Transcript Presentation #16 - the Middle East Seismological Forum

Seismicity, Major Structural
Elements and Required Tsunami
Early Warning System for Makran
(Sea of Oman) Region
Dr. Mohammad Mokhtari
Director of National Center for Earthquake Prediction.
International Institute of Earthquake Engineering and
Seismology (IIEES)
Iran
Gulf Seismic Forum
Muscat, Oman
19-22 February 2006
Outline
• Introduction
• Major structural Elements
• Seismicity
• Tsunami Early Warning System
• Conclusions
• An Invitation
Present plate boundaries in the Indian Ocean
1945
Makran Accretionary margin, location of 1945 Tsunami in this region
Island Arc Volcanics
A Mud Volcanoes
Characteristic of Makran Margin
• There is no obvious topographic trench
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associated with the present Accretionary front.
There is a thick sedimentary cover on oceanic
crust, 6-7 km of terrigenous sediments in the
abyssal plane.
There are no obvious magnetic anomalies
related to ocean floor spreading in the Oman
Sea. The oceanic crust formed during the
Cretaceous quiet zone (108-79 Ma)
Characteristic of Makran Margin
• The island arc volcanics are located where
the subducting plate is at ~100 km depth.
• There are no indications of active
volcanism or intrusions in the Accretionary
complex.
• The subducting plate has a northward dip.
Characteristic of Makran Margin
• Earthquake activity is low. Most major
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earthquakes appear to be associated with
wrench faults.
Earthquake fault plane solutions show
predominantly shallow northward dipping
thrusts, with dips increasing northward, away
from the Accretionary front.
The east-west oriented Accretionary complex is
more than 900 km long, bounded to the east
and west by large transform faults defining plate
boundaries.
Different
• Of all the Accretionary complexes active today,
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none of them is a direct “look-alike” to the
Makran Accretionary Complex.
Generally other Accretionary complexes have
more closely spaced thrusts compared to the
more open, simple structures in Makran.
This is ascribed to the thick sedimentary cover
(6-7 km) over the oceanic crust in the Gulf of
Oman.
Seismicity
Seismicity Map
North–south velocity along two profiles, together with the topography and the
seismicity. Top: profile crossing the continental collision; bottom: profile crossing
the subduction (F. Nilforoushan et. al. 2003)
SEISMIC REFLECTION DATA
OFFSHORE MAKRAN
OFFSHORE EAST MAKRAN
N-S 2D seismic data showing the Makran Accretionary Wedge (
OFFSHORE WEST MAKRAN
PC-2000 Seismic Reflection Data Offshore Oman Gulf
N
Back-Arc
Basin
S
Accreted mélange
Accretionary Wedge
North-south seismic line through the offshore part
of the Makran Accretionary Complex.
S
N
Oceanic crust
North-south seismic line through the Accretionary Wedge.
N
Fore-arc basin
Accreted melange
deep water thrust belt
(Base sediments)
North-south line recorded to 20 sec showing from left the fore-arc
basin, accreted melange zone and deep water thrust belt.
S
Zendan
Landsat image showing southern part of
the onshore Zendan-Minab Fault Complex.
W
Fore-Arc Basin
Offshore extension of Zendan Fault system (PC2000 seismic data, NIOC)
E
Landsat image showing coastal areas of Makran. Cuspate features are in line with
Offshore listric faults controlling the Fore-Arc Basin.
Dibba Zone
• The Dibba Zone is a prominent structural feature/lineament as defined in
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Oman, cutting across the Musendam Peninsula in a southwest/northeast
direction. In northern Oman the Dibba Zone defines the western and
northern extent of the ophiolite nappes. Onshore the Dibba Zone is also a
topographic feature.
The offshore continuation in Iranian waters lines up with a dog-leg system
of a north-south oriented lineament, interpreted as a thrust front, and a
conjugated set of northwest-southeast and northwest-southeast oriented
normal faults. The main structuring event pre-dates the Tertiary
unconformity, and might be correlated with the Late Cretaceous
(Campanian/Maastrichtian) event leading to emplacement of nappes in
Oman. To the north the Dibba Zone is bounded by a normal fault (down to
the east), close to the southern boundary of the Musendam High.
To the northeast the Dibba Zone terminates against the Zendan-Minab Fault
Complex.
Qesham Island
Landsat satellite image showing the Dibba Zone onshore
Oman, with offshore trends based on Seismic data.
E
W
East-west seismic line across the northern Dibba Zone showing
Late Cretaceous “folding”. Post-unconformity structuring is
limited to normal extensional faulting.
Cause of Tsunami
• Most tsunamis are caused by a rapid vertical
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movement along a break in the Earth's crust:
A tsunami is generated when a large mass of earth on
the bottom of the ocean drops or rises, thereby
displacing the column of water directly above it.
This type of displacement commonly occurs in large
subduction zones
Most Subduction occurs along most of the island
arcs and coastal areas of the Pacific and Makran
Region.
Other possible causes
• Other possible but less efficient methods of tsunami generation
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include:
Strong oscillations of the bottom of the ocean,
Transmission of energy to a column of water from a seismic
impulse (e.g., a deep-focus earthquake that has no surface
rupture)
Transmission of energy from a horizontal seismic impulse to
the water column through a vertical or inclined wall such as a
bathymetric ridge
Strong turbidity currents
Underwater and above-water explosions.
Typical values for a seismically generated tsunami
IRAN
Pakistan
1945 EQ
Oman Gulf
IRAN
Pakistan
1945 EQ
Oman Gulf
1h
2h
IRAN
Pakistan
1945 EQ
Oman Gulf
Tsunami In the coastal region of
Iran
• Caspian Sea (957 ?)
• Oman Sea (Makran Region) (1945)
• Magnitude 8.1
• Extensive damage specially in Pakistan
• Persian Gulf
• No proven major activity
Early Warning System for Makran
Region
Broadband Seismic Network (Established and operated by IIEES
IRAN
PAKISTAN
Gulf of Oman
Proposed Seismic stations
Proposed Sea-floor pressure sensors
Schematic drawing of Tsunami detection system with time scale
for distance earthquake.
Conclusions
• Tsunamis are not generated by all earthquakes. To generate a
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tsunami, the fault where the earthquake occur must be
underneath or near the ocean and cause vertical movement of
the seafloor over a large area.
The Mediterranean and Caribbean Seas both have few
Tsunami occurrence.
Only a few tsunamis have been generated in the Atlantic and
Indian Oceans.
Occurrence of 1945 Tsunami puts Makran in an area of prone
to Tsunami.
The largest Tsunamis have occurred in the Pacific Ocean.
The Tsunami can be detected using early warning System.
Move quickly to HIGHER PLACE.
The Invitation to Tehran for May
2007
More information
www.iiees.ac.ir/SEE5
• SEE5