Turkey Earthquake Hazard Map: Highest-Risk Cities and Regions

Introduction: Turkey's Seismic Reality

Turkey stands as one of the world's most seismically active nations, positioned at the junction of three major tectonic plates—the Eurasian, Arabian, and African plates. This precarious geologic location has shaped Turkey's earthquake history for millennia and continues to present significant challenges for modern urban planning and construction. Approximately 95% of Turkey's land area experiences some level of earthquake risk, making seismic hazard assessment not merely an academic exercise but a critical necessity for property owners, builders, engineers, and policymakers. The devastating 2023 earthquakes that claimed thousands of lives across Turkey and Syria underscored the critical importance of understanding and preparing for seismic risk.

Turkey's Complex Tectonic Setting

Turkey's position at the intersection of the Eurasian, Arabian, and African plates creates one of the most complex tectonic environments on Earth. The Anatolian Plate, the sliver upon which most of Turkey sits, is slowly moving westward relative to the Eurasian Plate, creating intense stress along major fault systems. This geodynamic setting has produced two dominant structural features: the North Anatolian Fault (NAF) and the East Anatolian Fault (EAF).

The North Anatolian Fault, approximately 1,200 kilometers in length, represents one of the world's most significant continental strike-slip faults. It extends from the Karaca Fault near the Turkish-Georgian border in the east, passing through northern Turkey, and terminating in the Aegean Sea west of Istanbul. The NAF is predominantly a right-lateral strike-slip fault, meaning the blocks on either side move horizontally past each other to the right. This fault has produced some of the most destructive earthquakes in recorded history, including the catastrophic 1999 İzmit earthquake (Mw 7.6).

The East Anatolian Fault extends approximately 580 kilometers from the Karliova triple junction in the north to the Mediterranean coast near Iskenderun in the south. The EAF is also predominantly right-lateral strike-slip in character and produces significant seismic events. The 2023 Kahramanmaraş earthquake sequence, beginning with a Mw 7.8 mainshock, demonstrated the EAF's continued hazard potential.

In addition to these major fault systems, Turkey is affected by the Aegean extensional zone to the west and the Hellenic subduction zone beneath the Aegean Sea. These regions are characterized by normal faulting and produce smaller but still significant earthquakes. Sengor et al. (2005) and Barka (1996) provided foundational work characterizing Turkey's seismotectonic framework, establishing that the country's seismic activity results from the ongoing collision and lateral escape of continental plates.

Historical Evolution of Turkey's Earthquake Hazard Maps

Earthquake hazard mapping in Turkey evolved significantly over the past century as scientific understanding and computational capabilities improved. The first systematic earthquake hazard map for Turkey was produced in 1945, identifying broad zones of relative seismic activity based on historical earthquake records. However, this approach was crude by modern standards, relying entirely on observed seismicity without incorporating fault models or probabilistic analysis.

A major update occurred in 1972, incorporating additional earthquake data and refined zoning boundaries. However, the most significant methodological shift came with the 1996 seismic hazard map, which introduced a five-zone classification system: Zone 1 (very high seismic risk), Zone 2a (high risk), Zone 2b (moderate risk), Zone 3 (low risk), and Zone 4 (very low risk). This zoning approach remained influential in Turkish building codes for over two decades.

The landmark 2018 update fundamentally transformed Turkey's approach to seismic hazard assessment. The Turkish Government's Directorate General for Disaster and Emergency Management (AFAD—Afet ve Acil Durum Yönetimi Başkanlığı) released the Türkiye Deprem Tehlike Haritaları (TDTH—Turkey Earthquake Hazard Maps), which abandoned the simplistic zoning approach in favor of a coordinate-based probabilistic seismic hazard analysis (PSHA). This represented a paradigm shift from categorical zoning to spatially continuous hazard estimates.

The advantages of the 2018 coordinate-based system are substantial. Rather than applying the same risk class to an entire zone regardless of location within it, the TDTH system provides precise hazard estimates for any latitude-longitude coordinate. This granularity enables more accurate site-specific building design, more informed insurance pricing, and better-calibrated land-use planning decisions.

Probabilistic Seismic Hazard Analysis: The Foundation of Modern Maps

The 2018 AFAD hazard maps employ Probabilistic Seismic Hazard Analysis (PSHA), a sophisticated methodology that combines earthquake science with probability theory to estimate ground motion intensity at specific locations. PSHA accounts for all plausible earthquakes that could affect a site, weighted by their probability of occurrence, and integrates their potential ground motion effects using attenuation relationships (also called ground-motion prediction equations or GMPEs).

