Q&A with UCLA Civil Engineer Jonathan Stewart on Earthquake in Turkey
Courtesy of U.S. Geological Survey
Macroseismic intensity map showing the East Anatolian Fault on which the 7.8 magnitude event occurred in Turkey near the border of Syria
The devastating 7.8 magnitude earthquake in Turkey on Feb. 6 has claimed the lives of more than 36,000 people and flattened thousands of buildings across southern Turkey and northern Syria. Since the catastrophic event, civil and environmental engineering professor Jonathan Stewart of the UCLA Samueli School of Engineering has been fielding media inquiries from around the world while helping coordinate the U.S. response, including mobilization of a reconnaissance team now deployed to the affected region and collaborating with colleagues in Turkey.
Stewart is affiliated with the Geotechnical Extreme Events Reconnaissance Association and the Learning from Earthquakes program in the Earthquake Engineering Research Institute. These organizations assembled a joint team of experts that arrived in Turkey recently, which will be surveying damage on-site and collecting perishable data that is essential for improving our understanding of the devastating impacts of large earthquakes.
“This was a very powerful earthquake with many structures close to the fault. In that sense, it is an exceptionally unfortunate circumstance in terms of seismic demand, but not unlike what we expect to see in portions of California for future events,” Jonathan Stewart said.
Following are some of the topline questions from journalists Stewart has addressed about the earthquake and its effects, with modifications for brevity and clarity. Journalists and the public are welcome to share such information with proper attribution to Jonathan Stewart and to the UCLA Samueli School of Engineering.
Q: Is Turkey prone to having earthquakes?
A: Turkey frequently experiences major earthquakes. The country has two major faults with high levels of activity — North Anatolian Fault and East Anatolian Fault. These faults are active because of plate movements on the surface of the earth, which is part of plate tectonics. The Arabian Plate is moving north towards the Eurasian Plate, which is squeezing a block of crust wedged between these to the west. The southern boundary of that block is the East Anatolian Fault on which the magnitude 7.8 event occurred.
Q: Can you describe the East Anatolian Fault and what is happening there with regard to earthquakes?
A: It is a long, left-lateral, strike-slip fault with a high slip rate (i.e, the rate with which crust on one side of the fault displaces in time with respect to the crust on the other side of the fault). It is exactly the kind of fault that will produce earthquakes like those we saw last week.
Q: Why were the aftershocks so strong following the earthquakes?
A: It is normal to have a high rate of aftershocks immediately after a large earthquake like the magnitude 7.8 event. The rate of aftershocks occurrence in time, and the size of the aftershocks in magnitude, should gradually decrease with time.
Q: In the days since the earthquake, are there patterns you are seeing emerge among buildings that collapsed? Do these failures point to specific construction flaws or the skirting of building codes?
A: We need to wait for data collected from on-the-ground inspections before drawing conclusions about specific patterns but in past earthquakes, we have found that patterns for construction similar to those in this part of Turkey often reflect ground conditions — that is, certain conditions can amplify ground shaking intensities or produce liquefaction that affects a foundation’s performance. In fact, we are expecting to see effects from liquefaction from this earthquake, as broad portions of this area have shallow groundwater and geologically young soils. I think we’re also going to see major effects from the rupture of the fault at the ground surface across an extended length of approximately 200 km, or 124 miles. Landslides in steep terrain are also likely. We should know more in the next month or so as results from the work of reconnaissance teams become available.
Q: Broadly, would you expect this degree of structural failure if building codes had been followed?
A: As for building standards, my understanding is that the Turkish building codes are quite good. There are issues with enforcement, even for modern buildings. I think as the specifics of various building collapses come to light, we are likely to see evidence for incidents of lack of enforcement. I have also read in a Guardian article of an amnesty program in which older buildings that were potentially unsafe were allowed to avoid retrofitting for a fee paid to the Turkish government.
Q: Are there similarly powerful earthquakes you would point to in countries with similarly sized buildings but which did not suffer such wide-scale failures?
