Transfer of stress from the 2004 M w9.2 Sumatra subduction earthquake promoted widespread seismicity and large strike‐slip events in the Wharton Basin

Continual interaction between the Minahassa subduction interface and the Palu-Koro strike-slip fault in Sulawesi, Indonesia.

10.5194/egusphere-egu2020-9831 ◽

2020 ◽

Author(s):

Nicolai Nijholt ◽

Wim Simons ◽

Riccardo Riva

Keyword(s):

Subduction Zone ◽

Fault Zone ◽

Slip Rate ◽

Strike Slip ◽

Strike Slip Fault ◽

Model Calculations ◽

Transient Deformation ◽

Subduction Earthquake ◽

Bay Area ◽

Gnss Velocities

Two major fault systems host Mw>7 earthquakes in Central and Northern Sulawesi, Indonesia: the Minahassa subduction interface and the Palu-Koro strike-slip fault. The Celebes Sea oceanic lithosphere subducts beneath the north arm of Sulawesi at the Minahassa subduction zone. At the western termination of the Minahassa subduction zone, it connects to the left-lateral Palu-Koro strike-slip fault zone. This fault strikes onshore at Palu Bay and then crosses Sulawesi. Interseismic GNSS velocities indicate that the Palu-Koro fault zone accommodates about 4 cm/yr of relative motion in the Palu Bay area, with a ~10 km locking depth. This shallowly locked segment of the Palu-Koro fault around the Palu Bay area ruptured during the devastating, tsunami-generating, 2018 Mw7.5 Palu earthquake. This complex event highlights the high seismic hazard for the island of Sulawesi.We have a >20-year record of GNSS velocities on Sulawesi, where the densest cluster of monument sites surrounds the Palu-Koro fault, specifically around Palu Bay, whereas the rest of the island is less densely covered. High quality estimates of interseismic velocities reveal second-order complex patterns of transient deformation in the wake of major earthquakes: the velocities in northern Sulawesi and around the Palu-Koro fault do not follow their interseismic trends after a major subduction earthquake has occurred, for several years after the event. This effect of transient deformation reaches more than 400km away from the epicentre of the major earthquakes. Surprisingly, a deviation from the background slip rate on the Palu-Koro fault is not accompanied by a deviation from the background (micro)seismic activity.We construct a 3D numerical model based on the structural and seismological data in the Sulawesi region. We investigate the post-seismic relaxation pattern from a subduction earthquake and determine whether the slip rate on the Palu-Koro fault changes due to this earthquake through forward model calculations. With a modelling focus on the 1996 Mw7.9 and 2008 Mw7.4 earthquakes that ruptured the Minahassa subduction interface, this study outlines the triggering of transient deformation and continual interaction between the Minahassa subduction interface and the Palu-Koro strike-slip fault.

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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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