The PSHA methodology involves several key steps. First, seismic sources—including faults, background seismicity zones, and subduction interfaces—are identified and characterized with parameters such as maximum magnitude, slip rate, and recurrence intervals. For Turkey's major faults like the NAF and EAF, decades of paleoseismic research, GPS geodetic measurements, and historical seismicity records inform these source models.

Second, magnitude-frequency relationships are established to describe how earthquake magnitude correlates with probability. The Gutenberg-Richter relationship, which states that smaller earthquakes occur far more frequently than larger ones, forms the basis for these estimates. For individual Turkish faults, local recurrence data refine these global relationships.

Third, attenuation relationships—empirical equations derived from strong-motion recordings of past earthquakes—predict ground motion intensity as a function of magnitude, distance, and site properties. For Turkish PSHA, the Akkar and Bommer (2010) attenuation relationships are widely employed, as they are specifically calibrated for Mediterranean and Middle Eastern tectonics.

Fourth, the analysis integrates all possible earthquake scenarios at all relevant distances, weighted by their probability, yielding a final probability distribution of ground motion intensity at the site of interest. This produces probabilistic estimates for multiple return periods—typically 475 years (a 10% probability of exceedance in 50 years, corresponding to building design standards) and 2,475 years (a 2% probability of exceedance in 50 years, a more conservative level used for critical infrastructure).

Key Seismic Parameters Explained

Peak Ground Acceleration (PGA) is the maximum rate of change of ground velocity during an earthquake, measured in units of gravitational acceleration (g). PGA represents the strongest single-directional shaking the ground experiences. A PGA of 0.10g, for example, means peak acceleration equals 10% of gravity. PGA is relevant for short-period structures and loose connections.

Short-Period Spectral Acceleration (SS) represents ground motion at a 0.2-second period, relevant for relatively stiff structures. Buildings with fundamental periods around 0.2 seconds—typically low-rise or very stiff buildings—respond most strongly to SS motion.

1-Second Spectral Acceleration (S1) represents ground motion at a 1-second period, governing response of more flexible structures with longer fundamental periods. Mid-rise buildings and structures on soft soils typically have periods in the 0.5 to 1.5-second range and respond primarily to S1 motion.

Design Spectral Acceleration for Short Period (SDS) and Design Spectral Acceleration at 1-second (SD1) are derived from SS and S1 after applying soil amplification factors and other adjustments. These are the parameters actually used in building code seismic design calculations. Soil class influences these parameters significantly—soft clay amplifies longer-period motion more than short-period motion.

Regional Risk Analysis: Where is Turkey Most Dangerous?

Istanbul and Marmara Region: The Highest Urban Risk

Istanbul and the Marmara region face the highest seismic hazard in Turkey, with PGA values at the 475-year return period often exceeding 0.30g. The North Anatolian Fault passes directly through this region, running offshore through the Sea of Marmara. Research by Parsons et al. (2004) calculated that the probability of a magnitude 7.0 or greater earthquake occurring on the Marmara segment of the NAF within 30 years is approximately 62%—an alarmingly high probability for a metropolitan region of over 15 million residents. The 1999 İzmit earthquake (Mw 7.6) killed approximately 17,000 people and displaced hundreds of thousands, providing a stark reminder of this region's seismic reality. Istanbul's dense urban environment, aging building stock, and concentration of critical infrastructure make earthquake risk here particularly consequential.

Eastern Turkey: The East Anatolian Fault Zone

Eastern Turkey along the East Anatolian Fault experiences significant seismic hazard. The 2023 Kahramanmaraş earthquake sequence, beginning on February 6, 2023 with a Mw 7.8 mainshock followed by thousands of aftershocks including a Mw 7.5 mainshock on February 7, devastated the Kahramanmaraş region and neighboring areas. Cumulative casualties exceeded 50,000 across Turkey and Syria. This sequence demonstrated that the EAF remains an active hazard and that eastern Turkey's building stock requires careful seismic design.

Aegean Coast: Extension and Seismicity

The Aegean coast, particularly around İzmir and Manisa, experiences moderate to high seismic hazard associated with normal faulting in the Aegean extensional zone. The 2020 İzmir earthquake (Mw 7.0) caused significant damage and demonstrated this region's continued seismic hazard. While hazard levels here are somewhat lower than in the Marmara region, the dense population in İzmir makes even moderate earthquakes consequential.

