2:30 PM - 2:45 PM
[G04-04] Descriptions of earthquakes in school science textbooks
Keywords:school science textbook, earthquake, Fracture in bedrock, active fault
I served as a specialist examiner for textbook approval for nine years until last year, and was mainly in charge of solid earth-related matters. During that time, there were several points that I repeatedly pointed out every year. Writing science textbooks is a difficult job that requires knowledge across a wide range of fields, and it is only natural that there are cases where something that experts consider to be “common sense” is not so in general. I would like to take this opportunity to introduce some common examples.
Are earthquakes the destruction of rocks?
There are many descriptions that say “earthquakes are a phenomenon in which rocks underground are destroyed”. Some even include photos of experiments in which rock samples are compressed and broken using a press. It is common knowledge among experts that earthquakes do not cause (intact) rocks to break, but rather that they cause pre-existing cracks, or faults, to re-activate. However, seismologists often describe the slipping of a fault as “the fault breaking”. This may be one of the causes of the misunderstanding.
In a related vein, we sometimes see statements to the effect that earthquakes are caused by very great forces. This seems to be directly related to the above view. In this area, progress has been made in recent decades. It has become widely known that not only plate boundary faults such as the San Andreas Fault, but also inland faults, are “weak”. By “weak”, we mean that the shear stress required to slip the fault is less than 0.3 in terms of the friction coefficient, and there is a possibility that it is around 0.05 (Copley, 2018). The coefficient of friction between ice and ice is around 0.1 (Wikipedia friction), so it can be said that the faults that generate earthquakes are very weak and prone to slipping. Active faults are weak planes within the earth's crust, and most textbooks correctly state that earthquakes occur repeatedly on them. It may be less misleading to say that earthquakes are more like landslides than rock fractures. I personally think that the reality of earthquakes is that very weak things collapse by themselves.
The science of earthquake occurrence is a field that is very behind the times when you look at the expectations of people around the world, and even the latest findings are likely to change in the future. We want to make sure that we convey the latest findings in as easy-to-understand a way as possible. In the lecture, I would also like to mention about the another problem that the northeast Japan belongs to the North American plate.
Are earthquakes the destruction of rocks?
There are many descriptions that say “earthquakes are a phenomenon in which rocks underground are destroyed”. Some even include photos of experiments in which rock samples are compressed and broken using a press. It is common knowledge among experts that earthquakes do not cause (intact) rocks to break, but rather that they cause pre-existing cracks, or faults, to re-activate. However, seismologists often describe the slipping of a fault as “the fault breaking”. This may be one of the causes of the misunderstanding.
In a related vein, we sometimes see statements to the effect that earthquakes are caused by very great forces. This seems to be directly related to the above view. In this area, progress has been made in recent decades. It has become widely known that not only plate boundary faults such as the San Andreas Fault, but also inland faults, are “weak”. By “weak”, we mean that the shear stress required to slip the fault is less than 0.3 in terms of the friction coefficient, and there is a possibility that it is around 0.05 (Copley, 2018). The coefficient of friction between ice and ice is around 0.1 (Wikipedia friction), so it can be said that the faults that generate earthquakes are very weak and prone to slipping. Active faults are weak planes within the earth's crust, and most textbooks correctly state that earthquakes occur repeatedly on them. It may be less misleading to say that earthquakes are more like landslides than rock fractures. I personally think that the reality of earthquakes is that very weak things collapse by themselves.
The science of earthquake occurrence is a field that is very behind the times when you look at the expectations of people around the world, and even the latest findings are likely to change in the future. We want to make sure that we convey the latest findings in as easy-to-understand a way as possible. In the lecture, I would also like to mention about the another problem that the northeast Japan belongs to the North American plate.