Comparison Between San Andreas Fault and North Anatolian Fault

Earthquake potential of the San Andreas and North Anatolian Fault Zones:

A comparative look

M. B. SørensenDepartment of Earth Science, University of Bergen, Norway,

Department of Earth Science

SCEC A. Barka

B. Bryant A. Barka

Department of Earth ScienceUniversity 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


Global earthquake distribution

Institutt for geovitenskap / Bergen Museum


SAFZ and NAFZ

USGS, 2000

N. Toksoz


SAFZ and NAFZ

SCEC A. Barka

B. Bryant A. Barka


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


San Andreas Fault Zone

Photo: R. Wallace



Wallace, 1990


San Andreas Fault Zone - evolution

AnimationIrwin, 1990


San Andreas Fault Zone - segmentation

Wallace, 1990

Four main segments:a) 1906 rupture and subparallel branchesb) Central California active (creeping) sectionc) 1857 rupture d) Southern section (south of Transverse ranges)

Additional faults are important parts of the system


San Andreas Fault Zone - geomorphology

Wallace, 1990


San Andreas Fault Zone - geomorphology

R. Wallace

R. Wallace M. Rymer

NASA USGS USGS/SCAMP


San Andreas Fault – major earthquakes

SCEC, 2006


San Andreas Fault Zone – creeping section

Schulz and Wallace, 1997


North Anatolian Fault Zone

Photo: S. Pucci



Armijo et al., 2005


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


North Anatolian Fault Zone - segmentation

Barka and Kadinsky-Cade, 1988


North Anatolian Fault Zone - geomorphology

Sengor et al., 2005


North Anatolian Fault Zone - geomorphology

Aksoy, 2004

Aksoy, 2004

Pucci, 2005

U. Arizona

U. Arizona


North Anatolian Fault Zone – major earthquakes

Barka et. al. (2002)


Factors affecting earthquake potential

SCEC A. Barka

B. Bryant A. Barka


Factors affecting earthquake potential

• Maximum expected magnitude

• Earthquake recurrence

• Time elapsed since last large earthquake

• Coulomb stress transfer

• Fault segmentation


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


Maximum expected magnitude - SAFZ

Schulz and Wallace, 1997

• Precence of creeping sections limits the maximum magnitude along SAF

• Maximum expected magnitude M=8+


Maximum expected magnitude - NAFZ


• Controlled by fault segmentation

• Limited by significant fault bends or offsets

• Maximum expected magnitude M=8.0


Earthquake recurrence

• San Andreas: M8 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)

M6 along the entire fault (e.g. Parkfield), larger events are

rare at creeping sections

Reflected in microseismicity

For entire SAF: M6 every 15 months, M7 every 12.5 years, M8 every 125 years (Ellsworth, 1990 based on 220 years earthquake catalogue)

1906

1857

??

Modified from Hill et al., 1990


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>5.5Toksoz et al., 1979


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


Time elapsed since last earthquakeRecent major earthquakes in California

Smith and Sandwell, 2006


Time elapsed since last earthquakeRecent major earthquakes along the North Anatolian Fault



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


Stress transfer – San Andreas Fault ZoneSouthern 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

AnimationToda et al., 2005


Stress transfer – North Anatolian Fault Zone

Westward migration of large earthquakes

Animation

Stein et al., 1996


Stress transfer – North Anatolian Fault ZoneEarthquake history of the North Anatolian Fault

AnimationStein et al., 1996


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


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


Fault segmentation - NAFZ

Barka and Kadinsky-Cade, 1988

Meghraoui, 2004


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


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


Seismic hazard – short term


• San Francisco bay area

• Southern California


• Istanbul

• East of Erzincan

Sengor et al., 2005

WGCEP, 1988


Seismic hazard – San Fransisco

USGS, 2003


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


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


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


Seismic hazard – short termSAFZ 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


Seismic hazard – long termCalifornia

Turkey

Petersen et al., 2003

Erdik et al., 1999


ConclusionsSAFZ 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




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

Education

Comparison Between San Andreas Fault and North Anatolian Fault