Fault kinematic investigations along the Panchkula-Morni region, NW Himalaya, India

2020 ◽  
Author(s):  
Ajay Kumar ◽  
Soumyajit Mukherjee ◽  
Mohamedharoon A. Shaikh ◽  
Seema Singh
Keyword(s):  
Fault Plane ◽  
Regional Scale ◽  
Fault Slip ◽  
Fault System ◽  
Inversion Algorithm ◽  
Stress Regime ◽  
Kinematic Indicators ◽  
Kinematic Evolution ◽  
Slip Planes ◽  
Paleostress Inversion

<p>The Morni hills located in the north-western Himalaya in Panchkula district, Haryana has undergone poly-phase deformation owing to its complex tectonic history. In order to better understand the kinematic evolution of study area, detailed structural analyses of the fault system at regional-scale is carried out. We perform paleostress analyses on the collected fault-slip data to derive the paleostress tensors. The fault-slip data includes attitudes of fault planes and slickenside lineations, and the sense of slip along the fault plane determined by observing various kinematic indicators. The study area mainly exposes compacted, fine- to medium-grained calcareous sandstones belonging to the lower Siwalik formation in the Himalayan foreland basin. The exposed sandstones contain numerous striated slip planes of varying slip-sense. As the fault planes are intra-formational and exposed in uniform lithology, sense of slip cannot be determined through offset markers. In such cases, the sense of slip of the fault plane is determined solely by observing various slickenside kinematic indicators and fracture types developed on the faulted surface. The slickenside kinematic indicators e.g., calcite mineral steps were found useful in deciphering the sense of movement of each of the slip plane. The paleostress inversion of fault-slip data was carried out by applying the open source software T-Tecto studio X5 to obtain the reduced stress tensor. The Paleostress inversion algorithm called the Right Dihedral Method (RDM) is executed to estimate the principal stress axes orientations. Temporally, the slip planes may have reactivated multiple times preserving multiple slickenside orientations superimposing one another. Such fault-slip data are called heterogeneous and therefore, multiple stress states are deduced to explain the heterogeneous fault-slip data. The paleostress analysis results indicate stress regime index (R’) range 1.25–2.25 and 0.20–1.00 suggesting pure strike-slip to transpressive and pure extensive to transtensive stress regime respectively prevailing in the study area.</p>

scholarly journals A functional tool to explore the reliability of micro-earthquake focal mechanism solution for seismotectonic purposes

2021 ◽  
Author(s):  
Guido Maria Adinolfi ◽  
Raffaella De Matteis ◽  
Rita De Nardis ◽  
Aldo Zollo
Keyword(s):  
Focal Mechanism ◽  
Fault Plane ◽  
Focal Mechanisms ◽  
Seismic Network ◽  
Fault System ◽  
Focal Mechanism Solution ◽  
Fault Plane Solutions ◽  
Stress Regime ◽  
Focal Mechanism Solutions ◽  
Earthquake Focal Mechanism

Abstract. Improving the knowledge of seismogenic faults requires the integration of geological, seismological, and geophysical information. Among several analyses, the definition of earthquake focal mechanisms plays an essential role in providing information about the geometry of individual faults and the stress regime acting in a region. Fault plane solutions can be retrieved by several techniques operating in specific magnitude ranges, both in the time and frequency domain and using different data. For earthquakes of low magnitude, the limited number of available data and their uncertainties can compromise the stability of fault plane solutions. In this work, we propose a useful methodology to evaluate how well a seismic network used to monitor natural and/or induced micro-seismicity estimates focal mechanisms as function of magnitude, location, and kinematics of seismic source and consequently their reliability in defining seismotectonic models. To study the consistency of focal mechanism solutions, we use a Bayesian approach that jointly inverts the P/S long-period spectral-level ratios and the P polarities to infer the fault-plane solutions. We applied this methodology, by computing synthetic data, to the local seismic network operated in the Campania-Lucania Apennines (Southern Italy) to monitor the complex normal fault system activated during the Ms 6.9, 1980 earthquake. We demonstrate that the method we propose can have a double purpose. It can be a valid tool to design or to test the performance of local seismic networks and more generally it can be used to assign an absolute uncertainty to focal mechanism solutions fundamental for seismotectonic studies.

