behind the scenes of the earthquake in the capital; “Water pumping” is a silent threat to the north fault of Tehran

Dr. Mehdi Zare, full professor of the International Research Institute of Seismology and Earthquake Engineering in an interview with ISNA By posing the question “Does water pumping have anything to do with triggering the north Tehran fault?” And how accurate is this claim that “according to the hydraulic conditions governing the underground water of the plain and the highlands north of Tehran, pumping water in Varamin and Ray and the plains of Tehran has nothing to do with stimulating and intensifying and accelerating the activity of the north Tehran fault”? He said: The claim made that the pumping of underground water in Varamin, Ray and Dasht of Tehran has nothing to do with stimulating, intensifying and accelerating the activity of the North Tehran fault is not accurate.

He added: Subsidence and change of tension and the connection of underground water pumping with the activity of faults are discussed in such a way that ground subsidence due to excessive extraction of underground water, especially in alluvial plains, causes a decrease in pore water pressure and, as a result, compression of soil and sediment layers (hydraulic compaction). Land subsidence, especially at high speed in the south and southwest of Tehran, which is reported to be more than 30 cm per year, can cause significant stress changes in the crust and in the adjacent fault zones. These stress changes can increase the shear stresses on the faults and bring them closer to the rupture threshold, which is called “earthquake triggering”.

Zare stated that earthquakes like the Mallard earthquake on 29 December 2016 occurred in the zone with severe subsidence and may be related to this phenomenon, and stated: This zone is located in the vicinity of the main faults of the region, including the North Tehran fault, and the change in stress due to subsidence is effective in transferring the Coulomb stress to the adjacent zones, including the North Tehran fault in Wardvard.

The professor of the International Research Institute of Seismology and Earthquake Engineering added: Drainage of underground water reduces pore pressure. A decrease in pore pressure in a water-saturated rock effectively increases the effective normal stress on the fault surface. An increase in normal stress usually causes fault containment, and stress changes caused by subsidence due to the compression of layers can also cause lateral changes in shear stress in deeper areas and far from the main pumping site, which can be irritating.

According to this risk researcher, the stress changes caused by the subsidence in the plains of Tehran area are transferred to the western end of the fault north of Tehran, as well as the range of Ray, Masha and Mahdasht-southern Karaj faults. This chain of stress changes can eventually affect the stress loading on the North Tehran fault and possibly accelerate it.

He emphasized: Therefore, even though pumping does not occur directly on the surface trace of the north Tehran fault, the hydraulic and mechanical changes caused by it in the alluvial plains are effective in stimulating and accelerating the activity of the north Tehran fault and other active faults in the region through the mechanisms of stress transfer and land subsidence.

Scientific evidence of the effects of water pumping on faults

Zare continued: On the other hand, it is claimed that the issue of water pumping is related to the surface layers up to a maximum of 200 to 300 meters, while the occurrence of earthquakes in the faults in the Tehran area is related to the depth of 5 to 20 kilometers, therefore, water pumping and subsidence cannot trigger the faults. The claim that pumping and subsidence cannot trigger faults is not correct according to scientific findings and local observations.

He explained about this: Indiscriminate pumping of groundwater with stress changes created on the surface of the earth and shallow layers can be mechanically transferred to the fault plane at depth. This phenomenon can be justified based on the principles of rock mechanics and the elasticity of the earth’s crust. Indiscriminate extraction of underground water in the alluvial plains of Varamin, Ray, Shahryar and Mallard causes a decrease in pore water pressure and as a result, clay and alluvial layers are compressed in low to medium depths. This compression is observed on the surface of the earth in the form of subsidence with high rates up to more than 30 cm per year.

The Professor of Seismological Research Institute pointed out: The massive displacement and deformation caused by subsidence in the surface layers creates mechanical loads and stress changes, especially shear stress and vertical stress in deeper layers, especially at the end of the north Tehran fault and the surface trace of the Mahdasht-South Karaj fault and the Pardisan fault. This phenomenon is called “Coulomb tension” change. The change of shear stresses can reduce the resistance of the fault against sliding and bring it closer to the rupture threshold.

He emphasized: Many recent small to medium earthquakes in Tehran region, such as the Mallard earthquake in 2016 (M=5), occurred in the Mallard subduction zone. These evidences strengthen the connection between the subsidence and the activation of faults such as the Mahdasht-South Karaj fault.

Zare added: Although the majority of pumping is from surface aquifers, in some areas, pumping deeper wells that reach deeper aquifers and sometimes close to bedrock can also have a more direct effect on pore pressure near faults. However, even without direct pumping at depth, the mechanism of subsidence and stress transfer is still active. Focusing only on the depth difference and ignoring the stress transfer mechanisms is a simplistic view. Huge volume changes on the scales of tens of cubic kilometers and high rates of subsidence, which have been reported in the south of Tehran up to more than 30 cm within the limits of Zone 1 of Tehran Municipality, are large enough to change the stress balance in deep faults.

Subsidence has a universal color

This professor of the International Research Institute of Seismology did not consider the issue of the connection between the pumping of underground water or the discharge of subsurface fluids and the stimulation of faults (induced seismicity) to be a purely local issue in Iran and continued: the extraction of underground water and subsidence in other countries is also a similar mechanism to what happened in Tehran, that is, the subsidence of the ground caused by the indiscriminate extraction of water and the transfer of stress to deeper faults is considered to be the cause of earthquake stimulation. will be

He regarded it as an example in Spain and added: Scientific and strong studies of the 2011 Lorca earthquake with a magnitude of 5.1, which resulted in human and financial losses, show that this earthquake was related to the intense extraction of underground water and changes in pore pressure in a shallow fault, and the close connection with the subsidence of the earth caused by the intense extraction of underground water led to a significant change in the shape of the earth, the sliding of a shallow fault and extensive damage in this city.

