Description of faults

Transcription

1 GLG310 Structural Geology Description of faults Horizontal stretch Crustal thickness Regional elevation Regional character Issues Normal Thrust/reverse Strike-slip >1 <1 >1 in one direction and < 1 in another Thin Thicken No change Usually lower Usually higher No change Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults Detachments, Listric, rotation, rifted margins Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults Layered rocks, reverse versus thrust Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems Transforms, bends and stepovers 4 November 2013 GLG310 Structural Geology 1

2 Strike-slip faults Horizontal motion dominantly Transforms and transfers Geomorphic evidence for sustained motion along the San Andreas Fault, including the 1857 Fort Tejon earthquake 35 mm/yr slip rate over the last 3700 yrs Wallace Creek in the Carrizo Plain, California 2

3 Noriega, et al Late Pleistocene-Holocene evolution of Wallace Creek (from Sieh and Jahns, 1984) Interseismic motion along the San Andreas Fault System (max arrow length=~50mm/yr relative to stable North America) 3

4 San Andreas Fault from 4

5 Transform faults Transform faults 26 October

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7 Areas Regions of contrasting of behavior contrasting along behavior the San Andreas in strain Fault release (from Allen, along 1968) the San Andreas Fault system (modified from Allen, 1968) Eurasian strike-slip faults and Continental escape Does continental lithosphere deform in a plate-like or more diffuse manner? 26 October Davis and Reynolds Structural Geology textbook 7

8 Geodetically measured strain accumulation in Eurasia Wang, et al., 2001 Strike-slip faults in intracontinental deformation: the Altyn Tagh left lateral strike-slip fault in Xinjiang, NW China Altyn Tagh fault system (Washburn and Arrowsmith) 8

9 Altyn Tagh fault system (Washburn and Arrowsmith) Altyn Tagh fault system (Washburn and Arrowsmith) 9

10 Altyn Tagh fault system (Washburn and Arrowsmith) Altyn Tagh fault system (Washburn and Arrowsmith) 10

11 Altyn Tagh fault system (Washburn and Arrowsmith) Altyn Tagh fault system (Washburn and Arrowsmith) 26 October 2004 GLG310 Structural Geology 11

12 M7.9 Denali Earthquake Main shock and aftershocks: Tectonic setting: Denali fault accommodates right lateral motion as south Alaska moves westward north of the Aleutian subduction zone Much of what follows comes from 12

13 Rupture map Slip distribution View to the south showing the edge of a swale (arrows) offset 1.4 +/- 0.1m right-laterally and /- 0.04m up to the south, across the Denali fault during the 2002 event. The white stadia rod lies along the rupture. P. Haeussler is standing in the swale on the south side of the fault, B. Sherrod at left. Site HSS-605, km Photo by D. Schwartz. 13

14 View to the east of the Denali fault scarp on the Black Rapids Glacier. Jon Laravee, helicopter pilot, stands at the fault scarp. Avalanche debris is visible in the distance. Offset snow and ice features showed that the fault in this area produced 3.9 +/- 0.05m of right-lateral slip and /- 0.05m vertical slip, up to the north. Site PH305, km Photo by P. Haeussler. View to the east of a pull-apart in ice of the Black Rapids Glacier. The Denali fault offsets snow and ice features 3.9 +/- 0.05m right-laterally and /- 0.05m up to the north. Avalanche debris is visible in the distance. Site PH305, km Photo by P. Haeussler. 14

15 View north of a small, dry rill (delineated with orange flags) offset a total of m along the Denali fault. Brittle offset occurs across one major fault strand (mid-foreground, with /- 0.1m right-lateral) and multiple minor strands (middleground), forming a rupture zone ~20m wide. Site , km Photo by H. Stenner. The Denali fault on the first prominent topographic saddle west of the Delta River. Photograph was taken in November, 2002, just after the earthquake. Here, offset is 5.0 +/- 1.0m, right-lateral, and /- 0.5m, up to the north. Note the push-up in the background. There is permafrost at the bottom of the cracks. Site PH031, km Photo by P. Haeussler. 15

16 Aerial view of the Denali fault trace west of Delta River, as seen in November, Offset in this area is 5.0 +/- 1.0m, right-lateral, and /- 0.5m, up to the north. Note push-up in the central part of the photograph, where the main trace steps left. Cracks perpendicular to the fault trace in the lower left are related to slope failure during ground shaking. Site PH031, km Photo by P. Haeussler. Cantwell glacier 16

17 View south of the Denali fault trace through the north side of the Cantwell Glacier. A crevasse is offset /-0.2m right-laterally and /- 0.2m up to the south. A stadia rod and 2-m-tall P. Haeussler for scale. This site had the largest vertical slip measured in ice along the rupture. Site PH312, km Photo by P. Haeussler. The crest of a rounded slope, adjacent to a shallow erosional swale, is offset 5.1 +/- 0.1m rightlaterally, and 0.56m up to the north, along the Denali fault near Slate Creek. View is to the north. Slip occurs across a 1-m-wide rupture zone. Orange flags mark the slope crest on either side of the rupture. Site DS-21, km Photo by T. Dawson. 17

18 Aerial view north of a stream channel right-laterally offset m along the Denali fault. Site Jack Cr-1, km 182. Photo by D. Schwartz. View southeast of a right-laterally offset stream bank edge at Cooper Creek, at the southeastern extent of the Totschunda fault. Offset is /- 0.25m, right-lateral, and /- 0.1m, up to the south. Site PH101, km Photo by P. Haeussler 18

19 Mud Volcano Shaking derived phenomena Debris flow Alaska Range Slide on Glacier Alaska Range Shaking derived phenomena 19

20 Landslide across Black Rapids Glacier. The landslide moved from right to left across the valley. The ridge in the center is a medial moraine. The fault scarp is not visible in the photo. Photo by Patty Craw, DGGS. Shaking derived phenomena Clay cake experiment simulating strike-slip faulting 20

21 Structures that develop in a dextral shear zone (and then rotate with continued deformation) Strike-slip steps and bends 21

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23 Description of faults Horizontal stretch Crustal thickness Regional elevation Regional character Issues Normal Thrust/reverse Strike-slip >1 <1 >1 in one direction and < 1 in another Thin Thicken No change Usually lower Usually higher No change Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults Detachments, Listric, rotation, rifted margins Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults Layered rocks, reverse versus thrust Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems Transforms, bends and stepovers 4 November 2013 GLG310 Structural Geology Description of faults Horizontal stretch Crustal thickness Regional elevation Regional character Issues Normal Thrust/reverse Strike-slip >1 <1 >1 in one direction and < 1 in another Thin Thicken No change Usually lower Usually higher No change Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults Detachments, Listric, rotation, rifted margins Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults Layered rocks, reverse versus thrust Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems Transforms, bends and stepovers 4 November 2013 GLG310 Structural Geology 23