scholarly journals Development of an inversion method to extract information on fault geometry from teleseismic data

2019 ◽  
Vol 220 (2) ◽  
pp. 1055-1065 ◽  
Author(s):  
Kousuke Shimizu ◽  
Yuji Yagi ◽  
Ryo Okuwaki ◽  
Yukitoshi Fukahata
Keyword(s):  
Fault Plane ◽  
Slip Rate ◽  
Rate Function ◽  
Fault Slip ◽  
Body Waves ◽  
Fault System ◽  
Inversion Method ◽  
Fault Geometry ◽  
Finite Fault ◽  
Extract Information

SUMMARY Teleseismic waveforms contain information on fault slip evolution during an earthquake, as well as on the fault geometry. A linear finite-fault inversion method is a tool for solving the slip-rate function distribution under an assumption of fault geometry as a single or multiple-fault-plane model. An inappropriate assumption of fault geometry would tend to distort the solution due to Green’s function modelling errors. We developed a new inversion method to extract information on fault geometry along with the slip-rate function from observed teleseismic waveforms. In this method, as in most previous studies, we assumed a flat fault plane, but we allowed arbitrary directions of slip not necessarily parallel to the assumed fault plane. More precisely, the method represents fault slip on the assumed fault by the superposition of five basis components of potency-density tensor, which can express arbitrary fault slip that occurs underground. We tested the developed method by applying it to real teleseismic P waveforms of the MW 7.7 2013 Balochistan, Pakistan, earthquake, which is thought to have occurred along a curved fault system. The obtained spatiotemporal distribution of potency-density tensors showed that the focal mechanism at each source knot was dominated by a strike-slip component with successive strike angle rotation from 205° to 240° as the rupture propagated unilaterally towards the south-west from the epicentre. This result is consistent with Earth’s surface deformation observed in optical satellite images. The success of the developed method is attributable to the fact that teleseismic body waves are not very sensitive to the spatial location of fault slip, whereas they are very sensitive to the direction of fault slip. The method may be a powerful tool to extract information on fault geometry along with the slip-rate function without requiring detailed assumptions about fault geometry.

Fault slip envelope: A new parametric investigation tool for fault system strength and slip

2020 ◽  
Author(s):  
Roger Soliva ◽  
Frantz Maerten ◽  
Laurent Maerten ◽  
Jussi Mattila
Keyword(s):  
Mechanical Properties ◽  
Fault Slip ◽  
Fault System ◽  
Nuclear Waste Repository ◽  
Computation Method ◽  
Strength Anisotropy ◽  
Stress Regime ◽  
Fault Systems ◽  
Geological Conditions ◽  
Wide Range

<p>The fact that inherited fault systems show strong variability in their 3D shape provides good reasons to consider the strength of the Earth’s brittle crust as variably anisotropic. In this work we quantify this strength anisotropy as a function of fault system complexity by combining 3D boundary element model, frictional slip theory and fast iterative computation method. This method allows to analyze together a very large number of scenarios of stress and fault mechanical properties variations through space and time. Using both synthetic and real fault system geometries we analyze a very large number of numerical simulations (125,000) to define for the first time macroscopic rupture envelopes for fault systems, referred to as “fault slip envelopes”. Fault slip envelopes are defined using variable friction, cohesion and stress state, and their shape is directly related to the fault system 3D geometry and the friction coefficient on fault surfaces. The obtained fault slip envelopes shows that very complex fault geometry implies low and isotropic strength of the fault system compared to geometry having limited fault orientations relative to the remote stresses, providing strong strength anisotropy. This technique is applied to the realistic geological conditions of the Olkiluoto high-level nuclear waste repository (Finland). The model results suggests that Olkiluoto fault system has a better probability to slip under the present day Andersonian thrust stress regime, than for the strike-slip and normal stress regimes expected in the future due to the probable presence of an ice sheet. This new tool allows to quantify the anisotropy of strength and probability of slip of 3D real fault networks as a function of a wide range of possible geological conditions an mechanical properties. This significantly helps to define the most conservative fault slip hazard case or to account for potential uncertainties in the input data for slip. This technique therefore applies to earthquakes hazard studies, geological storage, geothermal resources along faults and fault leaks/seals in geological reservoirs.</p>

scholarly journals A functional tool to explore the reliability of micro-earthquake focal mechanism solutions for seismotectonic purposes

