The nature of the Albstadt Shear Zone, Germany

2020 ◽  
Author(s):  
Sarah Mader ◽  
Klaus Reicherter ◽  
Joachim Ritter ◽  
the AlpArray Working Group
Keyword(s):  
Shear Zone ◽  
Seismic Velocity ◽  
Active Regions ◽  
Velocity Model ◽  
Strike Slip ◽  
Fault System ◽  
Earthquake Catalog ◽  
Depth Range ◽  
Study Region ◽  
The Town

<p><span>The region around the town of Albstadt, SW Germany, is one of the most seismically active regions in Central Europe. In the last century alone three earthquakes with a magnitude greater than five happened and caused major damage. The ruptures occur along the Albstadt Shear Zone (ASZ), an approx. 20-30 km long, N-S striking fault with left-lateral strike slip. As there is no evidence for surface rupture the nature of the Albstadt Shear Zone can only be studied by its seismicity.</span></p><p><span>To characterize the ASZ we </span><span>continuously</span><span> complement the earthquake catalog of the </span><span>State Earthquake Service</span><span> of Baden-Württemberg with additional seismic phase onsets. For the latter we use the station network of AlpArray as well as </span><span>5 </span><span>additional, </span><span>in 2018/2019</span><span> installed seismic stations from the KArlsruhe BroadBand Array. </span><span>W</span><span>e invert</span><span>ed</span><span> for </span><span>a </span><span>new minimum 1D </span><span>seismic </span><span>velocity model</span> <span>of the study region. </span><span>We use this seismic velocity model to relocalize the complemented catalog</span> <span>and to calculate focal mechanisms</span><span>. </span></p><p><span>The majority of the seismicity happens between the towns Tübingen and Albstadt at around 9°E in a depth range of </span><span>about 1.5 to 16 km </span><span>and aligns </span><span>n</span><span>orth-</span><span>s</span><span>outh</span><span>. </span><span>Additionally, we see </span><span>a </span><span>cluster</span><span>ing of events at the town</span><span>s</span><span> Hechingen and Albstadt.</span><span> The dominating focal mechanism is strike-slip, </span><span>but we also observe </span><span>minor components of </span><span>normal and reverse faulting.<br></span><span>Our results image the ASZ by its mainly micro-seismic activity b</span><span>etween</span><span> 2011 </span><span>and</span><span> 2018 </span><span>confirming the N-S striking character, but also indicating a more complex fault system.</span></p><p><span>We thank the </span><span>State Earthquake Service</span><span> in Freiburg for using their data (Az. 4784//18_3303). </span></p><p> </p>

Template matching applied to the seismicity of the Albstadt Shear Zone, SW Germany

2021 ◽  
Author(s):  
Sarah Mader ◽  
Andrea Brüstle ◽  
Joachim R. R. Ritter ◽  
Keyword(s):  
Shear Zone ◽  
Template Matching ◽  
Strong Motion ◽  
Active Regions ◽  
High Gain ◽  
Seismic Network ◽  
Seismogenic Zone ◽  
Earthquake Catalog ◽  
Active Structures ◽  
The Town

<p>The Swabian Alb near the town of Albstadt, SW Germany, is one of the seismically most active regions in Central Europe. Since the beginning of the twentieth century continuous seismic activity is observed. At least three earthquakes with magnitudes greater than 5 occurred, causing major damages on the buildings in the closer vicinity. Despite of the size of these earthquakes no rupture structures are visible on the Earth’s surface. Earthquake locations are concentrated along a N-S striking zone, the so-called Albstadt Shear Zone (ASZ), at focal depths of about 1 km to 18 km. The central part of this seismogenic zone has an extension of approximately 20 km to 30 km and is characterized by dominantly sinistral strike-slip focal mechanisms. <br><br>The State Earthquake Service of Baden-Württemberg (LED) operates a dense seismic network of 6 high-gain and 9 strong-motion stations in the area of the ASZ. In 2015 and in 2018, 9 temporary high-gain stations were deployed nearby the center structure of ASZ within the framework of AlpArray Project and StressTransfer Network. This densified seismic network gives a unique opportunity to detect and locate the seismically active structures of the ASZ in more detail.</p><p>Therefore, a template matching algorithm is applied for microseismic earthquake detections. Results are compared with the existing earthquake catalog of the LED and statistics of the outcome are presented.</p>

