Objectives Identify the different kinds of stressors and the difference between stress and strain Identify the 3 kinds of faults and where they re found Understand what earthquakes are and where they are found Identify types of earthquake body waves Identify what an epicenter and focus are and what defines magnitude How earthquakes are measured and predicted Tsunamis and how they relate to earthquake Earthquakes cause by anthropogenic influences Review Strains and what they can develop in a body Stress A way of producing a deformation on a body Strain A deformation of a body caused from the stress Measured as Force Area Types of Faults Normal Fault Tensional stress cause the hanging wall above the fault to move down relative to the foot wall Sierra Nevada is a normal fault Reverse Fault Compressional forces cause the hanging wall to move up relative to the footwall The Himalayas and Rocky Mountains are examples of Reverse Fault lines Strike slip Fault the movement of blocks along a fault is horizontal If the block on the far side of the fault moves to the left as shown in this animation the fault is called left lateral Right movement is right lateral Strike Slip is caused by shear force Most commonly found on ocean floor Definition of an Earthquake An Earthquake is when energy stored in elastically strained rocks is suddenly released with great force or by volcanic action They cause natural disasters and damage such as liquefaction of soil fires ground displacement subsidence lowering flooding To prevent larger damage in construction more attention has to be payed to construction materials height of building center of gravity base isolation shock absorbers and nature of ground The Epicenter is the point on Earth s surface that lies vertically above the focus of an Earthquake The Earthquake Focus is the point where an earthquake starts to release the elastic strain of surrounding rock Lies at some depth below Earth s Surface A convenient way to describe the location of an earthquake focus is to state the location of its epicenter and it s depth Seismic Waves Some seismic waves travel trough the Earth s interior These are body waves There are two forms of body waves These are referred to as P waves and S waves P stands for Primary this is the first wave recorded by seismographs since it travels faster than the S or Secondary waves P Waves A kind of body wave also known as Primary Wave of Compressional Wave It was the first kind of wave detected by a seismograph They vibrate in the same direction that they travel consisting of alternating compression and dilation Travel faster than S waves Speed depends on elastic moduli and density of the transmitting medium Particle motion is parallel to the direction of propagation longitudinal Material returns to its original shape after wave passes it travels slower through liquids and solids S Waves Also known as secondary or transverse wave It is a shear wave slow than P waves Vibrate transverse or perpendicular to the direction of travel Transverse particle motion shown here is vertical but can be in any direction however Earth s layers tend to cause mostly vertical SV or horizontal SH shear motions Not transmitted through liquids Material returns to original shape after wave passes S waves velocity depends on shear modulus and the density of the transmitting medium There are other types of seismic waves that travel on the surface of the Earth analogous to ripples on the surface of water that are set up by dropping a stone in the pond These are referred to as surface waves These cause the ground to rise and fall as the wave passes and frequently are responsible for the greatest damage during earthquakes Surface Waves Vibrations trapped near Earth s surface resulting ripples analogous to dropping a stone in a pond They cause actual rise and fall of the ground and the greatest amount of damage during an Earthquake Magnitude The magnitude of an earthquake refers to the amount of energy released Based on the Richter Magnitude scale It assigns a Magnitude number to quantify the energy released by an Earthquake defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary minor amplitude Measured with a seismometer 5 on Richter scale vs that of a level 4 Earthquake corresponding to an energy release 30x great Tsunami means great sea wave Slips along subduction zones on ocean floors can trigger and underwater earthquake displacing large volumes of water thus triggering a tsunami Can travel up to 500 mph Can reach wave heights of 100ft high Can also form from meteors volcanic activity and landslides Huge erosion potential Tsunami Predicting Tsunamis Earthquake prediction is an active area of research Yet to have accurate and dependable methods of detection Decrease of crustal seismic velocities in an area days to months prior Swelling in local volume of crustal rocks bulging or doming of area Ground tilting see above Changes in water level in wells and geyser activity Increased emissions of radon from crust Controversial methods animal behavior skewed radio frequencies Anthropogenic Earthquakes Water sand and chemicals are blasted at high pressures into shale rock to extract gas Disposal of toxic fraking fluid is stored in hollow concrete waste wells thousands of feet underground Oklahoma Ohio Texas are some states affected
View Full Document
Unlocking...