April 23 Istanbul Earthquake Not Linked to Major Expected Marmara Quake, Says Leading Geophysicist

Istanbul Technical University geophysics professor Tuncay Taymaz says the April 23 magnitude 6.2 earthquake off Silivri in the Marmara Sea and its aftershocks are not directly linked to the long-feared devastating Istanbul earthquake anticipated along the North Anatolian Fault (NAF).

“A Warning, Not a Catastrophe”

According to Prof. Taymaz, the April quake—estimated by his team at magnitude 6.3—originated from a previously unruptured fault segment in the Marmara Sea, at about 10 kilometers deep. The quake did not reach the seabed surface, but caused 90 cm of displacement at depth.

He noted that the quake’s strong shaking in northern Marmara, particularly Istanbul, was a result of poor soil quality in many districts. “The significant tremor, despite the relatively modest magnitude, reflects the presence of weak ground and structurally unsound buildings,” Taymaz emphasized.

The incident, he said, served as a “natural drill” for both residents and emergency responders, offering a real-time test of preparedness and highlighting critical questions: “Where do we stand? Is our building safe?”

No Direct Trigger for the Big One, But a Step Closer

Taymaz reassured the public that this earthquake does not pose the same level of threat as the major Marmara earthquake long expected. However, it did rupture a 20-25 km section near the Silivri-Kumburgaz ridge, leaving a remaining 10–15 km segment unbroken, which could still generate a magnitude 5.8 earthquake—similar to the September 26, 2019 event.

“It’s a bad scenario, but not catastrophic. If triggered, it may cause moderate damage,” he said.

Taymaz issued a critical warning: If this minor segment breaks, it could potentially activate the locked segments of the Yeşilköy-Bakırköy to Çınarcık fault lines, possibly initiating the long-feared magnitude 7+ Istanbul earthquake.

Seismic Energy Released, But Not Enough

The April 23 quake allowed for a partial release of seismic energy, Taymaz explained, meaning some stress has dissipated, and the fault is progressing in small increments rather than one devastating rupture. This is in contrast to the 2023 Kahramanmaraş twin earthquakes, which triggered multiple faults simultaneously.

Still, Taymaz cautioned against complacency. “While this quake may have nudged us closer to the big one, we can’t predict whether it will happen in three weeks, three years, or a decade.”

Weak Soils, Riverbeds, and Coastal Zones at Highest Risk

If a major Istanbul earthquake were to occur, the most vulnerable zones include weak soils, river valleys, coastal terraces, sediment basins, and landslide-prone areas. Districts closest to the NAF, like Bakırköy and Yeşilköy, lie only 8–9 kilometers from the fault.

Fortunately, Taymaz noted that modern seismic engineering solutions, such as seismic base isolators, can help mitigate risks—especially in public infrastructure like hospitals, schools, metros, viaducts, and dams. These systems, similar to shock absorbers, can limit structural damage and are becoming more cost-accessible, increasing total construction costs by only 10–15%.

“We Must Be as Selective Buying Homes as We Are Buying Tomatoes”

Calling for increased public awareness, Taymaz said that citizens must take as much care in choosing where they live as they do with everyday purchases. “The government, local authorities, and civil society are doing their part. Now, it’s our turn to ask: Is my home earthquake-safe?”

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