From Corinth gulf extension to Ionian subduction/collision (W. Greece): micro-seismicity survey to constrain local tectonics and regional geodynamics

2020 ◽  
Author(s):  
Valentine Lefils ◽  
Alexis Rigo ◽  
Efthimios Sokos
Keyword(s):  
Seismic Velocity ◽  
Deformation Mode ◽  
Velocity Model ◽  
Fault System ◽  
Normal Faults ◽  
Corinth Gulf ◽  
National Network ◽  
The North ◽  
Gulf Of Corinth ◽  
Seismological Network

<p>The North-Eastern zone of the Gulf of Corinth in Greece is characterized by the rotation of a micro-plate in formation. The Island Akarnanian Block (IAB) have been progressively individualized since the Pleistocene (less than ~ 1.5 My ago). This micro-plate is the result of a larger-scale tectonic context with, on one side the N-S extension of the Gulf of Corinth to the East, and on the other side the Hellenic subduction to the South and the Apulian collision to the West. To the Northeast, the IAB micro-plate is bounded by a large North-South sinistral strike-slip fault system, the Katouna-Stamna Fault (KSF) and by several normal faults. To the North, normal faults reach the limit between Apulian and Eurasian plates and to the East, they form the East-West graben of Trichonis lake.</p><p>Although the structures and dynamics behind the Gulf of Corinth extension are today relatively known, nevertheless, the set of faults linking the Gulf of Corinth to the Western subduction structures remain poorly studied. The seismicity recorded by the Greek national network shows discrepancies regarding to the faults mapped on the surface.</p><p>At the end of 2015, a new micro-seismicity campaign started with the deployment of a temporary seismological network in an area ranging from the Gulf of Patras to the Amvrakikos Gulf toward the North. This network includes 17 seismic stations, recording continuously, added to the permanent stations of the Corinth Rift Laboratory (CRL) and of the Hellenic Unified Seismic Network (HUSN).</p><p>The analysis of the seismological records is still in process for the 2016 and 2017 years. Our study consists first in picking the <em>P</em>- and <em>S</em>- waves, and then to precisely localize the seismic events recorded by our temporary seismological network combined with the permanent ones. We will present here the event location map obtained for the 2016-2017 period, a new seismic velocity model, and focal mechanisms. The seismic activity including thousands of events, is characterized by the presence of numerous clusters of few days to few weeks duration. The clusters are analysed in detail by relative relocations in order to appraise their physical processes and their implications in the fault activity. We will discuss the deformation mode of the region and build a seismotectonic model consistent with the regional geodynamics and observations.</p>

scholarly journals Seismic and Geodetic Crustal Moment-Rates Comparison: New Insights on the Seismic Hazard of Egypt

2021 ◽  
Vol 11 (17) ◽  
pp. 7836
Author(s):  
Rashad Sawires ◽  
José A. Peláez ◽  
Federica Sparacino ◽  
Ali M. Radwan ◽  
Mohamed Rashwan ◽  
...  
Keyword(s):  
Active Regions ◽  
Seismic Source ◽  
Satellite System ◽  
Dead Sea ◽  
Fault System ◽  
Gulf Of Aqaba ◽  
Seismic Sources ◽  
Earthquake Catalog ◽  
Focal Mechanism Solutions ◽  
Rate Ratios

