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Comparison Between San Andreas Fault and North Anatolian Fault
 

Comparison Between San Andreas Fault and North Anatolian Fault

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    Comparison Between San Andreas Fault and North Anatolian Fault Comparison Between San Andreas Fault and North Anatolian Fault Presentation Transcript

    • 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
    • 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
    • Department of Earth Science University of Bergen Global earthquake distribution Institutt for geovitenskap / Bergen Museum
    • Department of Earth Science University of Bergen SAFZ and NAFZ USGS, 2000 N. Toksoz
    • Department of Earth Science University of Bergen SAFZ and NAFZ
    • 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
    • Department of Earth Science University of Bergen San Andreas Fault Zone Photo: R. Wallace
    • Department of Earth Science University of Bergen San Andreas Fault Zone Wallace, 1990
    • Department of Earth Science University of Bergen San Andreas Fault Zone - evolution Animation Irwin, 1990
    • 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
    • Department of Earth Science University of Bergen San Andreas Fault Zone - geomorphology Wallace, 1990
    • Department of Earth Science University of Bergen San Andreas Fault Zone - geomorphology R. Wallace R. Wallace M. Rymer NASA USGS USGS/SCAMP
    • Department of Earth Science University of Bergen San Andreas Fault – major earthquakes SCEC, 2006
    • Department of Earth Science University of Bergen San Andreas Fault Zone – creeping section Schulz and Wallace, 1997
    • Department of Earth Science University of Bergen North Anatolian Fault Zone Photo: S. Pucci
    • Department of Earth Science University of Bergen North Anatolian Fault Zone Armijo et al., 2005
    • 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
    • Department of Earth Science University of Bergen North Anatolian Fault Zone - segmentation Barka and Kadinsky-Cade, 1988
    • Department of Earth Science University of Bergen North Anatolian Fault Zone - geomorphology Sengor et al., 2005
    • Department of Earth Science University of Bergen North Anatolian Fault Zone - geomorphology Aksoy, 2004 Aksoy, 2004 Pucci, 2005 U. Arizona U. Arizona
    • Department of Earth Science University of Bergen North Anatolian Fault Zone – major earthquakes Barka et. al. (2002)
    • Department of Earth Science University of Bergen Factors affecting earthquake potential
    • 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
    • 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
    • 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+
    • 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
    • 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
    • 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
    • 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
    • Department of Earth Science University of Bergen Time elapsed since last earthquake Recent major earthquakes in California Smith and Sandwell, 2006
    • Department of Earth Science University of Bergen Time elapsed since last earthquake Recent major earthquakes along the North Anatolian Fault Barka et. al. (2002)
    • 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
    • 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
    • Department of Earth Science University of Bergen Stress transfer – North Anatolian Fault Zone Westward migration of large earthquakes Animation Stein et al., 1996
    • 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
    • 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
    • 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
    • Department of Earth Science University of Bergen Fault segmentation - NAFZ Barka and Kadinsky-Cade, 1988
    • 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
    • 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
    • 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
    • Department of Earth Science University of Bergen Seismic hazard – San Fransisco USGS, 2003
    • 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
    • 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
    • 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
    • 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
    • Department of Earth Science University of Bergen Seismic hazard – long term California Turkey Petersen et al., 2003 Erdik et al., 1999
    • 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
    • Department of Earth Science University of Bergen
    • Department of Earth Science University of Bergen
    • 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