodies on earth is characterized by opening and closing. The opening-closing tectonic view can be used to explain some geological phenomena developing in continents which cannot be reasonably explained by the theory of plate tectonics. Based on the available basic geological data and combining with the opening-closing view, we analyzed the divisions and characteristics of tectonic units in South Tibet, and propose that Tibet can be divided into gravitational detachment and detachment fault zones, which are superimposed thrust fault zones and reconstructed normal fault zones, respectively. Although the mainstream opinion believed that the Tibetan Plateau is formed by collision-compression orogenesis, field investigation revealed the existence of the Rongbu Temple normal fault in the 1970s. We consider that the Rongbu Temple normal fault and the Main Central Thrust were formed earlier than the South Tibet detachment fault, and the former two faults constitute the two boundaries of the southern Tibet extrusion structure. The South Tibet detachment fault partially superimposes on the Main Central Thrust and manifests a relatively high angle in following the Rongbu Temple normal fault north of the Chomolangma. We suggest that the three fault systems are the products of different periods and tectonic backgrounds. The tectonic units, such as klippes and windows identified by previous researchers in southern Tibet, belong to thrust fault system but usually have no obvious extrusion or thrust characteristics; however, they are characterized by missing strata columns as younger strata overlapping the older ones. These klippes and windows should be the results of later gravitational decollement and must be characterized as extensions and slips, respectively. Based on opening-closing theory, we suggest that since the Cenozoic the study area had undergone multistage development, which can be divided into the oceanic crust expansion (opening) and subduction (closing) and the continental collision (closing) and intracontinental extension (opening) stages. Geothermal energy from the deep earth, gravitational potential energy from the earth’s interior, and additional stress energy from tectonic movements, all played a key role in the multistage tectonic evolutionary process.

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The Mw4.9 Le Teil surface-rupturing earthquake in southern France: New insight on seismic hazard assessment in stable continental regions

10.5194/egusphere-egu2020-8409 ◽

2020 ◽

Cited By ~ 1

Author(s):

Jean-François Ritz ◽

Stéphane Baize ◽

Matthieu Ferry ◽

Christophe Larroque ◽

Laurence Audin ◽

...

Keyword(s):

Seismic Hazard ◽

Hazard Assessment ◽

Seismic Hazard Assessment ◽

Airborne Lidar ◽

Fault System ◽

Epicentral Area ◽

Massif Central ◽

Southern France ◽

Seismological Data ◽

Stable Continental Regions

On November 11th 2019, a Mw 4.9 earthquake shook the Rhone River Valley in southern France, a rather densely populated area with many industrial facilities including several nuclear power plants. The &#8220;Le Teil&#8221; earthquake was felt as far as Montpellier and Grenoble, 120 km from the epicenter. Seismological data promptly showed that the earthquake corresponded to a reverse faulting event along a NE-SW trending fault with a focus at a very shallow depth (~1 km). In parallel, satellite-based radar observations (InSAR) showed the uplift of the SE compartment (up to 10 centimeters) along a sharp NE-SW trending ~4.5-km-long discontinuity. Field investigations conducted in the following days and weeks in the epicentral area uncovered several evidences of surface ruptures across roads and paths where the InSAR discontinuity is mapped. We also carried out airborne LiDAR surveys to map the rupture below the dense forest cover. Characteristics of surface deformations are fully consistent with InSAR and seismological data, and allow concluding to the reactivation of an Oligocene normal fault segment (i.e. La Rouvi&#232;re fault) that belongs to the C&#233;vennes fault system, a 120 km long polyphased system bounding the southern rim of the Massif Central. The absence of clear cumulative compressional deformation along the fault rupture, which on the contrary displays inherited extensional deformation (most likely Oligocene in age), suggests that the fault has not moved significantly since millions of years. These observations relaunch the question of seismic hazard assessment in stable continental regions such as continental France and most of Western Europe, where strain rates are very low.

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Active faulting, 3-D basin architecture and Plio-Quaternary structural evolution of extensional basins: a 4-D perspective on the central Apennine chain evolution, Italy

10.5194/se-2016-103 ◽

2016 ◽

Author(s):

Stefano Gori ◽

Emanuela Falcucci ◽

Chiara Ladina ◽

Simone Marzorati ◽

Fabrizio Galadini

Keyword(s):

Tectonic Setting ◽

Structural Evolution ◽

Normal Fault ◽

Basin And Range ◽

Early Pleistocene ◽

Fault System ◽

Late Pliocene ◽

North East ◽

The North ◽

Apennine Chain

Abstract. The general “basin and range” aspect of the Apennine relief is generally attributed to the presently active normal fault systems, whose activity throughout the Quaternary is supposed to have created alternating morphological/structural highs and lows. By coupling field geological survey and geophysical investigations, we reconstructed the 3-D geometry of one of the innermost tectonic basins of the central Apennines, the Subequana Valley, bounded to the north-east by an active and seismogenic normal fault. Our analyses revealed that, since the Late Pliocene, the depression experienced a double polarity, half graben-mode nucleation. An early phase, Late Pliocene-Early Pleistocene in age, was led by the ENE-WSW trending and SSE dipping Avezzano-Bussi fault, that determined the formation of an early depocentre towards the N-NW; subsequently, the main fault became the NW-SE trending, SW dipping and presently active normal fault system, that led the formation during the Quaternary of a new fault-related depocentre towards the NE. By considering the available geological information, a similar structural evolution has likely involved three close tectonic basins aligned along the Avezzano-Bussi fault, namely the Fucino basin, the Subequana Valley and the Sulmona basin, and it has been probably experienced by other tectonic basins of the chain. The present work therefore points out that the morpho-tectonic setting of the Apennine chain results from the superposition of deformation events whose “legacy” must be considered in a wider evolutionary perspective. Within this light, our results testify that a simple “basin and range” model – often adopted for morpho-tectonic and kinematic evaluations in active extensional contexts, as in the Apennines – may be actually simplistic, as it could not be applied everywhere, owing to peculiar complexities of the local tectonic histories.

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