A comparative analysis of geodetic versus seismic moment-rate estimations makes it possible to distinguish between seismic and aseismic deformation, define the style of deformation, and also to reveal potential seismic gaps. This analysis has been performed for Egypt where the present-day tectonics and seismicity result from the long-lasting interaction between the Nubian, Eurasian, and Arabian plates. The data used comprises all available geological and tectonic information, an updated Poissonian earthquake catalog (2200 B.C.–2020 A.D.) including historical and instrumental datasets, a focal-mechanism solutions catalog (1951–2019), and crustal geodetic strains from Global Navigation Satellite System (GNSS) data. The studied region was divided into ten (EG-01 to EG-10) crustal seismic sources based mainly on seismicity, focal mechanisms, and geodetic strain characteristics. The delimited seismic sources cover the Gulf of Aqaba–Dead Sea Transform Fault system, the Gulf of Suez­–Red Sea Rift, besides some potential seismic active regions along the Nile River and its delta. For each seismic source, the estimation of seismic and geodetic moment-rates has been performed. Although the obtained results cannot be considered to be definitive, among the delimited sources, four of them (EG-05, EG-06, EG-08, and EG-10) are characterized by low seismic-geodetic moment-rate ratios (<20%), reflecting a prevailing aseismic behavior. Intermediate moment-rate ratios (from 20% to 60%) have been obtained in four additional zones (EG-01, EG-04, EG-07, and EG-09), evidencing how the seismicity accounts for a minor to a moderate fraction of the total deformational budget. In the other two sources (EG-02 and EG-03), high seismic-geodetic moment-rates ratios (>60%) have been observed, reflecting a fully seismic deformation.

The moderate size 2019 September Mw 5.8 Silivri earthquake unveils the complexity of the Main Marmara Fault shear zone

2020 ◽  
Vol 224 (1) ◽  
pp. 377-388 ◽  
Author(s):  
Hayrullah Karabulut ◽  
Sezim Ezgi Güvercin ◽  
Figen Eskiköy ◽  
Ali Özgun Konca ◽  
Semih Ergintav
Keyword(s):  
Shear Zone ◽  
Sedimentary Cover ◽  
Marmara Sea ◽  
Depth Range ◽  
Stress Increase ◽  
The North ◽  
Finite Fault ◽  
Stress Changes ◽  
The City ◽  
The Town

SUMMARY The unbroken section of the North Anatolian Fault beneath the Sea of Marmara is a major source of seismic hazard for the city of İstanbul. The northern and currently the most active branch, the Main Marmara Fault (MMF), is segmented within a shear zone and exhibits both partially creeping and locked behaviour along its 150 km length. In 2019 September, a seismic activity initiated near MMF, off-coast the town of Silivri, generating 14 earthquakes ≥ Mw 3.5 in a week. The Mw 5.8 Silivri earthquake, is the largest in the Marmara Sea since the 1963 Mw 6.3 Çınarcık earthquake. Our analyses reveal that the activity started in a narrow zone (∼100 m) and spread to ∼7 km following an Mw 4.7 foreshock within ∼2 d. The distribution of relocated aftershocks and the focal mechanisms computed from regional waveforms reveal that the Mw 5.8 earthquake did not occur on the MMF, but it ruptured ∼60° north-dipping oblique strike-slip fault with significant thrust component located on the north of the MMF. Finite-fault slip model of the main shock shows 8 km long rupture with directivity toward east, where the ruptured fault merges to the MMF. The narrow depth range of the slip distribution (10–13 km) and the aftershock zone imply that the causative fault is below the deep sedimentary cover of the Marmara Basin. The distribution of aftershocks of the Mw 5.8 event is consistent with Coulomb stress increase. The stress changes along MMF include zones of both stress decrease due to clamping and right-lateral slip, and stress increase due to loading.

scholarly journals Polyphase deformation along the South Bohemian Batholith-Moldanubian nappes boundary – The Freyenstein Fault System (Bohemian Massif/Austria)

2020 ◽  
Vol 113 (1-2) ◽  
pp. 139-153
Author(s):  
Gerit E. U. Griesmeier ◽  
Christoph Iglseder ◽  
Ralf Schuster ◽  
Konstantin Petrakakis
Keyword(s):  
Shear Zone ◽  
Bohemian Massif ◽  
Potassium Feldspar ◽  
Strike Slip ◽  
Greenschist Facies ◽  
Fault System ◽  
Ductile Shear Zone ◽  
The South ◽  
Shear Sense ◽  
Ductile Shear

