For Goodness Sake, Let me Examine the Evidence, Ayhan!!!

Transcription

1 For Goodness Sake, Let me Examine the Evidence, Ayhan!!!

2 Deformation Belts and Fracture Belts along Earthquake Ruptures: INTRODUCTION The Ayhan and Arvid Comedy Hour and a Half!!! 13 February 2006

3 Kaynaşlı, Turkey Deformation Belts Along Earthquake Ruptures Damage Structures Phenomenon of Permanent Ground Distortion in an earthquake deformation belt, essentially a static phenomenon, can also damage structures. Such belts were recognized long ago, at least as early as the 1906 San Francisco, California, earthquake by G. K. Gilbert. A few earthquake geologists are rediscovering deformation belts today. Landers, California

4 1971 San Fernando E.Q Landers E.Q.

5 The Landers Johnson Valley Fault Emerson Lake Fault Homestead Valley Fault Rupture: A collage of old faults?

6 1992 EARTHQUAKE RUPTURES AT LANDERS

7 Happy Trail Fracture Zone

8 Setting of Happy Trail Fracture Zone

9 Happy Trail Fracture Zone N N

10 Types of Fractures at Happy Trail

11 Sequence of Fracture Events at Happy Trail 1. The fracture zone originated as N-S tension cracks caused by right lateral shearing, presumably over a shear zone or fault at depth. 2. Most of the tension cracks transformed into Mode I/Mode II, complex, left-lateral fractures, also a result of shearing below. 3. Also, as the separated blocks rotated, they were jammed against the ground on either side of the shear zone, producing small thrust faults and buckles. 4. Finally, a small, narrow right-lateral shear zone or fault formed last in the Happy Trail shear zone, cutting across the tension cracks and left-lateral complex fractures.

12 Back to Nov 1999 Dücze Earthquake

13 Back to Findikli

14 We saw this earlier (in Introduction to 1999 Dücze Earthquake Rupture)

15 Rupture Belt at Findikli (same place)

16 View East below View West along Rupture Belt at Findikli

17 Now, to the Deformation Zone at Kaynaşlı Viaduct

18 Viaduct Meets Fault! 360,000 Fault November 1999 Rupture To Istanbul and Duzce Dariyeri Kaynaşlı Viaduct Mahallesi 40 15' 500 Kaynasli km Contour Interval = 50 m

19 Piers of Viaduct within Deformation Zone

20 View East. Main Rupture Pier 44 R Pier 45 L Pier 45 R Pier 46 R

21 Main Trace Under the Viaduct

22 View West. One rupture under viaduct. Two beside the viaduct. Bolu Two Ruptures One Rupture

23 View West. Pair of fractures near piers 39, 40 and 41. Bolu 39 R 40 R 41 R 41 R 39 L 40 L

24 Survey Stations on a Pier Bolu PROJECT DIRECTION

25 Adjacent Piers Form a Surveyor s Quadrilateral (view south) Bolu a b d c

26 D d 44 L Left Pier a 45 L A Bolu c 44 R Right Pier C Footing b B 45 R A Quadri- lateral of Piers

27 Calculation of Deformation within Belt beneath Viaduct

28 Strain Measurements (Points) Compared to Strain Theory (Curved Line) Quad Strain (%) Quad Azimuth ( ) Quad Strain (%) Azimuth Strain (%) Azimuth

29 Strain Magnitudes of Maximum (extension) and Minimum (compression) along Viaduct Principal Strains along Viaduct 6E-02 5E-02 Maxumum Strain 4E-02 3E-02 Quad 45 2E-02 Quad 39 1E-02 Quad 35 Quad 50 0E+00-1E E E-02-4E-02 Minimum Strain Distance from Pier 38 (in m)

30 Directions of Maximum (extension) Directions of Maximum (extension) Strain along Viaduct LEFT-LATERAL SHEAR ZONE (ELASTIC REBOUND) RIGHT-LATERAL SHEAR ZONE (PLASTIC DEFORMATION) 44 LEFT-LATERAL SHEAR ZONE (ELASTIC REBOUND) N m

