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 February 2006

Outline Introduction Introduction Major structural Elements Major structural Elements Seismicity Seismicity Tsunami Early Warning System Tsunami Early Warning System Conclusions Conclusions An Invitation An 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 Margin There is no obvious topographic trench associated with the present Accretionary front. There is no obvious topographic trench 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 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 ( Ma) There are no obvious magnetic anomalies related to ocean floor spreading in the Oman Sea. The oceanic crust formed during the Cretaceous quiet zone ( Ma)

Characteristic of Makran Margin The island arc volcanics are located where the subducting plate is at ~100 km depth. 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. There are no indications of active volcanism or intrusions in the Accretionary complex. The subducting plate has a northward dip. The subducting plate has a northward dip.

Characteristic of Makran Margin Earthquake activity is low. Most major earthquakes appear to be associated with wrench faults. Earthquake activity is low. Most major 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. 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. 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, none of them is a direct “look-alike” to the Makran Accretionary Complex. Of all the Accretionary complexes active today, 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. 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. 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

S N Accretionary Wedge Accreted mélange Back-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 basinAccreted melangedeep water thrust belt

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

E W 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 Zone The Dibba Zone is a prominent structural feature/lineament as defined in 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 Dibba Zone is a prominent structural feature/lineament as defined in 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. 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. To the northeast the Dibba Zone terminates against the Zendan-Minab Fault Complex.

Landsat satellite image showing the Dibba Zone onshore Oman, with offshore trends based on Seismic data. Dibba Zone 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 Tsunami Most tsunamis are caused by a rapid vertical movement along a break in the Earth's crust: Most tsunamis are caused by a rapid vertical 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. 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 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. 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 include: Other possible but less efficient methods of tsunami 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 impulse (e.g., a deep-focus earthquake that has no surface rupture) 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 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 Strong turbidity currents Underwater and above-water explosions. Underwater and above-water explosions.

Typical values for a seismically generated tsunami

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 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

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.

Conclusions Tsunamis are not generated by all earthquakes. To generate a 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. Tsunamis are not generated by all earthquakes. To generate a 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. The Mediterranean and Caribbean Seas both have few Tsunami occurrence. Only a few tsunamis have been generated in the Atlantic and Indian Oceans. 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. Occurrence of 1945 Tsunami puts Makran in an area of prone 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 May 2007 More information SEE5 SEE5 SEE5