scholarly journals Crustal stress regime in Italy

1997 ◽  
Vol 40 (3) ◽  
Author(s):  
P. Montone ◽  
A. Amato ◽  
A. Frepoli ◽  
M. T. Mariucci ◽  
M. Cesaro
Keyword(s):  
Horizontal Stress ◽  
Focal Mechanisms ◽  
Plate Motion ◽  
Stress Regime ◽  
Deep Wells ◽  
Stress Directions ◽  
Geothermal Wells ◽  
Borehole Breakouts ◽  
Well Data ◽  
Messina Strait

In order to obtain a reliable map of the present-day stress field in Italy, needed to better understand the active tectonic processes and to contribute to the assessment of seismic hazard, in 1992 we started to collect and analyze new data from borehole breakouts in deep oil and geothermal wells and focal mechanisms of earthquakes (2.5 < M <5) occurred in Italy between 1988 and 1995. From about 200 deep wells and 300 focal mechanisms analyzed to date, we infer that: the internal (SW) sector of the Northern Apenninic arc is extending with minimum compressional stress (Shmin) oriented ? ENE, while the external front is thrusting over the Adriatic foreland (Shmin ? NW-SE). The entire Southern Apennine is extending in NE direction (from the Tyrrhenian margin to the Apulian foreland) and compression (in the foredeep) is no longer active at the outer (NE) thrust front. Between these two arcs, an abrupt change in the tectonic regime is detected with directions of horizontal stress changing by as much as 90º in the external front, around latitude 430N. Along the Ionian side of the Calabrian arc the stress directions inferred from breakouts and focal mechanisms are scattered with a hint of rotation from N-S Shmin close to the Southern Apennines, to ~ E-W directions in the Messina Strait. In Sicily, a NW-SE direction of SHmax is evident in the Hyblean foreland, parallel to the direction of plate motion between Africa and Europe. A more complex pattern of stress directions is observed in the thrust belt zone, with rotations from the regional trend (NW í directed SHmax) to NE oriented SHmax. A predominant NW direction of SHmax is also detected in mainland Sicily from earthquake focal mechanisms, but no well data are available in this region. In the northern part of Sicily (Aeolian Islands) a ~N-S direction of SHmax is observed.

New Focal Mechanisms for the New England Region: Constrains on the Regional Stress Regime

1988 ◽  
Vol 59 (4) ◽  
pp. 183-187 ◽  
Author(s):  
John E. Ebel ◽  
Bruce R. Bouck
Keyword(s):  
New York ◽  
New England ◽  
Maximum Stress ◽  
Focal Mechanisms ◽  
Stress Regime ◽  
Axis Orientation ◽  
Regional Stress ◽  
Stress Directions ◽  
Minimum Stress ◽  
Range Of Values

Abstract Single-event focal mechanisms for fifteen earthquakes in New England and New York have been determined. Thirteen of these are new focal mechanisms, while two are redeterminations for events with previously reported solutions. The focal mechanisms display considerable scatter in P-axis orientation, as has been reported in earlier studies. Some areas within the region, such as central New Hampshire and northeastern Massachusetts, show locally consistent principal stress directions. Other areas, such as central Maine, do not. All but one or two of the new focal mechanisms have P-axis and T-axis orientations which fall within the range of values calculated by Gephart and Forsyth (1985) for a regional stress field of horizontal, E-W maximum stress and vertical minimum stress in New England.

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.

Present-day tectonic stress regime in Egypt and surrounding area based on inversion of earthquake focal mechanisms

2013 ◽  
Vol 81 ◽  
pp. 1-15 ◽  
Author(s):  
H.M. Hussein ◽  
K.M. Abou Elenean ◽  
I.A. Marzouk ◽  
I.M. Korrat ◽  
I.F. Abu El-Nader ◽  
...  
Keyword(s):  
Tectonic Stress ◽  
Focal Mechanisms ◽  
Surrounding Area ◽  
Stress Regime ◽  
Earthquake Focal Mechanisms

scholarly journals A new method for correcting temperature log profiles in low-enthalpy plays

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Sandra Schumacher ◽  
Inga Moeck
Keyword(s):  
Input Parameter ◽  
New Method ◽  
Geothermal Resources ◽  
The North ◽  
Deep Wells ◽  
Thermal Disturbance ◽  
Drilling Operations ◽  
Crucial Information ◽  
Well Data ◽  
Drilling Time

Abstract Temperature logs recorded shortly after drilling operations can be the only temperature information from deep wells. However, these measurements are still influenced by the thermal disturbance caused by drilling and therefore do not represent true rock temperatures. The magnitude of the thermal disturbance is dependent on many factors such as drilling time, logging procedure or mud temperature. However, often old well reports lack this crucial information so that conventional corrections on temperature logs cannot be performed. This impedes the re-evaluation of well data for new exploration purposes, e.g. for geothermal resources. This study presents a new method to correct log temperatures in low-enthalpy play types which only requires a knowledge of the final depth of the well as an input parameter. The method was developed and verified using existing well data from an intracratonic sedimentary basin, the eastern part of the North German Basin. It can be transferred to other basins with little or no adjustment.

Fractures in the northern plains, stream patterns, and the midcontinent stress field

1987 ◽  
Vol 24 (6) ◽  
pp. 1086-1097 ◽  
Author(s):  
Mel R. Stauffer ◽  
Don J. Gendzwill
Keyword(s):  
Stress Field ◽  
Horizontal Stress ◽  
The Body ◽  
North American Plate ◽  
Plate Motion ◽  
Viscous Drag ◽  
Near Surface ◽  
The North ◽  
Elastic Rebound ◽  
Western North Dakota

Fractures in Late Cretaceous to Late Pleistocene sediments in Saskatchewan, eastern Montana, and western North Dakota form two vertical, orthogonal sets trending northeast–southwest and northwest–southeast. The pattern is consistent, regardless of rock type or age (except for concretionary sandstone). Both sets appear to be extensional in origin and are similar in character to joints in Alberta. Modem stream valleys also trend in the same two dominant directions and may be controlled by the underlying fractures.Elevation variations on the sub-Mannville (Early Cretaceous) unconformity form a rectilinear pattern also parallel to the fracture sets, suggesting that fracturing was initiated at least as early as Late Jurassic. It may have begun earlier, but there are insufficient data at present to extend the time of initiation.We interpret the fractures as the result of vertical uplift together with plate motion: the westward drift of North America. The northeast–southwest-directed maximum principal horizontal stress of the midcontinent stress field is generated by viscous drag effects between the North American plate and the mantle. Vertical uplift, erosion, or both together produce a horizontal tensile state in near-surface materials, and with the addition of a directed horizontal stress through plate motion, vertical tension cracks are generated parallel to that horizontal stress (northeast–southwest). Nearly instantaneous elastic rebound results in the production of second-order joints (northwest–southeast) perpendicular to the first. In this manner, the body of rock is being subjected with time to complex alternation of northeast–southwest and northwest–southeast horizontal stresses, resulting in the continuous and contemporaneous production of two perpendicular extensional joint sets.

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.

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