31 Strains within Pier Quadrilaterals

32 Piers of Viaduct within Deformation Zone

33 Magnitude of Maximum Shear Strain as Function of Distance along the Viaduct Maxumum Shear Strain Pier Number

34 Magnitude of Shear Strain as Function Across the Viaduct Distance Normal to Fault (m) Shearing Strain Pier No.

35 Summary of Interpretations of Deformation Belt at Viaduct: The earthquake deformation belt at Kaynaşlı is ~100 m wide. The belt has a zone of LARGE DEFORMATIONS, with a maximum width of ~35 m along the south side of the belt. (The estimated width of the zone of large strains is too high because of the large spacing of piers. The actual large strains are probably much m larger and the actual zone is probably much narrower (a few m) than could be measured.) Within this zone of large deformations, a little more than half of the offset (1.15 m) occurred along the main rupture, which is perhaps 3 to 5 m wide; the rest (0.9 m) was distributed in some fashion through the rest of the 100-m wide belt. The belt has a zone of smaller, but significant strains, across 65 to 95 m of the belt. (The strains were large enough to fracture brittle soil at Landers or brittle concrete or rock, but not the soft sand and gravel of the riverbed at Kaynasli.)

36 θ Deformation Belt along 1906 San Francisco EQ Rupture. At San Andreas Reservoir, a few km south of S.F. A A z C ψ c b SAN ANDREAS RESERVOIR crack fault line N m Brick Forebay crack Details of originally circular, now roughly elliptical, brick forebay and larger fractures within deformation belt.. C x Concrete Forebay crack Line of hole Brick Forebay Fault Concrete Shaft tunnel crack B 0 10 m

37 Are the Observations of Deformation Belts Consistent with Elastic Rebound?

38 ELASTIC REBOUND THEORY We go back to the ideas of elastic rebound theory introduced, perhaps, by G. K. Gilbert (1875?;1907) and Harry Reid (1910). In their early papers, an earthquake is considered to be a result of sudden slip on a fault in elastic ground that is under high enough stress to fail. It is supposed to be a result of a stress drop at a fault.

39 Let the dashed line in the figure below represent the trace on a map of a strike-slip slip fault and the solid line represent a passive marker inscribed across the fault just before earthquake rupture. When the traction on the fault suddenly drops, the ground will shake due to radiated energy, and the ground on either side of the fault will deform elastically.

40 After the earthquake, the passive marker will appear as two deformed line segments broken by the fault. Note that the offset on the fault is right-lateral lateral,, but the deformed line indicates that the rock on either side of the fault was distorted in a left-lateral lateral sense, due to the elastic rebound.

41 Thus, the Diagrams Below Represent the Idealized Concept of Elastic Rebound

42 Supposed Corollaries of Elastic Rebound Theory There are only three causes of earthquake damage worth consideration: Shaking of structures in excess of their design capabilities (Only cause considered by most structural engineers and geophysicists). Collapse of ground beneath structures due to landsliding or liquefaction of soil generated by shaking (Most important cause considered by (Most important cause considered by geotech engrs and engineering geologists). Direct offset across a line of the fault rupture (An important, but unlikely, cause according to all three groups of professionals).

43 Sketches of our disgusting interpretations of field measurements and observations.

44 Disgusting Implications: Elastic rebound, in some form, may be a good approximation, for now, to what happens near the hypocenter. The fault (or other source) fails catastrophically, generating the earthquake waves that are so dear to seismologists. If an earthquake rupture reaches the ground surface, however, there appears to be a belt of permanent deformation on either side or on only one side of a main rupture. The sense of permanent deformation is analogous to the sense of shift on the main rupture. Outside the belt of permanent deformation, there is elastic-like like deformation. The sense is opposite that of the shift across the main rupture.

45 Ooops W. does not like this or climate change!

46 End to Introduction to Belts of Permanent Deformation