AbstractThis work describes the Freyenstein Fault System, which extends over 45 km in the southeastern part of the Bohemian Massif (Lower Austria). It represents a ductile shear zone overprinted by a brittle fault located at the eastern edge of the South Bohemian Batholith towards the Moldanubian nappes. It affects Weinsberg- and a more “fine-grained” granite, interlayered aplitic granite and pegmatite dikes as well as paragneiss of the Ostrong Nappe System. The ductile shear zone is represented by approximately 500 m thick greenschist-facies mylonite dipping about 60° to the southeast. Shear-sense criteria like clast geometries, SCC`-type shear band fabrics as well as abundant microstructures show top to the south/ southsouthwest normal shearing with a dextral strike-slip component. Mineral assemblages in mylonitized granitoid consist of pre- to syntectonic muscovite- and biotite-porphyroclasts as well as dynamically recrystallized potassium feldspar, plagioclase and quartz. Dynamic recrystallization of potassium feldspar and the stability of biotite indicate upper green-schist-facies metamorphic conditions during the early phase of deformation. Fluid infiltration at lower greenschist-facies conditions led to local sericitization of feldspar and synmylonitic chloritisation of biotite during a later stage of ductile deformation. Finally, a brittle overprint by a north-south trending, subvertical, sinistral strike-slip fault that shows a normal component is observed. Ductile normal shearing along the Freyenstein Shear Zone is interpreted to have occurred between 320 Ma and c. 300 Ma. This time interval is indicated by literature data on the emplacement of the hostrock and cooling below c. 300°C inferred from two Rb-Sr biotite ages measured on undeformed granites close to the shear zone yielding 309.6 ± 3 Ma and 290.9 ± 2.9 Ma, respectively. Brittle sinistral strike-slip faulting at less than 300°C presumably took place not earlier than 300 Ma. Early ductile shearing along the Freyenstein Fault System may be genetically, but not kinematically linked to the Strudengau Shear Zone, as both acted in an extensional regime during late Variscan orogenic collapse. A relation to other major northeast-southwest trending faults of this part of the Bohemian Massif (e.g. the Vitis-Pribyslav Fault System) is indicated for the phase of brittle sinistral movement.

scholarly journals The Timing of Strike-Slip Deformation Along the Storstrømmen Shear Zone, Greenland Caledonides: U–Pb Zircon and Titanite Geochronology

2014 ◽  
Vol 41 (1) ◽  
pp. 19 ◽  
Author(s):  
Benjamin W. Hallett ◽  
William C. McClelland ◽  
Jane A. Gilotti
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Fault System ◽  
Oblique Collision ◽  
Plate Convergence ◽  
Ion Probe ◽  
Slip Displacement ◽  
Land Deformation ◽  
Lateral Escape

