Lecture 25

Namaskar. So, in the last lecture, we talked about the relation between stress and strain. And in this, we talked that if the deformation initially occurs, it will occur in an elastic pattern. That means, if the elastic limit is crossed, that will go into the plastic deformation, which we call irreversible, it will not come back. But the material of the earth, although it remains elastic, then in some portions, if we see the stress-strain relation, that how much the stress increased, how much the strain developed, then it remains in the elastic deformation or it goes into the plastic. And finally, when its threshold limit is crossed, then that will break. And this is what we tried to explain in this, that under condition representative of shallow crust, shallow crust will have brittle deformation and in deeper part, it will be ductile. So, let us see that if we take a block, a rock block and deform it, then we can deform it in uniform stress and the other is in differential stress, in which we talk about sigma 1, sigma 2, sigma 3, which mutually add each other perpendicularly. It is mainly taken in geological conditions. So, if this minimum is your sigma 3, intermediate will be your sigma 2 and the maximum will be sigma 1. And this is called directional stress. This directional stress and differential stress is seen in tectonic deformation. So, if we go to the deeper portion of the earth, usually we get to see uniform stresses, but close to the crust, close to the surface of the earth, usually we have seen, that they are differential stresses. So, in differential stresses, in the condition, if you take, these two examples are given that in uniform stress, there will be one kind of deformation, but in directional stress, we will get one alignment, we will get a preferred orientation. So, if we take this rock, for example, if it is granite, then it will look like this, which is in uniform stress, but if this material, rock, if we put it on differential stress, then we will get to see a typical alignment of minerals, which will be like this. And this is perpendicular to the maximum stress. So, this is an example, which is also a transformation of rocks, which is made of granite, which is made of granitic gneiss. So, this is a metamorphic rock, which we had studied earlier. So, this will be under differential stress conditions. So, we will keep this thing in mind, that this is a differential stress, because in your perpendicular direction, where there will be maximum stress, it will give a distinct foliation, or it will make your structures, it will be made in this way. Now, we have talked about this one, that we are deforming it, so it is being made in a differential stress condition, where we will get fractures, and we see such fractures, which I told earlier in a slide, that you will have brittle deformation. So, in brittle deformation, your fractures will be formed, cracks will be formed, so it makes a conjugate set of joints. Now, if we talk about earthquake protection, so we were basically seeing that failure happens, that is the time where you will have the strong ground shaking, and that ground shaking is, the vibrations are basically earthquake. So, this is a stress and stress, or strain diagram, we have seen, what is in its relation. Now, there is a lot of data available in this kind of literature, which says that we can forecast easily, but we believe that it is not so easy. But there are some earthquakes which were predicted and were successfully predicted. So, we will talk about some examples. So, mainly what is our forecasting? So, forecasting is basically, which identifies both earthquake prone areas and manmade structures that are especially vulnerable to damage from shaking. So, for this, we do forecasting. Mainly, our aim is that which areas will be affected by earthquakes, which will be affected by earthquakes, and what will be the things that will be affected? One will be mostly the manmade structures. So, we think a lot about how much damage will be done to the buildings, and how much damage will be done to the humanity. So, these things we always see, that which area is vulnerable and whatever structures are there, whether it will be affected or not, due to ground shaking. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, earthquake prediction refers to attempts to estimate precisely when the next earthquake will occur on particular fault is likely to occur. So, energy will be stored in elastically deformed rocks. So, seismologists use plate tectonic motion and GPS, global positioning system, they monitor the accumulation of strain. So, energy is the strain . is the strain .