On February 6, 2023, a powerful magnitude 7.7 earthquake struck south-central Turkey near the border with Syria at 4:15 a.m. local time, causing widespread damage and affecting many lives. The quake was quickly followed by a magnitude 6.7 aftershock just 11 minutes later, adding to the already chaotic situation. This earthquake is one of the strongest to hit the region in recent years, and its effects were felt far beyond the immediate area.
As a structural engineer, I was curious about the ground motion generated by the earthquake and decided to simulate it in the Shake Table at the Khwopa College of Engineering's research lab. To do this, I first needed the time series data of the earthquake, which I was able to download from the Disaster and Emergency Management Authority (AFAD) of Turkey. The data included East-West Acceleration, North-South Acceleration, and Up-Down Acceleration. The files are as follows:
Since the shake table can only simulate earthquakes in a single direction, the N-S direction was taken because it had a higher Peak Ground Acceleration (PGA) which is 0.51 g. The Acceleration time history is as shown below:
On integrating the acceleration data, we found that the peak displacement was 63 cm. However, our shake table could only give a maximum stroke of 9 cm so the data needed to be scaled down. While scaling down the data, there was a problem.
Scaling down the displacement of the earthquake would also decrease the acceleration in proportion, resulting in a weaker motion on the shake table platform. To accurately represent the actual inertial force during the actual earthquake, it was necessary to keep the acceleration constant. But in order to do so, the sample time had to be reduced proportionally, ultimately decreasing the total time duration of the earthquake. This compression of time can be seen in the graph below.
In the above graph, the top row displays the actual acceleration, velocity, and displacement time series, while the bottom row shows the scaled data. It can be observed that while the acceleration remains unchanged, the total time duration has been shortened. Conversely, both the velocity and displacement have been reduced.
An alternative approach would be to maintain the velocity constant while scaling down the displacement, which would result in a PGA of around 3g (which is very high). On the other hand, decreasing the displacement without compressing the total time would lower the PGA to 0.3g. However, for this particular simulation, we opted to keep the acceleration constant. A video of this simulation is presented below:
In this video, we can observe the devastating impact of a strong shock wave over a brief period, causing widespread damage to structures in Turkey and Syria.
The displacement of the shake table recorded by encoder is as shown below: