A rheologic model for wet crust applied to strike-slip faults

Frederick M. Chester

doi:10.1029/95jb00313

Failure Analysis Of Buried Gas Pipelines Crossing Seismic Faults

Academic Perspective Procedia ◽

10.33793/acperpro.03.02.2 ◽

2020 ◽

Vol 3 (2) ◽

pp. 781-790

Author(s):

M. Rizwan Akram ◽

Ali Yesilyurt ◽

A.Can. Zulfikar ◽

F. Göktepe

Keyword(s):

Ground Deformation ◽

Warning System ◽

Strike Slip ◽

Gas Pipelines ◽

Steel Pipes ◽

Seismic Fault ◽

Fault Parameters ◽

Dip Angle ◽

Permanent Ground Deformation ◽

Recent Earthquakes

Research on buried gas pipelines (BGPs) has taken an important consideration due to their failures in recent earthquakes. In permanent ground deformation (PGD) hazards, seismic faults are considered as one of the major causes of BGPs failure due to accumulation of impermissible tensile strains. In current research, four steel pipes such as X-42, X-52, X-60, and X-70 grades crossing through strike-slip, normal and reverse seismic faults have been investigated. Firstly, failure of BGPs due to change in soil-pipe parameters have been analyzed. Later, effects of seismic fault parameters such as change in dip angle and angle between pipe and fault plane are evaluated. Additionally, effects due to changing pipe class levels are also examined. The results of current study reveal that BGPs can resist until earthquake moment magnitude of 7.0 but fails above this limit under the assumed geotechnical properties of current study. In addition, strike-slip fault can trigger early damage in BGPs than normal and reverse faults. In the last stage, an early warning system is proposed based on the current procedure.&nbsp;

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Zircon geochronology and paleomagnetism of an Archean harzburgite intrusion, eastern Bighorn Mountains, Wyoming

The Mountain Geologist ◽

10.31582/rmag.mg.57.1.21 ◽

2020 ◽

Vol 57 (1) ◽

pp. 21-40

Author(s):

Alexandra Wallenberg ◽

Michelle Dafov ◽

David Malone ◽

John Craddock

Keyword(s):

Hanging Wall ◽

Vertical Axis ◽

Shear Zones ◽

Strike Slip ◽

Zircon Geochronology ◽

Weighted Mean ◽

Mafic Complex ◽

Laramide Orogeny ◽

Axis Rotation ◽

Bighorn Mountains

A harzburgite intrusion, which is part of the trailside mafic complex) intrudes ~2900-2950 Ma gneisses in the hanging wall of the Laramide Bighorn uplift west of Buffalo, Wyoming. The harzburgite is composed of pristine orthopyroxene (bronzite), clinopyroxene, serpentine after olivine and accessory magnetite-serpentinite seams, and strike-slip striated shear zones. The harzburgite is crosscut by a hydrothermally altered wehrlite dike (N20°E, 90°, 1 meter wide) with no zircons recovered. Zircons from the harzburgite reveal two ages: 1) a younger set that has a concordia upper intercept age of 2908±6 Ma and a weighted mean age of 2909.5±6.1 Ma; and 2) an older set that has a concordia upper intercept age of 2934.1±8.9 Ma and a weighted mean age 2940.5±5.8 Ma. Anisotropy of magnetic susceptibility (AMS) was used as a proxy for magmatic intrusion and the harzburgite preserves a sub-horizontal Kmax fabric (n=18) suggesting lateral intrusion. Alternating Field (AF) demagnetization for the harzburgite yielded a paleopole of 177.7 longitude, -14.4 latitude. The AF paleopole for the wehrlite dike has a vertical (90°) inclination suggesting intrusion at high latitude. The wehrlite dike preserves a Kmax fabric (n=19) that plots along the great circle of the dike and is difficult to interpret. The harzburgite has a two-component magnetization preserved that indicates a younger Cretaceous chemical overprint that may indicate a 90° clockwise vertical axis rotation of the Clear Creek thrust hanging wall, a range-bounding east-directed thrust fault that accommodated uplift of Bighorn Mountains during the Eocene Laramide Orogeny.

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