Active and recent structures

1. Active and recent structures Lecture 1/22/02 GEOS 304 Handouts and Powerpoint file

2. Objectives • Neotectonics vs. active tectonics • Earthquakes and faults • Methods used to measure amounts and rates of present day deformations • Geologic clues for young deformation • Deconstructing Hollywood and LA

3. Uniformitarianism Present is key to the past Or is it?

4. Time scales • Tectonics- analyses large scale deformations and Earth evolution processes at scales of millions to tens of millions of years • Neotectonics- time scale= thousand to tens of thousand years • Active tectonics = years to tens of years

5. 10,000,000- 100,000,000 = Orogenic scale Our main scale of interest in this class • 1,000-10,000 = Neotectonics • 1-10 = Active tectonics How do they compare?

6. Methods • ACTIVE deformation: study of earthquakes, monitoring with strainmeters and tiltmeters, other geodetival techniques. NEW techniques: continuous GPS and Radar interferometry • NEO-deformation, study of deformed historic sites of known ages , geochronology, + a variety of other techniques

7. Active structures

9. What are earthquakes? Obviously they are ruptures though the Earth’s crust. I.e. they are faults

11. Reverse fault Normal fault

12. Strike slip

14. = funding for geology

15. Indonesia (unknown loc)

16. San Gorgonio, CA

17. Izmit earthquake 1999

18. The bed of this major river at the northern end of the Chelungpu fault has been disarticulated by the fault.  The scarp hidden by the waterfall is about 7 meters high.  The bridge failed where it crosses the fault to the right a few hundred meters, out of the frame of the photo.  It is being reconstructed in the same location.

20. Long term plate motion- 5 cm/yr 400 m in 10000 yrs 40 mm per year

21. En echelon fault (compare to Fig 6.148 in text)

23. Folds

24. The wave of the future-GPS

28. Lessons from GPS and geodesy • Nothing is stable • Plate tectonics assumptions are ok as first order aprox. Within plate deformation can be huge! • Long term rates are comparable to short term - but keep in mind the sudden release of energy along earthquakes.

29. An example: faults in Los Angeles

33. View northward from the star-studded intersection of Hollywood and Vine.  The ramplike rise in the street just beyond the Capitol Records building is the scarp of the Hollywood fault.  Beyond the scarp and the freeway bridge are the Hollywood Hills, raised by innumerable ruptures of the fault.

34. The Hollywood fault and anticline

35. Anticline Fault tip Fault

36. Summary • Active and recent structures- provide the foundation of interpretative structural analysis; • Faults: reverse, normal and strike-slip • Folds: anticlines and synclines • Lithospheric plates are not entirely rigid • Structures form steady-state as well as catastrophically (in large increments separated by no deformation)

37. Please read the handout provided today- Chapter 2 in Dennis • It will give you additional information on active and recent structures, pre GPS. • Focuses on vertical deformation, and does a good job of distinguishing between climate vs. tectonic vertical motions.

38. Preview of Cottonwood