The Storstrømmen shear zone (SSZ) in the Greenland Caledonides is widely interpreted to have formed in a transpressional regime during sinistral, oblique collision between Baltica and Laurentia in the Silurian to Devonian. New mapping of the SSZ at Sanddal documents a 100 m thick, greenschistfacies mylonite zone cutting the eclogite to amphibolite-facies gneiss complex. We present U–Pb ion probe geochronology on zircon and titanite from a variety of lithologies that shows the SSZ was active from late Devonian to the Carboniferous (at least until 350 Ma). The age of thrusting in the foreland is not well known, but must be younger than the age of eclogite-facies metamorphism at ~400 Ma. It is, therefore, possible that contraction is the same age as strike-slip motion, and that transpression is a viable model. The timing of the SSZ is synchronous with dextral strike-slip displacement on the Germania Land deformation zone. Simultaneous displacement on sinistral and dextral, conjugate shear zones suggests that the SSZ is part of a strikeslip fault system that led to lateral escape of material northward (present day coordinates) during the waning stages of plate convergence between Laurentia and Baltica.SOMMAIRELa zone de cisaillement de Storstrømmen (SSZ) dans les Calédonides du Groenland est généralement comprise comme ayant été formée durant un régime de transpression sénestre lors de la collision oblique entre Baltica et Laurentie, du Silurien au Dévonien.  Une nouvelle cartographie de la SSZ à Sanddal décrit une zone de 100 m d’épaisseur de mylonite au faciès des schistes verts qui recoupe un complexe de gneiss au faciès éclogite à amphibolite.  Notre analyse géochronologique par sonde ionique U-Pb sur zircon et titanite sur diverses lithologies, montre que la SSZ a été active de la fin du Dévonien jusqu’au Carbonifère (au moins jusqu’à 350 Ma).  L’âge du chevauchement dans l’avant-pays n’est pas bien connue, mais il doit être plus jeune que le métamorphisme au faciès d’éclogite à ~400 Ma.  Il est donc possible que la contraction soit du même âge que le mouvement de coulissage, et que la transpression soit un modèle viable.  La chronologie de la SSZ est synchrone au mouvement de coulissage dextre de la zone de déformation de Germania Land.  Les déplacements simultanés, sénestre et dextre, sur des zones de cisaillement conjuguées permettent de penser que la SSZ fait partie d’un système de décrochement qui a engendré une éjection latérale de matériau vers le nord (selon les coordonnées actuelles) durant les stades de convergence des plaques Laurentie et Baltica.

Locations and focal mechanisms of recent microearthquakes and tectonics of Livermore Valley, California

1982 ◽  
Vol 72 (3) ◽  
pp. 821-840
Author(s):  
Fred E. Followill ◽  
Joseph M. Mills
Keyword(s):  
Linear Trend ◽  
Source Region ◽  
Velocity Model ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Fault System ◽  
Lateral Velocity ◽  
Thrust Faulting ◽  
Northern Regions ◽  
The Right

abstract Over 100 well-recorded microearthquakes (local magnitude less than 3), which occurred between January and September 1980, have been relocated, and focal mechanisms have been estimated for six regions of recent seismic activity for the Livermore Valley. Each of these microearthquakes had a minimum of 10 stations distributed in at least three quadrants around the epicenter. Data from these microearthquakes were combined with data from three USGS refraction experiments and used to develop a velocity model for Livermore Valley. Using this model, together with source region and station corrections to compensate for lateral velocity variations in the upper crust, we recalculated the locations and focal mechanisms. Comparing the results from these regions, we found differences in focal depths, patterns of epicenter locations, and focal mechanisms. Focal depths in the northern regions were usually between 5 and 11 km. These were slightly greater than focal depths (2 to 8 km) in the southern regions. The pattern of strike-slip focal mechanisms with P axes trending NNE and the linear trend of epicenters along the right-lateral strike-slip Greenville fault system in the northern regions is in contrast with the pattern of a mixture of focal mechanisms in southern regions (which includes about one-third with thrust-type mechanisms where the T axis is nearer vertical than horizontal). In the southern regions, there is some indication of short offset (en echelon) segments and an absence of the extended linear trend found in the northern regions. We speculate that this more diffuse pattern of locations and focal mechanisms in the southern regions of the valley results from general north-south compressional tectonics with both strikeslip and thrust faulting occurring in a localized zone of deformation between the Livermore Valley block and the Diablo Range block to the south.

Waveform Cross-Correlation Relocation and Focal Mechanisms for the 2019 Ridgecrest Earthquake Sequence

2020 ◽  
Vol 91 (4) ◽  
pp. 2055-2061 ◽  
Author(s):  
Guoqing Lin
Keyword(s):  
Cross Correlation ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Volcanic Field ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Earthquake Sequence ◽  
Waveform Data ◽  
Waveform Cross Correlation ◽  
First Motion

