LP10-SCI Fault G08 Richmindale PDF

Fault Science Course: G08-SCI-L10 Revision 0, updated on May 1, 2021 Form 5050 rev 0 | www.richmindale.com/standards/forms Richmindale® is a trademark of Richmindal...

Fault Science Course: G08-SCI-L10 Revision 0, updated on May 1, 2021 Form 5050 rev 0 | www.richmindale.com/standards/forms Richmindale® is a trademark of Richmindale College LLC, USA  Learning Outcomes Slide 2 At the end of this lecture the students are expected to: Use models or illustrations, explain how movements along faults generate earthquakes G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Earthquakes and Faults Slide 3 https://youtu.be/4Y55LUv6lN4?si=VbYWB7nXVLWCu_IM Richmindale® is a trademark of Richmindale College LLC, USA Fault Slide 4 The word “fault” refers to a defect. There may be greater defect than the San Andreas Fault across California. If the blocks of rock on one or both sides of a fracture move, the fracture is called a fault. Sudden motions along faults cause rocks to break and move suddenly. The energy released is an earthquake. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Fault Slide 5 The San Andreas Fault at Parkfield in central California. The person with the orange shirt is standing on the Pacific Plate and the person at the far side of the bridge is on the North American Plate. The bridge is designed to slide on its foundation. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Fault Slide 6 Schematic diagram of the India-Asia convergent boundary, showing examples of the types of faults along which earthquakes are focused. The devastating Nepal earthquake of May 2015 took place along one of these thrust faults. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Fault Slide 7 A fault (white dashed line) in intrusive rocks on Quadra Island, B.C. The pink dyke has been offset by the fault and the extent of the offset is shown by the white arrow (approximately 10 cm). Because the far side of the fault has moved to the right, this is a right-lateral fault. If the photo were taken from the other side, the fault would still appear to have a right-lateral offset. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA  Slip Slide 8 Slip is the distance rocks move along the fault. Slip can be up or down the fault plane. Slip is relative, because there is usually no way to know whether both sides move or only one. Faults lie at an angle to the horizontal surface of the Earth. The angle is called the fault’s dip. The dip defines which of two basic types a fault is. If the fault’s dip is inclined relative to the horizontal, the fault is a dip-slip fault. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA  Slip Slide 9 A rupture surface (dark pink), on a steeply dipping fault plane (light pink). The diagram represents a part of the crust that may be up to tens or hundreds of kilometers long. The rupture surface is the part of the fault plane along which displacement occurred. In this example, the near side of the fault is moving to the left, and the lengths of the arrows within the rupture surface represent relative amounts of displacement. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA  Slip Slide 10 G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA  Dip-Slip Faults Slide 11 There two types of dip-slip faults. In a normal fault, the hanging wall drops down relative to the footwall. In a reverse fault, the footwall drops down relative to the hanging wall. Dip-slip motion consists of relative up-and-down movement along a dipping fault between two blocks, the hanging wall and footwall. In a dip-slip system, the footwall is below the fault plane and the hanging wall is above the fault plane. A good way to remember this is to imagine a mine tunnel running along a fault; the hanging wall would be where a miner would hang a lantern and the footwall would be at the miner’s feet. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA  Normal Faults Slide 12 Normal faults move by a vertical motion where the hanging-wall moves downward relative to the footwall along the dip of the fault. Normal faults are created by tensional forces in the crust. Normal faults and tensional forces commonly occur at divergent plate boundaries, where the crust is being stretched by tensional stresses. Examples of normal faults in Utah are the Wasatch Fault, the Hurricane Fault, and other faults bounding the valleys in the Basin and Range province. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA  Normal Faults Slide 13 G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA  Reverse Faults Slide 14 In reverse faults, compressional forces cause the hanging wall to move up relative to the footwall. A thrust fault is a reverse fault where the fault plane has a low dip angle of less than 45°. Thrust faults carry older rocks on top of younger rocks and can even cause repetition of rock units in the stratigraphic record. Convergent plate boundaries with subduction zones create a special type of “reverse” fault called a megathrust fault where denser oceanic crust drives down beneath less dense overlying crust. Megathrust faults cause the largest magnitude earthquakes yet measured and commonly cause massive destruction and tsunamis. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA  Reverse Faults Slide 15 G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Thrust Fault Slide 16 A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Thrust Fault Slide 17 Terminology of thrust faults (low-angle reverse faults). A klippe is the remnant of the hanging wall (aka nappe), where the surrounding material has been eroded away. A window is where part of the hanging wall has been eroded away to expose the footwall (autochthon). Note the symbol shows flags on the overlying thrust plate. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Thrust Fault Slide 18 Thrust fault in the North Qilian Mountains (Qilian Shan). The blueish rock is a thick fault gouge of basement, the redish stuff is above the fault plane. Everything thrust over the brown quaternary conglomerates (right part of the picture). The fault plane dips 65 degrees to the South. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Thrust Fault Slide 19 Depiction a thrust fault. Top: prior to faulting. Bottom: after significant fault offset. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Thrust Fault Slide 20 Thrust faults at the leading edge of the Athabasca Glacier, Alberta. The arrows show how the trailing ice has been thrust over the leading ice. (The dark vertical stripes are mud from sediments that have been washed off of the lateral moraine lying on the surface of the ice.) G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Strike-Slip Faults Slide 21 A strike-slip fault is a dip-slip fault in which the dip of the fault plane is vertical. Strike-slip faults result from shear stresses. Depiction of reverse, normal, and strike-slip faults. Reverse faults happen during compression while normal faults happen during extension. Most strike-slip faults are related to transform boundaries. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA Strike-Slip Faults Slide 22 Flower structures created by strike-slip faults. Depending on the relative movement in relation to the bend in the fault, flower structures can create basins or mountains. G08-SCI-L10>Fault Richmindale® is a trademark of Richmindale College LLC, USA   END OF PRESENTATION  Fault Science Form 5050 rev 0 | www.richmindale.com/standards/forms Richmindale® is a trademark of Richmindale College LLC, USA