A: This was a very powerful earthquake with many structures close to the fault. In that sense, it is an exceptionally unfortunate circumstance in terms of seismic demand (the force imposed on structures from earthquake ground motion), but not unlike what we expect to see in portions of California for future events. The 2011 Tohoku earthquake (magnitude 9.0) off of the coast of Japan and the 2010 Maule earthquake in Chile (magnitude 8.8) were much larger in magnitude, but as subduction events, those site-to-source distances were larger than for this recent earthquake in Turkey. This means that the shaking intensities for the events in Japan and Chile were generally lower in amplitude, although longer in duration. Relative to this earthquake in Turkey, the performance of structures in those events was quite good. Both Japan and Chile are known to have quality building codes and good enforcement.
“The earthquakes in Turkey were not induced by humans, but are natural earthquakes associated with a known major fault zone,” Stewart explained.
A: There are strong similarities between Turkey and California regarding the regional tectonics, which controls the types of earthquakes that can happen. Both the San Andreas Fault in California and the North Anatolian Fault in Turkey are long strike-slip faults (about 1300 km/800 miles for San Andreas and 1500 km/900 miles for North Anatolian) with high slip rates — the average velocity with which one side of the fault moves relative to the other side. Long and active faults can produce large earthquakes (magnitude 7.5-8) at relatively frequent time intervals from geological perspective (every few hundred years).
As a result, it is critical that we collect valuable and perishable data following the disaster in Turkey and Syria so that we may learn from it and reduce long-term seismic risk in seismically vulnerable regions globally. This is the aim of the work being conducted collaboratively by researchers in Turkey and U.S. partners with the Geotechnical Extreme Events Reconnaissance Association and the Earthquake Engineering Research Institute.
Q: Given patterns of building collapse, do you expect that many of the structures still standing may be too dangerous for habitation?
A: My experience in past earthquakes is that some of the currently standing structures are likely compromised and unsafe. This can be assessed through inspections to examine the condition of load-bearing elements like columns and walls. In the United States, we have a tagging system (red-yellow-green) to evaluate this and I expect something similar will be done in Turkey.
Q: Aside from load-bearing elements, is there anything else to look into for why some buildings collapsed, while others nearby did not?
A: It is very important to know the basic typology of the building — typically in Turkey there are reinforced concrete buildings (which tend to be taller) and masonry buildings. Masonry buildings are usually highly vulnerable to earthquakes. Reinforced concrete buildings can be safe if they are well-designed and constructed, or can be very dangerous if that is not the case. Another important consideration is the condition of the foundation and the ground around the building. Is there evidence of the foundation having been tilted or settled into the ground or sandy soil having boiled to the surface? If this is observed, it is evidence of liquefaction of foundation soils, which can be very damaging.
Q: Can earthquakes in the Middle East be predicted?
A: We cannot predict earthquakes on short time horizons, like days or weeks. We can predict areas that have relatively high or low levels of seismic hazard. The area that experienced last week’s earthquakes is known to have high seismic hazard on Turkish national seismic hazard maps.
Q: Can humans cause an earthquake?
A: Humans can induce earthquakes in certain circumstances, such as via the filling of reservoirs for the first time or by injecting pressurized fluids deep into ground as in the case of some earthquakes in Oklahoma. These earthquakes tend to be small (up to mid-magnitude 5s). The earthquakes in Turkey were not induced by humans, but are natural earthquakes associated with a known major fault zone.
Q: What improvements would you like to see as far as earthquakes are handled?
A: Improvements in building codes and their enforcement would be helpful for new structures. Older structures with known vulnerabilities should either be retrofitted or replaced.
Stewart’s research interests include geotechnical engineering, earthquake engineering and engineering seismology. He has studied what happens to infrastructure during earthquakes around the world and is a co-director of the multidisciplinary, multi-university Natural Hazards Risk and Resiliency Research Center and a member of the UC Seismic Advisory Board. In 2020, Stewart was awarded the Erskine Fellowship from the University of Canterbury in Christchurch, New Zealand, where he collaborated with researchers on studies pertaining to earthquake ground motion and soil liquefaction. An October 2022 Q&A with Stewart, coinciding with the annual Shake Out program, focused on more general earthquake information.