Two Very Different Surface Ruptures and Some Generalizations about the Behavior of Strike-slip Faults: Denali 2002 Bulnay 1905

Transcription

1 Two Very Different Surface Ruptures and Some Generalizations about the Behavior of Strike-slip Faults: Denali 2002 Bulnay 1905

2 Tectonics of southern Alaska

3 Horizontal slip (m) West Fork Glacier Susitna - Black Rapids Glacier Canwell - Gakona Glaciers Chistochina Glacier Denali -Totschunda Fault Transfer Zone July 2004 measurements July 2003 measurements November 2002 measurements Culled measurements Distance from epicenter (km) Augustana Epicenter Susitna/Black Creek Richardson Slate Creek Slana River Mentasta Tok Little Tok Nabesna Blue Rapids Divide Delta River Highway Gillett Pass Cutoff River River Lake Pipeline Canwell/Gakona Divide Highway

4 Denali-Totschunda Slip Distribution Horizontal slip (m) West Fork Glacier Susitna - Black Rapids Glacier Canwell - Gakona Glaciers Chistochina Glacier Denali -Totschunda Fault Transfer Zone July 2004 measurements July 2003 measurements November 2002 measurements Culled measurements 0 Epicenter Distance from epicenter (km) 0 50 Augustana Creek Susitna/Black Rapids Divide Richardson Slate Creek Slana River Mentasta Delta River Highway Gillett Pass Pipeline Canwell/Gakona Divide Tok Cutoff Highway Little Tok River Nabesna River Blue Lake Haeussler et al (2004)

5 Horizontal Slip distribution Denali-Totschunda fault rupture 4 main sections

6 Estimates of Average Slip 4.5 m 1.6m M w m 1.7 m Haeussler et al (2004) BSSA 4.9m 1.8m

7 Short-lived glacial offsets Susitna glacier thrust, Nov Canwell glacier, Nov Chistochina glacier, July 2003 Chistochina glacier, July 2003

8 Km m

9 Km (1.5) 1.4

10 Slate Creek Km 140

11 5m

12 5m

13

14 5.3 m Penultimate m

15 Canwell - Gakona Glaciers Chistochina Glacier Denali -Totschunda Fault Transfer Zone July 2004 measurements July 2003 measurements November 2002 measurements Culled measurements penultimate Distance from epicenter (km) Richardson Slate Creek Slana River Mentasta Tok Little Tok Nabesna Blue Highway Gillett Pass Cutoff River River Lake ne Canwell/Gakona Divide Highway offset (8.1) Km 18

16 Km 184 Gillett Pas

17 8.1 m

18 November 2002 Bone Creek 5.5m 5.5 meter lateral offset at Bone Creek Km 197 July 2003

19 Tok Cutoff Highway Km m

20 m m Primary control of 2002 rupture path is timing of past earthquakes/ accumulated strain on the Totschunda

21 Totschunda fault 250 km east of 02 epicenter

22 Horizontal slip (m) 10 West Fork Susitna - Black Canwell - Chistochina Denali -Totschunda Glacier Rapids Glacier Gakona Glacier Fault Transfer Zone Glaciers 8 July 2004 measurements July 2003 measurements 6 November 2002 measurements Culled measurements 4 2 Distance from epicenter (km) Augustana Epicenter Susitna/Black Creek Richardson Slate Creek Slana River Mentasta Tok Little Tok Nabesna Blue Rapids Divide Delta River Highway Gillett Pass Cutoff River River Lake Pipeline Canwell/Gakona Divide Highway (3.0) Km 250

23

24 8.2m Western Denali paleo-offsets 50 km west of 02 epicenter 8m in 2 events 4m

25 Eastern, unruptured (02), Denali Bean Lake, Tetlin River 20 km east of Totschunda fault intersection

26 Denali Rupture Characteristics Rupture of multiple faults:connectivity Slip distribution asymmetric: Dmax 180 km east of epicenter Slip divided into distinct sections (4-9) of Davg Large changes in slip occur over short ( 400 m) distances Within distinct sections point-specific D can vary by 90% Rupture structurally simple except at bends and steps Width of fault zone typically narrow (1-5m); no correlation between width of zone and Dnet Paleo offsets similar in size to 2002

27 The July 23, 1905 Bulnay Fault, Mongolia Surface Rupture D.P. Schwartz, S. Hecker, D. Ponti, W.E. Lund, H.D. Stenner, A. Bayasgalan

28 July 9 July Schlupp and Cisternas (2007)

29 Bulnay fault

30

31 Fissure with horizontal displacement Rupture Photos by A.Voznesenskii, 1905 Overthrust

32 complex trace large% of rupture

33

34 100 m

35 Buust Nuur 8.8 ± 2.3 m

36 18 ± penultimate west of Buust Nuur 8 ± 0.6 (1905) 11 ± 2 (1905) 8.8 ± 1.0 (1905)

37 west of Oygon Nuur 8.75 ± 0.25

38 Zuun Hangay West 1905:8 ± 0.9 m m penultima yb05

39 Bulnay slip distribution e s?? Bilateral Slight asymmetry Dmax (11 m) near eastern end Davg (8 m) at surface Characteristic slip

40 Bulnay Rupture Characteristics Rupture of multiple faults: connectivity Slip distribution asymmetric: Dmax 170 km east of epicenter Similar amount of slip over long distances ( 200 km) Rupture commonly complex; multiple traces km apart Complexity may reflect long recurrence (~ 3ka) Paleo offsets similar in size to 1905