Istanbul Canal’s Impacts on Earthquakes
You can click on the titles below to get information about the seismic effects of the Istanbul Canal Project.
Istanbul is a city that expects a very severe earthquake with a moment magnitude greater than 7 at any time, and the Istanbul Canal is planned to be built starting only 11 kilometers apart from the extension of the North Anatolian Fault Line in the Marmara Sea.
The southern part of the Istanbul Canal will be built in one of the most active regions of the country in terms of earthquake hazards. Therefore, it is mandatory to consider the earthquake action in the Canal design and the engineering structures associated with the Canal. These structures are main canal structure, bridges (highway and railway bridges), tunnels (railway, subway, infrastructure tunnels), infrastructure transition structures (wastewater, potable water, energy transmission, natural gas, telecommunication lines), and coastal-port structures.
According to the EIA Report, among all these structures, the main canal structure is the only structure in which the earthquake risks were tried to be estimated rationally. The earthquake performance of the main canal structure largely depends on the dynamic properties of the base of the Canal, since it is a ground structure. In this context, the 16.2-kilometer southern part of the structure located between the Marmara Sea and the Sazlıdere Dam is over extremely weak ground composed of an alluvial type, a very suitable type for liquefaction during an earthquake.
The EIA report addresses the liquefaction and slope stability analysis applying approximate methods for various soil units in this part of the Canal. It has been understood from the results that the permanent soil deformations calculated on the slopes and base of the Canal are far above the acceptable damage limits. In other words, the main structure of the Canal is exposed to “high earthquake risk”.
Even though this critical result should have immensely affected the route selection, the EIA report only suggests unrelated, unacceptable, and conflicting solutions.
In the EIA Report, it is recommended to arrange the base and slopes of the Canal bscreening after each earthquake, furthermore, there are “crazy” suggestions such as removing the existing base of the Canal with a length of 16.2 kilometers and renewing or improving it with better material at all depths, as well. However, the costs of such suggestions are not provided.
The situation is critical. A section of the Canal, which constitutes one-third of the total length, is on an extremely weak ground environment. It is evident that this section will liquefy and face potential large permanent deformations, even infrequent earthquakes. All these things considered, the technical, operational, and financial feasibility of the selection of the route of the Istanbul Canal raises suspicions. This issue must be clarified with a more detailed analysis.
On the other hand, there are limestone formations located on the west side (left) slopes and partially at the bottom of the 5.2-kilometer part of the Canal, between the northern end of Küçükçekmece Lake and the body of Sazlıdere Dam of the above-mentioned 16.2-kilometer section of the Canal. Therefore, it is planned to apply impermeability coating with the geosynthetic concrete liner at the bottom and the slopes of the Canal to prevent the risk of the existing groundwater reserve getting salty. However, the EIA report does not mention the earthquake damage that will occur in the form of liquefaction on the slopes and the bottom of the same Canal section. Earthquake damages resulting in slope collapses will cause damage to the impermeability coating to be applied in this section. Similarly, it is evident that the team conducting the liquefaction analysis was not aware of such impermeability coating.
According to the EIA Report, estimation of the cost of the transition structures (highway and railway crossing bridges, railway and subway tunnels, infrastructure transition structures) is 20% (15 billion TL) of the total cost of Canal Istanbul, excluding the main channel structure and the coastal-port structures. However, no earthquake analysis, similar to that for the main Canal structure performed, has been tried for any of these transition structures. The EIA Report only contains the schematic drawings of the conceptual designs of these structures. All of the transition structures, especially the crossing bridges, are massive engineering structures that are very ambitious in terms of earthquake response. The foundations of seven towers of the large span bridges (out of eight), which go up to 220 meters, will be built in the alluvial grounds in the Canal section, which is stated above that it will liquefy. The EIA report does not contain any concrete solution suggestions for constructing these foundations or any realistic estimates on how much they will cost.
