1. Earthquake potential of the San Andreas
and North Anatolian Fault Zones:
A comparative look
M. B. Sørensen
Department of Earth Science, University of Bergen, Norway,
Department of Earth Science

2. SCEC A. Barka
B. Bryant A. Barka
Department of Earth Science
University of Bergen
Earthquake potential
• The likelihood of a given fault or fault zone to
generate an earthquake at a given time
• Controls largely the seismic hazard in a
region
• Controlled by factors such as maximum
expected magnitudes, recurrence times,
time elapsed since last large earthquake,
stress transfer from other earthquakes and
fault vs. rupture segmentation

3. Department of Earth Science
University of Bergen
Global earthquake distribution
Institutt for geovitenskap / Bergen Museum

4. Department of Earth Science
University of Bergen
SAFZ and NAFZ
USGS, 2000
N. Toksoz

5. Department of Earth Science
University of Bergen
SAFZ and NAFZ

6. SCEC A. Barka
B. Bryant A. Barka
Department of Earth Science
University of Bergen
This presentation
• San Andreas Fault Zone
• North Anatolian Fault Zone
• Comparison of earthquake potential
- maximum expected mangitude
- earthquake recurrence
- historical earthquakes
- coulomb stress
- rupture segmentation
• Implications for seismic hazard
• Conclusions

7. Department of Earth Science
University of Bergen
San Andreas Fault Zone
Photo: R. Wallace

8. Department of Earth Science
University of Bergen
San Andreas Fault Zone
Wallace, 1990

9. Department of Earth Science
University of Bergen
San Andreas Fault Zone - evolution
Animation
Irwin, 1990

10. Department of Earth Science
University of Bergen
San Andreas Fault Zone - segmentation
Wallace, 1990
Four main segments:
a) 1906 rupture and subparallel branches
b) Central California active (creeping) section
c) 1857 rupture
d) Southern section (south of Transverse ranges)
Additional faults are important parts of the system

11. Department of Earth Science
University of Bergen
San Andreas Fault Zone - geomorphology
Wallace, 1990

12. Department of Earth Science
University of Bergen
San Andreas Fault Zone - geomorphology
R. Wallace
R. Wallace M. Rymer
NASA USGS USGS/SCAMP

13. Department of Earth Science
University of Bergen
San Andreas Fault – major earthquakes
SCEC, 2006

14. Department of Earth Science
University of Bergen
San Andreas Fault Zone – creeping section
Schulz and Wallace, 1997

15. Department of Earth Science
University of Bergen
North Anatolian Fault Zone
Photo: S. Pucci

16. Department of Earth Science
University of Bergen
North Anatolian Fault Zone
Armijo et al., 2005

17. Department of Earth Science
University of Bergen
North Anatolian Fault Zone - evolution
• 11-13 My ago: Arabia/Eurasia collision →
Anatolia moves west → creation of NAF in
eastern Turkey
• NAF propagates westwards (~11 cm/yr)
• Marmara Sea segment is ~200 000 years old
Armijo et al., 2005

18. Department of Earth Science
University of Bergen
North Anatolian Fault Zone - segmentation
Barka and Kadinsky-Cade, 1988

19. Department of Earth Science
University of Bergen
North Anatolian Fault Zone - geomorphology
Sengor et al., 2005

20. Department of Earth Science
University of Bergen
North Anatolian Fault Zone - geomorphology
Aksoy, 2004
Aksoy, 2004
Pucci, 2005
U. Arizona
U. Arizona

21. Department of Earth Science
University of Bergen
North Anatolian Fault Zone – major earthquakes
Barka et. al. (2002)

22. Department of Earth Science
University of Bergen
Factors affecting earthquake potential

23. SCEC A. Barka
B. Bryant A. Barka
Department of Earth Science
University of Bergen
Factors affecting earthquake potential
• Maximum expected magnitude
• Earthquake recurrence
• Time elapsed since last large earthquake
• Coulomb stress transfer
• Fault segmentation