Solid Earth ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 65-83
Author(s):  
Guido Maria Adinolfi ◽  
Raffaella De Matteis ◽  
Rita de Nardis ◽  
Aldo Zollo
Keyword(s):  
Focal Mechanism ◽  
Fault Plane ◽  
Normal Fault ◽  
Focal Mechanisms ◽  
Seismic Network ◽  
Fault System ◽  
Fault Plane Solutions ◽  
Stress Regime ◽  
Focal Mechanism Solutions ◽  
Earthquake Focal Mechanism

Abstract. Improving the knowledge of seismogenic faults requires the integration of geological, seismological, and geophysical information. Among several analyses, the definition of earthquake focal mechanisms plays an essential role in providing information about the geometry of individual faults and the stress regime acting in a region. Fault plane solutions can be retrieved by several techniques operating in specific magnitude ranges, both in the time and frequency domain and using different data. For earthquakes of low magnitude, the limited number of available data and their uncertainties can compromise the stability of fault plane solutions. In this work, we propose a useful methodology to evaluate how well a seismic network, used to monitor natural and/or induced micro-seismicity, estimates focal mechanisms as a function of magnitude, location, and kinematics of seismic source and consequently their reliability in defining seismotectonic models. To study the consistency of focal mechanism solutions, we use a Bayesian approach that jointly inverts the P/S long-period spectral-level ratios and the P polarities to infer the fault plane solutions. We applied this methodology, by computing synthetic data, to the local seismic network operating in the Campania–Lucania Apennines (southern Italy) aimed to monitor the complex normal fault system activated during the Ms 6.9, 1980 earthquake. We demonstrate that the method we propose is effective and can be adapted for other case studies with a double purpose. It can be a valid tool to design or to test the performance of local seismic networks, and more generally it can be used to assign an absolute uncertainty to focal mechanism solutions fundamental for seismotectonic studies.

scholarly journals Present-day stress state in northwestern Syria

2020 ◽  
Vol 59 (4) ◽  
pp. 299-316
Author(s):  
Mohamad Khir Abdul-Wahed ◽  
Mohammed ALISSA
Keyword(s):  
Fault Plane ◽  
Eastern Mediterranean ◽  
Active Faults ◽  
Plate Boundary ◽  
Shear Zones ◽  
Stress Pattern ◽  
P Wave ◽  
Fault System ◽  
Fault Plane Solutions ◽  
Stress Regime

Northwestern Syria is a key area in the eastern Mediterranean to study the active tectonics and stress pattern across the Arabia-Eurasia convergent plate boundary. This study aims to outline the present-day stress regime in this region of Syria using the fault plane solutions of the largest events recorded by the Syrian National Seismological Network from 1995 to 2011. A dataset of fault-plane solutions was obtained for 48 events having at least 5 P-wave polarities. The tectonic regime for most of these events is extensional and produces normal mechanisms in agreement with the local configurations of the seismogenic faults in the region. Strike-slip mechanisms are more scarce and restricted to certain areas, such as the northern extension of the Dead Sea fault system. The results of the current study reveal the spatial variations of SHmax orientation across the northwestern Syria region. This spatial variation of the present-day stress field highlights the role of main geometrically complex shear zones in the present-day stress pattern of northwestern Syria. However, these results show, regardless of the relatively small magnitudes of the studied events, they provide a picture of the local stress deviations that have currently been taking place along the local active faults.

scholarly journals Fault slip envelope: a new parametric investigation tool for fault slip based on geomechanics and 3-D fault geometry

Solid Earth ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 1141-1154
Author(s):  
Roger Soliva ◽  
Frantz Maerten ◽  
Laurent Maerten ◽  
Jussi Mattila
Keyword(s):  
Earthquake Hazard ◽  
Fault Slip ◽  
Fault System ◽  
Nuclear Waste Repository ◽  
Computation Method ◽  
Fault Geometry ◽  
Stress Regime ◽  
Geothermal Resources ◽  
Geological Conditions ◽  
Wide Range

