Seismicity, Major Structural Seismicity, Major Structural Elements and Required Elements and Required Tsunami Early Warning Tsunami Early Warning

System for Makran (Sea of System for Makran (Sea of Oman) RegionOman) Region

Dr. Mohammad MokhtariDr. Mohammad MokhtariDirector of National Center for Earthquake Prediction.Director of National Center for Earthquake Prediction.

International Institute of Earthquake Engineering and International Institute of Earthquake Engineering and Seismology (IIEES)Seismology (IIEES)

IranIran

Gulf Seismic Forum Muscat, Oman 19-22 February 2006

OutlineOutline

• IntroductionIntroduction

• Major structural ElementsMajor structural Elements

• SeismicitySeismicity

• Tsunami Early Warning SystemTsunami Early Warning System

• ConclusionsConclusions

• An InvitationAn Invitation

Present plate boundaries in the Indian Ocean

Makran Accretionary margin, location of 1945 Tsunami in this region

Island Arc Volcanics Mud Volcanoes

1945

A

Characteristic of Makran Characteristic of Makran MarginMargin• There is no obvious topographic trench There is no obvious topographic trench

associated with the present Accretionary associated with the present Accretionary front.front.

• There is a thick sedimentary cover on oceanic There is a thick sedimentary cover on oceanic crust, 6-7 km of terrigenous sediments in the crust, 6-7 km of terrigenous sediments in the abyssal plane.abyssal plane.

• There are no obvious magnetic anomalies There are no obvious magnetic anomalies related to ocean floor spreading in the Oman related to ocean floor spreading in the Oman Sea. The oceanic crust formed during the Sea. The oceanic crust formed during the Cretaceous quiet zone (108-79 Ma)Cretaceous quiet zone (108-79 Ma)

Characteristic of Makran Characteristic of Makran MarginMargin

• The island arc volcanics are located The island arc volcanics are located where the subducting plate is at where the subducting plate is at ~100 km depth.~100 km depth.

• There are no indications of active There are no indications of active volcanism or intrusions in the volcanism or intrusions in the Accretionary complex.Accretionary complex.

• The subducting plate has a The subducting plate has a northward dip.northward dip.

Characteristic of Makran Characteristic of Makran MarginMargin• Earthquake activity is low. Most major Earthquake activity is low. Most major

earthquakes appear to be associated with earthquakes appear to be associated with wrench faults.wrench faults.

• Earthquake fault plane solutions show Earthquake fault plane solutions show predominantly shallow northward dipping predominantly shallow northward dipping thrusts, with dips increasing northward, thrusts, with dips increasing northward, away from the Accretionary front.away from the Accretionary front.

• The east-west oriented Accretionary The east-west oriented Accretionary complex is more than 900 km long, complex is more than 900 km long, bounded to the east and west by large bounded to the east and west by large transform faults defining plate boundaries.transform faults defining plate boundaries.

DifferentDifferent

• Of all the Accretionary complexes active Of all the Accretionary complexes active today, none of them is a direct “look-alike” to today, none of them is a direct “look-alike” to the Makran Accretionary Complex. the Makran Accretionary Complex.

• Generally other Accretionary complexes have Generally other Accretionary complexes have more closely spaced thrusts compared to the more closely spaced thrusts compared to the more open, simple structures in Makran.more open, simple structures in Makran.

• This is ascribed to the thick sedimentary This is ascribed to the thick sedimentary cover (6-7 km) over the oceanic crust in the cover (6-7 km) over the oceanic crust in the Gulf of Oman.Gulf of Oman.

SeismicitySeismicity

Seismicity Map

North–south velocity along two profiles, together with the topography and theseismicity. Top: profile crossing the continental collision; bottom: profile crossing the subduction (F. Nilforoushan et. al. 2003)

SEISMIC REFLECTION DATASEISMIC REFLECTION DATA

OFFSHORE MAKRANOFFSHORE MAKRAN

OFFSHORE EAST MAKRANOFFSHORE EAST MAKRAN

N-S 2D seismic data showing the Makran Accretionary Wedge (

OFFSHORE WEST MAKRANOFFSHORE WEST MAKRAN

PC-2000 Seismic Reflection Data Offshore Oman Gulf

SN

Accretionary WedgeAccreted mélangeBack-Arc

Basin

North-south seismic line through the offshore part of the Makran Accretionary Complex.

N

Oceanic crust

S

North-south seismic line through the Accretionary Wedge.

(Base sediments)

N S

North-south line recorded to 20 sec showing from left the fore-arc basin, accreted melange zone and deep water thrust belt.

Fore-arc basin

Accreted melange

deep water thrust belt

Zendan

Landsat image showing southern part of the onshore Zendan-Minab Fault Complex.

EW Fore-Arc Basin

Offshore extension of Zendan Fault system (PC2000 seismic data, NIOC)

Landsat image showing coastal areas of Makran. Cuspate features are in line with Offshore listric faults controlling the Fore-Arc Basin.