24. Department of Earth Science
University of Bergen
Maximum expected magnitude
• One factor controlling earthquake magnitude is
rupture area
• Empirical study by Wells and Coppersmith (1994)
gives relation between rupture length and magnitude
• For strike-slip faults:
Magnitude Rupture length
6 14 km
7 60 km
7.5 120 km
8 245 km

25. Department of Earth Science
University of Bergen
Maximum expected magnitude - SAFZ
Schulz and Wallace, 1997
• Precence of creeping sections
limits the maximum magnitude
along SAF
• Maximum expected
magnitude M=8+

26. Department of Earth Science
University of Bergen
Maximum expected magnitude - NAFZ
Barka et. al. (2002)
• Controlled by fault segmentation
• Limited by significant fault bends
or offsets
• Maximum expected magnitude
M=8.0

27. Department of Earth Science
University of Bergen
Earthquake recurrence
• San Andreas: M≈8 every several hundres years in N
and S sections (e.g. 1857,1906)
Also smaller events at these locked
sections (e.g. 1989 Loma
Prieta, M=7.1)
M≈6 along the entire fault (e.g.
Parkfield), larger events are rare at
creeping sections
Reflected in microseismicity
For entire SAF: M≥6 every 15 months,
M≥7 every 12.5 years, M≥8 every 125
years (Ellsworth, 1990 based on 220
years earthquake catalogue)
1906
1857
??
Modified from Hill et al., 1990

28. Department of Earth Science
University of Bergen
Earthquake recurrence
• North Anatolian: M=7+ events rupture all segments along the fault
with intervals of 450 ± 220 years
Creeping section near Ismetpasa (1 cm/yr) within
1944 rupture area
M=6 every 2-4 years, M=7 every ~10 years
quiescence before 1939 → sequence
Complete for M>5.5
Toksoz et al., 1979

29. Department of Earth Science
University of Bergen
Earthquake magnitude and recurrence
SAFZ NAFZ
Creeping segment in central
SAF limits the maximum
magnitude to the levels
observed for the 1857 and
1906 earthquakes (M~8)
Largest known earthquake
along NAF is 1668 (M~8),
most known earthquakes are
of smaller magnitude
M=7+ every ~ 12.5 years M=7+ every ~ 10 years
M~8 events occur regularly M~8 events are rare

30. Department of Earth Science
University of Bergen
Time elapsed since last earthquake
Recent major earthquakes in California
Smith and Sandwell, 2006

31. Department of Earth Science
University of Bergen
Time elapsed since last earthquake
Recent major earthquakes along the North Anatolian Fault
Barka et. al. (2002)

32. Department of Earth Science
University of Bergen
Coulomb stress change
•Effect of an earthquake on the
surrounding faults due to transfer of
stresses
•Typical level of stress change is a few
bars (few percent of typical
earthquake stress drop)
•Such a change affects the time
required for tectonic stressing to bring
a segment to faliure
•Can be implemented in hazard
assessment by converting the change
into a change in the probability of a
future earthquake
Stein and Lisowski

33. Department of Earth Science
University of Bergen
Stress transfer – San Andreas Fault Zone
Southern california example: the area of the M=7.3 1992 Landers earthquake
Several large earthquakes occurred here during 1975-1999
Short distance between neighboring faults gives complicated stress transfer
effects
Red: increased stress, blue: decreased stress, gray dots: aftershocks
Animation
Toda et al., 2005

34. Department of Earth Science
University of Bergen
Stress transfer – North Anatolian Fault Zone
Westward migration of large earthquakes
Animation
Stein et al., 1996

35. Department of Earth Science
University of Bergen
Stress transfer – North Anatolian Fault Zone
Earthquake history of the North Anatolian Fault
Animation
Stein et al., 1996

36. Department of Earth Science
University of Bergen
Coulomb stress change
SAFZ NAFZ
Coulomb stress transfer results are
complex
Coulomb stress transfer successful
in describing potential locations of
future earthquakes
Simple, straight geometry → efficient stress transfer
Short distance to other faults →
irregular and complex stress
transfer pattern
Isolated from other faults →
minimum transfer to competing
faults
Smooth trace → larger earthquakes En echelon geometry → keeps the
entire fault from rupturing at once

