Supporting the teaching of Earth sciences at all levels
VIRTUAL EXPERIMENTS
EARTH SCIENCE TEACHERS’ ASSOCIATION
Experiment: Mike Tuke              Realised by: Julian & Phillipa Priddle                  Sponsor: PESGB

EARTHQUAKE 2

The purpose of these activities is to simulate the movement of an earthquake and to investigate the relationship of the fault displacement to the following: 1. Elasticity of the crust.   The earth’s crust is slightly elastic, it can be stretched or compressed. Without this elasticity all movements along faults would be slow and continuous. This elasticity is simulated by using elastic bands. 2. Friction between sides of the fault.   This depends on the roughness of the sides of the fault and is simulated by using different grades of sandpaper. 3. Pressure acting at right angles to the fault plane.  These forces are due to the weight of the overlying rock and to other pressures in the earth. This pressure is simulated by adding weights to the top of the wooden block. 4. Stress acting parallel to the direction of movement. This is the stress which causes the movement. To measure this the elastic band is replaced by a stress meter and readings of the stress taken immediately before and after each movement. 5. Speed of movement of the crust.  This is simulated by turning the winch a different speeds. 6. Variability of the amount of displacement.  The size of the maximum displacement at each movement of a given real fault varies greatly.  In this activity all the variables are kept constant and the displacement at each movement measured. There is a good correlation between displacement and earthquake magnitude. The apparatus that these virtual experiments are based on is shown below.  Turning the handle on the winch pulls the wooden block.  The wooden block has sandpaper on its underside and this rests on a long sheet of sandpaper of the same grade.  The paper strip is used to mark the position of the front of the wooden block each time it stops. Measurements taken over many years on any one real fault of the maximum displacement at each fault movement show there is considerable variation in the size of displacement. There is also considerable variation in the amount of displacement on the apparatus above even when keeping all the variables the same and this variation is built into the virtual movements.  It is therefore necessary to make a least 100 displacement measurements in order to get a reliable average. Making 100 measurements takes less than 10 minutes. In these virtual activities once you press “start” or “next” the elastic band stretches and the block moves without you turning a winch. The screen displays the number of movements, the displacement and the total of all the displacements so far. Print out the tables for results and the instructions. Choose which factor you will investigate.  Print the instructions and then click on one of the activities to open the animations Once you have completed the activities make a summary of your results and suggest if any could help predict earthquakes.
INSTRUCTIONS INSTRUCTIONS TABLES TABLES elasticity of the crust elasticity of the crust friction between the side of the fault friction between the side of the fault pressure acting at right angles to the fault plane pressure acting at right angles to the fault plane stress acting parallel to the direction of movement stress acting parallel to the direction of movement speed of movement of the crust speed of movement of the crust variability of displacement variability of displacement