scholarly journals SEGMENTATION AND INTERACTION OF NORMAL FAULTS IN CENTRAL GREECE

2017 ◽  
Vol 43 (1) ◽  
pp. 428 ◽  
Author(s):  
S. Kokkalas
Keyword(s):  
Scaling Laws ◽  
Normal Fault ◽  
Fault Zones ◽  
Segment Length ◽  
Normal Faults ◽  
Mechanical Interaction ◽  
Fault Segment ◽  
Central Greece ◽  
Fault Length ◽  
Radial Propagation

The aim of this study is to improve our understanding on the mechanical interaction and linkage process between normal fault segments. Faults grow by the process of radial propagation and the linkage of segments, as strain increases, evolving to large fault systems. For this purpose we conducted a combined field and photogeological study on two major segmented fault zones in Central Greece, the Atalanti and Arkitsa fault zones. This approach includes effects of fault size and spatial distribution, scaling laws and footwall-hanginwall topography. Throw distribution and the geometry of the segmented fault arrays were analyzed in order to investigate the complexity of fault zones, the fault linkage process and the geometric characteristics of the relay zones formed between individual segments. The correlation of fault throw with fault length (D-L) and the ratios of overlap-separation (OL-S), separation-fault segment length (S-L) and relay displacement vs. separation (Dr-S) were examined in order to give an insight for fault segment interaction and linkage .

scholarly journals Mechanisms of clay smear formation in unconsolidated sediments – insights from 3-D observations of excavated normal faults

Solid Earth ◽  
2016 ◽  
Vol 7 (3) ◽  
pp. 789-815 ◽  
Author(s):  
Michael Kettermann ◽  
Sebastian Thronberens ◽  
Oscar Juarez ◽  
Janos Lajos Urai ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Microscopic Study ◽  
Thickness Distribution ◽  
Normal Fault ◽  
Fault Zones ◽  
Unconsolidated Sediments ◽  
Normal Faults ◽  
Low Permeability ◽  
Lignite Mine ◽  
Log Normal ◽  
Open Cast

Abstract. Clay smears in normal faults can form seals for hydrocarbons and groundwater, and their prediction in the subsurface is an important problem in applied and basic geoscience. However, neither their complex 3-D structure, nor their processes of formation or destruction are well understood, and outcrop studies to date are mainly 2-D. We present a 3-D study of an excavated normal fault with clay smear, together with both source layers, in unlithified sand and clay of the Hambach open-cast lignite mine in Germany. The faults formed at a depth of 150 m, and have shale gouge ratios between 0.1 and 0.3. The fault zones are layered, with sheared sand, sheared clay and tectonically mixed sand–clay gouge. The thickness of clay smears in two excavated fault zones of 1.8 and 3.8 m2 is approximately log-normal, with values between 5 mm and 5 cm, without holes. The 3-D thickness distribution is heterogeneous. We show that clay smears are strongly affected by R and R' shears, mostly at the footwall side. These shears can locally cross and offset clay smears, forming holes in the clay smear, while thinning of the clay smear by shearing in the fault core is less important. The thinnest parts of the clay smears are often located close to source layer cut-offs. Locally, the clay smear consists of overlapping patches of sheared clay, separated by sheared sand. More commonly, it is one amalgamated zone of sheared sand and clay. A microscopic study of fault-zone samples shows that grain-scale mixing can lead to thickening of the low permeability smears, which may lead to resealing of holes.

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

Geosciences ◽  
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.

scholarly journals Statistical Analysis of Displacement and Length Relation for Normal Faults in the Barents Sea

Geosciences ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 421
Author(s):  
Dmitriy Kolyukhin ◽  
Anita Torabi ◽  
Audun Libak ◽  
Behzad Alaei ◽  
Tatiana Khachkova
Keyword(s):  
Statistical Analysis ◽  
Linear Regression ◽  
Barents Sea ◽  
Segment Length ◽  
Normal Faults ◽  
Scaling Relations ◽  
3D Seismic ◽  
The Barents Sea ◽  
Regression Parameters ◽  
Fault Length