Abstract. By combining a 3-D boundary element model, frictional slip theory, and fast computation method, we propose a new tool to improve fault slip analysis that allows the user to analyze a very large number of scenarios of stress and fault mechanical property variations through space and time. Using both synthetic and real fault system geometries, we analyze a very large number of numerical simulations (125 000) using a fast iterative method to define for the first time macroscopic rupture envelopes for fault systems, referred to as “fault slip envelopes”. Fault slip envelopes are defined using variable friction, cohesion, and stress state, and their shape is directly related to the fault system 3-D geometry and the friction coefficient on fault surfaces. The obtained fault slip envelopes show that very complex fault geometry implies low and isotropic strength of the fault system compared to geometry having limited fault orientations relative to the remote stresses, providing strong strength anisotropy. This technique is applied to the realistic geological conditions of the Olkiluoto high-level nuclear waste repository (Finland). The model results suggest that the Olkiluoto fault system has a better ability to slip under the present-day Andersonian thrust stress regime than for the strike-slip and normal stress regimes expected in the future due to the probable presence of an ice sheet. This new tool allows the user to quantify the anisotropy of strength of 3-D real fault networks as a function of a wide range of possible geological conditions and mechanical properties. This can be useful to define the most conservative fault slip hazard case or to account for potential uncertainties in the input data for slip. This technique therefore applies to earthquake hazard studies, geological storage, geothermal resources along faults, and fault leaks or seals in geological reservoirs.

scholarly journals 20 July 2017 Bodrum-Kos Earthquake (Mw:6.6) in southwestern Anatolia, Turkey

2021 ◽  
Vol 25 (3) ◽  
pp. 309-321
Author(s):  
Semir Över ◽  
Süha Özden ◽  
Esra Kalkan Ertan ◽  
Fatih Turhan ◽  
Zeynep Coşkun ◽  
...  
Keyword(s):  
Fault Plane ◽  
Regional Scale ◽  
Aegean Sea ◽  
Horizontal Stress ◽  
Focal Mechanisms ◽  
Stress Axis ◽  
Small Scale ◽  
Normal Type ◽  
Fault Plane Solutions ◽  
Stress Regime

In the Aegean Sea, the western part of Gökova Gulf, Kos and Bodrum were struck by a 6.6 (Mw) earthquake on July 20, 2017. The fault plane solution for the main shock shows an E-W striking normal type fault with approximately N-S (N4°E) tensional axis (T-axis). Fault plane solutions of 33 aftershocks show two groups of normal type fault with E-W and NE-SW to ENE-WSW orientations. The inversion of the focal mechanisms of the aftershocks yields two different normal faulting stress regimes: one is characterized by an approximately N-S (N5°E) σ3 axis (minimum horizontal stress axis). This extension is obtained from 13 focal mechanisms of aftershocks with approximately E-W direction. The other is characterized by approximately NW-SE (N330°E) σ3 axis. The latter is calculated from 21 seismic faults of aftershocks with approximately NE-SW direction. These aftershocks occurred on relatively small-scale faults that were directed from NE-SW to ENE-WSW, and possibly contributed to expansion of the basin in the west. The 24 focal mechanisms of earthquakes which occurred since 1933 in and around Gökova Basin are introduced into the inversion analysis to obtain the stress state effective in a wider region. The inversion yields an extensional stress regime characterized by an approximately N-S (N355°E) σ3 axis. The E-W directional metric faults, measured in the central part of Gökova Fault Zone bordering the Gökova Gulf in the north, also indicate N-S extension. The NE-SW extension obtained from NE-SW aftershocks appears to be more local and is responsible for the expansion of the western part of the asymmetric Gökova Basin. This N-S extension which appears to act on a regional-scale may be attributed to the geodynamic effects related to the combined forces of the southwestward extrusion of Anatolia and the roll-back process of African subduction beneath Anatolia.

scholarly journals Fault slip envelope: A new parametric investigation tool for fault slip based on geomechanics and 3D fault geometry

