Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano

1989 ◽  
Vol 126 (6) ◽  
pp. 659-673 ◽  
Author(s):  
Håvard Gautneb ◽  
Agust Gudmundsson ◽  
Niels Oskarsson
Keyword(s):  
Stress Field ◽  
Magma Chamber ◽  
Host Rock ◽  
Local Stress ◽  
Mature Stage ◽  
Central Volcano ◽  
Shallow Magma Chamber ◽  
The Common ◽  
Crustal Magma ◽  
Local Stress Field

AbstractStrike, dip, and thickness were measured for 504 sheets (inclined sheets and dykes) in the 4–6 Ma old Hafnarfjall central volcano in southwest Iceland. The average dip of sheets is 65°, 80% are less than 1.2 m thick, and the thickness tends to decrease with decreasing dip. In 0.5 km long traverses perpendicular to the average strike of sheets, the percentage of sheets ranges from about 6 to 11.Of 140 chemically analysed sheets most are quartz-tholeiites; a few are intermediate or acid. The sheets are chemically more evolved than the host rock and were generated by a shallow crustal magma chamber at a mature stage of the central volcano, whereas the host rock was generated earlier before the chamber was established. Trace element results suggest that the sheet magmas evolved by low-pressure fractional crystallization as well as by mixing of primitive magmas and crustal melts.A model is proposed where most of the sheets are generated by a growing shallow magma chamber. As the chamber grows its shape changes, and so does the local stress field associated with it. Because the sheets follow the stress trajectories of the local stress field, the potential pathways of the sheets change with the growth of the chamber, which may explain the common occurrence of cross-cutting sheets. From the evolved chemistry of the sheets, as well as from the pattern of the stress trajectories, it is concluded that the bulk of the sheets were injected from the upper part of the shallow magma chamber.

scholarly journals Activation of optimally and unfavourably oriented faults in a uniform local stress field during the 2011 Prague, Oklahoma, sequence

2020 ◽  
Vol 222 (1) ◽  
pp. 153-168 ◽  
Author(s):  
Elizabeth S Cochran ◽  
Robert J Skoumal ◽  
Devin McPhillips ◽  
Zachary E Ross ◽  
Katie M Keranen
Keyword(s):  
Stress Field ◽  
Compressive Stress ◽  
Local Stress ◽  
Wastewater Disposal ◽  
Principal Compressive Stress ◽  
Vertical Fault ◽  
Major Fault ◽  
Pressure Changes ◽  
Earthquake Sequences ◽  
Local Stress Field

SUMMARY The orientations of faults activated relative to the local principal stress directions can provide insights into the role of pore pressure changes in induced earthquake sequences. Here, we examine the 2011 M 5.7 Prague earthquake sequence that was induced by nearby wastewater disposal. We estimate the local principal compressive stress direction near the rupture as inferred from shear wave splitting measurements at spatial resolutions as small as 750 m. We find that the dominant azimuth observed is parallel to previous estimates of the regional compressive stress with some secondary azimuths oriented subparallel to the strike of the major fault structures. From an extended catalogue, we map ten distinct fault segments activated during the sequence that exhibit a wide array of orientations. We assess whether the five near-vertical fault planes are optimally oriented to fail in the determined stress field. We find that only two of the fault planes, including the M   5.7 main shock fault, are optimally oriented. Both the M 4.8 foreshock and M   4.8 aftershock occur on fault planes that deviate 20–29° from the optimal orientation for slip. Our results confirm that induced event sequences can occur on faults not optimally oriented for failure in the local stress field. The results suggest elevated pore fluid pressures likely induced failure along several of the faults activated in the 2011 Prague sequence.

A simplified method to predict the local stress field and N-SIF of V-shaped notch

2020 ◽  
Vol 234 ◽  
pp. 107096 ◽  
Author(s):  
Wei Shen ◽  
Guiming Liang ◽  
Chunmei Li ◽  
Enqian Liu
Keyword(s):  
Stress Field ◽  
Local Stress ◽  
Simplified Method ◽  
Local Stress Field

Seismic anisotropy time variations at Mt Etna

2019 ◽  
Vol 220 (1) ◽  
pp. 450-460
Author(s):  
Lucia Nardone ◽  
Francesca Bianco ◽  
Lucia Zaccarelli ◽  
Domenico Patanè
Keyword(s):  
Time Delay ◽  
Stress Field ◽  
Shear Wave ◽  
Local Stress ◽  
Temporal Variations ◽  
Fast Wave ◽  
Polarization Direction ◽  
Stress Changes ◽  
Mt Etna ◽  
Local Stress Field