Mediterranean and Hatay Region

Southern coastal regions including Hatay, Adana, and Mersin lie near the Hellenic subduction zone and experience seismic hazard from both subduction earthquakes and crustal faults. The 2023 earthquake sequence affected Hatay significantly, with widespread building collapse and destruction. Seismic hazard in this region is generally moderate to high.

Central Anatolia: The Relative Low-Risk Region

Central Anatolia, while not entirely earthquake-free, experiences relatively lower seismic hazard compared to border regions. However, even here, PGA values for the 475-year return period typically exceed 0.15g, indicating that earthquake-resistant design remains essential. Ankara experiences lower seismic risk than Istanbul or İzmir, but historical earthquakes demonstrate that central Anatolia is not seismic-free.

How to Use the 2018 AFAD Hazard Maps

AFAD provides an interactive web portal for accessing site-specific seismic hazard estimates. The TDTH (Türkiye Deprem Tehlike Haritaları) interactive map at tdth.afad.gov.tr allows users to query any location within Turkey and retrieve design ground motion parameters.

Step 1: Navigate to tdth.afad.gov.tr in your web browser.

Step 2: Enter your specific address or latitude-longitude coordinates in the search function.

Step 3: The system displays seismic parameters for your location, including PGA, SS, S1, SDS, and SD1 at both 475-year and 2,475-year return periods.

Step 4: Record your site's soil classification (typically A, B, C, D, or E in Turkish building codes) and seismic parameters for design purposes.

Check your location: Our free analysis tool retrieves the exact AFAD seismic parameters for your specific address and calculates your building's earthquake risk.

Implications for Property Owners and Builders

Building Code Compliance

Turkey's seismic building code, TBDY 2018 (Türkiye Bina Deprem Yönetmeliği 2018), requires all new construction to comply with seismic design standards derived from AFAD hazard maps. The design seismic demand at any site depends directly on the AFAD parameters for that location. Buildings in high-hazard zones like Istanbul must be designed for higher acceleration demands than those in moderate-risk areas. Compliance with TBDY 2018 is mandatory for new construction and increasingly enforced through building permits and inspections.

Earthquake Insurance Considerations

Turkey requires compulsory earthquake insurance (DASK—Turkish Catastrophe Insurance Pool) for residential buildings. Insurance premiums reflect the seismic hazard of the property's location, directly informed by AFAD hazard maps. Properties with higher PGA values pay higher premiums. Understanding your property's hazard parameters can clarify why your insurance costs what it does.

Retrofit and Strengthening Decisions

Owners of older buildings constructed before seismic code enforcement can use AFAD hazard parameters to evaluate whether retrofit investment is justified. Buildings in high-hazard zones like Istanbul face greater risk and stronger economic case for strengthening, while those in lower-hazard areas may present weaker retrofit economics. Engineers use site-specific AFAD parameters to perform seismic risk assessments that guide retrofit decisions.

New Construction Decisions

For developers and property investors, site-specific seismic hazard directly affects construction costs and feasibility. High-hazard sites require more sophisticated and costly earthquake-resistant design (seismic base isolation, advanced damping systems, stronger concrete and steel). Some developers avoid high-hazard sites due to construction cost implications. Understanding AFAD parameters helps stakeholders make informed location and design decisions.

References and Further Reading

Key Scientific References:

• Sengor, A. M. C., Gorur, N., & Saroglu, F. (2005). "Strike-slip faulting and related basin formation in zones of tectonic escape." Life and Work of Akademiker Necip Atalay. Turkish Association of Geoscientists, Ankara. [Foundational work on Turkey's strike-slip tectonics]
• Barka, A. (1996). "Slip distribution along the North Anatolian Fault associated with the large earthquakes of the period 1939 to 1967." Bulletin of the Seismological Society of America, 86(5), 1238-1256. [Classic paper on NAF earthquake history]
• Parsons, T., Stein, R. S., Simpson, R. W., & Reasenberg, P. A. (2004). "Stress sensitivity of fault seismicity: A comparison between limited outcomes (STRESS) and time-dependent probabilistic analyses." Journal of Geophysical Research, 109, B02304. [Documents 62% probability of Marmara earthquake]
• Akkar, S., & Bommer, J. J. (2010). "Empirical equations for the prediction of PGA, PGV, and spectral accelerations for shallow crustal earthquakes." Earthquake Spectra, 26(4), 915-945. [Standard attenuation relationships used in Turkish PSHA]
• AFAD (2018). "Türkiye Deprem Tehlike Haritaları (TDTH)." Official interactive hazard map portal and documentation.

Also available in Turkish: Türkiye Deprem Tehlike Haritası Rehberi on sismikizolasyon.com