2019 ◽  
Author(s):  
Roger Soliva ◽  
Frantz Maerten ◽  
Laurent Maerten ◽  
Jussi Mattila
Keyword(s):  
Mechanical Properties ◽  
Fault Slip ◽  
Fault System ◽  
Nuclear Waste Repository ◽  
Computation Method ◽  
Fault Geometry ◽  
Stress Regime ◽  
Geothermal Resources ◽  
Geological Conditions ◽  
Wide Range

Abstract. By combining 3D boundary element model, frictional slip theory and fast computation method, we propose a new tool to improve fault slip analysis that allows to analyze a very large number of scenarios of stress and fault mechanical properties variations through space and time. Using both synthetic and real fault system geometries we analyze a very large number of numerical simulations (125,000) using fast iterative method to define for the first time macroscopic rupture envelopes for fault systems, referred to as “fault slip envelopes”. Fault slip envelopes are defined using variable friction, cohesion and stress state, and their shape is directly related to the fault system 3D geometry and the friction coefficient on fault surfaces. The obtained fault slip envelopes shows that very complex fault geometry implies low and isotropic strength of the fault system compared to geometry having limited fault orientations relative to the remote stresses, providing strong strength anisotropy. This technique is applied to the realistic geological conditions of the Olkiluoto high-level nuclear waste repository (Finland). The model results suggests that Olkiluoto fault system has a better probability to slip under the present day Andersonian thrust stress regime, than for the strike-slip and normal stress regimes expected in the future due to the probable presence of an ice sheet. This new tool allows to quantify the anisotropy of strength and probability of slip of 3D real fault networks as a function of a wide range of possible geological conditions an mechanical properties. This significantly helps to define the most conservative fault slip hazard case or to account for potential uncertainties in the input data for slip. This technique therefore applies to earthquakes hazard studies, geological storage, geothermal resources along faults and fault leaks/seals in geological reservoirs.

Microearthquake seismicity and tectonics of Coastal Northern California

1970 ◽  
Vol 60 (5) ◽  
pp. 1669-1699 ◽  
Author(s):  
Leonardo Seeber ◽  
Muawia Barazangi ◽  
Ali Nowroozi
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
San Andreas Fault ◽  
High Gain ◽  
Strike Slip ◽  
Fault System ◽  
Northern California ◽  
Fault Plane Solutions ◽  
Sharp Bend ◽  
San Andreas

Abstract This paper demonstrates that high-gain, high-frequency portable seismographs operated for short intervals can provide unique data on the details of the current tectonic activity in a very small area. Five high-frequency, high-gain seismographs were operated at 25 sites along the coast of northern California during the summer of 1968. Eighty per cent of 160 microearthquakes located in the Cape Mendocino area occurred at depths between 15 and 35 km in a well-defined, horizontal seismic layer. These depths are significantly greater than those reported for other areas along the San Andreas fault system in California. Many of the earthquakes of the Cape Mendocino area occurred in sequences that have approximately the same magnitude versus length of faulting characteristics as other California earthquakes. Consistent first-motion directions are recorded from microearthquakes located within suitably chosen subdivisions of the active area. Composite fault plane solutions indicate that right-lateral movement prevails on strike-slip faults that radiate from Cape Mendocino northwest toward the Gorda basin. This is evidence that the Gorda basin is undergoing internal deformation. Inland, east of Cape Mendocino, a significant component of thrust faulting prevails for all the composite fault plane solutions. Thrusting is predominant in the fault plane solution of the June 26 1968 earthquake located along the Gorda escarpement. In general, the pattern of slip is consistent with a north-south crustal shortening. The Gorda escarpment, the Mattole River Valley, and the 1906 fault break northwest of Shelter Cove define a sharp bend that forms a possible connection between the Mendocino escarpment and the San Andreas fault. The distribution of hypocenters, relative travel times of P waves, and focal mechanisms strongly indicate that the above three features are surface expressions of an important structural boundary. The sharp bend in this boundary, which is concave toward the southwest, would tend to lock the dextral slip along the San Andreas fault and thus cause the regional north-south compression observed at Cape Mendocino. The above conclusions support the hypothesis that dextral strike-slip motion along the San Andreas fault is currently being taken up by slip along the Mendocino escarpment as well as by slip along northwest trending faults in the Gorda basin.

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