Download neotectonics

NEOTECTONICS
Yrd.Doç.Dr. Ziyadin Çakır
14.03.2007
İTÜ
Earthquake Belts
95% of energy released by earthquakes
originates in narrow zones that wind
around the Earth
• These zones mark of edges of
tectonic plates
Locations of earthquakes
from 1980 to 1990
Broad bands are subduction zone earthquakes, narrow are MOR
Depths of Earthquakes
Earthquakes originate at depths ranging
from 5 to , rarely, nearly 700 kilometers
Definite patterns exist in depth
– Shallow focus 20 km faults between MOR
– Large Transform (San Andreas) fault 80 km
– Deep earthquakes occur in Pacific landward of
oceanic trenches 80 km down to about 600 km
associated with subduction zones
Earthquake Depth and Plate Tectonic Setting
Subduction Zones discovered by Benioff
Earthquake in subduction
zones
Most earthquakes occur at plate boundaries
A small percentage of earthquakes occur along old faults on the continents
‰ Divergent boundaries – normal faults
‰ Convergent boundaries – reverse and thrust faults
‰ Transform fault boundaries – strike slip faults
Most earthquakes occur at shallow depths ( less than 40 km depth)
The deepest earthquakes occur in the sinking lithosphere in subduction zones
(up to 600 km depth)
Seismic Hazard Map
The most destructive earthquakes occur at convergent boundaries
Earthquake prediction
• Long-range forecasts
• Calculates probability of a certain
magnitude earthquake occurring over a
given time period
• Short-range predictions
• Ongoing research, presently not much
success
Long Term Predictions
Seismic Gaps
Long Term Predictions
• Strain Energy - accumulates
uniformly - release irregularly
• Some locked by friction “Seismic
gaps”
–Prime candidates for major
earthquake
• Some release energy continuouslycreep
–No major earthquakes there
Seismic Gaps at the Aleutian Islands SUBDUCTION ZONE
Seismic Gap along Himalayas
2005
Can earthquakes be predicted?
Short Term, Not very well
• Short-range predictions
• Goal is to provide a warning of the location
and magnitude of a large earthquake within
a narrow time frame
• Research has concentrated on monitoring
possible precursors – phenomena that
precede a forthcoming earthquake such as
measuring uplift, subsidence, and strain in
the rocks
locked faults
• Stresses
build up in the
crust, usually
due to
lithospheric
plate motions
• Rock deform
(strain) as the
result of
stress. The
strain is
energy stored
in the rocks.
locked faults
• When the rocks
reach their elastic
limit, they break,
and energy is
released in the
form of seismic
waves, radiating
out from the
earthquake focus
• The rocks return
to their original
shape, with a
displacement
(slip) along the
fault
Creeping faults
Surface creep in İsmetpaşa
Creep rate along strike
No triggered slip