Zare pointed out: the draining of the aquifer has changed the stress on the Alhama de Murcia fault and caused shallow earthquakes, highlighting the role of human activities in seismic events and the need for sustainable water management. Decades of groundwater pumping in the Alto Guadalentín Basin caused a significant drop in the water level up to 250 meters and subsequent land subsidence and compaction of compactable soils. This crustal drainage caused by water withdrawal imposed stresses on the shallow parts of the Alhama de Murcia fault, which changed the frictional properties and made the fault more prone to slip.

According to him, the 5.1 earthquake Spain It included a shallow rupture of 4 km in this fault, which was associated with compressional and left-rotational movement and caused strong tremors and surface displacement.

Zare continued: This subsidence created conditions that facilitated the nucleation and sliding of the earthquake, making it a clear example of seismicity caused by human activities or induced seismicity. The shallow depth and stresses associated with the subsidence resulted in severe damage to buildings, including historic structures, and resulted in fatalities and injuries.

This researcher of the International Research Institute of Seismology found another example in United States of America He mentioned and said: California’s San Joaquin Valley has one of the most severe subsidence rates in the world due to water extraction for agriculture. While groundwater pumping in the San Joaquin Valley is associated with low-magnitude annual seismicity modulation (typically less than 1.3) and could potentially advance the timing of a major tectonic earthquake on the San Andreas Fault.

He emphasized: The seasonal fluctuation of the groundwater level (more pumping in the dry season) causes the surrounding coastal mountain ranges and the Sierra Nevada mountains to rise, which slightly reduces the vertical pressure on the San Andreas fault and increases the amount of small earthquakes. Changes in stress caused by long-term groundwater discharge could potentially cause the next major tectonic earthquake on the San Andreas Fault to occur a little earlier than previously expected, but it is not the main cause of the major earthquake itself. Some earthquakes with a magnitude of more than 4 tectonics in other parts of California (especially Kern County oil fields) have been linked to various human activities such as fluid injection into waste disposal wells, which are different from the groundwater pumping-subsidence mechanism.

Occurrences of earthquakes in occupied Palestine caused by excessive water extraction

The full professor of the International Research Institute of Seismology and Earthquake Engineering stated: In occupied Palestine, Lake Kinneret, clusters of earthquakes in this area have been associated with the continuous withdrawal of underground water and a sharp decrease in the water level. Modeling has shown that the reduction in pore pressure caused by pumping can create expansion stresses that cause faulting.

He stated: The drying up of Kinneret Lake (Sea of ​​Galilee) is the result of reduced rainfall and excessive water extraction, and this process is related to induced seismicity (earthquake waves) in the region. Kinneret Lake is the main natural fresh water reservoir of occupied Palestine and is located in the seismically active valley of the Dead Sea. A combination of declining rainfall patterns and over-harvesting of water to meet the needs of a growing population has caused the lake’s level to drop significantly over the decades. In a major policy change, the Israeli regime created a “reverse aqueduct” system to pump desalinated Mediterranean water into the lake as needed to maintain its level. There is a relationship between human activities related to water management and induced seismicity near the lake.

Zare added: The categories of small to medium earthquakes (magnitude 3 to 4) have been linked to periods of significant reduction in the level of underground water in the water tables around the lake. Removing large amounts of groundwater reduces the pressure in the rock’s pores, potentially making existing faults slip more easily. Significant earthquake clusters occurred in October 2013 and July–August 2018 in the northern part of the lake, with focal depths of mostly less than 10 km, supporting the human-induced hypothesis. This active tectonic zone on the Dead Sea fault has a history of large earthquakes such as 1202, 1759 and 1927 due to tectonic stress. It seems that changes in water pressure caused by human activities are capable of causing smaller and shallower earthquakes.

Oil and earthquake activities

The professor of the International Research Institute of Seismology and Earthquake Engineering, referring to the effect of oil activities on seismic excitation, said: In the Groningen gas field of the Netherlands, extensive gas extraction caused numerous earthquakes up to magnitude 3.6 and left significant damages. So that the active production of this field was stopped in 2023.

According to him, the decrease in the pressure and density of the tank in this field has caused a change in the stress in the surrounding rocks and induced seismicity.

Zare added: The increase in pore pressure is one of the most well-known consequences of human activities, including fluid injection, which can trigger faults and cause induced earthquakes. The effective stress is the force that is borne by the solid grains of the rock and determines its resistance to rupture and sliding. This stress is obtained from the difference of total stress and pore pressure.

Zare, emphasizing that fault rupture and sliding occurs when the applied shear stress exceeds the fault’s shear strength. Shear resistance is calculated based on the Coulomb-Moher law and is directly related to the effective normal stress on the fault surface. If a fault is already under tectonic shear stress, the reduction of its shear strength is enough to cause the existing stress to slip and as a result earthquake. Simply put, “the injected water acts like a lubricant and releases the fault.”

He further pointed to the experience of the state of Oklahoma and said: In this region, the injection of large volumes of wastewater from oil and gas production into deep wells increased pore pressure and stimulated passive faults; So that the number of magnitude 3 earthquakes in this state increased from about two events per year to hundreds of earthquakes per year.

Stating that this mechanism is the opposite of the process that occurs as a result of ground subsidence in Tehran, Zare explained: In Oklahoma, fluid injection increases pore pressure, reduces effective stress, and as a result reduces shear resistance of the fault and its stimulation. But in Tehran, pumping and draining the aquifer reduces the load on the aquifer, increases the shear stress and changes the total stress due to subsidence, which can stimulate faults in the region through stress transfer.

end of message