Abstract I present a high-precision earthquake relocation catalog and first-motion focal mechanisms before and during the 2019 Ridgecrest earthquake sequence in eastern California. I obtain phase arrivals, first-motion polarities, and waveform data from the Southern California Earthquake Data Center for more than 24,000 earthquakes with the magnitudes varying between −0.7 and 7.1 from 1 January to 31 July 2019. I first relocate all the earthquakes using phase arrivals through a previously developed 3D seismic-velocity model and then improve relative location accuracies using differential times from waveform cross correlation. The majority of the relocated seismicity is distributed above 12 km depth. The seismicity migration along the northwest–southeast direction can be clearly seen with an aseismic zone near the Coso volcanic field. Focal mechanisms are solved for all the relocated events based on the first-motion polarity data with dominant strike-slip fault solutions. The Mw 6.4 and 7.1 earthquakes are positioned at 12.45 and 4.16 km depths after the 3D relocation, respectively, with strike-slip focal solutions. These results can help our understanding of the 2019 Ridgecrest earthquake sequence and can be used in other seismological and geophysical studies.

scholarly journals Conjugate faulting and structural complexity on the young fault system associated with the 2000 Tottori earthquake

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Aitaro Kato ◽  
Shin’ichi Sakai ◽  
Satoshi Matsumoto ◽  
Yoshihisa Iio
Keyword(s):  
High Spatial Resolution ◽  
Seismic Velocity ◽  
Structural Complexity ◽  
Fault Zones ◽  
Fault System ◽  
Earthquake Catalog ◽  
Earthquake Occurrence ◽  
Southwest Japan ◽  
Multiple Length Scales ◽  
Fluid Diffusion

AbstractYoung faults display unique complexity associated with their evolution, but how this relates to earthquake occurrence is unclear. Unravelling the fine-scale complexity in these systems could lead to a greater understanding of ongoing strain localization in young fault zones. Here we present high-spatial-resolution images of seismic sources and structural properties along a young fault zone that hosted the Tottori earthquake (Mw 6.8) in southwest Japan in 2000, based on data from a hyperdense network of ~1,000 seismic stations. Our precise micro-earthquake catalog reveals conjugate faulting over multiple length scales. These conjugate faults are well developed in zones of low seismic velocity. A vertically dipping seismic cluster of about 200 m length occurs within a width of about 10 m. Earthquake migrations in this cluster have a speed of about 30 m per day, which suggests that fluid diffusion plays a role. We suggest that fine structural complexities influence the pattern of seismicity in a developing fault system.

Seismic tomography at a fire‐flood site

Geophysics ◽  
1989 ◽  
Vol 54 (9) ◽  
pp. 1082-1090 ◽  
Author(s):  
N. D. Bregman ◽  
P. A. Hurley ◽  
G. F. West
Keyword(s):  
Oil Recovery ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Pilot Project ◽  
Velocity Model ◽  
High Amplitude ◽  
Oil Sand ◽  
Low Velocity ◽  
Study Region ◽  
Velocity Channel

A crosshole seismic experiment was conducted to locate and characterize a firefront at an enhanced oil recovery (EOR) pilot project. The reservoir engineers involved in the project were interested in finding out why the burnfront apparently had stalled between two wells 51 m apart. In a noisy producing environment, good quality seismic data were recorded at depths ranging from 710 to 770 m. The frequency range of the data, 500 to 1500 Hz, allows resolution of the velocity structure on a scale of several meters. The moveout of first arrivals indicates that there are large velocity variations in the study region; a high‐amplitude, late arriving channel wave points to the existence of a low‐velocity channel connecting the boreholes. Using an iterative, nonlinear scheme which incorporates curved ray tracing and least‐squares inversion in each iteration, the first‐arrival times were inverted to obtain a two‐dimensional model of the compressional seismic velocity between the boreholes. The velocities range from 1.5 km/s to 3.2 km/s, with a low‐velocity channel at the depth of the producing oil sand. Sonic, core, and temperature logs lead us to conclude that the extremely low velocities in the model are probably due to gases produced by the burn. Increased velocities in an adjacent shale may be a secondary effect of the burn. The velocity model also indicates an irregularity in the topography at the bottom of the reservoir, an irregularity which may be responsible for blocking the progress of the burnfront.

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