It is highly doubtful that the transition structures, most of which will be built in the southern part of the Canal, where the earthquake effects will be the greatest, can be constructed at an estimated cost of TRY 15 billion. Transition buildings of the Canal, which include two large-span highway bridges with inclined hangers, two subway tunnels, various clean water transport pipes, wastewater pipes, and natural gas pipes, will not be built within the scope of the buildoperate investor. They will be reconstructed under the responsibility of MM, and will inevitably bring an unnecessary financial burden to IMM beyond the estimations.
In conclusion, it is an undeniable fact that the part of the Istanbul Canal that constitutes one-third of the main Canal structure in the south is exposed to a high risk of damage in case of earthquakes, due to liquefaction on the ground underneath. The earthquake risk is far above the acceptable limits for the main Canal structure and must be re-assessed. The issue is critical enough to affect the selection of the route of the Canal Istanbul. The other engineering structures associated with the Canal are also under possibly very high damage risks in earthquakes. Also, the EIA Report does not mention high construction costs in any way.
The Istanbul Canal is an extremely risky structure in terms of earthquakes. Especially the section of the Canal between Sazlıdere Dam and the Marmara Sea is exposed to the threads of an active fault, liquefaction, landslide, and tsunami. Apart from these natural hazards, the Canal itself has the potential of increasing the earthquake risk in a possible earthquake. These risks are briefly discussed in separate paragraphs below:
The continental shelf where the Canal Istanbul meets the Marmara Sea is fragmented by NW-SE and roughly E-W trending faults. These faults are active. Due to their size, they may not cause large earthquakes on their own, but it is definite that they form a zone of weakness.
The expected Marmara Earthquake will have a minimum magnitude of 7.2. When this earthquake occurs, the part of the Istanbul Canal between Küçükçekmece Lake and the Marmara Sea will be affected with an intensity of at least IX-X. It is tremendously difficult for this part of the Canal to withstand an earthquake of this magnitude without critical damage. During the earthquake, the faults within the continental shelf will move and will significantly increase the impact along the route of the Canal up to Küçükçekmece. The Canal will be largely destroyed by the probable lateral and vertical movements.
The ground of the Canal between the Sazlıdere Dam and the Marmara Sea has a high liquefaction potential. In a possible earthquake, it is certain that these sediments will act as liquids and cause deformations in the Istanbul Canal and related structures such as collapses, settlements, and rotations. These materials are impossible to be scraped off completely in the Küçükçekmece region due to their thickness. Such an action will cause another stability problem in the area. It should also be noted that apart from the recent alluvium and sand dunes, the sandy and silty levels within the Tertiary formations at the base of these units will also contribute to liquefaction.
Küçükçekmece region is the most active region of Istanbul in terms of landslides. There is a radical relationship between active faults within the continental shelf and these landslide zones. When the expected Marmara Earthquake hits, the main earthquake zone will first trigger the faults within the shelf, and they will trigger the landslide zones on the land. This risk should never be overlooked. If these landslides start, it is not possible for the Canal, which will pass through Küçükçekmece Lake, not to be significantly affected. This Canal, which is shallow and narrow, will possibly be destroyed and blocked by landslides.
The expected Marmara Earthquake will probably happen along with a tsunami. If the tsunami waves enter the Canal, they can act as if they are molded and grow, causing significant damage to the Canal. The rapidly flowing tsunami current may hit, carve, and cause the collapse on the sides and slopes of the Canal with great force. The materials from the sides will be carried into the Canal and drift alongside the structure. The base and insulations of the Canal can be severely damaged during this material flow and drift. If there are ships passing through the Canal during a tsunami, they may drift due to the current velocity. If the drifting materials form a dam, the water level will rise in the Canal, which may cause the sea to take over the land in places with appropriate topography.
