How did the 1999 İzmit earthquake shape earthquake risk in Turkey?

At 03:01 local time (00:01 UTC), on August 17, 1999, a Mw7.4 earthquake ruptured a segment of the North Anatolian Fault (NAF) in İzmit (pop. ~ 376,000), northwest Turkey, a city located on the Gulf of İzmit in the Sea of Marmara.

The earthquake propagated along more than 100 kilometers (70 miles) of the northernmost section of the NAF close to İzmit in Kocaeli Province, just 100 kilometers (62 miles) east of İstanbul.

One of the world's longest and most active fault systems, the NAF stretches 1,500 kilometers (930 miles) across northern Turkey, with some similar characteristics to the San Andreas Fault in California, such as its predominantly right-lateral strike-slip movement.

The far-reaching impacts from the 1999 İzmit earthquake were also reminiscent of the damage seen in San Francisco and Oakland after the Mw6.9 Loma Prieta earthquake in 1989.

The 1999 Izmit earthquake impacted the highly urbanized and industrialized region of Marmara, which consists of 11 provinces. These provinces surround the north and south coasts of the Sea of Marmara and link Turkey to Greece and Bulgaria to the west, the Black Sea to the north, the Aegean to the south, and include cities such as İstanbul, Bursa, and Balıkesir. (Scawthorn et al., 2000).

With an estimated 20 million people living in the region, approximately a third of Turkey's total population at the time of the event, the earthquake resulted in more than 18,000 fatalities and left over 400,000 residents unhoused (Scawthorn et al., 2000).

Damaging ground motions were felt up to 2,000 square kilometers (770 square miles) from the rupture, including in İstanbul. The ground motions caused great physical damage to residential buildings and commercial and industrial facilities.

Over 53,000 dwellings were destroyed and over 280,000 were damaged, most of which were multi-story apartment buildings (United Nations, 2001). The damage to the housing sector was estimated to be between US$1.1 billion and US$1.6 billion in material losses (United Nations, 2001).

At the time of the event, the Izmit region was responsible for over 40 percent of the annual manufacturing production in Turkey (United Nations, 2001). The earthquake struck several industrial facilities and while the impact was not as extensive as seen to residential structures, there was business interruption and physical damage (Scawthorn et al., 2000).

In addition, telecommunications were severed and the İstanbul-Ankara railroad and motorway were damaged. However, these impacts were minor as repairs were completed quickly (Scawthorn et al., 2000).

Revising building codes

The Turkish building code revision in 1997 did include regulations designed to withstand earthquakes of such a magnitude but was introduced just two years before the Izmit earthquake and coupled with rapid building development and strong demand, saw poor enforcement of these regulations (Scawthorn et al., 2000).

Many buildings in the impacted region were built before the code revision in 1997 and fell under the 1975 seismic building design code, which did not perform well in the Izmit earthquake.

Damage was also attributed to significant liquefaction and ground settlement in the city of Adapazari (pop. ~280,000), just 40 kilometers (25 miles) west of Izmit, causing the collapse of many buildings in the city center, and also along Izmit Bay, affecting the port and docks on the south shore (United Nations, 2001).

The total economic losses from the earthquake were estimated to be around US$20 billion with the insured losses only at US$900 million (AXCO, 2024).

Legislative change and development of the insurance market

The Izmit earthquake was pivotal for Turkey, exposing the need for enhanced seismic resilience from many perspectives.

For construction, the Turkish government reviewed the enforcement of their current building code after the earthquake, which they revised in 2007 and again in 2018.

However, discrepancies remained and it was estimated that more than 50 percent of structures were not compliant with building regulations in 2010. Turkey's Chamber of Commerce estimated that around 65 percent of all new buildings were either built without a permit or had a lenient inspection (AXCO, 2024).

The inconsistent performance of buildings during the 2023 Kahramanmaraş earthquakes in southern Turkey again highlighted the issues of enforcement of the building regulations.

From a financial perspective, the government established a property catastrophe risk insurance mechanism - DASK (Doğal Afet Sigortaları Kurumu), the Turkish Catastrophe Insurance Pool (TCIP) after the earthquake, as part of a larger effort to combat the impact of natural disasters.

The TCIP looked to reduce Turkey's private property exposure to natural disasters by effectively transferring the risk from the government to homeowners and the insurance market, and considerably increase the insurance penetration in Turkey.

According to the TCIP annual report published in 2000, there were an estimated 159,301 earthquake policies (Turk Reasurans, 2005). As of August 2024, the number of policies exceeded 11.2 million, covering 56.4 percent of residences within the country (DASK, 2024).

In Kocaeli, the province most impacted by the 1999 event, the penetration rate is up to 68.6 percent; a higher-than-average rate that can also be seen in other provinces that have experienced large earthquakes (DASK, 2024). The current penetration rate in Istanbul is 62.8 percent (DASK, 2024).

Before the introduction of the TCIP, residential insurance take-up was in the low single digits, making most people dependent on the government.

Imminent seismic risk in Turkey

As of 2023, 77.5 percent of the country's total population of 85.3 million live in urban areas, and 20 percent reside in Istanbul; approximately 15.85 million residents. A repeat of the 1999 Izmit earthquake would cause substantial damage across the Marmara region due to the increasing exposure.

While a repeat of the Izmit earthquake is concerning, a more imminent seismic risk is the potential for a major earthquake along the main Marmara fault, located south of Istanbul and beneath the Marmara Sea - a seismic gap that has remained unruptured for over 250 years.

Past studies indicate that the Princes' Islands fault segment is locked, making it a probable nucleation point for another major earthquake in the Marmara region (Bohnhoff et al., 2013). Located just north of Istanbul, such an overdue event would pose an immediate and severe threat to the city's 15 million residents.

Building earthquake resilience

Twenty-five years since the 1999 Izmit earthquake, we look back at this event as a defining moment in Turkey's history, underlining the need for increased seismic resilience not only in this region, one of the country's most populous and industrially vital, but more broadly across the country.

Looking beyond Izmit, there is a high potential for other large-magnitude events to occur along the NAF. Given the seismic landscape in Turkey, it is important to acknowledge that another significant earthquake is inevitable in this region. The question is not if, but when, such an event will occur.

In response to the 1999 earthquake, actions have been taken to improve the seismic performance of buildings and infrastructure through updated building codes and the establishment of the Turkish Catastrophe Insurance Pool (TCIP).

However, the losses from the 2023 Kahramanmaraş earthquakes in southern Turkey showed the persisting building stock deficiencies and gaps in insurance penetration.

The next significant earthquake will serve as a critical test of seismic preparedness, disaster response, and the overall resilience of the region. The role of the insurance industry will be essential in aiding recovery.

To learn more about our rebuild of Moody's RMS Europe Earthquake Model, or to read our white paper on the twenty-fifth anniversary of the Izmit earthquake along with greater insights into a possible Istanbul earthquake, please get in touch with your Moody's account manager.