37. Department of Earth Science
University of Bergen
Fault segmentation - SAFZ
• Major earthquakes rupture entire fault
sections limited by creeping central segment
• Smaller events occur along these segments
at locations with low slip during major event
• Highly regular earthquake occurrence is
observed at some places, e.g. Parkfield
• High number of parallel faults can rupture in
individual events
Smith and Sandwell, 2006

38. Department of Earth Science
University of Bergen
Fault segmentation - NAFZ
Barka and Kadinsky-Cade,
1988

39. Meghraoui, 2004
Department of Earth Science
University of Bergen
Fault segmentation - NAFZ
• Major earthquakes occur repeatedly but rupture
segmentation is not repeated
• Westward migration of earthquakes does not seem to
be a general trend
Stein et al., 1996

40. Department of Earth Science
University of Bergen
Fault segmentation
SAFZ NAFZ
The SAF is more smooth
and generally rupture in
larger events but parallel
faults take up part of the
accumulated strain
Many bends and offsets
controls the rupture
segmentation along
NAFZ
This results in large
characteristic
earthquakes along SAF
and smaller events on
neighbouring faults
This generally results in
smaller events than what
is observed along SAF

41. Department of Earth Science
University of Bergen
Seismic hazard – short term
San Andreas Fault Zone
• San Francisco bay area
• Southern California
North Anatolian Fault Zone
• Istanbul
• East of Erzincan
Sengor et al., 2005
WGCEP, 1988

42. Department of Earth Science
University of Bergen
Seismic hazard – San Fransisco
USGS, 2003

43. Department of Earth Science
University of Bergen
Seismic hazard – Southern California
• Many faults affect the hazard in the region
• Densely populated part of California including Los
Angeles
• Hidden (unknown) faults are present – for example
1994 M=6.7 Northridge earthquake
SCEC, 2006

44. Department of Earth Science
University of Bergen
Seismic hazard – Istanbul
(Pulido et al., 2004)
• 35-70% probability of a
M=7+ earthquake in the
Marmara Sea within the
next 30 years (Parsons,
2004)
• Scenario based ground
motion modelling
estimates ground shaking
level

45. Department of Earth Science
University of Bergen
Seismic hazard – Eastern Turkey
• Last rupture in 1784
• Confined by 1992 and 1949 ruptures (potential M=7+ earthquake)
• 1992 earthquake (M~6.7) caused significant damage in Erzincan
Photos: M. Yoshimine
Stein et al., 1996

46. Department of Earth Science
University of Bergen
Seismic hazard – short term
SAFZ NAFZ
Both fault zones are characterized by a significant seismic hazard towards a
big city
Risk mitigation efforts are important and should be prioritized (strengthening
of buildings, information to the pubic, disaster planning etc.)
earthquake forecasting IEEWRRS
Atakan and Sørensen, 2006USGS, 2006

47. Department of Earth Science
University of Bergen
Seismic hazard – long term
California
Turkey
Petersen et al., 2003
Erdik et al., 1999

48. Department of Earth Science
University of Bergen
Conclusions
SAFZ NAFZ
Two major fault systems with similar length, direction of motion, slip
rate, age and straightness
High seismic hazard in urban environments
Maximum expected magnitude
limited by creep
Maximum expected magnitude
limited by segmentation
M=6+ every 15 months
M=7+ every 12.5 years
M=8+ every 125 years
M=6+ every 2-4 years
M=7+ every 10 years
M=8+ rare
Smooth trace implies large
earthquakes
Strong segmentation implies
smaller events
Many parallel faults cause a
complicated stress transfer
pattern
Isolated fault gives little transfer
of stresses to competing faults

49. Department of Earth Science
University of Bergen

50. Department of Earth Science
University of Bergen

51. Department of Earth Science
University of Bergen
Earthquake recurrence
Time vs. distance plot of known
damaging earthquakes along NAF for
the time 400 BC to 2000 AD
Tendency of lower activity level prior
to 1500, may be due to incomplete
historical records
From Sengor et al., 2005