When the earth shakes – measuring vibrations on a large scale

We stepped outside of our comfort zone when we interviewed seismologist Dr. Sibylle Steimen. The director of the Natural Disaster Management department at Allianz SE gave us some interesting insights into early detection of earthquakes and how canaries play a part.

Dr. Steimen, thank you for taking the time to talk to PRÜFTECHNIK insight. Please tell us a little about yourself, your team and your work.

 

Thank you for inviting me. I‘d be glad to. I studied geophysics, specializing in earthquake sciences/seismology at the Swiss Federal Institute of Technology (ETH) in Zurich and was granted a doctorate in geophysics. Since 2005, I have been working at the Allianz SE in Munich and head the Natural Disaster Management department. My team is spread across the globe and consists of 18 specialists covering various disciplines of the natural sciences: Meteorologists focus on our climate and weather concerns, hydrologists specialize in flooding, geophysicists research earthquakes, geographers are generalists and mathematicians deal with the statistical aspects of natural disasters.

Our task is to predict and calculate the costs to Allianz in the event of a natural catastrophe, such as an earthquake, hurricane, flood, hail, etc. Natural disasters are distinctive in that they generally re- sult in extensive damage and that insurance companies like Allianz need large amounts of available funds to quickly pay claims from insured customers. Such was the case, for example, after the big floods in Germany or what could potentially happen following a large earthquake in San Francisco.

 

 

When the earth quakes, it often has disastrous consequences for man and nature. How do earthquakes come about?

 

The Earth‘s surface consists of numerous continental plates. Some of these plates – put simply – carry a continent and are referred to as the African plate, Australian plate, and so forth. The ocean floor is also subdivided into continental plates. These vary in size, are approximately 30 kilometers thick and float on a semi-fluid mass – the upper mantle. The plates meet either frontally with one plate diving beneath the other, or they slide past each other. The latter case describes the situation in the San Francisco region. This movement causes friction at the plate boundaries. An earthquake occurs when the plate boundaries catch on each other and then abruptly start moving again.

What are the regions with the highest risk of earthquakes?

 

In Germany, the susceptible regions are Baden-Württemberg, the Rheingraben, areas around Köln-Aachen and the region around Gera/Zwickau south of Leipzig. On a global scale, however, Germany has „moderate seismicity“. Worldwide, Japan, California and Turkey are examples of high risk regions since they are located along the boundaries of the continental plates.

 

When an earthquake occurs, the media often talks of an „earthquake with a magnitude of, for example, 8.0“. What does this mean?


This usually refers to the magnitude scale. Magnitude measures the energy released by an earthquake. It can be roughly translated as „The surface area on which rock moves“. In a relatively weak earthquake with a magnitude of 3, for example, rock movement occurs within a radius of approximately 300 meters. In contrast, during a magnitude 8 earthquake, the crust of the Earth splits through. In other words, it fractures 30 kilometers down and 350 kilometers in length. Of course, a fracture of this size results in a very strong earthquake.

 

How is the magnitude or the strength of an earthquake measured?

 

Earthquake waves – or seismic waves – are recorded using seismometers. Seismometers are devices that measure and record the Earth‘s vibrations using accelerometers and velocity transducers. The networked devices are distributed around the globe. When a quake occurs, these sensors send a signal to a central station and the seismometer is deflected. The exact location of the earthquake can be computed from the time measurement and the relative time of arrival of the seismic waves. Based on this information, alerts can be issued to the authorities or the general population by e-mail, text message, and through other forms of communication. This type of online monitoring is similar to that offered by PRUFTECHNIK and is a fully automated operation. In addition, re- ports are often received from the general population when weak tremors occur. Such observations include a canary inexplicably falling from its perch or dishes rattling in the cupboard.

 

At PRUFTECHNIK, we are interested in early detection of machine damage based on certain parameters. Are there any early warnings for earthquakes?

 

You will never hear a seismologist say the words „Tomorrow Istanbul will experience a large earthquake of magnitude 7“. Unfortunately, earthquakes cannot be foreseen in the way ma- chine or pump damage can be predicted by PRUFTECHNIK, for example. Generally, but not always, earthquakes are preceded by a single or many smaller fore shocks.

Unfortunately, it is only after a strong earthquake has occurred that we know that the weaker quakes were actually precursory events. Many methods have been tested and celebrated, but until now, none of them have proved reliable. Nature is simply not as predictable as a machine and will always find a loophole. I think that due to the complexity of the involved mechanisms, reliable predictions will continue to be very difficult in the future. Seismologists only have a limited glimpse into the third dimension
– towards the Earth‘s core.

 

 

How do you and your team proceed when predictions are almost impossible?

 

Based on statistical models, we calculate the probability of certain financial losses an earthquake in a given region will produce. This may sound rather unspectacular at first, but it is critical for gaining an overall picture. For example, there are prognoses that say,
„There is a 30% probability that an earthquake of magnitude 8 will occur in region XY in the next 30 years“. Such statements are very important in the insurance business because they allow us to define zones on Earth in which massive damage can be expected in the foreseeable future. This is relevant for insurers as well as for governments that need to prepare the population for disasters.

 

What happens in your department when an earthquake has occurred and there is damage?

 

As an insurer, we need to know „What did the earthquake cost?“ – and this immediately. On the day of Japan‘s severe earthquake in 2011, my team and I raced to create a damage estimate based on the data in our systems. This initial estimate is very important to quickly obtain a picture of how large the quake was and how high the damage is expected to be. This information goes straight to the top management. Next, we spend about one week fine-tuning this estimate. Soon after, the first concrete damage notifications arrive, and by then our work using model-based estimates is more or less over. When a natural disaster occurs in the region of one of our companies, we later compare the concrete damage data with our expectations based on the probability models to assess the quality and accuracy of our calculations and to improve them if necessary.

 


Just one more question: Do you decide where to spend your vacation based on the earthquake map?

 

It‘s not quite that bad, but because of my job I am aware that certain areas are more prone to disaster. I remember once when I was in Istanbul with friends. We had no sooner arrived at the hotel than I said: „Ok, now lets just see where the emergency exits are be- cause things can start rocking in Istanbul at any time.“ Of course, my friends were skeptical at first, but I had my way in the end.


Dr. Steimen, thank you very much for these interesting insights into your work.