This paper is devoted to the statistical analysis of dependence between fault length (L) and displacement (D). The main purpose of this work is to study the scaling relations between fault length and displacement using a database that includes datasets of 21 faults with geometric data extracted from 3D seismic coherence cubes of the Norwegian Barents Sea. Multiple linear regression and Bayesian and Akaike information criterions are applied to obtain optimal regression parameters. Our dataset is unique since it includes segment lengths of individual faults, unlike the previously published datasets. Hence, we studied both the dependence of fault segment length and accumulated fault length on displacement. The latter relation (accumulated fault length versus displacement) shows a general agreement (positive correlation and power-law relation) with the previously published results that are mainly obtained from outcrop studies, although the slopes vary for different lithologies. The differences could be attributed to the unique characteristics of our dataset that includes data of all segment lengths of individual faults.

scholarly journals Seismic and Geodetic Imaging (DInSAR) Investigation of the March 2021 Strong Earthquake Sequence in Thessaly, Central Greece

Geosciences ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 311
Author(s):  
Gerassimos A. Papadopoulos ◽  
Apostolos Agalos ◽  
Andreas Karavias ◽  
Ioanna Triantafyllou ◽  
Issaak Parcharidis ◽  
...  
Keyword(s):  
Moment Tensor ◽  
Normal Fault ◽  
Surface Subsidence ◽  
Ground Subsidence ◽  
Fault Models ◽  
Strong Earthquakes ◽  
Fault Segment ◽  
Central Greece ◽  
Seismic Slip ◽  
Instrumental Period

Three strong earthquakes ruptured the northwest Thessaly area, Central Greece, on the 3, 4 and 12 March 2021. Since the area did not rupture by strong earthquakes in the instrumental period of seismicity, it is of great interest to understand the seismotectonics and source properties of these earthquakes. We combined relocated hypocenters, inversions of teleseismic P-waveforms and of InSAR data, and moment tensor solutions to produce three fault models. The first shock (Mw = 6.3) occurred in a fault segment of strike 314° and dip NE41°. It caused surface subsidence −40 cm and seismic slip 1.2–1.5 m at depth ~10 km. The second earthquake (Mw = 6.2) occurred to the NW on an antithetic subparallel fault segment (strike 123°, dip SW44°). Seismic slip of 1.2 m occurred at depth of ~7 km, while surface subsidence −10 cm was determined. Possibly the same fault was ruptured further to the NW on 12 March (Mw = 5.7, strike 112°, dip SSW42°) that caused ground subsidence −5 cm and seismic slip of 1.0 m at depth ~10 km. We concluded that three blind, unknown and unmapped so far normal fault segments were activated, the entire system of which forms a graben-like structure in the area of northwest Thessaly.

STRUCTURAL AND SEISMIC DEFORMATIONS ALONG NORMAL FAULTS IN THE EASTERN VENEZUELAN BASIN

Geophysics ◽  
1956 ◽  
Vol 21 (2) ◽  
pp. 368-387 ◽  
Author(s):  
Hans P. Laubscher
Keyword(s):  
Fault Zone ◽  
Normal Fault ◽  
Fault Zones ◽  
Fault Analysis ◽  
Structural Deformation ◽  
Normal Faults ◽  
Seismic Deformations ◽  
Structural Deformations ◽  
Fault Structures ◽  
Seismic Reflections

Seismic reflections in normal fault zones in the Eastern Venezuelan basin usually appear distorted. Studies of reflections over fault structures delineated by drilling indicate that this is due to the similar effects of two entirely different phenomena: 1. True structural deformation of beds on the downthrown side. 2. Purely seismic distortion of reflections from underneath the fault. Analysis indicates that the structural deformations form an integral part of the fault zone; the purely seismic distortion is caused by passage of the wave through this zone of deformation.

scholarly journals Past earthquake timing and magnitude along the Inglewood fault, Taranaki, New Zealand

1994 ◽  
Vol 27 (2) ◽  
pp. 155-162 ◽  
Author(s):  
A. G. Hull
Keyword(s):  
Volcanic Ash ◽  
Surface Displacement ◽  
Normal Fault ◽  
Historical Earthquakes ◽  
Normal Faults ◽  
Single Event ◽  
Ground Shaking ◽  
Large Earthquakes ◽  
Fault Length ◽  
Strong Ground

Several active normal faults in the onshore and offshore regions of Taranaki are capable of generating large earthquakes and associated strong ground shaking. Historical earthquakes are concentrated offshore of Cape Egmont, and no significant earthquakes have been detected along the major onshore surface faults. The northeaststriking Inglewood fault is a major onshore, southward-dipping normal fault. It has a known length of c. 20 km and an average scarp height of c. 3 m on landforms less than about 15,000 yrs old. Three subsurface excavations at two sites along the Inglewood fault about 15 km from New Plymouth have revealed three surface fault displacements during the last c. 13,000 years. Earthquakes resulting in about 1.2 m of surface displacement occurred at c. 3,500 radiocarbon yrs BP; between 4,000 and 9,000 radiocarbon yrs BP; and between 10,000 and 13,000 radiocarbon yrs BP, judged by the amount of vertical offset of dated volcanic ash layers. Based on average single-event fault slip values of 1.2-3.0 m and a fault length of 20-30 km, the estimated earthquake magnitudes associated with these past movements range from Mw 6.7 to 7.2.

Large near-surface block rotations at normal faults of the Iceland rift: Evolution of tectonic caves and dilatancy

Geology ◽  
2019 ◽  
Vol 47 (8) ◽  
pp. 781-785 ◽  
Author(s):  
Michael Kettermann ◽  
Christopher Weismüller ◽  
Christoph von Hagke ◽  
Klaus Reicherter ◽  
Janos L. Urai
Keyword(s):  
High Resolution ◽  
Plate Boundary ◽  
Normal Fault ◽  
Fault Zones ◽  
Normal Faults ◽  
Failure Zone ◽  
Near Surface ◽  
Modeling Studies ◽  
The Family ◽  
Aerial Vehicle

Abstract Surface ramps in normal fault zones of the Iceland plate boundary have been described in many studies, but their structure and evolution are not well understood. We show that surface ramps are manifestations of large tilted blocks (TBs) formed in dip relays of normal faults. Based on existing modeling studies, we propose three classes of TBs defined by kinematics and location of the hinge of the TB. TBs are considered a member of the family of fault relay structures that form near the surface, commonly, but not exclusively, in columnar basalts with orthotropic strength. We present high-resolution aerial vehicle–based observations of a representative set of normal faults in Iceland and compare these with geometric models we derived from modeling studies. We predict extensive tectonic cave (fluid conduit) systems under the TB, which interact with magma and groundwater flow. The general fault structure is dominated by large, subvertical open fractures reactivating cooling joints that are locally filled by basalt rubble. We propose the existence of a hybrid failure zone at larger depths before the effective vertical stress is sufficient to initiate shear fractures in intact basalt.

scholarly journals Mechanisms of clay smear formation in unconsolidated sediments – insights from 3D observations of excavated normal faults

2016 ◽  
Author(s):  
Michael Kettermann ◽  
Sebastian Thronberens ◽  
Oscar Juarez ◽  
Janos Lajos Urai ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Thickness Distribution ◽  
3D Structure ◽  
Normal Fault ◽  
Fault Zones ◽  
Unconsolidated Sediments ◽  
Normal Faults ◽  
Low Permeability ◽  
Lignite Mine ◽  
Log Normal ◽  
Open Cast

Abstract. Clay smears in normal faults can form seals for hydrocarbons and groundwater, and their prediction in the subsurface is an important problem in applied and basic geoscience. However, neither their complex 3D structure, nor their processes of formation or destruction are well understood, and outcrop studies to date are mainly 2D. We present a 3D study of an excavated normal fault with clay smear, together with both source layers, in unlithified sand and clay of the Hambach open cast lignite mine in Germany. The faults formed at a depth of 150 m, and have Shale Gouge Ratios between 0.1 and 0.3. The fault zones are layered, with sheared sand, sheared clay and tectonically mixed sand-clay gouge. Thickness of clay smears in two excavated fault zones of 1.8 and 3.8 m2 is approximately log-normal, with values between 5 mm and 5 cm, without holes. The 3D thickness distribution is heterogeneous. We show that clay smears are strongly affected by R- and R'-shears, mostly at the footwall side. These shears can locally cross and offset clay smears, forming holes in the clay smear, while thinning of the clay smear by shearing in the fault core is less important. Thinnest parts of the clay smears are often located close to source layer cutoffs. Locally, the clay smear consists of overlapping patches of sheared clay, separated by sheared sand. More commonly, it is one amalgamated zone of shared sand and clay. Microscopic study of fault zone samples shows that grain-scale mixing can lead to thickening of the low permeability smears, which may lead to resealing of holes.

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