Many factors increase the risk in an earthquake-prone city. One of them is increasing the number of buildings and the population in that city. The more the structure and population increase, the higher the risk of a possible earthquake. The Istanbul Canal is such a project. Therefore, it will increase the risk of loss of life and property in Istanbul in a probable earthquake. Istanbul Canal will interrupt disaster management and emergency response activities in a possible earthquake if built. The reason for that is a significant part of Istanbul will turn into an island with this project, and this island and Thrace, and Anatolia will only be accessible by the sea, bridge, or tunnels. In an earthquake, emergency response and disaster management will be impossible if these roads are partially or completely damaged. Hence, the peak of loss of lives.
Available sources suggest that the number of earthquakes with a magnitude of M≥6.0 that affected the settlements in the Marmara Region and the European and Anatolian peninsulas of Istanbul in the last 1990 years is 85. 38 of these earthquakes had magnitude of 7.0 or higher. The number of tsunamis on the shores of the Marmara Sea is 37. As a matter of fact, the scientific studies conducted so far show that the probability of an earthquake with a magnitude of 7.0 or higher in the next 30 years has reached 65%. This danger increases by 2.5% every year. Istanbul is a city with a population of 16 million and is still under the pressure of population increase. There is a vital situation in terms of loss risks for the settlements and important engineering projects (bridge, viaduct, industrial facility, chemical and fuel storage facility, energy facility, dam, port, airport, high building, tunnel, pipeline, power line) of Istanbul.
The previous geological and geophysical surveys detected new active faults in the NNW-SSE trending and moving towards the right direction in Küçükçekmece Lake. According to the measurements of PS-InSAR observations made between 2002-2010, a new fault with a right-trending fault with a movement value of 5 mm/year was found. These studies published in international refereed journals were not cited or mentioned in the final EIA Report. The relevant annexes of the final EIA Report shows various faults in 28 of the geological-geophysical-geotechnical sections provided. However, there are no established relations between the types, ages, and tectonic movements of these faults, and no interpretation is provided in the report. The report should have assessed these faults and investigate their motion characteristics and active fault potentials.
In the EIA studies for the Istanbul Canal Project, which is planned to connect the Marmara Sea and the Black Sea, the maximum and spectral acceleration values that it will be exposed to in the Marmara Sea inlet section was calculated to be PGA:0.773 g, Ss: 1.975 g, and S1: 0.641 g for S wave velocity Vs30 = 760 m/sec (NEHRP standard B/C limit) according to the Safety Based Earthquake Level measure. These values show the magnitude of the impact of the earthquake will be on the parts of the Canal near the Marmara shores. Additionally, the previous geological and seismological studies reveal that the deep geological and geophysical structure towards the north, especially in the vicinity of the Marmara Sea, has liquefaction and landslide hazards, and the seismic movement during an earthquake causes soil amplification above the expectations. An analysis of the soil amplification specific to the region is not provided in the soil movement analysis in the EIA Report.
The tsunami that may occur on the shores of the Marmara Sea has two sources: earthquakes and sea bottom landslides. These two potential tsunami hazards are assessed in the EIA study. However, the earthquake and landslide-based tsunami triggering models envisaged by the same research group for the EIA study are different from models provided in the report submitted to IMM in 2018. The reason for this difference is not explained in the EIA Report.
16 million kilograms of ANFO will be detonated in 4 years during the excavation phase of the Canal, according to the predictions. The daily 11-ton denotations for 4 years will release a seismic energy equivalent to an earthquake with a magnitude of 3.8. There is no assessment of the stress and strain changes that such seismic energy will cause, considering the underground cracks, fractures, faults, and pore pressure changes.
The vicinity of the Istanbul Canal will be zoned for construction, causing an increase in the population and the number of buildings, thereby increasing the risk of loss of life and property in a possible earthquake. In such earthquake-prone regions, the aim should be to decrease the built environment and population density, not increase them. TRY 75 billion to be spent for the Istanbul Canal construction (cost according to 2019) should be used to reduce the earthquake loss risks of Istanbul and its vicinity. Istanbul is a city that expects the reduction of earthquake risks that will cause a tragic loss of life and property. Istanbul’s priority is not the Istanbul Canal, but an Istanbul that is Earthquake-Safe and Livable.