Dibba ZoneDibba Zone

• The Dibba Zone is a prominent structural feature/lineament as The Dibba Zone is a prominent structural feature/lineament as defined in Oman, cutting across the Musendam Peninsula in a defined in Oman, cutting across the Musendam Peninsula in a southwest/northeast direction. In northern Oman the Dibba Zone southwest/northeast direction. In northern Oman the Dibba Zone defines the western and northern extent of the ophiolite nappes. defines the western and northern extent of the ophiolite nappes. Onshore the Dibba Zone is also a topographic feature. Onshore the Dibba Zone is also a topographic feature.

• The offshore continuation in Iranian waters lines up with a dog-leg The offshore continuation in Iranian waters lines up with a dog-leg system of a north-south oriented lineament, interpreted as a system of a north-south oriented lineament, interpreted as a thrust front, and a conjugated set of northwest-southeast and thrust front, and a conjugated set of northwest-southeast and northwest-southeast oriented normal faults. The main structuring northwest-southeast oriented normal faults. The main structuring event pre-dates the Tertiary unconformity, and might be event pre-dates the Tertiary unconformity, and might be correlated with the Late Cretaceous (Campanian/Maastrichtian) correlated with the Late Cretaceous (Campanian/Maastrichtian) event leading to emplacement of nappes in Oman. event leading to emplacement of nappes in Oman. To the north To the north the Dibba Zone is bounded by a normal fault (down to the east), the Dibba Zone is bounded by a normal fault (down to the east), close to the southern boundary of the Musendam High.close to the southern boundary of the Musendam High.

• To the northeast the Dibba Zone terminates against the Zendan-To the northeast the Dibba Zone terminates against the Zendan-Minab Fault Complex. Minab Fault Complex.

Landsat satellite image showing the Dibba Zone onshore Oman, with offshore trends based on Seismic data.

Dibba

Zon

e

Qesham Island

W E

East-west seismic line across the northern Dibba Zone showing Late Cretaceous “folding”. Post-unconformity structuring is limited to normal extensional faulting.

Cause of TsunamiCause of Tsunami

• Most tsunamis are caused by a rapid vertical Most tsunamis are caused by a rapid vertical movement along a break in the Earth's crust:movement along a break in the Earth's crust:

• A tsunami is generated when a large mass of earth on A tsunami is generated when a large mass of earth on the bottom of the ocean drops or rises, thereby the bottom of the ocean drops or rises, thereby displacing the column of water directly above it. displacing the column of water directly above it.

• This type of displacement commonly occurs in large This type of displacement commonly occurs in large subduction zonessubduction zones

• Most Subduction occurs along most of the island Most Subduction occurs along most of the island arcs and coastal areas of the Pacific and Makran arcs and coastal areas of the Pacific and Makran Region. Region.

Other possible causesOther possible causes

• Other possible but less efficient methods of tsunami Other possible but less efficient methods of tsunami generation include:generation include:

• Strong oscillations of the bottom of the ocean,Strong oscillations of the bottom of the ocean,• Transmission of energy to a column of water from a seismic Transmission of energy to a column of water from a seismic

impulse (e.g., a deep-focus earthquake that has no surface impulse (e.g., a deep-focus earthquake that has no surface rupture)rupture)

• Transmission of energy from a horizontal seismic impulse to Transmission of energy from a horizontal seismic impulse to the water column through a vertical or inclined wall such as a the water column through a vertical or inclined wall such as a bathymetric ridgebathymetric ridge

• Strong turbidity currentsStrong turbidity currents• Underwater and above-water explosions.Underwater and above-water explosions.

Typical values for a seismically generated Typical values for a seismically generated tsunamitsunami

Persian

Gulf

Oman Gulf

IRAN

Pakistan

1945 EQ

Persian

Gulf

Oman Gulf

IRAN

Pakistan

1945 EQ

1h

2h

Persian

Gulf

Oman Gulf

IRAN

Pakistan 1945 EQ

Tsunami In the coastal region Tsunami In the coastal region of Iranof 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 Early Warning System for Makran RegionMakran Region

Broadband Seismic Network (Established and operated by IIEES

Proposed Seismic stations Proposed Sea-floor pressure sensors

IRAN

PAKISTAN

Persian Gulf

Gulf of Oman

Schematic drawing of Tsunami detection system with time scale for distance earthquake.

ConclusionsConclusions

• Tsunamis are not generated by all earthquakes. To generate a Tsunamis are not generated by all earthquakes. To generate a tsunami, the fault where the earthquake occur must be tsunami, the fault where the earthquake occur must be underneath or near the ocean and cause vertical movement of underneath or near the ocean and cause vertical movement of the seafloor over a large area.the seafloor over a large area.

• The Mediterranean and Caribbean Seas both have few The Mediterranean and Caribbean Seas both have few Tsunami occurrence.Tsunami occurrence.

• Only a few tsunamis have been generated in the Atlantic and Only a few tsunamis have been generated in the Atlantic and Indian Oceans. Indian Oceans.

• Occurrence of 1945 Tsunami puts Makran in an area of prone Occurrence of 1945 Tsunami puts Makran in an area of prone to Tsunami. to Tsunami.

• The largest Tsunamis have occurred in the Pacific Ocean. The largest Tsunamis have occurred in the Pacific Ocean. • The Tsunami can be detected using early warning System.The Tsunami can be detected using early warning System.• Move quickly to HIGHER PLACE.Move quickly to HIGHER PLACE.

The Invitation to Tehran for The Invitation to Tehran for May 2007 May 2007

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