SUMMARY The aim of this paper is to study the temporal variations in the seismic wavefield associated with the stress changes in the dynamic features of the Mt Etna volcanic activity. We used shear wave splitting analysis on a huge data set of local earthquakes, in order to identify changes of the local stress field at Mt Etna during the time interval from 2006 to 2011. This analysis allows us to obtain two parameters: the polarization direction of the fast shear wave (φ) and the time delay of the slow shear wave (Td,time delay between the split shear waves). Orientation of φ generally provides information about the anisotropic symmetry and stress direction whereas Td provide information about the average crack density along the ray path. Based on our findings it is possible to divide Etna Volcano in three different sectors, each one distinguished by typical fast wave polarization direction. We find that the western part of the volcano is controlled by the regional tectonic stress field having a NS and EW directions. Instead, the eastern part of the volcano is mainly controlled by the local volcanic stress, particularly an EW local stress field in the NE sector (Pernicana), and a quasi NS local stress field in the SE sector (Mascalucia, Timpe), where previous studies evidenced: (i) some low-Qp anomaly regions between 0 and about 6 km depth, probably associated with high pore pressure and the intense faulting and (ii) by magnetotelluric surveys, several high conductivity zones, up to 8 km depth, related to a diffuse presence of hydrothermal activity and fluid circulation. Temporal variations in time delay, mostly before the 2008–2009 lateral eruption, can be interpreted as stress accumulation increase with a consequent release of stress due to coalescing of microcracks in the conduit for the eruption of magma.

2D thermo-mechanical-chemical coupled numerical models of interactions between a cooling magma chamber and a visco-elastic host rock

2020 ◽  
Author(s):  
Dániel Kiss ◽  
Evangelos Moulas ◽  
Lisa Rummel ◽  
Boris Kaus
Keyword(s):  
Magma Chamber ◽  
Host Rock ◽  
Numerical Models ◽  
Bulk Composition ◽  
Inertial Forces ◽  
Volume Changes ◽  
Consistent System ◽  
Host Rocks ◽  
2D Numerical Model ◽  
Crustal Magma

<p>A recent focus of studies in geodynamic modeling and magmatic petrology is to understand the coupled behavior between deformation and magmatic processes. Here, we present a 2D numerical model of an upper crustal magma (or mush) chamber in a visco-elastic host rock, with coupled thermal, mechanical and chemical (TMC) processes. The magma chamber is isolated from deeper sources of magma and it is cooling, and thus shrinking. We quantify the mechanical interaction between the shrinking magma chamber and the surrounding host rock, using a compressible visco-elastic formulation, considering several geometries of the magma chamber.</p><p>We present a self-consistent system of the conservation equations for coupled TMC processes, under the assumptions of slow (negligible inertial forces), visco-elastic deformation and constant chemical bulk composition. The thermodynamic melting/crystallization model is based on a pelitic melting model calculated with Perple_X, assuming a granitic composition and is incorporated as a look-up table. We will discuss the numerical implementation, show the results of systematic numerical simulations, and illustrate the effect of volume changes due to crystallization on stresses in the host rocks.</p>

Modeling the local stress field and kinematics of the San Andreas fault system

1979 ◽  
Vol 52 (1-4) ◽  
pp. 647-663 ◽  
Author(s):  
D.N. Osokina ◽  
A.A. Nikonov ◽  
N.Yu. Tsvetkova
Keyword(s):  
Stress Field ◽  
San Andreas Fault ◽  
Local Stress ◽  
Fault System ◽  
San Andreas ◽  
San Andreas Fault System ◽  
Local Stress Field

Size Dependent Micro-Stress-Field of Fibers in Eutectic Ceramic Rod

2010 ◽  
Vol 168-170 ◽  
pp. 226-229
Author(s):  
Hai Xing Lu ◽  
Xie Quan Liu ◽  
Xin Hua Ni ◽  
Tao Sun ◽  
Bao Feng Li
Keyword(s):  
Stress Field ◽  
Local Stress ◽  
Apparent Size ◽  
Average Strain ◽  
Size Dependent ◽  
Three Phase ◽  
Stress Boundary Condition ◽  
Stress Boundary ◽  
Remote Stress ◽  
Local Stress Field

Considering the interaction between fiber-inclusion and strong constraining interphase, forth-phase model is suggested to determine the local stress field distribution of three-phase element in eutectic ceramic rod. On the basis of the volumetric average strain, the effective compliance tensor increment of eutectic ceramic rod is obtained. The remote stress boundary condition of the eutectic ceramic rod is accounted for getting the micro stress field of fibers in eutectic ceramic rod. The results show the micro stress field of the fiber-inclusion in eutectic ceramic rod is associated with the stiffness and the volume fractions of each component in eutectic ceramic rod, the shape of interphase and fiber. The micro stress field has apparent size effect: three direction stresses increase with the diameter of fiber- inclusion.

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